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→Contact Materials and Design of Contact Components
==<!--6.1 --> Application Ranges for Switching Contacts==
===<!--6.1.1 -->Low and Medium Electrical Loads===Switching processes at low and medium electrical loads are experienced for example in relays and switches for the measuring technology, telecommunications, automotive usage, and appliances. The switching voltage ranges from μV to 400V with currents between μA and about 100A.
Main ArticelArticle: [[Low and Medium Electrical Loads| Low and Medium Electrical Loads]]
===<!--6.1.2 -->High Electrical Loads===At With high electric electrical loads that , as usually occur occuring in power engineering devices equipment, the switching phenomena are mostly related usually due to arc formationarcing. For most applications the management of the switching arc is the key problem. Depending on the device type , different require-ments requirements are dominant , which influence the selection of the contact material. Similar to those in communications engineering, issues related to the switching characteristics and current path have to be considered.
Main ArticelArticle: [[High Electrical Loads| High Electrical Loads]]
==<!--6.2 -->Contact Materials and Design of Contact Components==The highest reliability and electrical life of electromechanical components and switching devices can only be achieved if both, the material selection and the design of the actual contact parts, are optimized. Economic Of course, economic considerations must of course also be applied when selecting the most suitable contact material and its way of application as an electrical contact. In the following <xr id="tab:Material Selection and Contact Component Design"/><!--Table 6.1 --> recommendations are made for selected application examples for contact materials and contact shape or configuration.
<figtable id="tab:Material Selection and Contact Component Design"><caption>'''<!--Table 6.1: -->Material Selection and Contact Component Design (2 teile!)'''</caption>
Table 1: '''Material Selection and Contact Component Design (Fortsetzung)'''
{| class="twocolortable" style="text-align: left; font-size: 12px"
|-
!Type of Contacts or Devices
!Characteristic Requirements for Contacts
!Contact Material
!Design Form of Contacts
|-
|Automatic staircase lighting switches
|High arc erosion and weld resistance
|Ag/Ni, Ag/SnO<sub>2</sub>, (Ag/CdO), Ag/C against Ag/SnO<sub>2</sub>
|Rivets, welded contact parts
|-
|Miniature Circuit breakers
|Extremely high weld resistance, low temperature rise in use, sufficient arc erosion resistance
|I< 50 A: Ag/C97/3 (Cu/C) against Cu, I> 50 A : Ag/C97/3 o. 95/5 against AgCu3, Ag/Ni90/10 o. 80/20, Ag/W, Ag/WC (USA)
|Welded contact parts (Ag/C), clad stamped parts
|-
|Fault current circuit breakers
|Extremely high weld resistance, low contact resistance, high arc erosion resistance
|Stationary contact: Ag/C96/4 o. 95/5 Movable contact: Ag/Ni, Ag/MeO, Ag/W, Ag/WC, Ag/WC/C
|Welded and brazed contact parts
|-
|Micro snap switches
|Low contact resistance, no sticking during make operation
|AgNi 0,15, Ag/Ni, Ag/SnO<sub>2</sub>, (Ag/CdO)
|Rivets, clad or welded contact parts
|-
|Control and auxiliary switches
|Low contact resistance over extended life span
|Ag, AgNi 0,15, AgCu, Ag/Ni
|Rivets, clad stamped parts, (gold plated rivets), welded contact parts
|-
|Auxiliary and control relays
|High reliability over extended life span, low contact resistance
|AgNi 0,15, Ag/Ni
|Rivets, clad profile parts, welded contact parts
|-
|Cam switches (higher loads)
|High arc erosion and weld resistance, low contact resistance
|AgCu, Ag/Ni, Ag/SnO<sub>2</sub>, Ag/ZnO, (Ag/CdO)
|Rivets, welded contact parts
|-
|Contactors
|High arc erosion and weld resistance, low contact resistance
|I< 20A : Ag/Ni, Ag/SnO<sub>2</sub> I>20A : Ag/SnO<sub>2</sub>, (AgCdO)
|Welded and brazed contact tips
|-
|Motor -protective circuit breakers
|Extremely high weld resistance, low contact resistance
|Ag/ZnO, Ag/C against Ag/Ni
|Welded contact parts, toplay stamping parts
|-
|Power switches and circuit breakers
|Extremely high arc erosion and weld resistance, low contact resistance
|Ag/ZnO, Ag/SnO<sub>2</sub> , Ag/C against Ag/Ni o. Ag/W, Ag/W, Ag/WC/C, Ag/W against Ag/CdO
|Brazed and welded contact tips and formed parts
|-
|Power switches with arcing and main contacts
|High weld resistance, low contact resistance, high arc erosion resistance
|Arcing contacts: W/Ag, W/Cu, (Cu) Main contacts: Ag/Ni, Ag/ZnO, Ag/W, Ag/WC
|Brazed and welded contact tips and formed parts
|-
|Disconnect switches
|Low contact resistance, sufficient mechanical strength
|AgNi 0,15, Ag/Ni, Ag (electroplated)
|Electroplated coatings, brazed contact parts
|-
