《SAE-ARP-4912B-2007.pdf》由会员分享，可在线阅读，更多相关《SAE-ARP-4912B-2007.pdf（8页珍藏版）》请在三一文库上搜索。
1、_ 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 arising there
2、from, 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 publication m
3、ay 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 (outside USA)
4、 Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org ARP4912 REV. B AEROSPACE RECOMMENDED PRACTICE Issued 1996-12 Revised 2007-04 Superseding ARP4912A Design Recommendations for Spare Seals in Landing Gear Shock Struts RATIONALE This SAE Aerospace Recommended Practice
5、is intended to provide comprehensive recommendations for the storage and selection of spare seals in landing gear shock struts. 1. SCOPE This SAE Aerospace Recommended Practice (ARP) provides recommendations on cavity design and the installation of elastomer type spare seals in these cavities. 2. AP
6、PLICABLE DOCUMENTS The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the
7、 text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1 SAE Publications Available from SAE International, 400 Commonwealth Drive,
8、Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. AMS-P-83461 Packing, Preformed, Petroleum Hydraulic Fluid Resistant, Improved Performance at 275F (135C) 2.2 U.S. Government Publications Available from the Document Automation and Produc
9、tion Service (DAPS), Building 4/D, 700 Robbins Avenue, Philadelphia, PA 19111-5094, Tel: 215-697-6257, http:/assist.daps.dla.mil/quicksearch/. MIL-PRF-5606 MIL-PRF-83282 MIL-P-25732 (Inactive) Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 No
10、t for Resale, 12/04/2007 18:20:56 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP4912 Revision B - 2 - 3. RECOMMENDATIONS 3.1 Spare seal cavities should be designed with maximum bottom radii, both to eliminate stress risers and to distinguish the spare seal cavity f
11、rom the actual seal glands. Half round cavities may be considered for rod type T-Seals or O-rings. 3.2 All spare seal cavity edges are to be smooth and free of sharp edges and burrs to eliminate seal damage during installation. 3.3 Design considerations must assure that spare seals cannot function a
12、s a static seal. Since MIL-Specs require seal elastomers to swell 10 to 20% in MIL-PRF-5606 and 5 to 15% in MIL-PRF-83282, these increases in volume must be considered. 3.4 Spare seal cavities should be located downstream (nonpressurized side) of the active static seals. This location minimizes flui
13、d contact, reducing seal swell which can make seal installation difficult or impossible. Seal swell in excess of 15% increase in circumference has been seen after 500 h in MIL-PRF-5606. 3.5 Seals should be lubricated and packed in grease in the spare seal cavities. A list of recommended greases with
14、 typical swell is included in Appendix A. 3.6 Seals are to be stored in their “as molded“ configuration. When seals are turned inside out and stretched over the lower bearing, excessive stress is applied to the dynamic sealing surfaces. 3.7 If seals are installed in separate grooves, backup rings ma
15、y be stored with the seals. 3.8 Several aircraft have recently been designed with active spare seals. This design as shown in Figure 1 uses two seals in tandem with a normally open valve arrangement between them to eliminate a pressure differential across the inboard or spare seal. When the outboard
16、 seal fails, the valve is closed and the inboard seal becomes the primary seal. Although the life of this seal is not as long as the outboard seal, it is a spare seal arrangement that should be considered. FIGURE 1 - DOWTY AEROSPACE LG-GLOUCESTER 3.9 This document addresses nitrile type seals used w
17、ith common mineral oil strut fluids, such as MIL-PRF-5606 and MIL-PRF-83282. Phosphate ester systems using Skydrol or Hyjet fluids with EPR type elastomers may exhibit different stretch and swell characteristics and require alternate compatible greases for installation. 3.10 Design considerations sh
18、ould include the prevention of pressure trapping between the static seal and spare seals. Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 18:20:56 MSTNo reproduction or networking permitted without license from IHS -
19、,-,- SAE ARP4912 Revision B - 3 - 3.11 Recommended spare seal cavity dimensions are shown in tabular form in Figure 2. 3.12 The spare seal gland size and location should not allow deformation of the lower bearing created by extended loads of the piston during aircraft take off. 4. TEST RESULTS Sever
