Seal for a joint or juncture – Seal between relatively movable parts – Relatively rotatable radially extending sealing face member
Reexamination Certificate
2001-08-10
2003-12-23
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Relatively rotatable radially extending sealing face member
C277S408000
Reexamination Certificate
active
06666457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a sealing device for sealing a cavity that can be rotated around a rotational axis, especially a cavity of a rotary film evaporator.
2. Description of the Prior Art
In order to evaporate substances, for example, in order to evaporate solvents during the concentration of pharmaceutical or chemical products, rotary film evaporators are used, such as for example, the commercially available rotary film evaporators made by Genser Wissenschaftliche Apparate (a scientific equipment company) based in Rothenburg o.d.T., Germany. With these known rotary film evaporators, the liquid substances to be evaporated are placed into the cavity of a rotating flask (evaporator vessel), usually in a heating bath. By rotating the flask, a thin liquid film is created on the inside of the rotating flask and the substance, especially the solvent, evaporates from said liquid film. A certain amount of the substance or of the solvent also evaporates directly out of the liquid surface in the rotating flask. The vapor is transported out of the rotating flask through a vapor line to a condenser, where it is condensed out again. In general, a negative pressure or vacuum is also generated in the rotating flask in order to increase the vapor pressure of the substances to be evaporated and in order to treat the product gently. The vapor line is connected in a passage area to the rotating flask via a rotatable connection. The connection site is sealed by means of an axial sliding ring sealing device that has a sliding ring arranged concentrically to the rotational axis on the rotating flask and a counter sealing face on the vapor line on which the sliding ring slides when the flask rotates. The sliding ring is made of a PTFE compound (PTFE/glass), the counter sealing face on which the sliding ring slides is often made of glass. However, it is also known to employ radial shaft seals, for example, radial sliding rings (shaft sealing rings) cooperating with a corresponding cylindrical counter sealing face to seal the system.
Extremely high demands are made to the sealing system of a rotary film evaporator. It has to be resistant to virtually all chemicals and has to remain leak-tight over a long period of time. Moreover, when leaks occur in the sealing system, sometimes spontaneously, the vacuum in the system deteriorates, that is to say, the pressure rises. This vacuum deterioration leads to an increase in the boiling temperature (or to a reduction of the vapor pressure) and thus to a rise in the product temperature. This is normally ameliorated by the fact that the heating bath temperature is set at a value that is not critical for the product. However, the drawback of this approach is that the evaporation performance is worse. Furthermore, as a result of a leak, product losses or even product destruction can occur, which is often associated with substantial financial losses in the case of sensitive and expensive products.
For these reasons, both sealing faces are machined mechanically precisely so that the leakiness at this sealing site is as small as possible. In the case of a sliding ring seal, there can also be an adjustment means for the sliding ring or for the opposite side in order to compensate for temperature differences and/or wear and tear of the seal. These known measures yield a final vacuum value of at least 0.1 mbar in the rotary film evaporator without any problems when a commercially available laboratory oil vacuum pump (rotary slide-valve pump) with a suction capacity of about 2500 liters per hour is used to evacuate the rotary film evaporator. EP 0,504,099 B1 discloses a rotary film evaporator with which the leak-tightness of a sealing system for carrying the vapor to the rotating flask is improved in that two tubular or annular parts are arranged coaxially to the rotational axis and adjacent to each other, whose front ends facing each other form sealing faces that slide on each other. These sealing tube parts or sealing ring parts are made of a sliding plastic, glass, ceramic or carbon material and especially of a PTFE composite material. A stationary sealing ring is additionally arranged on the outside of the lateral surface area of each of the two tubular or annular parts.
The object of the present invention is to provide a sealing device for a rotatable cavity, especially of a rotary film evaporator, with improved leak-tightness.
SUMMARY OF THE INVENTION
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a sealing device for sealing a rotatable cavity that can be rotated around a rotational axis, especially a cavity of a rotary film evaporator, which comprises
a) a number n≧2 of sealing areas that are separated from each other by n−1 intermediate zones (interspaces) that each lie between two sealing areas and in each of which two sealing faces, which run continuously (coherently) around the rotational axis, can be moved (rotated) slidingly (abrasively, prone to wear and tear) on each other when the cavity rotates, and
b) at least one, especially lockable, connection for at least one of the intermediate zones for charging and/or discharging and/or passing fluids (vapor) into or out of or through the intermediate zone.
The present invention is based on the notion of creating at least one additional buffer zone that is located in the seal between the cavity and an outer, generally air-filled, chamber and that is in the form of an intermediate zone which, in the flow direction for fluids flowing through the seal in case of a leak, is arranged in series with respect to the other sealing areas with the flat or curved sealing faces that slide on each other. This buffer zone or these buffer zones can be flow-connected via the appertaining connection to a fluid-filled chamber or a fluid conveying means. In this manner, the interfering influence of an existing leak can be diminished or compensated for in a desired manner, for example, by generating a defined pressure, especially a negative pressure, or a defined gas atmosphere in the intermediate zone.
Alternatively, the sealing device for sealing a cavity that can be rotated around a rotational axis, especially a cavity of a rotary film evaporator, can comprise
a) at least two sealing faces that slide on each other and can be rotated opposite from each other and
b) at least one surface-pressure control element to control the surface pressure with which the sealing faces that slide on each other can be pressed against each other,
whereby
c) the surface-pressure control element has a control connection to apply a controlling quantity.
Through these measures, it is possible to compensate for wear and tear or thermal expansion behavior of the sealing faces by an automatic setting or adjustment of the surface pressure of the sealing system. The formation of a gap between the sealing faces can be avoided.
In a first advantageous embodiment of the sealing device, the sealing areas are located radially, that is to say, perpendicular to the rotational axis, at a distance from each other relative to the rotational axis. This embodiment corresponds to an axial seal or axial shaft seal that has been improved according to the invention, including, for example, an axial sliding ring seal. The intermediate zones and the sealing areas are then preferably arranged concentrically around the rotational axis, but they can also be arranged eccentrically. In addition to the preferred annular or hollow-cylindrical shape, the intermediate zones and the sealing areas can also have a different closed shape, for example, an elliptical shape. Preferably the sealing faces are aligned essentially orthogonally relative to the rotational axis.
In a second and likewise advantageous embodiment of the sealing device, the sealing areas are arranged axially relative to the rotational axis, that is to say, parallel to the rotational axis, staggered with respect to each other. This embodiment corresponds to a radial seal or radial shaft
Knight Anthony
Kyle Michael J.
Sidley Austin Brown & Wood LLP
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