Building the foundation for green sand.Inside This Story: * The basic fundamentals of green sand preparation, such as additives to the system, mixing and mulling mulling (mul´ing), n the final step of mixing dental amalgam; a kneading of the triturated mass to complete the amalgamation. , and sand measurement methods, have a direct effect on the quality of castings. * Better green sand preparation methods lead to superior end-products. * This article identifies the basic concepts and provides a general guide to successful green sand preparation. Green sand preparation encompasses many aspects that may vary among metalcasting facilities, but there are basic fundamentals of sand preparation that bring success to the casting process. These fundamentals, such as additives to the system, mixing or mulling, and prepared sand measurement methods, are important building blocks to green sand molding. This article identifies the basic concepts and provides a general guide to successful green sand preparation. Optimizing Return Sand The basic additives in the green sand process are return sand, new sand, pre-blend (or individual ingredients, such as clay, seacoal, etc.) and water. The largest portion of this recipe is sand that returns to the muller Mul·ler , Hermann Joseph 1890-1967. American geneticist. He won a 1946 Nobel Prize for the study of the hereditary effect of x-rays on genes. Mül·ler , Johannes Peter 1801-1858. to be reused after shakeout Shakeout A situation in which many investors exit their positions, often at a loss, because of uncertainty or recent bad news circulating around a particular security or industry. Notes: During the dotcom boom and bust, numerous shakeouts occurred. . This return sand already has been prepared and used to make molds and castings, so the character of the sand has changed through the casting process. These changes need to be understood so the sand may be dealt with properly. Depending on the size of the casting, the metal temperature, the in-mold time and the sand-to-metal ratio, a proportional proportional values expressed as a proportion of the total number of values in a series. proportional dwarf the patient is a miniature without disproportionate reductions or enlargements of body parts. amount of the sand additives will be burned out. The best way to determine the amount of additives burned out is through actual practice. However, one method allows for direct calculation of the required clay based on the thermal degradation DEGRADATION, punishment, ecclesiastical law. A censure by which a clergy man is deprived of his holy orders, which he had as a priest or deacon. values of western (sodium) bentonite bentonite (bĕn`tənīt'): see clay. and southern (calcium) bentonite. Table 1 shows this method for iron casters casters the small rubber wheels on surgical trolleys, patient stretchers, mobile equipment. conductive casters the casters are impregnated with carbon to facilitate the dispersal of static electricity from equipment. . For example, to maintain 8% MB Clay, the equivalent of 9.72% new added clay is required. The addition for burned out clay then is 0.0972 x 0.1921 x 2000 = 37.34 lbs. (16.94 kg) clay per ton of iron poured. Another consideration in calculating the amount of additives to add to the returned sand is the amount of raw or unbonded sand returning as core sand and from new sand additions. This sand contains no clay, so it has to be brought up to the operating level. So, for an 8% MB clay system, the calculation would be 9.782 x 100 x 90.28 = 10.77 lbs. (4.89 kg) of new clay per 100 lbs. (45.36 kg) of sand dilution. This method provides a good guideline guideline Medtalk A series of recommendations by a body of experts in a particular discipline. See Cancer screening guidelines, Cardiac profile guidelines, Gatekeeper guidelines, Harvard guidelines, Transfusion guidelines. to follow in sand and clay replacement, but it is not absolute and should be used cautiously. Factors such as the amount of material removed by baghouses and exhaust systems Noun 1. exhaust system - system consisting of the parts of an engine through which burned gases or steam are discharged exhaust automobile engine - the engine that propels an automobile , casting section thickness, casting surface area, black water systems and returned collector fines can affect the results. The size of the return sand storage also can play a part in the character of the sand to be mulled mull 1 tr.v. mulled, mull·ing, mulls To heat and spice (wine, for example). [Origin unknown. and the resulting prepared sand. The larger the sand storage, the more time the sand has to be absorbed into the clay (temper). Sand that is allowed to temper often will result in improved green sand properties but ,nay nay adv. 1. No: All but four Democrats voted nay. 2. And moreover: He was ill-favored, nay, hideous. n. 1. A denial or refusal. exhibit lower flowability. If minimal storage is available, and the sand is cycled frequently during the shift, keeping the system full to minimize swings in sand properties is important. Replenishing with New Sand New sand must be added to the green sand mix to replenish re·plen·ish v. re·plen·ished, re·plen·ish·ing, re·plen·ish·es v.tr. 1. To fill or make complete again; add a new stock or supply to: replenish the larder. 