SAE ARP 1231B-2017 Gland Design Elastomeric O-Ring Seals General Considerations.pdf

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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 ther

2、efrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2017 SAE International All rights reserved. No part of this

3、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: +1 724-776-49

4、70 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/standards.sae.org/ARP1231B AEROSPACE RECOMMENDED PRACTICE ARP1231 REV. B Issued 1973-04 Reaffirmed 2012-10 Revis

5、ed 2017-05 Superseding ARP1231A Gland Design, Elastomeric O-Ring Seals, General Considerations RATIONALE Figures 1 and 2 redrawn for better clarity, Reference to ARP1235, ARP1236, and ARP1237 deleted as documents never produced, table 2 redrawn to remove metric dimensions, section added to show refe

6、rence documents and MILH-5606 corrected to MIL-PRF-5606. 1. SCOPE This document establishes general gland design criteria for static and dynamic O-ring seal applications used in fluid systems and at fluid pressures common to the aerospace industry. Detailed discussion of design criteria and tables o

7、f recommended gland dimensions are contained in the documents listed in Table 1. SI unit conversions for U.S. customary units have been provided for reference purposes. 1.1 Purpose The purpose of this document is to provide the aerospace industry with basic information pertinent to the design and se

8、lection of elastomeric O-ring seal glands. Table 1 DOCUMENT NUMBER DOCUMENT TITLE ARP1232 Gland Design, Elastomeric O-Ring Seals, Static Radial ARP1233 Gland Design, Elastomeric O-Ring Seals, Dynamic Radial, 1500 psi Max ARP1234 Gland Design, Elastomeric O-Ring Seals, Static Axial, without back-up r

9、ings SAE INTERNATIONAL ARP1231B Page 2 of 11 2. APPLICABLE 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 pu

10、rchase order. In the event of conflict between the 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 Availabl

11、e from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or +1 724-776-4970 (outside USA), www.sae.org. AS568 Aerospace Size Standard for O-rings AIR786 Elastomer Compatibility Considerations Relative to Elastomeric Sealant Selection 2.2

12、U.S. Government Publications Copies of these documents are available online at http:/quicksearch.dla.mil. MIL-PRF-5606 Performance Specification: Hydraulic Fluid, Petroleum Base; Aircraft, Missile, and Ordnance 3. GENERAL REQUIREMENTS 3.1 Gland Configuration 3.1.1 Radial O-Ring Seal Glands Figure 1

13、depicts rod-mounted and bore-mounted radial O-ring seal glands. The rod-mounted configuration is preferred. Fabrication costs are lower, assembly is easier, and there is less likelihood of the seal buckling or twisting and being pinched as the rod is installed. 3.1.2 Axial O-Ring Seal Glands Figure

14、2 illustrates an axial O-ring seal gland. In an axial gland, sealing occurs on the flat surfaces of the gland rather than on the gland diameters. 3.2 Gland Dimensions 3.2.1 General The best dimensions for a particular gland are functions of the fluids, elastomers, pressures, and temperatures employe

15、d in the system. However, the use of the best gland in each application is not always desirable or necessary. Within a given aerospace system, it is frequently necessary to change fluids or elastomers to achieve desired fluid system performance. When such a change is required, O-ring seal gland dime

16、nsions should not be changed. Therefore, it is preferable to design O-ring seal glands which will operate satisfactorily with a number of different fluids and materials in varying environmental conditions. 3.2.2 Standard Gland Dimensions Standard gland dimensions are provided in the ARP listed in Ta

17、ble 1 for the O-ring seal sizes covered by AS568. These dimensions are computed in accordance with criteria in the ARP adjusted to the needs of the specific gland classification (radial or axial, static or dynamic, etc.). SAE INTERNATIONAL ARP1231B Page 3 of 11 3.2.3 Modified Gland Dimensions The st

18、andard gland dimensions may be modified in a given application to achieve the best sealing configuration. In computing special gland configurations, the design criteria in Section 5 should be reviewed. 3.2.4 Lead-In Ramps Radial seal applications require lead-in ramps to prevent seal damage as the r

19、od is assembled into the bore. View K in Figure 1 depicts the preferred external and internal ramps. The entering diameters of the ramps should be sized such that the seals first contact the ramp slope. Figure 1 - Typical radial O-ring seal glands SAE INTERNATIONAL ARP1231B Page 4 of 11 TABLE 2 Nomi

