The Separation Phenomenon of Concrete in Textile Machines and the Development of Anti-Separation Devices

Concrete segregation in fabric machine and the development of anti-segregation devices

With the development of large-scale high-rise reinforced concrete structures, the vertical and horizontal transportation of concrete, as the main building material, has become a major issue in construction. In the past, concrete was primarily transported one truck at a time using tower cranes. This method was inefficient and resulted in poor casting quality. In recent years, continuous concrete pumping technology has effectively addressed the issue of vertical transportation, thanks to its short construction period, high quality, and low labor intensity, making it increasingly popular. The concrete placer, a new construction machine that pairs with concrete pumps, acts like a mechanical arm, quickly and accurately delivering concrete to any casting location on the work surface for continuous pouring, effectively solving the problem of horizontal concrete transportation. The concrete placer complements the vertical pumping technology, fully leveraging the strengths of both, achieving continuous concrete transportation, significantly reducing labor intensity, and improving construction progress and quality.

　1 The phenomenon of segregation in concrete used for fabricating machines and its causes

As a new type of construction machinery, the segregation phenomenon of concrete placer has long been a headache for construction units and research institutions, becoming an important factor制约ing the development of placers. The segregation of concrete in placers mainly manifests in several aspects:1)Segregation of concrete aggregates and mortar.(2)Concrete bleeding.

A concrete placer, as a large-scale manipulator, operates by extending its boom upwards towards the work surface and then pouring concrete downwards towards the pouring point. This method of operation dictates that the placer's conveying pipeline must be divided into an ascending section and a descending section.

The general working condition of a fabricating machine is typically with the large arm upward and the medium to small arms downward. At the ascending section of the pipeline.(Tower and Boom Pipeline)The concrete within the pipeline is propelled forward under the pressure of the concrete pump. The concrete fills the ascending pipeline, maintaining a stable flow rate and preventing segregation. As for the descending section of the pipeline...(Medium and lower arm)Due to the effect of gravity acceleration, the flow rate of concrete increases. As the flow rate of concrete in the descending section remains unchanged, the accelerated concrete cannot fill the conveying pipeline. Instead of being steadily "pushed" in the descending pipeline, concrete rapidly "falls." During the "falling" process, concrete continuously collides with the pipeline walls, causing aggregates to separate from the slurry, leading to the first form of segregation.

During downtime while waiting for materials, concrete in the descending pipeline of the fabricating machine leaks due to gravity, eventually settling at the top of the ascending pipeline. This is where the transition occurs between the ascending and descending sections of the machine's arm, marking the boundary within the pipeline where concrete is present. If the downtime is prolonged, water will separate from the concrete that has settled at this interface, resulting in the second type of segregation, known as bleeding.

2 The Dangers of Concrete Segregation

Aggregate segregation significantly impacts concrete mixers, being a major cause of blockages and tube issues. It severely affects the normal operation of mixers, the lifespan of tubes, and the quality of concrete pouring.

　1In the descending pipeline of the concrete pump, the segregated material in the concrete rapidly collides with the pipe wall, accelerating the wear of the conveying tube. Particularly at the bends in the pipeline, where the direction of speed changes, the impact on some curved pipes is especially great, thus leading to severe wear on these bends. This phenomenon is especially severe at the end of the pipeline, as the concrete is accelerated to its maximum value here. Test results and practical application situations indicate that the curved pipes at the end of the concrete pump's arm...(Utilizing standard materials)The transmission lifespan1000m3Left, sometimes even just a few hundredm3The输送arm of the fabric machine has a straight life span of approximately8000m2The conveying lifespan of the material handling pipeline in a fabricating machine is related to the machine's working posture. The greater the drop in the boom pipeline, the more intense the acceleration impact on the concrete, leading to a shorter lifespan for the pipeline. Frequent replacements of the pipeline at construction sites after wear-through not only increases construction costs but also hampers project progress.

　2During downtime waiting for materials, the concrete separates at the top of the arm pipeline, with the water and fine sand draining down the pipeline. If the downtime is prolonged, the pipeline at the top will become blocked due to the remaining coarse aggregate. Once a pipeline blockage occurs, it is quite labor-intensive and time-consuming to remove, and it also results in a significant waste of concrete.

3Concrete segregation has severely reduced7The quality of Kun concrete.

