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Sand testing of sand casting (4)

7) Shatter Index Test :

In this test, the AFS standard sand specimen is usually rammed by 10 blows and then it is allowed to fall a half inch mesh sieve from a height of 6 feet. The weight of sand retained on the sieve weighing. It then notified as a percentage of the total weight of the specimen is measured on the index shatter.

8) Mold Hardness Test:

The test is performed by mold hardness tester. The work on the tester based on the principle of Brinell hardness testing machine. In AFS hardness tester is a standard half-inch diameter steel ball hemispherical spring loaded with a load of 980 gm. The ball has to do to break into the sand mold or core sand surface. The spot is the point ball into the mold surface shown on dial in thousands of inches. The dial is calibrated to read the mold surface hardness directly ie offering no resistance to the steel ball hardness value would be zero and more rigid model and fully capable to prevent the ball from penetrating steel would hardness value of 100. The gauge can dial the hardness tester to provide direct readings.

9) Compactability flowability :

Compactability test is widely accepted as both a simple and directly related to the transport of sand in shape, especially when associated with compaction squeeze. A fixed amount of loose sand compacted under standard conditions and shows the percentage reduction in the amount of compactability.

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Sand testing of sand casting (3)

5) Strength test:

This is tempered sand strength expressed by its ability to hold model in shape. Sand molds are subject to compressive, tensile, shearing and transverse stress. The compressive strength test green and dry compressive strength of the test most commonly used in the foundry.

- Compression Tests A specimen of sand rammed produced Tempered shape is 2 inches in diameter and 2 inches tall. The sample is then rammed subject to load increase gradually until the sample breaks. The point where the sample taken breaks the compression strength.

- Shear Tests compressive loading system is modified to offset the specimen load to provide. Under most conditions the shear test results shown to be closely associated with the compression tests, although the latter property increases proportionately more high density ramming.

- The tensile test specimen is loaded in tension special waisted by a pair of grips. The test sample is rectangular plain transverse support by the end of knife edges and centrally loaded broken. And transverse tensile tests commonly applied to sand high strength, the conditions to be particularly associated with the stress incurred during handling cores and solutions.

6) Permeability Test:

Permeability is determined by measuring the air flow rate through compacted specimens under standard conditions. Roller sand sample is prepared using rammer and death. This sample (typically 2 inch dia and 2 inches tall) used for testing the permeability or porosity of the sand molding and core. The test is performed in permeability meters flat consists of a tank, water tank, nozzle, lever, adjusting the nose piece for fixing sand specimens and a manometer. The permeability is measured directly. Permeability number P is air volume (in cm 3) passing through sand specimen of 1 cm2 area and 1 cm cross-sectional height, a pressure difference of 1 gm / cm2 in one minute.

P = VH / ATP

Where,
P = permeability
v = volume of air passing through the specimen in c.c.
h = height of specimen in cm
p = pressure of air in gm/cm2
a = cross-sectional area of the specimen in cm2
t = time in minutes.

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Advantages and Disadvantages of Sand Casting

Advantages of sand casting:

1) solutions can be used to create complex geometries pad, including internal Goth external shapes arid.

2) Some parts casting operations produce net shape. Any additional manufacturing parts are needed.

3) can be used solutions.

4) casting process for any metal that can be heated to the liquid state.

5) There are several methods highly suitable solutions to this mass.

6) Resolution is the easiest and fastest (technique) from drawing (design) production.

Disadvantages of Sand Casting:

1) Limitation on mechanical properties.

2) Porosity (empty spaces inside the metal – metal strength decreases).

3) Poor precision dimensional and surface finishing.

4) safety hazards for people and environmental problems. A very difficult

5) Ending pattern of thin and small parts.

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Automated Sand Casting in Foundries

Today 70% of the processes to achieve solutions to automation. It is because of upto 200 sand casting components ideal, but in the case of long production lines arid higher number of components not much arid little economic sand casting components. For this purpose automated foundry is the right choice. High temperature melting metal used for castings. There are three types of producing

1) factory jobbing upto 100 parts but many of the

2) 500-1000 Batch factory part.

3) Mass production: lots of parts, can be more than 1000.

In foundries are automated conveyor continuously pouring into the pre-made models. This process is ongoing two levels.

1) Pooring the continuous metal into the molds.

