What are the special requirements for the injection molding process of PEEK products?
PEEK is a thermoplastic material high temperature special engineering plastic, which can be molded by injection molding. PEEK products generally injection dimensional accuracy can reach about 0.1mm, precision injection according to the different wall thickness of the product, different structures, dimensional accuracy can be controlled at about 0.015mm.
The melt fluidity of PEEK at high temperature is poor, and the melting temperature needs to be maintained at about 385 degrees. It is required that the heating section of the injection molding machine can continuously and stably provide a heating temperature of more than 350 degrees. The viscosity of PEEK in the molten state is larger, the injection pressure is higher, the wear of the screw is greater, and the injection machine needs to provide greater injection pressure.
The special requirements of PEEK injection molding process are as follows:
1. Injection requirements
Pressure: General injection pressure 70-140Mpa, injection speed: medium to high speed, back pressure: it is recommended to set the back pressure to 0-1.0MPa(0-10 kgf/cm2).
2, screw requirements
It is recommended that the minimum length to diameter ratio of the screw L/D is 16:1, but the L/D ratio between 18:1 and 24:1 should be preferred.
3. Injection machine:
Conventional machines that maintain the melt temperature at 360-400 ° C can be used.
4. Cylinder capacity
Due to the high processing temperature of PEEK polymers, the residence time of the material must be as short as possible. The ideal barrel capacity is 2-5 times the total injection weight.
5, nozzle and locking system
Install a heater large enough at the nozzle to prevent the cooling from producing "injection cold material". If the temperature drops below 343 ° C, the melt will cure very quickly.
6. Barrel temperature
The unenhanced level is 360-380 ° C, and the enhanced level is 380-400 ° C, and the ceramic heating ring is the best choice for the injection molding machine heating system. In order to smoothly feed, the charging area of the cylinder must be water-cooled to maintain the temperature at 70-100℃.
7, mold temperature
The surface temperature of the mold is 175-205 ° C, up to 220 ° C.
8. Mold design
The mold is heated by high temperature grease above 300℃, the mold steel is made of H13 or 8407 and other high temperature resistant grades, and the heat insulation board above 250℃ is installed on the mold (>8mm). In order to reduce heat dissipation, the thermal insulation layer can be added around the mold; The guide column adopts high temperature self-lubricating grade; The main channel is greater than 4mm, the taper is recommended to be 2°, the gate is ≥1mm(pure material), ≥2mm(reinforced material); The flow channel of the mold should be round or trapezoid.
9. Drying
The PEEK material is placed in an air circulation furnace and dried at 150 ° C for at least 3 hours, or at 160 ° C for 2 hours. The workshop must be kept clean, and other materials must be strictly prevented from mixing, PEEK processing temperature is as high as 350-400 ° C, and most other plastics will be seriously degraded when mixed, affecting product performance.
10. Thermal stability
The shutdown time of the melting process does not exceed 1 hour, and there is no obvious degradation of the material at 360 ° C. If the downtime exceeds 1 hour, the cylinder temperature should be reduced to 340 ° C, at which temperature the material can remain stable for several hours. If the down time is more than 3 hours, the barrel should be cleaned. It can be cleaned with some materials that can maintain stable properties at 380 ° C, such as polyether sulfone or polyether imide, or with low MFI polyethylene.
With the development of science and technology, people's requirements for materials will be more and more high, especially in the current energy shortage, weight reduction is a problem that each enterprise must consider, to plastic steel is the inevitable trend of future material development, for PEEK this "all-in-one" special engineering plastics demand will also be more and more, the application field will be more and more wide.
