GB2110594A

GB2110594A - Heat welding of thermoplastics

Info

Publication number: GB2110594A
Application number: GB08234473A
Authority: GB
Inventors: William Edmund Young; Ernst Walter Gerber; William Richard Pasco
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-12-03
Filing date: 1982-12-03
Publication date: 1983-06-22
Also published as: DE3249235T1; EP0095498A1; SE8304252D0; WO1983001926A1; SE8304252L

Abstract

The several embodiments illustrated in the Figures in which welding apparatus employs a conductive ribbon (40) that is heated above the melting temperature of plies of laminar plastic materials (90, 91) held in and by clamp jaws (64, 66). These jaws (64, 66) are cooler than the melting degree of said plies (90, 91) which are gripped by said jaws (64, 66) to locally weld said plies (90, 91) by melting their protruding edges to a determined degree and for a determined period of time by electrical energy passed through said ribbon (40). After welding is completed and the weld is cooled by the jaws (64, 66) are moved apart to release the now welded plies (90, 91). The jaws (64, 66) at their edges facing the heated ribbon (40) are substantially right angled and are disposedfrom these adges 1.2 to 1.98 mm.

Description

SPECIFICATION Heat welding of thermoplastics There are presently many patents and inventions relating to "bead" welding of plastic film with congruent edges. Most of these patents pertain to plastic film containing or coated with copolymers, various plasticizers and other additives which are substantially distinct from polyester film containing no additives. Polyester is the generic name for polyethylene terephthalate.

Mylar type (DuPont TM) having high clarity, balanced biaxially orientated heat set film is such a film.

The unique properties of this Mylar type D are a tensile strength of at least 1 757.6 kg. per sq. cm.

and has semi-rigidity; inertness; extremely long shelf life; contains no plasticizers; has a very high melt temperature, and is resistant to most chemicals, acids, alkalines, oils and other organics.

It is relatively impermeable to moisture and oxygen and has a heat conduction and is inert from fungus attacks. Has extremely high initial tear strength and has unique dielectric properties.

Mylar is used to store valuable documents and collectors' items, film negatives and many other items affected by volatile plasticizers and additive compounds of the many other types of plastic films.

It is commonly realized, in the present state of the art, that sealing this type of polyester film with ultrasonic welding can lead to one or more of the following problems; brittle seals; opaque recrystallization of the sealed bead (a milky white appearance); loss of strength of the seal; heat warping of the unsealed surfaces, and decomposition of the plastic on portions of the seal. The melt temperature is very close to the decomposition temperature, thus portions of the bead seal may become overheated and decompose.

Applying the known art such as shown in the U.S. Patent No. 2,679,469 to BEDFORE as issued on May 25, 1954; U.S. Patent No. 3,321,353 to ZELNICK as issued May 23, 1967; U.S. Patent No.

3,330,716 to ZELNICK as issued July 11, 1967; U.S. Patent No. 3,326,735 to BEASON, Jr. as issued June 20, 1976; U.S. Patent No. 3,355,337 to ZELNICK as issued November 28, 1967; U.S.

Patent No, 3,736,219 to MC TAGGART as issued May29, 1973; and U.S. Patent No.4,197,149 to FREITAG as issued April 8, 1 980 to the seal of Mylar film without using the distance, time and temperature control mentioned or suggested in the following description causes unsatisfactory results as listed above. Any or all of the above results are adverse to the intended use of Mylar film. It is a purpose of this invention to provide a seal to effectively eliminate all of the above adverse results. "Mylar" is a Registered Trade Mark.

Summary of the Invention In brief, the present invention provides an improved apparatus, to be hereinafter more fully described, which utilizes heating to bead weld two or more sheets of plastic, e.g. polyester to each other, the heating being provided by a hot ribbon which in use is located adjacent the edges of the films to be welded, but spaced therefrom, the edges being melted by the hot ribbon after being brought into and clamped in position. This apparatus includes means for clamping the films and with the congruent edge portions extending an established distance from the clamp, a heated ribbon spaced an established distance from these edges causes said edges to be bead welded. An eccentric apparatus when actuated moves the cold ribbon to and away from the clamped edges of the film providing locating means for the film edges prior to clamping.In another embodiment two or more sheets of film are clamped together and held between spaced apart pairs of clamp jaws, then the edge of a heated ribbon is moved through the films to effect the severing, melting and bead welding of the film plies. The heated ribbon is used to cut and weld the thermoplastic strips or sheets. Distance, time and heat are critical to successful bead welding, particularly when and after Mylar D or other highly orientated materials are welded.