2) Charges metal into the tables from the furnace (iron gray mostly) (all tables have six tones)

In automated sand casting sand automatically made arid pattern is made of metal. More water is added to the sand. But riot have become too damp sand otherwise it disintegrates easily. The pattern is pressed into the sand prepared by automatic hydraulic press and the mold is made. By the same procedure many models made then start operation solutions without stopping conveyor After the castings have cooled down arid completely, models have destroyed them passing through the drum recycling rotating sand removed arid up again with the sand transport system and the solutions have moved in the drum for additional operations such as the removal of the parts over (risers runner arid) from their bodies, and finishing operations arid burst. For a small number of large casted components with high melting temperature, metal, sand casting is suitable But this is a disadvantage every time you need a new model so that the technique would be economic for metals riot low melting temperature.

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Sand casting is simply melting the metal and pouring

Casting off the old technique is the quickest link Between 2nd manufacturing engineering drawing .It Provides us with the possibility of forming wide range of shapes with wide range of materials. sand casting is simply Melting the metal and pouring it INTO a preformed cavity, Called mold, allowing (the metal to solidify and Then breaking up the mold to remove casting. In sand casting expandable molds are Used. So for each casting operation are i have to form a new mold. Basic Requirements for metal casting

1. A mold cavity
2. Melting process
3. Pouring technique
4. Solidification process
5. Removal of casting
6. Finishing draft allowance.

Sand Casting is the MOST important ‘and mostly Cars casting technique. To Perform sand casting we do i have to form a pattern (a full sized model of the part), enlarged to account for shrinkage and machining allowances in the final casting. Materials Used to Make Patterns Include wood, plastics, aluminum, fiberglass, cast iron and Some other metals. Wood is a common pattern material Because it is easily. Worked INTO shape. Its disadvantages are That it tends to warp and the sand Being compacted around it abrades it, setup Limiting the number of times it whence be reused (Used for a small number of castings). Metal Patterns are more expensive to Make, BUT not * Much longer cargo. For example aluminum is the MOST common metal to be Used in f “work schedule castings are to be made by the Same pattern. So selection of the Appropriate pattern material depends to a large extent on the Total Quality of castings to be made. The size of the pattern depends upon the shrinkage Düring cooling and the Finishing allowance. Some special coating to Prevent Their Destruction shouldnt coat Patterns. Patterns i ar Some identifiers thrown out colors on dis, each of Which DG Different Meaning That represent Different treatments and requirements Far the Patterns. The casting will be Missing. To ensure That cores retain the Correct arrangement core Prints are placed Into the mold. Some metal springs Called densiments are placed Into the mold Io Provide Uniform solidification of the metal throughout the mold. Nails are inserted INTO thin parts of the mold to reinforce dis. After forming the mold cavity, the liquid is sprayed Alcoholic aver the cope (The upper part of the mold) and heated with flames to harden and to dry the surface.

Filling a metal box Having two halves, Which is Called the flask mold forms. So ar mold made up of two halves, Which is separated by a parting line. The Reason for this is to remove the part tasted easier for from the mold. The upper part of the mold Called the cope and the lower part Called the drag. The cope and drag are prepared separately and are ready not * not * When unites and metal is poured through a canal it INTO Called sprue, Which transmits the molten metal via Into the mold cavity runner. The runner shouldnt be big Because it will Increase the Amount of the waste metal. It shouldnt be small Because this enhances rapid solidification in the runner causing a blockage. At the bottom of the sprue there is a gap Far well Called the collection of the unwanted sand, Which comes with the flowing metal. There ar a riser system, Which acts from the inventory of molten metal When the mold cavity is fulfilled with the metal and Automatically feeds the cavity of the part I want to Get That we do.

Because this system is Essential for the molten metal cools it down this shrinks the Amount Needed to Replace the metal shrinked Comes fom the riser itself eliminating shrinkage cavities. A casting microporosity May show. This sing with directional solidification be eliminated either by incorporating a metal cell Into the mold or by tapering the thinnest section of the runner. You Chills ar Used around thicker parts of the casting to Provide Uniform cooling of the cooler parts These thinner parts to Prevent cracks. Chills, by this way, preserve the mechanical properties of the casting siar. The steel is melted in electric-arc Furnaces. The Advantage of electrical furnace, the scrap steel, Which wasnt Used Estimates for (metal risers and runners left In) sing in These Furnaces be melted and used again. When the furnace reaches the drink to temperature, it is Turned off. The molten metal is Filed Portable RESERVOIR Called Into the table and Then table is moved to just Above of the mold and metal is poured Into the mold’s pouring basin. A powder is added to the mold’s surface to Prevent metal’s rapid cooling pouring Düring. Another powder is sprayed aver the mold to form a blanket of inert gas to Prevent the oxidation of the molten metal. The steel is melted in electric-arc Furnaces. The Advantage of electrical furnace, the scrap steel, Which wasnt Used Estimates for (metal risers and runners left In) sing in These Furnaces be melted and used again.

