1. Criteria used for sand testing / properties:
Continued…….
Criteria used for sand testing / properties:
Moisture content,
green and dry sand permeabilities,
compression,
tension,
transverse and shear strengths,
deformation during compression tests,
green and dry hardness,
clay content,
grain-size distribution,
combustible content, pressure,
volume of gases evolved,
flowability,
sintering point,
resistance to spalling etc.
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2. Sand Testing For maintaining consistent quality of moulding sand
The sand or say blended sand is characterized by
Grain Size
Grain Shape
Surface smoothness
Density
Contaminants
Moisture content
Clay content
Compactibility
Final Mould key properties are mould hardness, permeability and strength.
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3. General Test performed to judge the moulding and casting characteristic are:
Moisture Content Test
Clay content Test
Chemical Composition of sand
Grain Shape and surface texture of sand
Grain Size distribution of sand
Specific Surface of sand grains.
Water absorption capacity of sand
Refractoriness of sand
Strength Test
Permeability Test
Flowability Test
Shatter Index Test
Mould Harness Test.
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4. Grain fineness test: (Sieve Analysis Method)
A sample of dry silica sand 50g free from clay taken
Place on topmost sieve bearing US series 6.
A set of 11 screens bearing the standard mesh number are 6,12,20,30,40,50,70,100,140,200,270 are mounted on mechanical shaker.
The series are place in order of fineness from top to bottom.
Shaking is done for 15 min.
Weight of retained sand in each sieve is measured.
The value of weight is multiply by 2 which gives % weight.
It will give the GFN number finally by simple mathematics.
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6. Sand Sieve analysis Tester for GFN
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Sand Sieve analysis Tester for GFN

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8. Moisture Content:
It is determined by special device that measures the electrical conductivity of small sample of compressed sand.
Direct method is to measure the weight loss by a 20g to 50g sample after it has been subjected to temperature of 100*C in oven for one hour time.
More speedily by instrument “ Speedy moisture teller”.
When water and calcium carbide react , they form acetylene gas which can be measured and which can be directly proportional to moisture.
CaC2+2H2O = Ca(OH)2+C2H2
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10. Clay content:
It is determined by washing the clay from 50-g sample of moulding sand , using water that contains sodium hydroxide to make it alkaline .
Several cycles of washing and agitation required to fully remove the clay.
The remaining sand is dried and weighed to determine the amount of clay removed from sample.
Clay in moulding sand of 50g is defined as particles which when suspended in water, fail to settle at a rate of 1inch per min. Clay consist of particle less than 20micron , per inch in diameter.
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Rapid Sand Washer

12. Refractoriness Test:
It is found by heating the AFS specimen to very high temperature ranges depending upon the types.
Sand test piece are cooled at room temperature .
Examined under microscope for surface characteristics or by scratching it with steel needle.
Every time sand heated above 1000*C with a step interval of 50*C temp rise.
Again it is examined under microscope and needle scratch , till the sintering is not seen.
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13. Strength Test:
The sand specimen is placed in the lugs and the pressure is applied using the hand wheel till the specimen breaks.
The reading of the needle of high and low pressure manometer indicates the compressive strength in kgf/sq.cm.
Bending, shear, compressive and tensile test are performed.
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14. Permeability test:
It is conducted on compacted sand , using standard rammed specimen.
A amount of sand is first placed in a 2-inch (50.8mm) diameter steel tube.
A 14-lb (6.35kg) weight is dropped on it 3 times from the height of 2 inch (50.8mm).
A rammed specimen is subjected to an air pressure of 10g/sq.cm
Test is performed in permeability meter consisting of balanced tank, water tank, nozzle, adjusting lever, nose piece for fixing the sand rammed specimen and a manometer.
AFS number can be calculated directly from calibrated permeability meter.
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15. v = Volume air passing through specimen h = Height of specimen in cm.
Permeability is the volume of air in cubic cm. passing through a sand specimen of 1sq.cm cross sectional area and 1cm height at a pressure difference of 1gm/sq.cm in one minute.
