Pulsation damper and concrete spraying device

Abstract

Proposed is a pulsation damping device (50) which is connectable to a conveying section (33) of a concrete spraying device, characterized in that the pulsation damping device (50) has a cylinder (1) with a piston rod (4) which is mounted therein and has a first piston (2) and a second piston (2'), wherein: one end of the cylinder (1) is open and is connectable to the conveying section (33) of the concrete spraying device; the other end of the cylinder (1) is closed; the cylinder (1) has a first guide (7) and a second guide (6) for the piston rod (4); the first piston (2) is arranged movably in the cylinder between the first guide (7) and the second guide (6); a first partial volume (V1) is formed between the first piston (2) and the first guide (7) and a second partial volume (V2) is formed between the first piston (2) and the second guide (6); the second piston (2') is arranged movably in the cylinder (1) between the second guide (6) and the open end of the cylinder (1); a third partial volume (V3) is formed between the second piston (2') and the second guide (6); the piston rod (4) is subjected to force by means of a spring (3) between the first guide (7) and the closed end of the cylinder (2); and the second guide (6) has two opposing check valves (10, 12) between the second partial volume (V2) and the third partial volume (V3).

Description

[0001] CONCRETE SPRAYER AND PULSATION DAMPER

[0002] The present invention relates to a concrete spraying machine comprising a reservoir for shotcrete, a first pump cylinder, a second pump cylinder, and an inlet for a setting accelerator, wherein the two pump cylinders are connected to the reservoir for receiving shotcrete, and wherein the two pump cylinders are connected to a delivery section for dispensing shotcrete. The invention further relates to a pulsation damping device for a concrete spraying machine. Finally, the invention relates to a method for applying shotcrete from a concrete spraying machine to a substrate, wherein a setting accelerator is added to the shotcrete and the shotcrete is alternately conveyed and dispensed via at least two pump cylinders along a delivery section of the concrete spraying machine.

[0003] BACKGROUND OF THE INVENTION

[0004] Shotcrete is pneumatically applied to a substrate using a spray nozzle. The application of shotcrete as an installation method has the advantage that the impact of the shotcrete on the substrate compacts it. A key application for shotcrete is in tunnel construction, where a homogeneous application is particularly important to ensure long-term stability.

[0005] State-of-the-art concrete spraying equipment often employs two pump cylinders (double-piston pumps) from which shotcrete is alternately applied to the substrate. In continuous operation, the shotcrete is first applied via the first filled pump cylinder and then via the second filled pump cylinder. As soon as the first pump cylinder is empty or nearly empty, the process switches from the first to the second. While the second pump cylinder is operating, the first pump cylinder can be filled, allowing a switch back from the second to the first pump cylinder without interrupting the shotcrete application process. Such a concrete spraying equipment is described, for example, in EP 0 669 462 A1.

[0006] Due to their design, concrete pumping with such concrete shotguns is possible without interruption. However, the concrete flow becomes briefly discontinuous during the changeover from one pump cylinder to the other. This is because a brief pressure drop occurs in the pumped concrete during the changeover, causing a change in velocity or an interruption of the concrete flow. This change in velocity is problematic because a setting accelerator is added to the concrete before it reaches the nozzle in concrete shotguns to accelerate the setting process. Since the accelerator is added continuously, the change in concrete flow velocity leads to an overdose of setting accelerator in the shotcrete during the changeover between the two pump cylinders.This effect, characterized by a brief drop in pressure and a corresponding decrease in flow rate, is called pulsation. The intermittent overdosing of setting accelerator in the concrete caused by pulsation leads to structural defects in the shotcrete, which are usually associated with a layer of concrete that can result in strength and durability problems.

[0007] This defect is described by the so-called pulsation degree. According to the draft guideline "Shotcrete 2024" (ÖVBB), the pulsation degree is defined as follows:

[0008] 100 x duration of the pressure drop in the concrete flow to below 90% of the maximum pressure in relation to the total duration of the piston stroke in %.

