Casting (1998) Part 6 ppsx

Pattern Heating. Although the use of a parting spray is effective, a better first step is to heat the patterns to 6 to 11 °C (10 to 20 °F) above the temperature of the molding sand. Cold patterns will cause the moisture in the molding sand to condense on the pattern face, which makes the sand stick to the pattern. Many molding machines do not have any provision for heating the pattern during the production run. Whether the molding machine has the heating capability or not, the pattern should be preheated to the proper temperature prior to the start of the production run to assist in a rapid start-up. References cited in this section 3. High Pressure Molding, 1st ed., American Foundrymen's Society, 1973 4. D. Boenisch, "Strength Problems in High Pressure Compacted Sand Molds," Paper presented at the Disamatic Convention, Disamatic Inc., 1971, p 69-84 5. D. Boenisch and B. Koehler, Sand Compaction and Grain Rupture in High Pressure Molding Machines, Giesserei, Vol 63 (No. 17), Aug 1976, p 453-464 Mold Finishing After the mold has been compacted and the pattern removed, the mold is ready for the finishing operations. These operations usually consist of blowing out any loose sand, looking for any molding defects, drilling the sprue cup (if applicable), and setting any necessary cores. Once the finishing operations are complete, the cope can be accurately placed on the drag and the mold sent to the pouring station. Mold blowoff is one of the areas that can cause surface finish problems if not property controlled. Excessive amounts of air blown onto the mold can cause localized drying of the mold surface. On the other hand, if the air contains large amounts of moisture, the mold face can become excessively wet, giving rise to rough finish and burn-in penetration, just as excessive amounts of water in the molding sand or excessive amounts of parting spray will. Core setting is another part of the process that has undergone tremendous change in the last few years. The increased demand for more accurate castings has affected cores and core setting just as it has molding. With mold hardness in the 85+ range, it is no longer possible to press an oversize core into undersize core prints. From the viewpoint of casting accuracy as well as cleaning room costs, it is equally unacceptable to place undersize cores in an oversize core print. Modern core processes allow the possibility of making the same size core every time, just as the same size mold can be made every time. Thus, it becomes apparent that every cavity in the corebox and every impression on the pattern must be as close as possible to the same dimensions. This obviously places greater demands on the supplier of patterns and coreboxes as well as on the process itself. Mold closing is the next step in the operation. Some molding machines close the mold inside the machine, while others close the mold just outside the machine. Still others utilize a separate piece of equipment to perform this function totally external to the molding machine. The halves should not be allowed to remain separated any longer than absolutely necessary. Separation of the mold halves for excessive periods of time will allow the mold faces to dry, and this can lead to cuts, washes, and a general degradation of the casting surface. Transportation of the mold to the closing station is critical. Jarring of the mold can cause green sand pockets to break away from the mold. In some cases, the pocket may not break away until the mold is poured; thus, the mold, the cores, and the metal are wasted. Rough transportation can easily cause heavy cores to shift off location, which can cause errors in casting dimensions, broken cores, and excessive metal around coreprints. Mold closing is just as critical as mold transportation, and the same basic rules apply. The mold must be treated as smoothly and gently as possible to avoid the same type of defects. The mold guiding mechanism is as important at mold closing as it is during manufacture of the mold. Too often the accuracy and smoothness with which the mold is closed is overlooked. Again, the results can be drops and core movement as well as mold shift, crush, casting dimension problems, and so on. After the mold is closed, mold transportation again becomes important. The finished mold