Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Very High-Pressure Liquid-Spraying Gun for a Very High-Pressure
Liquid-Spraying Machine, and Method for Manufacturing Same
The present invention relates to a method for manufacturing guns for
spraying liquid at a very high pressure, and in particular guns for machines
for
working pieces using a jet of liquid at a very high pressure, in particular
cutting
and/or machining machines. It extends to the spraying guns produced
according to this manufacturing method.
The technique of cutting and/or machining using a jet of liquid at a very
high pressure consists in spraying liquid at a pressure of from 1000 to 8000
bar. The liquid, generally pure water or water with additives, is then ejected
at
a very high speed, from 600 to more than 1000 m/s, and directed onto the
piece to be worked. Thus, the technique of machining using a jet of liquid at
a
very high pressure makes it possible to work numerous materials such as
plastics, paper or metal alloys, and to do so without emitting dust or
generating
heat. In order to make it easier to cut the materials, abrasive particles may
be
added to the sprayed water.
The cutting heads used according to this cutting method conventionally
comprise a collimation tube, a nozzle with a small internai diameter, a mixing
chamber and a gun for spraying liquid at a very high pressure.
The liquid at a very high pressure enters through the collimation tube.
The liquid is then sprayed through the nozzle and enters at a high speed into
the mixing chamber provided with an abrasive particle inlet. The mixture of
liquid and the abrasive particles is concentrated and the jet at a very high
pressure is directed onto the piece to be worked by a gun with a small
internai
diameter. This gun is generally known by the term focusing gun.
Conventionally, such focusing guns are manufactured by machining from
a solid piece.
These focusing guns, however, are pieces which have a large ratio of
length to diameter, which makes it difficuit to machine a duct from a solid
piece. In particular, the machining does not make it possible to go below a
certain internai diameter threshold for a given length. Yet the internai
diameter
of the focusing gun determines the precision of the liquid jet.
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Furthermore, according to this manufacturing technique, the focusing
guns are normally made of tungsten carbide. This is because this ceramic is
easy to use and has a reasonable cost for such an application. However, such
guns made of tungsten carbide can be used only with abrasives of the oxide
type, such as garnet or aluminum oxide with a low relative hardness. This is
because the use of abrasives with a hardness greater than that of tungsten
carbide, from 8 to 9 on the Mohs scale, would rapidiy wear the interior of the
gun, leading to a premature loss of precision and a lifetime incompatible with
the usual applications of machines for machining using a jet of liquid at a
very
high pressure.
Another method for manufacturing focusing guns consists in vapor
depositing a ceramic on a cylindrical graphite support, then removing the
cylindrical support by heating once the ceramic has formel a tubular structure
around the graphite.
This method makes it possible in particular to manufacture guns made of
silicon carbide, a ceramic which has a high hardness of the order of 9.5 on
the
Mohs scale, making it possible to work with a wide range of abrasives which
are no longer limited to oxides.
This manufacturing method, however, turns out to be compiex to
implement and the production cost of the guns thus produced is high.
In order to overcome the problems associated with the length to internai
diameter ratio of the gun, it has been envisaged to manufacture a focusing
gun by assembling a plurality of elements. These elements may be cylindrical
pieces of small height, and therefore with a low length to internai diameter
ratio, which are aiigned along the axis of the duct of the gun and kept
assembled by clamping with an external piece of the sleeve type. This
technique, however, is virtually unused. This is because it does not allow the
various elements of the gun to be aligned correctly, and the alignment
differences lead to perturbations of the flow of liquid at a very high
pressure.
Furthermore, the junction regions prove particularly sensitive to wear.
With a view to overcoming the drawbacks of the techniques above,
another manufacturing method has consisted, as described particularly in US
5 785 582 or DE 196 40 920, in producing focusing guns from two pieces
provided with assembly faces by which they are intended to be joined in order,
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in the assembled state, to form a focusing gun. According to this method, a
central groove is formed in the assembly face of each of the two pieces, this
being formed in a planar median region of said assembly face and adapted to
extend between the two ends thereof, said central grooves being adapted to
form the duct of the focusing gun in the assembled position of the two pieces.
The problem which such a technique needs to resolve resides in
obtaining precise positioning of the two pieces, making it possible to obtain
a
duct having perfectly controlled internai dimensions. At present, however, no
solution makes it possible to resolve this problem satisfactorily.
