Not only let you know good and bad of hot runner, but also let you know who is the best in hot runne

Time:2020-02-10 10:25:19 / Popularity: / Source:

Hot runner system 
Hot runner mold is a mold that does not solidify melt in runner by using a heating device. Because it has a shorter forming cycle than traditional molds and saves more raw materials, hot runner mold is widely used in industrialized countries and regions in the world today.


Hot runner system are divided into fully hot runner and semi hot runner systems. Design of fully hot runner is complicated, but effect is good and maintenance cost is very low. Structure of semi hot runner is simplified, stable, easy to use, and failure rate is low. Due to simple structure, maintenance cost is low, stability of production is more guaranteed.

Hot runner classification

Open type (for semi hot runner), needle valve type (for fully hot runner).
Hot runner system is generally composed of several parts such as thermal nozzle, manifold, temperature control box and accessories. Thermal nozzles generally include two types: open thermal nozzle and needle valve thermal nozzle. Because form of thermal nozzle directly determines selection of hot runner system and manufacture of mold, hot runner system is often divided into open hot runner system and needle valve hot runner system accordingly. Diverter plate is used for multi-cavity or multi-point feeding in a mold, single-point feeding, but offset material level. Material is usually P20 or H13. Manifold is generally divided into two types: standard and non-standard. Its structure is mainly determined by distribution of cavity on mold, nozzle layout and gate position. Temperature control box includes host, cables, connectors and wiring male and female sockets. Hot runner accessories usually include: heaters and thermocouples, runner seals, connectors and junction boxes.

Advantages of hot runner mold

Hot runner mold iswidely used in industrialized countries and regions in the world today. This is mainly because hot runner mold has following significant features:
1. Shorten molding cycle
Because there is no restriction on cooling time of runner system, product can be ejected in time after molding is solidified. Many thin-walled parts produced with hot runner mold can be molded in less than 5 seconds.
2. Save plastic raw materials
Because there is no cold runner in fully hot runner mold, there is no production waste. This is particularly significant for applications where plastic is expensive. In fact, major hot runner manufacturers in the world have developed rapidly in the era when world's oil and plastic raw materials were expensive. Because hot runner technology is an effective way to reduce materials and materials costs.
3. Reducing Expenses and Improving Product Quality
During hot runner molding process, temperature of plastic solution is accurately controlled in runner system. Plastic can flow into each cavity in a more uniform state, result is a consistent quality part. Gate of hot runner molding has good quality, low residual stress after demolding, and small part deformation. Therefore, many high-quality products on the market are produced by hot runner mold. For example, many plastic parts in MOTOROLA mobile phones, HP printers, and DELL laptops are made of hot runner molds.
4. Eliminating subsequent processes is conducive to production automation.
Product is finished after being molded by hot runner mold, and there is no need to trim gates and recycle cold runners, which is conducive to production automation. Many foreign product manufacturers have combined hot runner and automation to greatly increase production efficiency.
5. Expand scope of injection molding applications
Many advanced plastic molding process have been developed on the basis of hot runner technology. Such as PET pre-molding, multi-color co-injection in mold, co-injection of multiple materials, STACKMOLD, etc.

Disadvantages of hot runner mold

Although hot runner mold have many significant advantages compared to cold runner molds, mold users also need to understand disadvantages of hot runner mold. To sum up, there are following points.
1. Rising mold costs
Hot runner components are relatively expensive, and hot runner mold costs may increase significantly. If production of parts is small and cost ratio of mold tools is high, it will not be economical. For mold users in many developing countries, expensive hot runner system is one of main problems affecting widespread use of hot runner mold.
2. High requirements for hot runner mold making process equipment
Hot runner mold needs precision machining machinery for guarantee. Integration and cooperation requirements of hot runner system and mold are extremely strict, otherwise many serious problems will occur in production process of mold. For example, poor plastic sealing leads to plastic overflow and damage to hot runner component, which interrupt production. Relative position of nozzle inserts and gates is not good, resulting in a serious decline in product quality.
3. Complex operation and maintenance
Compared with cold runner mold, hot runner mold operation and maintenance are more complicated. If improper operation is used, it is easy to damage hot runner parts, making production impossible and causing huge economic losses. For new users of hot runner mold, it takes a long time to accumulate experience.

