Sand reclamation 1995: is it time for your foundry?

While process and economic variables dictate reclamation feasibility, some firms are saving money on their total sand costs.

While you hear many things about spent foundry sand reclamation, one that comes up often is "if you don't do it now, chances are you will have to in the next few years." The reasons are well documented: closing landfills; increased hauling, tipping and disposal fees; liability issues; changing environmental regulations; and increased materials costs.

Many foundries still have easy, inexpensive access to their local landfills. A few may be lucky enough to have a beneficial reuse alternative for their spent sands. But there is no guarantee of continued landfill access, and progress on reuse applications is slow.

Sand reclamation itself can be a confusing topic, with as many variables as any process in the foundry. D.J. Couture, GM Powertrain, Saginaw, Michigan, said of reclamation, "There is no general rule of thumb. It all depends on your needs. Do you want to reclaim core sand to molding sand, green sand to core sand, green sand to chemically bonded sand? Do you use high-purity silica or lake sand?"

For foundries considering a reclamation system, Couture suggests, "Do your own testing. What works for the foundry next door may not work for you."

Nevertheless, foundries are reclaiming their sand. To succeed, preparation and information are crucial.

According to Tom Jancek, RMT, Inc., Lansing, Michigan, "The first thing a foundry must do is reduce the number of waste streams coming from the plant." In-house process control steps such as reducing core room scrap and keeping a close inventory of binder use can cut waste and save money even before a decision on sand reclamation is made.

Jancek suggested drawing up comprehensive materials flow diagrams that list every thing coming into the foundry, and everything leaving it. Use your Material Safety Data Sheets (MSDSs) to know every constituent in every chemical you add to your sand, which will help you choose the right reclaimer for your operation.

Whatever you do with your spent sand must make economic sense. In many cases, traditional disposal may be the most cost-effective solution. External beneficial reuse almost always requires some processing before your sand leaves the foundry, and the foundry probably has to pay for hauling.

When considering reclamation, remember that you rarely purchase only the reclaimer. You will need other components for screening, classification, storage and handling, depending on how extensive your sand-handling system already is. It costs money to properly integrate a reclaimer into your existing operations.

Daryl Hoyt, Wedron Silica, Wedron, Illinois, said "No matter how large or small a reclaimer you're buying, the control system will cost between $50,000 and $75,000." Besides the initial capital investment, reclamation can be expensive in operation, factoring in energy costs and maintenance.

As with external reuse, a foundry must have the volume of sand necessary to make reclamation worthwhile. Do you use enough that the annual cost of disposal is high enough that your reclaimer will give you a reasonable return on investment? Do you have enough tonnage to operate the system continually if that is necessary for maintenance requirements and energy costs?

Also, once you have a reclamation system in place, it may restrict the types of changes you can make in your operations. "You can't suddenly change the rules on your reclaimer," Hoyt said. "Different machines do different things, and a change in sand composition could make the reclaimer useless."

No matter which method of reclamation is employed, lump crushing and sand granulation is the first essential reclamation step. After that, your choice of system rests on your specific requirements - sand/binder system, tonnage, energy costs and space limitations.

A basic framework for understanding which method is applicable to both your source sand and its desired reuse is: green sand to green sand - mechanical; chemically bonded to chemically bonded - mechanical or thermal; green to chemically bonded - thermal & mechanical.

What happens to the spent sand grain inside the reclaimer? Obviously, the objective is to remove the binder from the sand grain, leaving a "virgin" material ready for recoating. The various systems accomplish this in different ways, but all must have a way to remove tramp metal from the sand, classify and screen it, cool it if necessary, and transport and store it.

Wet Reclamation

Wet reclamation uses water as a solvent. Typically, the sand grains are vigorously stirred within a bath of water, which dissolves the binder. The method is only applicable with water-based binder systems, such as sodium silicates and clays.

Once the sand leaves the water, it must be dried - a very energy intensive, and therefore expensive, process. Another problem is that wet reclamation creates a new waste stream of high pH water, which requires its own handling system and leads into another set of environmental regulations.

Mechanical Reclamation

While mechanical reclamation can mean the simple breaking of lumps, it generally refers to the physical processing of the sand grains to remove residual materials. There are two ways of accomplishing this.

