Pin joints, Profile joints - Applied mechanics

Pin Connections

To transmit torque in lightly loaded gears, as well as to fix the position of one part relative to the other, use pin connections. The joints use pins (Figure 4.88): a - cylindrical smooth; b - with bared ends; in - insects; r - are spring-loaded; d - conical with a conicity of 1:50; e - with a threaded spigot. The dimensions of the pins are characterized by a diameter d pcs and a length l.

Make pins of carbon steels and non-ferrous metals. When installing the pins, the holes in both parts are drilled and unfolded assembled. Cylindrical pins are installed in the holes of the parts to be joined by interference fit (H7/n6, H7/n8, U8/n8). In connections requiring frequent assembly and disassembly, holes in the hub are machined to form the landing of the type K7/h8, H8/h8. From the fall, the pins are fixed in the collapsible joints by a spring ring (Figure 4.89, a), made of wire 0.5-0.8 mm in diameter. In non-separable joints, the cylindrical pins are corrugated (Fig. 4.89, b) or pins with drilled ends are used which expand after assembly. Nasal pins do not require the deployment of holes and additional fixation from falling out. They are used in non-essential joints of parts made of plastic materials. Spring pins are set in a small -

Fig. 4.88

Fig. 4.89

loaded connections; The interference is created by decreasing the diameter of the hole within

The connection of conical pins by the created interference provides the possibility of obtaining a no-slip connection. Self-locking of conical pins under the action of transverse force and torque is provided by frictional forces due to their conicity. However, under conditions of vibrations and sudden changes in temperature, the self-inhibition condition may not be fulfilled, and for its full guarantee against the dropout of the conical pin from the hole, its additional fastening is necessary.

The diameter of the pin in the "shaft-hub" type joints " in accordance with GOST designate, depending on the diameter of the shaft within (see Figure 4.89, b); The connection is checked for shear and crushing. Shear strength condition:

where - the torque; - allowable shear stresses.

For pins made of carbon steels,

where - the conditional area of ​​the collapse; 180 MPa - allowable stresses of crushing (for steel).

Profile Connections

In profile connections, the contact between the hub and the shaft is carried out along the contoured surface. The compounds can be with facets (Figure 4.90, a, b), with faces (Figure 4.90, c, d) and with an oval contour of the cross section (Figure 4.90, e). They can be collected for planting with interference, transitional and with clearance.

Advantages : lack of stress concentration, resulting in increased load capacity and fatigue strength; good self-centering; Improved noise performance.

Disadvantages : the need to expand the nomenclature of the cutting tool to form joints; difficulties in replacing parts during repair; The presence of spacer forces that cause the deformation of thin-walled hubs.

Profile joints are mainly used with an equiaxial profile with three, rarely five faces, which is the most technologically advanced. In an equiaxial profile, a constant distance is maintained between the parallel tangents and they have a common normal at the points of tangency. A quadrilateral section is applied to the profiles, which is widely used at the end sections of the turnkey shafts. Apply profile connections to transfer large torque. Their use in disk, worm, end and other cutters and tools instead of keyways increases the durability of mills and increases their strength.

Fig. 4.90

The calculation of the profile joints is carried out on the crushing of the working surfaces, on the tension in the hub and along the radial deformations of the bushing.

thematic pictures

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