WO2015059601A1

WO2015059601A1 - Assembly, precursor and process for forming hollow bodies

Info

Publication number: WO2015059601A1
Application number: PCT/IB2014/065255
Authority: WO
Inventors: Sandro Rabaioli; Luca Benedetti; Giuliano Bonomi
Original assignee: Rubinetterie Utensilerie Bonomi S.R.L.
Priority date: 2013-10-21
Filing date: 2014-10-13
Publication date: 2015-04-30
Also published as: ITBS20130148A1; TW201525332A

Abstract

Assembly (1, 1', 1") for forming a hollow metal body (2) comprising a precursor (4) having a substantially tubular wall (6), which extends about an axis (X) and delimits a body compartment (8), and a forming device (10, 10', 10"). Such device identifies one or more injection passageways (12, 12') of a pressurised liquid in the body compartment (8) to induce an expansion of the latter, and comprises a pair of half-moulds (14, 16), which jointly delimit a mould chamber (18) accommodating said precursor (4) and configured to contain plastic deformations of the tubular wall (6) following expansion. Such device comprises axial compression means (14, 16; 80, 80') of the precursor (4) to deform the tubular wall (6) radially externally and obtain the metal body (2).

Description

DESCRIPTION

"ASSEMBLY, PRECURSOR AND PROCESS FOR FORMING HOLLOW

BODIES"

[0001] The present invention relates to an assembly and process for forming hollow bodies, and a precursor that may be used in the above-mentioned assembly or process.

[0002] The use of ball valves is known in several fields of the art, in order to intercept the passage of fluids therein in a reversible manner.

[0003] Forging - high-temperature mechanical processing - or metal bar processing are the methods conventionally used for manufacturing^■ the balls of the above-mentioned valves .

[0004] Such known techniques, however, have the disadvantages of high energy consumption and various post-treatment steps, in particular mechanical operations of chip removal, to obtain a ball mountable in the valve body .

[0005] Therefore, the present invention falls within the foregoing context, seeking to provide an apparatus and method significantly simplified with respect to the systems of the prior art, so as to make the manufacturing of the above-mentioned components reproducible on a large scale .

[0006] Such objective is achieved thanks to an assembly according to claim 1, by means of a process according to claim 15, and by means of a precursor according to claim 19. The dependent claims show advantageous or preferred embodiment .

[0007] The object of the present invention will now be described in detail, with the aid of the attached drawing tables, wherein:

[0008] - figures 1, 2 and 10 show three assemblies object of the present invention, in accordance with different embodiments ;

[0009]- figures 3 and 4 show two enlargements of the half- moulds shown in figures 1 and 2, respectively;

[0010] - figure 5 shows a precursor according to a variant, while figures 5a, 5b, 5c show different embodiments of the end portion of such precursor;

[0011]- figure 6 shows a schematisation of the action of pressure between the closed half-moulds of the forming device, while figure 6a shows an enlargement of the area highlighted in figure 6;

[0012] - figures 7, 8 show a side view and a cutaway view of a hollow metal body according to a possible embodiment, while figure 8a shows an enlargement of the area highlighted in figure 8; and

[0013] - figure 9 shows a diagram of the pattern of pressure inside the precursor as a function of the stroke (c) of the movable half-mould;

[0014] - figure 11 shows a semi-finished hollow metal body obtainable by means of the equipment of figure 10.

[0015] With reference to the above-mentioned tables, reference numerals 1, 1', 1" globally indicate an assembly for forming a hollow metal body 2. Such assembly is particularly suitable for forming balls for ball valves, but may also be used for a set of further hollow metal bodies.

[0016] Such assembly 1, 1', 1" comprises a precursor 4 of the metal body 2 which comprises a substantially tubular wall 6, which extends about a central axis X to delimit a body compartment 8. For example, the above-mentioned precursor 4 only consists in the tubular wall 6.

[0017] Preferably, the precursor 4 is at least partially made from stainless steel according to the EN 10216-5 standard, preferably subjected to a thermal annealing treatment. By way of example, an AISI 316L steel was found suitable for this purpose.

