Metrology Instruments

 

Plain Limit Gauges

 

Dial Indicators

(what's calibrated?)

Height Gauges

(what's calibrated?)

Vernier Callipers

(what's calibrated?)

Micrometers

(what's calibrated?)

Surface Plates

 

Hardness Testing

 

 


Plain Limit Gauges

 

BS 969 : 1982

 

This standard specifies the tolerances and limits for simple forms of limit gauges, such as cylindrical plain plug, ring and gap gauges and is intended for reference by component producers and gauge makers when gauge limits have not been stipulated. It specifies gauge tolerances for work piece tolerances in ranges between 0.009mm and 3.200mm and how gauge limits are related to the work piece limits. It also specifies types of gauge according to size and minimum work piece tolerance, dimensions are expressed in millimetres but appropriate values in imperial units are given in appendix C. It may be uneconomical for any company or institution to invest in equipment to the level required in order to calibrate all types of plain limit gauges, particularly those with a small work piece tolerance and therefore small gauge tolerances. 

 

It is highly recommended that an appropriate authority such as a UKAS approved laboratory carries out a full calibration on plain limit gauges at least once a year. In between UKAS calibrations at a frequency based on usage, plain limit gauges should be calibrated in-house. A typical in-house calibration would include a written procedure and an associated calibration record sheet, which would contain as a minimum, the following listed information:

 

(a) Serial number

(b) Location

(c) Procedure number

(d) Workpiece tolerance

(e) Gauge tolerance

(f) Results

(g) Measurement uncertainty

(h) Sentence if appropriate

(i) Date and calibrators signature

(j) Traceability to National Standards

 

It is necessary that any person carrying out such calibration work should have received appropriate training and have shown the ability to be confident via a suitable training authority. Training records should be held and maintained.

Following are layouts for typical in-house calibrations for plain limit gauges:

Calibration to be carried out in accordance with in-house procedure number .......................

 

Serial Number: Make:

 

Calibration Date: Sizes:

 

FEATURE EXAMINED                      SPEC.                      MEASURED RESULTS

 

GO:

 

NOT GO:

 

The plain limit gap gauges were visually inspected for damage and the following faults were noted:

 

MEASUREMENT UNCERTAINTY +/- 0.00

 

Calibrators Signature: ........................................

 

A traceability statement in this section would be required for all items and their relevant certification utilised for the calibration of plain limit gap gauges.

 

Plain Plug Gauges

 

BS 969 : 1982

 

Calibration to be carried out in accordance with in-house procedure number .......................

 

Serial Number: Make:

 

Calibration Date: Sizes:

 

FEATURE EXAMINED                  SPEC.                  MEASURED RESULTS

                                                                                 FRONT     MIDDLE         BACK

GO:

@ 90 degrees:

NOT GO:

@ 90 degrees:

 

The plain limit plug gauges were visually inspected for damage and the following faults were noted:

 

MEASUREMENT UNCERTAINTY +/- 0.00

 

Calibrators Signature: ........................................

 

A traceability statement in this section would be required for all items and their relevant certification utilised for the calibration of plain limit plug gauges.

 


Dial Indicators (what' calibrated?)     Top of Page

 

The Use and Care Of Lever Dial Test Indicators

 

British Standard Reference : BS 2795 : 1981

1. Always select the dial test indicator that best fits the application.

2. Care should be taken while using a dial test indicator, try not to jolt the indicator, should you be unfortunate and drop a dial test indicator, get it re-calibrated/repaired before reusing it.

3. Replace worn contact points only with those of a similar length from the centre of the ball stylus to the abutment shoulder.

4. Always clean dial test indicators after use with a lint free paper or cloth and store the indicator in its box or in a dust free area.

5. When using a dial test indicator, always position the dial test indicator in a horizontal plane to the surface media.

6. Always use a rigid stand for mounting the dial test indicator.

7. When measuring a rotating object, either between centres or in a vee block, ensure that the object is rotating in the correct direction. Never rotate the workpiece towards the contact point.

8. When measuring a sliding object, only take readings when the object is moving directly towards the contact point, never away from the contact point or in a sideways manner.

9. Avoid parallax errors by reading the dial directly from the front and square on to the dial.

10. Never oil a dial test indicator as this attracts contamination, should the movement become erratic then the dial test indicator should be submitted to a reputable repair agent.

