Lubricants for Electrical Contacts in Household Appliances

Water intrusion can jeopardize the performance of electronic components and electrical connections as it leads to galvanic corrosion on the metal surface. Galvanic corrosion occurs when metal components come in contact with moisture. Metals are unstable under normal atmospheric conditions which allow them to be converted into their oxide form. When corrosion starts on the surface of an electrical contact, insulative oxides form on the surface which ultimately results in increased resistance and signal loss leading to component failure.

There have been several recalls by top appliance manufactures due to water intrusion into electrical connections that caused corrosion on contacts in refrigerators and dishwashers. There have also been several recalls for corrosion on contacts in refrigerators which resulted in intermittent interruption of ice production and melting of ice in the bin. Another recall was issued after dishwashers began to overheat due to the formation of corrosion on the electrical component which posed the potential to cause ­fires. Using the proper dielectric grease in electrical contacts will prevent corrosion from occurring and create an environmental barrier to keep moisture out which will increase component reliability, extend life of the component, reduce safety concerns, and reduce warranty costs.

Not all dielectric greases have the ability of preventing corrosion or water intrusion. Testing needs to be performed to know the grease’s limitations before it is selected for an application. Nye’s dielectric grease product line was carefully developed to protect against corrosion and to have good water resistance which is backed by extensive validation testing.

The SAE J2334 method is a common corrosion test used for tin-copper or nickel-brass contacts. This cyclic corrosion test replicates accelerated exposure conditions and relies on three segments the humid stage, the spray application, and the dry stage. These stages provide an accurate simulation of typical operating conditions for applications such as dishwashers and refrigerators. The wet and the dry part of the cycle mimic natural cyclic conditions while the spray application introduces the corrosive solution.

Each cycle totals 24 hours where the fi­rst segment is a 6-hour humid stage at 50°C, 100% relative humidity (RH) followed by a 15-minute salt application stage at 25°C and ­finally a drying stage at 60°C, 50% RH for 17.75 hours. A thin layer of grease is applied per the test method speci­fication to coupons before being placed in the test chamber. The automotive industry has found that 80 cycles correlates to 5 years in the field for their applications. The appliance industry could also utilize this testing to identify a correlation for speci­fic applications of interest. See images in Tables 1 and 2 for passing and failing results on tin-copper and nickel-brass coupons used in the testing of dielectric greases.

When looking at the failed coupons in Table 2 notice the range in color and degree of corrosion severity. When performing corrosion tests, it is important to obtain data on both the upper and base metal coatings of the component to evaluate a grease’s ability to protect the copper underplating that is traditionally used in electrical contacts and connectors. Nye performs copper corrosion testing per ASTM D-4048 at 100°C for 24 hours. The ratings cover a scale ranging from slight tarnish (1A/1B), moderate tarnish (2A-2E), dark tarnish (3A/3B), and corrosion (4A-4C).

The results seen in Figure 3 represents a dielectric grease that did not protect the copper surface from corrosion and is normally what one would see for a 3B result in the copper corrosion test that equates to dark tarnish described in the test method. The results seen in Figure 4, represent a dielectric grease that was properly forti­fied to protect the copper surface from corrosion and is typically what one would see for a 1A and 1B results on the corrosion scale. A dielectric grease that doesn’t offer protection against copper corrosion puts electrical contacts and connectors at risk for failure which can result in component malfunctions for customers and product recalls for manufacturers.

Greases have different water resistance capabilities depending on the thickener chemistry utilized in the formulation. ASTM D-1264, is a typical water washout test used to determine a greases’ resistance to water. In this test, a bearing is ­filled with a prescribed amount of grease and is inserted into a housing with speci­fied clearances and rotated at 600 rpm while water, controlled at 79 +/- 1°C, is sprayed on the bearing at a rate of 5 ml/second. After, the system is dried to remove water from testing components and the amount of grease remaining is recorded. The data in Table 3 shows the water washout characteristics of commonly used dielectric greases.

As previously mentioned, fretting corrosion can be detrimental to an electrical system. Nye Lubricants developed a custom fretting test rig to simulate fretting conditions. To test for fretting protection, 2.8 mm APEX tin copper connectors were used with testing conditions of 100 µm stroke amplitude and 10 hertz frequency until a failure (100 mΩ increase in resistance over the baseline initial readings) occurred.

When looking at electrical contacts or connectors if the upper metal coating has worn through to the base material as seen in Figure 5, this indicates that the component is experiencing a wear problem making it susceptible to oxidation which ultimately will lead to signal loss and component failure. Figure 4 represents a connector that was lubricated with one of Nye’s dielectric greases which contained an additive package that prevents fretting wear preserving the layered coatings on the contact to ensure the integrity of the electrical contact.