Maintaining Growth in the Wind Power Industry

You cannot say it’s a new industry because its been around for quite some time however, you can call it a growth industry because yes, it’s still growing. In fact, I can see it getting bigger. My reason for this is that I can see some remote communities taking advantage of this technology, technology that is improving with better power storage for example. I can also see some large manufacturing plants generating their own power to save on the costs because as we know, power is expensive to buy. I cannot say that we are there yet but as costs come down it looks like a viable alternative to what we do now in many cases.

Seeing wind turbines is common place these days and they are a large part of energy production. A wind turbine harnesses wind power to generate electricity. The most common is a horizontal axis wind turbine application which have three main components. A rotor, which the blades are attached to. A gearbox which increases the RPM of the rotor. And a generator, that is rotated and produces electricity, power.

Inside the nacelle. From left to right: rotor, gearbox and generator.

The rotor, which is relatively low speed (low RPM), converts the kinetic energy of the wind to rotate the shaft. Based on the length and width of the blade, this is a very powerful force. To generate enough power, we need it to be faster, hence the gearbox. The gearbox is a speed increaser having a ratio of 92 to 1. This powerful and now high speed rotational torque is passed through a coupling which turns the generator to make the electrical power. Easy right?

All of this plus a hydraulic system that allows the blade to tilt/pitch into the wind – much the same as a ships propeller can – and its all in a container called a Nacelle. This nacelle sits on top of a tower which can be several hundred feet in the air. The whole nacelle is geared so it can rotate or “yaw” into the wind as it’s called.  As you can imagine, it can get battered by the elements like heat, cold, wet, etc.

It’s a sophisticated asset that can pay for itself (we should all have one!). However, it requires high quality maintenance and this is critical to its life expectancy. Consider the cost of replacing one of these components that I listed out. Its not just man power that’s needed; for some items cranes need to be on site. So, think about what you don’t wont in the nacelle. One thing would be vibration. We all know that excessive vibration destroys machines, so making a reduction or elimination of vibration is very important. One of, if not, the most common cause of vibration is shaft misalignment. Therefore, it’s should be a priority that the gearbox to generator shaft is aligned correctly.

Some time ago I did some alignment work on a ship. The gentleman that I was working with described the ship as a floating upside-down bell. He pointed out that the vessel would ring (vibrate) when excited by the right natural vibration frequency. The vibration would travel through the steel structure of the ship. Transient vibrations do pass from one machine to another and it’s the same in a nacelle, like a ship, its one big steel frame. The reason is that there is no mass to absorb the vibration (no ground), at least not close by. We all know that mass dampens vibration. If you have a machine mounted on a platform or mezzanine it will most likely vibrate more than the same machine mounted on a concrete base.

One of two Easy-Laser PSD’s (aka measuring units) mounted with a magnetic bracket on the coupling hub closest to the generator.

The alignment procedure is quite simple. You normally use the gearbox as the stationary machine and align the generator to it. You use shims to adjust the misalignment in the vertical plane and jacking bolts for the misalignment in the horizontal plane. The OEM will normally give a tolerance as well as any offsets that may be required. For instance, on some models the sheer torque of the rotor when in service (online) will offset the gearbox. Because of this, a target value is set in the alignment laser system to compensate for the offset when aligning while offline.

Tolerances are based on RPM and this drive system would be variable speed, so you use the highest speed. A normal rotor input is 20 RPM which will give the gearbox an output of 1840 RPM. However, regardless of what the tolerance is we recommend that you minimize it to the best that you can get because in this case, less is more. Less vibration equals more exerted life of seals, bearings, gears, etc.

You still have all the other concerns to address such as base flatness, soft foot issues, etc. However, proper wind turbine alignment can minimize wasted energy, increase component life of the machines, and help reduce the possibility of catastrophic failure. With a customized Easy-Laser® shaft alignment system using special brackets, the gearbox and generator can be aligned even if the coupling is removed and the brake is locked. This way the maintenance technicians can make alignments even in bad weather conditions when the wind is stronger, but keep safe. Speaking of keeping safe, we had one of our own do some on-the job training for a customer in Southern, Ontario recently, see photo below.

John-Paul Lambert of Benchmark PDM on top of the nacelle, taking a break for a photo with a view.

All of this should give us food for thought. Is the lack of mass making these machines more sensitive to vibration a positive thing or a negative thing? I say it a positive thing because if you are aware of it you will do something about it. On land/ground-based machines the damaging forces are there but we do not see them as much because mass dampens the vibration. So often it is ignored which leads to machine failure in many cases. But that’s what I think, what do you think?

Dowel Pins: Should we be using them for pinning general purpose machines?

Figure 1 (above) – Can you see the dowel pin in this photo?

Dowels have been used by carpenters for centuries. They would have a length of rod which they would cut the required amount needed from it. It would have been inserted into a joint to give the joint more strength and to stop or reduce the share of forces that are on that joint. Basically, a pin to keep something in the same position. It is not designed to be fastener or a clamp, as something else would meet this requirement. So it’s no surprise that we see them in our industry.

Now let’s not confuse these dowel pins with locations pins. Location pins are used to position one component with another. The auto industry uses them a lot. For instance, the gearbox to block, cylinder head to block and timing chain covers to block uses location pins. We use location pins on split casing pumps, gearboxes and compressor covers and in many more places. We use similar devices such as step fit or rabbet fit on a flanged motor. We have other examples however, they all do the same thing which is marrying one component with the other and insuring they are in the correct position.

Dowel pins are different; they are used to lock/pin a machine in place after it has been positioned and aligned.

Figure 2 (left) – Dowel pin with thread, used to help for removal.

In some instances, I understand that on high speed/high torque machines such as large turbines they have to pin them down. They expect growth so they control the movement of the machine. One example that comes to mind is a turbine that is dowel pined at the front of the machine. This restricts the axial movement of the machine thus protecting the coupling. The back end is not pinned and allows the machine to grow along its length without restriction. It is an engineered design that works well for this application. This use of dowel pins makes sense to me.

However, on general purpose machines, I don’t like to see them used. I believe that just by using the correct grade and torque for the hold down bolts is adequate enough to keep the machine in place. And what’s more, many of the dowel pins that I see are incorrectly installed and are actually detrimental to the machines alignment.

Let me explain. We all know that a machine will move as it comes from offline to online reaching operating conditions. With this thermal growth, it will move axially (along its length) horizontally (side to side) and vertically (up or down).

We tend to focus on the vertical movement because as the machine heats and it wants/needs to expand down it cannot because the base restricts the movement. Instead, it moves up and creates misalignment between the two shafts and we compensate for this by shimming.

But what about horizontal movement? This is an interesting one as there are some machines that will move a large amount in the horizontal plane, such as reciprocating compressors, but this is known and should be compensated for.

