Tubular pile tube joint forming and rolling process

Abstract

The invention discloses a pipe pile pipe joint forming and rolling process, and belongs to the technical field of precast concrete component production. Aiming at the defects of serious layering and segregation of concrete, non-uniform compactness, low production efficiency and the like in traditional tubular pile centrifugal forming, the invention provides an integrated innovative process which takes hard concrete as a raw material basis, takes dynamic centrifugation and material distribution as a basis and takes stepped centrifugation and synchronous excitation rolling compounding as a core. According to the process, a traditional mode of firstly performing static material distribution and then performing centrifugation is abandoned, and belt conveyor continuous material distribution, mechanical excitation and external rolling limiting material supplementation are synchronously performed in the low-speed to medium-speed centrifugation stage. Starting from material adaptability and dynamics process collaboration, the process effectively eliminates the initial defects in the concrete, greatly reduces the layering phenomenon, remarkably improves the overall compactness, mechanical property uniformity, impermeability and durability of the pipe joint of the pipe pile, and is high in material distribution efficiency and high in process controllability.

Description

Technical Field

[0001] This invention relates to the manufacturing technology of prefabricated building components, and more specifically, to a centrifugal forming process for pipe pile sections. Background Technology

[0002] Prestressed high-strength concrete pipe piles are a widely used type of precast pile in foundation engineering. Their quality depends primarily on the density and uniformity of the concrete in the pipe section, its strength, and the bond performance between the concrete and the prestressed steel reinforcement. Currently, the mainstream pipe pile production process in the industry can be summarized as a static placement-step centrifugal process: First, plastic concrete with a certain degree of fluidity (slump typically greater than 50mm) is poured through a hopper into a slowly rotating or stationary steel mold, completing the initial placement; subsequently, the centrifuge is accelerated in stages (low speed, medium speed, high speed), using the gradually increasing centrifugal force to distribute and compact the concrete on the mold wall, while simultaneously removing excess water.

[0003] However, this traditional process has several inherent drawbacks, which have long hindered the further improvement of the quality of pipe piles: During the high-speed centrifugation stage, the coarse aggregate, fine aggregate, cement paste, and water in the plastic concrete undergo significant radial separation due to differences in specific gravity under the strong centrifugal force. Coarse aggregate accumulates on the outer side of the pipe wall, while cement paste and fine particles aggregate on the inner side, forming a layered structure with uneven chemical and physical properties. This results in increased brittleness on the outer side of the pipe pile, insufficient strength and high permeability on the inner side, and overall discrete mechanical properties, leading to poor impermeability and durability.

[0004] The hopper-based material distribution method involves accumulating concrete, resulting in uneven distribution of concrete in areas obscured by the reinforcing steel frame and on curved surfaces of the formwork. This can easily lead to initial voids and uneven thickness. Subsequent centrifugal processes rely primarily on material flow for filling, offering limited effectiveness in dry, dense areas or shaded zones behind the reinforcing steel. Initial defects are often preserved or only partially improved, becoming weak points in the structure.

[0005] Traditional processes rely entirely on centrifugal force to achieve compaction, which is a unidirectional volumetric force. For plastic concrete, centrifugal force mainly promotes the separation of the liquid and solid phases, but it is not very efficient at rearranging and interlocking solid particles and removing air, making it difficult to achieve optimal compaction. To achieve standard compaction, a long medium-to-high speed centrifugation time is often required, resulting in high energy consumption.

[0006] The main reason for using plastic concrete is to meet the fluidity requirements of hopper feeding. However, its high fluidity and easy segregation characteristics are contrary to the goal of centrifugal process to pursue uniformity and stability, thus forming an inherent contradiction in the process.

[0007] The material distribution in the hopper is discontinuous, involves many operational steps, makes it difficult to accurately control the material layer thickness, restricts production efficiency, and the stability of quality largely depends on the operator's experience.

