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CMW Inc. manufactures electrical contacts and contact assemblies from several material classes. A particular application generally requires one or more of the unique properties of class of material. Further analysis of a suitable material class often indicates that a single specific material will perform the best. Basic material classes are:
A listing of general CMW contact materials includes:
Ag Fine Silver Typical Properties Fine silver is used extensively for make and break contacts in the moderate current range. It has the highest electrical and thermal conductivity of all of the metals. These properties enable fine silver to have a low contact resistance and high heat dissipation capability. It is relatively tarnish resistant and does not form stable oxides under normal conditions. Disadvantages are that it forms sulfide films, which can affect the contact resistance adversely, especially where the contact closing force, current or voltage is low. The migration of silver ions across or through certain insulating materials occurs where there is a voltage difference across the insulation and it is in contact with silver. This effect accelerates with increasing humidity. It can cause dielectric failures and must be guarded against by device design. Fine silver contacts are found in a variety of switches and relays used in the appliance, automotive, aviation and industrial markets. They are used in both AC and DC circuits and at currents ranging from about 0.5 to 15 amperes. The oxidation resistance of the material permits it to be used with low contact forces ranging from about 1/2 ounce to a few ounces. It is often used in applications where the contacts remain closed for long periods of time. CMW furnishes fine silver with a minimum purity of 99.90% silver. It is a ductile material and can readily be formed into many shapes. Contact designs include solid rivets, composite rivets, composite weld buttons, solid weld buttons, composite screws, round or rectangular discs and assemblies. Availability:
Ag/C Silver Graphite Typical Properties The addition of graphite to silver provides a family of materials which is useful as make and break and brush contacts. The graphite provides good lubrication properties and, therefore, reduces the tendency for galling or scoring in sliding contacts, hinge joints, and slip ring applications. It also has high resistance to welding or sticking.
CMW® D582F (99.75% Silver / 0.25% Graphite) CMW® D581F (99.50% Silver / 0.50% Graphite) The materials containing the lower percentages of graphite such as CMW® D582F, D581F, D583F and D158F can be fabricated into wire form and headed into rivets over a limited size range. These materials are used in both AC and DC circuits and has been used primarily to reduce sticking. However, they are also used as brush contacts in some light force sliding applications.
CMW® D58 (95.0% Silver / 5.0% Graphite) The materials with the higher percentages of graphite, such as CMW® D58 and D1058, are used as make and break contacts usually operating in conjunction with silver nickel or other silver base alloys. CMW® D58 is used in industrial circuit breakers usually operating against CMW® D56. CMW® D58 and D1058 are usually furnished as a round or rectangular disc or as a special pressed shape. When brazing these materials, it is necessary to have a silver rich layer on the surface, which is to be brazed or tinned with, braze alloy. Ag/CdO Silver Cadmium Oxide Typical Properties CMW® D54 and CMW® D55 Silver-Cadmium Oxide Contacts Silver-semi-refractory materials are not true alloys, but rather mixtures of silver and other elements, metalloids, or metallic oxides. These materials are usually fabricated as mixtures of constituent powders by conventional powder metallurgy techniques. Powder metallurgy techniques are used because constituents do not have compatible melting temperatures or they are not soluble in each other. However, in the case of silver-cadmium oxides and silver-magnesium oxides, it is possible to form true alloys of the elements and then convert one or more of the elements into an oxide by internal oxidation techniques. The silver-semi-refractory materials have relatively high electrical conductivity combined with other desirable features such as low stable contact resistance and excellent resistance to sticking and welding. These properties are obtained by additions of cadmium