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What Is Mold Hot Runners ?

Edit: Smart Mold Technology Limited    Date: Feb 21, 2017

Hot runner is a set of heating components used in injection molds that inject melted plastics into the cavity of the mold. Also known as one of the mold standard parts.


What is hot runner?

Hot runner system is composed of hot mouth, runner board, temperature control box composed of three parts, is a plastic injection molding in a perfect form into the plastic structure.

Hot runner system works is installed in the plastic mold heater, the use of heating and temperature control of the principle of the mold to maintain the molten state of the runner. Like the injection molding machine directly into the cavity of the product cavity into the plastic point, so that the product more directly and easily forming.


Hot runner performance

Precise control of melt plastic temperature, to eliminate material degradation. Balanced flow channel design, parts cavity evenly filled. The runner has no dead zone to ensure rapid color change and prevent material degradation to minimize pressure loss.


Selection of hot runner

Many of the conditions are the factors to consider when choosing a hot mouth. For example, different plastic properties, shape, size, thickness, weight, cavity arrangement and gate position, we have several different shapes and sizes of hot mouth and runner Board to adapt to a variety of products.


Advantages and disadvantages of hot runner technology


So why is this hot runner technology appear? What are the benefits of hot runner technology? Familiar with the injection molding process friends know that conventional injection molding often have the following unfavorable factors:

 1, filling difficult;

 2, the deformation of thin-walled large parts;

 3, the waste of raw materials in the runner;

 4, multi-cavity mold injection of different quality.


Advantages of hot runner:


Hot runner technology, the problem is to provide a more complete solution, hot runner mold in today's world industrial developed countries and regions have been very widely used. This is mainly because the hot runner mold has the following many benefits:


 1. Save raw materials and reduce it.

 2. Shorten the molding cycle and improve the efficiency of the machine

 3. Improve the surface quality and mechanical properties.


 4. Do not use a three-plate mold that can use the point gate.

 5. A single product can be molded economically at a side gate.

 6. Improve the degree of automation.

 7. Needle valve gate can be used to control the gate frozen.

 8. Multi-cavity mold of the same quality of injection molded parts.

 9. Improve the surface aesthetics of injection molded products.


Hot runner shortcomings:


  However, each technology will have its own shortcomings exist, hot runner technology is no exception:

 1. Mold structure is complex, high cost, high maintenance costs.

 2. boot a period of time will be stable technology, resulting in more boot waste.

 3. Occurrence of melt leakage, heating element failure, the product quality and production schedule greater impact.


The third shortcomings above, especially need to pay attention, because compared with the cold runner mold, hot runner mold operation and maintenance complex. Such as the use of improper operation easily damaged hot runner parts, so that production can not be carried out, resulting in huge economic losses. For new users of hot runner molds, it takes a long time to accumulate experience. This can be reduced by purchasing quality upper heating elements, hot runner plates and nozzles and carefully maintained during use.


Which molds are suitable for hot runners



The above analysis of the advantages and disadvantages of so many hot runner, then whether each pair of molds can use hot runner? the answer is negative. In general, hot runner technology is only applicable to plastic molds, and not every plastic mold is suitable. Here are some of the commonly used plastic relative to the use of hot runner to explain:


Material - Model Crystalline

                    PP PE PBT PET POM PPA PPS LCP

Needle valve is very good very good may be very good may be very good possible

It is possible that there may be a possibility of contact with the inquiry

Big mouth very good mouth may be possible to contact the query can contact inquiries can contact inquiries do not recommend the use of materials - model non-crystalline

                    PS ABS PPO PC SAN PUR PVC PMMA

Needle valve is very good very good There may be likely to be very good

It is possible to contact the query may be possible to contact the query is not recommended to use

Large mouth mouth may be possible may be possible to contact the query can contact inquiries can contact inquiries may be possible material - model additives

                        FR GF ST

Needle valve may be possible

Point of the mouth can be linked to the query can contact inquiries can contact inquiries

It is possible that there may be a possibility


Hot runner technology in China

As an advanced injection molding technology, hot runner technology in Europe and the United States universal use can be traced back to the middle of the last century or even earlier, as early as December 1940, ERKnowles made a hot runner technology patents. In China, the real application of this technology is nothing more than what happened in recent years.

