Mixing drum, concrete mixer, and method for producing a mixing drum

Abstract

The invention relates to a mixing drum (1) for a concrete mixer, in particular a truck mixer (2). The mixing drum (1) is a rotating body which is made of a plurality of roll-bent sheet-metal blanks (4) that are welded together via welding seams (3). The aim of the invention is to provide an improved mixing drum which is less susceptible to wear and which can be easily produced even when harder steels are used for the sheet-metal blanks (4). For this purpose, the invention proposes that at least one of the welding seams (3) intersects an axial plane (5) of the rotating body (1) at an oblique angle (α) in the course of the welding seam, wherein at least two roll-bent sheet-metal blanks (4) that are welded together have a hardness of at least 400 HB at least in some regions. The invention additionally relates to a concrete mixer (2) comprising such a mixing drum (1) and to a method for producing such a mixing drum (1).

Description

[0001] Mixer drum. Concrete mixer and method for manufacturing a mixer drum

[0002] The invention relates to a mixer drum for a concrete mixer, in particular for a truck mixer. The mixer drum is a rotating body formed by several rolled, bended sheet metal blanks welded together via weld seams. Furthermore, the invention relates to a concrete mixer, in particular a truck mixer, with such a mixer drum, and to a method for producing a mixer drum.

[0003] Such a mixer drum is known, for example, from EP 1 950 017 B1. This proposes a mixer drum with an improved mixing spiral, wherein the mixing spiral is made of a steel with increased hardness to reduce wear. As already mentioned in EP 1 950 017 B1, such steels are difficult to process by rolling and bending. For this reason, correspondingly hard steels have not been used to date for the roll-bend sheet metal blanks of the rotating body of the mixer drum, which are welded together via weld seams and form the drum shell of the mixer drum. Accordingly, the drum shells of the previously known mixer drums are susceptible to wear.In addition to the springback resulting from the increased hardness of the sheet metal blanks, the lower hardness of the weld seams compared to the shell material is problematic for rolling and bending, leading to irregular and therefore undesirable deformations of the rotating body during the manufacturing process. The object of the invention is therefore to provide an improved mixer drum.

[0004] This object is achieved by a mixer drum having the features of claim 1, by a concrete mixer having the features of claim 8 and by a method according to the features of claim 9.

[0005] Because at least one of the weld seams intersects an axial plane of the rotating body at an oblique angle, i.e. in particular an angle different from 0° or an integer multiple of 90°, even harder steels, with a hardness of at least 400 HB at least in some regions, of the sheet metal blanks welded together via the weld seam can be rolled and bent very easily, without irregular and undesired deformations of the rotating body occurring. The at least one weld seam preferably has an elongated course that only intersects a plane of a generating curve of the at least one rotating body forming the mixer drum at certain points. The at least one weld seam thus intersects any axial plane of the rotating body at an oblique angle, i.e. an angle different from 0° or an integer multiple of 90°, along its course between the sheet metal blanks.The axial planes of the rotating body are the planes in which the longitudinal axis of the rotating body, i.e. the axis of rotation of the mixer drum, lies. The intersection of the rotating body with each of the axial planes represents the generating curve of the rotating body. The intersection of an axial plane of the rotating body at an oblique angle through at least one weld seam facilitates the manufacture of the mixer drum, as fewer irregular and undesired deformations of the rotating body of the mixer drum occur during the bending and rolling of the sheet metal blanks welded together via this weld seam. The more of the required weld seams intersect an axial plane of the rotating body at an oblique angle along their course, the better irregular and undesired deformations at the weld seams can be avoided during the bending and rolling of the rotating body of the mixer drum.However, the fewer weld seams required, the more evenly the rotating body of the mixer drum can be bent. The oblique cutting angle ensures uniform deformation of the welded sheet metal blanks during the bending process, forming the rotating body that forms the mixer drum. The rotating body of the mixer drum is thus formed by the drum shell, which consists of several sheet metal blanks welded together via weld seams.

