Shaft Alignment Basics Thermal Growth

[Music] thermal growth is the amount of the centerline's of a machine change both vertically and horizontally due to temperature changes this occurs because as the temperature of the machine Rises the metal expands it is important to note that the alignment of the machine can change from when it is offline to when it is running at its operating temperature during the shaft alignment process this change in temperature will need to be accounted for otherwise misalignment will occur in order to calculate thermal growth there are three pieces of information that we need to know one the differential temperature of the material being treated delta T to the linear dimension of the material being calculated health and three the coefficient of linear thermal expansion see these three elements are multiplied in the following equation delta T times L times C this is equal to the amount of thermal growth in the machine in order to find the coefficient of linear thermal expansion for common types of machine metals refer to the following chart thermal growth is not calculated by the fluid temperature it is calculated by the pump casing temperature which is holding the pump shaft up it almost never heats evenly from the bottom to the split line in order to calculate this temperature you must make an estimated calculation of the thermal growth by sampling the temperature in several places in getting an average temperature use the hot check function on your laser alignment tool if available to get a comparison between the hot and cold alignment values use a dynamic measuring process such as fixture lasers o L to R offline to running system to get an extremely accurate measurement of thermal growth which would also include dynamic factors such as piping changes lastly in order to check the linear dimension of the material being calculated L you need to measure the distance to the shaft centerline in inches thermal growth is not always a factor in aligning machinery but if your machine is large hot fast or must be aligned to a very close tolerance thermal growth must be factored in as a part of the alignment process [Music] you