2. the destruction or loss of sand from the molding process. The amount of new sand depends on the type of metal used. For example, the general recommendation for iron casting is a sand ratio of 300 lbs. (136.08 kg) of new sand per ton of metal poured (Table 2). New sand should be added at a controlled rate based on tons of metal poured. It also can be added anywhere in the system as long as it is blended with the return sand before return sand storage and mulling. Some binders deposit a carbon film on the core sand grains during the casting process. This occurs because of the reducing atmosphere in the mold mold, name for certain multicellular organisms of the various classes of the kingdom Fungi, characteristically having bodies composed of a cottony mycelium. The colors of molds are caused by the spores, which are borne on the mycelium. and the thermal decomposition For the biological process, see Decomposition. For chemical decomposition in general, see Chemical decomposition. Thermal decomposition is a chemical reaction whereby a chemical substance breaks up into at least two chemical substances when heated. of the binder binder: see combine. An earlier Microsoft Office workbook file that let users combine related documents from different Office applications. The documents could be viewed, saved, opened, e-mailed and printed as a group. system. The lack of oxygen allows a slow, smoldering smol·der also smoul·der intr.v. smol·dered, smol·der·ing, smol·ders 1. To burn with little smoke and no flame. 2. , smoky Smoky, river, c.250 mi (400 km) long, rising in Jasper National Park, W Alta., Canada, and flowing generally NE to the Peace River. It receives the Wapiti and Little Smoky rivers. It was explored (1792) by Alexander Mackenzie. environment that leaves a lot of the core sand with a carbon coating. This coating resists wetting and results in a weak bond between the clay and the sand grain, which can cause cause burn-in and sand inclusion defects. Addition of new sand to the system will help dilute di·lute v. To reduce a solution or mixture in concentration, quality, strength, or purity, as by adding water. adj. Thinned or weakened by diluting. the carbon coated sand and reduce the potential for these defects. Binding the Sand The binding agent in the green sand mold is found in the pre-blend mixture, which involves clay (such as western bentonite, southern bentonite or fireclay) and other additives, such as seacoal, to help achieve certain properties or eliminate specific problems (Table 3). The number of ingredients should be as minimal as possible to reduce variability in the sand system. Table 4 shows the different hot strengths that can be obtained by blending clays at the proportions indicated. The most common place to add pre-blend is at the muller. It should be noted the mixture is a fine material that fluidizes easily and can be pulled out by the muller exhaust. The best results occur if the pre-blend can be added as close as possible to the sand already in the muller. Additionally, knowing the amount of pre-blend going into the muller is important. This is one ingredient that defines the whole character of the prepared molding sand (Founding) a kind of sand containing clay, used in making molds. See also: Molding . The amount delivered should be known and verified, and the feeder feeder abbreviation for self-feeders. Used in feeding groups of animals at intervals of several days. Feed has to be dry and comminuted so that it will run down the spouts from the hopper into the troughs. mechanism used should be consistent in its delivery. Making It Stick Water is added to the sand mix in order to lend adhesive adhesive, substance capable of sticking to surfaces of other substances and bonding them to one another. The term adhesive cement is sometimes used in place of adhesive, especially when referring to a synthetic adhesive. characteristics to the clay for bonding the sand grains. The moisture content of a green sand system varies from 