WO1997040969A1

WO1997040969A1 - Apparatus to feed a constant flow of concrete containing additives

Info

Publication number: WO1997040969A1
Application number: PCT/EP1997/002226
Authority: WO
Inventors: Roberto Arpini; Ivano Fraccapani; Giorgio Moretti
Original assignee: Cifa S.P.A.
Priority date: 1996-04-30
Filing date: 1997-04-30
Publication date: 1997-11-06
Also published as: IT1282148B1; NZ332534A; NO985045L; CA2253247A1; ITMI960840A0; ITMI960840A1; NO985045D0; AU2775697A; CN1216946A; EP0904182A1

Abstract

An apparatus to feed a constant flow of concrete comprises two hydraulic cylinder-piston units (2, 3), acting alternately so as to operate two corresponding pistons (22, 23) feeding the concrete to a concrete delivery pipe (17) through a commutating valve (6), and a proportioning device to feed the additives having to be added to the concrete. The device proportioning the additives consists of a pump (5), which is operated by a hydraulic motor (4) driven by a hydraulic circuit derived from the main hydraulic circuit operating said cylinder-piston units (2, 3). Said derived hydraulic circuit consists of a circuit which connects said hydraulic motor (4) to the exhaust chambers of the cylinders of said cylinder-piston units (2, 3) through a valve system (20) apt to 'rectify' the hydraulic flow.

Description

"APPARATUS TO FEED A CONSTANT FLOW OF CONCRETE CONTAINING ADDITIVES"

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The present invention concerns an apparatus to feed a constant flow of concrete, particularly suited to be applied on machines for concrete castings in tunnels (so-called "spritz" machines).

The currently known concrete feeding systems generally comprise tv»o cylinder-piston units - alternately operated by corresponding hydraulic cylinder-piston units - which are filled with concrete and alternately emptied, to feed in a practically continuous manner the concrete delivery nozzle. The feeding of concrete to the single pipe with delivery nozzle is controlled by a commutating valve, commonly called S-valve due to its shape. The commutation of this valve requires times of the order of 0.2 seconds, during which the concrete flow is temporarily interrupted and continuity comes to fail.

Another cause for interruption of the concrete flow is the presence of a high percentage of air (up to 40%), produced in the cylinders of the cylinder-piston units while the concrete is being sucked in, and leading to a substantially "idle" initial stroke during delivery.

The direct consequence of these interruptions is a substantial dis- homogeneity of the concrete flow, which is undesirable from every point of view. In particular, said dishomogeneity makes it extremely difficult, if not impossible, to provide for a uniform proportioning of the concrete additives, at any moment of the feeding. In practice, the composition of the concrete is only roughly uniform, and it is suddenly apt to undergo big variations.

A further valid reason for wishing to always exactly proportion the percentage of additives in the concrete is the extremely high cost there¬ of, which may even exceed ten times the price of cement.

The object of the present invention is to thus supply a concrete feeding apparatus wherein the concrete flow is as uniform as possible and allowing to proportion the additives always exactly as required, even in the presence of the inevitable slight residual dishomogeneities. Said object is perfectly reached by the present invention thanks to the fact that, in an apparatus to feed a constant flow of concrete - of the type comprising two hydraulic cylinder-piston units, acting alterna¬ tely so as to operate two corresponding pistons feeding the concrete to a concrete delivery pipe through a cornmutating valve, and a proportioning device to feed the additives having to be added to the concrete - the device proportioning the additives consists of a pump, which is operated by a hydraulic motor driven by a hydraulic circuit derived from the main hydraulic circuit operating the two hydraulic cylinder-piston units.

According to the invention, said derived hydraulic circuit consists of a circuit which connects said hydraulic motor to the exhaust chambers of the cylinders of said cylinder-piston units through a valve system apt to "rectify" the hydraulic flow.

The invention is now described in further detail, with reference to a preferred embodiment thereof, illustrated by way of example on the single accompanying drawing, \\hich represents a general diagram of the concrete feeding apparatus according to the present invention.

As shown on the drawing, a pump 1 pumps oil into the main hydraulic circuit of the apparatus. The pump 1 is preferably of the double-powered type, as it comprises an electric motor and a diesel engine, this latter being used when operating in the absence of an electric supply mains.

Through the main hydraulic circuit and a distributor 9. the pump 1 feeds oil alternately to two cylinder-piston units 2, 3> which operate the concrete delivery pistons 22, 23; furthermore, through a secondary circuit and the distributor 10, the pump 1 feeds oil alternately to tuo cylinder-piston units 6a, 6b, vvhich directly control the cornmutating valve 6. Also an auxiliary circuit contributes to feed the units 6a. 6b, controlling the cornmutating valve 6, said auxiliary circuit being fed by a pump 7 to \\hich there is associated a known-type pressure accumulator 8; this latter is apt to keep in the auxiliary circuit a minimum prede¬ termined pressure (for instance 70 bar). Said auxiliary circuit and said accumulator 8 are meant to accelerate the movements of the cornmutating valve 6, as better specified hereinafter.

