INTRODUCTION:

The hardness of metals can be determined by measuring the resistance of the material to indentation. The two most common methods of measuring hardness of metals use Rockwell and Brinell hardness test machines. In this experiment, these machines will be used to measure the hardness of various metal samples.

OBJECTIVE:

Determine the Brinell, Rockwell "B", and Rockwell "C" hardness values for the samples provided.

EQUIPMENT:

Brinell Hardness Tester

Brinell Hardness Number Chart

Rockwell Hardness Tester

Brinell Hardness Tester

Brinell Hardness Number Chart

MATERIALS:

Various metal samples such as:

Aluminum alloy

Brass

Cast IronThin zinc sheet (0.010 inch)

Mild steel bar

Stainless steel

Brass

BRINELL HARDNESS TESTING:

PROCEDURE:

  1. Close the air control valve located on the right side of the machine near the dial face. (Turn CCW to the 100 mark on the dial.)

  2. CIf necessary, connect the air hose to the machine and open the shut-off valve at the wall.

  3. Use the air control valve to adjust the load to 500 kg for soft metals or 3000 kg for hard metals. (Turn CW to achieve setting.)

  4. Place the sample to be tested on the anvil and turn the capstan handwheel until the sample touches indenter.

  5. Apply the load by pulling the release valve knob. (Located on the left side of the machine near the dial face.)

  6. Release the load by pushing in the release valve. Lower the anvil and remove the specimen.

  7. Place the Brinell microscope over the indentation and read and record its diameter in mm. (Press button to turn on light to illuminate the specimen.)

  8. Repeat steps 3 through 7 for each specimen.

ROCKWELL HARDNESS TESTING:

PROCEDURE:

  1. Place 1/16" ball indenter in the Rockwell machine.

  2. Adjust the weights on the hanger on back of machine to show 100 kg. (NOTE: Weights fit together only in specific combinations. The number on the top weight is the total load being applied.)

  3. Place a sample on the anvil. (Start with aluminum.)

  4. Turn capstan handwheel until the test piece touches indenter. Continue turning the capstan until the small needle on the gage reaches the dot on the dial. The large hand should be nearly vertical. (The minor load now has been applied.)

  5. Turn the face of the gage until the large pointer coincides with the "set" point.

  6. Release the load lever with a light touch. When the handle stops moving, return the lever to its normal position.

  7. Record the applicable dial reading for each sample.:

OR

  1. Take three such readings and determine the average. (When doing Rockwell hardness tests, it is desirable to take at least three readings.)

  2. Repeat steps 3 through 8 for each sample.

  3. Replace the 1/16" ball with the diamond ("Brale") indenter.

  4. Adjust the weights to show 150 kg.

  5. Repeat steps 3 through 99.

REPORT:

Rockwell tests:

Present your data and results in tabular form.

Brinell tests:

Use the following formula to calculate the Brinell hardness number for one of the specimens (i.e ‘sample calculations’).

The actual Brinell hardness number is obtained from the following formula

BRINELL HARDNESS

which gives the hardness number in terms of kilograms load per square millimeter of impression area, where

P = Load applied (use 3000 kg for hard metals and 500 kg for soft metals

D = Diameter of steel ball (10 mm)

d = Diameter of depression.

Usually it is not necessary to compute the hardness number each time from the diameter obtained as charts are supplied with the instrument. These charts give direct Brinell hardness numbers for any depression with either load.

Use the chart on page 4 to determine the hardness number of each specimen tested. For impression diameters not included in the chart, use the formula to calculate the hardness numbers.

Present your data and results in tabular form.

For visual comparison purposes, create a bar chart (vertical bars) which shows the Brinell and average Rockwell Hardness values for each specimen.