A water meter pipe body, a water meter and a casting method thereof

Abstract

This invention discloses a water meter pipe body, a water meter, and its casting method, belonging to the field of precision casting technology for water meters. The water meter pipe body is an integrated cast structure, including a main body, an inlet end, an outlet end, and a transducer mounting base. The interior features a circular, uniform cross-section flow channel with straight-section rectifying structures at both ends. The inner hole of the transducer mounting base is flush with the inner wall of the flow channel, with rounded corners and process grooves at the root. The wall thickness is uniform and features a slope transition. The pipe body is made of modified austenitic stainless steel, with Al deoxidation and Ti micro-alloying to improve density and corrosion resistance. The casting method employs a composite mold of coated sand and metal molds, medium-frequency refining, inert gas blowing degassing, and a five-stage low-pressure casting process, combined with chilling and heat-insulating risers to achieve sequential solidification. This invention can significantly reduce porosity and shrinkage defects, improve dimensional accuracy, reduce internal roughness, and increase yield.

Description

Technical Field

[0001] This invention belongs to the field of water meter manufacturing and precision casting technology, specifically referring to a water meter tube body, a water meter, and its casting method. Background Technology

[0002] Ultrasonic water meters are core equipment in water metering systems. Their tubes, as key components carrying the transducer and constructing the measurement flow channel, directly determine the meter's measurement accuracy, sealing reliability, and service life through their structural design and manufacturing quality. Regarding materials, current water meter tubes are typically cast from standard grades of stainless steel (such as 304 stainless steel) or ordinary brass (such as H62 brass), directly adopting the standard range of common commercial grades without specific composition optimization for the particular operating conditions and casting process requirements of the water meter tube. In terms of manufacturing processes, mass production of these tubes often employs sand casting or gravity casting, relying on the natural flow of molten metal under gravity to complete cavity filling and solidification shrinkage.

[0003] However, from the perspective of material and process compatibility, gravity casting using conventional alloy compositions suffers from poor controllability of the filling process: the molten metal easily traps gas in the mold cavity, and due to insufficient feeding capacity during the solidification and shrinkage stage, internal defects such as porosity, shrinkage cavities, and shrinkage porosity are formed in the wall thickness variation area. As a result, the dimensional accuracy of the casting can usually only reach CT8 to CT10 level, and the surface roughness of the inner cavity can reach Ra12.5μm or more. This not only requires a lot of subsequent machining and finishing, but also leads to low material utilization. In addition, it is difficult to achieve system integration of strengthening feeding methods such as chilling and riser feeding under gravity casting conditions. Summary of the Invention

[0004] This invention provides a water meter pipe body, a water meter, and a casting method thereof, aiming to solve the technical problems of existing ultrasonic water meter pipe bodies, which are made of conventional commercial stainless steel and have not been optimized for casting process requirements, resulting in many internal defects, low dimensional accuracy, and insufficient material utilization. It also addresses the technical problems of uncontrollable filling and insufficient feeding in traditional casting methods, which lead to poor casting density.

[0005] The technical solution adopted by the present invention is as follows: The first aspect provides a water meter pipe body, including a pipe body body, an inlet end, an outlet end, and a transducer mounting base. The pipe body body, the inlet end, the outlet end, and the transducer mounting base are integrally cast structures. The interior of the pipe body body is a circular flow channel with equal cross-section. Both the inlet end and the outlet end are provided with straight section rectification structures. The bottom of the inner hole of the transducer mounting base is flush with the inner wall of the flow channel, and the root of the mounting base is provided with a rounded transition. The main body of the pipe has a uniform wall thickness, and the wall thickness changes are transitioned by a slope. The main body of the tube is made of austenitic stainless steel alloy, and the composition of the alloy by mass percentage is: C≤0.08%, Si≤1.0%, Mn≤2.0%, Cr18.0%~20.0%, Ni8.0%~11.0%, Al0.1%~0.2%, Ti0.05%~0.1%, with the balance being Fe and unavoidable impurities.

[0006] Furthermore, the Al content is 0.12% to 0.18%.

[0007] Furthermore, the content of Ti is 0.06% to 0.09%.

[0008] The second aspect provides a water meter, comprising a water meter tube body as described in any one of claims 1 to 3, a transducer installed in a transducer mounting base in the water meter tube body, a metering circuit electrically connected to the transducer, and a display device for displaying measurement results.

