DE102013104788A1 - magnetic stirrer - Google Patents

Abstract

The invention relates to a magnetic stirrer (1) with a can (3) and a stirrer (2), in which the can (3) has a drive section (5) in which a rotatable magnet arrangement (6) is arranged, which is magnetically connected to a Magnet arrangement (6A) is coupled, which is arranged in a drive ring (9) of the stirring head (2) surrounding the drive section, and a bearing section designed as a bearing journal (12), which has a pair of plain bearings with a bearing sleeve (11) arranged on the stirring head (2) forms, the bearing journal (11) having a tubular first bearing layer (15) with increased hardness, which is integrally connected to the bearing journal (11).

Description

FIELD OF THE INVENTION

The present invention relates to a magnetic stirrer with a split pot and a stirring head. In this case, the split pot on a drive portion in which a rotatable, coupled to a drive magnet assembly is arranged. This is magnetically coupled to a magnet arrangement which is arranged in a drive ring of the stirring head, which surrounds the drive section. At the split pot a bearing pin is arranged, which forms a plain bearing with a arranged on the mixing head bearing sleeve.

Such magnetic stirrers are mainly used in process technology and in particular in sterile technology. They are suitable for mixing liquid volumes from 2 liters to 50 m ³ in a hermetically sealed process chamber or process vessel. Such process vessels are usually designed as a stationary cylindrical container in which the magnetic agitator is arranged in the curved bottom a little eccentric and thus achieved by the asymmetric mixing effect complete mixing of the stirring medium. A magnetic stirrer for installation in the ground, for example, from EP 1 748 201 B1 known.

There are also versions (see eg EP 0 590 472 B1 ), in which the so-called split pot is designed as a longer unilaterally open tube, at the end of the drive and bearing section is arranged. Such a stirrer is then hung, for example, from above into the process container. The arranged at the lower end in the interior of the tube rotatable magnet assembly is then coupled, for example via an optionally mounted shaft with a drive motor, which can be arranged outside of the tube.

2 shows the structure of such a sliding bearing. The split pot, which is connected via its collar or flange with a container (welded or screwed), carries on its (upper) bottom a bearing pin on which a bearing bush L is pushed, which is secured by a bolt B against rotation, and with its shoulder in the foot area (transition bearing pin to the split pot bottom) is sealed via an O-ring O to the journal. The bushing is fixed by a retaining screw S, which is screwed via a thread introduced into the bearing journal with this. Between the head of the retaining screw and the end surface of the bearing bush, an O-ring O is also arranged to seal the cavities H in the interior of the bearing bush against the product environment.

The actual stirring head has a bearing ring R, which is shrunk onto a bearing sleeve, which is plugged onto the bearing bush L and is guided by this axially (down) and radially. About stirring elements of the bearing ring is coupled to a drive ring containing permanent magnets which are magnetically coupled to drive magnets which are arranged in a drive portion of the split pot.

In this bearing arrangement, there is the problem that in operation - for example due to temperature fluctuations, properties of the material to be stirred (creeping oils, etc.), cleaning operations, etc. - product residues, detergents or water vapor can get into the cavities H between bearing bush and journal despite the seals O. These contaminants can only be removed by completely disassembling the bearing. For this purpose, either the containment shell must be removed and dismantled or - in the case of a welded-in containment shell - the agitator must be entered. If the cavities H remain unpurified, the residues present there may possibly even be germinated and contaminate the material to be stirred. Such impurities are not acceptable in the largely aseptic manufacture of pharmaceutical products or foods.

In order to minimize such contamination, there is the approach to dispense with the bearing bush on the journal and store the mixing head directly with the bearing sleeve on the journal. However, the austenitic steel materials (1.4301, 1.4404, 1.4462) usually used in such stirred tanks have comparatively poor tribological properties. It may occur during operation of the agitator metallic abrasion, which would also contaminate the material to be stirred. The WO 2011/049492 A1 shows a separate bearing pin (possibly from another suitable for sliding bearing purposes more suitable material), which is placed on the gap pot. Again, however, there remains the problem of a joint, which is necessary between the containment shell and journals and may possibly be contaminated.