[0009] The pulsation level in shotcrete is therefore a measure of the discontinuity or interruption of the concrete flow during the spraying process.

[0010] The degree of pulsation is currently primarily influenced by changes in the material mix, the consistency and pumpability of the concrete, and the type of pump used. A high degree of pulsation can lead to uneven concrete application and potentially impair the quality of the concrete.

[0011] EP 0 669 462 A1 describes the problem of pulsation and attempts to solve it by observing and adjusting the characteristics of the pump cylinder's ejection motion until the pulsation reaches a tolerable level. The ejection motion is adjusted by varying the velocity during the piston's retraction within the pump cylinder. Consequently, the piston's retraction velocity is not constant throughout the stroke, but rather depends on the piston's position within the pump cylinder. However, varying the retraction velocity over the piston stroke is prone to errors, complex, and slow due to the intermittent reduction in retraction velocity, and therefore appears to have no practical application.

[0012] CN 102 297 312 B discloses a pulsation damping device connected to the delivery section of a concrete sprayer, wherein the pulsation damping device has two cylinders with a piston rod positioned between them. The piston rod is connected to a first piston in the first cylinder and a second piston in the second cylinder, one end of the first cylinder being open and connected to the delivery section of the concrete sprayer. A partial volume is formed between the second piston and the end of the second cylinder, which is connected to a hydraulic accumulator. The second piston can be acted upon by this accumulator to push the first piston towards the delivery section.

[0013] BRIEF DESCRIPTION OF THE INVENTION

[0014] For optimal application of shotcrete, a continuous and uniform concrete flow is essential to ensure the highest possible durability. However, local overdosing of accelerator reduces the concrete's durability, as it becomes less resistant to sulfates and can become porous in places due to leaching. This leaching can also clog drainage pipes.

[0015] At the same time, there is a strong desire to apply and set shotcrete very quickly in order to accelerate construction progress. Since the use of pulsation reduction methods – as described, for example, in EP 0 669 462 Al – has not proven successful in practice, more setting accelerator than necessary is added in tunnel construction due to time constraints, leading to the problems described.

[0016] The object of the present invention is therefore to reduce the problem of pulsation and the associated material impairment in the set shotcrete while still enabling rapid setting or rapid processing of the shotcrete.

[0017] This problem is solved, on the one hand, by a pulsation damping device which can be connected to a conveying section of a concrete spraying machine, characterized in that the pulsation damping device has a cylinder with a piston rod mounted therein, with a first piston and a second piston, wherein one end of the cylinder is open and can be connected to the conveying section of the concrete spraying machine, wherein the other end of the cylinder is closed, wherein the cylinder has a first guide and a second guide for the piston rod, wherein the first piston is movably arranged between the first guide and the second guide in the cylinder, wherein a first partial volume is formed between the first piston and the first guide and a second partial volume is formed between the first piston and the second guide, wherein the second piston is movably arranged between the second guide and the open end of the cylinder.wherein a third partial volume is formed between the second piston and the second guide, wherein the piston rod is subjected to a spring force between the first guide and the closed end of the cylinder, wherein the second guide has two opposing check valves between the second partial volume and the third partial volume.

[0018] On the other hand, the task is solved by a concrete spraying device, comprehensive

[0019] (i) a reservoir for receiving shotcrete,

[0020] (ii) a first pump cylinder,

[0021] (iii) a second pump cylinder and

[0022] (iv) an inlet for a setting accelerator, wherein the two pump cylinders are connected to the reservoir, wherein the two pump cylinders and the inlet are connected to a conveying section for the delivery of shotcrete, characterized in that a pulsation damping device of the type mentioned is provided, the open end of which opens into the conveying section.

[0023] Finally, the problem is solved by a method for applying shotcrete from a concrete spraying machine onto a substrate, wherein a setting accelerator is added to the shotcrete and wherein the shotcrete is conveyed along a conveying section of the concrete spraying machine via at least two alternately actuated pump cylinders and subsequently discharged, wherein, by means of a pulsation damping device of the aforementioned type, a compensation volume in the cylinder of the pulsation damping device is filled with shotcrete from the conveying section during the conveying of shotcrete along the conveying section by means of a pump cylinder and wherein, during the switching from one pump cylinder to the other pump cylinder, the shotcrete from the compensation volume in the cylinder of the pulsation damping device is discharged to the conveying section.

