JPS6216539Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is a mechanical seal that prevents fluid from leaking from a rotating shaft, especially when the sealed pressure fluid is a liquid or a mixture of liquid and gas, and the external fluid is a gas, generally air. This invention relates to an improvement in a mechanical seal that prevents leakage of a sealing fluid in cases where:

Normally, the above type of mechanical seal has a fixed seat ring through which the rotating shaft is inserted, and a driven ring that rotates with the rotating shaft makes sliding contact with the fixed seat ring. It has a configuration that prevents leakage. Therefore, in order to improve the sealing effect of the sliding surface, conventional methods have been to increase the pressing force of the driven ring against the seat ring to increase the pressure per unit area of the sliding surface, or to increase the pressure per unit area of the sliding surface, or to increase the pressure per unit area of the sliding surface. Countermeasures have been taken, such as selecting materials to form a robust sealing surface. However, surface roughness, deformation over time, etc. that occur in sliding contact parts cannot be avoided after all, and especially in harsh conditions where vibrations, temperature changes, etc. are applied, such as with mechanical seals applied to automobile cooler compressors, etc. When used under the hood, fluid leakage is significant and a fundamental improvement in the sealing means has been desired.

As a fundamental improvement to this sealing means, the inventors of the present invention have already invented a mechanical seal in which a dead-end thread groove with a closed outer end is formed on at least one of the sliding surfaces of the seat ring and the driven ring. They have filed patent applications for this (Japanese Patent Application No. 52-41838, Japanese Patent Application No. 53-24137).

The invention according to the above patent application focuses on the fact that radial pressure that can counter leakage flow can be applied to the fluid interposed in the minute gap between the sliding surfaces by using the relative rotation of the sliding surfaces. , characterized in that a yarn groove of a desired shape with a closed outer end is provided on at least one of the sliding contact surfaces, and the pumping action of the yarn groove as the driven ring rotates, or the side of the driven ring. It is believed that when a groove is formed in the yarn groove, the centrifugal force acting on the fluid that enters the yarn groove can prevent leakage.

By the way, in this mechanical seal, the inner end of the thread groove opens into the inner circumferential wall of the ring, and the connecting portion between the groove and the inner circumferential wall becomes a sharp edge. When the driven ring whose inner end of the thread groove has a sharp edge is rotated, cavitation occurs at and near the edge, and the edge also cracks.
When chipping occurs, this cavitation becomes stronger, which causes the sliding surface to become rough and reduces sealing performance.

Incidentally, in general, the influence of cavitation is small in mechanical seals, and even in the field of mechanical seals having grooves on the sliding surface to which the present invention belongs, the negative influence of cavitation is currently ignored. The reason why cavitation is not generally considered is that mechanical seals leak more due to wear and tear caused by long-term use, so even if the amount of leakage increases, it is usually assumed that it is due to the above-mentioned wear. This is thought to be one of the reasons.

In the present invention as well, the negative effects caused by cavitation were found to occur when ordinary leakage experiments regarding leakage from the thread groove were continued for a considerable period of time, especially when there was a chip in the open end portion on the rear side of the driven ring in the direction of rotation. This was discovered due to a relative increase in the amount of cavitation, and at the stage when we had just conducted a leakage experiment for about tens of hours on the yarn groove where the inner end of the yarn groove is a sharp edge, we found that there was no negative effect due to cavitation. was not taken into account.

However, for those with a chip in the opening end, the amount of leakage has increased relatively.
After examining the cause in detail, it was discovered that cavitation occurred in an unexpected area, which caused the leakage amount to increase.