We know that machines grow in the vertical plane so common sense should tell us that it will also grow in the horizontal. We don’t see too much movement horizontally when checking hot alignment. The reason I believe is that when machines expand outwards it is not restricted (by the base) so it can spread out equal amounts. I believe that there is also some movement between the motor feet and the base. I call it creep. Even if the bolts are torqued down I still think there is some movement or “creep” as the machine and the base grow or shrink. I know it’s possible to move a machine in the horizontal plane even after its tightened down as long as you apply the right amount of pressure with a good jacking bolt.  And that’s what thermal growth is, it’s constant pressure. If the growth is equal amounts and there is no restriction, we don’t see as much movement. But what if it is restricted?

The graphic on the right shows two dowel pins installed diagonally. These pins will restrict movement in one direction only. When the machines grow and push against the pin, it will have to move in the opposite direction. This means that this machine will rotate in the horizontal plane as it reaches operating temperature thus, misaligning the machine at the coupling.

Figure 3 (right) – Bird’s eye view of  a motor with potential horizontal movement due to dowel pin placement.

The machine that we removed these dowel pins from (Figure 4 below) was a large electric motor that was driving a gearbox which in turn was driving a roll. The dowels were installed diagonally as were the dowels in the gearbox. The gearbox dowels were the opposite to the motor so misalignment was compounded.

Figure 4 (above) – Dowel pins removed from a motor.

If you look at these two pins (Figure 4 above) you can see that there is a step (or indent) in one which to me means that there has been movement. The customer says that these machines have never been re-aligned since the original installation so I think the step has been caused by the thermal growth of the machine.

To remove these dowel pins can be a challenge. The simplest way is using a slide hammer (if the pin is threaded). You can make these up easily using a barrel nut, a length of threaded rod, a weight and a stop. They work very well as long as you have the room to get it in. If the area is obstructed, if there is a step in the pin or it’s bent, then the slide hammer does not work as well. That’s when the fun (and the wasted time) begins.

For example, I have seen the threaded end break off using a slide hammer. Then it was decided that they could punch it straight through not knowing that the pin was tapered. When that didn’t work they tried drilling it out which was taking a long time and not working. So eventually they pried the unit up and cut the pin with a Sawzall. This all takes time.

Figure 5 (left) – Two dowel pins removed from machines.

Have a look at these two pins (Figure 5 left). The first one (on the left) looks to have been cut short and you can see that it has not been installed deep enough because the step (where the joint will be) is very low to the bottom. You can also see that there was a lot of exposed pin at the top. The step is because someone moved the machine after it was pinned. However, that’s just a guess because no one is saying anything when we ask.

If you look at the next pin (on the right) you will see that its discolored. The reason for this I think is that it’s not making good contact with the sides on the tapered hole so that air can get in and the pin gets oxidized (discolored). This pin came out easily so that means it was probably loose.

The bottom line is that you have to install these pins correctly otherwise it’s a waste of time. And that begs the question of why they are being installed in the first place? If the reason is because of known circumstances such as to restrict movement of a machine in a certain direction, due to thermal growth movement, then it’s a good valid reason. In other words, there has been thought going into the decision. But if they are pinning the feet because someone thinks it would be a good idea and they have seen it somewhere else then I think you should review this “good idea.”

Now I admit that I haven’t done a lot of research or experimentation into this subject. My conclusions are based on many years of experience and my observations. This article was written in the form of a question. I have given you my opinion, so what’s yours? Do you have anything you can share? If so I would like to hear it from you and if appropriate, we can share it in our next newsletter.

Understanding Thermal Growth in Your Rotating Machinery – Part 3

There are other issues we should be aware of when talking about a machine’s thermal growth in our rotating machinery and how it affects the machine’s alignment at the coupling. One major factor affecting machinery alignment is Dynamic pipe strain caused by thermal growth. However, there are two types of pipe strain and the other type is also important to know about. Static pipe strain exists when the machines are not even operating. Static pipe strain is a major cause of machine failures and is the result of incorrect fabrication and/or installation, inadequate or missing support, or machine movement after piping is connected. Its effects are relatively simple to measure however, it’s often ignored because repairs or rework are perceived to be costly, but that’s not always the case.

Dynamic pipe strain is much more difficult to measure since it is present only after the machine and piping are at operating conditions. The word dynamic is characterized as constant change or movement (growth or shrinkage) and much of this movement is due to temperature change – hot or cold. If you are involved in some sort of machinery maintenance and repair or a condition monitoring program at your company/plant, you have probably seen some severe cases of machines increasing or decreasing in temperatures. For example, compressors can have ice forming at the inlet (suction) piping whereas the outlet (discharge) piping is often too hot to even touch. So some piping will grow and others may shrink. This is dynamic pipe strain and it can have a lot of influence on your machines.

Large temperature changes in piping will have a major effect on the machines they are attached to and usually result in moving these machines out of alignment. OEM (Original Equipment Manufacturers) can give you the expected amount of growth for their machines but in regards to piping, you are on your own. That is why the smart choice is to use flexible pipe joints between the piping system and the machine units (see photo below).

Piping runs can be very long and can have a big influence on the alignment of the machine units as well as creating case distortion. In the instance of offline to running (OLTR or OL2R), machine units can get to operating temperature relatively quickly but the temperature changes in piping can take a lot longer period of time.

For example, you may have a long run of pipe that is pumping cooling water from an outside source. The plant you are in may have a high ambient temperature (the temperature of the surrounding environment) so the length of pipe will shrink however, it will take a long time for the cooling water to bring down the temperature of the pipe. Obviously, with heat it will grow, hence the need for expansion joints. The point being is that it takes time for a machine unit to get to full operating temperature and even longer for the piping that is attached. Using a formula is impractical to measure pipe movement however you can use a good laser system. More on this later.

One other thing to consider is that temperature changes will vary over distance. You would expect that the further you get from the heat, the cooler the area. That is why it’s not easy using a formula to measure movement of long pipe runs. The best way to take temperature readings is to take a series of readings on each section of the piping in order to get an average of the growth. It’s not always that easy to do but taking an average is what we should be doing when trying to calculate a machine units’ growth.

In the following example, we take a temperature reading on the bearing housing of a pump just below the centre line. Pictured on the left, we can see where the laser pointer is for the location of the temperature reading. The reading we get a 171° F.

We know the ambient temperature is 70° F so the temperature difference is 101° F (T). The pump leg is 16 inches long (L) – the height from the foot to the center of the shaft. So if we want to know the thermal expansion of this pump we need to know one more thing: the coefficient of expansion (“/° F). In this example, the coefficient of expansion of mild steel is 0.0000063 (“/° F) (C). We multiply it by the length (height) of the leg (16 inches) and we get 0.0001. Now we multiply this by the temperature difference (101° F) and we have 0.010 inches (10 thou) of growth. Yes, 10 thou is a lot when the offset tolerance for this pump is 2 thou (0.002 inches).