[0024] According to the invention, the pulsation damping device comprises a mechanical-hydraulic piston-cylinder unit which, during the duration of a piston stroke of the concrete sprayer, continuously accumulates a compensation volume of shotcrete between the second piston and the open end of the cylinder. When switching to the second pump cylinder and the associated pressure drop occurs, this volume is very quickly fed into the concrete flow due to the spring action, thus smoothing the concrete pressure curve and reducing pulsation or, ideally, eliminating it entirely. The compensation volume depends on the pulsation level of the respective pump and can be adjusted by the stroke volume of the compensation cylinder.

[0025] A piston-cylinder unit is a basic mechanical assembly consisting of a cylinder, which is a hollow, cylindrical structure in which the piston moves up and down, or back and forth. The piston fits precisely into the cylinder and moves linearly up and down. The cylinder head closes off the cylinder at one end.

[0026] The piston rod is movably mounted in the first and second guides, with the two guides together with the piston rod movably mounted therein forming a tight barrier so that no fluid exchange can take place between the partial volumes - with the exception of the check valves.

[0027] The cylinder may be provided with a piston rod receptacle, whereby the piston rod and the receptacle are movable relative to each other and are subjected to spring force. This facilitates the application of spring force to the piston rod. The piston rod receptacle can, for example, be a tubular section in which the piston rod is mounted for linear movement. Alternatively, the piston rod receptacle can, for example, have a projection over which a tubular section of the piston rod is slid.

[0028] Furthermore, a spindle can be provided for adjusting the spring preload. In conjunction with a piston rod holder, even finer adjustment is possible.

[0029] It can be provided that the cross-sectional areas of the flow openings of the counter-rotating check valves between the second and third partial volumes are independently variable. This allows for optimization of the pulsation damping depending on the dimensions of the individual components of the pulsation damping device and the composition or flow properties of the shotcrete.

[0030] For example, the variable cross-sectional areas of the flow openings of the counter-rotating check valves can be adjusted via control valves.

[0031] The first partial volume can be connected to a hydraulic fluid reservoir via a pipe.

[0032] The second sub-volume can also be connected to the hydraulic fluid reservoir via a line, with a shut-off valve installed in the line. This shut-off valve is necessary to maintain a constant fluid flow between the second and third volumes during operation, ensuring the compensation volume is filled correctly.

[0033] To facilitate the assembly of the pulsation damping device, it has proven advantageous for the cylinder to be designed in at least two parts, with a detachable connection between the first and second parts of the cylinder within the volume of the first part. For this purpose, for example, the first and second parts of the cylinder can each have a flange, and the flanges can be connected to each other via screw connections.

[0034] The assembly of the pulsation damping device is also facilitated if the piston rod has at least piston rod sections that can be connected via two detachable connections, the first detachable connection being located in the section of the first partial volume and the second detachable connection being located in the section of the second partial volume. For example, the piston rod sections can have a detachable screw connection to each other.

[0035] The process according to the invention unfolds as follows during an entire piston stroke of the concrete pump:

[0036] Immediately after the previous change of the first pump cylinder to the second pump cylinder (or vice versa), due to the prevailing concrete pressure (approx. 30 ±10 bar), a compensation volume of shotcrete is accumulated in the pulsation damping device as evenly as possible over the entire stroke duration, controlled by the variable flow opening on the check valve, which is then released again to compensate for the pulsation, controlled by the variable flow opening on the check valve.

[0037] Once the piston of the concrete pump reaches its apex and the pump's diverter valve engages to switch to the other cylinder, causing a significant pressure drop in the concrete flow during delivery, the previously closed valve releases the oil flow. This allows the accumulated compensation volume of concrete, driven by the tensioned spring, to be released into the concrete flow, thus smoothing it out. The delivery rate can vary depending on the pump's capacity and can be adjusted via a setscrew to achieve optimal results.

