Patent Description:
More particularly, the impeder apparatus for welding according to the present invention comprises a system of nitrogen cooling of the impeder which makes it possible to guarantee a constant required temperature at the impeder itself, achieving greater system simplicity and, at the same time, improved quality of the weld that can be obtained.

The process implemented by said apparatus is also the subject of the present invention.

Using impeders for high-frequency welding of metal pipes is known from the state of the art.

An example of such apparatus is provided for example in international patent application <CIT>, which describes in particular impeders that can be used in electrical induction welding processes to form metal pipes or tubes.

With induction welding, the heat is electromagnetically induced into the workpiece. It is a high-precision, high-speed process, which makes this process ideal for welding the edges of pipes and tubes.

During this welding process, the pipes pass at high speed through an induction spool (also known as a Ruhmkorff spool), which electromagnetically induces the heat required to make the weld at the pipe to be welded.

The function of the impeder is to concentrate the magnetic flux that is generated by the inductor in the area of welding of the pipe. By lowering the reluctance of the magnetic path, the impeder, placed inside the pipe, enables energy to be saved and the efficiency of the entire welding process to be improved.

The impeder is therefore placed inside the pipe to be welded and concentrates the magnetic flux generated by the spool inductor, greatly improving the efficiency of the process itself.

Automated longitudinal induction welding that uses impeders is therefore a process characterised by high yield, low energy consumption and high efficiency, which enables costs to be reduced drastically. Furthermore, ease of control and reproducibility reduce scrap.

A disadvantage that affects apparatuses and methods for induction welding by impeder of the known type is however constituted by the risk of breakage of the impeder caused by the increase in temperature of the same.

In order to avoid breakage of the impeder, it is therefore necessary to cool the impeder itself to a temperature value that allows the properties of the magnetic field to be preserved.

The impeder is in fact made of ferrite, and therefore proper cooling of the impeder is essential also to ensure maximum welding efficiency and to keep the parameters of the production process stable, the Curie temperature of the ferrite being comprised between <NUM> and <NUM>.

To date, the impeder is generally cooled by water, disposable or recirculated within a circuit, and there are impeders specifically designed to optimise the cooling of the ferrite core by water.

In order to optimise the cooling of the impeder by means of water, the impeder is generally made with particular geometries, which also affect the structure of the user machine.

Furthermore, as mentioned, the use of water as a cooling medium entails the need to make a system for the recirculation and collection of the coolant and its disposal.

The need is therefore felt in the industry to use an impeder apparatus for high-frequency welding of pipes or the like that enables the disadvantages indicated above, in particular with reference to the simplification of the structure and features of the apparatus and of the impeder itself, to be overcome.

In light of the above, a task of the present invention is to provide an impeder apparatus for high-frequency welding of pipes or the like which enables the above-mentioned disadvantages to be overcome.

Within this task, an object of the present invention is to provide an impeder apparatus for high-frequency welding that ensures a certain constant temperature of the impeder and the possibility of setting the temperature value of the impeder and allows real-time monitoring of the value of this temperature.

Not least, the object of the present invention is to provide an impeder apparatus for high-frequency welding that allows the need to make impeders with particular geometries to be avoided and, consequently, does not require ad hoc modifications to the user machines, i.e. to the welding apparatus.

This task and these and other objects are achieved by an impeder apparatus for high-frequency welding according to claim <NUM> and by a high-frequency welding process according to claim <NUM>.

Further features of the apparatus according to the present invention are the subject of the dependent claims.

Further features and advantages will be made clearer by the following illustrative but non-limiting description of a preferred embodiment of the present invention which will be given here below with the aid of the accompanying drawing in which:
<FIG> shows a diagram of the apparatus according to the present invention in which the elements of the cooling system of said apparatus are shown in particular, among which the mixing chamber, the two circuits for feeding liquid and gaseous nitrogen respectively to said mixing chamber, and the elements that characterise and determine the functionality of this system can be noted.

With particular reference to the accompanying drawing, the impeder apparatus for high-frequency welding according to the present invention comprises at least one cooling system <NUM> for cooling at least one impeder <NUM>.

Said cooling system <NUM> of the apparatus according to the present invention comprises in turn at least one mixing chamber <NUM> fed by two separate circuits 30a, 30b, and at least one control and command panel 30c.

The first circuit 30a for feeding the chamber <NUM> is fed by nitrogen in the gaseous state.

