PC injection molding process of the big summary of the golden tips

PC has excellent characteristics, high clarity, good fracture toughness, stress relaxation resistance, a wide range of application temperatures. processing process characteristics of PC: melting viscosity to the cut-rate of sensitivity is small, but sensitive to temperature, no significant melting point, melt viscosity is high, high-temperature epoxy resin is easy to hydrolysis reaction, the product is easy to crack.

For this characteristic, we should especially pay attention to some differences.

1. To improve the flow of the melt, not with the expansion of injection pressure but should be selected to enhance the injection temperature to do;

2. To define the flow path of the mold shell. The gate should be short and thick to reduce the pressure damage of the liquid, and the injection pressure should be high;

3. The epoxy resin needs to be dried sufficiently before the molding production process so that its moisture content is manipulated below 0.02%. 4;

4. In addition, the epoxy resin should be used in the production process of thermal insulation measures to prevent moisture absorption again. 5;

5. Not only must be an effective product design plan but also should properly grasp the molding process, such as raising the temperature of the mold shell and carrying out a post-treatment process for the product, etc. can reduce or remove the thermal stress. Depending on the different conditions of the product, the main parameters of the process should be adjusted immediately.

Forming process

Raw material dryness

PC type plastic, even if it encounters very low moisture, will cause a hydrolysis reaction and break the bond. The content is reduced and the physical properties of compressive strength are reduced. Therefore, the moisture of polycarbonate should be strictly controlled at 0.02% or less before the molding process to prevent the impact toughness of the molded products from decreasing or the surface layer from causing vapor bubbles. The appearance of abnormal appearance such as silver lines.

PC is extremely sensitive to water, so it must be sufficiently dry before injection processing to reduce its moisture content to 0.02% below, PC general dry standard: 100 ~ 120 ℃, at least 4 hours above;

Injection temperature

The injection temperature must be integrated with the appearance of the product. Specification, mold design. Product characteristics. It can be made only after taking into consideration the conditions of each level such as regulations.

Generally, the temperature used in molding is between 270~320℃, if the material temperature exceeds 340℃, PC may be dissolved, the color of the product will become darker, and the surface layer will show silk strips. Dark strip. Small black spots. Vapor bubbles and other shortcomings, in addition to physical properties, are also significantly reduced. PC is also very sensitive to temperature, the viscosity of the solution with the temperature rises and significantly reduces the barrel temperature 250 ~ 320 ℃ (preferably not necessary to exceed 350 ℃), moderately raise the temperature barrel temperature of PC melt is beneficial. When necessary, thermal stress quenching, heating furnace temperature 125 ~ 135 ℃, time 2 hours, of course, cooling to room temperature.

Injection pressure

The physical properties of PC products, thermal stress. Forming shrinkage rate and other hazards to the appearance of the product and out of the mold has a great danger, the too low or too high injection pressure is the product will have some shortcomings, the general injection pressure manipulated in the middle of 80-120MPa, for thick-walled, long steps, look complicated, small gate products, to get rid of the friction resistance of the solute fluidity, to facilitate the immediate filling of the mold core, before using a higher injection pressure ( 120-145MPa). A product with a detailed and smooth surface is obtained.

Poor fluidity, to use high-pressure injection but need to care about plastic products residual large thermal stress (likely to cause cracking), injection rate: thickness to medium speed, thin wall to high speed.

Holding pressure and holding time

The size of the holding pressure and the length of the holding time are very harmful to the thermal stress of PC products. If the holding pressure is too small, the metal mold casting efficacy is small and easy to appear vacuum pump bubble or shrinkage concave on the surface layer. The selection of holding time should depend on the thickness of the product, the size of the gate, the mold temperature, and other conditions. The length of holding time can be clarified according to the experiment of gate sealing time.

Injection rate

There is no significant harm to the characteristics of PC products, except for thick wall, small gate, deep hole, long step products, generally choose medium speed or slow speed production processing, preferably multi-level injection, generally choose the slow-fast-slow multi-level injection method.

Molding temperature

Mold temperature manipulation: 85~120℃, generally manipulated at 80-100℃ can be, for complicated appearance, thinner, higher provisions of the products can also be raised to 100-120℃, but can not exceed the mold shell thermal deformation temperature. High die temperature to reduce the difference between the die temperature and PC die temperature, can reduce the thermal stress of the product.

Extruder screw speed ratio and condensing steam type

Because the PC solute viscosity is very large, from the beneficial melt, beneficial exhaust, beneficial maintenance of plastic machinery, to avoid excessive load on the extruder screw, the extruder screw speed ratio regulations can not be too high, generally manipulated in 30-60r / min is appropriate, while the condensate type manipulated in the middle of the injection pressure of 10-15% is appropriate.

Application of modifier

PC in the whole process of injection molding processing to strictly control the application of the release agent, in addition to the application of recycled particles can not exceed three times, the consumption should be 20% or less.

PC injection molding process, the mold shell regulations are high

1) Design program as thick and short as possible, bending bit less overflow channel, with ring cross-sectional separation channel and overflow channel grinding polishing, etc. to reduce the friction resistance of the flow of wear-resistant materials.

2) Injection gate can be used in all ways of the gate, but into the water level line diameter of not less than 1.5 mm.

For the production of PC products of plastic machinery regulations

Specify the larger injection volume of the product (including runners. Gates, etc.) should not exceed 70-80% of the nominal pressure injection volume;

Clamping pressure: 0.47 to 0.78 tons per square centimeter (or 3 to 5 tons per square inch) per square inch of the unfolded area of the finished product;

Machine and equipment size: the net weight of the finished product is about 40 to 60% of the volume of the plastic machine is the best, such as machinery and equipment to indicate the volume of polyethylene (ounce), it is necessary to reduce 10%, the volume of the application GUANG DA. 1 ounce = 28.3 grams.

Extruder screw: the length of the extruder screw needs to have at least 15 diameters long, its L / D is 20: 1 best. The engine compression ratio should be 1.5:1 to 30:1. The stop valve developed at the front of the extruder screw should be of the drag ring type, and the epoxy resin flowable gap should be at least 3.2 MM.

PC injection molding post-processing process

PE material should be used to pass through the machine.