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Screw Role And Working Principle
Sep 28, 2017

The screw is an important part of the injection molding machine. Its role is to transport the plastic, compaction, melting, stirring and pressure. All of which are done by the rotation of the screw in the barrel. In the rotation of the screw, the plastic for the barrel wall, the bottom of the screw groove, the edge of the screw and the plastic and plastic between the friction will produce friction and mutual movement. The advancement of the plastic is the result of this combination of movements, and the heat generated by the friction is also absorbed to increase the temperature of the plastic and to melt the plastic. The design of the screw will directly affect the extent of these effects.

1. The type and characteristics of the screw

(1) Gradient screw Features: Compression section is longer, accounting for 50% of the total length of the screw, plastic energy conversion when the ease of use, such as PVC and other poor thermal stability of the plastic. In the case of

(2) mutant screw characteristics: compression section is short, accounting for the total length of the screw about 5% to 15%, plastic energy conversion is more intense, and more for polyolefin, PA and other crystalline plastic. In the case of

(3) general-purpose screw Features: more adaptable general-purpose screw, can adapt to a variety of plastic processing.

2. Injection molding machine screw section description

Injection molding machine screw under normal circumstances can be divided into feeding section, compression section, equalization section (also known as the measurement section). (Note: different screw three sections of the ratio is not the same, the screw groove is not the same, the same form of the end of the screw diameter)

(1) Feeding section Description: This section of the groove depth of the fixed, its function is responsible for preheating and plastic solid transport and push. It must be ensured that the plastic begins to melt at the end of the feed section. In the case of

(2) Compression section Description: This section is tapered screw screw groove deep, its function is plastic raw material melting, mixing, shear compression and pressurized exhaust. Plastic in this paragraph will be completely dissolved, the volume will be reduced, the compression ratio of the design is very important.

(3) homogenization section Description: This section is screw groove groove fixed groove depth, the main function of mixing, melt transport, measurement, must also provide sufficient pressure to maintain the uniform temperature of molten rubber and stable flow of molten plastic.

3. Description of screw parameters

D-screw diameter (multi-use Φ said), the size of the screw directly affect the size of plasticizing capacity, affecting the size of the theoretical injection volume. In the case of

L / D-screw length to diameter ratio, L is the effective length of the screw thread part. The longer the length of the screw, the longer the length of the screw, the greater the length of the screw, the greater the length of the screw, the greater the length of the screw, the greater the length of the screw, the direct impact on the material in the hot history of the screw, but also affect the ability to absorb energy; if L / D is too small, Melting effect and melt quality; if L / D is too large, the transmission torque increases and the energy consumption increases. L1-feeding section length, the length of L1 should ensure that the material has sufficient transport space, because too short L1 will lead to premature melting of materials, which is difficult to guarantee the stability of the pressure delivery conditions, it is difficult to ensure that the screw after the plastic Quality and plasticizing capacity. In the case of

h1 - Feeding section groove depth. h1 deep, then the material to accommodate more to improve the amount of material and plasticizing capacity, but will affect the material plasticizing effect and the root of the screw shear strength, the general h1 ≈ (0.12 ~ 0.16) D

L3- melt length. The length of the L3 contributes to the fluctuation of the melt in the groove and has the effect of stabilizing the pressure so that the material is discharged from the screw head with a uniform amount of material. Generally L3 = (4 ~ 5) D. In the case of

h3 measuring the depth of the groove, h3 small, shallow snail, improve the plastic melt plastic effect, is conducive to the melt of the homogenization, but h3 too small will lead to high shear rate, and shear heat Large, causing the degradation of the molecular chain, affecting the melt quality; if h3 is too large, due to pre-plastic, the back pressure generated by the back pressure of the screw increased, will reduce the plasticizing capacity. In the case of

S-pitch, ε = h1 / h3, that is, the ratio of the depth h1 of the feed section to the groove depth h3 of the melting section is affected by the size of the helix angle, which affects the conveying efficiency of the groove.

Method of using screw for injection molding machine

1, the cartridge does not reach the pre-set temperature, do not start the machine. The new heat is generally required to reach the set temperature of 30 minutes after the operation of the screw. In the case of

2, each stop more than half an hour or more, it is best to close the blanking mouth and cleaning the material inside the barrel, set the insulation. 3, to avoid foreign matter falling into the material tube damage screw and barrel. To prevent metal debris and debris fall into the hopper, if the processing of recycled materials, need to add a magnetic hopper to prevent iron and other into the barrel. In the case of

4, the use of salivation when the barrel to determine the plastic completely melted, so as not to damage the drive back when the drive parts. 5, to avoid screw idling, slipping and so on. In the case of

6, the use of new plastic, the cartridge should be more than the remaining clean. Use POM, PVC, PA + GF and other materials to minimize the degradation of raw materials, after the shutdown with a timely rinse with ABS and other materials. In the case of

7, to avoid POM and PVC mixed with the barrel at the same time, the reaction will occur in the melting temperature caused serious industrial accidents. 8, when the molten plastic temperature is normal but continue to find molten plastic black spots or discoloration, should check the screw reverse ring (apron, meson) is damaged.

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