Seal for scroll pump

Abstract

A channel seal (200, 300) for a scroll pump (100). The channel seal comprises an inner portion (210, 310) and an outer portion (220, 320) located around the periphery of the inner portion. The outer portion is formed from a more wear resistant material than the inner portion. A surface of the inner portion which is subject to wear during operation of the scroll pump is axially offset from a surface of the outer portion which is subject to wear during operation of the scroll pump.

Description

[0001] SEAL FOR SCROLL PUMP

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to scroll pumps.

[0004] BACKGROUND

[0005] Scroll pumps are a known type of pump used in various different industries to pump fluid. Scroll pumps operate by using the relative motion of two intermeshed scrolls (known as a fixed scroll and an orbiting scroll) to pump fluid. Each of the fixed and orbiting scrolls includes a spiral wall extending from a base.

[0006] Scroll pumps include seals to prevent leakage of fluid from various parts of the scroll pump.

[0007] SUMMARY OF INVENTION

[0008] In an aspect, there is provided a channel seal for a scroll pump. The channel seal comprises an inner portion and an outer portion located around the periphery of the inner portion. The outer portion is formed from a more wear resistant material than the inner portion. A surface of the inner portion which is subject to wear during operation of the scroll pump is axially offset from a surface of the outer portion which is subject to wear during operation of the scroll pump.

[0009] The channel seal may further comprise a sacrificial bedding-in layer disposed on the outer portion.

[0010] The sacrificial bedding-in layer may be integrally formed with the inner portion.

[0011] The axial offset may be equal to a thickness of the sacrificial bedding-in layer. The inner portion may be formed from a different type of material to the outer portion.

[0012] The outer portion may be formed from a harder material than the inner portion.

[0013] The sacrificial bedding-in layer may be formed from the same material as the inner portion.

[0014] The channel seal may further comprise a base portion.

[0015] The base portion and the outer portion may together define a cavity within which the inner portion is located.

[0016] The base portion may be integrally formed with the outer portion.

[0017] The base portion may be formed from the same type of material as the outer portion.

[0018] The inner portion may be veneer bonded to the base portion and the outer portion.

[0019] The inner portion may be formed as a coating on the base portion and the outer portion.

[0020] The inner portion may comprise a spiral aperture.

[0021] In another aspect, there is provided a scroll pump comprising the channel seal of the above aspect.

[0022] In yet another aspect, there is provided a method of manufacturing a channel seal for a scroll pump. The method comprises forming an inner portion, and forming an outer portion around the periphery of the inner portion such that a surface of the inner portion which is subject to wear during operation of the scroll pump is axially offset from a surface of the outer portion which is subject to wear during operation of the scroll pump, wherein the outer portion is formed from a more wear resistant material than the inner portion.

[0023] BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic illustration (not to scale) showing a cross-sectional view of a scroll pump;

[0025] Figure 2 is a schematic illustration (not to scale) showing a plan view, a cross- sectional view and a zoomed-in cross-sectional view of a channel seal for the scroll pump; and

[0026] Figure 3 is a schematic illustration (not to scale) showing a plan view, a cross- sectional view and a zoomed-in cross-sectional view of another channel seal for the scroll pump.

[0027] DETAILED DESCRIPTION

[0028] Figure 1 is a schematic illustration (not to scale) showing a cross-sectional view of a scroll pump 100.

[0029] The scroll pump 100 comprises housing portions 110, a fixed scroll 120, an orbiting scroll 130, a drive shaft 140, an actuator 150, a bearing assembly 160, a first channel seal 170, and a second channel seal 180.

[0030] In this embodiment, the housing portions 110 and the fixed scroll 120 together define an overall housing of the scroll pump 100 within which other components of the scroll pump 100 are located. However, it will be appreciated that, in other embodiments, the fixed scroll 120 may not define any of the overall housing of the scroll pump 100 and instead may be located entirely within an overall housing. In this embodiment, the orbiting scroll 130 is located within the overall housing of the scroll pump 100.