However, if we take a series of readings (4) along the length at (roughly) equal spacing we can get an average of the temperature of the leg. See the laser spot on the leg as to where the reading is taken. We do this and the readings pictured below from left to right are 171° F, 164° F, 138° F and 119° F.

If we add them together and divide by four (4), we get the average of 148° F. When we take away ambient temperature (70° F) we get a temperature difference of 78° F. If we put these numbers into our thermal expansion formula from Part 2 of this article, it looks something like this:

T x L x C

= 78° F x 16″ x 0.0000063″ /° F
= 0.007″ (7 thou)

7 thou (using the average of four (4) temperature readings) and 10 thou (using the highest reading) only gives us a difference of 3 thou. Not a lot, but can make a difference when 2 thou is the tolerance.

We take temperature readings and average them for all four feet of each machine. After we input the info into our thermal growth expansion calculation (T x L x C), the results show:

Outboard pump feet – 0.007” (7 thou) of growth.

Inboard pump feet – 0.006” (6 thou) of growth.

Inboard motor feet – 0.004” (4 thou) of growth.

Outboard motor feet – 0.002” (2 thou) of growth.

If I graph these projections, you can see (below) by the dashed black center lines of each shaft that the offset and angle is very good, so we are in tolerance.

What’s important is if I had based the results on the one highest reading, I would have been out of tolerance. However, by averaging I am good to go. Not taking the correct temperature reading is a common mistake and it does make a difference.

Let’s look at another example. If we take temperature readings in the plane of the foot at the outlet of this blower (pictured below) we get 150° F, 150° F, 149° F and 146° F. The average of these readings becomes aprrox. 148° F. The ambient temperature is 75° F giving us a difference of 73° F. If we use the coefficient of expansion of mild steel 0.0000063 (“/° F) (C) and multiply it by 18 inches (L) – the height from the foot to the center of the shaft – and the temperature change (T x L x C), we should have 0.008” (8 thou) of thermal expansion/growth at the outlet.

The inlet has much lower readings of 67° F, 69° F, 78° F and 84° F. The average of this is 74° F. Taking away the ambient temperature, we get a difference of -1° F. If we do the thermal growth calculation (T x L x C) we have no growth. After doing a thermal growth calculation for the motor, we found that the results for the inboard feet were 0.003” (3 thou) of growth and the outboard feet was 0.002” (2 thou) of growth. This means that the outlet of the blower would grow, tilting the shaft down at the coupling, putting the machine out of alignment.

Attached to the machine is the OEM (Hoffman) guide to compensating for thermal growth of the Blower. After some pre-alignment checks, at # 5 it says to align the driver shaft (motor) parallel to the blower shaft (driven).

Then at # 5A, it says to add 0.008” (8 thou) of shim to all the motor feet lifting it up.

At # 5B it says to add .012” (12 thou) to the inlet end of the blower.

Finally, at # 5C, it says that a hot alignment measurement and correction must be done after the machine has been run up to full operating temperature.

To see this visually we can make a simple graph. The scale that we use is that each small box in the horizontal plane (going across the page) represent 2 inches. For the vertical plane each small box (going up and down the page) represents 0.002” inch (2 thou).

On the OEM guide, # 5 says to align the shaft which we have shown using the two black shafts along the red dotted line.

Then #5A and 5B said to add 0.008” (8 thou) to all of the motor’s feet and 0.012” (12 thou) to the inlet feet set of the blower. This you can see is represented by the red shafts for each machine.

Once the machine unit is started and runs up to full operating temperature, we can take the measurements and then calculate the thermal growth based on these measurements.  We get 0.008” (8 thou) at the outlet, 0.000” (0 thou) at the inlet, 0.003” (3 thou) at the motor front feet and 0.002” (2 thou) at the back feet. These growth numbers are represented by the green shaft and as you can see, it is very close to being within tolerance.

By doing a hot alignment (#5 C on the OEM guide) we will be able to trim this so that it’s a precision alignment. We think this is great information supplied by the OEM (Hoffman). You will not always have all the information you need to be able to get a good alignment with this guide because of, for example, what the ambient temperature is or the temperature of the air going into the inlet. However, based on a mechanic/millwrights experience with this machine the guide can give you a very good estimate so that you will be close at start up.

What we have been doing is giving you a practical look at thermal growth. How to be able to measure and calculate how much it will grow using a simple formula. The graph is a helpful way to see the machine’s growth visually. Its not an exact science however, it will get you very close. The reason why it is not exact is because of all the variables associated with the machine unit that can have an effect. We have already gone through some of them including pipe strain, incorrect temperature measurement readings, and following the proper OEM guides. Some others include the size of the machines feet, the design of the casing, and the airflow in and around the machine. Measuring thermal growth can he difficult with all of these variables influencing the machine unit, but it’s a lot better than the alternative – which is to ignore it!

Our professional level shaft alignment system can measure live time movement of the machines with specialized brackets attached to the machines. It can also give you live time readings in both the horizontal and vertical planes when mounted on a pipe as shown below left.

 

 

 

 

 

All of our shaft systems can give live time readings that can be used to measure pipe stress; for instance, when connecting or disconnecting piping. In fact, there are a lot of ways to measure machine movement because of thermal growth and machine casing stress, such as optical instruments or even inside micrometers and tooling ball set ups. We can also use geometric lasers to measure (photo above right). However, to set this type equipment up is time consuming and expensive. It is justifiable if there are issues with the machines but for the average machine this is not done. That is why we recommend a thermal growth calculation as well as a hot alignment measurement.

A hot alignment check is recommended by many OEM’s as part of their initial installation procedure. However, some companies tend to not do it as it is perceived as being unsafe. This is because the measurement should be done as quickly as you can after the machine unit is shut down. This does not mean that you have to be working in an unsafe manner. It does mean that it should be well planned and that all safety requirements are followed in a controlled manner. Yes, the machine will be hot so care does have to be taken – but as maintenance professionals, it’s what we do! I would like to make note that before this type of work is attempted, it should be reviewed by a safety committee so that all are aware of the requirements, procedures, etc.

Again, doing a hot alignment is not an exact science because there are many variables. I know some companies who will do one as soon as the machines are at operating temperature, then do another a day later just to confirm. For instance, thermal changes in gearboxes can be very difficult to calculate. Many large gearboxes will grow in the horizontal plane as well as the vertical plane. So a hot alignment would be seen as the best way to do this work. This article is intended to give you some idea of thermal growth and some simple ways on how to measure it, graph it and understand some of the major factors contributing to it ie. pipe strain.  It was written to bring a better awareness of this issue and how using some simple tips such as where to take proper temperature measurements while using an average and taking note of OEM guides, can help in the overall alignment process. These are things that we don’t often consider. Its not written to cover some of the more complex challenges that exist on some machines with very high operating temperature. One would expect that the machine manufacturer would have a documented procedure for such a machine. And if not, laser real time measurement would be taken in order to see the actual machine movement.

