WELDING WIRE CARTRIDGE WITH MOISTURE PROTECTION

Abstract

In order to reduce the accumulation of moisture on a welding wire (2, 2′, 2″) arranged in a welding wire cartridge (1, 1a, 1b) or to remove existing moisture in a simple and reliable manner, it is provided that a flow (D.sub.1) of purging air supplied to the welding wire cartridge (1, 1a, 1b) is adjusted by a flow control unit (14), the purging air is supplied to the flow control unit (14) at a first pressure (p) and is discharged at a purging air discharge (24) of the welding wire cartridge (1, 1a, 1b) at a third pressure (p.sub.at), and at a purging air feed (15) of the welding wire cartridge (1, 1a, 1b) a second pressure (p.sub.1) at the purging air feed (15) that is lower than the first pressure (p) results from the adjusted flow (D.sub.1), the third flow (p.sub.at) and a flow resistance between the purging air feed (15) and the purging air discharge (24), the relative humidity (rF.sub.1) of the purging air being reduced by the relief of pressure from the first pressure (p) to the second pressure (p.sub.1).

Claims

1. A welding wire cartridge for holding a welding wire (2, 2′, 2″) having a protective device (4) against moisture, wherein a purging air feed (15), into which a purging air supply line (13) for supplying dry purging air discharges, and a purging air discharge (16) having a purging air outlet (24) for discharging purging air out of the welding wire cartridge (1, 1a, 1b) are provided on the welding wire cartridge (1, 1a, 1b), characterized in that a flow control unit (14) is arranged in the purging air supply line (13) that adjusts a flow (D.sub.1) of purging air through the welding wire cartridge (1, 1a, 1b), in that a first pressure (p) is present upstream of the flow control unit (14) in the purging air supply line (13), in that a second pressure (p.sub.1), which is lower than the first pressure (p), is present downstream of the flow control unit (14) in the purging air supply line (13) and at the purging air feed (15), in that a third pressure (p.sub.at), which is lower than the second pressure (p.sub.1), is present at the purging air outlet (24), so that a pressure differential (p.sub.1−p.sub.at) results across the welding wire cartridge (1, 1a, 1b) and in that the second pressure (p.sub.1) at the purging air feed (15) results from the adjusted flow (D.sub.1), the third pressure (p.sub.at) and the flow resistance between the purging air feed (15) and the purging air outlet (24), whereby the relative humidity (rF.sub.1) of the purging air is reduced as a result of the relief of pressure from the first pressure (p) to the second pressure (p.sub.1).

2. The welding wire cartridge according to claim 1, characterized in that the pressure differential (p.sub.1−p.sub.at) between the second pressure (p.sub.1) and the third pressure (p.sub.at) is less than 0.2 bar.

3. The welding wire cartridge according to claim 1, characterized in that the purging air discharge (16) is connected to a purging air discharge line (17), the outlet of which forms the purging air outlet (24) and discharges into the environment.

4. The welding wire cartridge according to claim 1, characterized in that the flow (D.sub.1) of purging air through the welding wire cartridge (1, 1a, 1b) can be changed via the flow control unit (14) in order to adjust the relative humidity (rF.sub.2) of the purging air in the purging air discharge (16).

5. The welding wire cartridge according to claim 1, characterized in that an adjustable dehumidifier (12′) is arranged in the purging air supply line (13) upstream of the flow control unit (14), via which the relative humidity (rF) of the purging air upstream of the flow control unit (14) can be adjusted.

6. The welding wire cartridge according to claim 1, characterized in that a pressure regulating unit (25) is arranged in the purging air supply line (13) upstream of the flow control unit (14), via which the first pressure (p) of the purging air upstream of the pressure regulating unit (14) can be set.

7. The welding wire cartridge according to claim 1, characterized in that a moisture sensor (19) is arranged on the purging air discharge (16).

8. The welding wire cartridge according to claim 1, characterized in that a flow sensor (21) is arranged on the purging air discharge (16).

9. The welding wire cartridge according to claim 1, characterized in that a purging air guide device (18) is provided in the welding wire cartridge (1, 1a, 1b).

10. The welding wire cartridge according to claim 1, characterized in that a wire feed hose (26) is provided on the welding wire cartridge (1, 1a, 1b) as a purging air discharge (16).

11. A method for protecting a welding wire (2, 2′, 2″) in a welding wire cartridge (1, 1a, 1b) against humidity, characterized in that a flow (D1) of purging air supplied through the welding wire cartridge (1, 1a, 1b) is adjusted by means of a flow control unit (14), in that the purging air is supplied to the flow control unit (14) at a first pressure (p) and is discharged at a purging air discharge (24) of the welding wire cartridge (1, 1a, 1b) at a third pressure (p.sub.at), and in that, at a purging air feed (15) of the welding wire cartridge (1, 1a, 1b), a second pressure (p.sub.1) at the purging air feed (15) that is lower than the first pressure (p) results from the set flow (D.sub.1), the third pressure (p.sub.at) and a flow resistance between the purging air feed (15) and the purging air outlet (24), whereby a pressure differential (p.sub.1−p.sub.at) across the welding wire cartridge (1, 1a, 1b) results and the relative humidity (rF.sub.1) of the purging air is reduced by the relief of pressure from the first pressure (p) to the second pressure (p.sub.1).

12. The method according to claim 11, characterized in that the pressure differential (p1−pat) between the second pressure (p.sub.1) and the third pressure (p.sub.at) is set at less than 0.2 bar.

13. Method according to claim 11, characterized in that the flow of purging air through the welding wire cartridge (1, 1a, 1b) is set using the flow control unit (14) in order to set the relative humidity (rF.sub.2) of the purging air at the purging air discharge (16).

14. The method according to claim 11, characterized in that the first relative humidity (rF) of the purging air is altered using a dehumidifier (12′) upstream of the flow control unit (14).

15. The method according to claim 11, characterized in that the first pressure (p) of the purging air is altered upstream of the flow control unit (14) using a pressure regulating unit (25) upstream of the flow control unit (14).

16. The method according to claim 11, characterized in that the relative humidity (rF.sub.2) is measured downstream of the welding wire cartridge (1, 1a, 1b) and the flow control unit (14) or the dehumidifier (12′) or the pressure regulating unit (25) is controlled, in order to set a prescribed relative humidity (rF.sub.2,soll).

17. The method according to claim 16, characterized in that the flow (D.sub.1) supplied to the welding wire cartridge (1, 1a, 1b) is controlled so that the relative humidity (rF.sub.2) at the purging air discharge (16) is less than a prescribed maximum relative humidity (rF.sub.2,soll).

18. The method according to claim 11, characterized in that the flow (D.sub.2) is measured downstream of the welding wire cartridge (1, 1a, 1b) and an error is indicated if the measured flow (D.sub.2) remains below a prescribed, expected percentage of the supplied flow (D.sub.1).

Description

[0016] The present invention is explained below with reference to FIGS. 1 to 4, showing exemplary, schematic and non-restrictive advantageous embodiments of the invention. Shown are

[0017] FIG. 1 an welding wire cartridge having a safety device according to the invention,

[0018] FIG. 2 an arrangement having two welding wire cartridges connected in series,

[0019] FIG. 3 a simple control for the flow of dry purging air and

[0020] FIG. 4 a block diagram of a simple control concept.

[0021] A welding wire cartridge 1 is illustrated in FIG. 1, in which a welding wire 2 is inserted in a customary manner and is removed from the welding wire cartridge 1 in a welding process 3 (not depicted here in detail) and used for welding. A welding device having necessary additional equipment, such as an inert gas supply, for welding process 3 is well known and is not described or illustrated in detail here. A feed unit for conveying welding wire 2 can be provided in the welding wire cartridge 1 but can also be arranged in the welding device itself and/or in the welding torch. Welding wire 2 is generally inserted into welding wire cartridge 1 in the form of a welding wire coil 5, as indicated in FIG. 1. In order to protect the welding wire 2 from the moisture contained in the ambient air, a safety device 4 is provided that is described in detail below.

[0022] Via a compressor 10, ambient air is compressed and purging air with pressure p is created and made available via a compressed air line 11. A dehumidifier 12 is generally already contained in compressed air line 11, in the simplest case in the form of a water separator, which reduces the relative humidity rF of the created purging air or carries away the precipitated water. Compressed air is generally available in every manufacturing facility because many components in a manufacturing facility, such as various tools, require a compressed air supply and is, therefore, not normally a part of safety device 4 which in turn represents a cost savings. However, safety device 4 can, of course, also be equipped with its own compressor for creating compressed air from ambient air if no suitable compressed air supply is available on site.

[0023] Safety device 4 receives purging air from compressed air line 11 via a purging air supply line 13. If a dehumidifier 12 is provided in compressed air line 11 (which will generally be the case), purging air supply line 13 preferably branches off downstream from dehumidifier 12.

[0024] Purging air having a first pressure p and having a relative humidity rF is thus available in purging air supply line 13. An additional dehumidifier 12′ can also be arranged in purging air supply line 13. It is also conceivable that a pressure regulation unit 25 can be arranged in purging air supply line 13, for example in order to raise or lower pressure p in compressed air line 11 for safety device 4. Additional dehumidifier 12′ and/or pressure regulation unit 25 can also be controlled in order to set a desired first relative humidity rF or a desired first pressure p in purging air supply line 13.

[0025] Using a flow control unit 14 in purging air supply line 13, the need-based flow of purging air through welding wire cartridge 1 is set and prevailing first pressure p upstream of flow control unit 14 is thereby reduced to the second pressure p.sub.1 in purging air supply line 13 downstream from flow control unit 14. Flow control unit 14 can be designed as a mass flow regulator to regulate a mass flow or equivalently as a volumetric flow regulator to regulate a flow volume. In the following, flow D generally refers to mass flow or volumetric flow.

[0026] Purging air supply line 13 discharges downstream of flow control unit 14 via a purging air feed 15 into welding wire cartridge 1, through which welding wire cartridge 1 is supplied with purging air feed 15 having a specified flow D.sub.1, a specified second pressure p.sub.1 and a specified second relative humidity rF.sub.1. Welding wire cartridge 1 further has a purging air discharge 16, via which the purging air is removed from welding wire cartridge 1. Flow D.sub.2, pressure p.sub.2 and relative humidity rF.sub.2 are present at purging air discharge 16. Outgoing flow D.sub.2 is usually lower than incoming flow D.sub.1 because a sealed welding wire cartridge 1 is not required. This means that purging air can also leak from welding wire cartridge 1 at other places of the welding wire cartridge 1. Pressure p.sub.2 is only slightly lower than p.sub.1 because the flow cross sections in the wire cartridge are sufficiently large. Relative humidity rF.sub.2 at purging air discharge 16 is elevated in comparison to relative humidity rF.sub.1 at purging air feed 15 because the purging air is enriched with moisture in welding wire cartridge 1 and transports it away.

[0027] Purging air discharge 16 can also be connected to a purging air discharge line 17 that forms purging air outlet 24 of purging air discharge 16 and preferably discharges into the environment. Purging air discharge 16 can also discharge directly into the environment, however, and thereby form purging air outlet 24. A third pressure p.sub.at, preferably the ambient pressure, is present at purging air outlet 24 of purging air discharge 16. Purging air discharge line 17 or purging air discharge 16 itself preferably has a flow cross section large enough that, even at maximum flow D.sub.max in welding wire cartridge 1, only a small pressure differential forms between second pressure p.sub.1 on purging air feed 15 and third pressure p.sub.at at purging air outlet 24 of purging air discharge 16, preferably (p.sub.1−p.sub.at)≈(p.sub.2−p.sub.at)<0.2 bar. This means in particular that a sufficiently low flow resistance exists between purging air feed 15 and purging air outlet 24 because of the sufficiently large flow cross section. Second pressure p.sub.1 upstream of welding wire cartridge 1 is thus exclusively a function of currently prevailing third pressure p.sub.at at purging air outlet 24 of purging air discharge 16 of welding wire cartridge 1 and of the pressure differential (p.sub.1−p.sub.at), that ensues from the low flow resistance and in turn results from the adjusted flow. Second pressure p.sub.1 upstream of welding wire cartridge 1 is thus not adjusted, but results from the operation of welding wire cartridge 1. Because of the pressure reduction from first pressure p to second pressure p.sub.1 thus taking place, a reduction of moisture in the purging air also necessarily takes place, as is described in detail below.

[0028] In welding wire cartridge 1, a purging air guide device 18, in the form of baffles, nozzles, outflow openings, collecting devices, etc., can advantageously be provided in order to ensure as uniform a flow as possible of dehumidified or dried purging air through welding wire cartridge 1 and with it a uniform overflow of welding wire 2 with dehumidified purging air, as indicated in FIG. 1. A commercially available welding wire cartridge 1 (for example a welding wire package or a welding wire drum) is preferably used, however, in order to lower costs, wherein only a purging air feed 15 and a purging air discharge 16 may need to be provided. In the case of a welding wire coil 5, it can also be provided that welding wire coil 5 is radially purged simultaneously from the outside and the inside. It is also conceivable to provide a commercially available welding wire holder that has a welding wire 2 arranged therein with a sealed enclosure having a purging air feed 15 and a purging air discharge 16. An enclosure having a commercially available welding wire holder located therein is considered to be a welding wire cartridge 1 purged by means of dry purging air in the sense of the invention. The enclosure could also be a complete storage area in which a plurality of commercially available welding wire holders can also be stored. Thanks to openings in the welding wire holder, it is to also ensured in this case that welding wire 2 in the welding wire holder is flushed with dry purging air and is thus protected from moisture.

[0029] A flow of purging air that ideally corresponds to the need is adjusted in purging air supply line 13 by flow control unit 14, and first pressure p upstream of flow control unit 14 is decompressed to second pressure p.sub.1 downstream from flow control unit 14, whereby relative humidity rF of the purging air is changed in a known way in proportion to these two pressures p, p.sub.1 according to the (simplified) equation rF.sub.1=rF*p.sub.1/p, in particular reduced where p>p.sub.1. Flow control unit 14 therefore realizes a reduction of the relative humidity based upon the resulting pressure ratios.

[0030] For example, in purging air line 11 there is purging air having a first pressure p=6 bar (a possible drop in pressure in dehumidifier 12 or 12′ is disregarded in the description for reasons of simplicity) and a first relative humidity rF=32% (which corresponds to a pressure dew point of 3° C. and is a standard value of a common dehumidifier 12). Second pressure p.sub.1 in welding wire cartridge 1 results from the need-based flow set by flow control unit 14, the flow resistances and pressure differential (p.sub.1−p.sub.at) between purging air feed 15 of welding wire cartridge 1 and purging air outlet 24 of welding wire cartridge 1. Flow control unit 14 effects such a reduction of pressure p to pressure p1. At a third pressure, preferably the ambient pressure, p.sub.at=1.013 bar at purging air outlet 24 of purging air discharge 16, and at second pressure p.sub.1≈p.sub.2=1.1 bar at purging air feed 15, second relative humidity rF.sub.1 of the purging air in purging air supply line 13 downstream from flow control unit 14, and thus also at purging air feed 15, turns out to be rF.sub.1=rF*p.sub.1/p=6% (which corresponds to a pressure dew point of −18.6° C.). If it is assumed that there is a higher value for relative humidity in the environment of welding wire cartridge 1 than at purging air feed 15, the relative humidity at purging air outlet 24 and at purging air discharge 16 of welding wire cartridge 1 cannot drop below rF.sub.1, meaning rF.sub.1≦rF.sub.2.

[0031] Since second pressure p.sub.1 at purging air feed 15 for welding wire cartridge 1 ensues, second relative humidity rF.sub.1 of the dry purging air supplied to welding wire cartridge 1 is also predetermined, at least subject to the condition that a constant first pressure p and a constant first relative humidity rF are present. Thus flow D.sub.1 of dry purging air through welding wire cartridge 1 having relative humidity rF.sub.1 can be regulated by flow control unit 14 to adjust the humidity in welding wire cartridge 1.

[0032] If a moisture sensor 19 is arranged in purging air discharge line 17 that measures the prevailing relative humidity rF.sub.2 at purging air discharge 16 in flow D.sub.2, a simple flow control can be implemented that automatically determines the correct, need-based flow.

[0033] It can be assumed that first pressure p in compressed air line 11 always remains constant because other components in the manufacturing facility must also be supplied by it. The third pressure, generally the ambient pressure, p.sub.at, is also essentially constant because outlet 24 of the purging air preferably is into the environment. Thus a sufficient pressure differential (p.sub.1−p.sub.at) is always available so that flow control device 14 can ensure a need-based flow D from purging air feed 15 through welding wire cartridge 1 to purging air discharge 16.

[0034] That minimum flow D on falling below of the maximum permissible moisture at purging air discharge 16 is indicated as need-based flow D. This flow D is needed to comply with the requirements of the operator with respect to moisture. Furthermore, the need-based flow is influenced by the moisture that is introduced into welding wire cartridge 1 during a changing operation, by the moisture that penetrates through the surface of welding wire cartridge 1, by the relative humidity rF.sub.1 that the purging air at purging air feed 15 contains and by the maximum allowed humidity rF.sub.2 at purging air discharge 16.

[0035] Flow D.sub.1 supplied to welding wire cartridge 1 is thus regulated by flow control unit 14 in such a manner that relative humidity rF.sub.2 at purging air discharge 16 is maintained below a maximum value rF.sub.2,soll to be defined by the user. If prevailing humidity rF.sub.2 measured at purging air discharge 16 by moisture sensor 19 is below the maximum value, flow D.sub.1 can be reduced because less purging air is apparently sufficient to carry away the moisture from welding wire cartridge 1. The consumption of purging air is thus reduced and energy is saved. If, however, moisture enters into welding wire cartridge 1 because of leaks in welding wire cartridge 1 and the penetrating moisture cannot be removed by currently supplied flow D.sub.1, relative humidity rF.sub.2 present at purging air discharge 16 will rise. In this case, flow D.sub.1 of purging air is increased in order to be able to carry the excess moisture that is present away from welding wire cartridge 1 and to bring relative humidity rF.sub.2 back below the allowed maximum value rf.sub.2,soll.

[0036] In order to prevent a continuous switching of safety device 4, an upper threshold value rF.sub.2O (equal to maximum relative humidity rF.sub.2,soll) and a lower threshold rF.sub.2U (less than the maximum relative humidity rF.sub.2) can be defined or specified for prevailing relative humidity rF.sub.2 that specify the switching points for increasing or lowering flow D.sub.1, as shown in FIG. 3. However, relative humidity rF.sub.2 can also be regulated to a specified relative humidity rF.sub.2,soll in a closed-loop control via an implemented control rule. To do this, a control unit 20, which regulates flow D.sub.1, can be provided as indicated in FIG. 1.

[0037] It can also be provided that second relative humidity rF.sub.1 can be adjusted at purging air feed 15. If, for example, an additional adjustable dehumidifier 12′ or a pressure control unit 25 (indicated in FIG. 1) is arranged in purging air supply line 13, second relative humidity rF.sub.1 can be adjusted in accordance with the above relationship rF.sub.1=rF*p.sub.1/p, if first pressure p and/or first relative humidity rF is altered in purging air supply line 13 upstream of flow control unit 14. In this case, one could also completely omit control of flow D.sub.1 and set a constant flow D.sub.1, for example. It is also conceivable, however, to apply the adjustment of first relative humidity rF and/or of first pressure pin purging air supply line 13 in addition to control flow D. It is important to understand, however, that the pressure differential (p.sub.1−p.sub.at) between purging air feed 15 and purging air outlet 24 is not affected by controlling first pressure p, but rather only second relative humidity rF.sub.1.

