FEATURE | GANTRY CRANES
crane is transmitted to the floor through the casters – essentially as a point or line loads rather than being distributed - the flooring beneath a crane must be able to bear that load. Wallace suggests that it should be of 3,000 psi (7,000 N/m2) concrete at least 18” (45cm) deep with one or more courses of rebar. The standard Wallace casters, in either phenolic or steel core with polyurethane tread, are fully capable of smoothly running the crane across the floor at full load. An alternative option is to have the crane
track mounted. For these cranes, typically with an electric motor drive, the casters are replaced with V-groove steel, running on a track made of angle iron mounted on a plate. Wallace builds this track in-house with three different capacities, 1-5 tons, 8-10 tons, and 15 tons. The track sections are available in standard 5 and 10-ft lengths, with male and female sections for smooth running. Wallace also makes ta removable transition section for high-traffic areas. Many small portable gantries can be disassembled for storage, and Wallace cranes are no exception. The pinned joints
A 10-ton portable gantry by Wallace
make assembly and disassembly easier. Parts rotate and the design allows for some misalignment, which means that pins go in easily – the only tool needed is a small hammer – which speeds up initial and subsequent reassembly and reduces the likelihood of assembly-induced pre- stresses which could reduce crane life and reliability.
WHAT WHEELS?
An easy-to-overlook component of the small portable gantry is the set of wheels that support it. Spanco, of Pennsylvania make a wide range of gantry systems, some portable, some track-mounted, some adjustable in height and span, some from aluminium for lightness; and they set them A primary reason, they say, is ergonomics.
Having the correct casters for the application will allow less force to be used in moving them, so lessens the risk of strains and physical injuries. Pushing a gantry system rather than pulling, they say, is safer and unsupported positions of the arm and back – and walking backwards while pulling means you cannot see where you are going – and can even result in getting run over by the Polyurethane castors, say Spanco,
are simple low-maintenance option. Polyurethane can carry heavy loads; and it has a low rolling resistance, so allows the material to glide over smooth concrete surfaces with relative ease. The amount of force to initiate movement for a Spanco Gantry that uses polyurethane casters is approximately 5% of the system’s rated capacity; about 2% is needed to maintain
motion, and around 7% to 15% of the system’s rated capacity is needed to turn. Their level surfaces to run on. Polyurethane castors are solid and provide no cushioning. Pneumatic tyres fare better on rough surfaces, but their rated capacity – the load they can carry - is much less, and depends on the size of the wheel. Higher capacities need large-diameter wheels casters.
to push. Also, they do not give as smooth a around 15-20% of the system’s rated capacity to initiate and continue movement. It is harder for a pneumatic wheel to pivot, meaning more force is needed to turn the system. Additionally, the rated capacity depends on tires for greater capacities is necessary, while even small-diameter polyurethane casters can handle larger capacities. Yet another option is to use Nylacron Casters, which are best used for heavy- duty applications as an alternative to motorization. Nylacron is made from compressed cast polyamide and can handle heavy capacities at the lowest rolling with Nylacron is less than 1% of the system’s rated capacity; to continue movement it is less than half a percent; and to turn it is about 3% to 5% of the system’s rated capacity. Nylacron therefore moves the highest-rated capacities with the smallest can use them, Nylacron casters are typically motorization.
Wallace gantries are available in capacities from ½ ton to 15 tons, in fixed or adjustable heights and spans. Beam length and height can also be customised. So if it is a gantry that you need, there are
hundreds of different sizes and there will be one in your size available. But as for shape, one shape fits all. But still, it is a good shape. It will work for you.
30 | March 2025 |
www.hoistmagazine.com
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