<html><head></head><body><p dir="ltr">You get around the .8 factor by doing the exhaustive 100% NDT. If you can confirm negligible voids, you can design directly to the material specification. That may be more expensive than simply making the part thicker, but if your buoyancy margin is low, might be the only way to make castings work.</p>
<p dir="ltr">I didn't want to have any machined surfaces on parts that subsequently need to be welded, so that I can maintain design tolerances and not worry about heat induced distortion from welding. As such, all parts are welded first, with machining allowances (extra material) where I require machined surfaces, and then I can stress relieve the whole thing before doing the necessary facing (a handful of identical conical seats) in situ. This, of course, is not a DIY step and must be contracted.</p>
<p dir="ltr">As for your port seats, I'm not sure you would realize the advantage of casting by merely recreating your frames using a casting process - the seats need to be machined anyway, and that is a large part of the cost, and billet material will be higher quality than the cast material. Where the advantage comes into play is rethinking the insert to instead make a larger diameter casting which incorporates the smooth transition back to the hull thickness, so that you have a longer weld, but one which is just a butt weld as thick as the hull, and further away from the machined seat so you can get away with machining prior to welding without warping. Such a part would be loaded more lightly than a weld between the hull and a thick insert, and eliminates the stress concentration occurring at the abrupt change in geometry.</p>
<p dir="ltr">Sean<br>
</p>
<br><br><div class="gmail_quote">On April 19, 2016 6:25:14 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px"><div id="yui_3_16_0_ym19_1_1461067792128_3065"><span>Sean,</span></div><div id="yui_3_16_0_ym19_1_1461067792128_3572"><span id="yui_3_16_0_ym19_1_1461067792128_3571">By "over built" I meant just what you said, .08 quality factor. Good point though about the advantage of formability giving strength in itself. I still am amazed that there is a cost saving. It seems so complicated, but I know nothing about it either, other than high school Aluminum casting in metal shop. </span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1461067792128_3569"><span id="yui_3_16_0_ym19_1_1461067792128_3779">I went to a machine shop in Cranbrook to have a new land ring water jet cut and I mentioned how long it took me to machine my port frame. The owner (real nice guy) said he could C&C machine the remaining
two frames for 300 </span>dollars each. That is nothing, that makes each port frame 600 dollars for material and machining, ready to weld in. It will be interesting to see how that compares to having the part cast.</div><div dir="ltr" id="yui_3_16_0_ym19_1_1461067792128_3569">Hank</div> <div class="qtdSeparateBR"><br /><br /></div><div class="yahoo_quoted" style="display: block;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 12px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"><font size="2" face="Arial"> On Tuesday, April 19, 2016 5:51 AM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br /></font></div> <br /><br /> <div class="y_msg_container"><div id="yiv1593809770"><div><div dir="ltr">Not sure what you mean by overbuild? I only ever design things to be as
strong as they need to be. A casting is not a forging - you must accept that the strength gains you get by working as with forgings and plate materials don't exist in castings - all processes have tradeoffs.</div>
<div dir="ltr">I would specify an appropriate material, such as ASTM A352 LCC, which is analogous to the A516 grade 70 plate specification with regard to low temperature toughness. Also could use A216, but I note that the ABS steel vessel rules point out that all 216 castings should use a 0.8 quality factor unless NDT is carried out beyond that required by the material specification, which would necessitate the part being 25% larger for equivalent load carrying capacity. For a sub I would NDT the hell out of it anyway, so it comes down to a confidence thing. This is something I would work with the foundry on in order to minimize voids, and then a NDT professional in order to detect any that do exist.</div>
<div dir="ltr">It's always better to use a stringent material specification (i.e. A352), a reputable foundry who can discuss these issues with you, and do material testing (both exhaustive NDT on the completed part and e.g. notch toughness tests using samples from the same heat) so you can be assured of exactly what you have, versus not being confident and overbuilding to compensate.</div>
<div dir="ltr">In any case, cast parts don't necessarily need to be larger than machined equivalents. In fact, often the freedom of form afforded by casting allows you to eliminate geometric stress concentrations that would be unavoidable with plate fabrication and machining operations exclusively, such that even if you have less load carrying capacity in the material, you also have less load to carry because you can delocalize it.</div>
<div dir="ltr">I think the bigger consideration for the amateur is the tradeoff between the advantages of casting any particular part, versus the cost of doing the NDT.</div>
<div dir="ltr">Sean</div>
<br clear="none" /><br clear="none" /><div class="yiv1593809770yqt8698692043" id="yiv1593809770yqtfd55961"><div class="yiv1593809770gmail_quote">On April 18, 2016 7:58:12 PM MDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="yiv1593809770gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex;">
<div style="color:#000;background-color:#fff;font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px;"><div><span>Sean,</span></div><div dir="ltr" id="yiv1593809770yui_3_16_0_ym19_1_1461030467306_3492"><span id="yiv1593809770yui_3_16_0_ym19_1_1461030467306_3491">I have to admit,I find the process of mould making quite romantic. I think that is one of the reasons I keep looking at concrete. With concrete you have total freedom of form. I have it all worked out how I would make a perfect sphere. </span></div><div dir="ltr" id="yiv1593809770yui_3_16_0_ym19_1_1461030467306_3490"><span><br clear="none" /></span></div><div dir="ltr" id="yiv1593809770yui_3_16_0_ym19_1_1461030467306_3263"><span id="yiv1593809770yui_3_16_0_ym19_1_1461030467306_3262">I thought you had to over build when you cast parts, does this not mess with your buoyancy. That can be costly- your sub is likely big enough to handle the
weight. </span></div><div dir="ltr" id="yiv1593809770yui_3_16_0_ym19_1_1461030467306_3261"><span>Hank</span></div> <div class="yiv1593809770qtdSeparateBR"><br clear="none" /><br clear="none" /></div><div class="yiv1593809770yahoo_quoted" style="display:block;"> <div style="font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px;"> <div style="font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px;"> <div dir="ltr"><font size="2" face="Arial"> On Monday, April 18, 2016 7:18 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br clear="none" /></font></div> <br clear="none" /><br clear="none" /> <div class="yiv1593809770y_msg_container"><div id="yiv1593809770"><div><div dir="ltr">Actually, I would think that casting would be a useful process for a hands-on guy like you, Hank. You could probably do your own patterns from plywood and Bondo and
then deal with a foundry without having to pay for the pattern making. Just do some research first - you need to accommodate shrinkage, and !
