Anti-cracking process method for aluminate cement lining of nodular cast iron pipe

Abstract

The invention discloses a nodular cast iron pipe aluminate cement lining anti-cracking process method, which comprises the following steps: S1, aluminate cement slurry preparation and centrifugal lining coating operation: preparing aluminate cement mortar according to a pipe type, and stirring cement, sand and water for 5-15 minutes according to a ratio at 800-1000r / min; according to the method disclosed by the invention, the stable conversion of hydration products is realized by accurately matching the proportions of slurry with different pipe diameters and sectional centrifugal lining coating parameters and combining a sectional low-temperature and high-humidity curing process, cracking caused by thermal stress and volume mutation is effectively avoided, and the occurrence rate of macroscopic cracks is reduced; the water-based epoxy waterproof coating is additionally arranged for protection, the solid content of the coating is larger than or equal to 50%, the adhesive force is larger than or equal to 3 MPa, rainwater and moisture permeation paths can be tightly blocked, the structural integrity of the pipeline in the long-term storage and severe environment is guaranteed, and the service life is prolonged; by setting accurate process parameters for the whole series of DN100-DN2600 cast pipes, special complex equipment is not needed, the method can be matched with an existing production line, and the landing cost is low.

Description

Technical Field

[0001] This invention relates to the field of ductile iron pipe technology, specifically to a process for preventing cracking of aluminate cement lining in ductile iron pipes. Background Technology

[0002] In the 21st-century water supply and drainage industry, centrifugal ductile iron pipes are a primary water transmission pipe material due to their high cost-effectiveness. They possess the inherent properties of iron and the performance of steel, exhibiting excellent corrosion resistance, good ductility, good sealing performance, and easy installation. They are mainly used for water supply, gas transmission, and oil transmission in municipal and industrial enterprises. Centrifugal ductile iron pipes are an important water transmission pipe material. Due to the low cost of cement mortar and the excellent bonding performance between the cement mortar layer and the pipe, cement mortar is the preferred filling material for the inner wall of pipes, making it the first choice for most ductile iron pipe manufacturers and water supply networks.

[0003] Currently, in the market, due to its properties such as aluminate cement resistance to sulfate attack (≥0.85) and strong resistance to bio-adhesion in corrosive conditions (e.g., high-sulfate wastewater and groundwater transportation in coastal areas), aluminate cement is widely used in the lining of ductile iron sewage pipes. This type of lined pipe is widely used in chemical industrial parks and coastal city pipe networks. However, in traditional processes, aluminate cement linings are prone to cracking after curing, and during pipe storage, rainwater can cause the hydration products of aluminate cement to shrink, leading to a network of fine cracks.

[0004] To address this, we have developed a process for preventing cracking of aluminate cement linings in ductile iron pipes. This process involves curing and coating to prevent cracking of the aluminate cement linings in ductile iron pipes. Summary of the Invention

[0005] The purpose of this invention is to provide a process for preventing cracking of aluminate cement linings in ductile iron pipes, so as 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 preventing cracking of aluminate cement lining in ductile iron pipes, comprising: S1. Preparation of aluminate cement slurry and centrifugal lining operation: The aluminate cement slurry is prepared according to the pipe type. Cement, sand and water are mixed at 800-1000 r / min for 5-15 minutes according to the proportion. Centrifugal lining operation: The slurry is injected into the pipe at a uniform speed and centrifugal lining is carried out in segments to control the thickness and deviation of the cement lining layer. S2, sequentially through the natural conditioning stage, the steam heating conditioning stage, the constant temperature and humidity conditioning stage, and the static cooling stage, precisely controlling the temperature, humidity, and time parameters of each stage; S3, the water-milling and finishing of the inner lining and the coating and curing stage, a water-based epoxy waterproof coating is applied to the surface of the inner lining after water milling and then cured. A reinforcing layer is applied to the surface of the water-milled inner lining and then cured.

