oil wellhead ( Christmas tree) With gate valve is one of the largest dedicated gate, dosage of oil fields in the process of gate valve manufacturing, body hydrostatic strength test and sealing test pass rate is too low, 30% ~ 70%) And long plagued factory. Just above the crux of the problem are analyzed, and puts forward the solution.

1, gate blank casting process improvement

wellhead valve USES the sand mold cast steel blank, in the process of gate valve processing, often occurs in the internal thread with the seat with the casting defects such as blow hole, shrinkage, the macro analysis of the valve body section found that hot section area have different degrees of shrinkage phenomenon, in order to solve the above problems, the gate valve casting process to improve test many times.

1) To improve the water the riser system. Will be set up on either side of the body of the cylinder is poured riser system instead of the bottom of the valve body set with runner system;

2) Change of sand casting for the investment casting;

3) Change side pouring method for top pouring method, and make the flange down. Because the investment casting sand casting is better than the permeability, faster, more even cooling conditions, so the organization is more dense. Because of liquid steel poured in from the top, but also from the riser directly pouring in, pouring the location of the riser section near the hot area. Gate create the extremely good order for the casting solidification conditions, hot get timely feeding section area, so the production of casting organization density after process improvement, to eliminate the casting defects such as shrinkage, shrinkage, product qualification rate reached more than 99%.

2, gate valve, efforts to improve the machining accuracy of manufacture

the sealing effect is a key ingredient in a valve manufacturing. Gate valve seal mechanical processing industry has always been difficult to solve problems, to improve the manufacturing precision of the Industrial Valves, ensure that the Industrial Valves sealing effect, through theoretical research and production practice, summed up the following improvement measures.

the body is the key mechanical parts in the production of gate valve, due to the requirement of the structure, the Industrial Valves seat sealing surface and center symmetry plane tilted 30 ~ 60. For small and medium-sized gate valve body, the use of auxiliary curved plates with horizontal lathe tooling to complete the seat of the inclined plane processing. But must make the pledge that we shall make the plate Angle ( 30 ~ 60) Consistent with the body of technical requirements. At the same time, should be more strictly to ensure machine tool center high and bending tooling center high coincidence. Permissible error control in 0. 02mm～0. 4 mm between. In addition, the gate valve should be considered in the process of machining a clamping, positioning accuracy and reliability. By heavy face of lathe spindle's line should be as a reference, using vertical wedge grooves on the surface of the plate and the sliding body will end of the wedge block flange face looking for positive pressure tight, in two sides respectively. In addition, the gate valve body in the process of machining, the cost on the lathe tooling by rotate it back 1800 finish on both ends of the valve body cavity machining. The rotation accuracy is to rely on distribution in rotary flange two symmetrical distribution of conical repositioning to ensure that the positioning pin hole. Gate inversion error is 0. 1毫米~ 0。 02mm。

in addition, to choose appropriate gate valves with counterweight and bent plates. It is well known that curved plate on lathe tooling static balance directly affect the machining precision of lathe and the production efficiency, so in the plate shape and layout of balancing the up and down a lot of work, a is the radius of gyration gate valves as far as possible to reduce weight, the second is on the gate layout using the cylindrical inner structure, improve the performance of dynamic balance on the circumferential direction, the machine speed and workpiece machining accuracy to improve as soon as possible.

in the end, to ensure the parts in the gate valve seal coordination processing.

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