PVC Function And Injection Molding Process

Due to its high quality and low price, PVC material is valuable with anti-inflammatory properties, strong and firm, and has good resistance to organic chemical work, with a shrinkage rate of 0.2-0.6%. The use of packaging is becoming more and more common. For the characteristics of PVC materials, the analysis of the injection molding of products is as follows:

First, the characteristics of PVC material

The thermal stability of PVC is not good, the forming temperature is close to the dissolution temperature, the flowability is poor, and the appearance is very easy to produce defects. During processing, plasticizers can be added to improve its fluidity. Generally, preservatives must be added. Its compressive strength, dielectric strength of household appliances, and drug resistance are good.

2. Design scheme of abrasive tool and rubber inlet

In order to reduce the injection molding cycle time, the fewer the nozzles, the better, the cross section should be round, the diameter of the nozzle should be at least 6mm, it should be a circular cone, and the inner angle should be 6 degrees. Wells prevent poorly melted semi-solid raw materials from entering the core, which can compromise surface finishes and the compressive strength of the merchandise.

The draft angle should be between 0.50 and 10 to ensure that there is sufficient exhaust pipe equipment in the mold core. The common exhaust hole specifications are 0.03-0.05mm deep and 6mm wide, or the gap near the ejector pin of each mold is 0.03-0.05mm. Abrasives are manufactured from stainless steel or hard chrome plated.

PVC pipes

3. PVC forming process

PVC is a heat-sensitive plastic. Excessive temperature or excessive cutting will lead to dissolution and rapid diffusion. Since one of the dissolved substances (such as acid or HCI) will cause a catalytic reaction, the process will further dissolve, and the acidic substances will corrode metal materials. , making it into a dent, and the thickness of the protective layer of the metal material will fall off, causing rust, which is more harmful to the body.

The general screw length-diameter ratio is 18-24:1, the ratio of the three sections is 3:5:2, and the engine compression ratio is 1.8-2. When the screw is shot out in time, the distance between the top and the nozzle needs to be 0.7-1.8 mm, the screw must be made of stainless steel or treated with stainless steel.

Screw pad: The screw pad is in the middle of 2 to 3 mm, and the opportunities for large and medium-sized are greater.

Injection volume: The residence time of the specific cylinder should not exceed 3 minutes.

Barrel temperature setting: The temperature shown can only be used as a reference. It is very likely to exceed the strongly recommended range if appropriate adjustments are made according to the specific conditions of the equipment and raw materials.

Barrel residence time: under the temperature control of 2000C (plastic pellets), the maximum number of barrel residence times can exceed five minutes

Injection rate: The injection rate should be slow, otherwise the raw materials will be dissolved by excessive cutting. When using UPVC to produce extremely smooth thick-walled pipe products, multi-level injection rates should be used. Indicates that the shot rate is too fast.

Condensing type: The common surface value is 5bar. Lifting the condensing type is good for mixing colors and exhaust pipes, but the condensing type should be as low as possible.

Shutdown: Because of the low heat resistance of PVC, it is very important to shut down the machine. The barrel should be cleaned and tidy without leaving any PVC. Other thermosetting plastics with high heat resistance but not against PVC can be used (such as PMMA, PP, LDPE, or GPPS), do not mix POMTUPVC in the same barrel, otherwise it will cause excessive chemical changes and cause serious damage to the equipment.

Proportion of wrong materials: the maximum number of nozzle materials is 20%, otherwise it will endanger product quality.