Method and device for welding profiled elements in plastic material, in particular PVC

A method for welding profiled elements in plastic material, includes the steps of: preparing two profiled elements, arranged with respective zones to be facing one another; making a groove in correspondence to at least one zone, by a removal operation on a peripheral edge of at least one profiled element; heating the zones to be welded; coupling the zones to be welded to one another, pressing the profiled elements one against the other so as to keep the zones to be welded in reciprocal contact. The coupling step includes: melting the zones to be welded into one another in order to define a welding bead; making a containing compartment defined by the groove, the welding bead being made internally of the containing compartment; and arranging a containing presser in correspondence to the containing compartment for preventing exit of the welding bead from the compartment itself.

TECHNICAL FIELD

The present invention relates to a method and relative device for welding profiled elements in plastic material, in particular PVC.

BACKGROUND ART

In the state of the art, the PVC profiled elements, mainly used as window and door frames, are welded together by means of the melting of respective head surfaces in order to make a frame structure fittable to doors or windows.

In particular, the melting is done by heating the portions to be connected using suitable electric heating plates and then pressing the heated portions the one against the other to favor melting.

Generally, the heated portions are the head extremities of the profiled elements, suitably cut at 45° to define e.g. a right-angled portion of a respective window or door frame.

This method is carried out by welding machines equipped with respective retaining members of the profiled elements, mobile in a reciprocal closer moving direction to bring the heated extremities to be welded into contact.

Such machines are also equipped with finishing systems, suitable for removing the bead or welding bead which forms during the melting of the two profiled elements.

In fact, in correspondence to the joining line of the two profiled elements (surfaces cut at 45°), the portion of melted material in excess comes out and goes to form a bead protruding from the visible surface of the profiled elements. For this reason, in order to give the finished door or window frame an appreciable aesthetic appearance, once welded the profiled elements undergo a bead removal operation.

The known welding devices briefly described do however have major drawbacks mainly tied to the formation of the above-mentioned welding bead.

It must in fact be considered that the welding zone of the PVC profiled elements is not perfectly uniform and consequently, to make the profiled elements even, a lot of material is melted with the consequent formation of an abundant bead, and there is consequently a lot of waste material to be removed.

Furthermore, the finishing jobs for removing the bead and cleaning the welding zone have a strong effect on the total time required to machine the door or window frame. It should be realized in fact that for every door or window frame welding operation, the profiled elements have to be subsequently machined. Furthermore, in the case of spoked profiled elements, the removal of said bead is very complicated.

Furthermore, the machinery used for the above-mentioned finishing operations is cumbersome and particularly expensive.

This results in the need to sustain additional costs and work times because of the presence of further cumbersome equipment and tools.

DESCRIPTION OF THE INVENTION

In this context, the technical aim underlying the present invention is to propose a method and relative device for welding profiled elements in plastic material, in particular PVC, which overcomes the drawbacks of the above-mentioned state of the art.

In particular, the object of the present invention is to place at disposal a method and relative device for welding two profiled elements made in plastic material, in particular PVC able to eliminate all subsequent additional operations suitable for removing the welding bead.

Another object of the present invention is to envisage a method for welding profiled elements in plastic material, in particular PVC, that is fast, cheap and with reduced space.

The above objects are achieved by a method and relative device for welding profiled elements in plastic material, in particular PVC, comprising the technical specifications stated in any of the enclosed claims.

EMBODIMENTS OF THE INVENTION

With particular reference to figures from1ato3, indicated by1is a device or method for welding profiled elements in plastic material, in particular PVC.

Such device implements a method, or procedure, for welding profiled elements in plastic material, in particular PVC, wherein are arranged at least two profiled elements3, with respective zones to be welded4facing one another.

The plastic material from which the profiled elements3are made is, e.g., PVC, but plastic materials of the heat-sealable type other than PVC cannot be ruled out.

As will be better specified below according to the method, before the step of heating and welding the profiled elements3, a groove19is made in correspondence to at least one zone to be welded4of the profiled elements3by means of a removal operation (milling, melting, chamfering, etc.).

