Choosing Materials for Injection Molding

Applied Technical Services performs melt flow index testing to ensure clients’ design materials perform as required. One of the most prevalent ways that manufacturers utilize polymers in consumer products involves a process called injection molding. By filling metal dies with molten material and letting it cool into a solid, they can rapidly mass produce components. Certain polymers prove more efficient for this process than others, and thus product engineers choose from among them based not only on their performance characteristics as a solid, but also in their molten form.

 

What is Melt Flow Index and Why Does It Matter?

One of the key factors in a polymer’s suitability to the injection molding process is its melt flow index (MFI), a measure of how easily it flows when melted and subjected to pressure. Because it measures how much of a given sample flows through a capillary in a predetermined amount of time, a polymer’s melt flow index inversely correlates to its molecular weight — the higher its molecular weight, the slower it flows. Product engineers must choose a polymer with an appropriately high melt flow index to ensure that the article forms evenly during injection molding without allowing for air pockets and has sufficient strength once cooled for the final assembly’s intended use. To validate their chosen material for production, manufacturers send their samples to experienced polymer testing labs like ATS.

 

How the Method Works and Our Testing Capabilities

The ATS chemical analysis division performs all our melt flow index testing services. These experts bring cumulative decades of experience performing this method to ASTM D1238 and DIN EN ISO 1133-A, Code T — the two most recognized test standards. We conduct all such testing at our Marietta Lab, where we maintain ISO 17025 accreditation through the American Association for Laboratory Accreditation (A2LA) to perform this method to ASTM D1238.

 

Testing begins with chemists heating either virgin polymer pellets or ground finished product to a specified temperature, causing it to melt. They introduce this molten sample into our melt flow indexer, which uses a piston system to squeeze it through a minuscule aperture in a metal die for a specified period. By calculating the change in the sample’s weight after this process, our team can determine the flowability of the polymer sample. In addition to determining how a material will behave during processing, melt flow index data is also used in support of failure analysis.

 

This method represents only one facet of our polymer testing expertise. From quantifying other thermal characteristics to identifying polymeric compounds to determining mechanical performance traits, you can view the rest of our capabilities here.