That is, in the mechanical seal of the present invention, the thread groove is not opened toward the outer periphery where the sealing fluid made of liquid or a mixture of liquid and gas exists, but rather, the thread groove is not opened toward the outer periphery where the sealing fluid is present. The sealing fluid that leaks from the outer periphery of the sliding surface of the driven ring beyond the land portion flows into the thread groove from the outer peripheral end of the thread groove. It is thought that the fibers are caught and pushed back into the land portion from the outer peripheral end of the thread groove by the relative rotation between the seat ring and the driven ring. Therefore, it is thought that the flow rate of the sealing fluid to the thread groove is naturally large at the outer peripheral end of the thread groove, and is minimal or almost zero at the inner peripheral side of the mechanical seal where the thread groove opens. It is predicted that cavitation is more likely to occur at the outer peripheral end than at the inner peripheral end, and in addition, when the seat ring and driven ring rotate relative to each other, the peripheral speed at the outer peripheral end of the thread groove is lower than the inner peripheral end. The circumferential speed was higher than that of the open end portion, and from this point of view, it was predicted that cavitation would occur more easily at the outer circumferential end portion than at the inner circumferential end portion.

However, in reality, contrary to such predictions,
As shown in Fig. 5, which will be described later, cavitation occurs in the opening where the flow rate of the sealing fluid is small and the peripheral speed is relatively slow, and the occurrence of cavitation in the opening increases the amount of leakage. I confirmed that it was. Although cavitation appears to occur at the outer peripheral end portion of the thread groove, the effect is ultimately smaller than the cavitation occurring at the opening, so it is considered to be negligible.

The present invention was made based on such knowledge, and at the open end of the thread groove to the inner circumferential wall of the driven ring, at least the open end on the rear side in the rotational direction of the driven ring and the inner circumferential wall, which causes cavitation, are removed. A mechanical seal is obtained in which the connecting portions of the mechanical seals are connected with smooth curved surfaces to avoid the cavitation described above and the deterioration in sealing performance caused by the cavitation.

The invention will now be described with reference to the illustrated embodiments. Fig. 1 shows a compressor for an automobile cooler as an example of a rotary shaft with a mechanical seal, where 1 is the rotary shaft of the compressor, and 2 is an electromagnetic clutch coupled to the rotary shaft 1 with its rotation restrained by a key 3. The connecting body 4 is a rotating body that can freely rotate with respect to the casing 5. When the excitation coil 6 inserted into the space inside the rotating body 4 is energized, the rotating body 4 and the connecting body 2 are integrated, and the rotating body The rotating shaft 1 rotates together with the rotating shaft 4. 7 is a mechanical seal part that prevents the fluid in the compressor part 8, that is, liquid or a mixture of liquid and gas, from leaking toward the rotating shaft 1. As shown in an enlarged view in FIG.
A driven ring 10 rotating together with the rotating shaft 1 is brought into sliding contact with the seat ring 9 through which the seat ring 9 is inserted, and this sliding contact prevents oil and gas from leaking from the gap between the seat ring 9 and the rotating shaft 1. ing. 11 is a gasket that is in close contact with the rotating shaft 1; 12 is its holder; 1
3 is a knock ring, and 14 is a spring that applies a pressing force to the driven ring 10 toward the seat ring 9 side.

As shown in FIG. 3, the sliding surface 10A of the driven ring 10 with the seat ring 9 has a flat land portion 20 formed on its outer periphery and a plurality of thread grooves 21 on its inner periphery. It is perforated. The outer end of this thread groove 21 is closed by the land portion 20, but the inner end thereof is open to the inner circumferential wall 10B of the driven ring 10, and this open end includes:
In order to prevent the occurrence of cavitation, this groove 21 is formed on the rear side of the driven ring 10 in the rotational direction.
A curved surface 22 is formed that smoothly connects the inner circumferential wall 10B. The radius of curvature of this curved surface 22 varies depending on the inclination angle of the thread groove 21, the groove width, etc., but the radius of curvature (approximately 0.1 mm ), specifically, an appropriate value of 0.2 mmR or more, preferably 0.3 mmR or more. This curved surface 22 was formed by observing the sliding surface 10A in a plan view, but when the thread groove 21 is viewed from the inner circumferential wall 10B side, a curved surface 23 as shown in FIG. 4 is formed at the end of the groove. The groove can be smoothly connected to the inner circumferential wall also in the depth direction of the groove.

