IT202100025589A1 - SCREW COMPRESSOR. - Google Patents

Description

SCREW COMPRESSOR

The screw compressor? a volumetric rotary compressor consisting of two parallel rotors externally equipped with more? helical profiles (screws) such that they can mesh into each other. The two rotors are housed in a stator composed of two cylinders that intersect longitudinally, inside which the rotors rotate with a clearance that is not ? reducible beyond a certain limit.

The rotor shafts are supported by rolling bearings, and generally one rotor drives the other through the meshing of the same helical profiles. Sometimes both can be controlled by a pair of external gears, to reduce the friction otherwise present. During rotation, the profiles of the screws reveal a suction port, located at one end. of the stator, through which air or gas enters to fill the volume between the profiles themselves up to its maximum extension.

On the opposite side, the profiles penetrate into each other, reducing the volume and compressing the gas contained therein until revealing the delivery port. The operation of the screw compressor is based on the counter-rotating action of two helical rotors which compress the gas or air taken from the suction pipe and bring it towards the delivery pipe. During this journey the space is reduced and, consequently, the pressure rises.

The screw compressor? very widespread thanks to the diffusion of the technology of its construction. There are many manufacturers and assemblers who offer this product in the most different variants: single-stage, two-stage for high pressure with and without oil for "Oil free" applications. The speed? rotation normally? higher than that of the engine to which ? connected by multiplier gears or by the pulley ratio when a belt is present.

These types of industrial compressors supply compressed gas or air continuously, are very well controllable, extremely efficient and silent (in terms of workplace safety, environmental protection and noise emissions). Does the current technology involve the use of metallic materials (ductile cast iron or steel) for the production of screws and the correct functioning of the compressor? linked to the presence of clearances between the profile of the screws and the screws with the compression chamber. But the presence of such clearances still leads to a lower efficiency of the machine due to the leakages that bring the gas from high pressure areas (delivery) and areas with more? low pressure (suction).

As mentioned above, the compression ratios can be increased by injecting lubricating oil which helps both the surfaces of the profiles in contact, which acts as a refrigerant to maintain temperature limits suitable for the materials used, and as a sealing fluid between the elements in relative motion to each other. Patent CN1032383 describes propellers with a steel shaft, aluminum body and fiber-filled polyamide covering; this composition of different materials? used to guarantee a reduction in the overall weight of the finished body, fully exploit the peculiar characteristics of polymeric materials and also to use a more efficient lubricating fluid. performing.

For this purpose, patent CN107448383A uses water as lubricants and unfilled PEEK (polyether ether ketone) to coat the rotor.

In the patents cited, the production of the rotor, both as a coating and as a finished piece? obtained through injection molding.

The present invention aims to improve the performance of a compressor of this type by using entirely polymeric material for the propellers.

An aspect of the present invention concerns a screw compressor having the characteristics of the attached claim 1.

Further characteristics of the present invention are contained in the dependent claims.

The characteristics and advantages of the present invention will be more evident from the following description of an exemplifying and non-limiting embodiment of the invention, referring to the attached schematic drawings, in which:

? Figure 1 illustrates a side view of a screw compressor according to the present invention;

? figure 2 illustrates a section of the compressor of figure 1 taken along the line A-A;

? figure 3 illustrates a cross section of the compressor of figure 1,

? figure 4 illustrates the male rotor and the female rotor of the compressor of figure 1;

? figures 5a 5b and 5c illustrate respectively for male and female rotors and for coupled rotors the means for blocking the axial movement;

? figure 6 schematically illustrates the various parts of the screw compressor;

? figure 7 schematically illustrates a detail of a separate lubrication system for the mechanical parts (bearings, seals and gears) of the compressor.

With reference to the aforementioned figures, the screw compressor according to the present invention includes two rotors or helical screws, respectively male rotor 2 and female rotor 3 enclosed in a case 4 inside which they counter-rotate. A gas passes through a suction duct 5 created between the two rotors, and the rotation closes this suction duct and the compressed gas is pushed towards a delivery 6.

Each rotor includes a rotation shaft 21 and 31 which rotates in the case thanks to special bearings which are surrounded by helices 22 and 32 which engage with each other. The propellers are made in such a way as to progressively reduce the space between the rotors and the stator, so that the gas sucked in by the intake duct is compressed in the direction of the delivery 6.

