Mechanical seal, and agitating device and process using same

Details Mechanical seal, and agitating device and process using same Mechanical seal, and agitating device and process using same

1999-08-30

2003-02-11

Knight, Anthony (Department: 3676)

Seal for a joint or juncture

Seal between relatively movable parts

Relatively rotatable radially extending sealing face member

C277S370000, C277S377000, C277S387000

Reexamination Certificate

active

06517077

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention concerns improvements to the mechanical seal, and agitating device and process using same.
Mechanical seals are often used as a typical seal structure for use in rotary apparatuses. For example, if fluid is agitated in the agitating tank, rotary blades built in the agitating tank are rotated by means of a revolving shaft with its leading end portion received by the agitating tank, and the perimeter of the revolving shaft is rendered reliably liquidproof by the mechanical seal.
The pressure between the sliding faces of sliding rings in the mechanical seal greatly affects the sealability and the resistance to rotation of the revolving shaft. This pressure tends to fluctuate under the influence of various factors such as pressures of sealing fluid, spring, flushing liquid, etc.
More specifically, the flushing fluid is intended to be introduced into a seal box (stuffing box) as in order to cool the sliding rings. As the pressure of the flushing fluid increases, the pressure between the sliding faces tends to decrease. In this connection, for example, if the rotary speed of the revolving shaft is needed to increase, there is a limit to speeding up of the revolving shaft in terms of the flushing liquid. More specifically, it is necessary to increase the flow rate of flushing liquid for the purpose of cooling of the sliding rings as the revolving shaft is turned at higher speeds. The more the flow rate of flushing liquid, the higher the pressure of the flushing liquid, followed by the decrease of the pressure between the sliding faces. Since lowering of the pressure between the sliding faces may create liquid leaks, there would inevitably be a limit to the speed up of the revolving shaft in association of the flow rate of flushing liquid or the fluid pressure.
Desired pressure between the sliding faces is dependent on the pressures of a seal fluid used. Therefore, the mechanical seal is designed based on the pressure of the seal liquid being used that has been set within a predetermined range. If said pressure happens to deviate from the range, there would occur harmful effects such as liquid leaks, or increase of resistance to rotation.
In order to cope with such a problem, as the case may be, pressure-equalizing tubes are used to change the pressure of flushing liquid in response to the pressure change of seal fluid. However, such a solution needs to establish complicated requirements in connection with the rotary speed of the revolving shaft.
Many mechanical seals incorporate a spring acting to bias the sliding rings. The strength of said spring is designed in consideration of manifold factors. So, theoretically, the pressure between the sliding faces can be altered by changing the strength of spring. However, it is awfully difficult to change the spring strength into an adequate value in the mechanical seal fabricated from specific design. Particularly, it is safe to say that in operation, it is impossible to manipulate the spring in its inherent elasticity on the sliding rings.
On the other hand, nowadays, in the drugs or food industry, sterilization treatment must often be performed concurrently with the agitation treatment for fluid. In such a case, it is also necessary to clean and sterilize the mechanical seal in order to keep the interior of the agitating tank sterilized. In the past, such cleaning and sterilization operations had to be carried out after the mechanical seal had been disassembled. However, processes for performing cleaning or sterilization without disassembly, which are called CIP (cleaning in position) or SIP (sterilization in position) are becoming the mainstreams of today.
For example, Japanese Patent Publication No. 6-89872 proposed a process for keeping the sterilization medium constituted by a section surrounding the mechanical seal portion sterilized by subjecting this sterilization medium to sterilization by steam or introducing sterilized water into said medium.
However, said proposal has a problem that because the sliding faces of sliding rings in the mechanical seal portion are subjected to force fit by a predetermined pressure, steam never reaches the gap between the sliding faces, with the result that a complete sterilization can not be made. In cleaning only or in conjunction with sterilization also lies a similar problem.
Cleaning liquid, sterilization liquid, liquefied steam (water), or cooling liquid used for cooling the mechanical seal in operation may partially collect in the passage. Such a liquid pool is called “cold point”. Liquid gathered in this cold point may be an obstacle to reliable sterilization at the time when further sterlization takes place. In particular, the sterilization requirement on the basis of SIP needs passage of pure steam at a temperature higher than 121° C. for 20 minutes in order to sterilize the mechanical seal portion. However, if the introduced pure steam gets in touch with liquid such as water gathered in the cold point, the temperature of the pure steam will go down, thereby failing to meet said sterilization requirement.
An object of the present invention is the provision of a mechanical seal that may readily control the pressure between the sliding faces of sliding rings, and an agitating device and process using the mechanical seal.
Further object of the present invention is to widen the pressure range for seal liquid and the range of the rotary speed of revolving shaft in which the mechanical seal can be suitably used, by the provision of the mechanical seal enabling the pressure control between the sliding faces.
Further object of the present invention is to provide a mechanical seal that may control the pressure between the sliding faces in operation.
Another object of the present invention is to provide a mechanical seal, and an agitating device and process using same, in which a reliable cooling and sterilization of the sliding faces of sliding rings in the mechanical seal portion can also take place.
Further object of the present invention is to provide a mechanical seal, and an agitating device and process using same, in which a reliable sterilization may be carried out without creation of liquid pools (cold points) which constitute an obstacle, especially, to sterilization through steam.
BRIEF SUMMARY OF THE INVENTION
A first invention of the present application provides a mechanical seal for building a liquid seal between a plurality of sliding rings
2
,
3
opposed and rotatable relatively, namely sliding faces
2
a,
3
a
of said opposed sliding rings
2
,
3
, characterized in that it includes controlling mechanisms
6
,
53
of controlling force to bias at least one
3
of these sliding rings
2
,
3
against the other one
2
, so that the pressure or the gap between the sliding faces
2
a,
3
a
of the opposed sliding rings may be controlled. Said controlling mechanism is capable of controlling the pressure or the gap between the sliding faces
2
a,
3
a
regardless of the pressure of seal fluid or flushing liquid, or within the range wider than the range in which the pressure between the sliding faces may be changed by the seal fluid or flushing liquid.
A second invention of the present application provides the mechanical seal in accordance with the first invention, characterized in that at least one sliding ring
3
is pressed against the other sliding ring
2
by an elastic body, and that said controlling mechanisms
6
,
53
act to control the biassing force by applying force in the direction in which the pressing force due to said elastic body goes, or counter to said pressing force. In many conventional mechanical seals, one sliding ring
3
is pressed toward another sliding ring
2
by means of the elastic body. In this invention, the pressure or the gap between the sliding faces
2
a,
3
a
can be controlled by applying force in the direction in which the pressing force goes or counter to said direction.
A third invention of the present application provides the mechanical seal in accordance with the first or second invention, charac

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