A process for centrifugal forming of pipe piles

Abstract

This invention discloses a centrifugal forming process for pipe piles. By scientifically determining the effective filling volume based on the total mass of concrete, apparent density, and residual air porosity of the concrete fed into the mold, and combining this with a quantitative control method that calculates the radial distribution coefficient based on the apparent density of the hardened layer on the inner wall of the mold and the central core during multi-stage centrifugation, this invention effectively solves the technical problems of existing technologies that rely on experience-based judgment, leading to a lack of scientific basis for increasing rotational speed, easy segregation of concrete, uneven wall thickness, and excessively high internal porosity. It achieves precise monitoring and dynamic adjustment of the radial distribution state of the concrete, ensuring a tight bond between the aggregate skeleton and the cement paste, significantly improving the uniformity and density of the internal structure of the pipe pile. This avoids segregation while ensuring consistent wall thickness, a smooth surface, and stable mechanical properties in the finished pipe pile.

Description

Technical Field

[0001] This invention relates to the field of pipe pile technology, specifically to a pipe pile centrifugal forming process. Background Technology

[0002] Pipe piles, as an important foundation engineering material, are widely used in building, bridge, and port engineering. Their quality directly affects the load-bearing capacity and safety of the overall structure. Currently, the forming of pipe piles mainly adopts centrifugal technology, which involves injecting concrete into a mold and using the centrifugal force generated by a centrifuge to separate and rearrange the aggregate and slurry in the concrete, thereby removing excess water and air bubbles and improving the density and strength of the pipe pile.

[0003] Existing centrifugal molding processes for pipe piles typically employ a multi-stage variable-speed centrifugation method, generally including low-speed, medium-speed, and high-speed stages. In the low-speed stage, the main purpose is to initially shape the concrete and expel large air bubbles; in the medium-speed stage, the concrete is further compressed to remove free water; and in the high-speed stage, the powerful centrifugal force is used to achieve the final compaction of the pipe wall. However, existing technologies often suffer from the following problems in practical operation: the increase in rotational speed at each stage lacks scientific quantitative basis and relies heavily on the operator's experience and judgment, leading to segregation of the concrete during centrifugation—that is, the separation of the aggregate skeleton from the cement paste—resulting in uneven internal structure of the pipe pile. Particularly in the medium-speed stage, the inability to accurately grasp the radial distribution of the concrete makes it difficult to precisely control the degree of paste migration to the inner wall of the mold, resulting in uneven wall thickness, honeycomb-like surface defects, or excessively high internal porosity in some pipe piles, severely affecting the final mechanical properties and appearance quality of the pipe pile. Furthermore, the determination of the effective filling volume of concrete in traditional processes is rather crude, failing to fully consider the impact of residual air porosity after vibration on the final molding quality, further exacerbating fluctuations in the yield rate. Summary of the Invention

[0004] This invention aims to provide a centrifugal forming process for pipe piles that can accurately control the radial distribution of concrete, avoid segregation, and optimize the calculation of filling volume.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a centrifugal forming process for pipe piles, comprising: The stone is screened to obtain stones of a predetermined particle size. Cement and fine sand are prepared, and a self-prepared water-reducing agent containing polycarboxylate superplasticizer, defoamer and calcium nitrate is prepared. The stones, cement, fine sand and self-prepared water-reducing agent are mixed to obtain low slump concrete. The low-slump concrete is injected into the pipe pile mold and vibrated to compact it. The effective filling volume of the concrete is determined based on the total mass of the concrete injected into the mold, the apparent density of the concrete mixture, and the residual air porosity inside the concrete after vibration. The concrete-filled pipe pile mold is installed in a centrifuge and subjected to multi-stage centrifugation treatment, which includes a low-speed stage, a low-to-medium-speed stage, a medium-speed stage, a medium-to-high-speed stage, and a high-speed stage performed sequentially. During the medium-speed stage, the radial distribution coefficient is determined based on the apparent density of the hardened concrete layer on the inner wall of the mold and the apparent density of the concrete core in the central region. After the high-speed stage is completed, the mold is demolded.

[0006] Preferably, the stones of the predetermined particle size are stones with a particle size of 1 cm to 2 cm.

[0007] Preferably, the preparation of the self-prepared water-reducing agent includes: weighing polycarboxylate water-reducing agent powder and adding it to deionized water for pre-dissolution; adding defoamer and calcium nitrate to the pre-dissolved polycarboxylate water-reducing agent solution; and stirring to obtain the self-prepared water-reducing agent stock solution.

