METHOD AND APPARATUS FOR FORMING ITEMS MADE OF PLASTIC MATERIAL WHEREBY THE PLASTIC MATERIAL IS HEATED BY ULTRASONIC VIBRATIONS

Abstract: Method and apparatus for forming items (A) made of polymeric material, comprising the operations of bringing a mass of polymeric material (14) to a pre-set fluid or viscous condition suitable for obtaining the plastic item (A) and of forming into the desired predetermined shape said mass of polymeric material (14). In order to bring said mass into the pre-set viscous condition, the method entails sending ultrasound vibrations on said mass of polymeric material (14).

Description: 1 Description METHOD AND APPARATUS FOR FORMING ITEMS MADE OF PLASΗC MATERIAL WHEREBY THE PLASΗC MATERIAL IS HEATED BY ULTRASONIC VIBRATIONS Technical Field The present invention relates to a method and an apparatus for forming items made of polymeric plastic material. Background Art To obtain an item made of polymeric plastic material, apparatuses are currently employed that generally comprise a housing chamber for a mass of polymeric material - in general, fed in the form of powders or granular material - which is in connection with a mould or a nozzle for forming the item, where the plastic material is sent by means of compression imparted on the mass in said housing chamber, after said mass has been reduced to a plastic state suitable for forming. In said forming machines, in order to obtain the reduction to a desired fluid or viscous condition of the mass of polymeric plastic material, use is currently made of appropriate heating devices, generally in the form of electrical resistors and related control devices, whose employment however requires an excessive energy expenditure to obtain thermal energy through the Joule effect. A further excessive energy expenditure by prior art machines is due to the excessive use of compression force imparted on the plastic material in order to obtain, in contact with the pressing element, a honey-like state or viscous condition of the plastic material that favours the intervention of the heating means to bring the entire plastic mass into the fluid or plastic state suitable for the work process. Disclosure of Invention An aim of the present invention is therefore to provide a method and an apparatus for forming an item made of polymeric plastic material wherein the fluidisation phase of the plastic mass to be formed is accomplished with low energy expenditure. Moreover, in the aforementioned known apparatuses said electrical heating resistors, in order to obtain an effective heating of the plastic mass, are positioned circumferentially in correspondence with said chamber for the compression and fluidisation of the polymeric material with the further drawback of occupying a certain amount of space which makes said apparatuses bulky and complex. Other aims of the present invention therefore are those of providing an apparatus for forming an item made of polymeric plastic material that presents a simple, minimally sized and inexpensive structure. The above is attained thanks to a method according to claim 1 and, in particular, through a method for forming items made of polymeric material, comprising the phases of bringing a mass of polymeric material to a pre-set viscous condition suitable for obtaining the plastic item, and of forming said mass of polymeric material according to the desired shape to obtain said item; the method being characterised in that, in order to bring said mass of polymeric material into the pre-set viscous condition, ultrasonic vibrations are sent on the mass itself. The present invention further relates to an apparatus according to claim 5. The use of energy in the form of ultrasonic vibrations imparted to the plastic mass to be formed, to bring it to the desired fluid or viscous condition, advantageously allows to reduce energy expenditure with respect to apparatuses using traditional heating means, in particular electrical resistors, to perform this operation, as well as with respect to apparatuses using a high compression of the plastic mass to make it fluid in contact with the thrusting element. With the present invention it is possible to operate on a plastic mass to be formed in room temperature conditions with considerable energy savings. Moreover, all those bulky devices used in known apparatuses to perform such heating conditions and to obtain such high thrusts on the plastic material are eliminated. A considerable structural simplification and lowered set-up costs are obtained for the present apparatus . The secondary claims relate to advantageous embodiments of the present invention. Further technical features and advantages of the invention will become more readily apparent in the detailed description that follows, made with reference to the accompanying drawings, which represent embodiments provided purely by way of non limiting examples. - Figure 1 shows a schematic and exemplifying view of a first preferred apparatus for the realisation of the present method for forming an item made of polymeric plastic material; - Figure 2 shows a schematic and exemplifying view of a second preferred apparatus for the realisation of the present method for forming an item made of polymeric plastic material. In accordance with attached Figure 1, a preferred embodiment of the apparatus 10 for the realisation of the method of the present invention comprises a hermetically sealed chamber 12 for housing a mass 14 of polymeric material presenting at least one opening or a nozzle 16, used for the exit from chamber 12 of said mass 14 made of polymeric material in a viscous condition suitable to obtain an item, indicated by the generic reference A in the figure. The apparatus also comprises suitable means for feeding the plastic material into said chamber of the apparatus, exemplified in the present case by hopper T, whereon the plastic material is loaded in granular or powder form 18. Downstream of said feeding means are provided suitable means D for dosing the quantity of plastic material in granules to be introduced inside said chamber 12, which transfer to the chamber 12, through suitable one-way means 20 and a corresponding insertion opening 22 provided in the outer wall 23 contouring the chamber, the predetermined dose of load of plastic material to said chamber 12. Further provided are suitable means for forming said item; said forming means can comprise a suitably shaped nozzle 16 or an actual mould (not shown in the figure) within which said plastic material in fluid or viscous condition is introduced under pressure. To obtain the ejection of the plastic material in the fluid viscous state from the chamber 12, said fluid mass is compressed by suitable compression means, exemplified in the figure by the piston 24 able to slide longitudinally within said chamber 12. Said piston 24 being able, if need be, to be also used to create inside the chamber a vacuum suitable for drawing a subsequent dose of replenishment plastic material 18 in granular form into the chamber itself. The operations of actuating the compression means are performed thanks to suitable driving means M. In the present apparatus are further provided means for bringing a mass of polymeric material into a pre-set viscous condition suitable to obtain the forming of the plastic item A . Advantageously, said means to bring said mass of polymeric material to the pre-set viscous condition comprise a source of ultrasound energy or sonotrode device S which sends energy in the form of ultrasonic vibrations to said mass 14 of polymeric material. Preferably, said source of ultrasonic vibrations S is positioned on the side of the chamber 12 that is opposite to the one occupied by said compression means 24. Obviously, also other dispositions of the vibration source, for instance on a side wall of the housing chamber 12, can be imagined. The nozzle 16 for emitting the plastic in the viscous state is advantageously provided on the side wall of the chamber 12 in the vicinity of the surface of the vibrating element that is in contact with the plastic mass, where the polymeric material reaches its viscous condition. In the figure, the reference letter C indicates centralised control means preferably in the form of an electronic processing unit commanded with a program and, possibly, with the aid of suitable sensor means in appropriate areas of the machine. Thanks to such control means C it is possible to co-ordinate the intervention times of the dosing means D, of the means M for driving the piston 24 and of the ultrasound emission source S to obtain the production of the plastic material items A. In particular it is possible to provide said mass 14 of polymeric material, in combination with the sending of said ultrasonic vibrations thereon, with a pre-set compression state suitable to favour the attainment of the viscous condition on the part of the plastic material. Figure 2 shows a second preferred embodiment 100 of the apparatus for realising the method of the present invention. This second preferred embodiment presents most components that are wholly identical to those of the preceding first preferred realisation and hence are not commented again. The present second preferred embodiment 100 is distinguished from the first in that the emission of the plastic material from the chamber 12 takes place through a conduit 160 that is obtained inside the sonotrode S. In this way a greater transfer of ultrasonic device to the plastic mass can be obtained, thereby increasing the work efficiency of the apparatus. The plastic material that is preferably used is constituted by a thermoplastic plastic material. In any case, other plastic materials can be used as well, provided they are suitable for the present work processes. The method of the present invention could be applied to any kind of work process for the production of items made of plastic material, such as extrusion, compression moulding, injection moulding, transfer moulding, extrusion and blowing moulding and others . The invention thus conceived can be subject to numerous modifications and variations, without thereby departing from the scope of the inventive concept. Moreover, all details can be replaced with technically equivalent elements.

