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#204 - 01/28/09 04:55 PM Almen holder screws - nuisance
AircraftProps Offline
Member

Registered: 01/28/09
Posts: 3
Loc: O-H-I-O
We have one shot peening process in our facillity that wears out the Almen holder screws very quickly. This process is set for a nominal 17.8A intensity using AWS-62 per AMS 2431/4 media. My attitude towards this has always been to keep a box of spare (button head hex recess) screws for the operators to change as often as they desire. However, I am changing my opinion as we have done some time study work in that work area. Basically it slows down the operator greatly when he has to work to get the hex wrench into each screw recess. This particular process has a number of almen holders in various locations (lots of screws). The hex wrench actually no longer fits into the screw recess after a single intensity curve effort.

Recently I experimented by buying two batches of screws from vendors, we stripped them of black oxide in our plating department lab, then sent them to a vendor to carburized them to HRC57 at the surface (like J442 holder). Next we made a fixture from a perforated steel bar and installed a repeating pattern of Carburized A, Carburized B, stock, Carburized A, Carburized B, stock, etc. Next, begain exposing this to shot peening stream for increasing number of passes. We inspected and photographed the screws between each interval. I continued the test until the stock screw was completely unusable where both batches of carburized screws were still in excellent shape.

I have concluded that the carburized screws will save us valuable operator time and clearly make sense. Next we are either planning to A)start making our own hardened screws or B)find someone who is already selling these c) send my data to Jack Champaign and convince him that he should start offering bags of carburized screws for sale to anyone with the same need.

FEEDBACK PLEASE?? Realizing that others of you out there have everyday experience working with even higher intensities and unique situations, what are you doing? Has anyone ever hoped someone begins selling a hardened screw as a commodity? Anyone care to offer them for sale to me?

In case you are wondering, we also operate other processes at lower intensities and with smaller media sizes where the stock Almen screws last for weeks of use.

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#205 - 01/30/09 02:38 PM Re: Almen holder screws - nuisance
Mike W. Offline
Member

Registered: 10/25/06
Posts: 3
Loc: Seattle, WA USA
We shotpeen at similar intensities and gave up on socket head screws long ago. Our studies have shown that we get the best usage out of SS pan-head slotted screws.

However, I sure would be interested in testing hardened screws if they were available.

Mike W.

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#206 - 01/30/09 03:07 PM Re: Almen holder screws - nuisance
Socrates Offline


Registered: 02/20/06
Posts: 108
We gave up on standard screws thirty years ago - within four weeks of installing our university shot peening facility. Both pan-head and socket-head screws only lasted for a matter of hours. A local heat-treatment company carburised and quenched a gross of plain carbon pan-head screws for us. That batch lasted twenty years!

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#207 - 02/01/09 02:54 PM Re: Almen holder screws - nuisance
Pete Bailey Offline
Member

Registered: 01/12/05
Posts: 9
Loc: Hamilton, OH
Hard screws great idea. Has anyone tried masking the sockets in the screws with plastic plugs?

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#208 - 02/02/09 05:12 PM Re: Almen holder screws - nuisance
AircraftProps Offline
Member

Registered: 01/28/09
Posts: 3
Loc: O-H-I-O
An additional benefit was added to the goal today. That is we occasionaly get operator finger cuts from the periphery of the screw where it gets hammered out over the Almen strip to a knife-like edge. Every time we load/unload an Almen strip there is a chance of getting cut. I believe the carburized screw would prevent this from happening. Q:) Anyone seen this?? For us this always occurs on a rotary lance peening operation.

Mike W. - THANKS, I will add some SS slotted pan heads to the test sometime this week and see how they compare.

Socrates - THANKS, Confirmation is always a refreshing thing. I hoped someone has already tried this.

Pete - THANKS, our goal is to aim for avoiding all labor possible to keep costs to a minimum, I agree we could probably plug the hex, but it would cost us labor to install/remove them. We did verify that duct tape disks on the screws erroded away very quickly (and was slow to apply)

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