How does a plastic injection mold work?

1. Injection steps:

The raw material is melted by the high-speed rotation of the screw. The rotation speed is critical to the melting. If it is too slow, the plastic will not melt enough and if it is too fast, the plastic will be carbonized. Of course, the barrel is also important for heating.

After the raw material is melted, the melted material is injected into the mold. It also requires an injection molding machine to provide injection pressure to inject molten raw materials into the mold.

Then it takes some time to hold the pressure.

After that, cool the mold and close the gate of the mold. Finally, the mold is cooled by air and water.

Picking up the product: This is the last step. Some customers need a robot to pick up the product, and some let the product fall off automatically after molding.

Mainstream Road

It is a passage in the mold that connects the injection nozzle of the injection machine to the runner or cavity. The top of the main flow channel is concave so as to engage with the nozzle. The diameter of the inlet of the main flow channel should be slightly larger than the diameter of the nozzle (0.8mm) to avoid overflow and prevent blockage of the two due to inaccurate connection. The inlet diameter depends on the size of the product and is generally 4-8mm. The diameter of the main flow channel should be enlarged inward at an angle of 3 ° to 5 ° in order to facilitate the release of the flow path excess.

It is a cavity located at the end of the main flow channel, which is used to capture the cold material generated between the two injections at the end of the nozzle to prevent the clogging of the runner or the gate. If the cold material is once mixed into the cavity, internal stress will be easily generated in the manufactured product. The cold cavity has a diameter of about 8-10mm and a depth of 6mm. In order to facilitate demolding, the bottom is often borne by the demolding rod. The top of the demolding rod should be designed as a zigzag hook or a recessed groove so that the mainstream can be pulled out smoothly during demolding.

How injection molding works

Diversion channel

It is the channel connecting the main flow channel and each cavity in the multi-slot mold. In order to fill the cavity with the molten material at the same speed, the arrangement of the runners on the mold should be symmetrically and equally spaced. The shape and size of the cross-section of the shunt have an impact on the flow of the plastic melt, the release of the product, and the ease of mold manufacturing. If the flow is equal, the resistance of the flow channel with a circular cross-section is the smallest. However, the cylindrical flow channel is smaller than the surface, which is not good for the cooling of the shunts. Moreover, this shunt must be set on two mold halves, which are labor-intensive and easy to align. Therefore, a trapezoidal or semi-circular cross-section runner is often used and is opened on a half mold with a release rod. The runner surface must be polished to reduce the flow resistance and provide a faster filling speed. The size of the runner depends on the type of plastic injections, the size, and the thickness of the product. For most thermoplastics, the cross-section width of the diverter channel does not exceed 8m, the largest can reach 10-12m, and the smallest 2-3m. Under the premise of meeting the requirements, the cross-sectional area should be reduced as much as possible, so as not to increase the shunts and extend the cooling time.

Gate

It is the channel that connects the main channel (or the shunt channel) and the cavity. The cross-sectional area of ​​the channel can be equal to the mainstream channel (or the shunt channel), but it is usually reduced. Therefore, it is the smallest cross-sectional area in the entire flow channel system. The shape and size of the gate have a great impact on the quality of the product. The function of the gate is A. Control the flow rate: B. During the injection, the melt that exists in this part can be prevented from flowing backward. C. The molten material passing through is subjected to strong shear to increase the temperature. , Thereby reducing the apparent viscosity to improve fluidity: D, to facilitate the separation of the product from the flow channel system. The design of the gate shape, size and location depend on the nature of the plastic, the size and structure of the product. Generally, the cross-sectional shape of the gate is rectangular or circular, and the cross-sectional area should be small and the length should be short. This is not only based on the above-mentioned effects, but also because it is easier to make a small gate larger, and it is difficult to shrink a large gate. The gate location should generally be selected at the thickest part of the product without affecting the appearance. The design of the gate size should take into account the nature of the plastic melt.