==<!--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.

===<!--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.

==<!--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''' </caption>

|Brushes from flat rolled wire or stamped; collector hard gold electroplated or clad, or ; made from miniature profile segments

|Ag/Ni, Ag/SnO2SnO₂, (Ag/CdO), Ag/ZnO,AgNi0.15, (Ag)

|AgNi0.15, Ag/SnO2SnO₂, Ag/Ni

|PdCu15 and 40 (Anode) vs. AgNi0.15, AgCu3 (Cathode), Ag/ZnO, Ag/SnO2SnO₂

|W, Ag/SnO2SnO₂

|AgNi0.15, Ag/Ni, Ag/SnO2SnO₂, (Ag/CdO)

|AgNi0.15, Ag/Ni, Ag/SnO2SnO₂, (Ag/CdO)

 Table 6.1: '''Material Selection and Contact Component Design (Fortsetzung - 2 Teile!)'''

|Contacts for dry circuitsAutomatic staircase lighting switches|Reliable contacting at very High arc erosion and weld resistance|Ag/Ni, Ag/SnO₂, (Ag/CdO), Ag/C against Ag/SnO₂|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 currents 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/SnO₂, (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 voltages 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 mostly at alsoweld resistance, low contact resistance|AgCu, Ag/Ni, Ag/SnO<sub>2<br /sub>, Ag/ZnO, (Ag/CdO)|Rivets, welded contact parts|-|Contactors|High arc erosion and weld resistance, low contact forcesresistance|AuAg alloysI< 20A : Ag/Ni, Ag/SnO₂ I>20A : Ag/SnO₂, (AuPtAgCdO)|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, Aulow contact resistance|Contact rivetsAg/ZnO, Ag/SnO₂ , Ag/C against Ag/Ni o. Ag/W, Ag/W, Ag/WC/C, Ag/W against Ag/CdO|Brazed and welded miniature profiles 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, (tapesCu)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 Au)|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, sputtered Au layersbrazed or welded parts

|Switching contacts in measuring devicesVacuum contactors|Reliable switching at low voltages and currents at Low chopping current, high arc erosion resistance, low contact forcesresistance|Au and Pt alloysLow gas content W/Cu, W/CuSb, (AgPd alloys)WC/Ag, CuCr|Contact rivets, welded tipsdiscs, clad partsshaped rings

|Keyboard contactsVacuum circuit breakers|Defined contacting, close to bounce-free makeHigh switching capacity, high reliability at low switching loadscontact resistance|Au alloys, (AgPd), Au on Ni substrateLow gas content CuCr|Au plated snap Contact discs, Au clad wires and stamped parts, hard gold electroplated contact spots on printed circuit boards

|Rotary switches on printed circuit boardsTransformer tab changers|Good frictional wear High arc erosion resistance, low contact résistancein oil environment|Sliding track: hard gold on Ni substrate Slider: AgPd alloy, (Hard silver)W/Cu in filtrated with approx. 70%|Electroplated coatings on slide tracks; clad, welded, or riveted stamping partsBrazed contact tips

|Slip rings with Disconnect switches in high reliabilityvoltage circuits|Low and consistent contact resistance at , low contact forcesmechanical wear, sufficient arc erosion resistance during current commutation|Brushes: Au alloysAg (electroplated), AgPdAgNi0, AgPdCu; Slip rings: Au alloys15, Ag alloys (Rh); /SnO₂|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 higher currents: most of the contact materials, we deliberately did not indicate the exact composition and, as for Ag/C brushes against Ag slip ringsSnO₂ 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|Brush wiresManufacturing Technologies for Contact Parts]]). The desired contact shape however, stamped brushes; solidrequires specific material properties like formability and weldability, cladwhich cannot be fulfilled by all materials in the same way. In addition, or electroplated slip ringsthe 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, Agcontact material and specific applications.  <figtable id="tab:Design Technologies for Contacts"><caption>'''<!--Table 6.2:-->Design Technologies for Contacts'''</C formed partscaption> {| class="twocolortable" style="text-align: left; font-size: 12px"

|Sliding contacts in miniature motors|Very high frictional wear resistance!Contact Parts, sure contacting even at very low contact forcesSemi-finished Materials|Ag !Typical Contact Materials and Au alloys, Pd alloys, Au multi component alloysDimensions!Main Areas of Application|Brushes from flat rolled wire or stamped; collector hard gold electroplated or clad, or made from miniature profile segments!Remarks

