Engineering and technical people often use technical phrases that sound complicated. Thermal growth is one of those terms. It sounds like it could be an engineering marvel – one that would help us perform complicated alignments of high temperature, high speed machines. So, here’s the “secret” of thermal growth.
When metal gets hotter, it gets bigger.
Just how big is based on three things:
It is calculated using the following formula:
C x ∆T x L = amount of thermal growth
Still sounding complicated? Try this comparison.
12 inches of these commonly used materials, heated to 100°F above room temperature, yields the following growth:
Cast Iron 0.007”
Mild Steel 0.008”
12 in. of cast iron, heated 100° over room temperature = 0.007”. But we have 24”, so:
0.007 x 2 (12 inches twice) = 0.014”.
It sounds right, but not so fast!
Thermal growth is not calculated by the fluid temperature, but by the pump casing temperature. That’s what’s holding the pump shaft up. And it almost never heats evenly from the bottom to the split line. So you must either:
Thermal growth is not always a factor in aligning machinery, but if your machine is:
thermal growth must be factored as part of the alignment process.
How do you determine thermal growth factors and how they should be used?