The valve assembly is the last stage of the production process. Valve assembly is based on the premise of the delineation of technology, the combination of all parts and components of the valve, making it a product process. The whole machine is the most basic unit of valve assembly, and several components form components of valve, such as bonnet, disc parts, etc. The assembly process of several parts and components is called component assembly, and the assembly process of several parts and components is called general assembly. The assembly work has a great influence on the quality of the product. Even if the design is accurate and the parts are qualified, if the assembly is not properly assembled, the valve can not meet the required requirements, and even the sealing leakage is produced. Therefore, we should pay special attention to the fair assembly method to ensure the final quality of the valve. The assembly process described in file form is called assembly process rule in production.
Common assembly method of valve
There are three ways to assemble valves, that is, the complete replacement method, repair method and matching method.
(1) complete exchange method: when the valve is assembled by complete interchange method, each part of the valve can be assembled without any dressing or choice, and the product after assembly can meet the required technical requirements. At this point, the valve parts must be processed according to the design requirements, satisfying the requirements of dimensional accuracy and geometric tolerance. The advantage of the complete exchange method is that the assembly work is simple and economical, the workers do not need high skill level, the production efficiency of the assembly process is high, and it is easy to organize assembly line and organize specialized production. However, it is absolutely required that the machining accuracy of parts is higher when the assembly is completely changed. It is applied to valves that are absolutely simple and medium and small caliber valves, such as stop valves, check valves and ball valves.
(2) selection method: the valve is assembled by the selection method, the whole machine can be processed according to the economic precision, and the size of a certain adjustment and compensation effect is selected in assembly to reach the specified assembly precision. The principle of matching method is identical with the repair method, but only in the way of changing the size of the compensation ring. The former uses the way of selecting accessories to change the size of the compensation ring, and the latter uses the way of trimming parts to change the size of the compensation ring. For example, the top core and dressing gasket of the control valve type double gate wedge valve and the adjusting cushion between the two body of the ball valve are to take the special parts as compensation parts in the dimension chain related to the assembly precision, and to reach the required precision by adjusting the thickness of the gasket. In order to ensure that it can be selected with fixed compensator in different circumstances, a set of washer with different thickness and the type of hydraulic control valve for shaft sleeve compensator should be made in advance for selection.
(3) the repair method: the valve is assembled by the repair method, the parts can be machined according to the economic precision, and then the size of a certain adjustment and remedy is repaired in order to achieve the specified assembly target. For example, the gate and valve body of wedge gate valves are too expensive because most of the manufacturers need to apply the repair process. That is, in the final grinding gate seal face opening size when the size of the valve seal surface should be matched with the opening size of the valve, so as to achieve the ultimate seal requirements. Although this method adds the working procedure of the plate, it greatly simplifies the requirement of the dimension precision of the previous working procedure, and the special operation of the panel process is well done. In general, it will not affect the efficiency of production. Valve assembly process: valves are individually assembled in a fixed site. The zero, component assembly and assembly of the valves are carried out in the assembly workshop, and all the required parts and components are transported to the place of the assembly. Generally, the assembly and General Assembly resolution are carried out at the same time by the number of groups of workers, which not only shorten the assembly cycle, but also facilitate the application of special assembly tools, and the requirements for the workers' technical level are also low.
Some overseas manufacturers or high technology grade valves also adopt the mode of assembling suspension line or assembling turntable.
(1) preparatory work before assembly: before the valve parts are assembled, the burrs and residual welding residue should be removed, and the packing and gaskets are cleaned and cut.
(2) the cleaning of valve parts: as the valve installed by the fluid pipeline, the inner cavity must be clean. Especially for valves used in nuclear power, medicine and food industry, in order to ensure the purity of the medium and avoid the infection of medium, the requirement for the cleanliness of the inner cavity of the valve is more severe. Before assembly, the parts of the response valve are cleaned, and the debris, the remaining smooth oil, the coolant, the spur, the slag and the remaining dirt on the parts are cleaned. The cleaning of valves is usually done by washing with alkali or hot water or washing with kerosene. After the grinding and polishing of the parts, the final cleaning is required. Finally, the cleaning is usually used to clean the seal face position with gasoline, and then blow dry with tight air and wipe clean with cloth.
(3) preparation of fillers and gaskets: graphite packing is widely used due to its advantages such as corrosion resistance, good sealing and small friction coefficient. Packing and gaskets are used to prevent leakage of media through the joint between valve stem and bonnet and flange joint. All these accessories must be prepared before cutting valve and assembling.
(4) valve assembly: valve is usually assembled on the basis of valve body as a reference part and according to the order and method specified in the process. Before assembling, we must review the parts and components, avoid the parts that are not burr or not cleaned into the final assembly. In the assembly process, part tohandlegentlyand, avoid the bump and scratch processing staff. The active parts of valves, such as stem and bearing, should be coated with industrial butter. The valve cover is connected with the flange in the valve body, and when the bolt is fastened, the response is called, interlaced, repeated and tightened, otherwise the joint surface of the valve and valve cover will produce the leakage of the flow control valve due to the uneven force around the valve. The moving hands should not be too long when they are fastened, so that the pre tightening force is too large to affect the strength of bolts. For a valve that has severe request for pre tightening force, torque shall be applied to move the hand, and according to the specified torque requirement, the tightening bolt should be tightened. After completion of the assembly, the rotary control mechanism should be rotated to check whether the valve opening and closing parts are mobile or not. Whether the device direction of the valve cover, bracket and other parts meet the requirements of the drawings, can the valve be tested after passing all the reviews?
