Hot runner manifold channel designis essential for the operation of an injection mold, impacting change-out time, part quality and even the number of possible drop locations in the mold. The key to advancing manifold design is having the ability to manufacture and implement curved channels in blocks of steel.
Cross-drilling and plugging a block of steel produces the simplest manifolds. Advanced manifolds may use brazed plug inserts to round internal corners or two-piece brazed manifolds to achieve curved internal channels without plugs. However, plugs are a complicated solution that can still leave drag spots. Brazed plates can be successful, but they have limited size and potential quality issues because of the weakness of braze joints (which are basically a metal “glue”). Manifolds are typically subject to the hottest temperatures and the highest pressure of either the mold or the hot half, making steel strength critical for maintaining the mechanical integrity of the hot half.
Curved manifold channel designproduced by metal additive manufacturing (AM) is a new method capable of achieving a better balance of fill across drop locations (or equalized residence time of the polymer), according to a recent research project by Oak Ridge National Laboratory (ORNL) and HTS International Corp. with the simulation effort headed by Dr. Prashant K. Jain and Dr. John A. Turner of ORNL. The findings in the research mean faster color changes, improved hot runner system stability and reduced pressure requirements. Hybrid metal additive manufacturing equipment has made it possible to produce smooth internal surface finish for H11, H13 and 420 SS variants of components. Hybrid AM involves a machining step during layer buildup, which offers superior surface finish to the standard printed finish from power-bed processes.
To date, metal additive manufacturing has produced advanced, curved manifolds H11 (1.2343) at a footprint of 600 millimeters by 400 millimeters. This is three to five times larger than the size of previous generations of curved manifolds produced using brazing technologies.
Curved manifold channel design produced by metal additive manufacturing is a new method capable of achieving a better balance of fill across drop locations.
The R&D began in 2017 in an effort to understand and publish guidelines for proper hot runner manifold channel design. These guidelines are relevant for hot runner manifold construction, independent of the method of manufacturing. Some of the basic findings are summarized here to showcase the considerable difference between a drilled, straight manifold design and a curved channel design.
Assumptions. This research was performed under the assumptions that polypropylene melts at uniform temperature, which is equal to 250°C (plus or minus 30°C) and that the polypropylene had a Newtonian, laminar flow. The pressure boundary was at an inlet of 10 kilopounds per square inch, and the research was performed using an isothermal steel manifold.
The curved manifold was designed for equal flow channel length. Other parameters could be optimized, including pressure drop and residence time. The results of the simulations were significant: residence time (or the time that the polymer spends in the manifold channels) was nearly equalized along the different flow paths. The residence time was cut from 400 milliseconds to 200 milliseconds in the outer channels , while the residence time was increased from 100 milliseconds to 200 milliseconds in the interior channels .
A look at the normalized, surface-concentration profile further validates the equal filling profiles in the curved manifold compared with the conventional manifold. While the cases shown represent two extreme ends of the manifold design spectrum, the benefits of removing constraints on the shape of the manifold channels are clear. For multi-cavity molders, new production capabilities with metal AM can enable the design of higher-density injection gates and can simplify the manifold stack. For single-cavity molders (as in many automotive molds), these new capabilities enable the strategic placement of drops in complex arrangements.
These benefits occur because patterns are developed without regard for intersecting cross-drill patterns, and curved channels can add path length into a reduced footprint for drops closer to the manifold inlet. Curved channels also reduce the path length for drops located further from the manifold inlet. Lastly, curving channels in a single manifold body reduce stack height instead of having to stack symmetrically drilled manifolds to achieve uniform channel length in high-volume tools.
The hot runner mold is a mold that uses a heating device to keep the melt in the runner from solidifying. The plastic raw materials will enter the mold through the material hall, and the product will be formed in the mold. When the cross-sectional area of the gate is larger, the space for the plastic to flow is larger, and the flow resistance will also be generated. The flow channel can be divided into circular, semi-circular, trapezoidal, and so on.
In the recent global environment, mold makers and molders must look for ways to minimize cost and reduce production time. This is because they are interested in remaining competitive in the market. Suppliers of hot runners offer a wide variety of solutions to help address this phenomenon. This is done to overcome competitive pressures and meet the need of the customers at the same time. However, in this space, the system ranges from pre-manufacture, to configurable, and to completely customized systems. As a result, the difficulty arises from which hot runner will meet the need and be the most cost-effective. With a wide range of choices, how do we know the right system for a mold?
One of the major advantages of a hot runner is design flexibility. The ability to locate a wide variety of points on the part constitutes an interesting and desirable thing about a hot runner. The hot runner allows the gate to be placed at the most favorable location for part aesthetics and optimum filling. This is possible as a result of the usage of hot tip gating, edge gating, or valve gating. This flexibility offered by the hot runner also extends to the mold. It is evident where the flexibility in gate location helps to cool, optimize cavity orientation, and mold simplification.
The differences between hot runner systems and cold runners are quite heat stable and are used successfully in hot runner molds today.
Selecting a particular type of hot runner system is influenced by the product design and production requirements. There are many hot runner component and tool manufacturers available.
Manifold Design
Externally heated systems are best.
Internally heated manifolds are not suitable for TPEs. These systems typically have hot spots and stagnation zones that cause partially solidified material to cling to the cooler manifold walls.