[0009] The third aspect provides a casting method for the water meter pipe body as described above, including the following steps: Furnace charge pretreatment steps: The furnace charge is cleaned and then dried; Melting and composition control steps: Melt the furnace charge in a medium-frequency induction melting furnace at a melting temperature of 1550℃~1600℃ and hold for 10~15 minutes. Add aluminum for deoxidation treatment to make the aluminum content in the melt 0.1%~0.2%. Add titanium for micro-alloying treatment to make the titanium content in the melt 0.05%~0.1%. Use inert gas rotary blowing to degas for 5~8 minutes. After slag removal, let stand for 5~10 minutes. The casting preparation steps are as follows: A composite casting mold of coated sand and metal mold is used. Chills are placed at the corresponding positions at the root of the transducer mounting base, and heat-insulating risers are placed above the hot spot. Low-pressure casting process: Casting is carried out using a low-pressure casting machine, and the pressure and time are controlled according to the process curve of liquid raising, mold filling, pressurization, pressure holding and pressure release. Cooling, demolding and post-processing steps: After depressurization, cool to room temperature for demolding, remove the gating and riser, and perform surface treatment on the inner wall of the runner.

[0010] Furthermore, in the smelting and composition control steps, the order of adding materials is scrap steel → recycled material → ferrochrome → ferronickel → ferromanganese → ferrosilicon → aluminum → titanium. Aluminum is added 3 to 5 minutes before tapping, and titanium is added 1 to 2 minutes before tapping.

[0011] Furthermore, in the mold preparation step, the coated sand is made by hot mixing and coating process of 70 / 140 mesh quartz sand and phenolic resin powder. The phenolic resin content of the coated sand is 1.5% to 2.5%. The coated sand is filled into a metal mold heated to 200℃ to 250℃ and cured to form a coated sand shell mold. The cavity is coated with an alcohol-based zircon powder coating, with a total coating thickness of 0.2 mm to 0.3 mm; The parting surface is provided with venting grooves with a depth of 0.5mm to 1mm; The chills are made of HT200 material and are 1.5 to 2 times the thickness of the casting wall. The diameter of the insulation riser is 1.5 to 1.8 times the diameter of the thermal section.

[0012] Furthermore, in the low-pressure casting step, the mold preheating temperature is 200℃~300℃, the mold temperature is 150℃~250℃; the liquid lifting pressure is 0.01~0.02MPa, time is 5~8s, the filling pressure is 0.02~0.05MPa, time is 10~15s, the filling speed is 0.05~0.1m / s, the pressure boosting pressure is 0.05~0.08MPa, time is 3~5s, the holding pressure is 0.08MPa, time is 120~180s, and the pressure release time is 5~10s.

[0013] Beneficial effects: The water meter pipe body provided in this application is made of austenitic stainless steel alloy. The final deoxidation treatment by adding aluminum reduces the oxygen content of the melt to below 30 ppm, effectively reducing oxide inclusion defects in the casting. The addition of titanium for microalloying treatment allows titanium to form fine TiN and TiC particles with nitrogen and carbon in the melt. During solidification, these particles act as heterogeneous nucleation cores, improving the solidification and feeding ability of the alloy, while fixing free nitrogen and preventing grain boundary embrittlement.

[0014] In terms of manufacturing process, this application adopts a composite casting method that combines low-pressure filling with chilling and feeding via insulating risers. The pressure and time of the low-pressure filling process are controllable, and the molten metal fills the cavity smoothly in a laminar flow state under pressure, which significantly reduces filling defects such as porosity and inclusions. Chills are set at hot spots such as the root of the transducer mounting base to force this area to cool and solidify first. Combined with the continuous feeding via the insulating risers above under the holding pressure, sequential solidification conditions conducive to obtaining a dense structure are established.

[0015] Through the synergistic effect of the alloy composition, tube structure characteristics, and casting process, the internal defect rate of the tube casting is reduced, the dimensional accuracy is improved, and the material utilization rate is effectively increased. Attached Figure Description

[0016] Figure 1 This is a perspective view of the casting structure of the main body of the pipe proposed in an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of the main structure of the central tube; Figure 3 This is a schematic diagram of the casting method for the water meter pipe body proposed in an embodiment of the present invention.