[0018] Unless otherwise specified, in the present disclosure the terms "axial" and "radial" will refer to the central axis X.

[0019] Advantageously, the body compartment 8 is open on both axial ends 4', 4" of the precursor 4 by means of opposite access openings 42, 44. [0020] With reference to the embodiments shown in figures 3, 4 and 5, the precursor 4 may be characterised by different axial lengths L0 (which are the lengths of the tubular wall 6 parallel to the central axis X) , different wall thicknesses s and different transit sections of the body compartment 8.

[0021] Preferably, the tubular wall 6 delimits a body compartment 8 with a substantially circular cross section (i.e. orthogonally to the central axis X) .

[0022] The assembly 1, 1', 1" further comprises a forming device 10, 10', 10" which comprise at least a first 14 and a second 16 half-mould, which jointly delimit a mould chamber 18, wherein the latter accommodates the precursor 4 preferably in a reversible manner.

[0023] In fact, the precursor 4 is inserted in the mould chamber 18, then, after that such precursor has been transformed into the metal body through the operations described hereinafter, such body 2 is extracted from the chamber which may thus accommodate a new precursor to be subjected to a new forming process.

[0024] The forming device 10, 10', 10" identifies one or more injection passageways 12, 12' of a pressurised liquid in the body compartment 8 to induce an expansion of the latter. For example, the liquid used is water or oil. [0025] Advantageously, the injection passageway 12, 12' is identified at least in part by one of the half-moulds 14, 16; according to one embodiment, both half-moulds identify a separate injection passageway. For example, such passageway 12, 12' crosses at least partially the thickness of a mould wall 46, 48.

[0026] Preferably, the injection passageway 12, 12' communicates upstream with at least one pressurisation source 38, 40 of the pressurised liquid, only schematised in the tables, and communicates downstream with the mould chamber 18. Since the precursor lies inside such chamber 18, and due to the fact that the tubular wall 6 preferably creates a seal with an inner surface 30, 30' of at least one of the half-moulds 14, 16, the injection passageway 12, 12' end downstream inside the body compartment 8. More in particular, at least one outlet 20, 20' of the injection passageway 12, 12' in the mould chamber 18 ends at one of the access openings 42, 44 to the body compartment 8.

[0027] In such context, the terms "upstream" and "downstream" refer to the transit direction of the pressurised liquid.

[0028] In at least one operating condition thereof, the above-mentioned half-moulds 14, 16 are configured to contain the plastic deformations of the tubular wall 6 following the expansion of the body compartment. In fact, the tubular body 6 is deformed outwards by the pressurised liquid, in order to progressively adhere to the inner surfaces 30, 30' delimited by the half-moulds.

[0029] With reference to the variant schematised in figure 1, the forming device 10 comprises a pair of pressurisation sources 38, 40, wherein the first source 38 preferably acts as a feedback to the second source 40. For example, the second pressurisation source 40 comprises a pressure multiplier.

[0030] The forming device 10, 10', 10" further comprises axial compression means 14, 16; 80, 80' of the precursor 4 to deform the tubular wall 6 radially externally and obtain the metal body 2.

[0031 ] According to a first preferred variant, the axial compression means comprise at least one thrust member^' 80, 80', associated with at least one half-mould 14, 16 and translatable towards the mould chamber 18 to compress the above-mentioned precursor. Specifically, such translation occurs independently with respect to half-moulds. Preferably, the injection passageway 12, 12' is at least partially obtained within the thrust member 80, 80', such as for example schematised in figure 10, which may therefore be made in a generally tubular form.

[0032] According to a second preferred variant, the axial compression means comprise at least one of the above- mentioned half-moulds (14 or 16) , movable relative to the other half-mould (16 or 14) between an open configuration of the mould chamber 18 and a compression configuration, wherein the movable half-mould 14, 16 axially compresses the precursor 4.