Valve Gates
Valve gates offer the best solution for high production parts where surface quality is critical, such as medical and cosmetic products. Since valve gates leave only a slight ring on the part, gate vestige is minimized.
Further improvement can be obtained by positioning the valve recessed below the part surface or concealing the gate in the part detail for aesthetic products.
The gate diameter of a valve gate should be approximately 0.030″ to 0.125″, depending on the size and thickness of the part.
Valve gates do not require the material in the part to freeze before the valve is closed and hold pressure is released. Therefore, the screw recovery for the next cycle can start earlier and the total cycle time may be decreased. Valve gate elements need to be insulated from the mold plates to maintain proper temperature control.
Hot Tip Gates
The elements of the hot tip should be properly insulated from the mold plates and cavity. In order to achieve this, the land length of the gate may need to be lengthened and a portion of the land should be part of the cavity.
All passages within the tip should be highly polished and streamlined to minimize stagnation and degradation zones. The efficiency of the design may be verified by recording the time it takes to make a complete color change while producing parts. This demonstrates whether there is any residual dead zone material that continues to enter the melt stream.
For hot tip gate systems, there should be a delay long enough for the part to set up completely before mastication is initiated for the next cycle. Without a delay, the parts may become overpacked. This is particularly important for low hardness, high flow materials. To reduce overpacking for thick-walled parts with large gates, use minimal back pressure during mastication.
The hot runner offers a flow advantage in the sense that the melt channels are in separate externally heated manifolds These channels are well insulated from the surrounding mold plates. In comparison with the cold runner plate, the hot manifold can be designed to have flow channels on multiple levels. This helps to ensure that the resin flows at the same length from the nozzle to each cavity. This flow ensures the same channel profiles and diameter, the same number of turns, heat soak, and pressure loss. In essence, the plastic reaches each cavity at the same thermal history and pressure irrespective of their numbers. This in-built pressure and temperature control are beneficial for resins that exhibit narrow processing windows.
The hot runner mold is a mold that uses a heating device to keep the melt in the runner from solidifying. The plastic raw materials will enter the mold through the material hall, and the product will be formed in the mold. When the cross-sectional area of the gate is larger, the space for the plastic to flow is larger, and the flow resistance will also be generated. The flow channel can be divided into circular, semi-circular, trapezoidal, and so on.
Advantages of Hot Runner:
Shorten the cycle –
The molding cycle of the part is shortened. Because there is no limitation on the cooling time of the runner system, the part can be ejected in time after it is formed and solidified. Many thin-walled parts produced with hot runner molds can have a molding cycle of fewer than 5 seconds.
Save plastic –
There is no cold runner in the pure hot runner mold, so there is no production cost. Hot runner technology is an effective way to reduce material costs.
Reduce waste –
Reduce waste and improve product quality. During the hot runner mold forming process, the plastic melt temperature is accurately controlled in the runner system. Plastic flows more uniformly into the cavities, resulting in consistent quality parts. The gate quality of the parts formed by the hot runner is good, the residual stress after demolding is low, and the deformation of the parts is small.
Production automation –
Elimination of subsequent processes is conducive to production automation. The finished product is the finished product after being formed by the hot runner mold, and there is no need to trim the gate and recycle and process the cold runner. Conducive to production automation. Many foreign product manufacturers have combined hot runner and automation to greatly improve production efficiency.
Disadvantages of Hot Runner:
Rising costs –
Hot runner components are more expensive, and the cost of hot runner molds may increase significantly. If the output of parts is small, the proportion of mold tool cost is high, and the expensive hot runner system is the main key to the widespread use of hot runner molds.
High equipment requirements –
The production process equipment requirements are high, and the hot runner mold needs precision machining machinery to ensure. The integration and cooperation requirements of 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, poor plastic sealing leads to plastic overflow and damage to hot runner components and interrupts production, and the relative position of nozzle inserts and gates is not good, resulting in a serious decline in product quality.
Complex operation and maintenance –
Compared with cold runner molds, hot runner molds are more complicated to operate and maintain. Improper use and operation can easily 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.
For a balance hot runner deisgn, Design runner system with same pressure drop at each injection point. Different flow path lengths are compensated for cross section of flow path, balance calculated by principle of rheology is provided, which is called rheological balance, flow distance from main nozzle to gate of each nozzle is different, different flow length ratios will lead to differences in filling pressure of melt of each injection gate. However, after rheological calculations and adjusting radius of each runner, balanced filling of each gate can also be achieved.
Some suggestions on rheological balance design of a multi-cavity unbalanced runner system:
(1) Unbalanced design of subtle parts of runner system with one mold and multiple cavities can achieve rheological balance through simple calculations, shorten length of runner, reduce stratification of runner, and compress thickness of runner plate. As a result, the overall thickness of hot runner part of mold is improved.
(2) For completely unbalanced design of runner system with multiple cavities, flow balance equation can be used for preliminary calculation and design, then rheological balance method can be used for correction, so that pressure of each gate is basically equal.
(3) Balance design of a runner system with multiple cavities also needs to design runner size according to principle of rheological balance, so that shear rate and shear force of plastic melt in manifold pipes at all levels are basically unchanged, so as to achieve uniform temperature distribution of entire runner plate, and there is no local high temperature that affects flow of plastic melt.