Subsequently, the zones to be welded4are heated and coupled, or joined, by pressing the profiled elements3one against the other to keep the zones4in reciprocal contact. This way, the groove19or the grooves19of the two profiled elements3define a containing compartment19afor containing a bead or welding bead produced during the melting of the respective profiled elements3.

In the rest of the present description, a single welding device1will be illustrated suitable for welding the extremities of the two respective profiled elements. Nevertheless, the present invention can comprise a series of devices1, each of which operating on a respective extremity of a profiled element3. For example, to make a rectangular frame to be used as a door or window frame, four devices1are used, each intended to weld the profiled elements3in correspondence to right angles of the mentioned frame.

With reference toFIG. 1it should be noted that the device1comprises a base frame38that supports a pair of retaining members2of respective profiled elements3in PVC, suitable for engaging the profiled elements3themselves with corresponding zones to be welded4facing one another.

In particular, each retaining member comprises a base portion5on which the profiled element3is positioned, and a mobile portion6arranged above the base portion5. The mobile portion6is suitably moved to shift towards the base portion5and thus retain the profiled element3.

As can be seen on the attached illustrations, each profiled element3is therefore arranged between the base portion5and the mobile portion6, with the respective head extremity protruding. The head extremities of the profiled elements make up the zones to be welded4and for this reason they are facing one another.

It should also be noted that the zones to be welded4are suitably cut at 45° to define a coupling between two right-angled profiled elements.

Moreover, the device1comprises movement means7of the retaining members2, to shift the profiled elements3between a first reciprocal away direction and a second reciprocal closer direction wherein the zones to be welded4are coupled together.

In particular, for each retaining member2, the movement means7have a sliding guide8, extending parallel to the longitudinal extension of the profiled element3. On the sliding guide is fitted a carriage9integral with the aforementioned base portion5. Furthermore, each carriage9is coupled with a movement system10(not described in detail because of known type and not forming a part of the present invention) suitable for moving both the carriages9of the retaining members2reciprocally closer/away. The device1also comprises heating means11for heating the aforementioned zones to be welded4of the profiled elements3in PVC. The heating means11are preferably mobile between an active condition wherein they are placed between the profiled elements3, and a non-use condition wherein they are spaced at a distance from the profiled elements3.

In particular, it should be noted that when the profiled elements3are arranged by the movement means7in reciprocal away direction, they define a transit zone of the heating means11. This way, once the zones to be welded4have been heated, the profiled elements3are moved closer together and pressed with the respective extremity heads against one another.

Advantageously, the heating means11comprise a hot-plate heat-sealing element12, made up e.g. of a substantially plate-shaped electric resistance12, fitted on a movement system13. Preferably, the movement system13is composed of a pair of carriages14mounted sliding in respective rails15and each of which arranged on opposite sides of the aforementioned resistance12. This way, the resistance12is fastened to the carriages14and moved by these along the rails15. The carriages14are also operatively connected to a motor16, by means of a connecting rod-crank17. Advantageously, the connecting rod-crank17transforms the rotary motion given by the motor16into a back and forth motion of the carriages14and of the resistance12to insert/remove the resistance12between/from the above-mentioned profiled elements3.

The device1is also equipped with removal means18to make at least one groove19on the peripheral edge of at least one zone to be welded4.

The removal means18, e.g., are composed of means of removal by milling; alternative embodiments cannot however be ruled out wherein the removal means are of a different type and envisage, e.g., one or more hot points, which remove the plastic material by melting, or one or more ultrasonic points.

The removal means18by milling comprise a supporting frame20placed above the retaining members2, and at least one machining tool21(a cutter), facing a profiled element3to make the above-mentioned groove19on the zone to be welded4.

The tool21is moved by a motor part22preferably of the electric type and miniaturized, brushless sensorless with very high rotation speed.

Furthermore, the tool21is moved by a movement member23, between a first idle condition (position in which it is placed between the profiled elements3) and a second working condition in which it is placed between the profiled elements3in PVC.

In greater detail, the removal means18by milling preferably comprise a pair of machining tools21, each of which equipped with an active head21aon the peripheral edge of a respective zone to be welded4.

