EP0691901A1

EP0691901A1 - Cutting method and apparatus using a jet of cryogenic fluid

Info

Publication number: EP0691901A1
Application number: EP94912580A
Authority: EP
Inventors: R. Geo Res. S.A.R.L. Grudzinski
Original assignee: Geofinanciere SA
Current assignee: Geofinanciere SA
Priority date: 1993-04-02
Filing date: 1994-03-31
Publication date: 1996-01-17
Also published as: JPH08511205A; WO1994022646A1

Abstract

A cutting apparatus using a jet of cryogenic fluid and comprising a low pressure cryogenic fluid storage tank, a high pressure compressor (12), and a discharge nozzle (19) connected by lagged ducts. The operation of a heat exchanger (8) arranged between the storage tank (1) and the discharge nozzle (19) for cooling the discharged fluid to a constant set temperature is controlled by the output from a temperature sensor (31) at the inlet of the high pressure compressor (12). A cutting method carried out using said apparatus is also disclosed.

Description

INSTILLATION AND METHOD FOR CRYOGENIC FLUID JET CUTTING.

The present invention relates to an installation and a method of cutting by cryogenic fluid jet.

This cutting process is similar to cutting processes using a high-pressure water jet or a jet of fluid loaded with abrasive particles. It has the advantage of not moistening the cut material, which is particularly advantageous for cutting food, or hydrophilic materials. Furthermore, the boiling point of cryogenic fluids is generally significantly below 0 ° C at atmospheric pressure. The process is therefore particularly suitable for cutting frozen products.

A prior art volatile jet cutting process has been described. In particular, French Patent No. 2,647,049 describes a process for cutting materials with a fluid, maintained under low pressure in a tank, and compressed at high pressure to form a jet which volatilizes after cutting the material.

The object of the present invention is to improve this process, in particular by increasing the efficiency of cutting.

The invention relates more particularly to a cryogenic fluid jet cutting installation comprising a storage tank for cryogenic liquid at low pressure, a high-pressure compressor, an ejection nozzle connected by heat-insulating ducts, as well as a heat exchanger. heat disposed between the storage tank and the ejection nozzle for cooling the ejected fluid to a constant set temperature. The functioning 1 heat exchanger is slaved to the signal delivered by a temperature sensor disposed at the inlet of the high-pressure compressor.

This embodiment guarantees the permanence of the mechanical efficiency of the jet.

According to a preferred embodiment, the heat exchanger is arranged between the storage tank and the high-pressure compressor. According to a first variant, the heat exchanger consists of an enclosure containing liquid nitrogen connected to a vacuum pump causing the expansion of the liquid nitrogen contained in said enclosure.

According to a second variant, the heat exchanger comprises a primary circuit in which the cryogenic fluid circulating coming from the storage tank, said primary circuit being thermally connected to a secondary circuit in which circulates a fluid coming from a cryogenerator.

Advantageously, the heat exchanger is controlled by an electronic circuit connected to the temperature sensor disposed at the inlet of the high-pressure compressor, and comprising an adjustment means for the adjustment of a set point value fixed experimentally. Preferably, the electronic circuit includes a comparator, one of the inputs of which receives the signal from the temperature sensor and the other inverter input receives a setpoint voltage from the means for adjusting the setpoint temperature.

The invention also relates to a method of cutting by jet of cryogenic fluid compressed to a pressure greater than 500 bars and ejected through a calibrated orifice of small diameter. According to this process, the set temperature is determined experimentally cryogenic fluid at the inlet of the high-pressure compressor by optimizing the mechanical efficiency of the jet, and in that the temperature of the cryogenic fluid is kept equal to the set value by a controlled temperature exchanger.

Another object of the invention is to allow industrial cutting of a plurality of elements.

Cutting a part involves the relative displacement of the ejection nozzle relative to the part.

Given the pressure of the fluid at the outlet of the compressor which usually exceeds 1000 bars, and the very low temperature of the ejected fluid, it has been proposed in the prior art, to connect the nozzle to the compressor with a short length of pipe, and to move the part in a plane perpendicular to the axis of ejection of the fluid.

