TWI568935B - Screw-type vacuum pump - Google Patents

Description

Spiral vacuum pump

The present invention relates to a spiral vacuum pump.

The spiral vacuum pump includes two helical rotors that are arranged in a pumping chamber formed by a pump housing. Spiral rotors are typically supported on both sides and may have different pitch profiles. The rotor may have a symmetrical or asymmetrical tooth profile, as described, for example, in the 2010 Vacuum Technology Manual, Woods-Vacuum Technical Manual, 10th Edition, pages 270-277. The rotors typically have a built-in compression ratio of less than 4 (the so-called built-in compression ratio is the ratio of the chamber volume between the suction side chamber and the pressure side chamber. The higher compression ratio is at a higher suction pressure) This results in a very high power input value and requires a disproportionately large drive motor (refer to the above-mentioned "Woods-vacuum technology manual" on page 276). Increasing the compression will further cause high temperatures to occur in the pressure side area of the spiral rotor. In this case, it is impossible to dissipate heat through the pump casing, so heat dissipation must be performed by internal cooling of the spiral rotor. However, this is technically complicated and causes manufacturing costs and maintenance costs of the screw vacuum pump. improve.

In order to allow high built-in compression ratios, it was proposed to change the gap height in the 2006 VDI Report Journal No. 1932. It is stated in the report that the gap height on the suction side, especially the distance between the spiral rotor and the pump casing, should be designed to be larger than the gap height on the pressure side. Since the viscosity and the type of flow of the molecules are related to the pressure, the larger gap on the suction side is acceptable. In the case of high suction pressure, when this gap is combined with slowed rotor speed This will cause a reduction in internal compression. This results in less compression power and therefore less heat. Disadvantageously, however, a reduction in internal compression also results in a reduction in pumping capacity.

Furthermore, it is well known that the rotor can also be supported only on one side, i.e. in the form of a cantilever. A significant advantage of this type is that only one bearing needs to be placed. This bearing is placed on the pressure side, ie on the transmission side. Then, the second bearing disposed in the low pressure region on the suction side can be omitted. However, the helical rotor assembly supported in a cantilever manner must contain rotors of short construction length, otherwise there is a risk of mutual contact between the rotors during operation. If the structural length of the rotor is relatively short, the number of windings will be reduced. Also, the cantilevered rotor has a relatively large diameter. The ratio of the distance between the rotor length and the rotor axis is typically less than 2.5.

It is an object of the present invention to provide a spiral vacuum pump having a "built-in compression ratio" of at least 4.5, wherein the heat dissipation is achieved in a simple manner.

According to the present invention, the above object is achieved by the features defined in the first item of the patent application.

The spiral vacuum pump of the present invention includes a pump housing that defines a pumping chamber. Two spiral rotors are arranged in the pump housing. Since the length of the spiral rotor of the present invention is rather long, the rotors are of a type supported on both sides. Thus, each of the spiral rotors is configured with two bearings. Again, the helical rotor has a relatively small diameter such that the ratio of the distance between the length of the helical rotor and the axis of the rotor is greater than 3, preferably greater than 3.5, and more preferably greater than 4.0. Moreover, the spiral rotor of the present invention has a variable pitch and includes There are at least 7 windings, preferably at least 9, and more preferably at least 11 turns. The compression ratio of the present invention is at least 4.5, preferably at least 5. In order to avoid overheating of the rotor due to the high compression ratio provided by the present invention, the rotor includes a plurality of spiral turns on the pressure side with only a slight or no change in pitch. Thus, in accordance with the present invention, the pitch after the half of the turns is less than twice the pitch at the rotor exit, preferably less than 1.5 times the pitch at the rotor exit. Since in the present invention, the pitch of the pressure side of the rotor changes little, and the gap height is selected correspondingly, compression occurs along a longer area of the rotor. Thereby, the present invention can provide significant advantages in improving the heat dissipation effect. The waste heat caused by the compression work is generated substantially in the high pressure region, and the surface area of the casing for absorbing heat is now larger due to the occurrence of such high pressure respective extension regions in the present invention. . A preferred embodiment of a spiral vacuum pump in accordance with the present invention is provided with a helical rotor, each helical rotor comprising only one thread.

Therefore, since the pressure-side spiral rotor has a small pitch variation in the region on the pressure side according to the present invention, a compression ratio of at least 4.5 can be achieved, and the generated heat can be dissipated, and the rotor can be avoided. overheat. Here, it must be noted that heat dissipation can only be carried out in the pressure side region, since in the region of low pressure or high vacuum, due to the low gas density, there may not be sufficient heat to be transferred to the housing.