[0017] Among them, 1. top riser; 2. main gating system; 3. main body of the pipe; 31. water inlet end; 32. water outlet end; 33. transducer mounting base; 4. branch gating system.

[0018] The accompanying drawings are provided to further understand the embodiments and form part of the specification. They are used together with the embodiments for explanation and do not constitute a limitation on the embodiments. Detailed Implementation

[0019] The technical solutions in 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, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0020] In the description of the embodiments, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments.

[0021] Existing water meter pipes are typically cast from conventional commercial-grade stainless steel. The material composition is not optimized for low-pressure casting processes and the operating conditions of water meters. This results in high oxygen content in the molten metal and coarse grains in the as-cast state, leading to numerous internal porosity and inclusion defects in the casting, insufficient feeding capacity, and difficulty in achieving a balance between mechanical properties and corrosion resistance. To address these issues, this application provides a water meter pipe body, a water meter, and a casting method thereof.

[0022] like Figure 2 As shown, a water meter pipe body includes a main body 3, an inlet end 31, an outlet end 32, and a transducer mounting base 33. The main body 3 is the middle section of the pipe body, forming a measuring flow channel for fluid passage, with its axis extending horizontally. The inlet end 31 and the outlet end 32 are located at opposite ends of the main body 3, used for connection to an external piping system. The main body 3, inlet end 31, outlet end 32, and transducer mounting base 33 are integrally cast structures, meaning that all parts are simultaneously filled and solidified by the same alloy molten metal in the same casting process, with no threaded connections, welding, or adhesive bonding interfaces between them. This integral molding method eliminates assembly gaps at the manufacturing stage, ensuring the integrity and uniformity of the structure.

[0023] Inside the main body 3 is a circular, uniform cross-section flow channel. The circular cross-section facilitates uniform fluid filling within the channel. The uniform cross-section design ensures a constant channel diameter within the measuring section, consistent with the nominal diameter of the pipe body, thus avoiding flow field disturbances and pressure losses caused by diameter changes. Both the inlet end 31 and the outlet end 32 are equipped with straight-section rectification structures. The rectification section at the inlet end 31 eliminates swirling and asymmetrical flow introduced by upstream bends or valves, while the rectification section at the outlet end 32 prevents backflow interference at the measuring section outlet from propagating upstream, thereby establishing a stable and fully developed velocity profile within the measuring section.

[0024] The bottom of the inner hole of the transducer mounting base 33 is flush with the inner wall of the flow channel, meaning that the lower end face of the inner hole of the transducer mounting base 33 and the inner wall of the flow channel are on the same cylindrical surface, without forming bosses or pits, ensuring that there are no non-counting reflection interfaces on the ultrasonic wave propagation path. The root of the mounting base is provided with a rounded transition, with a rounded radius of not less than 3mm, to reduce stress concentration caused by abrupt changes in cross-section, and to facilitate the filling and solidification of molten metal during the casting process.

[0025] The main body of the pipe has a uniform wall thickness, and the difference in wall thickness at various points in the main body of the pipe does not exceed 10% of the average wall thickness. When the nominal wall thickness of the pipe is 3.5 mm, the actual wall thickness is allowed to be within the range of 3.15 mm to 3.85 mm. A slope transition is adopted at the wall thickness change points, and the slope is not greater than 1:3. That is, for every 1 mm increase in wall thickness, the length of the transition section is not less than 3 mm to avoid the formation of hot spots due to abrupt changes in local cross-section.

[0026] A process groove is provided at the root of the transducer mounting base 33. This groove extends circumferentially around the root of the transducer mounting base 33, with a rectangular cross-section. It divides the hot spot, which was originally concentrated in the thick cross-section at this location, into smaller hot spot areas, ensuring that the diameter of the hot spot circle does not exceed 1.5 times the thickness of the main body wall. The hot spot circle refers to the largest inscribed circle that can be drawn within the cross-section of the casting. The larger the diameter of this circle, the greater the tendency to form shrinkage cavities and porosity during solidification. The function of the process groove is to divide the large hot spot, originally concentrated at the root, into smaller hot spot areas.

