EP1891842B1

EP1891842B1 - Plasma cutting device with pneumatic striking

Info

Publication number: EP1891842B1
Application number: EP06744806A
Authority: EP
Inventors: Giorgio Bassi
Original assignee: Tecmo SRL
Current assignee: Tecmo SRL
Priority date: 2005-06-03
Filing date: 2006-06-01
Publication date: 2013-02-27
Anticipated expiration: 2026-06-01
Also published as: EP1891842A2; WO2006129179A3; ITBO20050386A1; WO2006129179A2

Description

TECHNICAL FIELD

The present invention relates to the devices to generate a plasma jet, such as for cutting and in particular it refers to a plasma cutting device with pneumatic contact striking, of torch type, which can be handled manually or can be associated with a robotized arm or with an automatic machine.

BACKGROUND ART

There are known plasma torch devices equipped with an electrode contained in a nozzle under a big electric potential difference. In an operational condition, the electrode and the nozzle are mutually separated by an interspace crossed by a gas flow, usually air flow, fit to form the plasma jet coming out from a hole of the nozzle and fit for cutting metallic pieces.
In the said pneumatic torches type, the jet striking is effected translating the electrode from a contact condition with the nozzle to a separation condition of this latter by means of pneumatic type driving means.
A drawback of said torches consists in that the conformation and the disposition of the known pneumatic type driving means are very bulky so reducing handling and/or causing limits in manual or machine applications.
Other drawback of some known torches with pneumatic striking consists in that they generally consume excessively air or other active fluid.
Further drawback of some known torches consists in that they have a fluid feeding connection laterally positioned and orientated in radial or inclined manner reducing the handling features of said torches.
Other drawback of some known torches with pneumatic striking consists in that they have some elements which are not sufficiently cooled.
The document US4914271 discloses a plasma cutting device with pneumatic striking provided with a cylinder for a pneumatic piston fit to move an electrode, inside a nozzle for the outlet of the plasma, between a rest condition and an operational condition in which the electrode and the nozzle are respectively in mutual contact and spaced apart. The piston is at a distance from the free end to the electrode bigger than four times the maximum transversal dimension of the electrode. The document WO 90/03243 discloses a plasma cutting device with pneumatic striking provided with a cylinder for a pneumatic piston fit to move an electrode. The lower chamber of the cylinder is fed of gas by a lateral duct, to translate the piston and to form the plasma.

DISCLOSURE OF THE INVENTION

An object of the present invention is to propose a plasma cutting device with pneumatic striking, consisting of a small sized and compact torch, allowing easy handling and that can be simply used manually or with automatic machines.
Other object is to propose a very efficient device having a low consumption of air or of a generic active fluid.
Further object is to propose a device provided with a fluid feeding connection back positioned and axial or inclined oriented.
Other object is to propose a device provided with a suitable cooling.
The above mentioned objects are achieved in accordance with the content of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of the present invention are high-lighted in the following with particular reference to the attached drawings, in which:

figure 1 shows a schematic longitudinal section view of the plasma cutting device with pneumatic striking, of the present invention, in a rest condition and in which some parts are removed for better evidencing others parts;
figure 2 shows a longitudinal section view of the device of figure 1 in an operational condition;
figure 3 shows a transversal section view according to the plane III - III of figure 2, of a cylinder of the device;
figure 4 shows a schematic longitudinal section view of a first variant of the device of figure 1 represented in the rest condition and in which some parts are removed for better evidencing others parts;
figure 5 shows a longitudinal section view of the variant of the device of figure 4 in the operational condition;
figure 6 shows a schematic longitudinal section view of a second variant of the device of figure 1 represented in the rest condition and in which some parts are removed for better evidencing other parts;
figure 7 shows a longitudinal section view of the variant of the device of figure 6 in the operational condition