Continuous welding is contemplated and is shown in three embodiments hereinafter more fully described. In one embodiment bead welding of the film edges is made using a heated ribbon spaced from the edges of the travelling film strips.

In another embodiment the heated ribbon is used as a knife and two or more films are bead welded to form a weld along and at the severed line. In another embodiment a knife is first used to split the films and then a weld of these edges is made using a heated ribbon.

In yet another embodiment film sheets are severed by a heated ribbon while the strips are clamped. The clamp jaws are then moved toward each other to form a bead weld of the two sheets of film at a given# position.

It is, of course, realized that the apparatus shown for bead welding of hard-to-weld plastic films such as Mylar may also be used for the welding of other films which are easier to weld together. Each embodiment satisfactorily produces a weld for both very difficult and easy to weld films. The precise spacing or positioning, the time interval and the amount of radiant heat supplied enables welding of films of less than one mil thick and more than ten mils thick.

Brief Description of the Drawings FIG. 1 represents an isometric view, partly diagrammatic and fragmentary and showing apparatus for eccentric movement of an intermittently heated ribbon positioned in way of and away from congruent film edges; FIG. 2 represents a side view, partly in section and diagrammatic and showing apparatus for gripping the film sheets in and by spring actuated arm means; FIG. 3 represents the apparatus of FIG. 2 in a side, partly sectional view, and partly diagrammatic and with spring means for urging the heating ribbon into an established position; FIGS. 4 A and 4 B represent diagrammatic sectional side views of the bead melting of the edges of the film; FIG. 5 represents a diagrammatic side view of the apparatus for clamping, severing and bead welding of two or more plies of sheet material;; FIGS. 6 A, 6 B, 6 C, 6 D, 6 E and 6 F represent progressive steps of the bead welding performed by the apparatus of FIG. 5, these several views diagrammatically showing step-by-step operation of said apparatus; FIG. 7 represents a side view, partly fragmentary and diagrammatic, and showing continuous edge welding of two plies of film; FIG. 8 represents a fragmentary sectional side view in an enlarged scale of the apparatus of FIG. 7, this view taken on the line 8-8 thereof and looking in the direction of the arrows; FIG. 9 represents a diagrammatic front view of apparatus and showing a heated ribbon member positioned in way of two plies of film and providing a cutting and welding operation performed with the same heated ribbon;; FIG. 10 represents a side view of the apparatus of FIG.9, partly diagrammatic and fragmentary; FIG. 11 represents a diagrammatic front view of an arrangement for advancing film strips to driving means and during the retention in and around a driving pulley the edges of the strips are bead welded; FIG. 12 represents a fragmentary side view, partly diagrammatic and showing the arrangement of apparatus of FIG. 11.

FIGS. 13 A, 13 B, 13 C, 13 D, 13 E, and 13 F represent step-by-step bead welding similar to that of FIGS. 5 and 6 but with the heated ribbon adapted to make a bead seal of two films without separation, and FIGS. 14 A, 14 B and 14 C represent step-bystep welding of arranged plies in a stacked insulated and clamped condition and diagrammatically showing edge welding of the plies as by heated air, flame or the like.

In the following description and in the claims various details are identified by specific names for convenience. These names are intended to be generic in their application. Corresponding reference characters refer to like members throughout the several figures of the drawings.

Embodiment of FIGS. 1 through 4 B Referring next to the drawings and the embodiment shown in the apparatus of FIGS. 1, 2 and 3, it is to be noted that the apparatus is of a length sufficient for bead welding two or more strips of sheets of material. A base plate 20 carries two end plates 22 of which only the near member is seen in FIG. 1. A protective guard 24 is indicated in phantom outline and is secured to the rear edge of the base 20. Carried by these end plates is a rotatable shaft 26. On this shaft is a plurality of like cams 28 which are secured to the shaft by key means 29 and/or the like. This key means not only aligns the cams as to a flat portion 30 formed on each but also insures that the several cams are not displaced from their mounted condition on the shaft.

The shaft 26 has one end (near) that extends from the end plate 22 at a determined amount and as depicted there is mounted therein a lever handle 32 which is adapted to rotate the shaft a selected amount. This rotation is usually about a quarter turn and stops are provided to establish the limits of rotation. Shown diagrammatically is a ribbon clamp assembly 36 which includes dovetail blocks 37 and 38. A ribbon 40 that is selectively heated by the passing of electrical current therethrough is carried by a clamp assembly generally identifed as 36 at each end of the apparatus. Only the near end clamp assembly 36 is shown in this FIG. 1. This near end clamp assembly spring tensions the ribbon to maintain it taut as its length increases during heating.

