Q. How are Vibro/Dynamics Isolators different from others on the market?
A. Vibro/Dynamics doesn’t use a “one size fits all” approach to isolator selection. Every Micro/Level Isolator size has a wide variety of different elastomeric inserts to precisely meet the isolator characteristics required to solve a particular problem.
Our design is unique. Look at a cross-section drawing of a Vibro/Dynamics Micro/Level® Isolator. Its design is unlike anything on the market. Notice that the isolator has pins or “fingers” that extend down from the support housing, pass through the bearing plate, and then fit into “grippers” molded into a custom-engineered elastomer. This feature, called “Glide/Damping™”, reduces the isolator’s horizontal stiffness and provides a greater degree of isolation. It also helps keep machines from walking by decoupling the support housing from the elastomer.
Q. Why don’t presses “walk” on isolators?
A. Presses don’t walk on properly selected free-standing isolators due to friction between the isolator and the foundation. To keep a machine from walking, the static deflection (compression) of the isolator under load must be greater than any dynamic unloading of the isolator caused by the operation of the machine. Properly selected and applied isolators always carry load, so the friction of the elastomer on the floor is usually sufficient to overcome any horizontal forces that cause a machine to walk.
Q. My press is rocking. Is this normal?
A. Yes, to an extent. A press with an unbalanced crankshaft or eccentric will generate a rocking force. Isolators compress and shear in reaction to these forces, so it is normal that a press will rock to some degree. The softer the isolator is, the more the press will rock. Depending on the press and isolators, one-quarter inch at the crown is not unusual. The human eye tends to magnify motion, so what looks like excessive motion may not be.
Q. How long will isolators last?
A. It is not uncommon for Vibro/Dynamics Isolators to last 30 years or more. When properly applied and installed, the isolators can last the life of a machine.
Chemicals can be harmful. Vibro/Dynamics has three alternate elastomeric compounds to handle most environments. Consult with us if your isolator installation will be subjected to a high degree of chemical exposure.
Q. Why are you recommending a larger isolator than your competitor?
A. It could be due to two reasons. One, Vibro/Dynamics manufactures vibration isolators as opposed to simple machinery mounts. Our goal is to provide the best isolation possible while keeping machinery motion to an acceptable level. A larger area isolator is usually a softer isolator. Due to the larger area, greater isolator deflection is possible without over stressing the isolator’s elastomeric element. Overstressing causes leveling instability (due to elastomeric creep) and the higher stress on the foundation.
Two, a larger isolator may have been recommended to provide better support coverage of the machine foot. The isolator support housing should span the foot gussets.
Q. Why does the isolator stick out from under the machine foot?
Is this a problem?
A. There are really two questions here. One, is it a problem for the isolators and two, is it a problem for the machine? In answer to the first question, the support housing of a Micro/Level® Isolator is designed to transfer the load on the isolator’s support housing to the leveling adjustment screw, which then distributes the load uniformly over a heavy-duty steel bearing plate. The isolator has a built-in swiveling capability that automatically compensates when the bottom of the machine foot is not parallel to the floor, assuring that the isolator’s elastomer is uniformly loaded.
In answer to the second question, most machines have foot and leg designs strong enough to allow them to be supported at the mounting hole. Of course, there are exceptions and the Applications Engineering Staff at Vibro/Dynamics can offer assistance in this regard. Vibro/Dynamics has a complete line of vibration isolators designed for almost every situation. If the machine cannot be supported at the mounting hole, then Vibro/Dynamics will recommend a wedge-style isolator that can be placed anywhere under the machine foot.
Q. How do isolators reduce noise?
A. Isolators are very effective at reducing structural-borne noise caused by transmitted vibration. Vibration causes noise when it excites the natural frequencies of a structure. This “sounding board” effect is directly related to vibration in the supporting surface. Since isolators reduce vibration, structural-borne noise is reduced.
Q. Is it OK to use isolators on a press with a rolling bolster or die cart?
A. Absolutely. This is very common. The alignment tolerance for most rolling bolster and die carts is sufficient so that it is not a problem.
Q. Where does the vibration go when I mount my press on isolators?
A. Internal forces caused by the stamping operation occur whether the press is bolted to a foundation or installed on isolators. However, the magnitude of the vibration within the press is lower when using vibration isolators.
It is a common misconception that bolting a press to a foundation somehow “sucks” the vibration out. Bolting a press to a foundaton actually subjects it to more vibration and impact force. Vibration isolators are cushions that transform a sudden shock pulse into a decaying series of longer duration forces.
Imagine hitting a brick wall with your fist. It would hurt! Now imagine hitting the wall with the same energy, but with your hand in a well padded boxing glove. It hurt less! Why? It’s because the impact duration is longer, effectively reducing the impact force. Short duration impacts mean higher force.
This is the same thing that happens on a hard-mounted press. The sudden release of potential energy at snap-through causes the press foot to slam against the foundation. This fast duration, high magnitude force hits the foundation and the foundation responds in kind, sending damaging forces back into the press.
