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Final Thesis of Mechanical Engineering

Title: Abrasive waterjet machine for stainless steel cutting

Engineer: Marcelo Francisco Bisciglia
Director: Eng. Roberto E. Mas
Adviser: Eng. Manuel Kupersmitt, Eng. Edgar Balbastro, Eng. Santiago Zanotti

I n d e x
Abstract Introduction Development Results Computer book AWJ Mail

Abstract: The conventional process of cutting stainless steel foils, is plasma beam. This type of cutting has the following disadvantages: a) It leaves scum. b) The cutting area is subjected to heating (area affected by the heat [ZAC]), that originates structural changes and c) In the ZAC an aureole that harms its aesthetic termination appearance.
   The objective of the following project is to eliminate the difficulties pointed in the previous process, carrying out the cutting (austenitic stainless steel foils up to 2 mm of thickness) by means of a jet of fluid to high speed.
   The cutting process can only be carry out mixing with, the flow of water, particles of abrasive material {M-K}. Can be used as element elevator of the pressure of the water, a lineal injection pump (Diesel motor), a series of transformations should be carried out to adapt it to the specific use.
   With regard to the circuit: a) the correct filtering of the water should be carried out to prolong the useful life of the nozzle {URI}. b) The regulation valve of pressure protects the circuit of over pressures and c) The accumulator of gas maintains the constant pressure.

Introduction: To carry out the cut of a certain material it is needed a certain quantity of energy. In the cutting process we denominate: transformation of the energy, to the energy that is delivered becomes deformation of the material to cut. Now, all fluid in movement is associate with certain quantity of energy (kinetics). Therefore, this fluid will have a bigger energy or similar to the necessary one to carry out the cut.
   As energy carrier in general, we can almost use all the liquid elements: oils, alcohols and also liquid metals for example the mercury. Now, the water presents a series of advantages with regard to the other ones: a) it Exists in enough quantity and in required quality (drinkable), in almost all the places. b) tiny cost, in their employment, with regard to the other fluids. c) Easily accessible. d) it doesn't generate fire. e) Good conditions of fluency (low viscosity), otherwise it would be very difficult to achieve the delivery of the jet through a small hole to high speed.
   On the other hand, the air is also completely discarded as energy carrier for the following reasons: a) High cost to achieve high speeds beams (tunnel of wind). b) Very low kinetic energy (Density of the air = Density of the water / 1000). c) Very difficult of achieving a punctual effect, high dispersion when leaving the nozzle.
   The project is delimited to the cutting of austenitic stainless steel up to 2 mm of thickness.

Development: For the cutting of foils of austenitic stainless steel (AISI 310) with 2 mm thickness it is needed a very high pressure of water, this is due to the drop density of the fluid. When adding an element elevator of the density (metal particles) to the flow of water, the necessary pressure of the pump is reduced to a third of the previous value. But it even continues being high.
   The appropriate alternative is to add particles of abrasive material (alumina, garnet, etc.) to the flow of water {M-K}, which produce the microcutting of the material {E-M}. Now the necessary pressure of the pump of water is located in 400 atmospheres.
   With regard to the system blending of water with abrasive, can be said: the suction of the abrasive, from the chute that contains it, is made by suction (Venturi effect) through a gauged badge hole, being necessary a depression of a tenth of atmosphere to obtain the appropriate flow (3.4 gr/s).
   {S} The more appropriate construction for the mixing tube, with alumina like abrasive, it is the carbide of boron with carbon 5 % (B4C-C 5 %). The interior profile of the tube should be smoothly convergent from the entrance mouth (diameter 4 mm) until the exit mouth (diameter 0.8 mm) . A bigger longitude of the tube (76 mm) it brings harnessed a better acceleration of the particles of abrasive.
   Can be used as element elevator of the pressure a lineal injection pump (Diesel motor), it should be carried out the following transformations: a) Change the material of construction of the pistons, cylinders, valves, valve seats and hole for martensitic stainless steel (AISI 440). b) The system of variation of the flow is omitted. c) It modifies the profile of each levy (tree of levies) so that the flow of water is continuous and non pulsating (characteristic of the Diesel injection). d) It is carved in each piston a groove circumferential with that which a hydrodynamic stamp is possible to avoid the fall of the yield with the elevation of the pressure.
   It is fundamental to carry out the correct filtrate of the water {URI} to prolong the useful life of the nozzle of water.
   A regulating valve of pressure is placed in the circuit of high pressure for: a) To protect the circuit of over pressure in the moment of closing (momentarily) the valve blockade solenoid. b) That the pump works to low pressure during that period.
   An accumulator of gas is placed (type membrane) for: a) To absorb the small variations of pressure, consequence of the discontinuous flow that gives the main pump, making it more constant. b) To absorb the picks of pressure due to the abrupt closing of the valve blockade solenoid and c) To maintain the circuit (between the anti-return valve and the valve blockade solenoid) on the working pressure (400 atmospheres), while the main pump works to low pressure (it closes momentary of the valve blockade solenoid).
   In the enclosed diagram can be observed the main components of the circuit.

The machine

   References:

Results: To carry out the cutting of austenitic stainless steel foils (up to 2 mm of thickness) by means of jet of water, it should be added to the fluid a certain flow of abrasive particles producing what we denominate microcutting of the material, since this particles they impact on the material to a high speed (460 km/h).
   You can use a lineal injection pump (Diesel motor) as element elevator of the pressure of the water, for it should be carried out it certain changes to guarantee their appropriate acting.
   A correct filtrate of the water prolongs the useful life of the nozzle of water. When including in the hydraulic circuit a valve regulator of pressure: a) it is protected to the same one of on pressures, b) it is saved energy and c) it diminishes the waste of the pump.
   On the other hand, the accumulator of gas helps to maintain constant the pressure of the water.

Computer book AWJ: If you are interested in this project, you can acquire the computer Book (Spanish language) on Machine of cut of foils of stainless steel for jet of water and abrasive. Here she/he will find, in 88 topics distributed in 94 pages (A4), all the information on this novel cut system, which was topic of my Final Thesis of Mechanical Engineering.
   If you require additional information in this respect, I recommend download the Demo: Awjd.zip (76 kb).
   If on the contrary, it is convinced of the kindness of this book, you can acquire it right now by means of some of the following links:

   Then, please, register by means of the following connection so that it can make the shipment: Registration form


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Traslation: Engineer Gustavo Bisciglia (ielpo@ielpo.com.ar)