Hot Runner Cleaning is Crucial in the Injection-Molding Business


Injection-molding is simple in concept, as long as the injection-molding equipment is kept clean and free of impurities. Hot runner cleaning is one of the critical steps in the ongoing maintenance of these machines. 

Injection-molding is performed in four steps. First, the plastic or polymer materials to be used are poured into a hopper above the hot runner injection chamber. A measured amount is then released into the hot runner. This chamber has a piston at one end and the mold at the other end. 

The hot runner performs as its name implies. The injection material is first heated up inside the hot runner until it’s liquefied. Then the piston moves through the chamber by means of a screw that pushes the piston to the end where the mold is attached. The threads of the screw are tight against the walls of the hot runner to completely remove all the material from the hot runner chamber. 

The injection mold is filled and removed until the material cools and regains its characteristics and intended strength. The mold is then replaced with another mold, and the process is repeated. 

Where Problems Occur

The reason why cleaning hot runners is so crucial is because as the screw moves the piston down the chamber, tiny pieces of dirt or other foreign material cause scratching along the walls of the chamber. These scratches can contain build-ups of the materials used in prior production runs and can be injected into the molds along with the intended materials. 

Some of the tell-tale signs that a hot runner needs cleaning are the presence of blemishes and discolorations in the final product left by different colored materials that have lodged in the scratches along the walls of the hot runner. 

Many different materials are used depending on the intended use of the final product. PVC, PS, ABS, PC polymers, and nylon are some of the more common materials used. These each have different characteristics in strength, rigidity, and hardness. 

Products intended to be 100% of one type of material may not be up to spec for the conditions they will ultimately be used for if the hot runner is not cleaned effectively. In the worst-case scenario, the product will be flawed in critical areas and crack or break when subjected to the stresses it was designed to handle. 

Taking Proper Preventive Measures

High-quality purging materials should be used in hot runner cleaning regularly whenever there is a change-over in injection materials. These materials will not only rid the hot runner of materials that have become embedded in the scratches; they can prevent the scratches from happening in the first place and prolong the effective lifespan of the machines. 

With proper hot runner cleaning, injection-molding businesses can get the true value out of their equipment. They can enjoy greater savings from less wastage on materials and increased customer satisfaction with the quality of their products.