1、 AEROSPACE INFORMATION REPORT Age Control of Age Sensitive Elastomeric Materials 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 suita
2、bility for any particular use, including any patent infringement 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. Copyri
3、ght 2003 SAE International All rights reserved. No part of this 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 ORD
4、ER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: custsvcsae.org SAE WEB ADDRESS: http:/www.sae.org Issued 1975-05 Revised 1995-11 Reaffirmed 2003-12 Superseding AIR1364 AIR1364 REV.A (R) FOREWORD MIL-STD-1523A, Age Controls of Age-Sensitive Elast
5、omeric Materiel, requiring maximum ages of age sensitive elastomeric items for use in military aircraft and missiles and for space vehicles at the time of acceptance, was canceled on 30 January 1995. U.S. military specifications for nitrile rubber O-rings such as MIL-P-5315, MIL-P-5510, MIL-P-25732,
6、 and MIL-P-83461 which were formerly controlled by MIL-STD-1523A are now released from age control. Certain hoses containing nitrile rubber continue to be age controlled by AS1933A, Age Controls for Hose Containing Age-Sensitive Elastomeric Material. The following text is unchanged from the 1975 rev
7、ision (except where indicated) and is republished for historical purposes. 1. SCOPE: This SAE Aerospace Information Report (AIR) summarizes data and background relative to age control of specific classes of those nitrile type synthetic elastomers used in sealing devices which are resistant to petrol
8、eum base hydraulic fluids, lubricating oils, and aircraft fuels. This includes, but is not limited to, those nitrile (NBR or BUNA-N) elastomers previously covered by Section I of MIL-STD-1523. 1.1 Purpose: To provide users with appropriate references and information correlating past need and use of
9、age controls with current needs and to provide summary guidelines for consideration when future use of age controls is required or contemplated. SAE AIR1364 Revision A - 2 - 2. REFERENCES: 2.1 SAE Publications: Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001. AS1933A Age Contro
10、ls for Hose Containing Age-Sensitive Elastomeric Material 2.2 U.S. Government Publications: Available from DODSSP, Subscription Services Desk, Building 4D, 700 Robbins Avenue, Philadelphia, PA 19111-5094. MIL-STD-1523 2.3 Other Publications: ANA 438 3. BACKGROUND: 3.1 ANA Bulletin 438: After World W
11、ar II, particular concern was expressed relative to the apparent aging characteristics of the then recently developed BUNA-N and nitrile/neoprene blended elastomers being used in critical sealing devices of aircraft hydraulic, lubricating, and fuel systems. These early compounds apparently possessed
12、 poor ozone and weather resistance characteristics and were soon classified as age sensitive. As a result, age controls were established on these materials, initially in various general coverage government documents; when this proved unwieldy, all requirements were collected in 1958 and published in
13、 a single document, ANA Bulletin 438. Unfortunately, subsequent interpretations of this document by various agencies and contractors resulted in additions and variations in its implementation with subsequent confusion, abuses, and cost increases being incurred during enforcement of these variations.
14、 3.2 MIL-STD-1523: At the same time age controls leading to ANA 438 were being promulgated, at least ten programs were initiated relative to evaluation of long term aging of elastomeric materials. Results of these evaluations have been summarized in an excellent Air Force report AFMA-TR-67-235. The
15、tests indicated that, while certain mechanical properties did undergo some change with time (i.e., increases in hardness, tensile, and modulus with a corresponding decrease in ultimate elongation), these property changes tended to level off after 4 or 5 years. Further, the changes that did occur wer
16、e not of sufficient magnitude to result in seal failure. SAE AIR1364 Revision A - 3 - 3.2 (Continued): In addition to the above test programs, a large amount of performance data for old components containing over-age elastomeric seals has also been generated over the years that further indicate elas
17、tomers are less affected by aging than originally expected. Several of the more widely publicized studies involved the analysis of equipment removed from two aircraft that had crashed during WW II, one in the Libyan desert and the other on the Arctic ice cap. Functional tests performed on assemblies
18、 and mechanical property data on O-rings from these aircraft indicated that the elastomeric seals were in remarkably good condition when tested and that most of these old units functioned within their original specification limits. As the elastomeric parts removed from these two planes had probably
19、been cured in 1941 or 1942, these materials represented the state of the art for very early nitrile or nitrile-neoprene blended compounds. In view of the above results and the fact that overall properties of current nitrile materials are much improved over those evaluated, it was concluded that the
20、then current age controls should be reconsidered and made less restrictive. Accordingly, MIL-STD-1523 was promulgated and when released in 1973, superseded ANA Bulletin 438. Among other considerations, this document basically provides for a cure date limitation of twelve quarters from cure date to a
21、cceptance of the seals or bulk hose by the original procuring activity, whether a government agency, a first or second tier subcontractor or kitter. In all cases, continued use of cure dates is intended to provide for good first-in/first-out warehousing procedures. 3.3 MIL-STD-1523A: (R) MIL-STD-152
22、3A was issued 1 February 1984, superseding MIL-STD-1523. This somewhat alleviated the burden imposed by the earlier versions. Limitation of time from cure date to acceptance was extended from 12 quarters to 40 quarters. In both ANA Bulletin 438c and MIL-STD-1523, ages were controlled as the items mo
23、ved through the development and production cycles. Acceptance for the government was done by procuring activities at intermediate stages as well as acceptance by the government of the completed system. Later acceptances depended upon previous age requirements having been met. O-rings were not contro
