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What is a plastic mold injection molding machine?

writer:LI SONG Share

The mechanical principle of the injection molding machine The injection molding machine is mainly divided into the injection part and the clamping part in the mechanical structure. The function of the injection part is to melt the plastic and inject it into the mold cavity, and the function of the clamping part is to control various actions such as opening and closing the mold and ejecting the product. The action program of the injection molding machine: nozzle forward→injection→holding pressure→pre-molding→reverse→nozzle backward→cooling→mould opening→ejection→needle withdrawal→door opening→door closing→mould closing→nozzle forward.

injection molding machine

1. The injection part of the injection molding machine mainly has two forms:
Piston type and reciprocating screw type. Piston-type injection molding machines are rare now, so I won’t introduce them here. The reciprocating screw injection molding machine melts and mixes solid plastic particles (or powder) through the rotation of the screw in the heating barrel, and squeezes it into the cavity at the front end of the barrel. Then the screw moves forward in the axial direction to remove the plastic in the cavity. The melt is injected into the mold cavity. During plasticization, the plastic is compacted in the screw groove under the push of the screw ridge, and receives the heat transferred from the barrel wall. In addition, the friction between the plastic and the plastic, the plastic and the barrel and the screw surface generates heat, and the temperature gradually rises. High to melting temperature. The melted plastic is stirred and further mixed by the screw, and enters the front of the barrel along the screw groove and pushes the screw back. The injection parts and plasticization-related components mainly include: screw, barrel, shunt shuttle, check ring, nozzle, flange, hopper, etc.

The following is an explanation of its role and influence in the plasticization process:
(1) Screw Screw is an important part of injection molding machine. Its function is to transport, compact, melt, stir and press plastic. All of this is accomplished by the rotation of the screw in the barrel. When the screw rotates, the plastic will generate friction and mutual movement on the inner wall of the barrel, the bottom surface of the screw groove, the screw edge advancement surface, and the plastic and the plastic. The advancement of plastic is the result of this combination of movements, and the heat generated by friction is also absorbed to increase the temperature of the plastic and melt the plastic. The structure of the screw will directly affect the extent of these effects. Ordinary injection screw structure is also designed as a separate screw, barrier screw or split screw in order to improve the quality of plasticization.

 (2) The structure of the barrel is actually a round tube with a discharge opening in the middle. In the plasticization process of plastics, the driving force for advancement and mixing comes from the relative rotation of the screw and barrel. According to the different forms of plastic in the screw groove, the screw is generally divided into three sections: solid conveying section (also called feeding section), melting section (also called compression section), and homogenizing section (also called metering section).

(3) Diversion shuttle (passing rubber head) Diversion shuttle is a torpedo-shaped part mounted on the front end of the screw. The function of the shunt shuttle in the plasticization of plastics is mainly to shunt and mix the plastic melt, so that the melt is further mixed evenly. At the same time, the shunt shuttle has the function of limiting the position of the anti-reverse ring during plasticization. In order to further strengthen the mixing effect, it is recommended to use barrier-type mixing structure shunt shuttles on injection molding machines with a clamping force of over 250 tons. Not only can the uniformity of the color of the product be improved, but also the mechanical strength of the product can be higher.

(4) The anti-reverse ring (over the rubber ring), as the name implies, the role of the anti-reverse ring is to prevent inversion. It is a part that prevents the plastic melt from leaking back during injection. When working, the non-return ring and the non-return washer (over-rubber washer) contact to form a closed structure to prevent the plastic melt from leaking. The precision of the weight of an injection molding machine's injection product has a great relationship with the speed of the anti-return ring's anti-reverse movement. The speed of a non-return ring action response is determined by its non-reverse movement stroke, seal pressing time, time to leave the shunt shuttle and other factors. We have tried a variety of non-return ring structures and part parameters, and finally determined the optimal non-reverse surface parameters, the non-reverse ring and the shunt shuttle fitting parameters, the non-reverse ring and the barrel gap parameters through experiments. High-precision injection volume control can be achieved.

(5) Nozzle The nozzle is the transitional part connecting the barrel and the mold. During injection, the molten material in the barrel is pushed by the screw to inject into the mold with high pressure and rapid flow through the nozzle. Therefore, the structure of the nozzle, the size of the nozzle, and the manufacturing accuracy will affect the pressure and temperature loss of the melt, the distance of the range, the pros and cons of the feeding effect, and whether the phenomenon of "salivation" occurs. There are many types of nozzles currently in use, and they all have their scope of application.

(6) Flanges & flanges are the parts that connect the nozzle and the barrel? It only serves as a channel during plastic injection. If there is a large gap or groove on the joint surface of the flange and the nozzle or the flange and the barrel, the black spots of the product will appear due to the decomposition of the plastic in the gap or groove for too long.

(7) Feeding hopper: The feeding hopper is a part that stores plastic raw materials, and some add heating and blowing devices to the feeding hopper to make a drying hopper. The shape of the hopper is generally a lower cone shape and an upper cylindrical shape. The cone-shaped cone slope has different optimal values ​​for plastic parts with different particle sizes, different particle shapes, and different friction coefficients and adhesion coefficients between particles. Otherwise, the storage capacity of the hopper is wasted or the feeding is not smooth. Or the phenomenon of "bridging" or "funneling into tubes" where the material is not discharged at all. The reason for the "bridging" phenomenon is that the plastic particles form an open bridge between the small cones that can support the material above it. It is easier to occur for recycled materials with larger particles and irregular shapes. "Funnel into tube" is because the particles flowing down are not enough to pull the adjacent particles to flow together, which often occurs when the plastic particle size is small. The general solution is to install a vibration device on the hopper or reduce the cone slope. If the heat from the barrel is transferred to the feeding hopper, the temperature of the feeding hopper is too high, the surface of the plastic particles will soften or stick into blocks, which is more likely to form "bridging" or blockage.

2. Mold clamping control:
Mold clamping is to close the mold tightly with a huge mechanical thrust to resist the huge opening force of the mold caused by the high pressure injection of molten plastic during the injection molding process and the filling of the mold. Close the safety door, each travel switch will give a signal, and the mold clamping action will start immediately. The first is that the movable template starts at a slow speed. After a short distance, the control rod pressing block that originally held the slow switch is released, and the movable plate rotates to advance quickly. When advancing to close to the end of mold clamping, the other end of the control rod presses the slow switch again, and the movable plate rotates at a slow speed and advances at a low pressure at this time. During the low-pressure mold clamping process, if there are no obstacles between the molds, they can be smoothly closed until the high-pressure switch is pressed. The high-pressure switch is to straighten the hinge of the machine to complete the mold clamping action. The distance is very short, generally only 0.3~1.0mm. The mold clamping termination limit switch is touched as soon as the high voltage is turned on. At this time, the action stops and the mold clamping process ends.

LISONG machine rofessional provide the plastic injection molding machine.Factory direct sales, quality assurance, and price concessions.~~~ Would you like it? Wellcome to contact us.The manufacturers email:kevin@lisonginc.com. 

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