Jade Bridges, European Technical Support Specialist at Electrolube explores how, by adding the ‘slick factor’ with contact lubricants, can enhance switch functionality and improve the lifecycle of components
Contact lubricants are an important factor for electrical components in order to maximise lifecycle and functionality. Specially formulated greases and oils, designed to reduce friction and wear enhance electrical performance of current carrying metal interfaces, such as those found in switches and connectors.
On a microscopic scale, contact surfaces have ‘peaks and troughs’, of which only the peaks touch when the two surfaces come together. As a result, current carrying surface area is greatly reduced, which causes heat generation and the formation of oxide layers.
Hot spots are also created which reduce the efficiency of the switch and can result in complete failure should the two surfaces weld together.
By filling in the air gaps between the contacts, contact lubricants have a great ability to increase the effective surface area, in turn preventing arcing, temperature rise and oxide formation. They also create a barrier against airborne contamination and reduce the effects of friction.
Connectors and closed contacts are generally exposed to small amplitude movements caused by vibration and temperature changes. As the surfaces fret, friction causes metal particles to be removed from the higher points on the surfaces of the connector, breaking through the plated surfaces. This exposes the underlying surfaces to the effects of oxidation and wear.
Air gaps that are present between the contact surfaces can become ionised and the associated temperature rise can cause metal transfer between the contacts.
This results in the formation of new peaks and troughs, increasing the surface roughness of the contacts. Arcing occurs as mini lightning strikes and leads to oxide formation and destruction of the plated contacts.
Contact lubricants have the potential to extend the lifetime of switches by more than 300 percent, enhancing performance in a variety of applications and can decrease maintenance needs.
There are many ways to ensure correct product selection. Included in this are elements such as whether plastics are present in the surrounding contact area. plastics compatibility can vary depending on the type of plastic and lubricant being used. More sensitive plastics, such as polycarbonate, require a specialist lubricant formulated using synthetic base oils.
In the case of less sensitive plastics, such as polyamide, mineral oil based lubricants may be suitable and in some cases can provide enhanced electrical performance capability.
Environmental effects
Environmental influences can include temperature changes, humidity exposure and corrosive atmospheres.
Changes in temperature can affect the consistency of the contact lubricant, for example, a lubricant may have a cone penetration value of 320 at 25°C but when exposed to temperatures of -40°C or lower, this value may significantly reduce, resulting in the lubricant stiffening.
This change can result in a reduction in performance, particularly in terms of reducing friction.
Temperature changes can also result in a difference in compatibility of materials; for example, at higher temperatures the plastics compatibility may be reduced.
It is therefore vital that the operating temperature range of the connector or switch is compared to the operating temperature range of the lubricant and for ‘in use’ tests to be performed.
Humid environments are common and most contact lubricants will withstand high humidity for prolonged periods.
When high humidity is combined with corrosive environments, differences between products can be observed.
Tests that can check compatibility include wetting, humidity followed by salt mist tests, chlorine resistance tests and consideration of different materials that come into contact.
In addition to considering environmental effects, Electrolube has evaluated the mechanical performance of their lubricants by conducting 4-ball wear tests. The test consists of loading the grease into specialist equipment that has four balls under a defined rotation and pressure loads are applied.
The values taken are the pass value and a wearing value at the pass value. The wearing value is measured in mm and quantifies the amount of wear observed on the test balls. The weld point is also determined as the point where the wearing is in excess of 4mm.
These tests clearly illustrated that the fluorinated materials offer superior mechanical protection. Lubricants such as the company’s EGF are proven to surpass standard synthetic and mineral based lubricants, typically using lithium and clay based thickeners. Figure 2, highlights the differences between these materials.
Careful consideration of the requirement for contact lubricants and the numerous benefits they bring to switch/connector applications can have a distinct impact on device performance for the variety of industries such components are used in.
When selecting the right lubricant it is essential that the final application environment is considered in detail as the added stress of corrosive environments or mechanical wear can greatly alter the product selection stage. Also to ensure maximum capability, no matter what the application or the lubricants used previously, testing is vital.
Whether it is a change in component material or an alteration to the environment or electrical requirements, many factors can alter the performance of a switch or connector.
Electrolube
