Skip to main content

Hardness and Hardness Testers



Every metal have its own physical, chemical and mechanical properties. Brittleness, Creep, Ductility, Elasticity, Fatigue, Hardness, Malleability, Plasticity, Resilience, Stiffness, Toughness, Yield strength are the some mechanical properties of metals. In this post I am specifically going to talk about Hardness.

Hardness

A material’s ability to withstand friction, essentially abrasion resistance, is known as hardness
 cutting tool would break apart if specimen have a more hardness than tool itself. That's why drill bits and cutting tools are made of hard metals, harder than the specimen.

More Hardness Doesn't Mean More Strength

Glass have a more hardness than steel in general. It is harder to scratch glass than the steel because glass have a higher hardness.

Hardness in Steel

Steel is an alloy of iron and carbon. Iron have a very low hardness but addition of carbon increases the hardness of iron making it steel. Heat Treatment (hardening, case hardening) methods are used to add carbon in a iron, Following Iron-Carbon Diagram is showing how iron reacts on different percentages of carbon (click on link below to study more about Iron-Carbon Diagram)

Hardness Testers

To measure hardness of metal, hardness testers are used. Different types of hardness testers are available. Rockwell Hardness Tester, Vicker Hardness Tester and Brinell Hardness Tester are the some types of Hardness testers.

Rockwell Hardness Tester

Rockwell Hardness Tester
Rockwell is the most commonly used hardness tester. This method is used on almost all metals. Rockwell use two different types of indentors. Ball Indentor and Diamond Indentor . Ball indentor is a hardened steel ball usually used for soft metals like aluminum, Diamond indentor is used for steel and all other hard metals. Rockwell measures the permanent depth of indentation produced by a load on an indenter. First, a pre-load of 3 kgf-10 kgf is applied to a sample using a diamond or ball indenter. After holding the pre-load for a specific time the major load is applied to reach the total required test load. Different loads are applied on different type of materials, after specific time the load is removed using crank. The dial face on the top shows the result after removing the load. No formula is required in Rockwell tester it shows the result on dial face unlike brinell. Usually the HRC and HRB scales are used, for diamond indentor HRC (Hardness Rockwell C-Scale) is used and for Ball indentor HRC (Hardness Rockwell B-Scale) is used.

Brinell Hardness Tester

This method is usually used on low hardened materials like aluminum, copper and low carbon steel. Brinell Hardness Tester applies a 300 kgf-3000 kgf  of load for a specific time of 10s-15s on a specimen. Indentor is made of Tungsten Carbide which shapes like a ball of 2.5mm-10mm in diameter. After the indentor penetrates.The dent is measured using microscope. 

following formula is used to find the value of hardness,

where the,
              BHN = Brinell Hardness Number
              F = Load applied
              D = Diameter of indenter
              d = Diameter if dent
Labels:

Comments

Post a Comment

Popular posts from this blog

Calculate Size of Capacitor Bank

Electrical Load of (1) 2 No’s of 120KW, 415V motor, 90% Efficiency, 0.8 P.F. (2) 2 No’s of 150KW, 415V motor, 90% Efficiency, 0.8 P.F. (3) 100KW, 415V Lighting Load. The targeted P.F. Of system is 0.98 Calculate Size of Discharge Resister for discharging of Capacitor Bank Discharge rate of capacitor is 55v in less than 1 minute. Also calculate reduction in KVAR Rating of capacitor if Capacitor bank is operated at frequency of 30Hz instead of 50Hz and if operating voltage is 390V instead of 415V Calculation:  For Connection (1): Total Load KW for Connection (1) =KW / Efficiency=(120×2) / 0.9=266.67KW  Total Load KVAR1= KW×([(√1-(Old P.F.)^2) / Old P.F.] - [(√1-(New P.F.)^2 / New P.F])   Total Load KVAR1=266.67×([(√1-(0.8)^2) / 0.8] - [(√1-(0.98)^2) / 0.98])    Total Load KVAR1=145.98 KVAR  OR  Total Load KVAR1= KW×(tanϕ1- tanϕ2) =266.67×(tan 36.87 - tan 11.48)                                                                     = 266.67×(0.75 - 0.203) 
Post a Comment
Read more

High Speed Rails and How they Work?

Railway is one of the most ancient form of long distance transportation. Many developments has been made to railway throughout the time. Wooden trains were the oldest and they're the first kind of trains which was used to pushed by animals and humans. Speed is always a concern for railway they always want to achieve higher speeds. To achieve high speed the High Speed Rails (HSR) has been developed. First High Speed Rail The first Electric HSR was introduced by Japan on 1 October 1964, Japanese national railways started the operation of a fully brand new 515 km standard gauge line, the Tokaido Shinkansen , from Tokyo Central to Shin Osaka. Tokaido Shinkansen had the Top Speed of 210km/hr. Development  After Japans Tokaido Shinkansen success, many other countries adopted HSR system. Now, only 16 nations have HSR system. China has done a lot to their transport system in last 15 years. China began planning for its current high-speed rail system in the early 1990s, mo
1 comment
Read more