oxide, nickel, carbon, magnesium, iron, or other elements or compounds. CMW® D54 (90% Silver / 10% Cadmium Oxide) and CMW® D55 (85% Silver / 15% Cadmium Oxide) are produced as individual contacts by traditional powder metallurgy techniques (mix - press - sinter - repress to density). Normally, the powder metallurgy type materials are used in disc or rectangular shapes. The powder metallurgy process provides and economical method of producing radii, projections for welding or locating, indentations for solder traps and round or irregularly shaped contacts without material loss. While the cadmium oxide content can be readily varied, the two standard materials (10% CdO and 15% CdO) satisfy most contact requirements. The contacts can be supplied with a "backing" layer of fine silver which is recommended for attachment by brazing. If omitted, the cadmium oxide can cause a brazing alloy to develop brittle phases and ultimately a detachment of the braze. Besides standard discs and rectangles, irregular shapes typical of powder metallurgy parts can be produced economically. The addition of cadmium oxide to silver greatly improves the anti-welding characteristic. Of Ag/CdO materials, the powder metallurgy type has the least tendency to welding or sticking of all. It is the material of choice for arcing contacts of medium-low to medium-high current rating where "non-sticking" primary concern and erosion rates higher than wrought type Ag/CdO can be tolerated. It is not used in "high reliability - low current" applications (where CMW Elkonium® materials are best), nor in "high current circuit breaking" (where Elkonite® materials are superior). Generally this makes it a choice for "high-end" household and "low-end" industrial relay and contactor applications. The cost of Ag/CdO materials are directly tied to the cost of silver and the silver content of the material. As would be expected, the conductivity (and therefore resistance to temperature rise) is better with higher silver content.
CMW® D54X (90% Silver / 10% Cadmium Oxide) The "X" is appended to the material names to denote that the material is cast and formed as an alloy of Silver and Cadmium. The cadmium within the contact is then "post-oxidized" by heating in the presence of oxygen to convert it to cadmium oxide. Because of the kinetics of the process (which involves both migration of oxygen and cadmium) there is a resulting high concentration of fine Cadmium Oxide phase near the surface of the contact, and a lower concentration of courser Cadmium Oxide as one approaches the core of the item. Sometimes this "core" is referred to as a "depleted zone" or "silver-rich zone" due to the fact that the cadmium oxide content at this point is in much lower concentration. This should not be confused with an "un-oxidized core" (failure of sufficient oxidation time to reach cadmium at the core) or "reduced layer" (a surface condition where cadmium oxide has been re-reduced to cadmium because of contact with a "reducing" atmosphere). In the latter two cases, the cadmium is still present, but not in its "oxidized" form. The kinetics of the situation, (and processing techniques at CMW) limit the "center-to-surface distance" for this type of material to about 1/16 inch. Contacts thicker than 1/8 inch will likely have an "un-oxidized core". Of Ag/CdO materials, the "post-oxidized type" has the least tendency to for early erosion. It is the material of choice for arcing contacts of medium-low to medium-high current rating both where early "erosion" primary concern and anti-welding is also a high priority. Magnetic contactors, relays, and industrial controls are common applications. It is often chosen for its manufacturing ease and economics. Prior to oxidation, the silver cadmium alloy is readily cold worked, and can be headed from wire (to make "rivet contacts"), or rolled and formed to exotic shapes from strip with very good manufacturing economics for high volume applications. It is not used in "high reliability - low current" applications (where CMW Elkonium® materials are best), nor in "high current circuit breaking" (where Elkonite® materials are superior). Generally this makes it a choice for "high-end" household and "low-end" industrial relay and contactor applications. The cost of Ag/CdO materials are directly tied to the cost of silver and the silver content of the material. As would be expected, the conductivity (and therefore resistance to temperature rise) is better with higher silver content.