With the increasing use of hot runner technology, hot runner mold in the proportion of plastic mold will gradually increase.As the above mentioned the use of hot runner technology mold many advantages, therefore, hot runner technology applications in foreign development faster, Many of the molds produced by plastic mold factory more than 50% of the hot runner technology used, or even 80% or more, the effect is very obvious. Hot runner in the country has also been used for production, but overall less than 10%, this gap is quite large, which means This industry has a considerable market space exists.

The following are the same as the "

In recent years, the gradual promotion of hot runner technology in China, which is largely due to the rapid development of China's mold exports to Europe and the United States. Hot runner technology in China's penetration rate is very low, the reason is many A lot of mold enterprises and injection companies have a wait-and-see attitude on the technology, and even do not even understand it, which is largely because of the hot runner supplier publicity is not enough.As a hot runner supplier, Its end customers (injection companies) understand that the use of hot runners is to help them profit, not only make their products more beautiful, raw materials are saved, more productive, but also can help it greatly improve the life of the mold. , Hot runner suppliers and mold enterprises as intermediate links have a lot of work to do; the other hand, is to teach customers the correct use of hot runner system. Many customers (including mold enterprises and injection enterprises) after the purchase of hot runner , Due to improper use, often burn the heating element and even the temperature controller, which lightly lead to product quality decline, heavy damage caused by mold damage, injection molding machine stall, etc., so that customers will mistakenly believe that the hot runner is So that the promotion of hot runner technology in China, the customer's propaganda work long way to go, so that injection companies to accept and really learn to use hot runner technology will be hot runner suppliers in the future the most important work.


Hot runner technology is widely used in plastic mold a major change in the injection molding, it has a considerable number of unparalleled advantages, it can be said that with the further development of its technology mature and reduce the cost of manufacturing, hot runner Technology will increasingly show its great advantages.To develop hot runner components of the national standard, and actively produce cheap high-quality components, do hot runner technology promotion, is the development of hot runner mold key


The structure of the hot runner system


Hot runner system is generally composed of hot nozzles, manifolds, temperature control boxes and accessories.


1, hot mouth back fixed to the manifold; the hot mouth fixed to the manifold on the high temperature bolts, can prevent leakage under cooling conditions. This system still requires a cold gap, because the steel edge at room temperature requires a certain expansion of space. Although this method can proactively prevent the leakage of the hot mouth to the manifold, it is not possible to prevent thermal expansion of the components under overheating conditions.


2, through the bolt fixed to the manifold on the nozzle with the manifold with the movement. This design has a minimum length requirement for the nozzle, and there is a limit to the cavity spacing. It is economical and effective way to prevent the leakage between the hot mouth and the manifold, and is suitable for a system with few cavities.


3, hot mouth edge with elastic rather than steel design, elastic edge in the cooling conditions to provide preload, and to prevent system damage. If accidentally heated too much, it can also absorb thermal expansion, so that the operating range expanded to ± 110 ℃.


Hot nozzles generally include two types: open hot nozzles and needle valve hot nozzles. As the hot nozzle form directly determines the hot runner system selection and mold manufacturing, and thus often the corresponding hot runner system is divided into open hot runner system and needle valve hot runner system. The manifold is used in a multi-cavity or multi-point feed, single point feed but level offset. Materials are usually P20 or H13. Split plate is generally divided into standard and non-standard two categories, its structure mainly by the cavity in the mold on the distribution of the nozzle arrangement and the location of the gate to decide. Temperature control box, including host, cable, connector and wiring male and female sockets. Hot runner accessories typically include: heaters and thermocouples, flow path seals, connectors and junction boxes.


Classification of hot runner systems


In general, the hot runner system is divided into single head hot runner system, long hot runner system and valve gate hot runner system. Single-head hot runner system consists of a single nozzle, nozzle head, nozzle connection plate, temperature control system and other components. Single head hot runner system Plastic mold structure is relatively simple. The molten state of the plastic from the injection molding machine into the nozzle connection plate, through the nozzle to reach the nozzle head, into the cavity. It is necessary to control the dimensions d, D, L and by adjusting the thickness dimension of the nozzle connecting plate so that the die fixing plate presses the end face of the nozzle connecting plate, controls the axial displacement of the nozzle, or directly engages the nozzle connection plate with the injection molding nozzle Face, but also to achieve the same purpose. A lead slot is provided at a suitable position on the stationary plate so that the power cord is led out of the mold and connected to the terminal block mounted on the mold.