[0008] While existing technologies have attempted to improve concrete performance by adding admixtures or by using simple vibrations during the placement stage, these are mostly repairs of a single aspect and fail to achieve synergistic innovation at the systemic level of materials, placement dynamics, and compaction mechanics. Therefore, they cannot fundamentally solve the core problems of segregation and uneven compaction. For example, simply increasing the hardness of concrete may lead to difficulties in placement; simply increasing placement vibration may exacerbate segregation in plastic concrete.

[0009] Therefore, it is necessary to develop a new molding process that can systematically optimize the internal structure of concrete, improve the overall performance of pipe piles, and is suitable for efficient and automated production. Summary of the Invention

[0010] The purpose of this invention is to provide a rolling process for forming pipe pile sections, overcoming the shortcomings of existing technologies. This process aims to achieve the following objectives: To the greatest extent possible, it can reduce or eliminate the segregation of concrete pipe walls during the forming process, obtain a concrete structure with uniform micro and macro properties, significantly improve the final density and microstructural integrity of concrete, thereby comprehensively enhancing the mechanical strength, impermeability and long-term durability of pipe piles; and achieve continuous, uniform and efficient material placement process, improving the automation level and process controllability of the production line.

[0011] Technical solution To achieve the above objectives, this invention proposes an integrated and innovative roller pressing process for forming pipe pile sections. Its core design concept is to transform passive centrifugation after static filling into dynamic construction and active compaction occurring simultaneously. Through the synergy of materials, methods, and processes, multi-field coupled composite forces are applied during the optimal window period of concrete's plastic state, guiding the formation of a uniform and dense initial skeleton. The specific technical solution is as follows: A rolling process for forming pipe pile sections includes the following steps: S1. Preparation of dry-hard concrete Abandoning traditional plastic concrete, a dry-hard concrete with extremely low slump is specially designed and formulated. This concrete has a low water-cement ratio, strong cohesion, and almost no fluidity. Its material properties bring fundamental advantages: First, it has strong resistance to segregation during conveying and placement, laying the foundation for subsequent use of non-traditional placement methods; second, under stress, it mainly exhibits friction and rearrangement between solid particles rather than liquid flow, which allows it to effectively respond to and utilize mechanical compaction methods such as vibration and roller pressing.

[0012] S2. Dynamic Fabric and Initial Attachment (Rotation Speed: 83 rpm) The assembled steel mold with its reinforcing steel frame and end plates is placed on a centrifugal device and rotated at a relatively low initial speed (approximately 83 rpm). At this speed, the generated centrifugal force is weak, its main function being to ensure that the poured concrete adheres to the mold wall and does not fall off. The key innovation lies in the material distribution method: a belt conveyor is used to precisely and evenly distribute dry, stiff concrete onto the inner wall of the rotating steel mold in a continuous flow. This rotating-while-distributing method mimics a spin coating process, ensuring that the concrete achieves a relatively uniform initial thin layer both circumferentially and axially from the moment it contacts the mold wall. This completely changes the random accumulation state caused by hopper distribution, creating near-ideal initial conditions for subsequent uniform compaction. This process lasts approximately 120 seconds, until the material layer completely covers the internal pre-drilled holes and other protrusions.

[0013] S3. Synchronous vibration, rolling and precise feeding (speed: 103 rpm) The rotation speed of the steel mold is increased to the second medium speed (approximately 103 rpm). At this point, the centrifugal force increases, providing the main driving force for the rearrangement of concrete particles. The core innovation of this step is the introduction of a time-synchronized, spatially coupled composite dense field: Vibration: The vibration device is activated synchronously to apply mechanical vibration to the rotating steel mold at a medium frequency of 60-75Hz. The vibration is transmitted into the concrete, producing a liquefaction effect, which significantly reduces the frictional resistance and interlocking force between particles, allowing the particles to move more easily to a more stable and compact position under centrifugal force. Vibration also effectively promotes the upward (towards the inner wall) migration and aggregation of microbubbles.

[0014] Continuous dynamic material distribution: The belt conveyor continues to feed material, so that the concrete layer increases in thickness evenly according to the design thickness.

