Changes

Tungsten is characterized by its advantageous properties of high melting and boiling points, sufficient electrical and thermal conductivity and high hardness and density ''(<xr id="tab:Mechanical_Properties_of_Tungsten_and_Molybdenum"/><!--(Table 2.35)''-->). It is mainly used in the form of brazed contact tips for switching duties , that require a rapid switching sequence , such as horn contacts for cars and trucks.

<figtable id="tab:Mechanical_Properties_of_Tungsten_and_Molybdenum"><caption>'''<!--Table 2.35: -->Mechanical Properties of Tungsten and Molybdenum'''</caption><table border="1" cellspacingclass="0" style="border-collapse:collapsetwocolortable"><tr><tdth><p class="s12">Material</p></tdth><tdth><p class="s12">Micro Structure Condition</p></tdth><tdth><p class="s12">Vickers</p><p class="s12">Hardness HV 10</p></tdth><tdth><p class="s12">Tensile Strength</p><p class="s12">[MPa]</p></tdth></tr><tr><td><p class="s12">WolframTungsten</p></td><td><p class="s12">Lightly worked structure</p><p class="s12">(wire and strip &gt; 1.0 mm thick)</p><p class="s12">Strongly worked structure</p><p class="s12">(wire and strip &lt; 1.0 mm thick)</p><p class="s12">Re-crystallized structure</p></td><td><p class="s12">300 - 500</p><p class="s12">500 - 750</p><p class="s12">360</p></td><td><p class="s12">1000 - 1800</p><p class="s12">1500 - 5000</p><p class="s12">1000 - 1200</p></td></tr><tr><td><p class="s12">MolybdänMolybdenum</p></td><td><p class="s12">Lightly worked structure</p><p class="s12">(wire and strip &gt; 1.0 mm thick)</p><p class="s12">Strongly worked structure</p><p class="s12">(wire and strip &lt; 1.0 mm thick)</p><p class="s12">Re-crystallized structure</p></td><td><p class="s12">140 - 320</p><p class="s12">260 - 550</p><p class="s12">140 - 160</p></td><td><p class="s12">600 - 1100</p><p class="s12">800 - 2500</p><p class="s12">600 - 900</p></td></tr></table></figtable>

=== Silver–Tungsten (SIWODUR) Materials===Ag/W (SIWODUR) contact materials combine the high electrical and thermal conductivity of silver with the high arc erosion resistance of the high meltingtungsten metal ''(<xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(Table 2.36)''-->). The manufacturing of materials with typically 50-80 wt% tungsten is performed by the powder metallurgical processes ofliquid phase sintering or by infiltration. Particle size and shape of the starting powders are determining the micro structure and the contact specific properties of this material group ''(Figs<xr id="fig:Micro structure of Ag W 25 75"/><!--(Fig. 2.134 and )-->, <xr id="fig:Micro structure of Ag WC 50 50"/><!--(Fig. 2.135) (Table 2.37--> and <xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/>)''.

During repeated switching under arcing loads , tungsten oxides and mixed oxides (silver tungstates – Ag₂ WO₄ ) are formed on the Ag/W surface , creating 2 4 poorly conducting layers which increase the contact resistance and by this the temperature rise during current carrying. Because of this fact the Ag/W is paired in many applications with Ag/C or Ag/WC/C contact parts.

switches and industrial circuit breakers ''(<xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(Table 2.38)''-->). In north and south america they are also used in large volumes in miniature circuit breakers of small to medium current ratings in domestic wiring as well as for commercial power distribution.

<figtable id=== Silver–Tungsten Carbide (SIWODUR C) "tab:Physical Properties of Contact Materials===This group of contact materials contains the typically 40Based on Silver-65 wtTungsten, Silver-% of the very hard Tungsten Carbide and erosion wear resistant tungsten carbide and the high conductivity silver Silver Molybdenum"><caption>'''(Fig. 2.135) (<!--Table 2.36)'7:-->Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum'. Compared to Ag/W the Ag/WC (SIWODUR C) materials exhibit a higher resistance against contact welding ''(Table 2.37)''. The rise in contact resistance experienced with Ag</W is less pronounced in Ag/WC because during arcing a protective gas layer of CO is formed which limits the reaction of oxygen on the contact surface and therefore the formation of metal oxides.caption>

