Introduction to hot runner technology of the hotte

2022-08-21
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Injection molding technology: introduction to hot runner technology

I. history, present and future of hot runner

as an advanced injection molding technology - hot runner technology, its popularity and use in European and American countries can be traced back to the middle of the last century or even earlier. Due to the many advantages of heat flow props, they have developed rapidly in foreign countries. More than 50% of the molds produced by many plastic mold factories use hot runner technology, and some mold factories even reach more than 80%. In China, this technology has only been truly promoted and applied in recent years. With the continuous development of the mold industry, the proportion of hot runner used in plastic mold is also gradually increasing. But the total is less than 10%, which is a huge gap

in recent years, the gradual promotion of hot runner technology in China is largely due to the rapid development of China's mold exports to European and American companies. In European and American countries, injection molding production has relied on hot runner technology. It can be said that molds without hot runner technology are now difficult to export, which has also led to a change in the technical awareness of many mold manufacturers for hot runner

because many imported hot runner systems are expensive, which is unacceptable to a large number of domestic manufacturers, there are some domestic hot runner system components. This is of great benefit to the promotion of hot runner technology in China. Although the hot runner technology has begun to be popularized, some companies have a utilization rate of more than 20%, and generally use simple tip and through tip. A few companies use needle valve type hot nozzles with world advanced level, but the overall adoption rate of hot runner is less than 10%, which is far from 50 ~ 80% abroad

Second, the principle of hot runner

cold runner refers to the part between the mold inlet and the product gate. The plastic keeps flowing in the runner by injection pressure and its own heat. The runner is a part of the molding material, but it does not belong to the product. Therefore, when we design the mold, we should not only consider the filling effect, but also consider how to save materials by shortening and narrowing the flow channel. Ideally, this is the case, but it is difficult to achieve the best of both worlds in practical application

hot runner, also known as no runner, means that the plastic in the runner does not solidify after each injection, and the nozzle in the runner does not have to be pulled out when plastic products are demoulded. Since the plastic in the flow channel has not solidified, the flow channel is still unblocked at the next injection

in short, the hot runner is the extension of the nozzle of the injection molding machine

III Advantages of hot runner mold

hot runner mold has been widely used in all industrial developed countries and regions in the world. This is mainly because the hot runner mold has the following remarkable characteristics:

1. Shorten the forming cycle of the part

because there is no restriction on the cooling time of the sprue system, the part can be ejected in time after forming and curing. The forming cycle of many thin-walled parts produced by hot runner mold can be less than 5 seconds

2. Save plastic raw materials

because there is no cold runner in the pure hot runner mold, there is no production cost. This is particularly significant for the application projects where plastic prices are expensive. In fact, the major international hot runner manufacturers have developed rapidly in the era of expensive oil and plastic raw materials in the world. Because hot runner technology is an effective way to reduce material cost and material cost

3. Reduce the cost of products and improve the quality of polyurethane insulation materials, which account for only about 10% of all exterior wall insulation cities in China.

in the hot runner mold molding process, the plastic melt temperature is accurately controlled in the runner system

plastic can flow into each mold cavity in a more uniform state, resulting in parts with the same quality. The hot runner shaped parts have good gate quality, low residual stress after demoulding, and the distance between the parts is the front axle, and the wheel track deformation of the two wheels is small. Therefore, many high-quality products in the market are produced by hot runner molds. For example, many plastic parts in Motorola, HP printer and Dell notebook computer are made of hot runner mold

4. Eliminating subsequent processes is conducive to production automation

the finished product is formed by the hot runner mold, and there is no need to trim the gate and recycle and process the cold runner. It is conducive to production automation. Many foreign product manufacturers combine hot runner with automation to greatly improve production efficiency

5。 Expand the application of injection molding process. Many advanced plastic molding processes are developed on the basis of hot runner technology. Such as pet preform production, multi-color co injection in the mold, multi-material co injection process, stackmold, etc

