1、 WORLDWIDE ENGINEERING STANDARDS General Specification GMW16722 Non-metallic Locking Element Type Prevailing Torque Requirements Copyright 2013 General Motors Company All Rights Reserved March 2013 Page 1 of 5 1 Introduction 1.1 Scope. This standard establishes engineering design and conformance tes
2、t procedures for the locking ability performance of prevailing torque type lock screws and nuts that utilize a non-metallic locking element (hereinafter called “lock screw” or “lock nut”). Note: “Lock” is a generic term used to identify the threaded products covered in this standard. The terms “lock
3、” and “locking” are not intended to imply an indefinite permanency of fixity. 1.2 Designation. Not applicable. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. ASME B1.1 ISO 725 ASME B18.2.2 ISO 4033 ISO 68 ISO 58
4、64 ISO 263 2.2 GM Standards/Specifications. GMW3059 GMW16551 3 Requirements 3.1 Purpose. 3.1.1 General. The prevailing torque values given in this standard are conformance requirements for lock screws and nuts and apply only to the combination of test conditions described in the locking ability test
5、 procedures 3.7.2.2 or 3.7.2.3. If the conditions of the actual service application differ from those of 3.7.2.2 or 3.7.2.3 (e.g., internally threaded hole in a different material, length of thread engagement, class of internal thread tolerance, speed of driving, different plating or coating on mati
6、ng part), the prevailing torque values may differ. Such values can only be determined through testing the lock in its application. 3.1.2 Restrictions. This standard is not concerned with dimensional features such as head styles or with other mechanical or performance capabilities such as strength pr
7、operties, corrosion resistance, sealing, suitability for use in low temperatures, or temperatures above 125 C, and/or consistency of torque-to-tension relationships during assembly. Such features and properties are covered in other standards and specifications and must be referenced when specifying
8、a lock screw/nut to assure that all of the service conditions of the particular engineering application are properly met. 3.1.3 Applicability. A prevailing torque lock screw or nut is a threaded fastener which is frictionally resistant to rotation due to a self-contained prevailing-torque feature, a
9、nd not because of a compressive load developed against the underhead bearing surface of the screw or a tensile load developed in the shank of the screw. 3.2 Material. Non-metallic locking element type prevailing torque lock fasteners are metallic fasteners to which a polyamide (nylon), polyester or
10、similar non-metallic locking element has been inserted in or bonded or fused to the threads. 3.3 Surface Treatment. Lock screws and nuts shall be furnished plain or with a protective coating as specified by the purchaser. When authorized by purchaser, lock screws may be provided with a supplementary
11、 lubricant. 3.4 Thread. 3.4.1 Thread Tolerances. Threads of metric lock screws or nuts shall comply with GMW16551. English threaded lock screws shall have class 2A tolerance as specified in ASME B1.1 or ISO 68, ISO 263, ISO 725 and ISO 5864. However, the length of the thread containing the locking e
12、lement need not conform to thread gaging requirements unless the locking element is removed. 3.4.2 Thread Start. The locking screws or nuts shall have a minimum of one full thread free of locking element so that the fastener can be finger started into any mating component having threads that conform
13、 to the referenced documents in paragraph 3.4.1. 3.5 Locking Element. 3.5.1 Other than a pelletized or strip locking element, the effective length of the locking element shall be a minimum of 1.2 times the lock Copyright General Motors Company Provided by IHS under license with General Motors Compan
14、yNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16722 Copyright 2013 General Motors Company All Rights Reserved March 2013 Page 2 of 5 screw/nuts nominal diameter with flash on one thread permissible on both ends. 3.5.2 Other
15、than a pelletized or strip locking element, the width of the locking element normally shall cover between 60 degrees and 180 degrees of the lock screws or nuts circumference. When authorized by the purchaser, wider locking elements up to full circumference (360 degrees) may be used, provided the tor
16、que requirements listed in Appendix A are met. 3.6 Locking Ability. 3.6.1 The prevailing torque of lock screws or nuts occurring during any installation or removal shall not exceed the maximum prevailing torque specified in Appendix A when tested as specified in 3.7.2.2 or 3.7.2.3. In addition, the
17、maximum prevailing torque developed by lock screw/nuts during first and fifth removals shall not be less than the minimum first and fifth removal torques, respectively, as specified in Appendix A when tested in accordance with 3.7.2.2 or 3.7.2.3; and at no time shall the minimum prevailing torque de
