PC performance, high transparency, impact toughness, creep resistance, the use of a wide temperature range.
PC process characteristics: the viscosity of the melt viscosity of the shear rate is small, and the sensitivity of the temperature, no significant melting point, high viscosity melt, high temperature resin hydrolysis, easy to crack products.
In view of these characteristics, we should pay special attention to distinguish between:
To increase the liquidity of the melt, not to increase the injection pressure should be used to increase the injection temperature to achieve;
Requirements of the mold of the runner, gate short and thick, in order to reduce fluid pressure loss, while higher injection pressure;
Resin in the molding process before the need for adequate drying, so that the water content controlled below 0.02%;
In addition, the resin should also be taken in the processing of insulation measures to prevent moisture absorption again;
Not only need a reasonable product design, but also the right to master the molding process, such as increasing the mold temperature, post-processing of products can reduce or eliminate internal stress depending on the product status of the timely correction of process parameters.
Here we talk about molding process:
1. Raw material is dry
PC plastic, even in the face of very low water will produce hydrolysis and broken keys, molecular weight reduction and physical strength reduction phenomenon.Therefore, before molding, should be strictly controlled the water content of polycarbonate below 0.02% In order to avoid the mechanical strength of the molded product is reduced or the surface of the abnormal appearance of bubbles, silver lines and the like.
PC is extremely sensitive to water, so it must be fully dried before injection to reduce the water content below 0.02%. PC general drying conditions: 100 ~ 120 ℃, time for at least 4 hours;
Injection temperature
Injection temperature must be integrated product shape, size, mold structure, product performance, requirements and other aspects of the situation to be considered before they can make.
Generally used in forming the temperature between 270 ~ 320 ℃, too high temperature of the material such as more than 340 ℃, the PC will be decomposed, the product color becomes dark, the surface silver, dark stripes, black spots, bubbles and other defects , While physical and mechanical properties also decreased significantly PC is also very sensitive to temperature, melt viscosity decreased with increasing temperature, barrel temperature 250 ~ 320 ℃ (preferably not more than 350 ℃), the appropriate temperature to increase the temperature of the barrel PC plasticization is beneficial if necessary, stress annealing, oven temperature 125 ~ 135 ℃, 2 hours, naturally cooled to room temperature.
Injection pressure
The physical and mechanical properties of PC products, internal stress, molding shrinkage and so have a certain impact on the appearance and release of products have a greater impact, too low or too high injection pressure will make the product some defects, the general Injection pressure control between 80-120MPa, the thin-walled, long process, complex shape, the gate smaller products, to overcome the melt flow resistance, in order to fill the cavity in time, only the choice of a higher injection pressure (120 -145MPa) .In order to obtain a complete and smooth surface products.
Liquidity is poor, the need for high-pressure injection, but to take into account the plastic residual large internal stress (which may lead to cracking), injection speed: take the wall thickness, thin wall to take high-speed.
4. Drip pressure and dwell time
Pressure holding pressure and the length of the length of the PC products have a greater impact on the internal stress, packing pressure is too small, the role of small shrinkage prone vacuum vacuole or surface shrinkage, packing pressure is too large, pouring Easy to produce large internal stress around the mouth, in the actual processing, often with high feed temperature, low pressure to solve the way. Pressure time should be selected depending on the thickness of the product, the gate size, mold temperature and other circumstances , Generally small and thin products do not need a long dwell time, on the contrary, large and thick products dwell time should be longer. Dwell time length can be determined by the gate seal time test.
5 injection speed
On the performance of PC products did not have a significant impact, in addition to thin-walled, small gates, deep holes, long process products, the general use of medium-speed or slow processing, preferably multi-level injection, the general slow - fast - slow Multi-stage injection.
Mold temperature
Mold temperature control: 85 ~ 120 ℃, the general control at 80-100 ℃ can be, the shape of complex, thin, demanding products, but also can be increased to 100-120 ℃, but can not exceed the mold heat distortion temperature. Die Temperature and temperature to reduce the mold temperature and PC material temperature differences, can reduce the internal stress components.
Screw speed and back pressure
As the PC melt viscosity, from the favorable plasticization, favorable exhaust, the maintenance of plastic presses, to prevent the screw load is too large, the screw speed requirements can not be too high, the general control of 30-60r / min is appropriate, The back pressure control in the injection pressure of 10-15% is appropriate.
8. Auxiliaries use
PC in the injection molding process to strictly control the use of release agent, while the use of recycled materials can not be more than three times the amount should be about 20%.
9.PC injection molding, higher requirements on the mold:
1) The design is as coarse and short as possible, the flow channel with a small number of bends is used, and the flow resistance of the melt is reduced by using circular cross-section flow channels and lapping and polishing.
2) Injection gate can be any type of gate, but into the water level diameter of not less than 1.5mm.
10 on the production of PC products, plastic machine requirements
Requirements for the maximum amount of injection products (including runners, gates, etc.) should not be greater than the nominal injection volume of 70-80%;
Mold clamping pressure: 0.47 to 0.78 ton (or 3 to 5 tons per square inch) per square centimeter of projected product area;
Machine size: the weight of the finished product is about 40-60% of the capacity of the injection molding machine. If the capacity of the machine in terms of polystyrene (oz) is reduced by 10%, the capacity of GUANG DA should be used. 1 oz = 28.3 grams.
Screw: the length of the screw should be at least 15 long diameter, the L / D is 20: 1 the best compression ratio should be 1.5: 1 to 30: 1. The front of the stop-flow valve should be used sliding ring, the resin can be Flow gap should be at least 3.2MM.
11.PC injection molding treatment: PE material over the machine