DE10019637B4 - Screw vacuum pump - Google Patents

Abstract

Screw vacuum pump with two meshing screw rotors (12, 14), the pump or working chambers (30, 31, 32) delimiting in the conveying direction smaller chamber volumes, characterized in that at least two adjacent pump or working chambers (30, 31, 32) a check valve (41a, 41b, 42a, 42b) are connected directly to each other with the passage direction to the pressure side.

Description

The invention relates to a screw vacuum pump with two meshing screw rotors delimiting chambers.

Vacuum pumps are used to generate vacuum in a container, which is generated by pumping a gas from the container into the atmosphere. In order to pump gas from the container from a low pressure of, for example, 0.01 mbar into the atmosphere, the gas in the pump must be compressed to at least atmospheric pressure of 1013 mbar. In screw vacuum pumps, a compression chamber achieves a compression ratio of typically 10. In order to produce a vacuum of 0.01 mbar with a single screw vacuum pump, the pump must therefore have multiple chambers with decreasing chamber volumes in the conveying direction. In stepwise design of the chambers of the pump about 5 to 6 stages are required to achieve the required total compaction of 10 ⁵ . Here, the chamber volume ratio of suction side to pressure side, that is, from the inlet side to the outlet side, the "built-in" volume ratio. In this case, one speaks of a machine with internal compression. It is advantageous if the chamber volume of the chambers continuously decreases in the direction of conveyance. If gas is sucked in at the beginning of the evacuation on the suction side of the pump at high inlet pressure, for example at atmospheric pressure of 1013 mbar, this pressure is increased to the pressure side of the pump according to the "built-in" compression ratio, so that high material loads would occur and especially one very high drive power would be required to produce the high gas pressures. To avoid such over-compression in the chambers, pressure relief valves are used which connect the chamber to the atmospheric environment as soon as the pressure in the chamber substantially exceeds the atmospheric pressure. Such screw vacuum pumps with pressure relief valves are disclosed in DE 197 45 615 and DE 197 36 017 , However, these screw vacuum pumps have the fundamental disadvantage that in the case of faulty leaks in the overpressure valves, the chamber is constantly ventilated with atmospheric pressure. The fact that then in the corresponding chamber no negative pressure can be built up, possibly leading to a complete failure of the pump, especially if a chamber near the suction side is affected.

The object of the invention is to provide a screw vacuum pump with pressure reduction, in which the reliability is increased.

This object is achieved with the features of claim 1 and 14, respectively.

In the screw vacuum pump according to the invention two adjacent chambers of different chamber volumes are connected directly to each other by a check valve, whose forward direction is directed to the pressure side and the reverse direction to the suction side. The overpressure valve thus connects two adjacent pump chambers with each other, so that no more direct connection exists from the chambers near the suction side to the surrounding atmosphere. If the pump has a "built-in" compression ratio in several stages, the chambers may be connected to the two adjacent chambers via a valve, i. H. the chambers are cascade-connected by valves. Even if one of the valves is defective and should be completely permeable in the reverse direction continuously, the maximum pressure loss is limited only to the pressure difference between two adjacent chambers of the pump. Nevertheless, by the continuous cascade-like arrangement of the pressure relief valves between all areas of different chamber volumes also a reduction of superatmospheric pressure from a chamber through the remaining chambers through possible. Since the valves only need to be designed for relatively low pressure conditions, they are at the same time technically simpler, longer-lasting and less expensive to implement with greater reliability. The check valve may be formed mechanically or without moving parts.

Preferably, the valve is formed by a continuous valve channel between two chambers. Valve channel is any form of an open passage to understand that has no moving valve members. The trained as a channel valve is extremely reliable in operation, in a simple manner and inexpensive to produce. In this case, the valve channel is formed asymmetrically in longitudinal section so that it has a different transmission behavior in the forward direction and in the reverse direction. The valve channel is chosen so narrow that the backflow from the pressure-side chamber in the suction-side chamber in the reverse direction is relatively low, while the valve channel is still far enough to be able to break down sufficiently fast in the direction of pressure adjacent chamber at large overpressure pressure peaks.