To provide for reciprocal and sliding motion the clamp assembly 36 is provided with a slide guide 42 that has an open forked end 43 engaged by a through rod 44. A U-shaped electrical insulator 46 of sheet material is disposed between block 37 and guide 42. Also seen is a cooling tube or conduit 48 which is carried in support block 50.

Between the end plates 22 and on a support bar 52 is mounted a plurality of pivot supports 54 which are mounted in threaded holes and extend upwardly from tapped holes formed in support bar 52. Nuts 55 are each mounted on the threaded shank of a socket headed cap screw 56. The screws are rotated so as to be moved up and down and are locked in position by the nut 55.

This adjustment is made so as to bring the movable clamp bar means in the desired arrangement.

As seen in FIG. 2, the underside of screw 56 is made with a circular groove which is sized to receive and retain a roll pin 57. This roll pin is carried in a transverse hole formed in an L-shaped support member 58. An elongated aperture 60 is formed in this L-shaped support member 58 and in this elongated aperture the shank of said screw is carried. The forward end of this L-shaped support is provided with a pair of through holes (not shown) and in these holes is positioned a pair of cap screws 62 and 63 as seen in FIG. 1 which enter threaded holes and secure a clamp bar portion 64. This clamp bar portion is normal to the L-shaped support 58 and is urged with and by said L-shaped support into a clamping condition against a fixed support plate 66 as seen in FIGS. 2 and 3. It is to be noted in FIG. 2 that this L-shaped support 58 is actuated toward a clamping position by a spring plunger 68 and compression spring 70. A sliding bar or strip 72 is moved into and out of compressing condition so as to load or unload spring 70 when the bar 64 is moved to bring the L-shaped support and the spring-bias into a gripping condition.

It is to be further noted that shaft 26 has a plurality of recesses and mounted in each is a ball 74 which is adapted to and does engage the L-shaped support 58 at its midlength and lifts said L-shaped support 58 and clamp bar portion 64 from gripping condition. The lift force applied by the ball 74 is provided by the rotation of shaft 26 when the lever handle is manipulated. It is also to be noted in FIG. 2 that about ninety degrees counterclockwise from the balls 74 are pins 76 which also engage the midlength of the L-shaped support when the shaft is further rotated counterclockwise. This additional lift causes the clamp bar portions 64 to be lifted for adjustment or other operations.

The cooling tube or conduit 48 as seen in FIGS.

1,2 and 3 is carried by and in block 50 and provides means for cooling this bar after heat has been applied to the ribbon or strip 40. In FIG. 3 there is depicted the apparatus for making the eccentric movement. The cams 28 have flat portions 30 and as the handle 32 and shaft 26 are rotated these circular cams are rotated so that the circular portion engages and pushes leftwardly an angle shaped shoe member 78. This member is adjustably positioned by means of a cap screw 79 and nut 80. A slot 81 is provided in member 78 for movement to the desired adjusting position. A channel-shaped member 82 having heat dissipation properties is shown and is moved by the angle-shaped shoe member 78 as this member is moved by the cams 28. Springs 83 are carried in formed recesses 84 in block 50 and urge the channel-shaped member 82 rearwardly.FIG. 2 shows a block which is secured to the base 20 and provides a rearward stop limit to the angleshaped shoe member 78. Also to be noted is a groove 88 formed in the top surface of the channel member 82 to provide a guideway for the angle-shaped shoe 78. This is particularly noted in FIG. 3.

As seen in FIG. 3 the ribbon 40 is a small distance from the face of channel-shaped member 82 and this ribbon is urged forwardly to provide a locating stop for the film stop for the film edges prior to welding as shown in FIG. 4 A. The clamp 64 then engages the films, after which the member 82 is retracted to the position of FIG. 3.