      Multi-head hot runner system Plastic mold structure is more complex. The molten plastic is injected into the nozzle connection plate by the injection molding machine, flows through the nozzle to the nozzle head and then into the cavity. Hot runner system nozzle and set the template radial size D with the requirements and axial size limit requirements. Nozzle head and die with a radial size d with the requirements to ensure that the molten state of the plastic does not overflow to the non-cavity parts, and requires the hardness of hardening die 50HRC around. The distance L between the parting surface and the axial positioning surface of the hot nozzle must be strictly controlled, which should be determined according to the actual distance L 'of the nozzle at room temperature and the actual extension ΔL of the nozzle at the normal working temperature of the mold. In order to ensure reliable attachment of the nozzle to the hot runner plate without deformation of the hot runner plate, an adjustment pad is provided above the top of the nozzle, which together with the axial positioning surface of the nozzle itself limits the axial movement of the nozzle, And the effective control of the hot runner plate may produce deformation. At room temperature, adjust the pad and the hot runner plate and fixed mold plate between the control 0.025mm gap so that the mold heated, the working temperature in the state when the adjustment pad just compact. The locating seat and the locating pin of the hot runner system together control the position of the hot runner plate in the mold. Positioning seat and the fixed plate with radial size D2 with the requirements, and the depth h must be controlled accurately, positioning the seat of the axial role of supporting the hot runner plate, directly to the injection machine injection pressure. Locating pin and hot runner plate fixing plate with the requirements. There should be enough clearance between the hot runner and the template to wrap the insulation. The hot runner plate and the mounting plate must be provided with sufficient wiring slots to allow the power cord to be led out of the mold and connected to the terminal block mounted on the mold. There is a radial dimension D1 between the nozzle connecting plate and the fixed mold fixing plate so that the injection head of the injection molding machine cooperates well with the nozzle connecting plate on the mold. In the vicinity of the hot runner plate, will set the template, hot runner plate fixed plate, fixed fixed plate with screws connected to enhance the rigidity of the hot runner board.


Valve gate hot runner system Plastic mold structure is the most complex. It has the same structure as the ordinary long hot runner system plastic mold, in addition to a set of valve needle drive control valve needle opening and closing movement. The transmission device is equivalent to a hydraulic cylinder, the use of injection device hydraulic device and die connected to form a hydraulic circuit to achieve the valve needle opening and closing movement, control the molten state of plastic injection cavity.



  Hot runner plastic mold design program


First, according to the plastic structure and the use of requirements, determine the feed port position. The inlet of the hot runner system can be placed in any position in the plastic part as long as the plastic structure allows the nozzles and nozzles in the mold insert not to interfere with the forming structure. Conventional plastic injection molding of the inlet position is usually selected according to experience. For large and complex shaped plastic parts, injection molding of the inlet position can be used computer-aided analysis (CAE) simulation of molten plastic in the cavity of the flow of the mold parts of the cooling effect, to determine the ideal feed Mouth position.


Then, determine the nozzle head form of the hot runner system. The use of plastic materials and products is a key factor in the choice of nozzle head form, the production of plastic parts and mold manufacturing costs is also an important factor in the choice of nozzle head


Third, according to the production of plastic parts and injection equipment tonnage size, to determine the number of cavity per model


Leakage treatment


Part of the leakage material situation, not because the system design is bad, but because the design parameters are not in accordance with the operation. Leakage usually occurs at the seal between the hot mouth and the manifold. According to the general design specifications of the hot runner, there is a steel edge at the hot Tsui to ensure that the height of the hot mouth assembly is less than the actual groove depth on the hot runner plate. The purpose of designing this size difference (commonly known as a cold gap) is to prevent the component from being damaged when the system is at operating temperature.