As illustrated in the detail views, the tools21are opposite one another to work at the same time on both the profiled elements3.

Furthermore, the frame20has a supporting bar24arranged above the retaining members2and designed to sustain the tools21which in this situation are mounted on a lower extremity of the bar24itself.

The bar24is operatively connected to the movement member23to be moved in correspondence to the zones to be welded4.

Advantageously, the tools21are positioned in correspondence to the side edge of the zone4by means of the movement of the above-mentioned movement member23.

In particular, the member23comprises a pair of supporting guides25on which the bar24is mounted sliding and moved by a known motor not described in detail.

Furthermore, the bar24is moved vertically by means of an axis with wormscrew26arranged in correspondence to the supporting frame20.

Advantageously, both the tools21and the motor part22are supported by the bar24and are mobile with it both horizontally (along the guides25) and vertically (by means of the wormscrew26).

The movement of the bar24is by means of a controlled-axis system which enables the tools21to shift along the peripheral edge of the profiled elements3to obtain the grooves19.

Thanks to the controlled-axis system, furthermore, the tools21are moved between an idle position, wherein they are not placed between the profiled elements3, and a working position, wherein they are placed between the profiled elements3.

The device1is also equipped with a containing presser27mobile along a direction transversal both to the direction of movement of the profiled elements3and to the lying plane on which they lie, to abut on the grooves19made in the respective zones to be welded. Such presser can be heated to better shape the plastic material underneath and can have protrusions or recesses to reproduce a special shape on the hot piece just machined. The still hot material is in fact easy to shape.

In particular, in the welding condition of the zones4, i.e., when they are brought into contact and pressed with each other, the grooves19define a containing compartment19ain reciprocal collaboration.

Depending on the shape of the grooves19, the compartment19acan be open or closed, as will be better described below.

In the event of the compartment19abeing open, it can be delimited by the containing presser27which prevents the melted material coming out of the compartment19a. Preferably, two containing pressers27are prepared, each of which associable with a respective pair of opposite grooves19to define two containing compartments19afor respective welding beads.

In particular, a first presser27is arranged above the profiled elements3, while a second presser27is arranged underneath the profiled elements3.

It will in fact be noted that the grooves19are applied for the externally visible portions of the profiled elements3, i.e., the side edges cut at 45° which when welded together determine the formation of a protruding welding bead.

In this situation, the bead does not come out of the compartment19abut is contained inside it.

In this context, the pressers27are mobile by means of suitable movement elements not described in detail and able to move closer to/away from the pressers27themselves during the various welding steps of the profiled elements3.

The device1is furthermore equipped with an electrostatic part28for retaining the shavings that form during the removal operation by milling.

The electrostatic part28is made up of an electrode connected to the work tool21and connected to a high-voltage generator. This way, the shavings charged with negative polarity are retained by the head21aof the cutter (which acts as an electrode) charged positively to avoid the dispersion of the mentioned shavings.

In collaboration with or alternatively to the electrostatic part28, the device1has a vortex suction system29a,29bconcentric with the tool21which permits removing the shavings which form during the removal operation by milling.

The suction system29a,29b, e.g., consists in a chamber29awhich is arranged around each tool21and which is connected to a suction duct29bwhich moves the shavings away.

For this purpose, furthermore, the tool21consists of a helical-shaped cutter that conveys the removed shavings towards the inside of the chamber29ato make suctioning the shavings easier.

Advantageously, all the PVC shavings produced by the removal operations by milling are easily suctioned.

The device1described above in prevalently structural terms implements a welding method which is also the subject of the present invention.

The method comprises the steps of preparing at least two profiled elements3, arranged with the respective zones to be welded4facing one another, in correspondence to the retaining members.

Then, the grooves19are made in correspondence to each zone to be welded4of the profiled elements3. The zones to be welded4are subsequently heated and coupled together by pressing the profiled elements3one against the other. This way the zones4are kept in reciprocal contact to melt the zones4together thus defining the welding bead.

