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.

<tr><th><p class="s12">Material</p></th><th><p class="s12">Micro Structure Condition</p></th><th><p class="s12">Vickers</p><p class="s12">Hardness HV 10</p></th><th><p class="s12">Tensile Strength</p><p class="s12">[MPa]</p></th></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>

=== 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 melting tungsten metal (<xr id="tab:Physical Properties of-Contact Materials Basedon 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 of liquid 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 (<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)-->, and <xr id="tab:Contact and Switching Physical Properties of Contact Materials Based on Silver – -Tungsten (SIWODUR), Silver–Tungsten Silver-Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(Table 2.37)-->.

During repeated switching under arcing loads , tungsten oxides and mixed oxides (silver tungstates – Ag₂ WO₄ ) are formed on the Ag/W surface , creating 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.

=== Silver–Tungsten Carbide (SIWODUR C) Materials===This group of contact materials contains the 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 Ag WC 50 50"/><!--(Fig. 2.135)--> <xr figtable id="tab:Physical Properties of-Contact Materials Basedon Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><caption>'''<!--(Table 2.36)7:-->. Compared to Ag/W the Ag/WC (SIWODUR C) materials exhibit a higher resistance against contact welding <xr id="tab:Contact and Switching Physical Properties of Contact Materials Based on Silver – -Tungsten (SIWODUR), Silver–Tungsten Silver-Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"'''</caption><!--(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.

Higher requirements on low temperature rise can be fulfilled by adding a small amount of graphite which however increases the arc erosion{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Material!Silver<br/>Content<br/>[wt. Silver–tungsten carbide–graphite materials with for example 27 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 16 wt% |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 and 70/28C2 [[#text-reference|^{2 wt% graphite are manufactured using the single tip press}]]|68 - 72|9,6 - 10,3|24 - 32|35 - 55|-|Ag/Mo 65/35 [[#text-reference|¹]]|62 - 68|9,9 - 10,9|16 - 28|140 -sinter130|-repress (PSR) process |}<xr div id="fig:Micro structure of text-Ag WC 27 C3reference">₁manufactured by infiltration<!/div><div id="text--(Fig. reference">_2.136)- manufactured by press sinter-repress</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"/WC contacts are similar ><!--(Fig. 2.135)--> and <xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(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 single tip press-sinter-repress (PSR) process (<xr id="fig:Micro structure of -Ag Mo 35 65WC 27 C3"/><!--(Fig. 2.137)--> <xr id="tab:Physical Properties of-Contact Materials Based"/><!--(Table 2.36)-->. Their contact properties are similar to those of Ag/W materials <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 2.37136)-->. 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 <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)-->.

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

=== 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 WC 50 50Mo 35 65"/><!--(Fig. 2.135:137)--> Micro structure of Ag/WC 50/50 and <xr id="figtab:Micro structure Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Ag WC 27 C3Tungsten Carbide and Silver Molybdenum"/><!--Fig. (Table 2.136:36)--> Micro structure ). Their contact properties are similar to those of Ag/WC27/C3 W materials (<xr id="figtab:Micro structure Contact and Switching Properties of Ag Mo 35 65Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--Fig. (Table 2.137:37)--> Micro structure ). 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 35however 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)"/65><!--(Table 2.38)-->).

<caption>'''<!--Table 2.37:-->Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''</caption>

<tr><th><p class="s12">Material/ DODUCO- Designation</p></th><th><p class="s12">Properties</p></th></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>

<caption>'''<!--Table 2.38:-->Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)'''</caption>

|Ag/W<br />SIWODUR

|Ag/W<br />SIWODUR<br />Ag/WC<br />SIWODUR C<br />Ag/WC/C<br />SIWODUR C/C

|Ag/Mo<br />SILMODUR

=== Copper–Tungsten (CUWODUR) Materials===Copper–tungsten (CUWODUR) materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selected according to the end application [[#figures4|(Figs. 5 – 86)]] <!--(Figs. 2.138 – 2.141)--> and (<xr id="tab:Physical Properties properties of Copper Tungsten CUWODUR Contact Materialscopper-tungsten materials"/><!--(Table 2.39)-->). To increase the wettability of the tungsten skeleton by copper a small amount of nickel < 1 wt% is added to the starting powder mix.