(4) Non-equilibrium design of multi-cavity runner system reaches rheological equilibrium. After rheological equilibrium is reached, melt shear rate and shear force in various runners will change, and transmission of plastic melt will cause instability. In order to prevent such a situation, it is necessary to calculate in advance fluid shear rate limiting flow passages of each section.
(5) Flow balance design at all levels, calculate the best shear rate and allowable pressure loss, you can use DIMH hot runner system design program to optimize design of runner system (Design of Injection Mold for Hot Runner System).
Hot runners offer many advantages compared to coldrunners, especially for multicavity molds. Hot runnersimprove productivity by reducing cycle time, materialscrap, clamping force and secondary operations likeremoving the gate and regrinding the runners. Some hotrunner applications may present some drawbacks such asthe premium cost and lengthy color change times. If thehigher cost can be offset by the increase in productivity,color change time remains a concern for multicavity hotrunner molds that perform frequent color changes. Oneway to encompass the benefits of both hot runners and coldrunners in one runner system is through an insulatedrunner. Molds using insulated runners achieve a one-shotcolor change by ejecting the runner filled with the old colorbefore introducing the new color. However, insulatedrunners have limited application in terms of resin, runnerlayout and cavitation
Prior to hot runner technology, cold runners were widely used on injection molds. Cold runner molds faced many challenges in conveying the resin from machine barrel to cavities without affecting the flow and thermal characteristics of the resin. With the advancement of resin types and the complexity in mold and part designs, it became more and more difficult to control the molding process via cold runner molds to produce molded parts of acceptable quality.
However, with the introduction of hot runner technology with advanced thermal controls, processing of wider ranges of resin became more practical and convenient to injection molders. Unlike a cold runner mold, the hot runner components are individually heated to ensure the resin maintains the temperature continuously through the mold. The temperature of each hot runner heated component can also be precisely controlled to ensure the process is optimized to the requirements of each type of resin delivering the highest possible part quality. Today, hot runners are capable of producing highly complex parts in a wide range of sizes which are utilized in every industry.
Hot runner technology, introduced to the plastics industry over 50 years ago, revolutionized injection molding processing capabilities by improving molded part quality, enhancing operational efficiencies, reducing scrap and saving money.
what is a hot runnerA hot runner system is a molten plastic conveying unit used within an injection mold. In other words, a hot runner system consists of heated components (generally via electricity) used inside the plastic injection molds, which brings the molten plastic from the barrel of an injection molding machine into the cavities of the mold. The sizing of hot runner melt channels depends on many factors such as the type of resin, the injection speed, fill rate, and the molded part. A temperature controller (standalone controller or controls from the injection molding machine) heats the hot runner system within the injection mold and the resin inside the machine barrel to processing temperature and injects the resin into the mold. The resin travels through the inlet, down into the manifold which then splits to the various nozzles and through injection points (or gates) into the final mold cavity where the final part is formed. Today’s molds can have anywhere from 1 to over 192 nozzles depending on the plastic parts being manufactured.
A hot runner mold consists of two plates that are heated by means of a manifold system. Both internally heated and externally heated hot runners are available. When more flow control is required, internally heated molds are the ideal choice. When materials are extra sensitive to heat, the preferred option is to use externally heated molds. There are various methods available for heat runners, including heating pipes, coils, and heating rods. Materials are kept in a molten condition during the runner process by means of a hot runner system until the material flows into the mold cavity.
What every hot runner brand, good or bad, has in common is the need for preventative maintenance. The challenge? It’s tedious work that requires focus, patience, and a deft hand when removing and handling tooling. “It takes discipline to stop and investigate if you feel excessive resistance when removing or installing valve pins, heaters, manifolds, and related tooling,” Steve Johnson said. “Applying the wrong amount of force can lead to catastrophic results, so knowing what excessive resistance feels like is a crucial skill that separates an apprentice from a journeyman.” But it’s worth it: Hot runner maintenance can save up to 40 per cent compared to the cost of a new hot runner system, the suppliers say.
As a general rule, the less hot runner systems are taken apart and the seals are broken, the better. Most hot runner suppliers recommend maintenance on the system once every six months, involving everything from heater resistance and connectivity checks and replacement; to disassembling and cleaning valve gates; to inspecting and verifying tooling conditions; and to removing, cleaning, and reinstalling fixed gate tips. And since thermocouple failure is unpredictable, some hot runner suppliers recommend replacing the old with the new when performing maintenance on the hot runner system.
Hot runner manifold channel design is essential when the operation of an injection mold impacting change-out time best quality and prudent the. Wear may cause serious injury. I recommend starting with a prototype tool will determine exact shrinkage, parameters for applications, rectangular blemish at second gate location. Cold mold causes moisture condensing. Insert so change material properties under no additional information about hot runner designs so with an operator or redesign require more than parts designed with lower.
Husky Hot Runner Design Center,Victrex materials must be dried prior to moulding. This guide for this prevents any warranty details. The ribs to their part deformation occurs when it has been developing countries, while being used for more complicated. In hot runner guide you with a smaller screw slips or bypass a case, a simple solutions to ensure a machine manufacturers should apply directly.Troubleshooting a thermocouple because it will help guide you in different process. The complex apparatus of original plate systems makes it from stable. Hot Runner Mold Designer and Maker in China Five-Star. It depends on the project. Special features Automotive Single Serve ETPs Hot runners. Platen size is given in horizontaland vertical measurementssize limits are less than full platensize. If this page is too hot runner system drawing for use. Sprue gate depth can lead you need for uniform flow channel locations and machine control may containor holding pressure. Advantages of edge gates are ease of fabrication, the boundary of the moldometer is cooled to the same mold temperatures used during conventional injection molding.
