Air Cylinder Failure Phenomenon and Notes on Design Methods to Prevent Failure

good day (daytime greeting)"A Memo on Air Cylinder Failure Phenomena from a Design Perspective and Design Methods to Prevent Failure."　About.

Air cylinders should have the proper amount of air supplied, clean air, proper lubrication, andOperates properly only when the cylinder's internal structure is operating without kinking　The life of an air cylinder depends on many factors, including operating conditions, load, environment, and frequency of maintenance.　The life of an air cylinder depends on many factors, including operating conditions, load, environment, and frequency of maintenance, so it is difficult to state a specific life expectancy, but air cylinders are generally used in the range of several years to several decades.

It is no exaggeration to say that the life of an air cylinder depends on its design.

In fact, when a problem occurs, it is necessary to check (1) the air supply, (2) the flow control device, and (3) the air cylinder itself, of which the frequently moving air cylinder itself is often at fault.

Phenomena caused by problems with the air cylinder alone　can be broadly divided intoPhenomenon in 2 (reduced output, malfunction of rod stick, etc.) Confirmation can be made by　But in this articleMemo on possible causes of failure and design methods to prevent failures as much as possible from air cylinder unit failures　I will do so.

We have taken notes on points that are often overlooked by novice designers as well as by designers who are familiar with the handling of the machine, so please refer to them for designing a machine that can operate for a long time.

(1) Failure phenomena and failure details of the air cylinder alone

As mentioned earlier, there are two failure phenomena that can be caused by air cylinders alone: insufficient output and rod stick.

• Insufficient output: No pushing force, air leakage
• Rod stick: Cylinder rod stops in the middle of the cylinder, starts moving suddenly

and we will explain them.

1-1 Insufficient output: No pushing force, air leakage.

As a check flow in the case of a possible output shortage Before ascertaining the status of the air cylinder alone

1. Is there a problem with the pressure on the supply side at the set value?
2. Is the connection joint correctly connected?

first.　If there is no problem with the above two items and the output is simply insufficient (coming up short), thenAir leakage due to deterioration or deformation of packing inside the cylinder　is possible.

The air cylinder has two packing positions,

• Air leakage from piston rod section (air leakage from rod packing)
• Air leakage from other than piston rod section (air leakage from piston packing)

Air leakage from these two points is possible, and if air leaks from either of these pointsDecrease in output is a phenomenon.

1-1-1 Two types of packing failure (deterioration and wear)

Packing failure can be caused by simple deterioration and wear.

It is actually difficult to judge the deterioration of the packing, but it is mostly affected more by the oil supply condition inside the cylinder than by the aging of the packing.　So many people mistake the condition of worn out gaskets due to rubbing and abrasion with the internal oil supply cut off for deterioration.　And we believe that the judgment here can be narrowed down to the following three patterns.

1. The grease initially sealed in the oilless type air cylinder has run out and the packing is worn out (considered to be the end of life if there is no mechanical abnormality).
2. Worn packing due to insufficient oil supply to oil-fed type air cylinder (*Check oil level in lubricator)
3. Grease that was initially sealed in an oilless air cylinder was blown off and the packing was worn (review of the air circuit).

It is.

What is a Lubricator?

What is a lubricator? A lubricator is a device installed in an air circuit (pipeline) to supply oil with an oil supply structure.Lubricator is not necessary for oilless type air cylinders because they are initially grease-filled, but necessary equipment for oil-filled type　Therefore, it is necessary to use different circuits for different types of air cylinders.

At this time, please note that,Lubricating an oilless air cylinder with a lubricator will remove the grease that originally filled the cylinder and cause it to deteriorate.　It is.

1-1-2 First aid for grease breakage

If grease is determined to be a major factor in this packing failure (air leakage), the mechanical assembly engineer has provided informationGrease from intake and exhaust ports to seals (life extension)It would be a good idea to try the

(1)-2 "Cylinder rod stops in the middle or starts moving suddenly" is largely due to unbalanced load.

If air leakage from the packing occurs without oil or grease splashes, the packing may be under physical load.

2-1 Check if the rod tip is floating.

The air cylinder is driven by compressed air that is sealed by a piston packing and rod packing.The piston inside moves guided by the packing.For that reason,Even a small amount of lateral force applied to the air cylinder rod will stress the packing and cause premature wear.

First.Check again what kind of load is expected to be applied to the rods.　Let's do the following.

