WO1992014600A1

WO1992014600A1 - A method of welding a material cotaining heat-weldable plastics, as well as a welding press and a welding electrode to be used when carrying out the method

Info

Publication number: WO1992014600A1
Application number: PCT/DK1992/000057
Authority: WO
Inventors: Henrik Nyborg
Original assignee: Weldan A/S
Priority date: 1991-02-25
Filing date: 1992-02-25
Publication date: 1992-09-03
Also published as: AU1378392A; DK136891A; DK136891D0

Abstract

A method for heat welding plastics (1, 2) between a holder-on (5) and an electrode (3) comprising a pulse heating element (9). A welding press (10) for carrying out the method comprises two planes (4, 5) relatively movable (6) towards and away from one another, and an adjustable depth stop. The welding plane (4) is non-heated and retains at least one pulse heating element (9) with an active area (R) separated from the plastic material (1, 2) by way of a partition layer (8) of a higher melting point. The profile and the pattern of the welding electrode are shaped in accordance with the welding to be performed. Each pulse heating element (9) is connected to a timer and an electronic regulator which can individually set and adjust very accurately the temperature and the welding period for each pulse heating element. The holder-on plane (5) is also non-heated and of a shape mating the shape of the welding pattern and the material (1, 2). A welding electrode to be used when carrying out the method comprises a laminate of two electrically insulating layers (7, 8) of a higher melting point than the plastic material (1, 2), and a pulse heating element (9) embedded between said two layers and communicating with outside current connectors (A, B).

Description

Title: A Method of Welding a Material Containing Heat-

Weldable Plastics, as well as a Welding Press and a We ding Electrode to be Used When Carrying Out the Meth¬ od f ( 5 Technical Field

The invention relates to a method of welding a material containing heat-weldable plastics by way of indirect heating thereof.

Background Art

10 Heat contact welding is traditionally used for welding thermoplastic materials, said welding involving a direct or an indirect heating. In case of plastic materials presenting a sufficiently high dielectric loss, such as PVC, HF-welding is used.

15 The HF-welding is advantageous in only using a single electrode, i.e. the welding electrode, which is cold in principle. Another advantage is found in the heating of the material, said heating being caused by the dielec¬ tric loss in the material with the result that the meth-

20 od is very easy and convenient to perform and does not require a production of exactly mating and accordingly expensive electrodes. The HF-generator of the machine is, however, very expensive and involves furthermore a high consumption of energy. The method has gradually

25 been extensively used especially for welding PVC.

A heat contact welding involving an indirect heating of the plastics employs usually a welding electrode and a counter electrode, where both electrodes are heated, the welding electrode being heated to a temperature about 30 the softening temperature of the plastics and the coun¬ ter electrode being heated to a temperature exceeding the melting temperature of the plastics. The welding electrode is of a solid, permanent shape and includes the particular welding profile acting directly on the possibly Teflon—coated top side of the plastics, and the counter electrode is also of a solid, permanent, espe— cially plane shape and is shielded from the plastics by means of a separation tape of a higher melting point than the plastics. The latter method has been extensive¬ ly used for welding thin sheets, but can only be used to a limited extent for welding thick sheets and materials because the heat must be conducted through the plastics in order to reach the welding spot, and accordingly the top side of the plastics is heated more than the welding spot. Thick materials require a comparatively long heat¬ ing period, and therefore critical problems of heat da- mages arise outside the welding seams. In order to ob¬ tain high production rates, attempts have been made at operating at temperatures being as high as possible, but such procedures only made the situation worse because the high temperatures and high amounts of heat, espe— cially in the bottom tool, involved a considerably in¬ creased risk of the sheets being damaged. A consequence of the unintended heating is that the sheets turn soft and form bulges, especially in connection with even very short breaks. Attempts have been made at solving this problem by establishing suitable screening devices and cooling devices, but these devices did not provide sa¬ tisfactory results when thick sheets were involved.

