Objective: To assess the Brinell Hardness number HB of the specified sample
Tool and Equipment
Brinell hardness tester RAB-250, Brinell microscope and indentors (2.5mm and 5mm ball)
Description of Machine
The Brinell Hardness Tester comprises of a loading system, a chief screw and additionally a dial gauge. The loading system which comprises various factors such as weights, leavers and also a hydraulic dashpot and a plunger arrangement is bounded in the cast iron body of the equipment. The chief screw is additionally sheltered from various hindering elements with the help of a rubber bellow. It transmits the test table on its topmost to support the sample and is activated by a pointer at the foundation, the equipment is specifically given with multiple ball indenters (of sizes 2.5mm&5mm) to convey the test load on to the chosen sample.
Theory and Principle
The test experimentation comprises of forcing a steel ball of diameter D beneath a load P into the sample for a given period of time and computing the mean diameter’d’ of the impression left on the surface after the process of elimination of the load. The Brinell Hardness Number (BHN) is then computed as load (in kg-f) dropped by surface area of indention (in mm2)
Depth of Indentation (h) is shown by,
Thus,
Where,
D = Diameter of wall in mm
-P = Applied load in kg-f, and
d = Diameter of indentation in mm.
The test load P, to be exerted is based on the diameter D of the indenter and the substance of the sample. For reference, a table might be utilized which will be helpful. The test surface has to be machined smooth, horizontal and even. The density of the sample should be minimum eight times the depth of indentation.
Procedure
Set up the equipment to the mandatory point of test load. Choose the intentor to be utilized and clasp it to the equipment. Position the sample on the test table and, exert a miner load of approximately 10-kg-f on it by rotating the hand wheel and brining all pointers on the dial gauge to the ‘set’ spots. Exert the major load (residual portion of the experimentation load) on the sample by turning the loading lever in the reverse positon. Sustain the load on the sample precisely for the given dwell time (15 second) and then suspended it by turning the loading lever onwards. Detach the sample and compute the diameter of the dent created on it by utilizing the Brinell Microscope.
Observation and calculation
The observations taken at the time of test are logged in table -2. Calculation for trial-1 of steel sample is given below.
Result
Brinell hardness of given steel sample is H B / 2.5 / 187.5/ = ———-
Brinell hardness of given brass sample is HB / 2.5 / 187.5/= ————
Questions
1. Name the type of hardness tests you have dome in the laboratory.
2. Explain the process of how is load applied to the sample in the Brinell hardness test.
3. State time of application of load in the Brinell hardness test.
4. State the load to be utilized in the Brinell hardness test for: (1) brass (2) Cropper (3) aluminum and (40 mild steel.
5. State the minimum thickness necessary for the sample to be utilized for Brinell hardness test.
6. What type of intender is us‘’60 in the Brinell hardness test?
7. Statw the least count of the scale in the Brinell microscope.