As an advanced injection molding processing technology, the popularization and use of hot runner technology in European and American countries can be traced back to the middle of the last century or even earlier. As early as December 1940, E.R. Knowles achieved hot runner technology. technology patent rights. In China, the real promotion and application of this technology has only happened in recent years.
With the increasing promotion and application of hot runner technology, the proportion of hot runner molds in plastic molds will gradually increase. Due to the many advantages of molds using hot runner technology mentioned above, the application of hot runner technology is developing rapidly abroad. Many plastic mold factories produce molds with hot runner technology for more than 50%, or even more than 80%, and the effect is very obvious. . Hot runner has also been used in production in China, but the total is less than 10. This gap is quite huge, which means that this industry has considerable market space.
The gradual promotion of hot runner technology in China is largely due to the rapid development of Chinese mold exports to European and American companies. In European and American countries, injection molding production has relied heavily on hot runner technology. It can be said that it is basically difficult to export molds that do not use hot runner technology, which has also caused a change in the awareness of many mold manufacturers about hot runner technology. However, because many hot runner systems imported from foreign countries are relatively expensive and cannot be accepted by a large number of domestic manufacturers, some domestically produced commercial hot runner system components have emerged. This is of great benefit to the promotion of hot runner technology in China. However, although hot runner technology has begun to be promoted, some factories have an adoption rate of more than 20%, generally using internal or external heating hot runner devices. A few units use world-leading and difficult needle valve hot runner devices, but overall The adoption rate of hot runner is less than 10, which is still far from enough compared with 50 to 80 in foreign countries.
In recent years, world-famous hot runner technology suppliers have successively entered the Chinese market in various forms, either establishing production bases, looking for agents, setting up offices, or establishing subsidiaries. They should Said that this trend has played a huge role in the rapid improvement of technology in China's mold industry. In this trend, Korean companies that are close to the water are undoubtedly the first to take advantage of it. South Korea's Yudo (Ryudo), SINO (R) (Xianrui) and other brands have considerable influence in China; there is also Synventive (Synventive) headquartered in the Netherlands. The factories established by Synventive and Mold Masters of Canada in Suzhou and Kunshan respectively will also be put into production successively; North American injection molding industry giant Husky has been committed to popularizing hot runner technology in China for many years. work, its wholly-owned Asian operations center - Husky Shanghai Technology Center also has strong hot runner provision capabilities; at the same time, a large number of emerging private enterprises in China have also recognized the unlimited business opportunities in this field and have established hot runner Manufacturing enterprises, this is of great significance for reducing the use cost of hot runner technology and promoting its application. However, in general, most of the technologies that Chinese local enterprises can provide are still relatively rudimentary, with small space for selection, unstable quality and long maintenance cycles. The emergence of short-term problems often affects the trust of downstream companies in their products.
The widespread application of hot runner technology is a major change in plastic molds. In terms of injection molding, it has many unparalleled advantages. It can be said that with the further development and maturity of its technology and the reduction of manufacturing costs, hot runner technology will increasingly show its huge advantages. Formulating national standards for hot runner components, actively producing low-cost and high-quality components, and promoting hot runner technology are the keys to developing hot runner molds.
Hot runner system is a relatively complex technology in the field of injection molding. When mold designers and mold users choose and purchase hot runner systems, there are many issues that need to be considered. When a mold manufacturing company designs and makes a hot runner mold, it does not simply go to the hot runner supplier to buy a hot runner system and install it on the mold.
In fact, there are many detailed and close technical and commercial differences between the mold manufacturing company and the hot runner supplier, from the conceptual design stage of the hot runner mold, to the actual manufacturing process of the mold, to the final use of the mold. Coordination and cooperation. Therefore, mold manufacturing companies and mold users should choose a good hot runner supplier. When choosing a hot runner supplier, you should focus on two basic aspects. One is the quantity and quality of the hot runner components produced by the hot runner supplier; the other is the technical support provided by the hot runner supplier in the area where the mold user is located. and after-sales service.