Higher requirements on low temperature rise can be fulfilled by adding a small amount of graphite which however increases the arc erosion. Silver–tungsten{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Materialcarbide–graphite materials with for example 27 !Silver<br/>Content<br/>[wt.% ]!Density<br/>[g/cm³]!Electrical<br/>Conductivity<br/>[MS/m]!Vickers<br/>Hardness<br/>[HV5]|-|Ag/W 50/50 [[#text-reference|¹]]<br/>|47 - 53|12,9 - 13,9|29 - 38|110 - 175|-|Ag/W 40/60 [[#text-reference|¹]]|37 - 43|13,9 - 14,5|21 - 32|150 - 240|-|Ag/W 35/65 [[#text-reference|¹]]|32 - 38|14,1 - 15,1|21 - 31|160 - 260|-|Ag/W 32/68 [[#text-reference|¹]]|29 - 35|14,3 - 15,2|21 - 30|180 - 265|-|Ag/WC and 60/40 [[#text-reference|¹]]|57 - 63|11,6 - 12,2|21 - 29|140 - 200|-|Ag/WC 40/60 [[#text-reference|¹]]|37 - 43|12,5 - 13,3 wt% graphite or |18 - 25|230 - 340|-|Ag/WC 80/16C2 [[#text-reference|²]]|80 - 84|9,2 - 9,9|30 - 38|35 - 55|-|Ag/WC 80/17C3 [[#text-reference|²]]|78 - 82|9,1 - 9,8|23 - 33|35 - 55|-|Ag/WC 80/19C1 [[#text-reference|²]]|78 - 82|9,5 - 10,5|28 - 43|40 - 60|-|Ag/WC 70/28C2 [[#text-reference|²]]|68 - 72|9,6 - 10,3|24 - 32|35 - 55|-|Ag/Mo 65/35 [[#text-reference|¹]]|62 - 68|9,9 - 10,9|16 wt% WC and - 28|140 - 130|-|}<div id="text-reference">₁manufactured by infiltration</div><div id="text-reference">_{2 wt% graphite are} manufactured using the single tip by press-sinter-repress (PSR) process ''(Fig. 2.136)''.</div></figtable>

The applications === Silver–Tungsten Carbide Materials===This group of contact materials contains typically 40-65 wt-% of the very hard and erosion wear resistant tungsten carbide and the high conductivity silver (<xr id="fig:Micro structure of AgWC 50 50"/><!--(Fig. 2.135)--> and <xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/WC contacts are similar ><!--(Table 2.36)-->). Compared to those for Ag/W ''the Ag/WC materials exhibit a higher resistance against contact welding (<xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(Table 2.3837)-->)''. The rise in contact resistance experienced with Ag/W is less pronounced in Ag/WC because during arcing, a protective gas layer of CO is formed, which limits the reaction of oxygen on the contact surface and therefore the formation of metal oxides.

=== Silver–Molybdenum (SILMODUR) Materials===Ag/Mo Higher requirements on low temperature rise can be fulfilled by adding a small amount of graphite, which however increases the arc erosion. Silver–tungsten-carbide–graphite materials with typically 50-70 for example 19 wt% WC and 1 wt% graphite or 16 wt% WC and 2 wt% molybdenum graphite are usually produced by manufactured using the powder metallurgical infiltration process ''single tip press-sinter-repress (Fig. 2.137PSR) process (Table 2.36)''. Their contact properties are similar to those <xr id="fig:Micro structure of -AgWC 27 C3"/W materials ''><!--(Table Fig. 2.37136)''. Since the molybdenum oxide is thermally less stable than tungsten oxide the self-cleaning effect of Ag/Mo contact surface during arcing is more pronounced and the contact resistance remains lower than that of Ag/W. The arc erosion resistance of Ag/Mo however is lower than the one for Ag/W materials. The main applications for Ag/Mo contacts are in equipment protecting switching devices ''(Table 2.38->)''.