[0031] The orbiting scroll 130 is intermeshed with the fixed scroll 120 to define a space (or channel) which is used by the scroll pump 100 during operation to pump fluid (e.g. a gas). The orbiting scroll 130 is configured to orbit relative to the fixed scroll 120 to pump fluid from an inlet (not shown) of the scroll pump 100 to an outlet (not shown) of the scroll pump 100. The precise physical mechanism by which fluid is pumped by the orbiting of the orbiting scroll 130 relative to the fixed scroll 120 is well understood and will not be described herein for the sake of brevity.

[0032] The fixed scroll 120 comprises a first base 122 and a first spiral wall 124. The orbiting scroll 130 comprises a second base 132 and a second spiral wall 134. The first spiral wall 124 and second spiral wall 134 are intermeshed with each other. Furthermore, the first spiral wall 124 extends perpendicularly from the first base 122 towards the second base 132 such that an end surface (also known as the tip) of the first spiral wall 124 is proximate to but not in contact with an opposing surface of the second base 132. The second spiral wall 134 extends perpendicularly from the second base 132 towards the first base 122 such that an end surface (or tip) of the second spiral wall 134 is proximate to but not in contact with an opposing surface of the first base 122. The first channel seal 170 is sandwiched between the end surface of the second spiral wall 134 and the opposing surface of the first base 122. The second channel seal 180 is sandwiched between the end surface of the first spiral wall 124 and the opposing surface of the second base 132. The fixed scroll 120 and orbiting scroll 130 may be biased together by a biasing apparatus (not shown) of the scroll pump (e.g. one or more springs).

[0033] In this embodiment, the first base 122 and first spiral wall 124 are integrally formed with each other, and the second base 132 and second spiral wall 134 are integrally formed with each other. However, in other embodiments, one or both of the spiral walls 124, 134 are not integrally formed with their respective bases 122, 132.

[0034] The drive shaft 140 is coupled to the orbiting scroll 130 and configured to rotate to drive the orbiting of the orbiting scroll 130. The drive shaft 140 is located within the overall housing of the scroll pump 100 and mounted via the bearing assembly 160 which facilitates rotation of the drive shaft 140. In this embodiment, the drive shaft 140 extends through both the fixed scroll 120 and the orbiting scroll 130 is mounted at an end of the draft shaft 140.

[0035] The actuator 150 (e.g. an electric motor) is coupled to the drive shaft 140 and configured to actuate the drive shaft 140 to cause the drive shaft 140 to rotate to drive the orbiting of the orbiting scroll 130. The actuator 150 is located within the overall housing of the scroll pump 100 and mounted around the drive shaft 140.

[0036] The bearing assembly 160 mechanically couples the drive shaft 140 to the orbiting scroll 130 and the overall housing of the scroll pump 100 such that the drive shaft 140 is able to rotate within the scroll pump 100 to drive the orbiting scroll 130.

[0037] The first channel seal 170 and the second channel seal 180 provide axial seals to prevent / oppose leakage of fluid axially between different sections of the space (or channel) which is used by the scroll pump 100 during operation to pump fluid. During operation of the scroll pump 100, due to the orbiting of the orbiting scroll 130, the end surface of the first spiral wall 124 rubs against the second channel seal 180 and the end surface of the second spiral wall 134 rubs against the first channel seal 170. Thus, the first and second channel seals 170, 180 are subject to wear from the rubbing over their lifetime. Seal structures which may be used for the first and second channel seals 170, 180 will now be described with reference to Figure 2 and Figure 3.

[0038] Figure 2 is a schematic illustration (not to scale) showing a plan view, a cross- sectional view and a zoomed-in cross-sectional view of a channel seal 200 for the scroll pump 100 of Figure 1 according to an embodiment. The channel seal 200 of Figure 2 may be used as the first channel seal 170 or the second channel seal 180 in the scroll pump 100 of Figure 1.

[0039] The channel seal 200 comprises an inner portion 210 and an outer portion 220 located around the periphery of the inner portion 210. The channel seal 200 defines a radial direction and an axial direction, and the outer portion 220 is located radially outwards of the inner portion 210. The outer portion 220 may be bonded to the inner portion 210. Alternatively, the outer portion 220 may be a separate piece to the inner portion 210 and not bonded or attached.