In the pneumatic or impingement method, the grains are pneumatically hurled against a target and each other while a dust collector removes the fines and dust generated by the impact.

Attrition is the grinding of the grains together (scrubbing). The binder is removed and the sharp edges of the sand grains become rounded, reducing surface area and necessitating less binder upon reuse. Again, a dust collection system must be employed to remove the residual materials, therefore generating a solid waste stream. It is important to note that impingement and attrition are never mutually exclusive; both mechanisms necessarily occur naturally within the same reclaimer.

Mechanical reclamation is effective in maximizing the life of green sand. Unlike thermal attrition, which kills and embrittles all the clay binder, it preserves the desirable active clay, which cannot be simply knocked off through physical contact.

In green sand to green sand applications, "pneumatic reclaimers are really purging systems that remove only the undesirable elements," said Matt Granlund, Foundry Systems Control, St. Joseph, Minnesota. "Because you still have active clay in there, you don't want to remove all of it. You just want to purge the sand and replace the spent clay with new addition."

Table 1. Bahr Bros. Reclaiming Costs Vs. Savings

Costs:

Maintenance                    $640.00/month
Gas for Thermal Unit          $2500.00/month
Electrical Costs                120.00/month
1 Sand Load to
Replace Dust Collecter         $804.44/month

Total                         $4064.44/month

Savings:

Dumping Costs
($19/ton x 520)               $9,880.00
New Sand ($30.94/ton)        $16,088.80
Less Actual Costs             $4,064.44

Total                        $21,904.36/month

Mechanical methods are also highly efficient in recycling chemically bonded sand for reuse in the same binder system - or one that is compatible - because a lesser degree of residual binder must be removed.

Thermal Reclamation

This method entails heating the grains to the point of oxidation, so that the coating combusts. Commercial systems differ in the configuration, heating method and the time the grain stays within the heating chamber (usually 30-60 minutes). Some employ a fluidized bed for uniform sand heating, while others rely on mechanical sand manipulation within the unit, such as rotary calcining. Power options include gas and electricity.

Thermal reclamation is most commonly used in reclaiming unlike binder systems, where all the binder must be removed before rebonding with the new system: acid catalyzed to basic, for example. Because calcining thoroughly kills clay, it is ideal for applications in which green sand is reclaimed for use in the core room. However, because desirable active clays remain in green sand, thermal reclamation is generally not suitable for green sand to green sand applications.

Another consideration with thermal use is that inorganics cannot be combusted. Sources of inorganics are some binders, iron oxides, inhibitors and other additives. While some binders may at first appear to be organic, they may have inorganic constituents, which will remain on the grain.

Though calcining is often used on green sand in conjunction with scrubbing, critics say that calcining temperatures - in the 1300-1400F (704-760c) range - actually fuse clays to the grain. Though attrition will still remove most of the binder, that which stays in hollows of the grain and cannot be physically reached will remain and actually build up. There are examples to suggest that using lower temperatures in combination systems will accomplish the same results of embrittling the coating for easy removal without "baking" the binder to the grain surface.

Granlund, however, said "If you have western (sodium) bentonite in there, you have to get it up to 1300F (704c) to embrittle it enough for removal."

Once the sand leaves the kiln, cooling is required before storage or reentry to the sand system, necessitating the purchase of cooling equipment. The thermal method - whether gas-fired or electric - is also energy intensive. Of course, the savings in new sand and disposal costs may outweigh the utility bill. Technological advancements in thermal reclamation in the last several years have largely focused on making the units more energy efficient, recuperating excess heat to help fire the systems and cut energy usage.

Environmental Factors

No matter what the method, reclamation generates waste streams. As mentioned above, wet reclamation generates high-pH water. Mechanical reclamation creates fines, dust and residuals that must be captured in a dust collector or baghouse. Thermal reclamation creates air exhaust contaminated with combustion by-products, as well as fines. When choosing a system, any by-product generated during operation should be considered with an eye toward current and future regulations.

For thermal reclamation, this is especially important. A recent policy determination by U.S. EPA potentially views thermal reclaimers used on brass foundry sands as hazardous waste incinerators. Should this determination be adopted as an enforced regulation, brass foundries with the units would be forced to apply for a part B permit - a two-year process during which the reclaimer may not be operated.