In general
P = vh / pat
P = Permeability
v = Volume air passing through specimen
h = Height of specimen in cm.
p = Pressure of air in gm/sq.cm
a = cross sectional area of specimen in sq.cm.
t = time in min.
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16. Permeability Meter (AFS)
For AFS standard permeability meter , 2000cc of air is passed through 5.08cm height specimen and sq.cm c/s area at a pressure of 10gms/sq.cm and total time measured is 10sec = 1/6 min.
P = Approximately.
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Permeability Meter (AFS)

17. Check that the open orifice is in position in the center post.
Prepare a standard specimen of sand. Before stripping from tube, place in position on the center post and seal by rotating the knurled ring anti- clockwise.
Turn air valve to vent and raise air drum until it is above the water level.
Turn valve to close and allow the drum to descend slowly into the water. Turn the air valve gradually towards vent and allow the air drum to descend until the „X‟ mark on the drum is level with the top edge of the tank. Turn valve to „closed‟
Allow the air drum to descend by turning the air valve to a position midway between closed and vent.
Time the descent of the air drum between the zero and the 2000 ml mark with a stop watch and record the pressure indicated on the manometer during the descent of the drum.
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18. Block Diagram of Permeability Meter
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Block Diagram of Permeability Meter

19. Green Compressive Strength
It is determined by removing the rammed from compacting tube and place in mechanical testing device.
A compressive load is applied until specimen breaks. Which usually occur in range of 10 to 30 psi.
Hardness:
It is determined by resistance of the sand to penetration of a 5.08mm diameter spring loaded steel ball.
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20. Flowability: Put the sand in the steel cylinder.
By movement of rammer plunger between the 4th and 5th drop
It is indicated in percentage.
This can be directly taken on the dial of the flow indicator.
Then the stem of this indicator again put on the top of the plunger of hammer .
It records the actual movement of plunger between 4th and 5th drops.
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21. Shatter Index Test: Put the sand in the steel cylinder.
AFS standard specimen is rammed by 10 blows
Allowed to fall on a 1/2 inch mesh sieve from height of 6 feet.
The weight of sand retained in sieve is measured.
It is expressed as percentage of total weight of the specimen which is a measure of shatter index.
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22. Mould Hardness test: Performed by mould hardness tester.
Principle is based on brinell hardness testing machine.
A ½ inch diameter steel hemi-spherical ball is loaded with spring load of 980gm.
The ball is made to penetrate the mould sand and core sand surface.
The dial indicates the penetration in thousands of inch, which directly reads the hardness value.
The penetration of the probe into the mould surface is registered on the dial and is read direct as Green Hardness „B‟ Scale.
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Dial gauge
Sand Rammer

24. CORE
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25. Compact mass of core sand prepared separately that when placed in mould cavity at required location with proper alignment does not allow the molten metal to occupy the space for solidification in that portion and hence help to produce hollowness in casting.
Hollowness – Holes, recesses, Projections , undercut, internal cavities etc.
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26. CORE must meet following functions/objectives:
Core produce hollowness in casting in the form of internal cavities.
It must be sufficiently permeable to allow the easy escape of gases during pouring and solidification.
It may form a part of green sand mould.
It may be deployed to improve mould surface.
It may provide external undercut feature in casting.
It may be inserted to achieve deep recesses in casting.
It may be used to strengthen the mould.
It may be used to form gating system of large size mould.
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27. CORE Sand:
Special Kind of moulding sand. Consideration in selection of Core sand are
Core sand should be High in refractory nature.
Permeability should be high compare to moulding sand.
It should not possesses any material which produce gas , while /during contact with molten metal.
It must be collapsible in nature.
Constituents are : SILICA SAND (COARSE GRAINS) + BINDER (ORGANIC)
Binders : Cereal , Protein, Thermosetting resin, Sulphite, Dextrin, Pitch,
Molasses, Core oil.
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28. Protein Binder : Used to increase collapsibility property of core.
Cereal Binder : It develops Green strength and collapsibility. Amount vary from 0.2 To 2%.
Protein Binder : Used to increase collapsibility property of core.
Thermo setting resin : It imparts high strength, collapsibility to core.
