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Rockwell Hardness Tester Operation Guide

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Rockwell Hardness Tester Operation Guide
Latest company news about Rockwell Hardness Tester Operation Guide

Rockwell Hardness Tester Operation Guide

 

What is the Rockwell Hardness Tester?

Rockwell hardness tester is the first Rockwell hardness tester designed according to the Rockwell hardness test principle in the world, which can test the metal hardness only by contacting the sample on one side. The Rockwell hardness tester probe is adsorbed on the steel surface by magnetic force, and there is no need to support the sample. The test accuracy meets the standards GB / t230 and iso6508, which is not lower than that of desktop Rockwell hardness tester.

 

The magnetic chuck is used to fix the hardness tester on the surface of steel workpiece without support, sampling and moving the workpiece. The test can be completed as long as one side contacts

What is the principle of the Rockwell Hardness Tester?

Unlike height, weight, and width, hardness is not a fundamental property of metal. Hardness is most closely related to tensile strength and is a reliable indicator of ductility and wear resistance. The principle of any hardness testing method is to force an indentor (penetrator) into a material sample under a specific load at a controlled rate and then measure the dimensions (depth or surface area) of the indentation. Unlike length, mass, or time which have exact measures, hardness testing is a comparative measure: accurate testing results can only be achieved with calibrated machines and previous test results taken from a material of known hardness.

In metallurgy, the hardness of a material depends on a combination of yield strength, tensile strength, and modulus of elasticity – the stiffness of a material and its ability to resist deformation under applied force. It is measured by indenting a small sample piece of material without destroying it.

Under the specified conditions, the Rockwell hardness tester indenter (diamond cone, steel ball or cemented carbide ball) is pressed into the surface of the sample in 2 steps. After removing the main test force, measure the residual depth h of the indentation under the initial test force. The level of hardness is represented by the residual depth h of the indentation. The principle of Rockwell hardness test is shown in Figure 1.Rockwell hardness test principle diagram

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1—The indentation depth under the initial test force F0;

2—The indentation depth under the total test force F0+F1;

3—The elastic recovery depth after removing the main test force F1;

4—residual indentation depth h;

5—Sample surface;

6—Measurement datum;

7—Indenter position

The Rockwell hardness value is calculated as follows:

N-constant, for A, C, D, N, T scales, N=100; for other scales, N=130;

h-residual indentation depth, mm;

S-constant, for Rockwell hardness, S=0.002mm, for surface Rockwell hardness, S=0.001mm. The indentation depth corresponding to each Rockwell hardness unit, the Rockwell hardness is 0.002mm, and the surface Rockwell hardness is 0.001mm. The shallower the indentation, the higher the hardness. Rockwell hardness test is divided into two types, one is ordinary Rockwell hardness test, and the other is surface Rockwell hardness test. The Rockwell hardness test uses three indenters of 1200 diamond cone and 1.587mm, 3.175mm steel ball, and three test forces of 60kg, 100kg and 150kg. There are nine combinations of them, corresponding to the nine scales of Rockwell hardness, namely HRA , HRB, HRC, HRD, HRE, HRF, HRG, HRH, HRK. The surface Rockwell hardness test uses two indenters, 1200 diamond cone and 1.587mm steel ball, and three test forces of 15kg, 30kg and 45kg. There are six combinations of them, corresponding to the six scales of the surface Rockwell, namely HR15N, HR30N , HR45N, HR15N, HR30T, HR45T.

 

 

 

Test Method Illustration

A = Depth reached by indenter after application of preload (minor load)

B = Position of indenter during Total load, Minor plus Major loads

C = Final position reached by indenter after elastic recovery of sample material

D = Distance measurement taken representing difference between preload and major load position. This distance is used to calculate the Rockwell Hardness Number.

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A variety of indenters may be used: conical diamond with a round tip for harder metals to ball indenters ranges with a diameter ranging from 1/16” to ½” for softer materials.