Fourth, the number of nozzles is determined by the determined feed port position and the number of cavities per mold. If you choose a product, choose a mold of a feed port, then as long as a nozzle, that is, the use of single-head hot runner system; if the formation of a product, choose a mold multi-cavity or a cavity more than two Mouth, it is necessary to multiple nozzles, that is, the choice of long hot runner system, but 

Except for mold structures with crossflowers.


Fifth, leakage material handling


Part of the leakage material situation, not because the system design is bad, but because the design parameters are not in accordance with the operation. Leakage usually occurs at the seal between the hot mouth and the manifold. According to the general design specifications of the hot runner, there is a steel edge at the hot Tsui to ensure that the height of the hot mouth assembly is less than the actual groove depth on the hot runner plate. The purpose of designing this size difference (commonly known as a cold gap) is to prevent the component from being damaged when the system is at operating temperature.


Sixth, according to the plastic structure to determine the size of the mold structure, and then according to the size of the fixed mold and set the thickness of the nozzle size of the standard length of the series size, and finally repair the thickness of the template size and other hot runner system-related size.


Seventh, according to the shape of the hot runner plate to determine the shape of the hot runner fixed plate, in its board layout power cord lead slot, and in the hot runner board, nozzle, nozzle head near the design of adequate cooling water loop.


Eighth, complete the hot runner system plastic mold design drawing.


The development direction of hot runner system


At present, the hot runner system there are some defects, such as the mold structure is complex, easy to damage the heater components, high manufacturing costs, the need for more sophisticated temperature control device, the molding resin must be clean without debris, resin replacement and color change more difficult, More complex, but these defects are gradually being overcome. At present, the main trends of domestic and foreign hot runner mold can be summarized as the following aspects.


The miniaturization of the components in order to achieve a small product of a multi-cavity and large products multi-gate filling. By reducing the nozzle space, more cavities can be configured on the mold to increase the yield of the product and the utilization of the injection machine. In the 1990s, Master developed a minimum nozzle to 15.875mm; Husky company developed a multi-gate nozzle, each nozzle has four gates, gate distance can be close to 9.067mm; Osco company developed a combination of compound nozzle, Each nozzle has 12 gate probes that can be used for 48 cavity molds. MoldMaters developed a nozzle for small parts in 2001, with a single heater, tip and melt channel, a smaller than 9mm diameter, a gate pitch of only 10mm and a molded weight of 1 to 30 g of the product.


Hot runner components are standardized and serialized. At present, the user requirements mold design and manufacturing cycle is shorter and shorter, the hot runner component standardization is not only conducive to reducing the design work to repeat and reduce the cost of the mold, and very easy to replace the parts and maintenance of vulnerable parts. According to reports, Polyshot has developed a quick-change hot runner mold system, especially for injection pressure of 70kN small injection machine. Husky, Presto and Moldmasters companies such as the nozzle, stem and manifold are available as standard for quick replacement and delivery of molds, and now only 4 weeks to deliver molds abroad.


Hot runner mold design overall reliability improvement. Now the major mold companies at home and abroad on the hot runner board design and thermal nozzle connected part of the pressure distribution, temperature distribution, sealing and other issues of research and development of great importance. The development and utilization of the laminated hot runner injection molds is also a hot spot. Stack mold can effectively increase the number of cavity, while the injection molding machine clamping force only need to increase 10% to 15%. Stacked hot runner molds in some foreign countries have been used in industrialized industrialization.


The purpose of improving the hot runner element material is to improve the wear resistance of the nozzle and hot runner and for the molding of sensitive materials. Such as the use of molybdenum titanium and other toughness alloy material manufacturing nozzle, metal powder injection molding by sintering into hot runner components has become possible.


Develop accurate temperature control system. In the hot runner mold molding, the development of more sophisticated temperature control device to control the hot runner board and the gate of the molten resin temperature is to prevent resin overheating degradation and product performance reduction effective measures.


Use the hot runner for co-injection. The combination of manifolds and hot nozzle elements allows for the combination of co-injection molding and hot runner technology, resulting in the formation of three layers, five layers or even more layers of composite plastic products. For example, Anole has developed a melt delivery system and a coin nozzle; Anole's multi-outlet, multi-cavity injection tube production line can be used for multi-material multi-component co-injection.



Smart Mold Technology Limited