Industrial Machinery Repair Episode 2 Part 13 potx

534 Maintenance Welding different voltages, it may save time to place lugs on the ends of all the stator leads. This eliminates the necessity for loosening and resoldering to make connections, since the lugs may be safely joined with a screw, nut, and lock washer. Exciter Generator If the machine has a separate exciter generator, its armature, coils, brushes, and brush holders will need the same general care recommended for the welder set. Keep the covers over the exciter armature, since the commutator can be damaged easily. Controls Inspect the controls frequently to ensure that the ground and electrode cables are connected tightly to the output terminals. Loose connections cause arcing that destroys the insulation around the terminals and burns them. Do not bump or hit the control handles—it damages the controls, resulting in poor electrical contacts. If the handles are tight or jammed, inspect them for the cause. Check the contact fingers of the magnetic starting switch regularly. Keep the fingers free from deep pits or other defects that will interfere with a smooth, sliding contact. Copper fingers may be filed lightly. All fingers should make contact simultaneously. Keep the switch clean and free from dust. Blow out the entire control box with low-pressure compressed air. Connections of the leads from the motor stator to the switch must be tight. Keep the lugs in a vertical position. The line voltage is high enough to jump between the lugs on the stator leads if they are allowed to become loose and cocked to one side or the other. Keep the cover on the control box at all times. Condensers Condensers may be placed in an AC welder to raise the power factor. When condensers fail, it is not readily apparent from the appearance of the con- denser. Consequently, to check a condenser, one should see if the input current reading corresponds to the nameplate amperes at the rated input voltage and with the welder drawing the rated output load current. If the reading is 10 to 20% more, at least one condenser has failed. Caution: Never touch the condenser terminals without first disconnecting the welder from the input power source; then discharge the condenser by touching the two terminals with an insulated screwdriver. Maintenance Welding 535 Delay Relays The delay relay contacts may be cleaned by passing a cloth soaked in naphtha between them. Do not force the contact arms or use any abrasives to clean the points. Do not file the silver contacts. The pilot relay is enclosed in a dust- proof box and should need no attention. Relays are usually adjusted at the factory and should not be tampered with unless faulty operation is obvious. Table 24.18, a troubleshooting chart, may prove to be a great timesaver. Table 24.18 Trouble Cause Remedy Welder will not start Power circuit dead Check voltage (Starter not operating) Broken power lead Repair Wrong supply voltage Check name plate against supply Open power switches Close Blown fuses Replace Overload relay tripped Let set cool. Remove cause of overloading Open circuit to starter button Repair Defective operating coil Replace Mechanical obstruction in contactor Remove Welder will not start Wrong motor connections Check connection diagram (Starter operating) Wrong supply voltage Check name plate against supply Rotor stuck Try turning by hand Power circuit single-phased Replace fuse; repair open line Starter single-phased Check contact of starter tips Poor motor connection Tighten Open circuit in windings Repair Starter operates and blows fuse Fuse too small Should be two to three times rated motor current Short circuit in motor connections Check starter and motor leads for insulation from ground and from each other Welder starts but will not deliver welding current Wrong direction of rotation Brushes worn or missing Check connection diagram Check that all brushes bear on commutator with sufficient tension Brush connections loose Tighten Open field circuit Check connection to rheostat, resistor, and auxiliary brush studs Series field and armature circuit open Check with test lamp or bell ringer Electric shock can kill Hazard Factors to consider Wetness Welder in or workpiece Confined space Electrode holder and cable insulation · · · · · · · · · · · · · · · · · · · · Precaution summary Insulate welder from workpiece and ground using dry insulation. Rubber mat or dry wood. Wear dry, hole-free gloves. (Change as necessary to keep dry.) Do not touch electrically “hot” parts or electrode with bare skin or wet clothing. If wet area and welder cannot be insulated from