In this respect, the fact is underlined that the step of making the grooves19also comprises leveling the parts of the zones to be welded4not occupied by the grooves19.

In practice, the tools21are made to pass over the substantial totality of the zones to be welded4at different work depths:in correspondence to the peripheral edges of the profiled elements3, the work depth of the tools21is greater and such as to define the grooves19;in correspondence to the remaining parts of the zones to be welded4, instead, the work depth of the tools21is less and such as to only remove a small layer of plastic material, enough to flatten and even out the zones4to be welded.

In other words, the purpose of the tools21is not only to shape the grooves19but these are also fundamental for evening out the walls and correcting any cutting errors. In the absence of such leveling, the zones to be welded4would be too irregular and therefore not weldable.

It is also underlined that the grooves19and the leveling of the zones to be welded4are made by the tools21of the device1when the profiled elements3are already mounted on the retaining members2and the zones to be welded4are coupled and melted together without demounting the profiled elements3from the retaining members2.

In other words, the tooling of the profiled elements3on the retaining members2occurs just once and the device1is able to execute all the steps of the method according to the invention without the profiled elements3having to be prepared and/or machined on other machines.

Such peculiarity, besides ensuring very fast execution, permits avoiding welding errors due to the incorrect mounting of the profiled elements3on the retaining members2.

In fact, if the zones to be welded4were leveled on a different machine and then mounted on the device1to be welded, the risk would exist of badly welding, the profiled elements3because the zones to be welded4might not be perfectly facing and parallel.

With reference to the solution schematically shown in theFIGS. 7aand 7b, the compartment19apreviously made by the grooves19is open, meaning it has a side turned towards the outside which remains substantially accessible and visible.

In the solution shown in theFIGS. 7aand 7b, therefore, the welding bead is retained within the volume of the compartment19aby means of the presser27which closes one of its sides.

It will be noted in fact that when the profiled elements3are moved closer, the grooves19coincide with one another to define the compartment19a. Furthermore, the presence of the presser27determines the closing of the compartment19awhich keeps the welding bead on the same level as the external visible surfaces of the profiled elements3.

The step of making the groove19is implemented by means of a removal operation of material on the peripheral edges defined by the head extremities of each profiled element3. This way, the groove19obtained has a substantially stepped conformation in square, i.e., shaped at 90°, which extends along the entire extension of the zone to be welded4. Before the step of heating the zones to be welded4, and in particular during the removal by milling step, the step is implemented of the retention of the shavings by means of the cutter tool21with helical shape and the axial suction which conveys the removed shavings towards the inside of the chamber29a.

With reference to the solution shown inFIGS. 8a, 8band 8c, the grooves19made in correspondence to each zone to be welded4comprise at least an undercut portion30to define at least a protruding corner31obtained on a visible surface portion32of the profiled elements3.

Also in this case the step of making the grooves19is performed by means of a removal operation on a peripheral edge of each profiled element3, with the difference that a tool21is used which is specifically shaped to make the undercut portion30.

The tool21, in particular, can be shaped so as to make the groove19and its undercut portion30with a single material removal stroke direct from the solid.

Alternative embodiments are however possible wherein the removal operation is done by means of two different tools21, one for shaping the groove19in a way similar to that shown in theFIG. 7a, and one for obtaining only the undercut portion30.

The groove19thus obtained has a stepped conformation in undercut, which extends along the entire extension of the zone to be welded4.

The undercut step is at least partially obtained underneath the visible surface portion32of the profiled elements3to define the undercut portion30of the groove19.

More in detail, it is underlined that, once the grooves19have been made:the zones to be welded4comprise a head surface33suitable for coining into contact with the head surface33of the other zone to be welded4during the coupling step of the profiled elements3; andthe protruding corners31are arranged at a predefined distance34from the lying plane on which the head surfaces33lie.

The predefined distance34is determined according to the quantity of plastic material to be melted during the coupling step of the profiled elements3and to the volume at disposal in the undercut portions30of the grooves19which, as will be better described below, is designed to collect the melted material at the end of the coupling step of the profiled elements3.

