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Information & Precautions

Shock Absorbers

Basic Structure and Principles: Shock Absorber
Shock absorbers have two types of structure: an adjustable type in which the absorption characteristics can be adjusted, and a fixed type, which is non-adjustable. Each structure is shown below.
Adjustable Type
Shock absorber basic structure By rotating the adjustment knob (adjustment shaft) located towards the rear of the main body, the amount of oil flowing out of the pressure chamber can be adjusted, which in turn adjusts the absorption characteristics. For the multiple types, the adjustment can only be made with the final orifice; therefore, the range of adjustment is limited. The adjustment range is wider in the single types. Because the orifice area changes in an analog manner, fine-tuning of the absorption characteristics is possible.
Fixed Type
Shock absorber basic structureBecause it has no adjustment mechanism, the overall length is shorter than the adjustable type. By customizing your orifice design, optimal absorption characteristics can be obtained. In addition, because the characteristics are fairly uniform, more than two of them can be used in parallel. For the fixed type FK series, high-speed, mid-speed, and low-speed types are generally available to accommodate various speeds.
Principles of Energy Absorption
As shown below, when an object hits the piston rod, the motion is transferred to the oil in the pressure chamber through the piston rod. As a result, the oil inside the pressure chamber flows out of the orifices located in the inner tube. This causes compression in the pressure chamber. The product of this hydraulic pressure and the pressure applied area of the piston is resistance, which acts on the colliding object. shock absorbers use this resistance to apply the brake to the colliding object, slowing it down. The hydraulic pressure generated inside the pressure chamber is proportional to the square velocity of the colliding object, as long as the orifice size, oil viscosity, etc. are constant. This is called velocity-squared resistance.
Shock absorber principles
What is a Shock Absorber?
In order to increase the productivity of industrial machines, such as automatic assembling machines, various transportation machines, machines tools, and so on, their operating parts have been made to work faster. However, the resulting impact, vibration, and noise have caused adverse effects on the machine's performance and on the working environment. A shock absorber is an extremely convenient hydraulic buffer that can solve such problems. There are similar devices made of rubber, springs, or devices that use pneumatic pressure, but none of them rival the impact absorption characteristics of the hydraulic type.
RubberThe rubber’s elastic deformation captures the impact energy, and this energy is then accumulated in the rubber. As a result, the accumulated energy works as a repulsive force, and there is a high risk of a rebound being tenerated. Therefore, it is not an efficient impact absorber. On the other hand, it is extremely affordable and its installation is easy.resistance chart
Spring ALike the rubber type, it captures the impact through elastic deformation and stores it as elastic energy. Once the impelling force is diminished, the stored energy is likely to repel as it does in the rubber type, causing a rebound.
Pneumatic pressure BIt uses pneumatic pressure to absorb impact similar to the rubber and spring types, but because the compressed air is released to the atmosphere through an orifice, the energy does not accumulate. However, unless the rapid compression and releasing action through the orifice is well balanced, a rebound occurs as it does in the spring type.
Hydraulic pressure
It uses oil’s velocity-squared resistance as well as viscosity resistance to absorb the energy, which is then converted into heat energy and released into the atmosphere. As a result, extremely efficient impact absorption is possible. A relatively compact design is capable of absorbing large impacts, and depending on its structure, the impact absorption characteristics can be modified as well.
Absorption characteristics There are three structures in a single-orifice type: a dashpot structure that utilizes the space between the piston and cylinder tube; a single tube structure in which orifices are provided in the piston; and a double tube type single orifice structure (adjustable). Their resistance characteristics are shown in the graph to the right. When the piston moves within the cylinder tube, the product of the pressure generated in the inner tube and the piston area becomes the resistance. Throughout the entire stroke, the orifice area is constant. The resistance spikes immediately after the impact, and as the stroke advances, the speed decreases and the resistance decreases with it. Absorption characteristics
It has a double structure comprising an outer tube and an inner tube. Similar to the single-orifice type, the resistance is the product of the pressure generated inside the inner tube when the piston is stroking and the piston area. The orifice area at the moment of impact is larger compared to the single type, and because it gradually decreases as the stroke advances, it can suppress the overall resistance. Theoretically, the resistance during a stroke can be maintained constant. Depending on the orifice design, the resistance characteristics can be modified according to the impact conditions.
Although it has the same structure as the multiple-orifice type, resistance characteristics that are suitable for the intended use can be obtained rather than a constant damping force. FWM series is designed to absorb the kinetic energy in the first half of the stroke and to perform speed control during the last half of the stroke. Because of this, ideal energy absorption with respect to the air-cylinder thrust can be obtained.