[0015] Mechanical Roller Pressing and Precise Material Feeding: When the material layer approaches the designed thickness, an external mechanical roller device is introduced. The roller presses down, contacting the outer wall of the steel mold, applying a continuous and controllable radial static pressure to the rotating mold. This pressure, combined with internal centrifugal force and vibration, forms a three-dimensional composite dense force field of centrifugal force, vibration, and roller pressing. Under this force field, the operator can perform targeted material feeding: that is, while the roller is pressing, targeted material is added to local depressions caused by vibration or initial unevenness, and the roller then compacts and levels them. This process achieves dynamic, online, and precise control of the pipe wall thickness, strictly limiting the final molding thickness to 6-10mm. This stage is the most critical period for forming a uniform and dense skeleton, taking approximately 270 seconds in total.

[0016] S4. The composite force field remains dense. Stop all feeding. However, maintain the second medium speed, vibration, and roller pressure unchanged for approximately 30 seconds. This is equivalent to pre-forming finishing of the formed material layer, ensuring that under the combined force field, the particles achieve the optimal configuration in the current energy state, internal pores are further compressed, and accumulated air bubbles are driven to the surface. Subsequently, turn off the vibrator, but maintain the speed and roller pressure for approximately 20 seconds. This helps eliminate microstructural rebound that may be caused by vibration cessation, allowing the particle skeleton to achieve a new equilibrium under continuous centrifugal force and hydrostatic pressure, thus achieving structural stability.

[0017] S5. Stepped high-speed centrifugal dehydration (speed: 312 rpm - 378 rpm) After sufficient structural reorganization and initial compaction in the aforementioned low-to-medium speed stage, the concrete has formed a skeleton with high strength and good stability, with most of the free water existing between the particle pores. At this point, a two-step high-speed centrifugation is performed: first, the speed is increased to a third rotation speed (approximately 312 rpm) for about 180 seconds, using strong centrifugal force to expel most of the free water and air bubble film; then, the speed is increased to a higher fourth rotation speed (approximately 378 rpm) for about 120 seconds for final and powerful dehydration, ensuring that the concrete reaches the design requirements of low moisture content and high density. Since a stable structure resistant to segregation has been established in the early stages, the main task of high-speed centrifugation in this stage is dehydration, without causing severe secondary particle sorting, thus protecting the established homogeneity.

[0018] S6. Smooth deceleration After dehydration, to prevent the formed dense structure from developing internal stress or microcracks due to sudden changes in inertial forces, the deceleration process must be strictly controlled. The rotation speed should be slowly and linearly reduced from the highest speed to zero over a period of no less than 60 seconds, allowing the concrete structure to smoothly transition to a static state in a gradually decreasing centrifugal force field.

[0019] Compared with the prior art, the pipe pile section forming roll forming process provided by the present invention has the following significant improvements and positive effects: 1. Improved the uniformity of concrete structure and basically eliminated segregation: The use of dry-hard concrete from the source, whose inherent anti-segregation characteristics laid the foundation for the entire process; dynamic material placement ensured the macroscopic uniformity of the initial distribution of concrete and eliminated initial defects.

[0020] 2. In the low-to-medium speed stage (steps S3 and S4) when concrete is most plastic and easily modified, the internal structure of the concrete is reshaped through the synergistic effect of the centrifugal-vibration-roller pressure composite force field. Vibration reduces compaction resistance, roller pressure provides additional static compaction, and centrifugal force guides directional alignment. The coupling of these three forces coarse and fine particles to fully interact and interlock in three-dimensional space, forming a uniform and dense skeleton, rather than stratifying according to specific gravity under a single centrifugal force. Experimental tests show that the concrete cross-section hardness distribution curve of the pipe piles produced using this process is smooth, the ratio of inner and outer layer strength is close to 1, and the uniformity indicators such as carbonation depth and chloride ion permeability coefficient are far superior to traditional products, significantly improving the ultimate performance and durability of the concrete. 3. The compaction efficiency under a composite force field far exceeds that of centrifugal force alone, enabling concrete to achieve extremely high density at relatively low rotational speeds. Porosity is significantly reduced, especially the proportion of harmful pores. This uniform and dense structure directly translates into excellent physical and mechanical properties: compressive strength and flexural strength are increased by 10%-25%; the impermeability grade can easily reach P12 and above; key durability indicators such as resistance to freeze-thaw cycles, sulfate attack, and chloride ion penetration are significantly enhanced, greatly extending the service life of pipe piles in harsh environments.

