Hot runners are heated to ensure that plastics in runners and gates remain molten. Because there is a heating rod and heating ring near or in the center of runner, entire runner from injection nozzle of injection molding machine to gate is in a high temperature state, so that plastic in runner remains molten. Generally, it is not necessary to open runner to take out condensation after shutdown, only need to heat runner to required temperature when machine is turned on again. Therefore, hot runner process is sometimes referred to as a hot header system, or as runnerless molding.
Hot runner (Hot Runner Systems) is a heating component system used in injection molds to inject molten plastic particles into cavity of mold. Hot runner mold is a brand new structure in which runner of a traditional mold or three plate mold are heated, and runner need not be taken out during each forming. We will discuss timing of using hot runner from following four aspects.

 

In order to form oversized products, hot runners must be used to make plastic flow balanced. For example, automobile inner linings and home appliance shells, etc., it is necessary to inject material at the same time or sequentially.
When injection material laterally away from center of injection molding machine, inject material  by hot runner will make structure of mold simple, easy to mold, speed up molding speed, reduce molding time, and have no material head.

In three-plate method, each time injection is carried out, heavy mother template must slide on guide post. Even new mold is difficult to use and life of mold is not long.
Each time three plate mold is ejected, amount of movement of runner material taken out from mold is greater than amount of mold plate movement necessary to take out molded product from mold.

Use when inject from ejector side, or when a longer vertical runner is required.
Can avoid problems caused by too long material head, such as: reduced mold stroke, saving material head residue, easy forming, no shrinkage, no flow marks, etc.
For some large products that allow eccentric feeding:
In use of three plate mold, mother mold plate must be moved to take out material head. If hot runner molding method is used, mold opening movement can shorten necessary movement for unloading material head. Therefore, three plate mold must be produced with a large molding machine. After using hot runner, you can switch to a small molding machine.
Objects that are difficult to mold, such as high viscosity, low viscosity, and high molding temperature, hot runner system can solve these problems. Specific examples: metal powder injection, ceramic powder injection, plastic magnet injection, plastic bearing injection, thermoplastic rubber, and so on.

 

As a simple example, if cold material head accounts for 68% of waste rate (at the time of manufacture, 1kg of material can only produce 320g of product, and remaining 680g is a cold material head). Although cold material head can still be recovered, due to influence of human factors and proportion of mixed material of the recycled material, in order to maintain normal operation, some cold material heads must be accumulated, resulting in retention of funds.

High-speed injection molding not only improves molding efficiency, such as cups, containers, and other thin-thickness moldings are indispensable.

For some shallow, large-volume products, such as CD shells and small-granular products, you only need to increase clamping force by 15% and increase output by 80% with same injection time.
Environmental protection and efficiency of hot runner:
Since hot runner does not generate "garbage", it does not matter how to deal with "garbage". So-called "garbage" means a waste of resources. Hot runner system is a low-carbon product and does not have any impact on environment.
It does not occupy space of storage material head, there is no problem of crushing noise and deterioration:
Because of wide variety of plastics and variety of colors, often because of accumulation of material head, it must be classified, dehumidified, dried, and sealed. At the same time, smashing must produce noise that affects tranquility, and poor working environment affects staff morale.
In summary, we can know that switching to a hot runner in a three-plate mold has following advantages:
Material head is easy to take out, and stroke for taking out material head can be reduced.
Plastic flow during injection is relatively average, and operating conditions of each injection point can be controlled separately, making plastic injection easier.
Save cost of plastic materials and labor costs.