Cross-head & Dies For Plastic Extrusion Machines

Cross-head Definition:

The extrusion head is the processing tool that shapes the extrudate i.e. the tool that determines shape, properties, structures and dimensions of the extrudate as well as mutual position of the elements in the extrusion process. The extrusion head is the tool with an open forming cavity i.e. the extrusion die. The extrusion head has to ensure the occurrence of proper physical and chemical processes in the polymer during its flow through the flow channels . 

The extrusion head is fixed to the end part of the plasticizing system of the plastic extrusion machines. Small extrusion heads are fixed mainly by means of bolt connections or bolt-pin connections (usually hinge-type connections) or by means of a screwed shape ring. Larger extrusion heads are fixed by means of bolt-pin connections, shape semi-rings that are attached and fixed with bolts as well as by means of bolt connections that are very often provided with a vertical support on the plastic extrusion machines foundation. More and more frequently, auxiliary preparatory devices such as a polymer filter, a gear pump or a static mixer (or a set of two or three such devices) are attached and fixed to the plasticizing system. The extrusion head, usually provided with a vertical support, is connected to the last preparatory supplementary device

Design of the extrusion head, regardless of its purpose, should take into account the following general requirements that guarantee correct extrudate production process. The above-mentioned requirements are as follows :

 ensuring proper polymer flow in the flow channels so as to obtain required shape and dimensions of the extrudate,  enabling the extrusion process characterized by the highest possible polymer flow intensity, 

 preventing polymer stagnation areas in the extrusion head by ensuring proper shape and geometric characteristics of the flow channels and ensuring adequate polymer flow resistance, 

 ensuring proper mixing and homogenisation of polymer as well as stabilization of pressure at an adequately high level, 

 ensuring adequate strength of specific design elements of the extrusion head and their connections in high pressure and temperature conditions, 

 ensuring adequate weight and compactness of design of the extrusion head due to required thermal stability and guaranteeing the lowest number of partition surfaces due to required leaktightness of the extrusion head, 

 protecting surfaces of the flow channels against aggressive impact of some polymers, 

 providing the possibility of adjustment of polymer flow rate from the extrusion head die if recommended extrusion process conditions are to be influenced, especially the conditions inside the extrusion head, 

Numerous extrusion head designs have been developed (including patented ones) that differ with regard to design of specific functional components of the extrusion head, operation mode, methods of polymer supply to the extrusion die and the purpose.

Dies Definition

A die is a specialized tool used in manufacturing industries to cut or shape material mostly using a press. Like molds, dies are generally customized to the item they are used to create. Products made with dies range from simple paper clips to complex pieces used in advanced technology. Here we are mainly talking about the dies used for wire & cable manufacturing industry including: extrusion dies,bunching dies,stranding dies,wire drawing dies etc.