TORQUE WRENCHES

 

This procedure covers calibration of flat beam, micrometer adjustable, dial and digital torque wrenches. Torque wrenches are used in many types of applications from automotive & industrial maintenance, production assembly & inspection to laboratory testing. Sturtevant-Richmont is one of the leading torque wrench manufacturers and the source for much of the information herein. There are many other manufacturers of quality torque wrenches such as Armstrong, Proto, Snap-on, etc., but Sturtevant-Richmont specializes in torque equipment.

 

 

The flat beam torque wrench is the oldest design and still the best all around choice. The flat beam torque wrench is classified in ASME Standard B107.14 as a Type I (Indicating), Class A, deflecting beam torque wrench. This type of torque wrench is very accurate (only digital is more accurate) and virtually indestructible. Sturtevant-Richmont states the following about their flat beam torque wrenches:

 

“Flat Beams Are Superior. The four most important characteristics of a torque wrench - accuracy, reliability, durability, and low ownership cost, are combined into these exceptional tools. Accuracy is literally ground into the wrench. The special alloy steel beam is ground to a rate of deflection with the use of dead weights, rather than to a dimensional tolerance. This process is time consuming and very labor intensive, but the result is a tool that remains accurate as long as the beam is intact and the pointer is on zero under no-load condition. The flat (actually tapered) shape of the beam insures the beam remains at a right angle to the fastener, reducing or eliminating side-load error. This unique taper grinding distributes stress evenly along the entire length of the beam, extending tool life indefinitely. With a minimum of moving parts, these tools are virtually repair and maintenance free.

 

“Incredibly durable design, with a service life frequently measured in decades! There are S/R flat beam wrenches in use today that have been used for hourly product testing two shifts per day every week since the 1970's. In 1998 the U. S. Government contacted us to provide a replacement wrench for one they had. It had been in service since World War 2!

 

“Ideal for prevailing-torque and destructive testing applications! Unlike dial-type wrenches, S/R flat beam wrenches can be used in destructive testing (as on fasteners) without damaging the tool. There are no gears or other delicate mechanisms to suffer from the sudden release of force when the test object breaks. The special alloy steel beam simply straightens out, ready for the next use.”

 

S-R’s flat beam torque wrenches have a stated accuracy of  ± 2% of indicated value from 20% to 100% of wrench capacity in both directions (flat beam wrenches have a fixed head). Flat beam wrenches are available in models from 0-32 in-oz range with 2 in-oz graduations to 0-300 ft-lbf range with 10 ft-lbf graduations. Drive sizes range from ¼” to ¾”. They are also available in Newton-meter units. The accuracy requirement in ASME Standard B107.14 for this type of torque wrench is ± 4% of indicated value from 20% to 100% of full range.

 

S-R’s micrometer adjustable torque wrenches are available with fixed and ratcheting heads and are a very durable tool. They are set at a desired torque and have “breakaway” or click type indication. These are the least accurate torque wrench with a stated accuracy of ± 4% of indicated value from 20% to 100% of capacity. The accuracy of this type torque wrench is highly dependent upon the operator’s skill. Torque should be applied in a slow and even manner until the wrench indicates that the set torque has been reached. The wrench should never be snatched or jerked while applying torque. If these wrenches are not used correctly, torque application will be highly inaccurate and inconsistent. Micrometer torque wrenches are available in models from 10-50 in-lbf range with 1 in-lbf graduations to 100-700 ft-lbf range with 5 ft-lbf graduations. Drive sizes range from ¼” to ¾”. They are also available in Newton-meter units.

 

The micrometer adjustable torque wrench is classified in ASME Standard B107.14 as a Type II (Toque Limiting), Class A (Graduated), torque wrench. ASME accuracy requirements for this type are ± 4% of indicated value from 20% to 100% of full range clockwise, and ± 6% of indicated value from 20% to 100% of full range.

 

S-R’s dial torque wrenches are more accurate than the micrometer type and less accurate than the flat beam type. Their stated accuracy is ± 3% of indicated value from 20% to 100% of capacity. This type wrench is easy to use and read, but they are the least durable of all the torque wrench models. Personal experience indicates that they do not hold up well in production environments. They would probably perform better when used by skilled craftsmen or technicians, but extra care would still be needed in their use and storage.

