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Foundations
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Virtual Machine Shop Forum  |  Machine Tool Technology  |  Questions, answers, ideas  |  Topic: Foundations « previous next »
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Author Topic: Foundations  (Read 358 times)
Geo.
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« on: December 12, 2016, 01:02:31 PM »

Dead Weight Compared to Live or Dynamic Weight
The load on the foundation has two components. First, there is the total machine static weight or dead weight. The foundation should not be designed based on this factor alone. There is also the live weight that is generally assumed to be 1.5 times the static or dead weight of the machine.

A number of factors determine press foundation requirements. machines subjected to sudden snap-through loads from cutting operations have more critical foundation requirements than similar machines developing increasing pressor loads like drawing or forming.

Many manufacturers and engineers allow a safety factor of 1.5 times the dead weight of the press and heaviest tooling for the live weight factor when designing the foundation. This is a rule of thumb. An individual case-by-case engineering analysis may result in a different actual live weight figure. Of course, it is wise to over-design the foundation if there is any doubt as to the actual live weight. The amount of live weight is greater in the case of machines having heavy slides and operated with long stroke lengths and at higher speeds.

Manufacturers may supply guidelines for foundation requirements. Because of the effects of applications, the final responsibility for a proper installation is the duty of the machine user. One of the most popular foundations is a rectangular slab of reinforced concrete placed on soil at least as good as firm well-drained clay.
Typically, the slab is isolated from the surrounding concrete flooring by an inch (25.4-mm) of insulation board and the top of the joint sealed with an oil resistant sealing compound

Soil Conditions

If the press is placed on a reinforced concrete floor, the thickness and strength of the concrete are important factors. However, the soil condition under the concrete is a very important consideration. Well-drained undisturbed clay over sound bedrock can support heavy loads. Foundations placed on solid bedrock are ideal.

The Slab or Inertia Block Foundation

Many types of machine foundations can be found in use throughout the industry. Variables such as soil conditions, machine weight, and dynamic loading all should be considered when developing a final plan for a foundation design.
Manufacturers may supply guidelines for foundation requirements. Because of the effects of applications, the final responsibility for a proper installation is the duty of the machine user. One of the most popular foundations is a rectangular slab of reinforced concrete placed on soil at least as good as firm well-drained clay.
Typically, the slab is isolated from the surrounding concrete flooring by an inch (25.4-mm) of insulation board and the top of the joint sealed with an oil resistant sealing compound

It is advisable that the slab should extend beyond each of the machines feet on all sides. And that less than ideal soil conditions may require a larger slab.

The slab thickness should provide a weight equal to or greater than that of the machine if soil conditions are ideal
If shock loads through energy release are expected, the weight should be increased to 1-1/2 to two times the machine weight. If the soil conditions are not ideal, it may be necessary to increase the foundation dimensions in all directions.
The concrete should be of high quality and have a minimum compressive strength of 3,500-psi (24,129 kPa) after curing 28 days. If anchor bolts or other fasteners are to be used, they should be cast into the slab at locations that line up with the mounting holes in the press feet. The weight of the machine  must be distributed evenly on the slab foundation.   

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