This concludes the three-part post regarding a reader’s question about machine maintenance…
What is the best method of measuring tie bar strain?
The most common method of measuring this is to follow the procedures of measuring parallelism as discussed in the previous post on measuring platen parallelism. The difference between the parallelism before and after clamping will give you important information regarding the change under strain. For instance, if the platens are parallel before clamping, but they are out of parallelism after clamping, the change indicates the amount of additional strain in a particular tie bar
When possible, you should try to measure the stretch using a ultrasonic strain gauges. These use sensors at each end of the tie bar which measure the actual stretch of the tie bar during mold clamping. This is much more accurate since it can measure the actual stretch of each tie bar.