Manufacturing at KOVOHUTĚ HOLDING DT, a joint-stock company, division Kovohutě Čelákovice, consists of three technological operations which proceed in order. There is also a series of preliminary and subsidiary operations involved. At the beginning, there is raw material input and the process ends with an output of semi-products ready for additional processing (semi-finished products). The basic technological operations are melting and casting, extrusion, and drawing.
Melting and casting is when an alloy of specified chemical composition is prepared as rolled semi-product. Electric induction furnaces are used for melting, and some special alloys are manufactured in a gas-fired crucible. Samples for material analysis are taken before actual casting. After cooling the castings are divided into various lengths according to the pressing shop's requirements.
Extrusion is a very demanding and expensive process and needs perfect equipment, high-quality tools, and accuracy within determined parameters. Extrusion is carried out by hydraulic extrusion presses from ingots, which are heated in electric induction furnaces at temperature ranging from 700 to 1000 degrees centigrade. Bars, tubes, wires, and sections in straight lengths or coils can be extruded. Easily oxidable metals, for example copper, are extruded into water. Dimensions, surface quality, and flatness are checked.
Cold drawing is a process in which raw material is drawn through a die at normal temperature. A die or punch is a tool which is made from steel, sintered carbide, or from other materials. Its dimensions and geometry and surfaces have to be very precise. The surfaces must be absolutely smooth in order not to mar the semi-product. The friction when drawing should be minimal.
In the drawing process, material properties change. The strength is higher, but the quality of the drawn product is reduced. The structure is adjusted and becomes finer. The drawing process is limited to a certain extent. Exceeding limits could damage the structure of most metals. Cracking can occur as well as tearing. Only a few metals are exceptions (e.g., pure copper). Its hardness is limited, but even then it is possible to draw it without danger of damage.
Drawing can be combined with rolling for a more regular shape. For this operation rolling machines are used. They can be pilger rolling machines or ordinary ones producing flat or grooved rolls. Drawing conveyor lines are often used for this purpose. They link several production steps one after the other. Conveyor lines save expense and lessen the dangers of handling material; they also increase labor productivity.