Injection Mold Hot Runner Technology

Injection molding hot runner gating system be interpreted as an extension of firearms. Hot runner system's function is taken insulation to mold the thermoplastic melt near or directly into the mold. Can be independently heated hot runner, and in the injection mold heat insulation, this can compensate for separately with the "cold" mold exposure caused by heat loss. Hot runner mold has been successfully used in processing all kinds of plastic materials can be used cold runner mold almost all of plastic materials can be hot runner mold. Their parts and the smallest 0.1 grams, the largest 30 kg. Hot runner molds in the electronics, automotive, medical, daily necessities, toys, packaging, construction, office equipment and other areas have a wide range of applications.
Hot runner mold of a successful application projects require multiple links to be protected. One of the most important are two technical factors: First, plastic temperature control; two plastic flow of control. A typical hot runner system is composed of several components as follows:
1) hot runner plate (MANIFOLD);
2) nozzle (NOZZLE);
3) temperature controller;
4) The auxiliary components.
Hot runner mold advantages:
) Shortening the workpiece forming cycle;
2) Save plastic raw materials;
3) reduce waste, improve product quality;
4) The elimination of the follow-up processes are conducive to production automation;
5) expanding the application of bamboo mold injection molding process Wai.
There is also mold the rising costs, production process equipment with high requirements, complicated operation and maintenance shortcomings.
In the more developed industrial countries and regions most active in the production of hot runner molds, hot runner mold ratio rising, and even some less than 10 people have carried out a small mold factory production of hot runner molds. But in our hot runner technology, research has only just begun, the application range of limited-scale enterprises, design capability is relatively empty, so the study of the technology of great significance.
A hot runner system types and application of
In the application of hot runner technology, the gate type of correct choice is essential. Directly determine the gate type hot runner system components selection and die manufacture and use. Consequently, under a different gate type hot runner system can be divided into hot-tip-type of hot runner systems, pouring sleeve hot runner systems, valve type of hot runner systems, three types, each type of hot runner systems have important applications of features and scope of application. In selecting the type of gate with the hot runner system, need to consider many factors, the most important thing is plastic substrate types and additives, parts of the weight and size of wall thickness, part of the quality requirements, tool life and part production requirements.
1.1 Hot Runner System Hot tip-type (HOT TIP)
The working principle is through the nozzle is located in front of the inserts HOT TIP and cooling system combined with the plastic molding on the gate at processing temperatures for precise adjustment and control. HOT TIP nozzle inserts and thus the manufacture of materials and shape of the design is very important.
Hot-tip style (HOT TIP) hot runner system can be used to process the vast majority of crystalline and non-crystalline plastics such as PP, PE, PS, LCP, PA, PET, PBT, PEEK, POM, PEI, PMMA, ABSPVC, PC , PSU, TPU and so on. In general, the hot-tip-type gates are used for small and medium size parts processing, especially for small parts machining. Mostly in the gate diameter of between 0.5mm-2.0mm. Gate cross-section diameter identify key decision by the part weight and thickness, of course, should also consider the quality requirements for materials and spare parts. If you use a smaller diameter of the gate, injection filling stage soon after the gates closed, parts of small traces of the gate, part surface appearance and good quality. If the gate diameter is too small, will lead to plastic flow through the gate when the shear rate is too high, will be severely damaged plastic melt of molecular chain structure of the added material or plastic, resulting in substandard product quality can not meet the use requirements. Gate size on the choice of a usual approach is based components to initially set the thickness of the gate at the gate size: gate diameter = (0.75-1.0) Part wall thickness of the gate at. Processing flow of plastic whichever is less easy to value, and processing of the flow of hard plastic or shear-sensitive plastic materials for whichever is greater.
Hot-tip-style gates are usually open directly on the parts can be opened in the cold and then cold-runner on the parts on the gate to open. This is the hot runner and cold runner mold system, a combination of. In the application of hot-tip-style production of plastic parts when the gate always more or less marks in part on the left gate. Very often, Hou gate trace will be higher than the parts surface, affecting the parts of the aesthetic or affecting other parts of the assembly. Therefore, the selection gate position, the gate should be placed on parts of the recessed shelter.