 

When selecting a Rockwell scale, a general guide is to select the scale that specifies the largest load and the largest indenter possible without exceeding defined operation conditions and accounting for conditions that may influence the test result. These conditions include test specimens that are below the minimum thickness for the depth of indentation; a test impression that falls too close to the edge of the specimen or another impression; or testing on cylindrical specimens.

 

Additionally, the test axis should be within 2-degress of perpendicular to ensure precise loading; there should be no deflection of the test sample or tester during the loading application from conditions such as dirt under the test specimen or on the elevating screw. It is important to keep the surface finish clean and decarburization from heat treatment should be removed.

 

Sheet metal can be too thin and too soft for testing on a particular Rockwell scale without exceeding minimum thickness requirements and potentially indenting the test anvil. In this case a diamond anvil can be used to provide a consistent influence of the result.

 

Another special case in testing cold rolled sheet metal is that work hardening can create a gradient of hardness through the sample so any test is measuring the average of the hardness over the depth of indentation effect. In this case any Rockwell test result is going to be subject to doubt, there is often a history of testing using a particular scale on a particular material that operators are used to and able to functionally interpret.

 

Test Procedure

(1) Wipe the top surface of the screw and the upper and lower end surfaces of the worktable, and place the worktable on the screw table;

(2) Clean the support surface of the specimen and place it on the workbench, rotate the handwheel to slowly raise the workbench and push up the indenter until the small pointer points to the red dot and the big pointer rotates 3 circles vertically upwards;

(3) Rotate the indicator shell to make the long engraved line between C and B align with the big pointer;

(4) Pull the loading handle, apply the main test force, and the large pointer of the indicator rotates counterclockwise;

(5) When the rotation of the indicator needle stops, the unloading handle can be pushed back to remove the main test force;

(6) Reading from the corresponding scale on the indicator;

(7) Turn the handwheel to lower the test piece, then move the test piece, and carry out a new test according to the above steps (2)-(6);

(8) After the test, cover the machine with a dust cover.

Precautions

Proximity

Penetrator indentions must be spaced at least two indentation diameters from the edge of the work piece and a minimum of two indentation diameters from any other indentations to determine true hardness.

 

    Material Thickness

Use a correct load/indentor combination relative to the thickness of the material. Tests will end up measuring anvil hardness and results will not be indicative of the true hardness of the sample piece.

 

    No Stacking

Never stack multiple pieces of sample material. The interfaces between the strip will negatively affect the reading. Testing strip thickness needs to be at least 10x greater than the expected major load indentation depth.

 

Do Not Test Plating

Plated and finished samples must be tested in cross sections so that indentations can be made entirely in the base metal. Plating and finishing materials are typically harder or softer than base metals.

 

    Calibration

Hardness testing devices must be kept in good working condition and calibrated every year. Use a test block of known hardness daily to verify that your equipment is calibrated correctly.

 

    Curves

Bowed or twisted material will generate erroneous test results. Sample material must be flat and placed so that the bottom surface of the tested materials sits directly on the anvil.

 

    Avoid Conversions

Converting test results from one hardness scale to another may produce faulty results. If a material is certified to a specific test's hardness, the final part should be tested on the same scale.

 

   Tolerances

Hardness testing is toleranced with variables for plus or minus results. Refer to ASTM E10, ASTM E18, ASTM 392, ASTM E140, or ASTME E384 for specific allowances for your testing equipment.

 

    Indentors

Round ball indentors must be round. While steel ball indentors are less expensive than their tungsten carbide counterparts, steel is more likely to flattern during tests of very hard material samples.

 

   Surface Preparation

Test surfaces need to be smooth in order to produce accurate results. Rough surfaces will not allow the penetrator to create clearly defined, measurable indentations.

 

   Test Surface

In order to achieve consistent, accurate results, the test surface must be parallel or perpendicular to the indentor.

 

    Portable Testers

Handheld testers are costeffective and convenient, but they are not reliable substitutes for bench testing. They are best suited for comparison testing of unknown samples vs. known samples of the same type.

 

Maintenance

(1) When the hardness tester is not used for a long time, cover the machine with a dust cover.

