In order to ensure that the machine or components can be assembled smoothly and meet the performance requirements specified in the design, and that disassembly and assembly are convenient, the assembly structure between the parts must meet the assembly process requirements. Therefore, when designing and drawing assembly drawings, reasonable assembly structure and process issues should be considered.
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1. Number of contact surfaces
1. The number of contact surfaces. Two parts can only have one pair of contact surfaces in the same direction (lateral, vertical or radial). This can not only ensure good contact, but also reduce processing requirements. Otherwise, processing will be difficult and it will not be possible. will be contacted at the same time. As shown in Figure 1, a >a must be made.
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Figure 1 How to draw the contact surface
2. The fit between the journal and the hole is as shown in Figure 2. Since the margin φA has already formed a fit, φB and φC should no longer form a matching relationship, that is, φB>φC must be maintained.
3. Cone surface fit Since the cone surface fit can simultaneously determine the axial and radial positions, when the taper hole is blocked, there must be a gap between the top of the cone and the bottom of the taper hole. As shown in Figure 2, L2>L1 must be maintained, otherwise a stable fit will not be obtained. The standard values of cone taper and taper angle.
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Figure 2 The fit between the journal and the hole and the fit between the taper surface
4. The contact surfaces of structural parts in both directions at the turning point should be chamfered, rounded or grooved to ensure good contact between the contact surfaces in both directions. The turning points should not be processed into right angles or rounded corners of the same size, because this will cause interference at the turning points during assembly, resulting in poor contact and affecting assembly accuracy. As shown in Figure 3.
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Figure 3 Structure at the turning point of the contact surface
2. Reasonable structure of threaded connection In order to ensure that the thread is tight, an undercut groove should be left at the end of the thread or a pit or chamfer should be processed at the end of the screw hole, as shown in Figure 4. In order to ensure good contact between the connecting piece and the connected piece, the connected piece should have a counterbore or boss, as shown in Figure 4. The diameter of the through hole of the connected parts should be larger than the major diameter of the thread or the diameter of the screw to facilitate assembly.
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Figure 4 Structure using thread tightening
3. Reasonable structure for axial fixation of rolling bearings. In order to prevent axial movement of rolling bearings, a certain structure must be used to fix the same ring and seat ring. Commonly used axial fixed structural forms include: shaft shoulder, shoulder, elastic retaining ring, correcting party cover flange, round nut and backstop washer, and shaft end retaining ring, as shown in Figure 5. The standard dimensions of retaining rings for holes and shafts can be found in the standards. In order to make the rolling bearing rotate flexibly and prevent it from getting stuck after thermal expansion, a small amount of axial clearance should be left (generally 0.2-0.3mm). Commonly used adjustment methods include: replacing metal gaskets of different thicknesses or using screw thrust plates, etc. .
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Figure 5 Structure of rolling bearing ring
4. Leak-proof structure Whether the machine or component can operate normally depends to a large extent on the reliability of the seal or leak-proof structure. For this reason, a stuffing box (culvert) is often made into a stuffing box (culvert) where the rotating shaft and sliding rod (valve rod, piston rod, etc.) of the machine or component protrude from the box (or valve body) and filled with soft materials with special properties. For packing, use a gland or nut to compress the packing so that the packing sticks to the shaft (rod) with appropriate pressure, so as not to hinder the movement of the shaft (rod) and prevent the working medium (fluid or gas) from moving along the shaft (rod). ) leakage, thus playing the role of sealing and leakage prevention, as shown in Figure 6. When drawing the picture, the gland is drawn at the position where the packing has just been filled and the packing starts to be tightened.
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