August 2022 Volume 4

MAINTENANCE

What You Need to Know About Forge Shop Foundations By Victor Salcedo

Forging machine foundations are an essential part to the long-term performance and reduced maintenance intervals of even the most robust forging hammers and presses. Experienced maintenance personnel will know the tireless effort to re-machine critical components to compensate for mismatch and misalignment. A properly designed foundation will effectively transfer the static and dynamic machine loads to a competent layer of soil while maintaining rigidity and levelness of the machine. It typically consists of reinforced concrete and is broader than the machine base to reduce pressure on the soil. Coupled with carefully selected vibration isolators, typical amplification of force can be reduced to minimize foundation size while also reducing the risk of settlement during the life of the machine installation. Pre-Dig Investigations Before embarking on the installation of new machinery, it is important to review the plant layout and available space to assess whether vibration will interfere with any other planned processes, such as machining of product or dies. Also, future use of the space should help dictate the minimum distance at which forging machinery should be placed, whether isolated or not. In either case, subsoil investigation by a geotechnical engineering firm should be a priority. Furthermore, differential settlement risks should be identified, as this will inevitably stress the machine frame and unevenly wear machine components such as ram guides and cause contact misalignment. As a rule of thumb: • Square mat foundations stress the soil to a depth equal to about twice the foundation width, so be certain to commission sufficiently deep borings. • Soil is generally not continuous, so take various samples at the designated location. • Beware of existing un-engineered fill of unknown history. These soils should be removed. • The bearing strength of the soil should be sufficient to avoid settlement. • Water table behavior can cause swelling and shrinkage. Furthermore, saturated soils can be settlement prone and result in vibration transmission proportional to water content fluctuation. • The Cyclic loading of soil due to forging can cause loss of shear strength, which can cause settlement.

• The greater the moisture, the weaker the shear strength in cohesive soils such as clay. • Proper drainage and use of granular soils such as stone are important to avoid that later water may penetrate andweaken the support. This is a common cause of post-construction settlement problems. Additionally, dynamic soil testing with a few vibration sensors can provide valuable information to determine if the foundation and isolation system will be sufficient to attenuate vibration at a given distance. This will help minimize excessively large plant layouts. Furthermore, high soil moisture content can lead to higher vibration transmission, or amplification of vibration due to inappropriate isolation system selection, such as elastomer or springs that are too stiff on relatively wet soil. Once the static and dynamic characteristics of the soil have been determined, several techniques can be employed to improve dynamic foundation performance. These include: • Increasing the surface area to decrease demands on the soil • Improving soil or implementing a deep foundation using piles/caissons • Increasing mass inertia of high tuned (conventional) foundations generally using timbers • Connecting foundation to other foundations (requires careful engineering consultation) • Using a low Tuned Isolation System (i.e. GERB Spring VISCODAMPERs) There are several key items to look for during construction that can help reduce the risk of settlement. Always consider that excavated soil expands and could introduce soils with much less bearing capacity into the site. Regular compaction during fill layers of no more than 8-12 inches will result in less settlement, as up to 0.5-in. of settlement can be expected in 6 inches of poorly compacted soil. Compact the pit bottom using a vibrating plate compactor for sand or gravel soils, and a jumping jack compactor for silt or clay the same day as the concrete pour.

FIA MAGAZINE | AUGUST 2022 20