[0008] Preferably, injecting the low-slump concrete into the pipe pile mold and compacting it includes: checking whether the inner wall of the pipe pile mold is coated with release agent and confirming that the mold joints are tight; slowly pouring concrete into the center of the mold through a chute; inserting a vibrator to perform initial compaction when the amount of concrete poured reaches one-third of the mold height; continuing to pour concrete until the mold is full and performing secondary compaction; and then using a scraper to level the excess concrete on the top surface of the mold.

[0009] Preferably, the centrifuge speed is set to a first speed and run for a first duration. The first speed is 50 revolutions per minute, and the first duration is 4 minutes.

[0010] Preferably, the low-to-medium speed stage includes: increasing the centrifuge speed to a second speed and running for a second duration; the medium speed stage includes: increasing the centrifuge speed to a third speed and running for a third duration; the medium-to-high speed stage includes: increasing the centrifuge speed to a fourth speed and running for a fourth duration; and the high speed stage includes: increasing the centrifuge speed to a fifth speed and running for a fifth duration.

[0011] Preferably, the second rotational speed is 120 revolutions per minute and the second duration is 1 to 2 minutes; the third rotational speed is 210 revolutions per minute and the third duration is 1 to 2 minutes; the fourth rotational speed is 290 revolutions per minute and the fourth duration is 1 minute; and the fifth rotational speed is 440 revolutions per minute and the fifth duration is 3 to 6 minutes.

[0012] Preferably, determining the radial distribution coefficient includes: collecting the apparent density of the hardened concrete layer on the inner wall of the mold and the apparent density of the concrete core in the central region; and combining the apparent density of the hardened concrete layer on the inner wall with the apparent density of the concrete core in the central region to determine the radial distribution coefficient.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention scientifically determines the effective filling volume based on the total mass, apparent density, and residual air porosity of the concrete fed into the mold. Combined with a quantitative control method that calculates the radial distribution coefficient based on the apparent density of the hardened layer on the inner wall of the mold and the central core during multi-stage centrifugation, it effectively solves the technical problems of existing technologies that rely on experience-based judgment, leading to a lack of scientific basis for increasing rotational speed, easy segregation of concrete, uneven wall thickness, and excessively high internal porosity. It achieves precise monitoring and dynamic adjustment of the radial distribution state of the concrete, ensuring a tight bond between the aggregate skeleton and the cement paste, significantly improving the uniformity and density of the internal structure of the pipe pile. This avoids segregation while ensuring consistent wall thickness, a smooth surface, and stable mechanical properties in the finished pipe pile. Attached Figure Description

[0014] Figure 1 This is a flowchart of the centrifugal forming process for pipe piles according to the present invention. Detailed Implementation

[0015] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0016] like Figure 1 As shown, this invention proposes a centrifugal forming process for pipe piles, comprising: The stone is screened to obtain stones of a predetermined particle size. Cement and fine sand are prepared, and a self-prepared water-reducing agent containing polycarboxylate superplasticizer, defoamer and calcium nitrate is prepared. The stones, cement, fine sand and self-prepared water-reducing agent are mixed to obtain low slump concrete. The stones of the predetermined particle size are stones with a particle size of 1 cm to 2 cm.

[0017] Furthermore, the steps for preparing the self-prepared water-reducing agent include: weighing polycarboxylate water-reducing agent powder and adding it to deionized water for pre-dissolution; adding defoamer and calcium nitrate to the pre-dissolved polycarboxylate water-reducing agent solution; and stirring to obtain the self-prepared water-reducing agent stock solution.

[0018] By limiting the stone particle size to 1-2 cm, the aggregate gradation was optimized, effectively improving the stability and anti-segregation ability of the concrete skeleton. With the synergistic compounding of polycarboxylate superplasticizer, defoamer and calcium nitrate, water consumption was significantly reduced and low slump workability was ensured, while internal air bubbles were greatly reduced and early strength formation was accelerated, thus ensuring that the pipe piles were densely formed, with a smooth surface and uniform structure.

