Field of the invention

The present invention relates in general to the sectors of the perforation of plastic films, whether they are composed of homogeneous material or composites/co- laminates, as well as aluminium papers and films. More particularly, the invention relates to making holes through a punching movable cutting tool operated by compressed air which, acting in combination with a suitable die in a fixed position, causes the detachment of a portion of film named scrap, leaving a hole on the same film.

State of the art

There are multiple varieties of perforating devices for perforating films on the market, including those with pneumatic or compressed air operation. Such perforating devices normally operate at rather high speeds and rates, and one of the most frequent problems is that the scraps produced during the cutting operation are not expelled and conveyed correctly into the appropriate suction pipe, but they tend to adhere to the punch by following it in its upstroke and disperse on the surface of the film. The fact of having the perforated film contaminated by the scraps is in itself already a problem, with the aggravating factor that if the scrap is not expelled correctly, it falls back or reappears in the cutting area at the next punching, thus causing burrs on the perimeter of the hole or an incomplete cut. Perforating devices are known, in which the ejection of the scraps is carried out through compressed air, where, however, the use of dedicated control solenoid valves and a rather complex construction is required, or solutions which do not allow to optimise the outgoing air both in terms of pressure and in terms of the position of the punch in which the air blow is controlled.

US 4,534,250 describes a perforating device with punch of the through type in which the punch is operated pneumatically through a piston moved inside a cylinder. The punch is axially hollow and is placed in fluid communication with the compressed air supplied into the cylinder to carry out the perforation, in such a way as to feed the same pressurised air into the hollow punch and thus eject the scrap. The compressed air supply to the hollow punch is carried out at the same time as the piston is operated or through a separate inlet, and only in pre-set positions of the piston, or by the control of a special solenoid valve. This results in a waste of compressed air since the air flow exiting the punch remains active for longer times than necessary (the useful time for a head-type punch is in the instant immediately following the perforation) or, alternatively, this results in the need for a solenoid valve dedicated to the air blow for the ejection of the scraps. In other words, for a through punch, the instant and/or the position for operating the air blow for the ejection is quite relative, meaning that it is effective from the moment in which the punch completes the cut up to the piston stop. After the impact, the head punch can only go back up and the air blow loses its effectiveness as it is exhausted into the environment and not through the die.

The present invention differs from what exists in that it uses the same solenoid valve controlling the perforating device, due to its constructive simplicity and the ability to insufflate air adapted for expelling the scraps at a predefined pressure and at the exact moment in which it is necessary and useful, that is to say at the moment of contact between punch and die.

Summary of the invention

The object of the present invention is therefore to provide a functional, effective and cheap solution for ejecting or easing the ejection of the punching scraps.

An embodiment of a compressed air perforating device comprises at least one head- type punch which abuts against the hole of a cutting die, in which the punch is constrained to the body of an actuator.

The perforating device according to the present invention has a compressed air accumulation chamber obtained in the body of the actuator. At least one one-way valve is arranged at an inlet for the compressed air in the accumulation chamber and at least one one-way valve is arranged at an outlet for the compressed air from the accumulation chamber.

The ejection of the scrap is carried out by the same flow of compressed air operating the perforation actuator, but with the compressed air that has been retained in an accumulation chamber. The one-way valves allow to regulate the air flow useful for the ejection of each scrap.

The object of the present invention is therefore achieved through a particular shape of the perforating assembly of the punch and with the aid of suitable valves adapted to channel and regulate the compressed air flow useful for the ejection of each scrap. A one-way valve is arranged at the inlet of the compressed air in the accumulation chamber and consists, for example, of a rubber elastic element. The rubber elastic element of the one-way valve arranged at the inlet of the compressed air in the accumulation chamber must preferably have an elasticity suitable for ensuring a very low opening pressure differential, that is to say, a pressure differential intended as a very low difference between the pressure in the compressed air passage holes towards the accumulation chamber and the pressure in the accumulation chamber.

A one-way valve is arranged at the outlet of the compressed air stored in the accumulation chamber. This valve comprises a ball and a spring, wherein the ball serves as an air flow sealing element and the spring is designed to maintain a pre-set residual pressure within the accumulation chamber.

The ball abuts against the conical surface located at the end of a screw. This screw comprises an axial through hole which places in fluid communication the accumulation chamber and the one-way valve arranged at the outlet of the compressed air in the accumulation chamber.

The one-way valve located at the outlet of the compressed air stored in the accumulation chamber is calibrated and/or sized to the characteristics of the ball and spring, in such a way as to maintain within the accumulation chamber an adequate reserve of compressed air sufficient to ensure the ejection of the scrap.

The punch comprises an axial through hole which is selectively placed in fluid communication with the accumulation chamber through the one-way valve arranged at the outlet of the compressed air in the accumulation chamber.

The air escape from the one-way valve that regulates the flow exiting the accumulation chamber occurs as a result of the inertial displacement of the ball resulting from the impact of the punch against the cutting die.