[0033] For example, in the open configuration the two half- moulds are spaced apart from each other, specifically sufficiently spaced apart to allow the introduction of a precursor in the mould chamber 18. On the contrary, in the compression configuration, the movable half-mould 14, 16 axially compresses the precursor 4 - in particular against the other half-mould - to deform the tubular wall 6 radially externally and obtain the metal body 2.

[0034] In other words, in the compression configuration, the distance between the inner surfaces 30 30' axially facing the precursor 4 is smaller than the axial length L0 thereof, and this is why the above-mentioned axial compression is generated. For this reason, the axial length L0 is a critical parameter to ensure the complete filling of the mould.

[0035] Therefore, innovatively, the metal body 2 is obtained by means of the combined action of the inner pressure of the pressurised liquid and the mechanical deformation of the movable half-mould or the thrust member on the precursor .4. Accordingly, the metal body is at least partially expanded outwards, meaning that at least one cross section of the body compartment has increased with respect to the initial condition of the precursor.

[0036] In the embodiment shown in figure 1, the half-mould identified by reference numeral 14 is fixed, while the other half-mould 16 is movable in approaching/distancing direction . .

[0037] In the variant shown in figure 2, both half-moulds 14, 16 are mutually movable, for example symmetrically relative to a median plane Z.

[0038] In the variant shown in figure 10, independent of the presence of one or two movable half-moulds - both technical solutions being implementable according to this embodiment - at least one thrust member 80, 80' is translatably accommodated in at least one half-mould 14, 16. Preferably, each half-mould comprises such a thrust member .

[0039] For the embodiments of the forming device 10" that provide one thrust member 80, 80', there may be further provided a closing system 82 acting at least on the movable half-mould to ensure the closing of the mould chamber 18 during the injection of liquid.

[0040] Preferably, the movable half-mould and/or thrust member 80, 80' is movable parallel or coaxially relative to the central axis X of the tubular wall 6.

[0041] For moving the mould, the forming device 10, 10', 10" may comprise one or more linear actuators 32, 34, for example of the electrical or hydraulic type.

[0042] According to the variant of figure 1, the forming device 10 comprises only one linear actuator 32 to move the movable half-mould by means of an elbow kinematic mechanism 36. According to the variant of figure 2, the forming device 10' may comprise two movable half-moulds, each of which pushed by a relative linear actuator 32, 34. Preferably, a first linear actuator 32 works in opposition to the action of the other actuator 34. According to the variant of figure 10, the thrust member 80, 80' and the movable half-mould 14, 16 may be moved by a different linear actuator.

[0043] According to one embodiment, at least one outlet 20, 20' of the injection passageway 12, 12' (or plurality thereof) is obtained on a portion 22 of half-mould 14, 16 projecting in the mould chamber 18. According to such variant, when the movable half-mould 14, 16 is in a closed configuration of the mould chamber 18 (that is, in a configuration wherein the half-moulds are in mutual abutment), the metal body 2 lies in abutment with said portion 22 or the pair of portions 22 such as for example schematised in figure 6.

[0044] More specifically, since the projecting portion 22 delimits an annular groove 50 with the inner surface 30, 30' thereof, at the base of the above-mentioned portion 22, in the closed configuration the metal body 2 wedges itself in such groove 50. In this regard, the inner surface 30, 30' may be partially concave to guide the metal body during such insertion into the groove 50.

[0045] As it can be seen for example from the schematisation of figure 6, where the arrows 52 schematise the action of inner pressure on the precursor which has already transformed into the metal body 2, both ends of the above-mentioned body 2 are inserted into respective annular grooves 50.

[0046] Therefore, it is easy to understand that the above- mentioned projecting portion 22 maintains the fluidic passageway 68 within the metal body since, independently of the degree of deformation of the precursor, the access openings 70, 72 to the fluidic passageway will be still maintained open by the portion 22.

[0047] Preferably, the annular groove 50 is delimited inferiorly by a substantially rectilinear surface 74, preferably extending from the base of the projecting portion and from an adjacent concave surface 76 which extends away from the portion 22. For example, such surf.aces are portions of the inner surface 30 30' of at least one of the half-moulds.