1. The variety, quantity and quality of hot runner components
It has been introduced that hot runner systems include hot tip (HOT TIP), sprue type (SPRUE GATING) and valves
Needle Three major types: VALVE GATING. In fact, each type can be subdivided into many product series. For example, the cross-sectional diameter of the sprue in a hot tip nozzle (NOZZLE) can often range from 4 mm to 12 mm, and the nozzles are also made into product series of different sizes. Nozzle gate inserts are also available in many variations to meet different application requirements. Therefore, the richer the product series of the hot runner supplier you want to choose, the better. In this way, users can have greater selectivity of hot runner components, and the types, sizes, weights and application ranges of plastic parts produced with hot runner will be wider, which is more conducive to optimizing the injection molding production process and improving product quality.
When plastic products are processed by injection molding, the hot runner system and hot runner mold work under high temperature and high dynamic load conditions
There are many factors that lead to hot runner system component failure. And injection molding processing is mainly used in the production of large quantities of plastic parts. Once production is stopped, the economic losses will be very serious. Therefore, the quality and reliability of the hot runner system are very important. Customers should thoroughly investigate the quality and application history of hot runner components produced by hot runner suppliers. Some outstanding hot runner manufacturers have obtained ISO quality standard certification from international organizations.
2. Technical support and after-sales service
When using hot runner molds, in addition to first selecting a reliable hot runner system, users must also consider whether they can receive timely and effective technical support in case of any problems with the hot runner. and after-sales service is an important factor. Many hot runner suppliers have strong technical support and service networks in the countries and regions where their company headquarters are located, and are equipped with dedicated service personnel who can visit customers at any time for troubleshooting. However, these manufacturers often only set up some offices focusing on the sales of hot runner products in other countries and regions far away from their company headquarters. Technical support is relatively poor. Users should be aware of this factor. There are many specific technical links involved when users select and purchase a hot runner system. If the user has good technical knowledge related to hot runner, it will be easy to select and purchase the most suitable hot runner system to ensure the smoothness of the subsequent injection molding production process and improve product quality.
1. The correct choice of hot runner product series
Hot runner suppliers often make their hot runner components into product series according to the size and weight of the plastic parts to be processed. For example, large plastic parts are processed with large-size nozzles, and small plastic parts are processed with small-size nozzles. Therefore, after the user correctly selects the hot runner type (either hot tip or valve system), it is the choice of the hot runner product series. This determines the structural dimensions, design and manufacturing of the mold. If the hot runner product series is incorrectly selected and is not discovered until the later stages of mold processing or plastic parts production, the error is very serious and difficult to save. To help select the correct hot runner product line, each hot runner supplier has some guiding technical documents for reference. Users should work closely with hot runner suppliers to select a good hot runner product series.
2. Injection pressure loss in hot runner system
Injection pressure loss in hot runner system cannot be ignored. Many hot runner mold users have a misunderstanding that the injection pressure loss of hot runner is much smaller than that of cold runner. The reason is that the plastic melt located in the hot runner is always hot during the entire injection molding process. In fact, often the situation is exactly the opposite.
In hot runner molds, due to the need for hot runner structural design, the flow distance of the melt in the hot runner system will be greatly increased. Therefore, the injection pressure loss in the hot runner system is often larger. In practical applications, there are many situations where injection molding is difficult due to excessive injection pressure loss in the hot runner system. Therefore, when processing plastics with poor fluidity (such as PC, POM, etc.), the flow distance of the solution in the hot runner system is large, or the parts are heavy, CAE software should be used for flow channel analysis and calculation. CAE software that focuses on flow channel analysis and calculation includes MoldCAE and so on.