[0006] The oblique cutting angle is preferably greater than 4 degrees and less than 90 degrees. The oblique course of the at least one weld seam facilitates the use of harder steels for the sheet metal blanks, since the orientation of the course of the at least one weld seam relative to an axial plane of the rotating body during the bending and rolling of the sheet metal blanks connected to one another by the at least one weld seam results in more uniform deformation of the sheet metal blanks and the weld seam. The course of the weld seam is thus automatically oriented obliquely to the rolling direction selected during the bending and rolling of the rotating body.The longitudinal extension of the at least one weld seam should therefore lie outside a plane orthogonal to the rolling direction so that irregular and undesired deformations of the rotating body of the mixer drum can be easily avoided when the sheet metal blanks connected to one another via the at least one weld seam are deformed into the rotating body in the rolling direction by bending rollers.

[0007] Advantageous embodiments and further developments of the invention emerge from the dependent claims. It should be noted that the features listed individually in the claims can also be combined with one another in any technologically expedient manner, thus revealing further embodiments of the invention.

[0008] According to an advantageous embodiment of the invention, the mixer drum comprises at least two rotary body sections of the rotary body designed as cones, wherein at least one weld seam connecting the sheet metal blanks of at least one of the cones intersects an axial plane of the respective rotary body section at an oblique angle along its length. The production of cones, which form rotary body sections of the rotary body, is particularly difficult with harder steels for the sheet metal blanks, since irregular and undesirable deformations are particularly likely to occur during the bending and rolling of the rotary body sections.Even with an oblique weld seam connecting the sheet metal blanks of the cones to an axial plane of the respective rotating body section, more regularly shaped cones can be produced for the sheet metal blanks, especially from harder steels, if these cones only intersect the axial plane of the rotating body at certain points. The more of the required weld seams intersect the axial plane of the cone-shaped rotating body sections at an oblique angle along their course, the better irregular and undesirable deformations at the weld seams can be avoided during the bending roll process of the rotating body sections of the rotating body. However, the fewer weld seams required, the more evenly the rotating body of the mixer drum can be bent.

[0009] Particularly preferred is an embodiment which provides that the mixer drum comprises at least one rotary body section designed as a cylinder, wherein a weld seam connecting the sheet metal blanks of the cylinder intersects an axial plane of the respective rotary body section at an oblique angle along its course. The production of cylinders which form rotary body sections of the rotary body is also difficult with harder steels for the sheet metal blanks, since irregular and undesirable deformations can easily arise during the bending and rolling of the rotary body sections. Even with an oblique cutting angle of the oblique course of a weld seam connecting the sheet metal blanks of the cylinders to an axial plane of the respective rotary body section, more regularly shaped cylinders can be produced, particularly from harder steels for the sheet metal blanks.The more of the required weld seams intersect an axial plane of the cylindrical rotational body sections at an oblique angle along their length, the better irregular and undesirable deformations at the weld seams can be avoided during bending and rolling of the rotational body sections of the rotational body. A particularly advantageous embodiment of the invention relates to the fact that at least one of the weld seams intersects an axial plane of the rotational body and / or a rotational body section of the rotational body at an angle of at least 4 degrees, preferably at least 12 degrees, more preferably at least 14 degrees, and at most 45 degrees, preferably at most 35 degrees, more preferably at most 30 degrees, more preferably at most 25 degrees, along its length.With such a cutting angle, the course of at least one weld seam can be optimally positioned with respect to the rolling direction, so that irregular and undesirable deformations during the bending rolling of the rotating body or the rotating body sections of the rotating body are avoided.

[0010] A particularly advantageous embodiment of the invention provides that the weld seams in the developed view of the rotating body and / or a rotating body section of the rotating body have a straight line. This straight line allows the sheet metal blanks to be welded together particularly easily before bending and rolling. This allows the sheet metal blanks to be joined together in one plane by means of the straight weld seam before bending and rolling to form the rotating body or the rotating body section.

[0011] An advantageous embodiment of the invention provides that at least two welded and roll-bent sheet metal blanks have, at least in some regions, a hardness of at least 420 HB, more preferably at least 450 HB, more preferably at least 475 HB, more preferably at least 490 HB, more preferably at least 500 HB. With these hardnesses for the steels of the sheet metal blanks, a drum shell of the mixer drum can be realized that is particularly wear-resistant. The greater the hardness, the less susceptible the mixer drum is to wear and abrasion by the concrete transported in the mixer drum, even with a comparatively small wall thickness and thus a low weight of the mixer drum. An embodiment is particularly advantageous which provides that at least two welded and roll-bent sheet metal blanks have, at least in some regions, a thickness of at most 3 mm, preferably at most 2.7 mm.The potentially higher hardness of the sheet metal blanks allows for a reduction in the thickness of the sheet metal blanks, as the mixer drum is subjected to less abrasion from the concrete transported in the mixer drum. This allows for significant weight savings on the mixer drum, allowing for a larger concrete load. Thanks to the increased hardness of the sheet metal blanks, the reduction in sheet thickness does not reduce the service life of the mixer drum, as it is less susceptible to wear and tear from abrasion caused by the concrete being transported.