When the furnace reaches the drink to temperature, it is Turned off. The molten metal is Filed Portable RESERVOIR Called Into the label and Then table is moved to just Above of the mold and metal is poured Into the mold’s pouring basin. A powder is added to the mold’s surface to Prevent metal’s rapid cooling pouring Düring. Another powder is sprayed aver the mold to form a blanket of inert gas to Prevent the oxidation of the molten metal. Completed The casting is left for cooling and When it completely cools down the siar flask is wrangled to a vibrating platform to remove the casting from the mold. Excess parts are cut either by oxygen in f the casting is of steel (high), or by hammering in f the casting is of cast iron.

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Sand testing of sand casting (2)

2) Test Material Clay:

The amount of clay is determined by the test subject of clay a clay in the sand molding of 50 grams defined as particles when suspended in water, fail to resolve at the rate of one inch per min to complete. Clay consists of particles smaller than 20 microns, against 0.0008 inch dia.

3) Test Finer Grain:

The AFS Grain Fineness number (AFS-NBA) is one means of measuring the fine grain of sand system. NBA is a measure of the average particle size (or grain) in a sample of sand. The finer grain of sand molding measured using a test called sieve analysis. The test is carried out in shaker power driven a number of sieves equipped with one over the other. 1. A representative sample of the sand is dried and weighed, then passed through a series of progressively finer sieves (screens) and they are agitated and tapped a 15-minute test cycle. The series is put in order from top to bottom fineness. 2. The sand keep each sieve (grain too large to pass through) is then weighed and recorded. 3. The weight of each sieve to keep out three calculations to get the AFS-NBA.

4) Test refractoriness:

Refractoriness is considered the molding sand by heating the specimen AFS standard sand to the high temperature ranges depending on the type of sand. The heated sand test pieces are cooled to room temperature and examined under a microscope where surface characteristics or by scratching it with a steel needle. If silica sand grains remains sharply defined and easily give way to the needle. Sintering is not yet set in. In the actual experiment the boat porcelain sand specimen submitted in electric furnaces. Is usual practice to start the test from l000 ° C and temperature in steps of 100 ° C raise to 1300 ° C and in steps of 50 ° over 1300 ° C till sintering the grain silica sand held . At each level of temperature, it is kept for at least three minutes and then taken out of the oven for examination under the microscope to evaluate the surface characteristics or by scratching it with a steel needle.

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Heterogeneous nucleation of sand casting

- Heterogeneous nucleation occurs at surfaces, imperfections, deformed regions, etc. which lowers the critical free energy.

- In the molten metal (castings) usually foreign particles are present as impurities lower the solid liquid interface energy and aid in nucleation and thereby reduce the amount of nucleation undercooling required to actuate.

- The basic requirement for heterogeneous nucleation in the capacity of the liquid metal to wet the foreign particles. Can forming solid impurities critical radius took a smaller increase in the surface energy. Therefore, heterogeneous nucleation can occur with relatively low undercoolings

- After the initial nuclei are formed.
1. more solid can be deposited on the first nuclei
2. More nuclei form,
3. different stage in the melt occurring.

- Has either very little or no supercooling at all in heterogeneous nucleation.

GROWTH:

- A growth following nucleation.

- Growth process determines the final crystallographic structure of the solid.

- Method depends growth of individual grains as well as the general mass of the solid on the thermal conditions prevalent in the solidification zone and the alloy composition.

- Growth is defined as the increase in size of the nucleus.

- The nuclei grow by additions of atoms.

- The nuclei reduce their total energy-free continuous growth

- During growth, material is transferred by diffusion.
a) In the old stage (ie liquid metal)
b) Across the liquid-solid interface.
c) In the nucleus – begins to grow on the grains already formed.

- The growth is controlled by the rate of heat transfer from the casting, since the temperature gradient toward the casting surface, the growth occurring in the opposite direction of heat flow, ie towards the center of the melt.

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Homogenous or self nucleatton of sand casting

- Formation of a critical solid from the liquid medium at the cluster together a large number of atoms at high undercooling (without external interface).

- Is one homogeneous nucleation occurs in perfectly homogeneous materials such as pure liquid metal.

