EP0672801A2 - Screen element for gullies and water recovery device for street and sewer cleaning vehicle - Google Patents

Abstract

The sieve component comprises a sieve plate with several systematically arranged trickle holes (17). These trickle holes are arranged in parallel, spaced, running horizontally and superimposed rows. They are screened by downwardly facing screen components (18) at an angle. Dewatering material or cleaning material (56) cannot accumulate directly in front of the trickle holes. It instead forms a trickle channel in the wedge-shaped corner between the sieve plate and the screening components.

Description

The invention relates to a sieve element in drainage troughs and, in an expanded form, to a device for water recovery for street and sewer cleaning vehicles according to the preamble of independent claim 1.

Drainage troughs serve as collection containers for cleaning goods or waste, which contain a lot of water, which should run off as much as possible. For example, screenings from sewage treatment plants or suctioned sewer cleaning material are collected in such troughs. Such goods still contain a substantial proportion of water which is to be separated before the troughs are removed in order to use the trough volume primarily for the solids and not to unnecessarily load them with water. At the same time, the dewatering of the goods during storage in the trough constitutes a preliminary drying stage if the goods are subsequently processed, e.g. is burned. In order to allow the water of the collected goods to flow out of the trough, drainage troughs have a perforated plate at least in one wall or corner. However, these perforated plates clog relatively quickly, so that the water drainage is inhibited and the drainage is insufficient. If at all possible, an attempt is then made to scratch out, poke or rinse the perforated plates from inside or outside. In practice, it helps to prevent the perforated plates from clogging too quickly by accumulating a stone layer acting as a coarse filter in front of the perforated plate.

A similar, but probably more important problem exists with the drainage of sweeping or sewer cleaning material aimed at water recovery, which street sweeping or sewer cleaning vehicles take up. First the development of road sweeping vehicles is discussed. In road sweeping vehicles, the sweepings are picked up by rotating brushes of various designs or via a suction mouth. The sweepings consist of a considerable amount of dust. In older sweepers, this dust was whirled around inside the machine and largely blown back into the free atmosphere with the exhaust air flow. A first improvement was achieved by sweepers, where water was sprayed onto the sweeping surface from a tank integrated into the vehicle body, on the one hand to flush contaminants, in particular from grooves in the road surface, and on the other hand to bind the dust to the water. As a result, the pollution caused by the whirled up dust could be significantly reduced. With this type of machine, however, a large-volume water tank had to be provided or the tank content was sprayed soon, because the water was sprayed only once and was therefore lost (see, for example, DE-AS 12 17 424).

A further development is known from DE-PS 25 45 137. The sweeper proposed therein is provided with a sieve in the debris collection chamber, on which the essential water portion is separated from the muddy debris and returned to the water cycle. In this way, multiple use of the water is achieved, whereby the water tank can be made smaller and at the same time the service life of the cleaning vehicle with one water tank filling is increased. Although the sieve arrangement retains most of the sweepings, the separated water is heavily contaminated, which leads to annoying deposits and blockages in the nozzles, as well as heavy wear in the flow-through units, especially pumps.

From DE-GM 91 11 692 a device is known which is intended to enable water of a higher degree of purity to be recovered in a sweeper, which then is used again. For this purpose, the water recovery device contains a multi-chamber system with fineness graded filter walls and downstream backwashable fine filters. The equipment required here is very complex and the device has only limited performance in terms of the volume flow rate of dirty water. In addition, the filter walls and the fine filter must be cleaned frequently or replaced frequently.

Often even larger amounts of dirty water have to be treated in sewer cleaning vehicles. Here too, efforts are made to recover the rinsing water from a reservoir integrated in the vehicle as far as possible. Deposits in a channel section are flushed out with a pressurized water jet and the flushing water contaminated with deposits is sucked back into the vehicle interior. There is a more or less rough separation between solids and water according to the principle also used in sweepers - with the same shortcomings. The water is separated using the known sieve walls and filter arrangements. The water, which has been roughly cleaned to this extent, is returned to the reservoir and used again from here for pressure flushing.

The previously known devices for water separation in drainage troughs or for water recovery in street sweeping and sewer cleaning vehicles can all not be rated as optimal in terms of their cost-benefit ratio. Disadvantages - they occur alternatively or in combination - are particularly noteworthy: insufficient purity of the recovered water, too fast clogging of the separators used, complex apparatus construction and insufficient power throughput.

