Hot Runner Systems – Selection and Usage in Injection Molding Service

Hot Runner Systems – Selection and Usage in Injection Molding Service makenica.com/hot-runner-systems-selection-and-usage-in-injection-molding-service February 12, 2021

The hot runner system is a comparatively complicated technology in the field of injection molding service. Many things need to be considered as makers of plastic injection molds/custom plastic mold manufacturers/mold users select and order hot runner systems.

This article lists 13 concepts that you need to know, especially for those who want to purchase a hot runner system for plastic injection molding service:

Hot runner system - supplier selection Customized plastic mold makers of injection molding companies do not merely go to the hot runner supplier to purchase a hot runner system and mount it on the mold.

From the preliminary design stage of hot runner molds to the actual manufacturing process, to the final use of molds, there is a great deal of close technological and commercial collaboration and cooperation between custom plastic injection molding companies and hot runner suppliers.

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Injection molding companies and mold users should then select a good hot runner supplier. Concentrate on two primary things when considering a hot runner supplier for plastic injection molding service:

#1 Number and the quality of hot runner components There are three types of hot runner systems: hot tip type, SPRUEGATING, and VALVE GATING. Each type can be subdivided into several product lines. For example, the runner cross-section diameter in the hot tip nozzle can alter between 4 mm and 12 mm, and the nozzle is also produced in a range of different sizes.

There are also many variations of the nozzle gate inserts to meet different application requirements, so the hot runner supplier's product range is as rich as possible.

In this way, the user can have a higher selectivity of hot runner components. The type, size, and weight of plastic molded parts produced by hot runners are wider, which is more conducive to optimizing the injection molding service and product quality.

Ordinary valve gating system Hot runner systems and molds are operated under high temperature and pressure load conditions in plastic molded parts' injection molding service. Many factors cause the hot runner system's components to fail. The process of plastic injection molding service is mainly applied to large-scale plastic molded parts; economic losses are severe once any shutdown occurs.

Ordinary open system The reliability and quality of the hot runner system are therefore essential. Customers should have a thorough understanding of the quality and application history of hot runner components manufactured by hot runner suppliers. Some of the reliable hot runner manufacturers have been certified as ISO quality standards by international organizations.

2. Technical support and after-sales services During the use of hot runner mold and the choice of a reliable hot runner system, users should also consider, if there is a problem with hot runners, whether they can obtain timely and good technical support and after-sales service.

Many hot-runner vendors have an extensive technical assistance and service network in the countries and regions where their business offices are based and are staffed with fulltime service personnel that can contact customers at any time for troubleshooting.

However, these companies also only have offices focused on sales of hot runner products in other countries and areas where their companies are away from their headquarters. It is comparatively inferior to technical support, and users should pay attention to this aspect.

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Hot Runner System - Technical Information Users would have several unique technological issues included in the selection and installation of hot runner systems. Suppose users have good technical knowledge of hot runners. In that case, they can easily pick and buy the most appropriate hot runner system to ensure smooth and improved product quality in the subsequent process of plastic injection molding service.

1. Right range of hot runner product series Hot runner manufacturers also put their hot runner components in the product line according to the size and weight of processed plastic molded pieces. E.g., large plastic molded parts are processed using large-scale nozzles, and small plastic molded parts are processed using small-scale nozzles.

So, after the user selects the hot runner type correctly (whether it is a hot tip or a valve system), the hot runner product series's choice is made and thus defines the mold's structural size and design.

If the hot runner product line is not chosen right, it will be discovered in later phases of mold manufacturing or the manufacture of plastic molded components. Error is severe and very difficult to save.

To help you pick the hot runner product line correctly, each hot runner supplier has some valuable technical documents for comparison purposes. Users should work together with hot runner vendors to pick a hot runner line of goods.

2. Injection Pressure loss in the hot runner systems In hot runner systems, injection Pressure loss cannot be overlooked. Most hot runner mold users believe that the injection pressure loss of hot runner pressure is much less than that of a cold runner. The reason is that the hot runner plastic solution is always hot during injection molding service.

Cylinder wire rack system In fact, in many situations, the condition is just the opposite: in hot runner mold, due to the configuration of the hot runner mechanism, the spectrum of solution operation in the hot runner system is greatly improved. Injection pressure loss is often consistently high in the hot runner system.

In practical applications, there are many scenarios in which the injection molding process is problematic due to an extreme lack of injection pressure in the hot runner system.

Therefore, for plastics with weak processing operations (such as PC, POM, etc.), large active solution spacing in hot runner systems, or large workpiece weights, CAE tools can be used to calculate and measure flow channels.

3. Selection - standard and non-standard hot runner systems

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Usually, every hot runner vendor provides both standard and non-standard hot runner systems. Users should aim to choose a standard hot runner system if possible.

The advantage is that the standard hot runner system is cheaper than the non-standard hot runner system, and the shipping time is much shorter. The parts are compatible and are beneficial to potential usage and repair. Once a part has been broken, buy another standard part and mount it. Popular standard hot runner plates are two cavities in one raw, four cavities in one raw, eight cavities in one raw, four x-shaped cavities, eight xxshaped cavities, and so on.

