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Porcelain enamel has been around for 4000 years and shows no signs of disappearing any time soon. Although alternative materials like stainless steel, plastics and paints continue to gain market share and have completely taken over some markets, such as dishwashers, the cooking and laundry appliance markets remain strong, and total frit production remains about the same. However, some manufacturers believe a huge revolution in materials technology is needed to ensure the continued success of the industry. Both suppliers and manufacturers are doing their share to help ensure that this revolution takes place.
Making the FritPorcelain enamel coatings are made from a frit based on low melting temperature (2000 to 2500°F) borosilicate glasses. After the glass raw materials are melted (generally in recuperative furnaces) at rates ranging from 5 to 50 tons per day, rapid quenching is used to shatter the resultant glass into small particles. Further particle size reduction is achieved by grinding. The coating is applied using wet suspension or dry electrostatic powder processes, and is then heated to about 1500°F to produce chemical bonding with the metal substrate.
Producers can achieve many colors and formulations in small melting units. Due to the low melting temperatures, the average dwell time is only a few hours. Since the frit is melted a second time with the metal substrate, seeds in the glass are not a concern as long as the melt is homogenized and all raw material reactions are completed.
Pre-milled frits now allow enamelers to custom blend their own enamel formulations without using costly milling equipment. The enameler can blend the exact amount required for the job, eliminating waste. Blends can be made almost "just in time," eliminating the need for a large wet enamel inventory.
Many frit manufacturers have switched from air/gas to oxygen/gas combustion systems to lower their emissions, and this trend is expected to continue. Smelters have become more automated, and larger capacities are being used as product volumes increase through the increased standardization of frits.
Frit manufacturers continue to research coatings to address new applications. For instance, unique appearance characteristics are under development, including metallic lusters to simulate copper metal or stainless steel appearances. Refinements in frit products are also being made to achieve "easy to clean" oven coatings, as well as infrared reflectivity for faster cooking. In addition, hybrid coatings are being investigated to take advantage of properties provided by both porcelain enamel and organic coatings.
Improvements in ManufacturingFirst developed over 50 years ago, the electrostatic dry powder process, in which dry powdered frit is sprayed onto the prepared metal surface, is now used by most companies since it is an environmentally friendly process, generating no waste. Tighter U.S. Environmental Protection Agency (EPA) regulations have also virtually eliminated the use of the pickle/nickel process, in which a pickling solution was used to nickel plate the steel substrate so that it bonded to the ground coat enamel. Today's "pickle free" enamels use frits that are designed to react chemically and mechanically to form a tight bond directly with the substrate.
The use of CNC robotics and other computer controlled automation equipment has greatly improved enameling efficiencies and protects workers from hazardous jobs. For instance, coating systems have been introduced with automatic product recognition and application program selection features. These trends will continue as manufacturers seek to increase their flexibility and range of products. Automated troubleshooting systems will become popular as well. New firing technologies, including those based on induction and infrared, are also being investigated to reduce costs.
In addition to installing automated coating equipment, other novel processes have been implemented to improve productivity. For instance, ultrasonic cleaning is being used at several plants. Switching to this method from a conventional acid/nickel system can reduce energy costs, eliminate hazardous chemicals and improve the degree of cleaning. Production costs can also be reduced, since the cleaning operation typically requires less time (nine hours vs. 12 hours in one instance).
Electrophoretic enameling, in which a wet porcelain slip is applied to the charged metal part, continues to gain wide acceptance in Europe and is making progress in the U.S. Since 1995, several new production lines have been installed in Italy, Germany and Yugoslavia. The advantages of this process include reduced coating costs, a smoother surface finish, precise thickness control, excellent edge coverage, minimum floor space requirements, and reduced wastewater requirements since porcelain usage is virtually 100%. (The coating does not have to be dried before it can be fired.) Applications include flatware, microwave ovens and burner grates.
