Re: [PSUBS-MAILIST] Horizontal Pressure Hull Weldment Supports?

Thanks much Dean

I forgot about the etching step. I've been looking at Rhino liner type coatings for many areas of my sub. One brand called Rattle Guard is claiming you can apply it directly to clean bare metal with out any primer since it is self etching and water proof. This type or coating is an elastic material, it can expand and contract with the metal surfaces. Of course rubber can burn and cause you trouble if a fire gets on it. With Rattle Guard you can leave the rubber out of the mix.

http://www.rattleguard.com/faqs.htm

For bolts and the like, I like the idea of using nylon washers. You could also use nylon washers backed up with stainless steal washers for strength with allot of none moving connections which help avoid chipping the paint there as well. I also like the idea of using the bluing agent. If you make bolt hole over sized you can use a nylon collar to take up the extra space for connections with more stress and vibrations then most.

On the hyperbaric chambers I worked on we used internally threaded stainless steal couplers for all are through hulls and welded them with stainless steel MIG wire. This was mainly done since treads if not made of stainless will rust badly.

I've seen a fair number of the large springs that are used to make hatches easier to lift and close, and they all look like a rust nightmare. Is there a stainless steal alternative? Some stainless steal will rust in saltwater so I would be interested in knowing which type(s) are best in saltwater? What about the non-magnetic types of stainless steal? I've heard electrolysis will eat away stainless steal at a pretty quick rate if you don't coat it properly with a good epoxy paint or the like and/or use the zinc plates.

I was thinking about the stitch welding mentioned earlier and as I understand it you'll get less heat warping on your weldments if you do that. You would have allot of exposed tight voids were rust loves to work unless you can seal it with a bed liner flexible coating or the like. I've never seen a spot welded support ring with spaces left between the welds on a submarine, so there must be a reason or I might need to get out more. How ever it maybe a good idea to stitch weld your rings onto the outer hull and continue to stitch weld until there are no spaces. This would limit your warping. That's the way I weld thin metal together on car bodies and control the heat.

I don't see to many PSUBers heat treating to stress re leave their weldments for what ever reason. Likely because of cost and availability of local companies able to do the service. Karl Stanley did heat treat his deep diving sub Idabel a couple of different times while he was building it. It seems that heat treating is not always necessary but would give you just that much more strength and/or areas that are so hard they would brake rather then flex.

Brent Hartwig

From: Recon1st@aol.com
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Horizontal Pressure Hull Weldment Supports?
Date: Tue, 9 Jan 2007 21:39:14 EST

In a message dated 1/8/2007 10:11:12 PM Central Standard Time, ShellyDalg@aol.com writes:

and minimize the pockets you can't reach with paint

just my two cents. I tend to agree with the kiss rule here. My design

started using both internal and external ribbing, thinking I would save money.

the further I got into it the more I realized, just use the thicker material and

be done with it. The mfgs I provided can handle just about any thickness

ya can imagine, my brother was involved with one pressure vessel that was

6 inches thick12ft wide and over 30 ft long (think that is a little out of my budgef)

one thing that has been discussed of late is rust. This is an area I

have played in since I was 14 started doing body work at a body

shop.

Few hints on paint.

First and most important is clean clean clean

Welds I would sugest grinding as smooth as possible

next sand blast with glass beads.

And the most important part use a metal prep cleaner.

This can be bought at any body supply store. It is usually

not much more then watered down hydrochloric acid. This will stop any

oxidation going on at the present and actually etches the

metal for a mechanical bind for the primer.

2 don't think more is better. You need to seal all the moisture and

air from the area, but too much is not good. Paint and other materials

expand and contract at much different rates. This constant uneven

motion will either crack the paint (if to brittle) or break down the

chemical and mechanical bond.

A poorly prepared rust area will rust thru, faster being covered incorrectly

than if it were just left bare. Look at bare metal left out in the elements

it surface rusts real fast, but will take many years to make any real

structural problems. Now look at how fast a fender can rust all the

way thru on a car.

Also be careful about the paint itself. Not all paints are water proof

these will quickly break down.

Another point is any drilled hole. the bare edges have to be taken care of.

When tolerances are a concern I have used gun bluing and has worked

pretty good. Bolts need to be painted in place and don't use lockwashers.

They tear up the paint underneath and will give you the ugly little rust

flows in days.

The last I will mention is rubbing panted surface. The best way I have

found is, say on the pivot pin on a hatch. glue reinforced nylon washers

at the contact points, this will give it a great deal more life than just

letting the painted surface rub together. The trick here is the glue

to washer, can not allow the washers to rotate.

Dean Ackman