Even if your latest shipment of resin is what you ordered, it may not be what you need.
It is curious that in a world that relies increasingly on documentation, the attention to the details of polymer composition receive so little attention. Companies will fill volumes with procedures for various aspects of their manufacturing processes. However, no serious consideration is given to verifying the composition of the raw materials that are used to produce the various molded parts until there is a problem. Instead, there is a tendency simply to refer back to whatever published information is available from the material supplier.
This series of articles is designed to help molders understand how a few analytical tools can help diagnose a part failure. Michael Sepe, our analyst and author, is an independent materials and processing consultant based in Sedona, AZ. Mike has provided analytical services to material suppliers, molders, and end users for 20-plus years. You can reach him at email@example.com.
When questioned about quality control procedures related to incoming raw materials, most processors will respond that they rely on provided certifications from the supplier. My response to this is that I have been looking at certifications for over 20 years and have yet to see one that warned me that I had just received a nonconforming batch of material.
Certifications are important because they document what the supplier says it shipped. And if all of a processor’s raw materials are provided by suppliers who have direct control over all aspects of the compound manufacturing process, then relying solely on certifications may be a low-risk approach. However, as the supply base expands to include compound suppliers who in turn purchase their feedstocks from a variety of sources, this approach becomes increasingly problematic. Lessons learned from the world of failure analysis suggest that a better approach would be to adopt the philosophy of Ronald Reagan, “Trust, but verify.”
This has proven to be even more necessary as products are sourced globally. Most of us have heard stories about products purchased from various locations around the world that turned out to be something other than what was advertised. Many of these deviations are simple to detect. A material that was supposed to contain 30% glass fiber actually contains 10%. A nylon 6 is found to be a mixture of nylon 6, nylon 6/6, polypropylene, and polyethylene. In the first case the end user notices that the material is not as rigid as expected and deflects excessively under the applied loads of the application. In the second case the material shows a wide range of problems including unmelted pellets and delamination.
The unmelt is due to the fact that the processing temperatures are set for nylon 6, a material with a melting point of 220-225°C that can be processed using melt temperatures of 235-255°C while the nylon 6/6 present in the compound melts at 260°C. There is nothing inherently wrong with blending nylon 6 and nylon 6/6, but the molder should be told about it so it can set its processing conditions accordingly. The