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Publication numberUS3922146 A
Publication typeGrant
Publication dateNov 25, 1975
Filing dateFeb 16, 1973
Priority dateFeb 16, 1972
Also published asDE2207207A1, DE2207207B2
Publication numberUS 3922146 A, US 3922146A, US-A-3922146, US3922146 A, US3922146A
InventorsKupka Dieter
Original AssigneeKupka Dieter
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Stirrer and cover for stirring corrosive charges
US 3922146 A
Abstract
The stirring shaft of a stirrer which is used for stirring charges in a corrosion resistant, high pressure reaction tank is subjected to corrosion by the charge material. A plastic cover is provided which covers that portion of the stirring shaft which contacts the charge material and protects it against corrosion. The cover is firmly secured at one end to the shaft at a portion thereof which does not contact the charge material, and at its other end between the stirring shaft and a stirring element to which the stirring shaft is mounted.
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Description  (OCR text may contain errors)

United States Patent Kupka 1 Nov. 25, 1975 [5 1 STIRRER AND COVER FOR STIRRING 3,246,882 4/1966 Clough 259/108 x CORROSIVE CHARGES 3,622,129 11/1971 Mazowski Inventor. Dieter Kupka, Binger Landstrasse 37a, 657 Kira, Nahe, Germany Filed: Feb. 16, 1973 Appl. No.: 333,002

Foreign Application Priority Data Feb, 16. 1972 German 2207207 11.5. C1 23/252 A; 259/107; 285/292 Int. Cl.'- BOIF 7/16 Field of Search 23/252 A, 285, 289, 290; 259/107, 108, 122; 285/292, 298, DIG. l0; 403/1, 50

[56] References Cited UNITED STATES PATENTS 2.958.517 11/1960 Harker ct al 23/259 X Primary E.\'uminerMorris O. Wolk Assistant E.\'mninerTimothy W. Hagan Attorney, Agent, or FirmEdwin E. Greigg 1 1 ABSTRACT The stirring shaft of a stirrer which is used for stirring charges in a corrosion resistant, high pressure reaction tank is subjected to corrosion by the charge material. A plastic cover is provided which covers that portion of the stirring shaft which contacts the charge material and protects it against Corrosion. The cover is firmly secured at one end to the shaft at a portion thereof which does not contact the charge material, and at its other end between the stirring shaft and a stirring element to which the stirring shaft is mounted.

20 Claims, 5 Drawing Figures US. Patent Novizs, 1975 Sheet20f2 3,922,146

STIRRER AND COVER FOR STIRRING CORROSIVE CHARGES BACKGROUND OF THE INVENTION The present invention relates to a stirrer with a plastic stirring member for stirring systems with a corrosion resistant lining, and especially for stirring charges in glasslined, high pressure reaction tanks, and more particularly to a stirrer in which the stirring member is fabricated as a one-piece element having several arms, with the stirring member being attached to one end of a metallic stirring shaft, which is provided with a plastic cover along that portion of the shaft which contacts the charge material.

For stirring charge material having heavy acid or lye concentrations, for example, the chemical industry uses corrosion resistant stirring tanks made of glasslined steel. Since the stirring elements operating in these stirring tanks must also be corrosion resistant, they are enameled just like the tanks.

During molding of the stirring elements, care must be taken that a uniform and solidly adhering enamel coating develops everywhere. As a result, those stirring elements which are enameled cannot be given the most favorable shape insofar as flow and stirring techniques are concerned. This is particularly true of propellerlike stirring elements where it has been noted that the stresses at the ends of the stirring arms produce vibrations which lead to chipping off of the enamel layer. This result is particularly pronounced with large dimension stirring elements. Also, enameled stirring elements can no longer be balanced after enameling, so that they become limited insofar as the rpms that can be achieved are concerned. That is, one cannot use as high an rpm as in the case of stirring elements which do not need to be corrosion resistant and therefore are not enameled. Then, too, it was found that in the case of the known designs, the enameled tanks had a considerably longer service life than the enameled stirring elements, so that it was necessary to provide the tanks during their service life with several new stirring elements. This, of course, represents a considerable financial burden.

