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Every injection molding machine makes use of various parts in its manufacturing process. These parts work with each other to ensure that anything that comes out as the end product is exactly in the condition it was intended to be in. Some of these essential parts are the hot and cold runners.
We are going to look in detail at what cold and hot runners are, how they function as far as mold design is concerned, why they are important, their advantages and disadvantages, and the considerations one has to consider when making a choice between either.
Hot Runner System in Injection Molding
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A hot runner system is made up of a minimum of two hot places that are heated through a manifold process. The hot runner system in injection molding is constructed using heat-sensitive materials for the purpose of controlling the flow of molten materials through the mold gates into the empty cavity. The heating is usually supplied through heating coils, pipes, and rods that are connected to the runners straight from the sources of heat. There are two types of hot runner systems that are used widely in the injection molding system.
Insulated Runners: These are the unheated type of hot runners that make use of thick runner channels to maintain the molten nature of the material being injected into the cavity. The molds that use this type of runners have extra-large passageways that support a more free and open molten flow, and this eliminates the need to have manifolds and drops, which in turn makes modifications easier.
Heated Runners: Heated runners, as the name suggests, make use of heated parts for injection molding to take place. Heated runners are further split into two parts: Externally heated runners make use of a cartridge-heated manifold with an interior system of passageways, while internally heated runners have their passages heated by a probe located within the same passageways.
How Does a Hot Runner System Work in Injection Molding
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A hot runner system injection molding makes use of heat to direct the molten material into the empty mold to start the molding process. The purpose of using this much heat is to ensure the material maintains that viscous state as it moves and spreads into the crate evenly before the cooling process kicks off. These runners act as controls and having different types of them helps the injection molding operators to make better products from auto plastic parts to plastic molded chairs . In a nutshell, the materials in a hot runner maintain their high heat that ensures they are in a viscous state until every part of the mold is filled properly. When the cooling finally begins, it happens uniformly across the board.
Advantages
- Hot runners are cheaper and easier to maintain n can be reused many times over
- Hot runners allow for modification to be done, like the altering of the color without interrupting the process in progress.
- The cycle times are much shorter, and this makes them ideal for mass production.
- Hot runner systems have an improved molding system efficiency making them a very cost-effective method.
- Hot runners produce wholesome products as the filling process is much better since no heat or pressure is lost.
- It integrates easily with automation, and this further improves the quality of production and brings down the cost.
Disadvantages
- The initial investment of setting up a hot runner can be crippling. It requires a high amount of capital.
- The cost of maintenance is also higher, especially if you are dealing with larger hot runner systems.
Cold Runner System in Injection Molding
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This is a system where the runners that feed the mold are operated at a low temperature. There are three or more plates used inside the mold. The working principle is almost identical to how a hot runner operates with the main difference being the use of lower temperature and pressures for the entire system. It is also a crucial part in mold making technology.
How Does a Cold Runner System Work in Injection Molding
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The entire channel used in a cold runner system is unheated. It is used to convey the molten material,be it metal or plastic, to the empty mold. Since it is devoid of the same level of heat as a hot runner, the cold runner system has to be bigger to accommodate a greater flow in each manufacturing cycle. For this reason, the cost of running a cold runner could be significantly higher, although it does come in handy when you are in need of making larger plastic injection molds.
Advantages
- It can handle bigger production needs, and this makes it ideal for mass production of large parts.
- Despite its high running costs, the cost of maintenance is lower compared to the hit runners since the lack of excessive heat and pressure means there’s less damage sustained to the mechanical parts.
- The entire system is also less complex and easy to operate.
Disadvantages
- Cold runner systems are extremely wasteful. It uses more materials in each cycle, and the amount of waste produced is monumental.
- They lack the capacity and the ability to hold tolerances.
- The initial cost of setting a cold runner system up is very high, the same as that of a hot runner, and this can be a stumbling block for many small manufacturers.
Considerations in Choosing Between Hot and Cold Runner System
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When it comes to making a choice between a hot runner and cold runner systems, there are certain factors that have to be considered. Each system is designed for a specific function, and jumping in blindly will cost you in the end. The following are some of the factors you have to keep in mind when making that selection.
For Hot Runners
- Injection Pressure: The injection pressure has to be high enough to keep up with the heat level. Any drop in temperature could lead to deformities. Therefore, find a hot runner system that is able to deliver both high pressure and heat.
- Heating Capacity: The eating system has to be sharp throughout the whole process. This includes the external and internal. The heat being supplied has to be uniform.
- Gate Type: Hot runner types have the luxury of using all types of gates. However, you have to pay attention to the gate marks, injection materials, and gate location.
- Types of Materials: The type of molten material being injected also plays a huge part. Some like plastics are able to maintain their heat in the right conditions, while some glass tends to drop that heat quickly. Create conditions that are right for each material used.
For Cold Runners
- Nozzles: The nozzles have to be removable to allow for maintenance and cleaning. Using the same nozzle for all the processes will affect the quality of the products.
- Manifolds: The type of manifold you go with will determine how easy the work will be. Gun-drilled manifolds are much harder to deal with compared to split-plate manifolds that allow for modifications.
- Pneumatic Connections: Cold runner systems can either have external airlines or air terminal boxes. All these come with their own unique disconnectors. They are what make it easy to control the amount of molten material being injected into the mold.
Conclusion
Hot runners and cold runners are necessary for the injection molding process. There are many variations being made every day to suit the needs of each injection mold manufacturer. For more information on how hot and cold runner systems operate and how you can integrate them into your production, check out our website at any time of the day and provide you professional plastic injection molding service by our team of experts.
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