Title

Sand Testing Preparation (GFN) (Foundry)

Objective

To determine the sand grain size and calculates the Grain Fineness Number (GFN) for moulding material of sand casting.

Introduction (Background and Theory)

Casting and Molding Processes

Molding processes can be divided into four main categories: sand casting processes;

permanent mold process, ceramic processes; and rapid prototyping. While determining the

best process for the product to suit needs, there are several factors to be considered:

• Surface quality

• Dimensional accuracy

• Type of pattern/core-box equipment

• Cost of making the mold

• Effect of selected casting process on design of the casting

Among these casting processes, sand casting method has been used extensively in industry;

therefore sand casting process will be the main issue of laboratory experiments during whole

semester.

Figure 1 : Typical Foundry Process Flow

Sand Casting Processes

A mold is produced by shaping a refractory material to form a cavity of a desired shape in

which the molten metal is poured. The mold cavity must retain its shape until the metal has

solidified and the product is removed. There are variety of different refractory materials as

casting sands including silica, olivine, chromite and zircon sands.

The mold made of one or combination of these sands must:

• Have sufficient strength to sustain the weight of the molten metal

• Be stripped away from casting cleanly and easily after it has sufficiently cooled

• Be inexpensive, because large amounts of sand are used in a casting facility.

Size and size distribution

The size and size distribution of sand grain is one of the most important factors for a healthy

casting process. The size of the sand grains affects the quality of the casting. The grain

fineness of molding sand is measured using a simple sieve analysis test. Grain Fineness

Number (GFN) is a measure of the average size of the grains in sand. Likewise, AFS Grain

Fineness Number (AFS-GFN), introduced by American Foundry Society, is a measure of

grain fineness of a sand system. AFS-GFN is used to verify the molding sand to be staying

within specification for the castings being produced to avoid potential casting problems. Too

fine grains may cause low permeability, results in gas defects; too coarse may create high

permeability which leads to metal penetration into mold, and affects surface roughness of the

casting. The ideal GFN depends on the type of metal poured, pouring temperatures, heavy or

light casting and required surface roughness.

The size distribution of sand grains is also related to the quality of the sand system. Porosity

is directly related to permeability which is the ability of the mold to permit gas escape

through the mold. If sand grains of the mold are having nearly same size, the porosity is

maximized. This may lead to poor surface quality and metal penetration into the mold.

Therefore one should decide on an optimum size distribution to avoid such defects.

Formula below used to calculate Grain Size Fineness;

GFN=Σ FΣC

×100 %

Apparatus

Num. Diagram Name

1.

Green Sand

2.

Sieve Shaker

3.

Digital Scale

Balance

Num. Diagram Name

4.

Sieve

5.

Steel Bowl

Industrial Apparatus

Num. Diagram Description

1. High Capacity Sieve Shakers A061-96

Activated by electromagnetic impulses using

triple vibrating action (vertical, lateral and

rotational) they are recommended to perform

sieving tests where high precision and

performance are important.

Simple and sturdy construction can hold up

to 10 sieves and they are suitable for wet

sieving test

The sieving time from 1 to 999 minutes

Power supply are 230V 50/60Hz 1ph

450/750W

2. Sieve Shaker Part No. 206650

The Sieve Shaker has a uniform mechanical

action comprising both a horizontal circular

motion and a vertical tapping motion that

allows particles to stratify and seek critical

openings, ensuring accurate, repeatable

results.

Test sieve size is 8 in. diameter (20.3cm). A

maximum of six 2 in. high (5.1cm) or

thirteen 1 in. high (2.5cm) sieves can be

used for testing at one time. Shaker features

vertically mounted 1/4hp motor and has a

built-in 99-minute digital timer/clock

accurate to 0.1 second.

Recommended for testing applications

requiring analysis of particles from 5 in.

(12.7cm) to 20 microns wide (635 mesh)

Experimental Procedures

a) The sieves was cleaned by turning the sieve face down and striking the rim evenly

on the table.

b) The sand sample is weighed to 100 grams.

c) The sieve is then stacked together by putting the biggest mesh size on top until the

smallest sieve on the bottom (35, 45, 60, 70, and 80,100,120,170,230) and next with

the sieve pan at the last one.

d) The stack of sieves is then put on top of the Sieve Shaker Octagon 2000 machine.

e) The silica sand was put into the sieve.

f) For a period of 10 minutes the sieve was shaken continuously.

g) After shaking for 10 minutes, the top sieve is taken apart and left over sand on the

sieve was wiped using a brass brush and carefully weighed. The weight then recorded

in column C.

h) The step in (g) was repeated until the last over sand in the sieve was weighed and

the value is recorded.

i) Using the Grain Fineness Number (GFN) formula at the below we could calculate

the Grain Fineness Number (GFN)

GFN=Σ FΣC

×100 %

Results And Data Analysis

A B C D E FNO Sieve no Opening (µ) Sand

mass(g)Sample % AFS

multiplierAFS Product

(C X E)1 35 500 0.00 0.00 10 0.002 45 355 0.00 0.00 20 0.003 60 250 29.00 29.59 30 870.004 70 212 17.00 17.35 40 680.005 80 180 9.00 9.18 50 450.006 100 150 15.00 15.31 70 1050.007 120 125 12.00 12.24 100 1200.008 170 90 9.00 9.18 145 1305.009 230 63 4.00 4.08 200 800.00