From German Utility Patent No. 1,847,818, published on Mar. 8, 1962, a circulation mixing head for motor driven mixing arrangements for liquid medii made up of welded together parts of plastic, such as polyvinylchloride, is known. The purpose of using plastic was the cost savings realized over the use of high grade metal. However, there is no indication that the peculiarities of the problem, the solution to which gives rise to the present invention, were ever taken into consideration; and especially not the requirements to ensure sealing under thermal strain, to avoid welding in the filling area and the possibility of using polytetrafluoroethylene.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, a general object of the present invention to overcome the adverse aspects associated with enameling the stirring elements of a stirrer utilized for stirring a corrosive material.

It is, therefore, a more specific object of the present invention to provide corrosion resistant stirring elements for the chemical industry which operate in high pressure tanks with a corrosion resistant lining, such as 2 glass, which have a service life corresponding to the service life of the tanks with which they are used.

It is a related object of the present invention to provide a corrosion resistant stirring element utilizing the known advantageous characteristics of plastics and in particular the advantageous characteristics of polytetrafluoroethylene (PTFE) which has been found to have a resistance to chemical attack and a temperature resistance comparable with corresponding characteristics of enamel.

These and other objects of the present invention are accomplished by covering that portion of the stirring shaft which contacts the corrosive charge material with a plastic cover, and by mounting the plastic cover so that one end is firmly secured to the stirring element and the other end is firmly secured to the stirring shaft.

Before proceeding to a detailed discussion of the present invention, it should be noted that attempts have already been made to make steel parts corrosion resistant by coating them with plastic in its liquid state. Protective coatings made from liquid plastic, however, always possess pores which are permeated by chemicals, so that after a short time the metal parts thus coated are attacked.

In addition, welded joints in plastic materials, including PTFE, can only with difficulty be produced in a sufficiently pore-free manner for use in the chemical industry for immersed parts, with the result that the problem also called for the avoidance of welded joints in the plastic material, at least in the area of immersion.

Another fact to consider is that PTFE, which is the most desirable plastic to use, isinclined to run (socalled cold flow). It can therefore be subjected only to low specific surface pressure, or it has to be encased. Also, it has no noteworthy elasticity. Therefore, it does not behave similarly to rubber with the result that it does not automatically return to its previous shape after the cause for its changed shape is eliminated.

The solution to this problem is to be found in the present invention in the fact that at least that part of the metallic stirring shaft which comes into contact with the charge material in the tank is covered by a plastic cover which is driven with the stirrer. The plastic cover represents a prefabricated special construction element, preferably an extruded pipe element which has one of its ends firmly secured to the stirring element of the stirrer and the other of its ends firmly secured to the stirring shaft of the stirrer.

One development according to the present invention lies in the fact that many plastics and particularly PTFE can be easily machined, so that the plastic cover can be configured into any desired shape, and particularly into those shapes which are effective for desirable flow and stirring characteristics. Thus, the need for enameling in order to shape the stirring elements is eliminated. Also, the advantageous characteristics of PTFE are particularly realized when used to fabricate the plastic cover. Like other plastics, however, PTFE contracts and expands in dependence upon temperature fluctuations, and it does so by much greater amounts than metals, and therefore also by a much greater amount than a metal such as steel, which is used for the stirring shafts for which the plastic-covering is to be used.

According to a further development of the present invention, the plastic cover is made particularly resilient over at least a part of its length between its secured ends, so that it is capable of returning to its initial shape even when it changes its shape as a result of changes in 3 temperature. In such an embodiment, the cover has a bellows shape over part of its length near that end which is secured to the stirring shaft.

According to another further development of the present invention, the plastic cover can be bulged out freely between its secured ends.

