August 2022 Volume 4

MAINTENANCE

Figure 3: Embedded frame required for conventional forging press foundation being positioned to receive its press Furthermore, ground vibration limits the placement of nearby machining lines (i.e., of crankshafts), where lower frequency vibration (typically in the range of 5 to 15 Hz depending on the size of the press) causes vibration waves that can travel long distance and even excite sway in 3-4 story buildings. Because damping of low frequency waves is typically small, vibration levels decrease only in proportion to distance. In contrast, the higher frequency vibrations of forging hammers undergo an additional decrease with distance caused by higher damping in the ground.

Figure 5: Press bed installed on outrigger frame on Spring-VISCODAMPERs

Screw Press Foundations Screw presses combine characteristics of both types of machines. Hence the benefit of spring support to the foundation is a mix of the two. The ram, driven by a spindle and horizontal flywheel, impacts the forging like a hammer, creating a vertical shock. As the rotating masses slow down, an additional rotational shock occurs (trying to twist the foundation). This repetitive function usually necessitates large shear keys and anchor bolts to keep the press and foundation free of relative displacement. Dynamically uncoupling the foundation from the machine requires a robust support system that can handle both vertical and high horizontal loads. Like a mechanical press, the addition of an outrigger structure increases rocking and rotational stability. It also provides additional stiffness to the press frame. In this case a steel plate (6-8 inches thick, depending on press size) is installed between the vibration isolation system and the feet of the press. In isolated cases, steel frames of standard profile beams can replace the steel plates.

Figure 4: Conventional versus spring-support approach Of perhaps greater benefit during the life of the machine, damage to anchors and subsequent concrete is eliminated by placing the press on a spring and viscous damped steel outrigger frame. This results in increased rocking stability in the direction of the crankshaft rotation. The dynamic uncoupling of the foundation and press results in no more broken bolts, and the transformation of dynamic load yields similar benefits to those listed above for forging hammers (i.e. lower soil bearing requirement, reduced settlement, leveling at any time, etc).

FIA MAGAZINE | AUGUST 2022 22