Film plies 90 and 91 are then heated and melted at their edges that extend rightwardly from the clamp 64 by heat radiated from ribbon 40, shown in FIG. 4 B. The electrical current is then stopped and cooling air from a source not shown is directed at the melted end of the film plies. The clamp 64 is lifted by rotating the arm 32 and the now welded film plies 90 and 91 are removed from the apparatus. The arm rotation returns the member 82 to the position in FIG. 4 A, cooling the ribbon as it urges it to this position. Usually the movement of the ribbon is less than 4.762 mm and the movement is controlled by the eccentric movement of the channel-shaped member 82.To obtain optimum weld properties the following parameters are critical and depend on the nature and thickness of the materials being welded: Length of material extending toward heat source from clamp members 64 and 66 (FIG. 4 A); spacing between ribbon and protruding material prior to heating the ribbon (FIG. 3); intensity and time of heating, and rate of cooling. The cooling provided by air directed at the weld and the water cooling, if used, establishes the period of time needed to cool the weld before unclamping and removal from the apparatus.

FIG. 1 is fragmentary and does not show the other end of the apparatus which may or may not have a handle 32. The clamping of the ribbon is by similar components but made as mirror images.

The length of the apparatus is made to suit the width of film plies and the extent of clamp movement is a matter of selection as is the number of eccentrics. The shaft 26 may be supported intermediate its ends by a support not shown. Bearings and stops are merely design selection.

Embodiments of FIGS. 5 and 6 through F The welding of very hard to join materials such as Mylar and spun bonded thermoplastics may include the joining of two or more plies intermediate their edges or ends. Two fixed jaw members 110 and 112 support two or more sheets or plies of materials. As shown in FIG. 6 A, plies 114 and 11 5 are secured in place by movable jaw members 11 6 and 117 which are adapted to be moved downwardly to a clamped condition as seen in the second step of FIG. 6 B.

While retained in the desired clamped condition a heated strip or ribbon 118 is moved downwardly to and through the clamped plies 114 and 11 5 as seen in FIG. 6 C. The means for supporting and moving this heated ribbon 11 8 is depicted as a cylinder 120 which carries a stretcher member 1 22 having its ends provided with biased outwardly support means 124 and 125. Insulating means or blocks 127 and 128 are provided so that an electrical current is not carried from the ribbon 11 8 to the actuating apparatus usually of metal.

In FIG. 5 the upper and movable jaw members 11 6 and 117 are carried by end members 130 and 131 which may be guided in their reciprocable movement by a base member 132.

Shown is a piston rod 134 that moves a member 122 downward. A member 136 follows 122 downward until its movement is stopped by engagement of clamps 116 and 117 with clamps 110 and 112. The piston is carried by a support 138. Members 136 and 122 are cycled up and down in response to the desired time operation.

In FIG. 6 the film plies 114 and 115 are shown as being severed by a heated ribbon 118.

This heated ribbon melts both plies and produces a bead weld. The plies remained clamped while the bead melt is cooled. During this period of cooling time for the weld the heated ribbon 11 8 is again moved upwardly as seen in FIG. 6 E. After a determined period of cooling time the jaw members 116 and 117 are again moved upwardly as in FIG. 6 F and the plies 114 and 11 5, now welded and severed, have a bead weld to join the plies at the severed position.

The thickness of the film plies and the composition of the material of the plastic film are critical to the desired welding of the plies together.

The temperature in the heated ribbon 11 8 and speed of movement of said ribbon is established in view of the thickness and composition of plies of material. The spacing of the jaw members from the heated ribbon is contemplated to be about 1.588 mm with the weld or bead formed by surface tension toward the clamp jaws as indicated in FIGS. 6 E and 6 F.

Embodiment of FIGS. 7 and 8 In FIGS. 7 and 8 is shown apparatus for continuous edge welding of strips of thermoplastic materials. As depicted, a base plate 150 carries the several components of this apparatus, and is a rather diagrammatic showing of the preferred arrangement and function of said apparatus. Film sheets 152 and 153 are brought between and moved forwardly by upper and lower belts 1 55 and 156. As shown, these belts are endless and are carried and advanced by grooved pulleys 158, 159, 160 and 161. The two right pulleys are designated as 158 and 159 and the pulleys to the left as viewed in FIG. 7 are designated as 160 and 161. The left pulleys are carried by a header member 163 and said member pivotally carries arms 165 and 166 and the rotatable pulleys 160 and 161.An adjusting screw 168 is carried in a threaded nut or member 169 in header member 1 63. Rotation of the screw 1 68 moves the pulleys 160 and 161 to the right or left to loosen or tighten the belts 155 and 156. The belts 155 and 156 are matched in their speed by a gear arrangement associated with pulleys 158 and 159. These gears have a like pitch and number of teeth. Driving means (not shown) cause the gears and their associated pulleys to drive the endless belts in synchronism.