[0040] In this embodiment, the channel seal 200 has an overall circular shape. In this embodiment, the inner portion 210 has a circular shape with a spiral aperture matching the shape of the spiral wall of the scroll onto which the channel seal 200 fits, and a circular aperture matching the shape of the part of the drive shaft of the scroll pump around which the channel seal 200 is placed. In this embodiment, the outer portion 220 has a ring shape. However, it will be appreciated that the channel seal 200 and its inner and outer portions 210, 220 may have other different shapes, as long as the functions described herein are fulfilled.

[0041] The outer portion 220 is formed from a material which is more wear resistant than the inner portion 210. For example, the outer portion 220 may be formed from a harder material than the inner portion 210. The outer portion 220 may be formed from a different type of material to the material from which the inner portion 210 is formed. For example, the inner portion 210 may be formed from Polytetrafluoroethylene (PTFE) with a certain filler and the outer portion 220 may be formed from PTFE with a different filler which makes the outer portion 220 more wear resistant. As another example, the inner portion 210 may be formed from PTFE with a certain filler and the outer portion 220 may be formed from PTFE with the same filler but at a different density which makes the outer portion 220 more wear resistant. In the context of this specification, a more wear resistant material for the channel seal is a material which wears down at a lower rate when used in a given scroll pump (e.g. the scroll pump 100 of Figure 1) in a given set of operating conditions, compared to a less wear resistant material for the channel seal in that same given scroll pump in the same given set of operating conditions.

[0042] In this embodiment, the inner portion 210 is thicker than the outer portion 220. In this embodiment, the channel seal 200 further comprises a sacrificial bedding-in layer 230 disposed on the outer portion 220. The sacrificial bedding- in layer 230 is located radially outwards of the inner portion 210 and is layered onto the outer portion 220 in the axial direction. The sacrificial bedding-in layer 230 has a thickness such that the thickness of the sacrificial bedding-in layer 230 added to the thickness of the outer portion 220 is substantially the same as the thickness of the inner portion 210. In other words, the sacrificial bedding-in layer 230 covers a side of the outer portion 220 such that the exposed surface of the sacrificial bedding-in layer 230 is substantially flush with a surface of a side of the inner portion 210. The sacrificial bedding-in layer 230 is integrally formed with the inner portion 210. In other words, the inner portion 210 and the sacrificial bedding-in layer 230 together form a single piece of material. The sacrificial bedding-in layer 230 is formed from the same material as the inner portion 210.

[0043] The above-described structure means that the surface of the inner portion 210 which is subject to wear during operation of the scroll pump is axially offset from the surface of the outer portion 220 which is subject to wear during operation of the scroll pump (after the sacrificial bedding-in layer 230 has been worn through). The axial offset is equal to the thickness of the sacrificial bedding-in layer 230.

[0044] When the channel seal 200 is initially installed in a scroll pump and the scroll pump is operated, the channel seal 200 goes through a bedding-in phase in which the inner portion 210 and the sacrificial bedding-in layer 230 are worn down (at the same rate) until the part of the scroll pump wearing down the sacrificial bedding-in layer 230 wears completely through the sacrificial beddingin layer 230 and reaches the outer portion 220. Following this bedding-in phase, during subsequent operation of the scroll pump, the more wear resistant outer portion 220 takes more load than the inner portion 210, and the wear rate is mostly determined by the outer portion 220.

[0045] Thus, the above described structure advantageously means that the channel seal 200 can be relatively quickly initially bedded-in on less wear resistant material (i.e. the material of the inner portion 210 and the sacrificial bedding-in layer 230), and then the more wear resistant material (i.e. the material of the outer portion 220) is subjected to the bulk of the load on the channel seal 200, thus providing longer overall service life for the channel seal 200. The abovedescribed quick bedding-in tends to be desirable for scroll pumps because it tends to allow the scroll pump to reach full operational capacity quickly and with less run-time. The above-described structure also tends to allow a manufacturer of the scroll pump to avoid the use of extra specialised bedding-in equipment. This in turn tends to reduce costs for the supplier. The above-described bedding-in process also tends to help mitigate the effects of the seal being manufactured with imperfect flatness as well as mitigating the effects of the scrolls being of different heights. The above-described use of the more wear resistant portion to take the bulk of the load on the channel seal tends to reduce friction during operation of the scroll pump, thus saving power and generating less waste heat.

