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 revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2015 SAE International All rights reserved. No part of this p
3、ublication 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: +1 724-776-497
4、0 (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:/www.sae.org/technical/standards/AIR5885 AEROSPACE INFORMATION REPORT AIR5885 Issued 2004-12 Reaffirmed 2015-04 La
5、nding Gear Common Repair RATIONALE AIR5885 has been reaffirmed to comply with the SAE five-year review policy. 1. SCOPE: This document outlines the most common repairs used on landing gear components. It is not the intention of this AIR to replace Overhaul/Component Maintenance or Technical Order Ma
6、nuals, but it can serve as a guide into their preparation. This document may also be used as a template to develop an MRB (Material Review Board) plan. The recommendations in this document apply to components made of metallic alloys. These recommendations are intended for new manufactured components
7、 as well as for overhauled components. The extent of repair allowed for new components as opposed to in-service components is left to the cognizant engineering authorities. Reference could be made to this document when justifying repairs on landing gears. For repairs outside the scope of this docume
8、nt, a detailed justification is necessary. It must be understood that all the repairs listed in this document are not to be applied without the involvement of the cognizant engineer. 2. APPLICABLE DOCUMENTS: The following publications form a part of this document to the extent specified herein. The
9、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 text of this document and references cited herein, the text of this document takes precedence. Nothing in this
10、 document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1 SAE Publications: Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001. ARP4915 Disposition of Landing Gears Components Involved in Accidents/Incidents 3. DEFINITIONS: R
11、EPAIR: An engineering disposition to restore a component to within acceptable limits of its design requirements without adversely affecting its interchangeability, its reliability and its maintainability while maintaining its functional and structural integrity. REWORK: An engineering disposition to
12、 restore a component to within its drawing requirements. ACCEPTABLE AS IS: An engineering disposition given to a part with a departure from its drawing requirements when it is judged that such deviation will have no effect on its functional and structural integrity, as well as on its reliability, in
13、terchangeability and maintainability. 4. CLASSIFICATION: Type I: Repair with functional plating, coating, surface modification. Type II: Repair with bushing. Type III: Repair of damaged marks. Type IV: Repair of localized heat damaged surface. Type V: Repair of damaged plating. Type VI: Repair of da
14、maged threads. Type VII: Repair of lubrication hole. Type VIII: Repair of lugs with spherical bearing Type IX: Repair of plastically deformed surface. Class 1: Ferrous alloys Class 2: Aluminum alloys Class 3: Titanium alloys SAE INTERNATIONAL AIR5885 2 OF 145. REPAIRS: 5.1 Type I: (Repair with funct
15、ional plating, coating, surface modification) 5.1.1 Plating: 5.1.1.1 Chrome Plating: Chrome plate repairs should be limited to a deposited thickness of 0.015 inch since a heavier plating thickness could severely affect the fatigue life of the part, because of the residual tensile stresses induced at
16、 the base metal surface. Shot peening (or other residual compressive surface stress process) prior to plating is required. If the affected section has a low margin of safety in fatigue strength, this repair should not be used. Reference to reliable data on the fatigue impact due to the application o
17、f the chrome plating is recommended. In general, chrome plate repair should be used only in locations where plating already exists or where the OHM / CMM allows it. This repair should be used when hard, wear resistant and low friction surface is required. It can be used over other softer plating, li
18、ke sulfamate nickel, when a hard wear surface is required. Chrome plating is widely used on all Class 1 materials including high strength up to 300 ksi. Precautions should be taken when applying on stainless steel components due to adhesion difficulties. For Class 2 materials, because of its metallu
19、rgical surface characteristics, multiple under coatings are normally required such as zinc, copper and nickel. Chrome plating should not be used on Class 3 because of poor adhesion. Reference to reliable data on the fatigue impact due to the application of the sulfamate nickel is recommended. 5.1.1.