The above problems have become particularly topical be¬ cause of the present requirements for restricting the use of PVC so as to reduce the environmental damages. Accordingly, a demand has arisen for using other types of plastics, especially polyolefines . These types of plastics cannot, however, be welded by way of HF—welding in a satisfactory manner, and accordingly it is neces— sary to use heat contact welding although such a welding does not provide satisfactory results. A more particular problem applies to the manufacture of urine bags, wound bags, blood plasma bags etc. of ther¬ moplastic materials. Such bags are provided with at least one tubing or valve, and accordingly these bags are constantly encumbered with the problem of establish¬ ing a sealing connection between the tubing or the valve and the bag. Ordinarily the bag is "pinch-welded" along the tubing/valve. By the expression "pinch-welding" is meant that the bag sheet is tightened about the tub- ing/the valve from both sides of said tubing/valve by means of a welding electrode with a so-called tubing block, whereafter the webs of the bag sheet are welded together along the tubing/the valve in such a manner that the bag is preferably welded onto the tubing/the valve along the two lines formed by the welding elec¬ trode parallel to said tubing/valve. However, such a pinch-welding seldomly suffizes for ensuring an abso¬ lutely sealed connection, and accordingly one of several possible processes is used for improving the sealing. One of the possible processes is treating the tubing/the valve with a substance, such as cyclohexanone , prior to the insertion thereof in the bag, said substance causing the PVC to swell and seal. The latter process is, howev¬ er, preferably not used due to the toxic cyclohexanone vapours and the presence of the foreign substance in the bag. It is also possible to use pin-welding involving a pole-changing for HF—weldable materials , which is a very efficient, but time—consuming, expensive, and sensitive method often leaving large marks in the tubings. The latter method can only be used in connection with short tubings, i.e. tubings of a length not exceeding 75 mm, in order to allow insertion of the pin in the tubing. Another method is heat contact welding by means of a hot welding shoe of a shape tightly fitting half the tubing and usually made of brass lined with Teflon-tape and constantly heated to 150 to 180^βC. Such a method allows per se a good welding, but a poor appearance of said welding because the welding shoe is pulled away from the tubing while subjected to maximum heat and while the process is still difficult to control. Another advantage of the latter method is that it is inexpensive. Finally, it is possible to use ultrasonic welding at 20 to 40 kHz, which is a very fast method applicable in almost any available material, but which is very cost-intensive to use. It is a condition for the latter method that tensions do not arise in the materials to be welded. This method involves furthermore a risk of small holes being formed in the sheet along the welding electrode.

The problems of carrying out a welding being satisfac¬ tory in all respects apply in particular to the use of polyolefines , where especially polypropylene is only weldable in a very restricted temperature range of ap- proxi ately 8^βC. The problems apply also to the manufac¬ ture of thick-walled products and/or to products of a varying thickness various locations therein and/or to material shapes deviating from the plane sheet or plate products .

Among other known welding methods, the pulse heat weld¬ ing has furthermore been used within the packing in¬ dustry, especially for the manufacture of bags. The heating is by this method carried out by means of elec¬ trically heated resistance wires. This method is, howev— er, only used for thin sheets, and as far as the appear¬ ance is concerned the quality of the weldings has been poor compared to the requirements that can be met by HF- welding PVC.

Description of the Invention

Accordingly, a distinct demand exists for a method over¬ coming the above problems of the known methods , and the object of the present invention is to provide such a new method being both easy and inexpensive to carry out, as well as being simple to adjust very accurately, and which in addition can be varied in many ways in response to the welding to be carried out and be used in connec¬ tion with combinations of all types of heat-weldable ma¬ terials, and finally which can easily be developed for welding on a wide range of non-plane surfaces.

The new and characteristic features of the method ac¬ cording to the invention are found in

- inserting the material between a holder-on and a welding electrode, where said welding electrode com- prises at least one electrically insulated pulse heating element with an active and an inactive area, and where each pulse heating element is connected to a power source through an electronic regulator con¬ trolled by a timer, and where the pulse heating ele- ment in the active area is separated from the plast¬ ic material by a partition layer of a higher melting point than the plastic material and is shaped in accordance with the material and the weld to be welded, - followed by transmitting a current through the pulse heating element and compressing of the material to a predetermined depth stop for the welding electrode, the timer and the electronic regulator being set such that in a period of time determined by the set- ting of the timer the regulator maintains a very accurately controlled temperature in the active area of the pulse heating element within a narrow tem¬ perature range immediately above the melting point of the plastic material in question by measuring the voltage across and the current intensity in the pulse heating element at short intervals, such as 20 milliseconds, and by adjusting for deviations from the set temperature,