[0019] The low-slump concrete is injected into the pipe pile mold and vibrated to compact it. The effective filling volume of the concrete is determined based on the total mass of the concrete injected into the mold, the apparent density of the concrete mixture, and the residual air porosity inside the concrete after vibration. Furthermore, the process of injecting low-slump concrete into the pipe pile mold and compacting it includes: checking whether the inner wall of the pipe pile mold is coated with release agent and confirming that the mold joints are tight; slowly pouring concrete into the center of the mold through a chute; inserting a vibrator to perform initial compaction when the amount of concrete poured reaches one-third of the mold height; continuing to pour concrete until the mold is full and performing a second compaction; and then using a scraper to level the excess concrete on the top surface of the mold.

[0020] By employing a multi-stage pouring and secondary vibration process, along with the use of release agents and checks on the tightness of joints, dead-angle air bubbles inside the concrete were effectively eliminated, and leakage was prevented, significantly improving the initial density of the concrete inside the mold. At the same time, by comprehensively calculating the effective filling volume based on the total mass, apparent density, and residual air porosity, precise quantitative control of the amount of concrete poured into the mold was achieved. This avoided wall thickness deviations and internal voids caused by insufficient or excessive filling from the source, providing a uniform and stable foundation for subsequent centrifugal molding.

[0021] The concrete-filled pipe pile mold is installed in a centrifuge and subjected to multi-stage centrifugation treatment, which includes a low-speed stage, a low-to-medium-speed stage, a medium-speed stage, a medium-to-high-speed stage, and a high-speed stage performed sequentially. The low-speed phase includes: setting the centrifuge speed to the first speed and running for the first duration; the first speed is 50 revolutions per minute and the first duration is 4 minutes.

[0022] The low-to-medium speed phase includes: increasing the centrifuge speed to a second speed and running for a second duration; the second speed is 120 revolutions per minute, and the second duration is 1 to 2 minutes; The medium-speed phase includes: increasing the centrifuge speed to the third speed and running for the third duration; the third speed is 210 revolutions per minute, and the third duration is 1 to 2 minutes; The medium-to-high speed phase includes: increasing the centrifuge speed to the fourth speed and running for the fourth duration; the fourth speed is 290 revolutions per minute, and the fourth duration is 1 minute; The high-speed phase includes: increasing the centrifuge speed to the fifth speed and running for the fifth duration; the fifth speed is 440 revolutions per minute, and the fifth duration is 3 to 6 minutes.

[0023] This five-stage gradient centrifugation process effectively avoids concrete segregation and stratification caused by sudden changes in rotation speed in traditional processes by controlling low-speed stabilization, low-to-medium-speed degassing, medium-speed conditioning, medium-to-high-speed densification, and high-speed final setting. In particular, the introduction of low-to-medium-speed and medium-to-high-speed transition stages ensures uniform settling of the aggregate skeleton in the slurry and orderly drainage of water, significantly improving the homogeneity of the radial structure of the pipe pile, and ultimately obtaining high-quality pipe piles with consistent wall thickness, no internal voids, and a dense surface.

[0024] During the medium-speed stage, the radial distribution coefficient is determined based on the apparent density of the hardened concrete layer on the inner wall of the mold and the apparent density of the concrete core in the central region. After the high-speed stage is completed, the mold is demolded. The determination of the radial distribution coefficient includes: collecting the apparent density of the hardened concrete layer on the inner wall of the mold and the apparent density of the concrete core in the central region; and combining the apparent density of the hardened concrete layer on the inner wall and the apparent density of the concrete core in the central region to determine the radial distribution coefficient.

[0025] By quantitatively comparing the apparent density of the hardened layer on the inner wall of the mold with that of the central core and calculating the radial distribution coefficient, a precise assessment of the radial density uniformity of concrete during centrifugation was achieved. This mechanism effectively solves the problem that traditional processes have difficulty monitoring internal structural differences, ensuring that the aggregate and slurry are highly consistent in radial distribution, thereby eliminating the hidden danger of uneven strength between inner and outer layers and significantly improving the homogeneity and mechanical stability of the overall pipe pile structure.

