Sand testing methodsFamiliarize yourself with the sand testing methods used in your operation to understand how those readings reflect both the consistency of your molding sand and the quality of your castings. The quality of a foundry's green sand has a definite impact on the quality of the castings. Maintenance and control of the system sand is not only an important job but also a demanding one, requiring a battery of tests aimed at improving consistency. Knowing why and how sand testing is performed, therefore, can offer important clues to improving quality in your foundry. Sand testing falls into two categories: checking consistency and evaluating physical and chemical properties of a sand mix. Tests such as moisture, permeability, green compression and compactibility are used to check consistency of the sand. Such tests, along with actual mold testing and physical tests like loss on ignition (LOI), AFS clay, 25 micron clay, methylene blue (MB) clay and screen analysis can explain casting quality. To obtain comparable results, each test must be run according to AFS standard methods. Testing equipment must be checked and calibrated. Samples, usually a quart or larger, should be taken nearest the point of use, and casting quality should be correlated to sand test results. It's important to follow statistical process control procedures, and graphing results makes them easier to track. CONSISTENCY TESTS Moisture Moisture in molding sand develops the plasticity of the clay bond, and different types and amounts of clay require different amounts of water to achieve the best properties. The water consumption in the sand system is directly related to the tons of metal poured. Water also acts as the main coolant and heat extractor in the system. 1 in conjunction with green compression. Compactibility duplicates how a fixed volume of sand will react to a fixed input of energy and is useful in controlling the clay-to-water ratio. Compactibility Compactibility is directly related to the performance of the sand in the molding operation and reflects the degree of temper of the sand mix.The percent moisture is determined by completely drying a given amount of green sand (50 g). and more sand can be riddled into the specimen tube. it is superior to the bulk density test for measuring the water requirement of the sand mix. it must be maintained within a narrow range. around) with riddled sand through a 0. Excess water produces an oxidizing atmosphere in the mold. screen mounted at a constant height above the tube. The distance from the top of the tube to the surface of the sand is read as percent compactibility [ILLUSTRATION FOR FIGURE 1 OMITTED]. Two factors that affect the moisture requirement are the type and amount of clay and the type and amount of additives in the sand mix. Procedure . The sand and the drying container are weighed before and after drying. 2 in. the water-clay coating thickness decreases.Procedure . and the weight loss is doubled to arrive at the percent moisture.The water content affects every property of green sand. The presence of water in excess of what is required to establish the minimum density point of the molding sand results in free water within the sand mass. As the moisture decreases. This test. with the exception of grain fineness number of the base sand.The test is run by filling a standard specimen tube (4. lower permeability. Significance . and the sand is rammed three times. can be used to determine the working bond or effective clay present in a sand mix. excess gas evolution. The excess sand is struck off the top of the tube. high. Significance . high dry and hot strength. Moisture content of a green sand is not an arbitrary figure. low mold hardness and poor flowability. 2 .75 in.Because the test is independent of the specific gravity of the sand.375-in. long) is formed by placing a weighed amount of sand in a tube and ramming the sand three times. An increase in permeability usually indicates a more open structure in the rammed sand. which has no units.The permeability number. The rammed cylindrical specimen (2 in. Green compression in conjunction with moisture can be used to determine the available bond. rammed AFS cylindrical specimen. Molding sand at higher or lower compactibility will produce varying green strengths.Green Compression Green compression has been the most widely used control tool to measure the rate of clay addition to a sand molding system. shape and distribution of the foundry sand. the type and quantity of bonding materials. through a 2 x 2-in. The instrument used for breaking the specimen must continuously register the increasing load until the specimen fractures. A decrease in permeability indicates tighter packing and could lead to blows and pinholes.The green compressive strength of green sand is the maximum compressive stress that a mixture is capable of sustaining when prepared. sand-to-metal ratio. is determined by the rate of flow of air. The compression reading should be read at comparable compactibility ranges.The grain size.The degree of mulling. Significance . Procedure . under standard pressure. compactibility range and type of additives have a significant effect on green compression. clay content. Permeability Permeability is a test of the venting characteristics of a rammed sand. the density to which the sand is rammed and the percentage of moisture used for tempering the sand are important factors in regulating the degree of permeability. Procedure . Significance . it will lead to penetration-type defects and rough castings. 