11. Try not to expose dial test indicators to direct sunlight or in a high humidity environment.

12. Never use a dial test indicator that has not been calibrated, if in doubt consult an appropriate authority.

 

The Use and Care Of Plunger Dial Test Indicators

 

British Standard Reference : BS 907 : 1965

 

1. Always select the dial test indicator that best fits the application.

2. Care should be taken while using a dial test indicator, try not to jolt the indicator, should you be unfortunate and drop a dial test indicator, get it re-calibrated/repaired before reusing it.

3. Replace worn contact points.

4. Always clean dial test indicators after use with a lint free paper or cloth and store the indicator in its box or in a dust free area.

5. When using a dial test indicator, always position the dial test indicator square in both planes to the surface media.

6. Always use a rigid stand for mounting the dial test indicator.

7. Avoid parallax errors by reading the dial directly from the front and square on to the dial.

8. Never oil a dial test indicator as this attracts contamination, should the movement become erratic then the dial test indicator should be submitted to a reputable repair agent.

9. Try not to expose dial test indicators to direct sunlight or in a high humidity environment.

10. Never use a dial test indicator that has not been calibrated, if in doubt consult an appropriate authority.

 


 

Lever Dial Test Indicators - what's calibrated?     Top of Page

 

BS 2795 : 1981

 

This standard covers lever type dial test indicators fitted with an adjustable stylus which may be displaced in either two opposite directions. Lever dial test indicators with metric graduations in scale divisions of 0.01mm with a minimum magnification of times 70 or 0.002mm with a minimum magnification of times 350, each having a measuring range of at least one revolution of the parameter. Imperial equivalence are shown in table 2 of the standard. It may be uneconomical for any company or institution to invest in equipment to the level required in order to calibrate lever dial test indicators fully in accordance with the standard.

 

It is highly recommended that an appropriate authority such as a UKAS approved laboratory carries out a full calibration on lever dial test indicators at least once a year. In between UKAS calibrations at a frequency based on usage, lever dial test indicators should be calibrated in-house. A typical in-house calibration would include a written procedure and an associated calibration record sheet, which would contain as a minimum, the following listed information:

 

(a) Serial number

(b) Location

(c) Procedure number

(d) Repeatability

(e) Discrimination

(f) Error of reading over the intervals specified in the standard

(g) Results

(h) Measurement uncertainty

(i) Sentence if appropriate

(j) Date and calibrators signature

(k) Traceability to National Standards

 

It is necessary that any person carrying out such calibration work should have received appropriate training and have shown the ability to be confident via a suitable training authority. Training records should be held and maintained. Following is a layout for a typical in-house calibration for a metric lever dial test indicator.

 

Calibration to be carried out in accordance with in-house procedure number ...........

 

Serial Number: Make:

Calibration Date: Graduation:

 

FEATURE EXAMINED                  SPEC.                      MEASURED RESULTS

 

Any one unit division:

Any five unit divisions:

Any half revolution:

Discrimination:

Repeatability:

The lever dial test indicator and the stylus were visually inspected for damage, wear and missing parts and the following faults were noted:

MEASUREMENT UNCERTAINTY +/- 0.00

Calibrators Signature: ........................................

 

A traceability statement in this section would be required for all items and their relevant certification utilised for the calibration of the lever dial test indicators.

Plunger Dial Test Indicators

 

BS 907 : 1965 

 

This standard covers plunger type dial test indicators whose movement is parallel to the plane of the dial. It applies to gauges having dial diameters from 1.7/8" to 2.1/2" as measured from the outside of the scale marks and scale divisions of 0.001" (sometimes sub-divided into half divisions of 0.000 05", in which case they are commonly designated as "half thou gauges"), one tenth or 0.01mm. It may be uneconomical for any company or institution to invest in equipment to the level required in order to calibrate lever dial test indicators fully in accordance with the standard.

 

It is highly recommended that an appropriate authority such as a UKAS approved laboratory carries out a full calibration on plunger dial test indicators at least once a year. In between UKAS calibrations at a frequency based on usage, plunger dial test indicators should be calibrated in-house. A typical in-house calibration would include a written procedure and an associated calibration record sheet, which would contain as a minimum, the following listed information: 

 

(a) Serial number

(b) Location

(c) Procedure number

(d) Repeatability

(e) Discrimination

(f) Error of reading over the intervals specified in the standard

(g) Results

(h) Measurement uncertainty

(i) Sentence if appropriate

(j) Date and calibrators signature

(k) Traceability to National Standards

 

It is necessary that any person carrying out such calibration work should have received appropriate training and have shown the ability to be confident via a suitable training authority. Training records should be held and maintained.