20、2 Sulfamate Nickel Plating: Although not proven through proper qualification testing, it is accepted that sulfamate nickel because of its lower hardness (low residual tensile or compressive stresses) is less detrimental to the fatigue life of major structural components than chrome. This is supporte
21、d by the fact that this method of repair has been widely used on many landing gears, especially during their overhaul cycle. However, if available, reference to reliable data on the fatigue impact due to the application of the sulfamate nickel is required. The allowable thickness is limited by the a
22、mount a particular plating shop can apply. Achievement of thick coating will normally require multiple plate-machine-plate operations. Shot peening (or other residual compressive surface stress process) prior to plating is required. SAE INTERNATIONAL AIR5885 3 OF 145.1.1.2 (Continued): This repair c
23、an be used to restore large out-of-tolerance dimensions. Bearing/shear loads on the build up coating should be evaluated, especially if the area is not a fully captured “fill” area. It can be used under hard plating, such as chrome, when the limits in 5.1.1 are exceeded and it is essential to obtain
24、 the chrome plating surface hardness. If the affected section has a low margin of safety in fatigue strength, sulfamate nickel under chrome repair should not be used. Reference to reliable data on the fatigue impact due to the application of the sulfamate nickel under chrome is required. If used und
25、er chrome, the sulfamate nickel should be shot peened to check for proper adhesion prior to chrome application. Nickel plating is widely used on all Class 1 materials including high strength up to 300 ksi. Precautions should be taken when applying on stainless steel components due adhesion difficult
26、ies. For Class 2 materials, because of its metallurgical surface characteristics, multiple under coatings are sometimes required such as zinc, tin and copper. Nickel plating should not be used on Class 3 because of poor adhesion. 5.1.1.3 Electroless Nickel Plating: This type of repair is widely used
27、 because of its few post-plating operations required after repair of discrepancies. Although it is normally limited to thickness of about .002 inch, build-ups of .010 inch are possible. Caution should be taken when applying heavier plating thickness since the fatigue life of the part could be affect
28、ed, because of the residual tensile stresses induced at the base metal surface. If the affected section has a low margin of safety in fatigue strength, this repair should not be used. Shot peening (or other residual compressive surface stress process) prior to plating is recommended. When using elec
29、troless nickel plating it is essential to specify the hardness required, since different solutions and different thermal treatment will result in different surface hardness. This repair could be used when a harder surface is required and chrome plating cannot be used (example: it is not recommended
30、that two chrome plated surfaces be in contact because of the danger of galling). Electroless nickel is widely used on all Class 1 materials including high strength up to 300 ksi. Precautions should be taken when applying on stainless steel components due adhesion difficulties. For Class 2 materials,
31、 because of its metallurgical surface characteristics, multiple under coatings are sometimes required such as zinc, copper and tin. Electroless Nickel plating should not be used on Class 3 because of poor adhesion. Reference to reliable data on the fatigue impact due to the application of the electr
32、oless nickel is recommended. SAE INTERNATIONAL AIR5885 4 OF 145.1.1.4 Hard Nickel Electro-Plating: This repair is used in lieu of chrome plating, i.e. whenever a harder surface is required and when chrome plating cannot be used (example: it is not recommended that two chrome plated surfaces be in co
33、ntact because of the danger of galling). The same procedure as in chrome plating is applicable whenever this process is used (refer to 5.1.1.1). Reference to reliable data on the fatigue impact due to the application of the hard nickel is recommended. 5.1.2 Thermal Spray: 5.1.2.1 Plasma Spray: Care
34、should be taken when selecting the thickness, type of process and alloy used. Plasma spray is very flexible because of the wide variety of materials that it can deposit. Particular attention should be made for contact stresses, since under point loading, on low cohesive strength thermal sprayed allo