[0012] Furthermore, the invention relates to a concrete mixer, in particular a truck mixer, as described above and in more detail below, with a mixer drum as described above and in more detail below. Particularly in truck mixers, the improved mixing drum offers the advantage of lower manufacturing costs, lower wear, and a higher concrete load.

[0013] Furthermore, the invention relates to a method for producing a mixer drum, in particular a mixer drum as described above and in more detail below, comprising the following successive steps:

[0014] Cutting of flat sheet metal blanks, whereby the sheet metal blanks have a hardness of at least 400 HB, at least in some areas,

[0015] Welding the cut sheet metal blanks using straight weld seams,

[0016] Bending the welded sheet metal blanks to form a rotary body section, wherein the course of at least one of the weld seams intersects an axial plane of the rotary body section at an oblique angle,

[0017] Welding the rolled and welded sheet metal blanks to the rotation body section and

[0018] Joining several rotating body sections to form a mixer drum. Cutting the sheet metal for the mixer drum is very easy, as the development of the rotating body and / or a rotating body section is formed by flat sheet metal blanks. The cut sheet metal blanks are then simply welded together using straight weld seams. The welded sheet metal blanks thus form a flat development of a rotating body section, which can be easily fed into a bending and rolling device. When the welded sheet metal blanks are bend-rolled, a rotating body section is created, with the course of at least one of the weld seams, as explained above, intersecting an axial plane of the rotating body section at an oblique angle. After bending, the bend-rolled and welded sheet metal blanks are welded together to form the rotating body section.This is preferably achieved via a straight weld seam running in an axial plane of the rotating body section. Such a weld seam can be easily created on the already rolled rotating body section. Subsequently, several correspondingly manufactured rotating body sections are joined to form a rotating body of the mixer drum. This is preferably achieved via circumferential weld seams between the rotating body sections.

[0019] An advantageous embodiment of the method provides that, during bending rolling, an auxiliary sheet is welded to a first sheet metal blank of each rotating body section, which is introduced into a bending rolling device, in order to introduce the first sheet metal blank into the bending rolling device at an angle and, together with the auxiliary sheet, in the rolling direction. Using the auxiliary sheet, the first sheet metal blank can be very easily inserted into the bending rolling device to define a rolling direction, so that the longitudinal extension of the at least one weld seam lies outside a plane orthogonal to the rolling direction. This makes it easy to avoid irregular and undesired deformations of the rotating body of the mixer drum.This is because the sheet metal blanks, connected to one another by at least one weld seam, are deformed into the rotating body by the bending process in the rolling direction, while the course of the weld seams intersects the plane orthogonal to the rolling direction at an oblique angle. The auxiliary sheet facilitates the correct insertion of the welded sheet metal blanks. It can be removed again after the first welded sheet metal blanks have been bended into a rotating body section, before the rotating body section is welded shut.

[0020] A preferred embodiment of the method provides that, during bending rolling, an auxiliary plate is welded to the last sheet metal blank of each rotating body section introduced into a bending rolling device in order to guide the last sheet metal blank out of the bending rolling device at an angle and, together with the auxiliary plate, in the rolling direction. Since the last sheet metal blank introduced at an angle into a bending rolling device no longer rests against the starting block of the bending rolling device, this sheet metal blank can no longer be reliably guided in the bending rolling device. Without a corresponding auxiliary plate on the last sheet metal blank of each rotating body section introduced into the bending rolling device, undefined deformation can occur, which can be easily and effectively avoided with the auxiliary plate.

