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
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3、blication 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: +1 724-776-4970
4、 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR5717AEROSPACEINFORMATION REPORTAIR5717Issued 2009-12 Reaffirmed 2014-12 Mitigati
5、ng Wire Insulation Damage During Processing and Handling RATIONALEAIR5717 has been reaffirmed to comply with the SAE five-year review policy. 1. SCOPE Wire and cable products progress through a series of handling or operational steps from the time they leave the manufacturer, and until a finished ha
6、rness or assembly is ready for installation on a vehicle. Throughout these many steps, environmental or processing conditions may be present which can generate damage detrimental to the wire or cable and/or its intended application. 1.1 Application This document discusses the various forms of wire a
7、nd cable damage that may occur in an aerospace manufacturing environment. Characteristics of the different types of processes and/or equipment are described and associated with the types of damage as applicable. Mitigating actions are suggested where possible. 2. RELATED DOCUMENTS There are no refer
8、enced publications specified herein. 3. EVIDENCE OR INDICATIONS OF DAMAGE 3.1 Insulation or Jacket Shrinkage Insulation shrinkage (snapback), normally, is not immediately evident and is only discovered later in processing, or harness fabrication when the wire is cut or heated and the insulation snap
9、s back. Excessive tension on the wire will stretch it causing the entire wire to elongate. Constant tension on the wire or jerking will yield the same results. The conductor will yield, but the insulation remains in the elastic region of its stress-strain curve. Thus, when tension is relieved, and t
10、he insulation is free to move, it will return to its original dimension exposing the conductor. Frequently, thisis the only evidence that the wire has been under too much tension. Measurement of conductor properties will usually not reveal the prior existence of too much tension. Wire manufacturers
11、routinely monitor insulation shrinkage as a check of their processing conditions in addition to a constant monitoring of tension. 3.2 Abrasion and Cuts Here, the surface of the insulation will show scuff marks from contact with rough surfaces. The culprits may be rough or improperly sized wire guide
12、s, sheaves that do not rotate, or counter wheels and pinch rollers, with rough or serrated surfaces. Serrated rollers/wheels, under too much pressure, frequently leave “tractor marks” along the surface of the insulation. If the serrations are sharp, and the impressions deep, it is possible to observ
13、e insulation cuts in some cases. 3.3 Crushing or Flattening Crushing and flattening can occur in many situations and processes and is frequently the result of the actions of careless personnel. It is usually the result of having too much force applied by a pinch roller and its corresponding wheel. N
14、ot all systems work in the same manner. Some may be set for a predetermined force that remains constant even with dimensional changes in the wire or cable. Some may lock into position once a preset force has been reached. There have been cases where processing twisted, shielded and jacketed cables,
15、with this type of mechanism, has caused crushing to the point of shorting the conductors of the twisted pair together without any external evidence of damage. Conductor exposure in primary wires, removed from cables, has also been observed. 3.4 Conductor Kinking The same conditions that lead to insu
16、lation shrinkage can cause conductor kinking. The most insidious cases are with small gauge, foam dielectric coaxial cables. In these cases, when the dielectric snaps back, it causes the conductor to compress and form an omega-shaped kink. Eventually, this kink will short to the shield or even penet
17、rate it. In very extreme cases, conductor kinks have been seen in primary wires. Small gauge, foam dielectric coaxial cables are subject to misidentification as to their true nature and are handled as if they were a large gauge, primary wire. They are then subjected to excessive tension and tight be
18、nd radii that can create internal damage and kinking. 3.5 Jacket Wrinkles Jacket wrinkles are a sign that the cable has been bent tighter than its specified minimum unsupported bend radius, as defined in AS50881. Wrinkles become a problem when pulling cables during an installation. Wrinkles are easi
19、ly caught, snagged, and ripped. Also, the use of a hot-air gun can heat-set the wrinkles such that, when unbent, the wrinkles crack. This is a heat-set problem, not a loss of jacket elongation. 3.6 Twisting (“Live” Cables) All wires, when bent over a radius, will tend to rotate (torque) axially due
20、to their stranded conductors. The same mechanism can be present in multi-conductor cables with twisted primaries. Thus, de-reeling of wires, and running them over sheaves, will tend to introduce a certain amount of twist in the wire. This is visible in wire marking systems as evidenced by a series o
21、f marks that slowly spiral around the axis of the wire. Reversing the direction of bend over successive pulleys or sheaves can minimize twisting. Extreme twisting will create a live wire, or cable, that tends to be unmanageable. Also, a live cable can be created during its manufacture if proper proc
22、esses are not used. 3.7 Reel Set This is usually evidenced by the wire or cable forming tight coils as it is removed from a spool. This is a result of respooling onto spools with hub diameters that are less than recommended by the specification. This can occur in a users shop or from a distributor t
23、hat breaks down large lots. 4. PROCESSES AND OPERATIONAL STEPS Many of these processes listed below can occur more than once, and in various sequences, during the journey from the wire and cable manufacturer and up to the final installation on the vehicle. Frequently, a specific type of damage can b
24、e associated with more than one process (see 3.). 4.1 Packaging, Transportation, and Storage This can be a potential area for abrasions and cuts. Manufacturers try to package reels and spools to survive reasonable transportation conditions, but the unexpected can always happen. Careless forklift ope