CMW® D54F (90% Silver / 10% Cadmium Oxide) The "F" is appended to the material names to denote that the material is cast as a grain alloy of Silver and Cadmium. This grain is then oxidized to become Silver-Cadmium oxide grain. After oxidation the grain is subsequently hot and cold worked into wire, bar, or strip, and ultimately headed, or blanked, or coined into contacts. CMW refers to this processing as "Pre-oxidized", because conversion to cadmium oxide "precedes" formation of the contacts. Generally pre-oxidized ("F") AgCdO material is quite similar in properties to post-oxidized ("X") material with the exception of microstructure. Pre-oxidized ("F") material has a uniform distribution of fine and coarse cadmium oxide phase, while the post-oxidized ("X") material does not (see above). Because of this, there is no fear of reduced resistance to sticking as one wears down the contact and approaches its core region. Pre-oxidized Silver Cadmium Oxide ("F") materials cannot be cold worked to the degree that post-oxidized "X" type material. There are definite limitations on the heading of wire to form rivets, as well as rolling and coining. Compositions greater than 13.3% CdO are not considered to be "headable" at all. Conversely, there is no "1/8 inch thickness" limitation on contacts with "F" materials, since kinetics of oxidation at the contacts geometry are not a consideration. Thus heavier duty contacts can be blanked from thick "F" type strip. In strip form, fine silver backing is recommended as a brazing surface to eliminate brazing problems that occur if it is omitted. This backing is readily applied during the hot rolling of the strip. Of Ag/CdO materials, the "pre-oxidized type" has the superior arcing properties for everything except "anti-sticking" where the "powder metal" type is superior. It is the material of choice for arcing contacts of medium-low to medium-high current rating both where economics for a heavier and high volume application is of primary concern. Magnetic contactors, relays, and industrial controls are common applications. It is not used in "high reliability - low current" applications (where CMW Elkonium®s are best), nor in "high current circuit breaking" (where Elkonite® materials are superior). Generally this makes it a choice for "high-end" household and "low-end" industrial relay and contactor applications. The cost of Ag/CdO materials are directly tied to the cost of silver and the silver content of the material. As would be expected, the conductivity (and therefore resistance to temperature rise) is better with higher silver content. Ag/Cu Silver Copper Typical Properties CMW® Coin Silver (90% Ag / 10% Cu) and Elkonium®1 (75% Ag / 24.5% Cu / 0.5% Ni) Coin Silver and Elkonium® 1 alloys are the most widely used materials of this group for electrical contacts. Elkonium® 1 material sold by CMW displays low transfer tendencies and high current switching capability in a number of automotive applications. Coin silver also has been used in a number of relays and switches because it is more economical than fine silver. It has been used in rotary switches and other sliding contact applications because it has good resistance to mechanical wear. Both coil silver and Elkonium® 1 materials are used in high contact force applications where fine silver has failed by mechanical wear or deformation due to its lower hardness. Availability:
ELKONIUM®23 (98.5% Ag / 1.5% Cu) Typical Properties Elkonium® 23 alloy has a tarnish resistance almost as good as fine silver and is a little harder. In low force devices, which have high inrush currents, this material has somewhat less tendency toward sticking than fine silver. Availability:
Ag/Mo Silver Molybdenum Typical Properties Elkonite® G17 is a 60%Mo/40%Ag Elkonite® material. It is used for arcing contacts in both air and oil circuit breakers. It has good arc erosion characteristics. Low contact resistance permits good transfer of current from current carrying to the arcing contacts. Its low contact resistance plus resistance to welding make it a suitable material for high inrush currents at low voltage. It is also used in heavy duty truck starting contactors where it operates against a copper shorting contact. Elkonite® G18 has the highest silver content of the Ag/Mo Elkonite® materials. It is used for contacts that both carry and interrupt current. It is used in low and intermediate rated household and industrial air circuit breakers. It is also used as arcing contacts in oil circuit breakers, as well as shoe contacts in transformer tap changers. Elkonite® 7065 has the highest refractory content of the of the Ag/Mo Elkonite® materials. It is the most economical of the silver infiltrated materials in this group. It is used for low rated circuit breakers. Elkonite® 7165 is a high refractory Ag/Mo Elkonite® material made by the press-sinter-repress method. Its primary advantage is the ease of manufacturing into thin and small shapes. It can be directly attached to a blank without special finishing operations and provides a cap with good resistance to erosion and good current carrying capabilities. Use in automotive truck starters is a typical application. Ag/Ni Silver Nickel Typical Properties CMW® D505F (95.0% Silver / 5% Nickel) and CMW® D510F (90.0% Silver / 10% Nickel)
