HK1237391A1 - Pumping system for generating a vacuum and pumping method by means of this pumping system - Google Patents

Description

Pumping system for generating vacuum and pumping method using same

Technical Field

The invention relates to the technical field of vacuum. More precisely, the invention relates to a pumping system comprising at least one claw pump (pompe pumps) and a pumping method using such a pumping system.

Prior Art

In industries such as chemical industry, pharmaceutical industry, vacuum deposition industry, semiconductor industry, etc., the general purpose of improving the performance of vacuum pumps, reducing installation costs and energy consumption has led to significant developments in performance, energy conservation, volume, drive, etc.

The prior art shows that in order to improve the final vacuum, for example, supplementary stages have to be added to the vacuum pump of a multistage roots pump or a multistage claw pump. For a dry vacuum pump of the screw type, it is necessary to provide additional rotation of the screw and/or increase the internal compression ratio.

The rotational speed of the pump plays a very important role by defining the operation of the pump during different successive phases in the evacuation process of the vacuum chamber. With the internal compressibility of commercially available pumps (e.g. of the order of between 2 and 20), the power required in the first pumping stage will be very high if the rotational speed of the pump cannot be reduced when the pressure at the suction end is between atmospheric pressure and about 100 mbar (in other words during high mass flow rate operation).

A common solution is to use a variable speed drive that can reduce or increase speed, and thus power, according to different types of pressure, maximum current, limit torque, temperature, etc. criteria. However, during periods of operation where the rotational speed is reduced, there is a reduction in the flow rate at high pressure, the flow rate being proportional to the rotational speed. Furthermore, the speed variation through the variable speed drive results in additional cost and greater bulk.

Another common solution is to use bypass-type valves at certain well-defined locations along the screw in certain stages in roots-type or claw-type multi-stage vacuum pumps, or in screw-type dry vacuum pumps. This solution requires many parts and has reliability issues.

The prior art on pumping systems aimed at improving the final vacuum and increasing the flow rate also includes booster pumps of the roots type arranged upstream of the main dry pump. This type of system is bulky and operates with bypass valves having reliability issues, or by employing means of measurement, control, regulation or servo control. However, these means of control, regulation or servo control must be controlled in an active manner, which entails an increase in the number of components of the system, its complexity and its cost.

Disclosure of Invention

The aim of the invention is to allow a better vacuum (of the order of 0.0001 mbar) to be obtained than can be generated in a vacuum chamber by a single claw pump.

It is also an object of the present invention to obtain a greater evacuation or evacuation rate at low pressures than can be obtained by means of a single claw pump to achieve a vacuum in a vacuum chamber during pumping.

The present invention also aims to allow a reduction in the electrical energy required to evacuate the vacuum chamber and maintain the vacuum, and to achieve a reduction in the temperature of the exhaust gases.

These objects of the invention are achieved by means of a pumping system for generating a vacuum, said pumping system comprising a primary vacuum pump which is a claw pump having a gas suction inlet connected to a vacuum chamber and a gas exhaust outlet which opens into a gas evacuation conduit in the direction of a gas exhaust outlet external to the pumping system. The pumping system further comprises:

-a check valve positioned between the gas discharge outlet and the gas discharge outlet, and

-an auxiliary vacuum pump connected in parallel to the check valve.

The auxiliary vacuum pump can be of different types, in particular another claw pump type, screw dry pump type, multistage roots pump type, diaphragm pump type, dry rotary vane pump type or lubricating rotary vane pump type or gas injector type.

The invention likewise has as subject a pumping method with a pumping system such as previously defined. The method comprises the following steps:

-the main vacuum pump is activated so as to pump the gases contained in the vacuum chamber and to discharge these gases through its gas discharge outlet;

-at the same time, the auxiliary vacuum pump is started; and

the auxiliary vacuum pump continues pumping during the entire time the main vacuum pump pumps the gas contained in the vacuum chamber and/or during the entire time the main vacuum pump maintains a defined pressure in the vacuum chamber.

In the method according to the invention, the auxiliary pump is operated continuously not only during the entire time the main claw vacuum pump evacuates the vacuum chamber, but also during the entire time the main claw vacuum pump maintains a defined pressure (e.g. a final vacuum) in the chamber via evacuation of air through its exhaust end.

Thanks to the method according to the invention, the coupling of the primary claw vacuum pump with the secondary pump can be performed without specific measures or devices (e.g. sensors of pressure, temperature, current, etc.), servo control, or data management and without calculations. Thus, a pumping system suitable for implementing the pumping method according to the invention can contain only a minimum number of parts, can have great simplicity, and can be considerably less expensive than existing systems.