It is also a containment shell made of plastic (see. EP 1 748 201 B1 ) proposed, to which the bearing pin is integrally formed. Although the joint problem is solved here, the abrasion problem remains, even if the tribological properties of a plastic in conjunction with a metallic or ceramic bearing ring can be improved. In addition, a split pot with a molded plastic bearing pin may not have the required strength to accommodate the transmitted over the bearing ring on the bearing pin bearing forces. this applies in particular for highly viscous, heterogeneous and / or hot material to be stirred.

It is therefore an object of the present invention to provide an improved magnetic stirrer in which the abovementioned disadvantages are at least partially eliminated.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, the present invention provides a magnetic stirrer having a split pot and a stirring head and the split pot includes a drive portion in which a rotatable magnet assembly is magnetically coupled to a magnet assembly that is in a drive portion surrounding drive ring of the stirring head is arranged, and designed as a bearing journal bearing portion which forms a sliding bearing pairing with a arranged on the mixing head bearing bush, wherein the bearing pin has a tubular first bearing layer with increased hardness, which is materially connected to the bearing pin.

Such an additional bearing layer, which is materially connected to the journal, on the one hand provides a stable and abrasion-resistant counter surface for the arranged in the mixing head bearing bush. On the other hand, the cohesive connection with the journal prevents any type of gaps or cavities that can lead to contamination of the material to be stirred. So it can be met both the high demands on the purity and the cleaning properties as well as those of a stable and low-abrasion bearing pairing in plain bearings.

Further aspects and features of the present invention will become apparent from the dependent claims, the accompanying drawings and the following description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the invention will now be described by way of example and with reference to the figures. Showing:

1 a partial sectional view of a magnetic stirrer according to the invention,

2 a partial sectional view of a known from the prior art magnetic stirrer.

DESCRIPTION OF EMBODIMENTS

1 shows a magnetic stirrer according to the invention. Before a detailed description first follows general explanations to the embodiments.

In one embodiment, in addition to the bearing journal itself, a foot region surrounding the bearing journal has an annular disc-shaped second bearing layer with increased hardness, which is connected in a material-locking manner to the foot region. This bearing layer forms when moving or braking the mixing head a sliding bearing pairing with the end face of the stirring head, which settles on this bearing surface when approaching or braking. This embodiment is particularly useful in such agitators where the impellers are configured to create an axial force upon agitation that lifts the agitator head axially on the journal. However, this lifting force only occurs at a certain speed and with certain properties of the stirring medium (viscosity, density).

In one embodiment, in which the 1st and 2nd bearing layer, namely the cylindrical and ring-shaped bearing layer, merge seamlessly with each other, it is possible to prevent stress-affecting notch effects from becoming noticeable in the transition or surface defects occur which could impair cleaning.

In an embodiment in which the containment shell and journal are formed of an austenitic stainless steel material, process containers are available to interior spaces everywhere surfaces that are resistant to a variety of chemical products and have excellent cleaning properties.

There are versions in which the bearing layer (layers) are designed as so-called DLC layers. Such an amorphous diamond-like carbon coating (ADLC) is homogeneous and well adherent, provides coefficients of friction ranging from 0.02 to 0.1 against different friction partners, is resistant to a variety of acids and bases, has high thermal conductivity, and is temperature resistant up to 300 ° C. Usual layer thicknesses are between 1 and 4 microns, preferably between 2 and 3 microns in steel materials.

There are also versions in which the bearing layer has a multilayer structure. In this case, outer layers of aluminum oxide or zirconium oxide have proven themselves. Such ceramic coatings are applied to the steel using plasma techniques. The layer thicknesses are between 2 microns and 2 mm.

There are also embodiments in which the bearing layer is applied via a hardening process, namely by low-temperature nitrocarburizing. In this case, a 10-30 .mu.m thick, nitrogen-enriched edge layer is formed in the starting material, which also has good sliding properties.