Specificaliy, the current methods either require an expensive external
mechanism (techniques described in DE 297 02 397 or US 2 332 407), or do
not guarantee perfect relative positioning and perfect holding of the two
pieces
during the phase of assembling them:
^ technique using a film enclosing the two pieces described in US 5
785 582
^ technique of bonding the assembly faces of the two pieces, described
in DE 196 40 920, according to which:
= in the assembly face of at least one of the two pieces, laterally
with respect to the planar median region thereof, at least one
bonding reservoir is formed, which is intended to be filled with
a quantity of adhesive substance adapted to adhere to the
portion of the assembiy face of the other piece lying opposite
said reservoir, in the assembled position of the two pieces,
= each bonding reservoir is filled with adhesive substance, and
the two pieces are placed in contact so that they are joined by
their assembiy face and connected by means of the adhesive
substance.
The present invention aims to overcome the various drawbacks of the
current techniques for manufacturing focusing guns, and its main object is to
provide a method which is simple to carry out and has a low cost price, making
it possible to control very precisely the shape and the dimensions of the
spraying duct of the focusing gun.
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It is another object of the invention to provide a method making it
possible to manufacture focusing guns by using any type of materials, and in
particular materials with a very high hardness such as ceramics of the silicon
carbide type.
It is another object of the invention to provide a method making it
possible to manufacture focusing guns which are compatible with a wide range
of abrasives and have an increased lifetime regardless of the type of abrasive
used.
To this end, the invention relates to a method for manufacturing focusing
guns using the bonding technique described above, according to which,
furthermore:
- on the assembly face of at least one piece, at least one rib referred to
as a centering rib is formed, which projects from said assembly face,
- and, for each centering rib formed on the assembly face of one piece, a
cavity referred to as a centering cavity is formed in the assembly face of the
other piece, this cavity having dimensions adapted to tightly receive said
centering rib in the assembled position of the two pieces, in which the
central
grooves form the duct of the focusing gun.
Thus, according to the invention, the focusing gun consists of two pieces
connected to one another by bonding, in which the prior relative positioning
of
the pieces is ensured by means of at least a centering rib and a centering
cavity which are designed so as to cooperate in order to guarantee precision
of the relative positioning, before the surfaces intended to be connected by
bonding corne in contact with one another. Thus, during the actual bonding,
the two pieces are perfectly guided and can in no way experience any
transverse relative displacement liable to affect their centering.
Furthermore, once assembled, the two pieces are directly in contact with
one another in the planar median regions which make it possible to separate
the bonding region and the duct of the focusing gun, and therefore lead to a
safeguard against transfer of adhesive substance to said duct.
However, in order to reliably ensure against any transfer of adhesive
substance to the duct of the focusing gun, according to the invention a
centering rib is advantageously associated with each reservoir formed in the
assembly face of a piece, this rib having a length at least equal to that of
said
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bonding reservoir and being interposed between the latter and the central
groove formed in said assembly face, so that each rib thus has the twofold
function of a centering element and a barrier protecting the duct of the
focusing gun.
5 It should also be noted that, owing to its position, this protective barrier
not only preserves the integrity of the duct of the focusing gun but also
leads
to prevention of any migration of the adhesive substance to the planar median
region, so that the two pieces corne in contact with one another via
"unpolluted" faces.
The contact between the two pieces thus consists in direct contact
without significant play. Specifically, this play turns out to be greatly less
than
the diameter of the abrasive particles, so that the latter cannot become fixed
in
the gap between the pieces and prematurely wear the focusing gun.
According to an advantageous embodiment of the invention, a space
referred to as an overflow space is associated with each reservoir formed in
the assembly face of a piece, such that it communicates with said reservoir
with a view to receiving the possible excess of adhesive substance during
assembly of the two pieces, each of said overflow spaces being formed
laterally on the other side of the associated reservoir from the planar median
region.
Furthermore, the assembly faces of the two pieces are advantageously
formed so that each overflow space consists of a slot extending from the
periphery of the focusing gun, in the assembled position of the two pieces,
and
formed between said assembly faces opposite each bonding reservoir.
Besides the absorption of an excess of adhesive substance, such an overflow
space makes it possible to distribute this excess between the assembly faces
of the two joined pieces and thus to increase the bonded surface of these
assembly faces.
