Anwendungstabellen und Richtwerte für den Einsatz elektrischer Kontakte

Anwendungsbereiche für schaltende Kontakte

Kleine und mittlere elektrische Last

Schaltvorgänge bei kleinen und mittleren elektrischen Lasten treten z.B. in Relais und Schaltern der Messtechnik, Informationstechnik, Kfz-Technik und Hausgerätetechnik auf. Die Schaltspannung liegt dabei üblicherweise zwischen μV und 400 V, der Schaltstrom zwischen μA und ca. 100 A.

siehe Artikle: Kleine und mittlere elektrische Last

Hohe elektrische Last

Bei hohen elektrischen Lasten, die überwiegend im Bereich der Energietechnik auftreten, sind die Schaltvorgänge weitgehend mit dem Auftreten von Lichtbögen verbunden. Die Beherrschung des Schaltlichtbogens ist in den meisten Anwendungen das zentrale Problem. Je nach Schaltgerätetyp stehen bestimmte Anforderungen im Vordergrund, nach denen die Wahl des Kontaktwerkstoffes erfolgt. Wie in der Informations- und Nachrichtentechnik sind dabei die Probleme zu berücksichtigen, die bei den Schaltvorgängen und der Stromführung auftreten.

siehe Artikle: Hohe elektrische Last

Werkstoffbestückung von Kontaktstellen

Eine hohe Kontaktzuverlässigkeit und hohe Lebensdauer von elektromechanischen Bauelementen und Schaltgeräten wird nur dann erreicht, wenn den Anforderungen entsprechend der optimale Kontaktwerkstoff und die geeignetste Kontaktform eingesetzt werden. Bei der Festlegung des Kontaktwerkstoffes und der technologischen Gestaltung der Kontaktstellen müssen allerdings auch wirtschaftliche Gesichtspunkte berücksichtigt werden. In der folgenden Tabelle (Table 1) sind anhand einiger Anwendungsbeispiele Vorschläge für die Wahl des Kontaktwerkstoffes und der Kontaktform aufgelistet.

Table 1: Werkstoffbestückung von Kontaktteilen

Type of Contacts or Devices	Characteristic Requirements for Contacts	Contact Material	Design Form of Contacts
Contacts for dry circuits	Reliable contacting at very low currents and voltages and mostly at also low contact forces	AuAg alloys, (AuPt), Au	Contact rivets, welded miniature profiles (tapes), electroplated Au, sputtered Au layers
Switching contacts in measuring devices	Reliable switching at low voltages and currents at low contact forces	Au and Pt alloys, (AgPd alloys)	Contact rivets, welded tips, clad parts
Keyboard contacts	Defined contacting, close to bounce-free make, high reliability at low switching loads	Au alloys, (AgPd), Au on Ni substrate	Au plated snap discs, Au clad wires and stamped parts, hard gold electroplated contact spots on printed circuit boards
Rotary switches on printed circuit boards	Good frictional wear resistance, low contact résistance	Sliding track: hard gold on Ni substrate Slider: AgPd alloy, (Hard silver)	Electroplated coatings on slide tracks; clad, welded, or riveted stamping parts
Slip rings with high reliability	Low and consistent contact resistance at low contact forces	Brushes: Au alloys, AgPd, AgPdCu; Slip rings: Au alloys, Ag alloys (Rh); For higher currents: Ag/C brushes against Ag slip rings	Brush wires, stamped brushes; solid, clad, or electroplated slip rings, Ag/C formed parts
Sliding contacts in miniature motors	Very high frictional wear resistance, sure contacting even at very low contact forces	Ag and Au alloys, Pd alloys, Au multi component alloys	Brushes from flat rolled wire or stamped; collector hard gold electroplated or clad, or made from miniature profile segments
Centrifugal controllers for small motors	Little shape changes, defined contacting at very low contact forces and high frequency of operation	Pd alloys	Contact rivets, contact screws, welded parts
Connectors	Low contact resistance, corrosion resistance, sufficient frictional wear resistance, good sliding capabilities	Ag and Au alloys, Pd, PdNi; For automotive and consumer electronic at low operation numbers: Sn and Sn alloys	Electroplated layers or clad, often Au flash plated, mostly with Ni substrate layer, stamped parts from hot tin dipped strip
Telecommunication relays	Reliable contacting even at high operational frequency	Ag, AgPd, Au alloys, PdRu	Rivets, welded profile segments
Reed relay contacts	High reliability at low currents independent of atmospheric environment	Au, (Rh)	Switch paddles FeNi with partially diffused Au, (electroplated Rh)
Relays in electronic circuits	High reliability at low switching loads and compact device design	Au alloys, AgPd, Ag alloys	Stamped springs from seam-welded profiles, welded miniature profile (tape) segments, contact rivets
GP relais (Elementary relays)	Low arc erosion, high weld resistance, low and consistent contact resistance	Ag/Ni, Ag/SnO2, (Ag/CdO), Ag/ZnO,AgNi0.15, (Ag)	Solid and composite contact rivets, welded miniature profile (tape) segments
Automotive relays	Low material transfer, low contact resistance, high weld resistance	AgNi0.15, Ag/SnO2, Ag/Ni	Contact rivets, welded miniature profile (tape) segments
Flasher relays (automotive, > 3 Mio operations)	Low material transfer, high arc erosion resistance, low contact resistance	PdCu15 and 40 (Anode) vs. AgNi0.15, AgCu3 (Cathode), Ag/ZnO, Ag/SnO2	Contact rivets, welded miniature profile (tape) and strip segments
Breaker points (automotive ignition)	Very high arc erosion resistance, high switching frequency	W	Tips or discs welded to formed parts or Fe supports
Automotive horn contacts	High arc erosion resistance at extremely high number of switching operations	W, Ag/SnO2	Contact rivets, W weld buttons, springs or formed parts with brazed or welded tips
Appliance switches	Low contact resistance, reasonable arc erosion and weld resistance	AgNi0.15, Ag/Ni, Ag/SnO2, (Ag/CdO)	Contact rivets, welded contact parts
Temperature controllers (Thermostats)	Defined contacting point even at slow motion make, high operating temperatures	AgNi0.15, Ag/Ni, Ag/SnO2, (Ag/CdO)	Contact rivets, welded contact parts, weld buttons
Wiring devices (Light switches)	Low contact resistance, reasonable arc erosion and weld resistance	AgNi0.15, AgCu, Ag/Ni, with make peaks also Ag/ZnO, (Ag/CdO)	Contact rivets, welded contact parts