[0027] The pipe body is made of austenitic stainless steel alloy. By mass percentage, the alloy composition is: C≤0.08%, Si≤1.0%, Mn≤2.0%, Cr18.0%~20.0%, Ni8.0%~11.0%, Al0.1%~0.2%, Ti0.05%~0.1%, with the balance being Fe and unavoidable impurities. This composition design is optimized based on standard 304 stainless steel: the carbon content is strictly controlled below 0.08%, which effectively suppresses Cr... 23The precipitation of C5 at grain boundaries prevents intergranular corrosion caused by chromium depletion, ensuring the long-term reliability of the pipe in tap water and slightly chlorinated water media. A chromium content of 18.0%–20.0% ensures the formation of a continuous and dense Cr2O3 passivation film on the stainless steel surface, providing basic corrosion resistance. A nickel content of 8.0%–11.0% stabilizes the austenite phase, maintaining the face-centered cubic structure of the pipe at room temperature, resulting in good toughness and machinability. Silicon and manganese are conventional deoxidizing and desulfurizing elements, controlled within their upper limits to avoid excessive non-metallic inclusions. The addition of aluminum is 0.1%–0.2%. Aluminum reacts with dissolved oxygen in the molten metal to form Al2O3, primarily acting as a final deoxidizer, reducing the oxygen content of the molten metal to below 30 ppm, significantly reducing oxide inclusions in the casting; simultaneously, Al2O3 can serve as a heterogeneous nucleation site during solidification, promoting the formation of equiaxed crystals. The amount of titanium added is 0.05% to 0.1%. In the melt, titanium preferentially combines with nitrogen and carbon to form fine TiN and TiC particles, which play a heterogeneous nucleation role during solidification, refining the grain size to ASTM 4-6 grade; at the same time, it fixes the free nitrogen in the melt and prevents strain-aging embrittlement caused by nitrogen segregation at the grain boundaries.

[0028] In the above structure, aluminum is added to the alloy for deoxidation during smelting, and titanium microalloying treatment is used to obtain high purity and fine grain structure of the alloy. When the tube body is subsequently prepared by integral casting molding process, good casting processability is ensured by composition control. After molding, all parts of the tube body are a continuous and unified whole of materials, which improves the product yield and extends the product service life.

[0029] In use, the fluid enters the measuring section from the inlet end 31 through the rectifying section, forming a stable flow velocity distribution; the transducer in the transducer mounting base 33 emits and receives ultrasonic signals, the signals are reflected and propagated between the inner walls of the flow channel, and are received by the transducer after passing through the fluid. The flow rate is calculated by measuring the propagation time difference between the downstream and upstream flows.

[0030] The beneficial effects of this tube structure are as follows: through the targeted design of the alloy composition, it ensures good fluidity and solidification feeding ability of the molten metal during the low-pressure filling process, while giving the tube sufficient corrosion resistance and mechanical properties; the integrated structure eliminates assembly gaps at the source, avoiding reflection and attenuation of ultrasonic signals at the interface; the transducer mounting base 33 cooperates with the rectifier section to make the flow field in the measurement section more uniform, and the measurement accuracy can be improved from Class B to Class A; the uniform wall thickness design, the root rounded corner transition and the combined setting of the process groove actively suppress the casting hot spot from the structural design point, forming a synergistic effect with the alloy composition optimization, providing dual material and structural guarantees for achieving high-quality castings.

[0031] To further optimize the deoxidation and grain refinement effects of the alloy, the Al content is 0.12%–0.18%. Within this range, the deoxidation effect of aluminum is sufficient, and the residual aluminum content is moderate. This ensures that the oxygen content of the melt is stably controlled below 30 ppm, without generating excessive chain-like Al2O3 inclusions due to excessive aluminum, which would affect the melt fluidity and casting toughness. The Ti content is 0.06%–0.09%. Within this range, titanium can form a sufficient number of TiN and TiC heterogeneous nucleation particles, refining the as-cast grains to ASTM 5-6 grade. At the same time, the addition of titanium will not be too high, causing TiN particles to coarsen and lose the refining effect.

[0032] Furthermore, this application also provides a water meter, including a water meter pipe body as described above, a transducer installed in a transducer mounting base 33 within the water meter pipe body, a metering circuit electrically connected to the transducer, and a display device for displaying measurement results. The transducer is a piezoelectric ceramic ultrasonic transducer, which is pushed in from the mounting base opening during installation until the corresponding stepped surface on its outer shell abuts against the stop surface of the positioning boss inside the mounting base, achieving precise axial positioning. The metering circuit includes an ultrasonic transmitting and receiving circuit, a time measurement circuit, and a flow calculation and processing unit, used to calculate instantaneous flow rate and cumulative flow rate based on the propagation time difference between downstream and upstream flows. The display device is a liquid crystal display screen used to display information such as instantaneous flow rate, cumulative flow rate, and operating status.

