Changes

described in DIN EN 1652 (<xr id="tab:MaterialDesignations"/> and <xr id="tab:Composition of Some Pure Copper Types"/><!--5.2-->). (<xr id="tab:Physical Properties of Some Copper Types"/><!--Tables 5.3.--> and <xr id="tab:Mechanical Properties of Some Copper Types"/><!--5.4-->) show the physical and mechanical properties of these copper materials. According to these, Cu-ETP, Cu-OFE and Cu-HCP are the types of copper for which minimum values for the electrical conductivity are guaranteed.

[[File:Influence of small additions on the electrical conductivity of copper.jpg|right|thumb|Figure 4: Influence of small additions on the electrical conductivity of copper]]

For spring contact components, the interdependent relations between electrical conductivity and fatigue strength, or electrical conductivity and relaxation behavior are of main importance. The first case is critical for higher load relay springs. CuAg2 plays an important role for these applications. The latter is critical for components that are exposed to continuing high mechanical stresses like for example in connectors. The spring force must stay close to constant over the expected life time of the parts, even at elevated temperatures from the environment or current carrying. In this case, the relaxation behavior of the copper materials, which may cause a decrease in spring force over time, must be considered. Besides this, easy forming during manufacturing must be possible; this means, that bending operations can also be performed at high mechanical strength values.

Because of its low electrical conductivity , NiCu30Fe is besides pure Ni and CuNi alloys the most widely used backing material for weldable contact components. With 1 – 2 wt% additives of Fe as well as 0.5 – 1 wt% Mn and Co, the mechanical strength of the binary alloy NiCu30 can be increased.

[[File:Strain hardening of NiCu30Fe by cold working.jpg|right|thumb|Figure 7: Strain hardening of NiCu30Fe by cold working]]

[[File:Softening of NiCu30Fe after annealing for 0.5 hrs.jpg|right|thumb|Figure 8: Softening of NiCu30Fe after annealing for 0.5 hrs and after 80% cold working]]

Because of decreasing solubility of beryllium in nickel with decreasing temperature, NiBe can be precipitation hardened similar to CuBe (<xr id="fig:Phase diagram of nickel beryllium"/><!--(Fig. 5.49)-->). The maximum soluble amount of Be in Ni is 2.7 wt% at the eutectic temperature of 1150°C. To achieve a high hardness by precipitation hardening, NiBe similar to CuBe, is annealed at 970 - 1030°C and rapidly quenched to room temperature. Soft annealed material is easily cold formed and after stamping and forming a hardening anneal is performed at 480 to 500°C for 1 to 2 hours.

[[File:Phase diagram of nickel beryllium.jpg|right|thumb|Figure 9: Phase diagram of nickel-beryllium]]

Commercial nickel-beryllium alloys contain 2 wt% Be. Compared to CuBe2 the NiBe2 materials have a significantly higher modulus of elasticity but a much lower electrical conductivity. The mechanical strength is higher than that of CuBe2 (<xr id="fig:Precipitation hardening of NiBe2 soft at 480C"/><!--(Fig. 5.50)-->), the spring bending force limit can exceed values of over 1400 MPa and the fatigue strength reaches approximately 400 MPa.

[[File:Precipitation hardening of NiBe2 soft at 480C.jpg|right|thumb|Figure 10: Precipitation hardening of NiBe2 (soft) at 480°C]]

A further advantage of NiBe2 is its high temperature stability. Cold worked and subsequently precipitation hardened , NiBe2 can withstand sustained

Manufacturing of triple-layer carrier materials is usually performed by cold rollcladding. The three materials cover each other completely. The advantage of this composite material group is, that the different mechanical and physical properties of the individual components can be combined with each other.

Thermostatic bimetals are composite materials , consisting of two or three layers of materials, with different coefficients of thermal expansion. They are usually bonded together by cladding. If such a material part is heated, either directly through current flow or indirectly through heat conduction or radiation, the different expansion between the active (strong expansion) and passive (low expansion) layer causes bending of the component part.

The wide variety of thermostatic bimetal types is specified mostly through DIN 1715 and/or applicable ASTM standards (<xr id="tab:Partial Selection from the Wide Range of Available Thermo-Bimetals"/><!--(Table 5.23)-->). The different types have varying material compositions for the active and passive side of the materials. The mostly used alloys are iron-nickel and manganese-copper-nickel. Mainly used in circuit protection switches (i.e. circuit breakers) , some thermo-bimetals include an intermediate layer of copper or nickel which allows to design parts with a closely controlled electrical resistance.

For the design and calculation of the most important thermostatic-bimetal parts, formulas are given in (<xr id="tab:Design Formulas for Thermostatic Bimetal Components"/><!--Table 5.24-->). The necessary properties can be extracted for the most common materials from (<xr id="tab:Partial Selection from the Wide Range of Available Thermo-Bimetals"/><!--Table 5.23-->). The values given are valid only for a temperature range up to approximately 150°C. For higher temperatures ; data can be obtained from the materials manufacturer.

For all calculations according to the formulas in (<xr id="tab:Design Formulas for Thermostatic Bimetal Components"/><!--Table 5.24--> ) one should check if the thermally or mechanically induced stress forces stay below the allowed bending force limit. The following formulas are applicable for calculating the allowable load (Force P_max or momentum M_max):