[TheForge] heavy metal math/c frame press

[Andy Vida]

xlch58@swbell.net wrote:
> 
> Thanks Andy...

	s'right

> One is allowing air to get into the system, the other is
> allowing your hydraulic fluid get hot enough to start vaporizing into a
> gas.

	In both cases you now have a compressible fluid present.
	Compressible fluids are mechanically equivalent to a
	metal spring in terms of energy storage.  If the system
	stores enough energy, its sudden release via catastrophic
	structural failure would pose serious danger to anyone in 
	the vicinity.

><  Both of these cases allow the system to "store" energy that could
> be a hazard. 

	Precisely so.

> The critical temp depends on the fluid.  When I built my
> front loader, I included a temp gauge on the resevoir.  Anothe point
> here, is since most hydraulic systems depend on the resevoir to cool the
> fluid, you need to size it large enough to do this.  You also need to
> seperate the pump pickup from the return.  Not an issue wiith low cycle
> devices, but for something like my loader that gets a continuous workout
> it is critical.

	I take it you mean to separate the hot incoming fluids from
	the comparatively cool outgoing so the system doesn't keep
	recycling the same fluid mass.
> 
> BTW, one inch plate should work fine for the press,  the trick is how
> much and in what specific configuration.  That is not a simple
> engineering exersize..

	Correct.  Bear in mind the nature of the forces.  In the
	ideal case, the forces are being applied ALONG THE PLANE
	of the plate.  The bending moments along the plane are
	huge because you are effectively applying force to a mass
	of steel that is many inches thick (perhaps 12 to 20?).
	
	In the real world, materials being the imperfect things
	that they are, a normal force component (90* to the line
	of force along the plate) will develop, partly due to the
	non uniform nature of the materials strength ACROSS the
	plate.  To wit:

                       _________
                      |         |   ^
                      |         |   |
                      |         |   |
                      |         |   |
                      |         |   |
                      |         |   |
                      | Perfect |   |
                      |  Plate  |   | force vector in ideal world
                  ^   |         |   |
                  |   |         |   |
                  |   |         |   |
   Applied force -|   |         |   |
                      |         |   |
                      |_________|   |

                          'A'

                       _________
                      |         |   ----->
                      |         |   ^    .   
                      |         |   |   ,
                      |         |   |   .
                      |         |   |  ,
                      |         |   |  .
                      |   Real  |   |  ,
                      |  Plate  |   |  .   possible vector in 
                  ^   |         |   | ,    real world
                  |   |         |   | .
                  |   |         |   |,
   Applied force -|   |         |   |.
                      |         |   |.
                      |_________|   |

                         'B'

	In 'A', the plate is under pure tension or pure compression
	because the ideal material is uniform in its properties across
	its width over the entire length.  Force, that is to say energy,
	in these matters is very predictable.  Apply it to a perfect
	material and you will perfect distribution and vectoring. If
	you do not exceed the strength capacities of the material,
	the forces will remain predictable.

	In 'B' we see a real plate, whose material characteristics
	are not uniform.  Even slight variations in strength across
	and along the plate will take the component out of pure
	compression and introduce bending force due to the (in this
	example) the normal component going to the right at the
	top of the diagram.  Tension is another story.  Tension
	produces a self balancing situation with regard to applied
	force, whereas compression is an inherent move towards
	imbalance, which all has to do with trying to make atoms
	occupy the same space at the same time, which we are taught
	is not possible under non relativistic conditions.

	Also note that another source of bending in compression is
	the imperfect nature of mechanical devices.  Round is never
	perfectly round and flat is never perfectly flat.  Any variance
	in these characteristics of geometry contribute in some way to
	variance from "perfect" resultants.  This is countered in real
	world applications by two means: increasing accuracy in materials
	and manufacture, and increasing component mass.  There are also
	all manner of tricky design twists intended to effectively 
	maximize these two methods.  One example are the fillets in  
	castings.  A small increase of mass in the immediate vicinity
	of what would otherwise be a sharp radius intersection of two
	geometric forms (e.g. a bearing boss for the power transmission
	shaft on a #9 Beaudry Champion power hammer) will redistribute
	the forces applied at that locus over an area that could be
	hundreds of times larger than that of the sharp radius, thereby
	greatly increasing improving the stress profile of that area
	and greatly increasing the effective strength and longevity
	of that casting with but a meager increase in overall mass.
	The more perfectly the sliding surfaces of the ram are machined,
	the more closely the actual forces applied to the frame will
	reflect the designed forces.

	-Andy