by Dick Topping, director of Appliance Research, TIAX, LLC
Jane noticed that the temperature in her refrigerator seemed to be rising. Since it was still under warranty, she called and asked for a manufacturer's service representative to investigate. By the time he arrived 2 days later, she had moved the majority of perishable foods into a cooler and emptied the freezer of half-thawed food. The refrigerator had clearly lost its ability to cool.
Upon close inspection, the service representative finds a green patina on the copper tubing. He attempts to recharge the system, but finds a system leak. He replaces the greenish tubing and successfully recharges the system. The undetected culprit? It was formicary or "ants nest" corrosion that resulted in pitting and pinholes where the refrigerant escaped.
Corrosion can be a very costly culprit for appliance producers. Heat exchangers are especially vulnerable to corrosion, and the causes are often ordinary household chemicals. With an average service sealed system repair costing more than U.S. $200 dollars, it doesn't take long for warranty costs to rack up into the hundreds of thousands or even millions of dollars to correct a design flaw. And as marketing departments search for ways to differentiate products from their competitors, they often push to lengthen warranty periods. Some of the higher-end lines now offer warranties that run 6, 8, even 10 years. The only defense against costly service repairs and customer dissatisfaction is to follow good design practices that address potential corrosion problems long before they occur.
Several years ago, the Gas Research Institute and a furnace manufacturer asked my company to investigate a problem with malfunctioning flame sensors. Basically, the flame sensors were becoming coated with SiO2, which resulted in a false message that the flame was out. This caused the system controller to go into lockout mode to disable the furnace. Unable to identify the mechanism causing the SiO2 coating, they turned to us.
Eric Carlson, a corrosion expert at TIAX, explained, "What we found was that minute concentrations of volatile organo-silicone-compounds in the household environment-were decomposing in the flame and depositing silicon dioxide on the sensor surface. And, surprisingly, the sources were quite common-furniture polishes, antistatic laundry materials, makeup, and hairspray."
Appliance producers can go a long way toward protecting themselves against the torments of corrosion by following preemptive design processes.
Understand the environment. For instance, food products can give off organic acids (e.g., formic and acetic) and bases (such as amines from fish products). Combine these with condensation, and the result can be aggressive corrosion. Even though they may start out as very diluted substances, as the solution evaporates, they can become very concentrated. Bleach is another potentially harmful substance that is found in many residences. And as appliances become increasingly loaded with electronics, special care has to be taken to ensure that sensors, switches, connectors, and circuit boards aren't compromised by corrosion of electrical contacts.
Select the appropriate materials. Though most appliance producers do not select every individual material that goes into their products, they need to monitor them. Has your component supplier adapted materials to your exact needs? Are they aware of how the operating conditions could affect their component? If you're contemplating using a new vendor, are they aware of the potential pitfalls of your environment? Vendors with experience in your area and who have developed good practices themselves will not run into problems because they will have engineered out potential materials issues before the product hits the market.
Ensure that components match your use. Component manufacturers should have intimate knowledge of your industry, and they should base their materials usage on this knowledge. Beyond that, they should be conducting accelerated testing methods to characterize suitability of their products for your applications. They need to conduct failure mode and effects analysis (FMEA), including consideration of corrosion failures. And you need to know how to interpret the reliability data that they provide you with.
Verify that QC has been performed. Quality control (QC) is vital to maintaining the quality of materials and their protective coatings. Depending on how well a vendor maintains and documents its intellectual property could greatly influence how well it transfers from one product to new designs and new products.
Despite good design, occasionally products will fail in unanticipated ways. When this occurs, it is essential to track field failures. If you see an abnormal failure rate for a component, rather than simply replace it, investigate further. Have service reps return the parts or get the supplying vendor involved. This is the only way you can see trends, conduct failure analysis, and prevent the problem from reoccurring.
Dick Topping is director of Appliance Research at TIAX LLC (www.tiax.biz), formerly Arthur D. Little’s Technology & Innovation business. He can be reached by phone at 617/498-6058, by fax at 617/498-7206, or e-mail at firstname.lastname@example.org. From the Top appears bimonthly in APPLIANCE ENGINEER.