Detailed Explanation of Elastomer TPE/TPR Process

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For TPE based on harder SEBS, for TPR based on SBS,

During processing and injection molding, the editor of Juye believes that the accuracy of temperature settings is key to affecting product appearance and performance. The following are some suggestions for temperature settings during TPE injection molding.

The temperature in the feed zone should be set relatively low to avoid clogging of the feed port and to allow entrained air to escape. After testing, usually TPE.TPR products have temperature settings between 160°C and 210°C in each zone, while in the nozzle it is set between 180°C and 230°C.

The mold temperature should be set higher with the condensation temperature of the injection zone, so as to avoid water contamination of the mold and prevent stripes on the product surface. Too high mold temperature usually leads to a longer production cycle, but it can improve product appearance. Therefore, the mold temperature range should be designed between 30 and 40.
During the molding process, during the filling of the mold cavity, if the filling performance of the product is poor, problems such as excessive decompression, too long filling time, and unqualified filling may occur, causing quality issues. To improve the filling performance of the product during molding, the quality of the molded product can be improved, and usually the following aspects can be considered:
1) Switch to another series of Keyue products;
2) Change the gate position;
3) Change the injection pressure;
4) Change the geometry of the part.
The control of injection pressure is usually divided into one injection pressure, two injection pressures (holding pressure) or three or more injection pressures. It is important that when the pressure switching timing is appropriate, to prevent excessive pressure in the mold, overflow, or material shortage. The specific volume of the mold depends on the melt pressure and temperature when the gate is closed during the holding phase. If the pressure and temperature from the pressure holding switch to the product cooling phase are consistent, the specific volume of the article will not change.
Holding pressure is the most important parameter for determining product dimensions at a constant molding temperature. Holding pressure and temperature are the most important variables affecting product dimensional tolerances. For example, after the mold filling is complete, immediately reduce the holding pressure, and when the surface layer reaches a certain thickness, increase the holding pressure again. By using low clamping force, eliminate sink marks and flash, forming thick-walled products.
Holding pressure and holding speed are usually 50% to 65% of the maximum pressure and holding speed for plastic cavity filling, that is, the holding pressure is about 0.6 to 0.8 MPa lower than the injection pressure. Since the holding pressure is lower than the injection pressure, the pump load is low, extending the service life of the fixed oil pump and also reducing the power consumption of the pump motor. Pre-adjust a certain amount of measurement so that the screw tip near the end of the injection stroke still has a small amount of melt (cushion). According to the filling situation in the mold, further apply injection pressure (secondary or tertiary injection pressure) to add a small amount of melt. This can prevent product sinking or adjust product shrinkage.
Cooling time mainly depends on melt temperature, product wall thickness, and cooling efficiency. In addition, the hardness of the material is also a factor. Harder grades solidify faster in the mold than softer grades. If cooling is done from both sides, the cooling time required for wall thickness is usually 10 to 15 seconds per 0.100 inch. Products coated with adhesive require longer cooling times because they can be effectively cooled by a smaller surface area. The cooling time required for wall thickness is about 15 to 25 seconds per 0.100 inch.
1. Incomplete plastic molding
1) Improper feed adjustment, shortage or excess material.
2) Injection pressure too low, injection time too short, plunger or screw returns prematurely.
3) Slow injection speed.
4) Material temperature too low.
2. Overflow (flash)
1) Injection pressure too high or injection speed too fast.
2) Too much material feed, causing flash.
3) Barrel, nozzle or mold temperature too high will reduce plastic viscosity, increase fluidity, and cause flash when smoothly entering the mold.
3. Flow marks, bubbles and voids
Main results: (1) Material temperature too high, causing decomposition.
2) Low injection pressure, short holding time, causing the melt not to approach the cavity surface.
3) Injection speed too fast causes the molten plastic to decompose under shear, generating decomposition gases; injection speed too slow cannot fill the cavity in time, resulting in insufficient surface density and cracks.
4) Insufficient material, excessive cushion, material temperature too low or mold temperature too low will all affect melt flow and molding pressure, creating bubbles.
5) During screw preforming, back pressure too low, screw speed too high, causing screw to retract too fast and easily pushing air to the front of the cylinder.
4. Burn marks
1) Barrel and nozzle temperature too high.
2) Injection pressure or preplasticizing back pressure too high.

3) Injection time too fast or too long

For more about TPE/TPR applications and solutions, contact Juye TPE, we will customize TPE/TPR application solutions for you for free; bring you more possibilities to increase product added value.

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Detailed Explanation of Elastomer TPE/TPR Process

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