Technical Field

The present invention relates to a machine to cut profiled elements of plastic material.

Background Art

The machine can cut any type of plastic profiled element and/or material, in particular (but not only) those made of PVC, possibly charged with glass fibers. Throughout the world, the PVC market is fast growing because many new homes have to be built according to energy-saving criteria: a PVC frame ensures excellent thermal insulation with low costs and practically no maintenance compared to traditional materials such as aluminum or wood.

PVC frames are made by cutting various profiled elements using a circular- blade miter saw, which are subsequently welded together to obtain the frame of a door or a window.

Though easy to implement and universally used, the cutting system which envisages the use of a circular-blade miter saw has a number of drawbacks, in particular when used to cut PVC profiled elements.

During cutting using a circular blade in fact, electrically-charged shavings and dusts are produced, which are then attracted by the surfaces of the extraction ducts and of the worked profiled elements.

The shavings are also hard to remove, require the periodical cleaning of the extraction ducts and increase work time due to the need to carefully clean the worked profiled elements; in this respect, it is underlined that a consistent part of the operator's work shift is used to clean the machine and the workplace. To this must be added that, over time, the shavings release chlorine which, albeit in very small quantities, is corrosive and can affect the electronic devices present in the work environment.

Nor should the fact be forgotten as well that the rotating blade not only represents a cutting hazard for the operator and can eject hazardous fragments into the environment, but it is also very noisy during cutting.

PVC dust, furthermore, is harmful for the human breathing tract and the operator is therefore required to wear suitable clothing, which does not only consist of protective eyewear and ear muffs, but also a mask to cover the mouth and nose.

Yet another drawback consists in the fact that the cutting operation by means of a rotating blade produces on the tool and on the profiled element a series of composite forces that make cutting unstable.

Finally, the built-up shavings have to be disposed of and this takes time and economic resources and the dusts, as is known, are hard to remove.

Description of the Invention

The main object of the present invention is to provide a machine to cut profiled elements of plastic material that solves one or more of said drawbacks.

A particular object of the present invention is to provide a machine that does not produce shavings of plastic material.

A particular object of the present invention is to provide a machine that reduces

(and, possibly, eliminates) the release of chlorine.

A particular object of the present invention is to provide a machine that reduces the risk of acoustic pollution and/or accidental cut for operators.

Another object of the present invention is to provide a machine to cut profiled elements of plastic material which allows to overcome the mentioned drawbacks of the prior art within the ambit of a simple, rational, easy and effective to use as well as affordable solution.

The above mentioned objects are achieved by a machine having the characteristics mentioned in claim 1.

The above mentioned objects are also achieved by a cutting method having the characteristics mentioned in claim 10.

Each characteristic operation of the machine may be a stage of the method. Brief Description of the Drawings

Other characteristics and advantages of the present invention will become more evident from the description of a preferred, but not exclusive embodiment of a machine to cut profiled elements of plastic material, illustrated by way of an indicative, but not limitative example in the accompanying drawings wherein: Figure 1 is an axonometric view of the machine according to the invention in the configuration prior to the execution of cut; Figure 2 is an axonometric view of the machine according to the invention in the configuration with the cut made.

Embodiments of the Invention

With particular reference to such illustrations, it is globally indicated by reference number 10 a cutting machine for a profiled element P of plastic material.

The plastic material is preferably PVC, although it is not ruled out that it may be a different plastic from PVC.

The machine 10 comprises at least a positioning assembly 12, 90 for the profiled element P.

The positioning assembly 12, 90, e.g., comprises a base 12, for resting on a worktable, and two or more tightenable jaws 90 mounted on the base 12 to secure the profiled element P.

On the positioning assembly 12, 90, a cutting assembly 28 is mounted, designed to cut the profiled element P.

The positioning assembly 12, 90 and the cutting assembly 28 can be moved the one with respect to the other by means of guide means 14, 16, 18.

In this respect, it is underlined that from the base 12 two columns 14 rise up perpendicular having linear guides, e.g., T shaped, indicated by 16.

On the guides 16 are sliding two complementary runners 18 on which the cutting assembly 28 is mounted.

The movement of the runners 18 on the guides 16 (arrow F of figure 2) may be manual or by means of known actuator means (not shown), e.g., a screw-screw nut or rack-pinion system.

The cutting assembly 28 comprises a casing or plate 19, e.g., C shaped, the extremities of which are associated with the runners 18.

The cutting assembly 28 also comprises at least a heated cutting wire 30, closed on itself in a loop and wound around at least two pulleys 20 able to rotate in order to make it slide.

The cutting wire 30 is made of a metallic material.