- Grain nucleation the super cooled depending on two factors:

Factor A 1. The free energy available from the solidification process; depending on the volume of the particle formed. 2. The replacement passes old stage (ie molten metal) of the new phase (ie solid) reduced free energy per unit volume and this is contributing to the stability of the region (a new stage). 3. In the case of spherical particles, if the temperature suddenly dropped below the freezing point, the change of free energy per unit volume of metal transformation (ie solidified), and it is negative (due to energy cuts free); r radius of the particle.

Factor B 1. The second factor is the energy required to form a liquid-solid interface. 2. The particles are made, in some melting surface area. Steps are solid-liquid surface in between the two. A positive free energy per unit of surface it such. 3. The creation of a new interface (surface) of increasing the free energy is proportional to the surface area of ​​the particle and the free energy increase is equal to the free energy change so reported for particle ray. ? – As the radius increases particle, the free energy, also increases till grows the particle radius of critical and subsequent increase in radius of particles attached to reduce energy free and so much so that the energy Free also a negative charge. – Particles of radius smaller than the critical radius tend to redissolve and thus lower the free energy. Such particles are called embryos. – Particulate radius exceeds the critical radius tends to grow and also lower the free energy. Such particles are called nuclei. – Must critical particle size to create before the stable nucleus for certain super cooling temperature.

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Sand testing of sand casting (1)

Molding sand and sand core depending on shape, size composition and distribution of grains of sand, clay size, moisture and additives. The increase in demand for good surface finish and higher accuracy in castings requires certainty in the quality of the mold and core sand. Sand often test allows the use of cheaper local sand. It also ensures reliable mixing sand and allow use of the natural properties of molding sand. Will deliver sand test no change from the standard quality, and adjust the mixture to detect sand immediately to the particular needs so that it can minimize the casting defects.

In general the following tests are performed to judge the molding and casting foundry sands characteristics:

1. Moisture content Test
2. Clay content Test
3. Chemical composition of sand
4. Grain shape and surface texture of sand.
5. Grain size distribution of sand
6. Refractoriness of sand
7. Strength Test
8. Permeability Test
9. Flowability Test
10. Shatter index Test
11. Mould hardness Test.

1) Test Moisture Content: can the moisture content of the mixture, molding sand is determined by drying the size weighing 20 to 50 grams of sand molding with constant temperature up to 100 ° C in an oven for about an hour . It is then cooled to room temperature and then reweighing the molding sand. The moisture content in molding sand thus evaporated. The loss in weight of molding sand due to loss of moisture, gives the amount of moisture that can be expressed as a percentage of the original sand sample. Can the percentage of moisture content in molding sand also decide more quickly indeed an instrument called quick teller moisture. The instrument is based on the principle that when water and calcium carbide react, they form acetylene gas can be measured and this will in accordance with the moisture content. The instrument is available with a calibrated pressure gauge to read exactly the percentage of humidity present in the molding sand.

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Sand conditioning of sand casting

Natural sand generally not well suited for casting purposes. On continued use of molding sand, the clay coating the sand particles causing gets thinned out to reduce its strength.

Thus conditioning right sand binder accomplish uniform distribution around the grains of sand, moisture content control, eliminate foreign particles and aerates the sand.

Therefore, sand conditioning is needed for better results be achieved.

- The foreign materials, such as nails, hard sand and metal lumps from the sand used to enjoy. For removing the metal pieces, particularly ferrous pieces, the sand from the station shake out subject magnetic separator, which separates out the pieces of iron, nails etc. from the sand used.

- Next, the sand is examined in a separate measuring out the hard sand lumps etc. The measurements can be manual as well as mechanical. Mechanical measurements may be operated compressed air or electricity works. But electricity measurements are faster and can handle large quantities of sand in a short time. – After all these foreign particles to remove and the sand free from hard lumps etc., proper amount of sand pure, clay and additives have added to for the loss due to the burned, clay and other materials. As the moisture content of the sand back on knowledge, it is tested and after knowing the moisture on the required amount of water added.

- There are two ways to add water to clay and sand. In the first method, the first water is added followed by clay sand, and other means, is clay followed by addition of water. It has been said that the best order of ingredients adding sand to clay bonded sand with water followed by the binders. In this way, the clay is faster and uniformly spread the sand grains. A further advantage of the mix order is less dust produced during the mulling operation. – Now, what mix well in muller mix. The main objectives of a mix muller to distribute the binders, additives and moisture or water content uniformly across every grain of sand and helps develop the best physical properties can by kneading the sand grains. Mulling makes inadequate weak sand mixture can be compensated only by more binder.

- The final step in the cooling sand conditioning mixture of sand about the fact that if the hot molding sand mixture, it will cause difficulties in molding.

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