Changes

Semi-finished contact pre-materials can be manufactured from solid preciousmetals, precious metal alloys, or precious metal containing composite materials.They are made in wire, strip, and profile form by known processing technologiessuch as extrusion and subsequent annealing and drawing or roll-forming. Theyare supplied following the manufacturer's internal standards usually related toDIN EN specifications for copper based materials. The most important materialsare two – or multiple material layered semi-finished materials with the contactmaterial bonded in its solid phase to non-precious carriers by cladding, brazing,or welding. The contact material can also be deposited on the carrier from the

800°C and clad (or “welded”"welded") together under high pressure <xr id="fig:Hot_cladding_of_pre-materialsHot_cladding_of_pre_materials"/> <!--(Fig. 3.3)-->. At the interface between the two materials a non-separable bond is formed by either diffusion of the reaction partners or in liquid phase by forming a AgCu eutectic alloy when an additional brazing alloy foil is placed between the two materials. Further processing is done by rolling with required annealing steps between subsequent thickness reductions. The disadvantage of this process is the usually limited short length of final material strips.

<figure id="fig:Hot_cladding_of_pre-materialsHot_cladding_of_pre_materials">

In the ''Cold Roll-Cladding'' process the bond between the contact and carrier material is achieved by cold deformation of > 50% in one rolling pass <xr id="fig:Cold roll-cladding of semi-finished strips (schematic)"/> <!-- (Fig. 3.4)-->. The high plastic deformation causes cold welding in the boundary layer between the two materials. To increase the quality and strength of the bond a subsequent diffusion annealing is performed in most cases. This process is most suitable for clad semi-finished strips with thin contact material layers (&ge; 2 μm) and large strip length (> 100 m).

*Typical configurations of clad contact strips (<xr id="fig:Typical configurations of clad contact strips"/>)

*Dimensions (<xr id="fig:Dimensions"/>)

Strength properties and dimensional tolerances of clad contact bi-metals are derived from the standards DIN EN 1652 and DIN EN 1654 for Cu alloys. Whenspecifying the width of the contact material layer it is recommended to use the minimum required value. All dimensions should be specified originating from one strip edge.

The toplay process starts with a flat or profile – shaped contact material strip which is fed together with the wider non-precious carrier material and in most cases an intermediate thin foil of brazing alloy into a induction brazing machine <xr id="fig:Toplay brazing with an inductive heating inline equipment (schematic)"/> <!--(Fig. 3.5)-->. An evenly distributed and reliable braze joint can be achieved this way between contact and carrier materials. The combined material strip is rather soft after the brazing process and re-hardened during a subsequent profile rolling step. In this way different shapes and configurations can easily be achieved.

*Typical configurations of toplay contact profiles (<xr id="fig:Typical configurations of toplay contact profiles2"/>)

*Quality criteria, dimensions and tolerances (<xr id="fig:Quality criteria dimensions and tolerances"/>)

Seam–welding is the process by which the contact material in the form of a solid wire, narrow clad strip, or profile is attached to the carrier strip by overlapping or continuous weld pulses between rolling electrodes <xr id="fig:Seam-welding process (schematic)"/> <!--(Fig. 3.6)-->. The weld joint is created by simultaneous effects of heat and pressure. Except for the very small actual weld joint area the original hardness of the carrier strip is maintained because of the limited short time of the heat supply. Therefore also spring-hard base materials can be used without loss of their mechanical strength. The use of clad contact pre-materials and profiles allows to minimize the use of the costly precious metal component tailored to the need for optimum reliability over the expected electrical life of the contact components.

*Typical configurations of seam–welded contact strips and stamped parts (<xr id="fig:Typical configurations of seam-welded contact strips"/>)

*Dimensions (<xr id="fig:Contact Profiles Dimensions"/>)

*Typical configurations of multi-layer contact profiles (<xr id="fig:Typical configurations of multi-layer contact profiles"/>)

*Dimensions and tolerances (<xr id="fig:Contact Profiles Dimensions and tolerances"/>)