Shaft seal for mixers

Details Shaft seal for mixers Shaft seal for mixers

1998-11-18

2001-01-02

Knight, Anthony (Department: 3626)

Seal for a joint or juncture

Seal between relatively movable parts

Close proximity seal

C277S418000, C277S420000, C277S421000, C277S348000

Utility Patent

active

06168163

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates broadly to shaft sealing structure and, more particularly, pertains to a sealing and feed through arrangement for a rotating shaft used in mixing equipment to prevent the ingress of contaminants and control the egress of lubricant regardless of the various forces subjected upon the shaft.
BACKGROUND AND SUMMARY OF THE INVENTION
Spiral blade horizontal drum mixers are used to provide highly viscous, wet mixtures of concrete, mortar and the like. Such horizontal drum mixers are commonly equipped with a low speed rotating shaft which extends across a mixing tank, and protrudes or feeds through the opposed end walls of the tank with one end of the shaft coupled to a drive arrangement and the other end of the shaft supported by a bearing structure. As is well known, sealing arrangements surrounding the shaft are positioned on the interior and exterior surfaces of each end wall. More particularly, a rotor is connected for rotation with the shaft and is mounted adjacent to a liner on each end wall, while a non-rotatable stator is fixed on the outside of each end wall. The rotor and stator cooperate to form a primary labyrinth seal into which grease is periodically delivered in a manner which will keep the shaft lubricated and, at the same time, trap contaminants so that they are restricted from entering the seal. In most cases, the labyrinth seal is formed by a single flange-like baffle extending into a formed recess to create a tortuous path that makes it difficult for contaminants to invade the seal to degrade lubricant effectiveness.
In the course of normal operation of the horizontal drum mixture, it has been found that the rotating shaft is subject to radial, axial and angular forces which can cause the labyrinth seals to bind and fail. One way to avoid this problem is to provide larger, more tolerable clearances between the baffle and its recess. However, such alternative is not desirable because it results in higher costs of machining the rotor and stator. Even if it were cost permissible, the larger labyrinth pathways would allow grease to flow more quickly into and out of the seal, such that the lubricating and trapping functions of the seal would be negatively affected.
A further problem with prior art seals is the exposure of the inner portions of the seal within the mixing tank to the setting or “freezing” of grout infiltrate during periods of mixer shut down at the interface between each rotor and end wall liner. Before mixing can resume, this problem must be rectified by breaking the newly formed grout seal such as by applying a grinding wheel thereto. Such remedy creates unwanted down time of the mixer and results in increased maintenance costs.
It should also be noted that the formation of shaft seals of the type described above involves machining methods that can create a troublesome gap between the rotor and stator which makes alignment between these components less than precise, so that the integrity of the seal is compromised.
Despite the existence of various shaft sealing devices, there remains a need for an enhanced sealing arrangement which will provide effective sealing action, whether the shaft is at rest or in rotation. Accordingly, it is desirable to provide a shaft seal which will effectively retain lubricant and prevent contamination therein. It is also desirable to provide a shaft seal in which a rotor and stator are manufactured and assembled in a more precise fashion. Likewise, it is desirable to provide a shaft seal which is unaffected by various forces applied to the shaft during the rotation thereof. Furthermore, it is desirable to provide a sealing device which will enable the holding of tighter tolerances in the formation of labyrinth seals. It is also desirable to provide a shaft seal which will improve the effectiveness of a horizontal drum mixing machine.
It is a general object of the present invention to provide an improved primary seal and feed through arrangement for mixing equipment having a mixing tank through which a rotatable shaft extends, such that a portion of the seal arrangement floats and self aligns to compensate for radial, axial, and angular misalignment between the rotating shaft and the seal arrangement.
It is also an object of the present invention to provide a double labyrinth type shaft seal which allows for the use of tighter tolerances along the labyrinth pathways minimizing wear and improving the sealing capabilities for a rotating shaft.
It is a further object of the present invention to provide a secondary face seal arrangement interposed between a seal rotor and a seal stator mounted along a low speed rotating shaft on a horizontal drum mixer.
Yet another object of the present invention is to provide a shaft seal of split construction which is easily manufactured, assembled and serviced.
Still another object of the present invention is to provide a shaft seal for a spiral blade mixer which is effective to control the setting of wet mixed material during periods of mixer shutdown.
Moreover, a further object of the present invention is to provide a shaft seal which employs a compressible gasket to facilitate set-up of labyrinth structure.
In accordance with one aspect of the present invention, a shaft seal is interposed between a tank and a rotating shaft extending through the tank, and has a non-rotatable stator fixed to the tank and a rotor fixed for rotation to the shaft. The seal is improved so as to include a multiple labyrinth structure formed between the rotor and the stator for preventing the ingress of contaminants from the tank and the egress of lubricant from the shaft. The invention is further improved by a self-aligning arrangement constructed and arranged to permit the stator to shift axially along the shaft and compensate for various forces inflicted on the shaft as the shaft rotates. In the preferred embodiment, the multiple labyrinth structure includes a pair of baffles oriented at substantially 90° to each other. The rotor is formed with an axially extending recess receiving one of the baffles and a radially extending groove receiving the other of the baffles. The tank includes an end wall and has a liner connected thereto. One of the baffles is defined by an axially extending flange formed on the stator, while the other of the baffles is formed by the liner. A compressible gasket is interposed between facing surfaces of the stator and rotor and is engaged against the end wall. A set of fastener assemblies extends through the tank liner, the tank end wall, the gasket and the stator for holding the rotor and stator together in a preload arrangement relative to the tank. A first rubber spring washer and ring are disposed for rotation between the rotor and the shaft, and a second rubber spring washer and a ring are fixedly disposed between the stator and the shaft. A stationary lip seal is also fixed between the stator and the shaft. The stator extends outwardly of the tank end wall and the rotor extends inwardly of the tank liner. A bearing device is supported on an end of the shaft outwardly of the stator. The tank liner is spaced from the walls forming the rotor groove. The self-aligning arrangement is defined by the spacing of the tank liner from the walls of the groove, the preload arrangement of the fastener assemblies and the compressibility of the gasket.
In another aspect of the invention, a seal is provided for use with a mixing tank provided with a rotating shaft extending across and protruding through opposed end walls, each end wall having an inner liner. The seal includes a stator fixed to one of the end walls and having a facing surface and an axially extending flange formed thereon. A rotor is connected to the shaft for rotation therewith, and has a facing surface as well as an axially extending recess for receiving the stator flange to define a first labyrinth passage. The rotor also has a groove extending radially inwardly from the periphery of the rotor for receiving the liner of the end wall to define a second labyrinth passage in c

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