[0021] According to a preferred embodiment of the method, at least one of the weld seams runs at an oblique angle to an axis of one or more rolls of the bending rolling device during bending rolling. The sheet metal blanks welded together via the weld seam are bend-rolled by the bending rolling device over the oblique angle with the lowest possible stress on the weld seam. The oblique angle of the weld seam, which is usually softer than the sheet metal blanks, makes it particularly easy to prevent irregular and therefore undesirable deformations of the rotating body, since the weld seam oriented obliquely to the rolling direction is continuously and evenly loaded and deformed by the roll of the bending rolling device or the rolls of the bending rolling device one after the other. The sheet metal blanks running obliquely in the rolling direction next to the weld seam stabilize the weld seam that is bend-rolled in sections along its course.In this way, differences in hardness between the sheet metal blanks and the usually softer weld seams can be easily compensated and irregular and therefore undesirable deformations of the rotating body can be avoided.

[0022] Further features, details, and advantages of the invention will become apparent from the following description and from the drawings, which show exemplary embodiments of the invention. Corresponding objects or elements are provided with the same reference numerals in all figures. They show:

[0023] Figure 1 Truck mixer according to the state of the art,

[0024] Figure 2 Side view of the mixer drum according to the invention,

[0025] Figure 3 Front view of the mixer drum according to the invention,

[0026] Figure 4 Rear view of the mixer drum according to the invention,

[0027] Figure 5 Welded sheet metal blanks and roller,

[0028] Figure 6 Development of a rotation body section,

[0029] Figure 7 further development of a rotation body section,

[0030] Figure 8 Bending rolling device and sheet metal cutting,

[0031] Figure 9 further bending rolling device and sheet metal cutting,

[0032] Figure 10 further development of a rotation body section, and

[0033] Figure 11 Detailed view of the development of the rotation body section.

[0034] Figure 1, designated by reference numeral 1, shows a mixer drum as is known from the prior art. The mixer drum 1 is rotatably mounted in the usual way on the chassis 15 of a truck mixer 2. With such a truck mixer 2, fresh concrete can be easily transported to a construction site to be used for the construction of buildings. The mixer drum 1 of the truck mixer 2 forms a rotating body around the axis of rotation 16, about which a drive 17 of the truck mixer 2 rotates the mixer drum to mix the concrete and empty the concrete. The rotating body 1 is formed by several bend-rolled sheet metal blanks 4 welded together via weld seams 3, which form the drum shell of the mixer drum 1. The weld seams 3 here all run in an axial plane 5 (Figs. 3, 4) of the rotating body 1.Thus, the weld seams 3 shown each extend in a plane of a generating curve of the at least one rotating body forming the mixer drum 1. With a corresponding alignment of the weld seams 3 to the rolling direction, larger differences in hardness between the sheet metal blanks 4 and the typically softer weld seams 3 lead to irregular and therefore undesirable deformations of the rotating body 1, since the weld seams 3, which are oriented parallel to the rolls of the bending roller device, exhibit a different deformation behavior during bending rolling than the harder sheet metal blanks 4.

[0035] This is where the invention comes in and proposes a mixer drum 1 for a truck mixer 2, as can be seen in Figure 1, for example in Figure 2. The mixer drum 1 according to Figure 2 is characterized in that one or more weld seams 3 intersect an axial plane 5 (Figs. 3, 4) of the rotating body 1 at an oblique angle along their course. This makes it very easy to roll and bend even harder steels of the sheet metal blanks 4 welded together via the weld seam 3, without irregular and undesired deformations of the rotating body 1 occurring. The mixer drum 1 shown has three rotating body sections 6, 7, 8 of the rotating body 1 designed as cones 6, 7, 8.A rotary body section 9 designed as a cylinder 9 is arranged between the front cone 6 and the two rear cones 7 and 8, wherein the interconnected rotary body sections 6, 7, 8 and 9 form the drum shell of the rotary body of the mixer drum 1. In the exemplary embodiment shown here, at least the sheet metal blanks 4 of the first cone 6 and the second cone 7 are connected via weld seams 3, which intersect an axial plane 5 (Figs. 3 and 4) of the respective rotary body section 6, 7 at an oblique angle along their course. The sheet metal blanks 4 of the further cone 8 or of the cylinder 9 can also be connected via corresponding weld seams, which intersect an axial plane 5 (Fig. 3) of the respective rotary body section 8, 9 at an oblique angle along their course. However, this is not the case in the exemplary embodiment shown.Depending on the selected hardness of the sheet metal blanks 4, the rotary body section of the cylinder 9 can also be manufactured from sheet metal blanks 4 that are connected via weld seams 3 oriented parallel to the rollers of the bending roller device, since irregular and undesired deformations occur less frequently during the bending roller process of the cylinder 9 or only occur with larger differences in hardness between the sheet metal blanks 4 and the weld seams 3, and are easier to control during the bending roller process of the cylinder 9. In the exemplary embodiment, the third cone 8, i.e., the cone adjoining the drum opening 18, is also manufactured from sheet metal blanks 4 that are connected via weld seams 3 oriented along the generating curve of the rotary body section 8. This is possible, for example, by selecting a lower hardness for the sheet metal blanks 4 of the cone 8 adjoining the drum opening 18 than for the sheet metal blanks 4 of the other cones 6, 7.Since wear on the cone 8 adjoining the drum opening 18 is typically lower, sheet metal blanks 4 with a lower hardness than in the other rotating body sections 6, 7, 9 can be used at this point without significantly compromising the service life of the remaining mixer drum 1. This allows material costs to be kept lower without compromising the service life of the improved mixer drum 1. However, the more weld seams 3 required due to the raw material intersect an axial plane 5 (Figs. 3 and 4) of the rotating body 1 at an oblique angle along their course, the better irregular and undesirable deformations can be avoided during the bending and rolling of the rotating body of the mixer drum 1.

