Basic understanding of plastic mold


General definition of mold: In industrial production, various presses and special tools installed on the press are used to make metal or non-metallic materials into parts or products of the required shape through pressure. Such special tools are collectively called molds.

Injection mold process: A mold is a tool for producing plastic products. It is composed of several groups of parts, and there is a molding cavity in this combination. During injection molding, the plastic mold is clamped on the injection molding machine, and the molten plastic is injected into the molding cavity and cooled and shaped in the cavity. Then the upper and lower molds are separated, and the product is ejected from the cavity and out of the mold through the ejection system. Closed for the next injection, the entire injection molding process is cyclical.

According to different types of gating system, molds can be divided into three categories:

(1) Large nozzle mold: The runner and gate are on the parting line, and they are demolded together with the product when the mold is opened. The design is the simplest, easy to process, and low cost, so more people use the large nozzle system to work.

(2) Fine nozzle mold: runners and gates are not on the parting line, generally directly on the product, so it is necessary to design an additional set of nozzle parting lines, the design is more complicated and the processing is more difficult, and generally depends on the product requirements. Fine nozzle system.

(3) Hot runner mold: The structure of this type of mold is roughly the same as that of the nozzle. The biggest difference is that the runner is in one or more hot runner plates and hot nozzles with constant temperature. There is no cold material demoulding, runner and pouring. The port is directly on the product, so the runner does not need to be demolded. This system is also called a nozzleless system, which can save raw materials and is suitable for situations where raw materials are more expensive and products require higher requirements. Design and processing are difficult, and mold costs are higher.

Hot runner system, also known as hot runner system, is mainly composed of hot sprue sleeve, hot runner plate and temperature control electric box. Our common hot runner system has two forms: single-point hot gate and multi-point hot gate. Single-point hot gate uses a single hot sprue sleeve to directly inject molten plastic into the cavity. It is suitable for plastic molds with a single cavity and single gate; multi-point hot gate branches the molten material to each The sub-heat sprue sleeve then enters the cavity. It is suitable for single cavity multi-point feeding or multi-cavity molds.

Advantages of hot runner system:

(1) No nozzle material, no need for post-processing, making the entire molding process fully automated, saving processing time and improving work efficiency.

(2) The pressure loss is small. The temperature of the hot runner is equal to the nozzle temperature of the injection molding machine, which avoids the surface condensation of the raw materials in the runner, and the injection pressure loss is small.

(3) The repeated use of the nozzle material will degrade the performance of the plastic, and the use of the hot runner system without nozzle material can reduce the loss of raw materials, thereby reducing product costs. The temperature and pressure in the cavity are uniform, the stress of the plastic part is small, and the density is uniform. Under a small injection pressure and a short molding time, a better product can be injected than the general injection molding system. For transparent parts, thin parts, large plastic parts or high-demand plastic parts, it can show its advantages, and can produce larger products with smaller models.

(4) The hot nozzle adopts standardized and serialized design, equipped with various nozzle heads to choose from, and has good interchangeability. The uniquely designed and processed electric heating ring can achieve uniform heating temperature and long service life. The hot runner system is equipped with hot runner plates, thermostats, etc., with exquisite design, diverse types, convenient use, and stable and reliable quality.

Shortcomings of hot runner system application:

(1) The closing height of the overall mold is increased, and the overall height of the mold has increased due to the addition of hot runner plates.

(2) The heat radiation is difficult to control. The biggest problem of the hot runner is the heat loss of the runner, which is a major issue that needs to be solved.

(3) There is thermal expansion, thermal expansion and contraction are issues that we must consider when designing.

(4) The manufacturing cost of plastic molds increases, and the price of standard parts of the hot runner system is higher, which affects the popularity of hot runner molds.