3. Standard and non-standard hot runner systems
Each hot runner manufacturer provides both standard and non-standard hot runner systems. If possible, users should try to choose a standard hot runner system. Try to choose nozzles, hot runner plates, gate inserts, etc. of standard length and size. The advantage is that the standard hot runner system is cheaper than the non-standard hot runner system and the delivery time is much shorter. And the parts are interchangeable, which is beneficial to future use and maintenance. Once a part breaks, just buy another standard part and install it. Common standard hot runner plate shapes include 2 cavities in a row, 4 cavities in a row, 8 cavities in a row, 4-cavity X shape, 8-cavity XX shape, etc.
4. Selection of the number and layout of cavities on the mold
When selecting the number of cavities when designing a hot runner mold, in addition to placing as many cavities as possible to improve production efficiency, users should also consider the design of the hot runner. The choice of the number and layout of the mold cavities should be conducive to the flow balance of the plastic melt in the hot runner system. For example, if several cavities with the same shape are arranged in a row, it is best to select 2 or 4 cavities instead of 3. Because for molds with 2 or 4 cavities in a row, the hot runner can be designed into a completely naturally balanced system. In contrast, a 3-cavity mold requires artificial flow balancing of the hot runner manifold. Different sprue sizes are used for different flow paths on the hot runner manifold in order to achieve flow balance. The quality of flow balance depends on the quality of work of the specific hot runner designer. Therefore, users should try to choose the number of cavities that is conducive to flow balance (such as choosing 16 cavities instead of 15 cavities, etc.) to eliminate any errors caused by artificial design of flow balance.
5. Limitations on the Minimum Cavity Distance
When designing molds for producing tiny parts, people generally want to arrange the cavities as close as possible so that the mold can be more compact and possibly contain more cavities. However, the minimum cavity distance will be limited by the minimum distance between hot runner components such as nozzles. Therefore, when designing a mold with very close cavities, users should pay attention to check the minimum allowable nozzle distance. To avoid mold design rework.
6. Type of plastic processed
The type of plastic processed is a very important consideration when selecting a hot runner system. If glass-reinforced plastics (such as glass-reinforced nylon materials, etc.) are processed, gate inserts with good wear resistance should be selected. If plastics that are prone to thermal decomposition (such as PVC) are processed, a hot runner system with smooth sprues and no flow dead corners should be used. If you are processing plastics with poor fluidity (such as PC), you should consider choosing a larger nozzle series and using a larger sprue cross-section size in the hot runner plate.
7. Maturity of hot runner products
The maturity and application history of each hot runner product are different. A newly launched hot runner product takes a long time to gradually improve. While hot runner manufacturers continue to introduce new products, they will also eliminate hot runner products that have been proven to be unsuitable in practice. Therefore, users should try to choose hot runner products that are mature, popular and have a long application history. For this type of product, both hot runner manufacturers and other hot runner users have a lot of experience and successful cases that new users with little experience can learn from.
8. The status of the hot runner system before shipment
Some hot runner suppliers will conduct certain tests on the system before shipping their hot runner systems to users. For very important applications there are even actual injection molding experiments. However, each hot runner supplier's testing scope before shipping the hot runner system is different.
Users should understand it and be aware of it.
9. Multi-zone temperature control of hot runner
If users need to purchase a large-scale and complex hot runner system, or process plastics that are temperature-sensitive and have a narrow range of processing parameters, they should choose a hot runner with multi-zone separate temperature control. Tao design plan. In this way, users can locally adjust and control the temperature distribution as needed. An ideal hot runner system should have uniform temperature distribution. But in fact, there are many reasons that lead to different temperatures in the hot runner. Such as the quality of the hot runner heating element, excessive heat loss at the joint between the hot runner system and the mold, and the difference in shear heat of the plastic melt in the hot runner. The larger and more complex the hot runner system is, the more you should choose a hot runner system with multi-zone temperature control.