|High voltage circuit breakers
|Arcing contacts: highest arc erosion resistance Main contacts: low contact resistance
|Arcing contacts: W/Cu-infiltrated Main contact CuCrZr silver plated,
|Cast-on, electron-beam welded (or brazed) formed parts, percussion welded pins
|-
|Load disconnect switches (medium and high voltage)
|Low contact resistance, sufficient mechanical strength, high arc erosion resistance of precontacts
|Arcing contact: W/Cu, Cu, Ag/C Main contact: Cu, CuCrZr silver plated, Ag/Ni, AgNi0,15, Ag/C
|Arcing contacts: brazed or welded parts Main contacts: silver plated, brazed or welded parts
|-
|Vacuum contactors
|Low chopping current, high arc erosion resistance, low contact resistance
|Low gas content W/Cu, W/CuSb, WC/Ag, CuCr
|Contact discs, shaped rings
|-
|Vacuum circuit breakers
|High switching capacity, low contact resistance
|Low gas content CuCr
|Contact discs
|-
|Transformer tab changers
|High arc erosion resistance in oil environment
|W/Cu in filtrated with approx. 70%
|Brazed contact tips
|-
|Disconnect switches in high voltage circuits
|Low contact resistance, low mechanical wear, sufficient arc erosion resistance during current commutation
|Ag (electroplated), AgNi0,15, Ag/SnO<sub>2</sub>
|Electroplated coatings, brazed parts, Toplay profile segments
|}
'''Notes:'''
<xr id="tab:Material Selection and Contact Component Design"/><!--Table 6.1 --> is meant to give suggestions for the use of contact materials for the specified devices. For most of the contact materials , we deliberately did not indicate the exact composition and, as for Ag/SnO<sub>2</sub> and AgZnO, did also not include specific additives. The final material composition depends on specific design parameters of the electrical device. Advise on the special properties of specific contact materials can be found in chapter 2[[Contact Materials for Electrical Engineering| Contact Materials for Electrical Engineering ]]. ==<!--6.3-->Design Technologies for Contacts==A multitude of technologies is available and used for the actual manufacturing of contact components (see chapter 3 [[Manufacturing Technologies for Contact Parts|Manufacturing Technologies for Contact Parts]]). The desired contact shape however, requires specific material properties like formability and weldability, which cannot be fulfilled by all materials in the same way.In addition, the design of the contact part must be compatible with the stresses and requirements of each switching device. The following <xr id="tab:Design Technologies for Contacts"/><!--table 6.2--> combines contact design, contact material and specific applications. <figtable id="tab:Design Technologies for Contacts"><caption>'''<!--Table 6.2:-->Design Technologies for Contacts'''</caption> {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Contact Parts, Semi-finished Materials!Typical Contact Materials and Dimensions!Main Areas of Application!Remarks|-|Contact rivets solid, inserted wire segments|Ag, Ag alloys, Au alloys, Pd alloys, Ag/Ni, Ag/C97/3, Ag/MeO (1.2 – 8 mm Ø)|All types of switches in the communications, automotive or power distribution technology simple contact component, universally applied, selection through economic aspects|Secure rivet attachment only with sufficiently thick shank (shank Ø = 1⁄2 head Ø); change-over contacts by forming secondary head from longer shanks|-|Contact rivets, clad (Composite Rivets)|Ag, Ag alloys, Ag/Ni, Ag/MeO on Cu base (2 ~ 10 mm Ø)|All types of switches in the communications, automotive or power engineering|Secure rivet attachment only with sufficiently thick shank (shank Ø = 1⁄2 head Ø)|-|Contact rivets with brazed surface layer|Tungsten and difficult to form powder metallurgical materials (i.e. Ag/C) on Cu or Fe bases (1 ~ 12 mm Ø)|Switches for power engineering, W layers mostly for controls|Tungsten contact to be staked (riveted) with moderate force or using orbital riveting; for Fe bases also warm-forming|-|Contact screws|Any contact material on Fe and CuZn screws, brazed, (1 ~ 10 mm Ø, M 2 ~ M 10)|Adjustable contacts for controls and horns|During brazing carrier may get soft|-|Vertically welded wire segments|Ag, Ag alloys, Ag/Ni, AgPd, Au alloys (wire 0.6 ~ 5 mm Ø)|Contact parts for control functions and power engineering; economical manufacturing at higher quantities|Welding and subsequently heading or orbital forming of head shape|-|Horizontally welded wire and profile segments|Au alloys, Pd alloys, Ag, Ag alloys, Ag/Ni, Ag/MeO, Ag/C in strip or profile form, Miniature profiles - also multi-layered (profile width 0.2 ~ 5 mm)|Contact parts for communication, measurement, controls and power engineering; very economical with respect to precious metal usage|Welding synchronized to stamping / forming on