A ductile cast iron pipe cement mortar lining spraying process method

Abstract

The present application relates to ductile cast iron pipe production and processing technical field, disclose a kind of ductile cast iron pipe cement mortar lining spraying process method;The method aims at the problems such as lining layer cement mortar body enrichment, thickness uneven and need internal grinding process caused by traditional centrifugal process;The present application uses spraying process to replace centrifugal process, including pipe body pretreatment, cement mortar preparation, inner wall spraying, smoothing and curing steps of shaping;Through the axial and circumferential linkage spraying of spray gun, control spraying parameters such as pressure 0.3~0.8MPa, spray gun and pipe wall distance 10~30cm, and combine with stratified spraying and post-processing, realize lining layer uniform and smooth, thickness deviation is controlled within ±1mm;The present application cancels internal grinding process, improves production efficiency by more than 30%, mortar utilization rate reaches 95%, enhances bonding strength by more than 10%, adapts to oval pipe body, with high durability, environmental protection and economy.

Description

Technical Field

[0001] This invention relates to the field of ductile iron pipe production and processing technology, and in particular to a cement mortar lining spraying process for ductile iron pipes. Background Technology

[0002] In the 21st-century water supply and drainage industry, centrifugal ductile iron pipes are the mainstream water transmission pipe material. They combine the properties of iron with the performance of steel, offering excellent corrosion resistance, good ductility, superior sealing, and easy installation. They are widely used in municipal and industrial water supply, gas transmission, and oil transportation projects. Cement mortar, due to its low cost and excellent bonding performance with the inner wall of ductile iron pipes, has become the preferred filling material for pipe linings, effectively improving the pipe's corrosion resistance and extending its service life.

[0003] Currently, most ductile iron pipe manufacturers use centrifugal processing to prepare cement mortar linings, using centrifugal force to evenly spread the cement mortar on the inner wall of the pipe to form a protective layer. However, this process has several technical drawbacks: First, under centrifugal action, cement and water in the cement mortar easily precipitate and accumulate on the surface of the inner wall of the pipe, resulting in excessive slurry on the surface of the cement lining. This can lead to problems such as powdering and peeling, and poor appearance quality, requiring an additional internal grinding process, which increases production steps and costs. Second, due to the ellipticity deviation during the production of ductile iron pipes, the thickness distribution of the cement mortar lining in the pipe is uneven under centrifugal processing, with significant differences in lining thickness between the minor and major axes of the elliptical pipe. Third, centrifugal processing can easily lead to quality problems such as loose sand and micro-cracks inside the lining layer, reducing the bonding strength between the lining and the pipe body and affecting the overall performance of the pipeline.

[0004] To address the aforementioned issues, eliminate the internal grinding process, improve production efficiency, reduce production costs, and adapt to elliptical pipe bodies to achieve uniform preparation of the inner lining, the development of a cement mortar lining preparation process for ductile iron pipes that replaces the traditional centrifugal process has become a pressing technical challenge in the ductile iron pipe production field. Summary of the Invention

[0005] The purpose of this invention is to provide a process for spraying cement mortar lining of ductile iron pipes to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for spraying cement mortar lining of ductile iron pipes, comprising the following steps: S1. Pipe body pretreatment: Clean and remove impurities from the inner wall of the ductile iron pipe, removing floating rust, oil and impurities, and ensuring that the inner wall of the pipe is dry and free of protruding foreign objects. S2. Cement mortar preparation: Prepare cement, medium sand, and water or add admixtures according to the mass ratio, and stir to make a uniform, lump-free special cement mortar for spraying. The mortar consistency is controlled at 80-160mm, and the initial setting time is controlled at 3-6h. S3. Inner wall spraying: Place the pretreated ductile iron pipe on a special tooling table, and use a mortar spraying equipment to spray along the axial and circumferential directions of the pipe body. The distance between the spray gun and the inner wall of the pipe should be 10-30cm, and the spraying pressure should be controlled at 0.3-0.8MPa. A single spraying will form a cement mortar inner lining base with a thickness of 2-20mm. The total thickness of the spraying can be completed in one spraying or in layers. S4. Smoothing and shaping: During the spraying process, the trowel provided with the equipment is used to smooth the circumferential and axial lining of the pipe, or after spraying, the tooling table is started to perform slow centrifugation. The centrifugation speed is controlled at 15-30 r / min for 5-10 min to make the surface of the inner lining smooth and flat, and to eliminate spraying drips and unevenness. S5. Curing and solidification: Place the shaped ductile iron pipe in a curing furnace for curing to complete the preparation of the cement mortar lining.

[0007] Preferably, the mass ratio of cement mortar in S2 is cement:medium sand:water = 1:1.5~2.5:0.4~0.5, and the admixtures are water-reducing agent and water-retaining agent, with a total addition amount of 0.5%~1.0% of the cement mass.