- whereafter the regulator and the current is inter- rupted by means of the timer, and the welded mate¬ rial is cooled and removed. In this manner it is possible to carry out weldings of a very high quality in all types of thermo-weldable ma¬ terials. The welding electrode is easily adjusted to the shape of the material to be welded, also when used in a non—plane course. The very accurately controlled temper¬ ature in the pulse heating element renders it possible to optimize the transfer of heat to the welding spot while it is ensured that heat is not transferred to other spots beyond the welding spot. The depth stop en— sures that the sof ened/melted plastic material is not pressed away from the welding seam with the result that a seam of a high quality without beads or holes is en¬ sured. The accurate temperature control renders it fur¬ thermore possible to weld through very thick material layers as the heat transfer can be restricted to the welding area, whereby the surrounding areas do not suf¬ fer from heat damages. It is furthermore possible to vary the temperature on various locations in the pulse heating element, said varying being performed merely by correspondingly varying the electric resistance in said element with the effect that it is possible to vary the melting degree of the plastic material on various loca¬ tions of the welding seam. Energy is only used for the heating of the pulse heating element during the welding and then only for briefly heating and melting very small areas of the material, and accordingly the method is very energy—saving. In addition, the method is very con¬ venient to use as all the parts involved are non—heated during the preparation step of each welding. It is fur- thermore very easy to alter the welding conditions, said alteration merely requiring a readjustment of the weld¬ ing temperature and/or the welding period. The method is very inexpensive with respect to expenses both for the electrodes and for the equipment controlling the time and the temperature. The dimensioning of the welding tool and the structure of the apparatus is uncomplicat¬ ed. The electrodes require no heating period because the temperature set appears almost instantaneously in the electrode when the welding is initiated. No foreign sub¬ stances form part of the welding, and no sound or con¬ tact problems arise due to the heat. The method can be used for welding both soft and hard plastic materials as well as combinations thereof, such as a soft tubing on a hard injection-moulded pipe. The welding period is ty¬ pically about 1 sec. When welding PVC, the temperature in the pulse heating element is typically about 190^βC, and when welding PE said temperature is typically about 140^βC.

By choosing an electronic regulator, such as of the type "Resistron Res.-220", it is according to the invention possible to control the fluctuations in the temperature in the pulse heating element within a range of ±. 4^βC, especially within ± 2^βC relative to the set temperature. As a result, it is possible to remain inside the tem¬ perature range allowing a welding of for instance poly¬ propylene without said material flowing ~n an uncon¬ trolled manner.

When the material over at least a portion of the length to be welded comprises a non—planar surface facing the welding electrode, it is according to the invention ad¬ vantageous to use a welding electrode with a pulse heat¬ ing element mating the shape of the surface, preferably a welding electrode with a bendable pulse heating ele¬ ment and a welding block suited for shaping and pressing the pulse heating element into abutment with the surface of the material. In this manner the welding block may either completely mate the non-planar material surface or merely be shaped so as to spotwise force the pulse heating element into the desired position.

In addition it is possible to use a holder-on comprising at least one additional electrically insulated pulse heating element connected to a power source and an elec- tronic regulator with an associated timer and with a partition layer between said element and the plastic material, where said partition layer is of a higher melting point than the plastic material, whereby it is possible in one operation to perform the welding from both sides of the material, which is advantageous when for instance an article is to be welded between two lay¬ ers of sheet.

For certain purposes, especially when more than one pulse heating element is used in the welding electrode and/or the holder-on, respectively, the method according to the invention is advantageous in individually setting and controlling the temperature and the welding time of each pulse heating element by means of an electronic regulator and timer for each pulse heating element. In this manner it is possible to compensate for possible variations in the welding conditions between the indivi¬ dual pulse heating wires. Thus one side of a welded product may for instance be provided with one or more layers of material exceeding the number of layers on the other side of said product, such as a soft fibre layer making the bag less unpleasant to wear against the skin.

When the method according to the invention is used for sealingly welding a rod or tubing-shaped or tubular ar¬ ticle into a material containing plastics, such as a bag or tubing material, said method is advantageously car¬ ried out by squeezing the article inserted between two opposing layers of bag material or in the tubing ma¬ terial, between a welding electrode and a holder—on, which together form a preferably cylindrical cavity and which individually comprises at least one pulse heating element and a partition layer, and by heating the pulse heating elements to the desired temperature(s) in the desired period(s) of time, followed by cooling and re¬ moving the welded material. As a result, an easy and simple sealing welding is achieved of the inserted rod or tubing—shaped or tubular article onto the bag or tub- Ing material. The sealing welding can be performed after a conventional pinch-welding or as a separate welding prior to the actual welding of the bag in question. By a particular setup or production line, the sealing welding can alternatively be performed simultaneously with the remaining welding of the bag, optionally as a step of the production line involved.

The completing cooling is according to the invention advantageously carried out by means of a cooling system, such as an automatically controlled water cooling system, built into the welding electrode and/or the holder-on with the result that a handling of the welding products is achieved, which is as lenient as possible.

The invention relates furthermore to a welding press for carrying out the method and comprising a welding plane and a holder-on plane, where at least one plane can be moved towards and away from the other plane, and an ad¬ justable depth stop for adjusting the minimum distance between the planes with a high accuracy. The new and characteristic features of the welding press according to the invention are found in the facts

- that the welding plane is a non-heated plane retain¬ ing a welding electrode, which comprises at least one electrically insulated pulse heating element with an active and an inactive area, where at least the active area is separated by a partition layer of a higher melting point than the plastics from the material to be welded, and where the profile and the pattern of the welding electrode is shaped in ac- cordance with the weld and the material to be weld¬ ed, and where each pulse heating element is connect¬ ed to a power source through an electronic regulator controlled by a timer, said regulator being such that it is possible to set and adjust the tempera- ture in the active area and the individual welding period for each pulse heating element with a high accuracy, the electronic regulator being capable of measuring the voltage across and the current inten¬ sity in each pulse heating element at short inter¬ vals, such as 20 milliseconds, and of adjusting for deviations from the set temperature,

— and where the holder—on plane is an also non—heated plane containing a holder—on of a shape mating the welding pattern and the shape of the material.

