As companies strive to increase productivity by operating machinery at higher speeds, often the results are increased noise, damage to machinery/products, and excessive vibration. At the same time, safety and machine reliability are decreased. A variety of products are commonly used to solve these problems. However, they vary greatly in effectiveness and operation. Typical products used include rubber bumpers, springs, cylinder cushions and industrial shock absorbers. The following video compares how the most common products perform and why ITT Enidine shock absorbers are the smart choice for your energy absoprtion needs:
Theory of Energy Absorption
All moving objects possess kinetic energy. The amount of energy is dependent upon weight and velocity. A mechanical device that produces forces diametrically opposed to the direction of motion must be used to bring a moving object to rest.
Rubber bumpers and springs -
although very inexpensive, have an undesirable recoil effect.
Most of the energy absorbed by these at impact is actually stored.
This stored energy is returned to the load, producing rebound and
the potential for damage to the load or machinery. Rubber
bumpers and springs initially provide low resisting force which
increases with the stroke.
Cylinder cushions -
are limited in their range of operation. Most often they are not capable of absorbing energy generated by the system. By design, cushions have a relatively short stroke and operate at low pressures resulting in very low energy absorption. The remaining energy is transferred to the system, causing shock loading and vibration.
Industrial Shock absorbers -
provide controlled, predictable deceleration. These products work by converting kinetic energy to thermal energy. More specifically, motion applied to the piston of a hydraulic shock absorber pressurizes the fluid and forces it to flow through restricting orifices, causing the fluid to heat rapidly. The thermal energy is then transferred to the cylinder body and harmlessly dissipated to the atmosphere.
The advantages of using shock absorbers include:
1. Longer Machine Life – The use of industrial shock absorbers significantly reduces shock and vibration to machinery. This eliminates machinery damage, reduces downtime and maintenance costs, while increasing machine life.
2. Higher Operating Speeds – Machines can be operated at higher speeds because industrial shock absorbers control or gently stop moving objects. Therefore, production rates can be increased.
3. Improved Production Quality – Harmful side effects of motion, such as noise, vibration and damaging impacts, are moderated or eliminated so the quality of production is improved. Therefore, tolerances and fits are easier to maintain.
4. Safer Machinery Operation – Industrial Shock absorbers protect machinery and equipment operators by offering predictable, reliable and controlled deceleration. They can also be designed to meet specified safety standards, when required.
5. Competitive Advantage – Machines become more valuable because of increased productivity, longer life, lower maintenance costs and safer operation.
Automotive vs. Industrial Shock Absorbers
It is important to understand the differences that exist between the standard automotive-style shock absorber and the industrial shock absorber. The automotive style employs the deflective beam and washer method of orificing. Industrial shock absorbers utilize single orifice, multi-orifice and metering pin configurations. The automotive type maintains a damping force which varies in direct proportion to the velocity
of the piston, while the damping force in the industrial
type varies in proportion to the square of the piston velocity. In addition, the damping force of the automotive type is independent of the stroke position while the damping force associated with the industrial type can be designed either dependent or independent of stroke position.
Equally as important, automotive-style
shock absorbers are designed to absorb only
a specific amount of input energy. This means that,
for any given geometric size of automotive shock absorber, it will have a limited amount of absorption capability compared to the industrial type. This is explained by observing the structural design of the automotive type and the lower strength of materials commonly used. These materials can withstand the lower pressures commonly found in this type. The industrial shock absorber uses higher strength materials, enabling itt to function at higher damping forces.
Adjustment Techniques
A properly adjusted industrial shock absorber safely dissipates energy, reducing damaging shock loads and noise levels. For optimum adjustment setting see useable adjustment setting graphs. Watching and “listening” to a shock absorber as it functions aids in proper adjustment.
To correctly adjust an industrial shock absorber, set the adjustment knob at zero (0) prior to system engagement.
Cycle the mechanism and observe deceleration of the system.
If damping appears too soft (unit strokes with no visual deceleration and bangs at end of stroke), move indicator to next largest number.
Adjustments must be made in gradual increments to avoid internal damage to the unit (e.g., adjust from 0 to 1, not 0 to 4).
Increase adjustment setting until smooth deceleration or control is achieved and negligible noise is heard when the system starts either to decelerate or comes to rest.
When abrupt deceleration occurs at the beginning of the stroke (banging at impact),
the adjustment setting must be moved to a lower number to allow smooth deceleration.
If the industrial shock absorber adjustment knob is set at the high end of the adjustment scale and abrupt deceleration occurs at the end of the stroke, a larger unit may be required.
Industrial Shock Absorber Performance When Weight or Impact Velocity Vary
When conditions change from the original calculated data or actual input, a shock absorber’s performance can be greatly affected, causing failure or degradation of performance. Variations in input conditions after a shock absorber has been installed can cause internal damage, or at the very least, can result in unwanted damping performance. Variations in weight or impact velocity can be seen by examining the following energy curves:
Varying Impact Weight: Increasing the impact weight (impact velocity remains unchanged), without reorificing or readjustment will result in increased damping force at the end of the stroke. Figure 1 depicts this undesirable bottoming peak force. This force is then transferred to the mounting structure and impacting load.
Varying Impact Velocity: Increasing impact velocity (weight remains the same) results in a radical change in the resultant shock force. Shock absorbers are velocity conscious products; therefore, the critical relationship to impact velocity must be carefully monitored. Figure 2 depicts the substantial change in shock force that occurs when the velocity is increased. Variations from original design data or errors in original data may cause damage to mounting structures and systems, or result in shock absorber failure if the shock force limits are exceeded.