Understanding Thermal Growth in Your Rotating Machinery – Part 2

In the first part of this article (click here for Understanding Thermal Growth in Your Rotating Machinery – Part 1), we defined what thermal growth in machines is. We used an example of a machine growing equal amounts in the vertical direction. The fix was to lift or lower the machine of choice by a total of 5 thou (0.005“) to compensate for the growth offset. To reiterate this example a little further see below the temperature readings we took on a motor running at approx. 1800 rpm. The first reading (PHOTO – below) the front foot is 51° C and the next reading (PHOTO – below) the back foot is 38° C.

To calculate the growth based on the temperature in the picture we need to know three things and multiply them: the change in Temperature (T), the length of material we are measuring (L) and the coefficient of thermal expansion of the material (C). For more information on why these three things, go to Part 1 of this article.

To find the temperature change, we first transform from Celsius to Fahrenheit so that we can use the same formula we started with in Part 1 of this article. 51° C becomes approx. 124° F and 38° C becomes approx. 100° F. Next, we take away the ambient temperature, which we know is 73° F. This gives us a temperature change of 51° F (124° F – 73° F = 51° F) at the front foot and  27° F (100° F – 73° F = 27° F) at the back foot – both of which are small amounts.

The length (height) of the section we are measuring – from the foot bolt to the centre of the shaft is 12 inches.

It is important we know what the material we are working with is. In this case, it is mild steel. The coefficient of mild steel is 0.0000063 (inch/° F).

We then plug our numbers into the Thermal Growth formula for each foot starting with the front foot (FF):

FF = T x L x C

= 51° F x 12” x 0.0000063 (“/° F)

= 0.003” (3 thou)

We do the same for the back foot (BF) and we get 0.002” (2 thou) which is not a lot.

A 0.001” (1 thou) difference across the distance between the feet is not an issue at all. The 0.003” (3 thou) in growth at the front feet could be an issue if the motor was running at high speed, but it is not, so we are good to go.

Machines can move and grow in equal amounts as we have just seen in this example, but more commonly, they move in unequal amounts. This can be more of a concern because now we are adding angle to the offset. So let’s look at what angle can do to the machines alignment.

How Machines Grow in Unequal Amounts

There are other issues that make machines move. For instance, the sheer torque at start up from the driver (ie. motor) to the driven machine, if either machine is not secured properly or the base is inadequate or flexible, can result in one or both of the machines to move. Even the power/force of liquids or air being forced though piping or duct work can make machines move – especially at start up. More often than not however, it’s because of temperature changes from ambient temperature when off line to operating temperature when online (running) – known as Offline To Running (OLTR or OL2R).

(PHOTO – Above) If you see paint blistering on pipe work, it’s more than likely because the product is very hot.

Now remember, machines may not always move (grow) in equal amounts so when considering if thermal growth is an issue for you, you have to be aware of different temperature readings from the machines you are working on. Have a good look at the machines you are working with. Think of an electric motor.  Many may have a cooling fan at the outboard end but nothing at the inboard end. Does that mean its cooler on the outboard end? Also, the inboard end is where the transfer of torque occurs at the coupling and there may be some heat transfer from the machine that’s being driven. Does this mean the inboard end will run hotter?

Recently a customer who works in the mechanical reliability group of his company asked me to have a look at some results from an alignment job. He had gone over it numerous times and confirmed that the numbers were in fact correct. However, he wanted us to review it and give an explanation of the corrections at the machines feet so he could pass it on to his technicians. He writes:

Our technicians recently did an alignment on a motor and centrifugal air compressor.  They were using an E420 laser alignment unit and got results of -1.0 thou offset and -0.5 thou/inch angular in the vertical plane.  The display was saying that the motors feet corrections were -10 thou low in the front and -29 thou low in the rear. Could you please take a look at these numbers and let me know if they make sense to you?  Also, if the final values are within tolerance, why does the alignment instrument show corrections?  Are they just to show us what we’d have to do to get the final values to zero?

He had included a photo of a basic diagram in his e-mail which is great because I’m a visual type person and like to see the problem. It had the misalignment at the coupling values (offset & angle), the feet corrections and the laser units and machines feet distances.

Well the answer is quite simple: we measure misalignment at the centre of the coupling and make the corrections at the machines feet. If you look at his picture diagram of the motor, the corrections at the feet are negative numbers meaning the motor is sitting low – so they have to add shim. Do they need to do a correction? No, the important numbers – which are the results at the coupling – are good. -1 thou (0.001“) of offset and -0.5 thou (0.0005“) per inch of angle is very good for this RPM.

If we constructed a graph based on the information given including distance between machine feet and the distance between the centre of the coupling to the front feet, we can then verify the results and his assessment of the alignment. The graph is to scale with the distance between each light blue line representing 2 inches and the distance between the heavy blue lines representing 10 inches – both going across the graph horizontally. In the vertical axis we have the distance between each light blue line representing 2 thou (0.002”) and the distance between the heavy blue lines representing 10 thou (0.010”). We can see that the projected centerline of the motors rotating shaft is in fact -1 thou low. And we can also see the angle is -0.5 thou per inch (see graph below).

It’s the angle, although small at the coupling, measured over a large distance that leaves a large number still at the foot. Under normal circumstances you do not have to correct this. However, this is where the plot thickens as they say.

It should be said that all the above is all based on measurement taken when the machine is down and at an offline temperature. It turns out that when they had started the machine, which did start well, after a few hours the vibration levels increased so they shut it down correctly suspecting thermal growth.

 

The compressor (Compr) runs at 150° F with the normal (ambient) temperature of 70° F – a difference of 80° F. This change in temperature (T) is multiplied by the length (L) from the foot bolt to the centre of the shaft – 25.5 inches – and then by the coefficient of mild steel, which is 0.0000063 (inch/° F). This works out to a thermal growth of 0.0128” – almost 13 thou.

Compr    = T x L x C

= 80° F x 25.5” x 0.0000063 (“/° F)

= 0.0128” (13 thou)

Once we know what the growth is the rest is easy. We simply make the corrections based on the projected position of the shaft which we can draw. Based on this, you may think you just have to add 13 thou to the driver (motor) so that when the driven (compressor) machine heats up, everything will be aligned and in many cases that is true.

However, the plot thickens again with the reliability group doing some more investigating. They found that there is a cooling system on the back of the compressor with an operating temperature of 70° F. In fact, you can put your hand on the back end and keep it there but you cannot do this at the front. This means it will grow at an angle.

To see this visually, on our graph (below) we add the distance from the centre of the coupling to the compressors front foot (16 inches) and the distance between the machines feet (49 inches). We can drop in the lines which represent the planes of the feet and plot the point 13 thou high as the growth is positive. We then place the shaft over the plotted points of the compressor and we can now see the projected position of the shaft when it’s in operation. You can also see that there is a lot of misalignment when it is running.

