The injection mold is composed of two parts: moving mold and fixed mold. The moving mold is installed on the moving formwork of the injection molding machine, and the fixed mold is installed on the fixed formwork of the injection molding machine. During injection molding, the dynamic mold and the fixed mold are closed to form a pouring system and cavity. When the mold is opened, the moving mold and the fixed mold are separated to take out the plastic products. In order to reduce the heavy work of mold design and manufacture, the standard die base is mostly used in injection mold.

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gating system

The pouring system refers to the flow passage before the plastic enters the cavity from the nozzle, including the main channel, the cold material hole, the shunt channel and the gate. The pouring system is also called the runner system. It is a group of feeding channels which lead the plastic melt from the injector nozzle to the cavity, which is usually composed of the main channel, the shunt channel, the gate and the cold material hole. It is directly related to the molding quality and production efficiency of plastic products.

The main channel is a passage connecting the injection nozzle of injection molding machine to the shunt channel or cavity in the mold. The top of the main channel is concave to connect with the nozzle. The diameter of the inlet of the main channel should be slightly larger than the nozzle diameter (0.8mm) to avoid overflow and prevent the blocking of the two due to the improper connection. The diameter of the import is determined by the size of the product, generally 4-8mm. The diameter of the main channel should be extended inwards at an angle of 3 ° to 5 ° to facilitate the release of the runner burden.

The cold material hole is a hole at the end of the main channel to catch the cold material produced between two injections at the end of the nozzle, so as to prevent the blocking of the shunt or gate. If the cold material is mixed into the cavity, the internal stress will easily be produced in the product. The diameter of cold material hole is about 8-10 mm and the depth is 6mm. In order to facilitate demoulding, the bottom of the demoulding rod is usually undertaken. The top of the release rod should be designed as a zigzag hook or a groove to allow the main channel to pull out the main duct burden smoothly.

The shunt channel is a channel in which the main channel and each cavity are connected in the multi slot mode. In order to make the molten material fill all cavities at equal speed, the distribution of the shunt channel on the mold should be symmetrical and equal distance. The shape and size of the cross section of the shunt channel have an influence on the flow of plastic melt, the release of products and the difficulty of mold manufacturing.

If the flow is equal, the flow resistance of the runner with circular section is the least. However, because the surface of the cylindrical runner is small, it is not good for the cooling of the burden of the shunt, and the shunt must be set on the two half die, which is not easy to align with and laborious.

Therefore, the trapezoidal or semicircular section of the shunt channel is often used and is set on the half mold with release rod. The surface of the runner must be polished to reduce the flow resistance to provide a faster mold filling speed. The size of the runner is determined by the plastic variety, the size and thickness of the product. For most thermoplastic, the width of the shunt channel is not more than 8m, the extra large can reach 10-12m and the extra small 2-3m. On the premise of meeting the needs, the cross-section area should be minimized to increase the burden of the diversion channel and prolong the cooling time.

Gate

It is a channel connecting the main channel (or shunt) and the cavity. The cross-section of the channel can be equal to the main channel (or shunt), but it is usually reduced. So it is the smallest section of the whole flow system. The shape and size of gate have great influence on the quality of products.

The gate is used to:

A. Control the flow speed:

B. Backflow can be prevented by early setting of the molten material stored in this part during injection:

C. The temperature of the molten material is increased by strong shear, thus reducing the apparent viscosity to improve the fluidity

D. It is convenient to separate the product from the runner system. The shape, size and location of gate are designed according to the nature of plastic, the size and structure of the product. The section shape of the gate is rectangular or circular, and the section area should be small and the length should be shorter. This is not only based on the above-mentioned function, but also because it is easier to grow the small gate, and it is difficult to reduce the large gate. Gate position should be selected in general the thickest part of the product without affecting the appearance.

The gate size shall be designed to take into account the properties of the plastic melt. Cavity is the space for forming plastic products in the mold. Components used to form cavities are collectively referred to as forming parts.

Each formed part often has a special name. The forming parts forming the product shape are called concave die (also called the female mold), and the inner shape (such as holes, grooves, etc.) of the products is called core or punch (also called the male mold). The overall structure of the cavity should be determined according to the performance of plastic, the geometry of the product, the tolerance of dimension and the requirement of using.

Secondly, according to the structure, the position of parting surface, gate and vent hole and demoulding mode are selected.

Finally, according to the size of the control products, the design of each part and the combination of the parts are determined. The plastic melt has high pressure when entering the cavity, so the forming parts should be selected reasonably and the strength and rigidity checked.

In order to ensure the smooth and beautiful surface of plastic products and easy to demould, the roughness of the surface contacting with plastic is ra > 0.32um, and it should be corrosion resistant. The forming parts are generally made of corrosion-resistant steel by heat treatment to improve the hardness.

Temperature regulating system

In order to meet the requirements of injection process on mold temperature, temperature regulating system is needed to adjust the temperature of the mold. For injection mold for thermoplastic, the cooling system is designed to cool the mold. The common method of mold cooling is to set up cooling water channel in the mold, and take away the heat of the mold by circulating cooling water; In addition to the hot water or steam in the cooling water channel, the heating element can be installed inside and around the mold.