The resulting welding press is inexpensive to manufac- ture, presents a flexible applicability, is easy to ad¬ just to the desired process, is easy and convenient to handle as well as energy—saving.

According to an embodiment of the welding press accord¬ ing to the invention, the welding electrode comprises a pulse heating element, which at least over a portion is formed according to a non—plane surface portion of the material, preferably by the electrode comprising a bend- able pulse heating element and a welding block, which over a portion is shaped according to the non—plane sur- face portion of the material, and which is suited for forming and pressing the pulse heating element so as to abut said non— lane surface portion of the material. The resulting electrode is very simple and inexpensive to use for welding non—planar surfaces, and it allows the use of the same pulse heating element for various non- planar surfaces.

When both sides of an article are to be welded simultan¬ eously, the welding press may according to the invention advantageously be such that the holder—on comprises at least one electrically insulated pulse heating element with an active and an inactive area and separately con¬ nected to the power source through an electronic regu¬ lator controlled by a timer, said pulse heating element being seperated from the material by means of a parti- tion layer of a higher melting point than the plastic material. In this manner it is possible simultaneously to weld on both sides of the material in welding periods and at welding temperatures being controlled individual¬ ly. The various pulse heating elements can, of course, also be interconnected in series and thereby be simul¬ taneously controlled by means of the same timer and re¬ gulator. The latter connection does not, however, pre¬ vent an operation at various temperatures on various locations by means of various electric resistances in the pulse heating elements.

The welding press according to the invention may fur¬ thermore be such that the pulse heating element situated on the holder-on is shaped according to a non—plane por¬ tion of the surface of the material facing the holder- on, preferable by said pulse heating element being bend- able, and such that the side of the holder-on facing the material is adapted to shape and press the pulse heating element into abutment with said surface. The resulting welding method renders it possible in one operation to two-sidedly weld articles having non-planar surfaces on opposing sides.

According to the invention the welding press may in par¬ ticular be adapted to sealingly weld a rod or tubing- shaped or tubular article into a plastic-containing ma- terial, such as a bag or tubing material. The latter welding press is characterised in that it comprises a welding electrode and a holder-on, which together form a preferably cylindrical cavity communicating with the article mould, and which individually comprises at least one pulse heating element and a partition layer of a higher melting point than the plastic material, whereby the individual pulse heating elements are connected to their respective electronic regulator controlled by a timer for an individual setting and adjustment of the temperature and the welding period. In this manner a simple and rational welding in of non-planar articles into sheet material is allowed in a sealing manner. The shape of the article to be welded in is not particularly important because the pulse heating elements are easy to bend and shape with the result that even very sharp di- rectional changes on the surface to be welded are ac¬ ceptable. The welding tools are easy to dimension with the result that it is possible for instance for the welding in of a soft tubing of a diameter of 10 mm into a bag material of a thickness of 200 μm to use a welding electrode with a welding block, which together with the holder—on form a cavity of a diameter of 10 mm. Subse¬ quently, the cavity is lined with a pulse heating ele¬ ment of a thickness of 100 μm and a Teflon—tape on both sides thereof and also of a thickness of 100 μm. In this manner each pulse heating element can be shaped com¬ pletely symmetrical as a semi-circular curve with dia¬ metrically arranged webs at the ends thereof. In order to ensure a good sealing between the tubing and the bag material in the triangular areas at the transition be- tween the serai—circular curve and the diametrically ar¬ ranged webs, it is possible to provide the pulse heating elements with a higher resistance and consequently a higher temperature in these areas , whereby the plastics more easily melt and merge in these areas.

According to the invention it is preferred that the electronic regulator used is such that during the weld¬ ing, such as at intervals of 20 milliseconds, said regu¬ lator can register the voltage across and the current intensity in the pulse heating element and consequently register a value of the temperature in the active area of the pulse heating element, and furthermore said regu¬ lator can adjust for deviations from the value set in such a manner that the fluctuations in the temperature of the pulse heating element during the running can be kept within a temperature range of + 2^βC. In this manner it is possible in a very reliable manner to control the temperature within the very restricted temperature range of 8^βC applying when polypropylene is to be welded with¬ out involving problems of the melted polypropylene flow¬ ing in an uncontrolled manner.

