Patent Application
20210270265
Vacuum boosters utilize rotors that rotate in opposite directions to compress a gas. One type of vacuum booster is the roots-type vacuum booster. Roots-type vacuum boosters utilize two rotors that are positioned within a booster housing. The rotors include lobes that intermesh with each other during rotation. The rotors rotate within the booster housing to convey mass and create a pressure differential between the two ports in the housing. Another type of vacuum booster is the screw type booster. Screw type boosters can include two or more screw rotors that are positioned within a booster housing. The rotors include helical flights that intermesh with each other during rotation.
In an aspect, a vacuum booster assembly includes, but is not limited to, a booster housing defining a booster chamber, the booster housing formed to include a gas inlet for allowing gas to enter the booster chamber and a gas outlet to allow gas to exit the booster chamber; a first rotor positioned within the booster chamber and adapted for rotation therein, the first rotor including a first shaft and at least two lobes having an outer surface that defines a first lobe profile; and a second rotor positioned within the booster chamber and adapted for rotation therein, the second rotor including a second shaft and at least two lobes having an outer surface that defines a second lobe profile, wherein the first and second rotors are formed from a metal having a coefficient of thermal expansion from about 1 (10−6 in/in*K) to about 13 (10−6 in/in*K), and wherein the outer surface of the first rotor and the outer surface of the second rotor each includes a coating including at least one of an abradable coating or a formable coating.
In an aspect, a vacuum booster assembly includes, but is not limited to, a booster housing defining a booster chamber, the booster housing formed to include a gas inlet for allowing gas to enter the booster chamber and a gas outlet to allow gas to exit the booster chamber; a first rotor positioned within the booster chamber and adapted for rotation therein, the first rotor including first shaft and at least two lobes having an outer surface that defines a first lobe profile; and a second rotor positioned within the booster chamber and adapted for rotation therein, the second rotor including a second shaft and at least two lobes having an outer surface that defines a second lobe profile, wherein the first and second rotors formed from metal having a coefficient of thermal expansion from about 1 (10−6 in/in*K) to about 13 (10−6 in/in*K), and wherein an inner surface of the booster housing includes a coating including at least one of an abradable coating or a formable coating.
In an aspect, a method for forming a vacuum booster assembly includes, but is not limited to, forming a booster housing from a metal via investment casting, the booster housing formed to include an interior chamber, a gas inlet for allowing gas to enter the booster chamber, and a gas outlet to allow gas to exit the booster chamber; forming a first rotor from a metal having a coefficient of thermal expansion from about 1 (10−6 in/in*K) to about 13 (10−6 in/in*K) via investment casting, the first rotor having an outer surface; machining a portion of the outer surface of the first rotor to remove a portion of the metal to define a first rotor profile; forming a second rotor from a metal having a coefficient of thermal expansion from about 1 (10−6 in/in*K) to about 13 (10−6 in/in*K) via investment casting, the second rotor having an outer surface; machining a portion of the outer surface of the second rotor to remove a portion of the metal to define a second rotor profile; applying a coating including at least one of an abradable coating or a formable coating to at least one of the rotors or the booster housing; and positioning the first rotor and the second rotor within the interior chamber for rotation therein.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The Detailed Description is described with reference to the accompanying figures. The use of the same reference numbers in different instances in the description and the figures may indicate similar or identical items.
Vacuum boosters have rotational components that intermesh during operation to compress gas received from an inlet to drive a pressurized gas through an outlet of the booster. During operation, the rotational components dimensionally expand as operating temperatures and pressures increase. Dimensional variation in rotational components limits operating efficiencies over various operating conditions and can result in damage at higher temperatures and pressures. Moreover, the rotational components can include smooth surface textures that permit gas to slip past the surfaces of the rotational components during operation, which can decrease vacuum booster efficiency and can increase operating temperatures of the vacuum booster.
Accordingly, the present disclosure is directed, at least in part, to systems and methods for providing rotors that have increased operating efficiencies over a wide range of operating temperatures and pressures. In an aspect, the rotors are formed from materials having low coefficients of thermal expansion within a vacuum booster housing and are provided with a coating to prevent gas slippage past the rotors during operation. In an aspect, the rotors are formed from an investment casting process and machined to include a precise outer profile to ensure strict tolerances between the rotors and between a given rotor and the housing. The rotor profiles and the coating can facilitate low dimensional variation in the rotational components, which can facilitate greater bearing life, higher speeds of rotation, and improved operating efficiencies and ranges.