4. Number of mold cavities and choice of layout When designing hot runner molds and selecting several cavities, in addition to increasing the cavity to improve production efficiency, the design of hot runners should also be considered. Choosing the number of mold and layout cavities should be beneficial in balancing the hot runner system's plastic solution activity.

For instance, in a row, it is preferable to choose 2 or 4 cavities instead of 3 if several cavities with the same design are arranged. It can be designed as a completely natural balanced system for 2-cavity or 4-cavity mold in a raw, hot runner. Conversely, a 3-cavity mold requires a manifold balance of human activities on a hot runner.

The balance of activity depends on the quality of the work of the specific hot runner design staff. The user should try to choose the number of cavities that contribute to the balance of activity (such as the selection of 16 cavities instead of 15 cavities, etc.) to eliminate any errors caused by the balance of human design activities.

5. Minimum cavity spacing limit When designing molds with injection molding service for small parts production, it is generally desirable to arrange the cavities as close as possible so that the molds are compact and can have more cavities. However, the minimum cavity spacing is limited by a minimum spacing between hot runner components such as nozzles.

Therefore, when designing molds with narrowly spaced cavities, plastic injection molding companies should pay attention to checking the minimum nozzle spacing to avoid rework of the mold design.

6. Forms of plastics processed The type of plastic processed by plastic injection molding companies is a significant factor when choosing a hot runner system. A wear-resistant gate insert can be used to handle glass reinforced plastics (such as glass-reinforced nylon materials, etc.). For handling plastics that are readily thermally decomposed (like PVC), one should use a hot runner system comprising smooth runners and no dead ends.

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When handling poor activity plastics (such as PCs), injection molding companies should pay attention to larger series of nozzles and the use of larger cross-section runner dimensions in hot runner plates.

7. Maturity of hot runner products It takes a long time for a new hot runner product to progress steadily. Hot runner suppliers will continue to launch new products and remove hot runner products unsuitable. Users and injection molding companies should also select hot runner goods with a substantial maturity, a prominent and broad background.

In the case of those goods, whether it is a hot runner maker or hot runner user, there are more experienced and successful events for new customers with less experience.

8. Hot runner system state before shipping Some hot runner vendors conduct certain device checks before supplying their hot runner system to the customer. The actual process of injection molding service tests is often performed on critical applications. However, before the hot runner system is delivered, each hot runner provider has a separate test set. Users and plastic injection molding companies should be aware of this.

9. Choosing multi-zone temperature regulation for hot runners Suppose users need to buy large and complex hot runner systems or handle plastics that are temperature sensitive and have limited processing parameters. In that case, they can prefer a hot runner configuration with multiple temperature control zones. In this way, the user can change and monitor the temperature distribution locally as desired.

10. What to do if I have a color change request?

Some users use the same mold to manufacture plastic molded parts of the same variety in different colors, a color shift technology project.

When ordering hot runners, consider selecting a hot runner device with a tiny sprue to speed up color change and minimize waste. Simultaneously, every runner turning in the hot runner system must be round and smooth with no dead ends.

Suppose the valve type hot runner system is used to manufacture plastic molded parts with color shift specifications. If that's the case, there will often be a dead angle (DEAD SPOT) behind the valve's needle, which must be paid careful attention!

11. One mold with multi-cavity When constructing a multi-cavity mold, the balance of operation must be considered.

Suppose the variation between the components' size and weight is so big and the difference of injection pressure of each cavity is greater than 200-300 BAR. In that case, it is impossible to obtain a balance of operation by adjusting the runner's size in the hot runner method.

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If the operation is unbalanced in a mold-shaped multi-cavity mold, there may be certain issues in that the parts' loading is inadequate, the other parts are overfilled, the flash is wide, and the residual tension is high.

Think about using a valved hot runner system or modifying the overall mold configuration at this stage. The valve system will shut the early filled cavity gates at the right time to prevent overfilling these cavities.

12. Proportion of cavity and volume of hot runner The hot runner system's runner volume must not be too high relative to the cavity volume.

Otherwise, the plastic solution will persist in the hot runner system for too long and decompose thermally. Unable to manufacture qualified molded plastic components.

If the molded plastic pieces' weight is too little, hot and cold runners should be used. The injection amount increases after using a cold runner, which strengthens the relative relationship between the cavity and the hot runner volume. It decreases the length of the liquid fluid in the hot runner system.

13. Usage of trial mold Hot runner molds are more precious, particularly hot runner molds with high cavity counts (such as 96, 128 cavities, etc.) and higher prices.

If you want to open a new operation area, have inadequate expertise, or try using more new hot runner components (like nozzles or new gates), consider creating a plain, singlecavity trial mold to check the feasibility report of the program. After having enough practice, you're going to make a precious and structured work mold.

Read More : What are the materials used in Injection Molding Service?

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