|Centrifugal controllers for small motorsContact rivets solid, inserted wire segments|Little shape changesAg, Ag alloys, Au alloys, defined contacting at very low contact forces and high frequency of operation|Pd alloys, Ag/Ni, Ag/C97/3, Ag/MeO (1.2 – 8 mm Ø)|Contact rivetsAll types of switches in the communications, automotive or power distribution technology simple contact screwscomponent, welded partsuniversally 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

|ConnectorsContact rivets, clad (Composite Rivets)|Low contact resistanceAg, corrosion resistanceAg alloys, sufficient frictional wear resistanceAg/Ni, good sliding capabilitiesAg/MeO on Cu base (2 ~ 10 mm Ø)|Ag and Au alloysAll types of switches in the communications, Pd, PdNi; For automotive and consumer electronic at low operation numbers: Sn and Sn alloysor power engineering|Electroplated layers or clad, often Au flash plated, mostly Secure rivet attachment only with Ni substrate layer, stamped parts from hot tin dipped stripsufficiently thick shank (shank Ø = 1⁄2 head Ø)

|Telecommunication relaysContact rivets with brazed surface layer|Reliable contacting even at high operational frequencyTungsten and difficult to form powder metallurgical materials (i.e. Ag/C) on Cu or Fe bases (1 ~ 12 mm Ø)|AgSwitches for power engineering, AgPd, Au alloys, PdRuW layers mostly for controls|Rivets, welded profile segmentsTungsten contact to be staked (riveted) with moderate force or using orbital riveting; for Fe bases also warm-forming

|Reed relay contactsContact screws|High reliability at low currents independent of atmospheric environment|AuAny contact material on Fe and CuZn screws, brazed, (Rh1 ~ 10 mm Ø, M 2 ~ M 10)|Switch paddles FeNi with partially diffused Au, (electroplated Rh)Adjustable contacts for controls and horns|During brazing carrier may get soft

|Relays in electronic circuitsVertically welded wire segments|High reliability at low switching loads and compact device design|Au Ag, Ag alloys, Ag/Ni, AgPd, Ag Au alloys(wire 0.6 ~ 5 mm Ø)|Stamped springs from seam-welded profiles, welded miniature profile (tape) segments, contact rivetsContact parts for control functions and power engineering; economical manufacturing at higher quantities|Welding and subsequently heading or orbital forming of head shape

|GP relais (Elementary relays)Horizontally welded wire and profile segments|Low arc erosionAu alloys, Pd alloys, high weld resistanceAg, low and consistent contact resistance|Ag/Nialloys, Ag/SnO2Ni, (Ag/CdO)MeO, Ag/ZnOC in strip or profile form,AgNi0Miniature profiles - also multi-layered (profile width 0.15, (Ag2 ~ 5 mm)|Solid Contact parts for communication, measurement, controls and composite contact rivets, welded miniature profile (tape) segmentspower engineering; very economical with respect to precious metal usage|Welding synchronized to stamping / forming on special equipment

|Automotive relaysWeld buttons|Low material transferAg, low contact resistanceAg alloys, high weld resistance|AgNi0.15Ag/Ni, Ag/SnO2MeO on Steel, Ni, Monel; Ag/Ni|Contact rivetsW, welded miniature profile Ag/Mo (tape1.5 ~ 10 mm Ø) segments|Welded for example to steel springs or thermostatic bimetals for temperature controls|Metallurgical bond through simple projection welding remains strong in temperature cycling applications

|Flasher relays Tungsten weld buttons|W on Ni or Ni-plated Fe, (automotive, > 3 Mio operations2 ~ 6 mm)with weld projections|Low material transferContacts for controls, high arc erosion resistance, low contact resistance|PdCu15 ignition points and 40 (Anode) vs. AgNi0.15, AgCu3 (Cathode), Ag/ZnO, Ag/SnO2horns; arcing contacts in special relays|Contact rivets, For change-over contact welded miniature profile (tape) and strip segmentson both sides of carrier

|Breaker points (automotive ignition)Brazed contact tips|Very high arc erosion resistanceAll materials and dimensions, high switching frequencyoxide and graphite containing materials with brazable backing, carrier parts from Fe, Cu and Cu alloys, at higher strength requirements also CuCrZr or CuBe|WMedium and higher load switching devices for power engineering|Tips or discs welded to formed parts or Fe supportsBraze alloy layer with low meting point, carriers may soften during brazing