BEST MODE OF CARRYING OUT THE INVENTION

With reference to figures 1 - 3, the numeral 1 indicates the plasma cutting device with pneumatic contact striking, object of the present invention.
The device 1 is provided with a cylinder 4, consisting of a metallic cylindrical wall for the sliding stroke of a pneumatic piston 5, made of electrically insulating material, fit to move an electrode 2, movable inside a nozzle 3, for the plasma outlet, between a rest condition R and an operational condition O, in which the electrode 2 and the nozzle 3 are respectively in mutual contact and spaced apart.
The electrode 2 and the nozzle 3 are electrically isolated and, in the operational condition O, are under a big electric potential difference necessary to support the plasma jet.
The piston 5 is connected to the electrode 2 directly or at a short distance from this latter; said distance is shorter than four times of the maximum transversal dimension of the electrode 2. Preferably, in case of electrode fixed by means of a threading to a stem as in figure 1 or 2, said distance is shorter than the maximum diameter of the electrode. Generally anembodiment provides that the piston is fixed at a distance to the free end of the electrode, or to the end of this latter contacting with the nozzle in the rest condition, shorter than the half, or one-third or one-fourth of the total length of the torch.
The device comprises elastic means 20 fit to provide the antagonistic elastic force against the pneumatic force of the piston 5 fit to move the electrode 2 between the operational condition O and the rest condition R.
The device comprises a metallic stem 6 of elongated tubular shape, whose one first end, faced toward the nozzle 3, has a female screw connection 7 for a thread connection portion of the electrode. The first end portion of the stem 6, comprising the respective first end, has a perimetrical thread for the fixing of the piston 5 by means of screwing its one central female screw.
The piston 5 is blocked the stem 6 by means of a block pin 27 inserted in diametrical holes of said piston and stem.
The electrode 2, the nozzle 3, the cylinder 4 for the sliding of the piston, the piston 5 and the stem 6 are coaxial positioned with the longitudinal axis of the device.
The active fluid, preferably consisting of compressed air fit to the plasma formation and to the cooling, is flowed along the longitudinal internal hollow of the tubular stem 6. To this purpose, the second end of the stem 6, opposite in respect to the first end connected to the electrode, has an inlet for the active fluid and its first end portion, comprising the respective first end, has a set of outlets 8 for said fluid, consisting of radial holes passing through the wall of the stem and flowing into a first chamber 9 of the cylinder 4.
Said first chamber 9 is delimited by the piston 5 and by a separator 10, made of insulating material and fixed in an irremovable manner to the cylinder 4 to form a head, and provided with a hole slidingly engaged by the stem 6 or by the electrode. The separator 10 is interposed between the piston and the electrode.
The cylinder 4 has at least a first outlet 11, constituted by a set of radial holes passing through the wall of the cylinder and lying on a plane orthogonal in respect to the stem. Said holes are made in a position approximately corresponding to the end of the first chamber opposite to the separator in a manner that the first outlet 11 is at least partially closed by the piston in the rest condition R and at least partially opened in the operational condition O.
The first outlet 11 of the first chamber 9 is in flow communication with a duct 12 externally delimited by an external sleeve 13 and internally delimited by portions of the separator 10, of a diffuser 14, of the nozzle 3, of the cylinder 4 and of the sleeve 13. The first outlet 11 flows in the volume between the nozzle 3 and the electrode 2 through said duct 12 and a plurality of passing holes of the diffuser 14 that is made of insulating material and is interposed between the separator 10 and the nozzle 3.
The first outlet 11 of the first chamber 9 is also in flow communication with the external volume around the nozzle 3 through the duct 12 and a plurality of passing holes 15 of the external sleeve 13.
A second portion of the stem 6, almost complementary respect to its first end portion comprising the respective first end, is slidingly housed in a fixed tubular member 16, made of insulating material, rigidly connected to a connection portion 17 of the cylinder 4.
An end of the fixed tubular member 16 is inside the cylinder 4 and it serves as end stroke 18 for the piston 5 in the operational condition O determining the maximum distance between the electrode and the nozzle in said condition.
The elastic means 20 are of metallic helicoidal shape type and are interposed between the piston 5 and a tubular shaped stop mean 19 inside the cylinder. Said stop mean is carried out by an abutment obtained internally in the connection portion 17 of the cylinder 4 or, in alternative, in the fixed tubular member 16.
In order to improve the pneumatic sealing between the piston and the cylinder, the piston 5 is provided with at least an annular sealing mean 28, for instance of O-Ring type.
