MAAD blog

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.

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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.

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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.

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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. However, many machinery manufacturers (for example, a Heat Pump Manufacturer) have to be aware of and take thermal growth into consideration when manufacturing such machines for home and commercial use. 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!

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