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Bicolour Injection Molding | Manufacturing Process Characteristics and Mold Structures
The Characteristics of Bicolour Injection Molding Manufacturing Process
1. Two sets of plastic injection devices
The bicolour injection molding machine is composed of two sets of plastic injection devices with identical structures and specifications. The nozzle should have a special structure according to the production method. Or it should be equipped with 2 molding dies with exactly the same structure that can be rotated and transposed.
When plasticizing injection, the melt temperature, injection pressure, injection melt volume and other process parameters of the two sets of plasticizing injection devices must be the same. What’s more, we should minimize the deviation of the process parameters in the two sets of devices.
2. Higher melt temperature and injection pressure
Compared with ordinary injection molded plastic products, the bicolour ones must adopt higher parameter values for the melt temperature and injection pressure during injection. The reason is that the mold runner in bicolour injection molding is relatively long. Besides, the structure is complicated, and the flow resistance of the injected melt is large.
3. Raw materials with great thermal stability
We should choose the raw materials with good thermal stability and low melt viscosity for the bicolour injection molding plastic products. So it can avoid the situation that the raw materials are decomposed due to the high temperature of the melt and the overly long residence time in the runner. The most widely used plastics are polyolefin resins, polystyrene and ABS materials.
4. Higher injection parameters
In the injection molding of bicolour plastic products, to make the two melts of different colors well welded in the mold during molding and ensure the molding quality of the injection molded products, we should use a higher melt temperature, mold temperature, injection pressure and injection rate.
Mold Structure of Bicolour Injection Molding
The Two forms of traditional bicolour injection molds:
- Punch translation
- Punch rotation
1. Punch translation
There are two concave molds and one convex mold inthe “punch translation” mold. When the first barrel shoots glue, the male mold is closed with the first female moldand then complete the injection of the first kind of plastic.
After the first kind of plastic is solidified, the concave and convex molds are separated. And the semi-finished product formed by the first plastic stays in the convex mold. Then, it moves with the convex mold to the position aligned with the second concave mold. After the injection molding machine is closed, the second barrel is injected with the second plastic. After the second plastic solidifies, the injection molding machine opens the mold and takes out the complete product.
2. Punch rotation
The bicolour mold in the form of “punch rotation” has two concave molds and two back-to-backconvex mold.This convex mold can rotate.
The bicolour injection molding machine has two barrels. We better design the second barrel in the vertical direction of the movement of the injection molding machine. Two different plastics can be injected at the same time. When the two kinds of injected plastics are solidified, the injection molding machine opens and automatically ejects the complete product. After taking out the product, the “rotatable punch” turns 180 degrees. And the injection molding machine is closed for the next cycle.
In the first and second barrels of the “punch translation” mode, the injection is taken in turn. While the first and second barrels of the “Punch rotation” mode are injected at the same time. Therefore, for the same product, the production efficiency of the “punch rotation” mode is twice of that the “punch translation” mode.
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