Iron Foundries SIC 3321,3322

Transcription

1 ron Foundries SC 3321,3322 OVERVEW The US. iron foundry industry in-, cludes manufacturers engaged in the production of gray iron (SC 3321) and malleable (plus ductile) iron castings (SC 3322). Major iron foundry products include castings for automotive, marine, agricultural, and construction equipment; ingot molds; cast iron pipe and pipe fixtures; mill rolls; and general public works fixtures-drain grates, manhole covers, light and sign pole bases. During the late 1970s and early 1980% changes in basic manufacturing technology in the construction, automotive, machine tool, and steelmaking industries, plus a manufacturing recession and environmental regulations produced adverse and lasting effects on the US. iron found- ry industry-particularly for gray iron producers. Total US. shipments of finished iron castings dropped by about 50% from 1978 to Since 1982, industry shipments have remained essentially constant, at about 8-9 million metric tons, despite modest growth in ductile iron production (Figure l), while malleable iron casting shipments have dropped to a commercially insignificant level. ndustry forecasts predict a flat trend in shipments throughout the 1990s, despite increased demand, due to ' continued closings of smaller, lessefficient foundries. ' By the late 1970s, concrete and plastics had replaced a portion of the cast iron used for municipal pipe lines and residential plumbing.' At about the same time, minimill steel plants first emerged, featuring electric arc furnaces and continuous casters. Vehicle weight and fuel-savings requirements led automakers to begin to substitute aluminum alloy castings for iron in engine blocks, heads, manifolds, transmission cases, and brake parts in some cases. For the US. iron foundry industry, demand for about 6.7 mil- Coreless nduction Furnace lion tons per year had rapidly and permanently disappeared. For the period, the Bureau of Labor Statistics reported that US. iron foundry employment fell about 25%, from 108,900 to 82,400. ronically, recent retirements among older iron foundry workers spared during the prior decade of layoffs have resulted in an industrywide shortage of skilled management, engineering, and operating personnel. Likewise, record numbers of foundry closings have created shortages of several critical industrial cast products. As the number of all US. ferrous and nonferrous foundries

2 hlaking ' Million Metric Tans 16 - CHARACTERGTCS Malleable Note: eetimate Saurce. Modem Casting continues to decrease (from about 6000 in 1955 to about 3000 currently), shortages of high-value iron castings are expected to continue. The integrated automaking operations of the United States, Canada, Figure 2 Basic ron Foundrv Process Sand Mold Casting Ductile and Mexico constitute the worlds largest producer and consumer of high-value iron castings. As demands for North American-made autos increase, imports of automobile and machine castings are ex- Except for the highly automated automotive engine parts foundries, the majority of US. iron foundries are small- to intermediate-sized jobbing shops engaged in the production of specialized parts for a range of industrial, agricultural, marine, farm, and construction equipment applications. ron foundries are scattered throughout the United States, with heavier concentrations located near automaking, equipment making, and steel plants in Michigan, llinois, Pennsylvania, California, Georgia, Texas, Ohio, and Tennessee. ron engine block castings are, by far, the single largest industry product line, accounting for more than half of all tonnage cast. Nearly all engine foundries are captive or subsidiary operations of major equipment or vehicle manufacturers. These and other US. iron foundries rely on purchased metallic feedstocks, in the form of pigs c + Clay Mold Core Smd Sand+ Binden Making Binders Redatmcd 5~nJ Disposal spent Sand Abrasives Shot Pigs scrap -+ Fluxes C Coke, Oxygen f Relurn~ (Gales and Risers) 2

3 and scrap, for their melting operations. Except for the major automotive parts casters, where highpowered coreless induction fumaces or hot blast cupolas are common, most iron foundries are relatively low-tonnage operations, with production rates of less than about 10 tons/ furnace / hour. The industry classifies its producers principally by the end uses of its finished castings, Le., automotive and marine engine foundries, pipe makers, and jobbing foundries. Regardless of classification, many foundries produce at least two of the four principal types of cast iron, with each type differentiated mainly by its internal graphite structure. Malleable iron features a globular form of graphite that gives more ductility and strength than gray cast iron. This graphite form is developed during a hour heat treatment. First, a brittle, hard whi'te iron is obtained on solidification by means of a closely controlled low carbon and low silicon chemistry. Upon long-term heat treatment, the excess carbon retained on solidification is precipitated into globular "cauliflower" form. Malleable iron has better ductility than gray iron, but has lower fluidity and castability, and is limited to relatively small castings with thin sections. n addition, the long, energy-intensive heat treatment has limited its use in recent years. Gray iron is the oldest and leastexpensive form of cast iron. t exhibits high wear and corrosion resistance, excellent castability and machineability, but relatively low strength, ductility, and toughness. Gray iron is metallurgically characterized by extensive internal networks of flake graphite precipitates that impart self-lubricating qualities to the material in service. Ductile iron. By treating molten cast irons of specific chemical composition with magnesium or rare earth metals, the morphology (shape) of the resulting carbon precipitates is radically changed. Figure 3 Diagram of 50 ton& Plasma Cupola Figure 4 Typical Coreless nduction Furnace Refractory Furnace - Coil Lid Molten Metal Spout ng Axis 3