Q. Why do I still feel vibration in the floor when my press is on your isolators?
A. Vibro/Dynamics rates isolation effectiveness as a percentage compared to the levels that would exist if the machine were anchored or “hard mounted”. It is not possible to obtain 100% with a passive isolation system, but you can come close.
When selecting isolators, many factors are taken into account. But it usually comes down to two issues: How much isolation is required and how much motion can be tolerated? Isolators are usually selected to achieve the highest amount of vibration isolation possible while keeping motion to an acceptable level. These are conflicting goals. To reduce machine motion, the stiffness of the isolator is often increased, at the detriment of isolation, resulting in some vibration being felt in the floor.
Inertia Force, which is the force generated by the motion of the press slide, is another possible cause of remaining vibration in the floor. Run the press without material to see if inertia is the cause of the vibration. If vibration is felt, then inertia is contributing to the vibration in the floor.
Elastomer isolators are not usually designed to isolate inertia force. These are high-tuned isolators, which means the isolator’s natural frequency is higher than the operating speed (SPM) of the press, resulting in no inertia force isolation. In order to isolate inertia force, the natural frequency of the isolator must be lower than the operating speed of the press. Vibro/Dynamics VS Series Spring Isolators have natural frequencies as low as 2.5 Hz., which is ideal for machines running over 250 SPM. Added weight is usually required to keep press motion to an acceptable level.
See the following question for information on reducing inertia force.
Q: What can I do to reduce the vibration in my press?
A: Vibro/Dynamics isolators have been installed on tens of thousands of presses. We have a lot of experience isolating machines with a wide variety of different press designs, jobs, and soil conditions. Lowering the shock level within the machine will improve tooling and machine life and will further improve the work environment with less vibration in the plant. The following list of suggestions will help reduce vibration and save a lot of downtime and money.
A: Once machines are installed and a vibration problem is discovered, it is often very difficult and expensive to relocate the offending machine or sensitive area. Surface vibration waves are typically the culprit. The amplitude, or severity, of surface waves decreases by a function of at least (1/distance from vibration source)0.5. High frequency waves will dissipate over shorter distances than longer wavelength, low frequency waves. Vibration waves are further attenuated by damping losses characteristic of the materials they are travelling within. Steel, concrete, and frozen water/soil are efficient conductors of vibration. Surface waves can thus travel significant distance and still cause problems. It is most effective to reduce the amplitude of the waves at the source and at the sensitive area. The most cost efficient way to achieve isolation of the vibration waves is by using passive vibration isolators.
Many other methods have been employed to attempt to reduce the surface wave vibrations, with generally limited success:
To avoid costly vibration mitigation measures it is best practice to be aware of vibration problems before a machine is installed. It is important to understand the frequency content of the source and the sensitive frequencies of the surroundings.
Q. Do I still need a foundation if I use machinery mounts or isolators?
A. Isolators do not eliminate the need for a well-designed foundation. The foundation must be strong enough to support the physical weight of the machinery, plus the dynamic forces generated by the machine. Dynamic forces vary with machine characteristics. Well-designed isolators will reduce the dynamic force transmitted into a foundation, but determining the amount going into a foundation is very difficult.
(See the following question).
Q. How much force is transmitted to the foundation when a machine is installed
A. This question is often asked by civil engineers and architects when designing machinery foundations. The short answer is, “we cannot determine the exact magnitude of the transmitted impact forces.”
In order to determine the transmitted force, the frequency and forces being generated must be known as well as the characteristics of the soil, foundation, and machine construction. Many of the variables influencing the magnitude of the input forces are not known or even measurable. Factors that strongly influence the transmitted force:
Estimates of transmitted forces can be made, but they are only estimates. Vibration isolators are the most important factor in reducing transmitted vibration. However, the vibration isolators must be given the proper conditions to function at peak efficiency.
Q. Is my current foundation or floor sufficient?
A. Local Civil Engineers or Architects are the best people to answer this question. They can assess the local soil conditions, the status of the existing concrete, and the status of the existing reinforcing steel. Areas with high water tables or that have been filled could potentially cause problems if the foundation design doesn’t take them into consideration.
Q. How do I measure the foundation stiffness (K) and natural frequency (Fn)?
A. The soil under the foundation will often be compacted during foundation construction and then further loaded and compacted as the installation ages and machines are run. So the finished installation is often very different from when the site was just a plant floor or an open field. Foundation Natural Frequency (Fn) can be determined by dropping a mass and recording the ground vibrations.
Two types of tests can be done by Civil Engineers to determine the soils present at unimproved sites:
A Red Flag is when the soil is found to be very poor with high amount of fine clays and high water table. The foundation will tend to have a lower natural frequency and lower bearing capacity if the soil is poor. In these cases, Vibro/Dynamics advises a larger foundation and "foot print" with the softest isolators permissible to avoid settling and to improve isolator effectiveness. If the foundation is under-sized, the isolators will have reduced effectiveness regardless of their stiffness.