 

S-R dial torque wrenches are available in models with 50 in-lbf range with 1 in-lbf graduations to

1000 ft-lbf range with 20 ft-lbf graduations. Drive sizes range from ¼” to 1”.

 

Dial torque wrenches are classified in ASME Standard B107.14 as a Type I (Indicating), Class C torque wrench. ASME accuracy requirements for this type torque wrench are ± 4% of indicated value from 20% to 100% of full range.  

 

S-R’s Exacta Digital Torque Wrench is the most accurate model series with a stated accuracy of  ± 1% of indicated value from 20% to 100% of capacity. The writer has no experience in the application of digital torque wrenches and can offer no opinion as to their durability. Experience with other digital measuring instruments indicates that these wrenches should be easy to use and read. Exacta digital torque wrenches are available in models from 25 ft-lbf capacity to 250 ft-lbf capacity.

 

ASME Standard B107.14 does not cover digital torque wrenches, but most likely, this type would be classified as a Type I indicating torque wrench.

 

The calibration equipment used in this procedure is an AKO Torque Master Calibration System with digital readout. The digital readout has scale options of in-lbf, ft-lbf, N-m and kg-m. Two load cells are used. One is for torque up to 10 ft-lbf, and the other is for torque up to 1000 ft-lbf. The torque calibrator model in the procedure is several years old. Today’s equivalent is probably AKO’s Model TSD 2050. More information can be found at www.akotorque.com.

 

Sturtevant-Richmont also manufactures torque calibration systems. Their two laboratory type

floor model systems are described in their literature as follows:

 

The System 4/5 provides the choice of two accuracy levels to meet your requirements; the System 4 has a +/- 0.5% Indicated Value accuracy, and the System 5 provides even greater accuracy at +/- 0.25% of Indicated Value to meet even the most stringent requirements.

 

Torque transducers in twelve capacities are available, providing calibration capability ranging from a low of 2.5 inch-ounces through 2000 foot-pounds.

 

CALIBRATION PROCEDURE – HCJ MACHINE COMPANY	PROCEDURE NO. CP-47
SUBJECT:                                               TORQUE WRENCHES                                   FLAT BEAM, MICROMETER ADJUSTABLE, DIAL & DIGITAL
PROCEDURE

 

 

1.0   REFERENCE DOCUMENTS

 

1.1   TORQUE WRENCH SPECIFICATIONS (VENDOR CATALOG, ETC.)

 

1.2   OPERATION MANUAL FOR A.K.O TORQUE MASTER CALIBRATION SYSTEM

 

1.3   CALIBRATION EQUIPMENT ACCURACY LIST

 

2.0   MATERIALS, EQUIPMENT REQUIRED

 

2.1   TORQUE MASTER CALIBRATION SYSTEM, A.K.O

 

3.0   PROCEDURE FLAT BEAM, DIAL & DIGITAL

 

3.1   VISUALLY INSPECT SUBJECT TORQUE WRENCH FOR OBVIOUS DAMAGE OR

        EXCESSIVE WEAR THAT MAY EFFECT ITS FUNCTION.

 

3.2   ASCERTAIN THE WRENCH NUMBER IS CORRECT AND LEGIBLE.

 

3.3   ASCERTAIN THE PROPER LOAD CELL TO BE USED (1000 FT-LB OR 10 FT-LB).

 

3.4   PLACE DIGITAL READOUT ON THE PROPER UNIT MODE (IN-LB, FT-LB, N-M, OR KG-M).

 

3.5   ZERO DIGITAL INDICATOR USING SCREWDRIVER TO ADJUST ZERO BUTTON.

 

3.6   PLACE TORQUE WRENCH SQUARE DRIVE INTO APPLICABLE TEST PLATE SOCKET

       ON THE MACHINE.

 

3.7   ADJUST SLIDE TABLE SO THAT THE FLAT SIDE OF THE POSITIVE STOP IS LOCATED

        AS NEAR THE CENTER OF WRENCH HANDLE AS POSSIBLE.

