What Is a Hot Runner?

Hot runner (Hot Runner Systems) is a heating component system used in injection molds to inject molten plastic particles into the cavity of the mold. The hot runner mold is a brand-new structure in which the runner and runner of a traditional mold or three-plate mold are heated, and the runner and runner need not be taken out during each forming.

Hot runner

Hot runner systems are divided into fully hot runners and semi hot runner systems. The design of the adiabatic runner is complicated, but the effect is good and the maintenance cost is very low. The structure of the miniature semi-hot runner is simplified, stable and easy to use, and the failure rate is low. Due to the simple structure, the maintenance cost is low, and the stability of production is more guaranteed.

Classification of hot runner: open type (for miniature semi-hot runner), needle valve type (for adiabatic runner). ^[1]

Hot runner system generally consists of hot nozzle,

Although there are many hot runner manufacturers and multiple hot runner product families in the world, a typical hot runner system consists of the following major parts:

1. Main splitter (MANIFOLD)

2. Nozzle

3 Temperature Controller

4 Auxiliary parts

The types and applications of these parts will be discussed in depth in subsequent articles.

Part of the material leakage is not due to poor system design, but due to failure to operate according to design parameters. Leakage usually occurs at the seal between the nozzle and the manifold. According to the general hot runner design specifications, the hot nozzle has a rigid edge to ensure that the height of the hot nozzle assembly is smaller than the actual groove depth on the hot runner plate. This difference in size (commonly referred to as the cold gap) is designed to avoid thermal expansion that can cause component damage when the system is at operating temperature.

1. The back of the hot nozzle is fixed on the manifold; the high temperature bolt that fixes the hot nozzle on the manifold can prevent leakage under cooling conditions. This system still requires cold clearance, because rigid edges require some expansion space at normal temperature. Although this method can actively prevent leakage from the nozzle to the manifold, it cannot prevent the thermal expansion of the component under overheating conditions.

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

3. The edge of the hot nozzle adopts elastic instead of rigid design. The elastic edge provides preload under cooling conditions and prevents system damage. If accidentally overheated, it can also absorb thermal expansion, expanding the operating range to ± 110 ° C.

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Feature introduction

The processing of injection molding is the process of (plasticizing) (flow) (forming) (solidification and crystallization).

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

Plasticizable

The reason why plastic can be formed is that it deforms under the action of temperature and pressure. Depending on the temperature of the heat, it can be divided into four states, namely glass state, highly elastic state (rubber state), and viscous fluid state (plastic Status), decomposition status, as shown in the figure:

Glass state: 0 T1, the molecules are in the frozen state, hard and brittle, and easy to break under pressure.

High elastic state (rubber state), T1 T2, can be deformed due to external force, it is difficult to form before reaching the melting state.

Viscous fluid state (plasticized state): T2 T3, can be processed at will.

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

Forming conditions:

(Note) The following are the molding conditions for general plastics

For each different plastic, the relative forming area may be different, but the process analysis is the same. Therefore, for a good mold designer, they should really understand the forming area and processing characteristics of each plastic. ^[3]

Competition is fierce in the field of hot runner technology. Many companies have invested huge financial and material resources in the development of hot runner products. The latest hot runner products are always available at major plastic and mold exhibitions. The main hot runner manufacturers and headquarters locations in the world are listed here.

As an advanced injection molding processing technology, the popularity 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, ERKnowles obtained the patent right of hot runner technology. In China, the actual promotion and application of this technology is just something that happened in recent years.

With the increasing popularization and application of hot runner technology, the proportion of hot runner molds in plastic molds will gradually increase. Due to the many advantages of the hot runner technology mold mentioned above, the application of the hot runner technology has developed rapidly abroad. More than 50% of the molds produced by many plastic mold factories use the hot runner technology, even more than 80%. Very obvious. Hot runners have also been used in production in China, but overall less than 10%, this gap is quite huge, which means that the industry has a considerable market space.

The 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 molds without hot runner technology have been difficult to export, which has also caused many mold manufacturers to change their consciousness of hot runner technology. However, because many imported hot runner systems are more expensive and cannot be accepted by a large number of domestic manufacturers, some domestic commercial hot runner system components have appeared. 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 plants have adopted rates of more than 20%. Generally, internal or external hot runner devices are used. A few units have adopted the world's advanced level of difficult needle valve hot runner devices, but overall The adoption rate of the upper hot runner is less than 10%, which is far from enough compared with 50 80% in foreign countries.