[0026] The following will describe in detail the process of centrifugal forming of pipe piles with specific embodiments, including: Step 1: Precise selection of raw materials and preparation of self-prepared water-reducing agent components This step focuses on strict control of aggregate particle shape and on-site preparation of the specialized water-reducing agent. First, the incoming stone materials must be inspected at the source, removing impurities containing soil, mica, and weathered particles to ensure the purity of the raw materials meets production requirements. Then, the screened stone is fed into crushing and screening equipment. Based on the previous screening results, crushed stone with a particle size of 1 to 2 cm is retained as the main coarse aggregate. This size of stone has sharp edges and continuous gradation, effectively improving the density of the concrete's internal structure. After obtaining the required stone, the preparation of the self-mixed water-reducing agent is immediately initiated. This process is not a simple mixing, but rather a precise proportioning based on the high molecular weight characteristics of polycarboxylate superplasticizer, combined with the synergistic effect of defoamer and calcium nitrate; the details are as follows: Collect stone samples and make a preliminary judgment on their surface cleanliness by visual inspection and touch. If obvious dust or mud is found, transfer them to the cleaning area for secondary rinsing until there are no visible stains on the stone surface, so as to provide pure raw materials for subsequent particle size control.

[0027] After washing, the stones are fed into a vibrating screen. The screen aperture parameters are set so that large stones are returned to the crushing port for reprocessing, while small stones enter the next stage. Finally, qualified stones with a particle size between 1 cm and 2 cm are collected and piled up in a designated dry area for later use.

[0028] Weigh out the predetermined mass of polycarboxylate superplasticizer powder, place it in a high-speed dispersion tank, add an appropriate amount of deionized water for pre-dissolution, and control the stirring speed to within 300 revolutions per minute to prevent the polymer chains from breaking due to excessive shear force and ensure the uniformity of the solution.

[0029] Add the calculated proportions of defoamer and calcium nitrate sequentially to the above polycarboxylate superplasticizer solution. The defoamer is used to eliminate air bubbles generated during concrete mixing, while the calcium nitrate is introduced as an early-strength component. After mixing the three, stir at low speed again for two minutes to form a uniform and transparent self-prepared superplasticizer stock solution, ready to be added to the next stage of concrete mixing.

[0030] Step Two: Concrete Mix Design and Low Slump Mixing The key point of this step is to determine the optimal water-cement ratio and to perform forced mixing of the low-slump concrete. Due to the special aggregate type and the significant water-reducing effect of the admixture, the cement and water dosages need to be recalculated to ensure the fresh concrete has suitable fluidity and cohesiveness, avoiding segregation during centrifugation. A twin-shaft forced mixer is used for mixing, with dry materials added first, followed by wet materials. The polycarboxylic acid component in the self-prepared water-reducing agent coats the cement particles, releasing free water, while calcium nitrate accelerates the early hydration reaction of the cement, as detailed below: Based on the bulk density and moisture content data of 1-2 cm pebbles obtained in step one, calculate the total mass of pebbles required for this mixing, deduct the free water adhering to the surface of the pebbles, and obtain the actual amount of dry pebbles to be used. Pour the dry pebbles into the mixer drum.

[0031] Add cement and fine sand according to the design ratio, turn on the dry mixing device of the mixer, set the rotation time to one minute, so that the solid materials are fully mixed evenly. At this time, observe whether the color of the materials is consistent. If a color difference is found, extend the dry mixing time by thirty seconds.

[0032] Slowly inject the self-prepared water-reducing agent stock solution prepared in step one into the mixer, while simultaneously turning on the water spray nozzle to replenish the remaining required amount of water. The water injection rate needs to be dynamically adjusted according to the water absorption of the stones to ensure that the water-cement ratio falls within the preset range and to prevent local areas from being too thin or too dry.

[0033] Start the high-speed mixing program and continue mixing for three minutes. During this time, observe the state of the concrete mixture. When the mixture is uniformly grayish-black, with no obvious bleeding and the stones are completely coated by the slurry, stop mixing and unload the mixed concrete into the transport truck, ready to be transported to the mold.

[0034] Step 3: Concrete pouring and initial vibration compaction This step involves pouring concrete into the steel pipe pile mold and using mechanical vibration to eliminate internal voids. Because defoamers are added to the concrete and specific aggregate sizes are used, the drop height must be controlled during pouring to reduce the risk of segregation. Simultaneously, a vibrator is used to vibrate the concrete in layers to ensure uniform aggregate distribution. During this process, special attention must be paid to the filling of the concrete at the bottom of the mold, as the bottom experiences the greatest stress; any voids will directly affect the bearing capacity of the pipe pile. Specifically: Check whether the inner wall of the pipe pile mold is coated with release agent, and confirm that the mold joints are tight and there is no risk of grout leakage. Then, slowly pour the concrete mixed in step two into the center of the mold through the chute, controlling the pouring speed to avoid the stones rolling off and causing stratification.