24、lled after installation. Both versions required that the history of an elastomeric item be known at installation. Therefore, not all elastomeric items already installed in an assembly or subassembly at acquisition were automatically acceptable for critical programs, i.e., for the acquisition of spac
25、e vehicles, military aircraft, and missiles. The history of each elastomeric item had to be known at the time it was installed and its age had to fall within the limit given in the table of each version. In MIL-STD-1523A the ages of both O-rings and hoses were controlled only at time of acceptance b
26、y the government. The limits were meant to apply to items installed in a system to be accepted by the government. Since the only age control was at acceptance, the cure date of each item had to be known at that time. The main reasons for changes from MIL-STD-1523 to MIL-STD-1523A were: SAE AIR1364 R
27、evision A - 4 - 3.3 (Continued): a. At the limits given in MIL-STD-1523, government inspectors were requiring the discarding of unused material. This culling and discarding increased costs and delayed ongoing programs. Therefore, a time longer than most development programs was specified to allow un
28、interrupted pursuit of a program. b. To assign age control responsibility to the prime contractor, who had to see that the age limits in MIL-STD-1523A fit into the missile, military aircraft, or space vehicle development program completion or production delivery schedule. c. Systems already accepted
29、 by the government were removed from control of the document. The elastomeric items for such systems were to be controlled by their managers in accordance with system needs and constraints. d. Specifying age limits for intermediate stages of a program as was done in MIL-STD-1523 were not consistent
30、with the then DoD standardization policy that documents give minimum performance requirements and not detailed methods. 4. SUMMARY GUIDELINES (OBSOLETE MIL-STD-1523): In conclusion and as a result of study and evaluation of the above and related data by both consumers and producers, the following po
31、ints are offered as a guide for use in justifying or otherwise considering future requirements for age controls where needed under MIL-STD-1523. 4.1 The general and detailed requirements of MIL-STD-1523 provide: 4.1.1 The necessary parameters needed for future procurement programs involving age cont
32、rols of those age sensitive elastomers included therein. 4.1.2 A cure date based on which good supply and warehousing procedures may be established. 4.1.3 An effective reference for use on contractual specifications and/or drawings. 4.1.4 An appropriate description of environmental limits for proper
33、 long term storage of items made from subject elastomers. 4.1.5 The reference document and authority for discontinuing use of, and deleting reference to, the now obsolete ANA Bulletin 438 at the earliest practicable date. SAE AIR1364 Revision A - 5 - 4.2 In considering storage of uninstalled items s
34、uch as spare seals in supply lines or large single buys by subcontractors against their own production schedules, optimum protection against circulating air, sunlight, fuel, oil, water, dust, and ozone may best be accomplished by use of packaging in sealed, polyethylene bags in covered containers or
35、 sealed poly-lined kraft bags. Inside storage of items so packaged at ambient temperatures not exceeding 120 F (100 F preferred) will minimize or eliminate any deteriorating effects of adverse environmental conditions. In this respect, past usage of age controls has placed so much emphasis on time f
36、actors, the need for proper storage conditions is too often overlooked or otherwise de-emphasized. To place storage conditions in their proper perspective, as much attention should be given them as is given to the selection of the proper elastomer for use in a specific fluid. To this end, the requir
37、ements of MIL-STD-1523, paragraph 5.4, are most important and should not be neglected or ignored. 5. CANCELLATION OF MIL-STD-1523A, REFERENCES: (R) The history of age control of elastomeric O-rings and hoses was marked with considerable controversy. Since its inception, there were many unsuccessful
38、attempts to clarify the requirements of age control in order to make uniform implementation possible. During the period of ANA 438 and MIL-STD-1523, numerous complaints about the practicability of O-ring control were raised by both members of industry and the government. They cited studies by the U.
39、S. Government (e.g., AFML-TR-67-235, AFML-TR-66-275, and WWFESM-60-21), the Rubber Manufacturers Association (RMA, Effect of Long Term Storage on O-ring Physical Properties, 1 March 1966; Revision 2, 9 September 1968), the SAE Committee A-6 (Effects of Age on the Serviceability of Hydraulic Componen
40、ts and Systems, October 23, 1973) and industry (Parker Seal Co. and Precision Rubber Products Corp., 20 years of data) all of which consistently showed that O-ring age either installed or uninstalled, is not a factor in seal failure when stored per the applicable storage requirements. More recently,
41、 the Washington Public Power Supply System of Richland, Washington published Report No. EPRI NP-6608, Shelf Life of Elastomeric Components, May, 1994, prepared for the Electric Power Research Institute, Charlotte, NC. This study presented results of tests for elastomer natural aging on O-rings that
42、are 25 to 32 years old, which assessed the military shelf life limitation standards. A conclusion was that shelf life for seals made from a variety of elastomers including nitrile could be extended to 32 years. It is the finding of the SAE AMS Elastomers Committee that based on the studies and histo
43、ry of age control for nitrile elastomers, the cancellation of MIL-STD-1523A is justified. 6. NOTES: The (R) is for the convenience of the user in locating areas where technical revisions, not editorial changes, have been made to the previous issue of this specification. If the symbol is next to the specification title, it indicates a complete revision of the specification. PREPARED BY AMS COMMITTEE “CE“
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