According to a preferred embodiment, the single piece stirring element of the stirrer and the plastic cover for the stirring shaft both consist of PTFE.

A further development of the present invention lies in the fact that between a connecting rod clamping together the stirring element and the stirring shaft, and one of the elements clamped together by it, a mechanism, preferably a spring, resiliently limiting the transferable clamping power has been inserted. This will counteract the cold flow of substance like PTFE.

Other further developments and details of embodiments of the invention will unfold from the embodiment described in the following paragraphs by way of example and in connection with the claims and the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates in elevation a partial cross-sectional view of a stirrer according to the present invention, with the outside ends of the stirring arms cut away;

FIG. 2 illustrates a partial top view of the stirring element of FIG. 1;

FIG. 3 is a view taken along the lines 3-3 of FIG. 2;

FIG. 4 is a top plan view of the mounting plate for mounting the tie rod and consequently the stirring shaft to the stirring element; and

FIG. 5 is a top plan view illustrating one set of relative positions of adjustable abutment elements which are mounted to the mounting plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more specifically to the drawing, FIG. 1 shows a stirring element 1 fabricated as a one-piece element of PTFE with two stirring arms 2 extending radially outward from a central hub 4. The arms 2 have, as best seen in FIG. 3, a cross section similar to propeller blades. This cross section is produced by a chipping treatment of a starting piece which has a square profile.

The stirring element 1 with its hub 4 is attached to the lower end of a stirring shaft 7 in a manner which will be explained in more detail in the following paragraphs. The stirring shaft 7 is developed as a hollow shaft and is made of a metal, such as steel, preferably high grade steel.

The shaft 7 comprises an upper portion 7, an intermediate metallic weld member 24 and an end seal 25. The lower end of the upper portion 7' has defined therein a recess 7" and the upper end of the end seal 25 has defined therein a recess 25. Both these recesses provide mounting areas for receiving respective ends of the weld member 24 for welding to the upper portion 7' and the end seal 25, respectively. Both the upper portion 7 and the end seal 25 are provided with shoulders which form a limit to the recesses 7" and 25, respectively, on one end, and define frusto-conical surfaces 22 and 19, respectively. In addition, the end seal is also provided with a torque transmitting extension 8 which has a square configuration.

The shaft 7 is constructed to have a larger diameter in its lower area that is, in the area thereof which comes into contact with the material with which the tank is charged, than in its area which does not contact the charge material. The larger diameter area is essentially formed by the weld member 24 which comprises a piece of pipe. In the area which comes into contact with the charge material, which for convenience will be designated as area A, the stirring shaft 7 is covered by a plastic cover 18.

The hub 4 defines a bore which is configured to have a first portion 4 which defines a conical surface 4", a second portion 5 in the form of a square recess and a third portion 6 in the form of a cylindrical counterbore which defines an abutment surface 17.

The cover 18 is a prefabricated, specially constructed element, that is, an element which is extruded in pipe form of PTFE. The upper end of the cover 18 is pressed tightly against the conical surface 22 by means of a screw cap 21, which is provided with a surface 21' and screw threads 20 for this purpose. The screw cap 21 is screwed onto the upper portion 7 of the stirring shaft 7. The lower end of the cover 18 is pressed tightly against the conical surface 4" of the hub portion 4', which generally corresponds to the surface 19. In the area between its tightly attached ends, that is, in area A, the cover 18 may be shrunk on. Alternatively, the cover 18 could also loosely surround the shaft 7 in the area A, so that it can expand or bulge out unimpeded with increasing temperatures, and can contract again in the case of shrinkage due to a drop in temperature. Yet another alternative exists in that the cover 18 can also be made resilient, by being developed in the manner of bellows near its upper secured end. The bellows can be produced originally as a separate part and can be welded together with the downwardly succeeding part of the cover, especially whenever the place of welding is above the filling level of the vessel.

The square recess of the second portion 5 has been so formed in order to engageably receive therein the square torque transmitting extension 8. As a result of this engagement, the stirring element 1 is driven by the stirring shaft 7.

