Mon Feb 27 18:20:27 CST 2023
The moulds can be divided into three categories according to the different types of pouring system.
(1) Large spout moulds: the runners and gates are on the parting line, and the product is demoulded together when the mould is opened. The design is the simplest, easy to process and less costly, so more people use the large spout system for their work.
(2) Fine spout moulds: runners and gates are not on the parting line, generally directly on the product, so to design more than one set of spout parting line, the design is more complex, processing is more difficult, generally depending on the product requirements and the choice of fine spout system.
(3) Hot runner moulds: the structure of such moulds is largely the same as that of fine spouts, the major difference is that the runners are in one or more hot runner plates and hot spouts with constant temperature, no cold material release, the runners and gates are directly on the product, so the runners do not need to be released, this system is also known as the no spout system, can save raw materials, suitable for raw materials are more expensive, the product requirements are higher, design and processing difficulties, mould costs are higher. High cost.
The hot runner system, also known as hot sprue system, consists of a hot sprue sleeve, a hot sprue plate and a temperature controlled electric box. Our common hot runner systems are single point hot gates and multi-point hot gates. Single point hot gate is to use a single hot gate sleeve to shoot the molten plastic directly into the cavity, it is suitable for single cavity single gate plastic mould; multi-point hot gate is to branch the molten material into each hot gate sleeve and then into the cavity through the hot gate plate, it is suitable for single cavity multi-point feeding or multi-cavity mould.
Advantages of the runner system
(1) No sprues, no post-processing, making the whole moulding process fully automatic, saving working time and improving work efficiency.
(2) Low pressure loss. The hot runner temperature is equal to the injection moulding machine nozzle temperature, avoiding surface condensation of the material in the runner and resulting in low injection pressure loss.
(3) Repeated use of sprues can degrade the plastic properties, whereas with a hot runner system there is no sprues, which reduces the loss of raw material and thus reduces the cost of the product. Uniform temperature and pressure in the cavity, low stress in the plastic part, uniform density, and better products than normal injection molding system can be injected in a shorter molding time under a smaller injection pressure. For transparent parts, thin parts, large plastic parts or highly demanding plastic parts can show its advantages, and can produce larger products with smaller models.
The nozzles are standardised and series designed, with a wide range of nozzle heads available for interchangeability. The unique design and processing of the electric heating ring can achieve uniform heating temperature and long service life. The hot runner system is equipped with hot runner plates, temperature controllers, etc. The design is exquisite, diverse, easy to use, stable and reliable in quality.
Shortcomings of the hot runner system application
(1) The overall mould closure height is increased, the overall height of the mould is increased due to the addition of hot runner plates etc.
(2) Heat radiation is difficult to control, the biggest fault of hot runners is the heat loss of the sprue, a major issue that needs to be addressed.
(3) There is thermal expansion, thermal expansion and contraction is a problem we have to consider when designing.
(4) The cost of mould manufacturing has increased, the higher price of standard fittings for hot sprue systems has affected the popularity of hot sprue moulds.