GB2595892A

GB2595892A - Vacuum pump

Info

Publication number: GB2595892A
Application number: GB2008768.0A
Authority: GB
Inventors: Jonathan Grant Nicolas; David Jones Peter; Charles Lamb Peter
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2020-06-10
Filing date: 2020-06-10
Publication date: 2021-12-15
Also published as: GB202008768D0; WO2021250400A1

Abstract

Vacuum scroll pump (fig.1A) with a housing, a first element 26,30 connected with the housing providing a stator, a second element 28, 32 rotating relative to the first element having at least one pump element interacting with the stator to convey a gas. A seal 38, 40 arranged between the first element and the second element has a base element 42 with a contact surface 46 against the opposite element, where the contact surface is non-flat and becomes flat after first use (fig.3) as running in has caused bedding-in and abrasion of the seal. Preferably the seal is a tip seal seated in a groove of the wrap’s end wall on the scroll and having a contact surface with a feature such as a protrusion 48 adjacent to the opposite scroll’s base 50; the protrusion being rectangular, triangular, or a partial ellipse in cross-section. Preferably the seal is from 1-5mm in width D and the protrusion is less than 1mm, or less than 0.01mm in width W and the feature varies along the length of the seal. Benefit: because of the smaller contact area a harder seal material can be used but run-in period can be kept below 24h.

Description

VACUUM PUMP

The present invention relates to a vacuum pump and in particular to a scroll pump.

Known vacuum pumps comprise a housing having an inlet and an outlet wherein in the housing a first element is disposed connected to the housing and acting as a stator. Further, a second element is disposed in the housing rotating or orbiting relative to the first element, wherein the second element has at least one pump element interacting with the stator in order to convey a gaseous medium from the inlet to the outlet.

In order to prevent backflow between regions of different pressures, seals are arranged between the first element and the second element in order to close the gaps and separate areas of different pressures. For this purpose, it is known to use tip seals made of plastic material. Tip seals are typically formed as a rectangle with one substantially flat face acting as a sliding seal against the moving element. During the initial running of pumps the tip seal must wear in to match the other element. During this process seal material is transferred from the tip seal to the surface of the other element in order to improve the sealing and friction properties between the two elements. This process is called "bedding-in". This bedding-in process takes a long time which is usually up to 24 hours. Therein, it would be possible to use a seal fabricated from a softer material. Then the bedding-in process would be shortened. However, wear during the use of the vacuum pump is then increased reducing the lifetime of the seal.

Thus, it is desirable to use harder material for the seal, thereby also increasing the necessary time for a sufficient bedding-in.

It is known to accelerate the bedding-in process and control the bedding-in pro-cess by either applying a force to the seal to increase the pressure of the seal to the other element or apply a pressure difference such that the seal is forced by the pressure difference to the other element. During the bedding process larger forces can be applied through the mechanical axial force, allowing more material to wear and speeding up the bedding in process. Because of the large surface area of seal material in contact with the opposing first and second elements, small changes to the axial position can have large effects on power, resulting in excessive heating of the tip seal. Thus, axial adjustment is less con-trollable, and an excessive axial force would cause skimming of the seal, damaging the seal and reducing the performance of the seal due to an inhomogeneous transfer of the material to the other element. The pressure difference across the seal will also support wear of the tip seal, though this force is dynamic through the scroll and relatively small. Methods to increase this pressure delta improve the bedding in speed but improvements to this would still be beneficial. Thus, applying gas pressure difference is more controllable but produces a relatively small force because of limited pressure difference available.

It is an object of the present invention to provide a vacuum pump with a reduced bedding-in time upon the initial running of the vacuum pump.

