ASME B18.21.3-2008 pdf – Double Coil Helical Spring Lock Washers for Wood Structures.
Vickers Hardness, Rockwell Hardness, Rockwell
Superficial Hardness, Knoop Hardness, and
Scieroscope Hardness)
Publisher: ASTM International (ASTM), 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA
SAE J403, Chemical Composition of SAE Carbon Steels
SAE J411, Carbon and Alloy Steels
SAE J419, Methods of Measuring Decarburization
Publisher: The Society of Automotive Engineers (SAE), 400 Commonwealth Drive, Warrendale, PA 15096-
1.7 Related Standards
Related lock washers and tests are included in
ASME B18.21.1.
1.8 Designation
Nominal washer sizes are intended for use with comparable nominal screw, bolt, and/or nut sizes. Fasteners conforming to this Standard shall he designated by the following data and sequence:
(a) product name
(b) ASME document number
(c) nominal size
EXAMPLE: Double coil helical spring lock washers for wood structures, ASME B18.21.3, 3q in.
1.9 Part Identifying Number
For a part identifying number, refer to ASME B18.24.
2.1 Application
The double coil helical spring lock washers for wood structures covered in this Standard are intended to be used with a curved flat washer or the standard hardware practice of the user against the wood. While not essential, it is a good practice to use a standard round washer between the double coil helical spring lock washer and the nut, then tighten the nut in accordance with the users’ standard practice, and back off the nut /4 (90 deg) turn. This is important to maintain an acceptable pressure on the hardware and the wood fibers which may shrink or swell during varying weather conditions.
Although these washers were designed specifically for use on bolts in wooden assemblies (poles, crossarms, etc.), they can also be used for general applications where a heavy duty double coil washer is needed.
2.2 Dimensions
The dimensions of standard and extended travel double coil helical spring lock washers for wood structures are specified in Tables 1 and 2 and are before coating. Selections should be made from standard or extended travel series in Tables I and 2, respectively, to suit design requirements.
2.3 Material and Hardness
2.3.1 Material Composition. Washers shall be made from material meeting the chemical composition requirements of the following standards:
(a) up to and including 3/4 in. carbon steel — SAE J403 1055-1065 (UNS G10550-G10650)
(b) /8 in. and above boron steel — SAE J411 10B55- 10B65
2.3.2 Hardness. All washer section hardness req uirements are 38 HRC to 46 HRC, 372 HV to 458 HV. To prepare washers for checking the material hardness, cut washer approximately in half so only one coil is used. Cold (water) grind or file both sides sufficiently flat and parallel to ensure a correct reading. If applicable, be sure to remove the decarburized and coated surface. During this operation, care shall be exercised to prevent the surface temperature from exceeding 250°F. Refer to ASTM E 140 for hardness conversion.
2.3.3 Decarburization. Carbon steel and boron steel shall meet the limits for decarburization shown in Table 3. The method for testing limits shall conform to
SAE J419.
2.4 Washer Section
The corners at the inner and outer peripheries of the washers shall be slightly rounded. The section of the finished washer shall be slightly trapezoidal with thickness at the inner periphery greater than the thickness at the outer periphery by a minimum of 0.0005 in. to a maximum of 0.001 in. per 0.0156 in. of the section width. The minimum section thickness specified in the dimensional tables represents the nominal mean thickness, T, of the trapezoid. The tolerance on the nominal mean thickness of the trapezoid shall be subject to the following:
2.10 Travel
Travel shall be measured by placing the washerbetween hardened steel plates,one of which is move-able, until the washer is being touched by both plates.From this point, measure the distance required to com-pletely close the washer. Minimum travel requirementsare shown in Tables 4 and 5.