Electrical Contacts

High Voltage contacts / Arc Tolerant Contacts

CMW is the forerunner in manufacturing high voltage contacts and arc tolerant electrical contact materials. Elkonite® is a family of materials developed by P.R. Mallory that employ the infiltration of copper or silver into a tungsten, tungsten carbide or molybdenum base. Elkonite® materials are hard and durable, with good conductivity and particularly resistant to the erosive damage of contact arcing.

Higher voltage applications bring a diverse set of challenges in design and wear of electrical contacts. Some of these high voltage contacts are operated in oil, others in air, others in a vacuum and still others in varying gases to deal with the unique requirements of high voltage applications. Some of the problems encountered will be high wear, arcing and sticking (or welding). In this section you’ll find a large number of CMW manufactured materials perfectly suited to meet these challenges.

Elkonite® Silver Tungsten

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® 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.

Elkonite® Copper Tungsten

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.

Elkonite® Copper Tungsten Carbide

Cu/WC Copper Tungsten Carbide Typical Properties

Elkonite® Copper Tungsten Carbide 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.