August 2004
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Having the right equipment is essential to succeed in just about any endeavor. If your plans for success include recycling aluminum, then owning a sweat furnace should be an important part of your plan as well.

A sweat furnace enables recyclers to convert piles of mixed aluminum scrap into more uniform, saleable ingots or sows. The advantage this affords the recycler, of course, is that buyers of aluminum ingots have a much better understanding of the material’s composition, which in turn affects the price it brings in the market. Mill buyers prefer ingots to mixed scrap because they make a cleaner product and are ready to go directly into their process.

An aluminum sweat furnace can generally process from several hundred pounds to as much as a ton of scrap aluminum per hour, depending on the size of the unit.

Sweat furnaces are bound by a number of government regulations. Buyers should be certain that any furnace they consider – whether new or used – complies with these regulations.

While compliance with government regulations can seem complicated, some sweat furnace manufacturers offer aluminum recyclers much needed help. Dave Conway, president of Recycling Services International, LLC (RSI) of Cohoes, New York near Albany said, “We include a package of information with every furnace we sell to help customers understand exactly what must be done – and when – in order to comply with the law. In the package is a manual for standard operating procedures, a second that covers maintenance and malfunction procedures, and another for emergency start up and shut down. It’s easy for customers to stay in compliance, because all of the key activities are listed on a calendar, also part of the package. There is weekly, bi-weekly, monthly and quarterly tasks plainly spelled out. We even supply the proper forms. They know when reports must be filed with the government, and when key service procedures must be performed to keep their furnace up and running more efficiently. It’s all right there on the calendar,” he said.

Jerome Mostek, owner of Aluminum King Manufacturing, LTD., a manufacturer of aluminum sweat furnaces, said his company consulted the Environmental Protection Agency when regulations concerning aluminum sweat furnaces were changed.

“All of the furnaces we manufacture feature a temperature probe in the combustion chamber to record the average temperature and a data logger. The data logger creates a permanent record of the critical information such as temperature and how long the gas is retained in the afterburner. It stores the information in a computer file. The file is then available for inspectors,” said Mr. Mostek.

When aluminum is melted, dioxins and furans are released in the form of gas. These compounds are known to cause or are suspected to cause cancer and other serious health threats. The afterburner contains these potentially harmful compounds for just under a second and incinerates them thoroughly before exhausting the spent gases to atmosphere. In addition to momentary containment, the temperature must average 1600°F to meet federal regulations.

This temperature will ensure that any potential harmful compounds are fully incinerated before exhausting to atmosphere. All commercially manufactured aluminum sweat furnaces today are equipped with afterburners. However, if a buyer is considering an older, used furnace, they should confirm that it is equipped with one.

Dave Conway of RSI, LLC added, “Some time ago, we began equipping our furnaces with a special interlock switch. The switch prevents the primary charge door from opening if the temperature in the afterburner is below the required 1600°F. That way, customers automatically stay in compliance with that part of the regulations,” he said.

Another consideration when shopping for a furnace is the general build quality of the unit. Anytime metals are exposed to extreme heat, stresses and wear will invariably occur. Generally speaking, the heavier the gauge of material the furnace is made from, the longer it is likely to last.

Jerome Mostek observed, “The weight of your furnace is a good indicator of its general quality. If there’s a big difference in weight between two different furnaces of the same size, you know you are getting a better value with the heavier furnace.”

Before choosing a furnace, recyclers should examine the typical mix of material they plan to recover. Whenever possible, recyclers should sort the material going in to minimize loss of material in the melt. Light gauge material will melt more quickly than heavy gauge at the same temperature. But the longer the recovered aluminum remains in a molten state, a certain portion is simply burned up. “Either too much heat, or too little heat creates problems,” said Mr. Mostek. “Too much burns up the aluminum and not enough heat fuel takes too long and can waste fuel. The furnace must be balanced with just the right amount of heat for the best results.”

As the content of aluminum continues to increase in most automobiles on the road today, recyclers must deal with an increasing variety of recovered components such as transmission castings, cylinder heads, manifolds and other chassis and interior parts.

EnviroAir, Inc., of Eagle, Wisconsin, offers a variation of the conventional aluminum sweat furnace. Company president Doug Stenz explains, “Our design is a rotary kiln. There is a lot of scrap metal recovered today that is either zinc plated or aluminum coated. With a rotary kiln design, recyclers can process a mixed load of scrap, and still get clean ingots. Zinc melts at a lower temperature, so the operator can bring the furnace to that point, spin the kiln and draw off the molten zinc. Then the temperature is increased until the aluminum melts off and it too is recovered in the same manner. That leaves just the ferrous base metal parts,” he said. EnviroAir purchased the assets of the former College Research Corporation, retaining the CORECO brand for its sweat furnace line.

Most aluminum sweat furnaces use natural gas, propane or diesel fuel to support combustion, and at today’s fuel costs – that accounts for the greatest expense in operating a furnace. Newer fuels such as biodiesel are also suitable. Permits can be granted for the use of waste gasoline and waste oil as well.

Burning waste fuel and recovered motor oil makes perfect sense for auto recyclers – a target market for aluminum sweat furnace makers. Cost savings are realized not only in fuel for the furnace, but by not having to pay for transportation and disposal of the recovered fluids. All that is required for auto recyclers to burn recovered oil is a permit from their respective state.

Maintenance of an aluminum sweat furnace includes the periodic inspection and repair of the lining of the smelter. Over time, small chips or cracks can appear in the firebrick lining that must be patched. Special putty for high refractory applications is used to repair any blemishes in the lining of the furnace. Provided no hostile material is melted down, a typical recycler can expect to process several million pounds of scrap aluminum before relining the furnace. According to Jerome Mostek, “The job isn’t that difficult to do. Most recyclers can reline their own furnace if it becomes necessary, without paying for a service call from the manufacturer.”

Burner maintenance is also an important element for longevity of a sweat furnace. In addition to the required annual inspection of the afterburner, recyclers should be sure the burner assemblies are kept clean and free of corrosion. A clean burner supports more efficient combustion, which can also impact fuel costs over extended periods of time.

Not surprisingly, the last factor in the successful operation of an aluminum sweat furnace is often the most overlooked - a properly trained staff. “It takes some experience to learn how to load a furnace, balance the heat and cycle material through the process most efficiently,” said Doug Stenz, of EnviroAir.

“Safety, maintenance, fuel costs and the quality of material produced are all the result of trained people knowing what they’re doing.” The effective operation of an aluminum sweat furnace is an area where employee training can pay big dividends for recyclers.