How Stable Are Such Plastic Parts

How Stable Are Such Plastic Parts

How Stable Are Such Plastic Parts

In our short series on the properties of the plastics we use for plastic parts, we would like to take a closer look at another important question today. How stable is a plastic part? As we have already described, there are about 90,000 different types of plastics and plastic compounds that are currently used commercially as plastic parts around the world.

They are classified into major categories such as thermosets, elastomers, and thermoplastics. There are even close to 120,000 possible compounds stored in a database that collects the technical components of other potential plastic parts. This is a dizzying number that developers of plastics technology have come up with. Before plastic can be considered for injection molding as a plastic part like ours, it must, of course, be extensively tested. As a medium-sized company, we prefer to rely on tested plastics that have been in use for many years when selecting materials, because we neither tend to experiment unnecessarily in plastic injection molding nor do we want to put our customers at any risk. We leave the technical development and experimentation of the most diverse requirements for plastic parts to universities and large industries.

Impact Loads and Impact Strength of Plastic Parts

In the manufacture of any plastic, there are a series of properties that determine its availability for different applications. One of the most important of these is, of course, the so-called impact strength. How strong this impact strength of plastic always depends on the temperature. If it is below the typical value for the plastic part to be tested, the material will become brittle and will then burst and shatter more easily.

This temperature limit depends, among other things, on the molecular weight of the plastic. In general, the higher the molecular weight, the better the plastic part will resist at low temperatures. However, if we look at the average temperature range of plastic, there are several accepted methods that researchers in plastics engineering laboratories use to measure impact strength.

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The Charpy Impact Test

The best-known and most widely used method of testing impact strength has probably been around for over 100 years. It is still in use today and has even gained its own standardization as a method for plastic or metal parts.ISO 179-1 standard specifies The Charpy Impact Test for measuring the impact strength of plastic parts under different temperature conditions. Perhaps you are thinking now that this sounds rather complicated. But once the principles are clear, it is actually relatively easy to understand. In order to perform this measurement procedure in plastics technology, you take a cube of plastic and cut a notch in advance on one of its long sides. Then, the sample is clamped and a pendulum is dropped from the frame onto the plastic cube, with the height, mass, and speed of the drop precisely calculated.

Like a pendulum, the hammer swings sideways from above to the unnotched side of the rectangular cube, smashing it into pieces. In the process, a certain amount of impact energy, or kinetic energy, is absorbed by the block and dissipated through the molecular bonds in the material. This dissipated energy slows down the pendulum. As a result, it reaches a lower height as it continues to swing on the other side of the block. By measuring the height still reached by the pendulum, it is possible to calculate exactly what the impact strength of the plastic is. The calculated value can then be used as a criterion for the load that the plastic must withstand when used as an injection molded part. To put it in technical terms. We determine the impact energy W of material in joules.

TX MOLD – Over 30 Years of Injection Molding Processes
If you would like to learn more about the process of injection molding plastics or especially thermosetting plastics processing, please contact us or visit our blog. As mentioned earlier, many episodes cover these topics. We look forward to getting to know you!

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