the
draft requirement. Also, you do need to 100% NDT the completed castings. Unlike billets / plates, voids can be quite common in cast parts, and these need to be detected and corrected for our application.</div>
<div dir="ltr">Sean<br clear="none" />
</div>
<br clear="none" /><br clear="none" /><div class="yiv1593809770yqt9548585235" id="yiv1593809770yqtfd75645"><div class="yiv1593809770gmail_quote">On April 18, 2016 7:05:01 PM MDT, "Sean T. Stevenson via Personal_Submersibles" <personal_submersibles@psubs.org> wrote:<blockquote class="yiv1593809770gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex;">
<div dir="ltr">There are a few reasons:</div>
<div dir="ltr">1) Economy of process. Creating a casting entails creating a master pattern, usually by a pattern maker at the foundry or associated with them. Once this is done, additional parts can be obtained for the cost of an additional heat / pour. For multiple similar parts (six identical hatches) this is cheaper than machining them all from billets.</div>
<div dir="ltr">2) Economy of waste. Machining from billets obviously is less material efficient, as much of the billet ends up as chips on the machine room floor. With a casting, extraneous material exists in the form of risers, flow channels and flash that must be trimmed, but in many cases these wastes can be cleaned and remelted in the furnace for reuse.</div>
<div dir="ltr">3) Suitability to size. Some parts which would be awkward to handle or difficult to machine without access to suitably large machines can be more readily cast at lesser cost.</div>
<div dir="ltr">4) Efficacy of form. The casting process allows you to readily incorporate large sweeping or compound curvatures and other features to reduce local stress concentrations or improve aesthetics, without necessitating multiple machining operations or tooling change outs to do so. Often, recreating a cast part with machining operations exclusively is prohibitively expensive. The design process is different for each - with machined parts, you need to think about machine envelope, repositioning, cutter clearances and interferences, tooling, avoiding impossible operations, and so forth. With castings, there is greater freedom of form, although you have to avoid thin-walled parts, apply draft to parallel edges to facilitate mold release, and consider material flow into the mold and how the part will cool to avoid warping. Often, combining processes gives you the best of both worlds: casting a blank to get the overall desired shape where surface profile is generally not
critical, and then subsequently machining specific faces or features to establish critical dimensions.</div>
<div dir="ltr">This is the approach I am taking - casting the transition rings from the hull shell thickness to the hatch seat thickness to get that smooth large curvature (and a sexier looking part, IMO), where the contact interface is machined in situ after stress relieving the hull, and then also casting the hatch blanks and machining their critical features (contact interface, O-ring grooves) into the blank.</div>
<div dir="ltr">Sean</div>
<br clear="none" /><br clear="none" /><div class="yiv1593809770gmail_quote">On April 18, 2016 4:11:09 PM MDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="yiv1593809770gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex;">
<div style="color:#000;background-color:#fff;font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px;"><div id="yiv1593809770yui_3_16_0_ym19_1_1461017365265_2579">Hi Sean,</div><div id="yiv1593809770yui_3_16_0_ym19_1_1461017365265_2579">I am curious why you wouldn't machine your hatch from a heavy disk, it would be one piece and any shape you want.</div><div id="yiv1593809770yui_3_16_0_ym19_1_1461017365265_2579">Hank</div></div><div style="margin-top:2.5em;margin-bottom:1em;border-bottom:1px solid #000;"></div><pre class="yiv1593809770k9mail"></pre><hr /><br clear="none" />Personal_Submersibles mailing list<br clear="none" />Personal_Submersibles@psubs.org<br clear="none" /><a rel="nofollow" shape="rect" target="_blank" href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none" /></blockquote></div><div
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