CHAPTER 12 CRANES AND ATTACHMENTS

Cranes and attachments are essential to the support of Naval Construction Force (NCF) operations. Lifting heavy objects, loading and unloading construction materials, excavating earthwork materials, and driving and extracting piles are typical tasks accomplished by the use of cranes and attachments.

Cranes and attachments procedures are a complex set of characteristics. Proper and efficient operation of cranes and their attachments requires more knowledge and skill than for any other piece of construction equipment you will operate.

NOTE: You must always be exceptionally safety conscious when working on or around crane operations of any type.

This chapter covers the characteristics and basic principles of operations of cranes and attachments. By reading the operator's manual and attending crane school, you can obtain detailed information about crane operations.

CRANES

Cranes are classified as weight-handling equipment and are designed primarily to perform weight-lifting and excavating operations under varied conditions. To make the most efficient use of a crane, you must know their capabilities and limitations.

TYPES OF CRANES

Cranes have evolved from many designs to satisfy the needs of construction and industrial operations. Operational characteristics of all cranes are basically the same. Although the superstructure is about the same on all makes and models of mobile cranes, the carrier, or mounting, may be one of three types: crawler, truck, or wheel (fig. 12-1).

Crawler-Mounted Cranes

The crawler-mounted crane is categorized under the 42-00000 USN number registration series. The crawler-mounted crane is slower and less mobile than the truck-mounted crane; however, the crawler-mount crane provides a stable base for operation of the revolving superstructure.

The travel unit of the crawler crane is shown in _{figure 12-2.} The travel unit includes the base, travel gears, clutches, travel brakes, sprockets, rollers, crawler chains, and crawler treads. The revolving superstructure rotates on the turntable (fig. 12-3).

Figure 12-1.-Crane carrier mountings.

Figure _12-2.-Crawler crane travel unit.

Figure 12-3.-Turntable assembly.

accessible to truck-mounted cranes because of terrain conditions. Also, the crawler crane has steering with positive traction that permits the crawler crane to travel and turn without cutting up the work area or roadway.

The size of the crawler treads spreads the weight of the crane over a large area. This feature gives the crawler crane a low ground bearing pressure of 5 to 12 psi, giving the crane the versatility needed to travel over soft terrain. When the crawler crane is climbing grades, the maximum grade capability is 30 percent on firm, dry material. The turning radius of the crawler crane is about the length of the tracks, which travel 1/2 to 2 mph. Because of the slow travel speed, it is not productive to try to travel more than 1 mile. Additionally, traveling the crane a long distance at one time causes extra wear to the tracks. When travel distance exceeds 1 mile, transport the crawler by tractor-trailer.

NOTE: Consult the operator's manual for detailed information if required to track travel for more than 1 mile,

Figure 12-4.-Crane radius measurement.

The primary advantage of the crawler crane over the truck-mounted crane is that it is better suited for continuous work in remote areas that are not readily accessible to truck-mounted cranes because of terrain conditions. Also, the crawler crane has steering with positive traction that permits the crawler crane to travel and turn without cutting up the work area or roadway.

The size of the crawler treads spreads the weight of the crane over a large area. This feature gives the crawler crane a low ground bearing pressure of 5 to 12 psi, giving the crane the versatility needed to travel over soft terrain. When the crawler crane is climbing grades, the maximum grade capability is 30 percent on firm, dry material. The turning radius of the crawler crane is about the length of the tracks, which travel 1/2 to 2 mph. Because of the slow travel speed, it is not productive to try to travel more than 1 mile. Additionally, traveling the crane a long distance at one time causes extra wear to the tracks. When travel distance exceeds 1 mile, transport the crawler by tractor-trailer.

NOTE: Consult the operators manual for detailed information if required to track travel for more than 1 mile, Steering of the crawler crane is performed by engaging the steering lever in the direction you want the crane to turn. Some models of crawler cranes have a swing-travel jaw clutch that is controlled by one lever

Figure 12-5.-Crawler-mounted crane quadrants of operation.

and provide power for either swinging the crane or _{traveling the crane.} The swing-travel jaw clutch requires the operator to engage a button or push a lever to select for swing or travel operations. Other models have a separate steering and swing lever, allowing both functions to be operated at the same time.

Use caution when traveling with a crawler crane on and around slopes. Some older types of crawler cranes do not have travel brakes and power could be disengaged, causing the crawler to freewheel.

On-the-job maneuvering is easy because of the small turning radius of the crawler crane. Additionally, the crawler crane does not require the use of outriggers for stability, so it requires less room for setting up. On some models of crawler cranes, the tracks can extend outward, providing the crane with more stability. Crawler crane models, on which the crawler tracks can extend, are rated at 85 percent of the minimum weight that can cause the crane to tip at a specified radius with the basic boom, Crawler models that do not have extendable tracks are rated at 75 percent. Crane radius measurement is measured from the center of rotation to the center of the hook after the boom deflects forward when under load, as shown in figure 12-4.

Depending on the make and model, most crawler cranes have a 360-degree working area. This working area is divided into operating areas called quadrants of _operation. The crane capacity is based on the quadrants, such as for over the side, over the drive end, and over the idler end, for a crawler-mounted crane (fig. 12-5). The capacity of the crane may change when rotating a load from one quadrant to another. This information is provided on the crane load chart.