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Overhead and gantry cranes represent major investment in equipment. Reliable functioning of such equipment is generally vital to operations performed in the areas served by the cranes. Proper installation, operation, inspection, and maintenance of the crane are necessary to ensure performance and to avoid premature breakdowns or accidents which might injure persons working on, under, or near the crane. This section is intended to outline recommended procedures. It’s by no means all-inclusive.
--- Typical heavy-duty overhead crane. UPPER SHEAVE BLOCK ROPE DRUM HOIST GEAR CASE HOIST MOTOR BRAKE TROLLEY TRAVERSE DRIVE UNIT FESTOON CROSS CONDUCTORS RAIL SWEEP TRUCK GIRDER BRIDGE WHEEL BUMPER CONTROL PANEL SERVICE PLATFORM CROSS SHAFT BRIDGE DRIVE UNIT; OPERATOR'S CAB
Manufacturer's instructions should be carefully read, retained, and followed. Attention also must be given to applicable federal standards, OSHA regulations, and state and local codes which include mandatory rules relating to crane inspection and maintenance.
Good maintenance begins with a good installation. Prior to, during, and following erection of the crane, the following precautions should be observed:
1. Crane runway rails should be straight and accurately aligned to the correct span the entire length of the runway.
2. Be sure the crane is assembled in accordance with the match marks and instructions provided by the manufacturer.
3. It’s of utmost importance that girders be square with the end trucks, that the trucks be parallel to each other, and that the bolts furnished with the crane be used for making the connection between the girders and end trucks. These bolts are usually of the ground-body type fitted into reamed holes.
4. Check all connecting bolts for tightness, and be sure lock washers or other locking means have been used as furnished.
5. Check for and remove any loose articles, such as bolts, hammers, or wrenches, which may have been left on top of the trolley or girders or on the platform.
6. Grease bearings on the crane as required. Check and add oil to gear housings as required.
7. Grease the hoisting cables.
8. Be sure the hoisting cable is reeved properly.
9. Check for any oil or grease spillage that may have occurred during erection, and wipe all oil spots dry.
Before the crane is placed in service:
1. Check operation of controllers for intended movement of each of the crane motions. In checking the hoisting unit, it’s particularly important to note that with a three-phase electrical supply it’s possible to have "reverse phasing," causing the hook to lower when the "up" push button, master switch, or controller is actuated. When this condition exists, the automatic limit switch will be inoperative, and hoist operation will be dangerous. To correct this condition, reverse one phase by interchanging any two of the supply wire leads. Don’t rewire push buttons or master switches to effect this correction.
2. Check adjustment and operation of all brakes.
3. Check hoist-limit stops, and adjust for proper operation. The trip setting of hoist-limit switches should be determined by tests with the empty hook traveling in increasing speeds up to the maximum speed. The actuating mechanism of the limit switch must be located so that it will trip the switch, under all conditions, in sufficient time to prevent contact of the hook or hook block with any part of the trolley.
4. Check operation of other limit stops or locking or safety devices which may be installed on the crane or runway.
5. Operate the crane slowly through all motions, over the entire length of runway, entire length of bridge, and entire length of lift, checking for proper performance throughout.
6. New cranes and those in which load-sustaining parts have been altered, replaced, or repaired should be subjected to a load test confirming the load rating of the crane. The load rating should be not more than 80 percent of the maximum load sustained during the test, and test loads should not be more than 125 percent of the rated load, unless otherwise recommended by the manufacturer.
The frequency of inspection and degree of maintenance required for cranes vary with the service to which the cranes are subjected, heavily used cranes requiring more attention than standby or lightly used cranes. Close attention should be given the crane in the first few days and weeks of operation, following which routine inspection procedures should be instituted.
Daily to monthly inspections are recommended to include
1. Operation of all limit switches, without load on hook (the crane motion should be inched or run into the limit position at slow speed for these checks)
2. All functional operating mechanisms for mis-adjustment, damage, or wear
3. Air and hydraulic systems components for deterioration or leakage
4. Hooks for deformations, cracks, and wear
5. Hoisting ropes for broken wires, abrasions, kinks, or evidence of not spooling properly on drum Monthly to yearly inspections should include checks on
1. Loose connections, bolts, nuts, rivets, keys, etc.
2. Cracked, worn, deformed, or corroded members, including rails or beam flanges on which the crane operates
3. Cracked, worn, or distorted mechanical parts such as shafts, bearings, pins, wheels, rollers, gears, pinions, and locking or clamping devices
4. Excessive wear on brake parts, pawls, pins, levers, ratchets, linings, etc.
5. Rope drums and sheaves for excessive wear or cracks
6. Electric or other types of motor for performance and wear of commutator, slip rings, brushes, etc.
7. Chain and sprockets for excessive wear or stretch
8. Crane hooks for cracks, by magnetic particle, dye penetrant, or other reliable crack-detection method; and hook-attaching means including hook nut, locking pin, etc., for security of hook attachment to lower block.
