The most frustrating problems are often the simplest solutions once you find them.
The life of a custom molder is full of adventure and daily challenges that can be frustrating at times, but also provide learning opportunities and great satisfaction when accomplished. Recently, we were running a general purpose natural ABS that was colored with color concentrate at the press. The material was dried and tumbled with the color and supplied to an autoloader at the machine. The process technician set up the machine and supplied first article samples to our quality department which were accepted for production. Soon thereafter the operator notices streaking in the color and notified QC.
Problem: Streaks and inconsistent color in the parts.
Initial Trouble shooting: The process technician noted concentrate in the site glass and in the feed section of the screw. The barrel was purged and restarted. It was noted that there was no evidence in the parts or purge that the material was wet. Following the purge and restart production parts were approved and resumed. Within the hour the problem resurfaced.
Second Trouble shooting: The process technician considered an incompatible melt index in the material and color concentrate that caused materials not to mix properly. Data sheets were reviewed and a melt index test was done to confirm that material and color were to specification. The machine was restarted and started running good parts. Within the hour the problem resurfaced again.
Third Trouble shooting: Scratching our heads we shut the machine down to tackle the next day. Upon coming in the morning the process technician was inspecting the equipment in preparation for another run and when he lowered the vacuum hose color concentrate spilled on the floor. The first clue to our problem.
Solution: It was determined that the specific gravity of the color concentrate was slightly greater than that of the ABS. As a result as the material travelled through the vacuum hose the heavier concentrate settled in the corrugations of the hose and starved the machine of color. Color concentrate was visibly present in the material presented to the throat of the press, but at the ratio blended prior to the vacuum loader. Upon recognizing the issue the vacuum pressure was increased to move the material with more force through the corrugated tube and the problem was resolved.
Sometimes the most frustrating and challenging problems are solved with the simplest of solutions. We hope you may park this experience in your memory bank and look like the smart guy when this happens in your shop. At Blackwell Plastics we believe it is important to do what you love and love what you do. If we can be of assistance, feel free to Ask an Engineer at firstname.lastname@example.org or call us at 713 643-6577.