US3170275A

US3170275A - Means for heat sealing lids on blisters

Info

Publication number: US3170275A
Application number: US308502A
Authority: US
Inventors: Howard A Rohdin; Adolph A Rohdin
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-09-12
Filing date: 1963-09-12
Publication date: 1965-02-23
Anticipated expiration: 1982-02-23
Also published as: SE313769B; DE1284888B; GB1083022A; GB1083023A

Description

Feb. 23, 1965 H. A. ROHDIN ETAL 3,170,275

MEANS FOR HEAT SEALING LIDS 0N BLISTERS Filed Sept. 12, 1963 5 Sheets-Sheet 1 FlG.2

FIG I INVENT 01B ADOLPH A. ROHDIN HOWARD A. ROHDIN BY 'Egaz'ifi ATTORNEY Feb. 23, 1965 H. A. ROHDlN ETAL 3,

MEANS FOR HEAT SEALING LIDS 0N BLISTERS Filed Sept. 12, 1963 5 Sheets-Sheet 2 FIG. 3

INVENTOIB ADOLPH A.ROHDIN HOWARD A. ROHQIN A'ITORNEY Feb. 23, 1965 H. A. ROHDIN ETAL 3,

MEANS FOR HEAT SEALING was on sus'rsas Filed Sept. 12, 1963 5 Sheets-Sheet 3' FIG 4A FIG .4C

mvmoas ADOLPH A. ROHDIN HOWARD A- ROHDIN FIG 48 BY F14 5- r m/z ATTORNEY Feb. 23, 1965 H. A. ROHDIN ETAL MEANS FOR HEAT SEALING LIDS ON BLISTERS Filed Sept.- 12, 1963 5 Sheets-Sheet 4 FIG-.5

YTrs N 9 LL.

INVENTORS ADOLFH A- ROHDIN HOWARD A ROHDIN ATTORNEY Feb. 23, 1965 H. A. ROHDIN ETAL 3,170,275

MEANS FOR HEAT SEALING mos on BLISTERS Filed Sept. 12, 1963 5 Sheets-Sheet 5 INVENTORS ADOlB-i A. ROH DIN w HOWARD AROHDIN BY Km [766/05 ATTORNEY United States Patent MEANS FOR HEAT SEALING LIDS 0N BLISTERS Howard A. Rohdin, 397 Forest Ave., and Adolph A. Rohdin, 385 Forest Ave., both of Glen Ridge, NJ. Filed Sept. 12, 1963, Ser. No. 308,502 12 Claims. (Cl. 53-373) It is an object of this invention to provide a method and apparatus for heat sealing lids onto preformed containers or blisters formed in a web of plastic. While it is perfectly possible to use this method and apparatus on a single web containing a plurality of such containers, the description will deal with individual blisters, since this is the more usual practice. It is not intended, therefore, to confine this invention to the sealing of individual (as distinct from web connected) blisters.

It is a further object of this invention to provide a method and apparatus as aforesaid in which the apparatus can be changed from one type of container to another ditfering in size, shape, caliper and kind of material with minimum down time and with a minimum requirement of selective judgement on the part of the person making the change.

It is a further object of this invention to provide in an apparatus aforesaid, heat sealing electrodes which will apply heat uniformly around the periphery of blisters of almost any peripheral outline.

The above and other objects will be made clear from the following detailed description taken in connection with the annexed drawings in which:

FIGURE 1 is a front elevation of the apparatus;

FIGURE 2 is a planview of the apparatus;

FIGURE 3 is a partial sectional view of the central heating and pressing part of the apparatus taken on the line 3-3 of FIGURE 2;

FIGURE 4 is a plan view of one of the heating electrodes;

FIGURES 4A and 4B illustrate other electrodes in forms that have been successfully used;

FIGURE 4C is a special electrode for non-hermetic Sealing;

FIGURE 5 is a section through one of the blister carrying trays showing how the electrode is secured in place;

FIGURE 6 is a schematic diagram illustrating a pre ferred and two alternative layouts for the machine adapted to heat sealing from the top;

FIGURE 7 is a view in partial section of a preferred form of machine for top sealing;

FIGURE 8 is a section on the line 88 of FIGURE FIGURE 9 is a schematic elevation of one form of sealing member and tray in loading position;

FIGURE 9A shows the parts of FIGURE 9 in sealing position;

FIGURE 10 shows an alternative to FIGURE 9 with the parts in loading position;

FIGURE 11 shows a further alternative to FIGURE 9 with the parts in loading position; and

FIGURE 12 is a preferred wiring diagram of the apparatus.

