MXPA99007240A - Easy-mount sealing element for packaging machines - Google Patents

Abstract

A heat sealing element (13) and related self aligning support jaw, for sealing at least two layers of thermoplastic film is disclosed. It may be used with a vertical form, fill and seal machine for packaging flowable materials, e.g. milk, chocolate fudge, or sundae topping, in pouches. Each end of the heat-sealing element has a plug which is preferably cylindrical, both pointing in the same direction, adapted to fit into spring-loaded sockets (14) which are slightly larger than the plugs, with openings toward the element. This permits unspringing the sockets and inserting the plugs, then letting the springs apply tension force to hold the elements taut.

Description

SEALANT ASSEMBLY ELEMENT FACILITATED FOR PACKAGING MACHINES FIELD OF THE INVENTION The present invention relates in general to film packaging equipment which periodically heats two or more films (or edges of the film) when the film is moved through a sealing station with heating. More specifically, the present invention is directed to an innovative facilitated mounting arrangement in which the heat sealing element can be safely changed and aligned with minimal effort.

BACKGROUND OF THE INVENTION Generally speaking, machines for "forming, filling and sealing, vertically" are well known and can be used, for example, for packaging milk in plastic bags. More recently, such packaging has been used for other flowable materials, such as mayonnaise, caramel, scrambled eggs, tomato sauce, chocolate candy, salad dressings, preserves and the like, REF, 31041 particularly for the market of users of institutions, that is, restaurants. In operation, such forming, filling and sealing machines, in a vertical manner, generally unwind a flat continuous roll of a synthetic thermoplastic film and then shape the film into a continuous tube by sealing the longitudinal edges with a coating seal or seal of fin. In general, the tube is then moved down to a station for filling. A sealing device below the filling station then creates an air-tight thermal seal through a cross-section of the tube, using a pair of sealing jaws. The material to be packaged will generally be introduced to the tube continuously, and therefore the film is generally sealed while some of the material is present between the surfaces for heat sealing in the tube. After the sealing operation has been completed, the jaws are generally opened and then the tube is caused to move down a predetermined distance. Such downward movement may be influenced by the weight of the material in the tube, and / or by a pulse mechanism in communication with the tube.

Once the tube moves down a predetermined distance, the jaws for heat sealing are closed once more to create a second transverse seal. Almost simultaneously, the second transverse seal also cuts the filled portion with the tube material, whereby a sealed bag of the material is created. The second transverse sealing operation also simultaneously creates the bottom seal so that the next bag is formed. One such form, fill and seal machine, of a vertical shape, of the type described above, is sold under the trademark PREPAC. Another filling and sealing equipment, in a vertical manner, causes the material to be packed to introduce the tube intermittently. In such cases, the material is introduced into the tube only after the jaws have closed to form the first transverse seal. The jaws then open, and the tube is moved down a predetermined distance. Then, before the second seal is made, the flow of material is stopped, so that the material will not be located between the surfaces for heat sealing in the tube. In other conventional machine designs, the sealing device does not cut the tube when the second seal is made with transverse heat, but instead, the tube is subsequently cut at a separate station. With still other machines, the heat sealing jaws move with the film as it moves downward, and then release the film at a predetermined distance. The jaws are then moved upwardly back to their original position to reattach the film. With such machines, the jaws secure, seal and cut the film tube while moving in the downward direction. The jaws then open and uncouple from the film and return to their original, upright position. The downward movement of the closed jaws also serves to advance the tubular film downwardly. The present invention relates to a heat sealing assembly for any of the aforementioned machines. Conventional "pulse sealer" devices utilize brief shocks of electric current to create sealing temperatures for only a fraction of the cycle time between operations.The pulse sealer may be a round wire, for example a "wire". piano "of approximately 2.0 mm to 2.29 mm in diameter, electrically insulated from a water-cooled support jaw Alternatively, the impulse sealant can be wound from the material in wire storage onto a ribbon or flat ribbon having a longitudinal flange in the center of a side referred to thereafter as a "solid flanged element." Impulse sealers having a round wire or solid flanged element are generally combined with flat, conventional, opposing heat sealing jaws and this design generally It will be satisfactory for forming and filling machines for packing milk, water or other ros highly aqueous products. Other forms of elements are generally more satisfactory in forming, filling and sealing machines when packing thick, flowable materials, such as mayonnaise, chocolate candies, scrambled egg mixes, dressings, jams and the like. Examples of other conventional sealants are described in U.S. Pat. No. 3,692,613, which was issued to R.E. Pederson, Pat. U.S. No. 4,115,182 which was issued to M. M. Wild oser and U.S. Pat. No. 4,744,845 which was issued to J. Posey.

