ASME B18-21.3 pdf download Double Coil Helical Spring Lock Washers for Wood Structures
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 dou- ble 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 1 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) 7 ⁄ 8 in. and above boron steel — SAE J411 10B55- 10B65 2.3.2 Hardness. All washer section hardness requirements 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 flatand parallel to ensure a correctreading. Ifapplicable, 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 thick- ness 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 dimen- sional 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:
2.5 Coiling Washers shall be coiled so that the gap between coils shall be such as to prevent washers from linking. The severed ends of the washers are to be cut so that the ends are less then two full coils as shown in Tables 1 and 2, dimension C. 2.6 Workmanship The flat surfaces (faces) of the double coil helical spring lock washers shall be free from such surface imperfections as knurling, serrations, die marks, deep scratches, loose scale, burrs, or other irregularities that would affect serviceability. Moderate feed roll marks shall be permissible on the outer periphery.
2.7 Grinding The face on both severed ends of the washer shall be ground prior to heat treating to provide a flat surface on each side as shown in Tables 1 and 2, dimensions D and F.
2.8 Finish All washers shall be mechanically coated and shall meet a minimum of 1,500 hr to red rust when tested in accordance with ASTM B 117.
2.9 Twist Test To prepare washers for twist testing, cut the washer approximately in half so only one coil is used. The washer shall be gripped in vice jaws. The ends of the washer shall be free, and the axis passing through the slot shall be parallel to and slightly above the top of the vice so that less then 50% of the washer is gripped. A 90 deg maximum segment of the free end of the washer shall be gripped in wrench jaws so that at least 25% of the washer is exposed when twisting, as shown in Fig. 1. The edges of the wrench jaws shall be in a plane parallel to the vice. Twisting the wrench increasing the free height of the washer section between 85 deg and 95 deg shall show no signs of fracture.
2.10 Travel Travel shall be measured by placing the washer between 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 requirements are shown in Tables 4 and 5.
2.11 Inspection and Quality Assurance Unless otherwise specified, products shall be fur- nished in accordance with ASME B18.18.1.