The nitrogen in the gaseous state advantageously comes from a liquid nitrogen storage tank (not shown in the drawing) via the passage in an air heat exchanger (also not shown in the drawing), which will be suitably dimensioned according to the flow rates that need to be supplied.

Said first circuit 30a for feeding nitrogen in the gaseous state to the mixing chamber <NUM> advantageously comprises at least the following elements.

The flow of nitrogen in the gaseous state is activated manually via said control panel 30c or directly and remotely via the activation command of the high-frequency welding machine to which the system is interlocked, advantageously by means of a PLC.

The pressure of the gaseous nitrogen flow is regulated to approx. <NUM> bar via a suitable pressure reducer <NUM>.

Between the solenoid valve <NUM> and the reducer <NUM> a ball valve <NUM> and a safety valve <NUM> for overpressure set at <NUM> bar are advantageously inserted.

The flow rate is preferably measured by means of a flowmeter <NUM>, optionally but not necessarily digital and connected to the control panel, with a scale of <NUM>-<NUM><NUM>/h, in that the maximum flow rate is advantageously <NUM><NUM>/h, with relative needle valve <NUM> for regulation of the flow rate.

A pressure gauge <NUM> for measurement of the pressure and a pressure transmitter <NUM> configured to transmit the value of the pressure measured by the pressure gauge <NUM> to the control panel 30c complete the line 30a.

The flow rate of gaseous nitrogen thus regulated, i.e. preferably to a pressure value of <NUM> bar and with a flow rate of approximately <NUM>-<NUM><NUM>/h, maximum <NUM><NUM>/h, is delivered into the mixing chamber <NUM>.

Similarly, the second circuit 30b feeding nitrogen in the liquid state to the mixing chamber <NUM> advantageously comprises at least the following elements:.

Also in this case, the flow of liquid nitrogen in the second circuit 30b is activated manually from the control panel 30c or remotely via the start command of the welding machine served via an on/off solenoid valve <NUM>.

Downstream of this on/off solenoid valve <NUM> a modulating pneumatic valve <NUM> is advantageously placed, capable of regulating the flow rate of liquid nitrogen in the second circuit 30b as a function of the temperature value of the nitrogen read by the temperature probe <NUM> inside the mixing chamber <NUM>.

Advantageously, said temperature value of the nitrogen inside the mixing chamber <NUM> may vary within a range of +/- <NUM> with respect to the required temperature value, which preferably may be about - <NUM>. The nitrogen inside the mixing chamber <NUM> will therefore advantageously be in the gaseous state.

For the cooling of the impeder <NUM>, nitrogen in the gaseous state exiting the mixing chamber <NUM> is used.

In order to reach the required temperature value of the gaseous nitrogen and keep it constant within the mixing chamber <NUM>, the cooling system <NUM> of the apparatus <NUM> according to the present invention therefore mixes liquid nitrogen preferably at a temperature TL between Tmin - <NUM> and Tmax - <NUM>, at a pressure value of <NUM> bar and a variable flow rate, and gaseous nitrogen at a temperature TG comprised between Tmin - <NUM> and Tmax + <NUM>, at a pressure value of <NUM> bar and a flow rate preferably of <NUM>/<NUM><NUM>/h to advantageously deliver gaseous nitrogen at the following conditions Tmax -<NUM>, Tmin - <NUM> at a pressure of <NUM> bar.

Said mixing chamber <NUM> is supplied simultaneously by liquid nitrogen and gaseous nitrogen, and more particularly the gaseous nitrogen will be advantageously at the indicated pressure and flow rate values that are those required by the user machine, while the flow of liquid nitrogen into the mixing chamber is regulated by a modulating valve <NUM> as a function of the temperature Te of the mixed nitrogen measured by means of the temperature probe <NUM> at the point of use.

The quantity of liquid nitrogen in the mixing chamber <NUM> is therefore regulated as a function of the temperature required at the point of use, measured by the temperature probe <NUM>.

The liquid nitrogen thus mixes in the chamber <NUM> provided with the gaseous nitrogen, creating the refrigerant gas at the optimum temperature for the functioning of the impeder <NUM>. The mixing chamber <NUM> is protected from the danger of overpressure thanks to the presence of a third safety valve <NUM>.

The nitrogen thus mixed is fed to the impeder <NUM> by means of suitable insulated piping <NUM>.