workpiece with dry insulation, use a semiautomatic, constant-voltage welder or stick welder with voltage redusing device. Keep electrode holder and cable insulation in good condition. Do not use if insulation damaged or missing. Use ventillation or exhaust to keep air breathing zone clear, comfortable. Use helmet and positioning of head to minimize fume in breathing zone. Read warnings on electrode container and material safety data sheet (MSDS) for electrode. Provide additional ventilation/exhaust where special ventillation requirements exist. Use special care when welding in a confined area. Do not weld unless ventillation is adequate. Fumes and gases can be dangerous Confined area Positioning of welder’s head Lack of general ventilation Electrode types, i.e., manganese, chromium, etc., see MSDS Base metal coatings, galvanize, paint Figure 24.46 · · · · · · · Do not weld on containers which have held combustible materials (unless strict AWS F4.1 procedures are followed). Check before welding. Remove flammable materiels from welding area or shield from sparks, heat. Keep a fire watch in area during and after welding. Keep a fire extinguisher in the welding area. Wear fire retardent clothing and hat. Use earplugs when welding overhead Containers which have held combustibiles Flammable materials Welding sparks can cause fire or explosion ·· · · · · · · · · · · · Select a filter lens which is comfortable for you while welding. Always use helmet when welding. Provide nonflammable shielding to protect others. Wear clothing which protects skin while welding. Carefully evaluvate adequacy of ventillation especially where electrode requires special ventillation or where gas may displace breathing air. If basic electric shock precautions cannot be follwed to insulate welder from work and electrode, use semiautomatic, constant-voltage equipment with cold electrode or stick welder with voltage reducing device. Provide welder helper and method of welder retrieval from outside enclosure. Process: gas-shielded arc most severe Arc rays can burn eyes and skin Confined space Metal enclosure Wetness Restricted entry Heavier than air gas Welder inside or on workpiece Figure 24.46 continued 538 Maintenance Welding Safety Arc welding can be done safely, provided that sufficient measures are taken to protect the operator from the potential hazards. If the proper measures are ignored or overlooked, welding operators can be exposed to such dan- gers as electrical shock and overexposure to radiation, fumes and gases, and fire and explosion, any of which could cause severe injury or even death. With the diversification of the welding that may be done by maintenance departments, it is vitally important that the appropriate safety measures be evaluated on a job-by-job basis and that they be rigidly enforced. A quick guide to welding safety is provided in Figure 24.46. All the potential hazards, as well as the proper safety measures, may be found in ANSI Z-49.1, published by the American National Standards Institute and the American Welding Society. A similar publication, “Arc Welding Safety,” is available from the Lincoln Electric Company. Appendix A Written Assessment Answers Safety Lubrication Bearings Chain Drives Belt Drives Hydraulics Couplings 1. C A A C D D A 2. A C A A A B A 3. C B A B A D A 4. A C D C A C A 5. C A D C C A D 6. A C D A C C C 7. B B A A C C C 8. C D B A D B A 9. A C A B B A C 10. D A A B C B C 11. B C C B C D D 12. C B A C C B C 13. D C D C C A C 14. A B B D A A A 15. B B B D D C B 16. B A A A A A B 17. A C C A D 18. D A A C 19. A B D A 20. B C C D Index A Accelerometers, 12 Aerodynamic instability, 276 Agitator failures, 359 Agitator installation, 357 Agitators, 353 Alignment, 215 Assembly errors, 57 Axial fans, 262 Axial flow pumps, 399 B Backlash, 294 Baghouse failures, 257 Baghouse installation, 252, 258 Baghouse performance, 251 Baghouses, 245 Balancing, 57, 64, 66 Balancing standards, 68 Ball valves, 180 Bearing failures, 111 Bearing installation, 104, 107 Bearing interchangability, 112 Bearings, 71, 166 Best Maintenance Repair Practices, 1, 2, 6 Best Maintenance Repair Practices Table, 3, 4 Bevel gears, 296 Blower failures, 280 Blowers, 250, 275 Blowers, 261 Bullgear compressors, 136 Butterfly valves, 182 C Calibration, 17 Caliper, measurement tool, 390, 394 Cavitation, 419, 422, 425 Center of rotation, 58 Centrifugal compressors, 133, 160 Centrifugal fan failures, 276 Centrifugal fans, 261 Centrifugal pump failures, 423 Centrifugal pumps, 395 Chain conveyors, 205 Chain Drives, 120 Chain Selection, 122 Chain Installation, 123 Circular pitch, 