1.2 Nested pouring hot runner system (SPRUE GATING)
Nested in the pouring of hot runner systems, plastic through the smooth flow channel (OPEN PIPE) into the mold cavity. Gate at the small plastic flow pressure loss. Nested pouring hot runner system is more suitable to the weight of the above medium size injection parts molding process. The use of nested pouring the advantages of hot runner system plastic mold filling in the flow through the gate when the shear rate experienced by the low residual stress after molding parts is small, less deformation, part mechanical strength is better. Compared with the thermal tip-style gate, pouring nested gate size should be larger, so the gate traces may also be relatively large. Thus, under normal circumstances the degree requirements for the beautiful gate of the mold usually more stringent plastic injection molding method; while the beautiful gate level can be less demanding of the internal structure of the piece nested by pouring hot runner system manufacturer. It is also often poured nested gate used in conjunction with the cold runner, that is pouring nozzle set as the main runner, will be poured by nested on the gate to open in the cold runner. In this application, the pouring gate can be opened by nested in order to facilitate a large number of plastic flow, because no one cares about the cold runner on the size of the gate marks.
And application of hot-tip-type hot runner system is similar to the gate at plastic temperature and mold temperature control of paramount importance. Need around the gate for an independent cooling circuit. Because pouring nested relatively large gate size, if the temperature-controlled gate is not good, more prone to die after the gate seals do not live in open plastic flow problems. Pouring hot runner system of nested inserts are also a variety of nozzle sizes shapes and manufacturing materials, changes in the light of want the plastic type of processing (eg, crystalline plastic or non-crystalline plastic) and the gate to the cooling of such a comprehensive consideration.
1.3 Valve Hot Runner System (VALVE GATING)
Valve (VALVE GATING) hot runner system is through the use of valve pin (VALVE PIN) in the valve pin control devices under the action of the scheduled time to mechanical movement of the ways to open or close the gate. This type of hot runner system has a lot of hot-tip type and pouring nested flow channel systems do not have advantages. For example a human-controlled gate switching time, gate smooth, hot-runner technology can expand the fields of applied technology.
Valve hot runner applications are more international in recent years, major automobile companies are using hot runner valve, combined with multi-color co-injection mold process to produce the overall lamp shade. Because the shade is transparent product, smooth gate necessary to meet the aesthetic requirements. This is only the use of valve gate hot runner can be achieved. Other parts required after the molding spray coloring. If these parts have a fusion of injection molding line, then, after coloring the color will be different parts and can not meet the quality requirements. To avoid such problems arise, many auto parts suppliers based on the order of switching valve gate hot runner production process, to the complete elimination of parts on the fusion of routes. In the medical field, people with plastic parts for medical quality requirements, the gate is extremely strict, and so can not have sharp bump. In this case, only to rely on gate valve flow channel system to improve product quality gate.
Due to valve gate valve needle through the closure of mechanical movement, free from the gate at plastic cooling time constraints, so valve gate runner system plastic parts can sometimes shorten the production cycle times. Gate size also could have been bigger, which is shear-sensitive plastics processing and is very good. Valve gate way to process small parts weighing a few grams, can be processed a few kilos of large parts. A variety of engineering plastics can, valve gate processing components. If there are a set of mold cavity a number of different sizes, using valve-type runner system can be through the control of the gate switching time, allowing the flow of each separate cavity to adjust and control. This difference in shape and size disparity in a multi-cavity mold mold of great importance. Also for high productivity with a multi-parting surface (STACK MOLD) die, and only through the use of valve type hot runner system to achieve. Valve pin mechanical movement device can be used hydraulic oil or compressed gas control. Using the method of hydraulic fluid moves the valve pin switch a powerful and accurate, but may in the production process dirty plastic workpieces. Therefore, in the production of plastic products for medical use, it must use compressed gas control method of production to ensure product cleanliness. Further, because of the use of valve pin control devices will increase the overall die die die set height. Conducting mold design and injection molding machine options, should be considered. In the installation of the valve pin control devices also need to set the cooling water on the template.
And hot tip type and pouring hot runner system nested application requirements, like the gate valve if the temperature control is not good, can also cause serious production problems. If the gate at high temperature, plastic mold from time to time in open glued to the valve pin on the risk. On the contrary, if the temperature is too low gate, gate plastic cooling, resulting in valve pin closure difficulties. Valve gate hot runner mold in price than the type and pouring hot tip nested hot runner molds expensive. If the valve type hot runner system and the valve pin control device itself is designed well, will appear in the valve needle formed after the flow of dead ends, or in the valve pin and other components with the surface of the sliding occurs between the overflow material behavior and other issues. Also, if the valve pin making good, close the operational control properly, there are serious consequences of damage to the gate. Therefore, valve hot runner systems, although there are many other two types of hot runner systems do not have advantages, but also increases the complexity of the mold.
