How to solve the problem of flow marks in injection molding products?

one. The effect of plastic materials on flow marks

The main reason for the flow marks is that the material is not slowed down due to the injection pressure and the rate of fire. The main reasons are the following two aspects:

The fluidity of plastic materials is not good

For injection molding products with relatively long flow length, materials with good fluidity must be selected. If the fluidity of the material is not good, the molten plastic will go slower and slower. The slower the temperature, the easier it is to cool. Because the flow length is too large, the injection pressure and pressure can not be maintained. The molten plastic is pressed against the surface of the mold to leave marks in the direction of material flow. When selecting materials, you can refer to the material property table parameters or let the material supplier make suggestions. If the glue is not easy to produce, try to use materials with good fluidity. At the same time, the mold flow analysis can also provide very accurate reference data. When the mold flow analysis data meets the requirements, the mold development is carried out, and it is impossible to take risks to make the back end difficult to handle.

Use a suitable molding material lubricant

For materials that do not meet the requirements for fluidity, a suitable proportion of molding lubricant can be added to improve the fluidity of the material. Refer to the material supplier's recommendations to increase the proportion of lubricant and increase the fluidity. In the case of sufficient injection pressure and pressure retention, the condensation layer of the material on the surface of the mold will not be generated until the material is shaped and no flow marks will be formed.

two. Effect of mold on flow marks

It is difficult to make injection molds difficult. The occurrence of many problems is not unilateral. It is caused by the interaction of many interrelated factors. It is necessary to systematically analyze and compare the advantages and disadvantages of various aspects to improve and solve.

1. The mold surface temperature is too low to cause flow marks

If the mold surface temperature is too low, the temperature of the material will drop too fast, and the material will quickly condense on the surface of the mold to form a trace of the flow direction. Therefore, it is necessary to increase the mold surface temperature and maintain a high material temperature so that the injection pressure can press the condensation layer tightly on the mold surface until the product is completely cooled. The mold temperature can be determined according to the mold flow analysis recommendations and the material property table, and the temperature of the ladder is used to gradually adjust the suitable product. For example: according to the recommended mold temperature start adjustment, each time increase 5 degrees, gradually adjust until the requirements are met, here pay attention to the actual mold surface temperature.

2. Factors affecting the size and quantity of runners and gates

The main purpose of the size and quantity of runners and gates is to increase the injection pressure, hold pressure and reduce the material flow ratio. The flow passage and the gate are too small to have a large pressure loss, and cannot provide sufficient injection pressure and pressure retention, and the injection speed is lowered, and the material easily forms a flow mark on the surface of the product. The specific flow path size and the number of gates can be referred to the mold flow analysis data.

3. Mold exhaust must be sufficient

The importance of mold exhaust to injection molding products, I wrote an article on the importance of exhaust on the platform, no longer talk about it here, interested friends can go and see. The end of the flow channel should have a large enough exhaust gas to prevent the flow of gas into the cavity. The poor cavity of the mold cavity will greatly reduce the flow speed of the material. The speed is slow, the material is easy to cool, and flow marks are prone to occur. The design of the exhaust gas can refer to the results of the mold flow analysis, and it can be judged that the flow end region and the severe flow blocking region can focus on increasing the exhaust gas. There is not much talk about exhausting here, please read the related reading at the end of the article.

three. Effect of molding conditions

The molding conditions are mainly affected by the following aspects:

When the temperature of the material tube is too low, the temperature of the molten plastic is also low, the fluidity of the material is lowered, and flow marks are easily formed in the flow direction;

The material cycle time is unreasonable. When the material cycle time is too short, the melt temperature will be low, and the fluidity of the material will be deteriorated during filling, which is prone to flow marks;

The material has insufficient residence time in the material tube, the material temperature is also too low, the material is not easy to be filled, and flow marks are also formed;

The injection injection pressure and holding pressure are insufficient, the material flow is slow, and it is easy to form cold glue on the surface of the mold, which will form flow marks. In this respect, the mold flow analysis data can also be referred to and gradually adjusted;

The temperature of the nozzle should not be too low, and it can be appropriately increased. It is more suitable than the temperature of the previous section.