|
Posted by Andrew Mawson on October 12, 2006, 3:17 pm
Please log in for more thread options
> On Thu, 12 Oct 2006 17:30:16 GMT, John Stevenson
>
>
> >
> >Sorry Peter but these don't work as they should because air is
> >compressible.
> >In Andrews case as the furnace tilts it's weight alters and
generally
> >stuffs any load calculations.
> >
> >What you have is an air / hydraulic damper in effect.
>
> John, point taken that the load is fairly large on Andrews furnace,
> but I've been fitting these flow controllers on pneumatic systems
for
> 20 years and they are very effective.
> If we had a particularly large download with possible shock impact
at
> the end I would either use a cylinder with cushioned end travel or
fit
> an Ace Linear Decelerator.
>
> I completely agree that air over hydraulic gives a far smoother and
> much more linear control, but my thoughts were that this is a
> relatively cheap way to get control where none exists at the moment.
>
> Peter
Now this is VERY interesting ! The two cylinders and valve say that
they are pneumatic fittings, but the scrap furnace man that I got it
from reckoned that the foundry had been using the cooling water for
the coil (pumped round at about 45 psi). Now that gives me two
problems. Firstly it leaks like a sieve - the cylinder end seals are
hissing. Secondly, my furnace coolant water is a sealed system to keep
air bubbles out - takes AGES to de-air it and is filled with expensive
special antifreeze. This furnace body plumbing is done in 15mm
stainless steel pipe and standard compression fittings between the
cylinders and spool valve which I had assumed was to be proof against
the odd splash of molten metal. I can see I'm going to have to strip
the cylinders and see if they are repairable, I don't fancy oil (as
per Johns cunning suggestion) or coolant spraying out at the wrong
time. ( a few weeks ago I was doing a melt when it was pouring down
outside, and a single rain drop dripped into the crucible of molten
iron - made a very impressive BANG ! )
AWEM
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap
>unit with crucible mounted in it so it tips just over 90 degrees to
>pour the molten metal. Tilting is by a pair of double acting pneumatic
>cylinders acting in parallel, with the air controlled by a single
>spool valve lever up/off /down thingy. This beast has been out in the
>open for too long and the bearings and pivots took quite some freeing
>to get the rust out. Now it 'sort off works' but the control is far
>too crude. Raising to tilt is ok'ish but the down stroke wacks it down
>far too roughly. Somehow I need to set the air flow rate so things are
>a little more gentle and controlled. Is it just a case of throttling
>the air with a valve, or is there an analogue version of the spool
>valve rather than the digital on/off type that is fitted?
>
>AWEM
>