There are also embodiments in which the electrical conductivity of the bearing layer is increased (the contact resistance is then less than 10 ⁶ ohms). Thus, electrostatic effects during stirring can be reduced (eg electrostatic charging of the surfaces on the bearing journal or on the bearing sleeve). This prevents critical spark discharges, which can lead to burns, explosions or deflagrations in combustible or explosive stirring media (especially bulk solids). In the case of coatings which have a very low conductance, the unwanted electrostatic charge can also be prevented by microcracks being present in the coating surface, which allow the charges to flow away via the containment shell.

In one embodiment, the bearing sleeve disposed in the bearing ring on a cylindrical Radialgleitfläche, which cooperates with the first bearing layer, and a planar Axialgleitfläche, which cooperates with the second bearing layer. This ensures the required slide bearing pairing with specially treated surfaces and materials under all operating conditions (starting, stopping, continuous operation).

The design of the bearing sleeve made of a silicon carbide material offers a particularly low-wear, durable, and dry-running storage of the stirring head, especially in conjunction with an ADLC coating on the journal.

The shrinking of the bearing sleeve in the bearing ring arranged on the stirring head stabilizes the bearing sleeve against impact stresses and provides a defined, centered seat on the bearing ring. For shrinking or pressing the bearing ring is heated, which expands thereby, the bearing sleeve is used, the bearing ring then cools down, shrinking in diameter, thus forming a positive connection to the bearing sleeve.

In an embodiment in which the bearing ring is connected via an impeller assembly to the drive ring, the impeller geometry and operation can be largely free. Moreover, it is also possible to constantly rinse the gap in the drive section between the magnet assembly of the stirring head and the inside of the gap pot when stirring with the stirring medium. In this way, contamination and product deposits in the area of the agitator can be reduced or completely prevented. When cleaning the agitator or the process container during operation of the agitator during cleaning, an additional rinsing effect can be achieved, which frees all agitator components completely from product buildup.

Coming back to 1 this shows the structure of a magnetic agitator according to the invention 1 in partial section. The magnetic agitator 1 includes a stirring head 2 and a containment shell 3 into a process container 4 is used. In a hollow drive section 5 , which is pot-shaped, sits inside a rotatable magnet assembly 6 via a drive shaft 7 is connected to a drive motor, not shown.

The stirring head 2 includes a bearing ring 8th , a drive ring 9 as well as several wing elements 10 , which each have the drive ring 8th with the bearing ring 9 connect. Inside the drive ring 9 is the magnet arrangement 6A arranged magnetically with the rotatable magnet assembly 6 is coupled. Between the inside of the drive ring 9 and the outside of the split pot 3 is a split S.

Inside the bearing ring 8th is a cylindrical bearing sleeve 11 arranged on a journal 12 sitting in one piece on the bottom of the split pot 3 is trained. The foot area of the trunnion 12 is as an annular disc-shaped, flat bearing surface 13 educated. The wall thickness of the bearing sleeve 11 is designed so that the end face 14 , which of the storage area 13 facing, this corresponds approximately.

The cylindrical outer surface of the journal 12 is with a tubular first bearing layer 15 provided, which is formed of an ADLC material and has a thickness of 1 to 2 microns. The storage area 13 is with a second bearing layer 16 provided - also from an ADLC material - and goes seamlessly into the bearing layer 15 above. Both bearing layers have a hardness of 1000 to 4000 HV, which exceeds the hardness of the base material of the gap pot 3 or the journal 12 which are made of an austenitic chromium-nickel steel (eg the quality 1.4301, 1.4404, 1.4435 BN2, etc.). The bearing sleeve 11 is formed of a silicon carbide material and forms with its inner surface or with its end face 14 a sliding bearing pairing with the first bearing layer 15 or the second bearing layer 16 ,

When operating the magnetic stirrer 1 becomes the magnet arrangement 6 over the drive shaft 7 placed in a rotational movement and takes through the magnetic coupling through the gap S in the interior of the bearing ring 8th arranged magnet arrangement 6A With. This is the entire stirring head 2 according to the rotation of the magnet assembly 6 . 6A turned.

