RO112492B1 - Bags making method and plant using the technique of the ultrasonic welding - Google Patents

Description

The present invention relates to a method and an installation for the manufacture of bags, in the filled state, using the technique of ultrasonic welding, starting from a foil. More specifically, the invention relates to the use of an ultrasonic welding system, both for forming the bags by sealing the joints between the sheets and for cutting the sheets for separating the bags.

There are various methods for making bags, starting from foils. Regardless of the technique applied, the need for sealing appears. The foil should be positioned so that a front and a posterior portion are obtained. This can be done in several ways. One of the most convenient ways is to make a tube, starting from a foil, which is then processed to obtain separate bags between them. Under the conditions of using this technology, a longitudinal joint appears, when the sheet is bent in the form of a tube, and end joints when the tube is transformed into bags. One of the advantages of this technology based on obtaining a tube, starting from a foil, is that the bag can be filled as the process of transforming the foil into a tube is carried out. The simultaneous filling and filling of bags has a number of advantages.

The formation of bags, by making watertight welds for joining the sheets, can be done using various methods, the joints can be made using adhesives. For gluing the thermoplastic sheets, a heated plate can be used. It is possible to use dielectric heating, also known as radio frequency (RF) heating. It is to be emphasized, however, that ultrasonic welding has a number of advantages over any of these methods, particularly during the filling and filling phases. In the case of the use of adhesives, the problem of solvent removal appears. There are also intervals for the adhesive hardening times. The use of a heated plate is not efficient, as the foil must be heated by conduction. In the case of the use of RF energy, instead of heating the surface of the foil, it is possible to heat the foil over its entire thickness. Thus, good quality welding can be achieved, but the method is limited only to those films that are capable of absorbing a sufficient amount of RF energy to reach the plasticizer. at the same time, given that the foil heats up to its full thickness, it is possible to overheat the foil, accompanied by depositing pieces of foil on the electrodes. In this way, the quality of the following welds is reached, until the electrodes are cleaned.

It has been found that by using the ultrasonic welding technique in the formation and modeling of bags, starting from thermoplastic sheets, there is progress towards methods based on the use of adhesives, heated plates or RF energy. In the case of ultrasonic welding, only the surfaces to be bonded are heated. The surfaces are heated by the shock energy absorption. The foil is no longer heated over its entire thickness, and this presents a number of advantages. Bags which do not have sufficient absorption capacity for RF energy can also be used in the manufacture of bags. The problems raised by the formation of electrode deposits are also avoided. There is no danger of detaching pieces of foil, since the heating takes place only at the level of the surfaces subject to the impact.

It has also been found that the use of ultrasonic welding presents a number of distinct advantages in terms of forming-filling operations. By these we mean those operations by which the bag is filled as the formation. A specific problem of these forming-filling operations is that, in the filling phase, the product shows the tendency to come into contact with that area of the bag to be subsequently welded. Other welding methods, including RF welding, may result in weak welds. In the case of ultrasonic welding, however, a cleaning prior to the welding operation takes place, of the surfaces to be welded. This is achieved by vibrating the adjacent surfaces. consequently, it was found that

The use of ultrasonic welding presents a number of specific advantages from the point of view of performing these combined forming-filling operations. In this way, welds with good strength can be obtained that correspond to the purpose pursued.

Ultrasonic technologies have been applied in welding operations of the most diverse materials. A patent welding machine based on the use of ultrasonic welding technology is presented in US Pat. The bags thus made are intended to be filled with meat or meat products. US Pat. No. 4,667,492 describes how to use ultrasonic technologies in welding operations of tubular containers. The containers are then sealed by another operation, after filling. U.S. Patent No. 4866914 discloses an ultrasonic bag welding device. The product is placed in the bag, after which the bag is sealed with the help of ultrasound, in a later technological phase. The patent emphasizes that during the welding operation any foreign substances are removed, which adhere to the surfaces to be welded together. These patents exemplify the current state of technical development in the field of sealing bags by ultrasonic techniques. However, none of these patents address the issue of ultrasonic welding of bags during the forming-filling operation.

There is also known an assembly consisting of a nicovalve ultrasonic transmitter, which serves both welding and cutting of sheets. In US patent 3939033, there is presented a process based on a fastener with a first embossed element for welding and a second embossed element for cutting. In other words, welding and cutting are not performed on the same surface. However, it was concluded that it is possible for one and the same surface to perform both the welding and the cutting operation. In this way a more efficient ultrasonic device is obtained.