Furthermore, in order to enhance the bonding and advantageously
according to the invention, for each bonding reservoir formed in one piece,
the
other piece has an assembly face comprising a planar region referred to as a
bonding region, coplanar with the planar median region and adapted to extend
in front of the associated bonding reservoir and to close the latter.
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According to another advantageous embodiment of the invention, a
focusing gun is produced from two identical pieces, each comprising at least
one centering assembly consisting of a centering rib and a centering cavity
which are arranged symmetrically on either side of the central groove.
Moreover, advantageously according to the invention, centering ribs are
formed and centering cavities are formed, which extend over the majority of
the pieces.
Thus, the positioning of the two pieces is perfectly secured over the
entire length of these pieces and their manufacture is simplified.
Bonding reservoirs are likewise advantageously formed, consisting of
grooves extending over the majority of the pieces.
With the bonding regions extending over the entire length of the focusing
gun, the contact surface of the adhesive substance is maximized and the
quality of the adhesion is therefore increased.
Furthermore, a bonding reservoir is advantageously formed in each
piece.
Moreover, advantageously and according to the invention, the assembly
faces of the pieces are cleaned before an adhesive substance is deposited.
Furthermore, the step of depositing an adhesive substance is
advantageously preceded by a step of improving the adhesion of each
reservoir and each bonding region, such as a step of erosion by attack by a
laser, an acid or plasma, or a step of depositing a preparation layer, in
particular based on silane.
During assembly, moreover, a pressure is advantageously exerted on
the pieces after they have been brought in contact.
Furthermore, after assembly, the step of bonding the pieces by an
adhesive substance is advantageously followed by a step of machining the
focusing gun.
Moreover, an adhesive substance selected from epoxies, methacrylates,
polyimides or a mixture thereof is advantageously used.
As regards the materials used, pieces made of a material with a
hardness of more than 8 on the Mohs scale are advantageously used, for
example and advantageously silicon carbide.
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The manufacture of focusing guns from materials having a hardness
greater than that of tungsten carbide, which is conventionally used, makes it
possible to widen the range of products worked with the machines for cutting
and/or machining using a jet of liquid at a very high pressure. This is
because
materials having a hardness of more than 8 on the Mohs scale can then be
cut, and abrasive particles likewise having a high hardness can be used in
order to facilitate this work without the risk of prematurely wearing the
focusing
gun.
The invention also extends to a gun for spraying liquid at a very high
pressure, for a machine for spraying liquid at a very high pressure, referred
to
as a focusing gun, consisting of two pieces comprising assembly faces by
which they are joined and in which the following are formed:
^ for each of the two pieces, a central groove formed in a planar
median region of said assembly face and adapted to extend
between the two ends thereof, so as to form the duct of the
focusing gun,
^ for at least one of the two pieces and laterally with respect to the
planar median region thereof, at least one bonding reservoir
intended to be filled with a quantity of adhesive substance
adapted to adhere to the portion of the assembly face of the
other piece lying opposite said reservoir.
According to the invention, this focusing gun furthermore comprises:
formed on the assembly face of at least one piece, at Ieast one rib,
referred to as a centering rib, which projects from said assembly face,
= and, for each centering rib formed on the assembly face of one piece
and arranged in the assembly face of the other piece, a cavity, referred
to as a centering cavity, tightly receiving said centering rib.
The invention also extends to a focusing gun comprising any of the
characteristics mentioned in the claims or the description of the present
application, taken individually or in combination.
Other objects, characteristics and advantages of the invention will
become apparent from the following detailed description referring to the
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appended drawings, which represent two preferred embodiments thereof by
way of nonlimiting examples. In these drawings:
- Figure 1 is a view from above of a piece according ta the invention,
used for the manufacture of a focusing gun according ta the invention,
- Figure 2 is a section on an enlarged scale of this piece through a
transverse plane A,
- Figures 3 and 4 are cross sections through the transverse plane A
representing two phases in the manufacture of the focusing gun according ta
the invention,
- and Figure 5 is a partial section through the transverse plane A of a
variant of a focusing gun according ta the invention during assembly.
The focusing gun represented in the figures is intended in the usual way
ta be mounted on a cutting head of a machine for spraying liquid at a very
high
pressure.