The goal is to have the machines shaft in line at operating temperature. As you can see, one way to do this is to add 32 thou to the motor front foot and 63 thou to the back.

So although the customers’ initial results were in tolerance for offline temperatures, the direction was pointing up which was the complete opposite of what it should be when you factor in the thermal growth of the compressor. It needs to be high and pointing down as you can see in the graph.

We measure thermal growth in the planes of the machines feet – from the base to the centre of the shaft (as depicted by the yellow arrows in the image below). If they are both the same the fix is quite simple; we simply lift or lower the chosen machine by the calculated amount. However, this is not always the case as machines grow at different amounts. If the outboard is hotter than the inboard, the shaft centre will be pointing down. If the inboard is hotter than the outboard, the shaft is pointing up.

 

This is important to know as even a small amount of angle can prove to be a big issue over a larger distance. Before you start your alignment work you need to know how much thermal growth is expected and in which direction. Look out for Part 3 of this article where we wrap up Understanding Thermal Growth.

For Part 3 of this article, click here.

Understanding Thermal Growth in Your Rotating Machinery – Part 1

Thermal growth is an issue that is very much ignored because many think it too complicated to calculate and compensate for. Some are even unaware that it is an important issue that should be considered. So our aim is to address this issue and hopefully simplify it so that it can be measured and compensated for on a more regular basis. We will do this over a three-part article – Part Two and Three will follow in the New Year. So excuse the pun but we want thermal growth to be the hot issue in 2016!

Fig.1 An example of how hot liquids in the piping could pull the pump up, creating a twist or bent base frame as well as a misalignment between the shafts of the pump and motor.

 

As you know when something gets hot, it gets bigger; it expands. It happens to most things or materials but in this case we are only interested in metal, specifically iron, so that’s what we will work with. The coefficient of linear thermal expansion (C) is what is used to explain this expansion of material. For cast iron, it is 0.0000059” per degree F. Looks like a small amount but it can add up – let me explain.

 

Material Coefficient of Linear Thermal Expansion (C) (inch/ ° F)
Aluminum 0.0000126
Bronze 0.0000101
Cast Iron 0.0000059
Copper 0.0000092
Mild Steel 0.0000063
Stainless Steel 0.0000074

Fig 2.  Common materials that would be used in the industry for rotating machinery and their known coefficient of linear thermal expansion (C) values.

 

The coefficient of the material (metal) to be measured is one of three things you need to know. The other two is how long the length of iron is and how hot it’s going to get. Let’s say it’s 12 inches long and will be heated to 100° F. Now, without writing out what looks like a complicated formula or equation in some textbooks, do this:

Take 0.0000059” (C) and multiply it by 12” (the length) and you get 0.00007”. Now multiply that by 100 (the temperature) and you should have 0.007” thou (or 7.0 mils). Put simple, that length of cast iron will grow 7 thou (7.0 mils) if you heat it to 100° F.

That’s it – that’s thermal growth. Now apply it to your application. Let’s say you have a compressor that has a cast iron housing. The only area of this machine that we are interested in is in the plane of the machines feet. Imagine a line going up from the foot bolt through the machine but it stops at the center of the shaft. This is the length of the piece we want to measure. The reason is when this area grows and tries to move down it cannot because of the base, so it moves up and lifts the shaft. Anything above the shaft center line has room to grow so we do not care about this. The height from the base to the center of the shaft is 12 inches.

Now we take temperature measurements in the planes of the machines feet. The ambient (normal) temperature is 70° F and that’s what the motor is running at. So no thermal growth. The compressor is operating at 140° F so we have growth. What we need to know is the temperature change from normal (ambient) to running So, 140° F running less 70° F offline (140 – 70 = 70).  So our temperature change is 70° Fahrenheit. This is known as offline to running (OLTR) temperature.

This means that the compressor will rise (or grow) 0.0049” – almost 5 thou (5.0 mils) – because 0.0000059” (C) X 12” (L) = 0.00007”. Now multiply 0.00007” by 70° (T) and you get 0.0049” (see Note 1 for a simple and common equation used in the industry).

To correct this is easy. You can put 5 thou (5.0 mils) under each of the four motor mounting feet so that as the compressor grows it will align the shaft centerlines. The other option is to set the compressor low by 5 thou (5.0 mils) – your choice.

This is just one simple example and the start of the thermal growth discussion that we can have. We would be happy to answer any questions you may have on the subject or even comment on information that you can send us so we can help you with this issue. Our goal is to make it simple at the start so we can all move forward together. Keep an eye out for Part 2 and 3 of Understanding Thermal Growth in Your Rotating Machinery where we will introduce other factors that can affect Thermal Growth.

 

Note 1: The formula or equation that is often used when calculating for thermal growth is T x L x C.

T = the temperature change of the material in Fahrenheit

L = the length in inches of the material

C = the coefficient of linear thermal expansion

For Part 2 of this article, click here.

Getting the Right Angle in Shaft Alignment

Getting the right angle can pull you out of a jam.

When we think of shaft alignment we usually think of one machine being the stationary and the other machine being the moveable. The normal preference is to use the driven (ie. pump) as the stationary and the driver (ie. motor) as the moveable. The reason behind this is that you don’t want to create pipe strain by moving the pump. Makes sense right? For some who don’t think beyond this, it limits their options. The reality is that you can move either machine and in fact, in the case of say, a diesel engine that is driving a generator, it’s the driven that is normally chosen to be the movable. However, very often moving a combination of both machines will give you the best option with the least amount of correction.

During our three day MAAD Training Machinery Installation program we can demonstrate this combination move during the reverse-dial indicator shaft alignment section.  MAAD is an acronym for Measure, Analyze, Act and Document and that is the process we promote during the training. This training covers it all from nuts and bolts to the geometric measurement of the base. We train participants in shaft alignment using dials and laser systems.

Currently, an organization that is taking the program had asked that we include both Rim and Face and Reverse Dial methods of shaft alignment as well as laser alignment which we accommodated.

One benefit of using the reverse-dial alignment procedure is that we can use the graphical method to calculate the necessary machine corrections. The graph is a pictorial view of the machines shafts which is to scale.

If we set up a graph and draw the machines shaft and leave out the dial plotting points you would have something like this below. The black solid lines represent each of the machines shafts plotted from the dial indicator readings (not shown). The red lines represent the plane of the machines feet (the adjustment points). The dashed line is a target line for traditional alignment graphing/plotting.
We are showing the vertical plane only and the scale we are using is such that going across the page each small box is equal to 1 inch. Moving up and down, each small box is equal to 0.001 inch (1 thou).

The stationary machine is on the left and as you can see we have 16 inches between the feet. It is drawn in the traditional manor as sitting in a level plane.