The two rotors are usually designed with different profiles. The male rotor? usually equipped with convex lobes, while the female rotor has cavities? usually concave. ? thanks to these characteristics that are grafted onto each other.

A special motor supplies the compressor with the necessary power. The motor is used to rotate the male rotor, which in turn drives the female rotor.

The cash register? equipped with special bearings which are used to keep the rotors in the correct position. Are they located at the ends? of both rotors, ensuring uniform rotation and constant balancing.

There are also intake and exhaust valves, which regulate the initial recovery and removal of gas from the compressor. The inlet valve opens to allow gas to enter the system, while the exhaust valve receives the compressed gas at the end of the process.

According to the present invention the propellers 22 and 32 are made of a polymeric material.

The choice of a polymeric material for the production of the propellers, in fact, brings significant advantages in terms of performance, exploiting the temperature behavior and the greater deformability. of the material itself, capable of leading to a reduction in clearances between the propellers during operation. Unlike metals, in fact, ? Is it possible to have greater contact, therefore adaptation of the profiles during the meshing process, in relation to the properties? reduction of surface friction and non-stick.

Furthermore, in order to minimize fatigue and/or deformation problems of the propeller shaft, in relation to more application critical, in terms of mechanical resistance, the central body of the screw, in particular the shaft 21 and 31 including external protrusions, can? be produced in more material? resistant and subsequently mechanically connected to the helical polymer parts. Polymer propellers can be produced starting from a 3D printing process (e.g. FDM) or starting from a solid profile.

The propeller manufacturing process can include both the use of FDM (Fused Deposition Modeling) and the mechanical processing of a solid cylinder. 3D printing, using FDM, has excellent piece finishes and good speed. of production, but at the same time, keeps the mechanical and chemical characteristics of the polymer unchanged. In the printing process it can? a further finishing phase of the rotor obtained may be necessary, to guarantee compliance with the geometric and dimensional tolerances of the piece necessary for the correct functioning of the machine, in transients and at operating speed.

The shaft is preferably made with a different material from that of the propellers, for example from a lighter material. resistant, in order to absorb most of the bending load generated by the compression and the torque imposed by the engine, minimizing the deformations that could be encountered using a body made solely from the same material.

The shafts are mechanically connected to the respective propellers in order to transmit the torque of the engine through an appropriate locking system. To obtain an effective transmission of the torque, this system includes tabs and related slots made both on the rotor and on the shaft, with a variable number based on the diameter of the shaft and the torque value to be transmitted, up to the use of a splined shaft.

As regards the transmission line of the axial and radial loads linked to the compression process itself, the coupling between the propeller and shaft requires the presence of contact surfaces designed to resist the forces involved. In particular, radial thrusts were taken into account by appropriately calibrating the diametric coupling between shaft and propeller. From the point of view of the axial thrusts, from delivery to suction, in operating conditions, means have been created to block the relative axial movement between the two parts including a protrusion 211 and 311 on the shaft which fits into a slot obtained in the propeller . In relation to the reversed axial thrusts (from suction to delivery), connected instead to transitory situations when starting direct-coupled and gear-driven machines,? a locking ring 212 and 312 of the delivery side propeller is provided on each rotor.

This system has the task of avoiding both slippage between the screw and shaft during torque transmission, and of preventing axial translations of the rotor along the shaft in both directions, in relation to the loads generated by the mechanics of the meshing between the two rotors and the fluid dynamics of the compression process itself, taking into consideration the expansions involved.

Considering the anisotropic behavior of the material obtained by 3D printing, the internal stator bodies (rotor case-diametric seat and delivery and suction surfaces) of the compressor can be coated with an abradable polymer film.

This film, in addition to reducing the space between the rotor and the respective cylinder, further reducing leakage, guarantees, in the event of contact of the rotor with the aforementioned surfaces, the formation of a groove, avoiding plastic deformation or breakage of the rotor tooth due to excessive overheating caused by the friction of the different materials. So the purpose of the polymer film? also that of creating a thin ?sacrificial? barrier between the rotors and the compressor bodies.

A suitable polymer that can be used for both male and female screws? PEEK (polyether ether ketone), loaded with both long and short fibers, which has the right properties? of compatibility? both with the tree and with the processed gases, as well as? the properties? mechanical and chemical such that it can? be subjected to both 3D printing (such as FDM) and traditional mechanical processing, starting from solid (bar or cylinder) and for geometric finishing. Even polyamides and polyolefins, adequately functionalized and/or loaded with appropriate fillers and fibers, can be used to obtain profiles. These polymers must have properties of compatibility? both with the processed fluids and with the trees on which they are installed, that an adequate affinity? among them.

A category of polymers suitable for coating stator bodies, however, are fluorinated or perfluorinated compounds, as well as adequately functionalized polyolefins and polyamides.

This coating must present, in addition to compatibility? chemistry with the propeller material, in order to guarantee good adhesion, complete compatibility? with the temperatures and gases processed, in order to avoid premature and unwanted deterioration.

For the application of the film you can? foresee the use of sprays, powders or plasma. The use of high-performance polymers allows the use, in the case of oil injection machines, of more efficient refrigerant fluids. performing, as well as? improve the mechanical and functional behavior in the presence of corrosive and/or aggressive components of the gas.

The polymer propellers are therefore compatible with:

- process gas;

- lubricating fluid;

- compressor operating conditions (temperature, pressure, loads generated); At the same time, in relation to the characteristics identified in relation to deformability? to the conditions of use, they are able to reduce the previously mentioned games, in order to improve performance without however? affect the correct mechanical functioning, thanks to a higher thermal expansion coefficient of the polymer compared to the metal.

The choice of a polymeric material for the production of the propellers, in fact, brings significant advantages in terms of performance, exploiting the temperature behavior and the greater deformability. of the material itself, capable of leading to a reduction in clearances between the propellers during operation. Unlike metals, in fact, ? Is it possible to have greater contact, therefore adaptation of the profiles during the meshing process, in relation to the properties? reduction of surface friction and non-stick.

These aspects are inevitably expressed, for the oil injection machine version, in a more flexible choice of lubricant, which, on the rotor side, performs less and less both the function of anti-friction/anti-seize film during the mechanical meshing process and the function of reducing clearances, more? effectively covered by materials/coatings.

In terms of quantity? and functionality, therefore the injected fluid becomes, as far as the compression chamber is concerned, mainly a thermodynamic vector for reducing the temperature in the process, in relation to purely energetic heat balances. Where it is not possible to modify the characteristics of the fluid also used for lubrication of other mechanical parts (e.g. bearings/gears/seals?)? It is possible to use separate lubrication solutions. The screw compressor of the present invention can include lubrication channels 7, accessible from the outside, which transport the suitable lubricant to such mechanical parts such as for example bearings 71, gears, or seals 73. In this machine configuration the chamber where the meshing between the rotors, thus being able? use different fluids for each specific purpose (rotor coolant only or lubricant/coolant for other mechanical parts). This insulation is created by placing internal seals between the compression chamber and bearings.

Claims (9)

COMPLAINTS 1. Screw compressor comprising a male rotor (2) and a female rotor (3) enclosed in a case (4) inside which they counter-rotate, for the drive of the male rotor by a motor, a gas passes through a suction duct (5) created between the two rotors, and the rotation closes this suction duct and the compressed gas is pushed towards a delivery (6), each rotor includes a rotation shaft (21,31) which rotates in the case thanks to special bearings which are surrounded by propellers (22,32) which engage with each other, the propellers being made in such a way as to progressively reduce the space between the rotors and the case, so that the gas sucked in by the intake duct is compressed in the direction of the delivery (6), characterized in that the propellers are made of a polymeric material. 2. Compressor according to claim 1, in which the shafts (21,31) of the rotors are made of lighter material? resistant than that of the propellers. 3. Compressor according to claim 1, in which the shafts (21,31) are mechanically connected to the respective propellers (22,32) in order to transmit the torque of the engine through a suitable locking system. 4. The compressor according to claim 1, wherein such polymeric propeller material is PEEK. 5. Compressor according to claim 1, wherein the propellers are made by 3D molding. 6. Compressor according to claim 1, wherein such 3D molding is made using the FDM technique. 7. Compressor according to claim 1, in which the internal stator bodies, rotor case-diametric seat and delivery and suction surfaces are coated with an abradable polymer film. 8. Compressor according to claim 1, comprising lubrication channels (7), accessible from the outside, which transport suitable lubricant to bearings and/or gears and/or seals. 9. Compressor according to claim 1, comprising means for blocking the relative axial movement between propellers and shafts, comprising a protrusion (211,311) on the shaft which fits into a slot obtained in the propeller and a locking ring (212,312) of the propeller side sent.