|Automotive horn contactsClad contact materials (Contact Bimetals), totally covered or with inlayed strips|High arc erosion resistance at extremely high number 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 switching operations|Wtotal, Ag/SnO2strip width starting at 2 mm|Contact rivets, W weld buttons, Clad contact springs or ; stamped and formed parts with brazed for communications and power engineering; aluminum clad for bonding capability|Metallurgical bond; inlayed strip stamped perpendicular or welded tipsat angle to strip direction; avoid bends at the cladding edges

|Appliance switchesStrips or profiles with brazed contact material layers (Toplay material)|Low contact resistanceAg, reasonable arc erosion and weld resistance|AgNi0.15Ag alloys, Ag/Ni, Ag/SnO2MeO on Cu and Cu alloy carriers, total width 10 ~ 100mm, carrier thickness 0.3 – 5 mm, (Agstrip cross section from 0.3 x 3 mm<sup>2</CdO)sup>, strip thickn. to be &le; carrier thickn.|Stationary and moving contact bridges for power engineering switching devices|Contact rivets, welded contact partslayers brazed with Ag brazing alloys; strips re-hardened during profile rolling

|Temperature controllers Seam-welded contact strips or profiles|Wire, strip, miniature profiles (Thermostatssolid or clad) welded to Cu alloy carrier strip (0.3 – 3 mm Ø or up to 5 mm width)|Defined contacting point even at slow motion makeSwitches, high operating temperatures|AgNi0.15pushbuttons, Ag/Nirelays, Ag/SnO2auxiliary contactors, (Ag/CdO)sliding contacts|Contact rivetsBroad usability, welded contact partshighly economical, weld buttonsthin spring hard carriers can be used

|Wiring devices Miniature profiles (Light switchesWeld tapes)|Low Mostly high precious contact resistancematerials, reasonable arc erosion and weld resistance|AgNi0.15double or multi layer, AgCu, Ag/Ni, with make peaks also Ag/ZnOMonel, (Ag/CdO)or Cu alloy carrier; miniature-profile width 0.2 – 2 mm|Contact rivetsWelded profile segments for contact parts in communication, welded measurement and control engineering|Manufacturing of cross-directional contact partsspots; most economical precious metal usage

Table 6.2: '''Design Technologies for Contacts (2 Teile!Fortsetzung)'''

Table {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Contact Parts, Semi-finished Materials!Typical Contact Materials and Dimensions!Main Areas of Application!Remarks|-|Clad profiles|Ag, Ag alloys, Ag/Ni, Ag/MeO, on Cu or Cu alloy carriers, all cross-sectional areas that can be drawn or rolled; Profile width: 2 ~ 10 mm|Profile segments as contact areas for low and high voltage switching devices|More complex shapes require costly tooling|-|Sintered and infiltrated parts|W-, WC-, Mo-based materials, in almost any contact shapes|Contact parts for low and high voltage switching devices|Single parts pressing; mostly with weld projec- tions and braze alloy coating on underside|-|Formed arc erosion parts|W/Cu infiltration materials, parts in almost any shapes|Arcing contacts for extreme duty switching devices, i.e. SF₆ circuit breakers|Attachment to Cu carriers by cast-on, percussion welding, electron-beam welding; rarely by brazing|-|Low gas content contact parts|W/Cu-, WC/Ag-, CuCr-based materials, rings and discs in almost any shape|Shaped contact parts for vacuum switches (contactors, power switches, circuit breakers)|Brazing to Cu carriers requires special brazing alloys|-|Cast-on contact parts|W/Cu cast on with Cu, shaped parts and rings up to 100 mm Ø|Arcing contacts in high voltage switchgear|Seamless bond interface, carriers get hardened through subsequent forming|-|Electron-beam welded contact parts|W/Cu on Cu or CuCrZr contact rods, tubes, tulips|Arcing contacts in high voltage circuit breakers|Seamless bond interface, withstands high mechanical and thermal stresses|-|Silver electroplating|Layer thickness up to 20 μm, mostly on Cu and Cu alloys|Connecting areas and no-load switching contacts in power engineering; rotary switches, sliding contacts, connectors|For switching contacts only under very low loads|-|Gold electroplating|Flash plating 0.1 – 0.2μm on Ag alloys, and Cu alloys; contact layers 0.5 – 5 μm mostly with intermediate Ni layer|Contacts with low current and voltage loads, connectors, rotary and sliding switches, contact areas on printed circuit boards|Flash plating only limited effective as corrosion resistant layer on silver contacts|-|Selectively electroplated strips|Stripe coatings: Tin plating 1- 10 μm, Ag plating 1 – 20 μm, Au plating 0.2 – 5 μm; stripe width 2 mm min, stripe distance > 2 mm; carrier material: Cu and Cu alloys, Ni alloys, stainless steel; strip thickness: 0.1 ~ 1 mm; strip width: Design Technologies 5 ~ 100 mm|Contact parts for Contacts connectors, keyboard switches, rotary and sliding switches; bondable areas (FortsetzungAu) for electronic components|Economic manufacturing for partially plated parts; hard gold with Ni intermediate layer possible but has limited formability|- |Selectively electroplated pre-stamped strips, Spot gold plating|Continuous partial electroplating of pre-stamped and coined contact spots; allprecious metals; intermediate layers of Cu or Ni; selective tinning of connector contact areas and terminal ends; carrier materials up to 1 mm thick, strip width up to ~ 80 mm|Precious metal plating of switching contacts, connector parts, and terminal pins in the communication technology|Crack-free and wear resistant layers possible since contact areas are already formed to final shape|-|Sputtered profiles|Au, Au alloys in any composition; layer thickness 0.1 – 5 μm|Contact profiles for relays, switches and keyboard contacts in the information and measuring technology|High purity contact layers for high reliability|-|Hot-dip tinned strips|All around or stripe tinning 1 ~ 15 μm|Connectors for automotive and consumer technology; screw and crimp connectors|Economic coating method; does not form (2 Teile!Sn)whiskers|}</figtable>