special equipment|-|Weld buttons|Ag, Ag alloys, Ag/Ni, Ag/MeO on Steel, Ni, Monel; Ag/W, Ag/Mo (1.5 ~ 10 mm Ø)|Welded for example to steel springs or thermostatic bimetals for temperature controls|Metallurgical bond through simple projection welding remains strong in temperature cycling applications|-|Tungsten weld buttons|W on Ni or Ni-plated Fe, (2 ~ 6 mm) with weld projections|Contacts for controls, ignition points and horns; arcing contacts in special relays|For change-over contact welded on both sides of carrier|-|Brazed contact tips|All materials and dimensions, oxide and graphite containing materials with brazable backing, carrier parts from Fe, Cu and Cu alloys, at higher strength requirements also CuCrZr or CuBe|Medium and higher load switching devices for power engineering|Braze alloy layer with low meting point, carriers may soften during brazing|-|Clad contact materials (Contact Bimetals), totally covered or with inlayed strips|Ductile precious metals on Cu and Cu alloys, minimum precious metal layer 2% of total strip thickness for Ag and Ag alloys, 0.5% of total strip thickness for Au alloys (with Ni intermediate layer), max. inlayed thickness 50% of total, strip width starting at 2 mm|Clad contact springs; stamped and formed parts for communications and power engineering; aluminum clad for bonding capability|Metallurgical bond; inlayed strip stamped perpendicular or at angle to strip direction; avoid bends at the cladding edges|-|Strips or profiles with brazed contact material layers (Toplay material)|Ag, Ag alloys, Ag/Ni, Ag/MeO on Cu and Cu alloy carriers, total width 10 ~ 100mm, carrier thickness 0.3 – 5 mm, Ag strip cross section from 0.3 x 3 mm<sup>2</sup>, strip thickn. to be ≤ carrier thickn.|Stationary and moving contact bridges for power engineering switching devices|Contact layers brazed with Ag brazing alloys; strips re-hardened during profile rolling|-|Seam-welded contact strips or profiles|Wire, strip, miniature profiles (solid or clad) welded to Cu alloy carrier strip (0.3 – 3 mm Ø or up to 5 mm width)|Switches, pushbuttons, relays, auxiliary contactors, sliding contacts|Broad usability, highly economical, thin spring hard carriers can be used|-|Miniature profiles (Weld tapes)|Mostly high precious contact materials, double or multi layer, Ni, Monel, or Cu alloy carrier; miniature-profile width 0.2 – 2 mm|Welded profile segments for contact parts in communication, measurement and control engineering|Manufacturing of cross-directional contact spots; most economical precious metal usage|}
Table 6.2: '''Design Technologies for Contacts (2 Teile!Fortsetzung)'''
==<!--6.4 -->Formulas and Design Rules==
===<!--6.4.1 -->Definition of Terms and Symbols===
Note: The symbols for electrical contact specific terms (i.e. contact area,
contact resistance, etc. have been retained from the german version of the Data
used here from german R<sub>k</sub>, in english mostly R<sub>c</sub>.
Main ArticelArticle: [[Definition of Terms and Symbols| Definition of Terms and Symbols]]
===<!--6.4.2 -->Contact Physics – Formulas===
Main ArticelArticle: [[Contact Physics – Formulas| Contact Physics – Formulas]]
===<!--6.4.3 -->Closed Contacts===
smooth flat surface; c) Schematic of the apparent, load bearing and effective
contact areas (not to scale; dashed lines are elevation lines)]]</figure>
<figtable id==="tab:Thermo-electrical Voltage of Contact Materials (against Copper)"><caption>'''<!--Table 6.4.4 Switching Contacts===3:-->Thermo-electrical Voltage of Contact Materials (against Copper)'''</caption>
===<!--6.4.5 Physical Effects in Sliding and Connector 4-->Switching Contacts===
Main ArticelArticle: [[Physical Effects in Sliding and Connector Switching Contacts| Physical Effects in Sliding and Connector Switching Contacts]]
===<!--6.4.6 General Rules for Dimensioning of 5-->Physical Effects in Sliding and Connector Contacts===
Main ArticelArticle: [[General Rules for Dimensioning of Physical Effects in Sliding and Connector Contacts| General Rules for Dimensioning of Physical Effects in Sliding and Connector Contacts]]
===<!--6.4.7 Contact Spring Calculations6-->General Rules for Dimensioning of Contacts===
Main ArticelArticle: [[Contact Spring CalculationsGeneral Rules for Dimensioning of Contacts| Contact Spring CalculationsGeneral Rules for Dimensioning of Contacts]]
===<!--6.4.7-->Contact Spring Calculations=== Main Article: [[Contact Spring Calculations| Contact Spring Calculations]] ==References===
Vinaricky, E. (Hrsg): Elektrische Kontakte-Werkstoffe und Anwendungen.
Kirchdorfer, J.: Schalter für elektrische Steuerkreise, Blaue TR-Reihe, Heft 91,
Verlag Hallwag, Bern und Stuttgart 1969
[[de:Anwendungstabellen_und_Richtwerte_für_den_Einsatz_elektrischer_Kontakte]]