Double acting cylinders with shock absorption
Double-acting cylinder with shock absorption
Their prevalence is huge. Virtually everything in the world of technology that moves in the vertical, horizontal and oblique plane to a greater or lesser extent uses the power of actuators. Their phenomenon lies in the fact that these devices are structurally very simple in terms of ideas, and at the same time irreplaceable. So far, no one has come up with a better way to move heavy elements of machines while being harmful to the environment. What are double-acting cylinders? In this article, we will reveal many secrets about them.
Double acting cylinder, what is it?
For the sake of order, it is worth mentioning that since there are double-acting cylinders, it means that they are also single-acting. The difference between them is in the way they use enormous forces.
Single-acting and double-acting actuator
One-sided cylinder is equipped with one working chamber, which means that the device can only work in one direction, away from or towards itself. The idle return movement is carried out by means of, for example, a spring.
This is how the categories of actuators arise:
They have much smaller dimensions than their double-sided counterparts, and are mostly compatible with double-sided cylinders. Their service is easier and cheaper, as are the prices of the devices.
A double-acting cylinder has two working chambers enabling working in both directions. Let us add that due to its greater functionality, this mechanism is more popular.
Double-acting pneumatic cylinder, functioning
The movements of the piston rod in both directions are possible thanks to the sequential supply of pressurized air to both sides of the actuator piston.
In one sentence, pneumatic actuators are devices that convert the energy contained in compressed air into force or moment.
The following elements contributed to the huge popularity of actuators:
Simplicity of the idea of action;
Standardization of performance;
Large ranges of obtained forces.
Standardization of performance refers to the dimensional standards contained in the documents ISO, CNOMO, UNITOP and so on. This type of solution makes it possible to effectively combine actuators from different sources, although it is not always the best solution.
Double acting cylinder symbol
Speaking of standards, one should be aware that, for reasons of operator safety, appropriate graphic symbols are used to inform the operator about the purpose, application and operation of all mechanical elements present in a given technical environment. The graphic symbols were developed on the basis of the PN / ISO-1219-1 standard. The operator, who is aware of the principle of operation of the device, knows how to, among other things, avoid the risk of contact with the machine, installation and devices.
The force of action of the cylinders
Before double-acting cylinders can be used in a mechanical system, the necessary operating force must be determined. Bearing in mind that the said force depends on the air pressure and the surface area of the piston under the pressure of compressed air, it is already possible to make appropriate calculations based on the following formula:
F = πD² / 4 xp [kg]
Where D in cm refers to the nominal diameter of the actuator, while p [bar] [atm] is the supply pressure. The diameter of the actuator is always specified in the product specification, it is specified in millimeters. It is therefore necessary to convert it into centimeters.
The pressure, on the other hand, is given in bars or atmospheres. Hence, the calculated force is measured in kilograms, as the most readable parameter, understandable even for people without specialized professional education.
Of course, you can also use pneumatic actuator force tables , which should be on the manufacturer's websites of the given equipment.
Push and pull force, differences
Let me remind you that we are constantly operating within the principles of operation of pneumatic actuators .
F1 = π (D²-d²) / 4 xp [kg]
For a deeper understanding of the above formula, we explain that the pushing force F is a result of the piston side of the actuator, while the amount of the pulling force F1 is influenced by the piston-side actuator. The sign of the equation after the F1 symbol means that the formula concerns the determination of the pulling force .
D [cm] - nominal diameter of the actuator
d [cm] - diameter of the piston rod
p [bar] [atm] - supply pressure
The invariable principle regarding the magnitude of individual forces is the fact that the force F is always greater than the force F1.
Control of double-acting cylinders
The article would be incomplete if we ignored the importance of valves in the actuators' work process. We already know the general principle of operation of these devices, so we are aware that to meet the needs related to the supply of air to the piston, diverting valves with two outputs to gas receivers are necessary. For this purpose, 5-way valves are most often used, although other solutions can also be found.
In turn, the stopping of the piston rod is possible thanks to the distributors. Due to the compressibility of air, this type of stop should not be treated as positioning. The piston rod will certainly not stop in a precisely defined place. This will require the use of additional equipment.
The working speed is governed by the throttle-check valves.
When selecting a manifold for a two-way actuator, one should remember about the principles of operation of spool valves. Taking into account the value of the flow rate.
Simply put, the manifold should have the same thread as the actuator.
Double-acting cylinder, application
It is really difficult to find an area of life in which these popular devices are missing.
They literally appear wherever something needs to be picked up, moved, held or passed.
Division by industries:
An extremely illustrative example of the use of actuators in industry is a production hall consisting of only robots. Thanks to the actuators, it is the mechanical workers who gain the ability of incredible precision and speed. They put together everything from microscopic integrated circuits to huge war machines. They solder, weld, stamp, press, transfer etc.
Rich amusement parks would be much poorer without all swaying, rocking, shaking devices, and trade could not stockpile and ship supplies to billions of customers.
Is it possible to imagine a construction site without hoists, girders and other construction machinery? Thanks to the operation of these devices, thousands of families can move into new apartments every year. It can be said without undue exaggeration that double-acting pneumatic cylinders are the unquestionable heroes of our time.
Due to the forces acting inside the mechanisms, the necessity to maintain tightness and numerous dangers threatening machine and device operators, there can be only one answer to the question of how to connect a double-acting cylinder . All assembly, service and maintenance works should be performed only by experienced persons who know the construction and requirements of the actuators. Under no circumstances should you start this work on your own.
Double acting cylinder with shock absorption, description
What is and what is the use of pneumatic cylinder cushioning ?
Attentive observers must have noticed and heard the loud banging of pistons inside the devices, coupled with powerful vibrations of entire mechanical systems. Needless to say, there is a risk of failure or even loss of expensive machinery. To prevent this from happening, the actuators use cushioning to soften and smooth the work of the pistons and piston rods, thus increasing their durability.
The cushioning works on the principle of an air cushion created inside the actuator. Its purpose is to mitigate the effects of the movement of the piston-piston rod assembly in the extreme positions.
As a rule, the compressed air zone forming the cushion is created thanks to the use of a special gasket having the features of a non-return valve that prevents air from escaping from the actuator chamber when the shock absorber sleeve installed on the piston rod penetrates into it. Air is directed outward through a small opening in the cover.
The design details of the solution may vary depending on the actuator manufacturer.
The impact of depreciation on the dynamics of work
Cushioning works much better when used in cylinders with long strokes. This is logical because the short-stroke actuator is not able to reach the required speeds because it is decelerated almost immediately after the start of the operating motion.
The dynamics can be increased by excluding the shock absorption from the seal system, which will require its disassembly, or by ordering an atypical cylinder, after consultation with experts in this industry.
Taking the above into account, two working theses can be formulated. Namely, cylinders with small strokes in combination with cushioning will show a reduced dynamics of work. And the second thesis, when selecting the actuator, you should absolutely pay attention to the stroke size of the device.
It is worth remembering that when selecting actuators to cooperate with each other in the future, it is good to follow the principle that devices from one source show the same technical and material parameters . This leads in a straight line to the extension of their durability and a significant increase in the degree of their mutual compatibility.
The wide spectrum of the presented information will certainly cause the need for more precise knowledge for many of you. For this purpose, it is worth using the contact form , thanks to which you will gain access to free advice and tips. Pneumatics experts will be happy to answer all technical questions related to the products you are looking for.