Therefore, the invention has set itself the goal of a device with improved efficiency at low to create equipment expenditure. Furthermore, it should be possible with the device to also separate large, muddy amounts of dirty water and debris with less water content with sufficient purity in water and solids without the need to use quickly clogging fine filters. It must be ensured that the filtration modules used cause little effort to clean them even under high loads.

The device according to the invention is defined in the characterizing part of independent patent claim 1. Preferred design variants result from the dependent patent claims.

Figur 1

: Prinzip der Vorrichtung zur Wasserrückgewinnung für Strassenkehrfahrzeuge;

Figur 2a

: Seitenansicht des Abscheidesiebes;

Figur 2b

: Frontansicht des Abscheidesiebes gemäss Figur 2a aus der Richtung des Pfeiles A;

Figur 2c

: Detailansicht des Abscheidesiebes gemäss dem Ausschnitt B aus Figur 2a, und

Figur 3

: Prinzip der Vorrichtung zur Wasserrückgewinnung für Kanalreinigungsfahrzeuge.

The invention is explained in more detail below, in specific embodiments, with reference to the attached schematic drawings. Show:

Figure 1

: Principle of the device for water recovery for road sweeping vehicles;

Figure 2a

: Side view of the separating sieve;

Figure 2b

: Front view of the separating sieve according to Figure 2a from the direction of arrow A;

Figure 2c

: Detailed view of the separating sieve according to section B of Figure 2a, and

Figure 3

: Principle of the device for water recovery for sewer cleaning vehicles.

The relevant part of the road sweeping vehicle consists of the dirt hopper 1, which is mounted on the vehicle frame 2 and can be tilted around a container axis 3 for the emptying process can swing open. A suction pipe 7 protrudes into the dirt hopper 1, the outer end of which is designed as a suction mouth 8 with which the water-sprayed sweepings are sucked from the street surface 9 into the sweepings hopper 1. The suction on the suction mouth 8 is generated by a high-performance blower 10, which communicates with the interior of the dirt hopper 1 via a suction duct 11 communicates. In the transition from the suction duct 11 to the dirt hopper 1, a coarse sieve 12 is arranged in the cover plate 13 of the dirt hopper 1, which in addition to the function as a container wall also serves as a baffle plate, whereupon the suctioned sweepings break down their essential share of kinetic energy. The coarse sieve 12 has the task of preventing that pieces of debris whirling around in the dirt hopper 1 do not get out again via the suction channel 11. The output of the high-performance blower 10 goes into the free atmosphere and can also be directed wholly or in part to support the sweeping process on the street surface 9. Upstream of the dirt hopper 1 is a trickle shaft 15 which is divided by a sieve wall 14. The sieve wall 14 is a vertical partition wall with a plurality of rows (see FIG. 2b) of trickle openings 17 which are shielded by shielding elements 18 aligned with these rows.

In the bottom 19 of the trickle shaft 15 there is a drain opening 20 with an attached drain connector 21 which opens into a settling tank 22 at the pool inlet 23. The sedimentation basin 22 has a bottom plate 24 which narrows conically downward and has a cone angle α of approximately 60 ° to 150 °. In the depression 25, the base plate 24 has a drain member 26, e.g. Tap, flap or slide open. A vertical wall 27 attaches to the funnel-like base plate 24, a container corner 28 being formed between the base plate 24 and the vertical wall 27. A guide element 29, which has the shape of a cover-like insert plate or is composed of segments, extends almost from the pool inlet 23 into the container corner 28. The guide element 29, which widens conically towards the vertical central axis of the settling basin 22 and downwards, spans at a guide element opening angle (γ) which is approximately in the range from 60 ° to 120 °.

Above the guide element 29 and near the vertical wall 27 there is a transfer pipe 30 which leads to the process water tank 31 and further to the consumers. In the course of the transfer pipe 30 there are two T-branches 33, 34 are provided, a magnetic valve 35 being positioned directly behind the settling basin 22 in the transfer pipe 30. The further course of the transfer pipe 30 leads to the first T-branch 33. From here, a vertical line branch runs as a suction line 36 into the lower connection 37 of the process water tank 31. At the lower connection 37, a drainage element 32, for example a tap or a flap, is installed. The solenoid valve 38 is arranged in the course of the suction line. The transfer pipe 30 extends from the T-branch 33 to the second T-branch 34, the service water pump 39 being located between the two T-branches 33, 34. At the second T-junction 34, a vertical branch branches off as a feed line 40 to the process water tank 31. The solenoid valve 41 is installed in the feed line 40. A consumer feed line 42 also extends from the second T-branch 34, a solenoid valve 43 also being located in this. Individual lines 45 to 47 lead from a distribution cross 44 to the various consumers 48 to 50. An actuator, for example a ball valve 51 to 53, is provided in each individual line to close or open the individual lines 45 to 47 to consumers 48 to 50.