On the following page is a layout for a typical in-house calibration for a metric plunger dial test indicator.

Calibration to be carried out in accordance with in-house procedure number ....................... 

 

Serial Number: Make:

 

Calibration Date: Graduation:

 

FEATURE EXAMINED                     SPEC.                             MEASURED RESULTS

 

Any 0.10mm:

Any half revolution:

Any one revolution:

Any two revolutions:

Any larger interval:

Discrimination:

Repeatability:

 

The plunger dial test indicator and the stylus were visually inspected for damage, wear and missing parts and the following faults were noted:

 

MEASUREMENT UNCERTAINTY +/- 0.00

 

Calibrators Signature: ........................................

 

A traceability statement in this section would be required for all items and their relevant certification utilised for the

calibration of the plunger dial test indicators

 


Height Gauges (What's calibrated?)     Top of Page

 

The Care and Use Of Vernier Height Gauges

 

British Standard Reference : BS 1643 : 1983

 

1. Select the height gauge that best fits your requirement. Ensure that the type, measuring range, graduation and other specifications of the height gauge are appropriate for your application.

2. Do not apply excessive force to the sliding and locking mechanisms of the height gauge. Should you be unfortunate and drop the height gauge, before reusing have the height gauge recalibration/repaired by an appropriate repair agent.

3. When using a scriber in conjunction with a height gauge, ensure that the scriber tip is not damaged.

4. Thoroughly clean the height gauge after use with a lint free paper or cloth ensuring the base and the scriber are cleaned.

5. Check the slider movement for smoothness, There should be no free play or intermittent restriction of movement. Report all non conformances to an appropriate authority.

6. Thoroughly clean the surface plate or surface table prior to placing the height gauge upon it, the height gauge and datum surface should be stabilised before use.

7. Adjust the zero line to the datum surface before use.

8. Avoid parallax errors by reading the scales directly from the front and square on.

9. During fine adjustment to a reference standard, ensure that the base remains stable on the measuring media, least this causes damage to either the reference standard or the height gauge.

10. When storing height gauges for long periods of time, or when they need oiling, use a lint free paper or cloth dampened with a rust preventative oil and lightly wipe each section, ensure that the oil is spread evenly over the surfaces.

11. Never leave or store the height gauge for long periods of time in a high humidity environment.

12. Never use a height gauge that has not been calibrated, if in doubt consult an appropriate authority.

 


 

Height Gauges - what's calibrated?     Top of Page

Vernier Height Gauges 

 

BS 1643 : 1983

 

This standard covers vernier height gauges which include a scriber for marking heights. Metric height gauges measure heights up to a maximum of 1000mm using a main scale and vernier scale graduated to read to 0.02mm. Imperial height gauges measure heights up to a maximum of 48" using a main scale and vernier scale graduated to read to 0.001". It may be uneconomical for any company or institution to invest in equipment to the level required in order to calibrate vernier height gauges fully in accordance with the standard. 

 

It is highly recommended that an appropriate authority such as a UKAS approved laboratory carries out a full calibration on vernier height gauges at least once a year. In between UKAS calibrations at a frequency based on usage, vernier height gauges should be calibrated in-house. A typical in-house calibration would include a written procedure and an associated calibration record sheet, which would contain as a minimum, the following listed information:

 

(a) Serial number

(b) Location

(c) Procedure number

(d) Flatness of base

(e) Flatness of measuring jaw

(f) Parallelism of measuring jaw to datum surface

(g) Flatness of measuring faces of the scriber

(h) Parallelism of measuring faces of the scriber

(i) Accuracy of readings

(j) Results

(k) Measurement uncertainty

(l) Sentence if appropriate

(m) Date and calibrators signature

(n) Traceability to National Standards

 

It is necessary that any person carrying out such calibration work should have received appropriate training and have shown the ability to be confident via a suitable training authority. Training records should be held and maintained.

On the following page is a layout for a typical in-house calibration for a 0 - 300mm vernier height gauge.

 

Calibration to be carried out in accordance with in-house procedure number .......................