Before the heating step, furthermore, the grooves19are delimited by a first surface35substantially at right angles to the head surfaces33and by a second surface36substantially oblique in correspondence to which said undercut portion30is defined. The second surface36is substantially sloped by an angle between 10° and 80° with respect to the visible surface portion32of the profiled elements3.

Alternative embodiments of the present invention cannot however be ruled out wherein the grooves19, and in particular the undercut portions30thereof, have a different conformation, e.g., curved or the like.

In the light of the specific conformation of the grooves19, during the step of approach and coupling of the zones to be welded4, the following sub-steps are completed:bringing the protruding corners31together so they substantially coincide without substantially melting them; andmaking a containing compartment19awhich is defined by the grooves19of each zone4and which, in correspondence to the visible surface portion32of the profiled elements3is closed by the protruding corners31brought close to one another.

In this configuration, therefore, the containing compartment19ais closed and the welding bead is made inside the containing compartment19a.

The plastic material melted in correspondence to the head surfaces33does in fact return up towards the visible surface portion32of the profiled elements3and remains trapped inside the containing compartment19a.

In the case shown in theFIGS. 8a, 8b, 8cthe containing pressers27are used resting on the profiled elements3in order to contain any leaking of the melted material through the protruding corners31.

With reference to the solution shown in theFIGS. 9a, 9b, 9cand 9d, the groove19is only obtained on one of the profiled elements to be welded.

For this purpose, the profiled elements3can be split up into a first profiled element3a, on which the groove19is made, and into a second profiled element3b, on which, instead, the groove19is not obtained.

The step of making the groove19moulds the zone to be welded4of the first profiled element3aso as to define a head surface40and a receding corner41obtained on a visible surface portion42of the first profiled element3a.

Just as in the previous cases, in the solution shown in theFIGS. 9a, 9b, 9c, 9das well, the step of making the groove19is implemented by means of a removal operation on a peripheral edge of the first profiled element3a.

After the step of making the groove19, an operation is performed consisting in the heating of the zones to be welded4, which is performed by bringing the profiled elements3a,3bcloser to the hot-plate heat-sealing element12.

During this step, a sub-step is carried out consisting in dissolving the head surface40of the first profiled element3aand only a part of the zone to be welded4of the second profiled element3b, so as to define a receding surface43of the second profiled element3band a relief corner44obtained on a visible surface portion42of the second profiled element3b.

For this purpose, in the solution shown in theFIGS. 9a, 9b, 9cand 9dthe hot-plate heat-sealing element12has a first face45, suitable for coming in contact with the head surface40of the first profiled element3a, and a second face46,47suitable for coming in contact with only one part of the zone to be welded4of the second profiled element3b.

More in detail, the second face46,47comprises at least one protruding part46, suitable for coming in contact with the second profiled element3bto define the receding surface43, and at least one receding part47, suitable for remaining spaced at a distance from the second profiled element3band for avoiding to come in contact with the relief corner44.

As can be seen inFIG. 9b, the second face46,47has two receding parts47which operate on opposite sides of the second profiled element3b.

The distance h between the receding parts47depends on the height of the second profiled element3b; higher the second profiled element3b, greater the distance between the receding parts47.

For this purpose, the hot-plate heat-sealing element12can be split into at least two sections12a,12breciprocally mobile to move the receding parts47close to and away from one another.

In the embodiment shown in theFIGS. 10aand 10b, e.g., each section12a,12bis wedge-shaped and has a sloping surface50which can slide on the sloping surface50of the other section12a,12bto change the distance h between the receding parts47. Alternative equivalent solutions cannot however be ruled out such as, e.g., the case in which the second face46,47consists of a kit of interchangeable sheets, shaped differently the one from the other (in particular, they have different distances h) and selectively associable with the hot-plate heat-sealing element12according to the height of the second profiled element3b.

After the heating step, a coupling step is performed of the zones to be welded4, which consists in reciprocally bringing the profiled elements3a,3bcloser along the sliding guides8and which contemplates the sub-step of melting the zones4together to define the above welding bead.