Intermediate the ends of the apparatus and between the pulleys and adapted to engage the film sheets 152 and 153 is the edge welding station. Upper and lower blocks 182 and 183 are carried on angle supports 185 and 186. Each block has a water cooled passageway with the upper passageway identified as 188 and the lower as 189. Carried by blocks 182 and 183 are guide members or strips 191 and 192 each adjustably secured by cap screws 194. Member 191 is spring biased toward member 192 (by means not shown) to clamp the material between the belts. A heated ribbon or strip 196 is shown in FIG. 8 and melts the protruding edges of the material strips or sheets 1 52 and 153. Since the spacing of the material edges relative to the heat source and clamping means is critical, cutting means (not shown) are provided between the endless belts and the material to be trimmed.Trim support rollers 197 and 198 carry the trim through the cutting station while the material to be welded is carried by the belts. Air cooling may be directed at the weld when the material emerges to region 199 of the belts path. Cooling clamp rollers may also be used on the soft weld in region 199, additionally re-orientating the weld material. With some materials the cutting step may be eliminated by lifting one end of the ribbon so its bottom edge is slightly above the plane of the advancing material where it first meets the ribbon.

Embodiment of FIGS. 9 and 10 FIGS. 9 and 10 are fragmentary and diagrammatic and show that in addition to the apparatus for welding as in FIGS. 7 and 8 the plies of film may be continuously welded intermediate their sides or edges. Depicted are upper rollers 200 and 201 carried and rotated by shaft 202.

Lower rollers 204 and 205 are carried on shaft 206. These rollers are intended to advance gripped film plies 208 and 209. In the space between upper rollers 200 and 201 and a like space between lower rollers 204 and 205 is carried a heated ribbon 210. Not shown, but of course contemplated, is electrical conducting means as well as spring tension and drive means.

The arrangement and application of this apparatus is subject to the requirements for each welding to be achieved. While the material is shown approaching the ribbon at an angle of about fortyfive degrees, the speed of cutting and sealing can be increased by reducing this angle of approach.

Embodiment of FIGS. 11 and 12 FIGS. 11 and 12 are fragmentary and diagrammatic. Depicted is an endless belt 216 as carried on pulleys or rollers 218,219, 200 and 221. A large roller 223 forms a U-path and is rotated to advance the film strips 225 and 226. A heater unit 228 is mounted adjacent the roller 223. The heated portion 230 of the mount is depicted along the circular path of the film strips 225 and 226 around the roller 223. The roller 223 is cooled to insure that the film strips do not adhere to it or to the belt 21 6. If required, the heated portion of unit 228 may not extend for the full one hundred-eighty degrees of material travel about the roller and the remaining clamped region of film travel may have the weld cooled by directed air flow.

It is to be noted that the apparatus of FIGS. 11 and 12 has a knife 231 to split the inward moving film strips instead of the heated ribbon of FIG. 9.

This knife assures congruent material edges and does not require heat to sever the materials.

Embodiments of FIGS. 12 A through 13 F The step-by-step showing of FIGS. 13 A through 13 F anticipates the use of apparatus very similar to that shown and described with respect to FIGS. 5 and 6 A through 6 F. As shown in this sequence, the apparatus of FIG. 5 is employed to effect a welding of two plies at an intermediate position. This concept anticipates that the melt weld will establish a seal or joining of the two plies at an intermediate position. As depicted, lower jaws 310 and 312 support two or more plies of plastic film which, as shown in FIG. 13 A, are identified as 314 and 31 5. Upper jaw members 316 and 317 are adapted to be moved downwardly to a clamped condition as seen in FIG. 13 B which shows the second of the progressive steps.These clamped plies are now melted by a heated ribbon 318 which is moved downwardly to and sufficiently through the plies to sever and melt as shown in FIG. 13 C.

In FIG. E the the jaw members 310 and 312 are moved towards each other after the ribbon 318 has been lifted upwardly. In a like manner and at the same speed and distance the upper jaw members 316 and 317 are moved toward each other to produce a common bead 31 9. After the bead weld 319 has cooled to the desired temperature the jaws 310,312,316 and 317 are moved to the condition and position of FIG. 13 A and as seen in FIG. 13 F the now joined film plies as an assembly are removed from the apparatus.

After the weld has been completed as shown in FIG. 13 E, cooled members 320 and 321 , shown in FIG. 13 D, may be introduced to clamp and flatten the soft weld. This tends to reorient the weld material, improving its physical properties.