This solution is satisfactory for experimental use or for low cutting rates. On the other hand, it does not allow large series of parts to be cut from a large material.

Another solution has been disclosed by the German patent PS3631116. This document discloses a cutting device comprising a movable nozzle in an X-Y plane.

The connection between the high pressure pump and the nozzle is carried out by a high pressure resistant conduit, articulated in a manner avoiding deformation.

The solution disclosed by patent PS3631116 consists in that the duct is movable in rotation around the Z axis thanks to a spiral element and a joint. It explicitly aims to avoid transverse deformations of the high-pressure resistant tube by using a conformation of the duct in the form of a spiral. This document PS363111β does not disclose the characteristic relating to the insulation of the duct, which is not very compatible with a spiral conformation, unless it results in excessive congestion of the cutting system and an unacceptable gap between the different nozzles. A second object of the invention is to remedy these drawbacks by allowing multi-cutting with a high performance cryogenic jet.

To this end, the invention relates more particularly to an installation in which the outlet of the high-pressure compressor is connected to a fixed ramp constituted by a tubular duct with thick insulating wall, to which is connected at least one tubular duct with thick insulating wall whose end opposite to the ramp is secured to a movable plate in a plane substantially perpendicular to the longitudinal axis of said conduit, the ejection nozzle being connected to the movable end of said conduit.

The force exerted by the plate on the end of the thick-walled conduit, the other end being fixed, causes deformation of the conduit, this deformation being reversible if the elastic limits of said conduit are respected.

According to a preferred embodiment, a plurality of thick-walled conduits is connected to the fixed ramp, the end of each of said conduits being integral with a movable plate in a plane substantially perpendicular to the longitudinal axis of said conduit, a nozzle ejection being connected to each of the movable ends of said conduits. Advantageously, the thick-walled conduits are surrounded by a sealed envelope, the volume between the sealed envelope and the conduit being connected to a vacuum pump. According to a preferred embodiment, each of the ejection nozzles is fixed to the plate so as to maintain a constant ejection direction whatever the position of said plate.

The invention will be better understood on reading the description which follows, referring to the drawings in which:

- Figure 1 shows a schematic view of the installation according to the invention;

- Figure 2 shows an embodiment of an electronic circuit for controlling the heat exchanger;

- Figure 3 shows the temperature-entropy diagram of the cryogenic fluid;

- Figure 4 shows a schematic view of a variant of the installation according to the invention;

- Figure 5 shows a schematic view of the installation according to the invention;

- Figure 6 shows a sectional view of the cryogenic fluid ejection system. The installation, an exemplary embodiment of which is described with reference to FIG. 1. This installation comprises a storage tank (1) for liquid nitrogen at low pressure and at a temperature corresponding substantially to the boiling temperature, ie at 77.3 ° K at atmospheric pressure. The temperature of liquid nitrogen increases during storage by about 0.5 ° per day due to the heat losses resulting from the lack of insulation. This reservoir (1) is constituted by a cylindrical body with thick walls closed by flanges. This tank is connected via a heat-insulating duct (2) to an intermediate tank (3) of smaller capacity. A valve (4) allows the filling of the intermediate tank (3) to be controlled. A nitrogen gas tank (5) containing nitrogen at low pressure, for example at around 30 bars, is also connected to the intermediate tank (3). This reservoir (5) of gaseous nitrogen makes it possible to raise the pressure of the liquid nitrogen contained in the intermediate reservoir (3) until a sufficient pressure is reached for the booster of the high-pressure compressor which follows. Conventionally, the booster pressure is around 30 bars. To reach this pressure, we start by filling the intermediate tank (3) by opening the valve (4). The valve (7) disposed at the outlet of the intermediate tank is closed during this time. When the equilibrium pressure is reached, the valve (4) disposed at the inlet of the intermediate tank (3) is closed and the valve (6) connecting the liquid nitrogen tank (5) to the intermediate tank is opened. ). The pressure of liquid nitrogen in the intermediate tank (3) thus increases up to the booster pressure. The outlet valve (7) can then be opened to start a high-pressure compression cycle.