The pulleys 20 are pivoted rotating at the opposite extremities of the plate 19 and can rotate around rotation axes A transversal to the sliding direction defined by the guide means 14, 16, 18.

The cutting wire 30, therefore, which is mounted around the pulleys 20, forms a first rectilinear section 32 which is turned towards the positioning assembly 12, 90, protrudes with respect to the plate 19 and is able to cut the profiled element P, and a second rectilinear section 34, which extends between the two pulleys 20 but on the opposite side with respect to the first rectilinear section 32.

The machine 10 comprises a device 40, 42 able to make electric current circulate within the cutting wire 30, so that the cutting wire 30 is heated by Joule effect.

The device 40, 42 comprises a magnetic core 40 able to generate a magnetic flux interconnected to the cutting wire 30.

More in detail, the central part of the plate 19 supports the magnetic core 40, which is closed (without air gap), e.g., toroidal, and is made of ferromagnetic or ferrite material.

On the magnetic core 40 is a winding 42 connected to a high-frequency power generator, not shown in detail in the illustrations.

The energizing of the magnetic core 40 by means of the winding 42 produces an electric current inside the cutting wire 30 by effect of the magnetic induction phenomenon, which runs along the whole length of the cutting wire 30 and heats it by Joule effect

The cutting wire 30 is fitted so as to interconnect with the central opening of the magnetic core 40 (equivalent to the hole of a ring-shaped object or toroid); in particular, in the embodiment shown in the illustrations, it is the second rectilinear section 34 of the cutting wire 30 which interconnects with the magnetic core 40, but alternative embodiments cannot be ruled out wherein the interconnection occurs in correspondence to the first rectilinear section 32.

The particular solution of providing a cutting wire 30 heated by magnetic induction permits avoiding the use of any sliding electric contacts and eliminating the wear these would cause on the cutting wire 30, and at the same time ensures utmost freedom as regards the choice of work parameters of the cutting wire 30, such as, e.g., the choice of a particularly high forward movement speed to keep the temperature of the cutting wire 30 uniform, as better described below.

Alternative embodiments cannot however be ruled out wherein the cutting wire 30 is electrified thanks to sliding electric contacts.

Alternative embodiments cannot be ruled out furthermore wherein the cutting wire 30 is heated by means of different heating systems, as in the case of conduction, convection and/or radiation heating plates, which heat the cutting wire 30 when this passes in the proximity of the plates themselves.

Another possible heating system consists in an open magnet with air gap.

In this latter case, an electrical winding is still wound on the magnet powered by a high-frequency voltage generator, and the cutting wire 30 transits in correspondence to the air gap, where the so-called field lines are generated. The part of the cutting wire 30 inside the air gap heats up due to the parasite currents, or Foucault currents.

Preferably, the cutting wire 30 is made in a single body piece, and has a homogeneous structure without joints.

In other words, the cutting wire 30 is made by cutting or shearing a thin metal plate, to obtain an uninterruptedly closed loop which is then laminated in the direction of thickness by two rollers to give it the circular section shape.

Such embodiment permits preventing the cutting wire 30 from being obtained starting from an initially open wire and then welded at a welding point which, during use, would cause a resistive peak for the transit of the electrical current and a consequent lack of heating uniformity due to the Joule effect of the cutting wire 30.

Considering that, in the embodiment shown in the illustrations, the heating of the cutting wire 30 is by transit of electric current, the pulleys 20, to last a long time, must be well resistant to the heat generated directly by the cutting wire 30 and, at the same time, must electrically insulate the cutting wire 30 from the rest of me machine 10.

To this purpose, the pulleys 20 comprise:

- an inner heart or central roller 20b, of an electrically insulating material (e.g. plastic) that electrically insulates the pulleys 20 preventing that the electric current of the cutting wire 30 from discharging to ground; and an outer disc 20a, conveniently made of a metallic material (e.g. aluminum) and arranged around the inner heart 20b.

The machine 1 also comprises at least a tensioning assembly 50, 52, 54, 56 able to tension the cutting wire 30 and keep it taut.

The tensioning assembly 50, 52, 54, 56 comprises movement means of at least one of the pulleys 20 in the opposite direction to the other pulley 20.

More in detail, one of the pulleys 20 is fitted on a support 54 integral with a slide 52 sliding on a linear guide, indicated by 50 and fitted on the plate 19. A spring 56 pushes the sliding pulley away from the other, to keep the cutting wire 30 taut also when this expands due to thermal deformation.

The operation of the machine 10 is the following.

The profiled element P to be cut is placed resting on the base 12 and fixed between the two tightenable jaws 90.

The pulleys 20 are set in equiverse rotation to drag the cutting wire 30 and the winding 42 is electrically powered to generate a variable magnetic field inside the magnetic core 40.