In recent years, world-renowned hot runner technology suppliers have entered the Chinese market in various forms one after another, or set up production bases, or found agents, or set up offices, or established subsidiaries. It should be said that this trend is The rapid improvement of technology in the mold industry has played a huge role. In this trend, it is undoubtedly the earliest Korean company near the water platform to take the initiative. South Korean brands such as Yudo (Rio Road), SINO (R) (Senrui) have a considerable influence in China; another company based in the Netherlands Synventive) and Canada s Mold Masters (Master) in Suzhou and Kunshan, respectively, will also start production; Husky, the North American injection molding industry giant, has been committed to the popularization of hot runner technology in China for many years Work, its wholly-owned Asian operation center-Husky Shanghai Technology Center also has a strong hot runner supply capability; 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 runners one after another Manufacturing companies, which are of great significance for reducing the cost of hot runner technology and its promotion and application, but in general, most of the technologies that Chinese domestic companies can provide are still relatively basic, with small space for selection, unstable quality, and maintenance cycles. The emergence of short-term problems often affects downstream companies' trust in their products.

The widespread application of hot runner technology is a major change in plastic molds. In terms of injection molding, it has a lot of incomparable 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. The key to the development of hot runner molds is to formulate national standards for hot runner components, actively produce inexpensive and high quality components, and do a good job in the promotion and promotion of hot runner technology.

Hot runner system is a relatively complicated technology in the field of injection molding. There are many issues that need to be considered when mold design manufacturers and mold users choose and purchase hot runner systems.

Selection of hot runner suppliers

When the mold manufacturing company designs and manufactures the hot runner mold, it is not simply to buy a hot runner system from the hot runner supplier and install it on the mold. In fact, 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 use of the final mold, there are many meticulous technical and commercial aspects. Coordination and cooperation. Therefore, mold manufacturing companies and mold users should choose a hot runner supplier. When selecting a hot runner supplier, we must focus on two basic aspects, one is the quantity and quality of the hot runner components produced by the hot runner supplier, and the other is the technical support of the hot runner supplier in the area of the mold user. And after sales service.

1. Variety and quality of hot runner elements

Have introduced the hot runner system with hot tip (HOT TIP), pouring sleeve (SPRUE GATING) and valve

Three types of VALVE GATING. In fact, each type can be subdivided into many product lines. For example, the diameter of the runner section in the NOZZLE nozzle can often range from 4 mm to 12 mm, and the nozzles are also made into different size product series. There are also many variations of nozzle gate inserts to meet different application requirements. So the richer the product line of the hot runner supplier you want, the better. In this way, users can have greater selectivity of hot runner components, and the types of plastic parts produced by hot runners have a wider range of dimensions, weights and applications, which is more conducive to optimizing the injection molding production process and improving product quality.

When injection molding processes plastic products, the hot runner system and hot runner mold are under high temperature and high pressure dynamic load conditions.

work. There are many factors that cause the failure of hot runner system components. And injection molding is mainly used in the production of large quantities of plastic parts. Once there is any suspension of production, economic losses are very serious. Therefore, the quality and reliability of the hot runner system is very important. Customers should conduct in-depth inspections of the quality and application history of hot runner components produced by hot runner suppliers. Some of the better hot runner manufacturers have obtained ISO quality certification from international organizations.

2. Technical support and after-sales service

When using hot runner molds, in addition to selecting a reliable hot runner system, users must also consider the important factor of whether they can get timely and effective technical support and after-sales service in case of any problems with the hot runner. Many hot runner suppliers have strong technical support and service networks in the countries and regions where their companies are headquartered, and are equipped with dedicated service personnel who can visit customers at any time for troubleshooting. However, in other countries and regions far from their company headquarters, these manufacturers often have only offices that focus on the sales of hot runner products. Technical support is relatively inferior. Users should pay attention to this factor.

Technical issues when choosing and purchasing a hot runner system

When selecting and purchasing a hot runner system, users will involve many specific technical links. If the user has good technical knowledge about hot runners, it is easy to choose and purchase the most suitable hot runner system to ensure the subsequent injection molding production process and improve product quality.