must be carefully transported to the pouring area, or problems such as those already mentioned will likely occur. After the mold has been poured, the molten metal must be given time to solidify and coot to the proper temperature before it is removed from the mold. During the solidifying process, the mold halves must be held solidly together. Any movement will introduce the possibility of casting inaccuracies or increased demands for feed metal or both. The loss of casting accuracy has obvious consequences. The requirement for additional feed metal has the consequence that shrinkage cavities may form and will probably not be evident from the casting exterior. Cooling time after solidification is critical for many casting/alloy combinations. Insufficient cooling time can lead not only to dimensional problems due to lack of casting rigidity but also to hardness and internal stress problems, even to the point of cracking the casting. Shakeout After the castings have cooled sufficiently, they can be shaken out, that is, separated from the sand mold. Shakeout devices are available in a number of different configurations. Many of the devices available are of the flat deck, vibratory type. They range from normal intensity, frequency, and travel to high-intensity units that utilize a very short travel but high frequency. Some shakeout units are rotary in nature and, depending on design, can also provide the added function of cooling the sand. Another type is the vibratory barrel. Deck-type shakeouts (Fig. 16) are available in a number of different configurations for various applications. The first is the stationary type. Stationary refers to the casting and sprue, not the shakeout itself. This type of shakeout is normally used by bringing the mold to the shakeout device; therefore, its primary application is for larger molds and low-to- medium production lines. The deck-type shakeout is also available as a unit that provides the function of conveying the castings from one end of the unit to the other. As mentioned earlier, either type is available in a variety of strokes, intensities, and frequencies. Selection of the shakeout is a function of casting design. Heavier castings can be quite successfully run using a longer-stroke shakeout, while thin-wall castings may require a short-stroke high-frequency unit to prevent breakage or damage to the casting. Rotary-type shakeouts (Fig. 17) are also available in different configurations. The sand may exit at the same end that the sand and castings enter the unit, or it may exit at the opposite end. This type of shakeout also provides the function of conveying the castings from one end of the unit to the other. Rotational speed is adjustable on most units to allow flexibility in shakeout intensity. In general, as rotational speed decreases, intensity decreases and castings are less likely to be damaged. Light thin-section castings may not be suitable for this type of shakeout. Although the castings themselves may not damage each other, the sprue is sometimes heavy enough that it can damage the castings. Fig. 17 Rotary-type shakeout system Rotary plus cooling type shakeouts are also available in a configuration that not only holds the sand and castings together for an extended period but also affords the opportunity to cool the molding aggregate. This type of device is designed such that the castings and sand are held together throughout the length of the drum (Fig. 18). The castings and sprue aid in the breakdown of lumps. Sand temperature samples are normally taken somewhere along the length of the Fig. 16 Flat deck vibratory type shakeout device drum to determine the amount of water necessary for cooling the sand. The cool sand in turn cools the castings, often down to a temperature that can be comfortably handled at the exit of the drum. Sand and castings are separated at the exit of the drum. As with rotary sh akeouts, sprue can damage certain types of castings, especially as wall sections become thinner. In-mold cooling time can become more critical when the castings and sand are kept together in the cooling device. When castings are too hot, hardness problems can result. In some cases, stresses can also be introduced into the castings because of the rapid quenching of the casting in the molding sand. Fig. 18 Rotary plus cooling type