Alternate for ShotPeening of 7075-T651 Fittings with Ceramic media 2

[ZeeS]

hello all

we had to perform a repair onto the wing to fuselage attachment fitting. the repair is also a fitting and a splice, which has been to be machined out of 7075-T651 Aluminium. Post machining, shot-peening with ceramic media is to be performed with AZB-425.

The problem is nonavailability of media.

Can somebody please elaborate or answer following:

a.

Any sourcing for this ceramic media AZB425?​

b.

Shot peening is carried out for imparting compression stresses and to increase fatigue resistance. Can i bypass this requirement, perform the repair and put a replacement interval onto this particular manufactured part alongwith some scheduled inspections till its next major overhauls (around 4~5 years and less than 1500 hours fly time)?​

c.

We have other medias avaialble for shot peening. Which is the nearest media i can use instead of this one?​

(we are at the verge of roll out and cannot afford delays... so alternates have to be searched for)

 

[TVP]

Have you inquired using a specification for ceramic media such as SAE AMS2431/7 (Z 425) rather than the proprietary designation AZB425? I would start by contacting Wheelabrator or Saint-Gobain ZirPro first, but there are other sources around the world, depending on where you are located:

http://www.straaltechniek.net/en/products/shot-peening/peening-media

http://www.wheelabratorgroup.com/us...s/content/parts_and_services/blast_media.aspx

http://www.zirpro.com/

http://www.alpha-blast.com/index.php/abrasives/ceramic

http://www.bnp.com.sg/blast-and-peen/25-abrasives/82-ceramic-beads

 

[ZeeS]

TVP! Thanks very much... its iaw AMS2431/7, from what all i could get uptill now, Z425 would suffice instaed of particluar AZB425.

Can u put any reference or may be paper, which can tell how to switch from one media to other, so as to achieve similar results? may be between glass bead and ceramic?

thanks....

 

[WKTaylor]

TVP...

I am confused...

Specification AMS2431/7 Peening Media, Ceramic Shot designations mandate use of 'AZBxxx' designations. There is NO SP media designation such as 'Zxxx' in that spec.

However, specification SAE J1830 Size Classification and Characteristics of Ceramic Shot for Peening does use the media designation 'Zxxx'.

It appears that SAE J1830 Z425 ceramic media is similar-enough to AMS2431/7 AZB425 ceramic media to be a direct substitute ["close-enough for government work"].

ZeeS...

CAUTION. Shot peening is a unique mechanical finish that provides significant benefits beyond just fatigue improvement [crushes surface to retard fatigue crack initiation].

IF applied properly, SP can also grossly reduce tendency for Stress Corrosion Cracking [SCC] initiation by "closing-up" [crushing/compressing] open end-grains on machined parts made from SCC prone materials: such [parts MF] 7075-T651 plate.

Also, SP compresses the surface reducing the potential for cracking due to application of a brittle anodic coating [anodized finish such as MIL-A-8625 Type I, IC or IIB]. Anodic coatings are generally superior to chromate conversion coatings [CCC, typical: MIL-DTL-5541 Class 1A] as an inorganic corrosion resistive] surface finish on aluminum alloys. In this case, there is an significant improvement in overall general corrosion resistance... with the application of chromated epoxy primer... relative to CCC coated parts [with same primer]. This factor may be especially important for delaying/preventing generalized and exfoliation corrosion on susceptible alloys such as 7075-T651.

The improvements in SCC and corrosion resistance may actually be a major underlying reason as to "why" the part needs to be SP'ed after machining.

CAUTION: you never mentioned what the required Intensity, Coverage and final shot-blasted surface finish [IE: roughness per ASME B46.1] is required for Your part. These are significant SP process requirements. IF a fairly low intensity is necessary, then You MIGHT be able to use glass beads ILO Ceramic beads. Also, requirement for 'single' or 'double' coverage would tend to indicate how critical this process was to the part designer/analyst. Final shot blasted finish may make a small difference in enhancing, or detracting from, Fatigue, SCC and EXCO resistance.

CAUTION.
7075-T6xx plate is generally prohibited for use on MILITARY aircraft parts due to poor SCC and EXCO properties in the ST [as-rolled thickness] direction. I have used this material [and -T6xxx extrusions or bar-stock] with significant reservations and attention to surface finish details, when and only when, the higher strength level of 7075-T6xxx is mandatory; and a newer high strength alloy, that is SCC and EXCO resistant, is simply NOT available.

Regards, Wil Taylor

Trust - But Verify!

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[tbuelna]

ZeeS-

As Wil Taylor pointed out, AMS 2431/7 AZB425 describes the size, shape, and physical properties of a particular shot media. What's more important is the specific process defined for shot peening this particular component. The process requirements are usually defined by a combination of engineering documentation and industry specifications like AMS 2430 for shot peening. The engineering documentation will define requirements like shot type/size, shot intensity, coverage, etc, as well as any QA requirements like use of almen strips and peen scan.

With a process like shot peening of aircraft structural components that relies heavily on tight process control to achieve the desired consistent result, it is usually frowned upon to deviate from the qualified process in any way. This would include substituting a consumable material in the process that has not passed the spec quality controls, even though the substitute material may very well be equivalent in every aspect. If the shot peen process described by the customers work order specifies a particular media then that is what you must use, unless they provide for an exception. As an example, AMS 2430R sec 3.1.1 states "As-received peening media shall conform to the requirements of AMS2431." AMS 24330R table 1 also lists only one type of ceramic shot, which is AZB.

Regards,
Terry

 

[TVP]

Wil,

My apologies, I was looking at SAE AMS 1830 when I typed that. Z 425 is from AMS 1830, while AZB425 is from AMS 2431/7. You have to wake up pretty early in the morning to get one by wktaylor...