W/Cu materials exhibit a very high arc erosion resistance <xr figtable id="tab:Contact and Switching Properties Physical properties of Copper–Tungsten (CUWODUR) Contact Materialscopper-tungsten materials"/><!--(Table 2.40)-caption>'''Physical properties of copper-tungsten materials'''</caption>. Compared to silver–tungsten materials they are however less suitable to carry permanent current.

With a solid tungsten skeleton as it is the case for {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Material!Tungsten<br/>Content<br/>[wt.%]!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/C infiltrated materials with Cu 60/40 <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 wt% tungsten the lower melting component copper melts and vaporizes in the intense electrical arc. At the boiling point of copper (2567°C) the still solid tungsten is efficiently “cooled” and remains pretty much unchanged.- 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|-|}</figtable>

During very high thermal stress on the W/Cu contacts, for example during short circuit currents > 40 kA the tungsten skeleton requires special materials exhibit a very high mechanical strengtharc erosion resistance. For such applications a high temperature sintering of tungsten from selected particle size powder is applied before the usual infiltration with copper (example: CUWODUR H)Compared to silver–tungsten materials, they are however less suitable to carry permanent current.

For high voltage load switches the most advantageous contact system consists of With a contact tulip and a contact rod. Both contact assemblies are made usually from solid tungsten skeleton, as it is the mechanically strong and high conductive CuCrZr material and case for W/Cu as C infiltrated materials with 70-85 wt% tungsten, the arcing tips. The thermally lower melting component copper melts and mechanically highly stressed attachment between vaporizes in the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion weldingintense electrical arc. Other attachment methods include brazing and cast-on At the boiling point of copper followed by cold forming steps to increase hardness (2567°C), the still solid tungsten is efficiently “cooled” and strengthremains pretty much unchanged.

The main application areas During very high thermal stress on the W/Cu contacts, for CUWODUR materials are as arcing contacts in load and example during short circuit currents > 40 kA, the tungsten skeleton requires special high power switching in medium and mechanical strength. For such applications, a high voltage switchgear as well as electrodes for spark gaps and over voltage arresters <xr id="tab:Application Examples and Forms temperature sintering of Supply for Tungsten– Copper (CUWODUR) Contact Materials"/><!--(Table 2.41)-->tungsten from selected particle size powder is applied before the usual infiltration with copper.

<figtable id="tab:Physical Properties For high voltage load switches, the most advantageous contact system consists of Copper Tungsten CUWODUR Contact Materials">[[File:Physical Properties of Copper Tungsten CUWODUR Contact Materialsa contact tulip and a contact rod.jpg|right|thumb|Physical Properties of Copper Tungsten (CUWODUR) Contact Materials]]<Both contact assemblies are usually made from the mechanically strong and high conductive CuCrZr material and W/figtable><div id="figures4"><xr id="fig:Micro structure of W Cu 70 30 G"/><!--Figas the arcing tips. 2The thermally and mechanically highly stressed attachment between the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion welding.139:-Other attachment methods include brazing and cast-> Micro structure on of W/Cu 70/30 Gcopper, followed by cold forming steps to increase hardness and strength.

<xr id="fig:Micro structure of The main application areas for W Cu 70 30 H"/><!--Fig. 2.140:--> Micro structure of W/Cu 70/30 H <xr id="fig:Micro structure of W Cu 70 30 F"/><!--Fig. 2.138:--> Micro structure of W/Cu 70/30 F  <xr id="fig:Micro structure of W Cu 80 20 H"/><!--Fig. 2materials are as arcing contacts in load and high power switching, in medium and high voltage switchgear as well as electrodes for spark gaps and over voltage arresters.141:--> Micro structure of W/Cu 80/20 H</div>

[[File:Micro structure of W Cu 70 30 G.jpg|left|thumb|<caption>Micro structure of W/Cu 70/30 G</caption>]]</figure> <figure id="fig:Micro structure of W Cu 70 30 H">[[File:Micro structure of W Cu 70 30 H.jpg|left|thumb|<caption>Micro structure of W/Cu 70/30 H(coarse)</caption>]]

[[File:Micro structure of W Cu 70 30 F.jpg|left|thumb|<caption>Micro structure of W/Cu 70/30 F(fine)</caption>]]