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1、AEROSPACE RECOMMENDED PRACTICE ARP688 REV. A Issued1962-07 Reaffirmed Revised2002-02 Reusable Lock for Spanner Nuts FOREWORD Changes in this Revision are format/editorial only. 1.SCOPE: This aerospace recommended practice is applicable to the design of a reusable locking device for cylindrical nuts
2、which are generally tightened with a spanner wrench. Nuts of this type are commonly used to pre-load, and/or position, anti-friction bearings. 1.1Purpose: To provide basic information relating to the design of a reusable lock for spanner and similar cylindrical nuts. 2.REFERENCES: MS172321 MS172236
3、B.S. 2090-1954 SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement
4、arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2007 SAE International All rights reserved. No part of this
5、publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970
6、(outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org RATIONALE This document has been reaffirmed to comply with the SAE 5-Year Review policy. 2007-06 Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 N
7、ot for Resale, 12/04/2007 19:52:02 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP688 Revision A - 2 - 3.INTRODUCTION: The problem of locking a pre-loading nut to prevent loosening during operation has met with a wide variety of solutions. Advantages of the design o
8、utlined herein are: a.All the parts are basically reusable for an unlimited number of installation and removal cycles. b.The design is basically unaffected by inertia loads which result when the nut is subjected to a gravitational field such as the rotating shaft application. c.The locking design is
9、 positive and is applicable for severe vibratory environment applications. d.Since the design does not require staking or deformation at the lock, there is no danger of inadvertently damaging the lock or the mating parts when setting the lock. e.The installation of the lock is simple and requires no
10、 special skill or tools. f.Since the lock is not in place during the torquing of the nut, the possibility of inadvertently damaging the lock during the torquing operation is eliminated. 4.DESCRIPTION OF THE DESIGN: 4.1The components of the assembly are as shown in Figure 1. FIGURE 1 Copyright SAE In
11、ternational Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 19:52:02 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP688 Revision A - 3 - 4.2The shaft is provided with a multiplicity of equally spaced slots of b
12、asic width W. See Figure 2. FIGURE 2 4.3The nut is provided with a multiplicity of equally spaced slots of basic width B. In addition, the nut has a groove for the retaining ring. See Figure 3. FIGURE 3 Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/591
13、3977001 Not for Resale, 12/04/2007 19:52:02 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP688 Revision A - 4 - 4.4The key washer is a flat annular plate with a single key of basic width W on its inside diameter, and a multiplicity of equally spaced keys of basic wi
14、dth B on its outside diameter. See Figure 4. FIGURE 4 4.4.1The single key on the inside diameter should be off-set from the outside diameter key by an angle equal to A. 4.4.2The number of keys on the outside diameter should be as few as possible but not less than three and wholly divisible into the
15、number of slots in the nut. 4.4.2.1One outside diameter key is the actual locking key and should be closely fitted to the slots in the nut. For convenience, the locking key should be the closest one to the inside diameter key 4.4.2.2The other outside diameter keys are for centrally locating the key
16、washer in the nut and to provide a surface to bear against the retaining ring. The width of these keys should be less than the locking key to provide for slot-to-slot and key-to-key positioning tolerance. 4.5The retaining ring can be a conventional split-ring designed to be under light compression w
17、hen installed in the ring groove. Rings of this type are available commercially. 5.MAXIMUM POSSIBLE INDEXING ERROR: 5.1After the nut is initially run down and torqued to the minimum value it is likely that it will not be possible to install the key washer because of a mis-match between the two sets
18、of keys and slots. 5.2The term “maximum indexing error“ as used here is the maximum angle in degrees that the nut might have to be rotated relative to the shaft to install the key washer. The maximum indexing error is measured in the direction of increasing torque, only; correction of the nut positi
19、on relative to the shaft will be considered as being possible only in direction of increasing torque. The maximum indexing error will be denoted by “I“. Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 19:52:02 MSTNo
20、reproduction or networking permitted without license from IHS -,-,- SAE ARP688 Revision A - 5 - 5.2.1The maximum indexing error, with the optimum value for angle A (see paragraph 5.3.1), is given by the following: (Eq. 1) where: G = Number of slots in the shaft. H = Number of slots in the nut. K = L