　　3 Development of anti-segregation device for fabric machines

　　3．1 Static堵料issue - The Key to Solving Concrete Segregation in Material Batching Machines

　 The analysis of the reasons for concrete segregation in fabric machine has been previously discussed.3. Whether it is the first type of separation or the second type of separation, it is due to the declineFThe key to solving the issue lies in addressing the gravitational effects encountered on the road.1How to eliminate the effect of gravity on the concrete in the descending pipeline.

Consider installing an adjustable anti-segregation device at the discharge outlet of the batching machine. This device requires a certain amount of thrust to open and automatically closes when the thrust is insufficient or disappears. During the operation of the batching machine, concrete is pushed out through the anti-segregation device under the action of the pumping pressure. When the batching machine stops, the anti-segregation device automatically closes, blocking the concrete in the descending pipeline from flowing out, which is known as the static blockage effect.

The key to this anti-segregation technology lies in the appropriate resistance at the discharge outlet, which balances the gravity within the descending pipeline, achieving so-called static blockage. During concrete pumping, the resistance balanced with gravity prevents acceleration of the concrete during its descent. Whether in the ascending or descending phase of the pipeline, the concrete fills the entire pipeline and is evenly distributed."Advancing at a steady pace, the 'push' prevents segregation of aggregates and mortar due to accelerated descent. When the hopper is idle, static blockage is achieved due to a resistance balanced with gravity, filling the entire conveyance pipeline with concrete. Consequently, only the concrete at the exit section may segregate moisture, and any minor blockage at the exit can be easily resolved.

The key to solving the concrete segregation issue in the concrete batching machine lies in applying an appropriate resistance at the outlet of the batching arm that can achieve static堵料 blocking.

3．2 Foreign anti-segregation devices and existing issues

GermanyPMThe concrete pump is equipped with a nylon anti-segregation device. This anti-segregation device is installed at the end of the pump's delivery arm hose, featuring a tapered tip that gradually narrows and is longitudinally scored with several slits.PMThe anti-segregation device exerts resistance on the concrete flow due to its gradually constricting conical structure. When the Pump Truck II is in operation, the conical structure expands due to the pressure exerted by the concrete pumping, allowing concrete to flow out through the open cone section. Upon the shutdown of the pump truck, the nylon cone section automatically retracts and closes due to its inherent elasticity, thus blocking the concrete within the descending pipeline from escaping.

3．4 Leaf Spring Double Door Anti-Disassembly Device

The large落差anti-segregation device suitable for fabric machines should have:1)Export resistance can be adjusted according to different pipeline gradients to balance the concrete gravity in the descending pipeline.2)Excellent wear resistance.3)Even after wear, the size of the export resistance will not change.

Based on the above three points, the so-called has been developed."Anti-segregation device with a full steel "sheet spring double door" structure. The device features two discharge doors, which are controlled by multiple stacked sheet springs for opening. The force required to open the discharge doors is adjusted by altering the number of stacked sheet springs, enabling different pipeline落差 static blockages. Since the sheet springs are not affected by concrete erosion, even if the discharge doors are worn, the device's performance is not compromised. To enhance the longevity of the device, wear-resistant surfacing is applied to its inner wall. During actual testing, this anti-segregation device fully met our expected requirements, with pipeline落差 reaching...16mAt the time, a full static blocking material system was fully realized. Whether static or dynamic, the entire pipeline was filled with concrete, achieving the anti-segregation goal of large gradients. To verify the role of the "sheet spring double door" anti-segregation device in reducing the wear of concrete pump pipelines, wear tests were conducted under the same concrete mix, working conditions, and test conditions on concrete pumps equipped with and without the anti-segregation device.LLTrial.

Test results show that the installation of anti-segregation devices on the fabricator significantly reduces the impact of concrete on the pipeline, resulting in a substantial increase in the lifespan of the arm bend pipes and straight pipes, with the lifespan of the arm-end bend pipes improving notably.8No Chinese content provided.

In the installation ofDuring the testing process of the "double door leaf spring" anti-segregation device on the cloth machine, the machine had to be stopped.40Minutes, observe for any pipeline blockage due to segregation effluent. Results indicate that although the anti-segregation device continuously produced clear water, no pipeline blockage occurred upon restarting the machine.