The vacuum pump in accordance to the present invention comprises a housing, a first element connected with the housing providing a stator and a second ele-ment rotating or orbiting relative to the first element having at least one pump element interacting with the stator to convey a gaseous medium from an inlet to an outlet of the housing. Further, a seal element is arranged between the first element and the second element to provide a seal between these two elements in order to prevent backflow from regions of higher pressure to regions of lower pressure. Therein, the seal element comprises a base element having a first end and a second end opposite to the first end, wherein the second end defines a contact surface. In accordance to the present invention, the contact surface is non-flat prior first use and substantially flat after first use. Thus, prior first use the contact surface is not in full contact with the other element of the vacuum pump, i.e. the first element or the second element. Due to the non-flat contact surface prior first use a contact area is reduced. Thus, contact pressure is increased, increasing the wear of the contact surface and transfer of the material from the seal element to the respective other element of the vacuum pump. At the same time, due to the reduced contact area, heat generation due to friction is reduced avoiding damage of the seal element. During first use, material of the seal element is transferred to the first element or second element of the vacuum pump, respectively. Thus, the contact surface of the seal element is subject to wear flattening the contact surface and thus providing full seal performance after the bedding-in process. Thus, also harder seal material can be used due to the improved bedding-in process time, increasing the lifetime of the seal element. In particular, the contact surface is substantially flat after first use in the meaning that a sufficient area of contact between the contact surface and the other element of the vacuum pump is provided not excluding a certain unevenness of the seal element as long as sufficient sealing effect is provided by the seal element.

Preferably, the first end of the base element is configured to abut against the first element of the vacuum pump wherein the contact surface is configured to abut against the second element of the vacuum pump. Alternatively, the first end is configured to abut against the second element of the vacuum pump while the contact surface is configured to abut against the first element of the vacuum pump.

Preferably, the vacuum pump can have more than one seal element, wherein in particular a first seal element is arranged at the first element of the vacuum pump, wherein the contact surface of the first seal element abuts against the second element of the vacuum pump while a second seal element is arranged at the second element of the vacuum pump, wherein the contact surface of the second seal element abuts against the first element of the vacuum pump.

Preferably, after first use the contact surface is in contact across almost full width of the base element with the first element or second element, respec-tively. Thus, after first use the non-flat contact surface is substantially leveled out or flattened such that the flat contact surface after first use is in full contact with the respective other element of the vacuum pump. Therein, a sufficient seal effect is provided.

Preferably, after first use the seal element has a rectangular shape. In particu-lar, the width of the seal element is between 5 mm and 1 mm, and more preferably between 3 mm and 2 mm. Therein, the term width can be here and in the following replaced by the term height in dependence on the orientation of the pump. In general, the term width refers to the extension of the seal element in the direction perpendicular to the length of the seal element. For a scroll pump the width of the seal element is defined perpendicular to the wall of the respective scroll member or by the extension perpendicular to the axis of rotation of the vacuum pump.

Preferably, prior first use the contact surface comprises at least one feature in order to provide a non-flat contact surface. Therein, the feature may have any shape or dimension in order to facilitate sufficient bedding-in and being able to provide a flat surface after first use. In particular, the ratio between the width of the feature and the width of the seal element is between 1:2 and 1:50, more preferably between 1:10 and 1:50 and most preferably between 1:20 and 1:50.

Preferably, the feature is made from a first material and the feature is at least partially surrounded by or adjacent to a second material, wherein first material and second material are different. In particular, first material and second material may have a different hardness. For example, the first material of the feature may be less hard and abraded during the bedding-in process while the second material is harder than the first material to provide a long lifetime. Preferably, if a two features are employed made from the same or a different material, then a second material might be arranged between the two features.

Preferably, the feature is a protrusion. Therein, the protrusion may have a cir-cular end face or a rectangular end face or any other shape as end face.

S

Preferably, the feature has a triangular shape wherein the triangular shape preferably extends across the full width of the base element or substantially the full width of the base element in order to create a sloped contact surface.

Preferably, one feature is arranged at the contact surface. Preferably, two or more features are arranged at the contact surface of the seal element.

Preferably, the feature extends along the full length of the seal element.

Preferably, the feature changes along the length of the seal element. Thus, in particular the number of features, shape of the one or more features and/or the material changes along the length of the seal element. For example, in areas of small pressure differences only one feature might be employed and sufficient to provide a sealing effect, while in areas of large pressure differences more than one feature might be employed to provide a sufficient sealing effect. Alterna-tively, the at least one feature is the same along the full length of the seal element.

Preferably, at least one intersection element is provided, extending along the width of the seal element preferably from one side of the seal element to the opposite side. By the intersection element a gas flow along the length of the seal element is prevented. Preferably, two or more intersection elements are distributed over the length of the seal element. Preferably, the intersection Preferably, the feature is abradable during first use. Thus, the first use the fea-ture is abraded in order to create a flat or at least substantially flat contact surface. Thus, the feature is abraded during first use resulting in a substantially rectangular shape of the seal element increasing the contact area of the contact surface and thereby providing the seal effect of the seal element.