[0035] When the amount of concrete poured reaches one-third of the height of the mold, insert a high-frequency vibrator for initial vibration. The vibrator should be inserted vertically and moved up and down, with a spacing of about 20 centimeters, until the concrete surface is covered with slurry and no more large amounts of air bubbles appear.

[0036] Continue pouring the remaining concrete until the mold is full, then use a vibrator to vibrate it a second time, focusing on strengthening the vibration around the edges of the mold and the reinforcing steel frame to ensure that the concrete adheres tightly to the inner wall of the mold.

[0037] After vibration, use a screed to level any excess concrete on the top surface of the mold and a trowel to smooth the surface. At this point, it is necessary to monitor the initial settlement of the concrete within the mold. If any minor depressions are found on the surface, add more concrete and vibrate lightly again to ensure overall volume stability. During this stage, the following parameter calculation model should be introduced to help determine the concrete filling density: ; in, Represents the effective filling volume of concrete. This refers to the total mass of concrete poured into the mold in step three. ρ is the apparent density of the concrete mixture, and n is the porosity of the residual air inside the concrete after vibration. This formula is used to quantitatively evaluate the filling efficiency under the current vibration process and guide whether the vibration time needs to be adjusted in subsequent operations.

[0038] Step 4: Centrifuge mold positioning and low-speed pre-stabilization operation This step involves transferring the mold to the centrifuge room and installing it inside the centrifuge drum for low-speed pre-stabilization. The core task at this stage is to ensure the mold is in absolute balance before high-speed rotation, preventing severe vibration of the equipment due to eccentricity. Since the concrete already contains calcium nitrate from the self-prepared water-reducing agent, its initial strength is slowly increasing but has not yet reached the level to withstand centrifugal force. Therefore, it is essential to strictly follow the set low-speed curve to further compact the concrete under the combined action of gravity and weak centrifugal force, expelling residual air bubbles; specifically as follows: Use a crane to smoothly lift the pipe pile mold completed in step three and move it to the centrifuge feeding platform. Check whether the mold number is consistent with the production plan. After confirming that there is no error, push the mold into the designated slot position of the centrifuge drum.

[0039] Start the hydraulic clamping device to apply uniform pressure to the mold base from all sides, tighten the fixing bolts, and check the level of the drum with a level. If the deviation exceeds the allowable range, the thickness of the shims needs to be finely adjusted until the drum is in an absolutely level state.

[0040] After confirming that all molds are installed and the drum is balanced, start the centrifuge drive motor and gradually increase the speed to fifty revolutions per minute. Maintain this speed throughout the process, and the operator must monitor the motor current and the vibration amplitude of the machine body.

[0041] After the rotation speed stabilizes at 50 revolutions per minute and continues to run for four minutes, observe the changes on the concrete surface. At this time, the concrete should have initially formed under the action of weak centrifugal force, and the surface slurry should be smooth with no signs of air bubbles escaping. Then the system will automatically send a signal to prepare to enter the next stage of speed increase. The entire low-speed pre-stabilization process ends here, laying a solid foundation for the subsequent medium-speed molding.

[0042] Step 5: Low-to-medium speed transition and initial coagulation of the slurry After the low-speed pre-stabilization run completed in step four, the concrete has initially formed an integral structure within the mold, and most of the internal air bubbles have been expelled. However, it has not yet reached sufficient density to withstand higher centrifugal forces. This step aims to further compress the water and air in the concrete by gradually increasing the rotation speed to the low-to-medium speed range, using the gradually increasing centrifugal force field to promote the migration of cement paste towards the inner wall of the mold and its initial coagulation. Because the 1-2 cm aggregate used in the previous steps has good gradation, and the polycarboxylate component in the self-prepared water-reducing agent effectively reduces the water-cement ratio, the concrete is less prone to segregation during the acceleration process. The key at this stage is to control the acceleration to avoid interlayer slippage or delamination cracks caused by sudden changes in rotation speed; specifically as follows: Based on the initial state of the concrete at the end of step four, the system automatically releases the motor speed limit protection, starts the frequency conversion speed control module, and smoothly increases the centrifuge speed from fifty revolutions per minute to one hundred and twenty revolutions per minute. The duration of the increase process is controlled within thirty seconds to ensure that the acceleration change is gradual.

