Teacher Dan Dan from Xiaosa School shared the five key points of spray-free injection molding process
Spray-free materials are more and more widely used, such as electric rice cookers, pressure cookers, electric kettles, soymilk machines, washing machines, air conditioners and other home appliances shells; automobile pedals, glove boxes, sun visors, pillar trims, side skirts and other interior and exterior trims are increasing Spray-free materials are applied locally, and spray-free materials are therefore favored by manufacturers. The injection molding process of spray-free plastics is a link that cannot be ignored. Let's take a look at the five main points of the injection molding process of spray-free materials.
1. Drying control: moisture content below 5%
Spray-free materials, like most materials, will absorb moisture in the air. It must be dried before molding, otherwise it may cause silver wire and water splash on the surface of the product and affect the surface gloss of the product.
It is usually required to control the moisture content of the spray-free material below 0.05 after drying. For example, for the spray-free material of ABS substrate, the drying temperature is usually 70°C-85°C, and the drying temperature is 3-4 hours.
Too high temperature will easily cause material performance degradation. Too low temperature, insufficient drying time, too high resin moisture content, and easy to produce gas marks on the surface of the product.
2. Injection temperature: medium and low temperature injection
Since the metal pigment is added to the spray-free material, it is easy to cause the discoloration of the metal pigment under the high shear of the screw. Therefore, the principle of setting the molding temperature for spray-free materials is to use medium and low temperature injection molding to prevent material degradation under the premise of ensuring that the material is fully plasticized.
For example, the processing temperature of spray-free materials with ABS as the base material is 210°C-230°C. If the temperature is too high, the material will degrade, and the product surface will have gas marks.
3. Injection speed: medium-speed stepwise control
When using spray-free materials for injection molding, the choice of injection speed mainly considers the appearance of the product, the exhaust of the mold, and the resistance of the resin flow in the cavity of the injection molding machine.
Faster injection speed generally lengthens the melt process, is suitable for filling thin-walled products, and forms a better surface finish and surface effect. However, a too fast injection speed will easily cause the melt to suffer strong shear, resulting in damage to the shape and particle size of the pearlescent toner and reducing the special color effect of the product. In addition, problems such as injection marks and poor exhaust are prone to occur near the gate.
Therefore, under the premise of ensuring the surface effect and quality of the product, it is recommended to choose a medium-speed stepped stepped speed control to ensure smooth filling and product appearance.
4. Injection pressure: lower pressure
The injection pressure is to overcome the resistance of the melt in the flow process, give the melt a certain filling speed and compact and feed the melt to ensure the smooth filling process. The actual injection pressure is related to many variables, such as melt temperature, mold temperature, part geometry, wall thickness, flow length, and other mold and equipment conditions.
Generally, it is best to choose a lower pressure that can meet the performance, appearance, and injection cycle. At the same time, pay attention to the difference between the actual injection peak pressure and the set value. In general, the appropriate holding pressure is 60-80% of the injection pressure.
5. Mold temperature: higher mold temperature
Mold temperature directly affects the surface brightness, weld line and strength of the final product. The use of high mold temperature can increase the fluidity of the material, obtain a higher bond line strength, and reduce the internal stress of the molded product, making it better heat resistance and chemical resistance, and at the same time improve the replication of the melt to the mold surface , Improve product gloss and special color effect.
In order to achieve the ideal surface quality effect, when using spray-free materials, higher mold temperature should be used as much as possible. For spray-free materials with ABS as the base material, the mold temperature is usually 70-90°C.
In short, only reasonable mold design, proper drying temperature, injection temperature, injection speed, and reasonable mold temperature are the indispensable conditions for spray-free materials to make beautiful appearance products.
In addition to the injection molding process, the choice of raw materials is also very important. Spray-free products have excellent aesthetic effects and excellent appearance. The materials have good heat resistance, good dimensional stability, creep resistance, excellent processing performance, reasonable cost performance and good mechanical properties.
Spray-free series plastics and their characteristics:
Spray-free PP material
High gloss, easy molding, scratch resistance, low cost, recyclable
Spray-free ABS material
High gloss, brilliant color, metallic effect, recyclable
Spray-free PC/ABS material
Rigid and tough balance, brilliant colors, easy to shape, low cost
Spray-free special materials for automobiles
Metal effect, high toughness, high flow, super weather resistance, recyclable