Figure 12-28.-Hook block.CLAMSHELLA clamshell consists of hoist drum lagging,clamshell bucket, tag line, and wire ropes to operateholding and closing lines. On some crane models, thehoist drum lagging (hoist drum diameter) can bechanged to meet the speed or pull requirements forclamshell operations. Once a crane is rigged with aclamshell, the crane is referred to by the name of theattachment.When changing attachments from a hook block to aclamshell, check the operator’s manual for the correctlength of wire rope reeving; for example, some cranemodels require 300 to 400 feet of wire rope for hookblock operations and only 100 to 200 feet of wire ropefor clamshell operations. Too much wire rope on thehoist drum during clamshell operations will cause thewraps of wire rope to loosen on the hoist drum and crosswind, resulting in crushed wires and kink spots in thewire rope. This is very expensive, because the wire ropeis usually no longer useful for hook block operations.Changing the length of rope requires unreeving thehook block wire rope and reeving the correct length ofwire rope for the clamshell. This may be atime-consuming effort, but saves you from having toreplace 300 to 400 feet of wire rope when the crane isrigged for hook block operations.The clamshell bucket (fig. 12-29) is two scoopshinged together in the center with counterweightsFigure 12-29.-Clamshell bucket.12-17
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business