Fig. 2.134: Micro structure The applications of Ag/W 25/75[[File:Micro structure of Ag W 25 75.jpg|right|thumb|Micro structure of WC contacts are similar to those for Ag/W 25/75]]Fig. 2.135(<xr id="tab: Micro structure Contact and Switching Properties of AgContact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/WC 50/50[[File:Micro structure of Ag WC 50 50.jpg|right|thumb|Micro structure of Ag/WC 50/50]]Fig. ><!--(Table 2.136: Micro structure of Ag/WC27/C3[[File:Micro structure of 38)--Ag WC 27 C3.jpg|right|thumb|Micro structure of Ag/WC27/C3]]Fig>). 2.137: Micro structure of Ag/Mo 35/65[[File:Micro structure of Ag Mo 35 65.jpg|right|thumb|Micro structure of Ag/Mo 35/65]]

'''=== Silver–Molybdenum Materials===Ag/Mo materials with typically 50-70 wt% molybdenum are usually produced by the powder metallurgical infiltration process (<xr id="fig:Micro structure of Ag Mo 35 65"/><!--(Fig. 2.137)--> and <xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(Table 2.36)-->). Their contact properties are similar to those of Ag/W materials (<xr id="tab: Physical Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(Table 2.37)-->). Since the molybdenum oxide is thermally less stable than tungsten oxide, the self-cleaning effect of Ag/Mo contact surface during arcing is more pronounced and the contact resistance remains lower than that of Ag/W. The arc erosion resistance of Ag/Mo however is lower than the one for Ag/W materials. The main applications for Ag/Mo contacts are in equipment protecting switching devices (<xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR),Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''"/><!--(Table 2.38)-->).

[[File:Physical Properties of<div class="multiple-Contact Materials Based.jpg|right|thumb|Physical Properties of Contact Materials Based on Silver–Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)]]images">

'''Table 2<figure id="fig:Micro structure of Ag W 25 75"> [[File:Micro structure of Ag W 25 75.37jpg|left|thumb|<caption>Micro structure of Ag/W 25/75</caption>]]</figure><figure id="fig: Contact and Switching Properties Micro structure of Contact Materials Based on Silver – TungstenAg WC 50 50"> [[File:Micro structure of Ag WC 50 50.jpg|left|thumb|<caption>Micro structure of Ag/WC 50/50</caption>]]</figure><figure id="fig:Micro structure of -Ag WC 27 C3"> [[File:Micro structure of -Ag WC 27 C3.jpg|left|thumb|<caption>Micro structure of Ag/WC27/C3</caption>]]</figure><figure id="fig:Micro structure of Ag Mo 35 65"> [[File:Micro structure of Ag Mo 35 65.jpg|left|thumb|<caption>Micro structure of Ag/Mo 35/65</caption>]]</figure></div>(SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''<div class="clear"></div>

<table borderfigtable id="1tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)" cellspacing="0" style><caption>'''<!--Table 2.37:-->Contact and Switching Properties of Contact Materials Based on Silver – Tungsten, Silver–Tungsten Carbide and Silver Molybdenum'''</caption><table class="border-collapse:collapsetwocolortable"><tr><tdth><p class="s12">Material/ DODUCO- Designation</p></tdth><tdth><p class="s12">Properties</p></tdth></tr><tr><td><p class="s12">Silver-Tungsten</p><p class="s12">SIWODUR</p><p class="s12">Silver-tungsten carbide SIWODUR C</p></td><td><p class="s12">Tendency to weld at high make currents in symmetrical pairing,</p><p class="s12">Higher contact resistance and higher temperature rise over increased number of operations through tungsten oxide and tungstate formation, especially for Ag/W,</p><p class="s12">High welding tendency of closed contacts during short circuit,</p><p class="s12">Very high arc erosion resistance, poor arc moving properties, High hardness and low formability,</p><p class="s12">Easy to braze and weld through Ag enriched backing layer</p></td></tr><tr><td><p class="s12">Silver-Tungsten Carbide plus Grafit SIWODUR C PlusGraphite</p></td><td><p class="s12">Low contact resistance and low temperature rise through graphite addition,</p><p class="s12">Lower tendency to contact welding, Lower arc erosion resistance than Ag/WWC</p></td></tr><tr><td><p class="s12">Silver-Molybdenum</p><p class="s12">SILMODUR</p></td><td><p class="s12">Better contact resistance stability due to less stable surface layers,</p><p class="s12">Lower arc erosion resistance than Ag/W</p></td></tr></table></figtable>