When a machine is stopped for adjustment to a different product, every element of cost, e.g.: labor, depreciation, etc., goes on exactly as though the machine were running productively. These shut-down costs must be added to the cost of the articles actually produced, and when the nature of the products is such that frequent stoppages for adjustment are required, such shutdown costs form a serious proportion of the total cost of the finished product.

It is also desirable that the adjustment require a ice j minimum of judgment or know-how on the part of the operator. Mistakes create Waste which adds to total costs, and potential mistakes are minimized as the field within which selective judgement must be exercised is restricted. Moreover, no matter how much the adjustment is simplified, a more expensive type of labor is revquircd to make adjustments than is required merely to supply the machine and to remove the product.

The present invention minimizes shut-down time as well as the exercise of judgement by employing a pinrality of trays, each having a plurality of openings therethrough, each of said openings being shaped to receive a particular form of blister. Each of the openings is surrounded by a heating electrode of the type shown in FIGURES 4, 4A and 4B which will be described hereinafter. The electrodes all are joined to a common return line which is connected to a contact mounted in the upper surface of the platen. This particular contact always has the same location, usually marginal, in the surface of the tray. The feed line of the several electrodes also goes to a marginal surface contact, but the location of the contact will vary from tray to tray. Mating contacts are provided in the pressure platen, a single contact for the return contacts of all the trays, and a plurality of contacts, though only one to a tray, at varying locations for the feed lines. On the feed side, depending on which of the contacts in the pressure platen is active a particular voltage will be applied selected especially for the blisters which the particular tray is designed to accommodate. Since the blister accommodating trays are merely resting in rolling contact with the machine as a whole, they can be removed and replaced easily and quickly and the replacing trays always will make contact with optimum voltage without necessity for the exercise of judgement on the part of the operator. Down time, therefore, is only a matter of seconds, and waste due to improper voltage application is avoided entirely.

It is, of course, perfectly possible to connect the heating elements of any tray to an appropriate voltage by means of jacks through a flexible conductor. Since both input and output would run through the flexible conductor, even the possibility of arcing through the platen to platen contacts hereinabove proposed would be avoided. A simple two wire jack would sufiice in most cases wherethe same voltage would be applied to the several heating elements. If, however, difierent voltages were required for the several heating elements, multiple conductors would and could be used in a single flexible cable, and the need for selective judgement can be avoided by appropriate markings and/ or mating lugs on the jacks and their respective sockets. The application of pressure and the energizing of the electrodes desirably are concomitants of the arrival of the tray in sealing position under the pressure unit. This will be brought out in detail in the discussion of FIGURE 12.

There are certain practical diiferences between the problem of sealing a cardboard lid to a blister type container, and sealing a plastic, impervious lid to the same type of container. Such differences are more manifest, however, in the machine than in the method which fundamentally, remains unchanged in either case. These differences, which are brought out in FIGURES 6-8, will be analyzed to afford a better understanding of the mechanical differentiation between the two operations which will be discussed in detail hereinafter.

In the first place, where the nature of the contents permits, there is almost universal preference for the cardboard lid as opposed to the impervious plastic lid. This is quite understandable. Cardboard, caliper for caliper, is stiffer than most thermoplastics and on the same basis arrears most plastics, and where it is suitable at all, it permits more imperfection of the seal, in the hermetic sense, than most plastics. Rejects therefore are less and net production is greater. Being fibrous, the cardboard usu ally has less heat conductivity than most plastics and it is usually best, quickest, and most effective to direct the heat through the flange of the container to the interface between flange and lid rather than through the cardboard. In such case, there is negligible tendency for the cardboard to stick .to the pressure die in contact therewith and no attention need be paid to this aspect of the operation.

