EP0840663A1

EP0840663A1 - Method and device for connecting wire ends of a hoop casing for packing material

Info

Publication number: EP0840663A1
Application number: EP96927591A
Authority: EP
Inventors: Rudolf Kuhn; Dieter Teutrine
Original assignee: Certus Maschinenbau GmbH
Current assignee: Certus Maschinenbau GmbH
Priority date: 1995-07-27
Filing date: 1996-07-24
Publication date: 1998-05-13
Also published as: WO1997004913A1; TW375585B; DE19527417A1

Abstract

The invention concerns a method and device for connecting wire ends (11, 12) of a hoop casing for packing material (3). The bracing wire (2) is passed around the packing material (3), pulled taut and cut off, the wire ends (11, 12) then being pressed flush together under high pressure and welded by the application of a welding current. In this respect the wire ends (11, 12) are pressed together with a controllable and substantially constant pressure at least before and/or during the welding process. For this purpose, a bracing device (8) with a feed drive (9) comprising a pressure-control system with pressure stages (19, 20) preferably of at least two different levels is provided.

Description

DESCRIPTION

Method and device for connecting wire ends of a strapping of packaging

The invention relates to a method and a Vorrichtur.g for connecting the wire ends of a strapping of packaged goods by resistance welding with the features in the preamble of the main method and device claim.

Such a method and device are known from DE-A 38 14 470. The tension wire is looped around the packaged goods via a wire guide and then cut off. By cutting off arise

Burrs on the wire ends. The wire ends are then butted together under pressure and welded together by applying a welding current. The welding point is then actively and quickly cooled down by switching on a cooling air flow. A tempering treatment follows the cooling process in order to remove undesired martensite hardness again. The previously known method and the device operate in a time-controlled manner. The pressure or feed movement of the wire ends takes place via a hydraulic cylinder, which during the

Melting the wire ends presses together at full pressure without control. The welding current source used only gives two different current levels for the welding current and the lower starting current. The welding current is only switched on and off. In practice it has been shown that the welding quality and the strength of the strapping are subject to considerable scatter and are not always of sufficient quality.

It is the object of the present invention to show a method and a device which meet higher quality requirements. The invention solves this problem with the features in the main method and device claim. With the method according to the invention and the associated device, the tolerances in the weld quality and strength can be more narrowly defined. The welding process is easier to control and less dependent on fluctuating boundary conditions. The welding results are more reproducible.

In this case, the targeted control of the pressure or the contact pressure is particularly advantageous, possibly in conjunction with a current control. In the prior art it could happen in practice that the weld failed because the duty cycle of the

Welding current and the associated plasticization of the wire ends was not properly matched to the feed movement of the wire ends and the constant contact pressure. With the pressure and / or current control according to the invention, these problems are eliminated.

In particular, the pressure control or the current control allow the uneven wire ends in front of the welder to be smoothed in a targeted manner and thus to create better current transitions and welding conditions. Smoothing is possible in different ways, e.g. by strong mechanical pressing or by melting

In the method according to the invention, the contact pressure of the wire ends is kept essentially constant in the various pressure stages. As a result, the wire ends can be melted undisturbed and more uniformly than in the prior art.

The initially high pressure is preferably reduced to a lower pressure level shortly before and / or during welding. The high pressure will only come back in the upsetting phase.

Slow cooling of the weld between the welding process and the tempering process results in better and more uniform strength of the weld and the strapping. The microstructure is cheaper and more uniform. Preferably, one

Cooling air support in favor of the slowest possible

No cooling down. The slow cooling can be promoted by a gradual reduction in the welding current and / or, if appropriate, by switching on a post-heating current.

The method according to the invention and the associated device can be used for any strapping of any packaging goods. A preferred area of application is pressed bales made of fiber materials.

Advantageous refinements of the invention are specified in the subclaims.

The invention is shown in the drawings, for example and schematically. Show in detail

FIG. 1: a strapping device in a schematic side view,

Figure 2: Flow diagram for flows and pressures during

Connection process and

FIGS. 3 and 4: Variants in the flow chart of FIG. 2.

FIG. 1 shows a strapping device (1) with which one or more straps are formed from a flexible tensioning wire (2) around a packaged product (3). The packaged goods (3) can be of any shape. In the shown and preferred embodiment, it is a press bale (3) made of fibers, which is produced in a baler (not shown) and is held under high pressure during strapping between two press rams (21).

