ORBITER VACUUM PUMP CAPABLE OF DRY-RUNNING

Abstract

The present invention relates to a dry-running, oil-free orbiter vacuum pump with an improved bearing arrangement consisting of a material pairing capable of dry-running A pivot bearing with a bearing cavity open towards the pump chamber for receiving a pivot head of a blocking slide is arranged inside the pump housing. The orbiter vacuum pump capable of dry-running is characterized in particular in that at least one sliding surface of the pivot bearing allocated to the bearing cavity or to the pivot head is made of a composite material including a solid lubricant.

Claims

1. A dry-running orbiter vacuum pump comprising: a pump housing with a cylindrical pump chamber; an orbiter eccentric piston with a guide slot and a cylindrical exterior surface, a cylindrical cross-section of the orbiter eccentric piston being smaller than a cylindrical cross-section of the pump chamber; a shaft for driving the orbiter eccentric piston by means of an eccentric disk with a crankpin that meshes with the orbiter eccentric piston; a blocking slide received in the guide slot of the orbiter eccentric piston, one end of the blocking slide being pivotably mounted at the pump housing between an inlet and an outlet; wherein a pivot bearing with a bearing cavity open towards the pump chamber for receiving a pivot head of the blocking slide is arranged inside the pump housing; wherein at least one sliding surface of the pivot bearing allocated to the bearing cavity or to the pivot head is made of a composite material including a solid lubricant.

2. The dry-running orbiter vacuum pump according to claim 1, wherein the composite material is based on a polymer matrix, and the composite material includes at least one of the solid lubricants molybdenum disulfide and/or graphite as a filler in a proportion of 10% to 30% of the weight.

3. The dry-running orbiter vacuum pump according to claim 2, wherein the polymer matrix consists of a thermoplastic.

4. The dry-running orbiter vacuum pump according to claim 3, wherein the thermoplastic is Polimid PA 6.

5. The dry-running orbiter vacuum pump according to claim 3, wherein the thermoplastic is polyamide, preferably PA 6.6.

6. The dry-running orbiter vacuum pump according to claim 2, wherein the polymer matrix consists of a thermosetting polymer, preferably a phenolic plastic.

7. The dry-running orbiter vacuum pump according to claim 1, wherein the polymer matrix includes, in a proportion of 20% to 50% of the polymer matrix, glass fibers or cullet as a filler.

8. The dry-running orbiter vacuum pump according to claim 1, wherein the entire pump housing or at least a portion of the pump housing surrounding the bearing cavity of the pivot bearing is made of the composite material including the solid lubricant.

9. The dry-running orbiter vacuum pump according to claim 1, wherein the pivot bearing furthermore includes a sliding bearing bushing with a C-shaped cross-section with respect to the pivot axis, and the sliding bearing bushing is made of the composite material including the solid lubricant.

10. The dry-running orbiter vacuum pump according to claim 1, wherein the blocking slide including the pivot head is made of a stainless steel as a bent sheet-metal part.

11. The dry-running orbiter vacuum pump according to claim 1, wherein the blocking slide including the pivot head is made of a stainless sintered steel as a sintered part.

12. The dry-running orbiter vacuum pump according to claim 1, wherein the blocking slide is made of a stainless steel; and the pivot head is made of the composite material including the solid lubricant.

13. The dry-running orbiter vacuum pump according to claim 1, wherein the blocking slide including the pivot head is made of the composite material including the solid lubricant.

14. The dry-running orbiter vacuum pump according to claim 1, wherein the entire pump housing or at least a portion of the pump housing surrounding the bearing cavity of the pivot bearing is made of a metal.

15. The dry-running orbiter vacuum pump according to claim 1, wherein the pivot bearing furthermore includes a sliding bearing bushing with a C-shaped cross-section with respect to the pivot axis, and the sliding bearing bushing is made of a stainless steel.

16. The dry-running orbiter vacuum pump according to claim 14, wherein the blocking slide is made of a stainless steel; and the pivot head is made of the composite material including the solid lubricant.