[0038] The relief valve can be designed in such a way that the speed of release of the compensation volume is dimensioned to achieve the most optimal uniformity of the concrete flow.

[0039] Since this process depends on the concrete pump's output, it will be necessary to adjust the cross-section of the relief orifice accordingly. Higher pump outputs result in higher delivery pressures, meaning that a simple dimensioning of the relief orifice ensures optimal pulsation minimization for only one specific pump output setting. If the device needs to be adaptable to any pump output, the cross-section of the relief orifice must be adjustable. This can be achieved with an adjusting screw that extends laterally into the relief orifice. The higher the pressure in the concrete flow, the smaller the cross-section of the relief orifice must be.

[0040] Depending on the pulsation, the required compensation volume is approximately 10 to 15% of the total delivery volume during a piston stroke. Since the delivery volume of a pump stroke varies between 25 and 30 liters depending on the machine, the compensation volume must be on the order of 2.5 to 4.5 liters.

[0041] DETAILED DESCRIPTION OF THE INVENTION

[0042] Further advantages and details of the invention are explained with reference to the accompanying figures and the following figure description.

[0043] Fig. 1 shows a rough schematic of a concrete spraying device according to the invention.

[0044] Fig. 2 schematically shows the piston-cylinder unit.

[0045] Figure 1 schematically illustrates a concrete spraying machine with a reservoir 30 for shotcrete and a first pump cylinder 31 and a second pump cylinder 32. The pump cylinders 31 and 32 are connected to both the reservoir 30 and a delivery section 33, through which the shotcrete is dispensed. To dispense the shotcrete, the shotcrete in the reservoir 30 is drawn into the pump cylinders 31 and 32. A driven piston then moves the shotcrete in the respective pump cylinder 31 or 32 to the delivery section 33. From the delivery section 33, the shotcrete can then be dispensed through a nozzle 34. As soon as the contents of the first pump cylinder 31 are empty, a switching unit (36), shown schematically, switches the pump to the second pump cylinder 32, which then dispenses the shotcrete through the delivery section 33 and nozzle 34.While the second pump cylinder 32 actively pumps shotcrete into the conveying section 33, the first pump cylinder 31 is filled with shotcrete from the reservoir 30. This process of alternately loading and unloading the pump cylinders 31, 32 can continue until the reservoir 30 is empty. An inlet 35 for setting accelerator is provided at a suitable location in the conveying section 33. The setting accelerator typically comes from a container and is added to the shotcrete in liquid form via the inlet 35. The addition of setting accelerator occurs at a largely constant rate. According to the invention, a pulsation damping device 50 is provided at the conveying section 33, which ensures that the conveying rate of the shotcrete does not drop when switching from one pump cylinder 31, 32 to the other pump cylinder 32, 31.If the shotcrete stagnates or slows down in conveying section 33, setting accelerator continues to be added via inlet 35 without the shotcrete moving (sufficiently) in conveying section 33. If this shotcrete, now containing an excess of setting accelerator, is then applied and hardens, the structure of the set shotcrete will be noticeably deteriorated.

[0046] Fig. 2 shows the pulsation damping device 50 according to the invention, which is connected to the conveying section 33 of the concrete spraying machine, in more detail. The flow direction of the shotcrete in the conveying section 33 is indicated by an arrow. The pulsation damping device 50 comprises a cylinder 1 with a piston rod 4 mounted therein. The piston rod 4 has two pistons, namely a first piston 2 and a second piston 2'. The pistons 2, 2' seal the space located upstream and downstream of the respective pistons 2, 2'. One end of the cylinder 1 (bottom in Fig. 2) is open and connected to the conveying section 33 of the concrete spraying machine. The other end of the cylinder 2 (top in Fig. 2) is closed.