<figtable id=== Copper–Tungsten "tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (CUWODURSIWODUR C) Materials===Copper–tungsten and Silver Molybdenum (CUWODURSILMODUR) materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selected">according to the end application <caption>'''(Figs. <!--Table 2.138 38:-->Contact and Switching Properties of Contact Materials Based on Silver – 2.141) (Table 2.39)Tungsten, Silver–Tungsten Carbide and Silver Molybdenum'''. To increase the wettability of the tungsten skeleton by copper a small amount of nickel < 1 wt% is added to the starting powder mix./caption>

{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Material !Application Examples!Form of Supply|-|Ag/W<br />|Circuit breakers (not current limiting)|rowspan="3" | Contact tips, brazed and welded<br />contact parts|-|Ag/W<br /><br />Ag/WC<br /><br />Ag/WC/C<br /Cu materials exhibit a very high arc erosion resistance ''> |(Table 2.40Main)''. Compared to silver–tungsten materials they are however less suitable to carryPower switches<br /> paired with Ag/C)<br />permanent Fault current.circuit breakers<br />(paired with Ag/C)|-|Ag/Mo<br />|Device protection switches|}</figtable>

With a solid tungsten skeleton as it is the case for W/C infiltrated === Copper–Tungsten Materials===Copper–tungsten materials with 70typically 50-85 wt% tungsten are produced by the infiltration process with the lower melting component copper melts and vaporizes in tungsten particle size selected according to the intense electrical arcend application [[#figures4|(Figs. At the boiling point 5 – 6)]] <!--(Figs. 2.138 – 2.141)--> and (<xr id="tab:Physical properties of copper -tungsten materials"/><!--(2567°CTable 2.39) -->). To increase the wettability of the still solid tungsten skeleton by copper a small amount of nickel < 1 wt% is efficiently “cooled” and remains pretty much unchangedadded to the starting powder mix.

During very high thermal stress on the W/Cu contacts, for example during short circuit currents <figtable id="tab:Physical properties of copper-tungsten materials"><caption> 40 kA the tungsten skeleton requires special high mechanical strength. For such applications a high temperature sintering '''Physical properties of copper-tungsten from selected particle size powder is applied before the usual infiltration with copper (example: CUWODUR H).materials'''</caption>

For high voltage load switches the most advantageous contact system consists of a contact tulip and a contact rod{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Material!Tungsten<br/>Content<br/>[wt. Both contact assemblies are made usually from the mechanically strong and high conductive CuCrZr material and %]!Density<br/>[g/cm³]!Melting Point<br/>[°C]!Electrical<br/>Resistivity<br/>[µΩ*cm]!Electrical<br/>Conductivity<br/>[% IACS]!Electrical<br/>Conductivity<br/>[MS/m]!Vickers<br/>Hardness<br/>[HV10]|-|W/Cu as the arcing tips. The thermally and mechanically highly stressed attachment between the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion welding. Other attachment methods include brazing and cast60/40 <br/>|57 - 63|12,9 - 13,3|1083|3,85 - 4,55|38 - 45|22 - 26|150 - 200|-|W/Cu 65/35|63 - 67|13,6 - 14,0|1083|4,17 - 5,0|34 - 41|20 - 24|160 - 210|-|W/Cu 70/30 |68 - 72|13,9 - 14,4|1083|3,85 - 5,56|31 - 38|18 - 22|160 - 230|-|W/Cu 75/25 |73 - 77|14,6 - 15,2|1083|4,76 - 5,88|29 - 36|17 - 21|180 - 210|-|W/Cu 80/20|78 - 82|15,3 - 15,9|1083|5,0 - 6,25|28 - 34|16 - 20|180 - 280|-on of copper followed by cold forming steps to increase hardness and strength.|}</figtable>

The main application areas for CUWODUR W/Cu materials are as arcing contacts in load and high power switching in medium and exhibit a very high voltage switchgear as wellas electrodes for spark gaps and over voltage arresters ''(Table 2arc erosion resistance.41)''Compared to silver–tungsten materials, they are however less suitable to carry permanent current.

'''Table 2With a solid tungsten skeleton, as it is the case for W/C infiltrated materials with 70-85 wt% tungsten, the lower melting component copper melts and vaporizes in the intense electrical arc.39: Physical Properties At the boiling point of Copper–Tungsten copper (CUWODUR2567°C) Contact Materials''', the still solid tungsten is efficiently “cooled” and remains pretty much unchanged.

