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Dongguan HongS Jingyan Hot Runner Technology Co., Ltd.
Shenzhen HongS Hot Runner Technology Co., Ltd.
Jiangxi HongS Mould Co., Ltd.

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What is a hot runner - the fifth
Issuing Time:2018-09-01

Composition editor


Although there are many hot runner manufacturers and a variety of hot runner products in the world, a typical hot runner system consists of the following major components:


1. Main splitter (MANIFOLD)


2. Nozzle (NOZZLE)


3. Temperature Controller


4. Auxiliary part


The types and applications of these parts will be discussed in depth in a future series of articles.


Technical key


A successful hot runner mold application project requires multiple links to be guaranteed. The most important of these are two technical factors. One is the control of plastic temperature, and the other is the control of plastic flow.


1. Plastic temperature control


The control of plastic temperature is extremely important in hot runner mold applications. Processing and product quality that occurs during many production processes


The problem is directly due to the poor temperature control of the hot runner system. For example, when the hot pin gate method is used for injection molding, the quality of the product gate is poor, the valve gate method is difficult to close the valve needle during molding, and the filling time and quality of the parts in the multi-cavity mold are inconsistent. If possible, try to choose a hot runner system with multiple zones for temperature control to increase flexibility and resilience.


2. Plastic flow control


The plastic is to be flow balanced in the hot runner system. The gates should be opened at the same time to allow the plastic to fill the cavities simultaneously. For the FAMILY MOLD, where the weight of the parts is very different, the runner size design balance is required. Otherwise, some parts will not be filled with mold and pressure, and some parts will be over-filled and over-filled. The hot runner sprue size should be reasonable. The size is too small and the filling pressure loss is too large. If the size is too large, the hot runner volume is too large, and the plastic stays in the hot runner system for too long, which may damage the material properties and cause the parts to be unable to meet the requirements after molding. There are already CAE software in the world that help users to design the best runners, such as MOLDCAE.


Application range


1. Plastic material type


Hot runner molds have been successfully used to process a variety of plastic materials. Such as PP, PE, PS, ABS, PBT, PA, PSU, PC, POM, LCP, PVC, PET, PMMA, PEI, ABS/PC, etc. Any plastic material that can be processed with a cold runner mold can be machined with a hot runner mold.


2. Part size and weight


Parts made with hot runner molds are as small as 0.1 gram or less. The largest is over 30 kg. The application is extremely flexible.


3. Industrial field


Hot runner molds are widely used in various industrial sectors such as electronics, automobiles, medical, daily necessities, toys, packaging, construction, and office equipment.


Production profile


Hot runner mold production is extremely active in countries and regions with more developed industries in the world. The proportion of hot runner molds continues to increase. Many small mold factories with less than 10 people are producing hot runner molds. Generally speaking, in North America, Europe uses hot runner technology for a long time and has a high level of experience. In Asia, Singapore, South Korea, Taiwan and Hong Kong are leading positions apart from Japan. In North America, Europe has a higher level of mold manufacturing, but the price is higher and the delivery time is longer. In contrast, hot runner mold manufacturers in Asia are more competitive in terms of price and delivery time. China's hot runner molds are still in their infancy, but they are growing rapidly and the proportion is increasing.


Missing processing edit


Part of the leakage situation is not due to poor system design, but because it does not operate according to design parameters. Leakage typically occurs at the seal between the hot nozzle and the manifold. According to the general hot runner design specification, the hot nozzle has a steel edge to ensure that the height of the nozzle assembly is less than the actual groove depth on the hot runner plate. The purpose of designing this dimensional difference (commonly referred to as a cold gap) is to avoid thermal damage resulting in component damage when the system is at operating temperature.


1. The back of the hot nozzle is fixed on the diverter plate; the high temperature bolt fixing the hot nozzle on the diverter plate can prevent leakage under cooling conditions. This system still requires a cold gap because the steel edge requires a certain amount of expansion space at normal temperature. Although this method can actively prevent the leakage of the nozzle to the manifold, it cannot prevent the thermal expansion of the component under overheating conditions.


2. The hot nozzle fixed to the manifold by bolts moves together with the manifold. This design has a minimum length requirement for the hot nozzle and a limit to the cavity spacing. It is an economical and effective way to prevent leakage between the hot nozzle and the manifold, and is suitable for systems with a small number of cavities.


3. The edge of the hot nozzle is elastic rather than steel, and the elastic edge provides preload under cooling conditions and prevents system damage. If accidentally overheated, it can also absorb thermal expansion, extending the operating range to ±110 °C.


Mold industry editor


Because the giants of the times are constantly, fast, and cruelly moving forward quickly, what is worse is that the manpower market is hard to find, and the mold industry is generally lacking in people... It is worrying! Therefore, under the limited human resources, how to improve your mold profit to cope with the increasing cost is the main problem that everyone faces, improving precision, automating mold making..., of course, it is a good way, but it needs Investing a lot of money to buy equipment, training personnel... The simplest and easiest way to achieve this is to have a thorough understanding of the use of hot runners.


Feature introduction


The processing of injection molding is a process of (plasticization) → (flow) → (forming) → (solidification crystallization).


Therefore, the characteristics of plastics are particularly important. For example, dissolution temperature, pressure, viscosity, specific heat, etc. must be taken seriously. Since the field of plastics is very broad, it is not possible to go deep into it, but we will explain the common sense part.


Plasticizable


The reason why plastic can be shaped and processed is that it is deformed under the action of temperature and pressure. According to the temperature of heat, it can be divided into four states, namely, glass state, high elasticity state (rubber state), and viscous flow state (plasticizable). State), decomposition state, as shown in the figure:


Glass state: 0 ~ T1, the molecule is in a frozen state, hard and brittle, and it is easy to break when subjected to pressure.


Highly elastic state (rubbery state), T1 to T2, deformable by external force, and not easily formed in a molten state.


Viscous flow state (plasticizable state): T2 ~ T3, can be freely formed.


Decomposition state: T3, the plastic begins to crack, gas decomposition products appear, and even burnt state.


Forming conditions:


(Note) The following are the forming conditions of general plastics.


For each different plastic, its relative.