Wheel-mounted cranes range in various sizes and have capacities from 5 to 35 tons or larger (fig. 12-9).
The wheel-mounted cranes shown in figure 12-9 are hydraulically operated, four-wheel drive, four-wheel steer, pneumatic-tired, engine-powered diesel. The superstructure consists of a telescoping boom, single-acting hydraulic lift cylinders, a hydraulically operated hoist drum, and a hook block attachment.
The wheel-mounted crane has a ground bearing pressure of about 35 psi and can travel at speeds ranging from 2 to 30 mph. It can turn in a 30-foot radius with two-wheel steering and in a 17-foot radius with four-wheel steering and can travel up a firm, dry 40-percent grade.
The wheel-mounted crane is a mobile and flexible crane that can be driven on or off roads over rough terrain. It is best suited for lifts around shops or for supporting fabrication projects that call for many varied, mobile lifts within a small working area.
Depending on the make and model, most wheel-mounted cranes have a 360-degree work area The quadrants of operation for wheel-mounted cranes are over the side, over the rear, and over the front (fig. 12-10). Remember that the capacity of the crane may
Figure 12-10.-Wheel-mounted crane quadrants of operation.
change when rotating a load from one quadrant to another. This information is provided on the crane load chart.
The major components of a lattice boom crane are shown in figure 12-11. Inspecting each of these components is part of the operator's prestart inspection. The lattice boom supports the working load and is the most common boom used in the NCF. It is used on all types and makes of cranes and is mounted at the boom butt on the revolving superstructure. The basic boom consists of the boom butt and boom tip, and the length is increased by adding boom extensions.
Lattice boom sections are made of lightweight, thin wall, high strength alloy tubular or angle steel and are designed to take compression loads. The most common boom is tubular. Terminology of a lattice boom section is shown in figure 12-12.
Manufacturers have set a zero tolerance on rust, bent lacings or cords, cracked welds, and other problems that affect the strength of the lattice boom. This zero tolerance requires crane crews to use extreme care when handling unused sections with forklifts, storing unused sections away from traffic areas, transporting and securing sections on tractor-trailers, and preventing equipment or obstacles from running into the boom while mounted on the crane during transport, performing operations, or when parked.
As outlined in the Management of Weight-Handling Equipment, Maintenance and Certification, NAVFAC P-307, all lattice boom cranes with structural damage to the main cords of the boom must be immediately
Figure 12-11.-Lattice boom crane components.
Figure 12-12.-Lattice boom terminology.
removed from service. When the main cords of tubular boom sections are damaged in any manner, including slight dents, they are severely weakened and have failed at loads significantly below capacities. As outlined in the 11200.1, structural repairs will not be made without written approval from COMSECOND/COM-THIRDNCB equipo offices.
In the NCF, sections normally come in 10- to 20-foot lengths. When adding several sections of different lengths, check the operator's manual for boom section configuration. If this information is not in the operator's manual, a rule of thumb used when mixing short boom sections with long sections, you install the shorter sections closest to the boom butt; for example, if you use two 10-foot sections and one 20-foot section, install the two 10-foot sections closest to the boom butt. The boom sections are bolted by plate (flange) connections (fig. 12-13, view A) or pin and clevis connections (fig. 12-13, view B). The most common is the pin and clevis.
All boom sections that come with a crane will have an attachment identification number attached that assigns the boom section to a specific crane.