[TowerTalk] Help identifying alloy in mast

[Jim Thomson]

Date: Mon, 10 Feb 2020 09:35:44 -0800
From: "Richard (Rick) Karlquist" <richard at karlquist.com>
To: john at kk9a.com, towertalk at contesting.com
Subject: Re: [TowerTalk] Help identifying alloy in mast

> For some reason hams seem to be obsessed with 2" chrome molly masts.
> John KK9A
 

<Can you expand on your comment about the chromoly obsession?
<I too keep reading the chromoly "hype" (?) here on TT.
<Is it possibly overrated? Or maybe it's the real deal.
<I don't have an opinion as a non-expert; just trying to learn about it.

<Rick N6RK

##  Pretty  simple  matter  to  calculate  all  the  loads  on  the  mast....including  the  mast  itself.
Before  you  overload  the  mast,  do  the  simple  calcs.

##  Bending  moment =  ......section  modulus X  yield  strength,  its  that  easy. 

##  A  3.0  inch OD   x   .25  wall   mast  weighs  the  same  as a 2.0 inch  x .375  wall  mast.....  BUT  the  3  inch  OD  mast  has a helluva  lot  bigger  section  modulus.  

## DOM  is  typ   75  to 87  ksi....and  can  not  be  heat  treated.

##  Chromolly from  the steel  yard  is  UN-HEAT  TREATED....and  is 70  ksi yield  strength. 
Once  heat  treated,  yield  strength is  typ  107  ksi....  up  to  a max  of  125  ksi. 
Heat   treatment  done  at  1100  deg  F.
Galvanizing  done  dead  last......and  done  at  900  F.    Galvanizing process  does  not  affect  the  heat  treatment process.

##  Can  the  XRF  gun  tell  how  much  heat  treatment  was  done  to a CM  mast ??    

## That  DXE  online  mast  calculator  is  based  on 222-F  specs....  which  are bogus  imo.  222-F  specs  are designed  to  sell  CM  masts. 
Instead  use the   ...  no-spec  method..which  is  the  basic wind  pressure  you  get  in  a wind  tunnel. 

##  DXEs....  yagi  mechanical  software  provides a choice  of    222-C  spec,  no  spec,   222-d,  222-e,  222-f,  222-G. 
JK  ants....and  myself  use  the...  no  spec.....  aka  basic  wind  speed  formulae.    Its  accurate and  more  stringent  than  222-C. 
222-F  results  in  a  204-BA   up  100  ft.... breaking  at 64  mph.....  which  is  nonsense  of  course.       

##  Think  of  the mast  as a giant  torque  wrench....  except with  loads applied   at  various  points.

##  wind  speed  device  really needs  to  go  at  top  of  mast....  not  on  the  side  of a tower.  Forget  the 6   oclock WX,  they  wont  get  it  right.

Jim  VE7RF