3 . diameter and 2 in. rammed and broken under standard conditions. and if the increase continues. An excessive amount of moistureabsorbing materials will decrease the dry strength. The specimen weight should be recorded at or near a predetermined compactibility. it is broken. Specimen Weight Variation in specimen weight indicates variation in the density of the rammed sand and changes in the system.When sand exhibits high dry compression. Example of a Sieve Analysis 4 .Dry compressive strength is the maximum load a dry specimen can sustain before fracturing. the type and amount of clay and the rammed mold density will affect the dry strength. Table 1. Procedure . An increase in moisture. Significance .When the specimen weight drops appreciably. hard lumps are present at shakeout and more sand carryout will take place. After cooling. a greater number of large. specimen is made and dried in a ventilated oven at 230F (110C) for 2 hr. A standard 2 x 2-in. burn-on and penetration defects.The weight of sand required to make a standard three-ram specimen should be recorded every time a test is run. it indicates a buildup of dead or oolitic material.2 x 2-in. Dry Compression Dry compression indicates the resistance of the mold to stresses during pouring and cooling of a casting and the ease of shakeout. Procedure . A trend to lower weight indicates not enough new sand is entering the system. and the strength is recorded. Significance . This buildup can lead to burn-in. The quality of a foundry's green sand has a definite impact on the quality of the castings. 25 micron clay. green compression and compactibility are used to check consistency of the sand.com Permeability & Porosity Affordable Manual Testers & Electronic Automated Testers www. can offer important clues to improving quality in your foundry. methylene blue (MB) clay and screen analysis can explain casting quality. AFS clay.frazierinstrument. requiring a battery of tests aimed at improving consistency. Compactability. Tests such as moisture. Molding & Pouring Equipment greensandcontrols. Ads by Google Moisture Absorb Agents Drierite Drying Agent Will Solve All Drying Problems . 5 . permeability.Familiarize yourself with the sand testing methods used in your operation to understand how those readings reflect both the consistency of your molding sand and the quality of your castings. Such tests.Order Online! www. therefore.com Maintenance and control of the system sand is not only an important job but also a demanding one. Knowing why and how sand testing is performed.com Foundry Equipment Mixers & Parts. along with actual mold testing and physical tests like loss on ignition (LOI).Drierite. Sand testing falls into two categories: checking consistency and evaluating physical and chemical properties of a sand mix. should be taken nearest the point of use. The sand and the drying container are weighed before and after drying. Excess water produces an oxidizing atmosphere in the mold. and casting quality should be correlated to sand test results. each test must be run according to AFS standard methods. Significance . high dry and hot strength. and different types and amounts of clay require different amounts of water to achieve the best properties. low mold hardness and poor flowability. it must be maintained within a narrow range. Water also acts as the main coolant and heat extractor in the system. Two factors that affect the moisture requirement are the type and amount of clay and the type and amount of additives in the sand mix. Procedure . The water consumption in the sand system is directly related to the tons of metal poured. Compactibility Compactibility is directly related to the performance of the sand in the molding operation and reflects the degree of temper of the sand mix. with the exception of grain fineness number of the base sand. Testing equipment must be checked and calibrated. Samples. It's important to follow statistical process control procedures. and graphing results makes them easier to track. Moisture content of a green sand is not an arbitrary figure. CONSISTENCY TESTS Moisture Moisture in molding sand develops the plasticity of the clay bond. 6 . lower permeability.The water content affects every property of green sand.The percent moisture is determined by completely drying a given amount of green sand (50 g). usually a quart or larger. and the weight loss is doubled to arrive at the percent moisture. excess gas evolution.To obtain comparable results. and the sand is rammed three times. The compression reading should be read at comparable 7 .Procedure .375-in. Significance . clay content. Significance . Compactibility duplicates how a fixed volume of sand will react to a fixed input of energy and is useful in controlling the clay-to-water ratio. the water-clay coating thickness decreases.Because the test is independent of the specific gravity of the sand. As the moisture decreases. The instrument used for breaking the specimen must continuously register the increasing load until the specimen fractures.The green compressive strength of green sand is the maximum compressive stress that