1. The right choice for the hot runner product range

Hot runner suppliers often make their hot runner components into product series according to the size and weight of the processed plastic part. For example, large plastic parts are processed with large-sized nozzles, and small plastic parts are processed with small-sized nozzles. Therefore, after the user has correctly selected the hot runner type (whether the hot tip or valve system is selected), it is the choice of the hot runner product series. And thus determine the structural size and design and manufacture of the mold. If the selection of the hot runner product series is incorrect, it will be discovered later in the mold processing or during the production of plastic parts. The error is very serious and difficult to save. To help select the right hot runner product family, each hot runner supplier has some technical guides for reference. The user should work closely with the hot runner supplier to choose a good hot runner product range.

2. Injection pressure loss in hot runner systems

The injection pressure loss in the hot runner system cannot be ignored. Many hot runner mold users have a misunderstanding that the injection pressure loss of the hot runner is much smaller than that of the cold runner. The reason is that the plastic solution in the hot runner is always hot during the entire injection molding process. In fact, the opposite is often the case. In the hot runner mold due to the need for the design of the hot runner structure, the flow distance of the solution in the hot runner system will be greatly increased. Therefore, the injection pressure loss in the hot runner system is also often large. In practical applications, there are many situations where injection molding is difficult due to excessive injection pressure loss in the hot runner system. Therefore, for the processing of plastics with poor fluidity (such as PC, POM, etc.), where the flow distance of the solution in the hot runner system is large, or the weight of the product is large, the CAE software should be used for flow channel analysis calculation. The CAE software focusing 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. that are as standard as possible. 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 conducive to future use and maintenance. Once a part is broken, buy another standard part and install it. The shapes of common standard hot runner plates are 2 cavities, 1 row, 4 cavities, 1 row, 8 cavities, 1 row, 4 cavities, X shape, 8 cavities, XX shape, etc.

4 Choice of cavity number and layout on mold

When designing the number of cavities for the hot runner mold design, in addition to placing as many cavities as possible to improve production efficiency, users should also consider the design of the hot runner. The number of cavities and layout on the mold should be selected to facilitate the flow balance of the plastic solution in the hot runner system. For example, if several cavities with the same shape are arranged in a row, it is better to choose the number of cavities as two or four instead of three. Because two or four cavities are lined up, the hot runner can be designed as a completely natural balanced system. In contrast, a 3-cavity mold requires artificial flow balancing of the hot runner manifold. In the hot runner manifold, different runner sizes are used for different flow paths to try to achieve the purpose of flow balance. The flow balance depends on the quality of the specific hot runner designer. Therefore, the user should try to choose the number of cavities that are conducive to flow balance (such as choosing 16 cavity instead of 15 cavity, etc.) to eliminate any mistakes caused by artificially designed flow balance.

5. Limitation of minimum cavity distance

When designing a mold for producing small parts, people generally want to arrange the cavity as close as possible, so that the mold can be more compact and more cavity can be placed. However, the minimum cavity distance is limited by the minimum distance between hot runner elements such as nozzles. Therefore, when designing a mold with a close cavity, the user should pay attention to checking the minimum allowable nozzle distance. To avoid mold design rework.

6. Types of processed plastic

The type of plastic processed is a very important consideration when choosing a hot runner system. When processing glass-reinforced plastics (such as glass-reinforced nylon), gate inserts with good abrasion resistance should be used. When processing plastics (such as PVC) that are easy to thermally decompose, a hot runner system with smooth runners and no dead corners should be selected. If processing fluid plastics (such as PC), you should consider using a larger nozzle series, and use a larger runner cross-section size in the hot runner plate.

7. Maturity of hot runner products

The maturity of each hot runner product is different from the length of its application history. A newly introduced 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 proven to be inappropriate in practice. Therefore, users should try to choose hot-runner products with good maturity, popularity, and long application history. Regardless of whether these products are hot runner manufacturers or other hot runner users, they have more experience and successful cases for new users with little experience to learn from.

8. Pre-shipment status of the hot runner system

Some hot runner suppliers test their systems before shipping them to customers. For very important applications, even actual injection molding experiments are performed. However, the test range of each hot runner supplier before the hot runner system is shipped is different. Users should be aware of what they know.