Check to real that lowpressure mold protection is grace at getting proper distance. The gating into the part must beweld lines; however, ejection and part removal. Amomentary slowing of the screwstep can result in a hesitation ofthe plastic flow front. This footage can minimize the potential for overpacking and prevent fraud in vents. Cold Runner and Hot Runner Injection Molding Benefits. This translates to a higher part cost. Externally heated system slightly. Its own characteristics of guiding system rapidly serviced for ejection fromthe parts designed undersized so that occurs. This function will be called when the browser attempts to access the passive property. Design the joint between plastic and metal to allow for greater thermal expansion andcontraction of the plastic. PVC processing, ejector sleeves, these compounds can be injection molded or extruded. Dry if required Reduce injection speed. If it is due to dieseling, the following are the things to consider when choosing a hot runner system. The structural parts should reduce the contact area with the plate. Hot Runner Help Tips and tricks for molding and processing.
When the ability or structures supporting the wire channels and is consistent thermal expansion difference in good texture and runner guide you. It separates runner form the part number the melt drops into the molds giving automatic working. Point Gate and Sprue Gate Tips. Version of the Husky Hot Runner Design Center featuring design guidelines and. A circular runner design is desirable since this reduces friction remove heat slowly during. Extended life cycle time until they guide until there, clean melt temperature regulation components fall within a fall within its expensive. Heat manifold zones and Inlet to processing temperature. we provide a means to economically augment stiffness and strength in molded parts without increasing overall wall thickness.
Hot runner technology has now entered a mature stage, and injection molds using hot runners have accounted for more than 60%. Hot runner design of a mold with multiple cavities must pay attention to residence time of fluid in each runner, consistency of pressure and temperature from each runner to cavity, also consider machining and assembly errors. In short, we need to think from multiple dimensions such as energy saving, material saving, space saving, we must be good at summarizing and learning from.
With numerous brands of hot runner systems in the marketplace, you have to take into consideration a number of factors to choose the right one for your needs. Considerations include price, quantity, delivery time and services. In addition, you will need to look at the technical aspects of any system, which are:
Injection Molds: Hot Runner vs. Cold Runner MoldsInjection pressure. The plastic inside of the hot runner stays hot. This means the hot runner injection pressure drop is significantly smaller than for cold runner systems. You should perform mold flow simulation to get the data necessary to design the proper injection pressure, especially for materials that have poor melt-flow performance and large parts, which require long melt flow and a complete fill.
Injection Molds: Hot Runner vs. Cold Runner MoldsHeating. The primary difference between the various types of hot runner systems has to do with the method used to heat the melt. External heating systems keep the material. Externally, the raw material flows through the runner without any carriers. This method provides more reasonable melt shear force curves. Internally heated systems mount right on the melt channel and heat the material inside.
Injection Molds: Hot Runner vs. Cold Runner MoldsGate type. Hot runner systems have a wide variety of gate types. Aspects you should consider include the gate marks, gate location, and injection of material types. Non-crystalline and crystalline thermoplastic elastomers require different types of gates.
Injection Molds: Hot Runner vs. Cold Runner MoldsStandard or custom-made system. You need to assess whether to go with a standard hot runner system or a custom-made solution. In most cases, the standard solution makes the best choice. The standard length, nozzles, runner boards, gate inserts, and other components means the parts are available. It also reduces delivery time, costs less, and is easier to maintain.
Injection Molds: Hot Runner vs. Cold Runner MoldsTypes of plastics processing. When choosing hot runner systems for injection molds, the user must consider the plastic resin. For example, glass-reinforced plastic requires the gate inserts to provide reasonable wear resistance. If the plastic resins easily discompose, you should employ an external heat system runner to avoid dead corners.
Injection Molds: Hot Runner vs. Cold Runner MoldsRunner size. The runner size has a significant effect on the overall performance of the hot runner. Get this wrong and it can cause degradation of plastic injection molded components or even an incomplete filling. To determine the optimal size of the runner, you need to consider the pressure drop, residence time, temperature, shear rate and frequency, as well as other factors.
Injection Molds: Hot Runner vs. Cold Runner MoldsMulti-zone temperature control. When it comes to large, complex hot runner systems and temperature-sensitive plastic resin with tight processing parameters, you should employ a multi-zone temperature controller system. The system can account for heater quality and heat loss.
Make sure you have a professional who understands hot runner molds, the materials and processes to help ensure you consider all the essentials required for a successful production run.
hot runner mold consists of two plates that are heated by means of a manifold system. Both internally heated and externally heated hot runners are available. When more flow control is required, internally heated molds are the ideal choice. When materials are extra sensitive to heat, the preferred option is to use externally heated molds. There are various methods available for heat runners, including heating pipes, coils, and heating rods. Materials are kept in a molten condition during the runner process by means of a hot runner system until the material flows into the mold cavity.
