/ep_edm/en/contect_1104.html SHINI PLASTICS TECHNOLOGIES, INC.

Special Reports

2016 Quarter 4 Issue 29

The Selection and Application of Hot Runner System

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The hot-runner moulds are heated to ensure the melting state of the runner and gate. As the heating rod and coil are set close to the runner or at center, the runner from IMM nozzle to gate is at high temperature state, keeping the melting of the plastic material. There’s no need to open the runner then take out the material, which only needs to heat up the runner to required temperature for next start. Therefore, the hot runner process is sometimes called the hot collecting pipe system or no runner mould.   


As an advanced injection processing technology, the hot runner technology has been popularized in European and American countries dating back to the middle of last century or even earlier. Since Dec. of 1940, E.R.Knowles has achieved the patent of hot-runner technology. However, the technology has actually been adopted in China was in 2000 or so.   

As hot runner technology is gradually popularized and applied, the proportion of hot runner mould in plastic mould is increasing. The adoption of hot-runner technology mould has various advantages, such as:  

1.Material saving and cost reduction.
2.Molding cycle reduction, and machine efficiency improvement.  
3.Product surface quality and mechanical property improvement.
4.Unnecessary to use three-plate mould for the pin-point gate. 
5.It can mold single product by side gate economically. 
6.Automation level improvement. 
7.It could use valve gate to control the gate freeze-up.   
8.It maintains the injection quality consistency of the multiple cavity mould. 
9.Plastic product surface improvement.   
10.With less injection pressure, it can reduce the post-deformation of the thin-wall product effectively.  

Each technology has its shortcoming, and the hot runner technology is no exception: 

1.complex mould structure, high construction and maintenance cost.
2.Require a certain process to become stable after start, which results lots of wastes at the beginning. 
3.When melt leakage and heating component failure happens, it will greatly affect product quality and production process. 

When the mould manufacturer designs and produces the hot-runner mould, it not only just to purchase the hot-runner system and install it on the mould. However, between the mould manufacturer and hot-runner supplier, from the concept design time of hot-runner mould, to actual production process, till the final application of the mould, there’s plenty of sophisticated close coordination and cooperation in the technology and business aspects. Therefore, the mould manufacturer and user should choose the correct hot-runner supplier, which requires special inspection on the variety quantity and quality of the hot-runner components that produced by the supplier as well as the technical support and after service provided by the supplier where user located. 

Shinzo hot runner system consists of pin-point, large gate and valve model, which could be subdivided into different product series in each model actually. Such as in hot nozzle of pin-point model, the sprue section diameter varies from 4mm to 12mm. Therefore, the hot nozzle is made into different product sizes of product correspondingly. The gate insert of hot nozzle also has multiple variations to satisfy different applications. Shinzo hot runner temperature control box has already achieved the CE certification of EU and grouped an experience after-sale sales team to provide strong technical service.  

Correct Selection of Hot-runner Product Series 

It involves many specific technical links when choosing and purchasing the hot runner system. If he/she gets enough hot runner related technical knowledge, it will be easy to choose and purchase the most suitable hot runner system, which ensures successful later injection process with improved quality. 

The hot runner manufacturer usually makes the hot runner component into product series as different sizes and weight of the plastic products. For processing, the large products use large size hot nozzle, while the small ones use the small size hot nozzle. As a result, after the user made correct selection of the hot runner model (either the pin-point or valve system), the next is to choose the series of the hot runner product and decide the mould structure size as well as design and manufacture. If the wrong hot-runner product series hasn’t been noticed before mould later processing or plastic product production, the mistake will be serious and can’t be offset. As to help the customer to chase suitable hot runner product, Shinzo hot runner will offer directive technical documents for the use of reference.

Injection Pressure Loss in Hot Runner System 

The injection pressure loss in hot runner system can’t be ignored. Most of the users misunderstand that the injection pressure loss in hot runner system is much lesser than cold runner as the plastic melt temperature in hot runner is always high. However, actually, the real situation is quite opposite. In hot runner mould, the melt flow distance will increase in the system as to cope with the hot runner structure of design. Therefore, the pressure loss in hot runner system is relatively larger. In actual application, the large losses result in lots of difficult molding occasions. So, when processing the plastic material (such as PC, POM) with poor fluidity, under the situation that the large flow distances of melt in hot runner system or large product weight, it should adopt the CAE software to analyze and calculate the runner, including the MoldCAE that is mainly for runner analysis and calculation etc.  

Standard and Nonstandard Hot Runner System 

Shinzo provides standard and nonstandard hot runner systems. If it is possible, the user had better to choose the standard hot runner system as well as the nozzle, hot runner plate, gate insert in standard length and dimension. The benefit is that the standard hot runner system is cheaper than the nonstandard model with much shorter delivery time. Besides, the parts are replaceable which are better for further use and maintenance. The common standard plate shape includes 2-cavity-1-row, 4-cavity-1-row, 8-cavity-1-row, 4-cavity-X and 8-cavity-XX models.  

Selection of Cavity No. and Layout on the Mould 

When it designs the mould and selects the cavity No., except to place more of the cavities for production efficiency improvement, it should consider the design of the hot runner. The selection of cavity No. and layout on the mould should be good for plastic melt flow balancing in the hot runner system. For example, if arranging several uniform cavities in a row, it had better to select the cavity No. as 2 or 4, other than 3. For the 2-cavity and 4-cavity mould, it can design the hot runner into full nature of balanced system. On the contrary, the 3-cavity mould requires manual flow balancing toward the hot runner manifold. That is to adopt different pouring gate dimensions according to different flow routes as to reach the flow balance purpose. The flow balance state is determined by hot runner quality designed by technical person. Therefore, the user s had better to choose the cavity No. (such as 16-cavity other than 15-cavity ) better for flow balancing to eliminate any mistakes due to man-made designed flow balance.   

Restriction of Minimum Cavity Distance 

When it designs and produces the micro-parts mould, the people generally incline to arrange the cavity distance closer, thus the mould would be more compacter with more cavities. However, the minimum cavity distance will be restricted by the hot runner component, as the minimum distance size between the nozzles. So, when the cavity distance is designed closely to mould, it should check the minimum allowable distance of the nozzle to avoid mould design rework.  

Processing Plastic Category

When designing the hot runner system, the processed plastics is an essential consideration factor. If processing the glass reinforced plastics (such as glass reinforced nylon), it should select the good wear-resistant gate insert. If processing the plastics (such as PVC) with easy thermal decomposition, it should select the smooth sprue runner without flow dead space in the system. If processing the plastics (such as PC) in poor liquidity, it should select large nozzle series with large section size of sprue runner for the hot runner plate.  

As the important element of plastic moulds, the hot runner system’ technical content is obvious. The fast developing of the plastic mould and unique features of hot runner mould enable the explosive growing of the domestic hot runner in these five years. However, the numerous manufacturers are at disordered competition state. They fight against the price and ignore the quality, which made the users lost their confident toward the domestic product. While the overseas hot-runner company who focused on quality and technology got sales increasing quarterly and annually. The hot runner requires high standard of technology. That is to say, it should input large capital on the technology research and production equipment aspects that can formulate the enterprise competitiveness. However, Shinzo Hot Runner achieved the core competitiveness in this field, which mastering the core technology, with high quality product as well as management system, effective coordination of staff quality within departments, making it gradually stands out of the disordered market. With consistent accumulation, research and developing as well as innovation, Shinzo Hot Runner customizes each unit of hot runner system as the spirit of craftsman, consistently providing the stable hot runner system for the user as to improve the maximum using value.