To mount the stirring element 1 to the shaft 7 so that the shaft 7 can drive the stirring element 1, a tie rod 13, a plate 9 and a plurality of adjustable abutment ele' ments 10 are provided. The tie rod 13 passes through a central bore 7' in the shaft 7 and extends outwardly from the end seal 25. The outwardly extending end of the tie rod 13 is provided with external threads which threadedly engage the tie rod 13 within a central bore 12 of the plate 9.

Referring to FIG. 4 it can be seen that the plate 9 is square in shape so that it can be engageable within the square shaped second portion 5 of the bore 4. Surrounding the bore 12 are bolt receiving bores 12'. Bolts 11 are provided with a head portion 11 which contains a hexagonal or polyhedral recess and a shank portion 11". An abutment element head 11" is provided for each bolt 11 on which a respective abutment element 10 is mounted. The head 11" may be a hexagonal nut or the like.

As shown in FIG. 5, the abutment elements 10 have longitudinal slots 26 therein through which the bolts 11 pass. As a result of the slots 26, the abutment elements 10 can be mounted by the bolts 1 1 to the plate 9 so that the plate 9 can be inserted into the recess formed by the second portion 5 of the bore 4 to the position shown in FIG. 1. The abutment elements 10 are then swiveled into the counterbore 6. Thereafter the bolts are held in turn by a tool (not shown), which engages within the hexagonal recesses, while the nuts 11" are rotated by a tool (not shown) which passes through the bore 12. This causes the abutment elements to be maintained in their swiveled position in the counterbore 6 so that they are firmly engaged against the abutment surface 17. Thereafter, the tie rod 13 is threadedly engaged within the bore 12 of the plate 9 to form the assembly.

A compression spring 16 is inserted between a head portion 15 of the rod 13 and an internal shoulder 23 in the upper portion 7' of the stirring shaft 7. The spring 16 is dimensioned such that its windings will not fit against each other, that is, the spring will not completely close, even if the tie rod 13 is tightened to a point where it clamps the stirring shaft 7 tightly together with the stirring element 1. The spring 16 is selected so that the clamping force will not produce too high a specific surface pressure between the abutment element 10 and the abutment surface 17, so that therefore, a cold flow of the PTFE of the stirring element 1 will be avoided.

I claim:

1. In a stirrer for stirring corrosive charges in corrosion resistant, high pressure reaction tanks, such as glass-lined tanks, the stirrer including a metallic stirring shaft and a plastic stirring element attached to one end of the stirring shaft, said stirring element being driven by said stirring shaft, the stirring element being fabricated as a one-piece element having a plurality of arms, the improvement comprising: a plastic cover covering a portion of the stirring shaft which contacts the corrosive charge, said cover having two end portions with one end portion being sealingly secured to the stirring element and the other end portion being sealingly secured to the stirring shaft wherein said cover has an intermediate portion between its secured end portions which is movable relative to said end portions, and wherein said cover is fabricated so that at least part of its length between its secured ends is resilient and thereby capable of returning to its initial shape as a result of temperature changes.

2. In a stirrer for stirring corrosive charges in corrosion resistant, high pressure reaction tanks, such as glass-lined tanks, the stirrer including a metallic stirring shaft and a plastic stirring element attached to one end of the stirring shaft, the stirring element being fabricated as a one-piece element having a plurality of arms, the improvement comprising: a plastic cover covering a portion of the stirring shaft which contacts the corrosive charge, said cover being fabricated as an extruded pipe and having two end portions with one end portion being sealingly secured to the stirring element and the other end portion being sealingly secured to the stirring shaft.