shakeout system in which the castings and water- cooled mold sand are separated at the drum exit Vibrating drum type shakeouts (Fig. 19) combine the operating principles of rotating drum and vibrating deck units. The vibrating section is round in cross section, but it does not rotate. Instead, a rotating action is imparted to the sand and castings by the vibratory action. As the drum vibrates, material is constantly agitated to produce particle migration in both axial and transverse directions. The drum can be designed to provide a very rapid blending action or a gentle folding action, depending on process requirements. Because air can be forcibly exhausted from the drum and because the surface of the sand within the drum is constantly changing, a limited amount of cooling is possible. Additional information on shakeout is available in the article "Shakeout and Core Knockout" in this Volume. Fig. 19 Front (a) and side (b) views of a vibratory drum type shakeout system Sand/Casting Recovery What happens to the sand after shakeout is of great importance to the design and operation of the system (see the section "Sand Reclamation" in this article). Historically, the sand is returned from the shakeout to a storage bin, where it is kept until the next time it is mixed with additional clay, water, and carbonaceous materials. Unfortunately, sand-to-metal ratios of 3:1 to 6:1 are quite common. Sand-to-metal ratios in this range, combined with cooling times that allow the castings to become cool enough to separate from the sand, can easily create return sand temperatures of 120 °C (250 °F) and above (Ref 6). High sand temperatures cause innumerable problems not only with regard to molding and surface finish but also for the system itself. Bentonite does not absorb water and become plastic to develop the necessary cohesive and adhesive strengths when sand is above 45 to 50 °C (115 to 120 °F). Therefore, the molding sand must be below these temperatures long enough for the muller to provide the necessary input of energy to coat the sand grains properly. Hot sand, usually above 50 °C (120 °F), is difficult to temper and bond, and when above 70 °C (160 °F), hot sands are impossible to rebond (Ref 7). Unfortunately, sand is not easily cooled, especially in the quantity necessary to keep a molding line running. Molding sand is a relatively good insulator and therefore tends to hold heat for long periods of time. Storage quantity is therefore not the answer. Not only does sand stored in a bin hold its heat for long periods of time but it also cools from the outside toward the center. As it cools in this manner, moisture tends to migrate toward the cooler sand, which causes it to cake on the outside walls. As time goes on, the caking on the outside wall becomes thicker until only a small portion of the sand is actually being circulated through the system. Vibrators and bin poppers have been designed and can be of some help in combatting this rat holing tendency of return sand bins, but the ideal situation would be to cool the sand prior to storage. Evaporative cooling is the only practical method of cooling the amount of sand needed in green sand systems. Hot sands must therefore have water added in amounts that exceed those required for tempering if both cooling and tempering are to take place. In addition, an ample supply of air must be present to carry away the heated water vapor. The cooling of molding sand may be regarded as a two-stage process, although no sharp line separates the stages. At temperatures in excess of approximately 70 °C (160 °F), added water causes a flash evaporation cooling effect (Ref 6). Temperature will continue to decrease fairly rapidly to about 60 °C (140 °F), but more slowly after that. As sand temperature approaches ambient temperature, further cooling becomes more difficult and time consuming. Conditions of high ambient temperature, especially when combined with high ambient humidity, can substantially reduce the effectiveness of cooling devices. Therefore, ambient conditions should be considered carefully when sand systems are being designed or modified. Some mullers have the capability of blowing air through the sand mixture and will cool the sand very effectively. However, there are some disadvantages to this method. It must be kept in mind that mulling (coating sand grains with bentonite) does not take place until the mixture is cool enough to be tempered and bonded (Ref 6). Cooling time must therefore be added to the mulling time. Although western bentonite provides the mold stability needed by most foundries, it does require more time and energy to absorb water and develop the necessary properties (Ref 8). Thus, the job of the muller or mixer becomes even more difficult and time consuming. The storage bin will still have the tendency to rat hole, thus returning sand more quickly and hotter to the muller and further aggravating the situation. Control of solid additives and water becomes more difficult as the molding sand becomes hotter. However, this is not an impossible situation; this method is used quite effectively in a number of foundries. A few steps can be taken to provide some amount of cooling to the return sand in an existing system and to keep equipment costs as low as possible. For example, water can be fogged on the return sand, preferably as early as possible. Chains can then be dragged through the aggregate and/or plows can be used to turn the mixture over. Additional air can be introduced by fans or other sources to enhance cooling. Elevators can be vented to enhance air flow, but this provides little help because the sand is being conveyed in solid buckets. The only assistance realized will be at the transfer points. Although these and similar methods do help to reduce return sand temperature, they are generally of only marginal value. An effective job of cooling return sand normally requires the addition of water, along with forced air being blown or pulled through the aggregate by some type of auxiliary cooling device. A number of auxiliary cooling devices are available that utilize forced air for evaporative cooling. These units should always be placed as close as possible to the casting shakeout. In fact, one type of unit, the shakeout-cooling drum, combines the functions of shakeout and sand cooling. Cooling the sand at or near the shakeout enables tighter control, reduces the tendency toward rat holing in the return sand bin, and reduces the demand for cooling on the muller. Because many muller designs make no provision for cooling, adequate external cooling is not only desirable but necessary. Cooling the sand as early as possible reduces the total cycle time of the muller by reducing or eliminating the time necessary for cooling and provides a method for making mulling time more efficient. Southern bentonite can be mulled in very quickly if the aggregate temperature is low enough. As mentioned earlier, western bentonite is not mulled in very quickly, because it must swell by such a large amount (Ref 8). For this reason, it is advisable to keep the bentonite swelled and as active as possible. Many of the auxiliary cooling devices can be controlled to the point where the level of return sand moisture will be such that the western bentonite will remain activated. Normally, a retained moisture level of 1.8 to 2.0% will not only keep bentonites activated but will also reduce the amount of dusting at transfer points, thus reducing the load on dust collection equipment. Cooling Devices. As mentioned earlier, it is possible to realize some cooling by adding water to a return sand belt and then using some method of turning the sand over at various places along the length of the belt. There are mechanized devices (Fig. 20) that perform similar functions and provide air flow through the sand. The effectiveness of these methods is often somewhat limited because of conveyor belt lengths; as belt lengths become shorter, the method becomes less effective. Difficult sand temperature problems will require more serious measures. Fig. 20 Mechanized sand cooler used in high-production molding lines Drums used as cooling units are among the oldest of the effective devices (Fig. 21). A cooling drum does not keep the sand and castings together; instead, this is a separate piece of equipment through which sand from the shakeout flows. As with other cooling devices, water must be added to the molding sand to allow the air moving through the drum to provide the necessary cooling by evaporation. Fig. 21 Cutaway view of a sand cooling drum system. Sequence of operations proceeds from right to left: 1, hot shakeout and