[0043] When the rotation speed stabilizes at 120 revolutions per minute, and this speed is maintained, the centrifugal force on the concrete increases significantly. The slurry begins to flow towards the outer wall of the mold, the stone skeleton rearranges under the action of centrifugal force, and the free water in the gaps between the aggregates is forced out and converges towards the center.

[0044] Operators must closely observe the vibration of the centrifuge body and listen to the sounds inside the concrete. If abnormal impact sounds or vibration amplitudes exceed the set threshold, the speed should be reduced immediately and the mold should be checked for fixation. Once confirmed to be correct, the current speed should be maintained.

[0045] Continue running in the low-to-medium speed stage for one to two minutes until a uniform water film layer is observed on the inner wall of the mold and the gloss of the concrete surface is significantly improved, indicating that the slurry has basically filled the aggregate voids and has initially solidified. At this point, the system is ready to enter the medium-speed molding stage, laying the foundation for subsequent high-speed slurry casting.

[0046] Step Six: Optimization of Medium-Speed ​​Molding and Slurry Distribution Continuing from the low-to-medium speed operation, this step further increases the rotation speed to the medium speed range. Stronger centrifugal force forces a large amount of free water out of the concrete, causing the slurry to form a dense, hardened layer on the inner wall of the mold. During this stage, the stress distribution within the concrete changes significantly. The aggregate particles are tightly bound together under centrifugal force, while the cement slurry is mainly distributed between the aggregate particles and on the inner wall of the mold, forming a stone-aggregate-slurry skin structure. To ensure the uniformity of the slurry distribution, a calculation model for the slurry thickness distribution is introduced. Monitoring the changes in slurry density at different radii guides the rotation speed adjustment strategy; specifically as follows: Based on the concrete density feedback at the end of step five, the variable frequency speed control is restarted, and the speed is linearly increased from 120 rpm to 210 rpm. The speed increase slope is dynamically adjusted according to the stability data of the previous stage to prevent excessive speed fluctuations.

[0047] Once the rotation speed stabilizes at 210 revolutions per minute, maintain this speed for one to two minutes. At this point, the water inside the concrete is forcefully ejected, and a uniform grayish-white slurry layer forms on the inner wall of the mold. The stone skeleton is completely wrapped and tightly arranged, and the hollow part of the pipe pile begins to be exposed.

[0048] During this process, it is necessary to collect temperature change data at different heights on the inner wall of the mold in real time, and calculate the radial distribution coefficient of the slurry using the following formula to evaluate the molding quality: ; in, Represents the radial distribution coefficient. This refers to the apparent density of the hardened concrete layer on the inner wall of the mold. The apparent density of the concrete core in the central area is used to quantify the degree of separation between the paste and the aggregate. The closer the value is to 1, the more uniform the paste distribution and the higher the density. Conversely, it indicates that there may be a risk of segregation.

[0049] Based on the distribution coefficient calculated in step six, if the value is within the ideal range, the current rotation speed will be maintained; if the value is too low, the medium-speed running time will be extended appropriately or the rotation speed will be finely adjusted to 215 revolutions per minute until the slurry is evenly distributed and there are no signs of local voids. Then the system will send a signal to prepare to enter the high-speed slurry throwing stage.

[0050] Step 7: Medium- and high-speed slurry deposition and initial curing of the pipe wall After the medium-speed molding process, the concrete pipe wall has formed a preliminary hardened structure, but it still has many pores and low strength. This step increases the rotation speed to the medium-high speed range, utilizing significant centrifugal force to further compress the remaining free water and some fine particles outwards, making the pipe wall thickness more uniform. Simultaneously, it accelerates the cement hydration reaction, improving the density and early strength of the pipe pile surface. Because calcium nitrate was used as an early-strength component in the previous step, the concrete sets faster at this stage and can withstand higher centrifugal forces without deformation; specifically as follows: Based on the distribution coefficient and the degree of slurry solidification calculated in step six, the system automatically instructs the motor to accelerate, rapidly increasing the speed from 210 revolutions per minute to 290 revolutions per minute. During the acceleration process, torque changes must be strictly controlled to prevent motor overload.

[0051] Once the rotation speed stabilizes at 290 revolutions per minute, maintain this speed for one minute. At this point, the enormous centrifugal force will almost completely remove the residual water from the concrete, resulting in a smooth, mirror-like surface on the pipe wall, clearly visible edges of the stones, and the slurry layer thickness reaching the design standard.