Especially for welding thick-walled materials, which, of course, are more heated by the welding than correspond¬ ing thin-walled materials, the welding press may advan¬ tageously be adapted to automatically perform a cooling after the welding, but before the opening of the press and the removal of the material, especially an internal water cooling of at least one of said means communicat¬ ing with the material by way of heat transmission. As a result, a fast cooling of the welded products is ensured in an easy manner.

The invention relates furthermore to a welding electrode to be used when carrying out the method. The welding electrode may according to the invention take a number of different shapes, all of which preferably comprising a lamin te of two electrically insulating layers of a higher melting point than the plastic material, at least one pulse heating element being embedded between said two layers, where said pulse heating element is of the shape of the welding pattern and communicates with outer current connectors.

A preferred embodiment of the welding electrode is ac- cording to the invention characterised in that the pulse heating element used is a pulse heating wire of an al¬ most linear temperature/resistance ratio in its active area and of a cross sectional dimension, which for inst¬ ance may be of a width of between about 2 mm and about 8 mm and a thickness of between about 0.1 mm and about 0.2 mm, and where the pulse heating wire outside its active area is copperplated or shaped in another manner so as to possess a higher conductivity.

According to a particularly advantageous embodiment of the welding electrode, the pulse heating element has been bent into a non—plane shape mating the shape of the material to be welded.

According to the invention the pulse heating element may advantageously comprise a metal—containing sheet, which is inexpensive to manufacture.

The pulse heating element may, however, also comprise an electrically conductive pattern arranged inside the la¬ minate by way of pressing or photochemical or electro- static transfer, in which case the electric resistance along the welding pattern has then been adapted to the desired generations of heat.

According to a particular embodiment of the pulse heat¬ ing element particularly suited for non—linear patterns, such as closed curves, said pulse heating element is a pulse heating wire extending in the longitudinal extent of the welding seam and winding within the width of said welding seam. As a result, it is immediately possible to shape the winding pulse heating wire in accordance with the pattern to be welded. In addition, the dimensional alterations of the heating wire caused by the tempera¬ ture changes can be directly absorbed as small movements within the individual curves and thereby prevent pro¬ blems from arising in connection with absorbtion of lon- gitudinal extensions when long portions of the heating wire are being heated.

The welding electrode may furthermore comprise a heat- conducting pattern layer mating the pattern of the weld¬ ing seam, said heat—conducting pattern layer communicat— ing by way of heat transmission with the pulse heating element while being electrically insulated relative thereto. As a result, a further distribution of the heat is allowed, said distribution for instance distributing the heat transferred from the pulse heating element to a comparatively broader and optionally more distinctly defined welding seam. In addition, the latter distribu¬ tion of heat can compensate for variations in the di¬ stribution of heat inside the welding seam. Thus it is for instance possible by means of such a layer also to establish a heat transferring bridge across a short por¬ tion where the pulse heating element must be interrupted for technical reasons although it is desired that the welding seam continues unchanged across said portion.

Brief Description of the Drawing

The invention is explained in greater detail below by means of embodiments and with reference to the accompa¬ nying drawing, in which-

Fig. 1 is a diagrammatic, side view of the fundamental structure of a welding press with a welding electrode according to the invention,

Fig. 2 illustrates the fundamental structure of the con¬ trol system of the welding process,

Fig. 3 is a side view of a typical arrangement of a sealing welding in of a tubing into a urine bag,

Fig. 4 is a sectional view on a larger scale through a portion of the bag of Fig. 3 with the welding shown,

Fig. 5 is a diagrammatic view of the structure of the welding tool to be used for carrying out the welding of Figs. 3 and 4,

Fig. 6 is a sectional view on a larger scale of a detail of the welding of Figs. 3 and 4, and

Figs. 7, 8 and 9 are exploded views of alternative embo¬ diments of the welding electrode according to the inven— tion intended for one—sided welding.

Best Mode for Carrying Out the Invention

Fig. 1 is a diagrammatic view of the fundamental struc¬ ture of a welding press 10 according to the invention for welding plane layers of material together, at least one of said layers containing thermoplastic material. The Figure shows two layers 1, 2 of material. The illu¬ strated press 10 comprises a welding plane 4 and a hold¬ er—on plane 5 as well as a welding electrode 3 associat— ed with a control system not shown. Both planes 4, 5 are non—heated and made of a hard, dimensionally stable ma¬ terial, such as aluminium. As indicated by the double arrow 6 , the welding plane 4 is shaped in a manner known per se so as to be movable towards and away from the holder—on plane 5. An adjustable depth stop not shown determines the minimum distance between the two planes with a very close accuracy. The welding electrode 3 ap¬ pears as a laminate comprising two electrically insulat¬ ing partition layers 7 , 8 of for instance Teflon—tape or another thermostable material of a higher melting point than the thermoplastic material of the layers 1, 2, as well as a pulse heating wire 9 embedded between the partition layers 7, 8. The pulse heating wire 9 compris¬ es a centrally active area R indicated by the symbol of an electric resistance for the sake of clarity, and two current connectors A, B for the connection with the con¬ trol system. The welding electrode 3 may be secured to the welding plane, such as by way of adhering, or be loosely arranged atop the layers 1, 2 of material or be secured thereto. According to a particular embodiment of the welding press 10, the welding plane 10 and/or the holder—on plane 5 may be provided with cooling channels for the internal cooling.