25、ration can penetrate boxes or protective wraps on large reels. Outdoor storage can invite water damage or ingress of moisture laden air into the conductor due to temperature cycling. Long-term storage should be in a temperature and humidity controlled environment. Always inspect packaging for mechan
26、ical or moisture damage upon receipt. SAE INTERNATIONAL AIR5717 2 OF 44.2 Handling Reels and Spools Abrasion, cuts, crushing, and tangles are prominent problems. Unrestrained wire or cable ends are prone to damage if not secured within the confines of the reel flanges. Loose ends may be crushed by t
27、he spool flange itself or actions by personnel who are not observant. If samples are removed from a spool, always rewind tightly and secure the ends. Handling of spools with unsecured wire or cable can cause layers to shift and create tangles.These types of problems also may cause personnel injuries
28、. 4.3 Payoffs, Take-ups, and Respooling These processes have the potential for creating all of the identified forms of damage. Start-stop processes, such as automated cut and strip operations, can also stretch wires due to jerking motions unless closed-loop controllers are used. Another source is th
29、e most basic of de-reeling set-ups where a spool, or reel, is supported on a horizontal shaft, and the wire, or cable, is pulled off by hand. If the weight of the total spool is very large, it can require considerable force to start the de-reeling process. Another complication is that the spool is u
30、sually left to revolve on its own, thus leading to loose, overlapping coils that then become tangled. This is identical to the birds-nests that occur on fishing reels. High-speed systems, such as marking lines, automated cut and strip operations, and commercial respooling lines, are often supplied a
31、s integrated packages. That is, they will have powered payoffs and take-ups, tension control via feedback loops, and, frequently, wire accumulators (dancers). These features are designed to control the acceleration and deceleration of the wire and ultimately the tension on the wire. When building an
32、 “in-house” system, these features should be incorporated. Failure to do so may result in wires being subjected to sharp jerks or excessive tension. When paying off from a revolving spool, always pay off from the bottom of the spool. Again, tightly secure the ends before removing the spool. As the q
33、uantity of wire on a large spool is used up in processing, it is frequently a common practice to respool it onto a smaller capacity spool. Care should be taken to use a spool with the same hub diameter as was used originally. Hubs that are too small will introduce “reel set” and will result in unman
34、ageable wire. The same precautions should be observed for take-up spools in “single-filament” operations where multiple lengths of wire are marked and taken up as one length to be cut up at the harness board level. In this sort of system, a closed-loop, tension control system is absolutely mandatory
35、.4.4 Marking, Measuring, Cutting, and Coiling These processes share many of the similarities found in Section 4.3. Some systems use driven wheels and pinch rollers to move the wire through the system. If the various parts of the system are not synchronized, the wheels may be trying to move the wire
36、while another part of the system has stopped the wire. This is not uncommon in rapid start-stop processes such as automated cut and strip operations. These systems may cause stretched, crushed, or abraded wire. If any damage is noted, trace the wire as it goes through the process to see where damage
37、 is occurring. The output of some systems may go into coiling pans while others may have takeup spools. In the latter is used, be aware of spool hubs that are too small. 4.5 Stripping and Termination Some of the concerns here are abrasions, cuts, and crushing. Sometimes these processes are semi-auto
38、mated. Attention should be directed at grippers used to hold the wire. Even in hand stripping, an incorrect gripper choice can damage the insulation of a wire. In a fully automated system, all of the previously noted processes come into play. SAE INTERNATIONAL AIR5717 3 OF 44.6 Routing and Tying (Ha
39、rness Boards) Since this is a very labor intensive operation, inattentive personnel are the source of most damage. This is a prime area for wire and cable to be bent on radii much smaller than specified minimums. A well designed harness board can preclude most occurrences. Also, harnesses on horizon
40、tal boards can be impacted by tools and other objects that are carelessly dropped. Be particularly observant for impact damage. Lacing tape and plastic mechanical straps are frequently used as temporary manufacturing aids and are cut off of the harness at some point during the total assembly process
41、. Personnel should be instructed to cut through the tape knot or strap hub rather than cutting into the harness. 4.7 Identification and Protection Practices here are usually dictated by engineering philosophy. Harnesses frequently carry markers (paint or ink) to aid in locating the harness within th
42、e airframe. Any such use should add only color to the harness and not a built-up coating. It is good practice to bag and box harnesses after assembly and until they can be installed. During fabrication, connectors should always be bagged or capped. 5. SUMMARY In a single word, awareness is the key t
43、o identifying and preventing damage. All shops are similar but unique due to the product and the culture. Many of the controls needed to prevent damage may be found in Materials and Process documents.6. NOTE A change bar (|) located in the left margin is for the convenience of the user in locating a
44、reas 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, including technical revisions. Change bars and (R) are not used in original publications, nor in documents that contain editorial changes only. PREPARED BY AE-8A SYSTEMS INSTALLATION COMMITTEE OF AE-8 AEROSPACE ELECTRONICS & ELECTRICAL SYSTEMS DIVISION SAE INTERNATIONAL AIR5717 4 OF 4