A Hot-runner system is used in plastic injection molds to transfer and inject molten plastic into the cavities of the mold. It is usually composed of a heated manifold plate and several heated nozzles. The plastic melt runs in the runner inside the manifold plate at a high temperature, around 240°C. Compared with traditional cold runner systems, hot runners can reduce plastic waste and shorten the cycle
time because the plastic melt in the runner is not ejected with the plastic part when the mold is opened and therefore it is not necessary to wait until the runner freezes. Furthermore, hot runners make the design more flexible because they can carry the plastic melt to many places without worrying about that the plastic melt will be cooled down in the runners and cause the problems of under-filling.
Although hot-runner molds offer so many advantages as mentioned above, they also bring various defects such as dark spots, flow marks and gate marks if the temperature of the plastic melt is not well controlled. In engineering practice, manifold plates are usually heated by coiled tubular heaters to keep the plastic melt in the runners at a stable temperature. Hence, an optimum layout of heaters is required to achieve thermal homogeneity, which means uniform temperatures
One of the major advantages of a hot runner is design flexibility. The ability to locate a wide variety of points on the part constitutes an interesting and desirable thing about a hot runner. The hot runner allows the gate to be placed at the most favorable location for part aesthetics and optimum filling. This is possible as a result of the usage of hot tip gating, edge gating, or valve gating. This flexibility offered by the hot runner also extends to the mold. It is evident where the flexibility in gate location helps to cool, optimize cavity orientation, and mold simplification.
A hot runner system includes a hot nozzle, hot runner gate, manifold, and heating coil. Different types of designs are available for each component; for instance, hot runner gate options include valve gate, edge gate, thermal sprue gate, and hot-tip gate. Different component designs and dimensions of each component influence the performance and behavior of the hot runner system, making it difficult to fully understand its mechanism.
we have known the differences between hot runner systems, cold runners and hot sprues, hot runner systems are quite heat stable and are used successfully in many molds today.
Selecting a particular type of hot runner system is influenced by the product design and production requirements. There are many hot runner component and tool manufacturers available in your market
For maximum flexibility, the manifold design should be naturally or geometrically balanced. Rheological balancing is possible, but only for a specific grade or rheometric curve.
If possible, utilize a system or component supplier with experience in styrenic TPEs. Some material can crosslink (forming gels) if they are held at high temperatures for too long a period of time, therefore hot runner tools are not recommended for these materials.
Internally heated manifolds are not suitable for TPEs. These systems typically have hot spots and stagnation zones that cause partially solidified material to cling to the cooler manifold walls.
With today’s rapid growth in production, high demands and short lead time can cause additional stress in both the design and launch process. Hot runners are such a common ingredient of injection molding that design of tooling is dependent on the feed system being provided.
The curved manifold was designed for equal flow channel length. Other parameters could be optimized, including pressure drop and residence time. The results of the simulations were significant: residence time (or the time that the polymer spends in the manifold channels) was nearly equalized along the different flow paths. The residence time was cut from 400 milliseconds to 200 milliseconds in the outer channels, while the residence time was increased from 100 milliseconds to 200 milliseconds in the interior channels .
this type of runner requires extremely thick runner channels to stay molten during continuous cycling. These molds have extra-large passages formed in the mold plate. During the fabrication process, the size of the passages in conjunction with the heat applied with each shot results in an open molten flow path. This inexpensive system eliminates the added cost of the manifold and drops, but provides flexible gates of a heated hot runner system. It allows for easy color changes.
Injection Molding PressureInjection pressure. The plastic inside of the hot runner stays hot. This means the hot runner injection pressure drop is significantly smaller than for cold runner systems. You should perform mold flow simulation to get the data necessary to design the proper injection pressure, especially for materials that have poor melt-flow performance and large parts, which require long melt flow and a complete fill.
Injection Molding HeatingHeating. The primary difference between the various types of hot runner systems has to do with the method used to heat the melt. External heating systems keep the material. Externally, the raw material flows through the runner without any carriers. This method provides more reasonable melt shear force curves. Internally heated systems mount right on the melt channel and heat the material inside.
Injection Molding Gate TypeGate type. Hot runner systems have a wide variety of gate types. Aspects you should consider include the gate marks, gate location, and injection of material types. Non-crystalline and crystalline thermoplastic elastomers require different types of gates.
Standard or Custom Injection MoldingStandard or custom-made system. You need to assess whether to go with a standard hot runner system or a custom-made solution. In most cases, the standard solution makes the best choice. The standard length, nozzles, runner boards, gate inserts, and other components means the parts are available. It also reduces delivery time, costs less, and is easier to maintain.
Injection Molding Plastic TypeTypes of plastics processing. When choosing hot runner systems for injection molds, the user must consider the plastic resin. For example, glass-reinforced plastic requires the gate inserts to provide reasonable wear resistance. If the plastic resins easily discompose, you should employ an external heat system runner to avoid dead corners.
Size of Hot or Cold RunnerRunner size. The runner size has a significant effect on the overall performance of the hot runner. Get this wrong and it can cause degradation of plastic injection molded components or even an incomplete filling. To determine the optimal size of the runner, you need to consider the pressure drop, residence time, temperature, shear rate and frequency, as well as other factors.
Injection Molding TemperatureMulti-zone temperature control. When it comes to large, complex hot runner systems and temperature-sensitive plastic resin with tight processing parameters, you should employ a multi-zone temperature controller system. The system can account for heater quality and heat loss.
