Why do plastic parts warp after processing?
When we process plastic parts, it can sometimes happen that they warp or twist after a while. This can be frustrating, especially if the parts are intended for precision applications. But why does this happen?
One of the most common reasons for plastic parts to warp is the internal stresses that exist in the material. These stresses can occur during the extrusion process, when the plastic is formed into its final shape. If the plastic is not aged or processed correctly, these internal stresses can remain and cause problems later.
Internal stresses from the extrusion process
When plastic is extruded, it can be exposed to different types of stresses, such as thermal and mechanical stresses. These stresses can cause the plastic to deform or warp. If the plastic is not processed correctly, these stresses can remain and cause problems later. For example, PE-HD and PE-UHMW can be more prone to developing internal stresses during the extrusion process.
Another reason for plastic parts to warp can be asymmetric processing. When we process plastic parts, we can unintentionally create asymmetry in the material, which can cause it to warp or twist. For example, a part that is cut with a circular saw can be more prone to warping if it is not symmetrical.
Annealing process
A method to reduce internal stresses in plastic parts is through the annealing process. Annealing involves heating the plastic to a certain temperature and then slowly cooling it down. This can help to reduce internal stresses and improve the plastic's properties. For example, PA6G and POM-C can benefit from the annealing process to reduce internal stresses.
But how does the annealing process actually work? When the plastic is heated to a certain temperature, the molecules begin to move more freely. This can help to reduce internal stresses and improve the plastic's properties. Then, when the plastic is slowly cooled down, the molecules can return to their original position, which can help to improve the plastic's stability.
Material-specific behavior
Different plastics have different properties and behaviors. For example, PA is sensitive to moisture and can swell if it is exposed to too much moisture. This can cause the parts to warp or twist. On the other hand, POM is more stable and less sensitive to moisture.
Another important factor to consider is the shore hardness. For example, PE-UHMW has a shore hardness of 65° Shore D, which can affect its behavior during processing. If we do not take into account the shore hardness, we can unintentionally create problems during processing.
But what can we do to prevent plastic parts from warping? One important strategy is to choose the right material for the application. For example, PE-HD can be a better choice for certain applications than PA. Another strategy is to process the parts correctly, for example by using symmetry and avoiding asymmetry.
- Choose the right material for the application
- Process the parts correctly
- Use the annealing process to reduce internal stresses
- Consider the shore hardness and the material's specific behavior
If we follow these strategies, we can reduce the risk of plastic parts warping or twisting. But what if we have already produced parts that have warped? In such cases, we may need to consider re-processing the parts or even producing new parts.
We hope that this article has given you a better understanding of why plastic parts warp and how you can prevent it. If you have more questions or need help with your plastic applications, do not hesitate to contact us. We are always here to help you.
Why not read more about our different plastic materials and how they can be used in your applications? We have a lot of information and resources available on our website.
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