According ta the invention, this focusing gun 1 consists of two elongate
pieces 2, 2' comprising assembly faces J by which they are intended ta be
joined in order, in the assembled state, ta form said focusing gun 1.
According ta the example represented, these two pieces 2, 2' are
identical. Over the majority of their length, they have a semicylindrical
shape
delimited by an assembly face J extending in a diametral plane (P), and they
end in a distal end segment 2a of semi-frustoconical shape.
The dimensions of this piece 2 are determined as a function of the
dimensions of the focusing gun 1 ta be produced. Thus, in order ta produce a
focusing gun 1 having a length of from 20 mm ta 150 mm with an external
diameter of from 5 ta 20 mm, pieces 2 having a length of from 20 ta 150 mm
with a width of from 5 mm ta 20 mm, i.e. a radius of from 2.5 mm ta 10 mm, for
a piece 2 of semicylindrical shape will be used.
These pieces 2 furthermore consist of a material having a high hardness,
preferably a hardness of more than 8 on the Mohs scale, with a view ta
making it possible ta work materials having a hardness greater than the
materials conventionally worked with tungsten carbide guns. Thus, these
pieces 2 may in particular be made of tungsten carbide.
Firstly, each piece 2 comprises, formed in the junction face J and
centered on the longitudinal symmetry plane (S) of said piece, a central
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groove 3 of semicylindrical cross section adapted to form a cylindrical duct
12
in the assembled state of two pieces 2.
This central groove 3 extends over all of the piece 2 and, at the proximal
end of this piece, comprises a semi-frustoconical widened segment 3a for
introducing the pressurized liquid into the duct 12.
It should be noted that the central grooves 3 may have shapes other than
semicylindrical, and may form ducts 12 having any cross sections, e.g.
parallelepipedal etc. For example, a duct 12 of parallelepipedal shape may be
selected for applications consisting in imparting a sweeping movement to the
liquid jet.
It should also be noted that a coating made of a material different to the
material constituting the pieces 2 may be deposited inside the central groove
3. This additional material preferably has a hardness greater than that of the
pieces 2, and may for example consist of diamond. This material may, in
particular, be applied by vapor deposition.
As represented particularly in Figure 2, the assembly face J of each
piece 2 has a planar median region 4, 5 divided into two half-regions 4, 5
extending respectively on either side of the central groove 3. This median
region 4, 5 is furthermore coplanar with the diametral plane (P), so that the
median regions of two assembled pieces 2 are in contact with one another.
Furthermore, along one of its longitudinal edges, this median region 4, 5
is bordered by a central rib 6 of rectangular parallelepipedal cross section
projecting from the assembly face J.
The other longitudinal edge of this median region 4, 5 is in turn bordered
by a centering groove 7 having a cross section complementary to that of the
centering rib 6, said centering rib and said centering groove being arranged
symmetrically on either side of the symmetry plane (S) so that, as represented
in Figures 3 and 4, the centering rib 6 of each piece 2, 2' is received in the
centering groove 7 of the other piece 2, 2' when said pieces are being
assembled.
Furthermore, the assembly face J of each piece 2 forms, between the
centering groove 7 and the corresponding longitudinal edge of said piece, a
planar lateral region 8 extending in the diametral plane (P) and therefore
coplanar with the planar median region 4, 5.
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This assembly face J furthermore comprises, laterally joined to the
centering rib 6 and separated from the median region 4, 5 by said centering
rib, a longitudinal groove 9 intended to form a reservoir for an adhesive
substance 11 and to be closed, in the assembled position of two pieces 2, 2'
5 and as represented in Figure 4, by the lateral region 8 of the opposing
piece 2.
As represented in Figure 1, each of the grooves 7, 9 and ribs 6 extends
longitudinally from the distal end of each piece 2, substantially over three
fourths of the length of said piece.
Lastly, the assembly face J of each piece 2 forms, between the reservoir
10 9 and the corresponding longitudinal edge of said piece, a planar lateral
region
10 extending substantially set back from the diametral plane (P) so that the
lateral region 10 of one piece 2 delimits a siot, opening laterally at one of
the
generatrices of the focusing gun 1, with the opposing lateral face 8 of the
second piece 2' forming said focusing gun.
This slot 8-10 thus forms a duct for discharge of the possible excess of
adhesive substance and for distributing this excess between the assembly
faces J of two assembled pieces 2, 2, thus making it possible to increase the
bonded surface of these assembly faces.
