Cold & Hot Runner

Cold runner and hot runner: A runner is the channel in the mold that conveys the plastic from the barrel of the injection molding machine to the part.

Cold Runner: In a cold runner mold, the runner is cooled and ejected with the part. Every cycle, a part and a runner are produced. The obvious disadvantage of this system is the waste plastic generated. The runners are either disposed of, or reground and reprocessed with the original material. This adds a step in the manufacturing process. Also, regrind will increase variation in the injection molding process, and could decrease the plastic's mechanical properties. Despite these disadvantages, there are many significant advantages to using a cold runner mold. The mold design is very simple, and much cheaper than a hot runner system. The mold requires less maintenance and less skill to set up and operate. Colour changes are also very easy, since all of the plastic in the mold is ejected with each cycle.

Types of Cold Runner Molds: There are two major types of cold runner molds:

1. Two plates: A two plate cold runner mold is the simplest type of mold. It is called a two plate mold because there is one parting plane, and the mold splits into two halves. The runner system must be located on this parting plane; thus the part can only be gated on its perimeter.

2. Three plates: A three plate mold differs from a two plate in that it has two parting planes, and the mold splits into three sections every time the part is ejected. Since the mold has two parting planes, the runner system can be located on one, and the part on the other. Three plate molds are used because of their flexibility in gating location. A part can be gated virtually anywhere along its surface.

Advantages of Cold runner mould:

1. Simple mold design.

2. Cold runner injection molds are Inexpensive compared to hot runner molds.

3. Low maintenance cost.

4. Less skills required for set up and operation.

5. Change of material and color of injection molded part is easy.

Disadvantages of Cold runner mould:

1. In cold runner mold, runner is attached to molded part. Therefore additional runner cutting operation is required.

2. Runner material is wasted. if runner is not recycled.

Hot Runner: In a hot runner mold, the runner is situated internally in the mold and kept a temperature above the melting point of the plastic. Runner scrap is reduced or eliminated. The major disadvantage of a hot runner is that it is much more expensive than a cold runner, it requires costly maintenance, and requires more skill to operate. Colour changes with hot runner molds can be difficult, since it is virtually impossible to remove all of the plastic from an internal runner system. Hot runners have many advantages. They can completely eliminate runner scrap, so there are no runners to sort from the parts, and no runners to throw away or regrind and remix into the original material. Hot runners are popular in high production parts, especially with a lot of cavities.

Types of Hot Runner Molds: Hot runner molds are two plate molds with a heated runner system inside one half of the mold. 

A hot runner system is divided into two parts:

1. The manifold: Have channels that convey the plastic on a single plane, parallel to the parting line, to a point above the cavity. 

2. The drops: situated perpendicular to the manifold, convey the plastic from the manifold to the part. 

There are many variations of hot runner systems. Generally, hot runner systems are designated by how the plastic is heated. There are internally and externally heated drops and manifolds. Externally heated hot runner channels have the lowest pressure drop of any runner system (because there is no heater obstructing flow and all the plastic is molten), and they are better for colour changes none of the plastic in the runner system freezes. There are no places for material to hang up and degrade, so externally heated systems are good for thermally sensitive materials. Internally heated runner systems require higher molding pressures, and colour changes are very difficult. There are many places for material to hang up and degrade, so thermally sensitive materials should not be used. Internally heated drops offer better gate tip control. 

1. Internally heated systems also better separate runner heat from the mold because an insulating frozen layer is formed against the steel wall on the inside of the flow channels.

2. A special type of hot runner system is an insulated runner. An insulated runner is not heated; the runner channels are extremely thick and stay molten during constant cycling. This system is very inexpensive, and offers the flexible gating advantages of other hot runners and the elimination of gates without the added cost of the manifold and drops of a heated hot runner system. Colour changes are very easy. Unfortunately, these runner systems offer no control, and only commodity plastics like PP and PE can be used. If the mold stops cycling for some reason, the runner system will freeze and the mold has to be split to remove it. Insulated runners are usually used to make low tolerance parts like cups and Frisbees.

Pet preform injection mold: Molding system plays an important role in food & beverage packaging industry. Kenplas adopts latest engineering innovation, metalworking technologies, and mold making know-how to design, manufacture and test PET preform molds. Kenplas' PET preform mold assures the customer to produce high-quality PET preforms at high productivity, but with most economical investment, shortest start-up time and lowest maintenance cost. With Kenplas' PET preform mold, medium and small size company can produce PET preforms by themselves and also satisfy the fresh brood's production requirement in PET field. We are enjoying a good reputation on manufacturing close tolerance molds manufactured to rigid customer specifications. 

1. PET Preform Injection Molding (Size: 1.45Mb, Duration 0'36") 

2. Setup of PET Preform Injection Mold (Size 11.8Mb, Duration: 5'06")

Professional pet preform design: (Make Imagination into Reality)

Based on the years' experience and integration with most advanced mold technology on the world, Kenplas can design preform with both standard and non-standard neck/shape/volume for water bottle, CSD bottle and oil bottle with perfect bottle blowing performance as per customer's bottle requirement.

Long Service Life : ( Over 2.5 Million Shots)

Kenplas' PET Preform Injection Mold enjoys a service life over 2.5 million shots, based on scores years' design/manufacture experience, mold making know-how, adoption of CNC machining center, high-precision EDM shaping machine and high precision Jig Boring machine.

Steel Material and Machining Tools - Precision:

High quality steel like special Anti-trust Mold Steel and Alloy Steel is used to build mold's different parts. High original hardness and nice machining performance is above steel's mutual features.

Heat Treatment for Mold Building – Strong:

Kenplas does twin heating treatment for mold's inner parts to enhance their strength and prolong their using life. After Treatment, the mold core's surface hardness can reach HRC 58~60 degree. After heat treatment, hard chrome plating will be adopted on Kenplas Preform Injection Mold's inner part. On normal condition, Kenplas Preform Injection Mold can go on 2.5 million times of injecting production cycle at least.

Gate-Free Preform: (Labor-Saving)

1. Valve-Gate Sealing System -- Gate-free Preform: Kenplas Preform Injection Mold adopts Pneumatic Valve-Gate Sealing System to produce gate-free PET preform,  which can save much labor and material cost, also reduce the mold's wear & tear extent for customer.

2. Hot Runner System: Kenplas Preform Injection Mold adopts specially designed Pin-Valve type Hot Runner System to achieve ideal and prompt heating effect for preform production. Moreover, such hot runner system reduces mold's each part's wear & tear and maintenance cost, and also saves 10~15%'s electricity.

3. Heating System -- Quick Response but Energy-saving: Kenplas Preform Injection Mold adopts double Heating system to ensure perfect heating effect and reliable quality control. The Heater Unit is used to heat the hot runner plate with long service life and powerful heating capacity. The Heating Ring System is used to ensure the mold nozzle's constant heating temperature.

4. Hydraulic Ejecting System -- Quiet, Long Service Life: Kenplas Preform Injection Mold adopts hydraulic ejecting mode to replace the mechanical type Hook Doffing System for smooth preform doffing process. The preform-doffing success ratio has achieved firm insurance and the whole preform ejecting process will become much quieter.

Advantages of Hot runner mould:

1. Runner is not attached with molded part. Therefore material cost is reduced.

2. Reduced Cycle time.

3.More control over injection process. Therefore part quality improves.

4. Low pressure is required to push molten plastic.

5. Recommended for larger parts.

Disadvantage of hot runner mould:

1. Higher mold cost.

2. Higher maintenance cost.

3. Complete mold cleaning is required to change material.

4. Not recommended for thermal sensitive materials.