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Scraper failure

Scraper failure

Scraper failure

(OP)
Hi to everybody,

I would like to know if anybody can make any guess on the root cause failure of the following metal screaper seal on a hydraulic cylinder.

Thanks

RE: Scraper failure

Pressure.
Bent rod.
Ice.

Ted

RE: Scraper failure

(OP)
Thanks Ted,

Can you tell me what is your idea behind ice as possible cause?

I will exclude pressure, while I still keep bent rod as
possible cause.

Thanks



 

RE: Scraper failure

If water entered and filled the void between the scraper and seal and froze, it may push the wiper out.

Ted

RE: Scraper failure

How long was the cylinder in operation till the scraper failed? Was it perhaps just a poor assembly? Why can you exclude high pressure?

RE: Scraper failure

IF the pressure is as high as the cylinder construction suggests, AND the control valve is closed-center, AND if the control valve has little internal leakage, it's possible for the cylinder to act as its own intensifier and build a -150 pct pressure in the oil trapped in the rod end.  

Put a pressure gage in the rod end.  Make sure it has a damper, and a full scale range at least twice the nominal system pressure.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Scraper failure

(OP)
Hi to everybody and thanks for your reply,


I will exlude pressure becasue that seal is just a scraper whose function is to keep dirt away from the main seal.

The failure accured after few weeks of the machine installation, and the load condition were below average.

As first level of analysis I will say that the scraper at some point was sticked to the rod surface and was pulled out from it's sit.

Thanks
 

RE: Scraper failure

Asking to determine the root cause for pulling the scraper out.
Why do you suppose it stuck to the rod?

Or was it not properly installed and the resulting low pressfit pressure could not resist normal rod drag force?

Ted

RE: Scraper failure

Wipers can fail early if they get paint under them, usually because the rod is slightly extended and not covered. ISZ

RE: Scraper failure

Where is the cylinder used?  What is the application?  The root cause could go back to the original design - not just the cylinder seal but knowing the big picture may help.  Is it on an excavator, a wheel loader, etc?

RE: Scraper failure

Hi!

After reading this post, I can give more ideas (considering the correct installation of the scraper):

Regarding ice. By the way, it's due to know where is working this cylinder. The scraper user, following the sketch (and beware, because, the housing is on the wrong side)this scraper is to be used when several mud, or ice can be expected.
Considering that this scraper is a 2 piece scraper, and both of them is just press fitted, it's very easy that, in case of ice formed close to the rubber part, it takes off on the first stroke.

Regarding pressure. Yes, by the way a scraper is not intended to withstand pressure (althougth lately many manufacturers are using double-scrapers as function of U-lip seal, and a scraper, but I think this is not the case here). As told before, the scraper here is a 2 piece encased wiper (being 1 of them made in rubber, and the other in metal), so, in case of just a minimal pressure received, it wouldn't seal, but neither it will damage the rubber-part of the scraper, unless the pressure is too high, so you need to check the closer seals.

http://www.hidromar.es

RE: Scraper failure

Depending on what type of seals are used, the wiper could have been displaced from poor lubrication.  It looks like an extruded seal/wiper, from poor installation practices, or perhaps the cylinder uses chevron type packings which were over-tightened.

RE: Scraper failure

Your drawing shows a single metal scraper, but your image shows extruded rubber.  My guess is the wrong scraper was installed flush (abmormal compression) or at some point, someone thought two scrapers would work better and compressed a rubber one behind the metal one.

RE: Scraper failure

(OP)
Hi Automatic2,

Would you like to explain further?

The scraper used is made of two part a metal housing and a rubber part. You can read the code in the sketch I provided (trelleborg brand).

Since I'm not the manufacturer of the cylinder by only the end user, I'm now wondering if they have installed a scraper different from what they have specified (altough to my eyes it looks correct).

Thanks

RE: Scraper failure

I'd simply measure the  gland and check with the scrpaer requirements. Also, it looks like a lot of extensibility so I would check if the rubber is swollen from compatibility issues.

RE: Scraper failure

It looks to me like the rod scraper was installed backwards and the wiping lip was compressed against the bottom of the step causing it to get hot and stick to the rod pulling it out.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: Scraper failure

(OP)
Hi EdDanzer,

Yaa..true, it look like is installed backward.

But I can't get when you say "wiping lip was compressed against the bottom of the step"

Would you like to explain it further?

Thanks
Regads

RE: Scraper failure

The scraper lip usually sticks out beyond the metal can so material will fall clear when scraped off. If you install it backwards and drive it down until it stops the lip will be driven into the chamfer and gap between the rod and the head creating grip between the rod and the lip causing it to wad up and push out.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

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