Through a single tube system, the orifice groove provided on the inside wall of the tube changes as the stroke advances. Similarl to the multiple type, it has a large orifice area at the beginning of the stroke. As the stroke advances, the orifice area becomes smaller, suppressing the resistance. In addition, because the orifice area can be changed on a continuous basis, the resistance fluctuates less compared to the multiple type. Because of this, optimal energy absorption can be realized.
Purpose of the Accumulator
As shown below, when work collides with a shock absorber, the piston rod initiates a stroke, causing the oil to flow into the other side of the piston through the orifices. In short, the capacity of oil chamber B is reduced by the piston rod, and not all of the oil in oil chamber A is able to flow into the oil chamber B. In order to secure the capacity reduced by the piston rod, a self-foaming nitrile rubber is provided. The pressure of the oil compresses the rubber so that it absorbs the capacity that is equivalent to the piston rod. This is the role of an accumulator. Although silicone oil is used in a shock absorber, there are certain types of hydraulic oils that do not work well with certain types of accumulator. Using improper hydraulic oil causes the nitrile rubber to harden, reducing the durability of the shock absorber.
Purpose of an accumulator
Shock Absorber's Cap: Securing Method and Materials
Diagrams illustrating how the caps are secured End cap 1 End cap 2 End cap 3 End cap 4 End cap 5
Cap material Resin Resin Resin Polyurethane rubber Metal
Securing method Directly press-fit onto the rod Press-fit on the metal holder Press-fit on the metal holder Press-fit on the metal holder Screwed into the piston rod
Applicable models FA-1212 series
FA-1010 series
FA-1215 series
FA-0805 series
FA-1005 series
FA-1008 series
FWM-1008 series
FK-1008 series
FK-1417 series
*Do not throw into a fire
As the products contain oil, throwing them into a fire may cause them to ignite, resulting in injuries.
*Do not operate without sufficient mounting strength
Operating with insufficient mounting strength may damage the main machine and cause injuries.Ensure sufficient mounting strength of maximum drag x safety factor (Regarding maximum drag, please refer to the catalogue or contact our sales department.)
*Do not operate without an external stopper
Without an external stopper, the main machine may become damaged due to bottoming. Ensure that an external stopper is set in the prescribed location for each type before operating the product. (For the locations of external stoppers, please refer to the catalogue or to the owner's manual.)
*Do not attach using incorrect tightening torque
Using an incorrect tightening torque when attaching may cause operational failure and damage to the main machine. When tightening an attachment screw for a shock absorber, please use the tightening torque as listed below.
External diameter of the screw (mm) M4X0.5 M6X0.75 M8X0.75 M10X1 M12X1
M20X1.5 M25X1.5
M30X1.5 M36X1.5 M42X1.5
Tightening torque for the bolt (N·m) 0.35 0.85 3.9 7.8 7.8 9.8 14.7 29.4 49 58.8 78.4 98 392
*Dislodged retaining ring
Failure to adhere to the specifications listed in the catalogue may cause the internal pressure of the inner tube to raise to a dangerous level where the retaining ring may become dislodged and interior parts may shoot out, causing injuries. Do not bring your face close to a shock absorber that has a retaining ring while it is operating.
*Do not discard oil more than is necesssary
Discarding the oil contained in dampers more than is necessary will pollute the environment.
Dispose the oil according to laws concerning waste management and cleaning.
Scattering pieces due to cap damage
Failure to adhere to the specifications listed in the catalogue may cause the cap to break, resulting in scattering pieces that may cause injuries.Please install an anti-scattering cover.
Eccentric load and eccentric angle
When a load collides at an eccentric angle of ±2.5° or larger, recovery failure due to a bent piston rod and performance degradation due to eccentric friction on the sliding part may occur, causing damage to the main machine.
Operating temperature
When using a shock absorber, ensure that it is used within the operating temperature. Failure to do so will have adverse effects on the packing and accumulator that will reduce the product life, which may damage the main machine. (For the appropriate operating temperature, please refer to the catalogue or to the owner's manual.)
Usage environment
This product cannot be used in a vacuum or under high pressure, as this will cause damage to the main machine.Do not use in an environment where chips, cutting oil, water, etc. can come in contact with the piston rod. This will damage the packing, resulting in oil leakage, which leads to operational failure and damage to the main machine.
Bansbach Easylift of North America is not responsible for any secondary accidents caused by a shock absorber. The following are two examples of such secondary accidents caused by a shock absorber:
(Example 1) An overload causes the piston rod to break, resulting in a facial injury. Countermeasure – install a cover.
(Example 2) The drag causes the cap to break. The cap then gets lodged inside the machine, damaging it.
Countermeasure – install a tray, etc. under the shock absorber. The user should implement preventative measures against such secondary accidents.