[0007] Preferably, in the preparation of aluminate cement slurry, the sand-cement ratio is 1.3-1.6 when the pipe diameter is ≤DN600, 1.6-2.0 when the pipe diameter is DN700-DN1200, and 1.7-2.5 when the pipe diameter is ≥DN1200. The amount of water added is 0.35-0.5 of the cement ratio.

[0008] Preferably, the segmented centrifugation parameters for the centrifugal coating operation are: low speed centrifugation speed 100-300 r / min, coating time 0.5-2 minutes; medium speed centrifugation speed 600-800 r / min, coating time 0.5-3 minutes; and maximum speed 1000-1500 r / min, coating time 5-20 minutes.

[0009] Preferably, the thickness of the cement lining in the centrifugal coating operation is controlled as follows: 3.0mm-5.0mm for DN100-DN300, 3.5mm-6.0mm for DN350-DN600, 4.0mm-7.0mm for DN700-DN1200, 7.0mm-11.0mm for DN1400-DN2000, and 8.0mm-14.0mm for DN2200-DN2600, with a thickness deviation not exceeding ±0.5mm.

[0010] Preferably, during the natural curing stage, the cast pipe is placed in a curing furnace at 20-30℃ and 60%-70% relative humidity for 0-3 hours, with a curing time of 0-1 hour in summer and 3 hours in winter.

[0011] Preferably, during the steam heating and curing stage, the temperature is increased to 40-50℃ at a rate of 5-15℃ / hour for 2-3 hours, while maintaining a relative humidity of ≥90% inside the furnace; during the constant temperature and humidity curing stage, the temperature is maintained at 40-50℃ and the relative humidity is maintained at ≥90%, and curing continues for 2-3 hours.

[0012] Preferably, during the static cooling stage, the steam supply is turned off, the top cover of the curing furnace is opened, and the furnace is allowed to stand naturally for 0.5-1 hours to allow the temperature of the cast pipe and the inner lining to drop to a temperature difference of ≤5℃ with the external environment.

[0013] Preferably, the inner lining is finished by water grinding equipment to remove surface laitance, burrs and local protrusions, so that the surface flatness error of the inner lining is ≤0.3mm.

[0014] Preferably, the water-based epoxy waterproof coating is applied by high-pressure airless spraying or roller brushing. The solid content of the water-based epoxy waterproof coating is ≥50%, the coating thickness is 0.3-0.6mm, and it is cured by standing in a ventilated environment at 15-30℃ for 12-24 hours after application.

[0015] Preferably, the water-based epoxy waterproof coating is JT-212H water-based epoxy sealing paint, whose main components are: 20%-60% epoxy resin, 1%-10% propylene glycol methyl ether, 1%-15% additives, 0.1%-4% thickener, 10%-70% water, and 5%-30% epoxy curing agent. After curing, the coating adhesion is ≥3MPa.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) By accurately matching the slurry ratio of different pipe diameters and the segmented centrifugal coating parameters, combined with the "segmented low temperature and high humidity curing" process, the hydration products are stably converted, effectively avoiding cracking caused by thermal stress and volume change, reducing the incidence of visible cracks, and overcoming the pain points of traditional processes from the core link. (2) By adding a water-based epoxy waterproof coating, the coating has a solid content of ≥50% and an adhesion of ≥3MPa, which can strictly block the penetration path of rainwater and moisture, avoid the volume shrinkage caused by the secondary reaction of hydration products, ensure the structural integrity of the pipeline in long-term storage and harsh environment, and greatly extend the service life. (3) By setting precise process parameters for the entire series of cast iron pipes from DN100 to DN2600, no special or complex equipment is required. It can be adapted to existing production lines, is easy to operate, and has low implementation costs. Attached Figure Description

[0017] Fig. 1 This is a structural diagram of the inner lining pipe body of the aluminate cement lining coated pipe of the present invention; Fig. 2 This is a process flow diagram of the present invention.

[0018] In the diagram: 1. Reinforcing layer; 2. Water-polished inner lining; 3. Water-based epoxy waterproof coating. Detailed Implementation

[0019] 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.