Generally speaking, the element for heat sealing must be electrically isolated from the metal clamp on which it is mounted. Additionally, the element for heat sealing is also frequently thermally isolated from the jaw. Typically, this is accomplished by placing a woven glass cloth which is impregnated with polytetrafluoroethylene (PTFE) between the jaw and the heat sealing element. The heat sealing element must be heated quickly when it comes into contact with the film to be sealed. Several problems with the initial prior art have been solved, as represented by U.S. Pat. 5,538,590 - Riley (July 23, 1996) and 5,415,724 - Perrett (May 16, 1995), both of which are incorporated herein for reference. A further problem is the difficulty of changing and replacing the sealing element with heat and aligning it exactly so that the seal is properly made. The change of the elements needs to be done in a regular manner, such as daily, in a high-speed, high-capacity operation, which could be found, for example, in large dairy operations. The glass cloth impregnated with PTFE such as that sold by DuPont Company as "Teflon", used up and down the element as in U.S. Pat. 5,538,590, it is subject to wear and has to be replaced when it is no longer effective in an adequate manner.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a heat sealing assembly for sealing at least two layers of thermoplastic film, comprising first and second jaws, a heat sealing element, electric impulses, electrical terminals, and an electrical and thermal insulating material between the first jaw and the heat sealing element, the heat sealing element is removably connected to said electrical terminals, at least one of said jaws is capable of transverse movement and is adapted to crush a tubular film made of the thermoplastic film and passing it between the jaws, wherein said element has at each end a male electrical contact plug oriented at approximately a 90 degree angle of said element, the plugs are parallel to each other and have curvilinear surfaces facing each other which approach a cylindrical shape, each of the electrical terminals comprises plugs They have a shape and size slightly larger than that of the pins, with an opening facing the element, and the plugs are retained by means of spring adapted to apply a tension force to said element when the plugs are in said plugs , the plugs which are adapted to fit the plugs when the spring means are bent (flexed) towards said element. In the preferred embodiments, the spring means are flat springs with their broad sides that are parallel to each other, each being fixed to the opposite ends of a cooled heat dissipating block, and the opening in each plug is at least one 15 ° arc to allow increased force on the connections with the pegs to facilitate the cleaning capacity. Also, the heat sealing element is one embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of the invention, showing the heat sealing element in place in the assembly. Figure 2 is an elevation of the same object as Figure 1.