35、y serious damage can result (peeling). Plasma sprayed coatings tend to be fairly porous, therefore unsuitable for many sealing surfaces. Plasma spray process is widely used on most Class 1 and Class 2 materials, but is normally limited to secondary structural member with lower ultimate tensile stren
36、gth. Meanwhile, some precautions should be taken when applying on stainless steel components, because adhesion can be more difficult. In all cases, an undercoated alloy (bond coat, 95Ni/5Al) is required on those materials to ensure minimum bond strength. Thermal spray coating is rarely used on Class
37、 3 material because of its poor adhesion. Care must be exercised to insure that the item being coated is not overheated during application. Reference to reliable data on the fatigue impact due to the application of the plasma spray is recommended. 5.1.2.2 HVOF: High Velocity Oxy-Fuel (HVOF), a relat
38、ively new thermal spray process, is being widely used to replace hard chrome plating with Tungsten Carbide (WC) based materials. Preliminary qualification results show an equal or better performance to chrome plating as well as shorter processing times. Study needs to be completed for the impact of
39、thicker HVOF coating to resist spalling in high stress/high load reversal fatigue applications. Different powder alloy combinations can be used depending on the application. HVOF can be applied over all Class 1, 2, and 3 materials with very good cohesive strength. In addition, it can be applied over
40、 Sulfamate Nickel repairs as referenced in 5.1.1.2. Because of the process variables involved, HVOF should be applied by a qualified applicator, particularly for fatigue sensitive components. HVOF is a line of sight process, therefore not suitable for some internal diameters applications. Also, thic
41、kness should be limited to 0.010 inches. Reference to reliable data on the fatigue impact due to the application of the coating is recommended. SAE INTERNATIONAL AIR5885 5 OF 145.1.2.2 (Continued): Caution: Due to spalling issues under high stress/strain/reverse-high-loading conditions, typically se
42、en on carrier-based aircraft, not all applications are appropriate for HVOF repairs. Therefore, HVOF must be a pre-approved repair process for each specific location prior to repair application. 5.1.3 Surface Modification of Aluminum Alloys: 5.1.3.1 Hard Anodize: Hard Anodizing is usually limited to
43、 a build-up of about .002 inch. A better hard anodizing success rate is usually achieved on 7XXX series Aluminum as compared to 2XXX Aluminum series. Some processors can build up hard anodize to .006 inch for 7XXX series Al alloys. Caution should be taken not to affect the fatigue properties of the
44、repaired section, since the harder surface of the anodize will downgrade the fatigue life. Reference to reliable data on the fatigue impact due to hard anodizing is recommended. It is important to note that a build-up of .001 inch represents a total hard anodize thickness of .002 inch. Shot peening
45、(or other residual compressive surface stress process) is required before plating. This repair can be used to restore out-of-tolerance dimension of anodized surfaces when fit and function are affected. Hard anodize is used on Class 2 materials only. 5.1.3.2 Chemical Conversion Coating: Mechanically
46、damaged areas on base metal and from which the anodize surface has been removed may be touched up using chemical conversion materials MIL-C-81706 Class 1A coating and an applicable method of application (brush or immersion). Normally, the reworked areas should not exceed 5 percent of the total anodi
47、zed area of the component. This repair can only be used to restore corrosion resistance of damaged surfaces where fit and function are not affected. This repair is used only on Class 2 materials. Chemical conversion coating can be used to repair chromic, sulfuric and hard anodize surfaces. For hard
48、anodized surfaces, chemical conversion touch up can be used in areas not subjected to abrasion. 5.2 Type II (Repair with Bushing): 5.2.1 Diameters: It is generally accepted that bushings can be installed up to an oversized diameter of .060 inch, since a rework allowance is usually included in the or
49、iginal design. This should be confirmed by OHM/CMM or suitable strength analysis. For new components, it is preferred to limit the oversize to .020 inch, since the rework allowance will be affected. Although the above limits can be exceeded (if structural strength analysis shows positive margins of safety), care should be taken not to reduce the flange support area. Also, potential “punch thru” of the mating nut or bolt head under axial thrust