[0020] Please see Figs. 1-2This invention provides a technical solution: a method for preventing cracking of aluminate cement lining in ductile iron pipes, comprising: S1, preparation of aluminate cement slurry and centrifugal coating operation; preparation of aluminate cement slurry: aluminate cement mortar is prepared according to the pipe type, and cement, sand and water are mixed at 800-1000 r / min for 5-15 minutes according to the proportion; centrifugal coating operation: the slurry is injected into the pipe at a uniform speed, and segmented centrifugal coating is performed to control the thickness and deviation of the cement lining layer; S2, sequentially through the natural conditioning stage, the steam heating conditioning stage, the constant temperature and humidity conditioning stage, and the static cooling stage, precisely controlling the temperature, humidity, and time parameters of each stage; S3, the inner lining water milling 2 finishing and coating application and curing stage, the water-based epoxy waterproof coating 3 is applied to the inner lining surface after the inner lining water milling 2 and cured, and the reinforcing layer 1 is applied to the inner lining water milling 2 and cured.

[0021] Preliminary preparation stage: Preparation of aluminate cement slurry: Aluminate cement mortar should be prepared according to the pipe type. For pipe diameter ≤ DN600, the sand-cement ratio is 1.3-1.6; for DN700-DN1200, the sand-cement ratio is 1.6-2.0; and for ≥ DN1200, the sand-cement ratio is 1.7-2.5. When the pipe specification is DN300, the ratio of cement, sand and water is cement:sand:water = 1:(1.4~1.5):(0.35~0.5). When the pipe specifications are DN500 or DN600, the ratio of cement, sand, and water is cement:sand:water = 1:(1.5~1.7):(0.35~0.5). When the pipe specification is DN1000, the ratio of cement, sand and water is cement:sand:water = 1:(1.7~1.9):(0.35~0.5). When the pipe specification is DN1400, the ratio of cement, sand and water is cement:sand:water = 1:(1.8~2.0):(0.35~0.5), where the amount of water added is 0.35-0.5 of the cement ratio. According to the ratio, the cement, sand and water are first stirred at 800-1000r / min for 5-15 minutes. After stirring, ensure that the slurry is free of lumps and has uniform fluidity, and then put the material onto the material placing vehicle to prepare for feeding into the pipe. Centrifugal lining operation: The stirred aluminate cement slurry is injected into the ductile iron pipe at a uniform speed and centrifuged in stages. The low speed centrifugation speed is maintained at 100-300 r / min and the lining time is 0.5-2 minutes. The medium speed centrifugation speed is maintained at 600-800 r / min and the lining time is 0.5-3 minutes. The maximum speed is maintained at 1000-1500 r / min and the lining time is 5-20 minutes. The thickness of the cement lining should be controlled as follows: 3.0mm-5.0mm for DN100-DN300 pipes, 3.5mm-6.0mm for DN350-DN600 pipes, 4.0mm-7.0mm for DN700-DN1200 pipes, 7.0mm-11.0mm for DN1400-DN2000 pipes, and 8.0mm-14.0mm for DN2200-DN2600 pipes, with a thickness deviation not exceeding ±0.5mm. After lining, the pipes should be placed in a curing furnace for curing.

[0022] Natural curing stage: After centrifugal coating, the cast pipe is placed in a curing furnace at 20-30℃ and 60%-70% relative humidity for 0-3 hours of natural curing (reduced to 0-1 hour in summer and extended to 3 hours in winter). The optimal curing time is 0 hours in summer and 2 hours in winter. This allows the slurry to initially solidify and set, preventing flow or local accumulation during subsequent heating.

[0023] Steam heating and curing stage: Saturated steam is introduced into the furnace for slow heating, with the heating rate controlled at 5-15℃ / hour. The furnace temperature is raised to 40-50℃ in 2-3 hours (the low temperature range can reduce the concentrated release of hydration heat). The optimal heating rate is controlled at 5℃ / hour, with a heating time of 3 hours and a curing temperature of 40℃. At the same time, the relative humidity in the furnace is maintained at ≥90% (the high humidity environment inhibits the rapid evaporation of moisture on the cement surface, avoids surface shrinkage cracks, and provides sufficient moisture for the hydration reaction).