21、argest common integer factor of G and H. 5.3The off-set angle “A“ (see paragraph 4.4.1) when properly selected, can minimize the maximum indexing error because of the additional combinations provided by reversing the key washer. 5.3.1The optimum value for angle A is given by the following: (Eq. 2) 6
22、.INSTALLATION PROCEDURE: 6.1The nut should be torqued to the minimum specified torque. 6.2By making trial installations of the key washer using each of the shaft slots, and by reversing the key washer, the closest position for accomplishing the installation can be determined 6.3The nut should then b
23、e rotated in the direction of increasing torque until the outside diameter locking key on the key washer lines up with the slot selected to accomplish the installation. If the correct torque allowance has been provided (see paragraph 8.4) the final torque should be equal to, or less than, the maximu
24、m specified torque. 6.4The installation of the retaining ring in the nut groove completes the operation. 7.MAXIMUM NUMBER OF SLOTS: 7.1The maximum indexing error can be reduced by increasing the number of slots in either the shaft, or nut, or both; within the limitations imposed by the factor K. (Se
25、e paragraph 5.2.1 - equation) 7.2The maximum number of slots in the shaft depends on the shaft diameter, and the width of the slots. 7.2.1Generally, a slot width of .10 inches on a .40 inch circular pitch is found to be satisfactory. 7.3The maximum number of slots in the nut depends on the basic nut
26、 size and the width of the slot. 7.3.1It is desirable for manufacturing reasons to have an even number of nut slots. I 180 K GH - -2A= A 90 K GH - -= Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 19:52:02 MSTNo rep
27、roduction or networking permitted without license from IHS -,-,- SAE ARP688 Revision A - 6 - 7.3.2The width of the slot is influenced by the strength requirements of the torquing wrench. 7.3.2.1In order to avoid a special wrench for each nut design, the nut OD and the slot dimensions should conform
28、to a standard. The preferred nut OD and slot dimensions are as used on the MS172321 and MS172236 series spanner nuts. NOTE:The United Kingdom standard B.S. 2090 - 1954 covering the standardization of C (or hook) spanner wrenches is now being considered for adoption in the United States. 7.3.2.2Gener
29、ally, slot widths given by the MS nuts used with a circular pitch of about 2.5 times the slot width will be satisfactory. 7.4As an example, Table 1 lists four nuts and the number of shaft and nut slots which result when the criteria given above are applied: TABLE 1 8.THE EFFECT OF THE MAXIMUM INDEXI
30、NG ERROR: 8.1As previously mentioned, a sufficient range of tightening torque must be allowed to ensure that it will be possible to install the key washer. This range of torque will result in a corresponding variation in the pre-load which the nut provides and in the pre-stress imposed on the clampe
31、d parts. 8.2The variation in the clamping load can be determined by the equation (Eq. 3) where: F = Variation in clamping load in pounds due to I. N = Number of threads per inch of length. e = Total strain induced in inches per unit clamping force. F I 360 Ne - -= Copyright SAE International Provide
32、d by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 19:52:02 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP688 Revision A - 7 - 8.2.1The value of e is given by where: L, A and E are length, cross sectional area, and modu
33、lus of elasticity of the i TH component of the strained, or stressed, element in the system due to the nut clamping force, “e“ is the summation of the quantity of all such elements. Complicated components such as a stepped or tapered shaft can be divided into several cylindrical elements. 8.3The inc
34、rement of stress resulting from the indexing error for any component of the strained system is (Eq. 5) where: f = Increment of stress in psi. F = As given in para. 8.2. A = Cross sectional area of the component of the strained system being investigated, in square inches. f F A - -= Copyright SAE Int
35、ernational Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 19:52:02 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP688 Revision A - 8 - 8.4The increment of torque corresponding to the indexing error can be foun
36、d from (Eq. 6) where: (Eq. 7) and: T = Torque increment in lb-inches. = Coefficient of friction. D = Mean diameter of contact face on nut. d = Thread pitch diameter. F = As given in paragraph 8.2. N = Threads per inch. b = Thread profile angle (60 for unified form threads). PREPARED UNDER THE JURISD
37、ICTION OF SAE COMMITTEE E-25, GENERAL STANDARDS FOR AEROSPACE PROPULSION SYSTEMS TDM+()F 2 - -= M .32 N - - d COSb 2 - - - -+= Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 19:52:02 MSTNo reproduction or networking permitted without license from IHS -,-,-