Improvements also continue in materials. These include the classification of cover coat powders, moisture-resistant base coat powders, and control of fleck size in ground coat powders. Ferro France has developed an 1100iF self-opacifying electrostatic powder for aluminized steel and aluminum alloys. These developments have helped improve coating uniformity and overall quality. Additionally, porcelain decals in multi-colors for range backgrounds and manifolds have replaced single color screening pastes.
Quality ControlA wide range of testing and analysis methods are being used to improve quality. Raman spectroscopy can be combined with scanning electron microscopy (SEM) for defect analysis. In a study of a one-coat enamel, a high percentage of iron was found, along with Cr2O3 and elements like silicon. An SEM equipped with an energy dispersive X-ray system can reduce the time needed to pinpoint defect causes and reduce overall defects.
Failure mode effects analysis (FMEA), an analytical technique that assesses the probability of failure and the effect of such failure, can improve reliability of products, reduce or eliminate defects, and improve design and manufacturing processes. Advanced product quality planning and cost-of-quality systems are other tools in use that achieve similar results.
In addition to these sophisticated techniques, traditional methods are finding their place as well. The 100-year-old pyrometric cone, in a fast-firing version, is being used to determine temperature differences within porcelain enamel furnaces, compare different furnaces, and/or check for changes in temperature readings that may have occurred because of thermocouple drift. Fast-fire cones are placed in different locations on a metal rack that passes through the furnace.
When used properly, cones can determine temperatures and temperature differences within two degrees Celsius. Ferro Corp. in Cleveland, Ohio, has found cones to be a rapid, economical means to monitor heat work on parts. The devices can quickly determine if changes in finished fire appearance or adhesion are caused by fluctuations during firing.
Standards like ISO 9000, or its equivalent (QS9000), are now widely used and have given manufacturers more confidence in their suppliers. "There are many misconceptions about porcelain enameling being more of an art than a definable, controllable process," says Kara Kopplin, president of Custom Ceramic Coatings, Inc. in Lenzburg, Ill. "ISO 9000 helps dispel those misconceptions. It gives documented evidence that enameling is a technical process that can be controlled and successfully executed."
Color standardization will also become more important on high end products, according to Maytag's Jeff Sellins (Cleveland, Ohio). "Thickness testing of unfired powders will become more popular," he adds. In addition, some porcelain enamel suppliers believe users need to develop simple in-process tests to determine the cause of defects. PEI's efforts are focusing on the characterization and testing of powder enamel. Once new test procedures are developed, they are submitted to ASTM for approval.
Another important trend in quality control is the review by appliance manufacturers of traditional/historic requirements for porcelain enamel, according to Jeff Wright, manager of market satisfaction for the Appliance Division of Ferro Corp.'s Industrial Coatings Group. Because this review is expected to result in relaxed porcelain enamel specifications to meet application requirements, porcelain enamel could be the coating of choice in place of alternatives. "This change could possibly allow for reduced cost of porcelain enamel systems and perhaps more robust, less stringent processing requirements," suggests Wright.
New ApplicationsMicrowave ovens may be one application that increases consumption of porcelain enamel, at least in international markets. In the last several years, new production lines for this application have been installed. Moulinex, a French manufacturer of small to medium-sized household appliances, has a plant in Cormelles-le-Royal in northern France that uses electrostatic powder. Its production capacity is 240 microwave ovens per hour.
Samsung has also installed a microwave oven line at its U.K. plant at Wynyard Park near Billingham. Using a special recycling system based on filter recovery and a squeegee system, up to 99% powder utilization is achievable. The advantages of using porcelain enamel include energy savings, better scratch resistance, ease of cleaning and improved nutritional value-food maintains a 5% higher level of vitamins C and D than with conventional cooking methods.
Aluminum cast grates for ranges can now be produced with superior heat resistance and performance by coating with porcelain enamel, and the service life of porcelain coatings for steel and cast iron grates has also improved. Special formulations for electronic and sanitaryware applications have been developed as well. Antimicrobial porcelain enamel coatings are popular in the Far East for bathtubs and other uses.