spill sand enter, and helical flights convey sand forward to begin blending process; 2, cascading effect provides s and cooling as well as sand homogenization; 3, blended and cooled sand is discharged onto perforated cylinder, which screens off tramp metal and core butts while passing sand; 4, replaceable screen passes sand to discharge onto conveyor; 5, lumps that do n ot pass final screen carry across to lifter paddles for discharge into overburden chamber The fluid bed cooler (Fig. 22) is a vibratory type of conveyor through which the sand flows in a more or less continuous but controlled stream. Air is pumped through the sand from underneath, causing the necessary evaporation and cooling. Fig. 22 Schematic of a fluid bed cooler Figure-Eight Cooler. Similar to the continuous muller shown in Fig. 13, the figure-eight cooler is designed so that air can be pumped through it and provide the necessary cooling. This device has been used directly above the muller, but a more desirable location would be as close to the shakeout as possible for the reasons already mentioned. Regardless of the equipment used, it is necessary to control the moisture additions so that sufficient moisture is available for cooling and bentonite activation without getting the return sand so wet that problems will be experienced with plugging up of the sand system. The movement of air through the aggregate will almost certainly remove some of the finer material. The higher the velocity of air movement, the better the cooling, but also the greater the loss of that fine material. The loss of a certain amount of that material (such as dead, burnt clay and ash) can be beneficial. Unfortunately, a number of beneficial materials can also be lost, such as the finer grains of sand, coal dust, and bentonite. Any cooling device should be planned with a solids separator on the exhaust air so that these materials can be collected and fed back into the system at a controlled rate. This will improve surface finish, and trapping and using the bentonites and coal dust will provide economic benefits. Metal Separation and Screening. The shakeout does the primary job of separating the sand from the sprue and castings. Smaller pieces of metal can easily slip through the grating of the shakeout device and be processed along with the sand. This will cause casting defects, and it may damage the equipment. Therefore, it is advisable to remove as much of the tramp metal as possible. When magnetic metals such as most irons and steels are being cast, the job is relatively easily accomplished with magnets. The suggested practice is to install an over-belt magnet somewhere along the length of a conveyor belt and a pulley magnet at the discharge end of the same belt. Placing both magnets on the same belt allows more complete separation of the magnetic particles. Nonmagnetic alloys present a different problem. Devices are available that separate the metallic particles based on density differences, but the most common method is to use screens. Multiple screens are often used, and the mesh size from screen to screen becomes progressively finer. Lumps are found in all sand systems and consist of system sand or core parts that have not been sufficiently heated to break down the binder. For this reason, it is necessary to have a good screen in all systems. The opening size in the screen should be as fine as is practical for the system involved. Two basic types of screens are in use: flat deck and rotary. The flat deck type is usually vibratory in nature and has the added function of providing further lump reduction as well as the screening function. The rotary type of screen is normally a large barrel that continually rotates. The exterior of the barrel has the desired size of holes in it to provide the screening action. Because of the tumbling action within the screen, lump reduction similar to that obtained with the vibrating flat deck can be expected. In both cases, the size of the screen should be as fine as is practical. After the sand has been cooled, the tramp metal removed, and the core butts and lumps removed, the sand is ready to be returned to the storage hopper to be used again. References cited in this section 6. J.S. Schumacher and R.W. Heine, The Problem of Hot Molding Sands 1958 Revisited, Trans. AFS, Vol 91, 1983, p 