IMPELLER FOR ASEPTIC PURPOSES

Abstract: An impeller for aseptic purposes which is rotatable by induc­ tive drive means in a predetermined direction within a vessel for stirring and mixing sterile fluids. The impeller (10) comprises a plurality of radially extending stirring blades (15) on an outer surface of the impeller and bearing means on an inner surface of said impeller for rotatably mounting the impeller on the vessel wall. The impeller is further provided with through-flow passages which outwardly extend from the inside of the impeller in a direction away from an axis of rotation, through orifices (25, 26) which are situated on the outer sr-face of the impeller immediately adjacent each blade (15), seen in said direction of rotation, so that cleaning fluid can be sucked through the passages due to a low pressure region occurring behind each blade.

Description: The present invention relates to an impeller for aseptic purposes, rotatable by inductive drive means in a predetermined direction within a vessel for stirring and mixing sterile fluids, comprising a plurality of radially extending stirring blades located on an outer surface of the impeller and bearing means on an inner surface of said impeller for rotatably mounting the impeller on the vessel wall. It is known to generate stirring motion in a fluid within a closed vessel by means of a magnetic coupling between an external drive unit and a completely separate internal impeller (see for example US 4209259). At the same time it is a recognized problem to carry out cleaning and sterilizing of the vessel interior with the impeller. It has been proposed to provide the impeller with radial passages, which make it possible for cleaning fluid, for example water or overheated steam, to force its way in to the impeller's inner surfaces and flow over the bearing means. However, a really effective sterilization is usually only achievable after a relatively prolonged cleaning cycle. The object of the invention is thus to provide an impeller with a considerably greater self-cleaning capability so that sterilization with steam or other fluids can occur in a considerably shorter time. This object is achieved according to the invention by an impeller which is characterized by through-flow passages which outwardly extend from the inside of the impeller in a direction away from the axis of rotation, to orifices situated on the outer surfaces of the impeller immediately adjacent and behind each blade, seen in said direction of rotation, so that cleaning fluid can be sucked through the passages due to the low pressure region occurring behind each blade. According to a preferred embodiment of the invention the bearing means includes a stub-axle centrally locatable on an end wall of an inwardly extending cylindrical recess in the vessel's bottom wall. The cylindrical recess is appropriately surrounded by a peripheral section having a particular small clearance which permits the flow of cleaning fluid between the cylindrical recess and the peripheral section of the impeller. The above-mentioned, and further characteristics of the invention will be described in more detail in the following, with reference to the attached drawings in which Figure 1 shows a plan view of an impeller according to the invention, Figure 2 is a partially sectioned side view of the impeller including its drive arrangement, and Figure 3 is a section along line III-III in figure 1. The impeller 10 shown in the drawing is located in a mixing vessel whose bottom wall 11 is shown in figure 2. The vessel is intended for use in a large process plant, for example for preparation of medicaments, and is provided with a number of inlets, outlets and regulating valves. Various sterile fluids are delivered to the vessel where they are mixed together by means of the impeller 10, after which the resulting mixture is drawn from the vessel. The bearing- and drive means of the impeller are shown in figure 2 and include an inwardly-directed cylindrical recess 12 in the vessel wall 11, the recess being welded in such a way that no opening or inlets occur in this section of the tank wall. The impeller 10 is rotatably supported by means of a bush 10a on a stub axle 13 which is centrally located on an end wall 14, which demarcates the cylindrical recess 12. The impeller 10 is, like the vessel 11, principally manufactured from acidproof stainless steel, with a number of angled blades 15 and a central lifting ring 16. The impeller presents a peripheral section 17 which surrounds the cylindrical recess 12 and contains a number of permanent magnets 18 which are inductively connected to a corresponding number of permanent magnets 19 which are located in a rotor 20. This rotor is arranged to be driven in the direction of arrow 21 (see figure 1) by a (not shown) conventional electric motor, whereby the impeller 10 surrounding the recess is caused to rotate. From figure 3 it can be seen that the impeller is provided with through-flow passages 22,23, which extend from within the impeller 10 in a direction away from the axis of rotation 24 to orifices 25 resp. 26, situated on the outer surface of the impeller immediately adjacent and behind each blade 15, seen in said direction of rotation. Through this arrangement, cleaning fluid will be sucked through the passages due to the low pressure region occurring behind each blade. In this way cleaning fluid can flow over the recess 12 and the stub axle 13 during rotation of the impeller, whereby the fluid can flow out from the impeller via the substantially radially directed passages 22, 23. The invention is not restricted to above described example, but may be varied within the scope of the following claims. For example the passages and the orifices can be greater or fewer in number. The device for driving the impeller can be differently designed.

Claims: An impeller for aseptic purposes, rotatable by inductive drive means (20) in a predetermined direction within a vessel (11) for stirring and mixing sterile fluids, comprising a plurality of radially extending stirring blades (15) located on an outer surface (10) of the impeller and bearing means (10a, 13) on an inner surface of said impeller for rotatably mounting the impeller on the vessel wall, characterized by through-flow passages (22, 23) which outwardly extend from the inside of the impeller (10) in a direction away from the axis of rotation (24), to orifices (25, 26) situated on the outer surface on the impeller immediately adjacent and behind each blade, (15) seen in said direction of the rotation, so that cleaning fluid can be sucked through the passages (22, 23) due to the low pressure region occurring behind each blade. Impeller according to claim 1, characterized in that the bearing means includes a stub axle (13) centrally locatable on an end wall (14) of an inwardly extending cylindrical recess (12) in the vessel's bottom wall (11). Impeller according to claim 2, characterized by a peripheral section (17) being able to surround the cylindrical recess (12) with a particular small clearance, which permits the flow of cleaning fluid between the cylindrical recess (12) and the peripheral section (17) of the impeller.

Inventors: ARTHUN, NILS
Applicants: STERIDOSE SYSTEMS AB
Application year: 1990
Main classification: B01F15
IPC codes: B01F13, B01F15, B01F3