Classification and Selection of Screws

Usually, screw can be divided into general type, gradual type, mutation type, mixing type, separation type, shunt type and various barrier type, pin type, DIS opening shunt type and exhaust type, etc. The number of screw heads can be single or variable.

Special screw must be used if plastic with special properties, special products or special particle shape is used.

General screw is not superior to special screw in plasticization and power consumption for a kind of plastic. The following is a description of the special screw manufactured for various special products and special needs.

PC special screw

PC is a high viscosity non-crystalline plastic with poor fluidity, easy degradation after long time heating, high feeding torque, difficult to melt, and easy to plug. It needs high temperature and high pressure injection. The range of material temperature adjustment is narrow, and the technological property is not as good as PMMA.

The screw is fully hardened with imported high alloy steel, which can effectively withstand high torsion, high pressure impact, wear resistance, surface electroplating, corrosion resistance, smooth without pore to reduce surface adhesion and degradation, meticulous treatment of detail structure, effective prevention of hiding glue, low shear design, and low heating. In general, small and medium diameters are used to form PCABS + PC, PP-R and flame retardant ABS. Ordinary plastics and PMMA products can also be moulded, but the mixing effect is poor. If plastics are added with colour powder, it is necessary to customize the reinforced colour mixing screw.

With ultra-thin precision forming in the industry, we can provide screw diameter to be larger or smaller, length to be shorter, injection pressure to be increased to more than 3000Kgf/cm, and the injection seat can be retrofitted forward (after retrofitting, it can be restored to its original state).

PMMA special screw

PMMA is a high-viscosity non-crystalline plastic with high quality, strong and tough feeding torque, difficult to melt, easy to plug, shear-sensitive and degradable, slightly poor fluidity. It must be injected at high temperature and high pressure. The range of material temperature adjustment is wide and the process is good. Screw compression is relatively large, using imported high alloy steel full hardening treatment, effectively withstanding high torsion, high pressure impact, surface electroplating hard chromium reduces surface adhesion and degradation, plasticizing uniform effect, good mixing, low shear design heat, low degradation rate. In general, the middle diameter is used to form PMMA, PP-R, PC, ABS and other additives with good effect.

CP, CA acid screw assemblies:

In view of the corrosive properties of acid plastics such as CP and CA, special designs have been made for screw, melt drum and other plasticized parts in structure and surface treatment. The screw assembly has good corrosion resistance. It is recommended to use double alloy barrel to resist corrosion.

PVC special screw

PVC plastics can be divided into granular and powdery. They are very sensitive to temperature and easy to decompose. They have high viscosity and strong corrosiveness. The design of screw has two characteristics: the surface must be chromium plated; there is no apron and meson. The screw has good plasticization, less shearing heat and acid corrosion resistance. Because there is no rubber ring, it can not be used for low viscosity plastics and products with more accurate classification of injection speed and pressure.

There are two kinds of screw design: screw and rubber head integrated; screw and rubber head separated. For high quality products and only making single plastic (PVC), it is most appropriate to use the conjoined type, and vice versa, the split type can be used. However, it should be noted that the separation of screw and rubber head can easily lead to material accumulation. But what kind of screw we recommend must add a special thermometer for precise temperature control. Because of the need for heat dissipation and cooling, when making PVC products, the melt drum should adopt forced air cooling measures to cooperate with the screw. Soft PVC for making toys is excluded.

Special screws for PU and TPU

Designed for PU shear sensitivity, easy to overfire, strong adhesion and characteristics, hard chromium plating on the surface, smooth feeding, high plasticizing efficiency, low temperature rise.

Soft glue and EVA foam screw

Low shear, high conveying efficiency design, hard chromium plating on the surface.

PET special pole

PET plastic is the common raw material of plastic bottled beverage at present. It has low viscosity, good fluidity, large specific heat capacity, easy to stick, high forming temperature, but narrow range of material temperature adjustment and poor process. It is easy to produce acetaldehyde when the material temperature is too high, the screw shear is too large or the rotating speed is too fast, which leads to acidification.

According to the characteristics of PET and PET bottle blank which require fast plasticization and uniform plasticization, the screw has good plasticization, high stability, non-stick, fast melt speed and high rate of finished bottle blank blowing. Ordinary plastics can also be formed. However, it should be noted that the general manufacturers in mainland China will add nozzle material when making PET bottle blanks. In this case, the special screw for PET is not very suitable, whereas the ordinary screw chrome plating is more suitable. It is necessary to attach an anti-salivation device to the nozzle.

PA6/66/46/6T Special Screw

PA is a low-viscosity crystalline plastic with high temperature, fast melting speed, good self-lubrication, good fluidity, water-borne and salivable, temperature-sensitive, cold-head, moisture absorption, easy to stick the screw groove in the feeding section, and difficult coloring.

The screw has large compression ratio, precise backstop, good mixing effect, stable feed rate, high plasticizing efficiency and good exhaust effect. Generally take the middle diameter, forming PA, PP, LCP and other crystalline low viscosity plastics has good effect. Ordinary plastics can also be formed. For PC, PMMA flame retardant ABS and other plastics with high viscosity and poor thermal stability, it is not suitable (the middle temperature is too high, decomposition), forming POM is necessary to electroplate hard chromium. The nozzle is best heated at constant temperature, and additional anti-salivation device is necessary.

PPO special screw

PPO is an amorphous material, which is difficult to melt, easy to plug, sensitive to shear and easy to degrade.

It is recommended to use double alloys to improve wear resistance and corrosion resistance. Class C is enough, screw feeding is smooth and pressure is stable.

PBT+GF special screw

PBT is a saturated resin, semi-crystalline material, with high melting degree, fast crystallization, easy decomposition, pressure sensitivity and glass fibers to be added.

Dual alloys must be used to improve wear resistance. According to the amount of knitting, there are three kinds of workmanship: C, B and A.