Thanks to the method according to the invention, the main claw vacuum pump can be operated at a single constant speed, mains, or rotated at variable speed, depending on its own operating mode. Thus, the complexity and cost of a pumping system suitable for implementing the pumping method according to the invention can be reduced even more.

By its nature, the auxiliary pump integrated in the pumping system is always able to operate according to the pumping method of the invention without suffering damage. Its size is adapted by the minimum energy consumption for the operation of the device. Its nominal flow rate is selected as a function of the volume of the evacuation conduit between the main claw vacuum pump and the check valve. This flow rate can advantageously be 1/500 to 1/20 of the nominal flow rate of the main claw vacuum pump, but can also be 1/500 to 1/10, or even 1/500 to 1/5 of less or more than these values, in particular of the nominal flow rate of the main vacuum pump.

The non-return valve placed in the conduit downstream of the main claw vacuum pump can for example be a standard commercially available element, but equally elements designed specifically for a specific application are conceivable. It is dimensioned according to the nominal flow rate of the main claw vacuum pump. In particular, it is foreseen that the check valve closes when the pressure at the suction end of the main claw vacuum pump is between 500 mbar absolute and the final vacuum (for example 100 mbar absolute).

According to another variant, the auxiliary pump can be made of a material and/or have a coating that can have a high chemical resistance to the substances and gases commonly used in the semiconductor industry.

The auxiliary pump is preferably of small size.

Preferably, according to the pumping method employing the pumping system according to the present invention, the auxiliary vacuum pump always pumps in the volume between the gas exhaust outlet of the main claw vacuum pump and the check valve.

According to another variant of the method of the invention, the actuation of the auxiliary vacuum pump is controlled in a "total (tout) or no (rien)" manner in order to meet specific requirements. Control includes measuring one or more parameters and actuating the auxiliary vacuum pump or stopping it in compliance with certain rules. The parameters provided by suitable sensors are, for example, the current of the motor of the main claw vacuum pump, the pressure or temperature of the gas at its exhaust end (i.e. in the space upstream of the check valve in the evacuation conduit), or a combination of these parameters.

The auxiliary vacuum pump is dimensioned to achieve a minimum energy consumption of its motor. Its nominal flow rate is selected as a function of the flow rate of the main claw vacuum pump, but also taking into account the volume of the gas evacuation line defined between the main vacuum pump and the check valve. This flow rate can be not only 1/500 to 1/20 of the nominal flow rate of the primary claw vacuum pump, but also less or greater than these values.

From the cycle of evacuation of the chamber, the pressure there is high, for example equal to atmospheric pressure. In view of the compression in the main claw vacuum pump, the pressure of the gas discharged at its outlet is higher than the atmospheric pressure (if the gas at the outlet of the main pump is directly discharged into the atmosphere) or higher than the pressure at the inlet of another device connected downstream. This causes the opening of the check valve.

When this check valve opens, the action of the auxiliary vacuum pump is felt very slightly, since the pressure at its suction end is almost equal to the pressure at its discharge end. On the other hand, when the check valve closes at a certain pressure (because the pressure in the chamber has dropped at the same time), the action of the auxiliary vacuum pump causes the pressure difference between the vacuum chamber and the evacuation conduit upstream of the valve to gradually decrease.

The pressure at the outlet of the main claw vacuum pump becomes the pressure at the inlet of the auxiliary vacuum pump, the pressure at its outlet always being the pressure in the pipe after the check valve. The more the auxiliary vacuum valve pumps, the more the pressure at the outlet of the main claw vacuum pump (in the space defined by the closed check valve) drops, and therefore the pressure difference between the chamber and the outlet of the main claw vacuum pump decreases. This slight difference reduces internal leakage in the main claw vacuum pump and results in a reduction in pressure in the chamber, which improves the final vacuum.

Furthermore, the main claw vacuum pump consumes less energy for compression and generates less heat of compression.

On the other hand, it is also evident that the research of the mechanical concept seeks to reduce the space between the gas discharge outlet of the main claw vacuum pump and the check valve, with the aim of being able to reduce the pressure there more rapidly.

Drawings

The features and advantages of the invention will appear in more detail in the context of the following description, which gives exemplary embodiments by way of illustration and not of limitation, with reference to the accompanying drawings:

figure 1 represents in a schematic way a pumping system suitable for implementing the pumping method according to a first embodiment of the invention; and

figure 2 represents in a schematic way a pumping system suitable for implementing the pumping method according to a second embodiment of the invention.

Detailed Description

Fig. 1 shows a pumping system SP for generating a vacuum suitable for implementing the pumping method according to a first embodiment of the present invention.