The strapped packaging goods may have a tendency to expand after relieving pressure. The strapping should then prevent the packaged goods (3) from breaking apart. If necessary, a packaging film, a sack or another packaging material can also be wrapped around the bale (3) or another item to be packed before the strapping is attached. The subsequent strapping fixes this packaging material.

The strapping device (1) has a feed device (4) for the tensioning wire (2), which is drawn off from a wire supply (7) by means of suitable drives. The tension wire (2) consists of a metal band a preferably circular or possibly also flat rectangular cross section. Preferably carbon-containing steels are used as material, which can also contain alloy components, such as. B. manganese or silicon.

The strapping device (1) also includes a wire guide (6) with which the tensioning wire (2) supplied is placed around the packaged goods (3). In the exemplary embodiment shown there are two

Strapping heads (6), which are placed on both sides of the press ram (21) and interact with the lacing grooves provided there to shoot through the tensioning wire (2).

A tensioning device (8) and a welding device (5) are arranged on one side of the wire guide (6). The tensioning device (8) has a separating device (10) for cutting or pinching off the tensioning wire (2) in the required length and one

Infeed drive (9) with which the wire ends (11, 12) can be butted together.

The feed drive (9) preferably has a hydraulic cylinder or another suitable one

Power generator with a pressure control for setting the contact pressure or the contact pressure acting on the wire ends (11, 12). The contact pressure can preferably be switched in two or more pressure stages (19, 20) (see FIG. 2). Those in the higher pressure stage (20) on the wire ends

(11,12) pressing force is, for example, approx. 1400 N at a cylinder pressure of approx. 100 bar. In the lower pressure stage (19) there is, for example, a contact pressure of approx. 140-280 N at a cylinder pressure of 10-20 bar. The lower pressure level (19) has a size of approximately 10-20% of the higher pressure level (20). The contact pressure at the wire ends (11, 12) can be kept or controlled essentially constant within the pressure stages (19, 20) by means of suitable sensors and drain valves (not shown). The cylinder pressure can vary. The feed drive (9) has a large-volume oil reservoir with a corresponding pressure generator for actuating the cylinder. As a result, the hydraulic oil flows at high speed even at low pressure and allows the piston to extend quickly at all pressure levels (19, 20).

The tensioning device (8) also has suitable tensioning means for holding the wire ends (11, 12). In addition, a suitable pulling device is present in the tensioning device (8) or the feeding device (4), with which the wire loop or strapping is tensioned and after the welding of the. Wire ends (11.1?) Can be released from the wire guide (6).

The components of the wire feeder (4) and the tensioning device (8) can be designed in any suitable manner. In particular, apart from the multi-stage delivery drive (9), the structural design can be the same as that in DE-A 38 14 470.

The welding device (5) has two or more electrodes (not shown) which are connected to the wire ends (11, 12) in a suitable manner and are connected to a welding current source (13) via lines. The welding current source (13) can emit three or more different current levels. For this purpose, it can be provided in a suitable manner with different taps on the welding transformer or can be controlled in another way. Apart from the three or more different current levels, the welding device (5) can otherwise be designed in a similar manner as in DE-A 38 174 470 his .

Transport means are optionally arranged on the wire guide (6) in order to move them relative to the packaged goods (3). Under certain circumstances, several straps can be placed at the same time, several wire guides (6) with associated tensioning and welding devices (8, 5) being provided.

To control and, if necessary, regulate the functional sequences described below, the

Strapping device (1) a suitable computer-based and preferably programmable controller (14), which e.g. housed in the control cabinet of the feed device (4). The controller (14) has one or more

Microprocessors with one or more data memories for program, process and other data as well as suitable ones

Input and output interfaces.

The connection or strapping process is preferably time-controlled in the manner described below. Figure 2 gives a timing diagram for the switching of the different currents and pressures. The clamping and welding device (8, 13) can have suitable sensors or other measuring devices (not shown) for monitoring, controlling and regulating the described processes, with which currents, pressures or forces, movements, speeds, positions etc. can be detected and measured become.

At the beginning of the strapping, the wire guide (6) is moved into position with respect to the packaged goods (3) and a tensioning wire (2) is shot through the guide channels by the feed device (4). The tension wire (2) is from above into the right wire guide shown in Figure 1

(6) inserted and guided clockwise around the packaged goods (3). The free upper wire end (11) is in the clamping device (8) stopped and held with suitable jaws. The wire loop is then tightened by moving the feed drive backwards. The separating device (10) then cuts off the supplied wire, the lower wire end (12) being held in place with suitable clamping means and aligned with the upper wire end (11). The two wire ends (11, 12) can then be brought closer together via the feed drive (9).

The wire ends (11, 12) can have uneven surfaces after the separation. These are smoothed before the actual welding. The welding and connection process takes place in the manner illustrated in FIGS. 2, 3 and 4.

Figures 2 and 3 show a variant with mechanical smoothing of the wire ends (11, 12). For this purpose, the two wire ends (11, 12) in section "A" are pressed together with pressure and over a selectable period of time. The high pressure stage (20) is switched at approx. 100 bar. The pressing can take place according to FIG. 2 without current or according to FIG. 3 with a low contact current (22). The pressure flow (22) can be lower than the preheating flow (15) and serves to facilitate the deformation of the wire ends

(11.12). With this pressure, the end faces of the wire ends (11, 12) are cold-formed and mechanically leveled, so that there is a sufficiently large current transfer area during the subsequent welding process.

In the variant according to FIG. 4, the smoothing in section "A" takes place by melting the wire ends (11, 12). The wire ends (11, 12) are pressed together with the low pressure stage (19) or essentially without pressure. For this purpose, a pre-melting stream (23) is switched on, which melts and flattens the protruding tips on the end faces. The pre-melt current (23) can be in the order of the preheating current (15).

Subsequently, in sections "B" and "C" the lower pressure stage (19) is switched to approximately 10 bar or 10% of the higher pressure stage (20). In FIGS. 2 and 3, with a certain time delay after the start of the lower pressure stage (19), the welding current source (13) switches a preheating current (15) in section "B". For example, this is approximately 27% of the maximum

Current. In Figure 2 it rises steeply from "0". In the variants of FIGS. 3 and 4, the preferably lower contact current (22) or premelting current (23) is increased. In all three variants, the preheating current (15) can also be switched without a time delay at the beginning of section "B".

After a selectable preheating time of approx. 0.2 see. the welding current (16) is switched while maintaining the low pressure level (19), which is approximately 83% of the maximum current, i.e. e.g. approx. 3.5 kA. The current can be increased in a ramp or abruptly. The welding current (16) is applied in section "C". It only lasts a short time, e.g. 0.1 see. A protective gas can be supplied during the preheating and welding process. This can be done in a similar manner as in DE-A 38 14 470. An inert gas or alternatively carbon dioxide or another suitable gas can be used as the protective gas.

After the predetermined exposure time, the welding current (16) is switched off again, which can also be ramped or abrupt. The low pressure level (19) is present and continues for a certain period after the welding current (16) has been switched off. Due to the low pressure level (19) only one during the preheating and plasticizing phase of the wire ends (11, 12) lower and substantially constant contact pressure exerted so that the wire ends can melt evenly and at rest.

Due to the low pressure and the high feed speed of the cylinder, the infeed drive (9) can react quickly and precisely to the plasticization of the wire ends (11, 12) and the wire ends (11, 12) can be brought closer together and at the appropriate speed without welding spatter and under Gradual lateral displacement of the weld pool form the desired weld bead. The microstructure formation in the melting range is influenced favorably. The stepwise connection of the preheating and welding current (15, 16) also has an advantageous effect.

When welding, the introduced welding energy or amount of heat can be adjusted and regulated. This is possible by measuring the current or resistance and tracking the current in the process.

In the subsequent section "D", the pressure is shifted up again to the higher pressure stage (20) with a time delay. This causes the melted wire ends (11, 12) to be compressed. The shielding gas is switched off in section "D".

After the wire ends (11, 12) have melted and during the upsetting process, the weld is slowly cooled. In this case, external cooling by a cooling air flow or the like is preferably dispensed with. The slow cooling takes place in the shown

Embodiment through the normal heat dissipation in the clamping device (8) and the ambient air. After the welding current (16) has been switched off, a post-heating current (17) can be delayed in section "E" for, for example, about 0.4 see. be switched, the z. B. reaches a height of about 17% of the maximum current. The post-heating current slows down the cooling and also ensures a slight post-heating of the welding point. The high pressure stage (20) is preferably still present during the reheating phase.

Alternatively, the welding current (16) can be gradually reduced and e.g. be gradually or smoothly lowered via sections "D" and "E". This depends on the type of welding current source (13) and the welding current control. With this lowering, reheating may also take place by temporarily increasing the current.

In the subsequent time period "F", pressure and current are switched off. The heat can be distributed evenly at the welding point and over the tension wire (2) and the structure can develop evenly.

