Lattice Boom Breakdown
The bridle assembly plays an important part when changing the length of the boom. If you forget to disconnect the boom pendants lines from the boom tip, and not connect the bridle assembly or pendant lines behind the boom section you plan to remove or install, and you drive out the bottom pins, the top pins will act as a hinge and the boom will fall, as shown in figure 12-23. If you make this mistake and a crew member is under the boom, a tragedy could result, as shown in figure 12-24.
NEVER WORK UNDER A CRANE BOOM. Because so many accidents have occurred while personnel were changing booms, some manufacturers have made a one-way connecting pin that can only be installed from the inside. This requires the pin to be removed only from the outside, keeping personnel from getting underneath the boom (fig. 12-25). A common practice in the NCF is to install the pins from the inside out to prevent personnel from maneuvering inside the boom to drive out the pins.
Several methods are used to break down lattice booms to add or take out sections. If the boom sections are bolt-connected, you must use dunnage for support under each section.
The most common boom connection is with pins.
To break down a pin-connected boom, make sure you
Figure 12-25.-Drive pins from the outside in.
Figure 12-23.-Incorrect way to disconnect the lattice boom.
have gloves, hardhats, safety glasses or goggles, and safety shoes for all hands, sledge hammers, pliers, crowbars, marlin spikes, extra cotter pins, and dunnage.
Always wear gloves when handling wire rope.
NOTE: When breaking down a lattice boom, take the opportunity this provides to inspect items thoroughly, such as the connecting pins, cotter keys, and inside the connecting lugs for wear, rust, and surface cracks.
A common method used to break down a pinconnected basic boom and add a section is as follows:
1. Set outriggers and swing the upper revolving unit over the rear or side, depending on the make and model of the crane.
2. Lower the hook block(s) to the ground and provide slack in the hoist line(s). Next, lower the boom and set the boom tip sheaves on a piece of dunnage.
3. Engage the boom hoist control lever to lower the bridle assembly or boom mast to slacken the pendant lines.
4. To prevent the pendant lines from falling on the ground, use tie wire or rope to secure the pendant lines to the boom. Then remove the cotter pins and drive out the main pins from the bridle assembly connections in the pendant lines.
5. Position the bridle assembly on top of the boom butt (fig. 12-26, view A). This is done by having the operator engage the boom hoist control lever to tighten the boom hoist lines until the bridle is positioned on top of the boom butt. To align the pinholes, manually position the bridle assembly using the crowbar. The pins that are used for the pendant line connections are
Figure 12-26.-Boom hoist assembly connected to boom butt.
normally the pins used to connect the bridle assembly to the boom butt. If the crane is equipped with a boom mast, the boom mast normally has a short set of pendants that connect to the boom butt pinholes (fig. 12-26, view B).
NOTE: Visually check the boom hoist drum to ensure the boom hoist wire rope does not loosen and cross wind on the hoist drum, resulting in crushing or kinking the wire rope.
6. Tighten the boom hoist lines to support the weight of the boom, but not so tight that the boom tip is lifted off the dunnage.
7. Remove the cotter pins from the boom connection pins and drive out the lower boom connection pins.
8. After the lower pins are removed, engage the boom hoist control lever and lower the bridle assembly or mast, allowing the boom to separate at the bottom by hinging on the top pins. hen lower the boom on a piece of dunnage.
9. Remove the top connecting pins. Once removed, engage the boom hoist enough to separate the boom connections lugs.
When the boom breakdown is performed over the rear of the crane, you separate the boom by (1) raising the outriggers enough to move forward with the travel unit and by (2) releasing the brakes on the hoist line(s) to slacken the hoist wire rope, as the travel unit moves forward to allow space to add a section(s).
When the boom breakdown is performed over the side of the crane, you separate the boom by ( 1) releasing the brakes on the hoist line(s) to slacken the hoist wire rope and by (2) using a forklift to pick up the boom tip carefully and maneuver it enough to provide adequate space to insert a boom section(s).
A method for adding a boom section is as follows:
1. Have a forklift align the boom section with the boom butt.
2. Reverse the crane until the boom butt top pin connection lugs are connected with the top pin connection lugs on the boom section. The boom breakdown performed over the side requires a forklift to maneuver the boom section until the pins are aligned.
3. Once the top lugs are aligned, drive the boom connection pins into the top lugs from the inside out and insert the cotter pins.
4. Engage the boom hoist control lever to raise the boom butt. This allows the top pins to perform as a hinge that draws the bottom pin connection lugs together.
5. Once the bottom lugs are aligned, drive the boom connection pins into the bottom lugs from the inside out and insert the cotter pins.
6. Raise the boom butt and boom section several inches to clear the ground. Reverse the crane until the top connection lugs of the boom section align with the top connection lugs of the boom tip. Final alignment of the lugs might require the use of a crowbar.
7. Once the lugs are aligned, drive the boom connection pins into the top lugs and insert the cotter pins.
8. Engage the boom hoist control lever to raise the boom section and boom tip. This results with the top pins performing as a hinge, drawing the bottom pin connection lugs together.
9. Once the bottom lugs are aligned, drive the boom connection pins into the bottom lugs from the inside out and insert the cotter pins.
10. Reset the outriggers.
The procedures for connecting the bridle assembly to the boom pendants are as follows:
1. Engage the boom hoist control lever to lower the bridle assembly or boom mast to produce slack in the boom hoist wire rope.
2. The next step is to connect the boom bridle assembly to the boom section pendant lines. This is done by disconnecting the bridle assembly from the boom butt and manually maneuvering the bridle assembly to connect with the boom pendants of the boom section. To produce slack in the bridle assembly may require manually feeding of the boom hoist wire rope through the sheaves.
For cranes equipped with a boom mast, lower the boom mast to connect the pendant lines.
3. When the pendants are connected to the bridle, it is a good practice to insert the pins from the inside out. This practice allows for a easier visual inspection of the cotter pins inserted in the pendant line pins when the boom is in the air.
4. The next step is to connect the boom section pendants to the boom tip pendants. This usually requires manual labor to align the boom section pendants to the boom tip pendants. You may also have to engage the boom hoist control lever to provide slack in the boom hoist lines to align the pendant lines. Once the pendants are aligned, insert the pendant connection pins and cotter pins.
5. Next, engage the boom hoist control lever to raise the bridle assembly and pendants. Before doing this, go back through and visually inspect all boom and pendant line pin connections and cotter pins. Have someone visually watch the boom hoist drum to ensure the wire rope does not cross wind, causing the wire rope to be crushed or kinked. Additionally, ensure all of the boom hoist wire rope is properly running on all of the sheaves. Once everything checks out, engage the boom hoist control lever and raise the bridle assembly and pendants until they are tight.
6. Visually check the boom suspension system before raising the boom off the ground As the boom is being raised, visually check the reeving of the boom hoist wire rope.
7. Once the boom is erected, check the hoist wire rope reeving. You want to ensure the wire rope is correctly flowing through the boom tip and hook block sheaves and winding properly on the hoist drum. Before the crane can be operated, as outlined in the NMCB, Equipment Management, COMSECOND/ COMTHIRDNCBINST 11200.1, and before putting the crane back in service, the crane test director must inspect the crane for correct installation of all components and verify the prior testing and mechanical condition of added components. The crane certifying officer may direct the crane to be load-tested at its safe load capacity at minimum and maximum radius.