 

Serial Number: Make:

 

Calibration Date: Range:

 

FEATURE EXAMINED                      SPEC.                              MEASURED RESULTS

 

                                                        Metric         Imperial                     Metric             Imperial

Flatness of base:

Flatness of measuring jaw:

Parallelism of measuring jaw to datum surface:

Flatness of measuring faces of the scriber:

Parallelism of measuring faces of the scriber:

Accuracy of readings:

 

                    METRIC                                                              IMPERIAL

Position                         Measured                              Position                  Measured

Checked                       Deviation                              Checked                  Deviation

0                                                                                         0

25.52mm                                                                         1.210

50.14mm                                                                         2.425

75.76mm                                                                         3.615

100.38mm                                                                       4.835

150.00mm                                                                       6.000

200.00mm                                                                       8.000

300.00mm                                                                      12.000

 

The vernier height gauge was mechanically and visually inspected for mechanical performance, damage, wear and missing parts and the following faults were noted:

 

MEASUREMENT UNCERTAINTY +/- 0.000

 

Calibrators Signature: ........................................

 

A traceability statement in this section would be required for all items and their relevant certification utilised for the

calibration of the vernier height gauge.

 


Vernier Calipers (What's Calibrated?)     Top of Page

 

The Care and Use Of Vernier Calliper Gauges

 

British Standard Reference : BS 887 : 1982

 

1. Select the caliper that best suits your requirement. Ensure that the type, measuring range, graduations and other specifications of the caliper are appropriate to your application.

2. Never apply excessive force to the slider or the locking screws, should you be unfortunate and drop a caliper gauge, do not use until the caliper has been re-calibrated/repaired by an appropriate repair agent.

3. Be careful not to damage the measuring jaws and always examine both the internal and external measuring jaws for damage prior to use.

4. After use, clean the caliper with a lint free paper or cloth.

5. Check the slider movements for smoothness of travel. There should be no free play or intermittent restriction of movement. Report all non conformances to an appropriate authority.

6. When taking external measurements, position the workpiece as deep inside the measuring jaws as possible.

7. When taking internal measurements, position the measuring jaws as deep inside the workpiece as possible.

8. Avoid parallax errors by reading the scale directly from the front and squarely on.

9. Care should be taken with the measurement of small diameter holes, as these are somewhat smaller than the actual diameter indicated (see appendix 1).

10. When storing calipers for long periods of time, or when it needs oil, use a lint free paper or cloth dampened with a rust preventative oil and lightly wipe each section, ensure that the oil is spread evenly over the surfaces.

11. Always leave the measuring faces separated and when not in use, always place caliper in its case.

12. Never leave or store the caliper for long periods of time in a high humidity environment.

13. Never use a caliper that has not been calibrated, if in doubt consult an appropriate authority.


Vernier Callipers - what's calibrated?     Top of Page

 

Vernier Calipers BS 887 : 1982 

 

This standard covers vernier calipers with external and internal contact faces from 0 - 48"/0 -1000mm. Metric calipers measure lengths up to a maximum of 1000mm using a main scale and vernier scale graduated to read to 0.02mm. Imperial calipers measure lengths up to a maximum of 48" using a main scale and vernier scale graduated to read to 0.001". It may be uneconomical for any company or institution to invest in equipment to the level required in order to calibrate vernier calipers fully in accordance with the standard.

 

It is highly recommended that an appropriate authority such as a UKAS approved laboratory carries out a full calibration on vernier calipers at least once a year. In between UKAS calibrations at a frequency based on usage vernier calipers should be calibrated in-house. A typical in-house calibration would include a written procedure and an associated calibration record sheet which would contain as a minimum the following listed information: 

 

(a) Serial number

(b) Location

(c) Procedure number

(d) The flatness of external measuring jaws

(e) The parallelism of external measuring jaws

(f) The parallelism of internal measuring jaws

(g) Linearity of the measuring scale

(h) Results

(i) Measurement uncertainty

(j) Sentence if appropriate

(k) Date and calibrators signature

(l) Traceability to National Standards

 

It is necessary that any person carrying out such calibration work should have received appropriate training and have shown the ability to be confident via a suitable training authority. Training records should be held and maintained.

The following is a layout for a typical in-house calibration for a 0 - 150mm vernier caliper.

Calibration to be carried out in accordance with in-house procedure number .......................