(2) Regularly inject a small amount of oil into the contact surface of the lead screw and the handwheel.

(3) Before using the hardness tester, the top surface of the lead screw and the upper end surface of the worktable should be cleaned.

(4) If the hardness indication error is found to be large:

① The worktable can be taken off to check whether the contact surface with the screw is clean;

②Check whether the lead screw protective cover is jacking up the workbench;

③ Check whether the indenter is damaged.

(5) If the main test force is applied, the indicator pointer starts to rotate quickly and then slowly rotates, indicating that the oil in the buffer is too low. At this time, lift the felt pad on the upper end of the buffer and slowly inject clean 20# oil . At the same time, pull and push the handle several times to make the piston move up and down several times to remove all the air in the buffer until the piston sinks to the bottom and oil overflows from it.

(6) Regularly check the accuracy of the hardness tester with the standard hardness block carried by the machine.

① Wipe the workbench and the standard hardness block, and conduct the test on the working surface of the hardness block, and never allow the test on the supporting surface.

②If the displayed value error is large, in addition to checking according to the fourth item in this section, check whether there are burrs on the supporting surface of the standard hardness block, and if there are burrs, polish with oil stone.

③When testing at different positions of the standard hardness block, the hardness block should be dragged on the workbench and should not be taken away from the workbench.

(7) The instrument should be checked regularly and verified periodically.

 

People also ask

1.How do you perform a hardness test?

(8) A hardness test is typically performed by pressing a specifically dimensioned and loaded object (indenter) into the surface of the material you are testing. The hardness is determined by measuring the depth of indenter penetration or by measuring the size of the impression left by an indenter.

 

2. How do you use a manual Rookwell hardness tester?

(1) Wipe the top surface of the screw and the upper and lower end surfaces of the worktable, and place the worktable on the screw table;

(2) Clean the support surface of the specimen and place it on the workbench, rotate the handwheel to slowly raise the workbench and push up the indenter until the small pointer points to the red dot and the big pointer rotates 3 circles vertically upwards;

(3) Rotate the indicator shell to make the long engraved line between C and B align with the big pointer;

(4) Pull the loading handle, apply the main test force, and the large pointer of the indicator rotates counterclockwise;

(5) When the rotation of the indicator needle stops, the unloading handle can be pushed back to remove the main test force;

(6) Reading from the corresponding scale on the indicator;

(7) Turn the handwheel to lower the test piece, then move the test piece, and carry out a new test according to the above steps (2)-(6);

(8) After the test, cover the machine with a dust cover.

 

3.How do I find my Rockwell hardness number?

The Rockwell hardness number is calculated from the depth of permanent deformation of the indenter into the sample, i.e. the difference in indenter position before and after application of the major load. The minor and major loads can be applied using dead weights or springs.

 

4.Is code for Rockwell hardness test?

ISO 6508-1:2015 specifies the method for Rockwell regular and Rockwell superficial hardness tests (scales and applicable range of application according to Table 1) for metallic materials and is applicable to stationary and portable hardness testing machines.

 

5.how do you calibrate a digital hardness tester?

PROCEDURE Take out the force gauge to be calibrated and hold vertically up. Adjust the zero on the force gauge. Standard Weights are then applied to the hook of force gauge and measure the tension of the spring on the force gauge. When 1 kg of standard weight is applied, scale on the force gauge should also show 1 kg tension produced from the initial point where the pointer is adjusted. Adjust the zero on the force gauge again. Follow the same procedure for other weights. The test to be carried out for 1.0 kg, 2.0 kg, 5.0 kg, 10.0 kg, 20.0 kg & 30.0 kg standard weights.

 

6.How ofen should a durometer be calibrated?

one year

Unless otherwise requested the calibration interval on your durometer will be one year. Several factors should be taken into consideration such as: the required accuracy vs. the instruments accuracy, the impact an out of tolerance reading will have on the process, and the performance history.

Pub Time : 2022-03-30 14:03:52 >> News list
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