10 Pan Pan 3.00 3.06 300 900.00Total accumulated sand mass (g) ∑C= 98.00 ∑F= 7255.00

Original Mass of Sample before Sieving (g)

100

GFN=Σ FΣC

×100 %=7255.0098.00

×100 %=74.03<100(course)

Discussion

In this experiment, we have to measure grain size and calculates grain fineness number

(GFN)., We have followed the procedures given on the manual lab and recorded the data in

the respective table and sample of calculations in order to measure and calculate the grain.

From the experiment, the value of GFN we obtained for the sand silica sand in the sieve

analysis is 74.02 which is the silica sand has type of course grain. So, it can be simply said

that it is a good quality of sand.

The total accumulated mass of the sand mass (g) is 98.00. This is to be expected from

the beginning due some sand have trap at each sieves and not 100% pass. From the original

mass we were weighed before the sieve testing, there was a little bit decrease in the mass

weight where the original sand mass on sieve shaking was 100g. This occur due to the some

errors like not wipe all the left over sand in each sieve. In addition, the digital balancing scale

also one of the factor that cause error where it is not perform in proper condition. The reading

value always change and not fixed. However the data still accepted since the error are not too

much. For this experiment, there are several precaution we must take to avoid and prevent

errors from occurring. The screen on the sieves should be clean carefully in order to avoid

any grain sands still stuck in the sieves. The stack of sieves on the Sieve Shaker must be

locked tidily to avoid them from moving away or fall over during shaking process. We also

must clean the area around digital scale balance to get accurate readings and avoid the

environmental effects. Student also can use a softer bristle brush to gently wipe the screen.

i) Explain briefly what is GFN?

The definition ‘Grain Fineness Number’ or also known as (GFN) is a system

developed by AFS for rapidly expressing the average grain size of given sand. It

approximates the number of meshes per inch of that sieve that would just pass the sample if

its grains of uniform size. It is approximately proportional to the surface area per unit of

weight of sand, exclusive of clay.

ii) Based on GFN value and the distribution obtained, suggest the suitability of the sand

for castings.

To get the perfect match and sand casting suitability, there are several factor and

qualities that can be used as a reference. Firstly, there is refractoriness, bond strength,

permeability, collapsibility, grain fineness and size and lastly grain shape and roundness. The

most suitable sand for casting should have good strength. It is important to avoid the mould

from broken during the process. It also has high refractoriness to withstand the high

temperature of the molten metal.

The sand also must have good permeability. The sand must be porous so that the

gases generated are allowed to escape. Size of the sand and its shape it’s depend on the

materials and casting process. The small size provided better surface finish but the large grain

size is more permeable. The sand should have good thermal conductivity, so that the heat

from casting is quickly transferred. From the experiment, we could say that our sand sample

is good to use for casting as it have a balance amount of porosity and permeability to be used

for small cast operation and it will also have a good surface quality.

Conclusion

From the experiment, we can found that the value of GFN of the silica sand specimen

by using the sieve analysis is 74.03. Hence, the sand sample used in the experiment has the

most suitable coarse number value not too low of value and not too high value. As too low

will had poor surface quality in casting and too fine will make it less permeability. However

some error did occur during the experiment as the total accumulates sand mass is differ from

the original mass which is 98.00 gram while the original mass is 100g. To minimize the error

we need to take extra precaution in order to get the accurate data in this experiment and avoid

errors. As a conclusion the objective of this experiment was achieved and successfully.

Recommendation

There is a couple of things and procedure than can be improved by modifying certain steps or

we may even remove it. Firstly, the cleaning process of the screen on the sieves should be

done carefully in order to remove all grain sands. It also imperative to avoid contact the

sieves screen with the fingers. In the cleaning process, we should also gently brush the sieves

to make sure the sieves are not damage. In the shaking process, the stack of sieves on the

Sieve Shaker must be locked tidily to avoid them from moving away during. Then, we have

to make sure the left over sand in each sieve is transferred to the container use in weighing

process. Lastly, the area around digital scale balance should also be cleaned to get accurate

readings and this would avoid the environmental effects.

References

Books

1. Serope Kalpakjian, Steven R. Schmid, Manufacturing Technology and Fundamental,

5th Edition, Prentice Hall, 2004.

2. M. Y. b. H. M. al-Rangi, Manufacturing Process, Malaysia, 2009

3. Rao, Manufacturing Technology Vol-I 3E, Volume 1, Tata McGraw-Hill Education,

2009

Internet

1. http://wiki.answers.com/Q/

What_is_the_important_about_grain_fineness_number_for_sand_casting.

[Accessed On 27 October 2015]

2. http://www.atilim.edu.tr/~kazim.tur/mate401/Dosyalar-LAB/MATE%20401-Lab-

Exp.01-AFS%20grain%20fineness%20number.pdf

[Accessed On 27 October 2015]