A roots type vacuum booster 100 is shown in
Vacuum booster 100 includes a first rotor 103 positioned within the booster chamber 101 that is adapted for rotation about a first axis of rotation. For example, the first axis of rotation can extend through ends 145, 147 of the first rotor 103 (e.g., as shown in
Vacuum booster 100 also includes a second rotor 105 positioned within the booster chamber 101 that is adapted for rotation about a second axis of rotation. For example, the second axis of rotation can extend through ends 141, 143 of the second rotor 105 (e.g., as shown in
First and second rotors 103 and 105 can include surface treatments, textures, or materials to facilitate operation of the vacuum booster 100 during a wide range of operating conditions while maintaining tolerances between the rotors 103, 105 and the booster housing 102. For example, the first rotor is shown in
In implementations, the coating 131 applied to outer surface 123, 127 and/or to the ends 141, 143 of first and second rotors 103, 105 has a surface roughness from about 125 Ra to about 1000 Ra. Surface roughness of rotors 103, 105 is important as testing indicates that a surface roughness in the range of about 125 Ra to about 1000 Ra limits the amount of gas that slips past the rotor lobes (e.g., 118 and 120, 122 and 124) of first and second rotors 103, 105 during operation of the vacuum booster 100. Reduction in the amount of gas that slips past the rotor lobes increases vacuum booster 100 efficiency and reduces operating temperatures.
In implementations, the coating 131 is applied in multiple layers. For example, the coating 131 can be applied in two coating layers, three coating layers, or greater than three coating layers. In implementations, the coating 131 is applied in multiple layers and the layers are formed from two or more different coating materials. In implementations, a surface of the booster housing 102 (e.g., forming a boundary of the booster chamber 101) includes an abradable and formable coating. Depending upon manufacturing tolerances between the rotors 103, 105 and the booster housing 102, rotor to rotor contact or rotor to housing contact can cause a portion of the coating 131 from the first and second rotors 103, 105 to partially transfer onto a portion of the booster housing 102 during operation of the vacuum booster 100. The coating 131 applied to the rotors 103, 105 preferably can include a coefficient of friction from about 0.04μ to about 0.2μ. In implementations, the coating 131 includes a lubricant including, but not limited to, polytetrafluoroethylene (PTFE), graphite, molybdenum disulfide, or combinations thereof, to provide lubricity between the rotors 103, 105. In various operating scenarios, the use of a lubricant in the coating 131 allows for tighter tolerances between the rotors 103, 105 and the booster housing 102 than if no lubricant is included. In implementations, the vacuum booster 100 is manufactured so that the operating clearances between the first and second rotors 103, 105 when assembled into booster housing 102 is from about 0.003 inches to about 0.032 inches and the operating clearances between the rotors 103, 105 and the booster housing 102 is from about 0.002 inches to about 0.025 inches.
Rotors 103, 105 used in the vacuum booster 100 are manufactured from a low CTE material, which limits thermal expansion of the rotors 103, 105 during operating the vacuum booster 100 at higher temperatures and pressures. In implementations, the first and second rotors 103, 105 are formed from a metal that includes from about 50% to about 100% iron. The first and second rotors 103, 105 can also include nickel, for example, nickel in an amount from about 20% to about 35% nickel. The first and second rotors 103, 105 can also include cobalt, for example, cobalt in an amount from about 10% to about 25% cobalt.