20、nal O-ring Cross Section (w) per AS568 Edge Break J Radius R L Min M .070 .005-.015 .010-.020 .002 .020 .103 .010-.020 .020-.030 .002 .020 .139 .010-.020 .020-.030 .003 .020 .210 .010-.020 .020-.030 .004 .020 .275 .010-.020 .020-.030 .005 .020 R ( SEE FIGURE 1)J ( SEE FIGURE 1)Figure 2 - O-ring axia

21、l seal gland 3.2.5 Edge Breaks The gland edges must be broken in accordance with Figures 1 and 2 to avoid damaging seals during assembly and disassembly. The edge break should be carefully blended to avoid any condition that will cut the mating seal. If desired by the design activity, a radius may b

22、e substituted for the edge break. 4. EFFECT OF O-RING SEAL SELECTION ON GLAND DESIGN 4.1 Fluid Material Compatibility 4.1.1 This document establishes gland design criteria and standards for use with nitrile (NBR), fluorocarbon (FPM), and fluorosilicone (FMQ), ethylenepropylene (EPM), or silicone (VM

23、Q) elastomers in systems containing hydrocarbon fuels, petroleum oils, ester base synthetic oils, phosphate ester hydraulic fluids, silicate ester fluids, or air. The realization that differences in compatibility exist between various fluid/seal material combinations is essential to good design. The

24、 selection of the fluid/seal combination is the task of the designer. For more specific information on compatibilities, see AIR786. 4.2 Effects of Fluid Pressure on Seal Wear 4.2.1 Extrusion Figure 3 shows the tendency of a pressurized O-ring seal to extrude into the clearance gap. This leads to inc

25、reased seal wear and premature seal failure. SAE INTERNATIONAL ARP1231B Page 5 of 11 Figure 3 - O-ring seal extrusion 4.2.2 Control of Extrusion Seal extrusion is a function of the O-ring seal hardness, the fluid system pressure and the bore/rod diametral clearance. Diametral clearance is defined as

26、 the numerical difference between the bore and piston diameters (per Figure 1: Dia A-Dia C or Dia H-Dia B). As fluid pressure increases or seal hardness decreases, diametral clearance must be reduced to avoid O-ring seal extrusion (see Figure 4). In using Figure 4, it must be taken into account that

27、 elastomer hardness will decrease at elevated temperature and under fluid immersion. The elastomer used to derive Figure 4 displayed average modulus values at the indicated hardness levels. 4.2.3 Use of Anti-Extrusion Devices As a general rule, systems at above 1500 psi should utilize backup rings o

28、r other devices of this nature. Also, if diametral clearances are larger than desired, an anti-extrusion device may be installed in the gland to reduce the diametral clearances (see 5.4). 4.3 Temperature Considerations 4.3.1 Effects of Temperature on Seal Squeeze The minimum squeezes (see 5.2) used

29、in developing standard gland dimensions are designed to be effective across the full range of temperatures which the seal materials are capable of withstanding. 4.3.1.1 Because elastomers contract faster than metals, if operation is to be only at low temperatures a better seal can be obtained by red

30、ucing the gland volume. Conversely, an increase in gland volume will generally improve a seal where the seal operates primarily in the higher temperature range. 4.3.2 Effect of Temperature on O-Ring Seal Materials A significant factor in the selection of an O-ring seal material is its ability to fun

31、ction within the operating temperature range of a given system. Temperature limitations can be found in applicable material specifications. SAE INTERNATIONAL ARP1231B Page 6 of 11 Figure 4 - Recommended maximum dia clearance under high pressure 4.4 Seal Size Selection 4.4.1 Standard O-Ring Seal Size

32、s The O-ring seal size is a function of the system performance requirements and must be compatible with the mating rod and bore sizing. Sizes should be selected from standard O-ring seal drawings which meet the dimensional requirements of AS568. SAE INTERNATIONAL ARP1231B Page 7 of 11 4.4.2 Cross-Se

33、ction Diameters The durability of the O-ring seal and its ability to seal are proportional to its cross section. The larger cross-section rings are less likely to twist during installation and operation although they may generate higher friction levels. Also, larger cross-section seals should be use

34、d where low temperature sealing problems are expected. 4.4.2.1 Specifically, the 0.103 inch cross-section seals in the larger ID sizes are recommended in preference to the 0.070 inch cross-section seals except in applications where size or weight considerations necessitate the use of 0.070 inch cros

