Sand Testing Methods | The 7 Testing Methods That You Should Know About Green Sand Testing | Why Is Everyone Talking About Molding Sand?

Sand Testing Methods:

Sand testing methods are used to assess the properties of foundry green sand or molding sand for casting. The moulding sand after it is prepared should be properly tested to see that the required properties are achieved. Tests were conducted on a sample of the standard sand. The moulding sand should be prepared exactly as it is done in the shop on the standard equipment and then carefully enclosed in a container to safeguard its moisture content.

Sand tests indicate the moulding sand performance and help the foundry men in controlling the properties of moulding sands. Moulding sand testing methods control the moulding sand properties and testing through the control of its composition.

Sand Control Test

Green Sand is composed of the following ingredients: basic sand, bentonite binding agent, pitch powder or coal dust, and silica debris. Although green sand qualities cannot be standardized across all castings and molds as a whole, standards may be defined from one location to another and from one work to another in order to keep a minimum level of rejection.

The following are the various types of moulding sand testing methods:

1. Moisture content test

2. Clay content test

3. Grain fitness test

4. Air Permeability Test

5. Strength test

6. Refractoriness test

7. Mould hardness test (Brinell Hardness, Rockwell)

Molding sand has the following characteristics:

Refractoriness:

Molding and mixture must be able to survive the high temperatures encountered during melting without displaying evidence of softening or fusing to be considered heat resistant. The existence of quartz substance, or silica, as well as the form and size of its grains, contribute significantly to this attribute of the mouldings and other products. Rough and coarse grains have higher refractoriness than fine grains. Additionally, a larger amount of silica leads to increased refractoriness of materials.

Porosity or permeability:

It is the characteristic of sand that allows steam and other substances to penetrate through the sand mould.

Plasticity:

The quality of sand whereby it flows to all parts of the moulding box or flask and takes on a specified form under ramming pressure, and then holds that shape when the pressure is released is known as flowability.

Adhesiveness:

Sand has a characteristic that causes it to attach to the sides of the moulding box, a phenomenon known as sticking or clinging.

Cohesiveness:

Cohesiveness is a property of sand that causes the sand grains to adhere together when ramming is performed.

Moisture content test of sand

Moisture is the property of the moulding sand. It is defined as the amount of water present in the moulding sand. Low moisture content in the moulding sand does not develop strength properties. High moisture content decreases permeability.

Procedures of the moisture content test for green sand molds are:

1. 20 to 50 gms of prepared sand placed in the pan and heated by an infrared heater bulb for 2 to 3 minutes.

2. The moisture in the moulding sand is thus evaporated.

3. Moulding sand is taken out of the pan and reweighed.

4. The percentage of moisture can be calculated from the difference in the weights, of the original moist and the consequently dried sand samples.

Percentage of moisture content = (W1-W2)/(W1) %

Where, W1-weight of the sand before drying,

W2-Weight of the sand after drying.

Clay content test

Clay influences strength, permeability, and other moulding properties. It is responsible for bonding sand particles together.

Procedures of the clay content test for mold sand are:

1. A small quantity of prepared moulding sand was dried.

2. Separate 50 gms of dry moulding sand and transfer it to a wash bottle.

3. Add 475cc of distilled water + 25cc of 3% NaOH.

4. Agitate this mixture for about 10 minutes with the help of a sand stirrer.

5. Fill the wash bottle with water up to the marker.

6. After the sand, etc., has settled for about 10 minutes, siphon out the water from the wash bottle.

7. Dry the settled sand.

8. The clay content is determined from the difference in weights of the initial and final sand samples.

Percentage of clay content = (W1-W2)/(W1) * 100

Where, W1-weight of the sand before drying,

W2-Weight of the sand after drying.

Grain fitness test (Sand Sieve Analysis)

The grain size, distribution, and grain fitness are determined with the help of the fitness testing of moulding sands. The apparatus consists of a number of standard sieves mounted one above the other, on a power-driven shaker.

The shaker vibrates the sieve’s plate and the sand placed on the top sieve gets screened and collects on different sieves depending upon the various sizes of grains present in the molding sand.

The top sieve is the coarsest, and the bottom-most sieve plate is the finest of all the sieves. In between, sieves are placed in order of fineness from top to bottom.

Procedures of the Grain Fitness Test is:

1. A sample of dry sand (clay removed sand) was placed in the upper sieve plate.

2. Sand vibrated for a definite period.

3. The amount of same retained on each sieve plate is weighted.

4. Percentage distribution of grain is computed.

Air Permeability test

The quantity of air that will pass through a standard specimen of the sand at a particular pressure condition is called the permeability test of moulding sand.