[0033] When the water meter is working, the metering circuit controls the transducer to emit ultrasonic pulses. The signal passes through the fluid medium in the flow channel and is received by the transducer. The metering circuit measures the propagation time difference between the upstream and downstream flows, calculates the fluid velocity and flow rate, and outputs the measurement results on the display device.

[0034] Traditional gravity casting processes, even with integrated structural designs, result in pipe bodies where the filling speed is uncontrollable due to reliance on the molten metal's own gravity to fill the mold cavity. This makes the molten metal prone to trapping gas and forming pores. Furthermore, during solidification, feeding relies solely on riser static pressure, leading to premature closure of the feeding channels and shrinkage cavities and porosity at hot spots. To fully leverage the advantages of an integrated pipe body structure and optimized alloy composition, this application provides a casting method for water meter pipe bodies.

[0035] like Figures 1-3 As shown, a casting method for a water meter pipe body includes the following steps: furnace charge pretreatment step, smelting and composition control step, mold preparation step, low-pressure casting step, cooling demolding and post-treatment step.

[0036] Furnace charge pretreatment steps: The furnace charge is cleaned and then dried. The cleaning method is shot blasting, using high-speed steel shot to remove oxide scale and oil stains from the surface of the furnace charge. The drying temperature is 150℃ to 200℃, and the drying time is more than 2 hours. The proportion of recycled material should not exceed 30%. The recycled material needs to be magnetically separated to remove any iron filings that may be mixed in. The purpose of limiting the proportion of recycled material is to prevent the loss of alloying elements and the accumulation of inclusions caused by repeated remelting.

[0037] Drying removes adsorbed moisture from the surface of the furnace charge, preventing it from decomposing during smelting and releasing hydrogen atoms into the molten metal, thus creating hydrogen pores. Preheating and cleaning the furnace charge before smelting is fundamental to ensuring the purity of the molten metal.

[0038] Melting and composition control steps: Melt the furnace charge in a medium-frequency induction melting furnace at a melting temperature of 1550℃ to 1600℃ and hold for 10 to 15 minutes. Add aluminum for deoxidation treatment to make the aluminum content in the melt 0.1% to 0.2%. Add titanium for microalloying treatment to make the titanium content in the melt 0.05% to 0.1%. Use inert gas rotary blowing to degas for 5 to 8 minutes. After slag removal, let stand for 5 to 10 minutes.

[0039] By controlling the melting temperature within the range of 1550℃ to 1600℃, which is 100℃ to 150℃ higher than the liquidus temperature of 304 series austenitic stainless steel (approximately 1450℃ to 1500℃), the provided superheat ensures sufficient diffusion and dissolution of alloying elements and homogenization of the melt composition. At the same time, the temperature not exceeding 1600℃ avoids excessive burning of easily oxidized elements such as chromium and titanium, as well as excessive erosion of the furnace lining material by the melt.

[0040] The purpose of holding the furnace at room temperature for 10-15 minutes is to ensure that all alloying elements in the molten metal are fully homogenized. The order of charging is scrap steel → recycled material → ferrochrome → ferronickel → ferromanganese → ferrosilicon → aluminum → titanium. Charges with high melting points and less prone to burn-off should be added first. Aluminum should be added 3-5 minutes before tapping, and titanium should be added 1-2 minutes before tapping to reduce the loss of aluminum and titanium. Aluminum reacts with dissolved oxygen in the molten metal to form Al2O3, most of which floats to the slag layer. A residual aluminum content of 0.1% to 0.2% ensures thorough deoxidation without producing excessive chain-like Al2O3 inclusions.

[0041] Titanium preferentially reacts with nitrogen and carbon in the molten steel to generate fine TiN and TiC particles. These particles act as heterogeneous nucleation sites during the solidification process of molten steel, which can refine the solidification structure.

[0042] Argon is used as the inert gas. During the rotary injection, the argon pressure is 0.2 MPa to 0.3 MPa and the flow rate is 3 to 5 L / min. The large number of tiny bubbles generated by the rotation carry out the dissolved hydrogen and other gases in the melt during the rising process. At the same time, they adsorb the suspended oxides and impurities and float to the surface of the liquid to form a slag layer.

[0043] After slag removal, allow the mixture to stand for 5 to 10 minutes to allow small inclusions to continue to float to the surface and the molten metal temperature to become more uniform. In practical applications, the specific amount added and the processing time can be finely adjusted within a given range according to the state of the furnace charge and the molten metal; this application does not limit this.

[0044] Mold preparation steps: A composite assembly of a coated sand shell mold and metal mold inserts is used. Chills are placed at the corresponding positions at the base of transducer mounting seat 33, and an insulating riser is placed above the hot spot. The mold cavity is coated with alcohol-based zircon powder paint, with a total coating thickness of 0.2mm to 0.3mm, applied in two coats, and then ignited and dried. The zircon powder paint has high refractoriness and good thermochemical stability, preventing sand adhesion and chemical sand adhesion on the surface of the stainless steel casting.

[0045] 70 / 140 mesh quartz sand is preheated to 140℃~160℃, 2.0% phenolic resin powder and 12% hexamethylenetetramine curing agent are added, and the mixture is hot-mixed in a sand mixer for 60~90 seconds to melt the resin and uniformly coat the surface of the sand particles. After cooling, the sand particles are crushed and screened to obtain coated sand particles.

[0046] The coated sand is filled into a metal mold preheated to 220°C. Upon heating, the resin in the coated sand melts and begins to solidify. After holding the mold under pressure for 90 seconds, it is demolded to obtain a coated sand shell. The shell is 6mm–8mm thick, with a smooth cavity surface and high dimensional accuracy.

[0047] The parting surface is equipped with venting grooves with a depth of 0.5mm to 1mm to expel gas from the mold cavity and prevent air from forming pores during filling.

[0048] Specifically, the chills are made of HT200 material and are 1.5 to 2 times the thickness of the casting wall. The surface of the chills is coated with aluminum powder to prevent carburization. The chills are used to rapidly cool the hot spot area at the root of the transducer mounting base 33, accelerate heat dissipation, and establish a temperature gradient pointing towards the riser.

[0049] The diameter of the heat-insulating riser is 1.5 to 1.8 times that of the hot spot. The use of an exothermic heat-insulating riser sleeve can maintain the liquid state of the molten metal inside the riser for a longer period of time, providing a feeding flow for the solidification and shrinkage of the casting below.

[0050] In practical applications, the specific dimensions of the chills and the specifications of the risers can be adjusted within a given range according to the specifications of the castings, and the embodiments of this application do not limit this.

[0051] Low-pressure casting process: Casting is carried out using a low-pressure casting machine, and the pressure and time are controlled according to the process curve of liquid raising, mold filling, pressurization, pressure holding and pressure release.

[0052] The low-pressure casting machine includes a sealed crucible and a riser pipe. The sealed crucible contains molten metal that has been properly melted. The lower end of the riser pipe is inserted below the surface of the molten metal, and the upper end is connected to the mold gate.

[0053] During casting, dry, oil-free compressed air (dew point ≤ -20℃) is introduced into the crucible, and the pressure is controlled between 0.4MPa and 0.6MPa.

[0054] The preheating temperature of the casting mold is 200℃ to 300℃, and the mold temperature is 150℃ to 250℃. The liquid rise pressure is 0.01MPa to 0.02MPa, and the time is 5s to 8s, so that the molten metal rises steadily in the riser at a speed of 30mm / s to 50mm / s, avoiding excessive pressure that could cause violent fluctuations in the liquid surface and air intake.

[0055] The filling pressure is 0.02MPa to 0.05MPa, the time is 10s to 15s, and the filling speed is 0.05m / s to 0.1m / s. Within this speed range, the molten metal fills the cavity from bottom to top in a laminar flow state. The Reynolds number is controlled below 2000 to avoid air entrapment and oxide entrapment.

[0056] The pressure is increased from 0.05MPa to 0.08MPa for 3s to 5s. After filling, the pressure is rapidly increased within 3s to 5s to make the molten metal in the riser exert a greater feeding pressure on the casting and drive the feeding fluid to flow to the hot spot area.

