EP2738779B1

EP2738779B1 - Welding process for actuator for hydraulic valves

Info

Publication number: EP2738779B1
Application number: EP13190698.4A
Authority: EP
Inventors: Eugenio Colombo; Davide Ives Davoli
Original assignee: Nixa Srl Windings & Coils
Current assignee: Nixa Srl Windings & Coils
Priority date: 2012-11-28
Filing date: 2013-10-29
Publication date: 2015-09-09
Anticipated expiration: 2033-10-29
Also published as: EP2738779A1; PL2738779T3; ITMO20120296A1

Description

The present invention relates to a welding process for an actuator for hydraulic valves.
In hydraulic applications, electrically-controlled valves are normally used for switching mechanical components. In these electrically-controlled valves, the basic components are a coil, with the function of transforming an electric current into a magnetic field, a coil plate, with the function of guiding the flow lines of the magnetic field, and an electric actuator (or sleeve) which transforms the magnetic field into a force exerted on a mobile component (mobile core) subject to linear movement; by means of the travel of the mobile core, a change in the status of the hydraulic system is obtained.
The welding process in question relates in particular to realisation of an electric actuator of which the principal requirements are transforming the magnetic field of the coil into a force as a function of the distance of the fixed core from the mobile core and containing the pressurised hydraulic fluid, of which the flow is regulated by the hydraulic valve.
These actuators have a widespread use, for example in ON-OFF valves or proportional valves.
The principal components of the electric actuator are a fixed core, which polarises if subjected to a magnetic field generated by a coil, a mobile core, which is attracted with a force towards the polarised fixed core, a sliding jacket, inside which the mobile core slides, and an non-magnetic part which realises the mechanical connection between the fixed core and the sliding jacket.
The force acting on the fixed core, all conditions being equal, depends on its distance (air gap) from the fixed core. Creation of a polar cone, with a characteristic shape on the fixed core, and, in certain cases, also on the mobile core, allows the characteristic typical force towards the sleeve to be changed.
Currently, the various parts of the sleeve of an actuator to be connected to each other are placed alongside each other and welded, in the contact zones between the fixed core and the non-magnetic part and the non-magnetic part and the sliding jacket, using various welding methods; for example, laser welding, TIG welding and braze welding are used. A method is also used consisting in a bath of non-magnetic material which performs the dual function of welding and an non-magnetic spacing element.
A welding process according to the preamble of present claim 1 is disclosed in any of DE 10 2009 008 458 , US 2006/0028311 , DE 10 2010 000 797 .
The welding methods used to obtain the sleeve must allow optimal use of the magnetic sections of the actuator without dispersion of the work areas, must not deform the polar cone or the sliding jacket and must allow certain determination of the length of the non-magnetic part. These methods must also be as simple and rapid as possible and allow inexpensive embodiment.
The currently known methods do not solve all these problems, since several of them cause reduction of the polar cone, others cause deformation of the sleeve parts, and yet others are complex and expensive.
The object of the present invention is providing a method which overcomes all the problems of the prior art.
An advantage of the present invention is providing an inexpensive and easily and safely repeatable method.
These objects and advantages are all achieved by the the welding process as defined by the claims.
Further preferred characteristics and advantages of the present invention will become more apparent from the following detailed description of the steps of the method in question and the parties to which said method is applied, illustrated in a non-limiting example in the appended figures, wherein:

Figure 1 shows an exploded and cross-section view of the parts forming the sleeve of the actuator detached from each other;
Figure 2 shows a cross-section view of the fixed core and the non-magnetic part of the sleeve connected to each other;
Figure 3 shows a cross-section view of the actuator with the parts forming the sleeve connected to each other;
Figure 4 shows a cross-section view of the actuator provided with the coil.