Thermal Success

Bahr Bros, Manufacturing Co., Inc., is a 70-employee foundry in Marion, Indiana, pouring 2500 tons a year of gray and ductile iron, as well as steel and stainless steel. The shop uses ester phenolic nobake molding to cast parts up to 2000 lb. In 1977, Bahr Bros. bought a mechanical reclamation unit. The attrition mill allowed Bahr Bros. to mold with mixes of 50% reclaimed sand, cutting disposal and new sand costs.

In the late 1980s, with landfilling costs rapidly escalating, foundry officials began to seriously consider investing in a thermal reclaimer. But at the time, the foundry wasn't using enough sand to lustily the investment, and felt that thermal reclamation hadn't yet been proven as a viable technology.

By 1992, however, Bahr Bros. was using up to five 26-ton truck loads of sand per week. Working out the cost of the new sand, along with freight and landfilling costs for the spent material, officials realized they were spending $204,750 per year on sand. It was time to shop for a system.

"At that time," said owner Jeff Jackson, "we realized that whatever the cost of dumping our sand was, it was certain to go up."

In looking for a reclamation system, Bahr Bros.' goal was 100% sand reuse. "Early on, we had decided to go with a thermal system," Jackson said. "Because mechanical reclamation couldn't remove old oil buildup from the sand, none of the mechanical system suppliers could guarantee us over 80% reclaimed sand utilization."

Officials shopped carefully, canvassing five thermal system manufacturers as to capital and operating costs, size and space requirements maintenance and efficiency. Eventually, a one ton per hour fluid-bed thermal reclaimer from Simplicity-Richards was selected because it had very few moving parts and appeared to require little maintenance. "Also, Simplicity was physically close to us," said Jackson. "We figured if we did have problems, we could get them resolved more quickly."

To minimize the capital outlay, foundry officials "tore their quote apart again, looking at what we could do ourselves and what we could do with them," Jackson said. Simplicity-Richards supplied the lumpbreaker, elevator, classifying equipment, air transporter, electronics and the furnace itself. The foundry purchased a cooling tower, air compressor and dust collector separately. The thermal system would require the construction of a separate building, and the foundry handled as much of its construction as possible to minimize costs.

In operation, the system runs 24 hr a day, seven days a week. "The unit is rated at one ton per hour, but we're getting 1.5. Though it must be shut down 2-3 times per day to change the filters and shake the bags in the baghouse, and there has occasionally been some clogging of the screens leading to the furnace, the foundry has experienced a minimum of problems with the system. "It's very simple," said Jackson. "There really isn't all that much that can go wrong with it."

The foundry's new sand requirements have gone from 520 tons per month to just 26. The original mechanical reclamation unit Bahr Bros. bought in 1977 is still in operation, and still performing half the reclamation duties. "We're fortunate enough to have one sand system and one binder," Jackson said. "We're reusing 100% of our sand.

"We make a few very intricate castings. In the past, we had to use 100% new sand for them, because the new sand molded in stronger than the new sand mixed with mechanically reclaimed sand," he explains. "We now produce these parts with 100% thermally reclaimed sand and get the same strong mold and good-looking castings."

Jackson said there are other benefits to the system. "We now have a dependable supply of sand, since we aren't subject to ice storms or truck strikes."

Table 1 shows the actual costs and savings Bahr Bros. has experienced since the installation was completed in September, 1993. The total capital investment was $450,000. Dividing that number by the $21,904.36 per month the foundry is saving, the return on investment was 20.54 months.

In gathering the cash for the initial investment, Bahr Bros. obtained a loan of $191,000 from the Indiana Commerce Dept. Office of Energy Policy, and Jackson recommends foundries considering a reclamation system look into this kind of funding for environmentally friendly investments.

A Switch to Attrition

With 40 employees, Wolverine Bronze, Roseville, Michigan, casts a variety of brass and bronze parts, as well as large aluminum castings weighing up to 30,000 lb. The Wolverine plant is actually composed of two separate foundries - one running phenolic urethane nobake molding for small castings, and the other using an alkyd oil binder system for large parts.