[0057] The holding pressure is 0.08 MPa and the time is 120 to 180 seconds, which is maintained until the gate is completely solidified. For stainless steel tubes with a wall thickness of 3 mm to 4 mm, the gate solidification time is about 90 to 120 seconds. The holding time is increased by 30 to 60 seconds on this basis to ensure that the feeding channel is fully effective.

[0058] The pressure relief time is 5 to 10 seconds. The pressure relief is carried out in stages and slowly. For example, first reduce the pressure from 0.08 MPa to 0.04 MPa and hold for 3 seconds, then reduce it to 0.02 MPa and hold for 2 seconds, and finally completely relieve the pressure. This avoids pressure changes that could cause backflow or thermal cracking in the incompletely solidified liquid phase inside the casting due to pressure difference.

[0059]

[0060] Cooling, demolding, and post-processing steps: After depressurization, the strip mold is cooled to below 150℃ before demolding. The cooling time is 300 to 400 minutes. Slow cooling of the strip mold can avoid casting deformation and thermal cracking caused by thermal stress due to high-temperature mold opening. After removing the gating gates, risers, and burrs, the inner wall of the runner is subjected to abrasive flow extrusion grinding and polishing treatment. The semi-solid medium containing abrasive particles is repeatedly extruded in the runner by pressure. The abrasive particles remove the oxide layer and micro-protrusions on the casting surface by micro-cutting action on the tube wall. The surface roughness Ra of the treated inner cavity can reach below 3.2μm.

[0061] During operation, the clean molten metal after melting and refining is smoothly filled into the mold cavity from bottom to top under the controlled pressure of the low-pressure casting machine. The controllable filling speed allows the molten metal to be filled in a laminar flow state, which significantly reduces gas entrainment and oxide entrapment. After the mold cavity is filled, the casting solidifies sequentially from the far end to the riser under the quenching action of the chill. The molten metal in the riser is continuously replenished by solidification and shrinkage under pressure. At hot spots, the combined action of the process groove and the chill prevents the formation of shrinkage porosity.

[0062] Taking the DN15 austenitic stainless steel pipe as an example: After shot blasting, the furnace charge was dried at 180℃ for 2 hours, with a recycled material ratio of 25%. A 100kg medium-frequency induction melting furnace was used, and the charge was added in the following order: scrap steel → recycled material → ferrochrome → ferronickel → ferromanganese → ferrosilicon → aluminum → titanium. The temperature was raised to 1580℃ and held for 12 minutes. 0.15% aluminum was added for deoxidation treatment, and 0.08% titanium was added for microalloying treatment. Argon gas was rotary blown for degassing for 6 minutes. After slag removal, the mixture was allowed to stand for 8 minutes, and the oxygen content of the melt was reduced to 28ppm.

[0063] The mold uses coated sand, specifically 70 / 140 mesh quartz sand, with a phenolic resin content of 2.5%. The metal mold is preheated to 250℃ and cured under pressure for 120 seconds. The shell thickness is 7mm–8mm. The cavity is coated with two layers of alcohol-based zircon powder paint, with a total coating thickness of 0.3mm. The venting grooves on the parting surface are 1.0mm deep and 2.0mm wide. Chill installation: Install HT200 external chills (22mm×22mm×7mm) at the base of each mounting bracket. Riser installation: φ18mm×25mm insulated exposed risers, with a riser diameter 1.8 times the diameter of the hot spot.

[0064] During casting, the mold is preheated to 250℃, the die is preheated to 200℃, the liquid pressure is increased to 0.015MPa in 8s, the filling pressure is increased to 0.03MPa in 12s, the filling speed is 0.08m / s, the pressure is increased to 0.07MPa in 4s, the pressure is held to 0.08MPa in 150s, and the pressure is released in stages in 8s.

[0065] After cooling for 350 minutes, the pipe was demolded, the risers and gates were removed, and the pipe was shot-blasted. The inner wall of the runner was polished with abrasive flow to Ra 2.8 μm. In this embodiment, the pipe casting yield was 96%, the dimensional accuracy was CT6, the as-cast grain size was ASTM 5.5, there was no leakage in the 1.6 MPa water pressure test, and the measurement accuracy was A after assembling a water meter.

[0066] Table 2: Comparison of Smelting and Refining Process Parameters

[0067] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0068] The embodiments have been described above, and such description is not restrictive. The figures shown are only one embodiment, and the actual structure is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the inventive spirit, they should all fall within the scope of protection.