[0046] Figure 3 is a schematic illustration (not to scale) showing a plan view, a cross- sectional view and a zoomed-in cross-sectional view of a channel seal 300 for the scroll pump 100 of Figure 1 according to another embodiment. The channel seal 300 of Figure 3 may be used as the first channel seal 170 or the second channel seal 180 in the scroll pump 100 of Figure 1.

[0047] The channel seal 300 comprises an inner portion 310 and an outer portion 320 located around the periphery of the inner portion 310. In other words, the channel seal 300 defines a radial direction and an axial direction, and the outer portion 320 is located radially outwards of the inner portion 310. The outer portion 320 is bonded to the inner portion 310. In this embodiment, the channel seal 300 has an overall circular shape. In this embodiment, the inner portion 310 has a circular shape with a spiral aperture matching the shape of the spiral wall of the scroll onto which the channel seal 300 fits, and a circular aperture matching the shape of the part of the drive shaft of the scroll pump around which the channel seal 300 is placed. In this embodiment, the outer portion 320 has a ring shape. However, it will be appreciated that the channel seal 300 and its inner and outer portions 310, 320 may have other different shapes, as long as the functions described herein are fulfilled. The outer portion 320 is formed from a material which is more wear resistant than the inner portion 310. For example, the outer portion 320 may be formed from a harder material than the inner portion 310. The outer portion 320 may be formed from a different type of material to the material from which the inner portion 310 is formed. For example, the inner portion 310 may be formed from Polytetrafluoroethylene (PTFE) with a certain filler and the outer portion 320 may be formed from PTFE with a different filler which makes the outer portion 220 more wear resistant. As another example, the inner portion 310 may be formed from PTFE with a certain filler and the outer portion 320 may be formed from PTFE with the same filler but at a different density which makes the outer portion 320 more wear resistant. In the context of this specification, a more wear resistant material for the channel seal is a material which wears down at a lower rate when used in a given scroll pump (e.g. the scroll pump 100 of Figure 1) in a given set of operating conditions, compared to a less wear resistant material for the channel seal in that same given scroll pump in the same given set of operating conditions.

[0048] In this embodiment, the channel seal 300 further comprises a sacrificial bedding-in layer 330 disposed on the outer portion 320. The sacrificial beddingin layer 330 is located radially outwards of the inner portion 310 and is layered onto the outer portion 320 in the axial direction. In this embodiment, the channel seal 300 also further comprises a base portion 340. The base portion 340 and the outer portion 320 together define a cavity within which the inner portion 310 is located. The inner portion 310 is layered onto the base portion 340 in the axial direction. In this embodiment, the base portion 340 is integrally formed with the outer portion 320 and is formed from the same material as the outer portion 320. In this embodiment, the thickness of the sacrificial bedding-in layer 330 added to the thickness of the outer portion 320 is substantially the same as the thickness of the inner portion 310 added to the thickness of the base portion 340. The sacrificial bedding-in layer 330 covers a side of the outer portion 320 such that the exposed surface of the sacrificial bedding-in layer 330 is substantially flush with a surface of a side of the inner portion 310. The sacrificial bedding-in layer 330 is integrally formed with the inner portion 310. In other words, the inner portion 310 and the sacrificial bedding-in layer 330 together form a single piece of material. The sacrificial bedding-in layer 330 is formed from the same material as the inner portion 310.

[0049] In this embodiment, the inner portion 310 may be veneer bonded to the outer portion 320 and the base portion 340 or the inner portion 310 may be formed as a coating on the outer portion 320 and the base portion 340.

[0050] The above-described structure means that, in the same way as the embodiment of Figure 2, the surface of the inner portion 310 which is subject to wear during operation of the scroll pump is axially offset from the surface of the outer portion 320 which is subject to wear during operation of the scroll pump (after the sacrificial bedding-in layer 330 has been worn through). The axial offset is equal to the thickness of the sacrificial bedding-in layer 330.

[0051] In the same way as described above for the embodiment of Figure 2, when the channel seal 300 is initially installed in a scroll pump and the scroll pump is operated, the channel seal 300 goes through a bedding-in phase in which the inner portion 310 and the sacrificial bedding-in layer 330 are worn down (at the same rate) until the part of the scroll pump wearing down the sacrificial beddingin layer 330 wears completely through the sacrificial bedding-in layer 330 and reaches the outer portion 320. Following this bedding-in phase, during subsequent operation of the scroll pump, the more wear resistant outer portion 320 takes more load than the inner portion 310, and the wear rate is mostly determined by the outer portion 220.