[0048] Accordingly, according to. an advantageous variant, at the access openings 70, 72 the metal body may delimit an outer connecting surface 66, in particular of complementary shape to the surfaces of the annular groove discussed above.

[0049] According to an advantageous embodiment, the tubular wall 6 comprises an end thickness s (which may be an intermediate thickness in the case of a wall with constant thickness) and at least one end thinning d of said thickness s. Said end thinning d is provided to obtain a fluid seal with the respective half-mould 14, 16.

[0050] According to a further advantageous variant, the precursor 4 or the tubular wall. 6 delimits at least one conical inlet surface 24, inclined by an angle β with respect to the central axis X to obtain a planar cylindrical surface 26 in the metal body 2, once deformation has ended. For example, such angle β is comprised within the range 30°-70°, preferably 40°-60°, advantageously 45°-55°, for example substantially 50°.

[0051] Preferably, the planar cylindrical surface 26 is connected to the external connecting surface 66 by means of a planar annular surface 78. For example, the planar cylindrical surface 26 and the planar annular surface 78 mutually extend at a right angle, such as for example schematised in figure 8a or 6a.

[0052] With reference to the embodiment of figure 5a, there may be provided a first 24 and a second 58 conical inlet surface, obtained at opposite surfaces - one inner surface and one outer surface, respectively - of the tubular wall 6. In such way, at least one axial end 4" of the precursor 4 is provided with a sharp edge or a tapered edge 56.

[0053] Preferably, the metal body 2 is a spherical body with a substantially constant wall thickness 54 and wherein the following trigonometric relations apply:

wherein :

[0054] - Lfinale (shown as "Lf" in figure 8) is the final length of the spherical body;

[0055] - Dint is the inner diameter of the spherical body;

[0056] - a/2 is the average angle subtended at the final length of the spherical body;

[0057] - L0 is the axial length of the precursor 4 as defined above.

[0058] According to a variant, at least one axial end 4', 4" of the precursor 4 is radially internally inclined or deformed in a conical shape, so that an outer surface 28 of such end creates a seal with the inner surface 30 30' of at least one of the half-moulds 14, 16. Such a feature is well shown in figure 5c, wherein the conicity 64 shown precedes the moving of the movable half-mould.

[0059] With respect to the variant of the assembly of figure 10, since a variant provides that the thrusting members do not penetrate within the mould chamber 18, the achievement of the hollow metal body passes through a semi-finished product 84 having at least one generally cylindrical extension 86, 86' at an axial end thereof. For example, figure 11 shows a pair of such extensions mutually extending in opposite directions. Preferably, the above-mentioned extensions 86, 86' will have to be removed in order to obtain the metal body for the use thereof.

[0060] According to a further variant, the forming device 10, 10' , 10" comprises the above-mentioned pressurisation source 38, 40 which may be controlled so that:

[0061] a) when the half-moulds 14, 16 are spaced apart, the source 38, 40 is adjusted to maintain a first constant pressure P0 in the body compartment 8; and

[0062] b) upon contact between the half-moulds 14, 16, such source promotes an increase of the first pressure P0 to a second pressure Pi. [0063] Such pressure trend is well shown in the diagram of figure 9, wherein the upper curve shows the travel of the movable mould, which at time tl remains constant due to the closing of the mould chamber. The lower curve, on the contrary shows the pressure trend, which within the time interval tO-tl (that is, during the closing of the above- mentioned chamber) remains constant at value P0 and which, subsequently, within the time interval tl-t2 gradually increases up to PI and then stabilises at such constant value until time t3. Optionally, following time t3-and before the travel inversion of the movable half- mould to open the mould chamber again, the pressure may be decreased again (for example at ambient pressure), in particular to avoid uncontrolled deformations of the metal body.