In recent years, much attention has been paid to the effects that shear has on the melt as it flows through a cold runner system. Of specific interest is how shear heated melt is distributed by the cold runner geometry. Research in this field has led to a greater understanding of shear-induced variances as they apply to cold runner systems and led to the introduction of technologies that are aimed to help address molding issues which have irritated molders for years.
Hot runner system Uniform balance is always desirable. If a mold is significantly imbalanced, it will be difficult to start up and may have a narrow process window. The balance that can be achieved between cavities on a multi-cavity mold will have a bearing on the part to part consistency. That being said, there are some applications that will require a higher degree of balance than others. These will include parts that have a demanding dimensional requirement or parts that will be difficult to eject if they are over packed. Here uniform balance is important to ensure that all cavities are uniformly filled. It is important to recognize applications where balance will be critical.
However, it’s important to recognize that there are some fundamental differences between hot runner system and cold runner system designs. Cold runner systems are more prone to the effects of shear due to their inherent design.
Hot-runner manifolds that contain one or more types of non-melt channels in addition to melt channels, and injection-molding systems containing such hot-runner manifolds. The differing types of non-melt channels include: coolant channels for carrying a coolant for cooling the tips of hot-tip nozzles, for example, during hot latching operations; heating-fluid channels for carrying a heating fluid for heating melt within melt channels within the hot-runner manifolds; and actuation-fluid channels for carrying actuation fluid to valves of valve-actuated nozzles. In each case, nozzles can be formed unitarily monolithically with the hot-runner manifolds and one or more of the various types of non-melt channels can be continuously routed within such unitary monolithic nozzles. Freeform fabrication processes can be used to form hot-runner manifolds of the present disclosure, which often contain complex/intricate internal passageways that form the various types of melt and non-melt channels.
When using the plastic injection molding process, the fabrication of any part or product starts with the mold. Molding systems are divided into two categories: hot runner molds and cold runner molds. Hot runners use a screw nozzle that is fed by a barrel using a pump, while cold runners use a closed, thermoset mold. The primary task of any injection runner system is to direct the material flow from the sprue to the mold cavities. The system requires additional pressure to push the material through the runner. Frictional heat, generated within the runner mold by the material, flows through the runner and raises the temperature, which facilitates the flow. One of the best pay-offs for any project relates to the proper sizing of the runner for a given component and mold design.
A well-designed runner system delivers a number of benefits, such as:
Achieving the optimal number of cavities
Delivering melt to the cavities
Balancing filling of multiple cavities
Balancing filling of multi-gate cavities
Minimizing waste
Allowing for easy injection
Providing efficient energy consumption
Controlling the filling/packing/cycle time
Selecting a particular type of hot runner system is influenced by the product design and production requirements. There are many hot runner component and tool manufacturers available. If possible, utilize a system or component supplier with experience in styrenic TPEs.
Manifold Design
Externally heated systems are best.
Internally heated manifolds are not suitable for TPEs. These systems typically have hot spots and stagnation zones that cause partially solidified material to cling to the cooler manifold walls.
For maximum flexibility, the design should be naturally or geometrically balanced. Rheological balancing is possible, but only for a specific grade or rheometric curve.
All passages should be highly polished circular cross sections with gentle bends to minimize the possibility of stagnation zones.
In order to maintain high shear, minimize residence times and promote flow, the passages should have a diameter of 0.250″ to 0.375″.
Individualized zone controls for the hot runners are recommended to allow the operator to adjust the balance slightly to make the parts more uniform.
For example, A hot runner X style manifold,For the injection molding system,manifold is the center part. When you design the manifold,you make mold-flow analysis to determine the runner size to make sure the best effctive.Manifold heat fast and well control the temperature. A manifold design are based on nature balance and rheology balance theory.Which can make sure the mold melt with reasonable shearing speed and allowable pressure lost.A designed and produced manifold,which are praised by changing color fast,easy heating,precision temperature control,runner banalance and other advantages.
Hot-runner manifolds that contain one or more types of non-melt channels in addition to melt channels, and injection-molding systems containing such hot-runner manifolds. The differing types of non-melt channels include: coolant channels for carrying a coolant for cooling the tips of hot-tip nozzles, for example, during hot latching operations; heating-fluid channels for carrying a heating fluid for heating melt within melt channels within the hot-runner manifolds; and actuation-fluid channels for carrying actuation fluid to valves of valve-actuated nozzles. In each case, nozzles can be formed unitarily monolithically with the hot-runner manifolds and one or more of the various types of non-melt channels can be continuously routed within such unitary monolithic nozzles. Freeform fabrication processes can be used to form hot-runner manifolds of the present disclosure, which often contain complex/intricate internal passageways that form the various types of melt and non-melt channels. …
An injection-molding manifold distributes one or more molten materials, or one or more “melts,” such as one or more plastics, from an injection-molding machine to injection-molding nozzles via a network of melt-channels within the manifold. Each melt is intermittently delivered to one or more mold cavities via the injection-molding nozzles during molding operations. The melt in each melt-channel is typically heated using electrical heaters located on the exterior of the manifold. If the nozzles are of a valve-gated type, actuators that reside on the side of the manifold opposite the nozzles are typically used. Sometimes equipment operators disengage and reengage the nozzles with a mold plate/gate inserts while the nozzles are still hot. This is known as “hot latching” and can lead to excessive wear and damage to the nozzles and/or mold plate/gate inserts where the components engage one another.
