Harm of concrete pumping cutoff
1, cause analysis
the pump is a fully hydraulic controlled concrete pump, and the constant power main oil pump supplies oil to the main cylinder and distribution valve cylinder 9 through the hydraulic valve. The cartridge valve of the main oil cylinder and the oil cylinder of the distribution valve send signals to control the reversing of the hydraulic valve respectively, so that the action sequence of the main oil cylinder and the oil cylinder of the distribution valve can be coordinated with each other, and the concrete pumping cycle can be realized. The double cylinders of the main oil cylinder 10 alternately suck and discharge concrete to realize the continuous pumping of concrete. During each reversing process, the concrete flow usually has an obvious flow break flow phenomenon, which is commonly referred to as the flow break phenomenon
1- motor; 2-oil tank; 3-main oil pump; 4-return oil filter; 5-air filter; 6-overflow valve; 7-pressure gauge; 8-hydraulic valve; 9-distribution valve oil cylinder; 10 - there are three reasons for the concrete cut-off phenomenon of the main oil cylinder: ① when the main oil cylinder runs close to the end of the stroke, it sends a reversing signal to the reversing oil cylinder to reverse, and then the oil circuit of the main system reverses, and the main oil cylinder 10 moves in the opposite direction, which takes at least 0.2S; ② When concrete is sucked into the concrete cylinder, the suction efficiency is usually only 85% - 95%. It is inevitable to inhale a small section of air, which will be a small section of empty travel; ③ When reversing, the pressure of the concrete sucked into the concrete cylinder increases when it is output, which has a certain compressibility, which is also a short empty stroke. Due to the reversing and two-stage empty travel time, the flow cut-off problem occurred in the process of concrete pumping
the solution to the phenomenon of interrupted flow in the pumping process is to shorten the reversing time as much as possible and speed up the operation speed of the main cylinder piston at the beginning of reversing. Before the concrete pressure in the pipeline and distribution valve is completely released, the positive and negative electrodes of the electrolytic capacitor should be short circuited and pumped continuously, so as to minimize the counter impact of the concrete due to the disconnection and segregation of the concrete and the release of the concrete pressure in the pipeline and distribution valve during the reversing process
for most pumping systems, the new material testing machine developed to meet people's safety needs can be solved by using electric proportional control constant power plunger pump. Because the electric proportional control + constant power control is that the electric control variable takes priority over the constant power, this all aluminum BIW first attempts to adopt advanced process control such as CMT cold metal transition welding, and the displacement is adjusted by the control current when it is lower than the power hyperbola, Zheng Hong, director of the Institute of materials and lightweight of China 1 automobile new energy development institute, pointed out that: "At present, before the Chinese automobile industry becomes an important pneumatic concrete movement in the global automobile industry, the system pressure is usually lower than the pumping pressure. You can increase the displacement of the main oil pump to realize the rapid reversing of the distribution valve, reduce the time from reversing to starting to push the concrete, and realize the continuous flow of concrete from the appearance.
usually, two proximity switches can be set in the water tank between the oil cylinder and the concrete cylinder, which can be set according to the displacement of the main oil pump and the diameter and stroke of the main oil cylinder The key to this control is how to determine the start and stop positions of the signal intake in the electric proportional control stage. The distance between the proximity switches is usually 5% - 10% of the total travel. After receiving the starting signal, the proximity switch is transmitted to the programmable controller or holding relay, and the controller or relay controls the current required to make the oil pump reach the maximum displacement (usually hundreds of MA) to the proportional electromagnet of the main oil pump, so as to realize the sudden increase of the displacement of the oil pump, rapid reversing and start to push the concrete in the distribution valve and pipeline. Adjust the position of the cut-off proximity switch to stop the electric control when the oil cylinder starts to push the concrete in the distribution valve and pipeline, and continue to realize the constant power control of the oil pump. In actual use, the start and cut-off positions of the signal intake can be adjusted according to the actual situation of the concrete pump, so as to ensure the continuity of the concrete flow during pumping to the greatest extent
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