[0064] For example, the above-mentioned pressures P0, PI may be determined according to the following equations:

_ ^flPl.° . 7,

wherein :

[0065] - Rp 1,0 is the yield strength needed to obtain a permanent deformation of 1% of the precursor 4;

[0066] - dint is the inner diameter of the tubular wall 6;

[0067] - s is the average thickness of the tubular wall 6; [0068] - kl is a coefficient numerically comprised between

1 and 1.5, and is sensitive in order to ensure the plastic deformation of the precursor and the support of the tubular wall during the closure of the half-moulds ;

[0069] - k2 is a coefficient numerically comprised between

2 and 4, and is particularly important in order to ensure the calibration of the workpiece and hardening of the metal body with subsequent improvement of mechanical properties.

[0070] The above-mentioned objective is further achieved by means of a process for forming a metal body 2, in particular a ball for. ball valves, comprising the following steps:

[0071] - providing a precursor 4 of the metal body 2 comprising a substantially tubular wall 6, which extends about a central axis X to delimit a body compartment 8;

[0072] - injecting a pressurised liquid in the body compartment 8 to induce an expansion of the latter;

[0073] - containing plastic deformations of the tubular wall 6 following such expansion;

[0074] - axially compressing the precursor 4 to deform the tubular wall 6 radially externally and obtain the metal body 2.

[0075] Since such process is advantageously implementable by means of the above-mentioned device and assembly, advantageous or preferred embodiments of the method comprise any step implicitly described by means of the foregoing structural features.

[0076] In accordance with one embodiment, the step of providing the precursor comprises one or more steps of dividing a tubular bar into portions of axial length L0 approximately corresponding to those of the above- mentioned precursor.

[0077] In other words, the precursors usable in the method and assembly may be separate by a single tubular bar of desired size, for example by means of cutting operations.

[0078] According to an advantageous variant, the injecting and compressing steps are at least partially concurrent.

[0079] According to a further advantageous variant, the injecting step and/or the compressing step are performed by cold processing, that is in the absence of heating. For example one or both such steps could be performed at room temperature. In fact, because of such cold processing the metal body is reinforced thanks to the resulting hardening.

[0080] Optionally, the injecting step comprises a first sub-step of injecting the pressurised liquid at a first constant pressure P0, and increasing the first pressure P0 to a second pressure PI when the compressing step is complete. As regards the determination of the values of pressure P0, PI, reference should be made to the foregoing description.

[0081] According to further embodiments, the process may comprise one or more butt workings of the precursor, and/or a step of making an outer crack 60 on the metal body.

[0082] For example, the butt may be used to create the end thinning d, one or more conical inlet surfaces 24, 58 and/or to obtain the conical shape of the axial end 4', 4".

[0083] As regards the outer crack 60, in particular it may be arranged to accommodate an operation rod (not shown) actuatable by a user lever to cause the spherical metal body to rotate inside a valve body, in order to allow/prevent the transit of liquid inside the valve. By way of an example, such outer crack 60 may be made by mechanical chip removal or by laser removal/cutting. According to a further variant (not shown) , the outer crack may be made by means of a shearing step performed by suitable means functionally interacting with the mould chamber 18. According to such variant, the pressure inside the metal body may be, for example, maintained in order to oppose an inner strength to the external mechanical forces exerted by the shearing.

[0084] According to further variants, the metal body may be subjected to at least one of a grinding step of the outer surface 62 of the metal body 2 (for example aimed to obtain a satisfactory circularity or a desired outer profile/diameter) , and/or a brushing step of the outer surface of the metal body, in particular to obtain a desired surface finish. Optionally, a step of at least partially removing the cylindrical extensions 86, 86' (when provided), and optionally a grinding step and/or a brushing step of the residual parts of such removal may be provided.

[0085] For example, the grinding step may be performed by a cup grinding wheel, or by a crushed grinding wheel.

[0086] Advantageously, the assembly and process object of the present invention allow obtaining important advantages in terms of costs.

[0087] In particular, with the same number of metal bodies made, the present invention allows obtaining significant savings of raw materials, since the ball valves do not require to be post-treated to eliminate excess material.

[0088] Moreover, a wall thickness of the metal body that is thin and substantially constant throughout the length allows reducing the metal material needed to manufacture such bodies.