17. The dry-running orbiter vacuum pump according to claim 14, wherein the blocking slide including the pivot head is made of the composite material including the solid lubricant.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0040] The invention will be explained hereinafter with reference to the accompanying drawing with the aid of a preferred embodiment of an orbiter vacuum pump. In the drawing:

[0041] FIG. 1 shows a cross-section of the pump chamber of an orbiter vacuum pump according to one embodiment of the invention;

[0042] FIG. 2 shows an axial cross-section through the cutting line A-A of the orbiter vacuum pump in FIG. 1.

DETAILED DESCRIPTION

[0043] As shown in FIGS. 1 and 2, the orbiter vacuum pump is formed from a pump housing 1 which comprises a pump chamber 2 which is closed by a pump cover and has a cylindrical chamber wall. In the pump housing 1, a shaft is arranged in such a manner as to be rotatably mounted by means of a shaft bearing (not illustrated). An eccentric disk 9 with an eccentrically arranged crankpin is fixed on the shaft. The eccentric disk 9 engages with the crankpin in the center point of a cylindrical orbiter eccentric piston 3 designed as a piston drum.

[0044] The eccentric disk 9 performs a circular movement of the orbiter eccentric piston 3 through the pump chamber 2, wherein circumferential sliding contact of the orbiter eccentric piston 3 with the cylindrical chamber wall is maintained. Arranged in the orbiter eccentric piston 3 is a guide slot 4 which slidably receives a blocking slide 5. The blocking slide 5 is pivotably mounted in the chamber wall at a free end and extends through the pump chamber 2 to the orbiter eccentric piston 3. For this purpose, a pivot bearing 8 which is described more precisely hereinafter is arranged between an inlet opening 6 and an outlet opening 7 in the chamber wall. In dependence upon the position of the orbiter eccentric piston 3 on the circular movement in the pump chamber 2, a portion of the blocking slide 5 located opposite the pivotably mounted end slides in and out in the guide slot 4. The pump chamber 2 is divided, either side of the blocking slide 5, into two volumes, of which one communicates with the inlet opening 6 and one communicates with the outlet opening 7.

[0045] The volumes on each side of the blocking slide 5 vary with the circumferential sliding contact between the orbiter eccentric piston 3 and the cylindrical chamber wall in equal proportions oppositely to one another such that a cyclical displacement procedure is completed within one revolution of the shaft or a circular movement of the orbiter eccentric piston 3. During the circular movement of the orbiter eccentric piston 3, a torque required for the displacement procedure rises during the increase in the volume communicating with the inlet 6 and falls abruptly when a maximum volume is reached. The illustration in FIG. 1 shows a position of the orbiter eccentric piston 3 approximately halfway prior to a top dead center, in which the volume of the pump chamber 2 communicating with the inlet 6 reaches an almost maximum volume and the content thereof is thereafter pushed out of the outlet 7. The shaft is driven preferably by an electric motor, not illustrated.

[0046] By means of the aforementioned pivot bearing 8, the blocking slide 5 which slides in and out in the guide slot 4 during the circular movement of the orbiter eccentric piston 3 simultaneously performs a pivoting movement. The pivot bearing 8 is formed substantially by means of two sliding surfaces which are provided on the one hand on a bearing cavity 18 open towards the pump chamber 2, and on the other hand on a roller-shaped pivot head 58 of the blocking slide 5. The bearing cavity 18 is formed in the pump housing. The pivot head 58 is formed at a free end of the blocking slide 5. At least one of two sliding surfaces on the side of the bearing cavity 18 or of the pivot head 58 consists of the composite material which is defined hereinafter and includes a solid lubricant.

[0047] Furthermore, in one structural embodiment of the invention illustrated in FIG. 1, the pivot bearing 8 has a sliding sleeve 85 with a C-shaped cross-section which is arranged about a pivot point of the pivot bearing 8 between the pivot head 58 and the bearing cavity 18. The sliding sleeve 85 consists of the composite material including the solid lubricant. Depending upon the fit, the radially inner surface of the sliding sleeve 85 forms or replaces the sliding surface of the bearing cavity 18, or the radially outer surface of the sliding sleeve 85 forms or replaces the sliding surface of the pivot head 58. It is likewise possible to have a variant, in which the two radial surfaces of the sliding sleeve 85 simultaneously form or replace both sliding surfaces of the pivot bearing 8.