The thickness and composition of the films are critical to the satisfactory welding or joining plies 314 and 135. As above noted, the temperature of the heated ribbon 318 and time of said ribbon between the welds establishes the bead welding procedure. The spacing between the clamps and the ribbon is also critical. The weld of the plies of film may be cooled by means other than clamps and/or chilled fluid. For example, in FIG. 13 E an air conduit 322 is shown and provides a blast of air to the melted films. Air nozzle means may be used in any and all of the embodiments and the disposition and number of blast controls is provided in accordance with the apparatus to be used.

Embodiment of FIGS. 14 A, 14 B and 14 C Referring next and finally to the step-by-step apparatus and operation as diagrammatically depicted in the FIGS. 14 A, B and C, it is to be noted that in addition to using heat from an electrical resistance heating element, preheated gasses such as air, or hot gaseous combustion products, may be employed to effect a weld in accordance with this disclosure. FIG. 14 A shows stacked pairs of materials 401 to be protruding simultaneously from multiple clamp members 400. When hot gasses are directed against the protruding congruent edges of the materials, the Y form into welds as shown in FIG. 14 B. Rapid cooling is effected by an air stream to avoid recrystallization as in the case of Mylar. This hot gas method is particularly useful when making shaped welds, rather than straight line welds as described herebefore.

It has been found that gas flow around the protruding material edges tends to keep the clamp edges cool enough to permit the use of combustible materials for the clamps, saving cost in their construction, particularly when shaped.

FIG. 14 C shows the clamped assembly of FIGS. 14 A and 14 B with the protruding material edges depending vertically over a heated platen 402. Forming a weld in this position allows gravity to substantially improve its symmetry and other properties. It has been found that two or more plies of thermoplastic felted materials can be quilted by clamping them between a pierced insulating member and a conductive member. A high voltage discharge is directed through the holes in the insulation member fusing the felt fibers together according to the hole pattern.

Interior shaped welds, including round holes, may be provided interiorly of the perimeters of stacked plies of material by suitably shaping the clamping means and providing heat in accordance with the methods of this disclosure.

Control heating is especially important when welding Mylar since it decomposes if heated much above its welding temperature. Since gas bubbles may form in the weld, some heat must be maintained long enough for the bubbles to reabsorb after which the weld must be quickly cooled to avoid recrystallization and brittleness.

The methods hereinbefore disclosed successfully address these problems.

The several embodiments above described contemplate welding two or more plies of thermoplastic film together. These depicted apparati contemplate that the very difficult to weld films will be successfully welded by localized melting of the plastic film. Whether two or more plies are joined at the ends, edges or intermediate thereof, the heated ribbon is brought to a temperature much greater than the melting temperature of the plastic. This achieves a very fast melting of the plastic. The clamping means provides a cooling means to prevent any of the films held in the gripping means from changing their characteristics.

Assuming Mylar D (TM DuPont) is to be welded, the melting temperature is 81 5 Centigrade. Depending on the thickness of the film strips, such as 0.0125 to 0.254 mm, the ribbon is heated from 1,112 to 4,532 Centigrade. The time of exposure is a very critical factor and the spacing from the ribbon to the edge of the plies, depending on their nature, when the ribbon is heated is about 0.79 mm. The spacing between the clamps and the edges of the plies to be heated is from 1.448 to 1.702 mm as applied to Mylar D. Production processes have indicated that 1.59 mm, with an extreme tolerance of plus or minus 0.397 mm, establishes the limits of parameters of satisfactory bead welding of the edge. The edges of the clamp members as shown are sharp so that the cooling effect of the clamp members is not dissipated.

It is to be noted that the plies of film may be brought to a cooled ribbon and then clamped.

After clamping, the ribbon is moved away from the film edges and the ribbon heated for a determined short interval of time. The weld is cooled by the clamp means and directed air flow and the welded portion released after which the process is repeated. When the ribbon is used as a knife, the heated ribbon causes the advancing plies to melt at this severed portion. The belt arrangement may have a heated ribbon or member made as a curved element and the remainder of the curved element adjacent the endless belt may be provided for cooling. Removal of the trim from the knife cut is effected by means not shown.It is to be noted that roller 223 in FIG. 11 and other rollers may be chilled to provide localized cooling to the melted film portions and the chilled rolls, in their selection, size and temperature, are a matter of selection directed toward the requirement of the apparatus and plies.