The structure of the screen wall 14 can be seen from FIGS. 2a to 2c, the most expedient geometric relationships being described with reference to FIG. 2c. The sieve wall 14 dividing the trickle shaft 15 from the dirt hopper 1 extends between the bottom 19 and the cover plate 13. The sieve wall 14 consists of the sieve plate 54 and the shielding elements 18, which are assigned to the systematic openings 17 provided in the sieve plate 54. Perforated lines 17 or longitudinal slots come into consideration as pouring openings 17. For specific applications, for example when separating sand or fine-grained debris, it can be advantageous to cover the trickle openings 17 with a mesh screen (not shown). It could also prove expedient to initially keep the trickle openings 17 in the vicinity of the bottom 19 very small and then to increase them in the direction of the To increase the size of the cover plate 13, since the finer debris 56 is more compacted towards the floor 19 due to the shaking movements when the sweeper is traveling, while the coarser solids accumulate on the debris mountain 57.

Above each perforated row 55 there is a shielding element 18, which, at an angle downward, canopy-like, shields the perforated row 55 from the dirt hopper 1. The accumulated debris 56 does not completely fill the space below the shielding element 18; an irregular trickle channel 58 remains. When the debris 56 is dammed against the sieve wall 14, the debris is held back to the extent that the immediate run-up to the trickle openings 17 remains free, that is, debris 56 can hardly accumulate directly in front of the trickle openings 17. The choice of material for the screen plate 54 and the shielding elements 18 will be based on economic criteria and the required strength. The screen plate 54 and the shielding elements 18 must withstand the dynamic pressure of the debris hill 57, the shielding elements 18 also having to have sufficient stability if, for example, larger stones hit.

• Die Abschirmelementenlänge l als Distanz vom Ansatz 59 des Abschirmelementes 18 an der Siebplatte 54 bis zur Aussenkante 60 des Abschirmelementes.
• Der Anstellwinkel β als vom Abschirmelement 18 und der Siebplatte 54 eingeschlossener Winkel.
• Der Abschirmelementenabstand a als Distanz vom Ansatz 59 eines Abschirmelementes 18 an der Siebplatte 54 zum Ansatz 59 des nächsten Abschirmelementes 18 an der Siebplatte 54.
• Der Durchbruchdurchmesser d als Durchmesser oder adäquates Mass für die Grösse der Rieseldurchbrüche 17.
• Die Durchbruchtieflage t als Distanz vom Ansatz 59 eines Abschirmelementes 18 an der Siebplatte 54 bis zur Unterkante 61 der unterhalb dieses Abschirmelementes in der Siebplatte 54 befindlichen Lochzeile 55.
• Das Projektionsmass p als Ankathetenabschnitt auf der Siebplatte 54 zum Anstellwinkel β und bezüglich der Abschirmelementenlänge l bzw. als Projektion der Abschirmelementenlänge l auf die Siebplatte 54.
• Der Bodenabstand b als senkrechte Distanz von der Aussenkante 60 des untersten Abschirmelementes 18 zum Boden 19.

So that the trickle channels 58 form properly and the dewatering of the debris 56 proceeds optimally, the geometric dimensions of the screen wall 14 must adhere to certain relationships. These relevant dimensions are:

• The shielding element length l as a distance from the shoulder 59 of the shielding element 18 on the sieve plate 54 to the outer edge 60 of the shielding element.
• The angle of attack β as the angle enclosed by the shielding element 18 and the sieve plate 54.
• The shielding element distance a as the distance from the shoulder 59 of a shielding element 18 on the sieve plate 54 to the shoulder 59 of the next shielding element 18 on the sieve plate 54.
• The breakthrough diameter d as the diameter or an adequate measure for the size of the trickle breakthroughs 17.
• The breakthrough depth t as the distance from the shoulder 59 of a shielding element 18 on the sieve plate 54 to the lower edge 61 of the perforated line 55 located below this shielding element in the sieve plate 54.
• The projection dimension p as a section of the catheter on the sieve plate 54 at the angle of incidence β and with respect to the shielding element length l or as a projection of the shielding element length l onto the sieve plate 54.
• The ground clearance b as a vertical distance from the outer edge 60 of the lowermost shielding element 18 to the floor 19.