In the light of the specific conformation of the receding corner41, of the relief corner44, of the head surface40and of the receding surface43, during the coupling step the following sub-steps are also performed:melting the head surface40together with the receding surface43; andbringing the receding corner41close to the relief corner44so they substantially coincide without substantially melting them, to define a confinement barrier of the welding bead.

For this purpose is it underlined that, after the heating step and before the coupling step of the profiled elements3a,3b, the receding corner41of the first profiled element3ais arranged at a first predefined distance48from the lying plane on which the head surface40of the first profiled element3alies.

In the same way, after heating and before coupling, the relief corner44of the second profiled element3bis arranged at a second predefined distance49from the lying plane on which said receding surface43of the second profiled element3blies.

Usefully, the first predefined distance48is greater or the same as the second predefined distance49and, preferably, it is slightly greater, so that at the time of the coupling of the profiled elements3a,3b, the head surface40and the receding surface43come into contact and melt together, while the receding corner41and the relief corner44simply rest against one another without melting.

The first predefined distance48and the second predefined distance49are established according to the quantity of plastic material to be melted during the coupling step of the profiled elements3a,3b.

In this configuration, therefore, the containing compartment19ain which the welding bead remains confined is defined by the space underneath the confinement barrier.

It is in fact underlined that the plastic material melted in correspondence to the head surface40and of the receding surface43remains contained inside the containing barrier defined by the receding corner41and by the relief corner44and has no way of surfacing outside the profiled elements3a,3b. In the case shown in theFIGS. 9a, 9b, 9cthe containing pressers27are used resting on the profiled elements3a,3bto curb any melted material leaking through the receding corner41and the relief corner44.

The adhesion capacity of the door or window frame in correspondence to the welded extremities depends on the extension of the working surfaces of the profiled elements3which is placed in reciprocal contact and which, other sizings being equal, is determined by the thickness of the wall of the profiled elements3.

The presence of the grooves19determines the reduction of the wall thickness of the profiled elements3and, other conditions being equal, the working surface to be melted and welded.

To ensure greater adhesion and increase the mechanical strength of the end door or window frames, the figures from11to18show an alternative embodiment of the device or machine1.

In this embodiment, the profiled elements worked by the machine1are split up into a first profiled element60and a second profiled element61, having a first zone to be welded62and a second zone to be welded63, respectively.

The machine1comprises a base frame38, retaining members2, movement means7, removal means18and containing pressers27exactly the same as those mentioned above, to the detailed description of which full reference is made.

The hot-plate heat-sealing element12shown in the embodiment of the figures from11to18has a first face64and a second face65opposite one another against which the zones to be welded62,63are placeable in contact to be heated.

Advantageously, the hot-plate heat-sealing element12consists of a single resistance, with a substantially plate-shaped conformation and which, by means of an electric circuit66, is supplied with electricity to produce heat by joule effect.

The first face64and the second face65are therefore defined by the main surfaces of the electric resistance12.

It is easy to understand however that alternatively the hot-plate heat-sealing element12can consist of a support plaque which, on opposite sides, supports two or more separate electrical resistances, one of which defines the first face64while the other defines the second face65.

Alternatively, it is possible to have a hot-plate heat-sealing element12made up of one or more electric resistances with flat faces covered with a series of shaped elements, in a heating conductive material, which define the first face64and the second face65; in this case, the shaped elements can usefully consist of a piece of metal plate subject to bending, pressing or other type of shaping useful to shape the faces64,65in a way that will be better described below.

In a further alternative embodiment, it is possible for the hot-plate heat-sealing element12not to consist of an electric resistance but, rather, of one or more induction heating plates.

According to the present invention, the hot-plate heat-sealing element12is shaped in such a way that:the first face64comprise a plurality of first recesses64aand of first protrusions64balternated the one with the other and suitable for making on the first zone to be welded62a plurality of first reliefs62aand of first cavities62brespectively;the second face65comprises a plurality of second recesses65aand of second protrusions65balternated the one with the other and suitable for making on the second zone to be welded63a plurality of second reliefs63aand of second cavities63brespectively.