4 ~ ~~ -~ nstead of flakes, graphite spheroids are formed. This microstructural modification results in a stronger, tougher, and more-ductile iron, but is more difficult to cast due to higher shrinkage and warpage, and its machineability is considerably inferior to gray iron. Compacted-graphite or "CG" iron. By carefully controlling the treatment with magnesium or rare earths, a hybrid, or rosette graphite morphology can be obtained. CG iron is characterized by good castability and intermediate strength and toughness. Developed during the past 15 years, CG iron is now being used in many smaller automotive castings, including brake rotor discs and drums, manifolds, supports, and housings. Automation within the industryvanes widely with the volume and type of parts cast. Virtually all en- s gine block, pipe making, machine parts, and other high-volume foundries are well automated. n such facilities, many stages of processing-from melting to finishing-are either automatically or robotically controlled. The smaller roll-making and jobbing shops are Figure 5 Tvoical Channel nduction Furnace more labor-intensive operations, relying on the hand work of highly skilled pattern makers, mold makers, castings finishers, etc... MAKUFACTL'RNG hethods... A\D ~ ENERGY USE ~~~ ~ The commercial production of iron castings varies somewhat by the type of iron cast and by the weight of the raw casting, but a number of process steps predominate: mold and core preparation, melting, casting, cleaning, and finishing. Figure 2 illustrates the basic production sequence for the sand mold operation. Mold preparation. n sand mold casting, replicas (patterns) made from wood, metal, or plastic foam are placed in a box called a flask. The flask has separate upper (cope) and lower (drag) halves. Precisely sized sand, mixed with clay or organic (resin) binders, is carefully packed around the pattern in each half. After packing, the pattern is removed from the flask. Any cores required for internal areas are then placed into the drag. After securing the cope over the drag, the mold is ready for pouring. n investment casting, wax or plastic patterns are coated with ceramic materials, then the mold is heated to melt away the patterns and cure the ceramic binders. Another common iron foundry practice is centrifugal casting, which is widely used for cast iron pipe production. Water-cooled metal molds, or metal casings containing sand molds, are prepared and placed in fixtures that permit the mold to be vertically or horizontally spun at several hundred rpm during casting. Melting. The two most common metal-making methods used by iron foundries are cupola melting and electric induction melting (Figure 3). Hot-blast cupolas closely resemble small blast furnaces, and their operation is remarkably similar. ron and steel scrap and high-stability coke are charged along with fluxes at the top of the cupola. High-pressure combustion air, often enriched with oxygen, is supplied at the base of the cupola through water-cooled copper tuyeres. Periodically, the accumulated melt is drained from the furnace through tap holes or tapping gates. Most recently, plasma-fired cupolas have begun operation. Plasma torches supplement (or replace) tuyeres within the hearth of the furnace, reducing (or eliminating) coke consumption. nduction melting in iron foundries is accomplished using coreless induction furnaces (Figure 4) or channel induction furnaces (Figure 5). A coreless induction furnace is essentially a refractory crucible surrounded by a massive, water-cooled copper (primary) winding. The metallic charge in the crucible acts as a single-turn secondary transformer winding. When ac current is applied to the primary winding, heat and stirring energy are generated in the charge by eddy currents. Highly efficient (5540%) as compared to fuel-fired furnaces (20-50%), coreless furnaces are classified as either line (60 Hz), medium ( Hr), 4

