Poldi Hardness Test 

*This technique is use for measuring hardness 

- In some application like large casting in shop floor, it is not possible to use brinell hardness tester so at that time, the another hardness tester which has same working principle like brinell but portable instrument is used.
- This hardness tester is nothing but a poldi hardness tester 
- It is small in size and it consist of hollow steel tube in which plunger is fitted whose top end is out of tube 
- A steel ball of 10 mm is fitted at bottom end of tube 
- A slot is provided above this ball for inserting a steel bar of known hardness which we called standard bar and on that bar  hardness is printed on the bar 

Test procedure :

- In this standard bar of known hardness number is inserted in the slot of the instrument 
- so that standard bar touches the ball indenter as well as lower end of plunger 
- Entire assebly is held with left hand and hammer is given on the top of plunger 
- Impact must be in exact vertical otherwise impression may in elliptical 
- Load is applied manually 
- As indenter is touching to standard bar and specimen simultaneously it create two impression i.e. on the specimen and on the standard bar 
- For measuring this diameter of indenter magniscope is used

Precautions taken during Poldi Hardness Test :

- To avoid elliptical impression, tube should be vertical on the specimen 
- To avoid rebound effect, specimen kept on hard platform 
- Hammer impact should be moderate 

Advantages :

- It is portable 
- Require less time for measuring hardness 
- Low cost 
- Can be use for heterogeneous materials 
- Can be use for soft materials 

Limitation :

- Dependent load 
- Skilled operator is required to conduct test 
- Result obtained from the test are approximate due ti manual error 
- Not use for hard and thin material 


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