The cylinder is equipped with a second outlet 22, constituted by one or more passing holes carried out in the cylindrical wall of the end opposite to the separator of the second chamber of the cylinder 4, in opposite to the first chamber 9 in respect to the piston 5. Said second outlet 22 is fit to maintain the second chamber almost at atmospheric pressure also in case of compressed air entering therein.
The separator 10, the diffuser 14 and the nozzle 3 are interposed between the cylinder 4 and the sleeve 13 and these two latter are mutually fixed by screw for clamping the diffuser and the nozzle.
In case of torches for applications that allow to increase the air consumption, for instance because of connection to compressors or to other compressed air sources having big capacity, the invention provides that the cylinder 4 can be provided with a set of optional openings 29, each of them being constituted by a passing hole flowing into the portion of second chamber of the cylinder, in which are housed the elastic means 20, and in flow communication with the duct 12 delimited by the sleeve 13, by means of respective optional longitudinal grooves 30 obtained on the external face of the cylinder 4. An annular seal mean 31, positioned between the optional openings 29 and the second outlet 22 and matching the external wall of the cylinder and internal wall of the sleeve, prevents the exit of the air from the grooves directly to outside.
The axis of the holes of the optional openings 29 are radial oriented or preferably, inclined in the same manner to generate a spiral air flow to improve the cooling.
The invention thus provides that the first outlet 11 of the first chamber 9 is in flow communication with the outside through the duct 12, the optional longitudinal grooves 30, the optional openings 29, the second chamber of the cylinder.4 and the second outlet 22 of the cylinder 4 producing an air flow for cooling the portions of the device adjacent to the elastic means 20.
Compared with another torch having the same features except said optional longitudinal grooves 30 and optional openings 29, the torch equipped with the latter increases the thermal dissipation and the electric power.
The invention provides to regulate the air capacity and then the cooling of the area near the elastic means by modifying the diameter and/or the number of the holes of the optional openings 29.
The operation of the device 1 provides that, for starting the operational condition, the device is supplied with electric power and with the compressed air that, flowing through the stem in the first chamber 9, it increases the internal pressure of this latter effecting a force on the piston causing the translation thereof overcoming the force of the elastic means 20. Said translation provokes the opening of the first outlet 11 of the cylinder and thus the air flow through the nozzle in which, thanks to the separation of the electrode, the arc strikes and produces the plasma coming out from the nozzle to allow the cutting. Said device requires a very low air consumption and is particularly suitable for devices with medium and low amperage level.
The variant of the device of figures 4 and 5 is particularly suitable for devices with medium and high amperage level and it provides that the first outlet 11 of the first chamber 9 is in flow communication with the outside through the duct 12, through a plurality of passing holes 21, made in inclined manner through the wall of the cylinder 4; said passing holes 21 connect the duct 12 with the second chamber of the cylinder 4 opposite to the first chamber 9 in respect to the piston 5. The flow communication proceeds from the second chamber of the cylinder 4, through the second outlet 22 of the cylinder 4 to the outside generating an air flow for cooling the portions of the device near the elastic means 20.
In the variant of figures 6 and 7 of the device 1, the elastic means 20, of helical metallic spring type, are interposed between the second end of the stem 6, opposite to the electrode 2, and an annular abutment 23 inside the fixed tubular member 16.
Furthermore, the stem 6 has a transversal pin 24 whose anti-rotation ends 25, protruding from the stem 6, are slidingly housed in the respective concave longitudinal housing 26 carried out in the fixed tubular member 16. Said variant also allows to further reduce the dimensions of the device.
The power supply of the electrode is provided by means of the spring of the elastic means 20 or by means of a flexible or sliding connecting conductor element of the electrode or of the stem, to the annular abutment 23 electrically connected to the power terminal or directly to said terminal.
The main advantage of the present invention is to provide a small and compact pneumatic striking plasma cutting device which can be handled in a very simple manner and that can be easily manually used or suitable for automatic machines.
Other advantage is to provide a very efficient device having a lower consumption of air or of other generic active fluid.
Further advantage is to provide a device provided with a rear fluid feeding connection axial or inclined positioned.
Other advantage is to provide a device equipped with a suitable cooling.