[0048] In one structural embodiment of the invention which is not illustrated, the pivot joint 8 does not have a sliding sleeve 85. The pump housing 1 and thus the sliding surface of the bearing cavity 18 consist of the composite material including the solid lubricant. In an alternative variant of this structural embodiment, only a portion of the pump housing 1, in which the bearing cavity 18 is formed, consists of the composite material including the solid lubricant.

[0049] In one not-illustrated, further structural embodiment of the invention, the pivot joint 8 does not have a sliding sleeve 85. The pivot head 58 and thus the sliding surface on the side of the blocking slide 5 consist of the composite material including the solid lubricant. The composite material is integrally formed as a roller-shaped cast body on the free end of the blocking slide 5 by means of over-moulding. In an alternative variant of this structural embodiment, the blocking slide 5 including the pivot head 58 consists completely of the composite material including the solid lubricant.

[0050] Furthermore, elements of the aforementioned structural embodiments can be combined with one another, wherein in particular as an alternative embodiment, provision can be made that both the pump housing 1 and the pivot head 58 or the sliding sleeve 85 and the pivot head 58 are made of the composite material including the solid lubricant.

[0051] The composite material which includes the solid lubricant and from which the pump housing 1, the sliding sleeve 85 or the pivot head 58 of the aforementioned structural embodiments is made will be defined in greater detail hereinafter.

[0052] The composite material is produced by means of a material melt, in which a solid lubricant, such as molybdenum disulfide or graphite as a filler is admixed and homogeneously mixed. The material melt which, in the solidified state, serves as a matrix for incorporating the solid lubricant is preferably a synthetic material on the basis of a polyamide or phenolic plastic having a high degree of solidity.

[0053] In the preferred first embodiment of the invention illustrated in FIG. 1 and relating to a composite material having a particularly high level of wear resistance and low coefficient of friction, a polymer matrix of the composite material consists of polyamide designated as PA 6.0 or Polimid, in which pure molybdenum disulfide as a filler with a preferred weight proportion of 15% relating to the weight of the resulting composite material is admixed in a homogeneously distributed manner The composite material is processed by means of an injection-moulding process to produce a corresponding bearing part of the pivot bearing 8.

[0054] After tests performed by the inventors, the preferred composite material, which includes a 15% weight proportion of molybdenum disulfide as a filler in a polymer matrix, which consists of the thermoplastic Polimid PA 6, demonstrated the best properties relating to the wear resistance and a low-friction operation.

[0055] The inventors found out that the behavior of the coefficient of friction of molybdenum disulfide gives rise to a considerable advantage for the application of solid lubrication in a dry-running vacuum pump. Furthermore, the inventors found out that this advantage is also retained and can be provided permanently if the molybdenum disulfide as a filler is homogeneously mixed in a synthetic material melt with the objective that a moving bearing part of the pivot bearing 8 consisting of the resulting composite material permanently ensures continuous solid lubrication on the corresponding sliding surface.

[0056] The molybdenum disulfide which is admixed with the synthetic material-based composite material and is homogeneously distributed therein is provided in powder form and consists of particles in the form of so-called flakes having a predominant size distribution of 1 μm or several μm up to 100 μm in length. When viewed under magnification, the molybdenum sulfide flakes consist of a plurality of alternating atomic layers of molybdenum atoms and sulphur atoms, i.e. a sandwich structure consisting of two-dimensional, so-called basal planes which slide against one another and can be displaced, resulting in the lubricating effect of the solid.