□ It is also concluded that the formation and filling of thermoplastic bags is advantageous to use the ultrasonic technique.

Ultrasonic welding has advantages over the use of adhesives, conduction heating or dielectric heating. A special advantage is the possibility to carry out simultaneously the cleaning operations and the surfaces engaged in the welding and heating of these surfaces at least to the melting point. This is of importance for the execution of the technological phases of formation-filling, when the bag is formed and filled in a single phase. In packing operations, where the packaged product is usually liquid, it gets to dirty part of the welding surface, that is when it is poured into the bag. In order to make a quality weld, the respective surface must be clean. This condition can be fulfilled in various ways. The most efficient way is the use of ultrasonic welding techniques. In this way, a clean welding surface is obtained when the welding operation takes place.

The present invention relates to the use of an ultrasonic welding device, made up of an ultrasonic transmitter and a nylon having a dual purpose, both the welding of the film and the cutting thereof. The operations are performed on the same surfaces belonging to the ultrasonic transmitter and the nicovale. The profiled cutting surface is preferably part of the nylon and has a triangular cross-section. The outer angles from the base of the triangle are approximately 120 ° to 160 °. In this way, the interior angles are from 20 ° to 60 °. The top of the profile ends with a straight edge.

The following is an example of an embodiment in connection with fiq. 1 ... 7. So:

FIG. 1 shows a rear view of a bag with a bore hole, shaped by ultrasonic technique.

FIG. 2 shows a welding device for welding the longitudinal joints

RO 112492 The flanges of the bag in fig. 1.

FIG. 3 shows a cross section through a nylon used for welding and cutting the film.

FIG. 4 shows a top view of the device consisting of the ultrasonic and nicovalve transmitter.

FIG. 5 shows a cross-section along the sectioning plane 5-5, through the device of FIG. 4.

FIG. 6 shows a side view of the device of FIG. 4, transverse arrangement.

FIG. 7 presents the bag manufacturing facility.

The present invention relates to a method of manufacturing bags using the ultrasonic welding technique of bags in the form of bags at the same time as filling these bags and an installation for the manufacture of bags by this method, consisting of an ultrasonic transmitter and a nylon, with which both welding and cutting of thermoplastic foil are ensured. Taking into account the above, it follows that the ultrasonic and / or nicoval emitter must have a certain profile determined to correspond to the stated double purpose of welding a thermoplastic foil followed by cutting the thermoplastic foil in the welding zone.

In order to ensure the necessary conditions for welding the thermoplastic sheet followed by the cutting of the respective film, at least one of the ultrasonic or nicovale transmitters will be profiled so as to allow the cutting operation to be carried out. It is also possible that both the ultrasonic transmitter and the nicovala transmitter belonging to the ultrasonic welding device are profiled for the cutting operation. But this is not necessary. Only the ultrasonic or nicovala transmitter should be profiled for cutting. In this respect, it is preferable that the nicovala is the profiled element. This is explained by the fact that the profiled part is the one with the highest wear. It is preferred that the nicovala and not the ultrasonic transmitter be the piece with more advanced wear.

The method described in this description refers to the manufacture of bags with drainpipe. in FIG. 1 is presented, by way of example, such a bag. The bag is marked with the numerical mark 10, it has a rear portion 11, a longitudinal joint 12, a lower connection 13 and a joint, upper 14. Note the emptying beak noted with 15, entering 17 and the corresponding connection 1G. What you see is the back side of the bag.

During the process of forming and filling the bags of the type of fig. 1, in a first technological phase, the foil is transformed into a tube by overlapping the edges of the foil with □, 1 cm to 1, □ cm for making a joint. the joint then passes between the ultrasonic transmitter and the nicovala of a longitudinal ultrasonic welding device. the joint now being between the ultrasonic and nicovalve transmitter, the thermoplastic material in the joint is heated and welded by applying pressure and using ultrasonic energy near the ultrasonic and / or nicovale transmitter. Preferably, the pressure is applied to the ultrasonic transmitter. After this phase, the film took the form of a tube. As the side joint is welded, the upper joint of the bag is formed and it is welded by a lower bag. It is also recommended that at this moment the drain bag of the lower bag be formed as well as the bottom joint of the next bag. This is done because the foil is immobile and, in order to increase the efficiency of the method, it is considered possible that the foil be subjected to more than one operation simultaneously. It is thus possible to execute at the same time, but at different bags, a lateral weld, a higher weld and a lower weld at the drain. The upper welding and the one related to the drainage bore are made by means of a separate ultrasonic welding device, arranged transversely and opposite to the lateral welding device. This transversely arranged ultrasonic welding device performs, in a first technological phase, the operations to bring in contact the inner faces of the tube and then to proceed to the execution of the top and around the joints.

