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Structure and Working Principle of Rotary Joint (Diagram 1)

Views: 1971     Author: Site Editor     Publish Time: 2024-10-11      Origin: Site

Structure and Working Principle of Rotary Joint (Diagram 1)

The working principle of a mechanical seal structure rotary joint (referred to as a rotary joint) is to use axial force to press the dynamic ring onto the compensating static ring or floating ring, or vice versa to press the compensating static ring or floating ring (intermediate ring) onto the non compensating dynamic ring, to maintain its seal.  The axial unsealed passage between the moving ring (hollow shaft) and the shell, end cover, and bottom cover is sealed by O-rings and various elastic sealing rings with different cross-sections. The structure is shown in Figures 2-4, 2-5, and 2-6


drawing1

In general, each type of rotary joint is composed of fixed, floating, or floating radial sealing elements, rotating dynamic rings (hollow shafts, spherical spring seats, etc.), and axial sealing elements.  It has the advantages of precise sealing surface processing, low cost, and elimination of hollow shaft wear.  In order to adjust and compensate for the axial thermal expansion of the friction joint body and the wear of the friction cut end face and spherical surface, at least one elastic element, such as a spring or bellows, should be included in the rotary joint.

Figure 2-1 shows a spherical or combined spherical and end face sealing structure, with a bi-directional inner tube rotary joint.

Why is the sealing surface made into a spherical surface?  This is because the spherical friction motion pair structure has more degrees of freedom within the allowable clearance range, and can adapt to the strong vibration and swing of the equipment used.

From Figure 2-1, it can be seen that the moving ring is a spherical body 4 fixed on the outer tube 2 and a spherical spring seat 17 driven by it to rotate together and move axially;  The compensating ring consists of two stationary or moving concave rings 3 and 5, which are oil-free sliding bearings.

This structure has six sealing points (faces), namely a, b, c, d, e, and f.

a. The sealing of point B (surface) relative rotation relies on the spring 18 and the sealed fluid pressure to generate a suitable clamping force on the contact surface (sphere) between the spherical bodies (moving rings) 4 and 17 (spherical spring seat) and the compensating ring (stationary ring or moving ring) 3 in relative motion, so that these two smooth spheres are tightly adhered to achieve the purpose of sealing  The reason why the two spherical surfaces must be smooth and the concentricity and sphericity of the parts are required is to create conditions for the spherical surfaces to fully or nearly fully fit and have uniform clamping force

c. Point D (face) is a seal between two end faces  When the vibration and swing of the equipment are not significant and the clamping force is appropriate, the two compensating rings 3 are generally in a static state, which belongs to a static sealing situation.  When the vibration and oscillation of the equipment are strong and the clamping force is large, due to the large gap between the outer diameter of the compensating ring 3 and the inner diameter of the housing 6, it will move relative to the spherical body (moving ring) 4 and 17 on the corresponding end face out of synchronization, but the matching contact end face must be smooth and straight.  Due to the action of axial force, the end face of compensation ring 3 is tightly adhered to the inner end face of housing 6 and the end face of middle cover 9, making it difficult for the two ends of c and d to leak.

e. The f-point (face) refers to the four static sealing points (faces) between the sealing gasket 15 and the end faces of the housing 6, middle cover 9, and end cover 12. This type of static seal is relatively easy to handle and generally does not leak or rarely leaks.

The function of the oil-free graphite bearing 5 configured is mainly for support.  Consider the thermal expansion situation and the ability to move axially to compensate for the axial wear and thinning of the compensating ring 3, so that the spherical surface a, end face b, and h always remain in close contact. There is an appropriate gap (gap fit range) between it and the hollow shaft (outer tube) 2 and shell 6  Due to the small gaps i and g, the fluid entering the cavity k is negligible.  Only when the hollow shaft of the rotary joint is installed with poor concentricity with the matching equipment, or after a period of operation and use, due to installation deviation, the inner and outer diameters of the oil-free bearing 5 are worn off and there is a large gap between the matching parts;  The cavity k will enter the fluid, but this fluid will not easily leak even if it is sealed by the sealing surfaces a and b.

The inner and outer tubes rotate at the same angular velocity as the matching machine (the shell is stationary), which means that the inner tube 1, outer tube 2, and ball spring seat 17 maintain a relatively stationary state.  To prevent the fluid from entering and exiting through the gap between part 14 and the inner tube l, a small section of packing seal is designed and configured between the spherical spring seat 17 and the inner tube 1. It is compressed with a cover plate 14 and then locked with a locking nut 10.  This section of the packing seal is located between the relatively stationary moving parts 14 and 1, which belongs to the static sealing situation, so it is not easy to leak and does not consume frictional work

When the compensating ring of the friction pair wears out during operation and use, the amount of wear is reduced. The sleeve pressure generated by the elastic element and the sealed fluid medium will constantly push the spherical spring seat 17 to move axially (there is a guide key 7 between the outer tube 2 and the spherical spring seat 17 that can transmit torque and slide along the axial direction), so that the sealing surfaces b and c always remain tightly attached.  The spherical body 4 fixed on the outer tube 2, under the action of the axial force generated by the elastic element and the sealed medium, will push the oil-free bearing 5 to move to the left (in the direction of the bottom of the shell). The spherical body 4 is rigidly connected to the outer tube 2, and the outer tube 2 is fixedly (rigidly) connected to the matching equipment, unable to move axially to the left to compensate for the wear and thinning of the friction motion pair (such as compensation ring 3) at the bottom of the shell.  On the contact surface d between the inner end face of the shell 6 and the compensating ring 3, due to the compensating ring 3 exerting an axial force to the left on the inner bottom moth surface of the shell 6, the inner bottom surface d of the shell 6 exerts an equal and opposite axial force to the right on the end face d 'of the compensating ring 3. Under the action of the axial force, since the outer tube 2 and the spherical body 4 cannot move to the left in the axis, the shell will automatically move to the right to compensate for this wear and thinning amount.  This is the reason why a flexible hose should be configured for the connection of fluid inlet and outlet pipelines during the installation and use of rotary joints.  This is also the reason why its supporting, hanging, and anti rotation structures cannot be rigidly fixed axially.

For the spherical friction motion pair structure, the structure and sealing working principle of the bidirectional inner tube fixed type and the unidirectional rotating joint are the same as this bidirectional inner tube rotating type structure (see Figure 2-2 and Figure 2-3). The difference is that for the bidirectional inner tube fixed type, the inner tube 10 is fixedly connected to the end cover 2 and does not rotate randomly, but is in a stationary state, with the outer tube rotating. Therefore, there is no sealing problem between the inner and outer tubes  Unidirectional rotary joint, the instrument has a hollow shaft (tube) that rotates with n spoons.


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