TPR / TPE thermoplastic elastomer molding

TPR dry
According to the material characteristics and feeding conditions, usually in response to the material before forming the appearance and performance testing process. The supply of pellets often contain different levels of moisture, flux, and other volatile low molecular weight materials, especially those with a tendency to TPR moisture absorption process is always more than the agreed limit. Therefore, the processing must be dried before processing, and determination of water content. TPR at high temperatures the moisture content requirement of 5% or less, or even 2% -3%, so the common vacuum oven dried at 75 ℃ -90 ℃ for 2 hours. Already dry material must be properly sealed to prevent the material from the air and then the loss of moisture and drying effects, can be used for this purpose hopper drying chamber for the injection molding machine to provide continuous hot, dry material, to simplify operations, clean, progressive quality increase in injection rate are favorable. Drying hopper loading weight and generally injection molding machine with a feeding amount of 2.5 times per hour.http://www.prmindustry.com/Abstract...Articles section TPR staining
To SBC in the color-based TPE TPR is better than most other materials. Therefore, they need only small amounts of masterbatch can achieve a particular color effect, and the resulting color is more pure than other TPR. In general, the viscosity masterbatch viscosity should be lower than the TPR, which is due to TPR melt index higher than the masterbatch, which will help spread the process, making the color more evenly distributed.
For SBS based TPE, recommended the use of polystyrene containing reagent.
For hard SEBS-based TPR, recommended the use of polypropylene (PP) containing reagent.
For softer SEBS-based TPR, can be low density polyethylene or ethylene vinyl acetate copolymer. For the softer varieties, is not recommended the use of PP containing reagent, due to the hardness of composite materials will be affected.
For some of the plastic injection molding application package, using polyethylene (PE) containing reagent and the substrate may have a negative impact on adhesion.
Need to clean the barrel before injection
The beginning of a new injection molding machines purchased before using, or need to change the product in production, replacement materials, color or exchange decomposition phenomena found in plastics, the need for the injection molding machine barrel to clean or washable.
Commonly used cleaning barrel heating barrel cleaning method. Cleaning materials in the plastic raw materials (or plastic recycled material). For TPR material, can be used by the processing of new materials replace the transitional cleaning materials.
TPR molding temperature
In the processing of the molding process, the temperature settings are correct appearance and performance is good or bad product key. Here is the TPR process injection temperature set some of the recommendations.
Feed zone temperature should be set quite low, to avoid clogging the inlet and allow entrained air to escape. When using the masterbatch mixing time in order to improve the state should set the temperature of the transition zone above the melting point in the masterbatch. Latest from the injection nozzle area should be set too close to the temperature needed to melt temperature. So, after testing, usually TPR products in different regions of the set temperature range are: barrel to 160 degrees Celsius to 210 degrees Celsius, the nozzle is 180 degrees Celsius to 230 degrees Celsius.
Mold temperature should be set high condensing temperature with the injection zone, which would avoid the pollution of water resulting in products of the mold surface of the stripes. Higher mold temperature will usually result in a longer cycle, but it can improve the appearance of weld lines and products, the effect, so the mold should be designed to set the temperature range 30 to 40.
Mold filling, packing, cooling
Fill the mold cavity in the molding process, if the products filling performance is not good, it will reduce the occurrence of excessive pressure, fill time is too long, filled with resentment, etc., and hence subject to the quality of products there. In order to progress in filling in the molding product performance, improve the quality of molded products, usually available from the following aspects to consider:1) Change Section Yue another series of products;2) change the location of the gate;3) changing the injection pressure;4) Change the part geometry.
Injection pressure control is usually divided into an injection pressure, the second injection pressure (pressure) or more than three times the injection pressure control. Pressure switch timing is appropriate, the pressure is too high to prevent mold, prevent excess material or material shortage, etc. are very important. Model depends on the specific volume of products closed the gate packing stage when the melt pressure and temperature. If the pressure switch to ensure each product from the cooling phase of the pressure and temperature the same, then the specific volume of products will not change. Molded in a constant temperature, determine the size of products, packing the most important parameter is the pressure on the product dimensional tolerances of the most important variable is the holding pressure and temperature. For example: after the end of the filling, packing pressure immediately decreased when the surface of a certain thickness, packing pressure to rise again, so you can use a low clamping force forming large thick-walled products, elimination of collapse pits and flash.
Holding pressure and speed are usually plastic when filling the cavity pressure and the maximum speed of 50% -65%, that is holding pressure lower than the injection pressure of about 0.6-0.8MPa. As the holding pressure lower than the injection pressure, holding pressure in the considerable time, the pump load is low, solid pump life is extended, and pump motor power consumption is also reduced. Regulate the use of certain pre-measured, so the injection end of the trip around the screw end is still a small amount of melt remaining (buffer capacity), according to the mold filling was further applied injection pressure (injection pressure of two or three times) , add little melt. In this way, you can adjust the products to prevent product depression or shrinkage.
Cooling time depends on the melt temperature, products, wall thickness and cooling efficiency. In addition, the hardness of the material is also a factor. Varieties with very soft, hard varieties in the mold will quickly solidified. If the cooling from both sides, then each 0.100 "wall thickness required cooling time is usually about 10 to 15 seconds. Lagging way the products will require a longer cooling time, due to their smaller surface area and can be effectively cooled. Each 0.100 "wall thickness required cooling time is about 15 to 25 seconds.
Injection molding process conditions, the impact
1 plastic molding incomplete
(1) improper feeding regulation, lack of material or materials.(2) low injection pressure, injection time is short, the plunger or screw back too early.(3) slow injection.(4) the material temperature is too low.
2 flash (flash)
(1) injection pressure is too high or injection speed too fast.(2) flash caused by excessive feeding.(3) barrel, the nozzle temperature is too high or too high will cause the plastic mold temperature decreased the viscosity, activity increased in the case of fluid into the mold caused by flash.
3 crazing, bubbles and pores
(1) the material temperature is too high, resulting in decomposition.(2) injection pressure is small, the holding time is short, so that melt and cavity surface dense paste.(3) Injection speed too fast, the molten plastic to break down the large shear, resulting decomposition gas; injection is too slow and can not result in products covered the surface of the cavity produce enough silver grain density.(4) Feeding inadequate feeding cushion is too large, the material temperature is too low or too low mold temperature will affect the activities and forming the melt pressure to produce bubbles.(5) when the pre-plastic screw back pressure is too low, too high speed, screw back too fast, the air easily into the barrel along with the material front.
4 charred Obscure
(1) barrel, the nozzle temperature is too high.(2) injection pressure or pre-plastic back pressure too high.(3) injection or injection speed too fast cycle is too long.

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              Peter Huang