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===3.2 Manufacturing of Semi-Finished Materials===
Semi-finished contact pre-materials can be manufactured from solid precious
metals, precious metal alloys, or precious metal containing composite materials.
They are made in wire, strip, and profile form by known processing technologies
such as extrusion and subsequent annealing and drawing or roll-forming. They
are supplied following the manufacturer's internal standards usually related to
DIN EN specifications for copper based materials. The most important materials
are two – or multiple material layered semi-finished materials with the contact
material 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
liquid or vapor phase.
===3.2.1 Clad Semi-Finished Pre-Materials (Contact-Bimetals)===
Clad materials consist of two or more layers of different materials, the contact
material and the carrier, which are firmly bonded to each other. Depending on
the electrical requirements the contact material is mainly an alloy of gold,
palladium, or silver based while the carrier material are mainly copper alloys. To
bond these materials various technologies are utilized, the two most important
ones being described in more detail below.
During ''hot cladding'', the classic process, the materials to be clad are
assembled into a cladding package in block or plate form, heated to about
800°C and clad (or “welded”) together under high pressure ''(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.
Fig. 3.3: Hot cladding of pre-materials (schematic)
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 ''(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 (> 2 μm) and large strip
length (> 100 m).
Fig. 3.4: Cold roll-cladding of semi-finished strips (schematic)
*Typical configurations of clad contact strips
bild
*Contact materials
bild
*Carrier materials
bild?
*Dimensions
bild
When specifying the contact material layer thickness it is recommended to use the
minimum required thickness.
*Quality criteria and tolerances
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. When
specifying 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.
===3.2.2 Brazed Semi-Finished Contact Materials (Toplay–Profiles)===