20、al tests have been run to guide the designer in addressing the permanent set and swell of stored seals. These tests all utilized an elastomer meeting the MIL-P-25732 specification. 4.1 In the first test typical seals were stretched on mandrels 5, 10, 15, and 20% larger than the standard rod diameter
21、 for these seals, then aged 500 h in MIL-PRF-5606 fluid at 160 F. The results are shown in Figure 3. This test was originally planned to extend to 1000 h but fluid swell expanded the seal diameter beyond the mandrel diameter after 500 h exposure. 4.2 Since seal swell was clearly the predominant fact
22、or, several nitrile seal materials were immersed in commercial strut fluids and volume swell results of long-term soaks are shown in Figure 4. 4.3 To isolate the effects of long-term tensile set without the effects of fluid, the test described in 4.1 was repeated in air at 160 F. The results of thes
23、e tests are shown in Figure 5. 4.4 In a further attempt to isolate stored seals from fluid swell, a 7441-ft T-Ring was installed with a typical 5% stretch and sealed in the groove with a viscous silicone grease (Dow Corning DC-55). The assembly was then dipped into MIL-PRF-5606 fluid once a week to
24、simulate downstream seal leakage. After six months the seal was removed and measured seal swell was only 1.5% of the original diameter. 4.5 The seals used in these tests were T-Seals of the following type as shown in Table 1: TABLE 1 Part Number Dimensions Application 7451FT 11.500 OD x .275 Cx 747
25、MLG Dynamic Strut Seal 7441FT 7.510 OD x .275 Cx DC-10 NLG Dynamic Strut Seal 7339FT 3.640 OD x .210 Cx 737 NLG Dynamic Strut Seal 5. CONCLUSIONS 5.1 Seal swell due to fluid contact is a major problem when attempting to install a seal that has been exposed to hydraulic fluid. 5.2 Tensile set, even i
26、f seal is stretched 20%, should not be cause for concern. 5.3 By locating the spare seal downstream from the static seal and packing it in a low swell grease, minimum swell and less installation difficulty will be encountered. 6. NOTES 6.1 The change bar ( l ) located in the left margin is for the c
27、onvenience of the user in locating areas where technical revisions, not editorial changes, have been made to the previous issue of this document. An (R) symbol to the left of the document title indicates a complete revision of the document. PREPARED BY SAE SUBCOMMITTEE A-5B, GEARS, STRUTS, AND COUPL
28、INGS OF COMMITTEE A-5, AEROSPACE LANDING GEAR SYSTEMS Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 18:20:56 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP4912 Revision B - 4 - FI
29、GURE 2 - TYPICAL SPARE SEAL STORAGE ARRANGEMENT (SEPARATE CAVITIES) Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 18:20:56 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP4912 Revis
30、ion B - 5 - FIGURE 3 - EFFECT OF STRETCH AND FLUID ON DIAMETRICAL CHANGE AT 160 F Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 18:20:56 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE
31、 ARP4912 Revision B - 6 - FIGURE 4 - EFFECT OF FLUID ON VOLUME CHANGE WITH TIME (AT TEMPERATURE = 165 F, WITH -214 O-RINGS) Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 18:20:56 MSTNo reproduction or networking pe
32、rmitted without license from IHS -,-,- SAE ARP4912 Revision B - 7 - FIGURE 5 - EFFECT OF EXPOSURE TIME ON STRETCHED T-RINGS AT 160 F (T-RING SIZES: 7339, 7441, AND 7451 FT) Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/
33、2007 18:20:56 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE ARP4912 Revision B - 8 - APPENDIX A Several installation lubricants have been evaluated and found to be compatible with AMS-P-83461 Type nitrile seals. These include, but are not limited to the following as s
34、hown in Table A1: TABLE A1 Test Time Test Temperature Swell (%) 1) Aeroshell-6 6 months Room Temperature 3.46 2) Aeroshell-14 6 months Room Temperature 6.33 3) Aeroshell-23C 6 months Room Temperature 3.88 4) White Petrolatum 6 months Room Temperature 3.10 5) DC-55 Silicone Grease* 6 months Room Temp
35、erature 5.53 6) AFS-682 Grease+ 6 months Room Temperature 2.50 * Dow Corning Molykote55M + Aviation Fluid Services Copyright SAE International Provided by IHS under license with SAELicensee=Defense Supply Ctr/5913977001 Not for Resale, 12/04/2007 18:20:56 MSTNo reproduction or networking permitted without license from IHS -,-,-