This group of silver nickel compositions is made from metal powder. The lower nickel compositions, CMW® D505F and CMW® D510F, have good ductility and are fabricated into wire and strip. These compositions can also be headed into rivets, discs, or solid weld buttons. CMW® D505F is used in some appliance switches where a higher resistance to wear than fine silver affords is required. CMW® D510F is used in both AC and DC applications. It is used in the lower rating line starters operating against fine SILVER. CMW® D510F is also used in polarized low voltage DC circuits as a positive contact operating against Elkonium®45. CMW® D50F (85.0% Silver / 15.0% Nickel) and CMW® D50 (85.0% Silver / 15.0% Nickel) CMW® D50F can also be fabricated into wire, rod and strip; however, the headability of CMW® D50F is limited to a narrow range. It is used for main contacts in circuit breakers and switching devices where auxiliary contacts are used. This type of material has good resistance to mechanical wear under high contact forces, and maintains a stable surface resistance. CMW® D50 is the same composition as CMW D50F, but it is furnished in the form of discs, rectangles, and special shapes produced by conventional powder metallurgy techniques. Ag/W Silver Tungsten Typical Properties This group of Elkonite® materials consists of a series of tungsten silver compositions with the tungsten content ranging from 10% to 88% by weight. Tungsten has the highest strength and the highest melting temperature of the refractory metals. This is the principal factor in determining a contact's resistance to arc erosion and mechanical wear. The strength, erosion and weld resistance characteristics of the contact increase with increasing tungsten content; the electrical and thermal characteristics decrease. In selecting a material composition for a given application, you choose the highest refractory content that will provide a satisfactory temperature rise and current interruption. Elkonite® 20S is one of the high refractory content tungsten-silver Elkonite® materials made by press-sinter-infiltration and normally a high resistance to arc erosion. It is generally used as arcing contacts in large air and oil circuit breakers, line disconnects, re-closures, and in high current switches and contactors. Contact resistance is low enough to protect the higher conductivity current carrying contacts from arc damage. Its resistance to welding makes it a good shorting contact for bimetal protection in circuit breakers. Elkonite® 30S and Elkonite® 35S have more silver than Elkonite® 20S, which provides higher conductivity and a lower contact resistance. They are used extensively in a large variety of circuit breakers. In this application, a single pair of contacts provides the dual function of carrying the current without overheating, and interrupting the current without excessive arc erosion. They are also used in high current contactors where resistance to contact welding and arc erosion are required. In a variety of DC applications, they offer resistance to metal transfer. Elkonite® 50S has the highest silver content of the press-sinter-repress tungsten-silver Elkonite® materials. It exhibits good resistance to contact welding and is used for current carrying contacts in power circuit breakers that encounter high momentary currents. Elkonite® 20SB is made by a "press-sinter" method with a small addition of nickel used to activate the sintering. Because of fewer steps in manufacture this material is more economical than the Elkonite® 20S (press-sinter-infiltrate) counterpart. Size of Elkonite® 20SB contacts are limited due to warping. They can be made with a serrated back and excess silver to facilitate attachment. Elkonite® 20SB with its high refractory content is used in certain lower rated circuit breakers where their temperature rise is adequate. Some automotive circuit protectors use Elkonite® 20SB operating against a silver alloy. Elkonite® 35SB is the most popular material made by the press-sinter process with a small addition of nickel used to activate the sintering. Because of fewer steps in manufacture, this material is more economical than the Elkonite® 35S (press-sinter-infiltrate) counterpart. Elkonite® 4050 is a high silver material that uses a special tungsten powder. It is made by the press-sinter-infiltrate method. It was developed especially for use as a combination current carrying and arcing contact for molded case circuit breakers. Its strong structure improves its arc erosion resistance while