[0038] However, precise control of prevailing relative humidity rF.sub.2 at purging air discharge 16 is mostly not mandatory, and a simplified method for operating safety device 4 can often be sufficient. This is because there is no “too dry” when storing welding wire, and it must therefore only be monitored that a maximum relative humidity rF.sub.2,soll at purging air discharge 16 is not exceeded. A possible, simple control concept is described below in reference to FIG. 4.

[0039] In step S1, after safety device 4 is switched on, a specified flow D.sub.1, preferably a minimum flow D.sub.min, is set. In step S2, it can be verified whether welding wire cartridge 1 is closed (D.sub.1=D.sub.2). If this is the case, a quick dehumidification can be provided in step S3. To do this, a specified maximum flow value D.sub.max is set for a specified, determined time or until measured relative humidity rF.sub.2 has dropped below a specified value in order to dehumidify the volume of welding wire cartridge 1 as quickly as possible. Steps S2 and S3 are optional. It is then continually checked if measured relative humidity rF.sub.2 exceeds upper threshold rF.sub.2O (step S4) or is below lower threshold rF.sub.2U (step S6). If upper threshold rF.sub.2O is exceeded, flow D.sub.1 is increased (step S5), preferably to the maximum flow D.sub.max. If lower threshold rF.sub.2U is not reached, flow D.sub.1 is lowered (step S7), preferably to minimum flow D.sub.min.

[0040] A flow D.sub.2 in purging air discharge line 17 can also be measured using flow sensor 21, by which seal tightness of welding wire cartridge 1 can be deduced because supplied flow D.sub.1 is known. If flow D.sub.2 as measured using flow sensor 21 is significantly lower than an expected or predetermined value (flow D.sub.1), a large portion of the purging air is escaping via leaks in welding wire cartridge 1, which can be indicated as fault, for example by control unit 20. It should be noted here that welding wire cartridge 1 is never completely sealed and it can also even be desirable that welding wire cartridge 1 leaks to a certain extent so that moisture penetrating into welding wire cartridge 1 can be quickly dissipated. Flow D.sub.2 in purging air discharge line 17 is thus generally lower than supplied flow D.sub.1, which is to be taken into account in control unit 20 in determining any unusual leakage in welding wire cartridge 1. A commercially available welding wire cartridge 1 (for example a welding wire package or a welding wire drum) can thus also be used without requiring specialized seals. Thus, there is also no additional expense.

[0041] An alternate test of the housing seal tightness can also be performed using moisture sensor 19. If the dry flow escapes at a different place because of leakage, the moisture sensor sooner or later then measures the generally higher ambient humidity and that leads to a fault message in the control/regulation.

[0042] It can be provided in an advantageous embodiment to use a wire feed hose 26, through which welding wire 2 is conveyed from welding wire cartridge 1 to welding process 3, as a, if required as an additional, purging air discharge 16 of welding wire cartridge 1. This would have the advantage that welding wire 2 would also be protected from excessive moisture in wire feed hose 26.

[0043] Using safety device 4 according to the invention, a plurality of welding wire cartridges 1a, 1b connected in series can also be operated, as illustrated in FIG. 2. Purging air discharge 16a of a first welding wire cartridge 1 is connected by a connecting line 22 to purging air feed 15b of a downstream, second welding wire cartridge 1b. Purging air discharge line 17 is connected to purging air discharge 16b of second welding wire cartridge 1b, and purging air supply line 13 is connected to purging air feed 15a of first welding wire cartridge 1a. In this manner, even more than two welding wire cartridges 1 can of course be connected together. Thus a plurality of welding wire cartridges 1a, 1b connected in series can be supplied with dehumidified purging air by one safety device 4. Otherwise, the above explanations apply analogously.

[0044] Instead of a purging air discharge 16, it could also be provided to use outlet 23 for welding wire 2 or wire feed hose 26 in welding wire cartridge 1 as, if required as additional, purging air discharge 16. In this case, moisture sensor 19 and/or mass flow sensor 21 could also be arranged in the area of outlet 23. Because the flow cross section is generally very low in outlet 23 for the welding wire, only a very low flow D.sub.1 can, however, be set if only this outlet 23 is used. Thus, this represents a possible, albeit not optimal, implementation.