2.4-4.5%, but should be adjusted as variables dictate TO DICTATE. To pronounce word for word what is destined to be at the same time written by another. Merlin Rep. mot Suggestion, p. 5 00; Toull. Dr. Civ. Fr. liv. 3, t. 2, c. 5, n. 410. to maintain the required green sand physical properties. Water needed to satisfy sand conditions could vary dramatically if return sand temperature and/or the amount of pre-blend is not controlled. Bentonite clay can absorb up to 20 times its weight in water. Wide swings of this material change the water demand. In general, it is customary to add more water than the ideal to allow for evaporation evaporation, change of a liquid into vapor at any temperature below its boiling point. For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at a rate that depends on the amount of surface exposed, the humidity or poor mulling. Hot sand, which comes from shakeout into the mixture, is a nemesis Nemesis (nĕm`ĭsĭs), in Greek religion and mythology, personification of the gods' retribution for violation of sacred law; the avenger. Sometimes she was said to be the goddess of good and ill fortune. in most metalcasting facilities because it causes problems in the muller due to the evaporation of water and later in the delivery of the prepared sand to the mold line as water evaporates en route. Sand should be cooled to at least 120F (48.9C). Measurable differences in green sand properties and casting defects can occur as the temperature of the sand climbs above 120F (48.9C) (Table 5). The ratio of sand to metal also affects the amount of water needed, because it can affect the temperature of the sand. Figure 1 depicts this relationship between sand-to-metal ratios and sand temperature. [FIGURE 1 OMITTED] Compactability percentage, which measures the water/clay relationship is more important than the moisture content. In high-density molding, a compactability of 30-40% is preferred. The best control for how much water to add to the green sand is by the compactability test method (see sidebar (1) A Windows Vista desktop panel that holds mini applications (gadgets) such as a calendar, calculator, stock ticker and Vonage phone dialer. It is the Windows counterpart to the Dashboard in the Mac. See Windows Vista and gadget. ). Excess water, which is water that is not absorbed into the sand, can cause oversize o·ver·size n. 1. A size that is larger than usual. 2. An oversize article or object. adj. o·ver·size also o·ver·sized Larger in size than usual or necessary. Adj. 1. castings due to high deformation deformation /de·for·ma·tion/ (de?for-ma´shun) 1. in dysmorphology, a type of structural defect characterized by the abnormal form or position of a body part, caused by a nondisruptive mechanical force. 2. as well as expansion-related casting defects. Figure 2 illustrates the effects of excess moisture on green sand physical properties. [FIGURE 2 OMITTED] Consideration also should be given to where to add water in the muller. During batch mixing, sand and water should be added and blended with the pre-blend added afterward af·ter·ward also af·ter·wards adv. At a later time; subsequently. Adv. 1. afterward - happening at a time subsequent to a reference time; "he apologized subsequently"; "he's going to the store but he'll be back here . When continous mixing, it is best if water can be added to the stream of sand as it enters the muller. One method that works well is using a pipe with drilled holes in line with the length of the pipe. The pipe is positioned parallel to the sand entering the muller and helps keep the dust down. Mixers with bowl configurations to disperse disperse /dis·perse/ (dis-pers´) to scatter the component parts, as of a tumor or the fine particles in a colloid system; also, the particles so dispersed. dis·perse v. 1. water work well if the outlets are directed downward into the sand and the turret speed is slow enough not to sling sling (sling) a bandage or suspensory for supporting a part. mandibular sling a structure suspending the mandible, formed by the medial pterygoid and masseter muscles and aiding in water on the sidewalls or into the discharge side of the muller. In the Mix Green sand properties, such as green compressive strength Compressive strength is the capacity of a material to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength, e.g. and compactability, are optimized during the mixing and mulling cycle, which brings all the ingredients together and homogenizes the sand. Continous mixers offer a continual flow of prepared sand, so the pipeline is always full. If they are stopped and started often, however, sand quality will suffer. The additive additive