Vibration isolation at the source – example of a mechanical press
Machine bearing – Why?
Industrial plants generate considerable vibrations that are transferred to floors, walls and ceilings. These are therefore perceived as disturbing not only in the immediate vicinity, but also at a greater distance. The transfer to neighbouring offices or – due to the growth of cities – to adjacent residential areas is particularly undesirable. At the same time, this vibration load can also cause damage to buildings or other machines. Here the well-known principle applies: constant dripping hollows out the stone.
How vibrations are transmitted
Noise from machines can reach the receiver directly through the air. Vibrations of the machine can also be transmitted to the building (so-called structure-borne sound) and thus be sensed or felt. At the same time, the components radiate the vibrations again elsewhere as airborne noise. This leads to an extensive impairment of the quality of life and work.
Polyurethane mats as a solution
Polyurethane (PUR) products from KRAIBURG have been used in vibration isolation for many years. There are two ways to do this:
The disturbing vibrations are only suppressed at the receiver. This may be necessary if the source of the interference is not or not sufficiently isolated. On the other hand, the insulation may only be required on a small area.
The vibrations are reduced here before they are transferred to the building. Structural changes in the environment are therefore not necessary.
Depending on the existing boundary conditions, one or the other variant can be aimed for. For various reasons, source insulation is particularly suitable for machines:
- The contact surface of the machine is usually comparatively small compared to the surfaces on which no disturbing vibrations are to occur.
- The solution is optimally adapted to the machine.
- The building is not exposed to harmful vibrations.
- Source insulation is usually cheaper than retrofitting the building and is also more flexible.
The design of the solution depends on various factors, including the geometry and weight of the machine. This means that bearing can be carried out under the machine in points or strips. A flat bearing or the insulation of only individual machine components can also be implemented.
Advantages of polyurethane products
- Favourable material
- Longer service life
- Can be cut to machine dimensions
- High insulation effect
- Low tuning frequencies
- Compensation of unevenness
- Easy to process, no maintenance
- Small sinking in
- Properties can be optimally adapted for application.
In contrast to rubber products, polyurethanes are characterized by significantly better insulation properties. This can also significantly reduce very low-frequency interference.
A practical example: High-speed press
In 2002, the previously rigidly installed high-speed press (approx. 100 punching strokes/minute) was subsequently installed to decouple vibrations from the hall floor. Due to the slim design of the press with a small floor plan and high centre of gravity, a foundation on a steel plate with underlaid insulation made of polyurethane elastomer was chosen.
Picture: Press rigidly screwed to the hall floor
Technical data of the press:
- Weight of the press: 2200 kg
- Dimensions of foundation slab: 2,20 m x 1,35 m
- Weight of the foundation plate: 900 kg
- Total weight: 3100 kg
- Speed: 100 Strokes per minute
Picture: Steel foundation plate
The insulation was 50 mm thick, consisting of Dipoelast 2.2 (today PURASYS vibrafoam SD 26), and PUR elastomers with different stiffnesses were chosen to compensate for an eccentric system centre of gravity. The present load caused the mats to deflect about 2.2 mm.
The selected material distribution resulted in the material pressures described in the photo. This area of application is demanding for an elastic mounting in so far as there is a permanent load for many years and strong vibrations occur.
PURASYS vibrafoam/vibradyn products have excellent properties to permanently withstand such requirements.
Abbildung: Isolierung mit unterschiedlichen Flächenpressungen und zugehörigen PURASYS-Materialien
The removal of PUR insulation after 14 years of use
The vibration-insulated press was operated without downtime until October 2016. After about 14 years, the mechanically stressed insulation, wetted at the edges with mineral oils, was replaced by a new one. The old insulation fulfilled its purpose even after 14 years.
The replacement was carried out to investigate the performance of the materials after a long period of use and their ageing behaviour in the KRAIBURG test laboratory.
Picture: Vibration isolated press
The exchange was supervised by the engineering office Moschner & Partner from Haiger. The laboratory test was then carried out by KRAIBURG PuraSys GmbH & Co. KG.
The figure shows an example of a change in the static spring characteristic curve of dipoelast 2.2 with a component height of 50 mm. The production parameters recorded as standard at the time of production of the installed materials served as a reference. In the example shown, a slight post-hardening could be measured over the service life of 14 years, which, however, hardly differs from the original material. This application example makes it clear that the material used has not lost its very good dynamic properties even after very long use.
The former dipoelast series was transferred to the PURASYS vibrafoam series to cover a continuous range of applications. The Dipoelast 2.2 variant corresponds to the new type SD 26, whose characteristics are printed on the right.
„PURASYS vibrafoam and vibradyn products are used for various machine bearings such as air conditioners, presses and punches. This demanding application in particular shows successfully that this is a high-quality material that repeatedly convinces us and our customers in its long-term behaviour.“
– Guido Moschner, Ingenieurbüro Moschner & Partner