Composition of hot runner system

Although there are many hot runner manufacturers and various hot runner product families in the world, a typical hot runner system is composed of following major parts:
2. Nozzle
3. Temperature Controller
4. Auxiliary parts

Main technical key of hot runner application

A successful hot runner mold application project needs multiple links to ensure it. The most important of these are two technical factors. One is control of plastic temperature, and the other is control of plastic flow.
1. Control of plastic temperature
Control of plastic temperature is extremely important in hot runner mold applications. Many processing and product quality problems that arise in production process directly stem from poor temperature control of hot runner system. For example, quality of product gate is poor during injection molding using hot-pin gate method, valve needle is difficult to close when valve-gate method is used for molding, filling time and quality of parts in a multi-cavity mold are not consistent. If possible, you should choose a hot runner system with separate temperature control in multiple areas to increase flexibility and adaptability.
2. Control of plastic flow
Plastics must be balanced in hot runner system. Gates should be opened at the same time so that plastic can fill various cavities simultaneously. For FAMILY MOLD with very different part weights, runner size design must be balanced. Otherwise, some parts will have insufficient filling and holding pressure, some parts will have excessive filling and holding pressure, flashes will be too large and poor in quality. Design of runner size should be reasonable. If size is too small, filling pressure loss is too large. If size is too large, volume of hot runner is too large, residence time of plastic in hot runner system is too long, which damages performance of material and causes parts to fail to meet use requirements. In the world, there are already CAE softwares such as MOLDCAE that help users perform the best flow channel design.

Application range of hot runner mold

Hot runner mold 
1. Type of plastic material
Hot runner mold have been successfully used to process various plastic materials such as PP, PE, PS, ABS, PBT, PA, PSU, PC, POM, LCP, PVC, PET, PMMA, PEI, ABS / PC, etc. Any plastic material that can be processed with a cold runner mold can be processed with a hot runner mold.
2. Part size and weight
The smallest parts manufactured with hot runner mold are less than 0.1 g. The largest is over 30 kg. Applications are extremely versatile.
3. Industry
Hot runner mold are widely used in electronics, automobiles, medical, daily necessities, toys, packaging, construction, office equipment and other industrial sectors.

Brief Introduction of Hot Runner Mold Production in the World

Hot runner mold production is extremely active in countries and regions where industry is more developed in the world. Proportion of hot runner mold is constantly increasing. Many small mold factories with less than 10 people produce hot runner mold. Generally speaking, North America and Europe have used hot runner technology for a long time and have more experience. In Asia, with exception of Japan, Singapore, South Korea, Taiwan, and Hong Kong take the lead. In North America and Europe, although mold manufacturing level is higher, price is higher and delivery time is longer. In contrast, hot runner mold factories in Asia are more competitive in terms of price and lead time.

Major Hot Runner Manufacturers and Headquarters in the World

Competition is fierce in the field of hot runner technology. Many companies have invested huge financial and material resources in development of hot runner products. The latest hot runner products are always available at major plastic and mold exhibitions. Main hot runner manufacturers and headquarters locations in the world are listed here.
1. North America
HUSKY United States
SYNVENTIVE United States
CACO United States
INCOE United States
FASTHEAT United States
D-M-E United States
HASCO United States
2. Europe
EWIKON Germany
SPEAR Germany
PLASTHING United Kingdom
3. Asia
YUDO South Korea
4. Australia 
MASTIP New Zealand
Eliminate or reduce faults during use as much as possible. Pay attention to following when selecting and applying hot runner system:

1.Selection of heating method

Internal heating method: Internal heating nozzle has a complicated structure, higher cost, difficult replacement of parts, and higher requirements for electric heating elements. Placing heater in the middle of runner will produce a circular flow, increase friction area of container, pressure drop may be three times that of externally heated nozzle.
However, since internal heating element is set in torpedo body in nozzle, heat is all supplied to material, so heat loss is small, and electrical energy can be saved. If a point gate is used, tip of torpedo body is kept in the center of gate, which is conducive to gate cut off after injection and residual stress of plastic part is lower due to late condensation of gate.
External heating method: Using external thermal nozzles can eliminate cold film and reduce pressure loss. At the same time, due to its simple structure, convenient processing, thermocouple installed in the middle of nozzle to make temperature control accurate, etc., it is currently widely used in production. However, external thermal nozzle has a large heat loss, which is not as energy-efficient as internal thermal nozzle.

2.Gate selection

Design and selection of gate directly affect quality of plastic part. When applying hot runner system, appropriate gate type should be selected according to resin's flow performance, molding temperature, and product quality requirements to prevent drooling, dripping, leakage, and poor color change.