Following are the major parts of the permeability test equipment:

1. An inverted bell jar, floats in water.

2. Specimen tube, for the purpose of holding the equipment

3. A manometer (measure the air pressure)

The steps involved are:

1. The air (2000 cc volume) held in the bell jar was forced to pass through the sand specimen.

2. At this time, air entering the specimen equals the air that escaped through the specimen.

3. Take the pressure reading in the manometer.

4. Note the time required for 2000cc of air to pass the sand

5. Calculate the permeability number

6. Permeability number (N) = ((V x H) / (A x P x T))

Where,

V-Volume of air (cc)

H-Height of the specimen (mm)

A-Area of the specimen (mm²)

P-Air pressure (gm / cm²)

T-Time was taken by the air to pass through the sand (seconds).

Strength test

Measurements of the strength of moulding sands were carried out on the universal sand strength testing machine. The strength is measured, such as compression, shear, and tension.

The sands that could be tested are green sand, dry sand, or core sand. The compression and shear tests involve the standard cylindrical specimen that was used for the green sand permeability test.

a. Green compression strength:

Green compression strength or simply green strength generally refers to the stress required to rupture the sand specimen under compressive loading. The sand specimen is taken out of the specimen tube and immediately (any delay causes the drying of the sample which increases the strength) put on the strength testing machine and the force required to cause the compression failure is determined. The green strength of sands is generally in the range of 30 to 160 KPa.

b. Green shear strength:

With a sand sample similar to the above test, a different adapter is fitted in the universal machine so that the loading now be made for the shearing of the sand sample. The stress required to shear the specimen along the axis is then represented as the green shear strength. It may vary from 10 to 50 KPa.

c. Dry strength:

This test uses the standard specimens dried between 105 and 1100 C for 2 hours. Since the strength increases with drying, it may be necessary to apply larger stresses than the previous tests. The range of dry compression strengths found in moulding sands is from 140 to 1800 KPa, depending on the sand sample.

The steps involved are:

1. Specimen held between the grips

2. Apply the hydraulic pressure by rotating the hand wheel

3. Taking the deformation use of the indicators.

Refractoriness test

The refractoriness is used to measure the ability of the sand to withstand the higher temperature.

The steps involved are:

1. Prepare a cylindrical specimen of sand

2. Heating the specimen at 1500 C for 2 hours

3. Observe the changes in dimension and appearance

4. If the sand is good, it retains specimen share and shows very little expansion. If the sand is poor, the specimen will shrink and distort.

Mould hardness test

The hardness of the mould surface was tested with the help of an “indentation hardness tester.” It consists of an indicator, a spring-loaded spherical indenter.

The spherical indenter penetrates into the mould surface at the time of testing. The depth of penetration w.r.t. the flat reference surface of the tester.

Mould hardness number = ((P) / (D – (D²-d²))

Where,

P- Applied Force (N)

D- Diameter of the indenter (mm)

d- Diameter of the indentation (mm)

In metal casting, we must select good green sand and achieve better castings with the use of high-quality foundry sand and sand testing methods.

FAQ

Refractoriness in the moulding sand is due to the presence of

1. clay
2. silica
3. additives and binders
4. dust

Answer:

The main constituents of moulding sand are:

Refractoriness is defined as the capacity of the mouldings and green sand mixtures to tolerate the heat of the melt without displaying any symptoms of softening or fusing. The presence of quartz or silica (80 to 90% weight) in the mouldings, as well as the form and size of the grains, contribute significantly to this refractoriness characteristic. Coarse and thicker grains have greater refractoriness than fine grains. Consequently, a larger concentration of silica leads to increased refractoriness.

What are the most typical tests that are conducted on foundry green sand testing?

A number of properties, including wet tensile strength and cone jolt; mouldability; friability; moisture content; sand permeability test; green compression strength; compactibility; loss on ignition; volatile content; grain size and distribution; dust (dead clay) content; and impact strength are measured in the fundamental tests.

How many different types of moulding sand tests are there?

Organic impurity testing – this testing is done in the field, for every 20 cubic meters, and the results are reported.
Silt content testing – this is also a field test that should be performed every 20 cubic meters.
Particle size distribution – this test may be performed on-site or in a laboratory for every 40 cm3 of sand and can be done on a sample basis.

Why is it necessary to examine the sand in the foundries?

A rapid and precise assessment of living clay in foundry sand is made feasible via the use of the foundry sand testing procedure. The most significant benefit of this test is that it helps to balance the clay in the moulding sand.

The air is passed through an inverted bell jar; name the sand testing process.

Before you can begin to do the sand permeability test on foundry sand, you must first learn about the permeability number of the material.

What exactly is the Permeability Number?

A permeability number is defined as the volume of air in cubic centimeters that will travel per minute through a typical sand specimen with a cross-section area of 1 cm2 and a depth of 1 cm when subjected to a pressure of 1 g/cm2.

The following are the essential components that are needed for the Sand Permeability Test of Moulding Sand: The inverted Bell jar, which may float on water, the specimen tube, and the manometer (for measuring air pressure).