[0008] Preferably, the mortar spraying equipment in S3 is a centrifugal spraying equipment for well chamber repair, equipped with a fan-shaped spray gun that can rotate 360°. During the spraying process, the spray gun moves at a constant speed of 0.2 to 1.0 m / s along the axial direction of the pipe.

[0009] Preferably, during the inner wall spraying in S3, the pipe body rotates at a constant speed of 5-8 r / min, and the interlayer interval of the layered spraying is controlled at 30-60 min.

[0010] Preferably, the slow centrifugation treatment and the smoothing treatment in S4 can be implemented separately or in combination. When implemented in combination, slow centrifugation is performed first, followed by fine smoothing.

[0011] Preferably, the relative humidity of the curing environment in S5 is controlled above 90%, and the pipe body is prevented from shaking and the inner lining layer is prevented from being impacted by external forces during the curing period.

[0012] Preferably, after the tube body pretreatment in S1, the allowable value of unevenness on the inner wall surface is ≤20mm.

[0013] The technical effects and advantages of this invention are as follows: 1. This invention uses a spraying process instead of a centrifugal process, fundamentally avoiding the cement slurry enrichment caused by centrifugal force. By directly spraying cement mortar onto the inner wall of the pipe, the uniform distribution of the lining composition is ensured, effectively eliminating the risk of powdering and detachment caused by excessive surface slurry. Simultaneously, by optimizing the mortar mix ratio and adding special admixtures, the workability and water retention of the mortar are significantly improved, eliminating quality hazards such as loose sand and micro-cracks within the lining layer, thereby greatly improving the density, uniformity, and long-term durability of the lining layer. 2. Because the spray-coated inner lining layer has a smooth and flat surface, this invention successfully eliminates the essential internal grinding process in traditional methods. This not only simplifies the production process and is expected to increase production efficiency by more than 30%, but also directly reduces equipment energy consumption, mold wear, and labor costs. Furthermore, the spray coating process has good material orientation, increasing mortar utilization to over 95%, greatly reducing raw material waste. From an environmental perspective, eliminating the internal grinding process eliminates dust pollution at its source, aligning with the industry trend of green manufacturing. 3. This invention, through axial and circumferential coordinated spraying with a spray gun, combined with post-treatment processes such as slow centrifugation or mechanical smoothing, demonstrates strong adaptability to pipe shapes (especially ellipticity deviations). This process can precisely control the thickness of the inner lining layer, stably controlling its deviation within ±1 mm, perfectly solving the industry problem of uneven inner lining thickness for elliptical pipes under traditional centrifugal processes. Combined with the control of substrate roughness through pipe pretreatment, the mechanical bonding force between the inner lining layer and the pipe wall is further enhanced, increasing the bonding strength by more than 10%, ensuring the overall service life and safety performance of the pipeline. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the overall process flow of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1: This invention provides, for example Figure 1 The illustrated method is a cement mortar lining spraying process for ductile iron pipes. This embodiment is for ordinary ductile iron pipes with a DN300 specification, and the total thickness of the cement mortar lining is designed to be 10mm. The specific process steps are as follows: Pipe pretreatment: The inner wall of the DN300 ductile iron pipe is cleaned by grinding to remove floating rust, oil and impurities, and the unevenness of the inner wall surface is controlled to be ≤5mm to ensure that the inner wall of the pipe is dry and free of protruding foreign objects. Cement mortar preparation: The raw materials are prepared according to the mass ratio of cement:medium sand:water = 1:1.5:0.4. Add 0.5% of the cement mass of admixture (including 0.3% water-reducing agent and 0.2% water-retaining agent). Mix with a forced mixer for 4 minutes to make a uniform spray-specific cement mortar with a consistency of 130 mm and an initial setting time of 4 hours. Inner wall spraying: The pretreated ductile iron pipe is placed on a rotatable special tooling table, and the pipe body is rotated at a uniform speed of 5 r / min. A centrifugal spraying equipment for well chamber repair is used, equipped with a 360° rotating fan-shaped spray gun. The distance between the spray gun and the inner wall of the pipe is maintained at 20 cm, and the spraying pressure is controlled at 0.3 MPa. The spray gun moves at a uniform speed of 0.2 m / s along the axial direction of the pipe body to achieve circumferential and axial linkage spraying. A single spray forms a 5 mm thick inner lining base layer, and two sprays are used to complete a total thickness of 10 mm, with an interval of 30 minutes between sprays. Smoothing and shaping: After the spraying is completed, the flexible trowel provided with the equipment is used to mechanically smooth the inner lining layer in the circumferential and axial directions to eliminate defects such as sagging and unevenness, and to ensure that the surface of the inner lining layer is smooth and flat. Curing and solidification: Place the shaped ductile iron pipe in a curing furnace and cure it for 8 hours at a relative humidity of 90% and a temperature of 60℃. During the curing period, avoid shaking the pipe and external impact.