[0021] 4. The parameters at each stage of the process can be quantified and precisely executed, resulting in good product quality consistency, reducing reliance on human experience, and achieving standardized and replicable production. Attached Figure Description

[0022] Figure 1 A schematic diagram of the process flow for forming and rolling pipe sections of a pipe pile provided by the present invention; Figure 2 A front view of a roller pressing device for a pipe pile section forming roller pressing process provided by the present invention; Figure 3 Test diagram of a roller pressing device for a pipe pile section forming roller pressing process provided by the present invention. Detailed Implementation

[0023] S1. Material preparation and connection The prepared dry-hardened concrete is quickly unloaded from a mixer truck or a dedicated conveyor system into the storage hopper of a belt conveyor connected above the centrifuge station. The storage hopper is designed to prevent concrete segregation, and the start-up and conveying speed of the belt conveyor below are controlled by a frequency converter to ensure seamless connection with step S2.

[0024] S2. Dynamic fabric and initial attachment (first rotational speed stage: 83 ± 5 rpm) Start-up: Start the centrifuge, drive the steel mold to accelerate smoothly to 83 rpm and run stably. Almost simultaneously, start the belt conveyor.

[0025] Concrete placement operation: The operator precisely adjusts the conveyor belt speed (e.g., 0.8-1.2 m / s) according to the rotation speed and diameter of the steel mold, ensuring that the concrete falls precisely into the rotating steel mold in a continuous, stable, and uniformly thick ribbon-like stream. The concrete flow should slightly lead the bottom centerline of the steel mold, utilizing the tangential force of the rotating mold to quickly spread the concrete onto the inner wall. Process monitoring: Operators monitor the entire process through an observation window. Under weak centrifugal force (approximately 5-8g) and rotation, the dry-hard concrete adheres tightly to the formwork wall, forming a uniform initial lining. This stage lasts approximately 120 seconds, and the goal is not only to cover the formwork wall but also to ensure that the concrete completely encapsulates the prestressed steel reinforcement upsetting heads and end plate connection areas, eliminating any potential defects caused by inadequate encapsulation.

[0026] S3. Synchronous excitation, rolling and precise feeding (second speed stage: 103 ± 5 rpm) Speed ​​and vibration start-up: Gradually increase the centrifuge speed to 103 rpm within 15-20 seconds (increase the centrifugal force to approximately 12-15g). After the speed stabilizes, immediately start the vibrator and set the frequency to 70Hz (this can be finely adjusted according to the concrete reaction) to generate stable axial and radial composite vibrations in the steel mold.

[0027] Dynamic thickening and initial compaction: Under vibration, the concrete continues to be fed evenly via a belt conveyor. Vibration significantly reduces the internal friction between concrete particles, and under the enhanced centrifugal force, the newly fed concrete can fill the existing material layer more smoothly, thus initially increasing the overall density of the material layer.

[0028] Roller pressing intervention and closed-loop control: When the material layer thickness approaches the preset reference surface of the inner ring of the steel mold end cap (which can be determined with the assistance of laser ranging or industrial camera vision system), a key operation is executed: a. Pressing down the pressure roller: Control the pressure roller device to press down smoothly, so that the surface of the pressure roller forms a preset contact pressure (e.g., 20kN) with the outer wall of the steel mold. The rotation of the pressure roller is driven by the friction of the steel mold.

