testing procedures

MME346/Expt #02/ of 7

MME 346: Foundry Engineering Sessional Course Tutor: Dr. A.K.M.B. Rashid

Professor, MME Department, BUET

Experiment Two Properties of Greensand Moulding Aggregate

AIM OF EXPERIMENT 1 To familiarise with the standard test procedures for moulding sand aggregates used in

foundry establishment e.g. sieve analysis, clay content test and moisture content test, permeability, mould hardness, green compressive strength and dry compressive strength.

2 To be able to calculate the AFS grain fineness number and learn about its significance.

3 To be able to differentiate between moulding sands for ferrous and non-ferrous castings, and for small and heavy castings.

4 To be able to understand the effects of moulding sand characteristics (clay and water contents and number of ramming) on the properties of greensand moulding mixture (permeability, mould hardness, green compressive strength and dry compressive strength).

EXPERIMENTAL PROCEDURE 1 Conduct sieve analysis of as-received sand (Appendix-A1).

2 Prepare two sand batches

(1) using as-received sand. Call this sand as Batch One (B-1).

(2) using only one or two sieve fractions that retained the maximum amount of sand. Mark this sand as Batch Two (B-2).

3 Take Batch One sand and determine its clay content (Appendix-A2) and moisture content (Appendix-A3).

4 Prepare the greensand mixtures (see Table 1) by adding, if necessary, appropriate amount of clay and moisture to Batch One sand.

5 Prepare AFS Standard moulding sand mixture specimens (cylindrical bars with 2 in diameter and 2 in length) using 3 numbers of ramming. Prepare 3 specimens for each ramming condition.

6 Determine the permeability, hardness (top and bottom of the specimen), and green and dry compressive strength of the sand mixture (see Appendices-A4, A5 and A6).

7 Continue steps 3 to 6 using Batch Two sand.

8 Complete the data sheet for this experiment.

DISCUSS THE FOLLOWING IN YOUR REPORT 1 (a) Determine the AFS grain fineness number of the sand. What does this number

represent? What this number does not tell the foundrymen?

(b) Comment on whether or not the sand is 2–mesh, 3–mesh or 4-mesh type.

MMMMEE materials & metallurgical engineering


(c) Present the sieve analysis data in graphical form (both percent retained on each sieve and cumulative percentage). What does this curve demonstrate?

(d) Comment on the suitability of the sand you tested for ferrous and nonferrous castings, and for small and heavy castings. [Hints: compare the calculated AFS grain fineness number with the value obtained from literature].

2 Plot the difference in hardness between the top and bottom of the specimen versus the number of ramming and discuss your result.

3 Plot the following properties as functions of clay and moisture content.

(a) Mould hardness

(b) Permeability

(c) Green compressive strength (GCS)

(d) Dry compressive strength (DCS)

4 With the help of suitable graphs, discuss the effects of the following foundry variables on the properties (permeability, hardness, GCS, DCS) of moulding sand aggregate.

(a) Size and distribution of sand grains.

(b) Clay content.

(c) Moisture content.

ACHIEVEMENT After completing this experiment, the students should be able to

1 know and perform different standard test procedures used for moulding sand aggregates in foundry establishment.

2 understand the influence of moulding sand characteristics on the properties of moulding sand aggregates.

Table 1: Experimental details.

Student Group Sand Batch Clay Content Moisture Content

S1

B1

6

1.5 S2 2.0 S3 2.5 S4

3.0 S5 8 S6 10 S7 12 S8

B2

6

1.5 S9 2.0 S10 2.5 S11

3.0 S12 8 S13 10 S14 12


Student Group: _________________

DATA SHEET FOR SIEVE ANALYSIS

Weight of sample taken = _______________ grams

U.S. Series Equivalent Sieve Number

Sand retained Multiplier (B)

Product (A x B) Grams Per Cent

(A) Cumulative Percentage

Total

AFS Grain Fineness Number = Retained Sand of Percentage Total

Product Total

DATA SHEET FOR CLAY CONTENT Sample Description

Reading Number

Clay Content Per Cent Average Per Cent

1 2 3

DATA SHEET FOR MOISTURE CONTENT Sample Description

Reading Number

Moisture Content Per Cent Average Per Cent

1 2 3


Student Group: _________________

DATA SHEET FOR PERMEABILITY Sample Description

Clay Content

Moisture Content

Time in Second

Permeability Reading Average

DATA SHEET FOR MOULD HARDNESS Sample Description

Clay Content

Moisture Content

Mould Hardness Top Bottom Average Difference

DATA SHEET FOR GREEN AND DRY COMPRESSIVE STRENGTH Sample Description

Clay Content

Moisture Content

GCS DCS g/cm2 Average g/cm2 Average

COMPLETE DATA SHEET FOR EXPT. NO. 1 Sand Group

Clay Content, %

Moisture Content, %

Permeability Reading

Hardness Number

GCS g/cm2

DCS g/cm2

B1

6

1.5

2.0

2.5

3.0

8

10

12

B2

6

1.5

2.0

2.5

3.0

8

10

12


Appendix A

LITERATURE REVIEW FOR SAND TESTING

Periodic tests are necessary to determine the essential qualities of foundry sand. The properties changes by contamination from foreign materials, by washing action in tempering, by gradual change and distribution of grain size and by continual subjection to high temperature. Test may be either chemical or mechanical in nature. Various tests are designed to determine the properties of moulding sand and these are described in the following appendices.