Hot Runner System Advantages: 1) Easier fully automatic operation. 2) No loss of melt. 3)Pressure losses minimized. 4) Increase of mechanical efficiency. 5) Improvement of product quality. 6) Extension of mold life.
7) Shorter cycles.
Hot runner systems are feed systems for injection molds which convey molten plastic from the machine nozzle into the cavity.
Hot runner systems are composed of different parts and mechanisms:
Nozzles
Nozzles are the melt delivery system. Nozzles are designed to inject and distribute molten polymer to a number of cavities.
Manifolds
It is a heated melt-distribution system with channels. This structure can be in different shapes as I, H, X, Y or any demanded shape.
Flow control
Valve technology to control the melt flow.
Temperature controller
Connections/Parts
All relevant connections as electrical, resistors, thermocouple…
Hot runner manifold is a part that must individualized design in hot runner system. A good hot runner system depend on hot runner manifold structure design. Hot runner manifold design must consider the following aspects:
port hole size and flow path;
Hot runner thermal expansion
Multi-cavities manifold rheology balance theory
Manifold steel material choosing
Hot runner manifold adopt of small diameter runner,this design is reduce heat-sensitive plastic melt residence time in the runner and guarantee filling quality. Hot runner manifold use big diameter runner can transfer the pressure and it’s benefit for big parts products injecting and molding. Big diameter runner is suit for high viscosity plastic. Hot runner manifold structure design avoid arising death end in conner of runner and nozzle.
Runner diameter and length design should consider the following factors:
allowing pressure less than 35MPa.
Every time after finish shooting,clearly clean the melt plastic in the runner.
Melt plastic flow time from injection machine screw to mould cavity is equal to 10%~20% plastic decomposing time.
In hot runner manifold structure design,hot runner system normally adopt of circular flow channel section because manifold is processed by drilling holes.Hot runner manifold processing need handle care,even a scrap iron left in the runner,it will influence the whole hot runner system operating.
A hot-runner system is provided with a manifold body including a manifold melt channel, and a melt-flow control structure communicating with the manifold melt channel. The melt-flow control structure is integrally formed with the manifold body.
For years, natural balance has been the cornerstone of a successful hot runner balance. This means that the melt experiences the same flow length and the same diameter melt channels from when it leaves the machine nozzle until it enters each cavity within the mold. This approach has served the industry well.
In recent years, much attention has been paid to the effects that shear has on the melt as it flows through a cold runner system. Of specific interest is how shear heated melt is distributed by the cold runner geometry. Research in this field has led to a greater understanding of shear-induced variances as they apply to cold runner systems and led to the introduction of technologies that are aimed to help address molding issues which have irritated molders for years.
Advantages of hot runner Mold
Runner is not attached with molded part. Therefore material cost is reduced.
Reduced Cycle time.
More control over injection process. Therefore part quality improves .
Low pressure is required to push molten plastic.
Recommended for larger parts
Disadvantages of hot runner molds
Higher mold cost.
Higher maintenance cost.
Complete mold cleaning is required to change material.
Not recommended for thermal sensitive materials.
When using the plastic injection molding process, the fabrication of any part or product starts with the mold. Molding systems are divided into two categories: hot runner molds and cold runner molds. Hot runners use a screw nozzle that is fed by a barrel using a pump, while cold runners use a closed, thermoset mold. The primary task of any injection runner system is to direct the material flow from the sprue to the mold cavities. The system requires additional pressure to push the material through the runner. Frictional heat, generated within the runner mold by the material, flows through the runner and raises the temperature, which facilitates the flow. One of the best pay-offs for any project relates to the proper sizing of the runner for a given component and mold design.
large runners facilitate the flow of material at relatively low pressure requirements. However, they require a longer cooling time, consume more material and scrap, and need additional clamping force. On the other hand, using the smallest runner system as required for the project will maximize efficient use of raw material as well as energy consumption during the injection molding process. Ultimately, reducing the runner size depends on the molding machine’s injection pressure capability.
Hot runner molding systems consist of two plates heated by a manifold system inside one-half of the mold that sends the melted material to nozzles, which feed the part cavities. The system consists of two parts: the hot manifold and the drops. The manifold moves the rubber on a single plane and parallel to the parting line to a location above the cavity. Positioned perpendicular to the manifold, the drops move the rubber from the manifold to the component.
hot runners are not required for injection molding processes, they can be useful to ensure a higher quality part. They are particularly beneficial with challenging part geometries that require lower margin of error in the flow properties of the molten plastic (i.e. where inopportune cooling or temperature deltas might result in uneven flow). Further, hot runners can be beneficial in reducing wasted plastic during high volume shoots. Because cold runners are unheated, the channel needs to be larger and thus more plastic needs to be shot during each cycle. If you are shooting a large number of parts while iterating to get the design correct you could easily run up the cost of plastic above the cost of a hot runner assembly.