5 high (over 1000 Hz), or variable-frequency units. A channel induction furnace is characterized by a refractory-lined channel (or tunnel) within the furnace, which is surrounded by a water-cooled induction coil. When ac current is applied to the coil, molten metal near the inductor is heated and circulated back to the main bath by eddy-current forces. While requiring a liquid metal "heel" for start up, they are extremely (YO- 97%) efficient. Channel induction heating is often used in high-volume, autopoured casting operations such as automotive and farm implement foundries. Electric melting has become increasingly popular due to its advantages of high-energy efficiency, reduced gas and dust emissions,.superior metal cleanliness, improved metallic yields, and precise bath, temperature control (see CMP Tech- Commentary, "nduction Melting," CMP-072,lYYl). Casting. Molten metal is transferred from the melting or holding furnaces to pouring vessels. n traditional sand mold foundry operations, ladles fitted with pouring lips or spouts are used to fill the molds, either directly, or in conjunction with a pouring basin (which minimizes turbulence and slag carryover). n high-volume operations, autopouring vessels are commonly employed. The latest autopour designs incorporate induction heating, pressurization, and flow metering. Cleaning. After solidification, small sand mold castings are separated from their molds using vibratory "shakeout" screens, while larger castings are manually cleaned using air or electric hammers. Gates and risers are then removed from the casting, which is then shot- or grit-blasted. Spent sand may be processed for reuse in gas-fired or electric sand reclaimers. Foundry sand must be free of excess clay, binders, and fines before it can be reused. Benchmark sand reclaimers use a combination of heat. mechanical impact, and screening to remove binders and resize the sand. Electric sand reclaimers, which use submerged resistance or infrared heating elements, are gaining popularity in foundries due to their superior cleaning capabilities, reduced heat loss, low sand contamination, and improved reliability. Finishing. Certain iron castings require heat treatment prior to finish machining. Such heat treatment is usually performed in batch-type, fuel-fired, or electric-resistance furnaces. After heat treatment, the castings are machined and assembled as required. With the rapid shift to induction melting, specific electric power consumption in the industry has increased rapidly during the past 15 years to approximately 900 kwh per finished ton, with more than half of the total used in primary melting. High-volume foundry operations that have replaced cupolas with large induction furnaces have experienced savings of $10-$60 per ton of metal produced, through the elimination of expensive foundry coke and oxygen fuels and reduced air treatment costs. Throughout the industry, gas-fired metal mixers and holding furnaces are being replaced with electric holders, which permit extremely precise temperature control and superior metal cleanliness. ELECTRCTY MARKETNG OPPORTUNTES Load shifting. By shifting induction furnace melting and electric sand reclamation operations to off-peak hours, producers can realize immediate cost savings. f such a strategy is impractical for a particular foundry, the scheduling and sequencing of melting and reclamation operations should be carefully controlled so as not to exceed demand limits. A number of foundries have recently combined load shifting with interruptible supply to achieve substantial energy cost savings. - Strategic load growth. As iron foundries replace fuel-fired cupolas, sand reclaimers, and curing ovens with electric processes, electrical demand is expected to increase. Ever stricter air pollution control requirements will force foundries to increase the capacity and efficiency of precipitators, baghouses, and other environmental systems. For foundries solely replacing cupolas with electric melting processes, the dramatic decrease in process air emissions will normally reduce the capacity requirements for melter dust collection systems. Utilities should cooperate with the industry to ensure that future electric demand can be met. Strategic conservation. A number of advanced process technologies now offer the iron foundry industry opportunities for energy and production cost reduction. The application of adjustable speed drives to sand mixers, shake out systems, combustion air and ventilation fans, and conveyors can provide both energy and maintenance cost savings. Existing line-frequency induction furnaces can be replaced with medium-frequency units, improving efficiency, production rates, and product quality. Even updating the power supplies of older induction melters with solid-state supplies will significantly increase power-use efficiency, and reduce maintenance costs. Applicable Electricity Marketing Opportunities for SC 3321,3322 Peak Clipping Valley Filling Strategic Load Growth Strategic Conservation t 5

6 TRADE ASSOCATONS American Foundrymen's Society (includes Cast Metals nstitute) 505 State Street Des Plaines, L (708) Foundry Educational Foundation 484 E. Northwest Highway Des Plaines, L (708) nvestment Casting nstitute 8350 N. Central Expressway Suite MlllO Dallas, TX (214) NFORMATON SOURCES....- U.S. Department of Commerce, nternational Trade Administration, 1994 US. ndustrial Outlook, Washington, DC, January 1994 EPR/CMP Techcommentaries "Twenty Ways That Electricity Can ncrease Productivity, mprove Quality, and Reduce Costs in Steel Mills and Foundries," Vol. 3, No. 1,1987 "nduction Melting for Higher Productivity," CMP , 1988 "Electric Resistance Melting," CMP ,1988 "Electricity in Foundries," CMl' ,1989 "Resistance Melting for Low Capital nvestment," CMP-045,1989 "nduction Melting," CMP-072, 1991 "Foundry Automation," CMP-073, 1991 Modern Casting, American Foundrymen's Society, Des Plains, L, various issues EPR/CMP lndustry Briefs "Steel ndustry," Vol. 1, No. 13, 1991 "Nonferrous Foundries," Vol. 1, No. 48,1995 ABOUT NDUSTRY BREFS -~.- Basic funding for this ndustry Brief is provided by the Electric Power Research nstitute (EPR), a nonprofit organization that conducts research and development on behalf of the electric utility industry. ndustry Briefs are designed to provide the utility marketing representative with an overview of industry trends, manufacturing methods, and energy-use characteristics for each industry. Such information will enable utilities to identify, evaluate, and implement industrial electricity marketing opportunities suitable for specific materials production groups. This ndustry Brief was developed by Qualex Systems ncorporated, Pittsburgh, Pennsylvania; CMP; and the EPR Foundry Office. For technical information, contact EPR Foundry Office 2340 South Arlington Heights Rd. Arlington Heights, L (708) Fax (708) For ordering information, call EPRAMP Customer Assistance Center AMP Copyright ndustry Brief, Vol. 1, No. 52 Electric Power Research nstitute Palo Alto, CA Printed wim soya lnks on Recycled Paper (50% recycled inoluding 20% po~lcons~mer waste) in the United S181es of America B-105: