NO20220794A1

NO20220794A1 - Welding system and method for welding thermoplastic

Info

Publication number: NO20220794A1
Application number: NO20220794A
Authority: NO
Inventors: Lasse Willumsen; Pål Meløysund; Joachim Tiedemann
Original assignee: Polarplast As
Priority date: 2020-01-31
Filing date: 2021-02-01
Publication date: 2022-07-12
Also published as: WO2021154094A1; NO20200117A1

Description

Title: WELDING SYSTEM AND METHOD FOR WELDING THERMOPLASTIC

Description

Field of invention

[001] The invention relates to the welding of thermoplastic, more particularly a welding system for welding thermoplastic by means of a welding wire or welding band of metal which is applied to a welding path and which is heated by means of current and resistance in the welding wire or welding band.

Background

[002] Inventor works on a daily basis with thermoplastic constructions and many working hours in the company are spent on welding thermoplastic. Today's welding method involves the use of a welding machine that heats a point by means of hot air and / or contact with a hot surface. The welding point is moved along the welding paths. So-called extruders are used where a heated / molten welding wire is pressed out on a heated thermoplastic welding web or the thermoplastic is heated and compressed without welding wire. This puts high demands on the skills and endurance of the operator.

[003] It is known from e.g. EP 0281347 B1 to attach thermoplastic by means of electrically conductive welding wires which are heated by means of resistance.

Furthermore, it is known from US2012 / 0231272 to use a 'welding electrode’ made of an electrically conductive welding wire wrapped in thermoplastic for so-called thermoplastic electrofusion welding.

[004] Generally, the strength of a weld is less than the strength of the parts to be welded. The inventor describes a welding system and method that increases the strength of the weld and reduces the level of skill needed to achieve a good welding.

Brief summary of the invention

[005] The invention describes a welding system for welding thermoplastic parts together along a welding path. The system comprises one or more pressure applicators for pressing the thermoplastic parts to be welded together, an adjustable electrical power source and electrical contact means for creating an electrical circuit by means of the power source. The system further comprises a thermoplastic welding list to be applied to an outside of one of the thermoplastic parts to be welded. The thermoplastic welding list comprises a thermoplastic body, at least one welding line baked into or mounted on to the thermoplastic body and an insulating layer fastened to a side to be directed away from the thermoplastic part to be welded. The system further comprises fastening means for fastening the welding list to one of the thermoplastic parts to be welded. The thermoplastic part, onto which the welding list is applied, must be thin enough for the heat from the welding line to penetrate through said thermoplastic part.

[006] The invention also describes a method for welding two thermoplastic parts together using the mentioned welding system.

Brief description of the figures

[007] For a better understanding of the invention, we have made some drawings showing different embodiments of the invention. In these figures, the same reference numerals refer to the same features in different figures.

Figure 1a - d shows different embodiments of a welding list.

Figure 2a and b shows an embodiment of a pressure device in a side view and top view respectively.

Figure 3 shows two thermoplastic parts to be welded with a welding list positioned at the lower side.

Figure 4 shows two parts to be welded with a welding list positioned at the upper side.

Fig. 4a shows the two parts after welding.

Figure 5 shows two parts to be welded with a connection part bridging a gap between them and two welding lists positioned at the lower side and a press beam on top of the connection part.

Figure 6 shows two parts to be welded with a connection part bridging a gap between them and two welding lists positioned at the upper side and a press beam on top.

Figure 7 shows an embodiment where a welding band is mounted on the press beam.

Figure 8 Shows a section of cloths that are joined by forcing two press beams and a power source with contact means.

Figure 9 shows an embodiment of a welding list.

Detailed description

[008] The invention describes a welding system for welding thermoplastic parts together along a welding path. In the absence of a common term for wire and band, we use the words 'welding line’ 1 , which in this text means one or more flexible welding wires 1 b or welding bands 1 a of metal which can be heated by means of a supplied current. A welding path is the path on the respective thermoplastic parts 2, 3 along which they are to be welded, or the line where the two parts are welded together.

[009] The system comprises a thermoplastic welding list 11 , as shown in fig. 1 a-d, to be applied to the outside of one of the thermoplastic parts to be welded as shown in fig. 2a. The welding list comprises a thermoplastic body 21 and at least one welding line 1 which is positioned inside or mounted on to the thermoplastic body 21. The welding line 1 can also be sandwiched between two thermoplastic body parts 21 a, 21 b, which together constitutes the thermoplastic body. In one embodiment, the thermoplastic body 21 of the welding list 11 is extruded with the welding line 1 inside. The welding list 11 further comprises an insulating layer 20 to prevent heat from escaping to the surrounding and to promote a more even heating. In one embodiment the insulating layer 20 is a welding cloth or welding blanket made of fiberglass and a layer of aluminum foil. Preferably the welding cloth is next to the thermoplastic body 20 of the welding list 11 , but the welding will also function if the aluminum layer is next to the thermoplastic body.

[010] The welding line 1 comprises at least one flexible welding band 1 a or welding wire 1 b which can be heated by electrical resistance. The welding band or welding wire can be made of many different types of metal, but it is a great advantage that the welding line 1 can bend and change direction when the thermoplastic to be welded is applied. The welding system can be used on both thinner sheets or plates of thermoplastics, such as geomembranes, and on solid thermoplastic structures, such as boats, fish farms or tubular structures. However, it is a great advantage that the welding path is linear. Experience shows that the welding system can handle a thickness up to at least 5 cm of thermoplastic.

[011] In one embodiment, the metal in the welding line is copper. A typical thickness of a copper welding band will be from 0.2 mm to 1 mm. Copper has been shown to work well in terms of price, electrical resistance, flexibility and sufficient resistance to mechanical influences.

[012] When using welding wire 1 b instead of welding band 1 a, we have achieved good results with welding wires of copper that are 0.5 - 2 mm in diameter. The advantage of welding wire over welding band is that a smaller proportion of the weld is canceled due to the smaller extent of the welding wire in width. Usually the welding line will not adhere very well to the thermoplastic.

[013] The width of the welding band is in the order of 2-20 mm. If it becomes too wide, it will be difficult to make a curve with the welding band without curling it and thus cause uneven heating of the thermoplastic. As mentioned, the welding band or welding line does not form a strong bod with the thermoplastic for this reason the welding line should not be positioned centrally between the two parts to be welded thus weakening the bond between the parts to be welded.

[014] In known thermoplastic welding methods, a heating tool is often used which heats a spot of the thermoplastic quickly and moves the heating tool along the welding path at a steady speed. This gives a strength in the weld of typically 60% of the unwelded material. The method according to the invention gives a strength of just over 80% of the unwelded material. The reason for this is that there is a slow and more homogeneous heating that takes place simultaneously over the entire welding path, while with spot welding there is a rapid heating that is difficult to get homogeneous. That is, welding with spot welding is to a greater extent dependent on a skilled and enduring craftsman / welder. If the structure to be welded allows, the thermoplastic can also be bent along the welding paths during welding to a desired angle, when using the welding system according to the invention. For obvious reasons, this cannot be done with ordinary welding where the entire length is not heated at the same time.

[015] The welding system further comprises fastening means for making it possible to fasten the welding list to one of the thermoplastic parts to be welded. In one embodiment the fastening means is an adhesive.

[016] To achieve a desired pressure during welding, the system comprises pressure applicators 4. The pressure applicators may be weights, clamps 4c, straps 4a or a specially developed pressing device 4b, preferably in combination with one or more press beams 7 to distribute the pressure along the welding path. The mentioned pressing device 4b will be described later. The pressure is calculated according to the standard for thermoplastic welding. Torque wrench may be used to control the pressure, when using a pressing device or clamps.

[017] The pressing device 4b, shown in fig. 2a and 2b comprises a pressing arm 16 with at least one suction cup 15 at each end and an adjustable pushing rod 14 in the middle. Preferably the suction cups 15 are mounted on a suction cup arm 18, preferably with adjustable length to allow for different thicknesses of the parts to be welded and possibly a press beam 7. Preferably the pushing rod 14 and suction cup arms are parallel. Both the suction cups 15 and the pushing rod 14 can be operable by hand, compressed air or hydraulics. The pushing rod can also be electrically operated. In one embodiment a number of pressing arms are mounted together on a longitudinal beam 17 as seen in fig 2b.

[018] The pushing rod 14 may be adjusted by a screwing or jacking mechanism pressing against the area to be welded either directly on the structure or via a press beam 7 distributing the pressure along the welding path. In other words, the longitudinal beam 17 and the press beam 7 can be the same beam or two different beams.

[019] Fig. 3 shows a welding list below two thermoplastic parts to be welded 2, 3 and pressure is applied from above. Fig. 4 shows a similar configuration with the welding list on top. Fig. 4b shows the two parts from fig. 4 after welding. The thermoplastic body 20 of the welding list has now to a large degree been pressed into the closet part to be welded and a welding line can be seen bulging out at the end of each part. The overall thickness of the weld is slightly more than the two parts to be welded due to the thermoplastic body of the welding list. The welding band 1a is now integrated into the welding path close to the top. In this way the presence of the welding band disturbs/weakens the weld to much lesser degree compared to the configuration where the welding band is positioned between the two parts to be welded. At the same time, it is possible to reheat if the welding needs to be adjusted.

[020] Fig. 5 and fig. 6 shows a configuration where a thermoplastic connection part 19 bridges the two thermoplastic parts to be welded. This configuration allows for a gap between the two parts 2, 3.

[021] In another embodiment, the welding line 1 , preferably a welding band 1 a, is fastened to at least one press beam 7 with a Teflon layer 8 attached to the outside of the welding band as seen in fig. 7. The Teflon layer prevents the welding band from sticking to the thermoplastic after heating. This embodiment has the advantage that the welding line 1 is attached to the press beam 7 and can be used again and again.

[022] When welding thermoplastics of a structural / stiff nature, the pressure applicators 4 are preferably at least one of weights, straps 4a, the mentioned pressing device and clamps 4c. It can also be advantageous to use these in combination with press beams 7 in order to distribute the pressure along the welding path.

[023] In the event of a power failure, the welding path must be cooled before the process is resumed, to ensure that the correct welding temperature is achieved and not exceeded.

[024] Furthermore, the welding system comprises an adjustable current source for heating the metal welding band to the desired temperature and contact means for creating an electrical circuit through the welding line 1 by means of the current source. The contact means 6 will typically be two electrically conductive terminals which are attached to each end of the welding wire and to each wire which leads to its own pole on the adjustable power source.

[025] In one embodiment, the welding list 11 has a cross section which is the same in the longitudinal direction of the band and which is shaped as one of: T-shape, H-shape, trapeze, rectangle or triangle. For example, an H-shape can be used to join plates together.

[026] In one embodiment, the welding line 1 in the welding list 11 is a plurality of parallel wires or bands distributed over the cross section of the welding line. In another embodiment, two welding lines 1 are running parallel along the length of the welding list, as shown in figure 9, with electrical contact, achieved by means of a connector 13, at one end. The figure also shows how welding lists can be connected together by means of male 12b and female 12a contacts.

[027] The welding system is used by means of a method for welding thermoplastic along a welding path, the method comprising the following steps:

a) Attaching a welding list 1 along the welding path to at least one of the thermoplastic parts to be welded. The insulating layer is directed away from the welding path.

b) To apply pressure along the welding path by means of pressure applicators. The size of the pressure applied must be in accordance with 'Standards for thermoplastic welding'. The pressure applicators may be weights, straps 4a, the described pressing device 4b or clamps 4c. If the structures to be welded are not sufficiently rigid, one or more pressure beams may be required which distribute the pressure along the welding path.

c) Connecting the welding wire 1 to the adjustable power source 5 by means of the contact means 6.

d) To weld the two thermoplastic parts 2, 3 together by energizing the welding line 1 with current parameters that are in accordance with ‘Standards for thermoplastic welding’. (Eg EN 13067, DS INF. 70-1-7, NS: 416-1-2: 2008, EN 12201 -2-3, ISO 12176-2, ISO 13950)

Table of contents

1 Welding line

1a Flexible welding band

1b Flexible welding wire

2, 3 The thermoplastic parts to be welded 4 Pressure applicators

4a Straps

4b Pressing device

4c Clamps

5 Adjustable power source

6 Contact means

7 Press beam

8 Teflon layer

9 Welding wire drain

10 Joint part

11 Welding list

12a and b Male and female contact

13 Connector

14 Pushing rod

15 Suction cup

16 Pressing arm

17 Longitudinal beam

18 Suction cup arm

19 Thermoplastic connection part

20 Insulating layer

21 Thermoplastic body

21a, b Thermoplastic body parts

Claims

1. Welding system for welding thermoplastic parts (2, 3, 19) together along a welding path comprising:

one or more pressure applicators (4) for pressing the thermoplastic parts to be welded together,

an adjustable electrical power source (5),

electrical contact means (6) for creating an electrical circuit by means of the power source,

characterized by a thermoplastic welding list (11) to be applied to an outside of one of the thermoplastic parts to be welded, wherein the thermoplastic welding list comprises:

a thermoplastic body (21 ),

at least one welding line (1 ) baked into or mounted on to the thermoplastic body (21),

an insulating layer (20) fastened to a side to be directed away from the thermoplastic part to be welded,

fastening means for fastening the welding list to one of the thermoplastic parts to be welded,

wherein the thermoplastic part, onto which the welding list is applied, is thin enough for the heat from the welding line (1) to penetrate through said thermoplastic part.

2. Welding system according to claim 1 , wherein the welding line 1 is at least one welding band (1b).

3. Welding system according to claim 1 , wherein the welding line 1 is at least one welding wire (1b).

4. Welding system according to claim 2, wherein the fastening means is an adhesive applied to the welding list (1a) on the opposite side from the insulating layer (20).

5. Welding system according to claim 1 , wherein the welding line (1 ) is made of copper.

6. Welding system according to claims 1 and 5, wherein the welding strip (1a) is 0.2 to 0.5 mm thick.

7. Welding system according to claims 1 and 5, wherein the welding strip (1a) is between 2 and 20 mm wide.

8. Welding system according to claims 1 and 5, wherein the welding wire (1 b) is 0.5 to 2 mm in diameter.

9. Welding system according to claim 1 , wherein the pressure applicator (4) are at least one of: weights, straps (4a) and clamps (4c).

10. Welding system according to claim 1 , wherein the pressure applicator (4) is a pressing device (4b) having at least one pressing arm (16) with at least one suction cup (15) mounted on each end of the pressing arm and having a pushing rod (14) in the middle, wherein the pushing rod (14) and suction cups (15) are operable to press the thermoplastic parts, that are to be welded, together along the welding path.

11 . Welding system according to claim 10 wherein the pressing device (4b) comprises a plurality of pressing arms (16) attached to a longitudinal beam (17) at right angles.

12. Welding system according to claim 1 wherein the welding system comprises a press beam (7) to distribute the pressure from the one or more pressure applicators (4).

13. Welding system according to claim 12, wherein a Teflon layer (8) is attached to the press beam (7) on the outside of the welding strip (s) (1 a) to avoid thermoplastic to stick to the press beam.

14. Welding system according to claim 1 , wherein the contact means (6) are two electrically conductive cords which are attached to each end of the welding line and to each pole on the adjustable current source.

15. A method of welding thermoplastic along a welding path with the welding system of claim 1 , wherein the method comprises the following steps:

a) fastening the welding list (11) along the welding path,

b) applying pressure by means of the pressure applicators (4),

c) connecting the welding line 1 to the adjustable power source 5 by means of the contact means 6, and

d) welding the thermoplastic parts 2, 3 together by energizing the welding line 1.

16. The method according to claim 15 wherein the method comprises positioning a press beam (7) along the welding path before executing step b.