Appendix-A1: Sieve Analysis The test of determining the AFS grain fineness number is performed on a dried sand sample from which all clay substances have been removed. A set of standard testing sieve is used to screen the sand. These sieves are stacked in sequence with the coarsest sieve at the top and placed in a sieve shaker. About 100 g sand is placed at the top sieve and, after 15 minutes of vibration, the weight of the sand retained in each sieve is obtained. The AFS grain fineness number of the sand tested can then be determined by taking the percentage of sand retained on each screen, multiplying each by a multiplier (which is simply the next available sieve old mesh number greater than the one being weighed out), adding the total, and then dividing by the total percentage of sand retained on the sieves. Typical calculation of the AFS fineness number, which includes the multiplier factor, is given in Table 1. Table 1. Typical calculation of AFS grain fineness number.

Size of sample: 50 g; AFS clay content: 5.9 g, or 11.8%; sand grains: 44.1 g, or 88.2%.

USA sieve series No.

Sand retained on each sieve, g

Percentage of sand retained (A)

Multiplier (B)

Product (A x B)

6 none 0.0 3 0 12 none 0.0 5 0 20 none 0.0 10 0 30 none 0.0 20 0 40 0.20 0.4 30 12 50 0.65 1.3 40 52 70 1.20 2.4 50 120 100 2.25 4.5 70 315 140 8.55 17.1 100 1710 200 11.05 22.1 140 3094 270 10.90 21.8 200 4360 Pan 9.30 18.6 300 5580 Total 44.10 88.2 15243

AFS grain fineness number = Retained Sand ofPercent Total

Product Total = 88.2

15243

= 172.8 or 173 AFS.

Appendix-A2: Test for Clay Content The equipment necessary for determining the percentage of clay in moulding sand consists of a drying oven, a balance and weights, and a sand washer. Clay content test is carried out as follows:


A portion of sand sample is thoroughly dried out at 220 C for about 4 h or until constant weight is attained. 50 g of this dried sand is placed in a wash bottle. To this sand, 475 c.c. of distilled water and 25 c.c. of 3.0 % caustic soda solution are added. The mixture is stirred for 5 min in a rapid sand washer. Sufficient water is added up to the level line marked on the bottle. The liquid is then siphoned off after 10 min. The bottle is refilled twice more and siphoned the liquid off. The sand is placed in the oven for drying. The sand is weighed when it is completely dried and the percentage of clay is determined by the difference in the initial and final weights of the sample.

Appendix-A3: Test for Moisture Content The most accurate method of moisture determination is to dry out the sand and to note weights before and after. Fifty grams of tempered sand, accurately weighed and placed in the pan. The timer for the blower of the moisture teller is set for the required time to dry the sand (approximately 5 min) and air at 110 C is blown over and through the sand. The sand is dried after this and weighed again. Note the difference in the initial and final readings and determine the percentage of moisture in the sand.

Appendix-A4: Permeability Test Permeability is defined as that physical property of the moulded mass of sand mixture which allows gas to pass through it. It is determined by measuring the quantity of air that passes through a given sample of sand in a prescribed time and under standard condition. Permeability of moulding sand depends on several factors including shape of sand grains, fineness, degree of packing, moisture content and amount of binder present. Hence coarse grained sands are more permeable than finer ones.

To determine permeability the AFS Standard sand specimen of 5.08 cm (2 inches) diameter and 5.08 cm in height is prepared by ramming the required quantity of sand in a smooth surface tube with three blows of standard rammer. This sand specimen is placed in the mercury cup of the permeability meter. The air drum is raised to take 2000 cm3 of air in to the air drum which will be indicated by the graduation on it. The whole air is then allowed to escape through the sand specimen with a pressure of about 10 g/cm3 and the time is recorded.

The permeability number of the sand sample can be calculated from the following equation:

P = p t A

h V

Where P = AFS standard permeability number V = Volume of air in cm3 = 2000 cm3

h = Height of specimen in cm = 5.08 cm (or, 2 inches) A = Cross sectional area of specimen in cm2 = 20.268 cm2

p = Air pressure in g/cm2 = 10 g/cm2 t = Time in minutes

The above equation may be simplified as

P = t

3007.2

where, t = time in seconds.

Appendix-A5: Sand Hardness Test The hardness achieved by ramming the moulding sand mixture can be measured by using an indentation-type mould hardness tester where a spring-loaded 1/2 inch diameter steel ball is pressed into the AFS Standard sand sample prepared by three blows of standard hammer. The hardness number is read directly from a dial gage which reads from 100 to 0. If no penetration occurs, the hardness reading is set arbitrarily to 100. If the ball sinks


completely into the sand up to the limiting surface of the tester, the reading is set to 0; i.e. the sand is very soft. A “hard rammed” mould generally reads 90, while a “soft” mould reads 50 to 60. Severe penetration by the liquid metal and washing of the sand occur when the hardness reading is bellow 50.

Appendix-A6: Sand Strength Test Sand strength test is the measure of holding power of various bonding materials in green and dry sand. It determines the cohesiveness or natural binding capacity of the sand grains. There are four types of test for sand strength: (1) compression, (2) shear, (3) tensile, and (4) over-hang bar test. Of these tests, the compression test is by far most widely used and is very convenient for routine testing of all types of national bonded and synthetic moulding sand.

For green compression strength test, the AFS Standard sand specimen is prepared. The test is performed on the sand specimen by using Universal sand strength machine. This machine consists of a pusher arm and weight arm, both hanging from a pivot bearing at the top of the machine. The weight arm applies load on the specimen while pusher arm pushes the specimen against the weight. As the weight arm is pushed up higher, the load increases until the specimen breaks. Then the compression strength in ton/in2 may be read at the magnetic marker whose left side shows the maximum upward travel of the weight arm.

For dry compression strength test, the AFS standard specimen is placed in the oven and dried it for about two hours at 110 C. The specimen is cooled and tested it on the same day they are made. The specimen is placed in the upper position of the sand strength machine and broken the specimen as in the case of green strength test. The dry strength values are read in psi off the dry strength scale.

testing procedures

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