18、veloped by lock screws/nuts during fifth removal be zero. 3.6.2 Lock screws that are too short or have thread lengths too short to permit testing in accordance with 3.7.2.2 or 3.7.2.3 shall have their prevailing torque requirements and test procedure established by agreement between the purchaser an
19、d manufacturer. 3.7 Acceptability. 3.7.1 Each material must be initially approved by GM Fastening Engineering to comply with this specification. Subsequent testing shall be periodically performed to insure conformance. 3.7.2 Locking Ability Test. 3.7.2.1 Test Procedure A is applicable to nylon type
20、patching elements, and Test Procedure B is applicable to all other types of patching elements. 3.7.2.2 Test Procedure A. The lock screw/nut shall be assembled with a mating fastener until the locking element is at the edge of engagement. The test nut/screw shall then be tightened five full turns wit
21、h a torque measuring device. During the first tightening, the maximum prevailing torque (first on torque) occurring while the lock screw or test nut is in motion shall be measured. The test nut/screw shall then be backed off. The maximum torque (first removal torque) occurring while the lock screw/n
22、ut or test nut/screw is being backed off throughout the first 360 degrees of rotation shall be measured. The lock screw/nut or test nut/screw shall then be backed off until the locking element is disengaged. The lock screw/nut and test nut/screw shall be disassembled and then reassembled four more t
23、imes using the same method. During the fifth removal, the maximum torque (fifth removal torque) occurring while the lock screw or test nut is being backed off throughout the first 360 degrees of rotation shall be measured. If at any time during the fifth removal the driving torque drop to zero, the
24、locking element failed. During the four additional installations and removals, the prevailing torque shall not exceed the maximum prevailing torque specified in Appendix A. Note: The intent of this requirement is to demonstrate that galling between the sample lock screw and test nut has not occurred
25、. With certain designs of lock screws there may be an increase in the prevailing torque during the five assembly cycles and, in rare instances, the specified maximum prevailing torque may be exceeded. In such instances the manufacturer, when requested, shall give evidence that galling was not a cont
26、ributing factor. Note: Sufficient time shall elapse between torquing cycles to prevent overheating of the test assembly. Driving speed shall not exceed 30 rpm. 3.7.2.3 Test Procedure B. The lock screw/nut shall be assembled with a test washer (3.7.2.3.3) and a test nut/screw (3.7.2.4) in a load meas
27、uring device (3.7.2.3.1), or spaced with washers for short length screws with the test washer located adjacent to the component to be turned. During the complete performance of the test, either the lock screw/nut or the test nut/screw shall be turned. When the lock screw/nut is turned, the restraini
28、ng mechanism shall not distort the test nut/screw. The lock screw/nut or test nut/screw shall be advanced until its bearing surface is seated against the test washer. The total thickness of spacer material in the test assembly shall be selected so that at seating, the mid-length of the locking eleme
29、nt of the screw/nut shall coincide as closely as practical with the mid-thickness of the test nut/screw and a minimum length of lock screw/nut equivalent to two thread pitches shall project through the top of the test nut/screw. During this first installation, the maximum prevailing torque (first on
30、 torque) occurring while the lock screw/nut or test nut/screw is in motion and prior to development of any axial load shall be measured and recorded. Tightening shall be continued until a clamp load equal to the load or torque for a short length screw/nut, as specified in Appendix A for the applicab
31、le screw/nut size and property class, is developed. The clamp load in the lock screw/nut shall be reduced to zero by backing the turned member off until the test washer is free (can be Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduc
32、tion or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16722 Copyright 2013 General Motors Company All Rights Reserved March 2013 Page 3 of 5 moved by finger). Following a pause (it is generally necessary to change the wrench to one of a lower torque capacity
33、), removal shall be continued and the maximum torque (first removal torque) occurring while the lock screw/nut or test nut/screw is being backed off throughout the next 360 degrees of rotation shall be measured. The lock screw/nut and test nut/screw shall be reassembled and disassembled four more ti