Having thus described the impeder apparatus <NUM> for high-frequency welding according to the present invention, we will now briefly describe the mode of functioning of this apparatus.

The apparatus according to the present invention can advantageously operate in manual or automated mode, with remote actuation.

As has been described, the apparatus <NUM> according to the present invention comprises a cooling system <NUM> in turn comprising said at least one mixing chamber <NUM> fed by the two circuits 30a, 30b, and at least one control and command panel 30c.

In automated mode with remote actuation, the command and control panel 30c will send a command to open on-off valves for injection of liquid nitrogen <NUM> and, respectively, gaseous nitrogen <NUM>, into the mixing chamber <NUM>.

When the on-off injection valves <NUM> and <NUM> are open, said modulating valve <NUM> will maintain the temperature of the mixture exiting the mixing chamber <NUM> at the set value of - <NUM> with reverse control operation: as the output temperature Te increases, the modulating valve <NUM> will increase its opening, causing more liquid nitrogen to flow to the chamber <NUM>, while as the temperature decreases the modulating valve <NUM> will gradually close causing less liquid nitrogen to flow to the mixing chamber <NUM>.

When the set temperature Te is reached and maintained within the required and programmable limits, the apparatus will send a system ready signal to the user machine.

The apparatus will maintain the regulation of the cooling system <NUM> of the impeder <NUM> until it receives the switch-off signal from the user machine. The user machine, i.e. the high-frequency induction welding machine, is in fact provided with a control panel from which the cooling apparatus <NUM> according to the present invention can also be operated preferably via PLC. It is therefore not necessary to operate on the cooling system <NUM> directly, but all commands can be managed from the control panel, for example equipped with a touch screen, of the high-frequency induction welding machine with which said cooling system <NUM> is associated.

In the event of an emergency or fault being detected, an emergency command will interrupt the supply by means of closure of the liquid nitrogen and gaseous nitrogen supply valves.

In manual operation mode (selector switch in MAN) the start-up procedure will begin as soon as the operator intervenes on the control panel 30c by positioning the appropriate selector switch in the start position (selector switch in position <NUM>). This operation will completely bypass the consent from the user machine, and it will be possible to dispense nitrogen without waiting for the solenoid valves opening consent from the user machine.

The modes of operation are similar to that described above.

The system will maintain the regulation operation until intervention by the operator, who must return the selector switch to position <NUM> to stop operation.

A welding process is also an object of the present invention, comprising at least the steps of:.

The welding process according to the present invention also advantageously comprises the steps of:.

It has thus been shown how the impeder apparatus <NUM> for high-frequency welding according to the present invention and the welding method implemented by means of said apparatus achieve the intended task and objects.

More particularly, it has been shown how said welding apparatus and said method ensure the control of a required and constant temperature on the impeder, without the need to provide systems for water recirculation and/or collection of refrigerant liquids, nor the disposal thereof.

Furthermore, the apparatus and method according to the present invention enable programming of the temperature of the refrigerant mixture that feeds the cooling circuit of the impeder by means of an electronic control (PLC); moreover, the apparatus and method according to the present invention enable real-time monitoring of the temperature on the impeder.

Last but not least, it has been shown how the apparatus and method according to the present invention enable minimisation of oxidative effects and possible welding cracks in that nitrogen also performs an inerting function and replaces oxygen (avoiding oxidation) and water vapour (avoiding cracks due to H<NUM>), furthermore, no particular geometries of the impeder are required and no modification of the user machine is necessary.

Claim 1:
Welding apparatus comprising an impeder welding machine (<NUM>) for high-frequency welding, particularly for welding pipes, and a cooling system (<NUM>) of said welding machine in turn comprising at least one mixing chamber (<NUM>) and at least two separate supply circuits (30a, 30b) suitable for feeding said mixing chamber (<NUM>), in which a first (30a) of said supply circuits feeds gaseous nitrogen to the mixing chamber (<NUM>), and a second (30b) of said supply circuits feeds nitrogen in the liquid state to said mixing chamber (<NUM>), said mixing chamber (<NUM>) being in connection with said impeder (<NUM>), characterized in that said cooling system (<NUM>) further comprises at least one storage tank containing liquid nitrogen, at least one heat exchanger, preferably an air heat exchanger, and at least one control panel (30c) suitable for controlling said welding apparatus and said cooling system (<NUM>).