When copying new products or carrying out technical transformation and maintenance of existing machinery and equipment, it is often necessary to conduct surveying and mapping. That is, by disassembling the parts for measurement, drawing the assembly diagram and parts sketch; then drawing the assembly drawing based on the parts sketch; and then drawing the parts drawing based on the assembly drawing and parts sketch to complete the entire set of assembly drawings and parts drawings. This process is called Assembly mapping.
1. Understand the surveying and mapping objects
Understand its use, performance, working principle, structural characteristics, assembly and disassembly sequence, etc. by observing the actual object, reading relevant technical information and similar product drawings. In the process of collecting data, special attention should be paid to the use and improvement opinions of the production workers and technical personnel to make full preparations for the smooth progress of the surveying and mapping work. On the basis of a preliminary understanding of the function of the assembly, through careful analysis of the functions and structures of the parts, we can further understand the assembly and connection relationships between the parts.
As shown in Figure 10-19, the valve core of the ball valve is spherical and is a component used to open and close and regulate flow. In the position shown in the picture, the valves are all open. When the wrench is rotated 90° clockwise, the valves are all closed.
The key part of this assembly is the valve core, which will be analyzed below from the aspects of motion relationship, sealing relationship, and containment relationship.
Kinematic relationship: wrench → valve stem → valve core.
Sealing relationship: The two sealing rings are the first line of defense, and the adjustment pad not only ensures the sealing between the valve body and the valve cover, but also ensures the flexible rotation of the valve core; the second line of defense is the packing to prevent Fluid leaks from gaps in the valve stem of rotating parts.
Inclusion relationship: The valve body and valve cover are the main parts of the ball valve, and they are connected with four sets of studs. The valve core is positioned in the valve through two sealing rings, and the packing made of polytetrafluoroethylene is fixed in the valve body through the thread of the packing compression sleeve and the valve body.
The left end of the valve body is connected to the valve cover through studs and nuts, forming a cavity for the ball valve to accommodate the valve core. The cylindrical groove on the left end of the valve body matches the cylindrical flange of the valve cover. The cylindrical groove on the right side of the valve body cavity is used to place the sealing ring to ensure that the ball valve does not leak fluid when it is closed. The right end of the valve body has external threads for connecting pipes in the system, and the internal stepped hole communicates with the cavity. In the cylinder at the upper part of the valve body, there is a stepped hole communicating with the cavity. The valve stem, packing compression sleeve, etc. are installed in the stepped hole. The 90° sector-shaped limit bump at the top of the stepped hole is used to control the rotation angle of the wrench and valve stem.
2. Disassemble the parts and draw the assembly diagram
Before disassembly, you should prepare the relevant disassembly tools, as well as the equipment and place for placing the parts, and then formulate a plan based on the characteristics of the assembly. Careful disassembly plan, remove parts in a certain order. During disassembly, each part should be numbered, registered and labeled. The disassembled parts should be divided into groups and placed in appropriate places to avoid damage, deformation, confusion and loss, so as to ensure smooth reassembly.
Pay attention when disassembling parts: some necessary original dimensions should be measured before disassembly, such as the relative positions between certain parts, etc. During the disassembly process, it is strictly prohibited to knock randomly to avoid damaging the original parts. For parts with non-detachable connections, high-precision fits or interference fits, they should be disassembled as little or as little as possible to avoid reducing the original fit accuracy or damaging the parts.
As shown in Figure 10-19, the disassembly sequence of the ball valve can be carried out as follows:
① Remove the wrench 13.
② Unscrew the packing compression sleeve 11, take out the valve stem 12, and take out the packing 9 and packing pad 8.
③ Use a wrench to unscrew the nuts 7 connected by the four sets of studs, and take out the valve cover 2 and the adjustment pad 5.
④ Take out the valve core 4 from the valve body and complete the disassembly.
The assembly schematic diagram is a simplified diagram that uses visual inspection and freehand to draw the rough outline of each part of the assembly with simple drawing lines to show its assembly position, assembly relationship, working principle, etc.
When drawing a schematic diagram, the parts can be regarded as transparent bodies, and their representation is not limited by the front and rear levels, and try to concentrate all the parts on one diagram. When drawing the schematic diagram of the transmission part of the mechanism, it should be drawn in accordance with the national standard "Mechanical Drawing - Simplified Diagram Symbols of Mechanism Movement". For general parts, the rough outline of the part can be vividly drawn according to its appearance and structural characteristics.
Figure 10-20 Assembly schematic diagram of a ball valve
The assembly schematic diagram should be drawn after a comprehensive understanding and analysis of the assembly, and the internal structure and internal structure of the assembly should be further understood during the disassembly process. Correct and supplement the relationship between the parts to prepare for the correct drawing of assembly drawings and reassembly of the assembly in the future. The assembly diagram of the ball valve is shown in Figure 10-20.
3. Draw sketches of parts
Draw freehand sketches of the disassembled parts one by one. Some standard parts, such as bolts, screws, nuts, washers, keys, pins, etc., do not need to be drawn, but their main specifications and dimensions should be measured to determine their prescribed markings. Other data can be obtained by consulting relevant standards. All non-standard parts must be sketched and measured accurately and completely.
The method of drawing part sketches has been introduced before. In assembly surveying and mapping, the following three points should be paid attention to when drawing part sketches:
(1) When drawing part sketches, in addition to drawings Except that the lines are done freehand, the other requirements are the same as drawing formal parts working drawings.
(2) Part sketches can be drawn sequentially according to the assembly relationship or disassembly sequence, so that the relevant dimensions between the parts can be verified and coordinated at any time.
(3) The dimensions related to fit, connection and positioning between parts must be coordinated and marked on the sketch of the relevant parts.