| | | | | | | | | | | | | | | | | | | | |
| | | |
| | | A very important clue in determining if a machine is support critical is the presence of a factory designed or specified anchoring system. In the cost conscious world of the machine manufacturer, an anchoring system is only provided or recommended if it is truly necessary to achieve design performance levels. This is not an absolute statement, but it is accurate most of the time. Once the requirement for an anchoring/alignment system has been established, the next step is to decide on the best approach, and of providing an adequate foundation. Exceptions: It should also be noted at this time that there are situations where the natural frequency of the required isolation system will be lower than those levels attainable with free-standing mounts. In these situations an isolated foundation may still be required for a non-support critical machine solely for the purpose of providing adequate isolation. The relationship of natural frequency and isolation will be discussed later, in the section on vibration theory. | | |
| | | Vibration Sources Shown in the illustration below are some of the typical sources of disturbing vibrations. Each of these sources will exhibit a different amplitude/frequency characteristic. Shown are railroads, truck traffic, fork trucks and metal stamping equipment | | |
| | | |
| | | |
| | | FACTORS TO CONSIDER IN DECIDING WHETHER TO ISOLATE | | |
| | | |
| | | These sources can adversely affect the machine to be isolated or may simply contribute energy to excite other system elements (i.e., the building structure and floor) to vibrate at their own natural frequencies, thus causing machine accuracy and maintenance problems. Each facility has its own individual machine location layout. When developing an isolation scheme, it will be necessary to decide whether it is more advantageous to isolate the source of a shock/vibration condition, or the sensitive equipment which is vulnerable to the disturbances. In the typical industrial environment, it would be normal to see building and plant floor natural frequencies starting as low as 18 to 24 Hz, and transmission from railroads, industrial presses and highways occurring at even lower natural frequencies. | | |
| | | • High traffic (external or internal) • Nearby presses or mills taking heavy interrupted cuts • To avoid disturbing the surrounding environment with enegy from machine being installed • Interference from nearby rail lines | | |
| | | |
| | | It is always a good idea to have a vibration survey done to determine actual vibratory energy levels in the area where the machine is to be located. The next considerations are the specific machine requirements. This would include reviewing any OEM specifications related to vibration acceptable at the equipment under operating conditions. It may be necessary to examine the soil conditions, which may vary greatly from stiff clay to very soft high organic content top soils with a high water table. Future facility considerations also need to be taken into account, such as expansion and moving plans. If dealing with a new facility, be sure to make good use of historical data. Unisorb's experience in this area is unequalled. The primary difference between approaches available for isolating the foundation is the characteristic natural frequency range attainable. As will be seen in the next section, it is extremely important to know what disturbing frequencies need to be isolated. | | |
| | | |
| | | VIBRATION THEORY | | |
| | | |
| | | The fundamental requirement for designing a functioning foundation isolation system is to establish the proper relationship between the forcing frequency and the natural frequency of the isolation system. In most cases our objective is to assure that the natural frequency is lower than the forcing frequency. Please refer to the Transmis- | | |
| | | |
| | | 3 | | |
| | | |
| | | | | | | | | | | | | | | | | | | | |