According to a preferred embodiment, the valve channel is formed by a gap between the pump housing wall and the tooth tip of the screw rotor. A valve in the pump housing is eliminated. The required for a non-contact pump running gap between the tooth head and the housing wall receives a defined level to act as a valve between the two separated by the screw tooth areas of different chamber volumes can. The design of the walls of the valve channel, ie the Pump housing wall and the tooth head is chosen so that the flow resistance in the reverse direction is higher than in the forward direction. This can be achieved by configuring the housing wall and / or the tooth head such that the gas flowing in the reverse direction through the channel is excited to turbulences which have a gas flow obstructing effect, while the gas flowing in the forward direction has an undisturbed flow behavior , In this way, a valve with a preferred direction in the forward direction can be realized by a continuous channel.

Preferably, the channel inlet of the valve channel narrows steeper than the channel outlet widens, d. H. the inlet-side edge is relatively sharp, so has a small edge radius, while the outlet has a large radius. The channel inlet may be formed as a stage and the channel outlet as a conically widening portion which widens in a funnel-like manner in the forward direction. The gas flowing in the forward direction also retains its non-detaching flow in the area of the conically or funnel-like widening channel outlet, so that the flow resistance is low. In the reverse flow direction, ie in the reverse direction of the valve channel, turbulences form during the outflow of the gas at the step-like channel inlet, which reduce the effective flow cross-section and thus increase the flow resistance. Due to the described configuration of the valve channel turbulences are only in the reverse direction causes, although not complete, but effect a sufficient barrier effect.

According to a preferred embodiment, the conical portion of the channel outlet is formed by a chamfer of the outside of the tooth tip. Since the pump housing wall must be circular in cross-section, the profile of the valve channel can essentially be designed only by a corresponding design of the tooth tip outside.

Preferably, the maximum opening angle of the conical channel outlet is less than 20 °, in particular less than 10 °. Only at a small opening angle of the channel outlet is ensured that the flow in the forward direction in the conical section does not break, so that no effective channel cross-section reducing turbulence in the direction of flow can occur.

According to a preferred embodiment, at least two stages of different chamber volumes are provided, wherein in each case a valve in the direction of conveyance is arranged from the first significant reduction. The reduction of the working space can generally be done in two or more stages or continuously. Both the rotor diameter and the thread pitch can be changed.

According to a preferred embodiment, each screw tooth of the screw rotor forms a valve channel over a plurality of turns with the housing wall. Alternatively, the valve channel can also be arranged only at specific winding points of the respective tooth head.

According to a preferred embodiment, the profiles of the pressure-side end sides of the teeth of the screw rotor are designed such that they also form a gap channel valve with the pump housing end wall. In this way, the chamber compressed to the highest pressure is secured by a valve against the atmosphere against excessive internal pressures.

Preferably, the ratio of the cross-section of the channel inlet opening to that of the channel outlet opening is between 1.0 and 0.2, in particular approximately 0.3. The gap width is preferably less than 400 μm at the narrowest point and in particular between 50 and 200 μm in the low-operating state. The total gap length is preferably between 5 and 50 mm.

According to independent claim 14, in a screw vacuum pump, a check valve is formed from the pump chamber to the pump exhaust from a continuous valve channel between a rotor tooth of the screw rotor and a wall of the pump housing. The valve channel thus forms a check valve between the pump chamber and the exhaust. A valve channel is to be understood as meaning any shape of an open passage which has no movable valve members. Trained as a channel pressure relief valve is easy to implement, reliable and inexpensive to produce. The valve channel is asymmetrical in cross section, so that it has a different transmission behavior in the forward direction and in the reverse direction.

In the following three embodiments of the invention will be explained in more detail with reference to the drawings.

Show it:

1 a screw vacuum pump with two screw rotors, wherein the gap between a rotor and the housing wall is designed as a valve channel,

2 an enlarged view of the rotor tooth head and the housing wall of 1 .

3 an enlarged view of the rotor tooth head of a rotor and the tooth root of the other rotor of 1 .

4 a second embodiment of a rotor head,

5 A third embodiment of a rotor head,

6 an end view of a rotor of 1 in which the end profile of the screw rotor forms a valve channel with the housing end wall,

7 a section along the line VII-VII of the end face of the rotor in the 6 , and

8th a schematic representation of the cascaded valve assembly of the screw vacuum pump of 1 ,

In 1 is a screw vacuum pump in longitudinal section 10 with two symmetrical screw rotors 12 . 14 shown, which are meshing with each other. The two rotors 12 . 14 are rotatable in a metal housing 16 stored and rotate in opposite directions to each other. The lower first rotor 12 is driven by a motor (not shown). About a simple transmission is the second rotor 14 , synchronous and opposite to the first rotor 12 driven. The rotors 12 . 14 are made of metal, but can also be made of plastic or ceramic.

Both rotors 12 and 14 each have three levels 20 . 21 . 22 different diameters and gradients of the helical circumferential teeth 24 . 25 . 26 on. From the screw teeth 24 . 25 . 26 of the first rotor 12 , the housing wall 16 and the second rotor 14 each become chambers 30 . 31 . 32 different volume included. Due to the multi-level training with three levels 20 . 21 . 22 Different chamber volumes can on the suction side, ie in the region of the suction 34 a negative pressure of z. B. 10 mbar are generated. The at the suction 34 sucked gas of 10 mbar pressure is in the three stages 20 . 21 . 22 compressed to at least atmospheric pressure to pass through the exhaust 36 to be ejected at the pressure side. Also the second rotor 14 forms with the housing wall a second parallel pump.

Screw vacuum pumps with internal compression can also be realized with screw rotors, which vary continuously over the length with respect to the diameter and / or the pitch, so that the working space volume from the suction to the pressure side is continuously smaller. The more chambers are arranged in series between inlet and outlet and the better sealed these chambers are, the lower the pressure that can be reached on the suction side. The continuous or stepwise reduction causes a significant reduction in the drive power and the drive motor size and especially short rotors.

At the beginning of the evacuation of a vessel, the suction pressure at the suction port 34 correspond to the atmospheric pressure of 1013 mbar. At a compression of the sucked gas in the middle stage 21 would the gas pressure in the corresponding workspace 31 without pressure equalization significantly above the atmospheric pressure rise, which would cause a considerable mechanical load and would require a high drive power. For pressure equalization are between two of the three stages 21 . 22 as valves valve channels 41a . 41b . 42a . 42b provided, each of a gap between the circular cylinder-like Pumpenraumgehäuseinnenwand 17 and the respective tooth head 45a . 45b . 46a . 46b the teeth 25 . 26 be formed. The first valve channel 40a is at a point where the first significant change in chamber volume occurs. The suction-side teeth 24 do not form a valve channel.

The one of the teeth heads 45a . 45b . 46a and 46b and the housing inner wall 17 formed valve channel is formed asymmetrically in longitudinal section, as in the 2a . 2 B . 4 and 5 shown. The tooth head 45b has in the cross-sectional view of 2a and 2 B a channel inlet 50 on the suction side, then a channel section 52 and at the pressure side a channel outlet 54 on. The leading edge 56 of the canal inlet 50 is strongly curved, ie has a radius or edge fracture of a few millimeters. To the strongly curved front edge 56 closes in the channel section 52 a gap with a constant gap height of about 150 μm. The gap length, ie the channel section length is z. B. 20 mm. To the canal section 52 with the tooth channel wall 58 closes the outlet wall 60 of the duct outlet 54 which is approximately 10 ° inclined to the channel wall 58 , This bevel of the tooth head 45b forms together with the housing inner wall 17 a conical, ie in longitudinal section a wedge-like channel outlet 54 , The transition from the canal wall 58 to the outlet wall 60 has a relatively large radius of z. B. 10 mm. The channel height can basically be in the range of approximately 50 to 300 μm, the opening angle of the channel outlet, ie the angle of inclination of the outlet wall 60 can be 5 ° to 20 °. The exact dimensions of the valve channel 41b depend strongly on the size of the pump or the tooth, on the pressures that occur, gas speeds, speeds and desired valve characteristics.

The ratio of the narrowest channel section and the end cross section of the channel outlet 54 is about 1: 3, but may generally be in the range of 1: 1.5 and 1: 5. The length of the channel outlet is about 20 mm here.

Although the valve is of a continuous valve in both directions 41b formed, but the valve channel by its asymmetric configuration has a preferred direction, ie a forward direction and an opposite locking direction.