9. Load-limiting or other safety devices installed on the crane
10. Electrical devices, controls, and wiring for signs of deterioration or wear; electrical contactor points for excessive pitting Standby cranes should be inspected at least semiannually, and more frequently in adverse environment.
Written, dated, and signed inspection reports and records need to be maintained, particularly on critical items such as crane hooks, hoisting ropes, sheaves, drums, and brakes. --- shows the first sheet from the Overhead Crane Inspection and Maintenance Checklist published by and avail able from the Crane Manufacturers Association of America, Inc., 8720 Red Oak Blvd., Suite 201, Charlotte, NC 28217. Use of this or similar checklist is recommended. Cranes with identified safety hazards should be removed from service until repairs are completed unless other appropriate pre cautions are taken to eliminate possibility of an accident or injury to personnel.
--- This inspection report is being employed by many users of cranes. (Partial checklist shown.)
A preventive-maintenance program should be established based on the manufacturer's or a qualified person's recommendations. Service schedules and dated detailed records should be maintained.
Since the original equipment manufacturer is usually in the better position to provide replacement parts and ensure their safety, interchangeability, and suitability for the application, it’s recommended that such parts be obtained from the original equipment manufacturer.
A good preventive-maintenance program identifies parts requiring replacement sufficiently in advance of actual need to permit ordering of parts after approaching need is identified; however, for cranes in regular service, it’s generally advisable to carry on hand a reasonable minimum inventory of repair parts. The needed inventory will vary with type and age of crane, service to which it’s subjected, repair history, and general availability of parts. The crane manufacturer can provide lists of recommended spares.
Typical recommended spare-parts lists are apt to include Brake solenoids, coils, disks, linings Hoist-limit switches Contactors Contact kits Timing relays Push-button stations or parts Crane wheels and guide rollers Motor couplings and brushes Current collectors or collector shoes Bearings Load hooks, nuts, and thrust bearings Hoisting ropes Load brake parts On-hand availability of parts such as these can often spell the difference between a long, costly wait for repair and efficient replacement at a convenient time in advance of actual breakdown.
When ordering parts for a crane, observation of the following points can save time and expense:
1. Identify the crane by manufacturer's serial number.
2. Refer to the parts manual furnished by the manufacturer, and identify parts by the numbers given.
3. For cranes with auxiliary hoists, specify whether parts are for main or auxiliary hoist; if for a bucket crane, if parts are for the holding-line or closing-line mechanism.
4. If the crane carries more than one trolley or hoist, specify which trolley or hoist the parts relate to.
5. When ordering brake parts, specify which brake, whether hoist (main or auxiliary), trolley, or bridge.
6. If parts are for electrical equipment or other equipment not shown on the parts lists, describe the part and identify the serial number of the unit for which it’s required.
Before adjustments or repairs are started, several precautions should be taken:
1. The crane to be repaired should be located where it will cause least interference with other operations in the area.
2. All controllers should be placed in the off position.
3. Main and emergency switches should be locked in the open position.
4. Warning signs should be placed on the crane and on the floor beneath the crane or on the crane hook if near the floor.
5. If other cranes are operating on the same runway, rail stops or other means should be provided to prevent collision with the idle crane, or a signal man may be employed to warn off approaching cranes.
Following completion of adjustments and repairs, all guards and safety devices must be rein stalled and maintenance equipment removed before the crane is returned to service.
Adjustments and repairs to cranes should be done by designated and qualified personnel as soon as possible after identification of need, and before further use of the crane if a safety hazard is involved. Adjustments should be maintained for optimal crane performance and to ensure the safe functioning of all systems and components.
Hook deformation is usually a sign of tip loading of the hook or overloading of the crane. If over loading is suspected, other load-bearing parts of the crane should be checked for possible damage due to overloading. Hooks with cracks, or having a throat opening in excess of normal, or with twist from the plane of the unbent hook should be considered for replacement (see ANSI and other applicable standards). Hooks showing wear in the saddle of the hook, which indicates reduction of strength of the hook, also should be considered for replacement.