34、mes. (It is not necessary to conduct this portion of the test in a load measuring device.) On each reassembly, the lock screw/nut shall be assembled with the test nut/screw until the turned element is seated against the test washer, but no tensile load shall be induced in the lock screw/nut. During
35、the fifth removal, the maximum torque (fifth removal torque) occurring while the lock screw/nut or test nut/screw is being backed off throughout the first 360 degrees of rotation shall be measured and, if at any time during the fifth removal the driving torque drops to zero, the locking element fail
36、ed. During the four additional installations and removals, the prevailing torque shall not exceed the maximum prevailing torque specified in Appendix A. Note: The intent of this requirement is to demonstrate that galling between the sample lock screw/nut and test nut/screw has not occurred. With cer
37、tain designs of lock screw/nut there may be an increase in the prevailing torque during the five assembly cycles and in rare instances the specified maximum prevailing torque may be exceeded. In such instances, the manufacturer, when requested, shall give evidence that galling was not a contributing
38、 factor. Sufficient time shall elapse between torquing cycles to prevent overheating of the test assembly. Driving speed shall not exceed 30 rpm. 3.7.2.3.1 Tensile Load Measuring Device. The tensile load measuring device shall be an instrument capable of measuring the actual tension induced in the l
39、ock screw/nut as it is being tightened. The device shall be accurate within 5% of the tensile clamp load to be induced. Diameter of the lock screw/nut clearance hole in hole in the backing plate shall be the lock screw/nut nominal size plus 0.4 mm for screw/nut sizes M5 and smaller, and plus 0.8 mm
40、for sizes M6 to M16 (included and 7/16 in). 3.7.2.3.2 Torque Wrench. Torque wrenches shall be accurate within 2% of the maximum of the specified torque range of the wrench. 3.7.2.3.3 Test Washer. Washers shall be made of steel and with dimensions, hardness and finish at option of the tester. 3.7.2.4
41、 Test Nut/Screw. 3.7.2.4.1 Test Fastener. The test nut/screw shall correspond to the size (diameter and pitch) and strength level of the locking part. 3.7.2.4.1.1 Nut. Metric heavy hex nuts conforming to style 2 ISO 4033 shall be used for these tests where metric parts are being tested. Unified heav
42、y hex nuts conforming to ASME B18.2.2 shall be used for these tests where English threaded parts are being tested. 3.7.2.4.1.2 Screw. Standard metric or unified bolts may be used as long as two full for threads protrude beyond the end of the nut to be tested. 3.7.2.4.2 The test nuts/screws shall be
43、made of plain finished carbon steel with a light oil coating. 3.7.2.4.3 A new test nut/screw shall be used for testing each lock screw/nut (one pair of lock and test fasteners for each five installation/removal run). 3.8 Heat Test. The first removal prevailing torque requirement described in 3.7.2.2
44、 or 3.7.2.3 shall be met after exposure to the following: 3.8.1 Assemble a new test nut to the prevailing torque first installation position per 3.7.2.2 or 3.7.2.3 using spacer washers instead of the load measuring device. 3.8.2 Place the assembled fastener in an oven or other heating device capable
45、 of a radiant, non-flame heat for 1 h at 122 C 3 C. 3.8.3 Remove the assembled fastener from the heating oven and immediately measure the maximum prevailing torque in the first 360 degrees of rotation. Driving speed shall not exceed 30 rpm. 4 Rules and Regulations 4.1 Legal Regulations. All material
46、s must satisfy applicable laws, rules, regulations and recommendations valid in the country of usage. 4.2 Language. In the event of conflict between the English and domestic language, the English language shall take precedence. 4.3 Inspection and Rejection. Samples of components or materials release
47、d to a GM general specification shall be tested for conformity with the requirements of this general specification and approved by the responsible Engineering department prior to commencement of delivery of bulk supplies. A new approval must be received for any changes, e.g., properties, manufacturi
48、ng process, location of manufacture, etc. If not otherwise agreed, all testing and documentation normally required for initial release must be completed. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted wi
49、thout license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16722 Copyright 2013 General Motors Company All Rights Reserved March 2013 Page 4 of 5 It is the responsibility of the supplier to inform the customer in a timely manner, without solicitation, and to include documentation of all modifications of materials and/or processes and to apply for a new release. If not otherwise agreed, all release tests shall be repeated and documented by the supplier prior to commencement of deliv