The intermediate tank (3) is connected to a temperature exchanger (8) supplied with low temperature primary fluid by a cryogenerator (9), for example helium stirling, or by expansion of liquid nitrogen.

This temperature exchanger (8) has the function of lowering the temperature of liquid nitrogen to a temperature below the boiling temperature, and of regulating the temperature of nitrogen supplying the high-pressure compressor. It is connected to the high-pressure compressor (12) by a pipe (10) provided with a thermally insulated valve (11).

A temperature sensor (31) measures the temperature of the cryogenic fluid at the inlet of the high-pressure compressor (12).

The signal delivered by the temperature sensor (31) is compared to a setpoint signal delivered by an adjustment device (32) by an electronic circuit (33). This electronic circuit (33) controls the operation of the temperature exchanger (8) so as to keep the temperature of the cryogenic fluid supplying the high-pressure compressor (12) constant and equal to the set temperature. The high-pressure compressor (12) consists of a pressure intensifier using a double-acting piston, having a head

(14) of large section actuated by compressed air from a reservoir (13) via a conduit (16) controlled by a valve (17). The other end of the piston consists of a plunger (15) of reduced section, communicating with a chamber (18) supplied with liquid nitrogen at low pressure. The outlet of the booster (12) feeds an ejection nozzle (19) comprising in a known manner a sapphire pierced by a calibrated orifice. The ejection head

(20) is surrounded by an insulating sleeve connected to a vacuum pump (39) by a conduit (22) surrounded by an insulating sleeve (23). Likewise, the various heat-insulating pipes are connected to the vacuum pump (39).

FIG. 2 represents an exemplary embodiment of an electronic circuit (33). It is composed of a differential operational amplifier (35) one of the inputs of which receives the signal from of the temperature sensor (31) and the other input of which is connected to a variable resistor (36) delivering a setpoint signal. The output of the operational amplifier (35) is connected to a power stage (36) controlling the operation of the engine of the cryogenerator.

The setting of the set temperature is carried out as follows:

After the cutting installation has been put into operation, a standardized sample, for example a plate made of a reference material, and of a standardized thickness, is placed on the cutting tray. The sample is then moved under the jet and the target value is modified by acting empirically on the control means

(32) by observing the modifications of the cut. The optimum setting will be considered as reached when the mechanical efficiency of the jet is maximized. One solution is to observe the maximum cutting speed as a function of the setting of the set value. The maximum cutting value is determined by a control of the movement of the plate supporting the sample to the passage of the sample by the jet of cryogenic fluid. When the setpoint is determined, the installation is operational for a duty cycle. The setting should be periodically reviewed, due to variations due to the heating of the cryogenic fluid in the storage tank. Figure 3 shows the temperature-entropy diagram of the installation.

At 1 bar, the temperature for liquid nitrogen in equilibrium with the vapor phase is 77.35 ° K.

If the installation was perfect and showed no heat loss, the cycle would be isentropic, and would correspond to the vertical line AA ', the path AA' representing the isentropic compression without any exchange with the outside at the level of the body of the booster (12), and the path A'A representing the nitrogen jet outlet isentropic liquid, without exchange with the outside at the nozzle (19).

In real conditions, each transformation leads to an increase in entropy. In order to obtain an outlet jet corresponding to a mixture of vapor phase and liquid phase, represented on the temperature-entropy diagram by a point B ', it is necessary to take account of the exchanges and therefore to set the initial operating point at a point C of the liquid-vapor separation curve corresponding to an initial temperature lower than the boiling temperature.

If we start from a point C corresponding to a temperature T _c below 77 ° K, for example 72 ° K for a pressure Pc less than 1 bar, for example 0.5 bar, the compression in the booster (12 ) is represented by the path CD, reflecting an increase in entropy by loss due to the heat exchanges between the nitrogen and the wall of the booster (12).

The expansion occurring at the nozzle (19) is represented by the path DB showing the thermal losses due to rolling. At point B, the vapor pressure is less than 1 bar, and the ejected fluid is therefore completely liquid, with no vapor phase.