The several embodiments show the joining or securing of two or more plies of materials by melting the materials at very local areas while gripping these same plies by clamp or belt means to hold together and cool the adjacent ply area and prevent melting of the plastic except in the protruding area. For this reason the protruding amount of the plies of film is usually from 1.448 to 1.702 mm. The total thickness of plies is usually 0.025 mm or greater. The cost of Mylar D and like plastic is usually high, so the thickness of the film is kept to a minimum.

Terms such as "left", "right", "up", "down", "bottom", "top", "front", "back", "in", "out", and the like are applicable to the embodiments shown and described in conjunction with the drawings.

These terms are merely for the purposes of description and do not necessarily apply to the position in which the welding apparatus for joining plies of film may be constructed or used.

Claims

1. A welding apparatus for joining the congruent edges of a plurality of laminar thermoplastic plies, said apparatus including: (a) means for gripping and holding in a predetermined position the congruent edges of the plies of material, said gripping means including means for applying a predetermined force and for relaxing said force and for releasing said gripping means after a period of time; (b) a ribbon of conductive metal and means for positioning the heated ribbon at a selected distance from the congruent edges of the gripped plies, and (c) means for passing an electric current through the ribbon when at said selected distance, thereby to heat the ribbon to a predetermined temperature effective to melt the adjacent congruent edges of the superimposed plies and thereby to form a bead weld joining said plies along their congruent edges.

2. A welding apparatus according to claim 1, in which the means for gripping and holding further includes a clamp assembly which has opposed jaws with one of the jaws movable to and away from a clamping condition and with the movable jaw applying a predetermined pressure.

3. A welding apparatus according to claim 2, in which the clamp assembly includes a fixed bottom support plate and an upper clamp bar portion, this upper bar portion being moved into and away from clamping condition by cam means carried on and by a shaft whose axis is substantially parallel to the effective weld of said plies.

4. A welding apparatus according to claim 3, in which the upper clamp bar is carried by a L-shaped support member and this support member is carried by a support bar and is removable therefrom by manipulation of a cap screw having a groove formed in a shank portion thereof and into this groove is mounted a pin carried in the L-shaped support member and pivotally retaining said L-shaped member.

5. A welding apparatus according to claims 1, 2, 3 or 4, additionally comprising means for applying a current of cooling air to the weld after the formation thereof.

6. A welding apparatus according to any one of claims 1 to 5, in which the cooled ribbon is employable as a stop to determine the distance the congruent plies protrude from their gripping means.

7. A welding apparatus according to claim 6, additionally comprising means to space the ribbon a predetermined distance from the congruent edges of the plies after the plies have been located by said ribbon acting as a stop and gripped by the clamping means ready for welding.

8. A welding apparatus according to any one of the preceding claims, in which the position of the ribbon is adjustable in accordance with the composition and thickness of the plies of film.

9. A welding apparatus according to any one of the preceding claims in which the ribbon is removably held in tension at its ends by clamp means with additional means to move most of its length into and away from the gripping means.

10. A welding apparatus according to any one of the preceding claims in which the gripping means includes two pairs of inturning rollers with a determined space therebetween, these rollers as pairs carried on common shaft means with means for turning said rollers at like peripheral speeds and in the space between said pair of rollers there is disposed said ribbon which provides both a severing means for the plies brought thereto for congruence of their edges and serving to melt the plies to form the desired weld.

11. Apparatus according to claim 10 which further includes a heating roller carried between pairs of rollers for heating the split plies.

12. A welding apparatus according to claim 1, including a knife which severs or splits the plies of films along a selected line and means are provided for feeding the now split plies to an endless and continuously advancing belt which not only clamps the plies but brings said plies to a position adjacent the ribbon for subsequent formation of the weld.

13. A welding apparatus according to claim 1 in which the apparatus includes upper and lower endless belts carried by and on opposed grooved pulleys with one pair of opposed pulleys adjustably carried by a header member, and a pair of pivotally attached arms movable with the header member by adjusting means, said endless belts serving to carry the superimposed plies between adjustably positioned slide blocks thereby to bring the edges of the plies into a determined proximity to the ribbon during the activation thereof thereby to heat said edges and for the weld.

14. Apparatus according to claim 13, in which the slide blocks provided with a cooling means and additional cooling means are provided to cool the weld while still clamped between the belts.

15. Apparatus according to claim 14 in which the cooling means for slide blocks comprise a liquid conduit extending therethrough.

16. Apparatus according to claim 13, 14 or 15, in which the pulleys carrying the other ends of the endless belts are connected with gear trains so that the endless belts travel at the same speed.