P
   b ≈ 20 mm.The following values were found to be advantageous in extensive test series:
l ≈ 150 mm to 300 mm
β ≈ 30 ° to 60 °
a ≈ 1.2 l
d ≈ 5 mm to 10 mm
t ≈ $$\frac{\text{1}}{\text{3rd}}$$

P
b ≈ 20 mm.

The dimensioning of the breakthrough depth t is crucially dependent on the length of the shielding element l and the angle of attack β, in which case it has been assumed that the sieve plate 54 is perpendicular to the floor 19, which serves for an appropriate use of space with regard to the dirt hopper 1 and the trickle shaft 15.

The device according to FIGS. 1 to 2c will now be described in operation. When a street cleaning tour begins, it is assumed that the process water tank 31 is filled while the settling tank 22 is empty. All drainage devices 26 and 32, all solenoid valves 35, 38, 41 and 43, ball valves 51 to 53 and the emptying flap 5 are closed Domestic water pump 39 activated; at the same time you open the solenoid valves 38 and 43 and the ball valve 52. Likewise the corresponding sweeping units, not shown here, are switched on. The moistened debris is picked up from the road surface 9 by the suction mouth 8 and drawn into the interior of the debris container 1 via the suction pipe 7. In the course of the cleaning tour, a debris mountain 57 will form in the dirt hopper 1, with debris 56 accumulating in front of the sieve wall 14. Due to the repellent shielding elements 18, the space directly underneath the shielding elements and near the sieve plate 54 will not be completely filled with debris 56, but trickle channels 58 will remain free. The debris 56 itself acts as a first filter layer for the escaping water, which accumulates in the trickle channels 58 and runs through the trickle openings 17 in the sieve plate 54 into the trickle shaft 15. Coarse debris parts are retained by the sieve plate 54, while fine-grained material is partially washed away. The water flowing out of the Kehrgutberg 57 passes through the trickle shaft 15 through the drain opening 20, via the drain connection 21 into the pool inlet 23 and finally into the settling basin 22. The fine-grained sweepings 56 that are washed away settles in the depression 25 of the settling basin 22 as a solid layer 62 , while a relatively clean water layer 63 forms over it.

The operator receives a changeover signal via contactors (not shown) in the settling tank 22 - triggered when the water level is high - and / or in the process water tank 31 - triggered when the water level is low. Now it is a matter of transferring the recovered water from the settling tank 22 into the process water tank 31. There is a fundamental change in the switching position of the solenoid valves 35, 38, 41 and 43. Now the solenoid valves 35 and 41 are opened and the solenoid valves 38 and 43 are closed. The service water pump 39 thus sucks the water layer 63 out of the settling basin 22 and conveys the water via the feed line 40 into the service water tank 31. During the pumping over, the sweeping process is briefly interrupted. If the pumping is finished, it will return to the previous operating state hazards. In this way, a large part of the water sprayed through the consumers 48 to 50 is circulated and used several times. Of course, the device can also be operated with two separate pumps and a corresponding valve arrangement, so that no switching or sweeping interruption is necessary.

The conical base plate 24 has a special function in the settling basin 22. This promotes the settling process, i.e. the precipitation of the fine-grained, swept-away sweepings. The guiding elements 29 are also of essential importance for promoting settling. The arrangement of the guiding elements 29 calms the accumulated solids in the settling basin 22 during the shocks caused by the travel movements and the inflowing flow. Furthermore, the shielding effect of the guide elements 29 prevents substance from the solid layer 62 from also being sucked out of the suction connecting piece of the transfer pipes 30.

If the depression 25 in the settling basin 22 has filled up very much with the solid layer, this can be drained off by opening the discharge member 26 at a place provided for this purpose. For cleaning purposes, the process water tank 31 also has a drainage element 32 at the bottom of the countersink 37. For special applications, a fine filter could also be provided in the course of the feed line 40. Thus, the first filtration stage would take place on the screen wall 14, the second filtration stage on the settling tank 22 and the third filtration stage on the possible fine filter.