When, on the other hand, an impervious plastic lid is used, and for perishables this is almost the universal case, the problems are quite different. The container or blister must be self sustaining in three dimensional form, whereas the lid presents only a plane surface with far less strength requirements'than those ofthe container proper. The caliper of the lid is dictated by the requirements of imperviousness and not of strength, for which reason the caliper of the lid may be as little as A that of the container body. Where any such differential exists, it is manifestly desirable, in order to shorten the sealing cycle, to direct the heat through the lid to the interface between the lid and the flange of the container. This involves a reversal of the sealing conditions found optimum for the cardboard lid, and this in turn raises the problem of sticking between the lid and the pressure member, which member in this case also carries the heating elements or electrodes. To secure in this case all the benefit of the fundamental concept of this invention requires quite special mechanical adaptation as will appear hereinafter.

Referring now to FIGURES 1, 2 and 3, there is shown a machine generally designated 1d having a pair of guide rails 12 at one side and a pair of similar guide rails 14 at the opposite side of a pressure unit 16. A pair of

blister receiving trays

18 and 20 are provided, each mounted on rollers 22 for rolling contact on the

rails

12 and 14. As shown in FIGURE 1, the tray 18 has been rolled along the rails 12 until it is squarely under the pressure unit 16, while a tray 2d lies exposed on the rails 14. All of the trays have a plurality of blister receiving openings 24, as schematically illustrated in FIGURE 2. Each of the openings 24 is surrounded by a heating electrode 26. These electrodes are connected by lines 28 to a return line contact 3t which usually will have the same location on the surface of the tray, and to a feed contact 32 which'may have any of several locations 32' on the platen. As will be noted in FIGURES 1 and 2, the tray 20, in the position shown, has no connection with the machine as a whole except the rolling contact between the rollers 22 and the rails 14. It may be removed and replaced by a tray having different openings 24 connected to a feed contact 32 to convey a different voltage especially suited to the blisters to be placed in the openings of the substituted tray. Such substitution is quick, easy and involves no releasing, fitting or adjustment.

As shown in FIGURE 1, while the tray 18 is being processed in the pressure unit 16, the tray 20 is exposed, enabling the operator at that side of the machine to remove the heat sealed product of the previous operation,

common to all trays is the provision of a pattern of spring pressed, retractable pins 3%, surrounding each of the openings 24. Their purpose is to guide a cover for each blister into its proper position relative to the sealing flange of the blister. When the tray is in the unit 16,and sealing pressure is applied, these pins retract to the level of the flanges and do not interfere with the pressing operation.

Referring to FIGURE 3, which is a partial section taken generally on the line 33 of FIGURE 2, the unit 16 contains a pneumatic pressure cylinder 40 actuating a pressure plate 32. The cylinder as is secured to a plate 4-4 which in turn is secured to the walls 46 of the unit 16. Suspended from the plate 44 are tension springs 48 which support a pressure platen 50 secured to the pressure plate 42. Brackets 52 are mounted on the platen 5t) and each contains a stripper pin 54 surrounded by a compression spring 56 and having an end 54 protruding through the platen 5%) which preferably has a surface layer 58 of somewhat resilient silicone rubber. Thepins 54 and their contact ends 54' are insulated from the rest of the machine by conventional means not shown. A tray 18 is supported on rails 12 with its supporting studs 34 in contact with the base plate 36. Upon actuation of the cylinder 40, the pressure plate presses down the platen 50 into contact with the tray 13. Guide pins 38 retract into the tray 13 and stripper pins 54 retract into the pressure platen 513 after having established electrical connection with contacts 30 and 32. When pressure is established between the pressure platen 5t) and the tray 18, a predetermined, selected voltage is applied to the electrodes 26 surrounding the openings 24 in the platen 18. The voltage is applied for a predetermined, but adjustable period of time. When the voltage is cut olf, usually the pressure cylinder is deactivated and the pressure plate 42 rises to the position shown in FIGURE 3 by tension springs drawing the pressure platen 50 away from the tray 18 while the stripper pins 54' assure separation between the pressure platen 50 and the tray 18 which is now and place new, filled blisters in the openings 24, and to i apply covers or lids to the blisters. On completion of a cycle by the pressure unit 16, the operator at the opposite side of the machine withdraws tray 18 from unit 16 onto rails 12, and his fellow operator pushes tray 24) into unit 16 in the position occupied by tray 18 in FIGURE 1. For this purpose, all of the trays are equipped with handles 34 as shown on tray 2% in FIGURE 2. Another feature common to all of the trays is the provision of adjustable pressure resisting studs 35, protruding from the undersides of the trays. The studs 35, when the tray is in the unit 16, make contact with a base plate 36 to resist the pressure applied in the unit 16. Another feature ready for withdrawal to the left hand side of FIGURE 1 to be replaced by the tray 20, whereupon the cycle is repeated.

