which backplate

[Sadamune]

Hello bradshsi,

I really do have full confidence in the quality Tobin's backplates. My questions stem from my curiosity about the metallurgical aspects of marine engineering. There are a variety of different backplate designs out there and I'm trying to understand the reasoning for each manufacturer's particular design. Unfortunately, most of my inquiries into design specifics have been ignored by the manufacturers I contact. So far only Tobin of Deep Sea Supply has been willing to answer my questions, a credit to his openess and patience. As for convincing him to make a backplate out of duplex stainless steel, well, if I really wanted to trouble him, I'd probably ask him to make one out of iridium, but I don't think he'd be too keen on that idea...even if I could afford it.

The cold workability of 316L being the reason some choose to use it sounds quite plausable, especially if a manufacturer is using a traditional punch and not a water jet/laser to make precise cuts.

Cheers!

Sadamune

 

[ProfessorAronnax]

Nice Backplates: http://zeagle.com/index.php?submenu=Backplate_BCs&src=gendocs&link=backplate_std&category=Heavy%20Duty%20BCs

 

[jvdk01]

I think we need a line of designer Inconel plates.

 

[cool_hardware52]

The cold workability of 316L being the reason some choose to use it sounds quite plausable, especially if a manufacturer is using a traditional punch and not a water jet/laser to make precise cuts.

Somewhat conterintuitively harder materials are easier to punch cleanly. It's hard to imagine that any minor difference in "workability" would make 316L a choice over 316 or 304 for that matter. 304 and 316 are both quite ductile, both work harden, etc. Given the scale and power of the machines needed to produce a backplate from any stainless the minor differences in workability just aren't a player.

There can be manufacturering reasons for selection 316 including:

Ready access to a supply, for example if your waterjet or lazer cutting vendor already stocks 316 sheet stock for some other customer. (We actually make our own backplates in house, but to the best of my knowledge no one else does)

Small batch processing. Passivation is not an inexpensive or trivial process. Tanks of heated nitric acid bring the watchful eye of the environmental authorities. We send our plates out for this step. This means mimimum charges are incurred for "one off" batches. That's less of a problem if you are processing 50-100 plate batches, but could be a real problem if you are making custom gear essentially one at time.

If passivation was impractical due to batch size using 316 without passivation might be attractive.

You have to remember that we are discussing a backplate, not the engine cooling water line for a Guided Missle Cruiser. The loads on a backplate are trivial, the impacts of minor corrosion, should it occur, are not "Mission Critical"

What if you developed a brown spot on your plate? Oh the horror. Abort the dive, alert the CPSC!

How many angels can dance on the head of a pin?


Tobin

 

[kidspot]

here's a list of BP manufacturers I've found so far http://www.kidspot.org/personal/scuba/bpwing.html

The most commonly recommended here on the board would probably be:

Fred T (most variety in sizes and weights)
DSS (most feature packed)
Hammerhead (least expensive)

Have fun shopping

 

[FredT]

I've not had my doubles on my DSS plate as yet but one of the things that sold me on this plate was the profile of it. I have had shoulder problems and having valves closer makes life much easier. I

Please be aware that "closer" with singles aind "closer" with doubles may be mutually exclusive. Every manufacturer uses a different "model" and assumption sets (except for Hammerhead, they just cloned mine, without asking) with various considerations. I optomized mine for underplate storage, drysuit clearance and doubles with tanks from 6.9" OD to 8.5" OD.

Tobin did his slightly different and eliminated a nasty finishing issue with his inserts. I don't have an injection molding line handy so I deal with the strap chafing issue the "old fashioned way." How well the inserts will hold up over time is still to be seen, but 30 years will pass before that answer is apparent and the "old fashioned way" is a suitable plan "B" option for those plates. While Tobin and I may compete in some minor product line areas I haven't caught him in a major engineering error anywhere yet.

As far as the 304/316 issue:

I've been designing things to be "thrown in seawater" professionally for over 38 years. After extracting 14" fangs from my *** several times due to that mistake I simply won't use 304 for anything that gets wet with seawater on a regular basis. The price delta is there but I don't consider it significant overall relative to the harrassment factor. I also do not assume my gear will EVER be rinsed so it's designed to deal with that issue if made of stainless, and priced to be disposable after a decade or so if made from aluminum. In the world of Ocean Engineering the basic TRUTH is "If you have to think about the gear, you've got the wrong gear." I design accordingly.

FT

 

[Homunculus]

Thank you all for your helpful inputs!!!

on the side note:
the 316 vs. 304 stainless steel discussion was interesting. I was quite ignorant about this aspect of the backplate. I talked to my friend who is a production manager in a small steel factory. He clarified the issue for me even more. Out of the 2 choices (see above), they only use SS 316 for the parts that are in constant contact with sea water. There is another kind of steel they use (i forgot the number but it's irreleven for this particular topic). Passivation of SS 304 makes it fine for diving purposes and it seems that SS 316 does not need any additional treatment. The price of SS 304 + passivation is still cheaper than SS 316 without any treatment. That may be the reason why there are a lot of companies using it.

 

[cool_hardware52]

The price of SS 304 + passivation is still cheaper than SS 316 without any treatment.

That's a blanket statement that may or may not be true. Passivation is an additional step, and in many cases incurrs minimum charges.

Processing batches large enough to avoid minimums incurrs costs, increases required stocking levels etc.

I would agree that on a continuous processing basis 304 + passivation will be cheaper, on a batch processing basis it might not be.

Tobin