Table 1: Werkstoffbestückung von Kontaktteilen (Fortsetzung)

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/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 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 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/SnO2, Ag/ZnO, (Ag/CdO)	Rivets, welded contact parts
Contactors	High arc erosion and weld resistance, low contact resistance	I< 20A : Ag/Ni, Ag/SnO2 I>20A : Ag/SnO2, (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/SnO2 , 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/SnO2	Electroplated coatings, brazed parts, Toplay profile segments

Anmerkungen: Table 1 soll Hinweise geben, welche Kontaktwerkstoffe grundsätzlich für den jeweiligen Gerätetyp eingesetzt werden. Bei den aufgeführten Kontaktwerkstoffen wurde teilweise bewusst auf die Angabe der genauen Zusammensetzung und, wie bei Ag/SnO₂ und Ag/ZnO, der Art der Zusätze verzichtet, da eine endgültige Werkstofffestlegung auch von spezifischen konstruktiven Gegebenheiten des Gerätes abhängt. Hinweise auf spezielle Eigenschaften der Kontaktwerkstoffe sind aus Kap. 2 Kontaktwerkstoffe für die Elektrotechnik zu entnehmen.

Technologische Gestaltung von Kontaktstellen

Für die Herstellung von Kontaktteilen steht eine große Vielfalt an Technologien zur Verfügung (Kap. 3 Technologien für die Herstellung von Kontaktteilen). Die gewünschte Kontaktform setzt allerdings bestimmte Werkstoffeigenschaften z.B. Umform-, Schweißbarkeit usw. voraus, die nicht von allen Kontaktwerkstoffen gleich gut erfüllt werden. Darüber hinaus muss die Gestaltung der Kontaktstelle auf die Beanspruchung im jeweiligen Schaltgerät abgestimmt werden. Die nachfolgende Tabelle (Table 2) stellt eine Verknüpfung von Kontaktteil, Kontaktwerkstoff und Anwendung dar.

