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===3.2.3 Seam–Welded Contact Strip Materials (FDR–Profiles)===
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 ''(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
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Fig. 3.6: Seam-welding process (schematic)
*Contact materials
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*Carrier materials
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*Dimensions
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*Quality criteria and tolerances
Strength properties and dimensional tolerances of toplay profiles are derived from the
standards DIN EN 1652 and DIN EN 1654 for Cu alloys..
===3.2.4 Contact Profiles (Contact Weld Tapes)===
Contact profiles span a broad range of dimensions. Width and thickness are typically
between 0.8 – 8.0 mm and 0.2 – 3.0 mm resp. Special configurations, often defined
as miniature-profiles or even micro–profiles can have a
width < 2.0 mm.
Miniature–profiles are mostly composed of a contact-bimetal material with the contact
material being a precious metal alloy or composite material clad, welded or coated by
electroplating or vacuum-deposition (sputtered) onto a weldable base material. Since
these profiles are attached to carrier strip materials usually by segment– or seam–
welding to the base materials, materials with good welding properties such as nickel,
copper-nickel, copper-tin, as well as copper-nickel-zinc alloys are used. The bottom
surface of the profiles usually has formed weld rails or similar patterns to ensure a
solid continuous metallurgical weld joint between the profile and the contact carrier.
Contact profiles in larger sizes are often used for switching devices in the low voltage
technology. For these the contact layer mostly consists of arc erosion resistant
materials such as silver–nickel, silver–metal oxides or the weld resistant silver–
graphite. The brazable or weldable underside of the metal oxide or silver–graphite
materials is usually pure silver with also quite often a thin layer of a phosphorous
containing brazing alloy applied to aid the welding process.
*Typical configurations of multi-layer contact profiles
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*Contact materials
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*Carrier materials
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*Brazing alloy
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*Quality criteria
Beause of the variety of configurations of contact profiles usually the quality
issues are separately agreed upon between the manufacturer and the user.
*Dimensions and tolerances
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The thickness of the Au top-layer, which is sputtered for example, is between 0.2
and 5 μm, depending on the requirements. Tolerance of thickness is about + 10%.
===3.3 Attachment of Single Contact Parts===