Fig. 2 illustrates the fundamental structure of the con- trol system for the welding process used in connection with an e ctronic regulator 20 of the type "Resistron Res-220" the company ROPEX Industrie-Elektronik GmbH, D 7120 Bietigheim, Bissingen, and mating pulse heating wires presenting constant temperature/resistance condi- tions. The control system is such that the pulse heating wire 9 with the connectors A, B, is coupled in a secon¬ dary circuit 11. The secondary circuit 11 is supplied with current from a primary circuit 13 through a welding transformer 12, said primary circuit 13 being supplied with current from the electronic regulator 20 communi¬ cating with the power supply, 220 V, 50 Hz. An adjust¬ able timer T is associated with the electronic regulator 20 and switches the current supply on and off to the primary circuit 13 and determines thereby the welding period. During the welding process the electronic regu¬ lator 20 measures automatically the voltage E₂ across the pulse heating wire 9 at intervals of 20 milliseconds as well as the current intensity I₂ through said pulse heat¬ ing wire 9 by means of a measuring transformer 14. In addition, the regulator compares automatically the cor¬ responding resistance in the pulse heating wire 9 as well as the desired temperature set on said regulator 20 with the result that as the regulator detects deviations from the set temperature it alters the effect in the primary circuit in up- or downward direction.

Fig. 3 illustrates a portion of a urine bag 15 with two layers 1, 2 of PVC sheet welded together along the rims apart from a small portion in the middle of one end, said portion having been subjected to a pinch-welding 16, 16' about a PVC tubing 17 and an additional trans¬ verse welding 18, 18' . A hatched ar 19 transverse to the inserted tubing 17 and the pi n-welding 16, 16' illustrates how a two-sided sealing welding is typically placed in connection with the tubing according to the invention, i.e. the so-called tubing-welding 19. The tubing—welding provides a melting together of the tubing material 17 and the bag material 1, 2 with the result that any leak along the tubing has been eliminated.

Fig. 4 is a sectional view taken along the arrows A-A of Fig. 3 through the shown two—sided tubing—welding 19, where the tubing 17, the two layers 1, 2 of bag material with the pinch-welding 16, 16' , and the tubing-welding 19 are indicated.

Fig. 5 is an exploded view of a portion of the fundamen¬ tal structure of the welding tool used for the tubing- welding 19. The portion includes the welding block 21 and the holder-on 22 with the two cavities 23, 24 mating the cross section of the tubing in question, as well as two identical welding electrodes 3, 3' placed on the welding block 21 and the holder-on 22, respectively. The identical welding electrodes 3, 3' comprise a pulse heating wire 9, 9' enclosed on both sides with a layer of Teflon—tape 7, 8 and 7' , 8' , respectively. The layers of Teflon-tape have an electrically insulating effect and at the same time a higher melting point than the PVC bag and the PVC tubing here being welded together.

Fig. 6 is a sectional view perpendicular to the tubing 17 of a portion of the completed product. For the sake of clarity, it has been set off where the two layers 1, 2 of bag material have melted together with the tubing 17 in the triangular areas 26, 26' , where said areas meet one another.

Figs. 7, 8, and 9 illustrate examples of embodiments of a welding electrode for a one-sided welding and in form of laminates of Teflon— ape layers surrounding the pulse heating element and interconnected by way of adhering or welding together.

Fig. 7 is an exploded view of a welding electrode 3. The welding electrode comprises a laminate of two layers 7, 8 of Teflon—tape and an intermediary layer 29 also of Teflon-tape embedding a pulse heating element in form of an imprinted, electrically conductive pattern 9 with connectors A, B. The pattern 9 may alternatively be im¬ printed on one of the layers 7, 8 with the result that the layer 29 can be left out. The connectors A, B inter¬ connect the welding electrode and the secondary circuit 11, cf. Fig. 2.

Fig. 8 is also an exploded view of a welding electrode 3. The welding electrode comprises here a laminate of two layers 7 , 8 of Teflon-tape and an intermediary layer 29 also of Teflon-tape and with a pulse heating element in form of a resistance wire 9. The resistance wire 9 is of a substantially circular cross section curving as a pattern between the connectors A and B. The resistance wire is suitably adhered to or pressed down into the layer 29.