288 Cocked rotor, 59 Compression couplings, 216 Compressor failures, 160, 164, 170, 176 Compressor installation, 139, 148, 156 Compressor performance, 137, 146 Compressors, 133 Control valves, 180 Conveyor installation, 204, 206, 212 Conveyor performance, 203, 206, 209 Conveyors, 203 Coordination, 23 Coupled imbalance, 63 Coupling installation, 230 Coupling lubrication, 233 Coupling selection, 227 542 Index Couplings, 215 Cyclone performance, 255 Cyclone separators, 253 D Diametrical pitch, 288 Discipline, 10 Dust collectors, 245 Dynamic imbalance, 61 E Elliptical bearings, 85 Estimating, 19 Estimating labor cost, 21 Estimating materials, 22 Estimating time, 21 F Fan failures, 276 Fan installation, 269 Fan laws, 267 Fan performance, 265 Fans, 250, 261 Flanged couplings, 215 Flexible couplings, 218, 235 Fluid power, 190 Fluidizers, 275 G Gate valves, 181 Gear couplings, 218 Gear damage, 304 Gear dynamics, 302 Gear failures, 302, 309 Gear pumps, 416 Gearboxes, 283 Gears, 283 Globe valves, 183 Grease, 335, 337 H Helical gears, 297, 308 Hydraulics, 314 Hydraulic troubleshooter, knowledge, 314 Hydraulic maintenance person, knowledge, 315 Hydraulic, best maintenance practices, 316, 317 Hydraulic maintenance improvements, 323, 324, 325, 326 Herringbone gears, 302, 309 Human senses, 11 I Imbalance, 60, 62, 63, 179 Inspections, 11 Installation, machinery, 348 K Key length, 60 Key stress calculations, 239 Keys and keyways, 236 Keyway tolerances, 238 Knowledge Assessment, 27 L Lockout/Tagout, 53 Lifting, 54 Lubricating fluids, 101 Lubrication, 14, 15, 101, 233, 327, B148 Lubrication, best maintenance practices, 346 Lubrication, storage, 346 Lubrication systems, 167 Index 543 M Machine Guarding, 55 Machinery, installation, 348 Machinery, foundation, 348 Maintenance, definition of, 5 Master schedule, 10 Mean-time-between-failure, 13 Mechanical conveyors, 205 Mechanical imbalance, 57 Mechanical seal installation, 379 Mechanical seals, 364, 367, 376, 405 Micrometers, 386, 387, 389, 391, 392 Miter gears, 296 Mixer failures, 359 Mixer installation, 357 Mixers, 353 MTBF, 13 Multistage pumps, 400 N Net positive suction head, 421 O Oil analysis, 12 Oil whip, 118 Oil whirl, 118 P Packed stuffing box, 363, 404 Packing, 361 Packing failures, 383 Packing installation, 369 Partial arc bearings, 86 Phase, 62, 67 Pitch diameter, 286, 291 Plain bearings, 76, 79, 84, 100, 101, 104 Planning, 19 Plate-out, 276 Pneumatic conveyors, 203, 246 Positive displacement compressors, 140, 164 Positive displacement pump failures, 431 Positive displacement pumps, 408 Predictive maintenance, 10 Pressure relief valves, 159 Preventive maintenance, 7, 8, 9, B16410 Preventive maintenance procedures for Chain Drives, 131 Preventive maintenance procedures for Hydraulics, 318, 319, 320 Preventive maintenance procedures for V-Belts, 48, 459 Process instability, 280 Pumps, 395 R Reciprocating compressors, 146 Reciprocating pumps, 409 Record keeping, 24 Rigid couplings, 215, 235 Rolling element bearings, 76, 87, 93, 100, 102, 105 Rotor balancing, 57 S Safety, 50 Safety, risk assessment, 51, 52 Scheduling, 22 Screw compressors, 143 Screw conveyors, 208 Seal failures, 383 Seals, 361 Sensors, 12 [...]... Valve problems, 20 0 Valves, 167, 194 Vibration sources, 57 Viscocity of oil, 3 32 T Thermodynamics, 138 Thresholds, 13 Tilting pad bearings, 86 Troubleshooting, 111, 160, 164, 170, 176, 20 0, 25 7, 27 6, 28 0, 3 02, 309, 359, 383, 423 , 431, 440 W Welding, maintenance type, 460 Welding, SMAW stick, 463, 464 , Welding, FCAW 466–471 , Welding, GMAW 471–475 , Welding, GTAW 476–491 , Worm gears, 29 9 ...544 Index Shaft speed calculations, 447 Shaft stress calculations, 24 3 Shaft and sheave alignment, 453, 454 Sheave inspection gauges, v-belt type, 454 Skills assessment, 26 Split couplings, 21 6 Spur gears, 28 3 Static imbalance, 61 Steam trap failures, 440 Steam traps, 4 32 Steam traps installation, 438 V V-Belt, 441 V-Belt, maintenance requirements, 451 V-Belt, selection . 21 Estimating materials, 22 Estimating time, 21 F Fan failures, 27 6 Fan installation, 26 9 Fan laws, 26 7 Fan performance, 26 5 Fans, 25 0, 26 1 Flanged couplings, 21 5 Flexible couplings, 21 8, 23 5 Fluid power,. performance, 20 3, 20 6, 20 9 Conveyors, 20 3 Coordination, 23 Coupled imbalance, 63 Coupling installation, 23 0 Coupling lubrication, 23 3 Coupling selection, 22 7 5 42 Index Couplings, 21 5 Cyclone performance,. interchangability, 1 12 Bearings, 71, 166 Best Maintenance Repair Practices, 1, 2, 6 Best Maintenance Repair Practices Table, 3, 4 Bevel gears, 29 6 Blower failures, 28 0 Blowers, 25 0, 27 5 Blowers, 26 1 Bullgear