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Rolling and annealing of copper block.

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Introduction

Title:Rolling and annealing of copper block.

Abstract:

The hardness of a soft copper block was tested at City University, of increasing lengths and decreasing thickness after undergoing cold rolling. After the maximum length was obtained the copper a cut section was annealed to different temperatures. From the experiment it was found that as the block got thinner and longer the hardness increased. The experiment also shows that when the long copper section was annealed as the temperature was increased the breaking or tensile stress decreased.

Introduction:

The purpose of this Lab exercise is to investigate the effects of cold working and of annealing on the crystal structure and the hardness of a sample of copper (dimensioned at 50x25x5mm). The experiment is designed to allow us to see first hand the changes that take place in the material as it is subjected to varying degrees of work (deformation) and heat treatment.

Cold working uses the concept of “strain hardening”, to “temper” the metal, which is based on increasing the dislocation density within the material.  These dislocations are misalignments of atoms in the crystal lattice

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Middle

19.80

40.12

64.07

76.26

89.09

The percentage increase in length:

  1. Measure the lengths of the original block and the rolled block.
  2. Subtract the rolled length from the original length and then divide it by the original length.
  3. This will give the percentage increase in length when multiplied by 100.

Table 2: % increases in length, for given length.

Length (mm)

51

56

65

86

146

224

470

% Increase in length

0

9.8

27.5

68.6

186.3

339.2

821.6

The Hounsfield Tensometer test is then carried out on the final sample that has been cut, two of which are annealed and another remained as rolled and no heat treatment.

When the Hounsfield Tensometer test is carried out the Maximum load is given from which you have to calculate the tensile strength with equation (1) and (2).

Table 3: Annealing temperature and tensile Strength

Annealing temperature (oC)

0

160

360

Tensile strength (N/mm)

490.3

476.2

246.7

The data is analysed by plotting three graphs, % reduction in area against  

Hardness, % increases in Length against hardness and Tensile strength Vs Annealing temperature.

The plot of data is shown in fig 1, fig 2 and fig 3.

Discussions:

From the graph of data shown in fig.1, it can be seen that the points are increasing consecutively until the maximum hardness is approached after this point the graph has an exponential affect.

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Conclusion

Relationship between Annealing and Hardness

The above plot also shows that samples #1 and #2 had similar hardness, and hence, crystal states.  

Note: after several passes, one group’s 60% sample was erroneously passed through the rollers transverse to the direction of the initial passes.  This caused a general cupping of the sample and subsequently brittle fractures occurred.  The effect on the sample is unclear, but it is likely that it has a different deformation of its crystal structure compared to the other two samples, which were rolled in the same orientation each time.  

Hardness Testing:

Each group performed hardness tests using Rockwell Hardness Testers (by Wilson) in the Polishing Lab in Meuller Hall.  Hardness is a measure of a material’s resistance to deformation by surface indentation or abrasion.  According to the Callister text, the Rockwell Hardness tester works by pressing 1/16 inch steel ball under an initial minor load of 10kg into the sample, followed by a second major load on 100kg (B scale) into the test sample and comparing the depth of the indentation made by each load to derive a relative number indicating the “hardness”.   Multiple readings are taken at various locations on each sample, which are then averaged to find and average hardness number for the specimen.

image02.png

Figure 1.

image03.png

Figure 2.

image04.png

Figure 3.

Appendix:

Raw data showing intermediate calculations:

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