Fig. 9 is also an exploded view of a welding electrode 3 fundamentally shaped like the electrodes of Fig. 7 or Fig. 8 with two outer layers 7, 8 and an intermediary layer 29 of Teflon-tape, where the layer 29 embeds the pulse heating element. In addition, an extra layer 25, preferably of Teflon-tape, has, however, been inserted on the side of the layer 29 which is to face the mate¬ rial to be welded. The extra layer 25 is provided with a patterned layer 9' of a highly heat—conductive material, such as a metal-containing printing paste. The layer 9' may alternatively be imprinted on the layer 29 on the opposite side thereof relative to the pulse heating ele¬ ment or on the inner side of one of the layers 7, 8 pro- vided it is carried out in such a manner that the layer 9' is electrically insulated from the pulse heating ele¬ ment .

Claims

Claims .

1. A method of welding a material containing heat-weld— able plastics by way of indirect heating thereof, c h a r a c t e r i s e d by — inserting the material between a holder-on and a welding electrode, where said welding electrode com¬ prises at least one electrically insulated pulse heating element with an active and an inactive area, and where each pulse heating element is connected to a power source through an electronic regulator con¬ trolled by a timer, and where the pulse heating ele¬ ment in the active area is separated from the plast¬ ic material by a partition layer of a higher melting point than the plastic material and is shaped in accordance with the material and the weld to be welded, — followed by transmitting a current through the pulse heating element and compressing of the material to a predetermined depth stop for the welding electrode, the timer and the electronic regulator being set such that in a period of time determined by the set¬ ting of the timer the regulator maintains a very accurately controlled temperature in the active area of the pulse heating element within a narrow tem- perature range immediately above the melting point of the plastic material in question by measuring the voltage across and the current intensity in the pulse heating element at short intervals, such as 20 milliseconds, and by adjusting for deviations from the set temperature,

— whereafter the regulator and the current is inter¬ rupted by means of the timer, and the welded mate¬ rial is cooled and removed.

2. A method as claimed in claim 1, c h a r a c t e r — i s e d by controlling by means of the electronic regu¬ lator the fluctuations in the temperature in the pulse heating element within a range of +. 4°C, especially thin i 2°C relative to the set temperature.

3. A method as claimed in claim 1 or 2 , where the ma¬ terial over at least a portion of the length to be weld- ed comprises a non-planar surface facing the welding electrode, c h a r a c t e r i s e d by using a weld¬ ing electrode with a pulse heating element mating the shape of the surface, preferably a welding electrode with a bendable pulse heating element and a welding block suited for shaping and pressing the pulse heating element into abutment with the surface of the material.

4. A method as claimed in one or more of the preceding claims 1 to 3 , c h a r a c t e r i s e d by using a holder-on comprising at least one additional electrical- ly insulated pulse heating element connected to a power source and an electronic regulator with an associated timer and with a partition layer between said element and the plastic material, where said partition layer is of a higher melting point than the plastic material.

5. A method as claimed in claim 4, where more than one pulse heating element is used in the welding electrode and/or the holder—on, respectively, c h a r a c t e r ¬ i s e d by individually setting and controlling the temperature and the welding time of each pulse heating element by means of an electronic regulator and timer for each pulse heating element.

6. A method as claimed in claim 4 or 5 for sealingly welding a rod or tubing—shaped or tubular article into a material containing plastics, such as a bag or tubing material, c h a r a c t e r i s e d by squeezing the article inserted between two opposing layers of bag ma¬ terial or in the tubing material, between a welding electrode and a holder-on, which together form a pre¬ ferably cylindrical cavity and which individually com- prises at least one pulse heating element and a parti¬ tion layer, and by heating the pulse heating elements to the desired temperature(s) in the desired period(s) of time, followed by cooling and removing the welded ma— terial.

7. A method as claimed in one or more of the preceding claims l to 6, c h a r a c t e r i s e d by carrying out the completing cooling by means of a cooling system, such as an automatically controlled water cooling system, built into the welding electrode and/or the holder—on.

8. A welding press for welding a material containing a heat— eldable platics by way of the method as claimed in claim 1, and comprising a welding plane and a holder-on plane, where at least one plane can be moved towards and away from the other plane, and an adjustable depth stop for adjusting the minimum distance between the planes with a high accuracy, c h a r a c t e r i s e d in — that the welding plane is a non—heated plane retain- ing a welding electrode, which comprises at least one electrically insulated pulse heating element with an active and an inactive area, where at least the active area is separated by a partition layer of a higher melting point than the plastics from the material to be welded, and where the profile and the pattern of the welding electrode is shaped in ac¬ cordance with the weld and the material to be weld¬ ed, and where each pulse heating element is connect¬ ed to a power source through an electronic regulator controlled by a timer, said regulator being such that it is possible to set and adjust the tempera¬ ture in the active area and the individual welding period for each pulse heating element with a high accuracy, the electronic regulator being capable of measuring the voltage across and the current inten¬ sity in each pulse heating element at short inter- vals, such as 20 milliseconds, and of adjusting for deviations from the set temperature, - and where the holder-on plane is an also non-heated plane containing a holder-on of a shape mating the welding pattern and the shape of the material.

