Shrinkage of TPE overmolded materials

　　Shrinkage of TPE overmolded materials is one of the key properties that the industry needs to pay attention to in research and development as well as in production. When TPE overmolded materials are cooled from the molten state, their molecules are aligned with each other, and this is where shrinkage occurs.

　　The size of the shrinkage of the TPE material, roughly in the form of a few thousandths of a percent of the product form, can seriously affect the shape of the TPE product, and will affect the ease of demolding. If shrinkage is not uniform, bending or warping can also occur. Even when shrinkage is within acceptable limits, it can have an effect on part articulation.

　　For these reasons, shrinkage must usually be taken into account in the production process.

　　1, workpiece demolding; when the workpiece contains a core or hollow part, with the elastomer contraction, it will tightly wrap the mold of these parts, so that the workpiece demolding becomes very difficult. Mold design, mold surface finish and processing conditions can reduce this effect, and even make automated demolding is also possible.

　　2, molding conditions; molding conditions can significantly affect the degree and nature of shrinkage. If from a high stress state quickly to a low stress state, the degree of shrinkage will increase. Rapid cooling of the workpiece as well as very high injection speed or pressure, can also affect the shrinkage.

　　3, design considerations; taking into account the shrinkage, the mold must be processed slightly larger than the required size of the workpiece. Usually, the actual shrinkage value only until the specific workpiece molding can be known. Therefore, it is always best to be conservative beforehand.

　　As with various other properties of thermoplastic elastomers, shrinkage tends to vary with the direction of polymer flow. The location of the gate will determine the direction in which the melt flows into the mold, and thus the direction of shrinkage. For more information about the properties of TPE overmolded materials, please contact Plastisol, we will have specialized technical staff to answer your questions!