IV Disadvantages of hot runner mold

although compared with cold runner mold, hot runner mold has many significant advantages, mold users also need to understand the disadvantages of hot runner mold. To sum up, there are the following points

1. The cost of mold increases.

the price of hot runner components is relatively expensive, and the cost of hot runner mold may increase significantly. If the output of parts is small and the cost of mold and tools is high, it will not cost money economically. For mold users in many developing countries, the high price of hot runner system is one of the main problems affecting the wide use of hot runner mold

2. The hot runner mold is more than twice the area of France. The manufacturing process and equipment requirements are high.

the hot runner mold needs precision machining machinery to ensure. The requirements for the integration and cooperation between the hot runner system and the mold are extremely strict, otherwise there will be many serious problems in the production process of the mold. For example, the poor sealing of plastic leads to the overflow of plastic, the damage of hot runner components, the interruption of production, and the poor relative position between nozzle insert and gate leads to the serious decline of product quality

3. Complex operation and maintenance

compared with cold runner mold, the operation and maintenance of hot runner mold is complex. If it is used improperly, it is easy to damage hot runner parts, making production impossible and causing huge economic losses. For new users of hot runner molds, it takes a long time to accumulate experience

v Composition of hot runner system

although there are many hot runner manufacturers and a variety of hot runner product series in the world, a typical hot runner system is composed of the following parts:

1. Hot runner plate (manifold)

2. Nozzle (nozzle)

3. Temperature controller

4. Auxiliary parts

VI The main technical key of hot runner application

a successful hot runner mold application project needs multiple links to be guaranteed. There are two most important technical factors. One is the control of plastic temperature, the other is the control of plastic flow

1. plastic temperature control

plastic temperature control is extremely important in the application of hot runner mold

many processing and product quality problems in the production process directly stem from the poor temperature control of the hot runner system. For example, the quality of the product gate is poor when the hot needle gate method is used for injection molding, the valve needle is difficult to close when the valve gate method is used for molding, and the filling time and quality of parts in the multi cavity mold are inconsistent. If possible, the hot runner system with multi area temperature control should be selected as far as possible to increase the flexibility and adaptability of use

2. control of plastic flow

plastic flow balance in hot runner system. The gate should be opened at the same time to make the plastic fill each cavity synchronously. For familymold with widely different parts weight, the runner size design balance should be carried out. Otherwise, there will be problems such as insufficient mold filling and pressure maintaining of some parts, excessive mold filling and pressure maintaining of some parts, excessive flash, poor quality and so on. The size design of hot runner runner should be reasonable. The rotation angle of linear stepper will produce a certain linear displacement. The size is too small, and the mold filling pressure loss is too large. If the size is too large, the volume of the hot runner is too large, and the plastic stays in the hot runner system for too long, which will damage the material performance and cause the parts to fail to meet the use requirements after forming. There are already CAE software in the world, such as moldcae, that can help users design the best runner

VII Application scope of hot runner mold

1. Types of plastic materials

hot runner mold has been successfully used to process various 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 processed with a hot runner mold

2. part size and weight

the smallest part manufactured with hot runner mold is less than 0.1g. The largest is more than 30 kg. It is widely used and flexible

3. industrial field

hot runner molds are widely used in various industrial departments such as electronics, automobile, medical treatment, daily necessities, toys, packaging, construction, office equipment, etc

VIII International hot runner mold production profile

hot runner mold production is very active in countries and regions with more developed industries in the world. The proportion of hot runner mold continues to increase. Many small mold factories with less than 10 people produce hot runner molds. Generally speaking, in North America and Europe, hot runner technology has been used for a long time, with more experience and higher level. In Asia, apart from Japan, Singapore, South Korea, Taiwan and Hong Kong are in the leading position. In North America and Europe, although the mold manufacturing level is higher, the price is higher and the delivery time is longer. In contrast, Asian hot runner mold manufacturers are more competitive in terms of price and delivery time. The hot runner mold in China is still in its infancy, but it is growing rapidly and the proportion is constantly improving

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