Developing a crane safety program
Published in: Plant Engineering
Date: 2/1/1996
By: Holzhauer, Ron
Cranes are equipped with redundant brake controls and overload detection systems as part of the preventive maintenance and safety programs initiated by crane manufacturers. Aside from preventive maintenance, proper operation and scheduled inspections are also vital in ensuring safety in industrial plants. A daily visual inspection of the equipment should include checking the different machine components for wear, cracks and other possible causes of accidents. Periodic wire rope inspection is also critical in safe crane operation.
Proper operation, preventive maintenance, and regular inspection are the key ingredients in a safe system
The overhead crane is one of the most common types of heavy equipment found in industrial plants. As a result, safe crane operation is an issue of paramount importance, and with good reason. Given work safety and liability issues, and all the regulations set by OSHA, AISE, CMMA, and other organizations, everyone responsible for operating, maintaining, purchasing, or reconditioning crane systems must put safety first.
Fortunately, reputable crane manufacturers think likewise in both engineering and support activities. Components such as redundant brake concepts for hoists, more reliable controls, and economical overload detection systems are engineered into the system. Standard diagnostic devices are available in conjunction with detailed preventive maintenance and safety training programs.
Safety
Safety starts with the operator. Whenever there is doubt as to safety, the operator should stop the crane, report the problem to his supervisor, and not operate the equipment until satisfied it is safe to do so; or is directed to proceed by a supervisor, who then assumes all responsibility for the safety of the lift.
Operators should be familiar with the principal parts of the crane. Employees should receive hands-on training, read all instruction materials, and have a thorough knowledge of crane control functions and movements. Both the operator and person hitching or rigging the load should be required to know the location and proper operation of the main runway conductor disconnect for all cranes in the area.
The operator should test all crane controls, such as limit switches [ILLUSTRATION FOR FIGURE 1 OMITTED], brakes, ropes, and hooks, to ensure proper functioning at the beginning of each shift. The area should be clear of personnel during the test.
Under no circumstances should anyone be permitted to ride on the hook or load.
Before commencing work, the operator should perform a walk-around check to look for loose or damaged parts, or a visual inspection should be made from a catwalk or other safe observation point. Table I indicates a number of daily visual checks that should be made on the crane system.
In general, a crane operator should not close the main switch or emergency contactor until checking to ensure that no one is on the crane and there are no warning signs. When the lift approaches the rated load, the operator should test the hoisting brakes by raising the load a few inches and applying the brakes.
A limit switch on a crane or hoist should not be used as an operator control unless a backup switch is available. A load should not be lowered below the point where less than two full wraps of wire rope remain on the hoist drum.
The operator should land any attached load and place the controllers in the “off” position when leaving a crane unattended. The sling should always be removed from the hook and stored where it is protected from damage. The operator should make sure all controllers are in the “off” position before closing a main switch. All controls should be placed in the “off” position in case of a power failure.
Loads should never be carried over workers’ heads. The crane should not be used for side pulling. This movement creates dangerous load swings, and creates potential damage and excessive wear to wire ropes, rope guides, and limit switches; and results in equipment deterioration. Wire rope hoists are designed for lifting loads in straight vertical paths; not for winching operations. Wire rope strength is calculated by straight line pull. Compressed gases should be lifted only by a cradle or enclosed platform.
Hand signals should be clearly agreed upon and understood before moving a load. The operator or hooker should make sure of several conditions when attaching or moving a load:
* Hoisting rope or chain is free of kinks or twists and not wrapped around the load
* Load is attached to the load block hook by a sling or other approved device
* Sling and load will clear all obstacles or obstructions
* Load is balanced and secured before lifting more than a few inches
* Multiple lines are not twisted around each other
* Hook is brought over the load in a manner to prevent swinging
* There is no sudden acceleration or deceleration of the moving load.
The operator should never lift two separately rigged loads at the same time. Whenever a movement is made, the operator should pay constant attention to controlling the load, never allowing the control pendant to swing freely. When possible, traveling and lifting movements should be carried out simultaneously to reduce operating time.
Table I. Daily Visual Checks
Component Detail
Operating mechanisms Function
Limit switches Operational for function
Hooks Deformation and cracks
Chains Wear, elongation, and twist
Wire rope Wear, broken wire, and kinks
Slings Wear, broken wire, and kinks
Rope reaving Proper seating in drum and sheave grooves
The operator should approach the desired position as far as possible at the main speed and use creeping for final positioning to avoid unnecessary inching, which negatively affects the service life of certain components. Pendulation of the load is avoided by moving the crane/hoist or trolley in the same direction as the load is swinging. The operator should not drive the crane against endstops and avoid bumper contact.
