BASE ASSEMBLY.- The anvil block in the base assembly group is held in place by buffer bolts and has compression rings identical to those on the ram piston (fig. 12-64). Radial thrust or side thrust to the hammer is transmitted to the leads through the thrust bearing. A vibration damper, concealed under a shroud, isolates the cylinder from the shock vibration of the anvil. Buffer bumpers absorb the recoil from the Belleville washer type of buffer springs connected to the anvil by buffer bolts, dampening overtravel and holding the hammer together. Pins lock the buffer compression nuts to the buffer bolts and are held captive by the buffer housing caps. The buffer nut bumpers absorb the recoil of the Belleville springs.

RAM-PISTON OVERSTRIKE.- The length of free travel (maximum stroke) of the ram from the bottom of the stroke to the safety catch lip at the top is 109 inches (fig. 12-65). When the ram is recoiled high enough, the ram rings will engage the safety catch lip and prevent it from going out of the top. If the upward force of the ram is too great, the whole hammer will be lifted off the pile, possibly causing the rings to shear. To prevent this danger, watch the projection of the ram above the hammer and reset the throttle when necessary.

Pile-Driving Caps

A pile-driving cap is a block (usually a steel block) that rests on the butt or head of the pile and protects it against damage by receiving and transmitting the blows _{of the hammer or ram.} In the steam, or pneumatic, hammer, the cap is a part of the hammer. The cap with a drop or diesel hammer is a separate casting with the lower part recessed to fit the head or butt of the pile and the upper part recessed to contain a hard cushion block that receives the blows of the hammer. The cap is fitted with a wire rope sling so that the cap, as well as the hammer, may be raised to the top of the leads when positioning a pile in the leads.

On the DE-10 hammer, you place one cushion block in the drive cap and lash the cap to the hammer front and

Figure 12-66.-H-beam pile-driving cap.

back with two pieces of 1/2-inch wire rope and clips. You must allow 3 to 4 inches of slack in the wire rope. The cap is normally lashed to the hammer after the hammer is placed in the leads.

NOTE: The top of the cushion block should be kept high enough to prevent the hammer shroud from fouling on the rim of the drive cap pocket.

Pile-driving caps are available for driving timber, concrete, sheet, and H-beam piles. Figure 12-66 shows a pile cap designed for driving a H-beam pile.

Placing Hammer in Leads

Placing the pile-driving hammer in the leads is performed two ways: while the leads are horizontal or ^vertical. Leads are not always used in pile-driving operations. Pile hammers can be used as a flying hammer, using special adapter caps attached to the hammer (fig. 12-67). This is far the most dangerous of all types of pile-driving operations and should be attempted only by experienced personnel.

Figure 12-67.-Pile driving using a flying hammer.

The steps required to install the hammer in the leads in the horizontal position are as follows:

1. Block the leads about 18 inches off the ground in several places, keeping them as level as possible.

2. Using a forklift, place the hammer at the base of the leads with the top of the hammer towards the top of the leads.

NOTE: On underhung leads, the fuel pump faces upward. On extended four-way leads, the fuel pump faces downward.

3. Have the forklift approach the hammer from the pile cap end.

4. Adjust the forks so they will just fit the lead guides on the hammer.

5. Pick the hammer up in this manner and guide the top end into the leads as far as it will go without hitting the forks.

6. Block up the hammer that protrudes and reposition the forklift to push the remainder of the hammer into the leads.

NOTE: The crane line may assist in pulling the hammer into the leads.

7. Secure the hammer to the bottom of the leads. This will keep the strain off of the leads, as they are raised to the vertical position by the crane boom.

Installing the hammer in the leads in the vertical position is as follows:

1. Raise the boom and leads from horizontal to vertical and install the catwalk. Continue to raise the boom as high as practical and safety permits.

2. Hoist the hammer to a vertical position and position it under the leads. It takes a combination of lowering the boom and hoisting the hammer to slide the hammer onto the lead guides.

If this does not allow enough clearance to install the hammer vertically, use the following:

1. Use a deep ditch or loading ramp for additional clearance for the hammer.

2, Set the hammer in an excavated hole to clear the bottom of the leads.

3. The hammer can be partially submerged in water to gain additional clearance.

PILE-DRIVING TECHNIQUES AND TERMINOLOGY

Care must be taken during pile driving to avoid damaging the pile, the hammer, or both. The pile driver must be securely anchored to avoid a shift of position. If the hammer shifts while driving, the blow of the hammer will be out of line with the axis of the pile and both the pile and hammer may be damaged.

Carefully watch the piles for any indication of a split or brake below the ground. If driving suddenly becomes easier or if the pile suddenly changes direction, a break or split has probably occurred. When this happens, the pile must be pulled.