[0047] Cylinder 1 has two guides 6 and 7 for the piston rod 4. The first guide 7 and the second guide 6 are designed to be located on the inside of cylinder 1 and have a recess in which the piston rod 4 is guided. The first piston 2 is movably arranged between the first guide 7 and the second guide 6 within the cylinder. A first partial volume VI is formed between the first piston 2 and the first guide 7. A second partial volume V2 is also formed between the first piston 2 and the second guide 6.

[0048] The second piston 2' is movably arranged between the second guide 6 and the open end of the cylinder 1 within the cylinder 1. This creates a third partial volume V3 between the second piston 2' and the second guide 6.

[0049] The piston rod 4 is biased by a spring 3 between the first guide 7 and the closed end of the cylinder 2. The spring 3 bears against the first piston 7 on one side and against the cylinder 1 on the other. In the illustrated embodiment, the contact with the cylinder 1 is indirect via a spindle 8, which is inserted into the closed end of the cylinder 1. The spindle 8 allows adjustment of the spring 3 preload. For improved guidance, a piston rod receptacle 14 is provided on the cylinder 1, whereby the piston rod 4 and the piston rod receptacle 14 are movable relative to each other. These two are biased against each other by the spring 3. The piston rod receptacle 14 has a tubular section into which a projection of the piston rod 4 can be inserted and moved linearly along the cylinder axis.

[0050] The first partial volume VI and the second partial volume V2 are connected to a hydraulic fluid reservoir 5, which preferably contains hydraulic oil.

[0051] The second guide 6 has two counter-rotating and controllable check valves 10 and 12, which control the flow between the second partial volume V2 and the third partial volume V3 during the intake and discharge of the compensation volume. The second partial volume V2 and the third partial volume V3 are connected to each other via two flow openings with variable cross-sectional areas. Two control valves 9, 11 in the flow openings allow the cross-sectional areas of the flow openings to be adjusted.

[0052] The flow of hydraulic oil at valve 10 can be changed using adjusting screw 9. The flow of hydraulic oil at valve 12 can be changed using adjusting screw 11.

[0053] To facilitate assembly of the pulsation damping device 50, the cylinder 1 can be designed in two parts, with a detachable connection between a first part 1' of the cylinder and a second part 1" of the cylinder in the section of the first partial volume VI. The piston rod 4 can also be divided into piston rod sections 4', 4", 4'" for easier assembly, which are connected by two detachable connections 16, 16' (here: screw connections). The first detachable connection 16 is located in the section of the first partial volume VI, and the second detachable connection 16' is located in the section of the second partial volume V2.

[0054] During operation, the prevailing concrete pressure (approx. 30 ±10 bar) in the pump cylinders 31 and 32 exerts pressure on the piston 2, which moves towards the closed end in cylinder 1. This pre-tensions the spring 3, filling the volume with concrete over the stroke height h. This compensation volume, filled with shotcrete, acts as a reservoir for the shotcrete. After the first pump cylinder 31 switches to the second pump cylinder 32 (or vice versa), a slight pressure drop occurs in the delivery section 33. The spring 3 relaxes and, to compensate for the pulsation, pushes the shotcrete collected in the compensation volume over the stroke height h back into the delivery section 33, thus compensating for the pressure drop.

[0055] The first partial volume V1 is connected to a hydraulic fluid reservoir 5 via a line. The second partial volume V2 is also connected to the hydraulic fluid reservoir 5 via a line, with a shut-off device 13 arranged in the line. During operation, the shut-off device 13 is closed to keep the sum of the partial volumes V2 and V3 constant while shotcrete is being added to or ejected from the compensation volume.

