Many process technicians and engineers have not been taught the fundamentals when it comes to basic troubleshooting. What must be understood in the first place is what really causes defective parts to happen. Too often the wrong thing is blamed and troubleshooting activities start out improperly. The first place to look for defect causes is the machine, followed by the mold, the material, and the operator in that order. In fact, 60% of the time defects are caused by machine problems, 20% by tooling, 10% by material, and only 10% by the operator.

The next thing is to make only one change at a time, and allow 10 to 20 cycles between changes to allow the process to stabilize again. If a person makes 2, 3, 4, or more changes at once, the entire process can go out of control very shortly and this can result in complete havoc. If a single change does not correct the problem, re-set that parameter to where it was and wait another 10 cycles before making any other change. While this sounds like it may take forever to find the problem, the opposite is true. Once the cause is understood (by examining the machine, then the mold, then the material, then the operator) the solution will be determined within a few iterations.

Don't be too quick to blame the material. Most often, what appears to be a material problem is actually a machine problem in disguise. For instance loose heater band on the nozzle will cause an overheating of that zone which could result in splay or burning. This may appear to be from material that is not dry or contaminated. But a change in material will only prolong the problem and result in running a great deal of scrap or purgings. If you understand that the machine is probably the culprit 6 out of 10 times, it will be easier to spot the loose heater band because you will be looking for machine problems, not material problems.

And finally, at least in this shortened version of training, the process person must understand the basic structure of the plastic material being molded. This includes information as to whether it is amorphous or crystalline; the intended shrinkage factor, recommended melt temperature, and recommended mold temperature. Proper machine size, water turbulence, and residence time are also major items that need to be considered.

We hope these thoughts help you. For additional help, you can order our Troubleshooting For Injection Molders at www.iplas.com in the Catalog section. It addresses the 24 most common defects, what causes them, and how to correct them.

This is a controversial subject. If you ask 5 different molders, you'll get 6 different answers. At TPT we don't prefer either time or distance, but rather, pressure.

Controlling the fill by monitoring pressure allows you to ensure that all the cavities FINISH filling at the same time. This is what balanced systems are all about. This monitoring can be accomplished with pressure transducers placed in each (or at least one) cavity, or by readouts on the control panel. Either way is effective. Proper readings indicate that the cavity is being filled at the highest pressure NECESSARY. In addition, this should usually occur rapidly, so the fastest fill possible is also desirable.

Hope this helps you, Carl. Good luck! And keep those questions coming in folks. I love it.