Crawler cranes are multipurpose lifting equipment and the safe operation of these cranes can ensure their optimum utilization. P.P. Basistha reports.
Utility of crawler lattice boom cranes remains uncontested as a versatile lifting machinery. The versatility of the cranes is based on the fact that it can be used for conventional general erection. More so, as construction projects are becoming more complex and bigger in sizes, like refineries, power plants and other industrial projects, role of crawler cranes are gaining further prominence as equipment that can undertake heavy lifting.
However, the machine remains technically complex to its core based on its engineering. To take on the technical complexity of the machine, it is essential that elaborate yard sticks are followed for operating the cranes. The benchmarks should be followed by contractors taking into account the assembling and commissioning of the cranes, operation of the cranes ultimately to its dismantling.
Vital in Operation
Assembling and dismantling is also an important component of operation. During assembling and dismantling of the crane, the space availability of the job site should be taken into consideration. If the job site is congested other machinery and materials should be rationa- lized to create room to setting up the crane and undoing it.
Extensive precautions have to be taken into while making the cranes work at night at congested construction sites, precisely during slewing operation. During slewing, there is always a danger of the boom to strike other objects. To bypass the danger, lights should be placed on the crane boom in a staggered position. This would ultimately lead to safe working.
The crane has to be placed on flat ground level position. This is as because placing the crane out of level even by 1 degree can cut down 10% of its capacity.
As a solution to have the right inclination on uneven surface, particularly while the crane is working on rocky surface or loose soil terrain gunny bags should be used to rightly position the crane. This will enable the surface to have better ground bearing pressure. Clay soil will provide better ground bearing pressure to the crane while sandy soil will provide lesser ground bearing pressure. The nature of the soil should be duly examined by the geotechnical engineer. The examination carried has to be duly certified. Based on the soil type blogging material has to be used. The area of blogging material would depend on the wideness of the crawler and the character of soil on which the crawler crane would be working. Timber mats can be ideally used as a blogging material apart from gunny bag material. Post laying of blogging material, it is essential to cross examine that the crane is not in an uneven position. To check the uneven positioning, it has to be equipped with level indicator.
Prior to starting operation of the crane, the Safe Load Indicator(SLI) has to be duly examined. It is important that overall the crane should be duly examined. The check list of the crane should include its wire rope conditions, pulley conditions, hook conditions all clutches and brakes. Most importantly, the boom conditions needs to be checked. It should be noticed whether there is corroded or bent bracing in between the lattice. Uneven boom can lead to accidents and steep loading variations.
Precautions in Heavy Lifting
During tandem lifting with two cranes, it is quite obvious that the psychological reflux state of mind of the crane operator is bound to differ. The mental difference can result in the uneven or disproportionate movement of the boom. This resultantly can create a difference in lifting and unloading. To arrest the operational difference, it would be essential to curtail the lifting capacity of the crawler crane. In accordance with this, 20-25% of the safe working load of the crane has to be cut down. Cutting down the lifting capacity will create an impression in the mind of operator that the crane is working at reduced capacity. To ensure cutting down of safe working load, the Safe Load Indicator (SLI) should be modified or reset.
During heavy lifting, care has to be taken that the boom lowering and raising is gradual. Gradual raising and lowering of boom has to be followed during tandem and general lifting operations as well. This would resultantly prevent accidents.
It is very important that while working with over head wires, the boom should be three metres away from the over head wires or more if possible. Making the boom stay away from the electric over head wires will prevent any chances of electrocution.
Crawler cranes are excellent support equipments. Optimum working results can be obtained from the machinery. To have sustained equipment uptime, it is prerequisite that routine checks should be carried on the crane. These precautions will go a long way to provide a long life to the equipment preventing the contractor to invest in new or used equipment. This is so because crawler lattice boom cranes are always known to be costly machinery.