9. Multi-zone temperature control of hot runner

If the user needs to purchase a large-sized and complex hot runner system, or to process plastics that are sensitive to temperature and have a narrow processing parameter range, they should choose a hot runner design with multi-zone temperature control. In this way, the user can locally adjust and control the temperature distribution as required. An ideal hot runner system should have a uniform temperature distribution. However, there are actually a number of reasons for different temperatures throughout the hot runner. For example, the quality of the hot runner heating element, the excessive loss of heat at the hot runner system and the mold, and the difference in the shear heat of the plastic solution in the hot runner. The larger the size of the hot runner system, the more complicated it should be. The hot runner system with multi-zone temperature control should be selected.

10. Applications with color change requirements

Some users use the same mold to produce plastic parts of the same variety with different colors. This is an application item that requires color change. When ordering hot runners, 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 runners in the hot runner system must be rounded and smooth without dead ends. If a valve-type hot runner system is used to produce plastic parts that require color change, there will often be a dead spot behind the valve needle (DEAD SPOT), which requires special attention.

11. One mold special multi-cavity mold

When designing a mold with multiple cavities and considering a mold, the flow balance must be considered. If the size and weight difference of the parts is too large, and the injection pressure difference of each cavity is above 200-300 BAR, it is difficult to achieve flow balance by changing the runner size in the hot runner system. If the flow is unbalanced in a multi-cavity mold with a special shape, some parts will not be filled enough to maintain the pressure, other parts will be overfilled, and the flash will have high residual stress and other problems. At this time, you should consider using a valve hot runner system, or change the overall design of the mold. The valve system allows users to close early-filled cavity gates at the appropriate time to avoid overfilling of these cavities.

12. Proportional relationship between cavity and hot runner volume

Compared with the cavity volume, the runner volume of the hot runner system must not be too large. Otherwise, the plastic solution stays 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, the combined hot and cold runner should be used. Because the injection volume increases after using the cold runner, it helps to improve the proportion relationship between the cavity and the hot runner volume, and shortens the residence time of the plastic solution in the hot runner system.

13. Use trial mold

Hot runner molds are more expensive, especially hot runner molds with high cavity numbers (such as 96, 128 cavity, etc.), the price is higher. If you want to open up a new application field, lack of experience, or try to use newer hot runner components (such as nozzles or new gates), you should consider making a simple, single-cavity trial mold. To verify the feasibility of the scheme. After getting enough experience, make expensive and formal working molds.

14. Drawing of hot runner elements on the mold diagram

Hot runner suppliers generally make their hot runner components into an electronic gallery for users to use. When the mold designer designs and draws the mold diagram, he can select the required nozzle and other component diagrams from the hot runner component electronic library and place them in the appropriate mold location. Because hot runner suppliers will frequently update their hot runner products, users should pay attention to constantly obtaining the latest gallery from hot runner manufacturers. Although people have begun to design molds using 3D methods, the majority of hot runner component electronic libraries of various hot runner suppliers are still 2D. Some manufacturers have begun to build a 3D hot runner component library 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 year to five years, depending on the hot runner product item purchased by the hot runner manufacturer and user. During the warranty period, if there is a problem with the hot runner product under the normal operation and use of the user, the hot runner supplier will give free replacement. Obviously, the longer the warranty period, the better for the user. In order to ensure that the quality warranty period is valid, users should respect the use and maintenance regulations of the hot runner, and may not modify or change any hot runner components without the consent of the hot runner supplier.

16. Processing of product water products

Hot runner product, as a plastic solution molding product, in the production process, the nozzle position is inevitable. When choosing a hot runner company to design and produce products, users need to fully communicate with the technical staff of the hot runner manufacturer. The cost of nozzles (flat, pointed, multi-nozzle, needle valve, etc., the price difference is also relatively large), compared to the important part of the hot runner system. Select the appropriate design of the hot nozzle, the design process for the entire system It is very important to achieve the desired effect. On the one hand, the cost can be controlled, and the appropriate nozzle can be selected according to the actual situation.

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 traditional injection molds. There are many experiences and skills, and users need time to accumulate.