[0036] Figure 3 shows the mixer drum 1 according to Figure 2 in a front view from the direction of the rotation axis 16 (Fig. 2). Here, it can be seen that the weld seams 3, which connect the sheet metal blanks 4 of the first cone 6 to one another, intersect any axial plane 5 of the rotating body 1 at an oblique angle during their run between the sheet metal blanks 4. The axial planes 5 are the planes in which the rotation axis 16 runs.

[0037] Also from Figure 4, which shows a rear view of the mixer drum 1 according to Figure 2, it can be seen from the perspective of the rotation axis 16 (Fig. 2) that the weld seams 3, which connect the sheet metal blanks 4 of the second cone 7 to one another, intersect any axial plane 5 of the rotation body 1 at an oblique angle during their course between the sheet metal blanks 4.

[0038] Figure 5 shows, by way of example, two sheet metal blanks 4 welded together by a weld seam 3. These are fed to a bending-rolling device 10 by means of a roller 14 for bending-rolling a rotary body section 6, 7, 8, 9 (Fig. 2) in the rolling direction 12. It can be seen that the weld seam 3 is oriented obliquely along its course to the rolling direction 12 selected during the bending-rolling of the rotary body. The longitudinal extent of the weld seam 3 lies outside a plane orthogonal to the rolling direction 12. This makes it easy to avoid irregular and undesired deformations of the rotary body of the mixer drum 1 (Fig. 2), since the sheet metal blanks 4 connected to one another by the weld seam 3 are deformed in the rolling direction 12 by bending rollers to form the rotary body. The weld seam 3, which is oriented obliquely to the rolling direction 12, is formed by the roll 14 or the rolls 14a, 14b, 14c, 14d of the bending rolling device 10 (Fig.9) are continuously loaded and deformed one after the other. The sheet metal blanks 4, which run obliquely next to the weld seam 3 in the rolling direction 12, stabilize the weld seam 3, which is continuously bend-rolled along its course, during the deformation of the sheet metal blanks 4 into a rotational body section 6, 7, 8, 9 (Fig. 2). In this way, differences in hardness between the weld seam 3, the edge regions 19 of the sheet metal blanks 4 at the weld seam 3, and the remaining sheet metal blanks 4 can be easily compensated for during the bending-rolling of the mixer drum 1 (Fig. 2). Even if the material of the weld seams 3 has the same hardness as the sheet metal blanks 4, the hardness in the edge regions 19 is reduced by the heating of the sheet metal during welding of the blanks.