 

Serial Number: Make:

Calibration Date: Range:

 

FEATURE EXAMINED              SPEC.                      MEASURED RESULTS

                                                Metric       Imperial                Metric         Imperial

Zero reading as received:

Parallelism of internal measuring jaws:

Flatness of external measuring jaws:

Parallelism of external measuring jaws:

Combination width of measuring jaws:

Accuracy of readings: 

METRIC                                                          IMPERIAL

Position      Measured                                      Position              Measured

Checked      Deviation                                      Checked              Deviation

       0                                                                         0

25.52mm                                                                 1.210

50.14mm                                                                  2.425

75.76mm                                                                  3.615

100.38mm                                                                4.835

150.00mm                                                                6.000

 

The vernier caliper was mechanically and visually inspected for mechanical performance, damage, wear and missing parts and the following faults were noted: 

 

MEASUREMENT UNCERTAINTY +/- 0.000

 

Calibrators Signature: ........................................

 

A traceability statement in this section would be required for all items and their relevant certification utilised for the

calibration of the vernier caliper.

 


Micrometers (What's calibrated?)     Top of Page

 

The Care and Use Of External Micrometers

 

British Standard Reference : BS 870 : 1950

 

1. Select the micrometer that best suits your requirement. Ensure that the type, measuring range, graduation and other relevant specifications of the micrometer are appropriate for your application.

2. Always use the ratchet or friction thimble in the appropriate manner, never rotate the micrometer thimble violently.

3. Avoid parallax errors by reading the micrometer and vernier scales directly from the front and square on.

4. Do not apply excessive force to the micrometer thimble. Should you be unfortunate and drop a micrometer, do not use until the micrometer has been re-calibrated/repaired by an appropriate repair agent.

5. Clean the micrometer after use with a lint free paper or cloth.

6. Always ensure that both the micrometer and workpiece have stabilised to ambient temperature before measurements are taken.

7. Adjust the zero line in the ambient temperature that the micrometer is going to be used, remember that a micrometer should be calibrated at 20 deg.C, it may be used in varying ambient temperatures.

8. Should you mount a micrometer in a stand, ensure that the micrometer frame is clamped at the centre, do not clamp it too tightly and in any case carry out a zero check in the clamped position. If in doubt consult an appropriate authority.

9. When storing micrometers for long periods of time, or when they need oiling, use a lint free paper or cloth dampened with a rust preventative oil and lightly wipe each section, ensure that the oil is spread evenly over the surfaces.

10. Always leave the measuring faces separated and when not in use, always place micrometer in its case.

11. Never leave or store the micrometer for long periods of time in a high humidity environment.

12. Never use a micrometer that has not been calibrated, if in doubt consult an appropriate authority.


Micrometers - what's calibrated?     Top of Page

 

External Micrometers BS 870 : 1950 

 

This standard covers external micrometers from 0 - 24"/0 - 600mm including micrometers with interchangeable anvils and also setting standards for micrometers. The manufacturing specifications and associate accuracy requirements of this standard are complex and it may be uneconomical for any company or institution to invest in equipment to the level required in order to calibrate micrometers fully in accordance with the standard. 

It is highly recommended that an appropriate authority such as a UKAS approved laboratory carries out a full calibration on micrometers at least once a year. In between UKAS calibrations at a frequency based on usage micrometers should be calibrated in-house. A typical in-house calibration would include a written procedure and an associated calibration record sheet which would contain as a minimum the following listed information: 

 

(a) Serial number

(b) Location

(c) Procedure number

(d) The flatness of anvils of new micrometers

(e) The flatness of anvils of used micrometers

(f) The linearity of the micrometer screw

(g) Results

(h) Measurement uncertainty

(i) Sentence if appropriate

(j) Date and calibrators signature

(k) Traceability to National Standards

 

It is necessary that any person carrying out such calibration work should have received appropriate training and have shown the ability to be confident via a suitable training authority. Training records should be held and maintained.

On the following page is a layout for a typical in-house calibration for a 0 - 25mm micrometer.

 

Calibration to be carried out in accordance with in-house procedure number .......................

 

Serial Number: Make:

 

Calibration Date: Range:

 

FEATURE EXAMINED                   SPEC.                      MEASURED RESULTS 

 

Zero reading as received:

Parallelism of measuring faces:

Flatness of fixed anvil:

Flatness of spindle anvil:

Error in traverse of micrometer screw: 

 

Position                                 Measured                             Vernier         Measured

Checked                                 Deviation                             Scale            Deviation

0

3,10mm

6,50mm

9,70mm

12,50mm

15,80mm

19,00mm

21,90mm

25,00mm 

 

The micrometer was mechanically and visually inspected for performance, damage, wear and missing parts and the

following faults were noted: 

 

MEASUREMENT UNCERTAINTY +/- 0.000

 

Calibrators Signature: ........................................ Sentence: ....................................