In 1984, as landfilling costs began to soar, Wolverine installed a thermal reclamation system. Unfortunately, once the system had been installed, some economic problems became apparent. As a jobbing foundry, Wolverine was subject to wide variations in the amount of sand used per day (8-90 tons per day). The thermal system they had required continuous throughput, and as a consequence, was often idle. However, it still needed to be kept hot to allow quick start-up without damaging the system. Repair was more frequent than had been expected, and the system was often unavailable.

Officials also discovered that the foundry's two binder systems were incompatible. Though both were considered organic, the metal salts in the alkyd oil binder could not be burned off and consequently built up, leading to problems in rebonding with the phenolic urethane system.

Though no records were kept, Wolverine estimates that it was spending $30 per ton on reclaimed sand - only slightly less than sand costs before installation.

In 1989, Wolverine began looking into replacing the thermal system. By June of 1991, the foundry had begun operation with a batch attrition system from Eirich Machines, Ltd. "The whole installation cost us somewhere in the neighborhood of $700,000," said Wolverine's Paul Smith. "Had we had a compatible sand-handling system in place, it probably would have been around $250,000." Despite the size of the capital investment, Smith said, "We looked at it in terms of how much money it would save us. We still have to haul some away at something like $18 per yd for disposal. But we reclaim 100 tons a week. Imagine what we'd spend if we didn't."

As seen in the inset photo in Fig. 1, within the attrition unit, a rotating outer drum and counter-rotating impeller arms cause two separate sand streams to repeatedly collide for five minutes, scrubbing the binder from the grains. Low pressure air is used to convey fines and eroded binder to a dedicated dust collector. Because the intensive attrition can raise the sand temperature 30-50F (1-10c) above ambient, a flow-through cooler with a closed-loop water system was installed to bring sand leaving the attrition unit to 85F (30c). The reclaimer also has the capability for thermal operation should Wolverine change binder systems.

Because of the difficulties in feeding sand to two separate foundries, great care was given to sand handling. The sand is pneumatically transported from the reclaimer to the storage silos using a high-volume, low-velocity air stream. Sand flow is held to fewer than 10 ft per rain to avoid fines generation and excessive pipe wear, and allowing no silica dust to escape into the air.

Wolverine's reclaimed sand displays excellent rebonding characteristics in the alkyd oil binder system, and shakeout and tensile strength characteristics have improved. "It doesn't rebond well at all in the nobake system, but that's not the reclaimer's fault, it's the lead in the binder system," Smith said. "On that line, which is only for smaller molds, we just use new sand." The new sand addition necessary is 8% of the total sand tonnage.

Using a PLC, the system usually runs unattended 13 hr per day, mostly at night and on weekends when power demand is lower. "We're so busy right now," Smith said, "it's running 24 hr a day." It reclaims four tons of sand an hour in 700-lb batches. Wolverine now reports reclaimed sand costs to be less than $10 per ton, with maintenance costs on the system at $2.40 per ton. Smith said, "The PLC lets us know of any problems before they happen."

A Combination System

R.H. Sheppard Co., Hanover, Pennsylvania, is a 200-employee green sand foundry, pouring 150 tons per day of compacted graphite, gray, ductile and austempered ductile iron for use in a variety of industries. Many of these castings are extremely complex, some requiring as many as 30 cores, all produced in the shell and phenolic ester coldbox processes.

Since its installation in 1989, when a new building was constructed on site to house it, a continuously running green sand recycling system has produced 12 tons of reclaimed material a day. About 70% of the sand now replaces new sand in the plant's coldbox system, resulting in core mixtures of 100% reclaimed sand and 2% binder. The other 30% goes back into the green sand system as new sand additive.

The Coreco system [ILLUSTRATION FOR FIGURE 2 OMITTED] is a 0.5 ton/hr unit consisting of an indirectly heated rotary kiln, a rotary sand cooler and a pneumatic scrubber and classifier. That setup is immediately followed by an identical one.

Shakeout sand, lumps from the screen and corebutts are first reduced with an auxilliary vibratory crusher. The sand is then run through a magnetic separator to remove tramp metal and transported via belt to the first rotary kiln, where it is indirectly heated to 1250F (676C) by natural gas. Inside the kiln, the sand is raised to the top by lifter bars and then cascaded down for maximum heat transfer. In this phase, the bulk of residue on the sand grain is dried and embrittled for easy scrubbing, and the low temperature avoids fusing the clay to the grain.