[0029] b. Precise Material Refilling and Compaction: A micro-refilling port with precisely controllable opening and position is installed in front of the contact point of the pressure roller (along the rotation direction of the steel mold). The operator or automatic control system instructs the refilling port to perform point-spray micro-refilling of locally low-lying areas based on the flatness (high / low signal) of the exposed material surface after the pressure roller compaction. c. Closed-Loop Feedback: The replenished concrete is immediately compacted and leveled by the rotating pressure roller. This closed-loop process of material surface → replenishment point / amount → replenishment and roller compaction repeats along the entire length of the steel mold. The pressure roller not only compacts the concrete but also acts as a thickness scraper. When the material layer along the entire length of the mold tube reaches a stable and flat state after roller pressing, and multiple sampling measurements show that the excess thickness of the concrete layer exceeding the theoretical inner diameter is evenly distributed within the range of 6-10mm (the target control in this example is 8±2mm), this stage is considered complete. This stage begins when the rotation speed is increased to 103 rpm, and the total time is strictly controlled within 270±10 seconds.

[0030] S4. Continuous Compaction in the Composite Force Field (Finishing and Fine Compaction: Stop all external material supply. Continue to rotate the steel mold at 103 rpm, operate the vibrator at 70 Hz, and maintain pressure with the pressure rollers. This pure compaction stage lasts for 30 seconds, the purpose of which is to give the concrete particles already in the composite force field a final adjustment opportunity, so that the internal structure reaches the lowest energy and densest arrangement under the assistance of vibration, while driving more micro air bubbles to the vicinity of the inner surface.

[0031] Vibration elimination and static pressure stabilization: Turn off the vibrator, but maintain the rotational speed and roller pressure, and continue running for 20 seconds. These 20 seconds are crucial; they eliminate the microscopic loosening of the structure that may have been caused by the cessation of vibration, allowing the concrete skeleton to settle and form a stable bond under the continuous centrifugal static load and roller pressure.

[0032] Removal of pressure roller: After 20 seconds, smoothly raise the pressure roller to completely detach it from the surface of the steel mold.

[0033] S5. Stepped high-speed centrifugal dehydration Medium-high speed dehydration (third speed: 312 ± 20 rpm): Under the command of the control system, the centrifuge smoothly accelerates to 312 rpm within 40 seconds. At this speed, the powerful centrifugal force forces out most of the free water from the capillary pores and between particles of the concrete. This stage lasts for 180 seconds, during which a large amount of clear segregated water can be seen continuously splashing out from both ends of the steel mold and the joint. This stage mainly removes macroscopic free water.

[0034] High-speed fine dehydration (fourth rotation speed: 378 ± 20 rpm): The rotation speed is further increased to 378 rpm within 30 seconds. At this extreme speed, centrifugal force acts on the more microscopic pore water, resulting in deep dehydration. This stage lasts for 120 seconds, during which the amount of water drained decreases significantly, eventually leaving only trace amounts of water vapor. At this point, an extremely dense cement stone structure has formed inside the concrete.

[0035] S6. Smooth deceleration After high-speed dehydration, immediately initiate the slow-deceleration procedure. Control the centrifuge to gradually reduce its rotational speed from 378 rpm to zero in an approximately linear manner over a period of no less than 70 seconds (75 seconds in this embodiment). Slow deceleration is a crucial step in preventing microcracks from forming in the already formed dense concrete structure due to sudden stress changes, and must be strictly followed.

[0036] (III) Follow-up processing The steel mold, after centrifugation, is smoothly lifted off the centrifuge station. At this point, the concrete of the pipe pile has sufficient initial structural strength to maintain its shape. It is then placed in a steam curing tank and steam-cured at normal pressure in a saturated steam environment at 65±5°C for about 8-10 hours, allowing the concrete strength to rapidly develop to the level required for demolding.

[0037] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Obviously, the embodiments described above are only some embodiments of this invention, not all embodiments. The accompanying drawings show preferred embodiments of this invention, but do not limit the patent scope of this invention. This invention can be implemented in many different forms; on the contrary, the purpose of providing these embodiments is to make the disclosure of this invention more thorough and complete. Although the invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this invention.