The space above plate as is more or less filled with equipment for carrying out the above described cycle. Such equipment is available in the open market, for which reason the transformers, timers, relays, limit switches, etc., will not be described in detail, but only in connection with FIGURE 12.

The heating electrodes, one example of which is shown in FIGURE 4, form a material and distinct part of this invention, and, indeed, such electrodes mark a major reak-through in the art of heat sealing whether or not used in the context of the combination in which they here appear.

Referring now to FIGURE 4, a generally rectangular electrode 26 is shown. This preferably is formed of highly resistant metal, e.g.: nicrome or stainless steel. Various non-metallic and semi-metallic conductors have been developed and the use of any of these in place of the metallic conductors described herein is within the purview of this invention. These electrodes could be stamped from sheet stock at low unit cost, but since only limited quantities of any particular design are required, the die cost would be prohibitive. The electrodes, therefore, are machined from sheet stock, and the accuracy of machining versus stamping materially improves the performance of the electrodes. The essential factor is that at all points around the electrode, the width be constant. This becomes a problem only at corners which are machined to an internal radius R both radii having a common center and having the relationship fi -R W. Of course, from the standpoint of electrical resistance, uniform heating requires uniform cross-section. Under modern production methods, however, thin sheet stock as here contemplated may be presumed, quite fairly, to be of uniform thickness within the rather limited area occupied by any electrode. FIGURES 4, 4A and 4B may be considered to be characteristic of the overwhelming bulk of present practice. In all of these figures, L represents the feed line and L represents the return line. The lines L and L should be attached to the electrodes at such location that the lineal extent of the electrode between L and L shall be the same whether to right or left of each connection as shown in FIGURES 4, 4A and 4B.

FIGURE 40 is a special case where hermetic scaling is not required. Here a rectangle is defined 'by top and bottom strips 27 and 29 and by

side strips

31 and 33. These several strips may abut or be welded together, but preferably a slight gap is permitted at each corner and each strip has its own L and L connections If necessary or desired, separate voltages may be applied to strips of the same length, e.g.: 31 and 33 on the one hand and to 27 and 29 on the other. Simple straight strips as shown can be produced without resort to expensive machining operations.

While in FIGURE 2 the contact 32 represents L and the contact 30 represents L and the lines 28 connect the electrodes, this is simply a matter of convenience when the several electrodes 24 are identical. It is perfectly possible, using, for example, the electrodes of FIGURES 4, 4A and 4B to hook these in parallel, and even, still using a common return, to use separate L lines for each as will be made clear in the discussion of FIGURE 12.

The trays have certain physical requirements. They must be rigid, substantially inert chemically, highly resistant, both thermally and electrically, and should have a high degree of dimensional stability under varying conditions of temperature and humidity. The thickness of the tray should be considerable since thickness contributes greatly to rigidity, regardless of the elastic modulous of the material, and for this reason a laminated rather than a homogeneous structure usually will provide an optimum combination of cost and rigidity. Formica is recommended as a base material, but reinforced phenol condensation products, hardboards of the Masonite type and even marine type plywood may be used.

In FIGURE 5 there is illustrated a tray 18 having a container receiving opening 24 surrounded by a heating electrode 26. The body of the tray 18 is formed of formica or equivalent as above described. Over the upper surface of the tray 18 is adhered a layer of Teflon coated or impregnated glass cloth cut away at 24 to conform to the openings 24 in the tray 18. The electrodes 26 are secured to the glass cloth 24. The electrodes usually will conform to the shape of the openings 24, but not necessarily. It is only essential that the electrode conform to the shape of the sealing flange of the container, and this, as a matter of choice, may or may not conform to the container outline. In fact, the opening 24 need not conform to the container outline. It is only necessary that the rim of the opening 24 conform to and support the container flange, and that it contain suflicient protrusions or other structure inwardly directed so as to tune-- tion as a locating means for the container body.