879-888 7. C.A. Sanders, Foundry Sand Practice, American Colloid Company, 1973, p 441 8. J.S. Schumacher, R.A. Green, G.D. Hanson, D.A. Hentz, and H.J. Galloway, Why Does Hot Sand Cause Problems?, Trans. AFS, 1974, p 181-188 Computer-Aided Manufacture Recent years have seen a rapid advancement in the use of data processing units and data communication. These advancements have made possible almost complete and instantaneous record keeping and, equally important, trend recognition. The technology is advancing rapidly; there are systems currently in place that record on a continual basis the amounts of return sand, new sand, bentonite (or premix), and water that go into each batch of sand. In many cases, mixing time and maximum current draw of the muller are also recorded. With some systems, compactability can also be recorded. In any case, output data, such as compactability and muller current draw, can be stored for a period of time, and a trend analysis can be done automatically. Molding machines have also become more sophisticated. With microcomputers and programmable controllers being used to control machine movements, it is possible to read the pattern number automatically when the pattern is installed. Using information that had previously been stored in the memory of the computer or controller, the molding machine can optimize its molding parameters for the individual pattern. A hypothetical case will illustrate the extent of the available information. During a shift, a new pattern is installed on the molding machine. The operator tells the machine that 1250 molds are needed. Optimum molding parameters, poured weight, necessary cooling time, and so on, have already been determined during earlier runs and stored in the computer. At any point during the run, the operator or someone operating a distant host computer can query the molding machine to find out which mold is going to reach shakeout next, how much cooling time it had, how much metal is required to complete the production run, how much time will be required to complete the production run based on existing molding rates, how many cores will be required to complete the run, how many molds have been made and/or poured, and so on. These outputs can be used as control signals. More water or less water can be added to the sand cooler when sand from the new molds reaches the cooling device. Molding sand compresses more in the molding chamber/flask as sand becomes wetter (higher compactability), thus trend analysis can be done by recording mold compression during compaction, and the resulting information can be fed back to the sand preparation equipment. The exact position required for an automatic pouring device can be set by the molding machine. Daily production data reports can be printed out that will give information on each run; this information includes the number of castings, production rate, productivity, number of cored molds, and reasons for downtime (such as waiting for sand or metal). In the event of machine difficulty, the machine can help troubleshoot itself. It is not only possible but practical to allow the molding machine to exchange data with a remote location (via telephone lines) if assistance in troubleshooting is needed. The quantity of information that is available and transmittable depends on the mechanical and electronic design of the equipment. Some units are designed to allow one-way communication (output), while others are designed to allow two- way communication (output and input). In the latter case, it is possible for a remote location to control some or all inputs to the production equipment. These remote locations can consist of keyboard inputs from a host computer or even data output from other pieces of equipment. The type of information available (either as inputs or outputs), the form the information is in, and the communication protocols may vary greatly among manufacturers. It is therefore necessary to research the technical information available from each manufacturer to determine the best way for the various pieces of equipment to communicate and the best way to handle the information obtained. Additional information on the role of computers in the manufacture of green sand molds is available in the Section "Computer Applications in Metal Casting" in this Volume. Sand Reclamation