According to a fundamental characteristic of the invention, a supplementary hydraulic circuit is moreover provided downstream of the cylinder-piston units 2, 3, said circuit comprising a hydraulic motor 4, apt to operate a pump 5 for the additives and being fed with the oil expelled alternately from the chambers downstream of the cylinder-piston units 2, 3 (exhaust chambers), during the steps corresponding to the res¬ pective operations of the concrete delivery pistons 22, 23■ The feeding of this supplementary circuit is carried out through a system of four check valves 20 positioned according to a two-way bridge diagram, or through a four-way valve system, such valves forming a kind of hydraulic flow "rectifier", as better illustrated hereinafter.

The uorking of the apparatus is controlled by a processor 11 equip¬ ped, for example, with a control system 12 having a touch-sensitive screen. In particular, the processor 11 controls the pump 1 through line 1 ' and a pouered speed converter 13 through line 13'. The speed converter 13 - for example of the disk type - is interposed, on the motion trans¬ mission, between the hydraulic motor 4 and the pump 5 for the additives; it preferably has a reduction ratio from 1 to 5-

Signals are sent to the processor 11, through lines 14' and 15'. by tv,o pressure transducers 14 and 15, each positioned in the hydraulic cir¬ cuit of the cylinder-piston units 2 and 3 respectively. A further signal reaches the processor 11 from a measurer 16, which measures the instant flow rate of the concrete fed in the pipe 17 towards the delivery nozzle (not shown). Said measurer lό preferably consists of a device to detect the concrete speed profile - according to Italian Patent application N. MI96A 000812, filed by the Applicant on April 24, 1996 - apt to supply the measurement of the concrete instant flow rate.

To each of the cylinder-piston units 2, 3, there is moreover asso¬ ciated an end-of-stroke sensor l8, 19, also connected to the processor 11 through respective lines 18', 19' ■

When concrete feeding is started, the pump 1 is operated and sends oil first to one of the cylinder-piston units 2, 3. and immediately after - at the end of its stroke - to the other one of said units, through com¬ mutation of the distributor 9- The two sensors 18, 19. detect the end-of- stroke position of the piston, respectively of the unit 2 or 3• and send the relative signal to the processor 11; this latter then controls the operation of the cornmutating valve 6 which, in known manner, establishes each time which of said

units is meant to perform the suction and uhich the ejection.

To ensure a continuity in the pumping action and accelerate commu¬ tation between the two units 2, 3 , the present invention provides for the auxiliary circuit with pump 7 and accumulator 8. The accumulator 8 is set at a minimum predetermined pressure - for example of 70 bar - guaranteed. required, by the auxiliary pump J . This arrangement allows to ensure preserving the wanted oil pressure both in the secondary circuit and in the main circuit also during the commutation step, the length of which is thus reduced to less than the 0.2 seconds of known technique.

A first improvement is thereby obtained for what concerns a uniform flow rate in concrete feeding.

A further improvement for what concerns a uniform flow rate in con¬ crete feeding is obtained thanks to the transducers 14) 15_> v>hich - as said - detect the instant feeding pressure of the cylinder-piston units 2 and 3 respectively. When the piston 22 or 23 compresses the concrete mass, the oil pressure in the respective feeding circuit rises, due to the resistance opposed by the highly thick and viscous concrete; vice- versa when said piston, at the start of its stroke, expels the air intro¬ duced into the cylinder-piston units in the suction step, the resistance is neglectable and the oil pressure remains low. Hence, in this step, since the corresponding transducer 14 or 15 detects no pressure increase, it sends a signal in this sense to the central processor 11. This latter then causes the pump 1 to work at top speed, so as to expel the air as quickly as possible. When the piston 22 or 23 starts to compress the concrete mass, the oil pressure rises, the transducer 14 or 15 detects said increase and sends a signal to the processor 11 which causes the pump 1 to work at a steady speed, so as to feed the concrete at the required uniform flow rate.

According to the fundamental characteristic mentioned heretofore, as concrete is being ejected, the oil expelled from the respective unit 2 or 3 is fed, through the system of four valves 20, to the supplementary circuit driving the hydraulic motor 4- As stated, said valves act so as to "rectify" the oil flow delivered alternatively from the unit 2 or 3. so that the direction of said flow remains unvaried and the hydraulic motor 4 is fed in a uniform way. As illustrated on the drawing, supposing the unit 3 to be in a delivery phase, the oil expelled from its cylinder passes through the valve 20a and flows into the length 4a to be delivered to the motor 4; subsequently, the oil flows back into the length 4b to be recovered and, passing through the valve 20b, it flous into the cylinder of the unit 2 being in a recovery phase. When commutation takes place and the cylinder of the unit 2 is in a delivery phase, the oil passes through the valve 20c, it again flows into the length 4a and then flows back into the length 4b and, passing through the valve 20d, it reaches the cylinder of the unit 3 which is now in a recovery phase.