The zones to be welded62,63, thus heated and shaped, can be joined together with the first reliefs62ainserted in correspondence to the second cavities63band with the second reliefs63ainserted in correspondence to the first cavities62b.

As can be seen inFIG. 13, the first recesses64aare arranged on the hot-plate heat-sealing element12opposite the second protrusions65band the first protrusions64bare arranged opposite the second recesses65a.

This means that where the first face64has a first recess64a, the second face65has a second protrusion65b, and where the first face64has a first protrusion64b, the second face65has a second recess65a.

Alternative embodiments cannot however be ruled out wherein the recesses64a,65aof one face64,65are not perfectly opposed to the protrusions64b,65bof the other face64,65and are more of less staggered with respect to these.

The first recesses64aare shaped substantially complementary to the second protrusions65band, in the same way, the first protrusions64bare shaped substantially complementary to the second recesses65a.

Embodiments are also possible, however, wherein the recesses64a,65aand the protrusions64b,65bare not perfectly complementary.

In the embodiment shown in the illustrations, the recesses64a,65aand the protrusions64b,65bof the two faces64,65extend along rectilinear lines parallel to one another. Usefully, the dimensions of the recesses64a,65aand protrusions64b,65bmade this way vary between 0.5 and 2 mm of thickness and between 1 and 4 mm of depth and are preferably equal to about 1 mm of thickness and 2 mm of depth.

Such sizing permits cutting the profiled elements60,61in the best way to obtain an intimate adhesion between the reliefs62a,63aand the cavities62b,63bduring their joining and welding.

For reasons of clarity and simplicity of representation, the illustrations do not always show the real dimensions of the recesses64a,65a, of the protrusions64b,65b, of the reliefs62a,63aand of the cavities62b,63b, which have sometimes been accentuated to permit a greater understanding of the present invention.

In the embodiment shown in the illustrations, the rectilinear lines along which the recesses64a,65a, of the protrusions64b,65bextend are substantially at right angles to the lying plane on which the profiled elements60,61lie and, in other words, are vertical.

It is however easy to understand that, alternatively, the above rectilinear lines can be positioned parallel to the lying plane on which the profiled elements60,61lie and therefore horizontally.

In another embodiment, instead, the rectilinear lines can be positioned oblique with respect to the lying plane on which the profiled elements60,61lie.

It cannot be ruled out that the recesses64a,65aand the protrusions64b,65bhave a different conformation with respect to the linear one and, e.g., be substantially punctiform.

In this latter case, the protrusions64b,65bare defined by an alternation of tapered cusps opposed to recesses64a,65adefined by a series of cavities, these too tapered, cusps and cavities being arranged in chequered fashion.

Usefully, the faces64,65of the hot-plate heat-sealing element12are covered with a non-slip material which prevents the plastic of the profiled elements60,61from adhering to the resistance12and remaining trapped inside the recesses64a,65a.

For any event, however, the machine1also comprises cleaning means67associated with the base frame38and suitable for removing any portion of plastic which has remained attached to the hot-plate heat-sealing element12.

The cleaning means67are composed, e.g., of a pair of brushes suitable for passing over the first face64and over the second face65respectively.

TheFIGS. 11 and 12only show the brush67intended to clean the second face65, but it is easy to appreciate that an identical brush67, is provided to clean the first face64. The brushes67are fitted on the base frame38of the machine1in a fixed way and on opposite sides with respect to the movement path of the hot-plate heat-sealing element12.

This way, the brushes67have the chance to pass over the faces64,65during the transit of the hot-plate heat-sealing element12between the active condition and the non-use condition operated by the movement system13.

Alternative embodiments cannot however be ruled out wherein the brushes67have a mobility such as to make the cleaning operation of the faces64,65easier.

Consistently with the embodiment of the machine1shown in the figures from11to18, the method or procedure according to the present invention contemplates heating the zones to be welded62,63moving them closer together and placing them in contact with the faces64,65of the hot-plate heat-sealing element12(FIGS. 15 and 16).

The conformation of the faces64,65results in the first reliefs62aand the first cavities62bbeing made on the first zone to be welded62and in the second reliefs63aand the second cavities63bbeing made on the second zone to be welded63(FIG. 17).