Michael Zatkoff, Sandtechnik, Inc. Reclamation is defined by the American Foundrymen's Society (AFS) Sand Reclamation and Reuse Committee 4-S as the physical, chemical, or thermal treatment of a refractory aggregate to allow its reuse without significantly lowering its original useful properties as required for the application involved. To achieve this objective, one must evaluate the type of sand entering the reclamation system, the binder system used, and the area for its reuse. This section will provide a brief review of sand reclamation systems for both chemically bonded (resin bonded) sands and clay-bonded sands (green sands). Detailed information on sand molding principles and processes can be found elsewhere in this Volume. Reclamation of Chemically Bonded Sand The primary requirement of any reclamation system is to remove the resin coating around the sand grains. This involves abrasion and attrition to break the bond, as well as classification to remove the fines that are generated. The three basic reclamation systems are thermal, dry, and wet. Selection of a system depends greatly on the type of organic binder to be removed from the sand grains. More detailed information on organically bonded sand systems can be found in the article "Resin Binder Processes" in this Volume. Wet Reclamation Systems Wet reclamation systems were used for clay-bonded system sands in the 1950s, but are now used for silicate binder systems only. Silicate systems are very difficult to reclaim by dry processes and are impossible to reclaim in thermal systems. This is because silicate is an inorganic system that melts rather than burns in the furnace. The complete system includes lump-breaking and crushing equipment, an attrition unit, wet scrubber, dewatering system, and dryer. The systems require about one pound of water per pound of sand reclaimed, and in some cases the water can be discharged directly into municipal sewer lines. Most installations allow 100% reuse of the reclaimed sand, with makeup sand as the only new sand addition. Dry Reclamation Systems Many factors determine the degree of cleanliness required in a reclaimed sand. These factors include the type of resin system used for rebonding, the sand-to-metal ratio, the type of metal poured, the condition of the reclaimed sand, the type of new sand used, and the ratio of new sand to reclaimed sand. Attrition reclaimers break down the sand lumps to a smaller grain size. Some fines are removed, but the binder is not removed completely from the surfaces of the sand grains. In most cases, these units produce a sand that requires a higher concentration of new sand when the attritor is coupled with a sand scrubber, as described below. Additional scrubbing is sometimes required, and there are basically two types of scrubbers: mechanical and pneumatic. Selection between the two types is primarily a question of wear, ease of maintenance, and energy consumption because the units provide comparable performance in terms of scrubbing action. Pneumatic Scrubbing. Figure 23 shows one cell of a pneumatic scrubber. Sand is introduced by gravity at the top of the unit, and it flows down around the blast tube. High-volume low-pressure air from a turbine blower flows through the nozzle and lifts the sand up through the blast tube to the target plate. The sand grains undergo intense attrition in the tube by impacting on each other; further attrition occurs at the target as binder is removed from the sand grains. These fines and resin husks are then removed from the system by a classification dust collection system. Scrubbed sand falls from the target and is deflected to the next cell or is kept within the same cell for further scrubbing. The degree of cleanliness attained is determined by the retention time in the cells (controlled by the deflector plate) and the number of cells. Sand exiting the final cell should be screened to remove any foreign material that may be present in the refuse sand. [...]... 1,800-3,300 13 .6 30 152 × 1220 6 × 48 3,500-5,800 37 .6 83 152 × 1520 6 × 60 3,500-5,800 47.1 104 178 × 1220 7 × 48 4,400-7,500 46. 3 102 178 × 1520 7 × 60 4,400-7,500 59.9 132 203 × 1220 8 × 48 5,500-9,300 62 .1 137 203 × 1520 8 × 60 5,500-9,300 77.1 170 229 × 1520 9 × 60 6, 700-11,300 96. 