3. Temperature control method

After gate form is determined, control of melt temperature fluctuations will play a key role in quality of plastic part. In many cases, phenomenon of scorch, degradation or blockage of runner is caused by improper temperature control, especially for heat-sensitive plastics, which often require rapid and accurate reaction to temperature fluctuations.
For this reason, heating element should be reasonably installed to prevent local overheating, ensure matching gap between heating element and runner plate or nozzle, minimize heat loss. At the same time, more advanced electronic temperature controllers should be selected to meet temperature control requirements.

4. Temperature and pressure balance calculation of each manifold

Purpose of hot runner system is to pass hot plastic injected from injection molding machine nozzle through hot runner at same temperature and distribute melt to gates of mold at a uniform pressure. Therefore, temperature distribution of heating zone of each runner and melt pressure flowing into each gate should be calculated.
Calculation of nozzle and gate sleeve offset caused by thermal expansion. That is, centerline of hot (expanded) nozzle and cold (non-expanded) gate sleeve should be accurately positioned and aligned.

5.Calculation of heat loss

Internally heated runner is surrounded and supported by a cooled mold sleeve, so heat loss due to heat radiation and direct contact (conduction) should be calculated as accurately as possible. Otherwise, actual runner diameter will become smaller due to thickening of condensation layer on channel wall.

6. Installation of runner plate

Full consideration should be given to both thermal insulation and injection pressure. Generally, a spacer and a support are provided between runner plate and template. On the one hand, it can withstand injection pressure to avoid deformation of runner plate and material leakage, on the other hand, it can reduce heat loss.

7. Maintenance of hot runner system

For hot runner mold, it is important to regularly perform preventive maintenance of hot runner components during use. This work includes electrical testing, inspection of sealing components and connecting wires, cleaning of component dirt.
Hot runner mold 

1. Thermal manifold cannot reach set temperature

Cause: Thermocouple has poor contact or failure, heating wire is open, wiring of heating wire is too loose or too short.
Solution: Check whether thermocouple contacts are normal and whether wiring is correct. Check heating wire circuit.

2. Temperature of heat shunt plate is too slow.

Cause: A certain heating wire is broken or wiring is too loose, air gap of heat shunt plate is insufficient, cooling pad is overcooled, and thermocouple is not in good contact.
Solution: Check all heating wires, increase air gap at least 10mm, or use a heat insulation plate, add a heat insulation plate on fixed mold plate (bottom plate) or reduce cooling of lower fixed mold plate, check whether thermoelectricity is good.

3. Temperature of thermal manifold is unstable

Cause: Poor thermocouple contact.
Solution: Check thermocouple.

4. Metal fragments are present in melt

Reason: fragments on the screw of injection molding machine, metal fragments in injection molding material
Solution: Remove metal debris and repair impurities in plastic filtering screw.

5. Leaking of material at junction surface of thermal manifold and thermal nozzle

Reasons: Calculation of expansion is not correct, W surface processing height is inconsistent, material of fixed mold fixing plate (bottom plate) is too soft, temperature of thermal manifold is too high for a short time, installation of "O" seal ring is problematic.
Solution: recalculate and check expansion amount, check and correct height of W surface, replace fixed mold fixing plate (bottom plate) with appropriate hardness, replace damaged parts and "O" seal

6. Thermal diverter compensation plug leak

Reason: No spacer.
Solution: Install spacer.

7. Oil (gas) cylinder is not working

Cause: No air / hydraulic oil enters cylinder, pneumatic / hydraulic cylinder system is stuck, and system pressure is insufficient.
Solution: Inspect pipeline, pump for leaks and blockages, check cooperation of cylinder and piston, check whether feed line is excessively bent, whether piston and valve needle are flexible.

8. Cylinder system was bitten to death

Reason: Cylinder body, thermal manifold, thermal nozzle, etc. are not concentric, fixed mold plate (bottom plate) has excessive heat accumulation.
Solution: Adjust concentricity of cylinder block, manifold, and hot nozzle to increase cooling around cylinder block.

9. Cylinder blockage after overheating

Reason: Cylinder body, thermal manifold, thermal nozzle, etc. are not concentric, fixed mold plate (bottom plate) has excessive heat accumulation. Gasket and valve pin fixing nut cause friction.
Solution: Adjust concentricity of cylinder block, hot shunt plate, and thermal nozzle, increase cooling around cylinder block, adjust gasket and valve pin fixing nut.

10. Leakage occurs around valve pin bushing

Cause: Needle bushing on hot manifold is too loose.
Solution: Check diameter and height of hot shunt hole and valve bushing.

11. Valve needle head sticky

Cause: Too much heat is not dissipated on valve needle.
Solution: Reduce temperature of hot nozzle and gate, increase cooling time.

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