NZ205834A - Preheating can lids before sealing compound is applied - Google Patents

Description

205834 Priority Date(s): Complete Specification Filed: -3s1.

Class: && & /,. /$& &J J Jj, PubBcrton Date: ... „ .

P.O. Journal, No: .. &'*NI 04 _3QSEn98S Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "IMPROVEMENTS IN AN INSTALLATION FOR LINING STEEL -AND/OR ALUMINUM ENDS WITH A SEALING COMPOUND" I,WE W.R. GRACE & CO., a Connecticut Corporation of „/L. .S forte o-P CrzlV-O o 62 Whittemore Avenue, Cambridge, Massachusetts/, Ohio,U.S.A. hereby declare the invention, for which i-/\ae pray that a patent may be granted to ine/us, and the method by which it is to be performed, to be particularly described in and by the following statement -1- (followed by page 1A.^ •») 205834 The present invention pertains to an installation for sealini steel and/or aluminum lids for cans with a sealing compound, which is used in the manufacture of cans.

Traditionally, metal cans for beverages, foods and other products have been fabricated from a cylindrical body over which are clamped two closing elements (generally known as can lids), one at each end. The manufacturer of the can clamps on one of th< lids of the can and sends the empty cans and the lids for the tops of the cans to the packer. When the cans have been filled with the product, the packer clamps on the other lid. In recent years, so-called two-piece cans have been introduced to a great extent. With this type of can, the body and one of the lids are formed of a single piece by means of a process of drawing and shaping the wall or of drawing and re-drawing, such that only one lid is required for the can. In any type of can, the can lie provides a hermetic seal for the body of the can, in order to prevent the entry of bacteria or the leakage of the contents of the can. In order to obtain said hermetic seal, it is necessary to coat the channel of the can lid with a materia] (generally known as a sealing or hermetizing compound) . This operation is performed by the can manufacturer during the process of manufacturing the lids. The material is applied to the channel of the can lid in liquid form, by injecting it'into the channel, when the latter is turning at high speed so that the centrifugal force permits proper distribution of the sealing compound in the lid channel. 2 0 5 83 4 Sealing or hermetizing compounds may be of two types, which are conventionally known as water-based compounds and solvent based compounds. The water-based compound consists of a dispersion of the components of the material in water, and the solvent-based compound consists of a solution of some of the components and a dispersion of others in an organic liquid medium, usually hexane.

When the lid of the can has been sealed with the liquid compound, it is necessary to separate the liquid phase in order to obtain a solid seam. In the case of solvent-based compounds, this is done simply by leaving the hexane to evaporate under / ambient conditions. In the case of water-based compounds, traditionally, the sealing compound has been dried by application of heat, by passing the previously sealed lids through some type of oven. Generally, two types of ovens are employed, which are known as tunnel ovens and vertical ovens.

The tunnel oven consists of a long oven heated by hot air, which usually comes from a gas burner, with a conveyor belt passing through the oven. Stacks of lids are placed on the belt, and they are conveyed through the oven, usually with a residence or elapsed time of approximately 20 minutes. At the oven outlet, the stacks of lids are separated by hand and stored in any suitable manner for internal use in the plant or for shipment to the packer.

The screw oven consists of pairs of endless rotating screws which are arranged vertically and contained within a hot-air oven. The can lids are fed from the sealing machine where the ■ " * 2 0 5 8 3 4 compound has already been automatically applied^ to the endless screws, and the gyratory movement of the latter conveys the lids vertically, with the lids being separated by the pitch of the thread of the screws. The residence time in a screw oven is generally 4 minutes. The customary length of the vertical screws is that required for providing a transport time of 1 min fc each can lid from the bottom to the top of the screws. Therefore, ovens of this type generally have four sets of screws, with alternate right-threaded and left-threaded sets. The can lids are mechanically transferred from the end of one set of screws to the beginning of the following set. At the oven outlet, the lids are fed automatically to be stacked according to a determined arrangement, from which they are transferred manually for use in the plant or for shipment to the packer.

The tunnel type oven is mechanically very reliable, since it consists simply of a conveyor belt which passes through the oven, but it requires a great deal of manpower due to the fact that the stacks of lids have to be loaded manually at one end f and collected at the other end. The screw-type ovens do not require as much manpower, but on the other hand, they are very susceptible to mechanical breakdowns, mainly due to the mechanism for transferring the can lids from one set of screws to the next set. These mechanical problems represent lost operating time, and thus reduce the overall efficiency of the can lid manufacturin process.