 

Report:

 

A traceability statement in this section would be required for all items and their relevant certification utilised for the calibration of the micrometer.


Surface Plates    Top of Page

 

The Care And Use of Surface Tables And Plates

 

British Standard Reference : BS 817 : 1988

 

1. A Surface Plate is a datum and should be protected against damage. The top should be frequently wiped clean from dust and other particles. When measurements are being made, a cloth should be spread on the Surface Plate to receive small tools and gauges. When the Surface Plate is not in use the top should always be kept covered.

2. A grade '0' or grade '1' Surface Plate should be located in a circulating atmosphere under constant temperature control. Accordingly, it should be kept clear of direct sunlight or sudden draughts, in particular it is important that these should not cause a vertical gradient of temperature such that the top and underside of the Surface Plate are at difference temperatures.

3. Stands should be located on a stable foundation. The Surface Plate should be supported firmly and levelled.

4. Care should be taken that, wherever possible, the load on a Surface Plate is distributed over the working surface.

5. Point contact should not be made with scraped or machined Surface Plates because of the high proportion of low, unrepresentative areas of the working surfaces. Contact should be made through an intermediate Gauge Block, preferably not more than 10mm in length, or a distance piece of similar precision and surface area.

6. Use should be made of the full available area of the working surface and not concentrated on any one area.

7. A common form of damage to Cast Iron Surface Plates is burrs on the working surface, the excess metal may be stoned away by attention confined to the burr. This operation should be followed by thoroughly cleaning away any abrasive dust. If the Surface Plate is not required for some days, the surface should be coated with a corrosion preventative such as petroleum jelly. 

Rusting is a sign of neglect and misuse. Its effect can be reduced by frequently wiping the top when in use and by occasionally gently rubbing with another Surface Plate using a paste of a little jewellers rouge and paraffin as a lubricant.

8. A common form of damage to Granite Surface Plates is cuts in the working surface, these can be minimised only by care in the use of the Surface Plates.

9. Cleaning of Granite Surface Plates should be performed with the use of the specialised compounds available from the manufacturers.

10. A border zone of 10mm on the edges of Surface Plates/Surface Tables should be avoided when taking measurements.

11. Never use a surface plate/surface table that has not been calibrated, if in doubt consult an appropriate authority.

 


Hardness Testing      Top of Page

 

INTRODUCTION TO VICKERS PYRAMID HARDNESS TESTING

 

The Vickers Pyramid Hardness Testing Machine was developed as a result of research for a thoroughly reliable and accurate means of testing the hardness of metals, and to be applicable to all classes of work.

The importance of metallurgist science to engineering practice is ever increasing, and modern requirements of high speeds and stress call for rigid metallurgical control of hardness, capable of interpretation in terms of an accepted quantative formula.

 

In the vickers test, hardness is calculated in terms of the internationally accepted ratio:-

 

LOAD

 

IMPRESSED AREA

 

The basic formula is only of value when you have an accurate means of interpreting the result of test.

 

By the introduction of the 136 degree diamond pyramid, which with its geometric form provided a clear indentation with no burrs, previous problems associated with reading indents was eliminated. Just as important as having a clear indent is maintaining accuracy whilst applying a load, it is for this reason a Vickers Hardness Testing Machine utilises only calibrated weights which are applied through a simple lever mechanism.

 

It is important that any indent produced, is produced in a controlled manner and that it is not subjected to shock loads, to this end an automatic damping mechanism is employed to control the rate at which the load is applied.

 

As it is possible to apply loads varying from 1 to 100 kgs utilising the calibrated weights provided, the machine can measure both relatively soft and hard materials. Unlike other types of hardness testing, a Vickers Hardness Test Machine is capable of providing hardness values on one continuous numeric scale.

 

VICKERS PYRAMID NUMBER HARDNESS TESTING

 

BRITISH STANDARD REFERENCE: BS 427 : 1990 

 

This standard covers the testing of material hardness in the Vickers range scales of HV1 to HV100 (1 Kg to 100 Kg force loads) and the hardness values between 5 and 3000 HV. The standard also covers the methods for determining and verifying the accuracy of hardness testing machine. The Vickers Hardness Machine is capable of measuring the softest and hardest of metals and depending on the machine model, varying metal thicknesses from say 0.010" to 18" can be measured.

