Electrical contact rivets are critical, but often overlooked components used in "make and break" switching applications. These can be found as the main contacting interfaces in the switches, relays, circuit breakers, and contactors found in automobiles, electric and hybrid vehicles, industrial systems, automation devices, smart electrical meters, and many other devices.
Contact rivets are custom-designed in a variety of sizes, geometries, and metal alloys depending on...
Electrical contacts come in many physical sizes, depending on the application, switching current, and voltage requirements. Deringer-Ney manufactures both high amperage and low amperage electrical contact rivets. The higher amperage ratings would be used in applications including industrial devices, power meters, smart power meters, electric & hybrid vehicles, and automotive applications. Micro contact rivets would be designed and manufactured for lower amperage ratings (typically, mA) and used in micro-switches, micro-relays, and other small switching devices.
At Deringer-Ney, we've been manufacturing and supplying electrical contacts for over 70 years with parts numbering in the billions. Our experience, manufacturing technologies, and in-house metallurgy expertise allows product engineers to tap into our vast wealth of knowledge in electrical switching applications. We work closely with our customers as "development partners" in order to help select the best alloy to meet the competing design factors of cost, performance, and contact life.
Our manufacturing facility in Marshall, North Carolina, is one of the largest electrical contact cold heading facilities in North America. Our products include bimetal contact rivets, solid electrical contacts, and non-electrical cold headed and cold formed parts.
Design Considerations for Electrical Contact Rivets
Make and break electrical contacts are those whose function is to establish, carry, and interrupt current for many cycles over the contact's lifetime without significant sliding. This mechanism is in direct contrast to other Deringer-Ney electrical contacts such as sliding contacts used in potentiometer and sensing applications, as well as slip ring contact surfaces.
In ideal conditions, the resistance between mating contacts would be close to zero when closed and infinite when they are open. The number of design factors that influence electrical contact performance is extensive and their interaction too complex to permit simple rules for overall design and material selection. Factors such as contact rivet shape, contact force and ambient conditions balanced with cost all affect material selection and the overall design of the electrical switch. The following is just a partial list of design considerations for an electrical contact system...
Mating members in contact systems can be made round to round, round to flat, cone to flat, and various other geometrical configurations depending on the operating conditions and general design requirements of the switch mechanism.
Contact Wiping Action
Make and break contacts usually have some degree of wiping present, if not by design, then by inherent flexing of the support members during the switching action. Wiping will have some benefits such as cleaning the surface of minor films and in brushing aside particulate contamination. It can also smooth out transferred material and lessen the tendency for electrical contact welding. Since wiping always causes some frictional wear, this design aspect needs to be carefully balanced with the required life of the part, metal alloy choice, and cost.
The amount of contact force on the mating surfaces will determine the constriction resistance between the contacts. Just as a constriction in a water pipe results in a pressure drop and therefore represents a resistance to flow, very light contact force will constrict electrical current paths causing an electrical resistance and corresponding voltage drop. Conventional wisdom would lead the design engineer to make the contact force as high as practical in order to minimize constriction resistance; however, the classic "engineering compromise" will require the engineer to be careful with this approach because it will more than likely conflict with other design criteria.
Effects of Contact "Bounce"
As an electrical contact mates with a stationary one, there is always some tendancy to "bounce" after initial impact causing momentary oscillations in the switch until settling. This will have differing effects on low energy compared with high energy circuits. With resistive loads (little to no inductance or capacitance) and the absence of arcing, contact bounce will not necessarily shorten the life of the electrical contacts, but can be a source of error when the associated circuitry senses these multiple switch states. In applications where an arc is present, even of short duration, bounce should be minimized since the contacts will reclose on molten metal resulting in possible microwelds and sticking. In addition to possible mechanical damage to the switch, the tendency to radiate energy resulting in EMI greatly increases.
Voltage, Current, Power, and Energy
The most simple application for a make and break electrical contact system would be one which the switched current and voltage can be selected by the designer. Unfortunately, this seldom happens. There is limited influence the engineer has in determining the voltage and current of a particular circuit being switched. The overall design of the electrical switch needs to begin with the voltage, current, and load characterisitcs. For example, a highly inductive load will have a lot of stored energy that needs to be released when the circuit is opened. This will dictate very different design criteria than a resistive load with little stored energy.
Which Contact Alloy Is Best?
Deringer-Ney's team of material scientists, metallurgists, and application engineers can guide you in the right direction. We can help you choose the best metal alloy or combination of metal alloys in the case of bi-metal rivets. In addition to our research and development lab, we also have a full chemistry lab for material characterization and product support.
We currently produce solid and bi-metal electrical contacts with many materials...
silver cadmium oxide
silver tin oxide
many others available...