The sand passes from the kiln to a rotary cooler, where it is cascaded through an ambient airstream until it is about 10F above the ambient temperature. Oversized material is separated out before the sand is fed through the first scrubber and classifier. High-velocity compressed air shoots it through the scrubbing tube, where sand-to-sand abrasion removes most of the clay.

At the end of the tube is an impact plate through which the sand dust and residues are dispersed into the classifying chamber. After that, the entire process is repeated through the second set of equipment. The second kiln operates at 1500F (815C) to remove any residual combustible material.

The reclaimed sand rebonds equally well in the nobake and green sand systems. "We have an electric eye mold handling system," said Sheppard's Steven Clark, "and unless the corners of our molds are sharp and precise, it won't register them. The reclaimed sand has very high hot and dry strength."

A year after the reclaimer's installation, R.H. Sheppard reported a sand disposal savings of over $130,000 and of $42,000 in new sand purchases, for a total yearly savings of nearly $173,000. Taking operating costs into consideration, the estimated return on investment was three years. According to Clark, however, "We beat that by 14-18 months, and we're reusing every pound of sand. This is the best investment I've ever made."

In fact, Sheppard is expanding its capabilities with the installation of an identical system, and raising the roof on part of the foundry from 20 to 50 ft, to bring both to a central location within the plant. The new unit will double capacity to one ton per hour.

Emissions from the first reclaimer have been monitored by the Dept. of Environmental Resources and are well under current limits. Permits have already been issued for the second reclaimer.

While construction costs are considerable, Clark again expects a 3-year return on investment. "You don't do it for a payback," he said, "you do it to make sure you're in business in five years."

RELATED ARTICLE:

The General Kinematics Vibra-Mill attrition mill (l) reduces sand lamps from a variety of binder systems down to the original grains while maintaining size distribution. Available in a variety of sizes, it automatically purges tramp metal and other materials, separates fines and reduces sand temperature. The self-contained, energy-efficient unit is useful as the first step in a comprehensive sand reclamation system or on its own. Units have been installed at more than 200 foundries in the last 15 years.

The Thermfire 1000 from Gudgeon Bros., Ltd. uses a calcining fluid-bed beside a cooling fluid-bed to thermally reclaim chemically bonded sand to an LOI of .02-.05%. With a capacity of 1/2 ton/hr, a full system with dust collector, pneumatic transporter, cooling tower and dilution duct is available for $150,000. Installations include; Cunningham Foundry & Machine Co., St. Catherine, Ontario; Castalloy Corp., Waukesha, Wisconsin; and Montupet, Ltd., Riviere Beaudette, Quebec.

For thermally reclaiming all types of sand and organic binders, Castec's Thermpak (r) uses electricity or gas indirect radiant heating. Sizes range from 700-6000 lb/hr and prices begin at $125,000 for the complete system, which includes sand pump, heat exchanger, calcining vessel, cooling system and PLC. Applicable in any foundry using more than 5 tons/day, the sub-base mounted system is prepiped, wired and fully assembled. Installations include Empire Steel Castings, Reading, Pennsylvania.

National Engineering Co.'s Simpson Pro-Claim pneumatically reclaims a variety of sands and binder systems. Ideal for green sand to green sand and compatible chemically bonded sands, it can be coupled with a thermal reclaimer for green sand to core sand applications. Over 500 installations include: ESCO Corp., Newton, Mississippi; NACO-National Castings, Melrose Park, Illinois; and Price Pfister, Inc., Pacoma, California.

For foundries whose total sand cost approaches $30/ton, Sand Systems, Inc.'s GR Kalciner II is a gas-fired rotary kiln that reclaims chemically bonded sands with 20% greater thermal efficiency than fluid-bed reclaimers, and is effective on green sand when coupled with a scrubber. Units are available in sizes from 1/2-3 tons/hr, at prices from $120,000-$350,000 with sand cooler. A unit has been installed at Elyria Foundry, Elyria, Ohio.