Maintenance
A preventive maintenance program should be based on the crane manufacturer’s recommendations. The crane should be taken out of service to a safe location before adjustments or repairs are begun. The crane should not be put back into operation until all guards are reinstalled, safety devices reactivated, and maintenance equipment removed. All inspection reports and repairs should be entered into a logbook with the service technician’s signature.
Mechanical connections should be checked, particularly the bolts between the main girder and endtruck. Nuts, welding, and riveting, including rivets on the electric hoist casing’s rope anchorage, should be checked to ensure they are secure.
Examine the rail endstops and seating of the bumpers and endstops. Crane wheels are clearly visible when the bumper plates are removed from the endtruck. Also inspect the flat cable used to supply current to the trolley, hoist, or crane. No visible damage or sharp bends should be present.
Collector heads of the downshop power supply should be free from oil, grease, paint, and dirt. Badly bent busbars must be straightened or replaced immediately. Carbon sliders should be regularly checked for wear and replaced immediately when worn to prevent damage to the busbars or short circuit conditions.
When heavy wear is found on wheel flanges, the crane runway should be examined to determine whether it still conforms to tolerances and requirements. Damaged cables, in particular the round cable to the push button pendant in the floor control, must be replaced immediately.
Inspection
A daily visual inspection is important to safe crane operation. In addition, a complete inspection at 1-to-12-month intervals is recommended. A crane idle for more than a month should be inspected thoroughly.
[TABULAR DATA FOR TABLE II OMITTED]
Several deficiencies should be looked for during this inspection:
* Deformed, cracked, or corroded members
* Loose bolts or rivets
* Cracked or worn sheaves or drums
* Worn, cracked, or distorted parts, such as pins, bearings, shafts, gears, rollers, and locking and clamping devices
* Excessive wear on brake system parts, lining, pawls, and ratchets
* Excessive wear of chain drive sprockets and excessive chain stretch
* Cracks on crane hooks using magnetic particle or other suitable methods
* Pitting or any deterioration of controller contactors, limit switches, pushbutton stations, or other electrical apparatus.
Table II provides a detailed inspection checklist.
Periodic inspections of wire ropes are not only necessary, but required by OSHA regulation, and, as a result, must be properly documented [ILLUSTRATION FOR FIGURE 2 OMITTED]. A thorough inspection should be performed at least monthly.
The reason for the critical nature of the inspection is that the wire rope itself is literally “consumed” during use. The rope gradually loses strength during its life and must be carefully checked to assure that it retains sufficient strength to perform the required work during the period before the next inspection.
Wire ropes should be relaxed and at rest when inspected. Each rope must be treated individually. There are several possible areas of deterioration:
* Reduction of rope size below nominal diameter due to loss of core support, internal or external corrosion, or wear of the outside wires
* Number of broken outside wires and degree of distribution or concentration of these wires
* Worn outside wires
* Corroded or broken wires at end connections
* Corroded, cracked, bent, worn, or improperly applied end connections
* Severe kinking, crushing, cutting, or unstranding.
Critical points along any given rope should receive more attention than others, because some areas are usually subjected to greater stresses, forces, and hazards. Critical areas include pickup points, or sections of rope which are repeatedly placed under stress when the initial load of each lift is applied, such as those sections in contact with sheaves. Other critical points include end attachments; equalizing sheaves or sections of a rope in contact with and adjacent to sheaves, as on boom hoist lines; drums; and sheaves.
The inspection should look for signs of heat exposure and “bright spots” which indicate abuse, such as contact with cross members of a trolley frame or load.
Regular lubrication extends the life and properties of wire rope. If in doubt as to safe working strength or condition, do not hesitate to install a new wire rope.
Make sure the equipment is right for the application when new purchases are required. Planned or Preventive maintenance contracts or repair service should be carried out by qualified technicians.
Employee safety and productivity both benefit with an awareness and concern for safe working practices.
– Edited by Ron Holzhauer, Material Handling Editor, 847-390-2668
For more information…
RON TALBOT, the author, is willing to answer technical questions concerning this article. Mr. Talbot is available at 216-248-4500.
RON TALBOT, National Service & Modernization Manager, Demag Material Handling Equipment Corp., Cleveland, OH
COPYRIGHT 1996 Reed Business Information