It also evolves minimum amount of core and mould gases, so less
defects in casting. ( Penol formaldehyde , urea formaldehyde)
Sulphite Binder : used with certain amount of clay.
Dextrin: For increasing bake strength and collapsibility.
Pitch : Increase the hot strength of the core.
Molasses : Used as secondary binder to increase the hardness on baking. It is in the form of molasses liquid and sprayed on the core before baking.
Core Oil: It is in liquid state when mixed with core. Forms Coherent Solid Films holding the grains together when baked.
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29. Core Types
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30. CORE MAKING It is carried out in four steps : Core Sand Preparation
Using Roller mills and core sand mixer.
Core Making:
It is mechanized using core blowing, core ramming and core drawing machines.
Small bench blowers , Large floor blowers.
Squeezing, jolting, slinging.
Core drawing for deep draws is used. (rapping action on vibrator).
Core Baking
To remove moisture and harden the binder.
To provide strength to core.
Core oven and di-electric baker is used as dryer.
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31. Core Finishing -
Rubbing or filing of the surface to remove projections.
Core are coated with refractory and protective material using brushing, Deeping, spraying to improve the refractoriness and surface finish.
Bars , Wires and arbors used to reinforce core from inside. Also lifting rings are provided for heavy core.
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32. Casting Defects Defects generated due to : Improper Pattern Design
Improper Mould Construction
Improper Melting Practice
Improper Pouring Practice
Also from Moulding and core making materials.
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33. Common Defects in casting: Blow Holes Misrun or Short run Cold Shut
Mismatch
Flashes
Metal Penetration
Drop
Runout
Cut or Wash
Scars and Blisters
Hard Spots
Pinhole Porosity
Shrinkage Cavities
Hot Tears
Sponginess
Scab
Swell
Buckle
Rat-Tail
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34. Classification of Casting Defects
Surface Defects
Internal Defects
Visible Defects
Blow
Blow Holes
Wash
Scars
Porosity
Rat Tail
Blisters
Pin Holes
Swell
Drop
Inclusions
Misrun
Scab
Dross
Cold Shut
Penetration
Hot Tear
Buckle
Shrinkage / Shit
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35. Classification of Defect in casting (IITB)
SHAPE DEFECTS
Flash , Mismatch, Core, Distortion
FILLING DEFECTS
Blow hole, Cold shut, Gas porosity, Inclusions
SOLIDIFICATION DEFECTS
Shrinkage, Sink mark, Hot Tear , Fettling
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36. BLOW HOLES: Well rounded cavities with clean and smooth surface.
Appear on casting surface or in body of casting (cavities).
Reason – Excessive evolved gas entrapped in mould.
It collects into a bubble at high point of mould cavity and prevents the liquid metal to fill that space.
Occur due to:
Excessive moisture content , organic content of sand
moisture on chills, chaplets or metal inserts
Less permeability of moulding sand
Poor venting of mould
Insufficient drying of mould and cores
Cores not properly vented
High gas content of molten metal
Low pouring temperature
Incorrect feeding of casting.
Usually occur on “COPE” of casting.
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38. BLOW HOLES DEFECTS EXAMPLES
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39. MIS RUN OR SHORT RUN: We call it as “Incomplete Filling of cavity”.
Reason can be :
Inadequate metal supply
Too Low mould or melt temperature
Improperly designed gates
Length to thickness ratio of casting is too large.
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40. COLD SHUT:
It is interface between casting , where two metal streams meet without complete fusion.
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41. MISMATCH:
It is the shift of individual parts of a casting with respect to each other.
This may occur due to mould shift or core shift.
Reasons:
In expert assembling of the two halves of the mould.
From wear of pin bushes and pins
Dimensional discrepancy between the core prints of the pattern and core prints of the core.
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43. FLASHES: Other name is Fins . It appear along the mould joints.
Reasons:
Mould halves do not fit together properly
Much wear of the two halves of the flasks
Improper fastening of cope and drag portion.
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45. METAL PENETRATION (BURNT ON SAND):
It is strong crust of fused sand on the surface of the casting.