[0057] Since the particles of the molybdenum disulfide are embedded in the polymer matrix of the Polimid, they are not transported away by the conveyed gas stream in the sense of a loosely distributed solid lubricant. Furthermore, the solid lubrication is not subject to consumption by a wear-induced superficial material abrasion. Since the particles of the molybdenum disulfide as a filler are distributed homogeneously in the polymer matrix of the Polimid, a concentration of the solid lubricant which is provided on the sliding surfaces of the pivot bearing 8 does not change even after wear occurs. In contrast to a superficial lubrication or coating, this applies even if long-term material abrasion of the composite material should occur partially or uniformly on the respective sliding surface of the pivot bearing 8 as a result of the friction.

[0058] Further embodiments of the invention relating to the composite material as well as alternative variants to the various embodiments will be described hereinafter.

[0059] In one variant of the first embodiment, the polymer matrix consisting of Polimid PA 6 includes a weight proportion of 10% molybdenum sulfide as a filler. In another variant of the first embodiment, the polymer matrix consisting of

[0060] Polimid PA 6 includes a weight proportion of 30% molybdenum sulfide as a filler. Within the scope of the invention, in further variants of the first embodiment, the polymer matrix consisting of Polimid PA 6 includes any weight proportion between 10% and 30% molybdenum sulfide as a filler.

[0061] In alternative variants of the first embodiment, the polymer matrix includes a further filler, namely a silicate filler in the form of glass fibers, cullet, glass spheres and/or hollow glass spheres. Such uniformly formed particles are mostly spherical or fibrous in configuration. For this purpose, it is possible to use very short glass fibers, of which the ratio of length to diameter is the factor of ca. 1 to 5, fragments having a corresponding ratio of length to diameter with the factor of ca. 1 or spherical particles consisting of micro-silicate. The fibers, similarly to the flakes of the molybdenum disulfide in powder form, have a dimension in the range of 1 μm to 100 μm. Said silicate fillers thus represent a preferred application-optimized selection over alternative fillers, such as talcum, chalk or silica dust.

[0062] In an alternative variant of the first embodiment, the polymer matrix consisting of Polimid PA 6 includes, in addition to the molybdenum disulfide, a weight proportion of 20% glass fibers or cullet as a silicate filler. In another alternative variant of the first embodiment, the polymer matrix consisting of

[0063] Polimid PA 6 includes, in addition to the molybdenum disulfide, a weight proportion of 50% glass fibers or cullet as a silicate filler. Within the scope of the invention, in further alternative variants of the first embodiment, the polymer matrix consisting of Polimid PA 6 includes, in addition to the molybdenum disulfide, any weight proportion between 20% and 50% glass fibers or cullet as a silicate filler.

[0064] In a second embodiment of the invention relating to the composite material, the polymer matrix consists of the thermoplastic polyamide PA 6.6 in which molybdenum disulfide is embedded as a filler. The polymer matrix consisting of polyamide PA 6.6 from the second embodiment includes a weight proportion of 15% molybdenum disulfide as a filler.

[0065] In one variant of this second embodiment, the polymer matrix consisting of polyamide PA 6.6 includes a weight proportion of 10% molybdenum sulfide as a filler. In another variant of the second embodiment, the polymer matrix consisting of polyamide PA 6.6 includes a weight proportion of 30% molybdenum sulfide as a filler. Within the scope of the invention, in further variants of the second embodiment, the polymer matrix consisting of polyamide PA 6.6 includes any weight proportion between 10% and 30% molybdenum sulfide as a filler.

[0066] In an alternative variant of the second embodiment, the polymer matrix consisting of polyamide PA 6.6 includes, in addition to the molybdenum disulfide, a weight proportion of 20% glass fibers or cullet as a silicate filler. In another alternative variant of the second embodiment, the polymer matrix consisting of polyamide PA 6.6 includes, in addition to the molybdenum disulfide, a weight proportion of 50% glass fibers or cullet as a silicate filler. Within the scope of the invention, in further alternative variants of the second embodiment, the polymer matrix consisting of polyamide PA 6.6 includes, in addition to the molybdenum disulfide, any weight proportion between 20% and 50% glass fibers or cullet as a silicate filler.