[0052] Thus, the above described structure advantageously means that the channel seal 300 can be relatively quickly initially bedded-in on less wear resistant material (i.e. the material of the inner portion 310 and the sacrificial bedding-in layer 330), and then the more wear resistant material (i.e. the material of the outer portion 320) is subjected to the bulk of the load on the channel seal 300, thus providing longer overall service life for the channel seal 300. The abovedescribed quick bedding-in tends to be desirable for scroll pumps because it tends to allow the scroll pump to reach full operational capacity quickly and with less run-time. The above-described structure also tends to allow a manufacturer of the scroll pump to avoid the use of extra specialised bedding-in equipment. This in turn tends to reduce costs for the supplier. The above-described bedding-in process also tends to help mitigate the effects of the seal being manufactured with imperfect flatness as well as mitigating the effects of the scrolls being of different heights. The above-described use of the more wear resistant portion to take the bulk of the load on the channel seal tends to reduce friction during operation of the scroll pump, thus saving power and generating less waste heat. It will be appreciated that various modifications / deviations may be made to the above described embodiments without departing from the scope of the invention.

[0053] REFERENCE NUMERAL LIST

[0054] 100: scroll pump

[0055] 110: housing portion

[0056] 120: fixed scroll

[0057] 122: first base

[0058] 124: first spiral wall

[0059] 130: orbiting scroll

[0060] 132: second base

[0061] 134: second spiral wall

[0062] 140: drive shaft

[0063] 150: actuator

[0064] 160: bearing assembly

[0065] 170: first channel seal

[0066] 180: second channel seal

[0067] 200, 300: channel seal

[0068] 210, 310: inner portion

[0069] 220, 320: outer portion

[0070] 230, 330: sacrificial bedding-in layer

[0071] 340: base portion

Claims

CLAIMS1. A channel seal for a scroll pump, the channel seal comprising: an inner portion; and an outer portion located around the periphery of the inner portion, wherein the outer portion is formed from a more wear resistant material than the inner portion, and wherein a surface of the inner portion which is subject to wear during operation of the scroll pump is axially offset from a surface of the outer portion which is subject to wear during operation of the scroll pump.

2. The channel seal of claim 1 , further comprising a sacrificial bedding-in layer disposed on the outer portion.

3. The channel seal of claim 2, wherein the sacrificial bedding-in layer is integrally formed with the inner portion.

4. The channel seal of claim 2 or 3, wherein the axial offset is equal to a thickness of the sacrificial bedding-in layer.

5. The channel seal of any preceding claim, wherein the inner portion is formed from a different type of material to the outer portion.

6. The channel seal of any preceding claim, wherein the outer portion is formed from a harder material than the inner portion.

7. The channel seal of any preceding claim when dependent on claim 2, wherein the sacrificial bedding-in layer is formed from the same material as the inner portion.

8. The channel seal of any preceding claim, further comprising a base portion, wherein the base portion and the outer portion together define a cavity within which the inner portion is located.

9. The channel seal of claim 8, wherein the base portion is integrally formed with the outer portion.

10. The channel seal of claim 8 or 9, wherein the base portion is formed from the same type of material as the outer portion.11 . The channel seal of any of claims 8 to 10, wherein the inner portion is veneer bonded to the base portion and the outer portion.

12. The channel seal of any of claims 8 to 10, wherein the inner portion is formed as a coating on the base portion and the outer portion.

13. The channel seal of any preceding claim, wherein the inner portion comprises a spiral aperture.

14. A scroll pump comprising the channel seal of any preceding claim.

15. A method of manufacturing a channel seal for a scroll pump, the method comprising: forming an inner portion; andforming an outer portion around the periphery of the inner portion such that a surface of the inner portion which is subject to wear during operation of the scroll pump is axially offset from a surface of the outer portion which is subject to wear during operation of the scroll pump, wherein the outer portion is formed from a more wear resistant material than the inner portion.

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