A spiral rotor having a high built-in volume ratio according to the invention has the additional advantage that the power input is small at low pressures. Thus, for output pressures below 10 mbar, a power input of less than 12 W/(m ³ h) relative to the suction capacity can be achieved.

According to a preferred embodiment, the heat dissipation system is exclusively carried out via the pump housing. In addition to heat dissipation via the medium itself, heat dissipation is preferably performed only via the pump housing. Therefore, it is not necessary to perform internal cooling of the rotor which is technically relatively complicated.

Further, according to the present invention, the provision of a plurality of spiral turns having a slight pitch variation in the pressure side region of the rotor has the advantage of significantly reducing noise. This is due to the compression over a longer area, resulting in a smaller pressure difference between the last chamber and the gas outlet region. Therefore, reverse ventilation is reduced; and reverse ventilation causes pressure waves. And noise occurs. Due to this low reverse ventilation, noise generation is also reduced by up to 3 to 6 db (A) when freely venting the exhaust. This provides the distinct advantage that a smaller size silencer element can be provided. Since the constituent volume of the sound absorbing member can be reduced, the increase in the length of the vacuum pump due to the longer spiral rotor can be at least partially compensated.

Further, the outer shape of the spiral rotor is preferably substantially symmetrical. Preferred here is a trapezoidal appearance, a cycloid appearance or an evolvent appearance. Preferably, the gap height, i.e., the distance between the helical rotor and the inner wall of the housing, is selected such that compression extends over a relatively long area of the rotor exit side. More preferably, in the cold state of the turbomolecular pump, the ratio of "cold gap height / distance between axes" is >2/1000. Further, it is preferable that the ratio of the "cold gap height / the distance between the axes" is >12/1000 when the operating temperature is reached in the operating state. In accordance with the present invention, the gap height is preferably selected such that during end pressure operation, the chamber pressure drops below the average chamber pressure of 100 mbar only after about 20% of the rotor length (measured from the outlet side).

According to a preferred embodiment, the spiral vacuum pump of the present invention has a rated rotational speed greater than 5000 revolutions per minute. Also, in order to avoid excessive compression, the overpressure valve may be provided in the pressure side region of the spiral rotor. In addition to the overpressure valve, the speed controller can be optionally or additionally provided. Excessive compression can be avoided by appropriately reducing the speed. Through the above two measures, the power input under high suction pressure can be effectively reduced, and thus the performance of the built-in motor.

The two spiral rotors shown in Fig. 1 are arranged in a pump housing (not shown). This pump housing defines a pump chamber 10 in which two helical rotors 12, 14 are arranged. On either side of the two helical rotors, they include a shaft stub 16, 18 rotatably disposed within the pump housing via the bearing element 20. In order to drive the two helical rotors 12, 14, the stub shaft 18 or the stub shaft 16 is connected directly to the drive motor in a conventional manner or to the drive motor via a transmission gear. The second helical rotor is driven by the same drive motor via a corresponding gear connection (not shown) such that the two helical rotors 12, 14 are synchronized with each other and rotate in opposite directions to each other. The helical rotors 12, 14 act to cause the medium to be transported to be drawn in on the suction side (arrow 22) and to discharge the medium on the pressure side (arrow 24).

The pitch of the helical rotor is indicated by a diagonal line 26. In Figure 1, it can be seen that the pitch varies over the length l of the rotor. In the pressure side region 28, the pitch is significantly smaller than in the suction side region 30. Here, according to the invention, the pitch in the pressure side region 28 is configured such that the pitch in the region 31 of the half turn is at most twice the pitch at the rotor outlet 24. Therefore, a relatively long pressure side region 28 can be formed by only slightly changing the pitch. in In the pressure side region 28, compression of most of the pressure difference between the inlet and the outlet is achieved. Thus, most of the compression work is also performed in this area 28. Therefore, the heat to be discharged is generated substantially in this area. According to the invention, the heat discharge is achieved via a housing of the helical rotors 12, 14 enclosed in the pressure side region.

According to the invention, the structural length of the helical rotors 12, 14 is long. Thus, as provided by the present invention, the ratio of the length l of the helical rotors 12, 14 to the distance d between the rotor axes is greater than 3.0.

