Tn 36 Armature Banding

L APPAICA R TR Tech Note No. 36 AT Armature Banding With Fiberglass C ELE US TECH NOTE NO. 36 Reliable Solutions Today! EA SA SER N IO IC V T E A IA SSOC ARMATURE BANDING WITH FIBERGLASS By Chuck Yung Technical Support Specialist Electrical Apparatus Service Association, Inc. St. Louis, Missouri INTRODUCTION When banding armatures or wound-rotors, the usual procedure is to duplicate the original band in appearance and size. Often, the winder has a great deal of discretion and may just put on what “looks right” and send the arma- ture on its way. Fortunately, the tensile strength of the polyester resin-impregnated fiberglass band products is high—enough so that this casual method is rarely a prob- lem with small armatures. Problems can occur with larger armatures, however, especially when converting armature banding from steel to fiberglass, or when redesigning for operation at higher speeds. In these circumstances, the following guidelines and “tricks of the trade” will help ensure a safe rewind while Wire band strength = Turns x Ultimate tensile strength minimizing material waste. GENERAL PROCEDURES Now divide the wire band strength by the tensile strength General procedures for converting steel armature band- of the selected fiberglass banding material to determine ing to fiberglass should include: the number of turns to use for an equivalent fiberglass band. • Calculate the weight of a coil extension (before install- ing the coils). Wire band strength = Turns (fiberglass) • Determine the required tensile strength of the band. Tensile strength (fiberglass) • Select the type of fiberglass banding material to use, depending upon the application. TABLE 1: WIRE BAND STRENGTH • Calculate the number of turns of fiberglass banding Ultimate Tensile Strength Elastic Limit Strength Non- Non- needed to replace the steel band. Size Magnetic magnetic Magnetic magnetic • Preheat the wound armature to 120° - 135° C (250° - (AWG) lbs kg lbs kg lbs kg lbs kg 275° F). 14 774 351 738 335 503 228 443 201 • Provide a ventilation gap between the band and the 15 615 279 585 265 400 181 321 146 core/commutator. 16 486 220 462 210 316 143 277 126 • Edge the band area with tadpole edging tape. 17 387 176 368 167 251 114 221 100 • Apply the banding material at the proper uniform 18 306 139 291 132 199 90 174 79 tension. 19 243 110 231 105 158 72 138 63 • Fuse the last turn to the underlying turns before re- 20 193 88 183 83 125 57 110 50 leasing the tension. • Wrap the band with heat-shrink mylar before curing. The choice of glass banding material should take into account the temperature and humidity of the application. CONVERTING STEEL BANDING TO FIBERGLASS High humidity banding material, for example, is manufac- When replacing a steel band with fiberglass, the required tured using special moisture-resistant yarn. Other glass turn calculations are straightforward. First, determine the banding materials may be better suited for different envi- wire band strength by multiplying the number of turns by ronmental conditions or for higher or lower speed the ultimate tensile strength of the wire. applications. (Update - 10/03) TN36-1 35 mm) width.015” (. F = Fraction of whole coil CALCULATING CENTRIFUGAL FORCE E = Length of coil extension L = Loop length of the coil (add all dimensions) Sometimes it is necessary to calculate the centrifugal w = Weight of one coil extension force acting on a band—e.66 x 1.125° C (250 . ensuring good r = Radius at the band fusion of the banding material layers. armature speed. Tensile strength is derived from the tion of the centrifugal force that is transferred number of fiber strands the tape has.436 Newtons] mum of 1/2” (12.35 mm) of banding material width.H 33. Hoop stress represents the por- Tensile strength. They are generally not under tension and there. To ensure proper air flow .822 lbs through the armature.g.4 mm) 1580 717 1055 479 ing material (see Table 2): This table is for . The following information is needed in order to calculate Some manufacturers and service centers use an “effec- the required banding for a given armature: tive turns” multiplier of 0.25 is a correction factor for hoop stress and other factors. as shown in Figure 2). robbing it of some of its content. not base speed) ture below 110° C (230° F) will not produce sufficient resin For example. be sure to discount the first two turns applied.25 is the inverse of 0. The centrifugal force acting on a rotating body is n = Number of coils represented by this formula: F = 0. That weight of the coil and then by the number of coils to get the means 1/2” (12. not base resulting calculation will be the same. Finally.25 x 33. If the banding material has a different thread count. (See Figure 1.) Provide ventilation gaps.7 mm) wide banding tape has 40 ends. F = L When it is necessary to calculate the required turns of W= Fxwxn E banding precisely.Armature Banding With Fiberglass Tech Note No.. speed) Estimating the weight of the coil extensions. 