At this point, the heated zones to be welded62,63are coupled together by pressing, with adequate pressure, the profiled elements one against the other to keep the zones to be welded62,63in reciprocal contact.

This step of the procedure occurs taking care to arrange the first reliefs62ain correspondence to the second cavities63band the second reliefs63ain correspondence to the first cavities62b.

Subsequently, the faces64,65of the hot-plate heat-sealing element12are cleaned so as to remove any portions of plastic which have remained attached to the hot-plate heat-sealing element12.

This part of the procedure is performed by passing the brushes67over the first face64and the second face65respectively during the movement of the hot-plate heat-sealing element12between the active condition and the non-use condition.

The present invention achieves the proposed objects. In particular, the possibility of maintaining the welding bead inside the compartment19aand the operation of the containing pressers27prevents excess material coming out. Consequently, all the surface finishing jobs suitable for removing excess material are eliminated, with the consequent advantages in terms of time, energy and saving relating to the use of further machinery.

Furthermore, the removal operation ensures the leveling of the surfaces of the profiled elements3in reciprocal contact, with the consequent saving of the material which, at present, has to be melted to obtain the required amount.

It is further underlined that the particular solution of providing recesses and protrusions on the welding plate and of making reliefs and cavities on the zones to be welded permits considerably increasing the strength and mechanical tightness of the welding.

The reciprocal coupling of the reliefs and cavities in the ways indicated by the present invention does in fact determine the intimate adhesion of the zones to be welded by virtue of the fact that the contact surface is greater compared to a traditional coupling between perfectly flat zones to be welded.

It must also be underlined that the moving away of the welding plate and the surface tension of the melted material usually determine the formation of a thin surface repellent layer, so-called “skin”, which at least in part hinders the subsequent adhesion of the extremities of the profiled elements; the presence of reliefs and cavities, alternated the one with the other, on the other hand, strongly hinders the formation of the “skin” surface layer, which tends to only form in the most exposed parts of the reliefs, without affecting the cavities.

For all these reasons, we witness an increase in the adhesion capacity between the two head extremities of the profiled elements which permits achieving a roughly 30% improvement in ultimate strength.

In this respect, a series of laboratory tests have been performed on several pairs of test profiled elements of the same shape and size and which, other conditions being equal, only differ in terms of the following characteristics:A) non-milled test profiled elements, i.e., without grooves19, and traditionally welded, i.e., by means of a welding plate without recesses64a,65aand protrusions64b,65b;B) non-milled test profiled elements but welded according to the invention, i.e., by means of a welding plate with the recesses64a,65aand the protrusions64b,65b;C) milled test profiled elements, i.e., having grooves19, but traditionally welded;D) test profiled elements milled and welded according to the invention.

By way of example, by indicating as 1 kg the ultimate strength value for case A) and comparing such reference value with the data acquired for the cases B), C) and D), the following results are obtained:

ultimate strength of case A):1 kgultimate strength of case B):1.3 kgultimate strength of case C):0.83 kgultimate strength of case D):1.1 kg

As can be seen from the obtained data, therefore, it appears evident that the use of a welding plate with recesses64a,65aand protrusions64b,65bpermits strengthening the connection between the profiled elements both when there are no grooves19(switch from 1 kg to 1.3 kg) and when there are grooves (switch from 0.83 kg to 1.1 kg).

It is also underlined that, compared to a traditional welding, the adoption of the grooves19intended to create a containing compartment for the welding bead determines a considerable reduction in strength (switch from 1 kg to 0.83 kg) due to the reduction in thickness of the wall of the profiled elements but, by means of the present invention, the strength limit can be returned to values above initial values (switch from 0.83.1 g to 1.1 kg).

The particular solution of combining the removal means18and the welding plate12with recesses64a,65aand protrusions64b,65bon a single welding machine, therefore permits obtaining a result never before achieved to make window and door frames in a plastic material of considerable sturdiness and with an appreciable aesthetic appearance, which do not require additional finishing operations.