The moveable machine is on the right and its position is based on the dial reading taken from each shaft. However, for simplicity we are not showing the plotting points. You can see we have 18 inches between the machines feet and the shaft is low at foot 3 (F3) but high at foot 4 (F4).

Now imagine that we are base bound – a common problem in the real-world. There is no shim under the back feet (F4) and based on this graph, it is telling us that we must lower the back feet by 10 thou. The problem is, however that we cannot lower the machine if there is no shim to take out.

So we have measured the misalignment and now we can use the graph to help analyze the base bound issue. Remember the goal is simply to have these two shaft as one. We need to move one or both to be opposite to each other, in line, the technical term is collinear. To be inline in both horizontal and vertical planes.

Because of the base bound issue, the traditional option is to lift the stationary machine up by equal amounts to be higher than the moveable machine – in this case above 0.010 inch (thou) which is the high point. You would then readjust the movable machine into alignment. However, this is a lot of work and you will be fighting the pipe if the stationary machine is a pump so you are better looking for an alternative option.

The fact is that there is more than just one option. The stationary/moveable method means that the stationary feet are “locked”, and usually fixed in position. However, you can choose which feet to “lock” in any combination so you can achieve your goal of collinear shafts. To see this on our graph we can draw a (green) line from one outbound foot to the other (Foot 1 to Foot 4). We draw the line through the point where the shaft intersects the foot plane. This green line is now our target line.

Now if we view these outbound feet to be the locked pair we can see that in order to achieve our alignment we will have to move the inbound feet up. In this case the Driven (stationary) has to go up 0.003 inch (3 thou) at Foot 2 and the Driver (moveable) has to go up 0.010 inch (10 thou) at Foot 3. Now that’s a lot less work than the first option and it gets you out of the base bound issue.

Now can this move cause other issues? The answer is yes it can but let’s continue with the analysis before we make the move. We can see that the front foot of the pump has to go up 0.003 inch (3 thou). If we want to find out how much of an angle we will be introducing by lifting the pump/pipe flange up we will use the rise over run principle. If we divide 3 thou by the distance between the machines feet (16 inches) we get 0.1875 per inch of angle that we will be introducing to this machine. If we multiply that by the distance across the pipe flange, which is let’s say 7 inches, we would be lifting it up 0.0013 inch (1.3 thou) which is very little indeed. Once we are satisfied with our analysis stage, we take action and make the move. But this is only one option – if we draw our line from Foot 2 through to Foot 4 we could tilt the pipe flange down instead.

The point is that you have options when moving machine units and very often a small amount of angle can make a big difference. You need to be able to see and understand this when you analyze the results of your measurement.  Understanding dial indicator shaft alignment methods as well as graphing or plotting helps you see the whole view – the bigger picture. This is why organizations like the American Petroleum Institute (API), who have produced their own pump and motor installation standards, highly recommend that tradesmen who use laser systems to align shafts be fully conversant with dial alignment methods.

Now a good laser system will give you different bolt bound and base bound options such as these examples below.

Above, we lock the inbound feet of the stationary (pump) and the inbound feet of the moveable (motor) in the vertical plane. If we were base bound, this would be a good option because we can add shim.

Above, we lock the outbound feet of the stationary (pump) and the outbound feet of the moveable (motor) in the vertical plane. If we were base-bound, this would not be a good option because it’s asking us to take shim out, and there is no shim to take out.

Above, we lock the outbound feet of the stationary (pump) and the inbound feet of the moveable (motor) in the vertical plane.

If you look at the different options you can see the amount of angle you are introducing to the machines – in this case, 1.5 thou per inch with each option. Multiply this by 7 inches (distance of pipe flange face) and you get 0.0105 inch. Yes 10.5 thou – can the pipe handle that much? The way to find out is to measure it and with this style of laser you can actually measure the effects of pipe strain but I will save that for another article.

Remember, the optimum move is the one that meets your needs the best but if we were base bound, option 1 would work the best.

Finally, documentation is a basic requirement for a machines history file. It is also being strongly requested by companies after an alignment is finished. So don’t short change the job. Finish it off by capturing this important information and don’t forget to include your graphs in the documentation and report section.

Alignment Problems: Dancing with a Soft Foot

Alignment of machinery is critical in plant operations, and soft foot conditions are especially troublesome. Here’s how various alignment systems can help.

You would probably think it foolish to have work done on the front end of your car and not have the alignment checked and if necessary adjusted. If the front end is out of alignment the car would start to vibrate, sometimes excessively, right up the steering column into your hands. This would undoubtedly put greater stress on the front suspension and steering, causing expensive damage. You will see this most of all in the tires. You can go through a set of tires pretty quickly when the front end is out of alignment. In addition, your fuel usage will increase because of the extra power required to push that misaligned car around.

You would not knowingly leave your car in a misaligned condition because you know what the consequences will be. Yet machinery is installed and left in a misaligned condition on a regular basis throughout all of North America’s industries.

When most maintenance personnel think about misalignment they think of shaft-to-shaft alignment such as an arrangement with two separate shafts and a flexible coupling. But it’s much more than that. I see misalignment in chains and sprockets, V-belts, pulleys, cylinders, and shafts of coupled driven machines. The reasons for this misalignment are: a lack of knowledge, a lack of tools (instruments), and in some cases a perceived lack of time in which to do the job. However, the cost of all this misalignment is in the billions of dollars.

For now, let us concentrate on shaft-to-shaft misalignment. To get a better understanding of the problem, visualize how many pieces of coupled driven machine units (pumps, compressors, etc.) there are in the industrial area that you work in. The number would be quite high. Can you imagine how many there are in a huge industrial area like the Great Lakes Region of North America, for example?

Now consider the following: The SKF Bearing Maintenance Handbook states “Investigations made in the U.S.A. have shown that misalignment can be traced as the cause of 50% of the breakdown in rotating machinery,” and “A 20% load increase from misalignment reduces the calculated bearing life by almost 50%.”

The initial installation of a piece of equipment has to be done right. The alignment of the shafts (or their misalignment) will have a big influence on the life of the machine. Strangely enough, if the machine goes down after 10 months of operation for a motor bearing or pump seal failure, the alignment is seldom questioned. It is usually equated to a bad bearing, or a poorly installed seal.

Maintenance people often say that couplings can handle a lot of misalignment, or that since a machine runs very slowly, they need not be concerned with alignment. I don’t buy that argument! Even with the most forgiving coupling, the constant flexing back and forth of a misaligned shaft causes forces to be transmitted back through the shafts and bearings. These forces can drastically reduce the life expectancy of shafts, bearings and couplings. Coupling manufacturers generally do not try to mislead you about the capability of their couplings. They simply point out that one of the benefits of their couplings is that they have a high tolerance to misalignment. However, to them, shafts, bearings and seals are someone else’s problem.

