A. It is known that the injection rate is closely related to the appearance of the finished product. The injection rate controls the filling state of the resin in order to improve the quality of the finished product, In particular, it improves the accuracy of appearance and size. Especially in the range, the injection mode of arbitrarily controlling the injection rate of resin is the representative work. According to the requirements of different quality, in the process of injection, different injection speed is given. The control of this shooting mode can not only prevent the rough edge, indefinite injection, bubble, crack and other appearance defects of the finished product, It can improve the precision of size, reduce the internal stress and increase the strength of finished products

B. The relationship between the quality and the injection conditions is that the surface layer of the finished product is solidified during filling. Therefore, the adverse phenomena on the surface of the finished product depend on whether the molding state of the surface layer is correct or not during filling. Therefore, proper control of the injection speed has an excellent effect on the following adverse phenomena

1. The flow mark formed by the sudden increase of the surrounding area or cross-section area of the exit is caused by the jet phenomenon, which makes the resin flow into turbulent flow, resulting in irregular skin layer. In this case, the injection speed is reduced, and the pressure is placed on the basis of being able to flow. Most of the problems can be solved,

2. Blurring, coarseness, sliver, scorching and other phenomena are produced around the injection products, most of which are thermal decomposition and gas generated by friction with the injection outlet at the initial stage of injection. Because the plastic is always filled and the exhaust effect at the rear end is poor, the gas pressure will be generated. In this way, the injection speed will be reduced and the injection pressure will be reduced, which has a significant improvement effect

3. The joint line mark is formed by the joint of the solidified epidermis layer. It is very difficult to make the mark disappear, change the flow mode, change the position where it occurs in the invisible place, or accelerate the injection speed when the surface layer is joined, make the surface layer thinner, and also reduce the joint mark to a certain extent. Other causes of the joint line include: the flow direction changes suddenly during the filling process, In this case, reduce the flow rate of this part. It will have different effects on preventing irregular flow rate

4. Burr: it is caused by poor mold or insufficient mechanical die closing force, but it may also be helpful to control the injection speed, that is, the resin flows to the place where the burr occurs, reducing the injection speed, making the cortex at the place where the burr occurs thicker, because of the solidified cortex, although the mold has some voids, making the resin inflow more difficult

5. Gas scorch (discoloration): the air or resin in the mold hole contains gas (gas). After being sealed, it will generate high temperature due to adiabatic compression. Therefore, when the air is sealed, if the injection speed is reduced, it will be effectively prevented

6. Dents: Plastic shrinks in the process of cooling and hardening. It is very difficult to completely avoid them, but at the moment of filling, the injection speed is reduced and the burr is difficult to produce. When cooling, the pressure maintaining is increased, which will improve to a certain extent. Moreover, the molds or finished products with pinholes are far away from the injection outlet, because of the poor pressure maintaining effect, dents are easy to occur, Reduce the ejection speed of the thick meat part, so that the epidermis of this part becomes thicker. When it cools and hardens, the inner core layer creates a concave nest, and the surface dent is invisible

7. Shrinkage: among the defects of injection molding products, shrinkage is a common occurrence. For products with longer sprue and larger thickness, and products with uneven glue position, it is even more common. For injection molding, the melted plastic starts to harden when it touches the mold surface, and the density of the heated plastic and the solidified plastic starts to distinguish, so shrinkage begins, In particular, the injection pressure of products with irregular thickness and glue position can not be supplemented and the shrinkage is more obvious. If necessary, glass fiber can be filled into composite materials, the shrinkage will be reduced, otherwise the shrinkage rate of all crystalline plastics is quite large, and the shrinkage at the downstream end is easy to occur, so the plastic is adjusted by pressure maintaining before hardening, but the pressure maintaining pressure is too often cracked, Therefore, the pressure must be reduced with the increase of time. When the sprue is larger or the thickness difference is reduced, it is also helpful for shrinkage

8. End burning: the air in the mold cavity is compressed to produce high temperature, while the filling of the machine is carried out all the time. If the injection pressure is increased and the injection speed is increased, blacking will occur. This condition can improve the porosity or reduce the injection pressure / reduce the injection speed of the end and the plastic temperature, avoid the use of raw materials and materials with better thermal stability. Of course, the sprue is increased, Reducing the end velocity or improving the exhaust port is helpful to improve the end burn

9. Silver bar: the phenomenon of white stripes on the surface of the molded product caused by the plastic flow when it is ejected. This is the phenomenon that the water in the plastic is compressed into a gas shape, which cannot evaporate under the pressure of the nozzle and is attached to the hardening process. Therefore, the drying of the water in the raw material can completely stop the occurrence

10. Melting line: when the plastic flows through the hole, it can be divided and then combined, which is caused by the air hazard, or there are too many release agents. Therefore, it is helpful to raise the temperature of the plastic or increase the speed of the plastic passing through the hole, increase the temperature of the mold, and stop using the materials with good fluidity and release agents

3、 Problems often occur in injection molding machine

1. The molding material supply is not smooth. Under the normal rotation condition, the plastic fails to supply the screw normally and there is idling. The most common reason for this is that the raw material temperature is not consistent with the actual raw material temperature, resulting in the screw caking of the machine. For a long time, the machine does not turn off the electric heating, resulting in the heating dispersion of the screw raw material, the gas of raw material (gas) is serious, the back pressure of the machine is too large, and the powder is caused by too much recycled material, Or the color powder uses too much viscous oil and so on, the forming conditions are not appropriate, there are also reasons such as incomplete dry materials or abnormal temperature setting, or excessive screw speed

2. In normal production, the temperature rise of material pipe is too high; the back pressure is too high or the screw material pipe is damaged abnormally

3. Insufficient plasticizing capacity: (cycle time is too short) that is, heating is not enough to dissipate heat, which can moderately increase the wattage of the electric heater, and the raw material itself has insufficient plasticizing differential thermal decomposition

4. The injection machine is unstable, the temperature is abnormal or the countercurrent system is broken, the starting point position of the injection point is different, the voltage at the manufacturing site is not stable, and the machinery has mature technical experience and product development ability in the precision injection molding process due to the adjustment of the variable voltage parameters, which has solved various process requirements for customers.