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How to Choose the Screw of Injection Molding Machine Correctly
Publisher : Wia Release time : 1/28/2019 2:51:18 PM
1. The characteristics of PC material (polycarbonate):
Amorphous plastics, no obvious melting point, glass transition temperature 140-160 degrees Celsius, melting temperature 215-225 degrees Celsius, forming temperature 230-320 degrees Celsius;
2. High viscosity, high processing temperature, narrow range, easy to decompose, avoid overheating when selecting screw;
3 is sensitive to water. The resin hydrolyzes easily at high temperature. The drying temperature is 120 - 130 degrees Celsius and the drying time is about 4 hours.
Selection of parameters:
L/D has the characteristics of good thermal stability and high viscosity. In order to improve the plasticizing effect, the ratio of length to diameter should be as large as possible.
Because of its wide melting temperature range, long feeding section, short homogenizing section and moderate compression ratio, barrier type rubber head can be used to increase plasticizing effect.
If flame retardant or glass fiber reinforced PC material is added, corrosion resistant, wear resistant and high quality stainless tool steel screw and three small pieces can be selected.
2. PMMA (plexiglass) characteristics:
The glass transition temperature is 105 degrees Celsius, the melting temperature is more than 160 degrees Celsius, the decomposition temperature is 270 degrees Celsius, and the forming temperature range is very wide 180-250 degrees Celsius.
Viscosity is high, fluidity is poor, and shear rate is sensitive. Temperature should be strictly controlled during processing.
When the barrel temperature is 240 - 250 degrees Celsius and exceeds 260 degrees Celsius, the retention time is not more than 8 minutes.
Water absorption is strong, drying temperature is 80-90 degrees Celsius, time is more than 3 hours.
Selection of parameters:
The ratio of length to diameter is 20-22 for L/D, and L1 = 35-45% for gradual screw and L2 = 35-40% for gradual screw.
The compression ratio is generally 2.3-2.6.
In view of its hydrophilicity, the mixing fire structure is adopted at the front end of the screw.
PA (polyamide), common PA6 (nylon 6), PA66 (nylon 66) characteristics:
There are many kinds of crystalline plastics with different kinds, different melting points and narrow upper melting point range. Generally, the melting point of PA66 is 260 - 270 degrees Celsius.
It has low viscosity, good fluidity, obvious melting point and poor thermal stability.
High water absorption, dryer temperature 80 degrees Celsius, not more than 120 degrees Celsius, time 16 hours. If the material is exposed to air for 8 hours, vacuum oven should be used for about 105 degrees Celsius for 12 hours.
The parameters are determined first:
L/D chooses mutant screw with length ratio of 18-20.
Compression ratio is generally 2.5-3.5, which prevents SUPERTHERMAL decomposition of h3:0.067-0.089D.
Because of its low viscosity, the clearance between the rubber ring and the barrel should be as small as 0.05-0.08, and the clearance between the screw and the barrel should be 0.08-0.12.
Spring self-locking nozzle can be fitted at the nozzle.
IV. Chemical name of PET (polyester): properties of polyethylene terephthalate:
The melting point of blowing PET is 250 - 260 C, the forming temperature of blowing PET is wide, about 255 - 290 C, and the GF - PET of reinforced grade can reach 290 - 315 C, etc.
High melting point, low viscosity, high adhesion to metal, easy hydrolysis;
It is hydrophilic. The adhesive is sensitive to water at high temperature. The drying temperature is 150 - 160 C and the drying time is more than 4 hours.
Parameter selection:
L/D generally takes 20-22, three-segment distribution L1 = 50-60%, L2 = 20-30%.
The compression ratio of screw with low shear and low compression ratio is 1.8-2.2, because shear overheating causes discoloration or opacity H3 = 0.09-0.10D.
When using recycled material (sheet material), the conveying capacity of feeding section should be increased and the forced feeding plasticizing system should be adopted.
V. PVC (polyvinyl chloride)
Thermosensitive materials are generally divided into hard and soft materials. The difference lies in how many plasticizers are added to the raw materials. Less than 10% of the materials are rigid and more than 30% are soft.
Characteristic:
There is no obvious melting point. The melting point softens at 60 and the viscoelastic state at 100 150 and the melting temperature range at 140 is narrow. The thermal stability is poor. It is easy to decompose. It decomposes rapidly at 170 and the softening point is close to the decomposition point. The Deco
Because UPVC melt has high viscosity, poor thermal stability, temperature and time will lead to decomposition, so it has corrosion effect on general steel.
Temperature control is strict, screw design should be as low as possible, to prevent overheating, the runner must be smooth, no dead angle, to prevent the decomposition of accumulated materials;
The screw barrel should be protected from corrosion.
Injection moulding process should be strictly controlled.
Parameter selection:
L/D=18-21, h3+0.067-0.08D, e-1.6-2, L1=40-45%, L2=35-45%. In order to prevent the storage material from passing through the rubber ring, the chrome-plated screw is used in the head at 20-30 degrees Celsius.