17. Apparatus according to any one of claims 13 to 1 6, additionally comprising means for blowing cold air on to the formed weld.

18. Apparatus according to any one of claims 13 to 16, comprising a cooperating pair of chillable rollers adjacent the belts for cooling the formed weld.

19. A method of joining the edges of a plurality of superimposed plies of thermoplastic material, which comprises placing the plies in superimposed relationship; clamping the superimposed plies adjacent the superimposed edges that are to be joined by said weld; positioning an electrically heatable ribbon adjacent said superimposed edges, and energising the ribbon to heat said edges to form said weld.

20. A method according to claim 19, including forcibly cooling the welded edges with a cooling air stream after formation of the weld.

21. A method according to claim 19 or 20 wherein the superimposed plies are gripped between two fixed and spaced apart jaw members and two like spaced apart movable jaw members, these movable jaw members disposed to move into a gripping condition and to secure a plurality of plies therebetween, and when said plies are so secured, passing a heated ribbon through the held plies thereby to melt and sever said plies and at said severed portion to form a two bead welds, cooling the two welds and moving the movable jaw members to an unloading condition thereby to release the welded plies.

22. A method according to claim 21 in which the ribbon and movable jaw members are moved by and with cylinder means.

23. A method according to claim 21 or 22, in which the ribbon is moved into and maintained in a taut condition by bias means and the ribbon is electrically insulated from conductivity with the remaining apparatus.

24. A method according to claim 21, 22 or 23 where the ribbon is maintained heated while disengaged from the plies by radiative, convective or conductive means.

25. A method according to any one of claims 21 to 24, in which the movement of the movable jaw and the movement of the heated ribbon is by independently actuated cylinders.

26. A method according to claim 21, in which the plies are brought and disposed between a first pair of jaw members and a second pair of movable jaw members which are spaced at like distances from each other and movable toward the first pair of jaws to provide the desired gripping, and after the plies are gripped the heated ribbon is brought to and partly through the held plies to melt and sever said plies, and at said severed portion the melted and oppositely disposed portions are brought into a common weld by moving the pair of jaw members toward each other to form and provide a common bead weld and after the weld is achieved the heated ribbon is moved therefrom and the plies are cooled and released and the jaws are moved again to a receiving condition.

27. A method according to claim 26, in which one of the first jaw members and an opposite movable jaw members are movable and moved toward and from the other first and second jaw members.

28. A method according to claim 26 or 27, in which the ribbon and the first and second jaw members are moved by cylinder means.

29. A method according to claim 26, 27 or 28 in which the weld is cooled by flowing air.

30. A method according to claim 26, 27 or 28 wherein the weld is cooled by chilled clamping plies.

31. Welding apparatus for joining the congruent edges of a plurality of plies of laminar thermoplastic materials and adapted to provide heat sufficient for melting locally said plies at a predetermined temperature and for a selected period of time, said apparatus including: (a) means for gripping the plies with their congruent edges protruding a predetermined distance from the gripping means; (b) means for supplying heat for a predetermined time to the protruding edges of the plies to effect a bead weld, and (c) means for cooling said weld.

32. Apparatus according to claim 31 where the heating means is a gaseous fluid.

33. Apparatus according to claim 31 where the heating means is a heated surface spaced away a predetermined distance from the edges of the plies.

34. Apparatus according to claim 31 in which the plies are fed to and past a knife which severs or splits the plies along a selected line and after severing along the prescribed path the now split plies are fed to an endless and continuously advancing belt which not only clamps the plies but brings said plies to a source of heat whereat and whereby the melt of the plies is achieved, followed by cooling means for the weld.

35. Apparatus according to claim 31 in which the plies are continuously edge welded and the welding apparatus includes upper and lower endless belts carried by and on opposed grooved pulleys with one pair of opposed pulleys adjustably carried by a header member, and a pair of pivotally attached arms moved with the header member by adjusting means and with the source of heat applied at a predetermined degree and with the plies carried adjacent and spaced from this heated ribbon by said endless belts and plies carried by and between slide blocks adjustably positioned to bring the edges of the plies into a determined proximity to the ribbons and with the slide blocks adapted to be cooled by external means and additional means to cool the weld while still clamped between the belts.

36. Apparatus according to claim 35, in which the weld cooling means is provided by a cooperating pair of chilled rollers adjacent the belts.

37. Apparatus according to claim 1 substantially as hereinafter described with reference to the accompanying drawings.

38. A method according to claim 19 substantially as hereinbefore described with reference to the accompanying drawings.