 

It is highly recommended that an appropriate authority carries out a full calibration on Vickers Hardness Test Machines at least once a year. In between such calibrations at a frequency based upon usage, the accuracy of vickers hardness test machines should be monitored in-house.

 

Principal of Vickers Hardness Measurement.

 

An indenter comprising of a diamond in the form of a 'symmetrical pyramid' mounted in a holder, the diamond having an angle of 136 degrees between opposing faces. The diamond is forced into the test piece at a controlled rate with an appropriate force for a standard 'Dwell' period of 10 to 15 seconds. The produced indent is then measured using a microscope that can measure the diagonal length of the indent with an accuracy within 0,001mm. From this figure, which should be the mean dimension calculated from measuring each diagonal, it is possible to calculate the load area of the sloping faces of the pyramid. Given this value it is easy to calculate the Vickers pyramid number for any force employed by dividing the test force by the sloping surface area of the indent viz:-

 

Vickers Hardness Pyramid No. (HV) = Constant (*) x Test Force

 

Surface Area of Indentation

 

(* Constant = 1 = 1 = 1 = 0.102)

 

9n gravitational force in newtons 9.807n

 

force = mass (load) x gravity, ie. constant compensates for gravitational effects on load.

 

2F Sin 136 deg. 2f Sin 136 deg.

 

Therefore: HV = 0.102 x 2 = 2

 

2 2

 

Where: g = Gravity in Newtons

 

F = Test Force in Newtons

 

f = Load Mass Symbol

 

d = Mean of the Diagonal Indents 

 

The acceleration effects of the dwell period of the indentation is ignored, as its contributing error is negated by being constant within a negligible limit between all measurements made, and the damping action of the automatic loading mechanism.

 

Representation of Hardness Values

 

When defining a hardness value, it is important that it is presented in an unambiguous form, to this end the scale that has been used for the test must be stated, and where necessary the dwell period if different from the standard dwell period of 10 to 15 seconds. The accepted method of illustrating such a measurement where a Vickers Hardness of 526 obtained using a test force of 30 Kgf and a non-standard dwell period of 25 seconds is: "526HV30/25".

 

Monitoring the Accuracy of Your Machine

 

It is recommended that the accuracy of your machine should be monitored on a regular basis, in addition to the more stringent test carried out by your calibrating agent. The regularity with which the accuracy monitoring tests are carried out depends upon the usage of the machine and the scales used. Should a machine be partially employed on every working day then daily tests should be carried out, the more frequent the use of the machine, ie/ on a shift system it is logical to confirm the machines accuracy at the start of every shift. Likewise if the machine is used only once or twice per week, then tests should be carried out on each day before the machine is used.

 

The results obtained from these tests should be recorded conveniently by the machine for examination, an example of a typical accuracy monitoring data sheet is attached.

 

The tests should be carried out with the machine in its normal operating condition and environment, and with its usual diamond indenter fitted. A test block calibrated in accordance with BS 427 : 1990 should be used, and its value be that of approximately the most measured value of test carried out and of the same scale. The test block should be tested for its value and the result recorded, where a second reading is taken, due to vibration being suspected during indenting for instance, this should be recorded. The mean value obtained should be within the assigned value for the test block within the following tolerances.

 

+/- 5% for HV1

+/- 4% for HV2.5

+/- 3% for HV5, 10 & 20

+/- 2% for HV30, 50 & 100

 

It is recommended that where the test machine is regularly used and utilises various load forces, the procedure should be repeated with test blocks of appropriate value to the measurement being conducted.

 

Typical Accuracy Monitoring Data Sheet

(for location convenient to machine) 

 

ACCURACY MONITORING DATA SHEET 

 

Machine Number: ..............................................

Test No. 1: Test Block Serial No./Value/Load Scale ..................../....................HV.....

Test No. 2: Test Block Serial No./Value/Load Scale ..................../....................HV.....

Test No. 3: Test Block Serial No./Value/Load Scale ..................../....................HV.....

Test No. 4: Test Block Serial No./Value/Load Scale ..................../....................HV.....

Date of Test 1st 2nd Error from O.K.

Test No. Reading Nominal % /X

 

If error from nominal exceeds tolerance below suspend use of machine and arrange corrective action via

+/- 5% HV1

+/- 4% HV25

+/- 3% HV6, 10 & 20

+/- 2% HV30, 50 & 100

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