[0024] Constant temperature and humidity curing stage: Maintain a stable furnace temperature of 40-50℃ and relative humidity of ≥90% for 2-3 hours. The optimal temperature is 40℃ and the curing time is 3 hours. This ensures full hydration of aluminate cement, promotes the stable transformation of hydration products, and reduces metastable CAH. 10 The volumetric abrupt changes during the transition from C2AH8 to steady-state C3AH6 and AH3.

[0025] During the settling and cooling stage: turn off the steam supply, open the top cover of the curing furnace, and let the cast pipe stand naturally in the furnace for 0.5-1 hour. The optimal settling time is 1 hour, so that the temperature of the cast pipe and the inner lining can slowly drop to close to the ambient temperature (temperature difference ≤5℃) to avoid thermal stress cracks caused by excessive temperature difference when directly taken out of the furnace.

[0026] After curing using this process, the incidence of visible cracks in the aluminate cement lining during the initial curing stage decreased from 9.8% in the traditional process (natural curing for 3 hours, heating for 2 hours, constant temperature curing for 3 hours, curing temperature 60℃, and standing time for 0.5 hours) to 0.1%, and the proportion of microcracks (width < 0.01mm, cracks that cannot be observed with the naked eye) was also controlled to within 5%.

[0027] The experimental curing parameters were: natural curing for 0 hours, heating for 2 hours, constant temperature curing for 3 hours, curing temperature 40℃, and settling time for 1 hour. The experiments were conducted using the same tube type, cement ratio, and lining parameters, with the only difference being the curing parameters. Both curing parameters were tested on 26 batches of tubes, totaling 520 tubes. Crack detection was performed using a high-precision film comparison card before the tubes were stored and loaded onto trucks.

[0028] After water grinding, a waterproof coating is added to block the path of rainwater penetration. The specific steps are as follows: Water grinding and finishing of the inner lining: After curing, the surface of the cement inner lining is ground with water grinding equipment to remove surface laitance, burrs and local protrusions, so that the surface flatness error of the inner lining is ≤0.3mm.

[0029] Coating application stage: After the inner lining has dried naturally or by baking after water grinding 2, apply a water-based epoxy waterproof coating 3 (Jitai-water-based epoxy sealing paint JT-212H, main components: epoxy resin 20%-60%, propylene glycol methyl ether 1%-10%, additives 1%-15%, thickener 0.1%-4%, water 10%-70%, epoxy curing agent 5%-30%) to its surface using high-pressure airless spraying or roller application. The coating solid content should be ≥50%, and the spraying thickness should be controlled at 0.3-0.6mm to ensure uniform coverage without any missed spraying or sagging.

[0030] Coating curing stage: Place the coated cast pipe in a well-ventilated environment at 15-30℃ and let it stand for 12-24 hours to allow the waterproof coating to fully cure (the optimal parameters are 16 hours at 30℃ with a thickness of 0.4mm). After curing, the coating adhesion is ≥3MPa (pull-out test), which can effectively prevent rainwater and moisture from penetrating into the lining and avoid the formation of network-like microcracks in the aluminate cement lining due to volume shrinkage caused by secondary reactions of hydration products during storage.

