Rockwell Hardness Test by ElAffa

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									Rockwell Hardness Test
Objectives
 To understand what hardness is, and
 how it can be used to indicate some
 properties of materials.
 To conduct typical engineering
 hardness tests and be able to
 recognize commonly used hardness
 scales and numbers.
 To be able to understand the
 correlation between hardness numbers
 and the properties of materials.
 To learn the advantages and
 limitations of the common hardness
 test methods.

Introduction
Hardness refers to the resistance, which
a body has to the penetration of
another. Accordingly, in
common hardness testing methods, a
hard test body is pressed into the
sample perpendicular to
its surface.
A three-dimensional stress forms in the
sample beneath the penetrating test
body. Lasting
impressions can be achieved in very
hard and brittle materials without
resulting in cracks. This
distinguishes hardness testing from
tensile testing in which only a mono-
axial stress is generated
in the sample and no plastic deformation
is possible with hard materials.
One advantageous aspect of hardness
testing is that, in contrast to tensile
testing, material
properties can be determined without
destroying the sample, apart from the
relatively small
impression made by the test body.
One disadvantageous of hardness
testing is that it is only possible to give a
number
corresponding to strength, which
depends on the test method used, but
not the strength itself. For
this reason, the test method used must
always be specified.




Procedure
1.Select the correct combination of weights (at the rear of the machine)
and penetrators (diamond brale, 1/16-inch ball, etc.) for the hardness
scale you wish to use. The numbers given in black represent the scales
that use brale and the numbers given in red represent the scales that use
ball penetrators.
2.Make certain that the crank is in forward position (nearest to you).
3.Place sample on the anvil.
4.Slowly turn the wheel spokes clockwise. This raises the anvil and
sample toward the penetrator tip.
5.After contact is gently made, continue raising sample until small
pointer is about in line with small black dot and large pointer is within
colored sector .
6.The minor load has now been applied to the sample.
7.After step 6, large pointer on the dial is nearly vertical.
8. Now, turn the knurled collar until set line on the dial scale is in line
with large pointer .
9. Depress trip lever. This will trigger the mechanism that applies the
major load.
10.Crank will automatically move away from you. After the crank has
come to rest , gently pull the crank toward you as far as it will go.
11.Now record the scale reading of large pointer.
12.Remove the minor load, which remains on the specimen, by lowering
the anvil (Turn the wheel counterclockwise).
13. Move the sample to position for next test and repeat the steps above.




  A.       IMPACT TEST
Cooling with nitrogen oxide(-180ºC)




Cooling in room tempreture(30ºC)




Heat in furnace(>450ºC)




Cooling in freezer(0ºC)
  B.    MALLEABILITY TEST


DIAMETER                    19.3mm
HEIGHT                       50mm
FORCE                        100KN
TEMPRETURE                    30ºC


ROOM TEMPRETURE
HEIGHT                       42.7
DIAMETER                    21mm


FURNACE (160ºC)
HEIGHT                        40.6
DIAMETER                    21.1mm
RESULT

  C.     Rockwell Hardness Test


Material        R1(HRB)     R2(HRB)   R3(HRB)
  Mild Steel      87.9        89.4      89.5
Medium carbon     58.8        89.2      81.5
    steel
 High carbon     66.9        128.9     70.8
    steel
 Tempering       97.5         98.1      97.3
 Quenching       99.4         94.7     101.0
  Annealing      73.0         73.2      72.2
 Normalizing     73.5         78.9      77.3

								
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