[0089] Furthermore, the above-mentioned device is constructively simple, since it allows reducing the number and complexity of the equipment used. Specifically, with respect to passive mould apparatuses, the device object of the present invention allows eliminating the components associated with the pushers wherein the fluidic passageways are made. Furthermore, it is possible to exclude a press to keep the moulds closed.

[0090] Advantageously, the device and process of the present invention allow obtaining hollow bodies in an extremely repeatable manner, as well as with excellent size tolerances.

[0091] Advantageously, the device object of the present invention is capable of ensuring the seal during the entire forming cycle both before closing and after closing the half-moulds.

[0092] Advantageously, the assembly object of the present invention allows obtaining, with the same technical arrangement, greater thrust forces and having a closing of the moulds ensured mechanically, without using the machine automation.

[0093] Advantageously, by using an electrical motor, it is possible to obtain high precision throughout the work cycle.

[0094] Advantageously, the assembly and process object of the present invention provide the use of alternative raw materials for manufacturing balls for valves, in particular metal materials that do not require galvanic coating treatments.

[0095] In fact, a nickel-free directive will soon come into force that will foist manufacturers to responsibly do without nickel in the conventional nickel-chrome coating system on the brass balls currently marketed.

[0096] Advantageously, the thermodynamic parameters previously discussed favourably influence the cost of metal, since such component ensures the mechanical properties required also with wall thicknesses smaller than conventional metal bodies.

[0097] Advantageously, the fluidic passageway inlets of the metal body were specially designed to prevent any damage to the fluidic seals which cooperate outside of such body. The result is an increased lifespan of the valve as compared to conventional balls.

[0098] Advantageously, the above-mentioned process was designed to always work in conditions of safety, and to ensure high repeatability of the forming operations.

[0099] A man skilled in the art may make several changes or replacements of elements with other functionally equivalent ones to the embodiments of the above assembly, process and precursor in order to meet specific needs.

[00100] Also such variants are included within the scope of protection as defined by the following claims. [00101] Moreover, each variant described as belonging to a possible embodiment may be implemented · independently of the other variants described.

Claims

1. An assembly (1, 1', 1") for forming a hollow metal body (2), in particular for forming a ball for ball valves, comprising:

i) a precursor (4) of said metal body (2) comprising a substantially tubular wall (6), which extends about a central axis (X) to delimit a body compartment (8); and ii) a forming device (10, 10', 10") which identifies one or more injection passageways (12, 12') of a pressurised liquid in the body compartment (8) to induce an expansion of the latter, and which comprises at least a first (14) and a second (16) half-mould, which jointly delimit a mould chamber (18) accommodating said precursor (4) and configured to contain plastic deformations of the tubular wall (6) following said expansion;

wherein said device comprises axial compression means (14, 16; 80, 80') of the precursor (4) to deform the tubular wall (6) radially externally and obtain the metal body (2) .

2. An assembly according to claim 1, wherein the axial compression means comprise at least one of said half- moulds (14; 16), movable relative to the other half mould between an open configuration of the mould chamber (18), and a compression configuration wherein the movable half mould (14; 16) axially compresses the precursor (4).

3. An assembly according to any one of the preceding claims, wherein at least one outlet (20, 20' ) of the injection passageway (12, 12') or of the plurality thereof is obtained on a portion (22) of half-mould (14, 16) projecting in the mould chamber (18) wherein, when the movable half-mould (14; 16) is in a closed configuration of the mould chamber (18), the metal body lies in abutment with said portion (22) .

4. An assembly according to claim 3, wherein said projecting portion (22) delimits an annular groove (50) with an inner surface (30, 30') of the half-mould (14, 16) , said groove (50) being delimited inferiorly by a substantially rectilinear surface (74) and by an adjacent concave surface (76) which extends away from the portion (22), the metal body delimiting an outer connecting surface (66) having a shape complementary to said groove.

5. An assembly according to claim 1, wherein the axial compression means comprise at least one thrust member (80, 80'), associated with at least one half-mould (14/ 16) and translatable towards the mould chamber (18) to compress said precursor.