A second ply or sheet of Teflon impregnated or coated glass cloth 24" is adhere to the ply 24' and to the electrodes 26. It also covers any and all lead wires or strips for the electrodes 26, and secures the electrodes against any possibility of dislodgment in use. Moreover, it inhibits any sticking between the electrodes and the container flange.

As will be made clear hereinafter, a similar arrangement will be used when a plastic lid is to be sealed to the blister flange by heat directed from above through the lid. In such case the general arrangement of parts and materials will be the same, omitting, however, the openings 2.4, and, usually, reducing the thickness of the board 18. In this case the boards are not trays in the sense that the part 18 is a tray, but are simply special carriers for the electrodes.

In FIGURE 6 the full lines at A indicate ordinary container supporting trays. These, alternately, move to full line positions B in which positions they underlie electrode bearing plates, the electrodes of which register with the flanges of containers placed on trays at A. The superimposed plates and trays then advance to position C Where pressure is applied to both and voltage is applied to the electrodes. The superimposed plates and trays are then withdrawn to position B where suitable stop means detains the electrode plate while the tray continues to position A for unloading and reloading. This is the preterred arrangement and is discussed in detail in connection with FIGURES 7 and 8.

An alternative arrangement is illustrated in dotted outline at positions B. In this case, positions A are eliminated and the trays are loaded and unloaded at positions B. Electrode plates are pivoted at one side of the trays at position B and occupy swung out or inactive positions B during loading of the trays. They are then swung into superimposition relationship at position B and in this superimposed relationship are advanced laterally to the sealing position C.

A further alternative arrangement is illustrated in dotted outline at positions A, which in this case represent the loading and unloading positions of the trays. The electrode plates are mounted in tray receiving frames at B. A loaded tray moves from A to B where it underlies an electrode plate. The assembly then moves to C for sealing, after which the assembly moves -to B from which position the tray moves to position A for loading and unloading. This alternative has the advantage, under some circumstances of permitting a single operator to load and unload trays at both positions A.

A preferred arrangement of parts for sealing a plastic lid from the top is shown in FIGURES 7 and 8, and several alternatives for use in this arrangement are shown in FIGURES 91l. These latter are auxiliary in nature, and for the purpose of simplicity are discussed independently of the showing of FIGURES 7 and 8. Indeed, as will be noted in the discussion of FIGURE 12, the forms of FIGURES 9-11 may be dispensed with by putting the duration of application of pressure under control of a separate timer from that controlling the duration of the voltage application to the electrodes. In FIG- URES 7-11 reference numerals as applied to basic parts are the same as in FIGURES 1-3.

Referring now to FIGURE 7, there are shown tray rails 12 and 14 supporting respectively

trays

18 and 20 with the latter in loading position and the former located in the pressure unit 16. The pressure unit 16 is provided with pressure cylinder 40 and pressure plate 42. Plate 42 is supported by springs 48.

An extension 14 of rails 14 is adapted to guide the-tray 18 into position under a sealing plate which itself is mounted on rollers 102 and carries spring biased stripper pins 14. Electrodes 26 are mounted in the lower surface of the sealing plate 100 as above discussed in connection with FIGURES 44C and FIGURE 5. Lines L and L connect the sealing plate 100 to a jack I which may be plugged selectively into a jack receptacle J to receive a selected voltage.

In FIGURE 7, the tray 18 has moved first to a position under its sealing plate where its openings 24 register with electrodes 26 on the plate 150. At this point it encountered a stop on the plate 150. Tray 18 and plate 150 then moved in a continuous movement under the pressure platen 42 which then descended to the position shown to bring the tray 18 and its plate 150 under sealing pressure.

Upon completion of sealing the pressure is relieved in the cylinder 40 and springs 48 then raise the pressure platen 42. The sealing plate 150 is pushed upwardly by pins 154 and tray 18, with sealing plate 150, are withdrawn to the left of FIGURE 7.

