Document XJw3Jgqor8we6JMdB3qxxVjK

1 Softlr*o shaft In cosi-steel rotor's A Hwliontal-ihoft essembly. Rotor mode of four cast-iteel sections hod in rtm'7 bore, oxponded by Induction hooting 4 heoted to about 255 F by Induction for removal from shoft, which was dem^td*;st A Little Heat Eases Press-Fit Rotors on Their Shafts Relatively small temperature Increase may expand a large-rotor bore more than its press-fit tolerance. N L Rea, noted erection engineer, telfs how to ovoid trouble In the heating of these rotors for assembly on or removal from their shafts '* To coi-O-pRtsvrit a large flywheel or generator rotor on its shah is a dif ficult and uncertain job. It is con* aidcrably simplified by heating the rotor or flywheel, and sometimes by cooling the shaft Contrary to common belief, only a comparatively small in crease In rotor temperature is needed for a eliding fit on a cold shaft. This temperature increase can be obtained by induction heating, electrical heaters, steam or hot water, as in the table. Induction Heating. Temperoturo of 212 F will not damage even the lower* ' grade of electrical insulations, but will expand the bore of many rotor hubs to where they are larger than their shafts. Where a light press fit is re quired a rotor can be heated by indue* lion so it slides oh its shoft For heavy press or shrink fits, induction heating materially reduces the work of press ing a rotor on its shaft This method heats ropidly, is clean and easily ap plied. It Is especially helpful when re moving a rotor from its shaft. Heating by induction is produced by electric currents induced in the rotor's outer eurfoce, end not by resistance in the electrical conductors around the rim. It is therefore possible to heat ond expand a rotor's rim and spider before the heat is conducted down into the shaft We have obtained over 212-F rim-temperature rise before the beat reached the theft Expansion of the rim stretched the hub away from the shaft under these conditions. Hooting Winding. Fig. 1, shows the shaft being lowered into the bore of a cast-steel rotor expanded by induction heating. Heating was done by bare rViv 250,000-cm cable, Insulated from wound around the rotor's rim betww^ spokes and hub, as at A, and connectm;-.. to a 60-cycle power source. Stop B are lashed to the shoft to correctly in the rotor hob. .-JV* All sections of the winding are in the some direction and connertm^** in scries to give them all the same (**'* ity. This makes the rolor ri equivalent of a single-turn *ecoDi*f7:H(- Experience proves there U no `Pjijof.vj ciable gain in putting the around the rim, Fig. 1 sad .**, winding the cable on the rim * w; conference. Also, insulated be used because heating U c4U*"f eddy-current and hysteresis the iron, end not from resists0* in the cable. jjr&i Electric-Oven Hearing, Inducth 76 (682) POWER Ne*emh*,fi tog should not be applied to steel-plate rotors because the heat buckles ond dishes the plates. Heat such rotors in iempor*ry oven of packing-case toro id lined with sheet iron or batters. Make the oven lorge enough to fit over the piece to be heated. In electric heaters 5- lo 10*kw is enough to best the largest rotor. Baffle the oven with.sheet iron so the rotor is bested by air circulation and not di* reel radiation from the heaters. This - insures uniform heating and avoids damaging the rotor by unequal besting in the different sections. Checking Bore Eaponslon. Provido the besting oven with s small hatch so the bore's expansion can be checked with out stopping the heeling operation. Make a pin gage to fit the bore before starting the heating. Keep the gage lying on the shaft when not in use so it remains at shaft temperature. Check the bore's expansion with feelers be tween one end of the gage ond bore. Electric Hcotcn. Any available healers ean be used if applied intelligently. One large rotor was covered with tar paulins and seven 750-wott lamps hung between the rotor's spokes several days. Theta provided enough heat to expand the rotor so it would slide easily onto the shaft. If heaters are not available they can be made from iron telephone wire. Wind 100 turns on a %*in. pipe mandtel. Slip the coil off the mandrel stretch to separate the toms ond try it on 11$ v. It should take about 10 tmp and get nearly red hot. If It doesn't, shorten or lengthen (he col) to get satisfactory temperatures and asks additional coils like the sample. String porcelain knobs on Iron rods or oitseh them to a strap-iron framework with insulators on stove bolts and con nect enough coils in multiple to give required heater capacity. Another method is to threod por celain knobs on three concentric rings. Fig. 3. Here four 400-fl telephone wires in multiple on 11$ v toko about 35 kw. At frequent intervals tie the wires together and to the knobs. To use the heaters, support the rotor horizontally on blocking with the heaters placed 90 deg apart around it, with sheet-iron baffles between the two. Have the baffles extend vertically to top of rotor. Lower a square oven box over rotor and healers, and natural air circulation will transfer the heat evenly to all parts of rolor. A standard transformer drier that takes heated air from the bottom of the oven box- ond delivers it to the top baa been used to advantage. Verticol-ShoH Rotors. To assemble a vertical-shaft rotor, first op-end the shaft ond bolt it to the dummy coup ling plate in the assembly pit If the station has one, as it should. Otherwise, set the coupling in some convenient spot that carries weight of complete rotor', protecting the coupling face, and block the shaft securely, Fig. $. Center the shaft as nearly vertical as condi tions permit. Place stop blocks on the coupling to locate rotor on shaft cor rectly, If the latter does not have a shoulder for this purpose. It may re quire several' hours for the rotor to coo) enough to grip the shaft, so make sure it Is supported in the correct lo cation. One erector neglected to put stop blocks on the shaft and had to hold the rotor with the crane several hours before he dared slack off. Adjust slings on the rotor's first section until it hangs level, then lower it over the shaft end far enough to center the bore on the shaft Rotote the rotor to align key and keyway. Put match marks of white paiot or chalk on end of crane and its track, end on crone carriage and girder where tho crane man can ace them. This saves time when lowering the hot' section on the shaft Put the rotor with the slings on its Relatively Small Increase In Temperature ot Rotor Man tipantf Its Bore More Than the Press-fit Tolerance H*itir> r . method ... ?j'. | !< 0J|............ <*"..... Bo> di#, In. 20 IB 90 40 24 24 Fretting Bor# ellowence, in. expanded. In. 0.005 0.012 0.005 0.017 0.015 0.017 0.040 0.030 0.039 0.035 0.023 0.029 Oven temp, F 356 275 248 257 212 212 Room temp, f 66 68 6B 77 68 60 3Heoter unit. Hooter wire end Insula tors cuemblod on 3 concentric rings 4 Rabbet In hub. If hub has a robbet, chip It out before-storting assembly support and place the heatera around it and heat until the bore has expanded the required amount Place the thrust block in the oven so it will expand if it must be used as a strong bock should the hot rotor hang up on the shaft Ar range jacks end blocking for instant use.- When bore has expanded, lubri cate the shaft lift off the oven box and quickly lower rotor over shaft Hooting the Rotor. Adjust tho slinga on next section and heat at least 24 hr, or until shaft and first section cool to room temperoturo. Check hubs of all sections, which may have rabbet fits (or manufactur ing purposes. If rolor sections have a rabbet like Fig. 4, chip out the recess or cut off the spigot so clearance Is ample to take care of expansion of the heated section. Shaft and keys locate and hold the rotor sections in correct relation so the rabbet fit serves no purpose after ahop machining. Rotor-Section Eipontlon. Remember that the rotor sections expand in length as well as In diameter. Weight of the first section holds it down against the shaft shoulder or atop blocks as ft cools. The first section being cold chills the lower end of the next hub i/0ws . November 1949 (683) 77