[0017] The inner lining prepared in this embodiment has a smooth and flat surface, without large slurry or powdering, and the thickness deviation is controlled within ±0.8mm. It has excellent bonding strength with the pipe body and is free from defects such as loose sand and internal cracks.

[0018] Example 2: This embodiment is for a DN800 ductile iron pipe, with a designed total cement mortar lining thickness of 8mm. The specific process steps are as follows: Pipe pretreatment: The inner wall of the DN800 ductile iron pipe is thoroughly cleaned to remove loose rust and oil stains, and the surface unevenness value is controlled to ≤7mm to ensure that the inner wall is dry and free of impurities; Cement mortar preparation: The raw materials are prepared according to the mass ratio of cement:medium sand:water = 1:2.0:0.45. Add 1.0% of the cement mass of admixture (including 0.6% water-reducing agent and 0.4% water-retaining agent). Mix with a forced mixer for 5 minutes to make a uniform cement mortar with a consistency of 120 mm and an initial setting time of 4 hours. Inner wall spraying: Place the pipe on the tooling table and rotate it at a constant speed of 8 r / min. Maintain a distance of 30 cm between the spray gun and the inner wall of the pipe, spray pressure of 0.6 MPa, and axial movement speed of the spray gun of 0.4 m / s. A single spray forms a 4 mm thick inner lining base layer, and two sprays are used to complete a total thickness of 8 mm, with an interval of 60 min between coats; Smoothing and shaping: After spraying, start the tooling table for slow centrifugation treatment. The centrifugation speed is controlled at 30r / min for 5min. The centrifugal force makes the inner lining layer spread evenly, further improving the smoothness. Curing and solidification: Place the pipe in a humid environment with a relative humidity of 90% and a temperature of 60℃ for 8 hours, avoiding external interference.

[0019] The lining layer obtained in this embodiment has a thickness deviation of ±1mm, high surface flatness, no loose sand or cracks, excellent bonding strength, and significantly improved production efficiency.

[0020] Example 3: This embodiment is designed for large ductile iron pipes with a specification of DN1200. The total thickness of the cement mortar lining is 12mm to demonstrate the adaptability of this invention to large-specification pipes. The specific process steps are as follows: Pipe pretreatment: The inner wall of the DN1200 ductile iron pipe is cleaned and impurities are removed, and the surface unevenness value is controlled to be ≤10mm. The casting residue is removed by grinding to ensure that the roughness of the base material meets the requirements. Cement mortar preparation: Prepare raw materials according to the mass ratio of cement:medium sand:water = 1:2.2:0.48, add 0.8% of cement mass of admixture (including 0.5% water-reducing agent and 0.3% water-retaining agent), stir for 4.5 minutes to make a special mortar for spraying with a consistency of 140 mm and an initial setting time of 5 hours. Inner wall spraying: Place the pipe on the tooling table and rotate it at a speed of 6 r / min. The spray gun spacing is 25 cm, the spraying pressure is 0.5 MPa, and the axial movement speed of the spray gun is 0.3 m / s. A single spray forms a 4 mm thick inner lining base layer, and three sprays are used to complete a total thickness of 12 mm, with an interval of 40 min between layers to ensure tight bonding between layers; Smoothing and shaping: A combined processing method is adopted. First, slow centrifugation is performed (20 r / min for 8 min), and then fine smoothing is performed using the equipment-matched trowel to adapt to the shaping requirements of the elliptical tube and ensure uniform thickness. Curing and solidification: Curing at room temperature with a relative humidity of 95% for 10 hours, avoiding pipe handling, to promote the curing of the inner lining.

[0021] The inner lining layer prepared in this embodiment has a uniform thickness with a deviation controlled within ±1mm, no surface defects, and high bonding strength, verifying the good applicability of the present invention to large-diameter pipes.

[0022] The above embodiments demonstrate that, through precise parameter control, this invention can be adapted to ductile iron pipes of different specifications, achieving high-quality and high-efficiency preparation of the inner lining. Any modifications made within the spirit and principles of this invention are within the scope of protection of this invention.