Claims

Plasma cutting device with pneumatic striking provided with at least a cylinder (4) for a pneumatic piston (5) fit to move an electrode (2), inside a nozzle (3) for the outlet of the plasma, between a rest condition (R) and an operational condition (O) in which the electrode (2) and the nozzle (3) are respectively in mutual contact and spaced apart; the device (1) further comprises a tubular type stem (6) having a first end facing the nozzle (3), said first end having a connection (7) for the electrode (2), a first end portion, comprising said first end at which the piston (5) is connected at a distance from the electrode (2) shorter than four times of the maximum transversal dimension of the electrode (2) and a second end having an inlet for an active fluid fit at least to the formation of the plasma; the device (1) is characterized in that : said stem has a set of outlets (8) carried out in the first end portion of the stem (6); said cylinder (4) has a first chamber (9) wherein said active fluid flows from said inlet through said set of outlets (8) through said first chamber (9), said first chamber (9) being delimited by the piston (5) and by a fixed separator (10) provided with a hole slidingly engaged by the stem (6); said cylinder (4) comprises at least a first outlet (11) at least partially closed by the piston (5) in the rest condition (R) and at least partially opened in the operational condition (O) and in flow communication with at least the volume comprised between the nozzle (3) and the electrode (2) through a duct (12).
Device according to claim 1 characterized in that it comprises elastic means (20) which provide an antagonistic elastic force against the pneumatic force of the piston (5) fit to move the electrode (2) between the operational condition (O) and the rest condition (R).
Device according to claim 1 characterized in that the electrode (2), the nozzle (3), the cylinder (4), the piston (5) and the stem (6) are coaxial.
Device according to claim 1 characterised in that the duct is externally delimited by an external sleeve (13) and it is in flow communication with the volume comprised between the nozzle (3) and the electrode (2) through a plurality of passing holes of a diffuser (14) made of insulating material interposed between the separator (10) and the nozzle (3).
Device according to claim 1 characterized in that at least a first outlet (11) of the first chamber (9) is in flow communication with at least the external volume around the nozzle (3) through the duct (12) externally delimited by an external sleeve (13) and a plurality of passing holes (15) of the external sleeve (13).
Device according to claim 1 characterized in that a second end portion of the stem (6), nearly complementary to the first end portion comprising the first end, said second end portion is sliding housed in a fixed tubular member (16) rigidly connected to a connecting portion (17) of the cylinder (4).
Device according to claim 6 characterized in that an end (18) of the fixed tubular member (16) is inside the cylinder (4) and serves as end stroke (18) for the piston (5) in the operational condition (O) determining the maximum distance between the electrode and the nozzle in said condition.
Device according to claims 2 and 6 characterized in that the elastic means (20) are of helicoidal type and are positioned between the piston (5) and a stop means (19) of the connecting portion (17) of the cylinder (4) or of the fixed tubular member (16).
Device according to claim 1 characterized in that at least a first outlet (11) of the first chamber (9) is in flow communication with the outside through the duct (12) externally delimited by an external sleeve (13), a plurality of passing holes (21), carried out through the wall of the cylinder (4), in connection with the duct (12) to the second chamber of the cylinder (4), opposite to the first chamber (9) in respect to the piston (5), and at laest a second outlet (22) of the cylinder (4) which connects the second chamber with the outside.
Device according to claim 1 characterized in that at least a first outlet (11) of the first chamber (9) is in flow communication with the outside through the duct (12) externally delimited by an external sleeve (13), a plurality of longitudinal grooves (30) connecting the duct (12) with openings (29) constituted by passing holes carried out through the wall of the cylinder (4) and flowing into a second chamber of the cylinder (4), opposite to the first chamber (9) in respect to the piston (5), and at least a second outlet (22) of the cylinder (4) which connects the second chamber with the outside.
Device according to claim 10 characterized in that the holes of the openings (29) are positioned in radial manner or inclined in the same manner.
Device according to claim 10 characterized in that the diameter and/or the number of the holes of the openings (29) can be modified for adjusting the total air flow passing there through.
Device according to claims 2 and 6 characterized in that the elastic means (20) are of helical type and they are positioned between the second end portion of the stem (6), opposite to the electrode (2), and an annular abutment (23) inside the fixed tubular member (16).
Device according to claim 13 characterized in that the stem (6) has a transversal pivot (24) whose anti-rotation ends (25), protruding from the stem (6), are housed in sliding manner in respective longitudinal concave housing (26) carried out in the fixed tubular member (16).
Device according to any one of the preceding claims characterized in that the piston (5) is screwed to the stem (6).
Device according to any one of the preceding claims characterized in that the piston (5) is blocked to the stem (6) by means of a block pin (27).
Device according to any one of the preceding claims characterized in that the piston (5) is provided with at least an annular sealing mean (28).
Device according to any one of the claims 4, 6 and 9 characterized in that the separator (10), the diffuser (14) and the nozzle (3) are positioned between the cylinder (4) and the sleeve (13), these two latter being mutually screw fixed.
Device according to claim 18 characterized in that the separator (10) is fixed in irremovable manner to the cylinder (4) constituting a head thereof
Device according to claim 18 characterized in that the duct (12) is completely delimited by portions of the separator (10), of the diffuser (14), of the nozzle (3), of the cylinder (4) and of the sleeve (13).
Device according to any one of the preceding claims characterized in that the piston (5) is connected to the electrode (2) directly or at a distance from this latter shorter than the maximum diameter of the electrode.