Screw of injection moulding machine has the functions of conveying, melting, mixing, compressing, measuring and exhausting, which is the key factor affecting the plasticizing quality. Here are the main points of screw selection in injection moulding of several commonly used plastics.
The characteristics of PA are as follows: crystalline plastics have many kinds, different kinds, different melting points, and narrow melting point range. The melting point of PA66 is 260~265 degrees C. Low viscosity, good fluidity, obvious melting point, poor thermal stability. Water absorption is general.
The characteristics of ABS are as follows: good comprehensive performance, high impact strength, chemical stability and good electrical performance; good fusion with 372 plexiglass, made into two-color plastic parts, and can be chromium plated on the surface, spray paint treatment; high impact resistance, high heat resistance, flame retardant, enhanced, transparent grade; poor mobility than HIPS, better than PMMA, PC, good flexibility.
PP has the following characteristics: odorless and non-toxic. Because of its regular structure and high crystallization, the melting point can be as high as 167 C. Heat-resistant, corrosion-resistant, products can be steam disinfection is its outstanding advantages. Low density, is the lightest general purpose plastic. The disadvantage is poor low temperature impact resistance and easy aging, but can be overcome by modification respectively.
The characteristics of PC are as follows: amorphous plastics without obvious melting point, glass transition temperature 140-150 C, melting temperature 215-225 C and forming temperature 250-320 C. Viscosity is high and sensitive to temperature. It has good thermal stability in the normal processing temperature range. It does not decompose for a long time at 300 C, and begins to decompose at more than 340 C. Viscosity is less affected by shear rate. Water absorption is strong.
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