RO 112492 Drainage block; then, after forming the joints, by applying pressure and using ultrasonic energy, the top joint of the bag is welded and the drain is formed by welding the surfaces of this profile. The foil now comes in the form of a bag in the upside-down position and open at the top end. In this phase, the bag is prepared to be filled with a product which is, in most cases, in a liquid state. After filling, the filled bag moves from top to bottom and the ultrasonic transverse welding device is put into operation for the next duty cycle. the joint from the bottom of the bag is formed on the bag in a filled state and the respective operation takes place in the next cycle. at the same time the upper joint of the adjacent bottom bag is shaped as well as a weld for shaping the drain bead. In each cycle, after the formation of the joints, the application of the ultrasonic energy is interrupted and the pressure of the nicovale on the ultrasonic transmitter is raised. In this way, the nicovala and the ultrasonic transmitter function as a cutting device for cutting the foil in order to form the emptying beak at the top bag and for separating the sealed and filled bag from the top bag from which the top seam was executed but which was not still full.

In summary, the transverse ultrasonic welding device simultaneously welds the bottom joint of a filled tubular bag as well as the upper joint of an upper bag and, at the same time, forms the draining beak of this upper bag. This technological phase can be carried out simultaneously with other welding phases, given that the foil is immobile. In this way, during this phase of formation-filling, three different welding operations can be carried out in each time interval in which a pause occurs when the film is moving. the side joint is welded to obtain a tube, the top joint and the drain hose are executed at a bag where the front joint was executed in an earlier phase and the bottom joint is welded to a lower bag that has just been filled with that content. After the upper seams and the drain socket at the upper socket as well as the lower socket of the lower socket have been formed, the ultrasonic energy supply is interrupted and the pressure at the contact between the nicovalue and the ultrasonic transmitter is raised so as to obtain the full lower socket separation, of the empty upper bag. The filled bottom bag is then directed to the packing section and proceeds to fill the formed top bag. In the technological phase presented above, as the formation of the transverse joints is formed the emptying beak.

One of the problems that always arise in the case of these bags in the form of a bag is the dirt of the areas around the transverse joints when filling the bag. This dirt is due to the content that is poured into each bag separately. It is due to the spray with the product that is poured into the bag and the drops that come off at the end of the filling process. Since the lower faces of the thermoplastic foil are to be welded to one another, any excessive dirt has negative effects on the integrity of the transverse joints. However, since ultrasonic welding heats the faces of the sheets near the joints and not the thermoplastic foil over its entire thickness, the sealing by ultrasonic welding of the bags is more efficient than under the conditions of other welding techniques. This is due to the fact that the ultrasonic energy is concentrated on the inner faces of the thermoplastic film and can ensure an efficient cleaning of them by removing any traces of dirt before moving to the sealing joint. By this, it is distinguished by radio frequency heating, also known as dielectric heating, where the thermoplastic foil is heated to its entire thickness. In the case of dielectric heating, the energy used for sealing does not focus exclusively on the faces of the thermoplastic joints. Also

RO 112492 Bl is not an energy which ensures the cleaning of the surfaces to be welded together.

in FIG. 2 shows a longitudinal welding device. Both the ultrasonic transmitter 20 and the nicovala 21 can have flat work surfaces. The respective surfaces can be both smooth or one can be smooth and the other textured. Under operating conditions, the surface 22 of the ultrasonic transmitter is located at a very small distance from the surface 23 of the nanowire. If deemed necessary, the nicovala can be cooled by causing water or other fluid to flow through the unit. Also, if necessary, the ultrasonic transmitter can be cooled with an air jet. In this case, each ultrasonic transmitter and device are expected to be all cooled. For this purpose, the nicovale is provided with an inlet port 27 and an outlet port 28 through which the circulation of the cooling fluid is ensured. Even if any of the usual frequencies can be used in ultrasonic welding, it is preferred to use a frequency ranging from about 10 kHz to 70 kHz or, more specifically, from 20 kHz to 40 kHz. The energy is transmitted to the ultrasonic transmitter via an overvoltage-returner 29

