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POLDI HARDNESS TEST AIM: To determine the hardness of a given sample by using poldi hardness tester . APPARATUS: Standard test bar, test specimen, moderate hammer, instrument. THEORY: Poldi hardness test is a dynamic hardness test and can be used at any stage of processing of metals. The instrument consists of a hardened steel ball of 10mm diameter fixed to a hollow cylindrical casing; a movable plunger is fixed rigidly in the casing by means of spring. A standard test bar is inserted in the gap provided between the plunger bottom and the steel ball. The test bar is hardened for a predetermined value and is tapered for easy insertion. ADVANTAGES:
1) 2) 3) 4) 5)
It is fast and simple The in indenta ntation on on th the ob object is is sm small. It is por portable an and ea easily ope operated. It can can be be use used d at at any any stag stagee of of proc proces essi sing ng of meta metals ls.. It is usef useful ul whe when n the the spec specim imen en is is too too lar large ge or or can canno nott be mou mount nted ed..
DISADVANTAGES:
1)
Pold Poldii hard hardne ness ss val value ue is is no subs substi titu tute te for for the the benc bench h valu value. e. It It is 10% 10% of acc accur urat atel ely y meas measur ured ed Hardness value.
2)
it is not accurate
PROCEDURE:
1)
The The sam sampl plee is is clea cleane ned d and and plac placed ed on a cle clean an,, smo smoot oth h and and flat flat surf surfac ace. e.
2)
The The sta stand ndar ard d tes testt bar bar is inse insert rted ed betw between een the the bot botto tom m of of the the plun plunge gerr and and the the ste steel el ball. ball.
3)
The The ins insttrume rument nt is pla place ced d ver vertticall cally y on on the the metal etal sur surface face..
4) A loa load d of of ½ kg is appl applie ied d by by ham hamme merr blo blow w on on the the spec specim imen en whic which h res resul ults ts in the the two two indentations, one on the metal surface and the other on the standard test bar. 5)
The The dia diame mete ters rs of inde indent ntat atio ions ns are are meas measur ured ed by a magni magnifi fier er suppl supplie ied d alo along ng with with the the tes teste ter. r.
6) The The har hardn dnes esss of of the the spec specim imen en is equa equall to to the the valu valuee giv given en in the the gri grid d for forme med d by by the the indentation diameters on the standard test bar a nd specimen respectively from a book supplied supp lied with the machine.
7)
Tensile st strength fo for steels ca can be calculat ulateed by by UTS (mpa) = 3.4×BHN
8) The hardness values of aluminum, brass and steel are determined. PRECAUTIONS:
1)
The hammer blow should be moderate.
2)
The instrument should be held vertically.
3)
The gap between the neighboring indentations should be at least 15mm.
RESULT AND DISCUSSION:
The hardness values of the given samples (BHN) are
AluminiumBrass
-
Steel
-
Tensile strength of steel is Hence an increasing trend is observed in the hardness values. Steel has the highest value while aluminum has the least hardness value.