In the case of solvent-based compounds, they do not require any type of oven, since the lids are automatically transferred 1.

V 205834 from the sealing machine to a short conveyor system, and from the conveyor, the lids are transferred manually to any form of packing which is suitable for their use in the plant or for shipmer to the packer. Most of the organic solvent is evaporated while the can lids are on the conveyor system, and the small quantity which remains evaporates during storage.

From the above description, it will be evident that the solvent-based compounds are the most suitable type of compound for use from the standpoint of the can manufacturer. However, the presence of the organic solvent constitutes a problem for those countries which have laws concerning environmental toxicology and safety conditions in the workplace. Obviously, there is hexane vapor in the atmosphere surrounding the coating machine, and the permissible concentration of hexane in the air is the subject of legislation in many countries. Furthermore, in many countries there are limits concerning the quantity of organic vapor which may be emitted from a plant, such as that coming from solvent-based lacquers and can-sealing compounds. Therefore, many countries are turning away from the use of solvent-based compounds. However, there is considerable resistance on the part of the manufacturers, with respect to changing over to ovens, with the above-mentioned associated problems, for drying water-based compounds. In addition, even those can manufacturers who generally use water-based compounds with conventional ovens obtain a considerable advantage if they can do without these ovens.

In view of these considerations, a new type of water-based compound with a high content of solids has been developed which 205834 u can be dried without the use of an oven, and which also provides a seam with all of the characteristics for hermetically sealing a can satisfactorily. However, in spite of the fact that this compound can be air-dried, the time required to dry the seam depends to a great extent on the ambient conditions in the can manufacturing plant, i.e., the temperature and relative humidit of the air, and the method by viiich the can lids are packed and stored after the sealing operation Due to this limitation, the invention pertains to a process developed to eliminate this uncertaint concerning drying time without using a conventional oven. This process thus combines the advantages of easy handling of a solvent-based compound, with the advantages of a water-based compound with regard to toxicity and environmental contamination.

The basic concept of this process consists in heating the lids before they are sealed, such th&t the compound is applied to a pre-heated lid. If the lid is sufficiently warm, some of the water present in the compound is evaporated immediately upon applying the compound to the lid, and most of the water is evaporated as the lids are transferred along the conveyor system, which is similar to the one used with the solvent-based compound. As a result, when the lids are removed from the conveyor system, and packed for storage, the moisture remaining in the seam is sufficiently low so that the remainder is evaporated during storage within a short period of time.

Due to the fact that the lids are heated before sealing instead of after sealing, as occurs with conventional ovens, the process is known as "pre-heating", and the unit that heats the lids is known as a "pre-heater". It could be concluded 2 05 83 4 ul 1.1 that there is no advantage in heating lids before sealing them instead of afterwards. However, this is not the case. In the conventional process, if the process of drying the sealing compound •occurs suddenly at very high temperature during a short period of time, the compound tends to form blisters. This is due to the fact that the surface of the compound dries first forming a skin which prevents the evaporation of the water from the inside, and therefore, causes the formation of blisters under the skin. Consequently, there is a limit with respect to the rapidity of drying the sealed lids in an oven, which means that there are limits to the temperature to be used. Also, with conventional water-based compounds, it is necessary to make certain that the sealing compound is completely dry when the lids leave the oven. These limitations impose a minimum limit on the size of the oven. However, with the pre-heater unit, and because the lids are not sealed when they are heated, there is no limit to the speed at which they can be heated, and therefoce, the heating can be carried out as rapidly as needed, such that the unit can be manufactured in a completely compact form. The pre-heater unit can be installed over the existing equipment used in sealing the can lids, in place of the machine where the lids are fed to the inside of the machine, which means that no additional floor space is required as in the case of the oven.

Depending on whether the lids are steel or aluminum, two different pre-heater designs are used. In both cases', the lids are heated by the action on them of hot air, wfilfch comes from a fan with the air passing through electrical resisters.