A suitable latch engages between the tray and the sealing plate and is released when the sealing plate 150 ar- Y 7 rives at leftward position equivalent to the right hand position shown for sealing plate ltlil. When tray 1% and sealing plate 150 are withdrawn, tray 2% moves to engage sealing plate 1% and the operation is repeated. It is to be noted that the sealing job for tray 1%; may be different from that of tray 29 which means that the products sealed may be different as between the two trays.

Preferably, as discussed hereinafter in connection with FIGURE 12, an adjustable timer is provided to regulate the duration of the application of voltage to the electrodes 25. Since the electrodes have low mass there is little thermal inertia and the duration of heating closely approximates the duration of voltage application. Moreover, when the timer timesout the pressure automatically is released. This works fine for bottom heat application where sticking between the lid and the pressure plate is not a factor, but it is not always satisfactory when heat is applied from above to a thermoplastic lid.

In the latter case, the problem can be solved by the addition of a second timer to control duration of pressure after the heating timer times out, This, however, complicates the circuitry and adds to the basic machine cost. FIGURES 9-11 show various ways of solving the probem without change of the basic circuitry of FIGURE 12.

In FIGURE 9, tray and sealing plate are shown toward the sealing plate Itltl, into registry therewith, as

shown in FIGURE 9A. In this condition the web 119 loosely overlies the entire upper surface of the tray 2%, including the lids and containers. When heat and pressure are applied, the heat passes through the web ill? and then through the lids to the interface between the lids and the container flanges. Any sticking occurs solely between the lids and the web 11%? and this disappears as the lid cools. The duration of heating becomes unimportant, and only the duration of the pressure matters. That is, the requisite voltage may be applied at all times to the electrodes and a timer may be used only to relieve pressure. The parts remain in undisturbed contact after the pressure is relieved and until the tray and sealing plate are removed from the pressure station To to the left hand position of FIGURE 9A. By this time the parts will have cooled so that continued movement of the tray 2% to the position of FIGURE 9 can peel the web 11% away from the tray without adverse effect on the seals.

InFIGURE 10, the left hand end 1T2 of the web 116 is attached to the left hand end of the tray 20. The right hand end 116 of the web remains free until the tray is fully loaded, then is secured by snap means ITS-lid to the right hand end of the tray N. This permits a longer cooling period to elapse before the web lift? is stripped from the lids of the sealed containers.

In FIGURE 11 the left hand end 112 of the web llltl is secured to the left hand end of the tray Ztl. The major portion of the web Iltl, however, is stored on a roll 120 rotatably mounted in brackets 122 secured to the sealing plate Mill. The roll 1129 is spring biased in the manner of the conventional window shade to its wound up condition as shown in FIGURE 11. Leftward advance of the tray 29 under the sealing plate lllltl unwinds the web lltl from the roll 1% to overlie the lids and containers placed on tray 29. On return of the tray 2t) to the position of FIGURE 11 the spring bias of the roll 120 peels the web lit from the sealed containers.

Referring now to FIGURE 12 which depicts the wiring preferred when the lid or cover is cardboard but is equally applicable to top sealing of plastic lids as above described,

line L is treated as the hot line and line L is treated as the return line. A main switch L conditions the entire plantfor operation. As a tray 13 is inserted into the pressure unit 16, it first encountersa tray switch TI'S. This, preferably, is a limit switch with a roller arm and is wired directly to a relay R which is conditioned to a normally open position (NO), and also to a normally closed position (NC) as shown at the right hand side of FIGURE 7. As the .tray continues from approximately its halfway position (TrS) to its final position defined by kerfs cut into the rails 12-14, it thereby closed a rail switch RS which is a limit switch of the plunger type. This energizes a line through the normally closed side of relay R and a solenoid SOL-I. The solenoid SOL-I operates a valve to actuate the pressure cylinder 40. When the pressure in the cylinder 4ft reaches a predetermined point, pressure switch PS closes to start timer T. The starting of timer T simultaneously energizes control relay G which closes normally open switch S which, in turn energizes the secondary coil TR (primary not shown) of a transformer and thereby energizes the several electrodes E mounted in the pressure platen all. These electrodes are retractable. A though all of the electrodes E; are energized, only one of them will make contact with a particular input electrode (3%32') on a particular tray 2t), thereby applying heating current to the sealing bands 26 (FIGURE 2). A simple electrode through the heat elements E completes the circuit to line L Since each of the electrodes E carries a different voltage the heating effect will vary from tray to tray depending on the character of the blister and its cover.