[0023] Traditional centrifugal processes result in cement and water separation, leading to slurry accumulation on the inner lining surface, which is prone to powdering and detachment, necessitating an internal grinding process for remediation. This invention employs direct spraying technology, using axial and circumferential coordinated spraying (spray gun spacing 10–30 cm, pressure 0.3–0.8 MPa) to avoid material segregation and eliminate the problem of excessive surface slurry at its source. Combined with a smoothing and shaping process (slow centrifugation or mechanical smoothing), the internal grinding step is completely eliminated, increasing production efficiency by over 30% and significantly reducing process costs. Addressing the issue of uneven lining thickness caused by ovality deviation in ductile iron pipes, this invention achieves lining thickness deviation control within ±1 mm through layered spraying (single layer thickness 2–20 mm) and parameter adjustment (e.g., spray gun travel speed 0.2–1.0 m / s). The combined application of slow centrifugation (15-30 r / min) and trowel smoothing is particularly suitable for elliptical pipes, ensuring uniformity of the lining along the major and minor axes and resolving defects such as loose sand and internal cracks found in traditional processes. Pipe pretreatment controls inner wall undulations to ≤20 mm, enhancing the mechanical bonding between the mortar and the pipe. Admixtures (water-reducing and water-retaining agents, added at 0.5%-1.0%) optimize mortar workability and prevent segregation. Experiments show that the adhesion of the lining layer is improved by more than 10%, significantly extending the service life of the pipeline; mortar utilization reaches over 95%, reducing raw material waste; the elimination of the internal grinding process reduces energy consumption and dust pollution, meeting green production requirements. The process is highly adaptable to equipment, requiring only matching spraying equipment and tooling tables, without large-scale production line modifications, making it easy to promote in the industry; process parameters (such as mortar consistency 80-160 mm, curing humidity ≥90%) cover different pipe sizes from DN300 to DN1200, and its universality is verified through examples. The standardized operation process reduces reliance on personnel experience and facilitates large-scale application. Through innovative spraying process and multi-parameter synergistic control, this invention significantly outperforms traditional centrifugal processes in terms of quality, efficiency, cost, and environmental protection, providing an advanced solution for the preparation of ductile iron pipe linings.

[0024] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present 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 embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for spraying cement mortar lining of ductile iron pipes, characterized in that, Includes the following steps: S1. Pipe body pretreatment: Clean and remove impurities from the inner wall of the ductile iron pipe, removing floating rust, oil and impurities, and ensuring that the inner wall of the pipe is dry and free of protruding foreign objects. S2. Cement mortar preparation: Prepare cement, medium sand, and water or add admixtures according to the mass ratio, and stir to make a uniform, lump-free special cement mortar for spraying. The mortar consistency is controlled at 80-160mm, and the initial setting time is controlled at 3-6h. S3. Inner wall spraying: Place the pretreated ductile iron pipe on a special tooling table, and use a mortar spraying equipment to spray along the axial and circumferential directions of the pipe body. The distance between the spray gun and the inner wall of the pipe should be 10-30cm, and the spraying pressure should be controlled at 0.3-0.8MPa. A single spraying will form a cement mortar inner lining base with a thickness of 2-20mm. The total thickness of the spraying can be completed in one spraying or in layers. S4. Smoothing and shaping: During the spraying process, the trowel provided with the equipment is used to smooth the circumferential and axial lining of the pipe, or after spraying, the tooling table is started to perform slow centrifugation. The centrifugation speed is controlled at 15-30 r / min for 5-10 min to make the surface of the inner lining smooth and flat, and to eliminate spraying drips and unevenness. S5. Curing and solidification: Place the shaped ductile iron pipe in a curing furnace for curing to complete the preparation of the cement mortar lining.

2. The method for spraying cement mortar lining of ductile iron pipes according to claim 1, characterized in that, The mass ratio of cement mortar in S2 is cement: medium sand: water = 1:1.5~2.5:0.4~0.5, and the admixtures are water-reducing agent and water-retaining agent, with a total addition amount of 0.5%~1.0% of the cement mass.

3. The method for spraying cement mortar lining of ductile iron pipes according to claim 1, characterized in that, The mortar spraying equipment in S3 is a centrifugal spraying equipment for well chamber repair, equipped with a fan-shaped spray gun that can rotate 360°. During the spraying process, the spray gun moves at a constant speed of 0.2 to 1.0 m / s along the axial direction of the pipe.

4. The method for spraying cement mortar lining of ductile iron pipes according to claim 3, characterized in that, During the inner wall spraying in S3, the tube rotates at a constant speed of 5-8 r / min, and the interlayer interval of the layered spraying is controlled at 30-60 min.

5. The method for spraying cement mortar lining of ductile iron pipes according to claim 1, characterized in that, The slow centrifugation process and the smoothing process in S4 can be implemented separately or in combination. When implemented in combination, slow centrifugation is performed first, followed by fine smoothing.

6. The method for spraying cement mortar lining of ductile iron pipes according to claim 1, characterized in that, The relative humidity of the curing environment in S5 is controlled above 90%, and the pipe body is prevented from shaking and the inner lining layer is prevented from being impacted by external forces during the curing period.

7. The method for spraying cement mortar lining of ductile iron pipes according to claim 1, characterized in that, After the tube body pretreatment in S1, the allowable value for unevenness on the inner wall surface is ≤20mm.

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