In the plastic injection molding industry, all plastic parts begin from a mold. There are two types of molding systems – cold runner and hot runner. If your production company deals with plastic parts, you should definitely know more about these molding systems. Both have their pros and cons, and understanding them will allow you to decide which system is best suited to mold your plastic parts.
Cold Runner Molding System
Typically, there are two or three plates located within the base of the mold. When plastic has to be injected into the mold, it has to be done through the sprue and thereafter the plastic moves into the runners before finally entering the mold cavity parts.
In a two-plate mold, the runner structure and cavity parts are attached and to separate the two from the mold, one has to use an ejection system. On the other hand, in a three-plate mold, the runner is located on a separate plate. As a result, the cavity parts can be ejected on their own.
It is important to note, regardless of a two- or three-plate mold, the runner always is recycled and reground. This helps to reduce plastic waste, but causes the cycle time to increase.
Hot Runner Molding System
In this type of molding system, there are two plates that are heated along with a manifold system. This system directs the molten plastic to special nozzles, which lead to cavity parts. The hot runner system can be internally or externally heated.
In the internally heated type, the technician can control the flow of the plastic; whereas the externally heated type is more apt for resins that are sensitive to changes in temperature.
In a hot runner molding system there are no runners whatsoever. So the question of regrinding and recycling does not have an effect on the cycle time.
Now that you are aware what the two types of molding systems the plastic injection molding industry uses, it is time to take a look at the pros and cons of each system.
Pros and Cons of Cold Runner System
- It is relatively cheaper to maintain and use
- It lets you change colors very quickly
- It can be used for commodity as well as engineered plastics and polymers
- If robotics are used to remove runners, the cycle time can be pretty fast
- It is slower than a hot runner system
- There is a possibility of plastic waste from the runners if they cannot be recycled and reground
Pros and Cons of Hot Runner System
- The cycle time is extremely fast
- Since there are no runners, there is no question of plastic waste
- There is no need to invest in robotics, as there are no runners
- It is ideal for making large parts
- It is more expensive to use a hot runner molding system to produce parts
- It is not easy to change color
- The maintenance cost is high
- There is a possibility of downtime
- Not the best molding system for polymers and resins that are heat sensitive
If you want to find out which is the ideal molding system to produce your plastic parts, it is best to consult professionals and experts from the plastic injection molding industry before making a decision.