In foods, any of various chemical substances added to produce desirable effects. Additives include such substances as artificial or natural colourings and flavourings; stabilizers, emulsifiers, and thickeners; preservatives and humectants (moisture-retainers); and stream must be regulated to the input sand volumes. As the sand input changes, so must the additives. The proper sand retention time in the muller is important to assure the green sand is mulled sufficiently to generate the required green sand properties without overmulling. Figure 3 shows the relative time necessary to achieve the maximum green strength properties of western and southern bentonite and fireclay. Mixers should be sized properly to provide the desired prepared sand properties. [FIGURE 3 OMITTED] For More Information "Tips for Auditing Your Green Sand System," AFS A distributed file system for large, widely dispersed Unix and Windows networks from Transarc Corporation, now part of IBM. It is noted for its ease of administration and expandability and stems from Carnegie-Mellon's Andrew File System. AFS - Andrew File System Green Sand Molding Committee (4-M), K.C. Pickrell, G.F. Sergeant, M. Wolfe, and M.D. Wrobel, MODERN CASTING, March 1999, p. 30-33. RELATED ARTICLE: Testing your green sand. The minimum requirement for testing and controlling prepared' green sand is the compactability test and the methylene blue methylene blue n. A basic aniline dye that forms a deep blue solution when dissolved in water and is used as a bacteriological stain and as an antidote for cyanide poisoning. clay test. The compactability test determines the rammed height of a fixed volume of prepared sand, which gives a good indication of how the sand will compact under load at the molding machine (Woodworking) A planing machine for making moldings (Founding) A machine to assist in making molds for castings. See also: Molding Molding . Compactability is primarily a result of how much water is in the sand, but it also is influenced by clay content and mulling. Well-mulled green sand for high density molding will often display a compactability-to-moisture ratio of 10.5:1 to 12:1. In other words Adv. 1. in other words - otherwise stated; "in other words, we are broke" put differently , the compactability number should be 10.5-12 times higher than the moisture number. The methylene blue clay test is a chemical titration titration (tītrā`shən), gradual addition of an acidic solution to a basic solution or vice versa (see acids and bases); titrations are used to determine the concentration of acids or bases in solution. to determine the amount of active clay in green sand. The process involves introducing methylene blue dye into the sand mixture. The dye reacts with the clay in the sand via ion exchange ion exchange n. A reversible chemical reaction occurring between an insoluble solid and a solution during which ions may be interchanged, used in the separation of radioactive isotopes. , and the percent of active clay in the sand can be calculated by endpoint determination. Both the compactability and methylene blue clay tests should be administered daily by the melting department as part of a basic program of testing green sand. Other steps that should be part of this program are tests for green compressive strength, moisture content, permeability permeability /per·me·a·bil·i·ty/ (per?me-ah-bil´i-te) the property or state of being permeable. per·me·a·bil·i·ty n. 1. The property or condition of being permeable. 2. , temperature and specimen weight. Weekly tests on AFS clay content, sieve analysis A sieve analysis is a practice or procedure used to assess the particle size distribution of a granular material. The size distribution is often of critical importance to the way the material performs in use. , combustibles and volatiles also should be performed.
Table 1. New Clay Replacement Requirements for Thermally Degraded Clay
Percent Clay lbs. of New Western lbs. of New Southern
Bentonite * Bentonite **
MB% New Per Ton Per 1% MB Per Ton Per 1% MB
Clay % Iron Clay per Iron Clay per
lb. Iron lb. Iron
3.0 3.08 11.83 0.001972 27.2 0.004533
4 4.41 16.94 0.002118 39.94 0.004868
5 5.74 22.1 0.002210 50.68 0.005068
6 7.06 27.13 0.002261 62.34 0.005195
7 8.39 32.23 0.002302 74.08 0.005292
8 9.72 37.34 0.002334 85.83 0.005364
9 11.05 42.44 0.002358 97.57 0.005421
10 12.37 47.53 0.002377 109.23 0.005462
11 13.7 52.63 0.002392 120.97 0.005499
12 15.03 57.74 0.002406
* 1100F (593C) assumed as clay degradation temperature (0.1921 lbs.
sand heated per lb. of metal cast).
** 650F (343C) assumed as clay degradation temperature (0.4415 lbs.
sand heated per lb. of metal cast).
