Contamination occurs when a foreign substance gets trapped in the molten plastic during the injection molding process. These substances can be anything from extra moisture to dirt, flecks of paint from the interior of your machinery to bugs.
Machinery Contamination
If your injection molding machinery is in disrepair or not being correctly operated, oil leaks, dirt, and other matter can get into the plastics. It is essential to repair any oil leaks as quickly as possible and clean up any grease drips as soon as they happen. Cleaning the hopper thoroughly between material changeovers will help reduce contamination.
Mold Contamination
Molds with moving parts need frequent lubrication to keep them in good working order. However, if too much lubrication is used, excess can find its way into the mold. Optimizing lubricants is the best way to prevent contamination that can impact the integrity and quality of your plastics.
Material Contamination
Raw materials used in the injection molding process can become contaminated and negatively impact the finished product. Regrind, or material from a previous process causes the equipment to become dirty. To prevent this, cleaning the equipment and carefully checking for regrind is key.
Extra moisture can cause contamination from water, therefore, thoroughly dry all raw material before putting it through the molding process.
Operator Contamination
Ensure that food and drink is not kept near the equipment, implement proper cleaning procedures, and ensure proper care to ensure operator contamination does not occur. Review cleaning and housekeeping procedures often with your employees, and spot check the floor to be sure the rules are being followed.
Splay
Splay is off-colored streaking in a finished product that’s caused by moisture being trapped in the material during the injection process, or a degradation of the material.
What Causes Splay?
Splay can be caused by excess moisture getting into the molten material as it’s being injected into the mold. As moisture turns into steam in the injection process, it discolors the finished product. If the defect does not occur in the same section each time, it is likely due to moisture splay.
Heat can also create splay. If you identify signs of stickiness or burning on the finished product, or if there’s an odor of overheated material, it’s likely Heat splay.
Shear during the injection process also can cause splay, and this type of splay often is repeatable on other molded parts as the issue occurs at the same point in the injection process each time.
Moisture-related Splay
Ensuring that all material is thoroughly dry before beginning the injection mold process is crucial. Mold leaks also can cause moisture-related splay, so check the mold carefully for any signs of damage or leakage.
Heat-related Splay
Check that the melting temperature is within the window defined by the materials manufacturer to prevent against overheating. Too much back pressure also can cause the material to overheat and cause splay, so carefully dialing in the amount of back pressure used in the process is important.
Shear-related Splay
If your piece has smaller gate sizes, you may want to decrease the beginning-of-fill pressure to avoid filling the mold too forcefully. Large changes in temperature from when the material leaves the nozzle and when it enters the mold also can create shear-related splay. Check and properly calibrate both temperatures.