a mixture is capable of sustaining when prepared. high. Procedure . and more sand can be riddled into the specimen tube. Green Compression Green compression has been the most widely used control tool to measure the rate of clay addition to a sand molding system. in conjunction with green compression. long) is formed by placing a weighed amount of sand in a tube and ramming the sand three times. can be used to determine the working bond or effective clay present in a sand mix.The test is run by filling a standard specimen tube (4. rammed and broken under standard conditions. The distance from the top of the tube to the surface of the sand is read as percent compactibility [ILLUSTRATION FOR FIGURE 1 OMITTED]. The excess sand is struck off the top of the tube. This test. The presence of water in excess of what is required to establish the minimum density point of the molding sand results in free water within the sand mass. diameter and 2 in.75 in. screen mounted at a constant height above the tube. sand-to-metal ratio. it is superior to the bulk density test for measuring the water requirement of the sand mix. The rammed cylindrical specimen (2 in.The degree of mulling. 2 in. around) with riddled sand through a 0. compactibility range and type of additives have a significant effect on green compression. A trend to lower weight indicates not enough new sand is entering the system. Molding sand at higher or lower compactibility will produce varying green strengths. Significance . rammed AFS cylindrical specimen.The grain size. and if the increase continues. it will lead to penetration-type defects and rough castings. the type and quantity of bonding materials.The weight of sand required to make a standard three-ram specimen should be recorded every time a test is run. This buildup can lead to burn-in. which has no units. it indicates a buildup of dead or oolitic material. 8 . A decrease in permeability indicates tighter packing and could lead to blows and pinholes.When the specimen weight drops appreciably. burn-on and penetration defects.compactibility ranges. Green compression in conjunction with moisture can be used to determine the available bond. Significance . An increase in permeability usually indicates a more open structure in the rammed sand. 2 x 2-in. through a 2 x 2-in. Procedure . The specimen weight should be recorded at or near a predetermined compactibility. Permeability Permeability is a test of the venting characteristics of a rammed sand. the density to which the sand is rammed and the percentage of moisture used for tempering the sand are important factors in regulating the degree of permeability. shape and distribution of the foundry sand. Procedure . under standard pressure.The permeability number. Specimen Weight Variation in specimen weight indicates variation in the density of the rammed sand and changes in the system. is determined by the rate of flow of air. An increase in moisture. Example of a Sieve Analysis U. a greater number of large. After cooling.0 7.0 22. Significance . hard lumps are present at shakeout and more sand carryout will take place. Table 1.0 0.0 2.7 0. it is broken.0 41.0 17.0 0.0 14.0 9 . the type and amount of clay and the rammed mold density will affect the dry strength. and the strength is recorded.0 24. Procedure .0 24. specimen is made and dried in a ventilated oven at 230F (110C) for 2 hr.Dry compressive strength is the maximum load a dry specimen can sustain before fracturing.0 4.Dry Compression Dry compression indicates the resistance of the mold to stresses during pouring and cooling of a casting and the ease of shakeout. A standard 2 x 2-in.0 1. Sieve Number Sand A Sand B 20 30 40 50 70 100 140 200 270 0.0 1.0 1.S.0 24. An excessive amount of moistureabsorbing materials will decrease the dry strength.0 16.When sand exhibits high dry compression. Water is added to the top level line.0 60. Significance . silt. The MB clay value varies 10 . indicating the base exchange capability of bentonite. The procedure is repeated until the water above the sample is clear.Clay that still has the ability to exchange ions will contribute to green.0 100. Significance .0 AFS Clay indicates the amount of fines and water-absorbing material in the sample.3 100.Pan Total 0. Procedure . seacoal. Methylene Blue Clay The MB clay test determines the amount of active clay. dead clay. MB clay values are not affected by the majority of other sand additives. Only the active clay gives active bonding capacity to the system. The sand then is dried. and the mixture is allowed to settle for 5 min. cellulose. dry and hot properties of molding sand mixes.0 AFS Grain Fineness Number AFS Clay 60.The amount of exchangeable ions present is determined by replacing these ions with MB dye.AFS Clay may contain active clay. before the top 5 in.0 1. cereal. and the weight loss is recorded as AFS Clay. Procedure .A known amount of dried molding sand mixed with a pyrophosphate solution is stirred with a high-speed mixer for 5 min. ash. fines and all materials that float in water. of the water is siphoned off. many foundries have installed thermocouples in the batch hopper above the muller. Sand Temperature Temperature readings from the hopper sand help to determine if more or less water is required for tempering. and the temperature is recorded for each test. Significance . high LOI can lead to carbon pickup on the casting surface.The sand sample is fired at 1800F (982C) until it reaches constant weight. Screen Analysis and GFN 11 .A thermometer is placed into the sand sample immediately after sampling. Procedure . Loss on Ignition LOI determines the total amount of combustible material in the sand.depending on the purity and nature of bentonite and can be used to check incoming shipments of bentonite or pre-mixes. To assist muller operators. Automatic controllers use the incoming sand temperature as one of the parameters to determine the correct water addition.Variations in temperature indicate a need for varying the amount of water added to the muller. The time of firing is directly related to the size of the sample. In steel castings. Scabbing also can be caused by excess gas formation.The quantity of gas-forming material in the sand will affect casting results. High LOI may produce gas defects such as pinholes and blows.only warm sand can be cooled in the time allowed by the mulling cycle. The muller is not the place to cool hot sand . Procedure . Significance . Procedure .The fineness of the sand has a bearing on the physical properties that can be developed by the sand system. scabs. Excessive hardness. and the sand retained on each screen is weighed. The percentage retained in each screen is multiplied by a factor to give a product for each screen. 12 .A dry sample of sand is screened through a "nest" of sieves (largest opening sieve on top and progressing down the nest). can cause cracks. MOLD PROPERTY TESTS Mold Hardness The mold hardness test indicates the resistance of the mold-to-metal damage as the metal contacts the mold surface. Also. The sample is shaken for 15 min in the screen shakers. A comparison of the dried and the washed screen analyses shows how much agglomeration takes place in the sand system. Significance .5 min . Significance .Mold hardness is measured by the resistance offered by the mold surface to a spring-loaded plunger.The fineness influences the bond required and the surface finish of the castings. drops and swells. meanwhile. blows. more accurate dimensions and reduced penetration.the time required to break up the lumps but not the agglomerates. very different sand mixes with different casting properties still may average out to the same GFN (Table 1).Proper mold hardness will give castings a better finish. The dried sand should be shaken for only 2. The test should be run on the washed system sand and the dried system sand. pinholes and penetration. but the "C" scale tester is more accurate at the high end of the hardness scale. and that sum is totaled to determine the AFS grain fineness number (GFN). Procedure . which are the basis of the entire system. Both "B" and "C" scale hardness testers are available. and the back pressure to an airflow is read. is placed on the mold face.Mold Strength This test measures uniformity of compaction on the mold face in production. Procedure . Procedure .This test shows changes in the venting ability of the molding sand. connected with tubing to the MQI unit. 13 .A rubber-faced contact head. Although they may not always agree. connected with rubber tubing to the perimeter.A robber-faced contact head.A spring-loaded plunger is driven into the mold face to a predetermined depth. Significance . Significance . and the sand's resistance is measured in psi. they should remain in a constant relationship. Procedure . indicating system changes.The tighter sand is compacted.This strength can be compared to the green compression on a three-ram specimen. Mold Quality Indicator The mold quality indicator (MQI) readings are an indirect density reading based on permeability. allows the mold face permeability to be read. Significance . Mold Permeability The mold permeability test measures the degree of compaction to which the mold has been rammed. the higher the MQI reading. Procedure .The live clay actively bonds the sand. Available Bond Available bond indicates the moisture-absorbing material in the sand system.Higher working bond indicates more efficient use of the clay present. Significance . 14 . the greater the clay utilization and the lower the clay content required.DERIVED PROPERTIES Working Bond The working bond percent indicates the amount of clay that actually is producing bond strength in the sand mix. The dead clay does not add to green tensile or green splitting strength. Significance . but does absorb moisture. Mulling Efficiency The higher percent mulling efficiency. Procedure . and the latent clay can be activated with further energy input. latent and dead clay and additives.The available bond value is derived by relating green compression to moisture using a prepared graph or a special slide rule.Working bond (or effective clay) is derived by relating green compression to compactibility via a prepared graph or special slide rule. Large variation indicates variation in the clay additions or in the effectiveness of the mulling. including live. Procedure . 15 . temperature. quality of the bond.The working bond value divided by the available bond value (and multiplied by 100) gives a percent mulling efficiency reading. muller or mixer condition all may affect mulling efficiency.Segregation in transport. loss or buildup of fines due to lack of dust collection. Significance .