Now the adjustable timer T runs out and in so doing reverses the indicated N0 and NC positions of the timer switch 77 to deenergize C and to energize C The latter breaks the circuit through switch R (NC), thereby deenergizing SOL-1 and exhausting air from the pressure cylinder 40 to permit rise of the pressure platen Ell. The reduction of pressure, of course, opens the pressure switch PS A further effect is to close normally open relay R to hold the timer T at zero and prevent recycling until the tray is withdrawn clear of the tray switch TrS when all circuits are broken and the timer T is reset for the next seal. It is to be noted that the timer T controls only the duration of the application of voltage to the heat sealing bands 26. It becomes effective only when a sealing pressure is attained, and when it times out, not only is heating terminated but the pressure is relieved.

It will be noted that in FIGURES 71 1, the electrode bearing sealing plates Tilt) and simply constitute removable substitutes for the pressure platen 5d of FIG- URE 3. The jack I and jack receptacle J of FIGURE 7 function precisely in the manner of the electrodes E 32-32 and E described in connection with FIGURE 12. The essential element is to bring the electrodes into registry with the containers to be sealed and is the same whether registry is attained by original assembly as in FIGURES 2 and 5 or by physical movement of the parts as in FIGURES 7-11.

It will be understood that the wiring diagram just discussed represents a preferred but not indispensable embodiment. Variations may be made depending on the engineering taste of the designer. This invention, therefore, is not to be limited to the precise details disclosed but only as set forth in the subjoined claims. In its method aspect, the sequence of steps recited in the claims is not material unless explicitly so stated.

We claim:

1. A machine for sealing lids onto preformed containers comprising: a pressure unit, said pressure unit having as sociated therewith a predetermined number of contacts, each of said contacts having a predetermined location, and each supplying a predetermined voltage differing from the voltage supplied by the others of said contacts; a tray supporting means; a tray having means to position a peripherally flanged container placed therein; a heat sealing electrode conforming generally tov the container flange, said electrode being formed of electrically conductive but resistant material and said electrode having a contact located to engage a predetermined one of said pressure unit associated contacts; said tray and its associated electrode being movable into position for engagement respectively with said pressure unit and a predetermined one of said pressure unit associated contacts; means for applying to said electrode through said engaged contacts a predetermined voltage while applying to a lid overlying the outer periphery of each container pressure sufficient to effect a seal between said lid and said peripheral flange; and means for relieving said pressure to permit the removal of said tray from said pressure position.

2. A machine as set forth in claim 1 in which the electrode is mounted on said tray.

3. A machine as set forth in claim 1 in which each tray has means to locate a lid in proper relationship to said container.

4. A machine as set forth in claim 1 in which the electrode is mounted on a carrier separate from the tray.

5. A machine as set forth in claim 1 in which the trays for differing types of containers are at all times freely interchangeable on the tray supporting means.

6. A tray for sealing lids onto preformed containers, said tray comprising: a rigid backing member, said member having at least one opening through its surface designed to position a preformed container therein; at least one sealing electrode surrounding said opening and defining a sealing area for the preformed container to be positioned therein, and retractable pins extending from the surfaces of said backing member adjacent said opening, said pins acting to position a lid for said container.

7. A tray for sealing lids onto preformed containers, said tray comprising: a rigid backing member, said member having at least one opening through its surface designed to position a preformed container therein; at least one sealing electrode surrounding said opening and defining a sealing area for the preformed container to be positioned therein, and adjustable pressure resisting studs protruding from the side of said tray opposite the side bearing said electrode.

8. A tray for sealing lids onto preformed containers, said tray comprising: a rigid backing member, said member having at least one opening through its surface designed to position a preformed container therein; at least one sealing electrode surrounding said opening and defining a sealing area for the preformed container to be positioned therein; a sheet of non-sticking material secured to said backing member and underlying said electrode and a second sheet of non-sticking material overlying said electrode and said first named sheet and being secured to said first named sheet and to said electrode.