If the losses in the nozzle (19) increase, the operating point moves to B 'corresponding to a vapor pressure higher than the atmospheric pressure. In this case, the jet at the outlet of the nozzle is completely vaporized, and therefore loses any mechanical cutting effect.

To obtain a maximum cutting effect, the operating point C of the nitrogen introduced into the booster is adjusted so that the operating point B "at the outlet of the nozzle (19) is very slightly beyond the equilibrium point corresponding to a temperature of 77.3 ° K at atmospheric pressure, so that the fluid has a proportion of gaseous phase between 1 and 20% by volume. The fluid will thus behave like a charged liquid bubbles producing a mechanical erosion effect on contact with the material to be cut. Maintaining the optimum operating point B "will be obtained by controlling the cooling temperature by the temperature exchanger (8).

Figure 4 shows an alternative embodiment of the installation. The liquid nitrogen is cooled before entering the booster (12) by circulation in an enclosure (41) containing liquid nitrogen coming from the storage tank (1). This enclosure is connected to a vacuum pump (42) creating a vacuum causing expansion of the liquid nitrogen, and therefore a lowering of the temperature. For example, a pressure of 0.3 bar causes the temperature to drop by 8 °.

The temperature sensor (31) delivers a signal to an electronic circuit (33) also receiving a signal from a means for adjusting (32) the set value. The output of the electronic circuit (33) controls the operation of the vacuum pump, as well as the operation of a valve disposed between the vacuum pump (42) and the enclosure (41). FIGS. 5 and 6 relate to an alternative embodiment of a multi-nozzle cryogenic jet cutting installation.

The nozzle (69) is supplied with cryogenic fluid under pressure through a thick-walled conduit (74). This conduit is constituted by a stainless steel tube having an internal diameter of 1.6 millimeters and an external diameter of 6.35 millimeters. The pipe (74) is surrounded by an insulating sleeve connected to the liquid nitrogen tank (53) by a pipe (72) insulated by an insulation sleeve (73).

The upstream end (75) of the duct (74) connecting the booster (62) to the nozzle (69) is fixed. The opposite end closest to the nozzle (69) is movable in a plane perpendicular to the longitudinal axis to the conduit (74).

A motor (77) mounted on a frame (not shown) causes the nozzle (69) to move in a direction perpendicular to the plane of the figure. The elasticity of the conduit (74) allows a lateral movement whose amplitude depends on the length of the conduit

(74) and the mechanical qualities of the material used. By way of example, a duct made of stainless steel, the internal diameter of which is 1.6 millimeters and the external diameter of which is 6.35 millimeters, allows lateral movement of the movable end of approximately 50 millimeters for a length of 80 centimeters.

The workpiece (80) is moved in a direction perpendicular to the axis of the jet and to the direction of movement of the nozzle (69) via a conveyor (81), for example a roller conveyor. The combination of the two movements makes it possible to follow any cutting line.

FIG. 6 represents a view of the ejection system comprising several ejection nozzles (90 to 93). The outlet of the booster (112) is connected to a supply ramp (94). This feed ramp consists of a plurality of tubular segments (95 to 98). The tubular segments (95 to 98) are connected together in a known manner. Each of the tubular segments (95 to 98) has a branch opening into a conduit (99 to 102) supplying one of the nozzles (90 to 93) with high pressure cryogenic fluid.

Each of the conduits (99 to 102) is surrounded by a bellows envelope (103 to 106), opening onto the sleeve (107 to 110) surrounding the corresponding tubular segment (95 to 98).

The nozzles (90 to 93) are integral with a plate (111) supporting the drive mechanisms (112 to 115). The plate (111) is fixed relative to the ramp (94).

The drive mechanism (112 to 115) ensures the lateral displacement of the corresponding nozzle (90 to 93), and therefore causes a deformation of the corresponding conduit (99 to 102). In the embodiment shown in Figure 6, the nozzle (92) disposed at the end of the conduit (101) is moved to the right, which causes a longitudinal deformation of the conduit (101) of which the two ends retain the original orientation. The upstream end remains perpendicular to the horizontal plane passing through the ramp (94). Similarly, the downstream end remains perpendicular to the plate (111). The intermediate part of the conduit (101) takes a regular curvature determined by the mechanical characteristics of the material constituting the conduit.

