August 2022 Volume 4

MAINTENANCE

Impression Die Hammer Foundations Forging hammers usually cause very high vibration levels that can be felt more than a quarter mile away! Below a conventional foundation, the dynamic load from a hammer blow is several times higher than the static load. These dynamic loads may compact the soil and cause settlement and often result in tilting of the hammer. Realignment in these cases is difficult and costly. Vibration isolation of hammers reduces the dynamic loads below the vibration isolation system to a fraction of the static loads so that settlement caused by hammer operation is unlikely. In the rare occasion in which settlement occurs, access to vibration isolators in an open pit allows easy shimming and releveling without removing the machine or any of its components. By directly placing a forging hammer on spring-viscous dampers, like those supplied by GERB, the reduced loads result in a base mat of minimal thickness as generally shown in Figure 1.

• Components can be removed for repair without removing the hammer in most cases. • Operator fatigue can be reduced and the work environment improved. • It works well with robots/automated cells. • A hammer of any size can benefit (500 to 50,000 lbs!).

Figure 2: Typical foundation and isolator selection for 3,000 lb hammer

Mechanical Press Foundations The benefits of proper foundation design and isolator selection are also relevant to mechanical forging presses. Different from forging hammers, in which deformation and hardening of the forging happen rapidly, a crank or wedge press deforms the material with high forces at slow speeds, resulting in significantly lower vibration levels. But presses must provide extremely high pressing forces, 12,000 tons or more, and require the movement of heavy masses. To limit the speed disadvantage of a forging press as compared to a hammer, the press must rapidly accelerate the slide during 0.05 to 0.10 seconds of each stroke. Experience has shown that vibrations caused during the acceleration phase may be higher than during the actual forging operation. Furthermore, a large moment about the crank causes rotation about the foundation, which is usually the cause of anchor bolt failure. To reduce the risk of localized foundation failures large steel structures are usually embedded into the concrete. Furthermore, the foundation needs to be very stiff to avoid amplification of vibration.

Figure 1: Conventional versus foundation implementing spring VISCODAMPER support

With direct spring support, the resulting foundation pit size is significantly reduced. Therefore, foundation costs (including the spring system) may be less than fixed based foundations while also benefiting from 70-90 percent vibration isolation efficiency (depending on soil). Furthermore: • Foundation excavations can be significantly smaller (e.g. 50%). • Soil bearing requirement is lowered due to isolation efficiency, which usually eliminates the need for piles! • The estimated foundation mass is only about 20 percent of a conventional foundation; where a 6,000 lb hammer requires a reinforced concrete pit that is only 10 ft deep and 120,000 lbs of RCC, versus 20 ft and ~600,000 lbs of RCC. • If settlement occurs, it can be fixed with shims without third party rigging!

FIA MAGAZINE | AUGUST 2022 21