1180 In the above equation. If preheating is with a 10” (254 mm) radius and a coil extension weighing not possible.000028416 x (40 x 10 x 17252) = 33. use fiberglass banding with a higher resin con- 40 lbs (18.8) when • Diameter at the band area calculating the overall retained tension of the band.822 = 54. A preheat tempera- n = rpm (max. The • Speed of rotation (max. Where: fore do not contribute to total band strength.7 mm) wide. 1. when redesigning for a higher W= Combined weight of coil extensions speed. armature speed. Apply the first turns. plus 2 sacrificial turns Tape Width lbs kg lbs kg 615 3/8” (9.4 mm) wide tape has 80 ends. multiply this fraction by the ends per 1/4” (6. first weigh one coil (before rewinding the armature). Then divide the • Number of ends in the banding tape (tensile strength length of the coil extension (add all dimensions) by the loop of the banding material) length of the coil (add all dimensions) to find what fraction Most. To find • Width of banding material the approximate weight of the coil extensions. but not all. strength.144 kg) would be: tent and add 2 hours to the cure cycle.99. banding-tape manufacturers use 20 of the whole coil it is. E Core length sented here do not apply.38 mm) thick banding tape with 20 ends 1. not from the resin circumferentially to the band. 36 Based on the ultimate tensile strength of #15 magnetic TABLE 2: FIBERGLASS BANDING TENSILE STRENGTH steel banding in Table 1. that amount of force would re- quire 57 turns: Insulation Class A .000028416 x Wrn2 BANDING PROCEDURE Where: Preheat the armature. the calculations pre. and 1” (25. Preheating the armature in a curing oven at about 120 . at 1725 rpm the centrifugal force on a band flow to fuse the layers of banding material. approximate combined weight of the coil extensions.8 (1.25 = 36 turns per 1/4” (6.525 mm) 590 268 395 179 Or 1/2” (12.10/03) TN36-2 . Wrap the first couple of turns of (Update . ventilation gaps should be a mini- [.7 mm) 1180 535 790 358 36 turns of 0.00001097 x (18.275° F) makes the W = Weight of the coil extension resin begin to flow as the banding is applied.822 = 28.B Class F .015 x 1/2” of Class A or B fiberglass band- 1” (25.144 x 254 x 17252) = 150. 275° F then shrink material under the first tensioned (120° . and band over it (see Figure 3). least the same area as the original steel band did. This can only be done with a tensioning device (see Figure 4). Remove armature from VPI or oven. remove dip and mylar (if used). 100%. (Update . bake. Use proper banding tension. Uniform application at the proper tension may be the most important (and most overlooked) factor when banding rotating equipment. This stretches or elongates the fiberglass banding material. Edging is best applied under the first tensioned turn of banding material.135° C). The banding material must be elongated 2 . machine to attain full strength. Tension device mounted on lathe. Insert edging. applied an excessive number of turns of banding. banding Edging is best applied 250° . there is virtually no tension or elastic Banding material must be applied under tension by response. This keeps the edging straight and prevents it from curling over.Tech Note No. FIGURE 4: TENSIONING DEVICE Note: Apply edging and banding so that they do not inter- fere with the bore or coils during motor assembly. move the band to one edge of the area to be banded and insert the edging under the banding material while applying the first tensioned turn. tuck the finish end under.10/03) TN36-3 . pro- ducing an elastic response. All that holds the arma. 36 Armature Banding With Fiberglass FIGURE 1: BANDING PROCESS FLOW CHART FIGURE 3: INSERTING EDGING Preheat Install edging Cure armature to and band. so the band is weaker. To do so.” the material tries to return to its original size. When an armature is banded by hand. banding tightly around the armature by hand. It also is important to band over the support rings and to cover at Armature mounted in lathe. For a professional look. check cure. turn of banding material.3% to achieve proper final band tension. Proper tension cannot ture together in such circumstances is that the winder be attained when an armature is banded by hand. creating