Carbon injection molding machine heating several degrees

Answer:

The physicochemical properties of PC plastics are as follows:One is amorphous plastic, Tg is 149~150 DEG C, Tf is 215~225 DEG C, molding temperature is 250~310 DEG C, and relative average molecular weight is 2~4.The thermal stability is better and increases with the increase of molecular weight.The rheological properties are close to Newton liquid, and the apparent viscosity is greatly affected by the temperature, which is less affected by the shear rate and increases with the relative average molecular weight. No obvious melting point, higher melt viscosity. PC molecule chain has benzene ring, so the rigidity of molecular chain is big.PC has good creep resistance and good dimensional stability, but it is difficult to eliminate internal stress.PC at high temperature, water easily degraded, molding requirements of moisture content below 0.02%.The product is easy to crack.Before molding, the PC resin must be fully dried. The fluidized bed drying method (drying temperature 120 to 130 DEG C, 1 ~ 2H), vacuum drying (110 degrees Celsius temperature, vacuum degree more than 96kPa, 10 ~ 25h), hot air circulation drying (above the temperature of 120 to 130 DEG C, 6h). In order to prevent the moisture absorption of the dry resin, it should be placed in the insulating box at 90 degrees. It should not be stored for a long time. When forming, the hopper must be closed, the hopper should be equipped with heating device, the temperature is not less than 100 degrees, and no heat insulation device hopper, a feeding amount is best less than half an hour of the amount of use, and should be stamped tightly.

The nozzle temperature is 260~310 degrees, and the temperature control of the two types of injection molding machine nozzles is different. The mold temperature has great influence on the mechanical properties of the products. With the increase of mold temperature. The temperature and the temperature difference between the temperature decreases, the shear stress decreases, can melt in the mold cavity slow cooling, the molecular chain orientation to relaxation reduced, thereby reducing the internal stress of products, but the impact strength and elongation of the products decreased significantly, while there will be demolding. When demoulding, it is easy to deform, prolong the molding cycle and reduce the production efficiency, while the lower mold temperature will increase the internal stress of the product. Therefore, the die temperature must be controlled. Normally, the mold temperature of PC is 80~120 degrees centigrade. Ordinary products are controlled at 80~100 degrees, while for complex shapes, thin walls and high requirements, the product is controlled at 100~120 degrees centigrade and is not allowed to exceed its thermal deformation temperature. Mold temperature control is particularly important when forming PC thick wall products.

The quick test method for judging drying effect is to use the "air injection" on the injection molding machine". If the material flowing slowly from the nozzle is uniform and transparent, light silver strips and bubbles, is qualified. This method applies to all plastics.The melt viscosity of PC is much larger than that of PA, PS, PE, and the flowability is poor. Melt flow properties close to Newtonian fluid. The viscosity of the melt shear rate had little effect, and is very sensitive to changes in temperature, therefore, only by adjusting the molding processing temperature, viscosity can effectively control PC.The selection of molding temperature is relative to the average molecular weight of the resin and its distribution, the shape and size of the product, the type of the injection molding machine, and so on. It is generally controlled in the range of 250~310 centigrade. For injection molding, the resin with relatively low average molecular weight should be selected, MFR is 5 to 7g/10min; complex shape or thin wall products. Molding temperature should be high, 285~305 degrees; and thick wall products, molding temperature is slightly lower, to 250~280 degrees. Different injection molding machine, molding temperature is not the same. The screw type is 260~285 degrees, and the plunger type is 270~310 degrees centigrade. The setting of the material temperature is in the form of front high and low, near the end of the hopper, the temperature of the barrel should be controlled above the softening temperature of PC, that is greater than 230 degrees, to reduce the material resistance and injection pressure loss. In spite of increasing molding temperature, melt filling is beneficial. But not more than 230 DEG C, otherwise PC will degrade, make the products become darker in color, appear on the surface of silver, dark, black spots, bubbles and other defects, at the same time, the physical and mechanical properties will be significantly decreased.

Polycarbonate (PC) is a colorless and transparent engineering plastics, the impact strength is high, the use of a wide temperature range, good creep resistance, electrical insulation and dimensional stability; the disadvantage is sensitive to the gap, environmental stress cracking resistance, with metal insert molding products is difficult.Polycarbonate, English name Polycarbonate, referred to as PC. PC is a kind of amorphous, odorless, non-toxic, highly transparent colorless or slightly yellow thermoplastic engineering plastics, has excellent physical and mechanical properties, especially excellent shock resistance, tensile strength, bending strength, compressive strength and high creep; small size stability; has good heat resistance and low temperature resistance and with mechanical properties, stable in a wide range of temperature dimensional stability, electrical properties and flame retardant properties, can be used for a long time at -60~120 deg.c; no obvious melting point, molten at 220-230 DEG C; because the molecular chain rigidity, resin melt viscosity; low water absorption, low shrinkage, size high precision, good dimensional stability, permeability of films is small; self extinguishing materials; stable to light, but not UV resistance, good weather resistance; oil resistance, acid and alkali resistance, non oxidizing acids and amines, ketones, solution Chlorinated hydrocarbons and aromatic solvents are prone to hydrolysis and cracking in water for a long time. The disadvantage is that they are prone to stress cracking due to poor fatigue resistance, poor solvent resistance and poor wear resistance.