2 Hot Runner Structural Design
Universal Mold Hot Runner in the design should consider the following parameters: product plastic parts, a variety of raw materials, technical parameters, the weight of plastic parts products, product wall thickness, cavity volume, the number of pre-gate, location, injection molding machine of the type ( mechanical, hydraulic, or manufacturers), pre-clamping force (unit: t), pre-injection pressure (kg/cm3), pre-injection speed (cm3/sec), pre-injection cycle (or adjust), temperature ( plastic melt temperature, injection nozzle temperature, the mold cavity temperature), pressure (plasticization pressure, injection pressure, mold cavity pressure), the corresponding role of the time (injection time, packing time, cooling time) and so on.
2.1 The selection of hot runner heating methods
For the internal heating systems, heaters installed in the center of flow path. Plastic melt at the appropriate size of the annular gap flow, and only close to the inner annular gap can be used as fluid cross-sectional area, because the gap in the outer annular region, the melt due to temperature gradient (process temperature / mold temperature) solidification occurs.
External heating system, the flow channel by an external heater to heat and maintain its processing temperature. Unimpeded flow channel, the flow of the melt without any obstruction. And the use of external heating system, due to plastic shear in the flow passage in the state of better products and lower levels of stress in injection molding, so products can be maintained more stringent tolerances. For some heat-sensitive materials such as polycarbonate, external heating system can eliminate heat-sensitive material degradation caused by the problems and the melt flow channel in the flow of residual spots.
Two kinds of heating systems have their own strengths, due to the advantages of external heating system is increasingly evident in the design of hot runner software more inclined to outer heating.
2.2 Select a balanced approach to hot runner
In fact hot runner aim is to transfer corresponding to the various gates of plastic melt. From the rheological point of view, the balance of hot runner should be the natural balance as much as possible, from the injection nozzle into the flow channel between the molding products should be the same diameter and length should be equal. Usually multi-mode cavity with a balance of mechanical design of hot runner manifold, that is, from the injection molding machine nozzle into the mold cavity before the gate of each one have the same length of flow channel length and diameter of flow channel.
Whether multi-cavity mold in the cavity layout is what bits and melt in a consistent quality assurance is the key. Well-balanced hot runner design has some difficulties, but a multi-level specifications of the shunt with the hot runner analysis of multi-material help to mold to determine a reasonable layout of the melt flow channel.
Hot Runner in some of the design process, there are special products that require non-equilibrium flow channel design, and even need to design products according to the sequence of process steps one by one pouring.
2.3 The hot runner injection nozzle Methods
Requirements: workpieces require a very clean, almost invisible pour point, as far as possible to avoid the follow-up processing.
General use bolts to connect the nozzle to facilitate the replacement. Needle jet will only leave the surface of the product ejection rod with a similar trace, is a product for the surface decoration with an effective way. In addition it can reduce the stress of the product and shorten the processing period and adaptable to a variety of materials processing (including material containing a relatively higher wear and heat-sensitive materials).
The nozzle with a torpedo core has the following advantages:
1) temperature easy to control, and the polymer can tear at the nozzle automatically disconnected.
2) Torpedo-core head for the drawing is easy to produce the material (such as PA, PC) can form a good tear-off role.
Torpedo core drawback is that they cause the head of shearing material. On the shear-sensitive materials, torpedo batteries and flow channel of the annular gap, as well as the core of the chamfer at the torpedo a result of strong shearing damage. If the processing of parts by a hard material, torpedo cores resulted in chamfer can be imprinted. Coloring of the polymer, due to pigment accumulation has occurred is particularly difficult to processed. Whether a non-crystalline materials, crystals or a thermoplastic elastomer, all the way into certain materials have certain limitations.
2.4 The structural design of hot runner plate
Of hot runner plate design and is processed materials and processing technology (especially the processing temperature) are closely linked. Hot runner plate in the processing temperature of the thermal expansion is one of the points of hot runner system design; and melt flow of Tao in its internal processing (usually using grinding method), in particular channel turns the extent of the melt layer smooth flow of state impact and corrosive materials right shunt material requirements and so should be taken into account. In order to benefit from the flow channel of fluid flow, the melt rotation at ease as far as possible.