==<!--6.4 -->Formulas and Design Rules==

===<!--6.4.1 -->Definition of Terms and Symbols===

===<!--6.4.2 -->Contact Physics – Formulas===

===<!--6.4.3 -->Closed Contacts===

Fig<div class="multiple-images"> <figure id="fig:Rough flat surface">[[File:Rough flat surface. 6.5jpg|left|thumb|Figure1: Rough flat surface. a) before and b) during making contact with an ideally

contact areas (not to scale; dashed lines are elevation lines)]]</figure> <figure id="fig:Contact-resistance-of-crossed-rods">[[File:Contact-resistance-of-crossed-rods.jpg|right|thumb|Figure 2: Contact resistance of crossed rods as a function of the contact force for gold, silver and silver-palladium alloys]]</figure></div><div class="clear"></div>

<figtable id="tab:Thermo-electrical Voltage of Contact Materials (against Copper)"><caption>'''<!--Table 6.3: -->Thermo-electrical Voltage of Contact Materials (against Copper)'''</caption>

{| class="twocolortable" style="text-align: left; font-size: 12px"|-!!Contact Materials!Thermo-electric Voltage (0 - 100°C) [mV]|-|Pure metals|Ag<br />Au<br />Pt<br />Ir<br />Pd<br />Rh<br />Re<br />Cu<br />W<br />Mo| + 0.04<br />+ 0.06<br />+ 0.78<br />+ 0.13<br />+ 1.35<br />+ 0.08<br />+ 0.78<br />0<br />- 0.46<br />- 0.73|-|Alloys/Composite materials|AgCu 3<br />AgPd 30<br />AgPd 40<br />AgPd 50<br />AgPd 60<br />Ag/Ni 10<br />Ag/Ni 20<br />Ag/W 65<br />AuNi 5<br />AuAg 20<br />AuPt 10<br />PtW 5<br />Ptlr 10<br />Ptlr 20<br />PtRu 5<br />PtRu 10<br />PdCu 15<br />PdCu 40| + 0.026<br />+ 0.125<br />+ 0.198<br />+ 0.321<br />+ 0.412<br />+ 0.23<br />+ 0.27<br />+ 0.01<br />+ 4.7<br />+ 2.76<br />+ 1.11<br />+ 0.67<br />+ 0.56<br />+ 0.60<br />+ 0.32<br />+ 0.13<br />+ 0.180<br />+ 0.247|}</figtable> ===<!--6.4.4 -->Switching Contacts===

===<!--6.4.5 -->Physical Effects in Sliding and Connector Contacts===

===<!--6.4.6 -->General Rules for Dimensioning of Contacts===

===<!--6.4.7 -->Contact Spring Calculations===