You see them everywhere – still. Mobile cranes are still about to lend a boom whenever the need arises, though as Arty Wartanain, general manager of Gallagher International – a regional mobile hire firm, points out: “A lot of our business at the moment is about removing tower cranes – it’s a growth industry at the moment.”
The fleet of more than 50 units at the firm is in constant use, with a number of brands and sizes and models in action, so it is important to keep the fleet going at all times. so constant maintenance is one of the key factors here.
As the facility in Jebel Ali has all the machines and facilities to maintain the fleet, cranes belonging to other customers are welcome to be booked in. During our visit a team of technicians were busy stripping the brake drums from a crane belonging to another rental company.
Many of the staff have been with the company a great number of years, with a few of the staff having been there from around the time of the company’s inception in the early 1970s.
Vans
Mobile servicing is also an important part of the business. To this end, the firm has purchased a pair of Iveco vans, which have been kitted out with a workbench and vice, as well as all the tools as well as the grease, fluids and materials needed to service the cranes on site.
“Being able to do this means no downtime. Keeping the cranes ‘up’ at all times helps the client, just as it helps us” said workshop manager Simon Abraham.
The vans can go anywhere the cranes are, and the technicians can work on practically anything, with one notable exception being the
Brakes
It’s not just the lifting gear that it is important to maintain. These are also vehicles that get driven in the region’s hectic road traffic, so keeping the cranes running is important.
There are four basic principles that govern a crane’s mobility and safety during lifting operations, namely the centre of gravity, the amount of leverage, stability and structural integrity.
The centre of gravity of any object is the point in the object where its weight can be assumed to be concentrated or, more simply put, it is the point in the object around which its weight is evenly distributed.
The location of the centre of gravity of a mobile crane depends primarily on the weight and location of its heaviest components (boom, carrier, upperworks and counterweight).
Leverage Cranes use the principle of leverage to lift loads. Rotation of the upperworks (cab, boom, counterweight, load) changes the location of the crane’s centre of gravity, its leverage point or ‘fulcrum’.
As the upperworks rotates, the leverage of a mobile crane fluctuates. This rotation causes the crane’s centre of gravity to change and causes the distance between the crane’s centre of gravity and its tipping axis to also change.
Stability can be affected by the fluctuating leverage the crane exerts on the load as it swings. The crane’s rated capacity is therefore altered in the load chart to compensate for those changes in leverage.
Stability is the relationship of the load weight, angle of the boom and its radius to the centre of gravity of the load. The stability of a crane could also be affected by the support on which the crane is resting.
A crane’s load rating is generally developed for operations under ideal conditions, i.e., a level firm surface.
Surfaces that are not level, or soft ground therefore must be avoided. In areas where soft ground poses a support problem for stability, mats and or blocking should be used to distribute a crane’s load and maintain a level stable condition.
Structure
In addition to overturning, the structure of cranes can fail if overloaded. Structural failure may occur before a stability failure.
In other words, a mobile crane’s structure may fail long before it tips. As loads are added beyond its rated capacity, a crane may fail structurally before there is any sign of tipping. Structural failure is not limited to total fracture; it includes all permanent damage such as overstressing, bending and twisting of any of the components.
When a crane is overstressed, the damage may not be apparent. Nevertheless, a structural failure has occurred and overstressed components are then subject to catastrophic failure at some future time.
The crane’s main frame, crawler track or outrigger supports, boom sections, and attachments are all considered part of the structural integrity of lifting.
In addition, all wire ropes, including stationary supports or attachment points, help determine lifting capacity and are part of the overall structural integrity of a crane’s lifting capacity.
The following elements may also affect structural integrity and these are the load chart capacity in relationship to stability and the boom angle limitations which affect stability and maximum capacity.
Additionally, the knowledge of the length of boom and radius in determining capacity.
Stability failures are foreseeable, but in structural failure it is almost impossible to predict what component will fail at any given time. No matter what the cause, if the crane is overloaded, structural failure can occur.
As stated above, cranes are carefully designed, tested, and manufactured for safe operations. When used properly they can provide safe reliable service to lift or move loads.
Because cranes have the ability to lift heavy loads to great heights, they also have an increased potential for catastrophic accidents if safe. operating practices are not followed.
Planning
Accidents can be avoided by careful job planning. The person in charge must have a clear understanding of the work to be performed and consider all potential dangers at the job site. A safety plan must be developed for the job and must be explained to all personnel involved in the lift.
Before operations begin for the day, a walk around inspection needs to be conducted to ensure that the machine is in proper working condition. Only qualified and properly designated people shall operate the crane.
Regular inspections are important, they provide a means of detecting potential hazards or conditions that could contribute to a sequence of events leading to an accident.
Safe, reliable, and the economic operation of lifting equipment, cannot be ensured without regular safety inspections and thorough preventive maintenance programs.
A thorough inspection program can forecast maintenance needs or potential equipment failures or malfunctions.
The lack of such a program could result in serious deterioration of the equipment which might lead to excessive replacement, or repair charges, as well as an increased potential for accidents.
Mobile crane maintenance checklist (as recommended by OSHA)
- Check that all exposed moving parts are guarded. A removed guard may indicate that a mechanic is still working on part of the crane.
- Visually inspect each component of the crane used in lifting, swinging, or lowering the load or boom for any defects that might result in unsafe operation.
- Inspect all wire rope (including standing ropes), sheaves, drums rigging, hardware, and attachments. Remember, any hook that is deformed or cracked must be removed from service. Hooks with cracks, excessive throat openings of 15%, or hook twists of 10 degrees or more, must be removed from service.
- Check for freedom of rotation of all swivels.
- Visually inspect the boom and jib for straightness and any evidence of physical damage, such as cracking, bending, or any other deformation of the welds. Look for corrosion under any attachments that are connected to the chords and lacing. Watch carefully for cracking or flaking of paint. This may indicate fatigue of the metal which often precedes a failure. On lattice booms, look for bent lacing. If they are kinked or bent, the main chord can lose substantial support in that area. When lacing is bent, the ends also tend to draw together which pulls the main chords out of shape. This precaution is especially important on tubular booms where every component must be straight and free from any dents.
- Do not attempt to straighten these members by hammering or heating them and drawing them out. They must be cut out and replaced with lacing to the manufacturer’s specifications, procedures, and approval.
- Inspect tires for cuts, tears, breaks, and proper inflation.
- Visually inspect the crane for fluid leaks, both air and hydraulic.
- Visually check that the crane is properly lubricated. The fuel, lubricating oil, coolant and hydraulic oil reservoirs should be filled to proper levels.
- Check that the crane is equipped with a fully charged fire extinguisher and that the operator knows how to use it.
- Check all functional operating mechanisms such as: sheaves, drums, brakes, locking mechanisms, hooks, the boom, jib, hook rollers brackets, outrigger components, limit switches, safety devices, hydraulic cylinders, instruments, and lights.