Vacuum booster 100 is shown with the booster housing 102 and two transverse end plates 104. The end plates 104 include apertures 106 through which two rotor shafts 108, 110 extend. Shafts 108, 110 are supported at each end by bearings 112. In implementations, a motor 114 drives rotation of one shaft 108 and a gear mechanism 116 transmits the rotational power to the other shaft 110. The gear mechanism causes the shafts 108, 110 to rotate in synchronization in opposite directions. The first rotor 103 with rotor lobes 112, 120 is mounted to the shaft 108, which provides rotation to the first rotor 103 during operation of the motor 114. The second rotor 105 with rotor lobes 122, 124 is mounted to the shaft 110, which provides rotation to the second rotor 105 during operation of the motor 114 (e.g., via the gear mechanism 116). As the shafts 108, 110 rotate, the lobes 118, 120 and 122, 124 sweep past an internal surface 126 of the booster chamber 101 thereby moving gas from a chamber inlet 128 to a chamber outlet 130 (e.g., shown in
Referring to
The lobes 118, 120 and 122, 124 of the first and second rotors 103, 105 can include structural features that provide structural stability of the lobes 118, 120 and 122, 124 under high operating temperatures, pressures, and speeds. For example, the lobe 118 of the first rotor 103 can be formed with a first sidewall segment 134 and a second side wall segment 136 (e.g., as shown in
Lobe 118 of the first rotor 103 may also include a tensile bar 142, examples of which are shown in
Base 132 of the first rotor 103 interconnects the first and second lobes 118, 120. Base 132 includes a first concave side wall 157 and an opposed second concave side wall 150. First concave side wall 157 interconnects the first sidewall segment 134 of first lobe 118 with a first sidewall segment 152 of the second lobe 120. Similarly, the second concave sidewall 150 interconnects the second sidewall segment 136 of the first lobe 118 with a second sidewall segment 154 of the second lobe 120. In implementations, the base 132 of the first rotor 103 is formed to include a cylindrical bore 156 that extends at least partially through the first rotor 103. Cylindrical bore 156 of the base 132 of the first rotor 103 is adapted to accept first and second rotor shaft segments 108a, 108b, as shown, for example, in
In implementations, the first and second rotors 103, 105 are investment cast from a material having a low coefficient of thermal expansion (CTE). Use of a low CTE material to form the first and second rotors 103, 105 reduces the thermal growth of the first and second rotors 103, 105 during operation, allowing for a higher temperature and pressure operation. Low CTE materials that can be used for investment casting the first and second rotors 103, 105 include cast iron, which has a CTE of about 11 (10−6 in/in*K). Materials with lower CTE can also be used to investment cast rotors such as the material KOVAR™, which has a CTE of about 6 (10−6 in/in*K), INVAR™, which has a CTE of about 4 (10−6 in/in*K), and SUPER INVAR™, which has a CTE of about 1.5 (10−6 in/in*K). Materials with a high CTE, such as aluminum, are generally avoided as the thermal expansion of the aluminum metal is too great to gain the desired efficiencies.
The vacuum booster 100 can include other rotor configurations to facilitate generating a vacuum for industrial applications. For example, referring to
Low CTE rotors have more dimensional stability than high CTE rotors across a broader range of temperatures and pressures. The dimensional stability allows the low CTE rotors to be used in combination with abradable and formable (A/F) coatings. Under extreme operating conditions of pressure and high temperatures, A/F coated traditionally-structured rotors would thermally grow in dimension and so abrade the coatings, creating larger coating gaps when the rotors return (and shrink) to normal operating conditions of temperature and pressure. The more thermally stable A/F coated low CTE rotors described herein have smaller gaps between the coated rotors and the housing under a range of operating temperatures and pressures, improving overall efficiencies and lower operating temperatures due to less slip between the rotors and housing. In implementations, the A/F coating is an ultra-thin closed cell polymer coating that includes polymide resin, wear resistant particles, and a solid lubricant (e.g., PTFE). One example A/F coating is DB L-908 by Orion Industries. The coating can be applied to the rotors using spraying, powder coating, or other coating techniques.
Reducing clearance between the rotors for a booster or screws or cylinder for a vacuum pump reduces the slip and blowby of the booster to improve efficiency. The A/F coating can be applied to one or more of the rotors, the housing, or the end plates to improve booster efficiency. A zero clearance in the booster is created by having a line on line contact or slight interference between the first and second rotors 103, 105. During an initial run-in of the vacuum booster 100, the first and second rotors 103, 105 are rotated, which abrades and forms the A/F coating to a near zero clearance condition. Using an A/F coating on the CTE rotors reduces the tolerances required in manufacturing the rotors, making the manufacturing of the rotors more cost effective. Additionally, having dimensionally stable, material-optimized rotors can facilitate greater bearing life and higher speeds of rotation.
Although the subject matter has been described in language specific to structural features and/or process operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.
| Number | Date | Country | |
|---|---|---|---|
| 62982420 | Feb 2020 | US |
