Presses the basic parameters of screw and barrel

Date：2011/12/6 17:55:55

Generally divided into three sections that screw feed zone, compression section, all of the segments.

Feed zone - at the end by a smaller, main role is to transport raw materials to the back, so the main problem is the transmission capacity, parameters (L1, h1), h1 = (0.12-0.14) D.

Compression Section - The change in the end, the main role is to compaction, the molten material, the establishment of pressure. Parameters of the compression ratio ε = h1/h3 and L2. Degree of accuracy should be graded A = (h1-h3) / L2.

All of paragraph (measured above) - the compression section has been quantitatively determined temperature to melt the material pushed the front of the screw, the parameter (L3, h3), h3 = (0.05-0.07) D.

Screw on the whole, the aspect ratio parameter L/D-

L / D pros and cons: L / D with speed n, ability and the effect of plasticizing screw is an important factor, L / D is the material in a large barrel in the long residence time, will help plastics, and pressure flow, leakage reduction improve the plasticizing capacity, while the temperature distribution materials require a higher benefit, but the after use of the manufacturing and assembly have a negative impact on the general L / D of (18 ~ 20), but there is a trend to increase .

Other pitch S, helix angle φ = πDtgφ, general D = S, then φ = 17 ° 40 '.

φ affect the ability of plastics, in general, the larger φ is faster transmission speed, so the materials of different shapes, the φ have changed. Powder desirable φ = 25 ° or so, cylindrical material φ = 17 ° or so, box material φ = 15 ° or so, but φ is different, in terms of processing, but also more difficult, it is generally φ take 17 ° 40 '.

Wide edge e, in terms of the viscosity of the material, e try to get bigger, too easy to leakage, but the Assembly to increase the power consumption is too easy to overheat, e = (0.08 ~ 0.12) D.

All in all, in the present circumstances, due to lack of the necessary test means of the screw design means the design is not complete. Most of the material should be based on different nature of their experience of different formulation parameters to meet the needs of each plant roughly the same.

One. PC material (polycarbonate)

Features: ① non-crystalline plastics, no melting point, glass transition temperature of 140 ° ~ 150 ℃, melting temperature of 215 ℃ ~ 225 ℃, mold temperature 250 ℃ ~ 320 ℃.

② viscosity, temperature sensitive, in the normal processing temperature range, good heat stability, 300 ℃ almost no decomposition of long-stay, more than 340 ℃ begins to decompose, the viscosity was less affected by the shear rate.

③ absorbent

Selected parameters:

a. L / D for its thermal stability, viscosity characteristics, selected to enhance the plasticizing effect as large aspect ratio, factory take 26.
Because of its wide range of melting temperature, compression can be longer, so the use of gradient-type screw. L1 = 30% full-length, L2 = 46% full length.

b. Graded by the degree of compression ratio ε A need to adapt with the melting rate, but not yet calculated melting rate, according to PC from 225 ℃ to 320 ℃ between melt processability characteristics, its degree of gradient taken relatively moderate value of A can be upper value, in the case of large L2, general gradient-type screw ε = 2 ~ 3, factory take the 2.6.

c. Because of its high viscosity, water absorption, it is in all of the segment before the segment after compression screw on the increase in the mixing structure, to enhance the dissolution of the solid bed, while the entrained water which can escape into a gas.

d. Other parameters such as e, s, φ, and the gap with the barrel can be the same as other ordinary screw.

Two. PMMA (plexiglass)

Features: ① glass transition temperature of 105 ℃, melting temperature greater than 160 ℃, the decomposition temperature of 270 ℃, forming a wide temperature range.

② viscosity, poor mobility, good thermal stability.

③ absorbent.

Preferences
a. L / D select the aspect ratio of 20 to 22 of the gradient-type screw, depending on the molding of precision general L1 = 40%, L2 = 40%.

b. Compression ratio ε, 2.3 to 2.6 is generally selected.

c. There are some for its hydrophilic, so the screw of the front-end mixing ring structure.

d. Other parameters are generally designed according to universal screw, and barrel gap is not too small.

Three. PA (nylon)

Features: ① crystalline plastics, more and different types is not the same, its not the same melting point and melting range is narrow, generally with PA66 the melting point of 260 ℃ ~ 265 ℃.

② low viscosity, good fluidity, there are more obvious melting point, poor thermal stability.

③ absorbent general.

Preferences
a. L / D aspect ratio of 18 to 20 selected mutant screw.

b. Compression ratio is generally selected 3 to 3.5, which prevent the overheating decomposition h3 = 0.07 ~ 0.08D.

c. Because of its low viscosity, so the check ring and barrel at the gap should be small, about 0.05, the screw and barrel gap of about 0.08, if necessary, depending on the material, the front can be equipped with check ring, at the nozzle should be self-locking.

d. Other parameters, according to universal screw design.

Four. PET (polyester)

Features: ① melting point 250 ℃ ~ 260 ℃, blow molding grade PET is a wider temperature point, about 255 ℃ ~ 290 ℃.

② PET blow molding grade high viscosity, the temperature impact on the viscosity, thermal stability.

Preferences
① L / D 20 general admission, three sections of the distribution of L1 = 50% -55%, L2 = 20%.

② low shear, low compression ratio of the screw, the compression ratio ε, and generally 1.8 to 2, while overheating cause discoloration or opaque shear h3 = 0.09D.

③ no mixing screw the front ring to prevent overheating, possession of materials.

④ because this material is more sensitive to temperature, and general manufacturers and more recycled materials, to increase production, our factory uses low shear screw, it may be appropriate to increase the motor speed to achieve the purpose. Use of recycled materials in the same time (most of the material for the film), the factory according to the actual situation, in order to increase the feed section of the transmission capacity, has taken to increase the blanking aperture in the slot in the barrel, etc., to obtain a better the effect.

V. PVC (polyvinyl chloride)

Heat-sensitive materials are generally divided into hard and soft, the difference is the amount of plasticizer added to raw materials, less than 10% for hard, soft more than 30%.

Features: ① no significant melting point, 60 ℃ soft, 100 ℃ ~ 150 ℃ viscoelastic state, 140 ℃ when the melt, while decomposition, 170 ℃ decompose rapidly, softening point close to the break point, decomposition gases released in the HC1.

② poor thermal stability, temperature, time will lead to decomposition, poor mobility.

A. Design Principles Strict temperature control, low shear screw design as much as possible to prevent overheating.

b. The screw and barrel to prevent corrosion.

c. Injection molding process to be strictly controlled.

Generally speaking, the screw parameters for the L / D = 16 ~ 20, h3 = 0.07D, ε = 1.6 ~ 2, L1 = 40%, L2 = 40%.

To prevent the possession of material, no check ring, the head taper 20 ° ~ 30 °, more adapted to the soft, such as the products are higher, and can be used without metering section, the separation-type screw, this screw for rigid PVC more suitable, but also with the temperature, the feeding section of the internal cooling water or screw hole, plus cold water barrel or tank, temperature control accuracy of ± 2 ℃ or so.

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