Hot runner

As a hot runner or hot runner system, a special design of the runner system is referred to in the processing of plastics, in particular in automatic injection molding of thermoplastics, which is compared to the remaining injection-molding tool is thermally insulated and heated up.

Need / benefit

Injection molding of thermoplastics, the plastics melt is transferred from the plasticizing unit of the injection molding machine through the gating system into the mold cavity (or cavities ). In traditional injection molding the sprue system is not thermally isolated from the rest of the tool. Thus, both the tool, and the sprue system therein, heated to temperatures well below the processing temperatures of the plastic.

Thereby, the thermoplastic material solidifies in the runner system during the production of a component. Thus some disadvantages for this type of gating system arise. The gate must be isolated from the component generally. This can be done manually or mechanically either by additional functional elements in the tool or after demolding. After the removal of the sprue, a marker left on the component.

A part of the raw material does not flow into the product and must either be recycled and disposed of ( recycled ) or. In addition, through the gate increases the shot volume, it must be plasticized as ultimately is present in the product more plastic. This can be both energetically and in terms of the necessary engine power play a role.

In a hot runner system, the gating system is thermally isolated from the rest of the tool and separately heated so that the plastic melt in the feed system is continuously flowing. Wherein there is no freezing of the plastic in the gate system, it does not remain on the gate member. Furthermore, long flow paths can be realized by the hot runner systems, because the pressure loss in the runner system is not increased by a cooling of the melt and the associated increase in viscosity.

Disadvantages are the higher investment costs, since the tool must be designed specifically for the inclusion of a hot runner system, hot runner system itself incurs costs and also the machinery for controlling the system need to be purchased. Contrast, however, are not uncommon - especially for expensive engineering thermoplastics - a significant savings in raw materials as well as savings in the post-processing of the product.

The same purpose is also cause Isolierkanalwerkzeuge, where the gate is widened so that in a plastic soul remains. When thermoset and elastomer during molding, where the plastic hardens under the influence of temperature, cold runner systems are used appropriately.

Construction

The hot runner terminating in the hot runner nozzle, which constitutes the transition between the heated and unheated zone in a mold. The hot runner nozzle and the manifold to be adjusted to the temperature window in which the plastic is processed thermoplastically. To control the temperature is given to a hot runner control cabinets that permanently reconcile and regulate the setpoint and actual temperature.

Hot runner systems are mainly divided into open or closed systems. In closed systems, the injection can be closed by a special technique. This is usually done by a valve stem which can usually be pneumatically, hydraulically or electrically operated by a separately controllable mechanics.

Hot runner systems are often purchased parts are therefore usually not made ​​by the toolmakers themselves.