Figure 3 shows that the invention - i.e. the screen wall 114 and the settling tank 122 - can also be used in a sewer cleaning vehicle 100. In the following explanation, therefore, the structure and function of the structural units essential to the invention are no longer discussed, but only their basic arrangement in a sewer cleaning vehicle 100 is described.

On the sewer cleaning vehicle 100 there is a process water tank 131, in the bottom of which there is a suction line 136 flows into. A process water pump 139 conveys the water from the tank 131 via a consumer feed line 142 to the consumer 150, here a spray nozzle in a channel 109 to be cleaned. The consumer feed line 142 is designed as a hose from the hose reel 170. With the spray nozzle, a water jet is introduced into the channel 109, and sludge that has settled is thus washed up. This water-solid mixture is sucked off from a suction nozzle 108 and passed through the suction pipe 107 into the cleaning material container 101. The cleaning material container 101 is separated from a trickle chamber 115 by a screen wall 114. The items to be cleaned 156 accumulate in the cleaning container 101, a concentrate layer 157 settling at the bottom, while a less concentrated thin sludge layer 171 forms above it.

The concentrate and thin sludge layer 157, 171 accumulate in front of the sieve wall 114, which likewise consists of a sieve plate 154 with flow openings 117 arranged in rows 155 and shielding elements 118 covering this in the manner of a canopy. The thin sludge layer 171, which essentially consists of water and is deposited at the top, will flow through the flow openings 117 in the screen wall 114 in the direction of the flow chamber 115 without a filtration process. On the other hand, the viscous concentrate layer 157 will accumulate on the screen wall 114, the shielding elements 118 not admitting the concentrate to the trickle openings 117; Here, too, 117 trickle channels 158 are formed immediately before the trickle openings. In this way, the concentrate layer 157 is dewatered without the sieve plate 154 clogging up immediately.

If a certain water level is exceeded in the trickle chamber 115, a dirty water pump 173 could be switched on, for example, by a float 172 in order to pump dirty water from the trickle chamber 115 through a connecting pipe 121 into the settling tank 122. As already described for FIG. 1, the second filtration stage takes place in the settling tank 122. In the depression 125 of the sedimentation basin 122 a solid layer 162 settles, while a water layer 163 forms over it. A transfer pipe 130 protrudes into the settling basin 122 into the water layer 163 - arranged above the guide elements 129. The clarified water is pumped from the settling basin 122 into the service water tank 131 by means of a clarification water pump 174. If necessary, a rewindable filter 176 can also be installed in the course of the transfer pipe 130. The solid layer 162 formed in the settling basin 122 can be drained cyclically via a downpipe 175 which attaches to the bottom 125 of the settling basin 122 and leads into the washware container 101.

If the washware container 101 is excessively filled with concentrate 157, the container is emptied in the usual way, e.g. by means of a pneumatic extension piston or by tipping back. There are other options for the arrangement of the screen wall 114 and the settling basin 122 on the sewer cleaning vehicle 100 than previously shown here. The screen wall 114 could also be provided in the front part of the vehicle and the settling basin 122 does not have to be placed in or near the service water tank 131. Thanks to the arrangement, it is now also possible to use the rinsing water in sewer cleaning vehicles 100 several times in a circuit with relatively simple means. The withdrawn water is treated with a sufficient degree of purity so that the affected conveying and distribution units are spared when the clarified water is reused.

The inventive screen element can also advantageously be used in drainage troughs. For this purpose, at least one outer wall of the drainage trough is formed by the screen wall, the nature and mode of operation of which has already been described with reference to FIGS. 1, 2a and 3. It is also conceivable to design all four walls of the drainage trough entirely or partially as a screen wall. For certain applications, it should be sufficient to provide one or more horizontal or vertical wall strips in the form of the screen wall. A window-like arrangement is also conceivable.