Brief description of the drawings

Further characteristics and advantages of the present invention will become more apparent from the detailed description of some preferred, but not exclusive, forms of implementation of an embodiment of the device according to the invention, are shown by way of non-limiting example in the accompanying drawings, wherein:

- Fig. 1 shows a schematic exploded view of a punch assembly operated by compressed air;

- Fig. 2 shows a plan view of the detail named "slider cap";

- Fig. 3 shows a sectional view of the slider cap;

- Fig. 4 shows a perspective view of the slider cap;

- Fig. 5 shows a perspective view of a one-way valve arranged at the inlet of the compressed air in the accumulation chamber, depicted for example in the form of an umbrella valve, in the rest position;

- Fig. 6 shows a plan view of the valve of Fig. 5 in the rest position;

- Fig. 7 shows an elevation view of the valve of Fig. 5 in the rest position;

- Fig. 8 shows a sectional view of the valve of Fig. 5 in the rest position;

- Fig. 9 shows a sectional view of the valve of Fig. 5 in the open position;

- Fig. 10 shows a perspective view of the valve of Fig. 5 in the open position;

- Fig. 11 shows an elevation view of the punch fastening screw;

- Fig. 12 shows a sectional view of the punch fastening screw;

- Fig. 13 shows a perspective view of the punch fastening screw;

- Fig. 14 shows a schematic sectional view of a complete perforating apparatus comprising the punching assembly and the die assembly in the rest position;

- Fig. 15 shows an enlargement of the detail D of Fig. 14;

- Fig. 16 shows an enlargement of the detail C of Fig. 14;

- Fig. 17 shows a schematic sectional view of a complete perforating apparatus comprising the punch assembly and the die assembly in the start position of the punch descent; and

- Fig. 18 shows a schematic sectional view of a complete perforating apparatus comprising the punch assembly and the die assembly in the end position of the punch descent, then in the film cutting position.

Detailed description of the invention

Referring to Fig. 1, it is inferred that the compressed air perforating assembly is essentially composed of a closing element 1, named plug, fastened to the perforating body 10, a guiding and sealing element named slider cap 2, a one-way valve 3, an actuator slider 5, a return spring 6, a fastening screw 4 of the punch 9, a ball 7, a spring for ball valve 8, a cutting punch 9 and a support 11 of the perforating body 10. Figs. 2, 3 and 4 show in detail the slider cap 2 where the holes 12 for the passage of the compressed air are emphasized.

Figs. 5, 6, 7 and 8 show in detail the one-way valve 3, for example of the umbrella type, in the rest position, where in the sectional view of Fig. 8 the contact of the valve lip with the plane of the closing surface 13 is emphasized.

Figs. 9 and 10 show in detail a one-way valve 3 of the umbrella type in the open position, where in the sectional view of Fig. 9 the detachment of the valve lip from the plane of the closing surface 13 is emphasized.

Figs. 11, 12 and 13 show in detail the fastening screw 4 of the punch, where the hole 14 for the passage of air and the conical surface 15 adapted to receive the supported ball 7, are emphasized.

From Figs. 14, 15 and 16, it is inferred that the punch assembly can be operated by feeding compressed air through the hole 33 in the plug 1. The air fed will exert a force on the slider cap 2 integral both with the actuator slider 5 and the punch 9, thus causing the latter to be launched against the cutting die 12. As shown in detail in Fig. 17, part of the operating air flow 18 will be channelled from the holes 12 through the slider cap 2 and through the one-way valve 3, accumulating in the chamber 16 obtained in the body of the actuator slider 5. The escape of air from the chamber 16 cannot occur along the entry path, the valve 3 being of the one-way type; the air can therefore only escape from the chamber 16 through a second one-way -type and flow- regulating valve composed of the spring 8 and the ball 7, the latter acting on the conical surface 15 of the fastening screw 4 of the punch 9. The outflow one-way regulating valve, composed of the spring 8 and the ball 7, is sized in such a way as to hold the air accumulated in the chamber 16 up to a determined pressure, which will be equal to or slightly lower than the operating and actuating pressure of the actuator slider 5, such that, once the chamber 16 has been filled, the air escapes from the latter are minimal or null until an activation factor of the one-way regulating valve composed of the spring 8 and the ball 7, occurs.

Upon perforating, therefore when the impact between the punch 9 and the cutting die 12 occurs, as shown in Fig. 18, as a result of the acquired speed and its inertia, the ball 7 suitably sized by using materials with suitable specific weights will tend to continue its stroke, compressing the spring 8 and detaching itself from the conical surface 15 on which it rested and which it sealed. It follows that, for a short instant following the impact between the punch 9 and the cutting die 12, the air accumulated in the chamber 16 will be free to flow in the direction of the arrow 23, passing in order through the hole 14 in the fastening screw 4 of the punch 9, the one-way regulating valve composed of the spring 8 and the ball 7, and a hole 19 obtained in the body of the punch 9. The air flow exiting the hole 19 will cause a pressure and force acting on the cutting area of the film 21, with the effect of expelling the cut scraps 20 through the hole present in the cutting die 12.