The titanium and aluminium investment casting specialist TITAL GmbH located in Bestwig, Germany, concludes its investment programme for the large titanium casting facility, which was put into operation in December 2008, with a new chemical milling facility. In the new facility titanium parts with an edge length of up to 60in and a weight of up to 661lb can be chemically milled. The old chemical milling facility which still exists is too small for finishing parts of this size.
The chemical milling of titanium castings is a necessary step in the production process to remove the brittle casting skin (alpha-case). As the gating material (leftover raw material that is not useable) can be completely due to the chemical milling facility, TITAL was able to further optimise the process flow. The investment for the new chemical milling facility was approximately $720,000. It was produced and delivered ready-for-use to TITAL by ADRIAN Galvanotechnik GmbH & Co. KG located in Hückeswagen, Germany.
Dr Ralf Gerke-Cantow, head of Titanium Production, said: “Although we use reaction-stable materials, oxygenation and accumulation of nitrogen in the casting surface cannot be completely avoided. Consequently the titanium material is reacting at the surface with the moulding material of the casting.” If the cast parts were not chemically milled after the casting process, alpha-case would occur. This means that the surface layer becomes brittle. Dr Gerke-Cantow said: “In this case the components are not suited for dynamic forces and cracks can form deriving from the brittle surface. Therefore a chemical milling facility with adequate dimensions was essential.”
The key element of the chemical milling facility is a basin filled with acid which is 5.9ft wide and 6.5ft long. This basin is located in a pit with a depth of 6.5ft and is partially enclosed so that the access is limited. Therefore the semi-automatic operation of the carriage is carried out from the switchboard. Up to 100 rough castings are placed into a pivot mounting and submerged into the acid for about half an hour. After the dip the castings are rinsed off with clear water and then dried in an oven with hot air.
The old chemical milling facility with dimensions of 3.9ft x 3.2ft is still in use. However, it can only accommodate parts with an edge length of up to 23in.
By using the newly added chemical milling facility more than twice as much gating material as before can be recycled. Thus the investment optimises the process flow at TITAL and reduces the costs. Dr Gerke-Cantow said: “Titanium scraps are machined, freed from impurities and as a result reusable. For this reason we have practically no material loss anymore.”