Temperature selection:
1) Multi-stage air-cooling device for melt rubber cylinder;
2) screw barrel device for UPVC with low shear and high mixing.
Amorphous plastics, no obvious melting point, glass transition temperature 140-160 degrees Celsius, melting temperature 215-225 degrees Celsius, forming temperature 230-320 degrees Celsius;
2. High viscosity, high processing temperature, narrow range, easy to decompose, avoid overheating when selecting screw;
3 is sensitive to water. The resin hydrolyzes easily at high temperature. The drying temperature is 120 - 130 degrees Celsius and the drying time is about 4 hours.
Selection of parameters:
L/D has the characteristics of good thermal stability and high viscosity. In order to improve the plasticizing effect, the ratio of length to diameter should be as large as possible.
Because of its wide melting temperature range, long feeding section, short homogenizing section and moderate compression ratio, barrier type rubber head can be used to increase plasticizing effect.
If flame retardant or glass fiber reinforced PC material is added, corrosion resistant, wear resistant and high quality stainless tool steel screw and three small pieces can be selected.
2. PMMA (plexiglass) characteristics:
The glass transition temperature is 105 degrees Celsius, the melting temperature is more than 160 degrees Celsius, the decomposition temperature is 270 degrees Celsius, and the forming temperature range is very wide 180-250 degrees Celsius.
Viscosity is high, fluidity is poor, and shear rate is sensitive. Temperature should be strictly controlled during processing.
When the barrel temperature is 240 - 250 degrees Celsius and exceeds 260 degrees Celsius, the retention time is not more than 8 minutes.
Water absorption is strong, drying temperature is 80-90 degrees Celsius, time is more than 3 hours.
Selection of parameters:
The ratio of length to diameter is 20-22 for L/D, and L1 = 35-45% for gradual screw and L2 = 35-40% for gradual screw.
The compression ratio is generally 2.3-2.6.
In view of its hydrophilicity, the mixing fire structure is adopted at the front end of the screw.
PA (polyamide), common PA6 (nylon 6), PA66 (nylon 66) characteristics:
There are many kinds of crystalline plastics with different kinds, different melting points and narrow upper melting point range. Generally, the melting point of PA66 is 260 - 270 degrees Celsius.
It has low viscosity, good fluidity, obvious melting point and poor thermal stability.
High water absorption, dryer temperature 80 degrees Celsius, not more than 120 degrees Celsius, time 16 hours. If the material is exposed to air for 8 hours, vacuum oven should be used for about 105 degrees Celsius for 12 hours.
The parameters are determined first:
L/D chooses mutant screw with length ratio of 18-20.
Compression ratio is generally 2.5-3.5, which prevents SUPERTHERMAL decomposition of h3:0.067-0.089D.
Because of its low viscosity, the clearance between the rubber ring and the barrel should be as small as 0.05-0.08, and the clearance between the screw and the barrel should be 0.08-0.12.
Spring self-locking nozzle can be fitted at the nozzle.
IV. Chemical name of PET (polyester): properties of polyethylene terephthalate:
The melting point of blowing PET is 250 - 260 C, the forming temperature of blowing PET is wide, about 255 - 290 C, and the GF - PET of reinforced grade can reach 290 - 315 C, etc.
High melting point, low viscosity, high adhesion to metal, easy hydrolysis;
It is hydrophilic. The adhesive is sensitive to water at high temperature. The drying temperature is 150 - 160 C and the drying time is more than 4 hours.
Parameter selection:
L/D generally takes 20-22, three-segment distribution L1 = 50-60%, L2 = 20-30%.
The compression ratio of screw with low shear and low compression ratio is 1.8-2.2, because shear overheating causes discoloration or opacity H3 = 0.09-0.10D.
When using recycled material (sheet material), the conveying capacity of feeding section should be increased and the forced feeding plasticizing system should be adopted.
V. PVC (polyvinyl chloride)
Thermosensitive materials are generally divided into hard and soft materials. The difference lies in how many plasticizers are added to the raw materials. Less than 10% of the materials are rigid and more than 30% are soft.
Characteristic:
There is no obvious melting point. The melting point softens at 60 and the viscoelastic state at 100 150 and the melting temperature range at 140 is narrow. The thermal stability is poor. It is easy to decompose. It decomposes rapidly at 170 and the softening point is close to the decomposition point. The Deco
Because UPVC melt has high viscosity, poor thermal stability, temperature and time will lead to decomposition, so it has corrosion effect on general steel.
Temperature control is strict, screw design should be as low as possible, to prevent overheating, the runner must be smooth, no dead angle, to prevent the decomposition of accumulated materials;
The screw barrel should be protected from corrosion.
Injection moulding process should be strictly controlled.
Parameter selection:
L/D=18-21, h3+0.067-0.08D, e-1.6-2, L1=40-45%, L2=35-45%. In order to prevent the storage material from passing through the rubber ring, the chrome-plated screw is used in the head at 20-30 degrees Celsius.
Temperature selection:
1) Multi-stage air-cooling device for melt rubber cylinder;
2) screw barrel device for UPVC with low shear and high mixing.
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