2.4.1 Selection of hot runner size
In order to withstand injection pressure, open flow channel, installation of heating systems, hot runner plate should have sufficient size, but in order to reduce power and heat loss, the volume of hot runner plate should not be too large. Of hot runner plate structure can be designed according to product structure and shape, its gate number of decisions; flow channel plate shape of many different, selected according to actual demand. To minimize the quality of hot runner plate, hot runner plate quality, the smaller the power of the smaller the heating system. Also ensure that the surface roughness within the flow passage within a certain range.
Each material flow characteristics and performance are not the same diameter. For heat sensitive materials, use of a smaller flow channel dimensions can reduce the capacity of the material within the hot runner, but the shear-sensitive material to the larger size of the flow channel to reduce shearing. The color of those requirements can be used to replace the smaller size of the flow channel can be quickly washed the color of the old. However, runner size too small to significantly increase the overall system pressure drop, which may affect the cavity filling. The design of hot runner mold melt-flow analysis can be used to determine the best flow channel size, this analysis takes into account the type of material and processing parameters. This particular application will be able to produce an optimized flow channel dimensions.
2.4.2 Hot Runner front panel selection
There is also a hot runner system is the ability to transfer its injection mold injection molding machine between the template and the clamping force necessary. So hot runner system, front and rear plates must have sufficient rigidity to support the mold without distortion.
Each set of system design details include the following: a balanced cavity filling, balanced material flow, balanced heating capacity can quickly change color and change easily applied to plastic pipe heater and balance multi-flow channel of the modular design.
3 hot runner temperature control
3.1 Nozzle temperature control
Determine the temperature of hot runner nozzle gate direct impact on product quality and processing technology. Each nozzle in a stable state of the temperature fluctuations and the temperature difference between the nozzle is a measure of the quality of hot runner system, one of the criteria. The use of thermal control of the gate opening and closing the state of pin-point nozzle, the requirement is that the nozzle temperature fluctuations and deviations as small as possible.
Nozzle and the interface between the injection molded parts - "Temperature" control is critical. If the nozzle temperature is too high will be drooling; low plastic will be cold consolidation. The nozzle tip and the gate contact that needs to have enough heat to balance the heat taken away because of mold cooling; in the nozzle is closed when the mold gate requires low temperatures can make plastic consolidation. In this hot and cold between the two states need to have insulation measures (insulation medium), while between the nozzle and the gate also need mechanical positioning (to have a certain contact area), for the melt seal (requires a certain force ) and the nozzle assembly to allow the overall capacity of thermal expansion. Also need to consider gate scars, gate location, products in the flow line and fusion line of the formation and processing of such factors as the type of material.
3.2 The flow channel plate temperature control
Injection molding hot runner temperature control system plays a vital role in success. Temperature control is also an excellent hot runner systems to determine whether or not an important condition, in particular, to choose a good place to install the temperature sensor. According to existing experience, it should be installed in the expected temperature of the highest point must not be placed in the heat loss occurs where, such as the pressurized ring, sealing ring and the hot runner body near the outer area. Where the heat loss in the event of the strip heater to make the necessary adjustments, which in turn could lead to overheating of polymers. Usually the temperature sensor installed in the correct, "the hottest" position and can be replaced.
3.3 The internal temperature of hot runner Numerical simulation shows
In the process of stable and unstable thermal conductivity, temperature and time and space relations can be mathematically approximate description of each.
The process of instability for the thermal conductivity, temperature, time and space relationship between the Fourier heat conduction equation can be established. According to hot runner features, and integration of a variety of hot runner single-value conditions to carry out the numerical solution. This will be a continuous temperature with spatial and temporal distribution of discrete points is transformed into a limited-domain numerical problems, and take advantage of these discrete points to approximate the distribution of domains, or simulate the real temperature distribution field.
4 Conclusion
As a result of the mold hot runner technology can improve productivity and quality products, and can be substantial savings products, raw materials and energy conservation, so this technology is widely used in plastic mold of a big change. According to statistics, in the injection molding process using hot runner systems, can save 10% -20% of raw materials, costs can be reduced by about 30%, while investment increased by only 10% -30%. In foreign hot runner technology, has developed rapidly, with half of the plastic mold factory production of hot runner technology, molds have been used, and some manufacturers even reached 80% or more, the effect is quite obvious. China in recent years has begun to promote the use of, but overall has not yet reached 10%, and actively develop the future of technology is a hot runner injection mold development.