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September 15, 2010

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What amounts to a sand bath can be used to great advantage in a number of heat treating procedures in the technologically challenged metal working shop. It can provide an environment of otherwise expensive and difficult to achieve thermal inertia over a very useful range of temperatures.

Forgive me for asking, but have you been inspired by the same Connections Muse as James Burke? :) That was an amazing journey.

Of course I'll forgive you for asking - particularly since you've hit one proverbial nail on the head. The James Burke series has stuck in my head ever since I watched it. [Burke was a science historian whose series, "Connections" aired in the UK and the US in the late 70s; each one wove a story thread between scientific discoveries and related (although often seemingly unrelated) events]. It was, to my mind, one of the most compelling and fascinating documentary series ever. I guess that you identify with this view?

Indeed, I do identify with that view. The Connections 2 & 3 series were also excellent, produced in the mid nineties. James Burke also had a Connections column in Scientific American magazine for a while. (I have been a subscriber on and off for so long, I am not sure when the column was running.)

It is interesting to know that there is a connection there, if you will excuse the pun. But, connection or no, the knowledge and presentation styles exhibited both by you and by James Burke are excellent and admirable.

I love seeing the interrelatedness of seemingly disparate things, for informing the way I look at the world, and just for a good story.

I also thank Walter for his comment, and I would appreciate any pointers for looking into this. I found this an interesting application:
http://taogem.ganoksin.com/blogs/uncategorized/heat-treating-lapidary-cabochon-minerals-for-silver-solder-jewelry-design/
and was excited by a reference to tempering metals here:
http://www7.taosnet.com/ebear/metal/heattreat0.html
from a 1924 handbook, but all the links throw 404 errors, unfortunately.
Fluidized sand baths seem very interesting as well:
http://www.techneusa.com/tempcalibration/howdoflsdbathswork.htm

I'll just keep digging. Time, perhaps, to see what the local library system may have.

Thanks for the connections - and the compliments - you've spotted exactly what I humbly try to do.

Walter is an old friend and I've let him know about your comment, in case he hadn't seen it.

F: I'm afraid I have no idea where to look for anything that will help you with this. If I find anything, I'll post it here. I work as a blacksmith in a small shop. I've been at it for more than 30 years (wow) and am self-taught. Trial and error with emphasis on error. Also immense help from a number of books.

My work has been mainly ornamental, as opposed to technical, industrial, etc. The need to make, try, modify and recondition tools of various sorts arises frequently. This has led to the need to harden, temper, anneal and normalize various steels. Straight from my readings comes the practice of heating a piece of hardened steel above its upper critical temperature and burying it in the coal ashes to allow it to cool very slowly. In here, that passes for annealing.

On a number of occasions, I had difficulty tempering parts that were of varied section, i.e. thick and heavy in one part, light and narrow in another. The challenge was to heat the heavy part adequately and uniformly without overheating or over oxidizing the lighter parts. I find myself very hesitant to recommend some of the things I have tried. In the early days I learned two important lessons. The first was how to avoid getting burned. The second was that you're going to get burned anyway. Often. I've survived doing some fairly dangerous things. That doesn't make it OK. So read this, but DON"T DO IT.

The reference in the post was to a technique I have evolved (very crudely) in which I imbed a part to be tempered (temperatures ranging up to about 600 degrees [F]) in a bed of sand. The sand is contained in a cast iron pot or bowl and is preheated to desired temperature (as measured by oxidation colors on polished test strips). I have used my coal fire as a heat source. The advantage has been that the already hardened and brittle steel is not subjected to an abrupt temperature gradient. It can then sit there and soak at its temperature and cool very gradually. This has worked very well for me on a number of occasions. This description is quite abbreviated and I have tried a number of variants for differing requirements.

BTW: I share your enjoyment of Michael's posts and the James Burke approach to world view. I believe that the Scientific American column was mid to late nineties. I enjoyed all of Burke's series immensely. Good Luck!

Walter,

Thank you so much for sharing your experience with me. The likelihood that I should ever attempt such a thing is very remote, so no worries. I know what things like molten glass can do, and I respect their natures. (Incidentally, my woman was very nearly vapourized by molten Monofrax many years ago when the graphite mold was broken open too soon, so there is always that anecdotal scariness to remind me, should I ever happen to work with such hot substances.)

Again, I appreciate you taking the time to describe your usage of sand baths. I'll try to poke around a bit more, as I seem to remember (correctly or not) reading something on a similar technique used a bit further back in history, perhaps in China, for metallurgical or metalworking purposes. Perhaps I can find a copy of the handbook from 1924, a reference to which I had found at one of the links I posted previously.

Cheers,

Sean

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