The longitudinal welding device has the role of performing welds and does not need to be provided with possibilities for cutting the film. However, when it is desired that the unit can be used also for cutting operations, the nicovala and the ultrasonic transmitter should be provided with contact surfaces of the type shown in the cross section in fig. 3. The angle A of the surface 30 is approximately between 120 ° and 1 60 °, preferably between about 150 ° and 175 °. Broadly, this leads to an internal angle of 20 ° at 6CP. The top face 23 (a) is presented as an edge and is sufficient to ensure sufficient sealing, but at a pressure rise between the ultrasonic and nicovalve transmitter the film can be sectioned.

in FIG. 4 presents the nicovala designed for the execution of the top and bottom joints and those related to the drainage bore in fig. 1. The device is capable of concurrently executing the bottom seam of a lower bag, as well as the upper and surrounding seams of the drain bag belonging to the adjacent upper bags. After these joints are formed, the pressure between the ultrasonic and nicovalve transmitter is raised and the thermoplastic material is cut between the bottom joint of one bag and the upper joint of the other bag as well as the excess material in the drainage zone. The ultrasonic welding device must have sufficient energy to complete the welding operation and to thin the material for further cutting of the thermoplastic sheet.

The shape of these surfaces also allows a thin film. Ultrasonic frequencies between 10 kHz and 70 kHz are preferred, and in particular between 20 kHz and 40 kHz.

The device shown in FIG. 4 represents the nicovala 40 of a transverse ultrasonic welding device. The device is formed by a support plate 41 on which the recess 42 supports for welding the top and bottom joints and the recess 43 for welding the joints belonging to the drain. Each of these niches is slightly raised above the surface of the motherboard. The welding plate 42 has a surface 44 which contacts the corresponding surface of the ultrasonic transmitter, and the plate 43 has a surface 45 which contacts the corresponding surface of the ultrasonic transmitter. The base plate can be cooled by means of a cooling fluid circulating through the plate between the holes 46 and 47

The contact surfaces 44 and 45 are edge-shaped and effectively ensure welding and then sectioning the film. In view of the intended sealing effect, edge-shaped sections should be adopted for these surfaces. The shape of the niches in this ultrasonic welding device is shown in detail in FIG. 5. The outer angle A of the recess with the horizontal axis which, in fig. 5 coincides with the support plate, is about 120 ° to 1 60 ° and preferably about

RO 112492 Bl

135 ° to 15CP. This leads to internal angles of about 2 ° to 60 ° and preferably from about 30 ° to 45 °. The nippers are shaped so that they ensure an effective sealing and an effective section of the foil after welding. During the welding operation, the pressure between the nylon and the ultrasonic transmitter is about 10 kg / cm ² to 50 kg / cm ² . In order to cut the film, this pressure increases from about 20 kg / cm ² to 100 kg / cm ² . The increase in pressure is a function of the pressure used during welding operations. The lifting of the pressure can be achieved by moving the nicovale to the ultrasonic transmitter or by moving the ultrasonic transmitter to the nicovalone.

in FIG. 6 shows a complete cross-section through such an ultrasonic welding device by means of which the welded joints from the top and bottom of the bag as well as those from the drainage bore area are executed. The welding device consists mainly of the assembly called nicovalas 40 and the ultrasonic transmitter 35. The device serves to execute the welded joints from the top and bottom of the bags as well as the welded joints from the drainage area. The ultrasonic transmitter has the flat surfaces 36 which come into contact with the profiled surfaces 44 and 45 of the nicovale. The ultrasonic energy is transmitted from the overvoltage-returner 37 to the ultrasonic transmitter. As mentioned above, it is preferred to give the ultrasonic transmitter and not the specific shape suitable for the purpose of performing the film sectioning operations. The ultrasonic or nicovala transmitter should be profiled accordingly to perform the function of cutting the foil after welding. If the ultrasonic transmitter is the element that takes over the sectioning function of the foil, the contact area 36 of the ultrasonic transmitter must be in the shape shown for the nylon. In this case, the nicovala will have a flat surface.