The Soft Foot Problem

There is more involved in effective machinery maintenance than just shaft misalignment. Soft foot is also a major problem that results in premature machinery failure. Soft foot is a condition that occurs when the mounting feet on the machine do not lie in the same plane as the base to which they are bolted. Soft foot not only makes it impossible to align the shaft, but also causes misalignment internally within the machine.

This problem occurs not only in coupled driven machines, but can also be found in many other pieces of equipment, such as chain and belt driven machine units, air motors, cylinders, gearboxes, etc. In a discussion I had with an engineer from Timken Bearings, he said they would like to see internal misalignment down to 0.001 in., and he wasn’t joking. You can spend a lot of time finding and correcting soft foot, but it can be frustrating because you can create soft foot just as easily as you can correct it. However, the effort to correct it is time well spent. There is much more that can be discussed on this subject, but for now let us say that the problem mainly is one of poor machinery installation practices.

To demonstrate some of the poor installation practices, let us consider the installation of a belt driven machine unit. The machines are moved into position and the sheaves are installed loosely on the shafts. The mechanic roughly aligns the sheaves and then tightens them on to the taper lock bushings. To align the sheaves, a straight edge, or quite commonly a piece of string, is used to align the four edges of the sheaves. Then the belts are installed and adjusted to the correct tension. After a quick re-check the job is considered finished.

Now consider this. The frame that this machine unit sits on is probably bolted to the floor, and because the floor probably is not level, the frame will take on the same contour as the floor. If you bolt the machine to a twisted frame you will distort the machine’s casing as well. In most cases the bearings which support the shaft inside the machine have extremely close clearances, and the distortion in the casing can result in the reduction or removal of these clearances. Therefore, a soft foot correction should be done.

Another common problem can occur when tightening the taper lock. If you tighten one side slightly more then the other, it will skew the sheave. This causes the drive to shimmy when rotated and to vibrate axially along the shaft, hammering at the supporting bearings. The belts may be able to withstand these forces, but what about the rest of the equipment? To avoid this problem, a simple dial indicator should be used to check the run-out. A complete discussion of the proper alignment and belt tension is best left for another article, but note that there are low-cost instruments on the market today that will do a much better job than the string or straight edge–and do it faster.

One of the constant themes in vogue these days is “doing it right the first time.” Rework, repair, or replacement is very expensive, not only in dollars but in time, especially lost production time. What you need, to do the job right, is the right attitude. You need to be committed to the belief that “I will get the full life expectancy from all of our equipment.” Once you are committed to this belief, the majority of the instruments, tools and training you choose will be aimed at prevention. The primary focus will no longer be predicting the time of failure so that you can do a breakdown analysis. Your goal will be to prevent failure.

At a minimum standard, you should have the knowledge (training) of complete installation procedures, including shaft-to-shaft alignment. Even if you choose to have someone else do the work, such as a hired contractor, either you or someone on your staff should be able to verify that the work has been done correctly the first time.

Defining your requirements and goals for your machinery installation should be your starting point. Once you know what it is that you want to achieve, you can buy the right tools or training for the job. For instance, there is not much point in buying a dial set that will only allow you to do rim and face alignment, when for many pieces of equipment the reverse dial procedure is the one that is recommended. You may want to consider a laser alignment system, and if so you will want to make certain that you choose the system which best suits your requirements.

Student Millwrights: Why not hire one for the summer?

Summer is upon us and hopefully the livin’ is easy! For some in the mechanical maintenance world the summer time is a slow time; for others, it’s go go go. For instance, in cement plants they have their maintenance shut down in the winter months when it’s slow because their summer is full steam ahead for production. No matter what industry you’re in, one of your pressing problems is making sure that you have adequate maintenance coverage or man-power over the vacation period. You need the coverage because break downs can happen and do happen when least expected. And how are your staffing levels going into the summer? Most companies I see are still very lean and mean and could actually add one or two new staff members. However, this is deferred. Why? Well because it’s the summer and someone said lets hold off until the fall to get the extra bodies!

So if you are in maintenance supervision you could be in the juggling mode right about now. And if something does go down when you are short staffed you can always use the local union hall such as the Millwright Regional Council of Ontario who always provide great cover. I know because back in my time as a supervisor I used them a lot. But for your everyday requirements, have you thought about a summer student? Not just any student but one who is training to become a Millwright when his/her college days are through?

This is a great benefit for you because these kids come with a lot of shop knowledge already. They have a better understanding of safety which as we all know is one of the big concerns when hiring students. The greatest benefit is that it’s a Win-Win for both parties. Let’s face it, quite often you just need an extra pair of hands to work with one of your tradesmen but one who knows hand tools, hardware, etc. This means if you send him/her to the shop, they come back with the right parts. You also get to observe them on the job because this may be someone you want to hire as an apprentice in the future. In fact, you may want more than one if you look at the average age of your current staff. And for the student, they receive the work experience they need in their chosen career. A Win-Win.

I recently joined the Program Advisory Committee for the Mechanical Technician – Mechanical Maintenance and Control Program at Durham College. It was an honor to be asked because to me it’s a prestigious committee which is chaired by Chris Tozer of Ontario Power Generation (OPG). OPG as we all know is a community supportive company as is the Millwright Regional Council of Ontario, Local 2309, represented on the committee by Drew Chittenden. Both of these organizations also have a vested interest in making sure that we have a steady supply of quality tradesmen and women that can help grow Canadian industries. Which looks like another Win-Win. Will your organization be needing millwrights/maintenance mechanics in the future?

Durham College has one of the best training facilities that I have seen and is matched by the quality of their training instructors. Their machine shop is very well tooled as is their workshop which has received many donations of actual pumps and motor sets so that the students get to work in real world applications. Money as you can imagine is always tight but when available they invest in some top end equipment. For instance, they have a full precision Laser based geometric measurement system that can measure straightness, flatness, square, plumb, level and parallel (see photo below). They also use optical equipment, such as an optical level and jig transit to take similar measurements giving the student an understanding of old and new technologies. But the bottom line at this college is they offer one, if not the best millwright apprenticeship and pre-apprenticeship programs in Ontario.

Perhaps it’s time to look into a Win-Win situation for your maintenance department this summer?

Get MAAD about Maintenance!

How getting a little MAAD can help you with your Maintenance Processes

Most of us have heard enough about Reactive, Preventive, and Predictive Maintenance practices. Well how about Insane Maintenance? Yes that’s right, Insane Maintenance. You see, a definition of insanity is “to do the same thing over and over and to expect a different result”. If you think about it, do we – in the maintenance world – repair equipment only to have it breakdown again and again? How many bearings will be replaced this year in say an industrial area such as Fort McMurray Alberta – the center of Canada’s oil? Or say Sarnia Ontario, known as the chemical valley?  To be honest, I don’t know but an educated guess would be in the millions. This can be surprising to some because it is said that a bearings life is infinite as long as you can keep lubricant between the ball and the race. Belts, sheaves, chains, and sprockets have a life span so we expect to replace them. However, most do not reach their full life expectancy. Bearings, on the other hand, should last a long, long time – but they don’t. The reason they don’t is because of the static and dynamic stress that they have to operate under.

