How injection molding influence plastic product performance(2)?

>>How injection molding influence plastic product performance(2)?

How injection molding influence plastic product performance(2)?

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  • Plasticizing pressure

Plasticizing pressure refers to the screw top melt in the screw back when the pressure. Its influence on injection molding is mainly reflected in the plasticizing effect of the injection machine on the material and its plasticizing ability. Generally speaking, increasing the plasticizing pressure, the screw retreat speed decreases, the melt pressure in the barrel increases. As a result, the sheer effect is strengthened and the plasticizing effect is improved. However, it should be noted that, when the back pressure is increased, the excessive plasticizing pressure, on the one hand, reduces the plasticizing amount due to the reverse flow and leakage flow of the melt at the edge of the screw groove, which may cause insufficient measurement; on the other hand, it may cause excessive shear heat and excessive shear stress, which may degrade the material, cause bubbles or burns, and affect the quality of the plastic parts.

 

  • Mold temperature

Mold temperature refers to the temperature of the cavity surface during the molding process. The mold temperature affects the melt filling flow, the product cooling speed and product performance. The setting of the mold temperature mainly depends on the viscosity of the melt. Low mold temperature injection can be used to shorten the cooling time and improve production efficiency. Melt viscosity should be high – temperature injection molding. Raising the temperature of the mould can make the cooling rate of the workpiece uniform and prevent the forming defects such as indentation and crack. Mold temperature control directly determines the rate of cooling and further determines the rate of crystallization. When the mold temperature is high, the cooling rate is low and the crystallization rate is high. Mold temperature is too high, will extend the molding cycle and make the product brittle. In the case of low mold temperature and large cooling rate, the flow of molten material and crystallization occur simultaneously. The residence time of molten material in the crystallization temperature range is shortened, which is not conducive to crystal growth, resulting in a low degree of molecular crystallization of the product and affecting its performance. The mold temperature is too low, the plastic melt flow resistance is very large, the flow rate becomes slow, and even in the filling of the mold solidification hinders the subsequent feeding, making the parts short shot, forced orientation, often cause plastic parts to lack of material, sag, weld defects.

 

  • Barrel temperature

In order to ensure the normal flow of plastic melt and do not make it metamorphic decomposition, it is necessary to choose a suitable cylinder temperature, the average molecular weight is large, the distribution of concentrated plastic and glass reinforced plastic should choose a higher temperature cylinder temperature. The temperature of the cylinder is generally arranged according to the principle of high before and low after, but when the plastic contains too much water, the temperature of the rear end can be appropriately increased.

 

  • Nozzle temperature

In order to avoid the melt at the nozzle to produce flow delay, need to make the nozzle temperature slightly lower than the maximum temperature of the cylinder. Generally, in the case of low-speed air injection, the efflux is smooth without bubbles, which is considered as the appropriate temperature standard.

 

  • Melt temperature

The melt temperature mainly depends on the temperature of the barrel and the nozzle, which affects the plasticization of the material and the injection filling of the melt. The increase of injection temperature is mainly conducive to improving the fluidity of melt, which is related to many characteristics of products. With the increase of melt temperature, the mechanical properties of plastic parts, such as internal stress, impact strength in streamline direction, flexibility and tensile strength, can be reduced, while the impact strength, flow length and surface roughness perpendicular to streamline direction can be improved, and the POST-SHRINKAGE of products can be reduced.

Increasing melt temperature is conducive to improving the filling condition and the transfer in the die cavity, reducing the orientation and so on, and improving the comprehensive properties of plastic products. But too high temperature is not feasible, because when the melt temperature is close to the upper limit of the injection temperature range, it is easy to produce more gas, which makes the plastic parts produce bubbles, voids, discoloration, burning, flying edges, etc. On the other hand, it will degrade the plastic, reduce the strength of the plastic parts and lose elasticity.

 

  1. Special Process Impact

Under high vibration pressure, with the increase of vibration frequency, the tensile properties and notched impact strength of plastic products are obviously improved. In addition, the addition of ultrasonic technology can also play a good role.

 

Injection moulding process plays an important role in the quality of products. In the process of moulding, the defects of moulding machinery, die design and material properties can sometimes be remedied by appropriate moulding process settings. In a word, the processing conditions of injection moulding have an important impact on the appearance and mechanical properties of plastic products. Each process parameter is not independent of each other, and some defects of products are the result of interaction.

By | 2019-03-20T06:24:48+00:00 March 11th, 2019|Industry News|0 Comments

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