Ultrasonic transmitters can be made of titanium, Monel alloys, aluminum alloys or aluminum alloys. Titanium is a metal that is well suited for the execution of ultrasonic emitters. Nicovala can be of the same metal or of a metal different from the one from which the ultrasonic transmitter is made. Nicovala can also be made of stainless steel. It is necessary that the nicovala has a low degree of wear.

in FIG. 7 is a preferred embodiment of a filling system. With the help of this type of forming-filling system the bag shown in fig. 1 is formed and filled in the inverted position. first, the drainpipe and the upper joint, ie in the lower area of the tube, are formed, then the partially formed bag is filled, after which the bottom joint is executed. This technology was adopted because of the need to form the bag and the drain so that the bag can then be filled after the drain is executed. The sheet 51 runs from the feed drum 50. The sheet is then taken up by the stretch drum 52 and the guide rollers 53 and 54, then passes over the drum 56 and is directed down to the forming-filling section. In element 57 the foil is formed with an open tubular profile. The element 57 rests on the filling pipe 59 which is supplied with the product to be packaged, usually a liquid product provided by the supply pipe 58. The open profile sheet passes along the supply pipe 58 and reaches section 60 where the longitudinal joint is formed and welded. In this welding section, guide 61 guides the foil to a profile and when it reaches the ultrasonic longitudinal welding device, the overlapping edges form the joint ready for welding. The longitudinal ultrasonic transmitter 63 is supplied with ultrasonic energy from the transducer 62. Nicovala rests on the filling pipe 59. The sheet, which now has a tubular shape, leaves the longitudinal welding section 60 and moves down with the help of the regulator 64. The regulator 64 moves foil and stop it with ends

EN 112492 Blends for welding, cutting and filling operations. This regulator is equipped with driving rollers 65 which ensures the movement of the film.

In the area under the regulator, the tube is welded transversely to the device 67. The operation is performed by the lower welding device shown in Figures 4,5 and 6. This inferior welding device performs the top welding and the drainage bore on the tube, obtaining there is an open bag at the top end. This bag is in the upside down position. at the same time, the bottom bag that was filled is welded to the bottom. These operations are first performed by the reciprocal pressing of the ultrasonic transmitter and the nicovale followed by the application of ultrasonic energy. In a second phase, by raising the pressure between the ultrasonic and nicovalve transmitter and without applying the ultrasonic energy, the sectioning of the foil for separating the bottom pouch is performed, as well as the sectioning of the foil to obtain the emptying beaker at the top bag. In this phase, after the top welding is completed and the drain hole is formed, the bag is filled through the mouth 66 of the filling pipe 59. After the filling phase, the filled bag moves down and the transverse welding unit performs a new cycle during which the bottom of the bag is soldered as well as the top weld and the beak of another bag.

As pointed out, the foil goes through an intermittent technological flow. The continuous movement of the foil is interrupted for welding operations and for filling the bags. Thus, whenever the movement of the film is interrupted, the longitudinal ultrasonic welding device 63 and the transverse ultrasonic welding device 67 simultaneously enter into operation. Also, when the movement of the film is interrupted, the bag that was formed is filled.

In principle, any kind of film that can be welded by ultrasonic energy can be used to manufacture these bags. The various thermoplastic sheets can be either amorphous or crystalline. The appropriate types of foils include those based on acrylic copolymers, phenylene oxide, polycarbonates, polystyrene as well as cellulose sheets. In general, crystalline resins do not weld as easily as amorphous resins by ultrasonic welding. Flexible sheets are preferred. However, acetal resins, fluorinated polymer resins, nylon resins and polyester resins can be used under ultrasonic welding techniques. Preferred are the films which include in their composition at least one layer of ethylene vinyl acetate. The other layer or layers may be polyolefins such as polyethylene, polypropylene, polybutylene and polybutadiene.

In principle, the bags obtained by applying the presented ultrasonic welding techniques can have any size. However, the preferred dimensions are between approx. 50 cc and approx. 2 liters. These are the dimensions that can be handled conveniently from the point of view of the packaging technique. Products packaged in these types of bags can be body care products, household products as well as food products. In the category of body care products include liquid soap, shampoo and various lotions. The category of household products includes various cleaning and polishing products, fabric bleaching products and various types of soaps for general use. The food category includes various sauces for steaks, fruit flavor extracts and the like.

Example 1. In this example, the forming and filling operations of the bags are detailed using the forming-filling apparatus of FIG. 7.

