Injection mold principle

Plastic injection mold is given to the shape and size of the molding member. Although the structure of the mold and performance of varieties of plastic, shape, and configuration and the type of plastics injection molding machine may be different and changing, but the basic structure is the same. Die mainly by gating system, molded parts and structural parts of three parts. Gating system and molded parts which are in direct contact with the plastic part, and with the plastics and products change, the mold is the most complex and the biggest change, the most demanding part of the process finish and accuracy.

Gating system refers to the plastic from the nozzle portion of the cavity before entering the flow path, including the main channel, cold-slug, diversion channel and the gate and so on. Forming part refers to the shape of the various parts constituting products, including dynamic simulation, the fixed mold and cavity, core,  air popper forming rod and exhaust ports and so on. 

Sprue

   

  It is mold injection machine nozzle connected to a shunt or cavity section channel. Sprue concave top to the nozzle convergence. Sprue inlet diameter should be slightly larger than the diameter of the nozzle (O.8mm) to avoid overflow and prevent the interception of convergence between the two are not allowed to occur due. Imported products according to the size of the diameter, usually 4-8mm. Expanding the diameter of the main channel at an angle of 3 ° to 5 ° should be within in order to release the flow channel thereof is superfluous.

Cold slug

    

It is located in the main channel at the end of a hole to trap shoot between the ends of two injections of mouth generated by cold material, thereby preventing the diversion channel or gate blocked. If cold material once mixed with the cavity, then the system is easy to produce products in the internal stress. Cold slug diameter of about eight a lOmm, depth of 6mm. In order to facilitate mold release, normally borne by the bottom of the release lever. Top release lever should be designed to zigzag trench subsidence hook or set up in order to successfully pull the sprue superfluous matter when stripping.

Shunt

It is a multi-slot die cavity connecting the main channel and each channel. In order to melt each cavity is filled with equal speed, diversion channel on the mold arrangement should be symmetrical and equidistant distribution. Runner-sectional shape and size of the plastic melt flow, and ease of mold release products has an impact. If the feeding amount in equal flow, it places the smallest cross-section of the flow path resistance. But because of the cylindrical flow channel surface area is small, the cooling of the shunt superfluous material adverse, and this shunt must be opened on the two halves of the mold, both labor-and easy alignment. Therefore, regular use of the trapezoidal or semi-circular cross-section of the runner, and the opening on one half of the mold with a release lever. Channel surface polished to reduce flow resistance must provide faster filling speeds. Depends on the size of the plastic flow channel variety, size and thickness of the article. For most thermoplastics, the shunt section width does not exceed 8m, up to 10 a large 12m, special small 2-3m. Under the premise of meeting the needs of the cross-sectional area should be minimized to avoid increasing the shunt Warts and extend the cooling time.

Gate

It is on the main road (or shunt) and the cavity of the channel. Sectional area of ​​the channel can be with the mainstream channel (or shunt) are equal, but are usually reduced. So it is the smallest part of the whole system, the cross-sectional area of ​​the flow path. The shape and size of the gate great impact on product quality. The role of the gate is: A, control the material flow velocity: B, due to the injection can be stored in this part of the condensate and prevent melt back earlier: C, so that the melt by strong shear by increasing the temperature , thereby reducing the apparent viscosity to increase flowability: D, easy separation of products, and the flow channel system. Gate design shape, size and position depend on the nature, size and structure of the article of plastics. The gate of the cross-sectional shape is generally rectangular or circular cross-sectional area should be small and the length should be short, not only based on the above effects, but also because larger than the small gate easy, and it is very difficult to reduce the large gate. Gate location should generally be selected in the products do not affect the appearance of the thick places. Gate size should be designed to take into account the nature of the plastic melt.

Cavity

It is the mold space molded plastic products. Component as constituting the cavity collectively referred to as molded parts. Various molded parts are often specific names. The molded article constituting the shape of the concave part called a die (also known as the female mold) to form the internal shape of the article (such as holes, slots, etc.) is referred to as core or convex mold (also known as the male mold). First, the overall structure of the cavity to be determined according to performance, the geometry of products, dimensional tolerances and use requirements designed plastic molded part time. Second, to select sub-surface, the gate and the vent mode position, and release according to the determined structure. Finally, press the control product dimensions of each part of the design and determine the combinations between the various components. Plastic melt with high pressure into the cavity, so the molded parts to be reasonable selection and check the strength and stiffness. To ensure the smooth plastic surface appearance and easy stripping, where contact with the plastic surface roughness Ra> 0.32um, but also resistant to corrosion. Molded parts are generally by heat treatment to improve the hardness and corrosion-resistant steel manufacturing.

Vent

A groove which is open in a mold outlet, and for discharging the original gas into the melt. When the molten material into the cavity, the original is stored in the cavity from the melt into the air and gas must be discharged through the exhaust port to die at the end of the stream outside, otherwise it will make products with holes, bad splices, filling dissatisfaction, even accumulated compressed air due to high temperature and the product burns. In general, both exhaust holes provided in the cavity of the melt flow at the end, may be provided on the mold parting surface. The latter was set up at the side of the die deep 0.03-0.2mm, wide shallow groove 1.5-6mm's. Injection, the vent does not have a lot of melt leakage, because the melt is cooled and solidified in where the channel blocked. Never open position toward the exhaust port operator, to prevent accidental discharge wounding melt. It will also use the top of the bar with the gap with the top of the hole, the top block and the stripper plate and with the gap cores like exhaust.

Structural parts

  

  It refers to the various parts constituting the mold structure, including: orientation, ejection, core pulling and genotyping of various parts. As the front and rear plates, after deduction templates, pressure plate, bearing columns, guide posts, stripper, stripping pole and the return pole and so on.

Heating or cooling means

   

  This is to make the melt solidified in the mold shape of the device for thermoplastic male and female mold is typically a cooling medium passage, and by circulating cooling medium to the cooling purposes. Pass into the cooling medium and the structure of an article with the type of plastic and the like, cold water, hot water, hot oil and steam. The key is uniform cooling high efficiency, uneven cooling products will directly affect the quality and size. Should be based on the thermal properties of the melt (including crystallization), the shape of the article and the mold structure, consider selecting the arrangement of the cooling passage and the cooling medium.