Connections of the leads from the motor stator to the switch must be tight.. The line voltage is high enough to jump between the lugs on the stator leads if they are allowed to become lo
Trang 1534 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
Trang 2Maintenance 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
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 Check with test lamp or bell
Trang 3Electric shock
can kill
Hazard Factors to consider
Wetness Welder in or workpiece Confined space Electrode holder and cable insulation
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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
Trang 4·
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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
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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
Trang 5538 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
Trang 6Appendix A Written Assessment Answers
Safety Lubrication Bearings Chain Drives Belt Drives Hydraulics Couplings
Trang 8A
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
Trang 9542 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
Trang 10Index 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
Trang 11544 Index
Shaft speed calculations, 447
Shaft stress calculations, 243
Shaft and sheave alignment, 453,
454
Sheave inspection gauges, v-belt
type, 454
Skills assessment, 26
Split couplings, 216
Spur gears, 283
Static imbalance, 61
Steam trap failures, 440
Steam traps, 432
Steam traps installation, 438
T
Thermodynamics, 138
Thresholds, 13
Tilting pad bearings, 86
Troubleshooting, 111, 160, 164,
170, 176, 200, 257, 276, 280,
302, 309, 359, 383, 423, 431,
440
V
V-Belt, 441 V-Belt, maintenance requirements, 451
V-Belt, selection of, 443, 444 V-Belt tension guage, 453, 457 Valve actuators, 187, 198 Valve capacity rating, 185 Valve installation, 193 Valve performance, 185, 186, 193 Valve problems, 200
Valves, 167, 194 Vibration sources, 57 Viscocity of oil, 332
W
Welding, maintenance type, 460 Welding, SMAW, stick, 463, 464 Welding, FCAW, 466–471 Welding, GMAW, 471–475 Welding, GTAW, 476–491 Worm gears, 299