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Hardness Testing

For information regarding this presentation, please contact Dan Emelander (Metallurgist) 713-939-2672

Hardness Testing Equipment

Part 3: Rockwell, Verification, and

Miscellaneous Equipment

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Rockwell Hardness Testing

The Rockwell method typically usually uses one oftwo scales HRC, or C-scale uses a 150kg major load, and a diamond

cone indenter

HRB, or B-scale uses a 100kg major load, and a 1/16Tungsten Carbide ball indenter

Other scales are available, but are not recommended

The method involves applying a minor load (10kg) toremove some error from surface imperfections, then

applying a major load. The distance the indenter travels between when the minor

and major loads are applied, is used to determine thehardness.

Rockwell hardness testing is governed by ASTM E18

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Bench Rockwell

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Versitron (Rockwell)

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Magnetic Rockwell

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Rockwell - Clamp

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Key Points in ASTM E18 Use the correct scale

HRC is preferred

Test using the HRB scale if the hardness is

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Prior to Performing a Rockwell Test

Cylindrical pieces should be tested using a V-notch anvil or onhard, parallel twin cylinders properly positioned so that the apexof the specimen cylinder is directly under the indenter

Flat pieces should be tested using a flat anvil so that the test

surface is perpendicular to the indenter Since a Rockwell uses a relatively small load, it makes the test

sensitive to test setup

Any small burr or piece of dirt could influence the results

Perform 1-2 preliminary tests on the part, to make sure that thebottom is free from debris

Slide the sample around on the anvil

Any rocking or if the part does not sit level is an indication of debris

Once this check has been performed, continue with the test

Unexpected hardness values could also indicate a setupproblem

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Rockwell

Advantages and Limitations

Advantages

Very accurate

Direct reading off of thescale, no need to measure

the impression

Can test small or thin parts

NACE requirements are in

Rockwell can avoid error in

conversions

Disadvantages

Requires more surface prep

than Brinell Must use different scales for

different hardness ranges

Cannot re-read the

indentations at a later time

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Verification of all Hardness Testers

How often? Hardness testing equipment should be verified on a test

block a minimum of once on each day that it is used

Make 3 indentations Brinell: The result must be within 3% of the

hardness of the test block 197 HB: 6HB

237 HB: 7HB

Rockwell: The result must be within 1.0 point

Record the average and keep a log

Make 3+ punches on a scrap piece prior toperforming a test, to assure all equipment is properly

seated

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Calibration / Verification Equipment

Stage Micrometer

Brinell Test Block

Load Ring

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Verifying the Setup

Many times, it is beneficial to test the setup of the

part

Place the calibration block on top of the part to be

tested, and then make the indentation on the block

This not only checks the calibration of the machine, it also

checks that the part is properly seated on the anvil

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Miscellaneous Hardness Testers

There are other methods of hardness testing besides

Rockwell, Brinell, or the King Portable.

These include:

Equotip Rebound type tester, measures how a object

bounces off the surface of a material

Shear-pin Uses a ball penetrator

Telebrineller Uses a ball penetrator

Ultrasonic Uses sound waves to determine the hardness Vickers (for Laboratory use only)

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Equotip

The Equotip hardness tester is a very quick way to

approximate the hardness

It is only a recognized method on steel

API does NOT permit the use of the Equotip to certify

parts

This is why is not allowed for final acceptance (or rejection)

Subject to variation from part geometry, and is very

sensitive to surface preparation.

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Equotip

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Shear-Pin

Hardened ShearBlock

Hardened Support

Block

Handle

Mallet

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Shear-Pin

Shear Pins

Hardened Shear

Block

Hardened Support

Block

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Shear-Pin

The Shear-Pin type tester, sometimes referred to as

a Newage, is another quick method

Like the Equotip, it is NOT permitted by API for

certification

It can not be used for final acceptance, or rejection

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Telebrineller

Diameter of indentation on the bar

Diameter of the indentation on the partHBW =( ) x HBW of the test bar2

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Ultrasonic Hardness Tester

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Other Methods

The Telebrineller and Ultrasonic methods are two

other methods available. However, neither produces

any type of reliable results, and should not be used.

This is the same for other methods. Any new

methods that are found should not be used without

approval from Quality and Metallurgy.

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Comparison of Other Methods

Equotip Shear-Pin Vickers Ultrasonic Tele-

brineller

Advantages Very portable;

Can be used in

hard to reachareas;

Direct read-out

Very

portable;

Quick andeasy

Very

accurate

Measures the average

hardness through the

whole thickness

None

Limitations Requires a lot ofsurface prep;

Not highly

accurate;Not recognized by

API

Only measures

surface properties

Not

recognized

by API;

Variability inthe test

method

Must be

done in a

Laboratory;

Onlymeasures

surface

properties

Not recognized by

API;

Measures the

hardness through theentire thickness

Not

recognized by

API;

Large amountof variability