At present, concrete pump has been widely used in concrete construction. The concrete pump is mainly used for the double-cylinder driven concrete pump, which is commonly found in the moment of pumping reversal. This cut-off phenomenon has two major hazards, one is easily lead to concrete segregation, some concrete dehydration into a hard and hard concrete caused by blocking, especially in pumping concrete with low slump even more so; the second is to change the moment of the pipeline And distribution valve in the concrete pressure release, the concrete pump hydraulic system impact, resulting in damage to some parts and increase energy loss. Cut off the vertical upward especially 50m above the height of the pump when the hazard is obvious.
1, the reason analysis
Figure 1 is an open hydraulic system of two-cylinder drive concrete pump hydraulic system diagram. The pump is a full hydraulic control concrete pump, constant power main pump through the hydraulic valve 8-1, 8-2 to the main cylinder 10-1, 10-2 and distribution valve cylinder 9 oil. The main cylinder cartridge valve and the distribution valve cylinder were issued a signal to control the hydraulic valve commutation, so that the main cylinder and the distribution valve cylinder action sequence coordinated with each other to achieve concrete pumping cycle, in which the main cylinder 10 alternately suction suction - concrete row To achieve continuous pumping of concrete. During each commutation process, the flow of concrete often shows obvious phenomenon of flow-break-flow, which is commonly referred to as the phenomenon of breaking flow.
figure 1
Figure 1 concrete pump hydraulic system diagram
1 motor 2 oil tank 3 main oil pump 4 oil return filter 5 air cleaner 6 pressure relief valve 7 pressure gauge 8 hydraulic valve 9 distribution valve cylinder 10-main cylinder
Concrete cut-off phenomenon for three reasons: â‘ When the main fuel tank to run near the end of the stroke when the commutation signal is issued to the commutation cylinder commutation, and then the main system of oil for commutation, the main cylinder 10 to the opposite direction, this process at least 0.2 s; â‘¡ concrete is inhaled concrete cylinder suction efficiency is usually only 85% to 95%, inevitably inhaled a short period of air, which will be a short period of empty travel; â‘¢ commutation concrete cylinder suction in the outward pressure Rise, there is a certain degree of compressibility, this is also a short period of empty travel. Due to the commutation and two empty travel time, so there was a problem during the concrete pumping.
2, solution
The solution to the problem of interrupting flow in the pumping process is to minimize commutation time and speed up the main cylinder piston at the start of the commutation and to achieve continuous pumping of concrete before the concrete pressure in the piping and distribution valves is fully released, Reduce concrete segregation due to the flow and the diverting process of pipe and distribution valve in the concrete pressure release of the anti-impact.
For most pumping systems, the problem of shut-off can be solved by using electro-proportional controlled constant power piston pumps. As the electric proportional control + constant power control is the priority of the electronic control variable constant power control, below the power hyperbolic displacement by the control of the current adjustment, after the commutation process and reversing cylinder piston push the pipe before the concrete movement , The system pressure is usually lower than the pump pressure, you can increase the displacement of the main pump valve to achieve rapid commutation, reducing the commutation to the beginning to promote concrete time to achieve continuous flow of concrete from the apparent.
Usually in the tank between the cylinder and concrete tanks set up two proximity switches, according to the main oil pump displacement and the main cylinder bore and stroke set the starting and ending point to take the location of the letter of mouth, the key to this control is how to determine the electrical ratio In the control phase, the opening and closing positions of the fobs are taken. The distance between the proximity switches is usually 5% -10% of the total travel. The proximity switch receives a start signal and transmits it to the programmable logic controller or relay. The controller or relay controls the current required to reach the maximum displacement of the pump (typically a few hundred mA) to the main pump proportional solenoid, The volume soared, quickly commutated and began to push the distribution valve and pipe in the concrete. Adjust the position close to the switch so that the cylinder starts to push the distribution valve and concrete in the pipeline to stop the electric control, continue to achieve constant power pump control. The actual use of fiduciary mouth start and end position can be adjusted according to the actual situation of concrete pump to ensure the maximum increase in the continuity of pumping concrete flow.
In foreign countries, especially in Europe and the United States due to the use of more pump, displacement, concrete aggregate and grading more stringent control, building size and height are small, cut-off problems and hazards are not obvious; the domestic widespread use of pump , Displacement of more than 80m3 / h below, building size and height are larger, the phenomenon of cut-off more obvious. Through the selection and setting of the main pump control mode, it can effectively solve the problem of interrupted flow of concrete delivery, reduce the commutation impact and greatly improve the pumping performance of concrete pump.
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