Injection molding is generally divided into single-color injection molding and two-color injection molding. Here, we are introducing the two-color injection molding machine, so you can find out how it works.
As the name implies, this machine can process two colors of plastic materials at the same time. It usually has 2 injection units that process one material at a time. The two materials can be injected simultaneously or at different times according to the product requirements.
The features of a two-color injection molding machine can be simplified as follows: independent adjustable, high accuracy of measurement, stable plasticization quality, stable back pressure, and fast response.
Through a certain injection device and process, two different materials are injected into the same set of molds to get finished products. The two-color punching mold comprises two kinds of plastic materials that are punched on the same two-color punching machine. After the plastic mold is molded twice, the product will stick only once.
The two-color machine has both a parallel type and a vertical type injection molding machine, based on the type. It can also be divided into core rotating type, core receding type, and push plate rotating type, according to the structure.
At present, the core rotary type is more widely used in the market than the core rotary split type. The latter is applied to two split molds on a set of injection molding machines, which can release the injection molding of two-color products by alternate rotation.
The core rotation type is used in two separate molds on one set of injection molding machines, and it is also used for two-color injection molding by alternate rotation. The other form of core rotation type is the core rotation continuous type, and it is used for two-color injection molding in one set of mold.
Features of two-color injection molding
1. High energy saving with strong function
2. Good stability
3. Good rapid response
4. High precision
5. Energy saving
6. Dynamic mold is the same
The disadvantages of two-color injection molding
- Vapor bubbles in the product
In the whole process of a two-color injection molding machine, there are sometimes many products with vapor bubbles, which will jeopardize the compressive strength and physical properties of the products, and also greatly affect the appearance of the products.
General products due to uneven thickness, or mold shells have a prominent rib. Also, the raw material in the mold shell cooling rate is not the same, resulting in the uneven collection. Since it is very easy to produce bubbles, the stamping mold must pay special attention to avoid the problem.
In addition, the raw material is not dry enough. In the worn material when heat is converted into vapor, it is very easy to get into the core of the mold to produce bubbles. Therefore, when the product happens to be blistered, we can check the following factors and do the solution.
- The product has cracks
Cracks are the fatal condition of TPU products, which are mainly manifested as hair-like cracks on the surface of the product. When the product has sharp edges, the disc injection molding machine in this position isn’t easy to see the fine cracks, which is very risky for the product.
To prevent cracks caused by poor release, the space inside the molding chamber of the mold shell must be equipped with sufficient release inclination, and the size, part, and way of the mold ejector must be appropriate.
The frictional resistance of each part of the finished product should be proportional when pressing and shooting. The excessive filling is due to the increase of additional injection work pressure or too much raw material metering check, so the internal stress of the product is too large, resulting in cracks when demolding.
In this case, the deformation of the mold standard parts also expands, resulting in a two-color mold injection more difficult to de-mold, thus promoting the creation of cracks (and even cracking). Hence, in that case, the injection work pressure should be reduced to avoid excessive filling.
- The product gets shrinks or deforms
Injection molding processing products’ shrinkage and deformation are caused due to short refrigeration shaping time, high mold temperature, and different overflow channel system software.
- The product has scorched spots or black lines
Scorch spot or black pattern means that the product has a gray-black color spot or gray-black pattern. The key reason is that the heat resistance of raw materials is not good, caused by the decomposition reaction of raw materials.
Reasonable avoidance of scorched spots or black lines generated by the preventive measures is to avoid wear-resistant material barrels if the raw material temperature is too high, thus slowing down the injection rate.
If the inner cavity of the barrel or the screw of the extruder has scars or vacancies, some of the raw materials will stick to the barrel and this part of the raw materials will be decomposed due to the over temperature.
In addition, the check valve can also cause decomposition due to the retention of the material. Therefore, it is important to avoid scorching or black lines when applying materials with high viscosity or very easy to dissolve.
Advantages compared with conventional injection molding machine
- Two colors can be produced at the same time.
- The more environment-friendly core material can be applied to the secondary material of the manuscript.
- Produce products with a more delicate shape such as marble pattern.
- The skin layer material and core material can cooperate to reduce internal stress/impact toughness.