[0039] Figure 6 shows a developed view of a conical rotary body section 6, 7, 8 (Fig. 2) of the mixer drum 1. It can be seen that the weld seams 3 in the developed view of the rotary body section 6, 7, 8 (Fig. 2) of the mixer drum have a straight line. This straight line makes it possible to easily weld the flat sheet metal blanks 4 together before bending and rolling. For this purpose, the plate-shaped sheet metal blanks 4 are simply positioned butt-to-end. Figure 6 also shows an angle α, which characterizes the oblique course of the weld seams 3, which intersect an axial plane (Fig. 3) of the bend-rolled rotary body of the mixer drum 1 at a corresponding angle after the welded sheet metal blanks 4 have been bended and rolled. For this purpose, the sheet metal blanks 4 are cut to size. Preferably, the weld seams 3 intersect an axial plane 5 (Fig. 3, 4) of the rotating body of the mixer drum 1 ora rotational body section 6, 7, 8, 9 (Fig. 2) of the rotational body 1 at an angle of at least 4 degrees and at most 45 degrees. This allows the weld seams 3 to be optimally positioned with respect to the rolling direction 12 (Fig. 5), so that irregular and undesirable deformations during the bending-rolling of the rotational body 1 (Fig. 2) or the rotational body sections 6, 7, 8, 9 (Fig. 2) of the rotational body are avoided. Depending on the size of the rotational bodies 6, 7, 8, 9 (Fig. 2) and the bending-rolling device, a minimum angle results so that irregular and undesirable deformations during the bending-rolling of the rotational body 1 (Fig. 2) can be effectively prevented. Further explanations follow to simplify the determination of this minimum angle. After the sheets have been cut to size for the mixer drum 1 (Fig. 2), the cut sheet metal blanks 4 can be easily welded using straight weld seams 3.The flat development of the rotating body section shown in Figure 6 can be easily fed to a bending-rolling device 10 (Fig. 9). The rotating body section 6, 7, 8, 9 (Fig. 2) is thus created by bending-rolling the welded sheet metal blanks 4, whereby the course of the weld seams 3 intersects an axial plane 5 (Figs. 3, 4) of the rotating body section 6, 7, 8, 9 (Fig. 2) at an oblique angle α. The bend-rolled and welded sheet metal blanks 4 are then welded together to form the rotating body section 6, 7, 8, 9 (Fig. 2). To produce the mixer drum 1, several correspondingly manufactured rotating body sections 6, 7, 8, 9 (Fig. 2) are combined to form a rotating body.

[0040] I. This is preferably carried out via weld seams running in the circumferential direction between the rotation body sections 6, 7, 8, 9 (Fig. 2), which can be seen in Figure 2. Figure 6 also shows auxiliary sheets 11, which are attached to the sheet metal blanks 4 introduced into the bending rolling device 10 (Fig. 8) before the bending rolling. Via this auxiliary sheet 11, the first sheet metal blank 4 can be very easily introduced obliquely together with the auxiliary sheet 11 in the rolling direction 12 (Fig. 8) into the bending rolling device 10 (Fig. 8). This makes it particularly easy to ensure that the weld seams 4 run at an oblique angle (a) to an axis 13 of one or more rolls 14, 14a, 14b, 14c, 14d of the bending rolling device 10 (Fig. 9) during the bending rolling process. In this exemplary embodiment, the auxiliary sheet

[0041] II is formed in the shape of a triangle and can preferably consist of cutting remnants of the sheet metal blanks 4.

[0042] Figure 7 shows a further developed view of a conical rotary body section 6, 7, 8 (Fig. 2) of the mixer drum 1. This developed view differs from the developed view shown in Figure 6 in that the courses of the weld seams 3 between the sheet metal blanks 4 are not oriented uniformly obliquely to the rolling direction 12 (Fig. 5), but alternately run at a positive and a negative angle α to the rolling direction 12 (Fig. 5). The positive and negative angles α do not have to be the same size. For this purpose, the sheet metal blanks 4 are cut to size accordingly. Furthermore, the auxiliary sheet 11 is not designed as a triangle here, but rather as a preferably rectangular sheet metal strip.

[0043] Figure 8 schematically shows a bending-rolling device 10 with three rollers for bending-rolling the rotating body sections 6, 7, 8, 9 (Fig. 2) of the mixer drum 1 (Fig. 2) and a sheet metal blank 4, which is fed to the bending-rolling device 10. The deformation process during the bending-rolling of the welded sheet metal blanks 4 is carried out primarily by three rollers of the bending-rolling device 10, which form a feed roller 14a, an upper roller 14b, and a lower roller 14c.