 

3.8   INSURE TORQUE WRENCH INDICATES ZERO. IF NOT, CORRECT IF POSSIBLE.

 

3.9   MANUALLY TURN TORQUE APPLICATION WHEEL IN THE APPROPRIATE DIRECTION

        TO APPLY TORQUE TO HANDLE. WHEN USING THE 10 FT-LB LOAD CELL, THE

        APPLICATION WHEEL CAN'T BE USED. APPLY THE TORQUE MANUALLY.

 

3.10  CALIBRATE TORQUE WRENCH FROM LOWER 20% TO 100% OF RANGE.

 

3.11  TURN TORQUE APPLICATION WHEEL IN THE OPPOSITE DIRECTION TO RELEASE

         TORQUE FROM WRENCH AND RETURN DIGITAL INDICATOR TO ZERO.

 

3.12  TURN THE POSITIVE STOP 180°.  POSITION WRENCH FOR INSPECTION OF THE

         OPPOSITE END OF THE TORQUE WRENCH SCALE IF APPLICABLE.

 

3.13  ASCERTAIN THE TORQUE WRENCH DOES NOT EXCEED THE MAXIMUM

        ALLOWABLE INACCURACY FOR THE WRENCH BEING CALIBRATED.

 

3.14 ACCEPT/REJECT ACCORDINGLY.

 

3.15 UPDATE GAGE RECORDS.

 

4.0   PROCEDURE MICROMETER ADJUSTABLE

 

4.1   VISUALLY INSPECT SUBJECT TORQUE WRENCH FOR OBVIOUS DAMAGE OR

        EXCESSIVE WEAR THAT MAY EFFECT ITS FUNCTION.

 

4.2   ASCERTAIN THE WRENCH NUMBER IS CORRECT AND LEGIBLE.

 

4.3   ASCERTAIN THE PROPER LOAD CELL TO BE USED (1000 FT-LB OR 10 FT-LB).

 

4.4   PLACE DIGITAL READOUT ON THE PROPER UNIT MODE TO BE INSPECTED

       (IN-LB, FT-LB, N-M, OR KG-M).

 

4.5   ZERO DIGITAL INDICATOR USING SCREWDRIVER TO ADJUST ZERO BUTTON.

 

4.6   PLACE TORQUE WRENCH SQUARE DRIVE INTO APPLICABLE TEST PLATE SOCKET

       ON THE MACHINE.

 

4.7   ADJUST SLIDE TABLE SO THAT THE FLAT SIDE OF THE POSITIVE STOP IS LOCATED

        AS NEAR THE CENTER OF WRENCH HANDLE AS POSSIBLE.

 

4.8   ADJUST THE MICROMETER HANDLE UNTIL IT IS AT DESIRED TORQUE SETTING.

 

4.9   MANUALLY TURN TORQUE APPLICATION WHEEL IN THE APPROPRIATE DIRECTION,

        UNTIL TORQUE WRENCH "BREAKS" AT THE SET VALUE, COMPARE WITH DIGITAL

        READOUT.  WHEN USING THE 10 FT-LB LOAD CELL, THE APPLICATION WHEEL

        CAN'T BE USED. APPLY THE TORQUE MANUALLY.

 

4.10 TURN TORQUE APPLICATION WHEEL IN THE OPPOSITE DIRECTION TO RELEASE

        TORQUE FROM WRENCH AND RETURN DIGITAL INDICATOR TO ZERO.

 

4.11 ADJUST THE WRENCH TO ANOTHER TORQUE SETTING AND REPEAT THE ABOVE

       STEPS FOR CHECKING THE TORQUE. CALIBRATE TORQUE WRENCH FROM LOWER

       20% TO 100% OF RANGE FOR SEVERAL SETTINGS (AT LEAST FIVE).

 

4.12 TURN THE POSITIVE STOP 180°.  POSITION WRENCH FOR INSPECTION OF THE

        OPPOSITE DIRECTION.

 

4.13  ASCERTAIN THE TORQUE WRENCH DOES NOT EXCEED THE MAXIMUM

        ALLOWABLE INACCURACY FOR THE WRENCH BEING CALIBRATED.

 

4.14 ACCEPT/REJECT ACCORDINGLY.

 

4.15 UPDATE GAGE RECORDS.

 

 

APPROVAL	REV.	X
			CP-47
INITIALS	DATE:	X-XX-XX
XXX			SHEET  X OF  X