This is the first of many articles that will be published through our newsletter and website that we hope will be of interest to you and will help you find the causes of these stresses. We will also provide some simple condition monitoring tips to help you through your maintenance processes. You see, in order to stop doing the same thing over and over we have to change the process. Sort of like trying to lose weight; it’s a lifestyle change one has to make. Some call it Precision Maintenance but it basically means “Doing the job right and to a tolerance”. Yes, you will have to get better at break-down analysis but hopefully not as many times as before.

Now I don’t think maintenance is anything one should be crazy about but I would like to suggest that you get MAAD about it. MAAD stands for Measure, Analyze, Action and Document. This is something you should be doing throughout your condition monitoring program and when you are installing a machine. Actually, you can do this for any measurement that is important to you. We have gone as far as changing the name of our training program to MAAD (see below our first MAAD Training session on the road in Timmins, ON) as well as our brand new to MAAD Maintenance newsletter (click here to subscribe).

The following is an example of how we would use the MAAD process to do a shaft to shaft alignment. Now normally on a machine installation we would start with base measurements but for now we will focus briefly on the shafts just to give you the idea of the MAAD process.

Measurement. What’s important? Obviously accuracy for one. This means it has to be quantifiable (a known measure) seen by all. It also has to be repeatable. We all know about “measure twice and cut once.” Well it’s the same in this case. If the results are not repeatable you don’t have a good measurement. And why stop at two? There is nothing wrong with taking three readings to make sure that you have correct results. Repeatability is very important and this reading should be recorded as an “as found” (AF) result. Remember, to control a process you have to measure something but is has to be accurate and repeatable.

Analyze. The analysis section starts when you have the AF result, it’s seeing what you have and planning the optimum move for machine units. You may look at previous documentation (the machines history), temperature readings for thermal growth considerations, vibration data and so on. You ask the question, can the correction be done? Do we have the means? And of course the answer may be simple that yes you’re good to go.

Action. Now you should have a plan and the action is to implement that plan. Even if it’s to do nothing, that in itself is an action. However, if you are moving the machine, it has to be a controlled move using jacking bolts – not hitting the machine with a mallet (or something worse). Now let’s say you come up with a problem such as being bolt-bound, which may mean you have to go back to the Analysis stage. If you are using dials to align, you may have to graph it to see your options or if you are using a laser, you can use the bolt/base bound options to get around the problem.

Documentation, if done right, has been going on through the whole process. This is a very valuable record that should be added to the machines history. Why is it valuable? Well because in order to move forward it is said we must look at our history. Which means to improve your maintenance process you need to look at the documented data in the machines history file.

Soft Product, Harsh Conditions

In my business of providing alignment services, I get to see and work in a lot of harsh environments. In the past, I have written about doing this work in cement plants, which I think are some of the toughest because not only does the cement dust plug up the machines, it’s so abrasive that it wears them out quickly. Recently, I calibrated a laser system that had been used for a long time in a coke plant at a steel mill and I was reminded of just how harsh and very dirty these facilities are. Another example is a plant that makes a nice soft product – but the environment is anything but – it’s a tissue mill. Can you imagine how much nice, soft tissue is used in North America per day? Per hour? Tons! It’s a large industry. In one of the tissue plants I am working in currently, you could see some of the tissue or pulp floating in the air. It would get into every corner of the plant – including the machines. The motors would draw it in, adding a layer of insulation they did not need. Unseen components of this harsh environment are the chemicals used in the process. They attack the motors by adding a coating that degrades them – and all the machines over time. The main machine in the plant we are working on now is called a Yankee Dryer. Imagine a large drum as big as a living room that is heated by steam and is spinning. The wet pulp is sprayed onto the drum as it rotates and the steam heat dries the pulp and creates the tissue. The operators can control the density (the thickness) of the tissue by adjusting the speed of the dryer. This dryer had a higher than normal vibration at different speeds, so Steve Cameron of Advanced Balancing had made the call that the drive shafts needed to be aligned. My company went in to support the alignment work.

This Yankee Dryer was driven by two separate motors that drive a single gearbox, which in turn drives the dryer. The connecting drive shafts are universal jointed shafts (also known as Cardan shafts). The shafts are designed to compensate for offset misalignment. With offset, the shaft will run in an angled position (it will be slanted), but the shaft will compensate for the offset (up and down or left to right). However, the two connecting flange faces, one on the motor and the other on the gearbox, have to be parallel with each other in both the vertical and horizontal plane. Yes, they can be offset with each other, but if there is any angle involved, they will move in the axial plane and vibrate if running at speed. In essence, the shaft is opening and closing along its length as it rotates. These shafts have a splined slip assembly to compensate for this movement. It works at very low rpm (even so, it will still wear out), but at higher speeds it will vibrate and eventually damage the motor, shaft and gearbox. The solution is easy: align the flange faces. Most good laser systems provide Cardan (universal joint) shaft alignment programs. In this case, we used an Easy-Laser E710 with specially ground, flat, anodized aluminum mounting brackets. These brackets were attached to the flange faces because that’s what we were aligning – not the outer edge. This meant that we had to remove the shaft (PHOTO – left), which was worth doing if we wanted to get it right. The dimensions and distances were input into the system. The heads were rotated after each measurement was taken and then we read the results live on the device’s display.

We made the vertical correction by shimming the moveable machine (in this case, the motor) at either the front or back feet. Then we adjusted horizontally at the front or back feet while watching the movement results live on the device’s screen. We only had to adjust the machines at one foot pairing because we were only correcting angular misalignment – not offset. The next day, after the shutdown was over and the Yankee Dryer had been restarted, there were some happy faces in the plant. Why? Because we had removed the high vibration level. This vibration had been restricting the speed of the dryer, so now that it was gone, the big bonus was that production could now speed up the process. This meant it has increased capacity and production output. In other words, the plant has more opportunity for more throughput, if it wants. This is a win-win scenario. The maintenance department increased the reliability of a machine unit and production added potential capacity.

One note of caution is to be observed when aligning universal jointed shafts. They are not designed to be perfectly in line. In fact, if they are aligned, they will damage the bearings in the joint. This is because they need a certain amount of misalignment to draw the lubricant through the bearing – the same way a gear coupling does. This happens more so in shafts that have needle rollers as opposed to the ball bearings used in many industrial applications — but don’t worry, as a small amount of offset will look after this. (If you have the need to have a shaft inline, you should be using a jack shaft.) There is also another winner – us. By doing the work correctly and working to the correct tolerances, we have achieved very good results that should prove to management that precision driven maintenance techniques should always be used.