[[File:Physical Properties During very high thermal stress on the W/Cu contacts, for example during short circuit currents > 40 kA, the tungsten skeleton requires special high mechanical strength. For such applications, a high temperature sintering of Copper Tungsten CUWODUR Contact Materialstungsten from selected particle size powder is applied before the usual infiltration with copper.jpg|right|thumb|Physical Properties of Copper Tungsten (CUWODUR) Contact Materials]]2-teilig

Fig. 2.139: Micro structure of W/Cu 70/30 G[[File:Micro structure For high voltage load switches, the most advantageous contact system consists of W Cu 70 30 Ga contact tulip and a contact rod.jpg|right|thumb|Micro structure of Both contact assemblies are usually made from the mechanically strong and high conductive CuCrZr material and W/Cu 70/30 G]]Figas the arcing tips. 2.140: Micro structure of W/Cu 70/30 H[[File:Micro structure of W Cu 70 30 HThe thermally and mechanically highly stressed attachment between the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion welding.jpg|right|thumb|Micro structure Other attachment methods include brazing and cast-on of W/Cu 70/30 H]]Figcopper, followed by cold forming steps to increase hardness and strength. 2.138: Micro structure of W/Cu 70/30 F [[File:Micro structure of W Cu 70 30 F.jpg|right|thumb|Micro structure of W/Cu 70/30 F]]Fig. 2.141: Micro structure of W/Cu 80/20 H[[File:Micro structure of W Cu 80 20 H.jpg|right|thumb|Micro structure of W/Cu 80/20 H]]

'''Table 2.40:''' Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s12">Material/ DODUCO- Designation</p></td><td><p class="s12">Properties</p></td></tr><tr><td><p class="s12">The main application areas for W/Cu F</p><p class="s12">CUWODUR F</p></td><td><p class="s12">Very high arc erosion resistance,</p><p class="s12">Uniform erosion pattern after high operation frequency, Very high mechanical strength,</p><p class="s12">Highly resistant against thermal materials are as arcing contacts in load and mechanical shock</p></td></tr><tr><td><p class="s12">W/Cu G</p><p class="s12">CUWODUR G</p></td><td><p class="s12">Very high arc erosion resistance, Very high mechanical strengthpower switching,</p><p class="s12">Highly resistant against thermal in medium and mechanical shock.</p></td></tr><tr><td><p class="s12">W/Cu H</p><p class="s12">CUWODUR H</p></td><td><p class="s12">Very high arc erosion resistance, very high mechanical strength, Especially high resistance against thermal voltage switchgear as well as electrodes for spark gaps and mechanical shockover voltage arresters.</p></td></tr></table>

'''Table 2.41: Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials'''<table border="1" cellspacing="0" stylediv class="bordermultiple-collapse:collapseimages"><tr><td><p classfigure id="s12">Material</p></td><td><p class="s12">Application Examples</p></td><td><p class="s12">Form fig:Micro structure of Supply</p></td></tr><tr><td><p class="s12">W/Cu F</p></td><td><p class="s12">Transformer tap changers,</p><p class="s12">Medium voltage circuit breakers</p></td><td><p class="s12">Contact tips, formed parts, brazed</p><p class="s12">and welded contact parts</p></td></tr><tr><td><p class="s1270 30 G">[[File:Micro structure of W/Cu 70 30 G.jpg|left|thumb|</pcaption><Micro structure of W/td><td><p class="s12">Overvoltage arresters with spark gap,<Cu 70/p><p class="s12">Medium voltage circuit breakers, Medium voltage power switches, High voltage power switches and circuit breakers30 (coarse)</pcaption>]]</td><tdfigure> <p classfigure id="s12fig:Micro structure of W Cu 70 30 F">Contact tips, formed parts, brazed</p>[[File:Micro structure of W Cu 70 30 F.jpg|left|thumb|<p class="s12">and welded contact parts; Contact tulips, rods and tubes</p></td></tr><tr><td><p class="s12"caption>Micro structure of W/Cu H<70/p>30 (fine)</tdcaption><td><p class="s12">High voltage power switches and circuit]]</pfigure><p class="s12">breakers for very high short circuit currents </p></td><tddiv><p div class="s12clear">Welded contact parts; Contact tulips,</p><p class="s12">rods</p></td></tr></tablediv>