[0052] Operators need to closely monitor the slurry backflow on the top and bottom of the mold. If excessive slurry loss is found at the top or uneven accumulation at the bottom, the rotation speed can be temporarily paused for adjustment or minor corrections can be made to ensure that the wall thickness of the upper and lower sections of the pipe pile is consistent and to avoid quality defects such as uneven thickness.

[0053] After completing one minute of medium-high speed slurry spraying, the gloss and hardness of the concrete surface are observed. At this point, the surface of the pipe pile has a certain smoothness and compressive strength, and the internal structure is basically finalized. The system is then ready to enter the final high-speed finishing stage to completely eliminate internal micropores and enhance overall performance.

[0054] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A process for centrifugal forming of a pipe pile, characterized in that, include: The stone is screened to obtain stones of a predetermined particle size. Cement and fine sand are prepared, and a self-prepared water-reducing agent containing polycarboxylate superplasticizer, defoamer and calcium nitrate is prepared. The stones, cement, fine sand and self-prepared water-reducing agent are mixed to obtain low slump concrete. The low-slump concrete is injected into the pipe pile mold and vibrated to compact it. The effective filling volume of the concrete is determined based on the total mass of the concrete injected into the mold, the apparent density of the concrete mixture, and the residual air porosity inside the concrete after vibration. The concrete-filled pipe pile mold is installed in a centrifuge and subjected to multi-stage centrifugation treatment, which includes a low-speed stage, a low-to-medium-speed stage, a medium-speed stage, a medium-to-high-speed stage, and a high-speed stage performed sequentially. During the medium-speed stage, the radial distribution coefficient is determined based on the apparent density of the hardened concrete layer on the inner wall of the mold and the apparent density of the concrete core in the central region. After the high-speed stage is completed, the mold is demolded.

2. A tubular pile centrifugal forming process according to claim 1, characterised in that, The stones with the predetermined particle size are stones with a particle size of 1 cm to 2 cm.

3. A tubular pile centrifugal forming process according to claim 1, wherein, The preparation of the self-prepared water-reducing agent includes: weighing polycarboxylate water-reducing agent powder and adding it to deionized water for pre-dissolution; adding defoamer and calcium nitrate to the pre-dissolved polycarboxylate water-reducing agent solution; and stirring to obtain the self-prepared water-reducing agent stock solution.

4. A tubular pile centrifugal forming process according to claim 1, wherein, The process of injecting the low-slump concrete into the pipe pile mold and compacting it includes: Check whether the inner wall of the pipe pile mold is coated with release agent and confirm that the mold joints are tight. Slowly pour concrete into the center of the mold through the chute. When the concrete volume reaches one-third of the mold height, insert a vibrator for initial vibration. Continue pouring concrete until the mold is full and then vibrate it a second time. Then use a scraper to smooth out any excess concrete on the top surface of the mold.

5. A process for centrifugal forming of pipe piles according to claim 1, characterized in that, The low-speed phase includes setting the centrifuge speed to a first speed and running it for a first duration.

6. A process for centrifugally forming a pipe pile according to claim 5, wherein The first rotational speed is 50 revolutions per minute, and the first duration is 4 minutes.

7. The centrifugal forming process for pipe piles according to claim 1, characterized in that, The low-to-medium speed phase includes: increasing the centrifuge speed to a second speed and running for a second duration; the medium speed phase includes: increasing the centrifuge speed to a third speed and running for a third duration; the medium-to-high speed phase includes: increasing the centrifuge speed to a fourth speed and running for a fourth duration; the high speed phase includes: increasing the centrifuge speed to a fifth speed and running for a fifth duration.

8. The centrifugal forming process for pipe piles according to claim 7, characterized in that, The second rotational speed is 120 revolutions per minute, and the second duration is 1 to 2 minutes; the third rotational speed is 210 revolutions per minute, and the third duration is 1 to 2 minutes; the fourth rotational speed is 290 revolutions per minute, and the fourth duration is 1 minute; the fifth rotational speed is 440 revolutions per minute, and the fifth duration is 3 to 6 minutes.

9. The centrifugal forming process for pipe piles according to claim 1, characterized in that, The determination of the radial distribution coefficient includes: The apparent density of the hardened concrete layer on the inner wall of the mold and the apparent density of the concrete core in the central region are collected; the radial distribution coefficient is determined by combining the apparent density of the hardened concrete layer on the inner wall and the apparent density of the concrete core in the central region.

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