Figure 3 is a plan view of a plug of the invention. Figure 4 is an elevation of the same object as Figure 3. Figure 5 is an elevation of a heat sealing element of the invention, separate from the assembly. Figure 6 is a side view of a preferred flat spring for use with the invention. Figure 7 is a front view of the same object as Figure 6. Figure 8 is a perspective view of a heat sealing assembly, usually commercial.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES A common commercial design of the horizontal sealing bar or jaw 1 is shown in Figure 8. It uses a pulse sealing cycle, ie there is a discharge of sealing energy that lasts approximately 220 milliseconds when the jaws are closed. The filler makes a bag each time the jaws close which is about once every second. The heating element 2 is an electric resistance wire of 17 AWG "Chro" C rolled up to a special shape to promote sealing and cutting completely in a closing action of the jaw. Chromel C is the registered trademark of Hoskins Manufacturing Co. Another useful wire is "Tophet" Alloy C made by Carpenter Technology Corp. These are nickel-chrome electrical resistance wires that conform to ASTM B-344. The active length of the element is preferably approximately 200 mm. The heating element can operate at a temperature as high as 300 ° C and this causes a substantial thermal expansion. This thermal expansion is absorbed by the springs 8 which are tensioned when the element is secured in place by end joining posts 7. The heating element is thermally and electrically insulated from the aluminum sealing bar by two layers of fabric. 3 and 6 fiberglass coated with PTFE. Another layer of coated glass fiber cloth 5 is placed above the surface of the element to help retain it in place and to act as a release sheet when sealing with heat. The fabric is often in the form of an adhesive tape. Although PTFE is an excellent release agent, it is quite soft or soft and will wear out in this service. Therefore it becomes necessary for the operator to periodically replace the layers of the upper and lower tape. This is a job that requires some experience for the operator who must provide the heating element properly aligned and flat against the sealing bar, the correct amount of tension in the springs and the tapes properly applied. Improper gag service will likely lead to leaking seals. What is more difficult to do is provide the flat element against the sealing bar 4 and this is more critical. An improperly aligned element will quickly develop a hot spot which will cause premature failure of PTFE coated fiberglass tape which will lead to sealing problems. This type of sealing jaw service should be done at least once a day in a dairy filler, and many filler operators find it difficult, particularly new operators. The openings 9 for the cooling water are provided in the jaw 1. The improvements to the sealing jaw which will now be described, are an attempt to provide service to the sealing jaw in an easier manner and less prone to improper installation. and therefore the potential for "leaks or leaks".