maintaining good temperature rise and current interruption characteristics. Elkonite® 4050 has approximately the same silver content as Elkonite® 50S, but has higher mechanical properties due to its higher sintered strength. It is used in the higher rated household breakers. Elkonite® 2088 has a very high refractory content and is not considered in the normal family of make and break contacts. It is used in special applications where weight or hardness together with corrosion resistance may be of primary importance. It has also found use as a rocket nozzle material. Elkonite® 2150 has the same composition as Elkonite® 50S but is made by the press sinter repress method. The final repressing operating produces a contact facing which is ready for attachment to backings by silver brazing, without subsequent finishing operations. This press sinter repress material has a higher erosion rate than Elkonite® 50S. This is used to an advantage in some industrial breakers. The surface refractory metal erodes along with the silver and presents new tungsten silver surfaces which are more stable in temperature rise. Elkonite® 2150 is also used in distribution circuit breakers, small relays and switches, where resistance to metal transfer or contact welding is required. Elkonite® 2110 is a sintered tungsten-silver material that is made into wire. This wire can be cold headed into rivet contacts or discs, which can be brazed, to rivets or other backings. Elkonite® 2110 provides resistance to sticking and has uniform surface wear. Elkonite® 2110 does not resist erosion nearly as greatly as other members of the tungsten-silver family. This material is used in automotive circuit protectors generally operating against a Molybdenum silver Elkonite® mating contact. Elkonite® 2110 is used in wall switches and thermostats such as blanket thermostats. Its uniform surface wear helps maintain a uniform calibration in thermostats. Ag/WC Silver Tungsten Carbide Typical Properties Elkonite® G14 has the highest refractory content of the Tungsten Carbide/Silver Elkonite® materials. Electrically similar to Tungsten/Silver Elkonite® materials, the Tungsten Carbide versions have a higher resistance to mechanical wear. Elkonite® G14 is used in industrial type molded case circuit breakers. It has good resistance to welding, a stable contact resistance and good erosion resistance. The high hardness of Elkonite® G13 gives it a resistance to mechanical wear and deformation in high speed relays. Elkonite® G13 has a higher percentage of silver than G14 and is used in both industrial and high rated household breakers. Electrically similar to Tungsten/Silver Elkonite® materials, the Tungsten Carbide versions have a higher resistance to mechanical wear. Normally G13 contacts carry the current as well as make and break the circuit. Elkonite® G13 has good anti-weld characteristics and a low stable contact resistance. It is used in lighting relays where it resists welding at high inrush currents. It is also used in high current aircraft relays where it is normally operated against CMW D-54® contact material. This combination provides low contact resistance and good weld resistance. Because of its good resistance to mechanical wear, it is used in sliding contact applications such as commutators for aircraft generators. Elkonite® 3042 has the highest silver content of the of the Tungsten Carbide/Silver Elkonite® and is used in high rated household circuit breakers. It offers the unique combination of good current interruption, a low contact resistance to prevent overheating and a high resistance to contact sticking and welding. Elkonite® 3150 is a Tungsten Carbide/Silver Elkonite® made by the press-sinter-repress method. It is economical for facings on smaller rivets, screw type contacts and other assemblies. This press-singer-repress material is suitable for many "less severe" relay and switching applications where good resistance to sticking and welding is required. Elkonite® 1060 ElkoniteŽ 1060 was developed for vacuum interrupter applications. The tungsten carbide refractory material provides good anti-welding and resistance to erosion. The silver provides low, stable contact resistance and the cobalt is effective in reducing current chopping. Au Gold Based Materials Typical Properties Elkonium® 76 (90% Au / 10% Cu) and Pure Gold (99.9% Au min) Elkonium® 76 is CMW's gold-copper alloy that is completely tarnish resistant at ordinary atmospheric temperatures. Compared to the other CMW® gold Elkonium® alloys, it has improved resistance to welding, and particularly cold welding. When used as a positive contact operating against an Elkonium 32® alloy negative contact in low voltage DC applications, the combination resists transfer and sticking at currents up to 4 amperes. Availability:
Pure Gold has complete resistance to atmospheric tarnish and oxidation. It does not contribute to polymer formations like platinum and palladium alloys. Wrought gold metal is very soft and prone to welding and has very few contact applications. Electroplated coatings of gold on silver and other base metals are used in dry circuit application and to provide long shelf life reliability. Gold is alloyed with other metals to improve hardness, contact performance, and reduce cost. Cu Copper Alloys CMW Copper Alloys have excellent electrical and thermal conductivity, excellent resistance to corrosion, good fabrication characteristic, and fatigue resistance. They come in a broad spectrum of mechanical, and physical properties to match specific requirements. Links listed below are in order from highest electrical conductivity to lowest: CMW® 3 material is a high strength, high conductivity copper base alloy. CMW® 3 material is heat treatable. Optimum mechanical and physical properties of CMW® 3 material are developed by heat treatment or through a combination of heat treatment and cold working. CMW® 3 material is available in the following forms:
CMW® 3 material in wrought and cast shapes is used in numerous applications where a high strength, high conductivity material is required as a structural member. Examples are: Current carrying parts for circuit breakers, backing for circuit breaker arcing contacts, and bridging contact backings in heavy duty relays. In addition, CMW® 3 material is superior for use as a back up bar for arc welding applications. It is also extensively used as a component in electrical devices, where high strength and high conductivity are required. CMW® 28 material is a copper base alloy having very high electrical and thermal conductivity and medium strength and toughness. It is a heat treatable alloy and develops its strength and hardness through a combination of heat treatment and cold working. In more massive sections it will have reduced strength and hardness. CMW® 28 material is supplied in rod form. CMW® 28 material is used very successfully in the form of resistance welding electrodes. It is recommended for the welding of coated steel and materials of high conductivity excluding silver and copper. CMW® 73 material is a heat treatable copper base alloy having extremely high hardness and strength coupled with fair electrical and thermal conductivity. The extremely high hardness, strength and wear resistance is obtained in both cast and wrought material largely by means of heat treatment. It is generally useful where high stress is encountered or where high abrasion resistance is desired but where temperatures are not excessive. The annealing temperature is somewhat less than for other heat treatable high strength copper base alloys. The hardness of CMW® 73 material in the fully heat treated condition is sufficiently high to make machining somewhat difficult particularly in drilling and tapping of small holes. Where extensive machining or forming is to be done, CMW® 73 material can be supplied in the solution annealed (soft) condition and then hardened by a simple heat treatment following machining. CMW® 73 material is available in the following raw forms:
CMW® 73 material is useful where extremely high hardness, strength and abrasion resistance is required. It may be advantageously used where current density and heat are not excessive. Current carrying structural members of CMW® 73 material provide extremely high strength. CMW® 100 material is a heat treatable, high strength, high conductivity copper base alloy. Its properties are a combination of highest strength and hardness with relatively high electrical and thermal conductivity. CMW® 100 material has excellent properties. The properties are developed largely by heat treatment although in some wrought forms, the alloy is additionally cold worked. CMW® 100 material is available in the following forms:
The high hardness, good wear resistance and high annealing temperatures of CMW® 100 material, coupled with sufficiently high electrical conductivity, make it ideal for many electrical applications. CMW® 100 material is ideal for current carrying springs and structural parts where high conductivity and high strengths are required. Copper Tungsten (Cu/W) Typical Properties Elkonite® Copper Tungsten is a press-sinter-infiltrated material with the tungsten content ranging from 50% to 90% by weight. The balance is copper. Elkonite® Copper Tungsten costs less than Elkonite® Silver Tungsten. As with Silver Elkonite® material, Copper Elkonite® material has good resistance to arc erosion, mechanical wear, contact welding and good conductivity. They are usually selected for oil, gas, or vacuum, devices. Their contact surfaces will oxidize when switched in air. These press-sinter-infiltrate materials should only be considered for arcing surfaces in air when used as arcing tips, arc plates and arc runners. When switching with moderate contact arcing, the Elkonite® material with a high copper content may give the lowest