The wing elements 10 , which form an impeller arrangement, put the stirring medium in the interior of the process container 4 so moving that it gets mixed up. The wing elements 10 are designed so that a buoyancy effect is created, the stirring head 10 via a lifting force on the bearing journal 12 raises, leaving the front face 14 the bearing sleeve 11 from the second storage layer 16 dissolves and there a gap s is formed. During further operation of the stirring head 2 The storage is then exclusively on the sliding bearing pairing between the bearing sleeve 11 and the camp layer 15 on the journal 12 , When stopping the magnetic stirrer 1 leaves the buoyancy effect and the end face 14 sits down again on the second storage layer 16 from where it is then stored again sliding.

To optimally adjust the sliding properties, the surfaces are covered with a bearing layer 13 14 to be provided, processed accordingly. For this purpose, mechanical (grinding, lapping, etc.) but also electrochemical processes such as electropolishing serve.

Further embodiments and variants of the invention will become apparent to those skilled in the scope of the claims.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1748201 B1 [0002, 0008]
• EP 0590472 B1 [0003]
• WO 2011/049492 A1 [0007]

Claims (12)

Magnetic stirrer ( 1 ) with a containment shell ( 3 ) and a stirring head ( 2 ), in which the containment shell ( 3 ) a drive section ( 5 ), in which a rotatable magnet arrangement ( 6 ) arranged magnetically with a magnet arrangement ( 6A ), which in a drive section surrounding the drive ring ( 9 ) of the stirring head ( 2 ) is arranged, and as a journal ( 12 ) formed bearing section, with a on the mixing head ( 2 ) arranged bearing sleeve ( 11 ) forms a sliding bearing pairing, wherein the bearing journal ( 11 ) a tubular first bearing layer ( 15 ) having increased hardness, which cohesively with the bearing journal ( 11 ) connected is. Magnetic stirrer ( 1 ) according to claim 1, wherein the journal ( 11 ) surrounding foot area ( 13 ) an annular disc-shaped second bearing layer ( 16 ) having increased hardness, which cohesively with the foot area ( 13 ) connected is. Magnetic stirrer ( 1 ) according to claim 1 or 2, wherein the first and second storage layers ( 15 . 16 ) seamlessly merge. Magnetic stirrer ( 1 ) according to claim 1, 2 or 3, in which split pot ( 3 ) and journals ( 11 ) are integrally formed of an austenitic stainless steel material. Magnetic stirrer ( 1 ) according to claim 1, 2, 3 or 4, wherein the bearing layer ( 15 . 16 ) is designed as a DLC coating. Magnetic stirrer ( 1 ) according to claim 1, 2, 3 or 4, wherein the bearing layer ( 15 . 16 ) has a multilayer structure and an outer layer comprises one of the materials: aluminum oxide, zirconium oxide. Magnetic stirrer ( 1 ) according to claim 5 or 6, wherein the bearing layer thickness is between 2 microns and 2 mm, preferably between 2 microns and 30 microns. Magnetic stirrer ( 1 ) according to claim 1, 2 or 3, in which the electrical breakdown resistance of the bearing layer ( 15 . 16 ) is less than 10 ⁶ ohms. Magnetic stirrer ( 1 ) according to one of the preceding claims, in which the bearing sleeve ( 11 ) has a cylindrical Radialgleitfläche which with the first bearing layer ( 15 ) and a plane axial sliding surface ( 14 ), which with the second storage layer ( 16 ) cooperates Magnetic stirrer ( 1 ) according to one of the preceding claims, in which the bearing sleeve ( 11 ) is formed of a silicon carbide material. Magnetic stirrer ( 1 ) one of the preceding claims, wherein the bearing sleeve ( 11 ) in one of the stirring head ( 2 ) arranged bearing ring ( 8th ) has shrunk. Magnetic stirrer according to Claim 11, in which the bearing ring ( 8th ) via an impeller arrangement ( 10 ) with the drive ring ( 9 ) connected is.

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