Experiment 01 Manual-Determination of AFS Grain Fineness Number

Fall, 2014
MATE 401-Casting Processes and Applications
MATE 401
CASTING PROCESSES AND APPLICATIONS
Experiment 01:
Determination of AFS Grain Fineness Number
Asst.Pof.Dr. Kâzım TUR
Res.Asst. Rauf AKSU
Fall, 2014
MATE 401-Casting Processes and Applications
1. Introduction
1.1 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
Metallurgical and Materials Engineering Department, Atılım University
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Fall, 2014
MATE 401-Casting Processes and Applications
1.2 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
•
Permit any gases formed inside and allow it to escape outside
•
Resist to erosion by molten metal flow during pouring and high heat of the molten metal until it
solidifies
•
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
Silica Sand
Silica sand (SiO2) is used extensively for sand casting processes. Silica sand is defined as a product of the
disintegration of rocks over very long periods of time. It is preferred due to its low cost and resistance to
elevated temperatures.
Silica sand can be natural or synthetic. Natural sand contains naturally occurring clays whereas synthetic sand
is washed to dispose clay and other impurities. Then washed sand is screened and classified for desired size
distribution. Finally processed sand can be mixed with clay and other materials.
Silica sand consists of SiO2 in the form of quartz. There may be some impurities present such as ilmenite (FeOTiO2), magnetite (Fe3O4) or olivine ((Mg,Fe).SiO4). Pure silica has melting point of approximately 1700 oC.
1.2.1 Grain shape
Shape of a single sand grain is defined in terms of angularity and sphericity. Sand grains may be well rounded,
rounded, sub-rounded, sub-angular, angular and very angular. Grains may also have high, medium or low
sphericity within each angularity band.
Ideal foundry sand is rounded with medium to high sphericity. This enables to have good flowability and
permeability with high strength at low binder additions.
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Metallurgical and Materials Engineering Department, Atılım University
MATE 401-Casting Processes and Applications
Fall, 2014
Figure 2: Different shapes of a foundry sand grain
Surface area of the sand and other additives are important for controlling and preparing green sand. The
mixture may require more or less water depending on the surface area of the molding sand. As the size of the
sand decreases, its surface area increases.
Grain shape affects the amount of sand surface area. Rounded grains, having low surface area to volume
ratio, require the least amount of binder. Angular sands, however, have the greatest surface area. They
require more binder and moisture.
1.2.2 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.
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Fall, 2014
MATE 401-Casting Processes and Applications
2. Aim of Experiment
•
To learn and to conduct a standard sieve analysis test for sand used in molding processes.
•
To be able to calculate AFS Grain Fineness Number and size distribution of the sand and to
comprehend their importance.
3. Test Apparatus
•
Silica sand
•
Analytical balance (see appendix Figure 3)
•
Sieves (conforms to ISO R565 standard)
•
Mechanical sieve shaker (see appendix Figure 3 and 4)
4. Test Procedure
•
If the sand is wet, dry the sand sample in oven at approximately 110 oC to eliminate weight errors
caused by moisture.
IMPORTANT: Test sand must be free of clay and other additives. If not, wash the sand with “Rapid
Sand Washer” several times and oven-dry, then continue steps below.
•
Select appropriate sieves for silica sand, and stack sieves in sequence according to the coarsest
opening be at top, the finest be at the bottom.
•
Weigh 50±0,1 (or 50±0,1 )grams of dried silica sand with analytical balance and pour it down into the
top sieve, then place clamp plate on the top sieve and screw hand wheels and side handle levers on
the clamp plate.
•
IMPORTANT: The sieve shaker should be placed on a flat surface to ensure symmetrical distribution
of the sample over the sieve mesh.
•
IMPORTANT : Make sure that there is no any other equipment or objects placed on the surface
where the shaker stands. Otherwise, vibration might cause accidents and/or failure of the other
equipment.
•
Set vibration time to 15 minutes, vibration amplitude to 5, cyclic time to 10 seconds and waiting time
for intermitted shaking to 5 seconds in the Mode Function.
•
Remove the clamp plate, in same manner with placing, and the sieves beginning with top sieve.
IMPORTANT: Do not attempt to remove any component while the shaker is vibrating.
4
•
Collect the retained sand on each sieve with a brush on a paper.
•
Weigh the sand collected on papers of each sieve and record on table given below.
Metallurgical and Materials Engineering Department, Atılım University
MATE 401-Casting Processes and Applications
Fall, 2014
5. Calculation of AFS Grain Fineness Number
•
Divide the weight of sand retained on each sieve by total sand weight and multiply by 100 to
calculate the percentage of sand on each sieve.
•
Multiply the percentage of retained sand by corresponding AFS and add all them up then divide it by
total percentage retained.
Weight of sample taken = _______ grams.
Sieve Series
No
Aperture size
in mm
Sand retained
on each sieve
Percentage of
sand retained
1
1,400
6
2
1,000
9
3
0,710
15
4
0,500
25
5
0,355
35
6
0,250
45
7
0,180
60
8
0,125
81
9
0,090
118
10
0,063
164
Pan
-
275
Multiplier
Product
Total
AFS Grain Fineness Number =
Total Product
Total Percent of Sand Retained
Metallurgical and Materials Engineering Department, Atılım University
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Fall, 2014
MATE 401-Casting Processes and Applications
6. Result and Discussion
•
Calculate AFS Grain Fineness Number of sand sample of your group.
•
Present the size distribution of the sand in a bar chart. (use Excel)
•
Answer following questions:
 What does AFS Grain Fineness Number represent? And why is it important?
 What does the size distribution of sand grains tell? Which properties are being affected by
size distribution?
7. Equipment Visuals in the Lab for this Experiment
Figure 3: Mechanical Sieve Shaker (left), Balance and Analytical Balance (right)
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Metallurgical and Materials Engineering Department, Atılım University
MATE 401-Casting Processes and Applications
Fall, 2014
Figure 4: Mechanical Sieve Shaker and its components
8. References
[1] AFS | American Foundry Society. (2006). Guide to Casting and Molding Processes. Retrieved from
http://www.afsinc.org/files/methods.pdf
[2] ASTM International | American Society for Testing and Materials. (2014). Sieving Methods, Guidelines for Establishing Sieve
th
Analysis Procedures. 5 Edition by Smith T.
[3] Strobl S. (Simpson Technologies Corporation). (2000). The Fundamentals of Green Sand Preparation and Control. Retrieved
http://www.simpsongroup.com/tech/rpt-sales-Fundamentals%20of%20Sand%20Control.pdf
[4] The Library of Manufacturing. (n.d.). Sand Casting (For Manufacture). Retrieved from
http://thelibraryofmanufacturing.com/metalcasting_sand.html
[5] Endecotts Limited. The Octagon Digital User Guide: Variable Amplitude Test Sieve Shaker
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