3. In a stirrer for stirring corrosive charges in corrosion resistant, high pressure reaction tanks, such as glass-lined tanks, the stirrer including a metallic stirring shaft having a frusto-conical portion and a plastic stirring element attached to one end of the stirring shaft, the stirring element being fabricated as a one-piece element having a plurality of arms, the improvement comprising: a plastic cover covering a portion of the stirring shaft which contacts the corrosive charge, said cover having two end portions with one end portion being sealingly secured to the stirring element and the other end portion being sealingly secured to the stirring shaft; a screw cap which threadedly engages said stirring shaft, said screw cap having a surface which is generally parellel to the outer surface of said frusto-conical portion, said threaded engagement being such that said one end portion of said cover can be received and secured between said surfacesv 4. In a stirrer for stirring corrosive charges in corrosion resistant, high pressure reaction tanks, such as glass-lined tanks, the stirrer including a metallic stirring shaft and a plastic stirring element attached to one end of the stirring shaft, the stirring element being fabricated as a one-piece element having a plurality of arms, the improvement comprising: a plastic cover covering a portion of the stirring shaft which contacts the corrosive charge, said cover having two end portions with one end portion being sealingly secured to the stirring element and the other end portion being sealingly secured t0 the stirring shaft, wherein the diameter of said stirring shaft along the portion thereof which is covered by said cover and is in the area of the corrosive charge is larger than the diameter of said stirring shaft along the portion thereof which is not covered by said cover.

5. A stirrer as defined in claim 4, wherein the larger diameter portion of said stirring shaft includes an end seal and a metallic weld member, said end seal having a recess for receiving and having welded therein one end of said weld member, and wherein said end seal includes a frusto-conical sealing portion and a torque transmitting extension.

6. In a stirrer for stirring corrosive charges in corrosion resistant, high pressure reaction tanks, such as glass-lined tanks, the stirrer including a metallic stirring shaft and a plastic stirring element attached to one end of the stirring shaft, the stirring element being fabricated as a one-piece element having a plurality of arms, the improvement comprising: a plastic cover covering a portion of the stirring shaft which contacts the corrosive charge, said cover having two end portions with one end portions with one end portion being sealingly secured to the stirring element and the other end portion being sealingly secured to the stirring shaft; a tie rod; and a holding mechanism, said tie rod being adapted to attach said stirring shaft to said stirring element and said holding mechanism being adapted to effect said attachement, wherein said stirring element includes a bore defining hub portion at its center, and said stirring shaft includes an end seal having a frustoconical sealing portion and a torque transmitting extension, and wherein said bore is configured to define a first portion having a surface which is generally parallel to the outer surface of said frusto-conical portion and defining a receiving space for said frusto-conical portion, a second portion defining a receiving space for said torque transmitting extension and a third portion defining an abutment surface for said holding mechanism.

7. A stirrer as defined in claim 6, wherein said holding mechanism comprises: a mounting plate having a central threaded bore within which said tie rod is threadedly received and a plurality of bolt receiving bores, said plate being adapted for reception within said second bore portion; and a plurality of adjustable abutment elements, each being rotatably mounted by a bolt to said plate at a respective one of said bolt receiving bores, and each being positioned relative to said plate so that said plate can be received into said second bore portion and thereafter each is positioned within said third bore portion and in engagement with said abutment surface.

8. In a stirrer for stirring corrosive charges in corrosion resistant, high pressure reaction tanks, such as glass-lined tanks, the stirrer including a hollow metallic stirring shaft and a plastic stirring element attached to one end of the stirring shaft, the stirring element being fabricated as a one-piece element having a hub portion and a plurality of arms, the improvement comprising: a plastic cover covering a portion of the stirring shaft which contacts the corrosive charge, said cover having two end portions with one end portion being sealingly secured to the stirring element and the other end portion being sealingly secured to the stirring shaft; a tie rod which passes through said hollow stirring shaft; and means mounting said tie rod within said hub portion to said stirring element to thereby clamp together said cover, said stirring shaft and said stirring element and effect one of the secured ends of said cover.

9. A stirrer as defined in claim 8, wherein the improvement further comprises: resilient means mounted between said tie rod and said stirring element thereby resiliently limiting the transferable clamping force.