Claims

1. A water meter pipe body, comprising a pipe body main body, an inlet end, an outlet end, and a transducer mounting base, characterized in that, The main body of the pipe, the inlet end, the outlet end, and the transducer mounting base are integrally cast structures; the inside of the main body of the pipe is a circular flow channel with a constant cross-section, and both the inlet end and the outlet end are equipped with straight section rectification structures. The bottom of the inner hole of the transducer mounting base is flush with the inner wall of the flow channel, and the root of the transducer mounting base is provided with a rounded transition. The main body of the pipe has a uniform wall thickness, and the sections where the wall thickness changes are transitioned by a slope. The main body of the tube is made of austenitic stainless steel alloy, and the composition of the alloy by mass percentage is: C≤0.06%, Si0.6%~0.8%, Mn1.0%~1.5%, Cr18.0%~20.0%, Ni8.0%~11.0%, Al0.1%~0.2%, Ti0.05%~0.1%, with the balance being Fe and unavoidable impurities.

2. The water meter pipe body according to claim 1, characterized in that, The content of Al is 0.12% to 0.18%.

3. The water meter pipe body according to claim 1, characterized in that, The content of Ti is 0.06% to 0.09%.

4. A water meter, characterized in that, It includes a water meter pipe body as described in any one of claims 1 to 3, a transducer installed in a transducer mounting base in the water meter pipe body, a metering circuit electrically connected to the transducer, and a display device for displaying measurement results.

5. The casting method for the water meter pipe body according to any one of claims 1 to 3, characterized in that, Includes the following steps: Furnace charge pretreatment steps: The furnace charge is cleaned and then dried; Melting and composition control steps: Melt the furnace charge in a medium-frequency induction melting furnace at a melting temperature of 1550℃~1600℃ and hold for 10~15 minutes. Add aluminum for deoxidation treatment to make the aluminum content in the melt 0.1%~0.2%. Add titanium for micro-alloying treatment to make the titanium content in the melt 0.05%~0.1%. Use inert gas rotary blowing to degas for 5~8 minutes. After slag removal, let stand for 5~10 minutes. The casting preparation steps are as follows: A composite casting mold of coated sand and metal mold is used. Chills are placed at the corresponding positions at the root of the transducer mounting base, and heat-insulating risers are placed above the hot spot. Low-pressure casting process: Casting is carried out using a low-pressure casting machine, and the pressure and time are controlled according to the process curve of liquid raising, mold filling, pressurization, pressure holding and pressure release. Cooling, demolding and post-processing steps: After depressurization, cool to room temperature for demolding, remove the gating and riser, and perform surface treatment on the inner wall of the runner.

6. The casting method according to claim 5, characterized in that, In the smelting and composition control steps, the order of adding materials is scrap steel → recycled material → ferrochrome → ferronickel → ferromanganese → ferrosilicon → aluminum → titanium. Aluminum is added 3 to 5 minutes before tapping, and titanium is added 1 to 2 minutes before tapping.

7. The casting method according to claim 5, characterized in that, In the mold preparation step, the coated sand is made by hot mixing and coating process of 70 / 140 mesh quartz sand and phenolic resin powder. The phenolic resin content of the coated sand is 1.5% to 2.5%. The coated sand is filled into a metal mold heated to 200℃ to 250℃ and cured to form a coated sand shell. The cavity is coated with an alcohol-based zircon powder coating with a total coating thickness of 0.2 mm to 0.3 mm; The parting surface is provided with venting grooves with a depth of 0.5mm to 1mm; The chills are made of HT200 material and are 1.5 to 2 times the thickness of the casting wall; the diameter of the insulation riser is 1.5 to 1.8 times the diameter of the hot spot.

8. The casting method according to claim 5, characterized in that, In the low-pressure casting step, the mold preheating temperature is 200℃~300℃, the mold temperature is 150℃~250℃; the liquid lifting pressure is 0.01~0.02MPa, time is 5~8s, the filling pressure is 0.02~0.05MPa, time is 10~15s, the filling speed is 0.05~0.1m / s, the pressure boosting pressure is 0.05~0.08MPa, time is 3~5s, the holding pressure is 0.08MPa, time is 120~180s, and the pressure release time is 5~10s.

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