In the case of the steel lids, and due to the low thermal conductivi 2 0 5 8 3^ of steel, it is necessary to separate the lids so that the hot air is blown between them. This is done by using a magnetic hopper. The magnetic hopper consists of a cylindrical stainles steel tube with a set of permanent magnets placed on either sid of the tube. The magnetic field created between the two magnet induces magnetism in the steel lids, such that they repel one another and are automatically separated. The distance between the individual lids may be controlled by means of the separatio of the magnets. The lids are removed from the bottom of this magnetic hopper by the feed mechanism of the sealing machine an* are fed to the sealing station, and at the same time, the lids are fed at the top by a conveyor belt, proceeding from the press which produces the lids. During the passage from the top to the bottom of the magnetic hopper, the lids are heated by hot air which is blown through them.

In the case of aluminum lids, and due to their much greatei thermal conductivity by comparison with steel lids, it is not necessary to separate them, and therefore, the pre—heater for aluminum lids consists essentially of an insulated cylindrical jacket into which the hot air is blown laterally, and then leaves through the top. A series of partitions is used within this cylindrical chamber in order to ensure proper circulation o the air. In both types of pre-heaters, the hot air which leaves the pre-heater can be recirculated again to the blower in order to improve the overall thermal efficiency of the process. 205834 In the case of the pre-heater for steel lids, the transfer of heat from the hot air to the lids depends to a great extent on the separation between the lids. Consequently, in order to ensure good temperature control, it is necessary to control this separation precisely. The normal method of operating the sealing machine, which is supplied automatically with lids from a press, consists in operating the sealing machine at a speed slightly greater than that of the press. For example, if the press produces 300 lids per minute, the sealing machine will be regulated to produce 310 lids per minute. The lid feed from the sealer is provided with proximity detectors in order to detect the height of the stack of lids. When the stack reaches a fixed lower limit, feeding of the lids from the stack to the sealing station is automatically delayed until the end of the stack reaches a a fixed upper limit. In this way, the press operates continuously, but the sealing machine operates intermittently. Obviously, it is impossible to match the velocity of the two pieces of equipment exactly. It is more difficult to make a press operate intermittently and it is preferable that the sealing machine operate more rapidly than the press, instead of the opposite. When said system is used with the pre-heater for steel lids, the number of lids in the magnetic hopper will vary continually, which in turn will vary the separation between the individual lids. In order to-. solve this problem, a bi-directional electronic counter has been developed which operates in the following manner: one proximity 0 detector detects the lids as they are fed to the upper part of the magnetic hopper, and the other proximity detector detects the 205834 lids as they leave the sealing machine. The required number of lids is fed into the pre-heater in order to provide the necessar separation between the lids, and next, when the press and the sealing machine have been made to operate, the bi-directional counter counts the number of lids fed to the pre-heater and those which are leaving the sealing machine. When these numbers deviate from a pre-established quantity, for example 4, the feed from the base of the hopper is interrupted and is started up again when four lids have been fed to the top of the hopper. As a result, the number of lids in the hopper never varies by more than 4, such that the separation between the ends does not change significantly.

It should be pointed out that the magnetic hopper used with a pre-heating unit for steel lids is not new in itself. Magnetic hoppers have been used commercially for several years as a means for reducing the weight of the stack of lids on the feed mechanism of a sealing machine.

When the lids have been sealed and leave the sealing machine, they are moved along a conveyor system to the packing station.

This conveyor system usually consists of a semi-circular trough. If said trough is used with the pre-heater process, the water vapor which evaporates from the hot lids cannot escape and condenses on the bottom of the trough, and so,in order to ensure rapid evaporation of the water on the conveyor, the conveyor system will be such that it permits good air circulation around the lids.. It has been found that the best way of ensuring 205834 O) 11 this circulation consists in replacing the semi-cylindrical trough with a 4-rail system, as indicated in the attached drawing.

The normal operating conditions for the pre-heater for steel lids is based on heating the lids to a temperature between 60-120°C at the time of sealing. However, the actual temperature needed to ensure that the lids are dry within the specified time depends on several factors, such as the size of the lid, the weight of the compound in the lid, and the actual method of packing and storing the lids used in the particular plant.

In the case of aluminum lids, very low temperatures can be used, generally from 50-120°C, due to the fact that when the aluminum lids are sealed, the conveyor system from the sealing machine is usually very long, since the lids are fed to the other installa tion in order to insert the easy-opening feature.

