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Silver Metcar Material for Electrical Contacts & Brushes

Metallized Carbon Corp. has been producing silver impregnated, carbon-graphite materials for electrical applications for over sixty years. These materials are called “Silver Metcar."

Silver Metcar materials are solid carbon-graphite based with a controlled amount of interconnected porosity which is impregnated with molten silver. The carbon-graphite rings or blocks are submerged in pure, molten silver and the silver is forced into the porosity of the carbon-graphite material using extremely high gas pressure. Most of the Silver Metcar grades contain approximately fifty percent silver by weight.

The Carbon-graphite substrate provides the self-lubricating properties, while the pure silver provides high and constant electrical conductivity. Additives to the carbon-graphite base material are made to improve the self lubricating properties of the material in dry atmospheres that occur at high altitude and in outer space. Silver Metcar can not melt or weld to another metal surface because the carbon-graphite base material will not melt. The carbon-graphite matrix material will sublime (go directly from solid to gas), at approximately 6100°F. Silver Metcar can be silver or copper plated for easy solder ability to metal parts such as leaf springs or conventional brush holders.

Silver Metcar has the following properties that make it ideal for DC motor brushes, non-welding electrical contacts, and rotary slip ring brushes or contacts.
  • Self-lubricating
  • Low and constant electrical resistivity
  • Low and constant contact drop
  • Non-welding
  • Corrosion Resistant
  • Dimensionally Stable
  • Heavy overload capacity
  • High heat resistance
  • Wear resistant
  • High thermal conductivity
What we Supply
We supply brush and contact tips made from Silver Metcar materials. These tips can be machined to customer specifications and they are available with or without silver plating. Most Silver Metcar brush tips and contact tips are purchased by manufactures of low noise slip ring assemblies, non-welding contact assemblies, and high altitude DC electric motors.

Application Tips
  • Coin silver slip rings give the lowest noise level
  • The surface finish on the slip ring should be 20 micro inch or better
  • For long wear life, the spring load on the Silver Metcar brush should be 4 to 6 psi
  • Spring loads up to 120 psi can be used to reduce the noise level
Silver Metcar products can be provided with a variety of plating options. Metallized Carbon Corporations technical staff can recommend the optimal Metcar grade.

Brushes or Contacts for Low Noise Slip Ring Assemblies  · Non-Welding Contact Tips  · DC Motor Brushes for High Altitude

Brushes or Contacts for Low Noise Slip Ring Assemblies
Slip ring assemblies are used to transmit electrical signals from a rotating shaft to a stationary receiver. The slip ring is attached to the rotating shaft and is usually made of coin silver, silver plated copper, copper or bronze. If a connection with low resistance, low voltage drop, and low electrical noise is required, the stationary brush or contact can be made of Silver Metcar. These assemblies are also called rotary joints, microwave rotary couplings and RF rotary joints.

Low noise slip ring assemblies are used to transmit minute electrical signals in rotating equipment like microwave antennas, radar receivers, sonar receivers, rotating thermocouple read-outs, and rotating strain gauge read-outs. Applications include air traffic control radar, telecommunications systems, and satellite communication systems. A noise level a low as 0.01 mv is possible on a 5 mv signal. Rotating shaft speeds can be as high as 10,000 ft/min.

Non-Welding Contact Tips
Silver Metcar non-welding contact tips are used to interrupt critical circuits where there is the possibility that heavy overload could cause other contact materials to arc and weld in the closed position. The situation occurs in circuit breakers, controllers, contactors and relays because of possible short circuits or lighting strikes. A good example of this is in railroad signal relays where it is essential that the crossing gates always come down when a train is approaching, even after a direct lightning strike to the control system.

Silver Metcar is also good for sliding contacts where long wear life and low contact resistance is required. This occurs in elevator contacts where high amperage circuits must be reliably opened and closed.

DC Motor Brushes for High Altitude
Ordinary carbon-graphite brushes show a high wear rate when running at high altitude (over 20,000 ft), in vacuum, or in dry atmospheres (dew point -30°F, or -34°C). Silver Metcar brushes, with additive film formers, can overcome this problem. Silver Metcar Grades can run on coin silver, silver, copper or bronze commutators and provide long wear life, low voltage drop and high current carrying capacity.


·  Miniature Silver Metcar Parts

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