enough friction to hold the material in place as tension is applied. Note: It is not always possible to use edging due to insuffi- cient clearance between the armature and the stator bore. FIGURE 2: VENTILATION GAPS Inner ventilation gaps should be 1/2” minimum. mylar (if used). Starting these first turns where the finished band will cover them improves the appearance of the final band. Because fiberglass has a “memory. MO 63132 U. Many service centers use shrink. This minimizes the Jasper Fisher.easa. Although this does not mylar over the uncured band... The after an armature has been dipped. Inc. Direct the heat onto the band at the point where 2000.Armature Banding With Fiberglass Tech Note No. Balancing large armatures. This banding seats them flush with the top of the slots. Cold banding Von Roll Isola USA. Traverse quickly to each subsequent groove. The tape serves as a smoother surface finish.A. the material is being applied. on the finished band. Anderson..7 mm) 1” (25. TABLE 3: RECOMMENDED BANDING TENSION Temperature Width of material Rating 1/2” (12. it does produce a and tape over it with an opaque tape. Industrial Motor Repair. Adjust weakens the band. The smoother the finish. a timesaving trick is to band one end. it is essential to avoid sharp edges. If the banding rests directly on the top of the core.) This saves time and in- For random-wound armatures. then to the other end extension. and then traverse the banding material quickly to the first groove and fill it. Fuse the last turn. sures that proper tension is maintained on each band. SC Starting resin flow with cold banding. More shrinkage can cause ridges damage if carbon tracking results in a flashover. the top cause it ensures that the band will not slip. ing coils or slot insulation. Armatures with banding grooves. VPI or dip-and-bake cycles are Fibertek. less bulk on the armature and better heat dissipation. moisture and carbon. Fusing the last turn is important be. the slot fill when inserting the coils to accomplish this. it helps to tie the last turn increase the tensile strength of the band. Place correction weights beneath the Special thanks goes to the following individuals and com- coil extensions.10/03) TN36-4 Version 1100DP35C-1030 . Steve Darby. Inc. Special mylar tapes with a release agent TRICKS OF THE TRADE are available to simplify removal. NY requires a longer bake cycle to fully cure the banding ma- terial. Another technique for avoiding the preheat cycle is to use a heat-gun to start the resin flow during the banding Note: This article was originally published in November process.25 lbs or 11 kg). prevent failures of this kind. available for final balance.S. the less susceptible and-bake cycle. It is much more difficult to remove mylar the band is to a buildup of dirt. Darby Electric Co. TN best done with the armature vertical. IL unbalance caused by varnish buildup. When banding an armature with banding grooves on the armature core (Fig- ure 5). If the banding is edge of a slot may cut the banding and cause it to fail. Large armatures may be ACKNOWLEDGMENTS pre-balanced prior to coil insertion. Heat-seal the top turn of each band. The benefit is not limited solely to visible reminder to remove the mylar before the VPI/dip- appearance. 36 Besides assuring the required band strength. AT C ELE US EA SA 1331 Baur Boulevard • St. Be sure to remove old balance weights first. as the curing resin is extruded be- tween mylar turns. baked and cooled! Mylar band on the commutator end is especially vulnerable to with 5% shrink works best. use of FIGURE 5: ARMATURE WITH BANDING proper banding tension has an another advantage—less GROOVES banding material is needed. Franklin. Avoiding sharp edges. reduce tension to avoid damag. Apply shrink mylar. Schenectady. To cut before the end is heat-fused to the underlying turns. Louis. When applying shrink mylar over the banding material. Inc.4 mm) 180° C 450 lbs (204 kg)* 600 lbs (272 kg)* 220° C 500 lbs (227 kg)* 650 lbs (295 kg)* and then trim off the excess material between bands (the * Maximum recommended banding tension (+/. • (314) 993-2220 • Fax (314) 993-1269 • www. L APPA ICA R TR Electrical Apparatus Service Association. Any time the band is applied over the armature core. Alton. position the coils so that the the tension on the last several turns will be relaxed. Tying and taping shrink mylar. leaving the customary balance weight areas panies for providing information for this article. spirals created by the traverse. That means lower costs.com SER N IO IC V T E A SSOC IA Reliable Solutions Today! Copyright © 2003 (Update .