This pumping system SP comprises a chamber 1, the chamber 1 being connected to the suction end 2 of a main vacuum pump constituted by a claw pump 3. The gas exhaust outlet of the main claw vacuum pump 3 is connected to an exhaust pipe 5. A non-return discharge valve 6 is placed in the evacuation pipe 5, after which the evacuation pipe 5 continues into the gas discharge pipe 8. The non-return valve 6, when it is closed, allows the formation of the volume 4 contained between the gas discharge outlet of the primary vacuum pump 3 and itself.

The pumping system SP also comprises an auxiliary vacuum pump 7, the auxiliary vacuum pump 7 being connected in parallel to the non-return valve 6. The suction end of the auxiliary vacuum pump is connected to the space 4 of the evacuation duct 5, and the discharge end thereof is connected to the duct 8.

The auxiliary vacuum pump 7 itself has been actuated by actuation of the primary claw vacuum pump 3. The main claw vacuum pump 3 sucks the gases in the chamber 1 through the duct 2 connected at its inlet and compresses them in order to subsequently discharge them at its outlet to the evacuation duct 5, passing through the non-return valve 6. When the closing pressure of the non-return valve 6 is reached, it closes. From this point on, the pumping of the auxiliary vacuum pump 7 causes the pressure in the space 4 to gradually drop to the value of its pressure limit. In parallel, the power consumed by the main claw vacuum pump 3 is gradually reduced. This occurs in a short period of time, for example, some cycle of 5 to 10 seconds, but may also last longer, depending on the relationship between the volume 4 and the nominal flow rate of the auxiliary vacuum pump 7.

With a smart adjustment of the flow rate of the auxiliary vacuum pump 7 and with a smart adjustment of the closing pressure of the non-return valve 6 as a function of the flow rate of the main claw vacuum pump 3 and the volume of the chamber 1, it is possible to additionally reduce the time before closing of the non-return valve 6 with respect to the duration of the evacuation cycle and therefore to reduce the amount of energy consumed during this operating time of the auxiliary pump 7, with the advantage of simplicity and reliability of the system.

Depending on the different possibilities of combination, the auxiliary vacuum pump 7 may be another claw pump, a dry screw-type pump, a multistage roots pump, a diaphragm pump, a dry rotary vane pump, a lubricated rotary vane pump or even an ejector. In the last case, the ejector may be a "simple" ejector, in the sense that its flow rate of propulsion gas comes from the distribution network of the industrial site, or a compressor that can be equipped to provide the ejector with a flow of driving gas at the pressure required for its operation. More specifically, this compressor can be driven by the main pump, or alternatively or additionally in a spontaneous manner independently of the main pump. This compressor is capable of drawing atmospheric air or gas in a gas discharge line after the check valve. The presence of such a compressor results in a system of pumps independent of the source of compressed gas, which can meet the requirements of certain industrial environments.

Fig. 2 shows a pumping system SPP suitable for implementing a pumping method according to a second embodiment of the present invention.

With respect to the system shown in fig. 1, the system shown in fig. 2 represents a controlled pumping system SPP, which also contains suitable sensors 11, 12, 13 which check the current of the motor of the main claw vacuum pump 3 (sensor 11), or the pressure of the gas in the space of the exhaust conduit of the main claw vacuum pump limited by the non-return valve 6 (sensor 13), or the temperature of the gas in the space of the exhaust conduit at the outlet of the main claw vacuum pump limited by the non-return valve 6 (sensor 12), or a combination of these parameters. In fact, when the main claw vacuum pump 3 starts pumping the gas of the vacuum chamber 1, parameters such as the current of its motor, the temperature and the pressure of the gas in the space 4 of the exhaust duct start to change and reach the threshold value detected by the sensor. After a time delay this results in the start-up of the auxiliary vacuum pump 7. When these parameters return to the initial range (outside the set point), the auxiliary vacuum pump is stopped with a time delay.

In the second embodiment of the invention of fig. 2, the auxiliary vacuum pump can also be of the claw type, dry screw type, multistage roots type, diaphragm type, dry rotary vane type, lubricated rotary vane type or ejector (with or without a compressor providing its propulsion gas), as in the first embodiment of the invention of fig. 1.

While various embodiments have been described, it will be well understood that not all possible embodiments are exhaustively contemplated. It is, of course, contemplated that equivalent means may be substituted for those described without departing from the scope of the invention. All of these modifications form part of the common general knowledge of a person skilled in the art of vacuum technology.

Claims (27)

1. A pumping System (SP) for generating a vacuum, the pumping system comprising a primary vacuum pump which is a claw pump (3) having a gas suction inlet (2) and a gas exhaust outlet (4), the gas suction inlet (2) being connected to a vacuum chamber (1), the gas exhaust outlet (4) opening into a gas exhaust duct (5) in the direction of a gas exhaust outlet (8) outside the pumping system,

the pumping system is characterized in that: the pumping system comprises:

-a check valve (6) positioned between the gas discharge outlet (4) and the gas discharge outlet (8), and

-an auxiliary vacuum pump (7) connected in parallel to the check valve.