[0031] The thickness of the reinforcing layer of ductile iron pipe is as follows: 4.7mm-5.6mm for pipe specifications DN100-DN300, 6.0mm-8.0mm for pipe specifications DN350-DN600, 8.8mm-12.8mm for pipe specifications DN700-DN1200, 14.4mm-19.2mm for pipe specifications DN1400-DN2000, and 20.8mm-24.0mm for pipe specifications DN2200-DN2600. The thickness of the aluminate cement layer (i.e., the inner lining water mill 2) is as follows: when the cast pipe specification is DN100-DN300, the thickness is 3.0mm-5.0mm; when the cast pipe specification is DN350-DN600, the thickness is 3.5mm-6.0mm; when the cast pipe specification is DN700-DN1200, the thickness is 4.0mm-7.0mm; when the cast pipe specification is DN1400-DN2000, the thickness is 7.0mm-11.0mm; and when the cast pipe specification is DN2200-DN2600, the thickness is 8.0mm-14.0mm. Water-based epoxy waterproof coating 3, with a thickness of 0.3mm-0.6mm.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preventing cracking of aluminate cement lining in ductile iron pipes, characterized in that, include: S1. Preparation of aluminate cement slurry and centrifugal lining operation: The aluminate cement slurry is prepared according to the pipe type. Cement, sand and water are mixed at 800-1000 r / min for 5-15 minutes according to the proportion. Centrifugal lining operation: The slurry is injected into the pipe at a uniform speed and centrifugal lining is carried out in segments to control the thickness and deviation of the cement lining layer. S2, sequentially through the natural conditioning stage, the steam heating conditioning stage, the constant temperature and humidity conditioning stage, and the static cooling stage, precisely controlling the temperature, humidity, and time parameters of each stage; S3, Inner lining water milling (2) finishing and coating application and curing stage, water-based epoxy waterproof coating (3) is applied to the inner lining surface after inner lining water milling (2) and cured, and a reinforcing layer (1) is applied to the inner lining surface after inner lining water milling (2) and cured.

2. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: In the preparation of aluminate cement slurry, the sand-cement ratio is 1.3-1.6 when the pipe diameter is ≤DN600, 1.6-2.0 when the pipe diameter is DN700-DN1200, and 1.7-2.5 when the pipe diameter is ≥DN1200. The amount of water added is 0.35-0.5 of the cement ratio.

3. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: The segmented centrifugation parameters for centrifugal coating operations are as follows: low speed centrifugation speed 100-300 r / min, coating time 0.5-2 minutes; medium speed centrifugation speed 600-800 r / min, coating time 0.5-3 minutes; maximum speed 1000-1500 r / min, coating time 5-20 minutes.

4. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: The thickness of the cement lining in centrifugal coating operations is controlled as follows: DN100-DN300: 3.0mm-5.0mm, DN350-DN600: 3.5mm-6.0mm, DN700-DN1200: 4.0mm-7.0mm, DN1400-DN2000: 7.0mm-11.0mm, DN2200-DN2600: 8.0mm-14.0mm, with a thickness deviation not exceeding ±0.5mm.

5. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: During the natural curing stage, the cast pipe is placed in a curing furnace at 20-30℃ and 60%-70% relative humidity for 0-3 hours. In summer, the curing time is 0-1 hour, and in winter, the curing time is 3 hours.

6. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: During the steam heating and curing stage, the temperature is increased to 40-50℃ at a rate of 5-15℃ / hour for 2-3 hours, while maintaining a relative humidity of ≥90% inside the furnace; during the constant temperature and humidity curing stage, the temperature is maintained at 40-50℃ and the relative humidity is ≥90%, and curing continues for 2-3 hours.

7. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: During the static cooling stage, turn off the steam supply, open the top cover of the curing furnace, and let it stand naturally for 0.5-1 hours to allow the temperature of the cast pipe and the inner lining to drop to a temperature difference of ≤5℃ with the outside environment.

8. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: (2) The inner lining is finished by using a water grinding machine to remove surface slurry, burrs and local protrusions, so that the surface flatness error of the inner lining is ≤0.3mm.

9. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: The water-based epoxy waterproof coating (3) is applied by high-pressure airless spraying or roller brushing. The solid content of the water-based epoxy waterproof coating (3) is ≥50%, the coating thickness is 0.3-0.6mm, and it is cured by standing in a ventilated environment at 15-30℃ for 12-24 hours after application.

10. The anti-cracking process for aluminate cement lining of ductile iron pipes according to claim 1, characterized in that: The water-based epoxy waterproof coating (3) is JT-212H water-based epoxy sealing paint, whose main components are: epoxy resin 20%-60%, propylene glycol methyl ether 1%-10%, additives 1%-15%, thickener 0.1%-4%, water 10%-70%, epoxy curing agent 5%-30%, and the coating adhesion after curing is ≥3MPa.

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