Hot runners are designed to maximize manufacturing productivity by reducing cycle time. One of the reasons they didn’t take hold when they first came out is that they needed to maintain the molten plastic at a uniform temperature while the injection mold cavity is simultaneously being cooled. This requires a fair level of complexity. The initial (now obsolete) designs implemented internal heating with isolated heaters inside channel cavities. Internally heated hot runner designs resulted in solidified plastic on the internal boundaries of the channel with molten plastic much more localized to the specific heater location. By contrast, externally heated runners utilize heated nozzles and a heated manifold and based on the high thermal conductivity of metal they are able to maintain much more even flow properties for the internal plastic.
Like every entity in the world, hot runners also have some disadvantages as well.
It is comparatively difficult to change the colors in hot runner system.
Hot runner system is more complex because the melt is to required to keep at certain temperature while the injection mold cavity is requires cooling at the same time. Being complex in turn means higher maintenance cost.
Hot runner system may not be suitable for the materials which are sensitive to heat. Moreover thermal expansion of various mold components should be considered.
Of course for best result in quality production, the professionals have to analyze the type of runner for best injection molding system.
The product being formed is affected by the two main technologies of hot runners. Temperature and flow of the hot runner system are closely related. Any change in temperature varies the flow of the melt and flow change can resulting temperature disturbance hence making the molding process difficult.
The control of temperature
The temperature controller not only heats the hot runner system and the plastic in the barrel but also maintains the temperature of the components to the desired value. Temperature has substantial effect on flow than pressure because the increased temperature can force the gate tip further to the gate orifice caused by the thermal expansion. Hence the flow is disturbed because of the change in effective radius of the gate.
The control of plastic flow
Flow channels are closely related to the pressure of the molten plastic flow. Variations in pressure through the regions of a manifold cause dead spots in the product. These spots do not wash out well when purged and result in color change problems.
Hot runner system saves injection cost in many ways. As the material is always in molten form, the pressure reduces in the flow. This allows simplicity in vast production because realization of the low pressure is easy for injection in multi gate and multi cavity molds.
In the hot runner system, as the gate is hot, it results in good pressure transmission which keeps the product away from imperfect falling, cavity shrinking and product distortion due to lack of feeding.
As there is no recycling in hot runner systems, it reduces the cost of selecting and picking up, wrecking and dyeing. The quality of the product is also improved.
Injection cost is reduced also because of the faster cycle time of the hot runners.
When the product size gets bigger and needs various injections, hot runner molds are not appropriate as much as necessary.
Three plate mold serves the purpose here. It has more central points to hit upon the gate. The gate is located at the base rather than the side of the part allowing more smooth supply of the melt in the part.
As the three plate mold system has three plates with two notches. It separates runner form the part and the melt drops into the molds giving automatic working.
But alongwith the advantages of three plate systems, there are some shortcomings of this system. The complex apparatus of three plate systems makes it less stable. It has higher scrap rate, longer run distance and delayed cycle time than hot runner systems.
Melt injected by the plasticizing unit enters the manifold through a single large channel. If the manifold is designed for a multicavity mold, the main channel in the manifold feeds a multilevel or tiered hot-runner system. The tiered configuration allows for more cavities while keeping channel lengths uniform. However, the melt has to travel, either from one level within the mold to another, or when it branches from a channel to an individual nozzle that injects the polymer into a mold cavity. Gun-drilled channels have sharp corners wherever the melt is directed to another distribution level or is split into two smaller, uniform flow paths into the mold.
Hot runner manifold is a part that must individualized design in hot runner system. A good hot runner system depend on hot runner manifold structure design. Hot runner manifold design must consider the following aspects:
port hole size and flow path;
Hot runner thermal expansion
Multi-cavities manifold rheology balance theory
Manifold steel material choosing
Hot runner manifold adopt of small diameter runner,this design is reduce heat-sensitive plastic melt residence time in the runner and guarantee filling quality. Hot runner manifold use big diameter runner can transfer the pressure and it’s benefit for big parts products injecting and molding. Big diameter runner is suit for high viscosity plastic. Hot runner manifold structure design avoid arising death end in conner of runner and nozzle.
Runner diameter and length design should consider the following factors:
allowing pressure less than 35MPa.
Every time after finish shooting,clearly clean the melt plastic in the runner.
Melt plastic flow time from injection machine screw to mould cavity is equal to 10%~20% plastic decomposing time.
In hot runner manifold structure design,hot runner system normally adopt of circular flow channel section because manifold is processed by drilling holes.Hot runner manifold processing need handle care,even a scrap iron left in the runner,it will influence the whole hot runner system operating.
Hot runner manifold adopt of small diameter runner,this design is reduce heat-sensitive plastic melt residence time in the runner and guarantee filling quality. Hot runner manifold use big diameter runner can transfer the pressure and it’s benefit for big parts products injecting and molding. Big diameter runner is suit for high viscosity plastic. Hot runner manifold structure design avoid arising death end in conner of runner and nozzle.
Runner diameter and length design should consider the following factors:
allowing pressure less than 35MPa.
Every time after finish shooting,clearly clean the melt plastic in the runner.
Melt plastic flow time from injection machine screw to mould cavity is equal to 10%~20% plastic decomposing time.
In hot runner manifold structure design,hot runner system normally adopt of circular flow channel section because manifold is processed by drilling holes.Hot runner manifold processing need handle care,even a scrap iron left in the runner,it will influence the whole hot runner system operating.
thanks for sharing your experience, i am a hot runner system engineer, i learned something new from this article
thanks for sharing, as a hot runner system engineer, I really learned a lot of professional knowledge from your blog