Preferably, the contact area of the contact surface prior first use is smaller than after first use. Prior first use the contact surface is in contact with the other element of the vacuum pump only by the one or more features. During the first use these features are preferably abraded and consequently after first use the contact surface is in complete contact with the other element of the vacuum Pump.

Preferably, the vacuum pump is a scroll pump and the first element is a first scroll member having a first base and a generally spiral first wall that extends from the first base. Further, the second element is a scroll member having a second base and a generally spiral second wall that extends from second base meshing with the first wall to define at least a portion of a pump member.

Preferably, the seal element is arranged at the tip of the first wall in contact with the second base element. Additionally or alternatively, the seal element is arranged on the tip of the second wall in contact with the first base in order to 15 seal the respective pump chambers.

Preferably, the feature is along the complete length of the first wall and/or second wall.

Further, it is an object of the present invention to provide a method for initially running in a vacuum pump with the steps: - providing a vacuum pump as previously described, - starting a bedding-in process; -abrading the non-flat contact surface of the seal element during the bedding-in process in order to transfer material of the seal element to the respective other element of the vacuum pump until a flat or at least substantially flat surface of the seal element and/or sufficient seal effect is achieved; - stopping the bedding-in process.

Thus, during the bedding-in process the non-flat contact surface is subject of abrasion such that the non-flat contact surface is transformed into a substantially flat contact surface providing a sufficient sealing effect.

Preferably, a pressure difference or an axial force between the first element and the second element can be applied in order to enhance or improve the bedding-in process.

Preferably, the bedding-in process takes less than 24 hours preferably less than 12 hours.

In the following embodiments of the present invention will be described in more detail with reference to the accompanied drawings. It is shown: Fig. 1 a schematic drawing of a scroll pump, Figs. 2a-e different embodiments of the seal element according to the pre-sent invention prior first use and Fig. 3 the seal element of Figs. 2a-2e after first use.

Fig. la shows a cross section of the scroll pump having a housing 10 defining an inlet 12 and an outlet 14. Connected with the housing is a first scroll member 16 and a second scroll member 18, wherein the second scroll member 18 is orbiting around the first scroll member 16. Therein, the second scroll member 18 is connected to a shaft 20 which is rotated by an electro motor 22 to orbit around a common axis 24.

The first scroll member 16 has a first base 26 and a spiral first wall 28 extending 30 from the first base 26. Further, the second scroll member 18 has a second base 30 and a generally spiral second wall 32 extending from the second base 30 and meshing or nested within the first wall 28. First wall 28 and second wall 32 define at least a portion of the pump chamber 33 such that during movement of the second scroll member 18 a gaseous medium is conveyed from the inlet 12 to the outlet 14. In order to prevent backflow from one pump chamber 34 with higher pressure to a second pump chamber 36 of lower pressure at the tip of the first wall 28 a seal element 38 is arranged wherein the seal element 38 defines a contact surface in contact with the base 30 of the first scroll member 18. Similar, a seal element 40 is arranged at the tip of the second wall 32 wherein a contact surface of the seal element 40 is in contact with the first base 26 of the first scroll member 16.

Fig. 2a shows a detailed view of any of the seal elements 38, 40 arranged at the first scroll member 16 or second scroll member 18. Therein, the seal elements might be identical to each other. Alternatively, different configurations might be used for each of the seal elements 38, 40.

The seal element 38, 40 comprises a base element 42 having a first end 44 being in contact with the first scroll member 16 or second scroll member 18 and a contact surface 46 being in contact with the remaining scroll member, i.e. the second scroll member 18 or the first scroll member 16, respectively. Therein, Figs. 2a to 2e show the seal element prior first use. Prior first use the contact surface 46 of the seal element 38, 40 is non-flat. In the example of Fig. 2a the contact surface 46 comprises two rectangular shaped features 48 which are in contact with the other element of the vacuum pump. The features 48 define the contact area between the seal element and the respective base element 26, 30 of the other element prior first use, wherein this contact area is reduced com-pared to the full width of the base element 42. During initial running of the vacuum pump the features 48 are abraded, thereby transferring material of the seal element 38, 40 to the surface 50 of the respective first base or second base 26, 30. After first use the contact surface 46 becomes substantially flat as shown in Fig. 3. Thus, the contact area of the contact surface 46 is increased and spanning almost across the complete width of the base element 42 of the seal element 38, 40. Thus, sufficient seal effect is provided.