Any load-bearing parts which are cracked, bent, or excessively worn must be repaired or replaced.
Pitted or burned electrical contacts should be corrected only by replacement and only in sets.
All control stations should be kept clean with function labels intact. Missing or illegible warning labels must be replaced promptly.
Lubrication should be applied regularly to all moving parts for which lubrication is specified and/or indicated by lubrication fittings. Follow the manufacturer's recommendations as to frequency and types of lubricants to be used. Avoid over-greasing of bearings and overfilling of gear cases.
Unless the crane is equipped with automatic lubricators, the same preliminary precautions should be taken for lubricating the crane as for making repairs.
Hoisting ropes require special attention. On cranes in continuous service, ropes should be inspected visually daily, and a thorough inspection should be made at least once a month, with writ ten record made as to rope condition and possible need for replacement. All inspections should be made by an appointed or authorized person. Any form of rope deterioration which could result in appreciable loss of original rope strength should be carefully noted. Conditions such as the following require a determination as to whether continued use constitutes a safety hazard.
1. Kinked, crushed, cut, or unstranded sections
2. Broken, worn, or corroded outside wires
3. Reduction of rope diameter due to loss of core support, corrosion, or wear
4. Damaged end connections or damaged rope wires at the connections Ropes which have been out of service for long periods of time should be checked carefully before service is resumed.
Replacement rope should be the same size, grade, and construction as the original rope furnished by the crane manufacturer, unless otherwise recommended by the crane manufacturer.
Rules governing replacement of ropes are not precise and hence require judgment by an appointed person as to whether the remaining strength and life in the rope are sufficient to permit continued use. This judgment should take into account the service to which the crane is subjected, as well as the observed condition of the rope. For example, many users consider the following to be conditions which produce serious question as to safety of rope for continued use:
1. Crushed, kinked, bird-caged, or otherwise distorted rope
2. Twelve or more randomly distributed broken wires in one rope lay or four or more broken wires in one strand of one rope lay
3. Wear on outside individual wires exceeding one-third of the original wire diameter
4. Evidence of heat damage
5. Reductions in nominal rope diameters of more than 1/64 in. for ropes of 5/16 in. diameter and smaller 1/32 in. for ropes of 3/8 to and including 1/2 in.
3/64 in. for ropes 9/16 to and including 3/4 in.
1/16 in. for ropes of 7/8 to and including 1 1/8 in.
3/32 in. for ropes of 1 1/4 to and including 1 1/2 in.
Wire rope should be stored and handled in a manner which avoids damage or deterioration.
Unreeling or uncoiling rope requires care to avoid damaging the rope or introducing twist.
Before a rope is cut, seizings must be places on each side of the cut location to prevent unraveling of the rope when cut. Apply seizings as follows:
Preformed rope: one seizing each side of cut.
Nonpreformed rope 7/8 in. or smaller: two seizings each side of cut Nonpreformed rope 1 in. or larger: three seizings each side of cut Hoisting ropes should be maintained in well-lubricated condition to reduce internal friction and prevent corrosion. See crane and/or rope manufacturer's recommendations.
The reader is cautioned to recognize that a great many of the recommendations presented in this section are now mandatory under OSHA regulations which became effective in 1972 and are also likely to be mandatory under various state safety codes. It should be further noted that OSHA regulations require cranes to conform to the National Electrical Code (ANSI C1). These various regulations are subject to change. OSHA and other regulations applicable to your location should therefore be carefully checked for current requirements. Such codes generally deal with the crane equipment and its operation as well as with maintenance.
For further information on crane maintenance, the reader is referred to the following standards, codes, and regulations:
American National Safety Standards, published by The American Society of Mechanical Engineers, United Engineering Center, 345 East 47th Street, New York, NY 10017:
ANSI B30.2.0: Overhead and Gantry Cranes (Top Running Bridge, Multiple Girder) ANSI B30.9: Slings ANSI B30.11: Monorails and Underhung Cranes ANSI B30.16: Overhead Hoists ANSI B30.17: Overhead and Gantry Cranes (Top Running Bridge, Single Girder Underhung Hoist) CMAA Crane Specifications, published by The Crane Manufacturers Association of America, Inc., 8720 Red Oak Blvd., Suite 201, Charlotte, NC 28217 HST Performance Standards for Hoists, Published by ASME, 345 East 47th St., New York, NY 10017 OSHA regulations as published in the Federal Register. (Note: Portions of ANSI standards, such as ANSI B30.2.0, have been adopted as OSHA regulations.)