Understanding Thermal Growth with John Lambert
In this episode, the thermal growth and the understanding of the phenomenon—how it occurs and how to prevent and calculate it—is being discussed by John Lambert. So, first of all, we have to know what actually the thermal growth is. The answer is simple. This phenomenon occurs when the rotating machines get hot due to the difference in temperature and they start to expand in every direction. As these machines are mostly metal so their thermal growth is explained by the coefficient of linear thermal expansion that is already known for many different materials.
Now what happens is that organizations don’t do the necessary calculations even though these are pretty simple. You can calculate it easily if you have the coefficient of thermal expansion of the material, to what temperature it is to be heated, and the length of material. Their product is what helps you to apply the calculations that you have made for thermal growth and help you prevent the thermal expansion in your machines. You should not think of it as a common issue because it can get critical if you do not address it properly. Measuring it not only makes your shaft alignment better, it also compensates for losses on a regular basis.
Next thing you should know is the temperature change in the machine. This can be calculated by the difference of normal temperature from the current or running temperature of your machine. This difference in the temperature is also known as offline to running temperature—or OLTR temperature. When you have calculated this temperature, you should be able to set the compressor—if it grows or anything—so that the shaft is aligned correctly as it is supposed to. You can also make some easy calculations by contacting the OEMs and that is always the first place to start.
If you don’t do all of this, your equipment is going to fail due to a variety of reasons that stress on your machine causes in the components like ceilings, bearings, shafts etc. There could be other reasons for failure in the machines as well like torque issues, liquid power issues and so on but when there are two machines kept at the same temperature then they are always fine unless there is a difference between the temperature when they are offline and then go to the operating condition after the start up movements.
Thermal growth basically starts with a small angle movement and causes some serious damage in the longer distances. So, take the temperature readings from the machine you are working on and make sure that there is not even a little movement because machines don’t always grow in equal amounts. The corrections are always made in the planes of the machines’ feet and that is from the base to the center of the shaft. Whether it is a hot alignment check while you are setting it up or during alignment work, always take thermal growth in every direction into the account.
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