Reasons:
Insufficient refractoriness of moulding materials.
Large content of impurities
Inadequate mould packing
Poor quality of mould wash.
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46. DROP ( or CRUSH):
These are irregularly projections on the cope surface of the casting.
Reasons:
Break away a part of mould sand as a result of weak packing of mould.
Low strength of moulding sand.
Malfunctioning of moulding equipment.
Strong jolts and strikes at flask during assembling the mould.
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47. RUNOUT: In this metal is leaking out of a mould during pouring.
Reason:
Faulty moulding procedure or process.
Faulty flask equipment.
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48. CUT or WASH:
A low projection on drag face of a casting that extends along the surface.
It is decreasing in height as it extends from one side of the casting to the other end.
Reason:
It occurs in the casting having bottom gating system , having insufficient hot strength
When more amount of metal allowed to flow through one gate into the mould cavity.
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49. SCARS & BLISTERS: Scar is a shallow blow.
Generally occurs on flat surface.
Whereas blow occurs on convex casting surface.
Blister is a shallow blow like a scar with a thin metal layer covering it.
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51. HARD SPOTS:
Only occur with certain metals – like C.I with insufficient silicon.
Metal becomes hardened by the chilling effect of moulding sand.
Hard spots creates a difficulty while machining of casting.
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52. PINHOLE POROSITY: Small gas holes on or below the surface.
They occur in large numbers and fairly uniformly distributed over the surface.
Reason:
Due to dissolved gas in alloy
Alloy not properly degassed.
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53. Gas porosity / pin hole porosity
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54. SHRINKAGE CAVITIES:
Internal void or depression in casting due to volume contraction on solidification.
It occurs at hot spot.
Open shrinkage defects are open to the atmosphere, therefore as the shrinkage cavity forms air compensates.
open air defects: pipes and caved surfaces.
Pipes form at the surface of the casting and burrow into the casting, while caved surfaces are shallow cavities that form across the surface of the casting.
Closed shrinkage defects, also known as shrinkage porosity, are defects that form within the casting.
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56. HOT TEARS:
Hot cracks appear in the form of irregular crevices with a dark oxidized fracture surface.
Is a crack on casting surface usually near a thick (hot, weak) section, caused by resistance of a hard mold or core to casting contraction.
Reason:
When metal does not have sufficient strength to resist tensile forces during solidification.
Excessively high temperature of cast metal.
Increased metal contraction.
Incorrect design of gating system and casting as a whole.
Poor deformability / Collapsibility of the core.
Internal stresses due to non-uniform cooling.
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59. SPONGINESS (honeycombing):
Large number of small cavities in close proximity.
Apparently occur on surface.
Reason:
Suspension of dirt or inclusion in molten metal.
Imperfect skimming of slag in the ladle.
Incorrect gating system design.
Impurities being lighter comes up with evolved gases in the cavity.
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61. SCAB:
It occurs when a portion of face of a mould lifts or breaks down and the gap/recess is filled by metal.
Reason:
Very Fine Sand particles.
Low permeability of sand.
High moisture content of sand.
Uneven mould ramming.
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62. SWELL:
It is a smooth , slight/small bulge found on the vertical faces of casting.
It results from the pressure of liquid metal.
Reason:
Low strength of mould.
Mould with too high water content.
Improper / insufficient mould ramming.
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63. BUCKLE:
Long , shallow , V-shaped depression on surface of flat casting.
It extends in straight line on entire flat surface.
Reason:
Sand Expansion due to heat of metal.
Poor casting design – Too much large flat area/ surface in mould cavity.
Prevention:
Adding cereal or wood flour to sand .
On burning / oxidation by molten metal a void are created in mould which give space for expansion of sand particles and reduce compressive stresses.
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64. SINK MARK:
is a smooth depression seen on the top of a thick section caused by volumetric contraction occurring inside the section pulling the top surface.
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65. RAT TAIL: (or Veins Defect)
Long , Shallow , Angular depression in the surface of flat casting.
Reason are same as buckle.
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66. References
/lecture1.htm
Core preparing -
pictures.html
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