Table 2. Recommended Rates of New Sand Per Ton of Metal Poured
Metal lb./ton poured (kg/ton poured)
Aluminum 100 (45.36)
Brass/bronze 250 (90.7)
Iron 300 (136.07)
Steel 500 (226.8)
Table 3. Effect of Additives on Sand Properties
Additive Rammed Water
density required
Asphalt and gilsonite D I
Bentonite (southern) D I
Bentonite (western) D I
Cellulose D I
Cereal D I
Dextrin D I
Fireclay D I
Iron oxide I I
Light petroleum distillate D D
Lignite (caustized) D I
Olivine flour I I
Seacoal D I
Silica flour I I
Soda ash L L
Zircon flour I I
Additive Permeability Green
Compression
Strength
Asphalt and gilsonite D I
Bentonite (southern) D I
Bentonite (western) D I
Cellulose D D
Cereal D I
Dextrin D D
Fireclay D I
Iron oxide D I
Light petroleum distillate D D
Lignite (caustized) D I
Olivine flour D I
Seacoal D I
Silica flour D I
Soda ash L I
Zircon flour D I
Additive Dry Hot
Compression Compression
Strength Strength
Asphalt and gilsonite I D
Bentonite (southern) I I
Bentonite (western) I I
Cellulose D D
Cereal I D
Dextrin I D
Fireclay I I
Iron oxide I I
Light petroleum distillate D D
Lignite (caustized) I D
Olivine flour I I
Seacoal I D
Silica flour I I
Soda ash I I
Zircon flour I I
Additive Methylene Volatile
blue material at
requirement 1,200F (849C)
Asphalt and gilsonite L I
Bentonite (southern) I I
Bentonite (western) I I
Cellulose L I
Cereal L I
Dextrin L I
Fireclay I I
Iron oxide L L
Light petroleum distillate L I
Lignite (caustized) I I
Olivine flour L L
Seacoal L I
Silica flour L L
Soda ash I L
Zircon flour L L
Additive L01
1,800F
(902C)
Asphalt and gilsonite I
Bentonite (southern) I
Bentonite (western) I
Cellulose I
Cereal I
Dextrin I
Fireclay I
Iron oxide L
Light petroleum distillate I
Lignite (caustized) I
Olivine flour L
Seacoal I
Silica flour L
Soda ash L
Zircon flour L
I--increase D--Decrease L--Little or no effect
Table 4. Hot Strength (in psi) of Various Clay Blends
Blend 1,000F 1,500F 1,850F 2,000F 2,500F
(537.2C) (814.7C) (1,004C) (1,092.2C) (1,369.7C)
75%SB/25%CB 70 185 395 227 3
50%SB/50%CB 67 185 280 155 3
25%SB/75%CB 60 110 150 105 2
75%SB/25%FC 215 350 575 545 10
50%SB/50%FC 190 300 535 470 11
25%SB/75%FC 270 350 775 910 24
75%CB/25%FC 76 140 255 210 8
50%CB/50%FC 100 110 265 325 21
25%CB/75%FC 120 155 240 400 18
SB-Sodium bentonite CB-Calcium bentonite FC-Fireclay
All clays were adjusted to provide a typical proportion for each of the
respective clays.
Table 5. Effect of Hot Sand on Physical Properties
Sand Temperature Sand Physical Characteristics
100-120F (38-49C) Stable green properties
120-140F (49-60C) Relationships between physical properties
deteriorates; extra mulling required
140-160F (60-71C) Physical properties uncontrollable; weak,
friable molds
Above 160F (71C) Sand not capable of being mulled due to high
evaporation rate; clay not wetted
Stephen Baker For other persons of the same name, see Steven Baker (disambiguation). Stephen Baker (born August 30, 1964 in San Antonio, Texas) was a former professional American football player who was selected by the New York Giants in the 3rd round of the 1987 NFL Draft. is the senior materials engineer for Indianapolis Casting Corp., Indianapolis. |
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