35、s-section seals. 5. DESIGN CRITERIA 5.1 Seal Stretch 5.1.1 Designing for Seal Stretch Glands should be designed to assure that the O-ring seal is stretched when installed in order to avoid buckling of the seal. This is particularly important in the cases of rod-mounted static and low relative motion

36、 dynamic seals/1/. Buckling allows the seal to be pinched locally when the rod is installed in the mating bore. /1/Consult ARP1233, Gland Design, “Elastomeric O-ring Seals Dynamic Radial 1500PSI Max,“ for factors defining seal stretch requirements in other dynamic seal applications. 5.1.2 Computing

37、Seal Stretch Seal stretch is measured as a percentage increase in diameter and is calculated as follows: (Eq. 1) 5.1.3 Allowable Seal Stretch For allowable seal stretch in specific applications consult the documents listed in Table 1. 5.2 O-Ring Seal Squeeze 5.2.1 Importance of Squeeze Proper sealin

38、g depends on the amount of squeeze (compression) imposed on the seal cross section. 5.2.2 Factors Affecting Squeeze The amount of squeeze selected for a given application is a compromise of the following factors: 5.2.2.1 Friction Increased squeezes tend to improve sealing, but the force required to

39、install a seal or to move a dynamic seal is increased substantially as the amount of squeeze increases. 5.2.2.2 Seal Hardness Seal hardness affects squeeze. Soft seals perform better with increased squeeze because of the greater elastomer to metal contact. Soft seals can tolerate more squeeze than h

40、ard seals and still assemble well. Percent Stretchinstalled seal ID free seal IDfree seal ID-100=SAE INTERNATIONAL ARP1231B Page 8 of 11 5.2.2.3 Compression Set/Stress Relaxation Elastomers are subject to compression set or stress relaxation which causes a reduction in the amount of sealing force du

41、ring service. The amount varies with temperature and with each elastomer. 5.2.2.4 Thermal Expansion The thermal expansion rates of the elastomer and the metallic gland components differ. Often the rod and bore are made of different materials. The effect of these varying thermal expansion rates must

42、be considered (see 4.3.1.1). 5.2.2.5 Gland Breathing Expansion of the gland due to system pressure, known as gland breathing, affects squeeze and diametral clearances. Sufficient structural rigidity must be designed into the gland to confine such breathing to acceptable limits. 5.2.2.6 Seal Stretch

43、The seal cross section is reduced whenever the seal is stretched. The following formulas have been established empirically for many seal materials and provide a suitable method of adjusting the seal cross section for the effects of stretch: For rod-mounted applications (Eq. 2) For bore-mounted appli

44、cations (Eq. 3) where: W = seal cross-section diameter (uninstalled) F = gland diameter (see Figure 1) B = rod diameter (see Figure 1) K = seal ID (uninstalled) Reduction in cross section diameterW10-6F KK-=Reduction in cross section diameterW10-6B KK-=SAE INTERNATIONAL ARP1231B Page 9 of 11 5.2.2.7

45、 Nominal Squeeze Squeeze is normally expressed as a percentage of seal cross section and is computed by the following formula: (Eq. 4) where: W = free cross section diameter of seal S = gland height (see Figure 3) 5.3 O-Ring Seal Swell 5.3.1 Fluid Absorption Rates of Elastomers All O-ring seal mater

46、ials absorb some amount of fluid when installed in a fluid application. The amount of absorption depends on the elastomer and the fluid. Fluorocarbon elastomers installed in MIL- PRF-5606 hydraulic fluid will absorb enough fluid to increase the O-ring seal volume to 105% of the unsoaked volume. Some

47、 nitrile elastomeric O-ring seals installed in JP4 fuel will swell to 160% of their original (unsoaked) volume. 5.3.2 Designing for Seal Swell The volume of the O-ring seal gland should be large enough to accommodate a fully soaked seal in its intended application. This volume is controlled by the s

48、election of an appropriate gland width. Formulas for computing gland width are as follows: Rod-Mounted Applications (Eq. 5) Bore-Mounted Applications (Eq. 6) All Applications (Eq. 7) Percentage Squeeze (Nominal)W SW-100=G minMV NR+.7854 A2min F2max( )-=G minMV NB+.7854 E2min B2max( )-=GmaxGmindesired tolerance+=SAE INTERNATIONAL ARP1231B Page 10 of 11 where: A, B, E, F, G, and R are gland dimensions per Figure 1 V = maximum unsoaked seal volume = 2.4674 (Kmax + Wmax) (W2max) K = s