Table 2: Technologische Gestaltung von Kontaktstellen

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 engine- ering; 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 mm2, 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 2: Technologische Gestaltung von Kontaktstellen (Fortsetzung)

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 – 0.2 μm 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: 5 ~ 100 mm	Contact parts for connectors, keyboard switches, rotary and sliding switches; bondable areas (Au) 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; all precious 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 (Sn) whiskers

Formeln und Regeln

Begriffe

siehe Artikel: Begriffe

Formeln aus der Kontaktphysik

Main Artikel: Formeln aus der Kontaktphysik

Geschlossene Kontakte

Figure 1 Raue ebene Oberfläche. a) vor und b) während der Berührung mit einer ideal glatten, ebenen Fläche; c) Darstellung der scheinbaren, tragenden und wirksamen Kontaktfläche (Maßstäbe willkürlich; gestrichelte Linien sind Höhenlinien)

Figure 2 Kontaktwiderstand gekreuzter Rundstäbe in Abhängigkeit von der Kontaktkraft für Gold, Silber und Silber-Palladium-Legierungen

Raue ebene Oberfläche. a) vor und b) während der Berührung mit einer ideal glatten, ebenen Fläche; c) Darstellung der scheinbaren, tragenden und wirksamen Kontaktfläche (Maßstäbe willkürlich; gestrichelte Linien sind Höhenlinien)

Kontaktwiderstand gekreuzter Rundstäbe in Abhängigkeit von der Kontaktkraft für Gold, Silber und Silber-Palladium-Legierungen

Table 3: Thermospannung von Kontaktwerkstoffen (gegen Kupfer)

	Contact Materials	Thermo-electric Voltage (0 - 100°C) [mV]
Pure metals	Ag Au Pt Ir Pd Rh Re Cu W Mo	+ 0.04 + 0.06 + 0.78 + 0.13 + 1.35 + 0.08 + 0.78 0 - 0.46 - 0.73
Alloys/Composite materials	AgCu 3 AgPd 30 AgPd 40 AgPd 50 AgPd 60 Ag/Ni 10 Ag/Ni 20 Ag/W 65 AuNi 5 AuAg 20 AuPt 10 PtW 5 Ptlr 10 Ptlr 20 PtRu 5 PtRu 10 PdCu 15 PdCu 40	+ 0.026 + 0.125 + 0.198 + 0.321 + 0.412 + 0.23 + 0.27 + 0.01 + 4.7 + 2.76 + 1.11 + 0.67 + 0.56 + 0.60 + 0.32 + 0.13 + 0.180 + 0.247

Schaltende Kontakte

siehe Artikel: Schaltende Kontakte

Physikalische Effekte bei Gleit- und Steckkontakten

siehe Artikel: Physikalische Effekte bei Gleit- und Steckkontakten

Faustregeln für die Kontaktdimensionierung

siehe Artikel: Faustregeln für die Kontaktdimensionierung

Berechnung von Kontaktfedern

siehe Artikel: Berechnung von Kontaktfedern

Referenzen

Vinaricky, E. (Hrsg): Elektrische Kontakte-Werkstoffe und Anwendungen. Springer-Verlag, Berlin, Heidelberg 2002

Schröder, K.-H.: Grundlagen der Werkstoffauswahl für elektrische Kontakte. Buchreihe „Kontakt & Studium“, Band 366:zit. in „Werkstoffe für elektrische Kontakte und ihre Anwendungen“, Expert Verlag, Renningen, Bd. 366, (1997) 1-30

Horn, J.: „Steckverbinder“. zit. in Vinaricky, E. (Hrsg): „Elektrische Kontakte- Werkstoffe und Anwendungen“, Springer-Verlag, Berlin, Heidelberg 2002, 401- 419

Holm, R.: Electric Contacts, Springer-Verlag, Berlin, Heidelberg, New York 1967

Sauer, H. (Hrsg): Relais-Lexikon. 2. Aufl. Hüthig-Verlag, Heidelberg 1985

Greenwood J.A.: Constriction Resistance and the Area of Contact, Brit.J.Appl.Phys. 17 (1966) 1621

Biefer, H.: Elektrische Kontakte, Technische Rundschau (Bern) (1954/10) 17

Thielecke, K.: Anwendung von Kontakten in Schwachstromschaltern, in “Kontaktwerkstoffe in der Elektrotechnik”, Akademie-Verlag Berlin 1962, 107

Kirchdorfer, J.: Schalter für elektrische Steuerkreise, Blaue TR-Reihe, Heft 91, Verlag Hallwag, Bern und Stuttgart 1969