Injection molding process of PVC material

PVC material is inexpensive, inherently anti-inflammatory, hard and strong, good chemical resistance, shrinkage rate of 0.2-0.6%, the products are increasingly used in electrical appliances, machinery, construction, daily necessities, toys, packaging, for the characteristics of PVC material, analysis of the product injection molding process is as follows:

一、Properties of PVC materials

PVC thermal stability is poor, molding temperature and decomposition temperature is close to, poor mobility, the appearance of easy to form bad defects, PVC material heat resistance is not good, the most easy to burn, acidic gas and corrosion of the mold, processing can add plasticizer to increase its fluidity, - generally must add additives to use, its strength, electrical insulation, good chemical resistance.

二、Mold and gate design

In order to shorten the injection cycle, the shorter the injection port the better, the cross-section should be garden-shaped, the minimum diameter of the injection port is 6 mm, into the garden cone, the inner angle of 5 degrees, preferably with cold wells, cold wells can prevent poorly melted semi-solid materials into the cavity, and these materials will affect the surface finishing and product strength.

The die slope should be between 0.50 and 10 to ensure that the cavity has sufficient venting equipment. The common venting hole size is 0.03-0.05mm deep and 6mm wide, or 0.03-0.05mm clearance around each ejector pin. The die should be made of stainless steel or hard chrome plated.

三、PVC molding process

PVC is a heat-sensitive plastic. Overheating or excessive shearing will cause decomposition and spread rapidly, because one of the decomposition products (such as acid or HCI) will have a catalytic effect, resulting in further decomposition of the process, and the acid will erode the metal and make it change. If it is dented, the protective layer of the metal will peel off, causing rust, which is more harmful to the human body. The common screw length-diameter ratio is 18~24:1, the three-stage ratio is 3:5:2, and the compression ratio is 1.8~2. The depth of the screw groove in the feeding section is recommended as follows:

The injection speed should be slow, otherwise excessive shearing will degrade the material. When using UPVC to produce extremely smooth thick-walled products, multi-level injection speeds should be used. If light brown stripes radiate from the gate, it means that the injection speed is too high. quick.

The tip of the screw should have an internal angle of 25~30 degrees. When the screw is in place, the distance between the tip and the nozzle should be 0.7~1.8mm. The screw must be made of stainless steel or chrome-plated.

1) Screw gasket: The screw gasket is between 2~3mm, and the large-scale opportunity is larger

2) Injection volume: The actual residence time should not exceed 3 minutes.

3) Barrel temperature setting:

The temperatures provided are for reference only, and appropriate adjustments are made according to the actual conditions of the machine and raw materials, which may also exceed the recommended range.

The temperature of the middle feeding section in the front section of the mold nozzle (0C) 30-60 170-190 160-180 150-170

The injection volume used for 140-160 is 20~85% of the theoretical injection volume of the machine. The smaller the injection volume actually used, the longer the retention time of the material and the greater the risk of deterioration after heating. cin.com

4) Barrel residence time:

Under the temperature control of 2000C (rubber material), the maximum residence time of the barrel can exceed 5 minutes, when the temperature is 2100C.

5) Injection speed:

The injection speed should be slow, otherwise, the material will degrade due to excessive shearing. Multi-stage injection speed should be used when using UPVC to produce extremely smooth thick wall products. If there are light brown stripes radiating from the gate, it means that the injection speed is too high. quick.