Claims: 7 Claims 1. Method for forming items made of polymeric material, comprising the phases of bringing a mass (14) of polymeric material into a pre-set viscous condition suitable for obtaining the plastic item, forming into the desired predetermined shape said mass (14) of polymeric material, characterised in that in order to bring said mass (14) of polymeric material into the pre-set viscous condition, ultrasonic vibrations are sent on said mass. 2. Method according to claim 1 , characterised in that in order to bring said mass (14) of polymeric material into the pre-set viscous condition, in combination with the sending of said ultrasonic vibration on said mass, a compressed state is provided to said mass (14) of polymeric material. 3. Method according to any of the previous claims, characterised in that said viscous state of the plastic material is a state of complete fluidisation of the plastic mass. 4. Method according to any of the previous claims, characterised in that the viscous state of the plastic mass is obtained inside a chamber (12) for housing said plastic mass and wherein the plastic mass in the viscous state exits through the means (S) that send the ultrasonic vibrations into said chamber (12). 5. Apparatus for forming items made of polymeric material, comprising a chamber (12) for housing a mass (16) of polymeric material, means for bringing a mass of polymeric material into a pre-set viscous condition suitable for obtaining the plastic item, at least one opening (16) connected to said chamber (12) for the exit from the chamber (12) of said mass (14) of polymeric material in the 8 predetermined viscous condition, means (M, 24) for exerting a compression in said chamber (12) of said mass (14) in viscous condition to cause its exit from said opening (16), characterised in that said means for bringing into the pre-set viscous condition said mass (14) of polymeric material comprise a source of ultrasonic energy (S) that sends energy in the form of ultrasonic vibrations to said mass (14) of polymeric material. 6. Apparatus according to claim 5, characterised in that it comprises control means (C), said control means (C), in order to bring said mass of polymeric material into the pre-set viscous condition, activating in combination said source (S) to send said ultrasonic vibrations on said mass and said pressure means (M, 24) to induce a pre-set compression state in said mass (14) of polymeric material during the phase wherein the viscous state is reached. 7. Apparatus according to any of the previous claims from 5 to 6, characterised in that the opening (16) for the exit from the chamber (12) of said mass (14) of polymeric material in the predetermined viscous condition is located in the vicinity of the surface of said source (S) for sending the ultrasonic vibrations which is in contact with the mass (14) of polymeric material. 8. Apparatus according to any of the previous claims from 5 to 7, characterised in that a conduit (160) for the exit from the chamber (12) of said mass (14) of polymeric material in the predetermined viscous condition is located inside said source (S) for sending the ultrasonic vibrations. 9. Apparatus according to any of the previous claims from 5 to 8, characterised in that it comprises means (16) for directly forming said item starting from said mass in viscous condition. 10. Apparatus according to any of the previous claims from 5 to 9, characterised in that said source of ultrasonic energy (S) which sends energy in the form of ultrasonic vibrations to said mass (14) of polymeric material is located in said chamber (12) on the opposite side to that occupied by said compression means (24). 11. Method and apparatus according to the previous claims, characterised in that it operates at room temperature.

Inventors: DIOLAITI ERMINIO, RIVI GIULIANO, DIOLAITI, ERMINIO, RIVI, GIULIANO
Applicants: DIOLAITI ERMINIO, DIOLAITI LUIGI, RIVI GIULIANO, DIOLAITI, ERMINIO, DIOLAITI, LUIGI, RIVI, GIULIANO
Application year: 1999
Main classification: B29C35
IPC codes: B29B13, B29C35