The driven ring 10 in which the curved surface 22 (and curved surface 23) is formed at the end of the thread groove 21 in this way does not suffer from cracks 24 or chips like the conventional product shown in FIG. 5 in which the curved surface 22 portion is a sharp edge. This results in improved processability and mass production. At the same time, since cavitation does not occur on the sliding surface in the shaded area 25 in FIG. 5 due to turbulence caused by the shear edge or its cracks or chips, the sealing performance can be improved and stabilized.

Note that the thread groove 21 is preferably inclined toward the rear in the rotational movement direction of the sliding surface as shown by the arrow in FIG. 3, since it is thought that a leakage prevention effect can be obtained by the pumping action of this groove. However, as a result of research, the angle of inclination of this groove was found to be
It is recognized that almost the same effect can be obtained even if the driven ring 10 is radially moved as shown in Figure a, and furthermore, depending on the usage conditions, it may be possible to move the driven ring 10 at a certain angle forward in the rotational movement direction as shown in Figure b. Even when tilted by α (for example, about 5°), a sealing effect without any practical problem was observed. This is considered to be because, up to a certain limit angle of inclination of the yarn groove 21, the centrifugal force acting on the fluid in this groove generates a radial pressure capable of counteracting the leakage flow from the sliding surface.

In addition, the width of these thread grooves 21 is approximately 0.2 to 0.6 mm, and a nearly satisfactory sealing effect can be obtained, and the depth is preferably shallow enough to avoid being buried by abrasion powder during rotation, and experiments have shown that this There was a tendency for seals to decrease when it became about 0.05 mm. Of course, these values may change depending on the number of yarn grooves 21 to be set and the width of the sliding contact area.

It should be noted that the structure of the mechanical seal shown in FIGS. 1 and 2 is merely an example, and it is clear that the present invention does not concern these structures.

As described above, the present invention provides a mechanical seal in which a thread groove that opens in the inner circumferential wall of the driven ring is formed in the inner circumferential portion of the sliding surface of the driven ring. By connecting the inner peripheral wall with a smooth curved surface, cavitation can be prevented and stable sealing performance can be obtained. Further, by forming the above-mentioned curved surface, it is possible to prevent chipping and cracking of the sharp edge portion, and it is also possible to prevent cavitation from occurring more easily due to the chipping and cracking.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing an example of a rotating shaft having a mechanical seal, Fig. 2 is an enlarged view of the mechanical seal portion of Fig. 1, and Fig. 3 is a sliding contact surface of the driven ring of the mechanical seal according to the present invention. 4 is a plan view showing an example of the shape; FIG. 4 is a view taken in the direction of the arrow in FIG. 3; FIG. 5 is a plan view corresponding to an enlarged portion of FIG. The figure is a plan view of the driven ring showing another example of the direction of inclination of the thread groove. 1: Rotating shaft, 9: Seat ring, 10: Driven ring, 10A: Sliding surface, 10B: Inner peripheral wall, 20:
Land portion, 21: Yarn groove, 22, 23: Curved surface.

Claims (1)

[Scope of utility model registration request] It includes a seat ring through which a rotating shaft is inserted to form a stationary side member, and a driven ring that rotates together with the rotating shaft and slides into contact with this seat ring, and a liquid or a mixture of liquid and gas is provided on the outer circumferential side of the driven ring. In a mechanical seal that encloses a sealing pressure fluid consisting of a mixture and uses an external gas on the inner circumference side, the outer circumference of the sliding surface of the driven ring is a flat land, and the inner circumference has an inner end. has a plurality of thread grooves that communicate with the inner circumferential wall of the driven ring, and at the open end of the thread groove toward the inner circumferential wall of the driven ring, at least the open end on the rear side in the rotational direction of the driven ring and the inner circumferential wall. A mechanical seal that prevents cavitation by connecting with a smooth curved surface.