APPARATUS OF THE INVENTION The apparatus of this invention is shown in Figures 1 and 2, with the parts in Figures 3-7. This is a direct replacement for the clamp 1 shown in Figure 8 and can indeed use the same basic parts of the sealing bar or clamp 1 and 12. The L-shaped end springs 8 have been replaced by helical beam springs 11 in cantilever, brief, to which stainless steel plugs 14 have been fixed. Each plug 14 contains a through slot 25 in the form of a keyhole. The heating elements 13 have generally cylindrical pins 15 on the ends that are sized to fit snugly in the grooves 25 of the keyhole at approximately right angles to the wire (heating element) 13. The springs 11 are bent slightly outwards so that it is necessary to bend them (bend them) together so that the cylindrical pins 15 fit into the grooves 25. The deflection of the total spring is up to about 3 rnm. This is sufficient to accommodate the thermal expansion of the element during a heating cycle and still maintains the tension in the element. The plug 14 is held in place and electrically isolated from the spring 11 (and the rest of the jaw 12) by a notched insulating part 15 which fits or adapts around the spring 11., a bushing or bushing with protrusions 16, and locating hole 27 in the spring 11. The plug has the threaded stud 21 which passes through the insulating parts 15 and 16 through a hole in the bushing or bushing 16, which passes its smallest diameter through the hole 27 in the spring 11. The insulating parts 15 and 16 are held together by the flat washer 20 and a hexagonal nut 31. Then, the heavy electric cable 17 which supplies the energy to the jaw is secured to this stud 21 by the fixing washer 19, the flat washer 20, and a threaded plug 18. As in the common design, the active length of the element is electrically isolated from the sealing bar by two layers of fiberglass tape coated with PTFE under the element, with another layer on top of the top layer, to act as a release sheet, similar to 5 and 6 in Figure 8. The design of the slot 25 in the plug is very important. For the described sealing jaw 12, a current of about 40 amperes is needed during the pulse heating cycle to generate the temperature necessary to heat seal and cut the bags. This requires a fairly strong or rugged electrical connector. A good design of the electric heater requires a high force between the connecting parts to keep the contact resistance low and prevent heating. However, because of the thinness of the wire of the heating element and the difficulty of handling it, a great force can be exerted to insert or remove the plug in the plug without the risk of bending or damaging the wire. This problem was overcome by making the width of the slot 25 in the plug 14 almost equal to the width of the pin 15. The short coil springs are quite rigid and require good force (bending moment) to bend them. Once the plug 15 has been inserted into the plug 14 and the spring 11 has been released, the force of the full spring comes to rest against the support or projected area of the receptacle 14, which was reduced by making it wide to the slot 25. The resulting voltage between the plug 15 and the plug 14 is thus raised, just what is needed for a low contact resistance. But the slot 25 is not so wide that the plug 15 actually jams in the slot 25. Accordingly the plug 15 can be easily inserted or removed from the plug 14 without excessive force by simply bending (flexing) the spring 11 to take the pin 15 without strength. The high tension between the plug 15 and the plug 14 effectively causes oxidation on the surfaces to be removed by scraping when the plug 15 is pushed down towards the plug 14. There is a classic problem with the design of electric heater at the ends of the heating element. Because of the inherent electrical resistivity of the heating element, the heat will be generated directly at the end of the wire. But somehow eventually you should connect the resistance wire to a lower resistance conductor and take care of the heat. The best conductors of low resistance and almost universally used are copper or copper alloy but they do not tolerate high temperatures either. In general, the electrical connections must be kept relatively cold to avoid oxidation of the surfaces and high contact resistance. Once an electrical connection begins to deteriorate, it can get worse quickly. A poor connection generates heat which in turn causes additional oxidation and deterioration of the connection which in turn generates even more heat. In this design the problem is overcome by the plating of the ends 22 of the element wire with copper or silver. The plating, if thick enough, eliminates effectively the resistance of the wire near the plug and socket connection and keeps it relatively cold. The plating needs to cover the length of the wire of the element 22 between the end pin and the sealing bar 12. It is also desirable that the plating be even longer so that it continues on the active side of the sealing bar 12 over a short distance . The reason for this is that the sealing bar 12 is cooled with water and operates at or near room temperature. Accordingly the length of the veneered element 22 which is superimposed on the sealing bar 12, provides a path for heat to escape from the end of the hot or non-plated part 23 of the element wire and reduces heating of the connector by thermal conduction down the wire. Although copper and silver veneers work well, coating the element wire with silver solder is another good way to reduce electrical resistance or heating over the ends. Silver welding tolerates high temperatures well. However, due to its higher electrical resistivity, a thicker coating is required than for copper or silver. Superimposed on all of the other design issues is the sanitary requirement that the main assembly can be easily cleaned. The horizontal jaw on a form, fill and seal filler in vertical form, is just below the nozzle of the filling tube. Any problems with the filler which allow product leakage will likely mean that the product will spill onto the horizontal jaw. In a dairy, this situation is usually cleaned with a spray of hot water. At the end of a production day, the filler is cleaned again with hot water and cleaning and sanitary solutions. There should be no cavities to trap milk, water or cleaning chemicals. The preferred material of construction in a dairy filler is stainless steel of the 300 series and certain approved plastics. Threaded fasteners exposed are undesirable. An examination of the apparatus of this invention will show that the design is easily cleanable and that the stainless steel has been used for the plug 14, the worm wheel 11 and the fasteners 18, 19, 20, 21 and 31 and the insulators 15 and 16 are made of resin, such as vinyl acetal. The threads on fasteners 18, 21 and 31 are all covered. Brass has been considered acceptable for the pins of element 15 because the elements are removed daily to provide the service. The elements also have a finite utility life of several days so that any deterioration of the brass surface over time is not important. There are few commercial, high capacity electrical connectors. Which satisfy the sanitary requirements. The main feature of the device is the ease of installing the elements correctly. To install the element in the jaw, the operator inserts a plug 15 into a slotted plug 14 and then, while bending (flexing) the spring 11 over the opposite end, the remaining plug 15 is inserted into its socket 14. Does not exist force applied to the element so that it is not distorted in any way. Once the pins 15 are in the plugs 14, the operator then pushes them to the "base position" until the element rests flat against the active face of the sealing bar 12. There is no "waste" and "adjustment" which is required with the common design to provide the flat element downwardly against the sealing bar 12.