Consequently, the electric current is induced inside the cutting wire 30 and this heats up.

The plate 19 is then gradually lowered towards the base 12, so that the first rectilinear section 32 first of all touches the profiled element P and then gradually cuts it by melting of the plastic material, until a part of it becomes detached.

In this respect, it must be specified that, in the context of the present discussion, the fact that cutting is done by melting means that the temperature of the cutting wire 30 is such as to locally melt the plastic material.

To this must be added that even if, during cutting, the cutting wire 30 comes into direct contact with the profiled element P, in itself the cut is not made by rubbing between the surfaces of the profiled element P and of the cutting wire 30 but rather, as has been said, by melting of the plastic.

The particular solution of using a cutting wire 30 that slides and continues moving thanks to the rotation of the pulleys 20 permits keeping the temperature of the wire itself as uniform as possible during the cut, and therefore improving me control of me operation and cutting quality.

In this respect, it is underlined in fact mat the sliding of the cutting wire 30 enables it to cross the profiled element P at a pre-established temperature without overheating or cooling too much.

In the event of the cutting wire 30 not sliding longitudinally, on the other hand, only a short section of the cutting wire 30 would cross the profiled element P, which would therefore be subject to even very considerable and hard to control temperature variations.

It is further specified that it is best for the cutting wire 30 to have a particularly reduced thickness, e.g., between 0.2 and 2 mm, so as to reduce the quantity of heat required for cutting and the quantity of melted material.

In this respect, it should be remembered that many plastic materials, including PVC, once melted tend to adhere to the surfaces with which they come into contact; it is therefore best to reduce the surface and the thickness of the cutting wire 30 as much as possible and if necessary apply suitable surface treatments, with the aim of reducing the removed material to zero.

The use of the cutting wire 30, preferably made of multi-strand steel, satisfies this requirement and reduces surfaces and thicknesses to the utmost.

Every plastic material has a melting temperature beyond which it degenerates. For example, PVC melts at around 250°C and even at slightly higher temperatures it tends to become yellow and then burn.

It is therefore best to regulate and control the temperature of the cutting wire 30. If the plastic from which the profiled element is made is PVC, then it is best mat the temperature of the cutting wire 30 remain between 250°C (melting point of PVC) and 260°C.

To control the temperature of the cutting wire 30 a temperature control device 48 may be used, preferably of the type without contact, e.g. an infrared thermal camera.

The temperature control device 48 is connected to an electronic management and control unit, not shown in the illustrations, which increases or decreases the excitation of the winding 42 according to the temperature of the cutting wire 30 detected by the device itself, for the purpose of keeping it within the pre- established values.

It is best for the cutting of the profiled element P to be quick (e.g., around 2 seconds) and for the surface resulting on the pieces to be perfectly flat, to permit the perfect coupling of the pieces during subsequent operatioris/machining operations.

The use of the cutting wire 30 also has this advantage, i.e., it ensures a precise and quick cut.

With the same purpose, the cutting wire 30 is made to move forward at a fast forward speed, e.g., between 1 m/s and 2 m/s, such as to ensure, on the one hand, that the cut is made quickly and, on the other, that the heat is transferred correctly from the cutting wire 30 to the profiled element P.

To make the cutting wire 30 move forward at the required speed, the machine 1 has operating means, not shown in the illustrations, which are able to make the pulleys 20 rotate and are connected to the electronic control unit that determines the rotation speed thereof.

The operating means can motorize both the pulleys 20 in a synchronous way or motorize just one, the other being dragged in rotation by the cutting wire 30. The method according to the invention is implemented through the machine 1 and comprises the steps of:

- placing the profiled element P to be cut onto the positioning assembly 12, 90;

moving forward the cutting wire 30 making the pulleys 20 rotate, preferably so that the speed of forward movement of the cutting wire 30 is between 1 m/s and 2 m/s;

- heating the cutting wire 30. Such step comprises making electric current circulate within the cutting wire 30, which is therefore heated by Joule effect. The circulation of the electric current is by magnetic induction;

moving the positioning assembly 12, 90 and the cutting wire 30 one with respect to the other to cut the profiled element P through melting of the plastic material.

During cutting, the method according to the invention envisages, on the one hand, controlling the temperature of the cutting wire 30 and, on the other, tensioning the cutting wire 30 between the pulleys 20, in the ways previously illustrated.

From what has been said above, it can be appreciated that the machine 10 and the relevant method have the following advantages:

- they prevent the generation of cutting shavings, with all related problems; - they avoid acoustic pollution;

they avoid any risk of the operator cutting Mm herself;

they prevent hazardous fragments from being ejected into the environment; they avoid the creation of dusts;

- they provide a precise and affordable system for cutting plastic material.