Claims (8)

Sieve element in drainage troughs and in devices for water recovery for street and sewer cleaning vehicles consisting of a sieve plate (54, 154) with a large number of systematically arranged drainage openings (17, 117), characterized in that the drainage openings (17, 117) are arranged in parallel, horizontally spaced extending and one above the other rows (55, 155) are provided, the trickle openings (17, 117) being shielded by canopy-like shielding elements (18, 118) pointing downwards at an angle of attack (β), whereby drainage or cleaning material (56, 156) in the case of a sieve wall (14, 114) formed by the sieve element in a drainage trough, a street cleaning vehicle or a sewer cleaning vehicle (100), it cannot accumulate directly in front of the trickle openings (17, 117), but can instead accumulate in the wedge-shaped corner between the sieve plate (54, 154) and the shielding element (18, 118) a trickle channel (58 , 158) forms;
and that when the sieve element is used as a separating sieve wall (14, 114) in a street cleaning vehicle or sewer cleaning vehicle (100) to the department between a dirt hopper (1) and a trickle shaft (15) or between a cleaning goods container (101) and a trickle chamber (115 ) the water separated by means of the sieve wall (14, 114) is fed to a settling tank (22, 122) for further cleaning, which has a bottom plate (24) narrowing downwards at a cone angle (α) and a vertical wall (27) attached to it which together form a container corner (28); and from the pool inlet (23) to almost into the container corner (28) a diagonally downward-pointing guide element (29, 129) is installed, which extends like a hood at an opening angle (γ). Sieve element according to claim 1, characterized in that the same has the following relevant geometric dimensions: - A shielding element length ( l ) as the distance from the shoulder (59) of the shielding element (18) on the screen plate (54) to the outer edge (60) of the shielding element; - An angle of attack (β) as the angle enclosed by the shielding element (18) and the sieve plate (54); - A shielding element distance ( a ) as the distance from the shoulder (59) of a shielding element (18) on the sieve plate (54) to the shoulder (59) of the next shielding element (18) on the sieve plate (54); - A breakthrough diameter ( d ) as a diameter or adequate measure for the size of the trickle breakthroughs (17); - A breakthrough depth as the distance from the shoulder (59) of a shielding element (18) on the sieve plate (54) to the lower edge (61) of the perforated row (55) located below this shielding element (18) in the sieve plate (54); - A projection dimension ( p ) as a section on the screen plate (54) to the angle of attack (β) and with respect to the length of the shielding element ( l ) or as a projection of the length of the shielding element ( l ) onto the screen plate (54); and - A floor distance ( b ) as a vertical distance from the outer edge (60) of the lowest shielding element (18) to the floor (19); the following conditions apply:
l ≈ 150 mm to 300 mm
β ≈ 30 ° to 60 °;
a ≈ 1.2 l
d ≈ 5 mm to 10 mm;
t ≈ $$\frac{\text{1}}{\text{3rd}}$$

p and
b ≈ 20 mm. Sieve element according to claim 1 or 2, characterized in that it is designed as a sieve wall (14, 114) perpendicular to the bottom (19) of the dirt hopper (1) or the cleaning goods container (101). Sieve element according to one of claims 1 to 3, characterized in that the trickle openings (17, 117) in the sieve plate (54, 154) are designed as bores or slots, the trickle openings (17, 117) from the rows (55, 155 ) near the bottom (19) to the cover plate (13) can be made increasingly larger. Sieve element according to one of claims 1 to 4, characterized in that the shielding elements (18, 118) can be protected against bending and deformation by reinforcements. Sieve element according to one of claims 1 to 5, characterized in that it is provided in drainage troughs for designing at least one complete outer wall or as a single or multiple horizontal or vertical wall strip or as a trough corner or in a window-like arrangement. Sedimentation basin (22, 122) according to claim 1, characterized in that the conical base plate (24) forms a depression (25, 125), at the lowest position of which a drainage element (26) is provided, the sedimentation basin (22, 122) below a solid layer (62, 162) and above it a water layer (63, 163) and the water through a transfer pipe (30, 130), the nozzle above the guide element (29, 129) near the vertical wall (27) and the Container corner (28) attaches, removed and passed into a service water tank (31, 131) and thus the waste or cleaning goods (56, 156) was de-zone and again in circulation at the consumers (48 to 50) of the street cleaning vehicle or on Consumer (150) of the sewer cleaning vehicle (100) is available. Sedimentation basin according to one of claims 1 or 7, characterized in that the cone angle (α) is approximately between 60 ° and 150 ° and the guide element (29, 129) is formed in one piece in a lid-like manner or consists of several surface segments, the guide element opening angle (γ ) is approximately between 60 ° and 120 °.

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