6. An assembly according to any one of the preceding claims, wherein the tubular wall (6) comprises an end thickness (s), or an intermediate thickness, and at least one end thinning (d) of said thickness (s) to obtain a fluid seal with the at least one half-mould (14, 16) identifying the injection passageway (12, 12').

7. An assembly according to any one of the preceding claims, wherein the precursor (4) or the tubular wall (6) delimits at least one conical inlet surface (24), inclined by an angle (β) with respect to the central axis (X) to obtain a planar cylindrical surface (26) in the metal body (2 ) .

8. An assembly according to claim 7, wherein the angle (β) is comprised within the range 30°-70°, preferably 40°-60°, advantageously 45°-55°, for example substantially 50°.

9. An assembly according to any one of the preceding claims, wherein the metal body (2) is a spherical body with a substantially constant wall thickness (54), and wherein the followin trigonometric relations apply:

wherein :

- Lfinale is the final length the spherical body;

- Dint is the inner diameter of the spherical body;

- a/2 is the average angle subtended at the final, length of the spherical body;

- L0 is the axial length of the precursor (4) .

10. An assembly according to any one of the preceding claims, wherein at least one axial end (4'; 4") of the precursor (4) is radially internally inclined or deformed in a conical shape so that an outer surface (28) of said end creates a seal with the inner surface (30; 30' ) of at least one of the half-moulds (14; 16).

11. An assembly according to any one of the preceding claims, wherein:

- the forming device (10) comprises a linear actuator (32) to move the movable half-mould (14; 16) by means of an elbow kinematic mechanism (36);

- the forming device (10') comprises two movable half- moulds (14, 16), each being pushed by their own linear actuator (32, 34), of the electrical or hydraulic type; or

- the forming device (10") comprises at least one thrust member (80, 80') translatably accommodated in at least one half-mould (14, 16), said member (80, 80') and the movable half-mould (.14; 16) being moved by a different linear actuator..

12. An assembly according to any one of the preceding claims, wherein the forming device (10, 10', 10") comprise at least one pressurisation source (38, 40) of the pressurised liquid and wherein, when the half-moulds (14, 16) are spaced apart, said source (38, 40) is adjusted to maintain a first constant pressure (P0) in the body compartment (8) and wherein, upon contact between the two half-moulds (14, 16), said source promotes an increase of the first pressure (P0) to a second pressure (PI).

13. An assembly according to claim 12, wherein said pressures (P0, PI) are determined as follows:

wherein :

Rp 1,0 is the yield strength needed to obtain a permanent deformation of 1% of the precursor (4);

- dint is the inner diameter of the tubular wall (6);

- s is the average thickness of the tubular wall (6);

- kl is a coefficient numerically comprised between 1 and 1.5;

- kl is a coefficient numerically comprised between 2 and 4.

14. An assembly according to any one of the preceding claims, wherein the precursor (4) is at least partially made from stainless steel according to the EN 10216-5 standard, for example an AISI 316L steel, subjected to a thermal annealing treatment.

15. A process for forming a hollow metal body (2), in particular for forming a ball for ball valves, comprising the steps of:

providing a precursor (4) of said metal body (2) comprising a substantially tubular wall (6) , which extends about a central axis (X) to delimit a body compartment (8);

- injecting a pressurised liquid in the body compartment (8) to induce an expansion of the latter;

- containing plastic deformations of the tubular wall (6) following such expansion;

- axially compressing the precursor (4) to deform the tubular wall (6) radially externally and obtain the metal body (2) .

16. A process according to claim 15, wherein the injecting and compressing steps are at least partially concurrent .

17. A process according to claim 15 or 16, wherein the injecting step and/or the compressing step are performed in the absence of heating, for example at room temperature .

18. A process according to any one for claims 15-17, wherein the injecting step comprises a first sub-step of injecting at a first constant pressure (P0), and increasing the first pressure (P0) to a second pressure (PI) when the compressing step is complete.