Figure 5 represents an alternative embodiment according to which the
planar lateral region bordering the reservoir 9 consists of a planar face 25
making an obtuse angle of the order of 120 degrees with the diametral plane
(P).
Identically, the lateral region 8 bordering the centering groove 7 forms a
dihedron having an apex angle of the order of 120 degrees, one of the two
half-planes 23 of which is adapted to extend parallel to the plane face 25 and
to delimit therewith a volume for retaining the excess of adhesive substance,
which is closed at the periphery of the focusing gun 1 by a longitudinal
border
24 projecting from said half-plane 23.
According to this alternative embodiment, the amount of adhesive
substance filling the retention volume is made to work in shear and not in
tension, so that it increases the adhesion power of said adhesive substance.
The steps in the manufacture of a focusing gun 1 by means of two
identical pieces 2, which are represented in Figures 1 and 2, will be
described
below particularly with reference to Figures 3 and 4.
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First, after having produced the pieces 2, 2' and before filling the
reservoirs 9 with adhesive substance 11, a preliminary step consists in
carrying out cleaning of the assembly faces J of the two pieces. Residues
which may have been generated by the manufacture of the latter are thus
eliminated.
It should furthermore be noted that this cleaning is essential at the
reservoirs 9 and the planar lateral regions 8 for closing said reservoirs.
Specifically, this cleaning prevents residues present on these surfaces from
reducing the adhesion of the adhesive substance 11.
The cleaning may, for example, comprise a first step of degreasing the
pieces 2 followed by pickiing with an acid, and final cleaning with a solvent
in
order to remove the residues generated by the acid attack.
Furthermore, before the reservoirs 9 are filled with the adhesive
substance 11, a second operation consists in improving the adhesion of the
bonding surfaces, namely walis of the reservoirs 9, lateral regions 8 and
lateral
regions 10.
This improvement of the adhesion may be carried out by erosion of said
bonding surfaces, for example by attack using a laser, an acid or plasma. The
improvement of the adhesion may also be carried out by depositing a
preparation layer, for example based on silane.
The next operation consists in filling each reservoir with an adhesive
substance 11. This deposition may in particular be carried out by
screenprinting, by depositing an adhesive film, by depositing a bead or by any
other known way of depositing an adhesive substance 11.
Furthermore, the adhesive substance 11 may be an epoxy,
methacrylates, polyamides or a mixture of these components. Preferably, the
substance used thus consists of a film of epoxy or bismaleide.
As represented in Figures 3 and 4, the junction faces J of the two pieces
2 and 2' are then positioned opposite one another, and the two pieces 2, 2'
are
brought together until the centering ribs 6 penetrate into the centering
grooves
7, a position from which the two pieces 2, 2' are then perfectly guided and
can
in no way experience any transverse relative dispiacement liable to affect
their
centering.
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They then continue to be brought together until the regions of the
assembly faces J Iying in the diametral plane (P) are respectively either in
contact with one another or in their position closing the reservoirs 9.
Furthermore, during contact of the adhesive substance with the planar
faces 8 opposite the reservoirs 9, the possible flow of this substance
necessarily takes place in the direction of the slot 8-10 owing to the
presence
of the protective barrier which, in the opposite direction, is constituted by
the
centering rib 6. Thus, not only does this flow not affect the cleanness of the
median regions 4, 5, but furthermore it leads to an increase of the bonding
surfaces.
At the end of assembly, the contact obtained between the two pieces 2,
2', particularly in the median regions 4, 5, thus consists in direct contact
without significant play, so that the dimensions of the duct 12 of the
focusing
gun 1 depend only on the dimensions of the central grooves 3.
The next operation consists in exerting a pressure on the pieces 2, 2'
brought in contact in this way, and in maintaining this pressure for the time
necessary for satisfactory fixing of the pieces by the adhesive substance 11.
This time depends in particular on the nature of the adhesive substance,
the temperature and the humidity. It will be determined according to the
instructions provided by the manufacturer of the adhesive substance 11.
Once connected by means of the adhesive substance 11, the pieces 2, 2'
form a focusing gun 1 ready for use.
Nevertheless, the bonding step may be followed by a step of machining
or finishing the exterior of the focusing gun 1 in order to modify its shape,
modify its external diameter or remove the residues generated by the bonding.
