In the fields of coal chemical industry and ultra-high pressure pipeline transportation, the sealing surface accuracy of the gate plate of the Φ 200-500mm chromium molybdenum steel (A105N, F91) high-pressure gate valve (requiring flatness ≤ 0.015mm/100mm, roughness Ra ≤ 0.6 μ m) and the coaxiality of the valve chamber and flange (≤ 0.025mm) directly determine the pressure sealing performance - this type of valve needs to withstand high pressure of 42MPa and high temperature of 350 ℃ for a long time. If the processing accuracy does not meet the standard, it will cause the leakage rate of the medium (such as coal to olefin synthesis gas) to exceed 0.001% specified in API 602 standard, leading to equipment corrosion or safety hazards. When a domestic high-end valve manufacturer processes this type of gate valve, it faces a traditional process bottleneck: it needs to go through three processes: "horizontal lathe roughing valve chamber → vertical grinder precision grinding gate sealing surface → rocker arm drilling machine drilling flange bolt hole". Multiple clamping causes the coaxiality between the valve chamber and the flange to exceed 0.05-0.07mm, the flatness error of the gate sealing surface to be 0.03-0.05mm, and the product pressure test pass rate is only 88%; Chromium molybdenum steel (F91) has high chromium content and high high-temperature strength. The tool wear rate during cutting is 2.5 times that of ordinary carbon steel. The service life of hard alloy tools is only 25-30 pieces/blade, and the cost of single valve tools exceeds 320 yuan; The single piece processing cycle is as long as 50 minutes, making it difficult to meet the "short cycle delivery" requirements of coal chemical projects.
To overcome the difficulties, the company introduced the Shenyang Machine Tool CK525 CNC vertical lathe and built a dedicated processing system for gate valves with "difficult to machine material adaptation+high-pressure sealing accuracy control". The equipment adopts an integral high-strength cast iron bed body (with a casting wall thickness of 80mm), which has undergone dual stress relief of "natural aging for 12 months+vibration aging for 72 hours". Combined with the design of box type sliding pillows and four point support static pressure guide rails, the rigidity distribution is optimized through finite element analysis. The radial cutting stiffness reaches 38kN/mm, which can stably withstand the 22kN radial force during chromium molybdenum steel cutting; Equipped with Fanuc 31i-B5 CNC system and fully closed-loop control of grating ruler (resolution 0.01 μ m), it achieves ± 0.008mm positioning accuracy and ± 0.005mm repeated positioning accuracy, accurately matching the H6 level tolerance requirements of the gate sealing surface. In response to the high temperature strength and easy work hardening characteristics of chromium molybdenum steel, the equipment is equipped with a high-pressure internal cooling spindle (cooling pressure 1.8MPa, flow rate 45L/min) and ultrafine grain CBN cubic boron nitride cutting tools (hardness HV3200, high temperature wear resistance improved by 40%), combined with the "low-temperature oil mist assisted cooling" technology (cutting zone temperature controlled below 60 ℃), effectively suppressing tool edge collapse and chip formation.
Customer usage scenarios
In terms of technological innovation, the equipment has achieved a breakthrough in "precision machining of high-pressure gate valves in one clamping process": integrating a Φ 750mm four jaw hydraulic chuck (clamping force of up to 100kN, suitable for Φ 200-500mm valve bodies), an 8-station servo turret (tool change time of 1.4 seconds) and a radial power drilling and tapping unit, which can complete precise boring of the valve chamber (cylindricity ≤ 0.006mm), precise turning of the sealing surface mirror of the gate plate (using the "constant line speed+micro feed" process, line speed of 80-120m/min, back cutting amount of 0.03-0.05mm, flatness ≤ 0.012mm/100mm), precise turning of the flange end face (flatness ≤ 0.018mm), and drilling and tapping of 8-16 flange bolt holes (positional accuracy ≤ 0.018mm) in one go. 0.08mm, compliant with API 602 valve bolt hole symmetry standard). In response to the demand for "high-precision mirror effect" on the sealing surface of the gate plate, we innovatively adopt the "multi pass progressive precision machining process": the first pass removes 70% of the excess, the second pass adjusts the form and position errors with a back cutting amount of 0.08mm, and the last pass achieves mirror cutting with a back cutting amount of 0.02mm. Combined with Renishaw's on machine measuring probe (measurement accuracy ± 0.0005mm), it compensates for the thermal deformation of the workpiece in real time, making the roughness of the sealing surface stable at Ra0.4 μ m; For multi specification gate valve replacement (such as PN25-PN42 pressure rating), the equipment is equipped with 35 sets of process parameter templates, reducing the replacement time from traditional 2 hours to 18 minutes.
Three sided special fixture for three-way machining
The implementation results fully comply with the industry standards for high-pressure valves: the single piece processing cycle has been compressed from 50 minutes to 26 minutes, and the daily production capacity has been increased from 160 units to 280 units; The coaxiality stability between the valve chamber and the flange is ≤ 0.02mm, and the flatness of the gate sealing surface is ≤ 0.012mm/100mm, fully meeting the requirements of API 602 "Compact Steel Gate Valve" and GB/T 12234 "Steel Gate Valve with Stud Connected Valve Cover for Petroleum and Natural Gas Industry"; The pass rate of product pressure test has increased from 88% to 99.2%, and the leakage rate has been controlled below 0.0008%, meeting the Shell Coal Chemical "zero leakage" technical standard; The service life of chromium molybdenum steel (F91) machining tools has been extended by 80% (up to 45-54 pieces/blade), and the cost of single valve cutting tools has been reduced to 180 yuan; The intelligent operation and maintenance module equipped on the equipment can collect cutting force (accuracy ± 0.5%) and spindle vibration (sampling frequency 1kHz) in real time. Combined with a tool wear prediction model, the comprehensive utilization rate of the equipment has been increased from 76% to 94%, and the annual downtime has been reduced by 400 hours.
CK525 has completely solved the industry pain point of 'difficult processing+high precision' for high-pressure chromium molybdenum steel gate valves. ”The technical director of the company stated, 'Our gate valves have been successfully applied in large-scale coal chemical projects such as Baofeng in Ningxia and Tianye in Xinjiang. They have not only passed Shell's global supplier certification, but also meet the strict requirement of' continuous operation for 8000 hours without maintenance ', which has established a technical barrier for us in the high-pressure valve segment market.'. ”This case confirms that CNC vertical lathes have become the core equipment for breaking through quality and efficiency bottlenecks in the field of high-pressure valve manufacturing through the deep integration of "customized processing of difficult to machine materials, closed-loop control of high-pressure sealing accuracy, and efficient process integration".
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