Mold Maintenance & Repair

OCT 2014

Mold Maintenance & Repair

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October 2014 5 If you have already implemented a control system and checked the grounding for the thermocouple, but still believe there may be a discrepancy between the temperatures dis- played and the actual temperature, do a manual check. It is possible that the computers are misrepresenting data for one reason or another. To do such a manual check, connect a handheld pyrometer electrically in parallel to the same thermocouple to see if it shows the same tem- perature as the control. 4. Check heater ohm readings. On new hot runner systems, make a record of all the ohm readings for the heaters, then check those read- ings again during maintenance of the tool. Any reading higher or lower than baseline usually indicates an impending failure. While the tool is down for preventive maintenance, you may want to change those heaters. In most cases, front-loaded heaters can be changed out in the press. If you have to disassemble the hot runner to change nozzle heaters and the tool is already out of the press, you'll prevent a lot of down- time if you just change the heater immediately. 5. Cycle new heaters three times before use. When you install a new heater, test it on the bench before trusting it. If a brand new heater is going to fail, it usually does so on one of the frst three starts. So start it up, cool it down and repeat two more times before giving the mold a clean bill of health. This practice also bakes out damaging moisture. 6. Ensure machine settings match material specifcations. Material gas-off during molding is commonly caused by machines that are not set to the material manufacturer's recommen- dations. The material, therefore, overheats, causing hot runner problems. Materials often have so many additives that no one can know all the correct machine set- tings and critical material gas-off temperatures without the documentation. Previous jobs that Images courtesy of DME Co. Don't let this happen to you: Leaking nozzles are a common and messy problem that comes from improper setup and operation.

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