Pangborn Corp.'s ISS includes a rotocrusher, rotoconditioner scrubber, sand cooler, magnetic separator and recirculation components to mechanically scrub nobake sands for any size foundry. It is available in sizes from 1-40 tons/hr, and controls residual binder and sand grain size. Installed systems include: Buckeye Steel Castings, Columbus, Ohio; Atchison Castings, Atchison, Kansas; and Amite Foundry, Amite, Louisiana.

George Fischer Foundry Systems, Inc.'s Gamma-Vator 3 (l) shakes out, scrubs and classifies chemically bonded sand at rates of up to 3 tons/hr. It eliminates a separate shakeout, and affordable installation requires no pits. It can be arranged with a standard classification unit and sand cooler, and the attrition chamber is fully protected with replaceable wear liners. The unit has been installed at 50 foundries worldwide.

Beardsley & Piper's two-compartment Pneu-Reclaim uses pneumatic scrubbing to reclaim 1.5 tons/hr of green and nobake sands. It has an adjustable baffle, rubber-lined deflector and controlled discharge. The reclaimer costs $28,235, and can be purchased with a complete system, including dust collector. Installations include: Lodi Iron Works, Lodi, California; and Pacific Steel Castings, Berkeley, California.

Calcifire thermal reclaimers (r) from Dependable Foundry Equipment Co. are gas-powered, directly fired, fluid-bed systems with a compact design, built-in after-burner and air-to-air heat exchanger. With a self-diagnostic, fully automatic control system, it can be supplied with a cooler/classifier and other components. Available from 1-25 tons/hr, prices begin at $100,000. Designed for all chemically-bonded systems, it can be coupled with a Rotaclaim sand scrubber to reclaim green sand for core use. Installations include: Armstrong Mold Corp., Syracuse, New York; and Fansteel Wellman Dynamics, Creston, Iowa.

The GMD Thermo-Scrubber is designed to reclaim green sand for core room use. It incorporates the Thermo-Minder graphics monitor display control system and the PNU cooler/scrubber to effectively remove clays from sand grains. Among its 13 installations are: Gregg Industries, El Monte, California; Johnstown Corp., Johnstown, Pennsylvania; and Schlumberger Industries, Tallahassee, Alabama.

Consolidated Engineering Co.'s Sand Lion Three-In-One system (l) simultaneously shakes out and heat treats castings, and thermally reclaims the sand using a roller hearth furnace and high velocity air. It can also accept spent sand from other parts of the foundry for thermal reclaiming. The fluidized sand bed operates at a variety of temperatures, on all organic binders. Installations include: Honda of America, Anna, Ohio; Teksid, Dickinson, Tennessee; and VAW Alucast, West Yorkshire, U.K.

For demanding applications, the Didion Rotary Lump Crusher/Sand Reclaimer crushes, scrubs, screens and classifies large chemically bonded mold lumps into reusable grain size while automatically discharging tramp metal and debris. Installation requires no pits or special foundations. It is available in standard models from 2-50 tons/hr, for $48,000-$165,000. Over 130 have been installed, including: CMI-Wabash, Wabash, Indiana; General Motors Corp. Saginaw Malleable Iron Plant, Saginaw, Michigan; and Quality Electric Steel, Houston, Texas.

The Whirl-A Claim Model 72 from Whirl-Air-Flow crushes, scrubs, and screens nobake mold lumps of up to 42 sq in., while separating tramp metal and fines. The unit returns up to 95% of sand to the system, and is available in sizes from 1-20 tons/hr, with a standard price of $82,542. Fourteen installations include: Slaver Foundry, Virginia, Minnesota; Waunakee Alloy, Waunakee, Wisconsin; and HICA Steel, Shreveport, Louisiana.

ALB. Klein Co.'s Therm-A-Claim fluidized bed calciners reclaim 3-15 tons/hr of all types of organically bonded sand. It has built-in retention time to burn off all combustibles without the use of an afterburner. Total systems include crushing, screening, and classification, and standard prices range from $850,000-$4 million. Units have been installed at Halbergerhutte, Germany; and General Motors Corp.-Saginaw Malleable Iron Plant, Saginaw, Michigan.

Simplicity Engineering; Inc.'s gas fired thermal reclaimer (r) reclaims chemically bonded and green sands at rates from 1/4 ton-5 tons/hr. With 30 units installed in Europe and the U.S., costs range from $150,000-$450,000.