In past blogs we have examined how processing conditions can lead to contamination issues. Heats, residence time, layering, and difficult changeovers can all cause contamination that leads to rejected parts. Although these are the "usual suspects" when you are struggling with contamination, sometimes the cause of contamination has more to do with your environment than with your process. Once the "usual suspects" are crossed off your list, the cause of your headache will probably be one of the following:
Roofs and surfaces above and below the machine that are dirty. As time goes by, it is common for the production areas to form dust and dirt. Due to the effect of gravity, sooner or later these particles will fall into molds, boxes or hoppers. It is recommended that roofs be cleaned frequently, either annually or biannually. The same goes for the tops of the machines.* The static inherent to the plastic process will attract all types of particles from the nearby ceiling, walls or floor.
Silos and filters in plastic feed systems should also be cleaned to prevent fine particles from accumulating.
Feeding hoses and ducts are usually not a problem as long as they are dedicated to a single resin. What is important is to check that they have no wear; this would feed metal to the machine. Temporary tape patches should be removed as quickly as possible because pellets and other debris get stuck here.
Boxes, sacks, and feed hoppers must be kept covered at all times. Above all, educate your staff to value ground and waste or recycled material as much as virgin resin. They often throw garbage in these containers thinking that this is a waste product.
Water and oil leaks or other spills. They are not common but these leaks can lead to contamination points. They are often not visible, but in a thermoforming process they would multiply to a great extent.
Handling by personnel or robots. Some parts are critical, so gloves should be worn so as not to leave greasy marks. Some fabrics, such as denim, can also cause lint to adhere; make sure that the fabrics of the uniforms do not release lint. The suction cups and grips of the robots must be made of materials that do not leave residues and can withstand heat.
Keep these 6 external causes of contamination in the back of your mind and you will be better prepared to find the root cause of your processing issues.
Asaclean Purging Compounds will remove your contamination and lower your scrap-rate. That said, these external factors are self-inflicted wounds that can, and should, be avoided.
With the right tools and the right process, you can overcome any processing challenges associated with difficult changeovers. Get your free consultation today and make sure you're getting the most out of your process.
* For safety reasons it should be mandatory because dust is known as a material that can turn a fire into a catastrophe.
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