2. A pumping system according to claim 1, characterized in that the auxiliary vacuum pump (7) is selected from dry screw-type pumps, claw pumps, multistage roots pumps, diaphragm pumps, dry rotary vane pumps, lubricated rotary vane pumps and injectors.

3. Pumping system according to claim 1 or 2, characterized in that the auxiliary vacuum pump (7) is a dry screw type pump.

4. Pumping system according to claim 1 or 2, characterized in that the auxiliary vacuum pump (7) is a claw pump.

5. Pumping system according to claim 1 or 2, characterized in that the auxiliary vacuum pump (7) is a multistage roots pump.

6. A pumping system according to claim 1 or 2, characterized in that the auxiliary vacuum pump (7) is a diaphragm pump.

7. Pumping system according to claim 1 or 2, characterized in that the auxiliary vacuum pump (7) is a dry rotary vane pump.

8. Pumping system according to claim 1 or 2, characterized in that the auxiliary vacuum pump (7) is a lubricating rotary vane pump.

9. A pumping system according to claim 1 or 2, characterized in that the auxiliary vacuum pump (7) is an ejector.

10. Pumping system according to claim 9, characterized in that the working fluid of the ejector (7) is compressed air or nitrogen.

11. A pumping system according to claim 9 or 10, wherein the flow of gas at the pressure required for the operation of the ejector (7) is provided by a compressor.

12. A pumping system according to claim 11, characterized in that the compressor is driven by the main pump (3).

13. A pumping system according to claim 11, wherein the compressor is driven autonomously independently of the primary pump.

14. Pumping system according to any of the preceding claims, characterized in that the auxiliary vacuum pump (7) is designed to be able to pump during the entire time the main vacuum pump (3) pumps the gas contained in the vacuum chamber (1) and/or during the entire time the main vacuum pump (3) maintains a defined pressure in the vacuum chamber (1).

15. Pumping system according to any one of the preceding claims, characterized in that the auxiliary vacuum pump (7) comprises an exhaust end connected to the gas evacuation conduit (5) downstream of the non-return valve (6).

16. Pumping system according to any one of the preceding claims, characterized in that the nominal flow rate of the auxiliary vacuum pump (7) is chosen as a function of the volume defined by the gas evacuation duct (5) between the primary vacuum pump (3) and the non-return valve (6).

17. Pumping system according to any of the preceding claims, characterized in that the nominal flow rate of the auxiliary vacuum pump (7) is 1/500 to 1/5 of the nominal flow rate of the primary vacuum pump (3).

18. Pumping system according to any of the preceding claims, characterized in that the auxiliary vacuum pump (7) is single-stage or multi-stage.

19. Pumping system according to any of the preceding claims, characterized in that the check valve (6) is configured to close when the pressure at the suction end of the primary vacuum pump (3) is less than 500 mbar absolute.

20. Pumping system according to any one of the preceding claims, characterized in that the auxiliary vacuum pump (7) is made of a material having a high chemical resistance to the substances and gases commonly used in the semiconductor industry.

21. A pumping method using a pumping System (SP) according to any one of the preceding claims,

-the primary vacuum pump (3) is activated so as to pump the gases contained in the vacuum chamber (1) and to discharge these gases through a gas discharge outlet (4) of the primary vacuum pump (3);

-at the same time, the auxiliary vacuum pump (7) is activated; and

-the auxiliary vacuum pump (7) continuously pumps during the entire time the main vacuum pump (3) pumps the gas contained in the vacuum chamber (1), and/or continuously pumps during the entire time the main vacuum pump (3) maintains a defined pressure in the vacuum chamber (1).

22. Pumping method according to claim 21, characterized in that the auxiliary vacuum pump (7) pumps at a flow rate of the order of 1/500 to 1/20 of the nominal flow rate of the primary vacuum pump (3).

23. Pumping method according to claim 21 or 22, characterized in that the non-return valve (6) is closed when the pressure at the suction end of the primary vacuum pump (3) is less than 500 mbar absolute.

24. A pumping method according to any one of claims 21 to 23, wherein the auxiliary vacuum pump is an ejector.

25. A pumping method according to claim 24, characterized in that the flow of gas at the pressure required for the operation of the ejector (7) is provided by a compressor.

26. Pumping method according to claim 25, characterized in that the compressor is driven by the main pump (3).

27. A pumping method according to claim 25, wherein the compressor is driven autonomously independently of the primary pump.