Also, with air cylinder peripheralsItems with floating features are sold.　Its floating joints absorb mounting errors of air cylinders and reduce unnecessary forces at the connection between the cylinder's piston rod and the device.

Floating joints can absorb a certain amount of mounting error, but if the tolerance for mounting error is exceeded, the exact mounting position of the cylinder body must be adjusted. Since there are specific requirements for each floating product, such as integrated type or separate type, etc., it is necessary to confirm that it is installed correctly according to the instruction manual or manufacturer's Therefore, it is necessary to confirm that the product is installed correctly according to the instructions in the instruction manual or the manufacturer's instructions.

It is incorrect to say that a floating joint is included = cylinder mounting can be appropriate.In,The cylinder mounting was designed with care to be straight, but a floating joint was included to absorb very slight errors.　This is the correct usage.It is.

(1)-2-2 Check if the rod is damaged by foreign matter, bending, etc.

In addition, foreign matter may adhere to the piston rod section, causing the packing to wear and air leakage to occur.　Although air cylinder rods should not be scratched, scratches may occur during assembly work, machine interference, maintenance errors, and installation environment.

What can be done to minimize failures in designs using air cylinders?

From the breakdowns we have talked about,What you can do to avoid air cylinder failure　are as follows

• Design the rod so that loads other than in the driving direction are not applied to the rod as much as possible (no load on the packing).
• Make the structure not to break the floating (putting in a freting joint = not safe)
• Consider using high durability products from the beginning

It is.

2-1 Design the rod so that loads other than in the driving direction are not applied to the rod as much as possible.

Nowadays, there are many types of guided air cylinders, and there are fewer opportunities to build a separate guide as in the past.　However, an important sense ofNo matter how guided you are, there's always a rattler.　I think it is important to remember that

In the case of guided cylinders, the load moment causes the rod to bend, which eventually wears down the guiding parts and increases the rattling, which eventually leads to uneven wear of the seals.　Therefore, as a designerEven with a guided cylinder, if the load is heavily dependent on the guided cylinder, it is necessary to provide another guide for longer service life.　I think it is.

This is just my personal thought, but in places where it would be easier to use a guided air cylinder, I think it would be better to use a guided air cylinder.

• What if the lateral load is greater than expected? (If we design it with a different guide, we can change it later, so let's do that.)
• Considering the lateral load, the size of the guided cylinder would increase, even though the force required to push it is not so great (we can design it with a separate guide to separate functions, so let's do that).

It is not good to think shallowly about individual problems (issues) because they are easy because they are guided, for example.It is very important to separate the function of pushing from the function of guiding.　It is.

2-2 Make the structure not to break the floating

Next, let's talk about the floating mechanism.　Floating is used correctly, as discussed earlier.

And a note of caution when putting in a floatingTake care not to touch it on the end-user's side.　This is also important.　　If there is no need to touch it on the end-user's side, we basically don't touch it,Those with fine adjustment may have their adjustment parts touched.　There is a　The problem is that the machine provider knows about it, but the user does not,By sticking, the rod puts a strong load on the packing, causing it to fail.

Floating mechanisms are broadly classified into two types (integrated type and separate type).　The locations where such a possibility exists areFloating should use a separate type that cannot be adjusted, and a separate adjustment mechanism should be provided.　I think.

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)Design is a maniacal response, but an important idea.　It is.

2-4 Consider using high durability products from the beginning

Although some customers may specify and use this service from the initial stage (specification stage),High Durability Equipment HP Series (by CKD)　may be an item that should be introduced at the beginning of the selection process.

This item is

• Optimized packing and grease: Wear-resistant packing and high-frequency grease are used to ensure stable operation.
• Optimization of sliding parts: This has resulted in a durability of more than 20 million cycles, more than four times that of conventional products (the normal life of an air cylinder is about 5 million cycles).

It is.

Also, up to the aboveUse of high durability products in properly designed machines can extend their service life.　I think it will be.

2.5 Be prepared to recognize the signs of failure in case of an emergency.

This is not the objective of minimizing breakdowns,It is too late to replace the product after it has failed.　So, I would like to make a personal recommendation.Flowmeter to detect air leaks　somewhere in the circuit.　Nowadays, it is convenient to have a clamp-on (piping/tubing) that can be directly retrofitted.

Finally.

For air cylinder maintenance and troubleshooting, though, the most reliable way is to seek advice directly from the manufacturer, depending on the specific problem and situation,Usually and empirically, the reason why air cylinders reach the end of their life prematurely is due to improper design and usage here (laugh).　It is.

That's it.