[0067] In a third alternative embodiment of the invention relating to the composite material, the polymer matrix consists of a phenolic plastic, in which molybdenum disulfide is embedded as a filler, The polymer matrix consisting of phenolic plastic from the third embodiment includes a weight proportion of 15% molybdenum disulfide as a filler.

[0068] In one variant of this third embodiment, the polymer matrix consisting of phenolic plastic includes a weight proportion of 10% molybdenum sulfide as a filler. In another variant of the third embodiment, the polymer matrix consisting of phenolic plastic includes a weight proportion of 30% molybdenum sulfide as a filler. Within the scope of the invention, in further variants of the third embodiment, the polymer matrix consisting of phenolic plastic includes any weight proportion between 10% and 30% molybdenum sulfide as a filler.

[0069] In an alternative variant of the third embodiment, the polymer matrix consisting of phenolic plastic includes, in addition to the molybdenum disulfide, a weight proportion of 20% glass fibers or cullet as a silicate filler. In another alternative variant of the third embodiment, the polymer matrix consisting of phenolic plastic includes, in addition to the molybdenum disulfide, a weight proportion of 50% glass fibers or cullet as a silicate filler. Within the scope of the invention, in further alternative variants of the third embodiment, the polymer matrix consisting of phenolic plastic includes, in addition to the molybdenum disulfide, any weight proportion between 20% and 50% glass fibers or cullet as a silicate filler.

[0070] In an alternative variant of the first to third embodiment relating to the composite material, it is also possible to use, instead of or in addition to the molybdenum disulfide, graphite as a solid lubricant in the polymer matrix.

[0071] An opposing sliding surface of the pivot bearing 8 which does not consist of the composite material can be provided from a material conventionally provided for the respective component, such as e.g. a metal.

[0072] In the preferred embodiment illustrated in FIG. 1 and relating to a friction pairing of the sliding surfaces of the pivot joint 8, the pump housing 1 or even the blocking slide 5 consist of a stainless sintered steel designated as Sint-C40 or Sint-D40 as a material for the pump housing 1. A steel which can be sintered provides a preferred processing technique for producing a housing part having a generally complex shape. After sintering, regions of a housing part, such as a cylindrical inner surface of the pump chamber 2 can be subsequently machined, whereby a high degree of dimensional stability can be ensured with respect to the movement sequence of the orbiter eccentric piston 3 and the resulting circumferential sealing gap. In one variant of this embodiment relating to the friction pairing, the pump housing 1 is made of a more cost-effective alloy in the form of a sintered steel designated as Sint-C32, Sint-C36 or even Sint-C39.

[0073] In another embodiment relating to the friction pairing of the sliding surfaces of the pivot joint 8, the pump housing 1 or even the blocking slide 5 consist of a stainless steel with the standard designation X17CrNi16-2 which provides a suitable, low-wear friction pairing at economically advantageous cost.

[0074] In alternative embodiments relating to a friction pairing of the sliding surfaces of the pivot joint 8, the pump housing consists of an aluminium alloy designated as AlSi.sub.9Cu.sub.3, or a ceramic consisting of aluminium oxide Al.sub.2O.sub.3.

[0075] It is necessary to take into account that the different embodiments relating to the composite material, just like the embodiments relating to a friction pairing of the sliding surfaces of the pivot joint 8 or components thereof can be interchanged and combined with the various aforementioned structural embodiments relating to the pivot bearing 8 and the elements or bearing parts thereof. That is to say in particular that any material-related aspects of the embodiments can be transferred to any structural aspect of the embodiments, according to which the core of the invention with its advantageous effects, as described above, is still achieved.

LIST OF REFERENCE NUMERALS

[0076] 1 pump housing [0077] 2 pump chamber [0078] 3 orbiter eccentric piston [0079] 4 guide slot [0080] 5 blocking slide [0081] 6 inlet [0082] 7 outlet [0083] 8 pivot bearing [0084] 9 eccentric disk with crankpin [0085] 18 bearing cavity [0086] 58 pivot head [0087] 85 sliding sleeve