Plastic Material Problems: Plastics Drying, Defects, Lot Changes, Material Changes, Properties and Solutions

A company's material handling methods and supplier choices can be their best friend or biggest nightmare. This article addresses typical material problems and solutions for approaching issues as they arrise. As I'm sure many of you are well aware, this is a monstrous topic...and my being able to identify and offer solutions to every material topic in a single article are slim to none. I will touch on a few topics at a time, and as time goes by I will expand on these in greater detail.

This particular article will touch on the various issues that plague our daily operations and offer some brief information on potential causes and solutions.

It is important to understand the variety of properties that are associated with different material categories. There are many different grades and types of plastics, and each grade has its own set of rules and potential defects. It is important to always be aware of what type of material you are running and you should always refer to your MSDS when issues arrise that could be directly related to a material issue. A good material supplier performs extensive testing on the materials they produce, and you should always be able to get resource information from them regarding the molding properties associated with the material they are providing you. Some examples of data they should be able to offer you are as follows:

• Mean melt temperature
• Melt Window
• Specific gravity
• Temperature settings (Window
• Potential Problems
• Velocities
• Back Pressure/ Hold Pressure settings
• Mold Temperature setpoints

These are the basic ones of importance...there are others that sometimes need to be addressed as well. You can get some pretty intensive information regarding a specific material's properties from the following website:

http://www.ides.com

Materials sometimes require drying, and even removing the moisture for extended periods beyond manufacturer specs can lead to an array of other problems, such as splay and process variances. It is important to know what the minimum/ maximum drying times for your material should be, and when choosing a dryer you should calculate what the throughput of that dryer will be. There is a throughput calculator on the site that can help you determine this.

Drying temperatures are also important. I've seen situations where a material seemed to be performing incorrectly, and the cause was an individual trying to run at a higher temperature on the dryer for a shorter length of time. Sure, this may work on occasion...but it is not a good approach. Material specifications exist because people put a significant amount of testing and time determining how a material performed optimally. I will say that there are times you can push those specs to their limit...but any such action should be approached with caution and as a sample first. Changing your material procedure can affect your end product's functional, aesthetic and dimensional properties.

Materials that are susceptible to moisture should be considered when there are changes to your normal process. It is important to know what moisture level your material runs best at (moisture analyzer) and one of the first things you should check when moisture-specific defects arrise is the moisture content.

Another thing that can result in a drastic process change is a change from one lot of material to a new lot. I cannot stress how important it is for you to track your lots! There have been a number of times that I have witnessed a huge crisis that was identified as a change in lot properties.

I've just barely scratched the surface on this topic. Material can make or break consistency and profitability in a company. Buying the cheapest does not concrete being the most economic approach. If there are huge variances in your processes (resulting in scrap) that can be resolved by buying a better brand or a specific blend, then this may be the best approach to a long term solution.