Consumers also want more colors to choose from. Thus, new enameling materials for color electrostatic coatings that do not require a coloring frit are under development to expand the color palette from the current six to eight colors. Direct one-cover coats for specially processed steel are also being investigated.
PE in CyberspaceAnother relatively new technology that may help the industry grow is the Internet. The new BuyPorcelain.org website for consumers, sponsored by PEI, has seen traffic continue to build. In the first 83 days online, the site received 29,803 total hits and 2028 pages viewed (these are requests beyond the home page for further information or links to the membership).
The website is also mentioned on television ads, which brings more hits. "We have had around 70,000 hits since February," says Cullen Hackler, executive vice president of PEI, "and several hundred people a day that go deeper into the website and link up with others." Traffic continues to increase as more visitors find and begin to use the site.
Career centers for the porcelain enamel industry are also expected to go online. A business-to-business purchasing site, where all material can be bought in an exchange, is currently being set up by the industry. Buying and selling excess material and equipment in auction formats online, the E-Bay equivalent for porcelain enamel, is also predicted. "The Internet will provide a marketing and educational base for porcelain enamel," says Maytag's Sellins.
The Internet is also becoming a valuable tool for improving customer satisfaction. Electronic transfer of laboratory results (image analysis of defects) to salespeople or customers can be done in almost real time. By capturing images digitally and using e-mail or online/live video conferencing, the quality of photomicrographs and the speed of sending results are both drastically improved. The frit supplier, steel mill, enameler, and customer now can all be online discussing their analyses of the problems and working together to find a solution.
Future ChallengesLike the rest of the ceramic industry, the porcelain enamel industry continues to shrink as companies merge or plants close. As of April of this year, PEMCO Corp., headquartered in Baltimore, Md., completed the acquisition of C.V. Materials, Ltd. in Urbana, Ohio. Company sources indicated that the complementary nature of the C.V. Materials business in North America, along with export business to Central America and Asia, made the acquisition a good fit with PEMCO's worldwide growth plans. This acquisition is PEMCO's third in the past two years; the others being PEMCO Emailtechnik in Germany and PEMCO Emelier in Argentina.
Alternative materials will also continue to threaten the porcelain enamel industry. For instance, high-temperature paints may replace porcelain on cooking grates and burners. PEI continues to fight back with its marketing program and is increasing its advertising efforts in 2001. This program seems to be helping as the industry has recaptured the market for certain appliance parts.
"The use of porcelain enamel for barbecue grills and wood burning stoves is increasing, as well as interest in architectural panels for modular cities and other applications," says PEI's Hackler. "Alternative materials may be the choice for some products," he adds, "but high end products will require the heat resistance, durability, and performance of porcelain enamel." Porcelain enamel also continues to be the most reliable, cost effective coating for water heater interiors.
However, Robert Long, president of American Porcelain Enamel Co. in Muskegon, Mich., points out another major problem. "There is a high turnover of production workers in the industry and there is also a lack of technicians," he explains. "More vocational training is needed." Although PEI has a back-to-basics course, Long believes PEI should do more in this area.
Some believe environmental regulations will become stricter, especially regarding metals in powders and wet groundcoats. Fewer EPA studies and surveys could lead to more unrealistic regulations. Regulations in the metal processing and machining areas may also have some impact. PEI is working with the National Sanitation Foundation on water quality regulations, and is also working with a number of other trade and professional associations, including those representing the gas and home appliance manufacturers, to address some of the other challenges. How these efforts ultimately help the porcelain enamel industry remains to be seen. But Long still believes porcelain enamel is here to stay. "As long as there is steel and iron [that needs protection], there will be a need for it," he says.
The quality that porcelain enamel brings to appliances and other items is once again being recognized as the population becomes more "quality driven," says Wright. "I expect that we will continue to see significant new product and process developments throughout the next decade," he predicts. These developments will help expand market opportunities in aluminum cookware, architectural marker boards, and sanitaryware, and will help ensure the future of the porcelain enamel market for decades to come.
Editor's note: All photos in this article were supplied courtesy of the Porcelain Enamel Institute.