The coextruded sheet 51 of polyethylene / ethylene vinyl acetate, having a thickness of 0.20 mm and a width of 16 cm, is provided by the feed drum 50 and directed to the device for forming and filling the bags with the help of rollers 52, 53 , 54 and 56. The foil is fed in the form of a continuous strip 51 directed to the forming-filling device. As it passes through the upper formation die 57, the foil acquires a tube shape

RO 112492 Bl

The year whose longitudinal joint is presented with overlapping edges. The edges of the film overlap about 1 mm. The film then passes between the G3 longitudinal ultrasonic transmitter and a fixed part. The applied pressure is about 40 km / cm ² . During this operation, the continuous movement of the foil is interrupted. The longitudinal joint is executed by fixing the edges of the foil between the longitudinal and nicovalve ultrasonic transmitter (as shown in Fig. 2) and applying ultrasonic energy at the frequency of 2Q kHz. At the same time, the transverse joints in the bottom of the tube are executed as well as the drain hose. The latter is executed with the aid of a G7 device (shown in Figures 4 to 6) consisting of a transverse ultrasonic transmitter and a mobile nicovalone. Simultaneously with the execution of the top joint and the emptying spout of this bag, the joint from the bottom of the bottom bag that was previously filled is executed. An ultrasonic frequency of 35 kHz is used to perform these joints. During the welding, a pressure of approximately 40 kg / cm ² is applied between the transverse and nicovalve ultrasonic transmitter. After executing the side and top joints as well as the drainpipe belonging to the newly formed bags with the bottom still knotted, it is filled by introducing a quantity of 250 cc of bleach. The lower bag at which the closing weld was performed is separated by sectioning and directed to the packaging sector. The sectioning operation is performed by lifting to about 90 kg / cm ² the pressure exerted by the ultrasonic transmitter on the nicovale. Ultrasonic energy is not used in this phase. In this way, a manufacturing cycle is completed which is then repeated identically.

welded joints, executed on a representative lot of bags, are tested under pressure. The pressure test device consists of a fixed and a movable plate. The sample is placed between the two plates and the pressure applied to the bag is raised. A burst pressure of more than 150 kg indicates a filling under acceptable conditions. Usually, the bags comfortably exceed this limit.

Claims (13)

1. Method of manufacturing the bags, using the ultrasonic welding technique, characterized in that it consists in the partial tubular formation of the flexible sheet as a bag, with a portion of the edges overlapping 0.1 to 1.0 cm; applying an ultrasonic energy for watertight welding with a frequency between 10 and 50 kHz and a pressure of 10 to 70 kg / cm ² on the superimposed portion; sealing with the help of ultrasonic energy, the lower portion of the tube; filling the bag with liquid substance; tightly seal the filled bag with a contact pressure of 10 to 70 kg / cm ² and ultrasonic energy with a frequency of 10 to 50 kHz and section the bag with a pressure of 20 to 100 kg / cm ² . The method according to claim 1, characterized in that the flexible foil has at least one insert which can be welded itself, using ultrasonic energy. Method according to claims 1-2, characterized in that the flexible foil has at least one layer of pollen and one layer of ethylene-vinyl acetate. Method according to claim 3, characterized in that the pollen layer is selected from the group consisting of polyethylene, polypropylene, polybutylene and polybutadiene. Method according to one of claims 1-4, characterized in that the flexible foil is fed as a continuous foil, shaped in a tubular, continuous and watertight form. Method according to one of claims 1-5, characterized in that, during the sealing step of the lower and upper portions of the bag and during the sectioning thereof, the flexible foil is stationary. Method according to claim 6, characterized in that, after the sealing step of the lower portion, a beak is formed by cutting the excess film. RO 112492 Bl 8. Method according to claim 7, characterized in that the bag with liquid substance is filled by maintaining the filling mouth above the liquid level in the bag and actuating the suction elements when the filling operation ceases. Method according to claim 8, characterized in that the liquid substance for filling the bag is selected from the group of detergents, bleaches, soaking agents and lotions. 10. A bag manufacturing plant according to the method of claims 1-9, characterized in that it is composed of an element (57) for molding the sheet in the form of a tube; a longitudinal welding device (63) comprising an ultrasonic transmitter (20) and a nicovalve (21) having molded surfaces (30), either on the transmitter or on the nicovalve; some positioning elements (22, 23) of the film; drive elements (29) of said device (63); some filling elements of the bag; a transversal welding device (67) located after the longitudinal welding device (63) and comprising an ultrasonic transmitter (35) and a nicovalve (40), these having a shape that allows the film to be cut with high pressure; drive elements (37) of the device (67). An installation according to claim 10, characterized in that the molded surfaces (30) are preferably on the recess (21) and have a triangular shape in section, with the outer angle from the base from 120 ° to 175 °. 12. Installation according to claims 12-13, characterized in that the bag filling elements consist of an elongated tubular element (59) provided at the upper end with a feed pipe (58) and at the lower end with some suction elements. An installation according to claim 12, characterized in that the element (57) for forming the molding is a formator which fills the cross-section of the flexible foil bag.