Injection Mold Types: Cold runner molds

Cold runner molds are often used for different plastic injection mold processes. Heated plastic is cooled before it passes from the nozzle to the cavity. Once it is through this part of the process, both the part and the material are  ejected from the system. Compared with the  hot runner mold process, cold runner molds area  considerably cheaper and simpler alternative for smaller projects.

Components and Process

The average cold runner system can have either two or three plate molds. In two plate systems, there is a parting line that divides the mold in two.

Systems that have three plates have two of these lines so that the mold splits into three different sections once the part is ejected. Though more difficult, three plates offer more flexibility, as well as having more gates when directed  by the final requirements.

Things to Consider

When you begin with cold runner molds, here are some additional things to consider:

■                Thicker dimensions than the starting component will allow the heated plastics to be added during the cooling process.

■                Round runner is the most common cold runner system design. It is a two-plate system with each plate containing exactly half of the runner’s diameter.

■                Round trapezoid is another design; it allows for the milling of the cavity (or core side) of the tool.

■                Gates are important to the process as a primary reason for choosing this particular system. They are removed from the part once the mold opens or once the part ejects from it.