10. Application projects with color change requirements
Some users use the same mold to produce the same type of plastic parts with different colors. This is an application project with color change requirements. When ordering a hot runner, you should try to choose a hot runner system with a small runner volume to speed up the color change process and reduce waste. At the same time, any runner turns in the hot runner system must be round and smooth, with no flow dead corners. If a valve-type hot runner system is used to produce plastic parts that require color change, there will often be a flow dead spot (DEAD SPOT) behind the valve needle, so special attention must be paid.
11. One-mode special-shaped multi-cavity mold
When designing a special-shaped multi-cavity mold, the flow balance issue must be considered. If the size and weight of the parts are too different and the injection pressure difference in each cavity is more than 200-300 BAR, it will be difficult to achieve flow balance by changing the runner size in the hot runner system. If the flow in a special-shaped multi-cavity mold is unbalanced, there will be problems such as insufficient filling and pressure holding of some parts, over-filling of other parts, large flash, and high residual stress. At this time, you should consider using a valve hot runner system or changing the overall design of the mold. The valve system allows the user to gate early filling cavities at the appropriate moment to avoid overfilling issues in these cavities.
12． The proportional relationship between the cavity and the hot runner volume
Compared with the cavity volume, the runner volume of the hot runner system should not be too large. Otherwise, the plastic melt will stay in the hot runner system for too long and thermal decomposition will occur. Unable to produce qualified plastic parts. If the weight of the plastic part is too small, a solution that uses both hot and cold runners should be used. Because the injection volume increases after using the cold runner, it helps to improve the proportional relationship between the cavity and the hot runner volume and shorten the residence time of the plastic melt in the hot runner system.
13. Use trial molds
Hot runner molds are more expensive, especially hot runner molds with a high number of cavities (such as 96, 128 cavities, etc.), the price is even higher. If you want to open up a new application field, have insufficient experience, or are trying to use newer hot runner components (such as nozzles or new gates), you should consider making a simple, single-cavity trial mold first. to conduct feasibility study verification of the plan. After gaining enough experience, expensive and formal working molds can be made.
14. Drawing of hot runner components on the mold diagram
Hot runner suppliers generally make electronic libraries of their hot runner components for users to use. When designing and drawing mold drawings, mold designers can select the required component drawings such as nozzles from the electronic library of hot runner components and place them in the appropriate mold position. Since hot runner suppliers will frequently update their hot runner products, users should pay attention to constantly request the latest image galleries from hot runner manufacturers. Although people have begun to use 3D methods to design molds, the vast majority of hot runner component electronic libraries of various hot runner suppliers are still 2D. Some manufacturers have begun to establish 3D hot runner component libraries to adapt to the development of 3D mold design
15. Quality warranty period
Hot runner suppliers will provide some warranty periods for their hot runner products. The warranty period ranges from one to five years, depending on the hot runner manufacturer and the specific hot runner product purchased by the user. During the warranty period, if a problem occurs with the hot runner product under normal operation and use by the user, the hot runner supplier will replace it free of charge.
Obviously the longer the warranty period, the more beneficial it is to the user. In order to ensure that the quality warranty period is valid, users should respect the usage and maintenance regulations of hot runner and shall not modify or change any hot runner components without the consent of the hot runner supplier.
16. Handling the water position of the product
Hot runner products, as a plastic melt molded product, inevitably have water outlet positions during the production process. When users choose a hot runner company to design and produce products, they need to work with them Fully communicate with the technical staff of the hot runner manufacturer. The cost of the hot runner hot nozzle (flat nozzle, pointed nozzle, multi-head nozzle, needle valve nozzle, etc., the price difference is also relatively large) accounts for an important part of the hot runner system. Choose the design A suitable hot nozzle is very important for the operation of the entire system to achieve the desired effect during the design process. On the one hand, it can control the cost and select the appropriate hot nozzle according to the actual situation. On the other hand, it can reduce the occurrence of secondary design during production and use. Probability.
This article discusses several issues that need to be considered when selecting and purchasing a hot runner system. The production and use of hot runner molds is the same as that of traditional injection molds. There is a lot of experience and skills involved, and users need time to gradually accumulate them.