10. A stirrer as defined in claim 9, wherein said resilient means is a spring.

11. A stirrer as defined in claim 8, wherein said hub portion defines a bore and said stirring shaft includes an end seal having a frusto-conical sealing portion and a torque transmitting extension, and wherein said mounting means comprises: a holding mechanism which is adapted to mount said tie rod to said stirring element within the bore of said hub portion, said bore being configured to define a first portion having a surface which is generally parallel to the outer surface of said frusto-conical portion and defining a receiving space for said frusto-conical portion, a second portion defining a receiving space for said torque transmitting extension and a third portion defining an abutment surface for said holding mechanism.

12. A stirrer as defined in claim 11, wherein said holding mechanism comprises: a mounting plate having a central threaded bore within which said tie rod is threadedly received and a plurality of bolt receiving bores, said plate being adapted for reception within said second bore portion; and a plurality of adjustable abutment-elements, each being rotatably mounted by a bolt to said plate at a respective one of said bolt receiving bores, and each being positioned relative to said 8 plate so that said plate can be received into said second bore portion and thereafter each is positioned within said third bore portion and in engagement with said abutment surface.

13. A stirrer as defined in claim 8, wherein the improvement further comprises: resilient means mounted between said tie rod and said stirring shaft thereby resiliently limiting the transferable clamping force.

14. A stirrer as defined in claim 13, wherein said resilient means is a spring.

15. A stirrer as defined in claim 13, wherein said tie rod is provided with a head and said stirring shaft is provided with a shoulder, and wherein said resilient means is mounted between said head and said shoulder.

16. In a stirrer for stirring corrosive charges in corrosion resistant, high pressure reaction tanks, such as glass-lined tanks, the stirrer including a metallic stirring shaft and a plastic stirring element attached to one end of the stirring shaft, the stirring element being fabricated as a one-piece element having a plurality of arms, the improvement comprising: a plastic cover covering a portion of the stirring shaft which contacts the corrosive charge, said cover having two end portions with one end portion being sealingly secured to the stirring element and the other portion being sealingly secured to the stirring shaft; a tie rod for clampably mounting said stirring shaft to said stirring element; and resilient means mounted between said tie rod and said stirring shaft thereby resiliently limiting the transferable clamping force.

17. A stirrer as defined in claim 16, wherein said resilient means is a spring.

18. A stirrer as defined in claim 16, wherein said cover has an intermediate portion between its secured end portions which is movable relative to said end portions.

19. A stirrer as defined in claim 18, wherein said cover is fabricated so that at least part of its length between its secured ends is resilient and thereby capable of returning to its initial shape when it changes its shape as a result of temperature changes.

20. A stirrer as defined in claim 16, wherein both said stirring element and said cover consist of polytetrafluoroethylene.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2958517 *Apr 28, 1958Nov 1, 1960Bellco Glass IncVessel for tissue culture and the like comprising a magnetic stirrer
US3246882 *Feb 19, 1964Apr 19, 1966Carves Simon LtdApparatus for the aeration of liquids
US3622129 *May 14, 1969Nov 23, 1971Bellco Glass IncMagnetic stirrer apparatus
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4575253 *Nov 22, 1983Mar 11, 1986Dipl. Ing. H. List, Industrielle VerfahrenstechnikStirring apparatus
US7427449 *Oct 22, 2002Sep 23, 2008General Dynamics Information Technology, Inc.Proton exhange membrane fuel cells using reformates from hydrocarbon fuel combustion combined with hydrogen peroxide and a permanganate salt to produce oxygen, an insoluble carbonate and manganese (II) which further reacts with sulfur in the fuel to form insoluble sulfides, sulfites, or sulfates; cars
Classifications
U.S. Classification422/310, 422/226, 366/279, 366/343, 422/240
International ClassificationB01F7/00, B01F15/00
Cooperative ClassificationB01F7/00016, B01F7/00041
European ClassificationB01F7/00B10, B01F7/00B10B2