The subject of the invention will be better understood by reading the text of the description in conjunction with the attach drawings, where: Figure 1 is a schematic view in elevation of the installation according to the invention.

Figure 2 is a schematic view in elevation of the pre-heater for aluminum lids.

Figure 3 is a schematic view in elevation and laterally of the pre-heater for steel lids.

Figure 4 is a view similar to Figure 3, in which the machine control sensors appear.

Figure 1 is a schematic view where the press that forms the lids is represented by 1; 2 is the device for conveying the lids 2 0 5 8 3 4 from the press to the pre-heater unit; 3 is the sealing machine; 4 is the pro-heater unit; and 5 is a second conveyor devjcc which collects the lids for packaging.

Figure 2 represents the pre-heater unit for aluminum lids, where 6 represents the cylindrical jacket in which the lids are deposited; 7 represents the blower that heats the lids by driving air through the heating elements 8.

Figure 3 represents the schematic view in lateral elevation of the pre-heater for steel lids, where 9 represents the permanen magnets, 10 the blower, and 11 the heating elements.

Figure 4 illustrates, in elevation and . laterally, the different pre-heater control elements, where A represents a thermocouple, B the detector of the hopper for lids when they are blocked in the hopper, C the counter for lids•coming into the hopper, and D the counter for lids leaving it.

The nature of the invention is sufficiently described, as well as the manner of implementing it; it should be stated that details of the above-mentioned configurations can be changed, which does not alter the fundamental principle of the invention.

Claims (10)

205234 What we claim is:

1. An installation for sealing steel and/or aluminum lids of cans with a sealing compound, characterized in that the installation includes; a conveyor device at ambient temperature for lids coming from a manufacturing press; a sealing machine; a pre-heater unit installed in the machine which heats the lids coming from the conveyor, before sealing; a counting device which counts the lids fed to the pre-heater, and those leaving the sealing machine; a second conveyor device which collects the lids from the sealing machine and carries them to a packing station, where they are suitably arranged to finish the drying process.

2. An installation according to claim 1, characterized in that the pre-heater unit for steel lids comprises a magnetic hopper for lids, comprising a cylindrical tube or chamber of stainless steel, with two permanent magnets placed facing one another and on the outside of che chamber, and which, by means of the magnetic field created between the two, separates the lids from one another automatically in order to permit air to be blown between the lids; while the lids are heated with the air, which, proceeding from a blower, has been heated previously.

3. An installation according to claim 2, characterized in that the heating of the lids takes place laterally by means of the blower passing air through at least one vertical opening in the cylindrical chamber of the pre-heaLci. . ^—...

4. An installation according to claim 1 characterized 'ir that the pre-heater unit for aluminum lids comprises an !|h£ i -2APRI insulated cylindrical chamber, in which hot air is blown incto* ' "f o p i \! the bottom and leaves by the top, and the chamber has a series'^—- -12- ■20SX3H -of partitions which ensure proper circulation of the air.

5. An installation according to claim 2 or 3 characterized in that the counting device comprises a bidirectional electronic device and includes a proximity detector for the height of the stack of lids, which detects the lids as they are fed to the top of the magnetic hopper of the pre-heater, and a second proximity detector which detects the lids as they leave the sealing machine; and in that when the press and the compounding machine operate, the bidirectional device counts the number of lids fed to the pre-heater and those leaving the sealing machine.

6. An installation according to any one of the preceeding claims, characterized in that the normal operating conditions of the steel lid pre-heater comprise heating the lids to a temperature of 60-120°C, at the time they are sealed, while the temperature for aluminum lids is between 50-120°C.

7. An installation for sealing steel and/or aluminum lids for cans with a sealing compound, substantially as herein described with reference to the accompanying drawings.

8. A process of applying a water-based sealing compound to steel and/or aluminum lids of cans prior to joining said lids to said cans, characterized in that the lids are heated prior to application of the sealing compound thereto to initiate immediately evaporation of the water from the compound. -13- GP 205834

9. A process according to claim 8 wherein after application of the sealing compound to the preheated lid, the lids are transferred along a conveyor during which further evaporation of the water from the compound occurs.

10. A process according to claim 8 substantially as herein described with reference to the accompanying drawings.