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Torque specifications - Watertight Enclosures


(Wayne Holtzclaw) #1

We finally tested our ROV successfully, however upon reinstalling the 3" end cap, I was not able to get the machine screw to tighten, investigation revealed that the internal threads on the flange for one of the holes was stripped. Luckily we have finished our initial testing, but I was hoping to know what the torque specs were on the screws so that I don’t bugger it up again.

Thanks!


(Harold Scadden) #2

Frankly since the end cap has a “Radial” seal on it … in my opinion you should only have to go hand tight with the screws. Anything above that and you will start stripping threads. I use helicoil inserts with soft metal but in this case, you are stuck without it because the blasted things get real expensive when you are trying to mitigate cathodic corrosion between the two metals. The cap and the helicoil.


(Wayne Holtzclaw) #3

Thanks Harold,

Unfortunately, I have big hands, and am used to working on fast-attack submarines lol, sometimes I get carried away, but I ALWAYS use a small screw-driver. I was just hoping to get the specs so I could actually use a torque screwdriver instead of guessing lol.

Thank-you!

Wayne


(Harold Scadden) #4

You sound like an A-Ganger :slight_smile: I rode fast boats and still work on stuff for them after leaving Uncle Sam’s canoe club a long time ago.

Really … if you have to deal with a torque screwdriver then think in inch pounds. Those screws are to just keep the cap on. If it was a “face seal” race then that would be a totally different story. With the radial seal it only needs to keep the cap from coming off. Besides, water pressure is going to help that part out a lot.


(Wayne Holtzclaw) #5

LOL, you guessed it,… well was, 9 years 1989-1998 - back in the good ole’ days.

Yeah, I was figuring 10-50in-lbs; I guess I can look it up in the Standards, just didn’t know if there was one recommended by Blue Robotics specifically for the enclosures.

Thanks again!


(Harold Scadden) #6

Just remember … soft metal and softer material that it is threading into. Something very light like 10 inch pounds would more than likely be a good stop point. Only time will tell on the wear and tear factor.


(Harold Scadden) #7

I just realized that you are talking about the penetrator holes! I was thinking of the perimeter holes. Nevertheless; if you get to the point that you are compressing the o-ring you should be just fine.

If you are crazy … go to Parker’s site for their O-ring calculator software.
http://divappstest.parker.com/divapps/seal/mobile/MaterialSelection/MobileinPHorm.aspx?Panel=pnlPageMPH

You can select the type of seal that you are dealing with … the o-ring, which should be a buna-n material, and I believe it is a face seal on those penetrators (my memory is offline) and if so you can see how much torque it takes to get “x” amount of compression and run the numbers to see how much pressure that seal will handle.

With a full metal to metal mate, the seal will outlast the metal forming it. I have heard of 100,000+ psi holding pressures with a face seal face.

But back to the soft metal thing, the aluminum is “SOFT” and you will end up screwing up the threads over time. That is why I would be gentle on it. My molds I use at work are made from 6061 and we utilize helicoil inserts wherever we are using attaching hardware to help extend the life on the thread area. As I stated before … I don’t have to tell you the hell that seawater will play on dissimilar metals. Also, be real careful with anti-seize grease if you are thinking of trying that to reduce stress on the threads.

Bottom line, the o-ring doesn’t take a lot for it to create the seal that you need for the depth that the Acrylic can handle.