The blocking valve channel 41b is in 2a shown in the suction-side chamber 31 a lower pressure prevails than in the chamber 32 on the print side. In this case, compressed gas flows out of the pressure-side chamber 32 through the conical channel outlet 54 in the channel 52 one. The inflowing gas is due to the funnel-like narrowing of the channel outlet 54 in the flow direction in the channel section 52 considerably accelerated. The accelerated gas in the channel section 52 flows at high speed to the channel inlet 50 where the flow is at the strongly curved leading edge 56 breaks off, which forms the inlet area. As a result, turbulence is generated in this area. This effect is further enhanced by the fact that the head of the tooth 46 and thus also the strongly curved front edge 56 against the flow direction of the gas in the channel section 58 emotional. The turbulences fluidically reduce the effective flow cross-section of the channel inlet 50 , so that the flow resistance of the Kanaleinlassses 50 increases. The described effects cause in the valve channel 41b a barrier effect for gas flows from the pressure side 32 to the suction side 31 ,

The reverse case is in 2 B shown. Because of a high suction pressure and the reduction of the chambers in promotion prevails in the suction-side chamber 31 a significantly higher gas pressure than in the pressure-side chamber 32 , In this case, the supercharged gas flows at the leading edge 56 of the canal inlet 50 over and is considerably accelerated. The accelerated gas passes through the channel section 52 in which it depending on the length and surface condition of the housing inner wall 17 and the canal wall 58 is throttled to some extent. The gas flows out of the channel section 52 in the slightly conical channel outlet 54 one. The channel outlet 54 is designed in any case such that when the gas flows out of the channel section 52 no detachment occur in the forward direction, but always maintains a voltage applied to the wall flow. In this way, the flow resistance of the entire valve channel is kept small in the forward direction. The extension of the channel cross-section in the outlet area 54 acts as a diffuser, in which the flow is delayed and the pressure is increased to the outlet.

It is expedient to provide valves only where an over-compression must actually be prevented during operation. This is z. B. in the tooth heads 45a . 45b . 46a . 46b the case, not the teeth 24 the first stage 20 ,

A valve between areas of different working volume can also be done by providing a valve channel in the form of a longitudinal bore through a screw tooth or in the form of a groove in the tooth tip. The valve channel can basically also as a bore or groove in the housing 16 be educated. Regardless of the specific design and arrangement, the valve channel connects 11 in each case always two chambers 31 . 32 with each other, as in 8th shown and not a chamber directly to the exhaust 36 or the atmosphere. In this way, a cascade-like valve arrangement in the pump 10 realized, so that even with malfunction of a valve approximately by wear the pressure loss on the pressure difference between two adjacent chambers 31 . 32 is limited.

In 3 is the situation when meshing a rotor tooth 25 with a tooth root 64 of the counter-rotor 14 shown. The tooth base 64 is in its contour of the contour of the rotor tooth head 45a adjusted so that the sealing gap between Rotorzahnfuß 64 and rotor tooth head 45 as small as possible to avoid unwanted leakage at this point.

In the 4 and 5 two further embodiments of the design of the tooth head contour are shown.

The in 4 illustrated tooth head 70 has a channel inlet with a small radius 71 , a relatively long channel section 72 constant channel cross-section and an arcuate opening channel outlet 73 , While the canal intake 71 only a few millimeters long, the channel section can 72 a length of about 20 mm and the channel outlet 73 have a length of significantly more than 20 mm. The opening width of the duct outlet 73 is many times, preferably about three times larger than that of the channel inlet 71 ,

In 5 is another embodiment of a tooth head 80 shown having a channel inlet 81 having a leading edge radius of about 5 mm. The subsequent channel section of constant cross-section has a very small length of about 10 mm. The adjoining the canal section 82 subsequent channel outlet 83 has a length of about 30 mm and is arc-shaped curved over its entire length. In extreme cases, z. B. with narrow tooth tips, the constant channel section 52 or 82 drop away, leaving the entry radius 81 directly into the outlet diffuser 54 or 83 passes.

