[TheForge] heavy metal math/c frame press

[Andy Vida]

"David E. Smucker" wrote:
> 
> Andy,  First there is no such thing as NON-compressible fluid 

	Yes, there is.  A non compressible fluid is one where the 
	fluid density is independent of pressure. Water is non 
	compressible.  As far as I know there is no terrestrially 
	attainable pressure that will compress a body of pure water. 
	If we speak in terms of fifth-state conditions (what was
	once called "super-dense" matter, AKA black holes) then
	the fundamental structures of mundane matter are being
	defeated and all bets are off.

	Hydraulic fluids are either noncompressible or virtually
	so.  The amount of stored energy in such a fluid is, for
	all intents and purposes non-appreciable.  As far as I know
	ALL measurable stored energy in such systems resides
	in the containment structures.  Whether micro-miniscule
	compressibility is an issue in the design of high pressure
	systems as you state, I will defer to your assertions as I
	am by mo means an expert in this field.  But I'm curious
	then, because the stored energy in the containment structures
	of the system is still going to be far and away greater.
	Can you say what the precise issues are?  I find this idea
	fascinating.

> Stored energy is no where near what it is in an
> air or steam system  at low pressure such as 100 psi.

	Precisely, and in order to do mass damage, you need volume.

>  
> The amount of compression and stored energy in very high pressure hydraulic
> systems at 5000 to 10,000 psi is another story but for systems that
> blacksmiths and bladesmiths use this would be unrealistic. 

	Unless you happen into a good deal on a press that uses an
	11 KPSI Enerpac setup. :)

> The stored energy in a hydraulic press is another issue all together.  As a
> press is loaded there is store energy in not only the oil but in the stretch
> of the press itself.

	Well now this is a very different kettle of fish, and I completely
	agree.  The mass of the press constitutes a huge spring, mainly
	due to the tension (as opposed to compression)

> The real danger is from a smaller leak that
> causes a misting flow of the hydraulic oil -- which that comes in contact
> with the hot metal being worked and causes a fire / explosion of the mist
> cloud.  Hydraulic oil in liquid form is quite safe but in mist form it is
> much more like a gas.

	Oh yes, very definitely so.  This was a major problem with
	commercial aircraft regarding collisions.  An aircraft in
	troulble dumps fuel (ideally) prior to "landing" to prevent
	or at least minimize the fire hazard which as I recall is a
	greater threat to survival than initial impact in most cases.
	The problem lay in the hydraulic systems where breaches of
	containment of the high pressure lines would cause atomization
	of the fluids, which would in turn ignite.  The resulting
	conflagration was effectively as bad for the passengers as if
	the fuel had not been dumped.  There are now flame retardent
	hydraulic fluids specifically designed for aviation applications
	but my recollection is that they are not perfect and can in
	fact ignite under certain conditions.
> 
> The point of my referencing the pump failure that you noted is that it is
> very rare and I have never seen one caused by the hydraulic pressure itself.
> None the less in the industrial system that this pump fail there was a large
> amount of stored energy because this system -- as do most high performance
> industrial systems -- included major gas hydraulic accumulators to provide
> high volume flow for short duration as required by the system.

	Ah, I think I understand you.  Basically you are referring to
	gas cylinder capacitance for low pressure burst flow, no?  I
	gather that the accumulator is solidly isolated from the rest
	of the system via valving during high pressure operation, yes?
	If so, then we are talking about hybrid systems, which are 
	different from the purely hydraulic.

>  None the less I think it is important to not give the
> impression that hydraulic system don't have cases of high stored energy.

	Yes, I completely agree here.  I was unaware that there were
	such mechanisms in place, but it makes perfect sense.

> Another example of high stored energy is when a load is support by a blocked
> hydraulic cylinder such as in a fork lift or pay loader lift.  Failure to
> understand this possible stored energy can result in serious injury or death
> to those working on these type of systems.

	Could you elaborate?  I'm not sure what you mean here.
> 
> I still want to come back and once again make the point that there is real
> risk of fire / explosion between a hydraulic system and hot metal were a
> small leak can create a mist that then can become a major fire ball.  Just
> make sure your fittings, pipe, and hose are correctly rated for the
> pressures you are using.  You don't want to spray / mist hydraulic oil on
> hot metal !!

	One solution is to design a failsafe point into
	the system.  That is to say, you over engineer the entire
	system to some degree and place a "weak" element in a
	location where failure is deemed to pose the lowest threat.
	You might, for example, over-engineer all the conduits and
	place the failsafe point inside the reservoir on the high
	pressure side of the pump so that if there is a failure due
	to over pressurization, it will occur at the weak point and
	be contained by the structure of the reservoir.  No mess,
	and damger is contained.  The only mess will be the hands
	of the mechanic that has to replace the failsafe point. :)

	I'm not sure there is a lot to be done to protect against
	failures due to damage to the containment structure (e.g.
	driving your forklift into a concrete abuttment and nicking
	a line that fails later on).  Perhaps digital monitoring
	such that any sudden pressure drop that crosses a predetermined
	threshold triggers a release or deluge valve (deluge valves
	are super high speed opening and closing, microseconds from
	full closed to full open) to depressurize the system immediately.
	But things get so over complicated... :(

	-Andy