way to record accurate, controlled measurements. Temperatures should be measured in various areas of the cavitation, runner, bushing and hot drop areas. A good way to record this data is to take a picture of the mold faces themselves, then record the temperature data defining the correct positioning of the temperature probe/band. An example of this data helping to identify a problem is a poorly performing water circuit with reduced flow. The flow reduction would cause an increase in mold temperature in a specific area. Increasing historical data for the mold surfaces can help to identify these types of changes.
Support equipment, such as thermolators and hot runners, is frequently overlooked as a key source of variation that requires control to achieve process standardization. Two identical pieces of equipment—same brand, same make—may perform completely differently. Whenever possible, marry this type of equipment to a specific press to reduce potential variances.
Thermolator performance can be measured by recording GPM/LPM on both the supply and return of the unit itself. It is also important to verify that actual temperatures meet setpoints. For instance, if a thermolator pump starts to fail, lower GPM would be a clear indicator that a change has occurred.
Hot-runner performance is another key measurable that can be used to analyze variance. Actuals should be the same as setpoints. Another key recordable is temperature variance. Preferably, there should be no swing above and below actual setpoints. In cases where swing is inevitable, the normal swing should be recorded to help identify future variances. The hot runner itself should be measured similarly to barrel temperature recording. With the hot runner exposed, temperatures between bands should be measured and recorded for future reference. It is important to note that when bands on the hot runner are replaced, great care should be taken to install the new band in the same location that the old band was in.
These are only a few examples of how historical data can help improve a molder’s ability to quickly identify and respond to changing molding conditions. Increasing the amount of data recorded improves analysis capabilities and response time to process change. There is a clear difference between black-and-white and colorized photos. Similarly, change response is fully dependent upon the amount of data available to identify process variance. Record all data available when a process has been validated to ensure that, when future variances arise, the changes can be quickly addressed using the proper approach.
Garrett MacKenzie is the owner/editor of www.plastic411.com and a technical writer for PlasticsToday. His 31- year plastic injection career includes engineering and management for the automotive, medical and handgun industries. He currently offers in-plant processor training programs and training-based webinars. E-mail [email protected] for more information or a quote.
MacKenzie is organizing a two-day scientific molding workshop in Dalton, GA, on March 24 and 25. Read "Scientific molding workshop provides hands-on training" for detailed information about the course.