Claims

REQUIREMENTS 1. Pulsation damping device (50) which is connectable to a conveying section (33) of a concrete spraying device, wherein the pulsation damping device (50) has a cylinder (1) with a piston rod (4) mounted therein, having a first piston (2) and a second piston (2'), wherein one end of the cylinder (1) is open and connectable to the conveying section (33) of the concrete spraying device, wherein the other end of the cylinder (1) is closed, wherein the cylinder (1) has a first guide (7) and a second guide (6) for the piston rod (4), wherein the first piston (2) is movably arranged between the first guide (7) and the second guide (6) in the cylinder, wherein a first partial volume (VI) is formed between the first piston (2) and the first guide (7) and a second partial volume (V2) is formed between the first piston (2) and the second guide (6),wherein the second piston (2') is movably arranged between the second guide (6) and the open end of the cylinder (1) in the cylinder (1), wherein a third partial volume (V3) is formed between the second piston (2') and the second guide (6), wherein the piston rod (4) between the first guide (7) and the closed end of the cylinder (2) is acted upon by a spring (3), wherein the second guide (6) has two opposing check valves (10, 12) between the second partial volume (V2) and the third partial volume (V3).

2. Pulsation damping device according to claim 1, wherein a piston rod receptacle (14) is provided on the cylinder (1), wherein the piston rod (4) and the piston rod receptacle (14) are movable relative to each other and are subjected to force via the spring (3).

3. Pulsation damping device according to claim 1 or claim 2, wherein a spindle (8) is provided for adjusting the preload for the spring (3).

4. Pulsation damping device according to one of claims 1 to 3, wherein the cross-sectional areas of the flow openings of the counter-rotating check valves (10, 12) between the second subvolume (V2) and the third subvolume (V3) are independently variable.

5. Pulsation damping device according to claim 4, wherein the variable cross-sectional areas of the flow openings of the counter-rotating check valves (10, 12) are adjustable via control valves (9, 11).

6. Pulsation damping device according to one of claims 1 to 5, wherein the cylinder (1) is formed in at least two parts with a detachable connection (15) of a first part (1') of the cylinder (1) and a second part (1") of the cylinder (1) in the section of the first partial volume (VI).

7. Pulsation damping device according to one of claims 1 to 6, wherein the piston rod (4) has at least three piston rod sections (4', 4", 4'") which can be connected via two detachable connections (16, 16'), wherein the first detachable connection (16) is arranged in the section of the first partial volume (VI) and the second detachable connection (16') is arranged in the section of the second partial volume (V2).

8. Pulsation damping device according to one of claims 1 to 7, wherein the first partial volume (VI) is connected to a hydraulic fluid reservoir (5) via a line.

9. Pulsation damping device according to claim 8, wherein the second partial volume (V2) is connected to the hydraulic fluid reservoir (5) via a line, wherein a shut-off device (13) is arranged in the line.

10. Concrete spraying machine, including (i) a reservoir (30) for receiving shotcrete, (ii) a first pump cylinder (31), (iii) a second pump cylinder (32), and (iv) an inlet (35) for a setting accelerator, wherein the two pump cylinders (31, 32) are connected to the reservoir (30), wherein the two pump cylinders (31, 32) and the inlet (35) are connected to a conveying section (33) for dispensing shotcrete, wherein a pulsation damping device (50) according to one of claims 1 to 9 is provided, the open end of which opens into the conveying section (33).

11. Concrete spraying device according to claim 10, wherein the inlet (35) is for a Setting accelerator in the flow direction of the shotcrete between the a pulsation damping device (50) and a nozzle (34) for spraying the shotcrete is arranged.

12. Method for applying shotcrete from a concrete spraying machine onto a substrate, wherein a setting accelerator is added to the shotcrete and wherein the shotcrete is conveyed along a conveying section (33) of the concrete spraying machine via at least two alternately actuated pump cylinders (31, 32) and subsequently discharged, wherein, by means of a pulsation damping device (50) according to one of claims 1 to 9, a compensation volume in the cylinder (1) of the pulsation damping device (50) is filled with shotcrete from the conveying section (33) during the conveying of shotcrete along the conveying section (33) by means of one of the pump cylinders (31, 32) and wherein, during the switching from one of the pump cylinders (31, 32) to the other of the pump cylinders (32, 31), the shotcrete is discharged from the compensation volume in the cylinder (1) of the pulsation damping device (50) to the conveying section (33).

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