6 213 254 × 1220 10 × 48 8,000-13,300 97.1 214 254 × 1520 10 × 60 8,000-13,300 118 261 305 × 1520 12 × 60 11,300-17,000... 4,0005 ,60 0 254 10 457 18 6, 080 13,400 8,120 17,900 203 8 3,000-5,000 8.75 2.01 6. 58 22703,180 5,0007,000 368 14.5 483 19 9,070 20,000 12,100 26, 700 229 9 4,000 -6, 000 2.74 9.0 2. 06 6.75 27203,810 6, 0008,400 368 14.5 483 19 9,840 21,700 13,200 29,000 229 9 4,000 -6, 000 3.05 10.0 2.3 7.5 363 05,440 8,00012,000 368 14.5 508 20 14,500 32,000 19,100 42,000 254 10 5,000-9,000 3.35 11.0 2.51 8.25 54408, 160 12,00018,000... 11,300-17,000 171 378 305 × 1830 12 × 72 11,300-17,000 201 444 3 56 × 1520 14 × 60 18,000-25,000 228 502 3 56 × 1830 14 × 72 18,000-25,000 273 60 2 Carbon electrodes 203 × 1520 8 × 60 2,500-4,500 79.8 1 76 254 × 1520 10 × 60 3,100 -6, 300 125 275 305 × 1520 12 × 60 4,500-7,900 178 392 3 56 × 1520 14 × 60 5,400-10,000 240 528 3 56 × 1830 14 × 72 5,400-10,000 293 64 7 The electrodes are supported on three separate arms... 1.88 White 0. 56 2.01 Acid slag Basic slag White 0.51 2.53 Table 1 Refractories as a source of slag based on typical composition Type Composition, % Softening point SiO2 Al2O3 Cr2O3 TiO2 CaO MgO Fe2O3 Other °C °F Super duty 49- 56 40-44 1.52.5 2.5-4.0 17451 765 31753210 Medium duty 57-70 25-38 1.32.1 4.0-7.0 166 0 168 5 30203 065 Semi silica 72-80 18- 26 1.01.5 1.0-3.0 164 0 168 5 29853 065 1 -52 2... 0.15-0.35 2.53.5 0.32.2 0.020.10 168 01700 3 060 3090 Conventional 94-97 0.45-1.20 1.83.5 0.30.9 0.100.30 163 5 166 5 29753025 Chrome 3.0 -6. 0 15-34 28-33 14-19 11-17 1.0-2.0 12901425 2350 260 0 Magnesite 0.7-1.0 0.3-1.5 1.03.5 85-93 0.37.0 0.5-1.0 1480 167 5 27003050 0.5-5.0 0.2-1.0 0.51.5 92-98 0.21.0 0.0-0 .6 15951705 29003100 4-8 16- 27 18-28 0.71.5 27-53 1595 167 5 29003050 Silica type Basic type... 1.8 6. 0 1.4 2.20 7.25 2.4 2 .67 Electrode diameter Transformer capacity, kVA Dimensions Sidewall Bottom Normal Maximum lb/h mm in mm in kg lb kg lb mm in 45 064 0 1,0001,400 254 10 305 12 1, 360 3,000 1,810 4,000 75 3 1,000-1,500 4.5 9101,270 2,0002,800 254 10 381 15 2,810 6, 200 3,750 8, 260 152 6 1,500-2,000 1.7 5.5 1 360 1,910 3,0004,200 254 10 432 17 4, 260 9,400 5 ,67 0 12,500 178 7 2,000-3,000 8.0 1.8 6. 0... 3.0-4.0 1785 3245 1 -62 2 2.03.3 3.0-4.0 18051820 32803310 1 -72 2 3.04.0 3.0-4.0 18201850 33103 360 1 -82 2 3.04.0 3.0-4.0 1 865 3390 0.40.8 1.0-2.0 1930 3505 Fireclay Alumina type (high) 50% 41-47 47 1 2 60 % 31-37 57 1 2 70% 20- 26 67 1 2 80% 11-15 77 1 2 90% 7 1 2 89-91 9 Mullite 18-34 60 -78 0.53.1 1.0-3.0 1850 3 360 Corundum 0.2-1.0 98-99.5 Trace 0.3-1.0 2000 363 0 Silica super... 363 05,440 8,00012,000 368 14.5 508 20 14,500 32,000 19,100 42,000 254 10 5,000-9,000 3.35 11.0 2.51 8.25 54408, 160 12,00018,000 368 14.5 508 20 22,700 50,000 29,900 66 ,000 305 12 7,500-12,500 3.81 12.5 2.84 9.33 7 260 10,900 16, 00024,000 368 14.5 533 21 29,900 66 ,000 39,900 88,000 3 56 14 10,00015,000 The electrode can be graphite or carbon The graphite electrode has greater current capacity than the carbon... 27(b) Screen analysis Before Reclaimed Cyclone and dust reclaim sand collector 20 30 40 1.0 0.4 50 34.9 27.1 0.4 70 40.3 37.1 4.9 100 16. 8 22 .6 6.7 140 3.3 7.3 17 .6 200 2.1 3 .6 15.9 270 0.8 1.1 15.1 Pan 0.8 0.4 39.1 Total 100.0 99 .6 99.7 GFN(a) 56. 41 63 .31 195.25 Yield 77.5% 22.5% Source: Ref 9 (a) American Foundrymen's Society grain fineness number Table 3 Screen analysis of a base chromite... analysis Before reclaim Reclaimed sand Cyclone and dust collector 20 30 Trace Trace 40 2.3 2.4 50 28.9 30.7 0.1 70 35.4 36. 5 3.0 100 22.2 21 .6 9.2 140 7.8 6. 4 41.2 200 2.9 1.8 21.2 270 0.4 0.3 9.3 Pan 0.2 0.1 15.7 Total 100.1 99.8 99.7 GFN(a) 58 .69 56. 30 144.99 Yield 93.9% 6. 1% Source: Ref 9 (a) American Foundrymen's Society grain fineness number See the article "Aggregate Molding Materials" in . 27.1 0.4 70 40.3 37.1 4.9 100 16. 8 22 .6 6.7 140 3.3 7.3 17 .6 200 2.1 3 .6 15.9 270 0.8 1.1 15.1 Pan 0.8 0.4 39.1 Total 100.0 99 .6 99.7 GFN (a) 56. 41 63 .31 195.25 Yield . . . 77.5% 22.5%. 0.1 70 35.4 36. 5 3.0 100 22.2 21 .6 9.2 140 7.8 6. 4 41.2 200 2.9 1.8 21.2 270 0.4 0.3 9.3 Pan 0.2 0.1 15.7 Total 100.1 99.8 99.7 GFN (a) 58 .69 56. 30 144.99 Yield . . . 93.9% 6. 1% Source:. . . . 50 28.3 26. 9 . . . 70 25.2 25.2 0.7 100 17.1 18.5 4.2 140 6. 6 8.3 13.3 200 1.7 3.4 19.7 270 0.2 0.8 15.3 Pan 0.1 0.4 46. 9 Total 99.7 99.7 100.1 GFN (a) 51.53 56. 97 215.25 Yield