Likewise, the conduit (102) is deformed in the opposite direction due to the displacement of the corresponding nozzle (93) to the right.

The material to be cut (116) is moved in the plane parallel to the plate (111) by a conveyor (117). The device shown in Figure 6 allows for four simultaneous cutting lines. The control of the drive mechanisms (112 to 115) of the nozzles (90 to 93) as well as of the conveyor (117) can be controlled by a computer, optionally controlled by the cutting speed.

The invention is described in the foregoing by way of nonlimiting example. It is understood that the skilled person will be able to produce various variants without departing from the scope of

The invention.

Claims

1 - Cryogenic fluid jet cutting installation comprising a low-pressure cryogenic liquid storage tank, a high-pressure compressor (12), an ejection nozzle (19) connected by heat-insulating conduits, characterized in that it further comprises a heat exchanger (8) disposed between the storage tank (1) and the ejection nozzle (19) for cooling the ejected fluid to a constant set temperature, said heat exchanger being controlled by the signal delivered by a temperature sensor (31) disposed at the inlet of the high-pressure compressor (12).

2 - Installation for cutting by cryogenic fluid jet according to claim 1, characterized in that the heat exchanger (8) is disposed between the storage tank (1) and the high-pressure compressor (12).

3 - cryogenic fluid jet cutting installation according to claim 1 or according to claim 2 characterized in that the heat exchanger (8) consists of an enclosure (41) containing liquid nitrogen connected to a pump vacuum (42) causing the expansion of the liquid nitrogen contained in said enclosure.

4 - Cryogenic fluid jet cutting installation according to claim 1 or according to claim 2 characterized in that the heat exchanger (8) comprises a primary circuit in which the cryogenic fluid from the storage tank (1) circulates, said primary circuit being connected thermally to a secondary circuit in which a fluid from a cryogenerator circulates.

5 - Installation for cutting by cryogenic fluid jet according to any one of the preceding claims, characterized in that the heat exchanger (8) is controlled by an electronic circuit connected to the temperature sensor (31) disposed at the inlet of the high-pressure compressor, and comprising an adjustment means for adjusting an experimentally setpoint value.

6 - Cryogenic fluid jet cutting installation according to the preceding claim characterized in that the electronic circuit comprises a differential amplifier (37) one of the inputs of which receives the signal from the temperature sensor (31) and the other input reversing machine receives a setpoint signal (35) from the setpoint temperature adjusting means.

7 - Process for cutting by cryogenic fluid jet compressed to a pressure greater than 500 bars and ejected through a calibrated orifice of small diameter, characterized in that the target temperature of the cryogenic fluid at the inlet of the high-pressure compressor by optimizing the mechanical efficiency of the jet, and in that the temperature of the cryogenic fluid is kept equal to the set value by a controlled temperature exchanger.

8 - Cryogenic fluid jet cutting installation according to any one of the preceding claims, characterized in that it comprises at least one ejection nozzle (90 to 93) secured to a plate (111) movable in a plane substantially perpendicular to the longitudinal axis of said conduit (99 to 102), the ejection nozzle (90 to 93) being connected to the high-pressure compressor by a tubular duct (99 to 102) with a thick insulating wall connected to a fixed ramp (94) constituted by a tubular duct with a thick insulating wall.

9 - cryogenic fluid jet cutting installation according to claim 8 characterized in that a plurality of conduits (99 to 102) with thick walls are recorded on the fixed ramp (94), the end of each of said conduits being integral a movable plate in a plane substantially perpendicular to the longitudinal axis of said conduit, an ejection nozzle being connected to each of the movable ends of said conduits.

10 - Cryogenic fluid jet cutting installation according to claim 8 or according to claim 9 characterized in that the thick walled conduits are surrounded by a rigid waterproof envelope with bellows made of a thermally insulating material.

11 - Installation for cutting by cryogenic fluid jet according to claim 10 characterized in that the volume between the bellows envelope and the tubular conduit is connected to a vacuum pump.