In some embodiments, the seal element is running along the complete first wall 28 and/or second wall 32. Therein, the shape and/or the number of features and/or the material of the respective one or more features might change along the first and/or second wall 28, 32. Thus, in a region of low pressure difference only one feature 48 is arranged at the first end or second end while in regions of larger pressure difference at a different position of the same wall, two features 48 are present at the first end 44, respectively, in order to provide a sufficient sealing effect.

As shown in the Figs. 2b to 2e the feature can have various forms. Fig. 2b shows a single feature having a rectangular shape. Fig. 2c shows a single feature having a triangular shape. Fig. 2d showing a protrusion having a circular end face. Fig. 2e shows a feature having a triangular shape wherein the triangle spans across the full width of the base element 42 creating a sloped non-flat contact surface 46 prior first use of the seal element 38, 40. Therein, the feature 48 may have a width W that is smaller than the width D of the base element 42. In particular, the width D of the feature 48 is less than 1 mm preferably less than 0,1 mm and more preferably less than 0,01 mm. Therein, the width W of the base element 42 is preferably between 5 mm and 1 mm, more preferably between 3 mm and 2 mm.

Thus, during initial running in bedding-in of the seal element is performed. Therein, only the feature 48 is in direct contact with the base element of the other base, i.e. first base 26 or second base 30. Thus, the contact area is re- duced, increasing the wear of the feature and thereby accelerating transfer of the material from the seal element 38, 40 to the respective first or second base 26, 30. At the same time generation of heat is reduced. As a consequence and further benefit, a harder material of the seal element 38, 40 can be used im-proving the lifetime of the seal element without increase of the necessary time for a sufficient bedding-in process.

Claims

CLAIMS1. Vacuum pump, in particular a scroll pump, comprising a housing, a first element connected with the housing providing a stator, a second element rotating relative to the first element having at least one pump element interacting with the stator to convey a gaseous medium, a seal element arranged between the first element and the second element to provide a seal, wherein the seal element comprising: a base element having a first end and a second end opposite to the first end defining a contact surface, wherein the contact surface is none-flat prior first use and substantially flat after first use.
2. Vacuum pump according to claim 1, characterized in that after first use the contact surface is in contact with the first element and/or second element across full width of the base element.
3. Vacuum pump according to claims 1 or 2, characterized in that prior first use the contact surface comprises at least one feature.
4. Vacuum pump according to claim 3, characterized in that the feature is a protrusion.
5. Vacuum pump according to claim 3 or 4, characterized in that the at least one feature changes along the length of the seal element. 6. 7. 8. 9. 10. 11.
Vacuum pump according to any of claims 3 to 5, characterized in that the feature has a triangular shape, wherein preferably the triangular shape extends across the full width of the base element to create a sloped contact surface.
Vacuum pump according to any of claims 3 to 6, characterized in that the feature is abradable during first use.
Vacuum pump according to any of claims 1 to 7, characterized in that the contact area prior first use is smaller than after first use.
Vacuum pump according to any of claims 1 to 8, characterized in that the vacuum pump is a scroll pump and the first element is a first scroll member having a first base and a generally spiral first wall that extends from said first base and the second element is a second scroll member having a second base and a generally spiral second wall that extends from said second base meshing with the first wall to define at least a portion of a pump chamber.
Vacuum pump according to claim 9, characterized in that the seal element is arranged at the tip of the first wall in contact with the second base element and/or arranged at the tip of the second wall in contact with the first base to seal the pump chamber.
Method for initially running in a vacuum pump with the steps: Providing a vacuum pump according to any of claims 1 to 10; Starting a bedding-in process; Abrading the non-flat contact surface of the seal element during the bedding-in process until a flat contact surface of the seal element and/or sufficient seal effect is achieved; and Stopping the bedding-in process.
12. Method according to claim 11, characterized in that the bedding-in process takes less than 24h, preferably less than 12h.