Plastic Crate Box Mold

Precautions for mold design:

⑴ The shape and wall thickness design of the plastic parts should be particularly considered to facilitate the smooth flow of the filling cavity and avoid sharp corners and gaps.



⑵ The release angle should be large, 15% with glass fiber can be 1 ° ～ 2 °, 30% with glass fiber can be 2 ° ～ 3 ° When the draft angle is not allowed, forcible demoulding should be avoided, and the horizontal parting structure should be adopted.



⑶ The cross-section of the pouring system should be large, and the process should be straight and short to facilitate the even dispersion of the fibers.



⑷The design of the feed inlet should consider the prevention of insufficient filling, anisotropic deformation, uneven distribution of glass fibers, and easy to produce weld marks and other adverse consequences. The feed port should be thin, wide, fan-shaped, ring-shaped and multi-point feed ports to make the flow turbulent and the glass fibers evenly dispersed to reduce anisotropy. It is best not to use needle-shaped feed ports. The mouth section can be increased appropriately, and its length should be short.



⑸The mold core and cavity should have sufficient rigidity and strength.

⑹The mold should be hardened, polished, and wear-resistant steel should be selected, and the parts that are easy to wear should be easy to repair.

⑺Ejection should be even and strong, convenient for replacement.

⑻The mold should be equipped with exhaust overflow trough, and should be set at the place where welding marks easily occur.

Mold temperature setting

⑴Mold temperature affects the molding cycle and molding quality. In actual operation, the lowest appropriate mold temperature of the material used is set, and then adjusted appropriately according to the quality status.

⑵ Correctly speaking, the mold temperature refers to the temperature of the cavity surface when forming is being carried out. In mold design and forming engineering condition setting, it is important not only to maintain an appropriate temperature, but also to allow it to be evenly distributed .

(3) Uneven mold temperature distribution will cause uneven shrinkage and internal stress, thus making the molding port easy to deform and warp



⑷ Increasing the mold temperature can obtain the following effects;

① Increase the crystallinity and more uniform structure of the molded product.

②Make the molding shrinkage more fully, and reduce the shrinkage afterwards.

③ Improve the strength and heat resistance of molded products.

④Reduce internal stress residual, molecular alignment and deformation.

⑤ Reduce the flow resistance during filling and reduce the pressure loss.

⑥ Make the appearance of the molded product more shiny.

⑦ Increase the chance of burrs in molded products.

⑧ Increase the near-gate position and reduce the chance of depression at the far-gate position.

⑨Reduce the obvious degree of binding line

⑩ Increase the cooling time.

Measurement and plasticization

⑴In the molding process, the injection quantity control (measurement) and the uniform melting of the plastic (plasticization) are performed by the plasticizing unit (Plasticizing unit) of the injection machine.



①Barrel Temperature

Although the melting of plastic is about 60--85% due to the heat energy generated by the rotation of the screw, the melting state of the plastic is still affected by the temperature of the heating cylinder, especially the temperature near the front area of the nozzle-the temperature in the front area When it is high, it is easy to cause the phenomenon of dripping and pulling the parts when pulling out.



②screw speed

A. The melting of plastic is mainly due to the heat generated by the rotation of the screw, so the screw speed is too fast, it has the following effects:

a. Thermal decomposition of plastics.

b. Glass fiber (plus fiber plastic) is shortened.

c. The wear of the screw or heating cylinder is accelerated.

B. The speed setting can be measured by its circumferential speed:

Peripheral speed = n (speed) * d (diameter) * π (circumferential)

Generally, for low-viscosity plastics with good thermal stability, the peripheral speed of the screw rod rotation can be set to about 1m / s, but for plastics with poor thermal stability, it should be as low as about 0.1.

C. In practical applications, we can reduce the screw speed as much as possible, so that the rotary feeding can be completed before the mold is opened.



③BACK PRESSURE

A. When the screw rotates and feeds, the pressure accumulated by the melt advancing to the front end of the screw is called back pressure. During injection molding, it can be adjusted by adjusting the return pressure of the injection hydraulic cylinder. effect:

a. Melt melts more evenly.

b. The toner and filler are more evenly dispersed.

c. Make the gas exit from the blanking port.

d. The measurement of the feed is accurate.

B. The level of the back pressure is determined by the viscosity and thermal stability of the plastic. Too high a back pressure increases the feeding time, and due to the increase of the rotating shear force, it is easy to cause the plastic to overheat. Generally, 5--15kg / cm2 is suitable.



④Slack back (SUCK BACK, DECOMPRESSION)

A. Before the screw feed starts, the screw can be properly retracted, which can reduce the pressure of the melt at the front end of the mold. This is called front loosening. Its effect can prevent the pressure of the melt on the nozzle of the nozzle. Molding.

B. After the screw feed is completed, the screw can be properly retracted to reduce the melt pressure at the front end of the screw. This is called back loosening, and its effect can prevent the nozzle from dripping.

C. The shortcoming is that it is easy to stick the mainstream (SPRUE) mold; while too much loosening, it can suck in the air and make the molded product have air marks.