The welding process in question is used to realise actuators for hydraulic valves, and, in particular, for realisation of the sleeve 1 of said actuators.
The process is used for sleeves, normally cylindrical, which comprise a fixed core 2 provided at its end with a polar cone 3; the sleeve also comprises a mobile core 4 which is sliding inside a sliding jacket 5 and may be made to slide following a command which generates a magnetic field which causes attraction of the mobile core by the fixed core. The sliding jacket has the primary function of containing the pressurised hydraulic fluid.
The sleeve also comprises an non-magnetic part 6 which realises the mechanical connection between the fixed core and the sliding jacket and which also realises magnetic isolation between the fixed core and the sliding jacket, so that the magnetic field is forced to attract the mobile core 4 and does not discharge through the sliding jacket 5. An electric coil 8 is also envisaged, containing in a metal plate 9. These elements are shared with actuators of the known type.
For realisation of the actuator sleeve, the process in question envisages a first braze welding step performed to anchor the fixed core to the non-magnetic part. Both these elements have a cylindrical shape; the fixed core is a full cylinder, whereas the non-magnetic part is realised by means of a ring of non-magnetic material having substantially the same outer diameter of the fixed core; the outer diameter of the non-magnetic part is also substantially equal to the outer diameter of the sliding jacket.
This first welding step is performed with the known method of braze welding and allows a semi-finished product 7 to be obtained, formed of union of the fixed core with the non-magnetic part.
Before the first braze welding step, a processing step is performed of the surfaces of the fixed core 2 and the non-magnetic part 6, which must be welded to each other in the first welding step. This processing step obtains, on both the fixed core 2 and on the non-magnetic part 6, processed surfaces, respectively a surface 2a afforded on the fixed core and a surface 6a afforded on the non-magnetic part; these surfaces do not develop on a radial plane of the respective elements, and are fitted together.
In particular, said processed surfaces are at least partially conical and are afforded, respectively, 2a outside the fixed core 2 and surface 6a inside the non-magnetic part 6. In particular, the processed surface 2a is afforded on a protrusion of the fixed core which defines the polar cone 3.
In the contact zone of said processed surfaces 2a and 6a, there is also an annular niche, which may be variously arranged and which is not shown in the figure, and which is destined to house the material to be used for braze welding.
This first welding step is performed in an environment at a high temperature capable of melting the material used for braze welding; on melting, the braze welding material enters between the surfaces 2a and 6a facing each other in contact, thus causing close and firm connection once said material is once again solidified and guaranteeing the seal towards the outside of the pressurised fluid when the sleeve is completed. The particular shape of the fixed core and the non-magnetic part allows a semi-processed part 7 to be obtained which presents characterisation and optimisation of the polar cone; with this process, the working area of the fixed core is maximum and consequently does not reduce the efficiency of the actuator.
The process in question also envisages a second welding step to anchor the semi-finished part 7 to the sliding jacket; said second welding step is performed with a method of the known type, which allows localised welding, in an environment at room temperature, of the edges of the sliding jacket with the non-magnetic part; to perform said second welding step, laser welding or TIG welding, for example, may be used. Subsequently to the second welding step, the sleeve may be subjected to a turning step to remove any excess material and render the inner diameter of the non-magnetic part equal to the inner diameter of the sliding jacket.
The complete sleeve is thus obtained which, provided with the mobile core inside it, is ready for its final use.
Obviously, all the welding steps described may be performed so that the elements connected to each other are coaxial, so as to realise, inside them, a "sliding chamber" represented by the cavity defined by the polar cone, by the inner zone of the non-magnetic part and by the inner zone of the sliding jacket.
Performance of connection welding of the various elements forming the sleeve performed at two different moments and with two different welding methods, typical of the process in question, offers various advantages. In the first place, the first welding step, which is performed with the elements to be connected remaining at a high temperature, does not cause significant deformations of said elements; in particular, it avoids deformation of the polar cone which, furthermore, is maintained at its nominal dimensions, with consequent optimal use of the magnetic sections of the actuator, without dispersion of the work areas. Furthermore, said step may be performed simultaneously on a high number of pieces and allows semi-processed parts 7 to be obtained which may be stored and used for realisation of various sleeves.
The sliding jacket is not involved in the thermal cycle of the first welding and consequently its mechanical characteristics are not altered by the thermal cycle.
Performance of the second welding step occurs with the elements to be connected at room temperature, clearly with the exception of the edges of the non-magnetic part and the sliding jacket, which must be welded to each other. This allows semi-finished parts to be obtained, with clear advantages of repeatability of the process, but which may be welded to sliding jackets with different interfaces 5a, according to the customer's requirements.
In conclusion, unlike traditional welding systems, which use the coating of an non-magnetic bath with the dual function of both welding and an non-magnetic spacing element, the process described allows a considerable reduction of the material to be removed in the subsequent mechanical processing operation and therefore further reduces production costs.

Claims

Welding process for an actuator for hydraulic valves, the actuator comprising a sleeve (1) which in turn comprises a fixed core (2) provided with a polar cone (3), a sliding jacket (5) inside which a mobile core (4) slides, and an non-magnetic part (6) that makes the mechanical connection between the fixed core and the sliding jacket, characterised in that it comprises: a first braze welding step to anchor the fixed core to the non-magnetic part, in order to obtain a semi-processed part (7) made by joining the fixed core to the non-magnetic part; a second welding step to anchor the semi-processed part to the sliding jacket, performed with a known method that allows localised welding, in an environment at room temperature, of the edges of the sliding jacket to the non-magnetic part in order to obtain the complete sleeve.
Process according to claim 1, characterised in that it comprises a processing step of the surfaces of the fixed core (2) and of the non-magnetic part (6) to be welded together in the first braze welding step, adapted to obtain, on the fixed core (2) and on the non-magnetic part (6), processed surfaces (2a,6a) fitting together, which processed surfaces (2a,6a) do not extend on a plane radially arranged with respect to a longitudinal axis of said elements.
Process according to claim 2, characterised in that: the outer diameter of the fixed core (2) is the same as the outer diameter of the non-magnetic part (6); the outer diameter of the non-magnetic part is the same as the outer diameter of the sliding jacket; the inner diameter of the non-magnetic part is made the same, through a mechanical processing step performed on the finished sleeve, as the inner diameter of the sliding jacket; the said processed surfaces are at least partly conical and are obtained on the outer side of the fixed core (2) for the processed surface (2a) of the fixed core (2), and on the inner side of the non-magnetic part (6) for the processed surface (6a) of the non-magnetic part (6), respectively; in the contact zone of the processed surfaces (2a, 6a) an annular niche is obtained intended to house the material to be used for the braze welding.
Process according to claim 3, characterised in that: the processed surface (2a) of the fixed core (2) is obtained on a protrusion of the fixed core that defines the polar cone (3); the inside of the said protrusion has the same diameter as the inner diameter of the sliding jacket.