In the following section "G" there is another tempering treatment. Here, a starting current (18) switched, the z. B. 30% of the maximum current. In this period "G" the pressure can also be switched on again, e.g. with the low pressure rating (19). Depending on the application, the pressure can also remain switched off or the high pressure level (20) can be switched.

After starting, the connection process is complete and the strapping is wrapped around the packaged goods (3). The strapping device (1) can then continue to the next strapping point or after the end of

Release the strapping process of the packaged goods (3) for removal. The strapping device (1) can be suitably placed on packaging devices or similar other machines. In the preferred embodiment, it is located on a

Baler (not shown). This can be a carousel press or a central press in a baler with multiple pre-presses.

Modifications of the exemplary embodiment shown are possible in various ways with regard to the method and the device. The specified sections, current levels and pressures may vary depending on the wire material and boundary conditions. The current and pressure levels can also be graduated and changed even more finely. The structural configurations of the components of the strapping device (1) can also be changed. In principle, the type of wire guidance during the strapping can also be different than in the exemplary embodiment shown.

REFERENCE SIGN LIST

1 strapping tool

2 tension wire 3 packaged goods, pressed bales

4 feed device

5 welding device

6 wire guide, strapping head

7 wire supply 8 clamping device

9 feed drive

10 separating device

11 wire end

12 wire end 13 welding power source

14 control

15 preheating current

16 welding current

17 reheating current 18 starting current

19 pressure rating, low

20 pressure level, high

21 ram

22 Contact current 23 Premelt current

Claims

PATENT CLAIMS

1.) Method for connecting the wire ends of a strapping of packaged goods by resistance welding, in particular in a

Baling press, the wire separated from a wire supply being butt-pressed together at the ends under pressure and welded by applying a welding current, characterized in that the wire ends (11, 12) before and / or during welding with a height-controlled contact pressure be pressed together.

⁵ 2.) Method according to claim 1, characterized in that the contact pressure is switched in different levels (19, 20).

3.) Method according to claim 2, characterized in that the contact pressure in the various stages (19, 20) is kept essentially constant.

4.) Method according to claim 1, 2 or 3, characterized ^{5 in} that the wire ends (11, 12) are subjected to differently high currents (15, 16) before and / or during the welding process.

0 Method according to one of claims 1 to 4, characterized in that the wire ends (11, 12) are pressed together before welding under high contact pressure and without current or with a low contact current (22).

5

6.) Method according to one of claims 1 to 4, characterized in that the wire ends (11, 12) are pressed together with a low contact pressure and a pre-melt stream (23) is applied to them.

7.) Method according to claim 1 or one of the following, characterized in that the contact pressure in the lower pressure stage (19) is approximately 10-20% of the pressure in the higher pressure stage (20).

8.) Method according to claim 1 or one of the following, characterized in that a lower preheating current (15) and then the higher welding current (16) are switched when welding.

9.) Method according to claim 8, characterized in that the welding current (16) is approximately two to three times as high as the preheating current (15).

10.) Method according to claim 1 or one of the following, characterized in that the wire ends (11, 12) are subjected to an annealing treatment after welding, the welding point being slowly cooled between the welding process and the starting process.

11.) The method according to claim 10, characterized in that the weld between the welding process and the starting process is electrically reheated.

12.) Method according to claim 10 or 11, characterized in that the welding current (16) is gradually reduced or a post-heating current (17) is switched.

13.) Method according to claim 10, 11 or 12, characterized in that the wire ends (11, 12) are pressed together under contact pressure in the cooling or reheating phase.

14.) Method according to claim 1 or one of the following, characterized in that the starting current (18) is approximately the same as the preheating current (15) and the post-heating current (17) is approximately one to two thirds as high.

15.) Method according to claim 1 or one of the following, characterized in that the contact pressure is at least temporarily increased again in the cooling or reheating phase.

16.) Device for connecting the wire ends of a strapping of packaged goods by resistance welding, in particular in a baler, with a feed and tensioning device for the tensioning wire and a welding device with a welding current source and a control, characterized in that the tensioning device (8) has a feed drive (9) with a pressure control.

17.) Device according to claim 16, characterized in that the feed drive (9) has at least two different pressure levels (19, 20).

18.) Device according to claim 16 or 17, characterized in that the welding current source (13) emits at least three different current levels, the welding current (16) being switchable in steps or sliding and / or a reheating current (17) being switchable.