[0044] Figure 9 shows a further schematic bending rolling device 10 with four rollers 14a, 14b, 14c, 14d for bending the rotary body sections 6, 7, 8, 9 (Fig. 2) of the mixer drum 1 and a sheet metal blank which is fed to the bending rolling device 10. The bending rolling process begins with the pre-bending. In this case, the feed roller 14a is initially at the bottom, as can be seen in Figure 9. The discharge roller 14d is moved upwards and the sheet metal blank 4 is pushed between the upper roller 14b and the lower roller 14c until it rests on the discharge roller 14d. When bending a cone 6, 7, 8 (Fig. 2), a surface line I (Fig. 11) should be at the discharge roller 14d. This "standing" is necessary to ensure the correct alignment of the welded sheet metal blanks 4. If the first sheet metal blank 4 is cut at an angle, an alternative support point must be available. The aforementioned auxiliary sheet 11 (Fig.) can be used for this purpose.6 or 7) can be used. An extension in the form of an auxiliary sheet 11 (Figs. 6 and 7) is also useful on the outlet side of the sheet metal blanks 4, since the sheet metal is no longer in contact with the starting block of the bending roll device 10 and is therefore no longer guided in the bending roll device 10. In this way, undefined deformation can be easily avoided. The sheet metal blank 4 is moved back for bending until it is just resting on the lower roll 14c (Fig. 8). The actual bending process follows. In this case, the first sheet metal blank 4 is initially clamped between the upper roll 14b and the lower roll 14c with the feed roll 14a at the bottom, as can be seen in Figure 9. The feed roll 14a is then raised, as shown in Figure 8. The area of ​​the sheet metal blank 4 between points P2 and P3 (Fig. 8) remains undeformed - here a straight piece is obtained.The actual deformation process takes place between point P1 and point P2, where P2 marks the point where the sheet metal blank 4 rests on the top roll 14b. However, the position of point P2 is not precisely known. Since the feed roll 14a is inclined when bending a cone 6, 7, 8 (Fig. 2), the distance d between points P1 and P2 or P3 cannot be determined exactly or varies across the entire width of the rolls 14, 14a, 14b, 14c in the bending roll device 10. In order to determine the minimum oblique angle a (Figs. 6, 7, 10, 11) required for the course of the weld seams 3 in order to avoid irregular deformations during bending, the projected length p (Fig. 10) of the weld seams 3 (Fig. 10) should be determined. For this purpose, one can start from the geometric conditions when inserting the sheet metal blank 4 into the bending rolling device 10.The feed roller 14a and the bottom roller 14c are, as can be seen in Figure 9, at the same height and the distance between the bottom roller 14c and the feed roller 14a is very small. Preferably, the distance between the feed roller 14a and the bottom roller 14c is at most 10 mm. The simplified approach results in a projection length p that is in any case greater than the distance between the points P1 and P3 (Fig. 8). In the simplified approach for determining the minimum angle α, the contact point between the feed roller 14a and the sheet metal blank 4 is at 12 o'clock and during the actual rolling process (see Figure 8) it is well to the right of 12 o'clock, which in this case then results in a shorter projection line. This results in a minimum angle α for the intended course of the weld seams 3 connecting the sheet metal blanks 4 of.

[0045] In this regard, reference is also made to the detailed view in Figure 11, which shows the length I of the surface line of the cone, which results from the appropriate sheet metal cuts.

[0046] Figure 10 also shows a further development of a conical rotary body section 6, 7, 8 (Fig. 2) of the mixer drum 1. In this development, the welding of the bend-rolled and welded sheet metal blanks to the rotary body section 6, 7, 8 (Fig. 2) takes place via a straight weld seam that runs in an axial plane (5 (Figs. 3, 4) of the rotary body section 6, 7, 8 (Fig. 2). This eliminates the need for auxiliary sheets, and such a weld seam can be more easily implemented on the bend-rolled rotary body section 6, 7, 8 (Fig. 2) than a weld seam running spatially obliquely along the drum shell to close the rotary body section 6, 7, 8 (Fig. 2).

[0047] - List of reference symbols -

[0048] List of reference symbols

[0049] 1 mixer drum (rotating body)

[0050] 2 truck mixers 3 welds

[0051] 4 sheet metal blanks

[0052] 5 Axial plane

[0053] 6 First cone (first rotation body section)

[0054] 7 Second cone (second rotation body section) 8 Third cone (third rotation body section)

[0055] 9 cylinders (fourth rotation body section)

[0056] 10 Bending rolling device

[0057] 11 Auxiliary sheet

[0058] 12 Rolling direction 13 Axis

[0059] 14 roller, 14a feed roller, 14b top roller, 14c bottom roller, 14d

[0060] Discharge roller 15 chassis

[0061] 16 Rotation axis

[0062] 17 Drive

[0063] 18 Drum opening 19 Edge area a oblique angle d distance P1 - P2 p projection length

