Main Gear paint\surface rust removal

[mongo2]

In regards to the removal of surface rust and paint, is it acceptable to use extra fine black beauty instead of sanding, or will that cause
a problem with the peened surface and \or temper? No a whole lots of rust, just a few layers of paint here.

Rick

[mongo2]

I have removed one leg for the p-ponk mod so far and have read the posts regarding inspection of the legs, and I see chemicals are not recommended for stripping . Would it be accceptable to instead of sanding,use extra fine black beauty blast media, or would this compromise the peening and\or temper. Several layers of paint and some light surface corrosion here. Any help appreciated.

Rick

[GAHorn]

Bead blasting is good.

[mongo2]

George ,
Thankyou for the reply. I currently only have the extra fine Black beauty that Ive used on some other steel parts,
that is why I was wondering if I could use the same on the gear. Is that posssible? in the mean time I will look for some
plastic bead media.

Rick

[GAHorn]

I'm unfamiliar with the product you have. Obviously you want to use the least invasive method available, and if the shot-peening surface is removed it should be renewed. The shot peen specification is to be Almen intensity of 0.012 to 0.016 with 330 steel shot.

[alaskan99669]

I'm reading that only the lower section of the gear leg is hardened which gives it more stringent tolerances for corrosion. But it does not define what they call the "lower section". How many inches of the bottom section is hardened?

Here is a picture of a gear leg that was taken down to metal (all paint removed) and then primed. You can see scrapes, pits, (manufacturing flaws?) in the metal. Is it really expected that these all be sanded down and blended in to such a degree that once painted it would be "show room" quality?

(The big divot at the top of the picture is for the brake line clip)

[GAHorn]

It is not intended that all surface imperfections be removed. It is intended only that rust/corrosion be removed, and only to the extent necessary, as excessive or aggressive removal techniques will obviously degrade the surface hardening. (The small imperfections I see in the photo appear to be debris strikes.)

[c170b53]

How much damage is one issue but equally important consideration is where the damage is. Flap or shot peening is a means to uniformly compress the surface of the material to make it more resistant to failure. It is often used as a manufacturing process to harden bores in a material where machining was used to create the bore. In other words the area of weakness where failure is most likely to occur due to a loss of material or the concentration of stress. In the commercial fleet, a gouge in aluminum skin (depending on size and location) would require blending to remove the damage so the remaining material would have no stress concentration point. The area may require flap peening to place the surface in compression making it harder and more resistant to cracking as it would now be required to transmit the same loads as the thicker skin (non damaged area). Areas of the gear leg most susceptible will be the attachment points of the axle where corrosion occurs in the holes, on the edges of the gear where the radius has been deformed due to impact and again corrosion be the initiation point of failure. In that case, blending out the damage to a smooth contour would be a good maintenance practice, shot peening after blending would enhance the repair and of course restoring the protective covering (primer and paint). Looking at your picture, I'll guess its a mixture of the original finish and some surface corrosion, all in an area in my opinion that poses no more threat of failure than any other area. Probably (again in my opinion) if your going to the trouble to remove the leg and clean it up, you might as well go all the way and get it mag particle inspected. The spring steel is dense and a crack will be hard to detect by visual inspection until the latter stages of failure. George was communicating with the FAA over their concerns of gear problems in the Cessna Fleet. I'm not sure where that went but he probably has a better handle on the issue. I'll try to post a picture of high strength steel gear failure.

[c170b53]

Here's one thats not going to fly again.




Here's one thats had a bit of time spent on it
These are 737 MLG the broken one was found during a walkaround
Care to guess why it failed?

[ronjenx]

alaskan99669,

The "lower section" you read was really the "lower surface". My interpretation is the underside of the leg, its entire length. The shot peened surface will be easy to distinguish from the non-shot peened surface.
On the high strength steel gear components of the KC-135, it is mandatory to remove all damage,(corrosion, dents, gouges, scratches, etc.). Because of the much lower stress the 170 gear sees (compared to the -135), I would guess it is more damage tolerant, excluding corrosion. The proper thing to do would be to ask the experts at Cessna what to do about mechanical damage to the gear legs.

[c170b53]

Ah I guess none cares about the 737 gear but it failed due to hydrogen embrittlement. The gear had not spent enough time in the ovens after the chroming process to bake out the hydrogen. Your right a 10x should be sufficient to determine where on the piece the shot peening has taken place.

[Aviator54]

I came across a set of gear legs that the owner says were cleaned with a Wheelabrator machine using cast iron beads.
Is this an acceptable method?
What are the thoughts on this process?
Thanks