9. A tray for sealing lids onto preformed containers, said tray comprising: a rigid backing member, said member having at least one opening through its surface designed to position a preformed container therein; at least one sealing electrode surrounding said opening and defining a sealing area for the preformed container to be positioned therein, said electrode being formed of thin, flat sheet metal of constant width throughout the lineal extent of said electrode, said width being measured on lines normal to the edge of said electrode at any point in said lineal extent; a sheet of Teflon-like material adhered to said backing member and underlying and being adhered to said electrode and a sheet of Teflon-like material overlying said first named sheet and being adhered to said sheet and to said electrode.

10. A tray for sealing lids onto preformed containers, said tray comprising: a rigid backing member, said member having at least one opening through its surface designed to position a preformed container therein; at least one sealing electrode substantially surrounding said opening and defining a sealing area for a preformed container to be positioned therein, and means on said tray adjacent said electrode for positioning a lid in predetermined relationship to said container and said electrode.

11. A machine for sealing lids onto preformed containers comprising: a pressure unit, said pressure unit having associated therewith sources of predetermined voltages; a carrier having means to position a container and means to position a lid thereon; a carrier supporting means having a container and lid positioning station and a pressure unit station; an electrode formed of electrically conductive but resistant material, said electrode being sized, shaped and located to effect a seal between said lid and said container; said carrier being movable on said carrier supporting means from said container and lid positioning station to said pressure unit station; means operative concomitantly with arrival of said carrier at said pressure unit for selecting a predetermined one of said predetermined voltages and means for applying sealing pressure between said lid and said container; means controlling the duration of said pressure application, and means controlling the application of said predetermined voltage to said electrode.

12. A machine for sealing lids onto preformed containers comprising: a pressure unit, said pressure unit having associated therewith sources of predetermined voltages; a carrier having means to position a container and means to position a lid thereon; electrode means formed of electrically conductive but resistant material, said electrode means being sized, shaped and located to effect a seal between said lid and said container; said carrier being movable into active relationship with said pressure unit station; means operative concomitantly with arrival of said carrier at said pressure unit for selecting a predetermined one of said predetermined voltages and means for applying sealing pressure between said lid and said container; means controlling the duration of said pressure application, and means controlling the application of said predetermined voltage to said electrode.

References Cited by the Examiner UNITED STATES PATENTS 2,590,379 3/52 Cloud 53--30 X 2,714,416 ,8/55 Fener 2l9-243 X 3,018,594 1/62 Phillips et al. 53373 X 3,057,988 10/62 Roder 53329 X 3,092,945 6/63 Wizelman 53373 FRANK E. BAILEY, Primary Examiner.

TRAVIS S. McGEHEE, Examiner.

Claims

12. A MACHINE FOR SEALING LIDS ONTO PREFORMED CONTAINERS COMPRISING: A PRESSURE UNIT, SAID PRESSURE UNIT HAVING ASSOCIATED THEREWITH SOURCES OF PREDETERMINED VOLTAGES; A CARRIER HAVING MEANS TO POSITON A CONTAINER AND MEANS TO POSITION A LID THEREON; ELECTRODE MEANS FORMED OF ELECTRICALLY CONDUCTIVE BUT RESISTANT MATERIAL, SAID ELECTRODE MEANS BEING SIZED, SHAPED AND LOCATED TO EFFECT A SEAL BETWEEN SAID LID AND SAID CONTAINER; SAID CARRIER BEING MOVABLE INTO ACTIVE RELATIONSHIP WITH SAID PRESSURE UNIT STATION; MEANS OPERATIVE CONCOMITANTLY WITH ARRIVAL OF SAID CARRIER AT SAID PRESSURE UNIT FOR SELECTING A PREDETERMINED ONE OF SAID PREDETERMINED VOLTAGES AND MEANS FOR APPLYING SEALING PRESSURES BETWEEN SAID LID AND SAID CONTAINER; MEANS CONTROLLING THE DURATION OF SAID PRESSURE APPLICATION, AND MEANS CONTROLLING THE APPLICATION OF SAID PREDETERMINED VOLTAGE TO SAID ELECTRODE.