Claims

1. A rolling process for forming pipe pile sections, characterized in that, Includes the following steps: S1. Preparation of dry-hard concrete: Prepare a dry-hard concrete mixture with a slump of less than 10 mm; S2. Dynamic material placement and initial attachment: The steel mold containing the prestressed steel reinforcement cage and end plate is placed on a centrifugal device and driven to rotate at a first speed (83±15 rpm); at the same time, the dry hard concrete prepared in step S1 is continuously and uniformly fed into the inner wall of the rotating steel mold through a belt conveyor to form an initial material layer until the thickness of the concrete material layer covers the sealing component of the reserved hole in the inner wall of the steel mold. S3. Synchronous Vibration, Roller Pressing and Precise Material Replenishment: Increase the steel mold rotation speed to the second speed (103±15 rpm) and start the vibration device to apply vibration to the rotating steel mold at a frequency of 60-75Hz; keep the belt conveyor feeding continuously to thicken the material layer to be flush with the reference surface of the inner ring of the steel mold end cap; then, introduce the mechanical pressure roller device, and apply radial roller pressure to the outer wall of the steel mold while rotating at the second speed and continuously vibrating, and simultaneously perform the limit over-thickness replenishment operation, that is, while applying roller pressure, replenish the low-lying areas of the material layer, and control the final concrete layer over-thickness within the range of 6-10mm; S4. Composite force field remains dense: Stop all fabric and replenishment operations, and maintain the second rotation speed, excitation effect and mechanical roller pressing effect for a first preset time; Afterward, the excitation is stopped, and the second rotational speed and mechanical roller pressing action are maintained for a second preset time. S5. Stepped high-speed centrifugal dewatering: The steel mold speed is sequentially increased to the third speed (312±30 rpm) and maintained for the third preset time, then increased to the fourth speed (378±30 rpm) and maintained for the fourth preset time, so that the excess water inside the concrete is fully discharged through centrifugal force; S6. Smooth speed reduction maintenance: Slowly and evenly reduce the speed of the steel mold until it stops completely, and the entire speed reduction process should last for no less than 60 seconds.

2. The pipe pile section forming roll forming process according to claim 1, characterized in that, In step S2, the duration of the dynamic fabric application and initial attachment process at the first rotation speed is 110-130 seconds.

3. The pipe pile section forming roll forming process according to claim 1, characterized in that, In step S3, from the moment the rotational speed is increased to the second rotational speed until the entire process of synchronous excitation, rolling and precise feeding is completed, the total duration is 260-280 seconds.

4. The pipe pile section forming roll forming process according to claim 1, characterized in that, In step S4, the first preset time is 25-35 seconds, and the second preset time is 15-25 seconds.

5. The pipe pile section forming roll forming process according to claim 1, characterized in that, In step S5, the third preset time is 170-190 seconds, and the fourth preset time is 110-130 seconds.

6. The pipe pile section forming roll forming process according to claim 1, characterized in that, In steps S2 and S3, the conveying speed of the belt conveyor is dynamically matched with the rotation speed of the steel mold to ensure that the dry hard concrete can be evenly distributed on the inner wall of the steel mold and steadily thicken as the rotation speed increases, without collapsing or being thrown away prematurely.

7. The pipe pile section forming roll forming process according to claim 1, characterized in that, In step S3, the radial roller pressure applied by the mechanical roller device can be dynamically adjusted according to the state of the concrete layer to ensure the compaction effect without damaging the steel mold or causing damage to the concrete structure.

8. A prestressed concrete pipe pile section produced using the process described in any one of claims 1-7, characterized in that, Its pipe wall concrete structure is uniform and dense, the radial strength gradient is significantly reduced, and the cement stone porosity is low. It has higher compressive strength, flexural performance, impermeability grade and durability index than pipe piles produced by traditional centrifugal plastic concrete process.

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