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Topic: Using springs in BBQ drum roaster. (9 msgs / 754 lines)
1) From: Roger Shoaf
<Snip>
I see a potential problem for using any sort of spring in a BBQ drum roster.
The temperature these springs are subjected to are likely to cause the
springs to loose temper.
I considered this when I designed my drum and opted to forgo the use of any
springs.  My rod is a stainless pipe with a 1/2 inch OD and one end slides
on the rod allowing the beans to be dumped rapidly into the cooling tray.
I will see if I can get some photos posted.
Roger Shoaf

2) From: Brian Hyde
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500 degrees F is only 260 degrees C.  This is well below creep temperatures
or any sort of phase transformation.  There is something called temper embrittlement
which occurs in most steels at temperatures above 575C.  But that is 1067F
and you won't be going near that.  So use a quality spring and you should
be fine.  
Brian  
Roger Shoaf wrote:
  
    Message: 7
From: "dewardh" <dewardh>
To: <homeroast>
Subject: RE: +RK Drum Roasting...
Date: Sat, 27 Sep 2003 18:34:08 -0700
Reply-To: homeroast
Ron:
I'd skip the set screw altogether, and drill a hole in the shaft for
http://www.pivotpins.com/catalog/hair_pin.shtmlOr
http://www.pivotpins.com/catalog/dbl_loop.shtmlOr even
http://www.pivotpins.com/catalog/bow_tie.shtmlPositive detent, easy to remove, dare I say "a snap to install" <g> . . .
Deward
    
  
  
I see a potential problem for using any sort of spring in a BBQ drum roster.
The temperature these springs are subjected to are likely to cause the
springs to loose temper.
I considered this when I designed my drum and opted to forgo the use of any
springs.  My rod is a stainless pipe with a 1/2 inch OD and one end slides
on the rod allowing the beans to be dumped rapidly into the cooling tray.
I will see if I can get some photos posted.
Roger Shoaf
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3) From: Oaxaca Charlie
--- Roger Shoaf  wrote:
<Snip>
 Just for the record, My first roasting drum used a ss spring to
hold the door latch closed. I roasted every day for 4 years with
it, often 6 hours a day, in the brick oven. Every bit as hot as
the biggest gas grill. That spring still holds the drum door
closed just fine. The pin that holds the door closed on the drum
I got from Ron (the same kind  pin that Deward recomended) is a
more elegant solution and is working great so far, but I used
some ss wire to connect it to the drum after almost losing it
every time I removed it to dump the beans. They're not coiled
springs, though, so I check the pin every day to see if it needs
a little re-bending. So far the only bean spilling trouble I've
had was one time that I forgot to put the pin in it's shaft.
 Your idea for holding the drum to the roticery shaft might be a
good one, I'll have to see those photos to be sure I understand
it, though.
  Charlie
=====
Brick Oven Roasting in British Columbia
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4) From: Dan Bollinger
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Springs are tempered, 
hardened carbon steel.  Above 570F (dark blue temper) you will begin 
to remove the qualities from steel that make us call them springs. Too hot and 
you'll turn that spring into soft, steel wire.  
 

5) From: Brian Hyde
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There are many different types of springs and many different alloys (and
other materials) from which the spring can be made.  There is no set rule
that it has to be a martensitic steel.  How about an austenitic steel which
does not require temper to maintain its ductility?  I bet the springs that
are on my brake pads and shoes in my car get to that temperature, especially
considering they do indeed blue.  Haven't seen a problem in 140K miles of
cycling them and 10 years of heating and cooling.  Now if the spring isn't
steel, then maybe you will get a soft wire from a complete anneal.
For a plain carbon (1080) steel tempered at 600F it would take 1.15 days
to lower the hardness from 62HRC to about 55HRC (Rockwell).  Not a significant
softening of the material.       
 
Dan Bollinger wrote:
  
  
  
 
  
 
    
  Springs are tempered,  hardened
carbon steel.  Above 570°F (dark blue temper) you will begin  to remove the
qualities from steel that make us call them springs. Too hot and  you'll
turn that spring into soft, steel wire.  
 
   

6) From: Dan Bollinger
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  Ed's experience is more solid than your maybe, so I'll go with that. 
  My concern was someone getting burnt or wasting $6 of beans for the sake 
  of a 25 hardware store quality spring. 
   
   
   
   
   

7) From: Brian Hyde
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I didn't think that he tried it?   I'm a theoretical metallurgist so I haven't
tried it either.  But it did give me a break from my atomistic simulation
of steels to look back at some of this old stuff!  
Brian
Dan Bollinger wrote:
  
  
  
 
  
 
   
  
    Ed's experience is more solid
than your maybe, so I'll go with that.    My concern was someone getting
burnt or wasting $6 of beans for the sake    of a 25¢ hardware store quality
spring. 
   
     
   
     
   
     
   
     
   
     

8) From: dewardh
Roger:
<Snip>
are subjected to are likely to cause the springs to loose temper.
Maybe, but I doubt it.  First off, though, it is not their "springiness" that
retains them, but their geometry.  If they lost their "springiness" they would
not fail in use, but on removal (bend open and stay bent open).  It might be
annoying, but that is not, in and of itself, a hazard.  Second, if the
temperatures (in the grill) are getting high enough to damage the cotter you
probably have other, and much more serious, safety considerations . . . like
failure of the enclosure or other structural parts, or combustion of the beans .
. . in which case loss of "springiness" in the cotter could be regarded as a
safety *warning*.
Dan:
<Snip>
Springs can be carbon steel, stainless steel, other steels, bronze, plastic,
wood (as in a bow, or look at fishing rods for a variety of "springy"
materials), and like everything at some temperature (or extreme flexure) they
fail . . . but above 570 your beans are burning and the cover of the grill is
probably slumping or itself turning into a fine white powder.  If it came to
betting (and I only bet on sure things ) I'd bet you'd find, in the ashes,
the drum still retained by the cotter on the shaft. I'd certainly trust it more
than a set screw that had been similarly thermal (and mechanically) cycled.  If
in doubt you can always "tunnel up" the links I provided and ask the
manufacturers tech support.
Brian:
What you said . . . .  I have disassembled things that failed by overheating
or in fires and still had to struggle (in the *normal* ways ) to get the
"spring" clips off . . . But, to be fair, I've also seen hairpin cotters so
cheaply made that they lost their "springiness" at room temperature just from
taking them on and off (and maybe bending them a bit too far?).  Bad material,
failure to properly "temper", who knows?.
Deward

9) From: Ed Needham
I really think an indent or a small hole and pin would work.  The spit rod is
5/16" square plated cold rolled steel, and a 3/32" hole would not compromise
the strength enough to worry about in my opinion.  Now if we were designing a
structural member of a bridge or a weight bearing beam, I'd think a few calcs
might be in order, but not for this.
***********************************************
Ed Needham
To Absurdity and Beyond!
homeroaster ... d.o.t ... com
***********************************************


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