9. A welding press as claimed in claim 8, c h a r a c¬ t e r i s e d in that the welding electrode comprises a pulse heating element, which at least over a portion is formed according to a non-plane surface portion of the material, preferably by the electrode comprising a bend- able pulse heating element and a welding block, which over a portion is shaped according to the non-plane sur¬ face portion of the material, and which is suited for forming and pressing the pulse heating element so as to abut said non-plane surface portion of the material.

10. A welding press as claimed in claim 8 or 9 , c h a r a c t e r i s e d in that the holder—on com¬ prises at least one electrically insulated pulse heating element with an active and an inactive area and sepa- rately connected to the power source through an elec¬ tronic regulator controlled by a timer, said pulse heat¬ ing element being seperated from the material by means of a partition layer of a higher melting point than the plastic material.

11. A welding press as claimed in claim 10, c h r ¬ a c t e r i s e d in that the pulse heating element situated on the holder—on is shaped according to a non- plane portion of the surface of the material facing the holder-on, preferable by said pulse heating element be- ing bendable, and that the side of the holder-on facing the material is adapted to shape and press the pulse heating element into abutment with said surface.

12. A welding press as claimed in one or more of the preceding claims 8 to 11 for a sealing welding in of a rod or tubing—shaped or tubular article in a plastic- containing material, such as a bag or tubing material, acccording to the method as claimed in claim 7 , c h a r a c t e r i s e d in that it comprises a welding electrode and a holder—on, which together form a preferably cylindrical cavity communicating with the article mould, and which individually comprises at least one pulse heating element and a partition layer of a higher melting point than the plastic material, whereby the individual pulse heating elements are connected to their respective electronic regulator controlled by a timer for an individual setting and adjustment of the temperature and the welding period.

13. A welding press as claimed in one or more of the preceding claims 8 to 12, c h a r a c t e r i s e d in that the used electronic regulator is such that during the welding, such as at intervals of 20 milliseconds, said regulator can register the voltage across and the current intensity in the pulse heating element and con— sequently register a value of the temperature in the active area of the pulse heating element, and further¬ more said regulator can adjust for deviations from the value set in such a manner that the fluctuations in the temperature of the pulse heating element during the run— ning can be kept within a temperature range of +. 2^βC.

14. A welding press as claimed in one or more of the preceding claims 8 to 13, c h a r a c t e r i s e d in that it is adapted to automatically perform a cooling after the welding, but before the opening of the press and the removal of the material, especially an internal water cooling of at least one of said means communicat¬ ing with the material by way of heat transmission.

15. A welding electrode to be used when carrying out the method as claimed in one or more of the preceding claims 1 to 7 , c h a r a c t e r i s e d in that it comprises a laminate of two electrically insulating layers of a higher melting point than the plastic material, at least one pulse heating element being embedded between said two layers, where said pulse heating element is of the shape of the welding pattern and communicates with outer current connectors.

16. A welding electrode to be used when carrying out the method as claimed in one or more of the preceding claims l to 7, c h a r a c t e r i s e d in that the pulse heating element used is a pulse heating wire of an al¬ most linear temperature/resistance ratio in its active area and of a cross sectional dimension, which for inst¬ ance may be of a width of between about 2 mm and about 8 mm and a thickness of between about 0.1 mm and about 0.2 mm, and where the pulse heating wire outside its active area is copperplated or shaped in another manner so as to possess a higher conductivity.

17. A welding electrode as claimed in claim 15 or 16, c h a r a c t e r i s e d in that the pulse heating element has been bent into a non-plane shape mating the shape of the material to be welded.

18. A welding electrode as claimed in claim 15, 16 or 17, c h a r a c t e r i s e d in that the pulse heat¬ ing element comprises a metal-containing sheet.

19. A welding electrode as claimed in claim 16, c h a r a c t e r i s e d in that the pulse heating element comprises an electrically conductive pattern arranged inside the laminate by way of pressing or pho¬ tochemical or electrostatic transfer.

20. A welding electrode as claimed in claim 15 or 16, c h a r a c t e r i s e d in that the pulse heating element is a pulse heating wire extending in the longi¬ tudinal extent of the welding seam and winding within the width of said welding seam.

21. A welding electrode as claimed in one or more of the preceding claims 15 to 20, c h a r a c t e r i s e d in that in addition it comprises a heat—conducting pat— tern layer mating the pattern of the welding seam, said heat—conducting patter layer communicating by way of heat transmission with the pulse heating element while being electrically insulated relative thereto.