Example 1 The pins on the ends of the heating element are made of a common yellow brass rod 0.635 cm in diameter and are 15 mm in length. Plugs are made of 304 stainless steel and the hole is enlarged to 0.6388 cm. The slot in the plug is 4.50 mm wide. The element is wound on a flanged band of 2 mm wide 17 AWG Chromel C wire and 10 mm on each end are coated with silver solder. Using the techniques described in ASTM B359-90"Standard Test Methods for Measuring Contact Resistance of Electrical Connections", the element resistances and the plug / plug connector measured approximately 0.4 to 0.5 milliohms. The 10 mm silver solder coating measured approximately 7 to 8 milliohms. The apparatus was installed on a filling machine, not shown, with a minimum required effort to install it. In a test bags of 1-1 / 3 liters of water are made at 6 ° C to 47 bags per minute, the temperature of the plug rises to an equilibrium temperature of about 75 ° C after 20 minutes. The electrical impulse to seal the bags was approximately 39 amps at a duty cycle of 22%. With the measured resistances, the wasted heat generated by the plug connection was considerably less than 1 watt. After the test there was no evidence of thermal or electrical voltage at the plug / plug connector. The rise in temperature was mainly due to the heat generated in the silver solder coating and due to the conion of the active length of the element.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, property is claimed as contained in the following

Claims (8)

1. A heat seal assembly, for sealing at least two layers of thermoplastic film, characterized in that it comprises first and second jaws, a heat sealing element by electrical impulses, electrical terminals, and an electrical and thermal insulating material between the first jaw and the element of heat sealing, the thermal sealing element is removably connected to the electrical terminals, at least one of the jaws is capable of transverse movement and is adapted to crush a tubular film made of the thermoplastic film and passing between the jaws, where the element has at each end a male electrical contact pin oriented at an angle of approximately 90 degrees from the element, the pins are parallel to each other and have curvilinear surfaces facing each other which are of approximately cylindrical shape, each of the terminals electrical systems comprising female plugs that have a shape and size slightly larger than that of the pins, with an opening facing the element, and the plugs are retained by means of spring adapted to apply a force in the tension to the element when the plugs are in the plugs, the plugs are adapted to fit into the plugs when the spring means are flexed towards the element.

2. The assembly according to claim 1, characterized in that the spring means are flat springs with their wide sides that are parallel to each other, each being fixed to the opposite ends of a cooled heat dissipating block.

3. A heat sealing assembly according to claim 1, characterized in that the opening in each plug is at least one 15 ° arc to allow an increased force on the connections with the pins and to facilitate the cleaning capacity.

4. A thermal sealing element adapted to be removably mounted in a clamp of the heat sealing assembly of claim 1, by the connection to the electrical terminals thereof, characterized in that the element has at each end thereof, a male electrical contact plug oriented approximately 90 ° with respect to the element, the male plugs are parallel to each other and have curvilinear surfaces facing each other which approach a cylindrical shape, the male plugs are sized and shaped to be easily received in and easily removed from pegs slightly larger female on each of the electrical terminals, the male plugs and female plugs are fixed or secured together by spring means that apply tension to them when the element is mounted on the jaw, thus ensuring a good electrical contact, and during flexure release the resort e allows the disassembly of the jaw element.

5. The element according to claim 4, characterized in that the pins and the portions of the element adjacent to the pins are covered with a material that conducts electricity.

6. The element according to claim 5, characterized in that the material is silver.

7. The element according to claim 5, characterized in that the material is a silver solder.

8. The element according to claim 5, characterized in that the material is copper.