erosion. As arcing severity increases, the Elkonite® material with the higher refractory content withstand arc erosion better. However, the Elkonite® material with the higher refractory content is more susceptible to cracking due to thermal shock. This cracking can lead to chunks of material eroding form the contact. Elkonite® 2050C and Elkonite® 1W3 have the highest copper contents. As contact materials both are good switching materials in oil filled devices. In addition, Elkonite® 1W3 is used for arcing contacts in oil circuit breakers. It is also used as arcing edges of selector switchblades in transformer tap changers. Elkonite® 3W3 and Elkonite® 5W3, with a higher percentage of refractory, are used as contact materials in severe arcing applications. Arcing contacts in gas filled, oil and some air circuit breakers are often Elkonite® 3W3 and 5W3. They are used for arcing edges on both selector and reversing switch blades and wiper shoe contacts in tap changers. These press-sinter-infiltrated materials also find applications as transfer switch contacts in the higher rated tap changers. Elkonite® 10W3 and Elkonite® 30W3, with still higher tungsten content are used as contact materials under extreme arcing conditions. Applications include arcing contacts in gas and oil circuit breakers, contractors and transformer tap changers. Elkonite® 10W3 and 30W3 are also used for arcing plates and arc runners in power switching equipment. Elkonite® 40W3 and Elkonite® 50W3 have the highest tungsten content. They are used as contact materials where resistance to contact welding, sticking and arc erosion are important. They also provide satisfactory conductivity and good current interruption capabilities. A typical application is power vacuum switches. Elkonite® 40W3 and Elkonite® 50W3 make excellent high power spark gap electrodes. They are best for arcing which is moderate and repetitive. Because of their very high density, excellent machinability, and totally non-magnetic nature Elkonite® 3W53 and Elkonite® 10W53 are volumetrically the same composition as their 3W3 and 10W3 counterparts. The difference is that an "age hardenable" copper (instead of pure copper) is used when the parts are infiltrated. This allows significantly higher hardnesses to be developed if the material is "aged". Because this significantly lowers the electrical and thermal conductivities of these materials, they seldom see use as electrical contacts. However where low wear, high strength at elevated temperature, and satisfactory electrical transfer is required, these materials are chosen. They are usually used in resistance welding, electrical upsetting, and electro-forging applications. Cu/WC Copper Tungsten Carbide Typical Properties Elkonite® Tungsten Carbide-Copper is a press-sinter-infiltrated material with a refractory content ranging from 50% to 70% by weight. They are strong materials with high mechanical properties. They also have good resistance to arc erosion and contact welding. These materials are generally used in oil devices to protect the contact from oxidation. Elkonite® TC5 and Elkonite® TC10 are the grades most commonly used for electrical contacts primarily for their resistance to mechanical wear. Elkonite® TC5 with the higher copper content and electrical conductivity is used for wiper shoe contacts in tap changers. It is also used for transfer switches and heavy duty contactors. Elkonite® TC10 is a harder material and is used where greater wear resistance is desired. Applications include tap changer shoes and arcing contacts in oil breakers where high impact forces may be encountered. Elkonite® TC20 and Elkonite® TC53 are used in some of the more severe electrical upsetting and electro forging applications, where their very high hardness and strength properties are required. A major drawback of these materials is the difficulty of machining them due to their very high wear resistance. Pd Palladium Materials Typical Properties Elkonium® 40 (99.9% Pd min.) Elkonium® 40 is CMW's trademark for commercially pure palladium (9.90 minimum purity). Its good corrosion resistance and low hardness makes it a desirable contact for low current applications where forces are relatively low and reliability of making circuit is important. It is used in aircraft relays at currents under 1 ampere, in telephone relays and in instruments. It is often chosen for applications where contacts area open for long periods of time. Availability:
Pt Platinum Materials Typical Properties Elkonium® 30 (99.9% Pt min.) Elkonium® 30 material by CMW is commercially pure platinum (99.90% minimum purity) Freedom from tarnish and low hardness makes it a very reliable contact in low force, low current AC and DC applications. It is recommended for sensitive instruments and relays, particularly where contacts are open for long periods of time. Availability:
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