In the 6 is a plan view of the pressure-side end wall 18 of the housing 16 shown. In the front wall 18 is a circular segment-like outlet opening 28 provided by which the compressed gas from the chamber 32 in the exhaust 36 can flow. In the in 7 shown section of the line VII-VII of 6 It can be seen that the outlet-side end profile 90 in the manner described above as a diffuser-type and asymmetric valve channel 92 is trained. In this way, also between the last pressure-side chamber 32 and the exhaust 36 or the atmosphere realized a valve, which at a working space pressure via exhaust pressure, a pressure equalization of the chamber 32 allows before the working space the outlet opening 28 reached.

The chambers have a pressure relief valve, which does not lead to the atmosphere, but to an adjacent chamber. Even if the valve is defective, ie in the blocking direction, the affected chamber is ventilated with the gas pressure of the adjacent chamber, but not with atmospheric pressure.

Claims (15)

Screw vacuum pump with two meshing screw rotors ( 12 . 14 ), the pump or working chambers ( 30 . 31 . 32 ) with smaller in the conveying direction chamber volumes, characterized in that at least two adjacent pump or working chambers ( 30 . 31 . 32 ) by a check valve ( 41a . 41b . 42a . 42b ) are connected directly to each other with the passage direction to the pressure side. Screw vacuum pump according to claim 1, characterized in that the check valve by a continuous valve channel ( 41a . 41b . 42a . 42b ) is formed, wherein the valve channel ( 41a . 41b . 42a . 42b ) is formed asymmetrically in longitudinal section such that it has different transmission characteristics in both directions of flow. Screw vacuum pump according to claim 2, characterized in that the valve channel ( 41a . 41 . 42a . 42 ) is formed by at least one gap of a pump housing wall ( 17 ) and a tooth head ( 45a . 45b . 46a . 46b ) one of the screw rotors ( 12 ) is limited. Screw vacuum pump according to claim 3, characterized in that in the passage direction of the check valve ( 41a . 41b . 42a . 42b ) the channel inlet ( 50 ) narrows more steeply than the channel outlet ( 54 ) is expanding. Screw vacuum pump according to claim 4, characterized in that between channel inlet ( 50 ) and channel outlet ( 54 ) a channel section ( 52 ) is provided with a constant gap height. Screw vacuum pump according to claim 4 or 5, characterized in that the channel inlet ( 50 ) as a rounded edge and the channel outlet ( 54 ) is designed as a conical diffuser section, which widens in the forward direction. Screw vacuum pump according to claim 6, characterized in that the conical section ( 54 ) by a chamfer of the outside of the tooth head ( 45a . 45b . 46a . 46b ) is formed. Screw vacuum pump according to claim 7, characterized in that the opening angle of the conical section ( 54 ) is less than 20 °, in particular approximately equal to 10 °. Screw vacuum pump according to one of claims 3-8, characterized in that each tooth ( 24 . 25 . 26 ) of the screw rotor ( 12 ) is designed such that it with the housing wall over several turns a valve channel ( 40 . 41 . 42 ). Screw vacuum pump according to one of claims 1-9, characterized in that the outlet-side end profile ( 90 ) the teeth ( 26 ) of the screw rotor ( 12 ) is in each case designed such that the end profile ( 90 ) with the pump housing wall ( 18 ) a gap channel valve ( 92 ). Screw vacuum pump according to one of claims 1-10, characterized in that the ratio of the cross-sectional area of the channel inlet ( 52 ) to the cross-sectional area of the opening of the channel outlet ( 54 ) is between 1.0 and 0.2 and in particular about 0.3. Screw vacuum pump according to one of claims 3-11, characterized in that the gap height of the channel section ( 52 ) is less than 400 microns at the narrowest point, in particular 50 to 200 microns in operation. Screw vacuum pump according to one of claims 3-12, characterized in that the gap length is 5 to 50 mm. Screw vacuum pump with two meshing screw rotors ( 12 . 14 ) in a pump housing with its rotor teeth ( 26 ) Pumping chambers ( 32 ), at least one of which through a check valve with passage direction to the pressure side directly with the exhaust ( 28 ) or the surrounding atmosphere, characterized in that the check valve from a continuous valve channel ( 92 ) between a wall ( 18 ) of the pump housing and a rotor tooth ( 26 ), wherein the valve channel is formed asymmetrically in longitudinal section such that it has different passage behavior in both directions. Screw vacuum pump according to claim 14, having the features of any of claims 4-8 and 11-13.

Images