[0064] I Length of the surface line (cone)

[0065] D Sheet thickness

[0066] - Patent claims -

Claims

Patent claims 1. Mixer drum (1) for a concrete mixer, in particular for a truck mixer (2), wherein the mixer drum (1) is a rotating body formed by a plurality of bend-rolled sheet metal blanks (4) welded together via weld seams (3), characterized in that at least one of the weld seams (3) intersects an axial plane (5) of the rotating body (1) at an oblique angle (α) along its course, wherein at least two welded and bend-rolled sheet metal blanks (4) have a hardness of at least 400 HB, at least in some regions.

2. Mixer drum (1) according to claim 1, characterized in that the mixer drum (1) comprises at least two rotary body sections (6, 7, 8) of the rotary body (1) designed as cones (6, 7, 8), wherein at least one weld seam (3) connecting the sheet metal blanks (4) of at least one of the cones (6, 7, 8) intersects an axial plane (5) of the respective rotary body section (6, 7, 8) at an oblique angle (α) along its course.

3. Mixer drum (1) according to claim 1 or 2, characterized in that the mixer drum (1) comprises at least one rotary body section (9) designed as a cylinder (9), wherein a weld seam (3) connecting the sheet metal blanks (4) of the cylinder (9) intersects an axial plane (5) of the respective rotary body section (9) at an angle (α) along its course.

4. Mixer drum (1) according to one of the preceding claims, characterized in that at least one of the weld seams (3) intersects an axial plane (5) of the rotating body (1) and / or a rotating body section (6, 7, 8, 9) of the rotating body at an oblique angle of at least 4 degrees and at most 45 degrees along its course.

5. Mixer drum (1) according to one of the preceding claims, characterized in that the weld seams (3) have a straight line in the development of the rotating body (1) and / or a rotating body section (6, 7, 8, 9) of the rotating body.

6. Mixer drum (1) according to one of the preceding claims, characterized in that at least two welded and bend-rolled sheet metal blanks (4) have, at least in some regions, a hardness of at least 420 HB, more preferably at least 450 HB, more preferably at least 475 HB, more preferably at least 490 HB, more preferably at least 500 HB.

7. Mixer drum (1) according to one of the preceding claims, characterized in that at least two welded and rolled sheet metal blanks (4) have, at least in some regions, a thickness (D) of at most 3 mm, preferably at most 2.7 mm.

8. Concrete mixer, in particular a truck mixer (2), with a mixer drum (1) according to one of the preceding claims.

9. A method for producing a mixer drum (1), in particular a mixer drum (1) according to one of the preceding claims 1 to 7, comprising the following successive steps: Cutting of flat sheet metal blanks (4), wherein the sheet metal blanks (4) have a hardness of at least 400 HB at least in some areas, Welding the cut sheet metal blanks (4) via straight weld seams (3), Bending rolls of the welded sheet metal blanks (4) to a Rotational body section (6, 7, 8, 9), wherein the course of at least one of the weld seams (3) intersects an axial plane (5) of the rotational body section (6, 7, 8, 9) at an oblique angle (a), Welding the rolled and welded sheet metal blanks (4) to the rotation body section (6, 7, 8, 9) and Connecting several rotation body sections (6, 7, 8, 9) to form a mixer drum (1).

10. Method according to claim 9, characterized in that during bending rolling, an auxiliary sheet (11) is welded to a first sheet metal blank (4) of each rotary body section (6, 7, 8, 9) introduced into a bending rolling device (10) in order to introduce the first sheet metal blank (4) obliquely and together with the auxiliary sheet (11) in the rolling direction (12) into the bending rolling device (10).

11. Method according to claim 9 or 10, characterized in that during bending rolling, an auxiliary sheet (11) is welded to a last sheet metal blank (4) of each rotary body section (6, 7, 8, 9) introduced into a bending rolling device (10) in order to guide the last sheet metal blank (4) obliquely and together with the auxiliary sheet (11) in the rolling direction (12) out of the bending rolling device (10).

12. Method according to one of claims 9 to 11, characterized in that at least one of the weld seams (4) during bending rolls runs at an oblique angle (a) to an axis (13) of one or more rolls (14, 14a, 14b, 14c, 14d) of the bending roll device (10). - Summary -

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