Seen that, in this way, the flow rate of the oil fed to the motor 4 is directly tied to the speed of the forward stroke of the units 2, 3- and thus to the flow rate of concrete delivery, it ensues that the flou rate of the additive fed by the pump 5, operated by the motor A, is always strictly tied to the concrete flow rate.

A more precise adjustment can however be obtained by presetting, in the processor 11, the desired percentage of concrete additive, and by using the signal sent by the concrete flow rate measurer 16. On the basis of the preset percentage value and of the instant flow rate measured in 16, the processor 11 indicates to the pov,ered speed converter 13• time after time, the ratio between the speed of the motor 4 and the speed of the pump 5, so as to obtain the additive flow rate required to reach the preset percentage. One thereby obtains an even percentage of additive in the concrete, allowing to feed a concrete of uniform quality.

As can be easily understood from the previous description, the con¬ crete feeding apparatus according to the present invention allows, on one hand, to establish a uniform flow rate in concrete feeding, reducing to a minimum all the dishomogeneities present in the known feeding systems. and it enables, on the other hand, to exactly proportion the amount of additives according to the concrete flow rate, thereby notably reducing costs.

It is evident that the invention is not limited to the embodiment described heretofore, which merely forms a non-limiting example of its scope, but that various modifications can be introduced, all within reach of a person skilled in the art, without thereby departing from the scope of the present invention.

In particular, it is possible to associate to the processor 11 any printing unit, allowing to print on a special card the characteristics of the concrete being fed, in order to supply a quality certificate thereof.

Claims

1 ) Apparatus to feed a constant flow of concrete - of the type comprising two hydraulic cylinder-piston units (2, 3) acting alternately so as to operate two corresponding pistons (22, 23) feeding the concrete to a concrete delivery pipe (17) through a cornmutating valve (6), and a proportioning device to feed the additives having to be added to the concrete - characterized in that the device proportioning the additives consists of a pump (5). and in that said pump is operated by a hydraulic motor (4) driven by a hydraulic circuit derived from the main hydraulic circuit operating said cylinder-piston units (2, 3)-

2) Apparatus as in claim l), wherein said derived hydraulic circuit consists of a circuit which connects said hydraulic motor (4) to the exhaust chambers of the cylinders of said cylinder-piston units (2, 3) through a valve system apt to "rectify" the hydraulic flow.

3) Apparatus as in claim 2), wherein said "rectifying" valve system comprises four check valves (20) connected as a two-way bridge.

4) Apparatus as in claim 2), wherein said "rectifying" valve system consists of a four-way valve.

5) Apparatus as in claim l), wherein on the motion transmission, between said hydraulic motor (4) and said proportioning pump (5), there is interposed a speed converter (13) operated by means to control the proportion of additives.

6) Apparatus as in claim 5), wherein said means to control the proportion of additives comprise, on one hand, a measurer (l6) to measure the concrete instant flow rate in the concrete delivery pipe (17) and. on the other hand, a processor (11) which controls said speed converter (13) according to the signals sent by said measurer (l6).

7) Apparatus as in claim 5), wherein said speed converter (13), interposed between the motor (4) and the pump (5), is a mechanical disk- type converter.

8) Apparatus as in claim 5) or 7), wherein said speed converter (13) has a reduction ratio from 1 to 5- 9) Apparatus as in claim l), wherein the main hydraulic circuit feeding oil to each of the cylinder-piston units (2, 3) comprises tvio pressure transducers (14. 15) 1 the signals of which are sent to the processor (11 ) in order to control the motor which operates the pump ( 1 ) feeding oil to said main hydraulic circuit.

10) Apparatus as in any one of the previous claims, therein the cornmutating valve (6) between the tvvo concrete delivery pistons (22, 23) is controlled by said processor (ll) on the basis of the signals received from end-of-stroke sensors (18, 19) of said cylinder-piston units (2, 3).

11) Apparatus as in any one of the previous claims, comprising moreover means to accelerate the movements of the cornmutating valve (6).

12) Apparatus as in claim 11). wherein said means to accelerate the movements of the cornmutating valve (6) comprise an auxiliary circuit feeding oil to the main hydraulic circuit, said auxiliary circuit inclu¬ ding an auxiliary pump (7) and a pressure accumulator (8).

13) Apparatus as in claim 12), wherein said pressure accumulator (8) is kept at a minimum pressure of 70 bar.

14) Apparatus as in any one of the previous claims, wherein a printing unit is associated to said processor (11) .