The upper portion of Fig. 2 shows the helical rotor 12 according to the present invention corresponding to the helical rotors 12, 14 of Fig. 1. Below it is shown a spiral rotor 32 of the prior art. Conventional helical rotors 32 are relatively short and include a smaller number of helical turns whose pitch is only slightly altered in their pressure side regions. In the conventional helical rotor 32, its pressure profile is as outlined by line 34. As can be seen, a strong pressure rise occurs in the pressure side region 36 of the helical rotor 32.

Due to the structure of the rotor 12 according to the invention, the pressure side region 28 is significantly longer. In addition, the gap height is also selected correspondingly (cold gap height / distance between axes > 2 / 1000, and hot gap height / distance between axes > 1 / 1000). Thus, in the present invention, the rise in pressure follows a relatively flat track, as shown by line 38 in the figure.

Although the present invention has been described and illustrated with reference to the specific illustrated embodiments, the invention is not limited to the illustrated embodiments. It will be apparent to those skilled in the art that many variations and modifications can be made without departing from the true scope of the invention as defined by the scope of the appended claims. Therefore, if it falls on the subsequent patent application The present invention includes all such changes and modifications as it is intended.

10‧‧‧ pump room

12,14‧‧‧Spiral rotor

16,18‧‧‧ short axis

20‧‧‧ bearing components

22‧‧‧Medium suction side

24‧‧‧Media discharge side

26‧‧‧Slash

l‧‧‧The length of the rotor

28‧‧‧ Pressure side area

30‧‧‧ suction side area

31‧‧‧ in the area of half of the spiral

24‧‧‧Rotor exit

32‧‧‧Spiral rotors of conventional technology

34, 38‧‧" line

36‧‧‧ Pressure side area

D‧‧‧distance between rotor axes

The complete and exemplified disclosure of the present invention, including the best mode of the invention, which is to be understood by those skilled in the art, will be understood by the following detailed description with reference to the accompanying drawings in which: FIG. A schematic plan view of two spiral rotors. And Fig. 2 is a schematic diagram showing a comparison between a spiral rotor according to the prior art and a spiral rotor according to the present invention, accompanied by a schematic diagram of pressure development.

10‧‧‧ pump room

12,14‧‧‧Spiral rotor

16,18‧‧‧ short axis

20‧‧‧ bearing components

22‧‧‧Arrow (medium suction side)

24‧‧‧Arrow (media discharge side)

26‧‧‧Slash

D‧‧‧distance between rotor axes

l‧‧‧The length of the rotor

28‧‧‧ Pressure side area

30‧‧‧ suction side area

31‧‧‧ in the area of half of the spiral circle

24‧‧‧Rotor exit

Claims (12)

A spiral vacuum pump comprising: a pump housing defining a pump chamber (10), two helical rotors (12, 14) disposed in the pump chamber (10), the spiral rotors (12, 14) Supported in the pump housing by two bearing elements (20), and the ratio of the rotor length (l) of the helical rotor to the distance (d) between the rotor axes is greater than 3, the spiral rotors (12) , 14) having: a variable pitch, at least 7 turns and a built-in compression ratio of at least 4.5, and wherein the pitch in the region of the half turn is at most on the pressure side rotor outlet (24) Double the pitch. A spiral vacuum pump according to claim 1, wherein each of the spiral rotors (12, 14) has only one thread. A spiral vacuum pump according to claim 1, wherein the spiral rotors (12, 14) are substantially symmetrical in shape. A spiral vacuum pump according to claim 1, wherein the spiral rotors (12, 14) are substantially asymmetrical in shape. A spiral vacuum pump according to claim 1, wherein the ratio between the length (1) of the rotor and the distance (d) between the rotor axes is greater than 3.5. A spiral vacuum pump according to claim 1, wherein the ratio between the length (l) of the rotor and the distance (d) between the rotor axes is greater than four. A spiral vacuum pump according to claim 1, wherein each of the spiral rotors (12, 14) is provided with at least 9 spiral turns. A spiral vacuum pump according to claim 1, wherein each of the spiral rotors (12, 14) is provided with at least 11 spiral turns. A spiral vacuum pump according to claim 1, wherein the compression ratio is at least 5. A spiral vacuum pump according to claim 1, wherein the compression ratio is at least 6. A spiral vacuum pump according to claim 1, wherein at least one overpressure valve is provided in the pressure side region (28) in order to avoid excessive compression. A spiral type vacuum pump according to any one of claims 1 to 11, wherein the rotational speed is controlled by a rotational speed control unit.