WO2007030898A1

WO2007030898A1 - Improved screw of a water-injected screw compressor and a method for making such a screw

Info

Publication number: WO2007030898A1
Application number: PCT/BE2006/000098
Authority: WO
Inventors: Guido Jozef Christiian Peeters; Jozef Maria Segers; Sven Rogiest
Original assignee: Atlas Copco Airpower, Naamloze Vennootschap
Priority date: 2005-09-13
Filing date: 2006-09-11
Publication date: 2007-03-22
Also published as: BE1016762A3

Abstract

Improved screw of a water-injected screw-type compressor which mainly consists of a metal shaft around which has been cast a rotor made of a composite material, characterised in that at or near at least one far end (13-14) of the rotor (9) has been provided a sealing (12) between the rotor (9) and the shaft (8).

Description

Improved screw of a water-injected screw-type compressor and method for its production.

The present invention concerns a screw of a water- injected screw-type compressor, in particular a screw which consists of a metal shaft around which has been cast a rotor made of composite material.

Water-injected screw-type compressors whose screws are formed of a metal shaft around which has been provided a rotor made of a composite material are already known.

Although such water-injected compressors function very well, it is found that, after a long life, the quality of the screws may possibly represent some faults, such as for example the shaft that comes off.

The present invention aims an improved compressor which has a significantly longer life than the current water-injected compressors which are mainly composed of a metal shaft around which has been cast a rotor made of a composite material.

To this end, the invention concerns an improved screw of a water-injected screw-type compressor which mainly consists of a metal shaft around which has been cast a rotor made of a composite material, whereby a sealing is provided between the rotor and the shaft at or near at lea-st one far end of the rotor. Intensive research has indicated that providing a sealing at or near at least one far end of the rotor of an improved screw according to the invention results in a considerably longer life of said screw.

The present invention also concerns a method for manufacturing a screw according to the invention, which method consists in providing one or several sealings round the shaft, in providing the shaft in a mould together with the sealings and in casting a composite material in the mould so as to form the rotor round the shaft by making the composite material cure.

According to this preferred embodiment, the rotor is at least partly in direct contact with the metal shaft.

This embodiment is advantageous in that the rotor can be mechanically fixed round the shaft, such that a rotation of the rotor in relation to the shaft can be excluded, which is necessary in the case of screw-type compressors to maintain the set play between the rotors and between the rotors and the housing.

According to another preferred embodiment of the present invention, the sealing is formed of a layer made of an elastic synthetic material which is provided entirely round the shaft and which is embedded in the composite material of the rotor, whereby this layer extends over at least a part of the rotor. An advantage of this preferred embodiment is that the sealing can at least partly absorb the difference in the coefficient of expansion between the metal shaft and the composite material of the rotor, such that the fastening between both materials is maintained relatively well.

It should be noted that also a coating can be used as a sealing. In order to provide such a coating on the shaft, the shaft is preferably subjected to a number of pre-treatments first to optimize the adhesion between the coating and the shaft, such as for example mechanical roughening, cutting grooves, sandblasting or the like.

The actual application of the coating on the shaft can be done in many ways, such as by means of a brush or a spray gun.

Finally, composite material for forming the rotor round the shaft is provided, whereby, in order to obtain an optimal adhesion, the time of application of the composite material can be selected as a function of the drying or curing of the coating, for example after the coating has cured completely or, preferably, after the coating has dried but before it has cured completely, such that any solvents or water have disappeared and the coating has been immobilized on the shaft, and such that further chemical bonds can be formed between the coating and the composite material.

A coating on the basis of a two-component paint may have partially undergone the curing process at the time the composite material is applied for example. The coating is hereby selected such that a good adhesion and compatibility with the composite material are guaranteed, such as for example a phenol/epoxy or a polyurethane coating. A small amount of composite material may possibly have already been added to the base material for the coating so as to improve the compatibility.

In order to better explain the characteristics of the present invention, the following preferred embodiments of a screw according to the invention for a water-injected screw-type compressor are given as an example only without being limitative in any way, with reference to the accompanying drawings, in which:

figure 1 represents a water-injected screw-type compressor;

figure 2 represents a section according to line II-

II in figure 1; figure 3 represents a section according to line III-

III in figure 2 to a larger scale; figures 4 and 5 represent different variants of figure 3; figure 6 represents the part indicated by F6 in figure 5 to a larger scale; figure 7 represents another variant of figure 3.

Figures 1 and 2 represent a water-injected screw-type compressor 1 with a male screw 2 and a female screw 3 working in conjunction with the latter, provided in a housing 4 in a rotating manner, with an inlet 5 and an outlet 6.

As is known, one or several openings 7 are provided in the housing 4 through which water can be injected in the rotor chamber of the screw-type compressor 1, among others to lubricate and cool the screws 2, 3.

As is represented in more detail in figure 3, each of the above-mentioned screws 2 and 3 mainly consists of a metal shaft 8 around which is cast a rotor 9 in composite material .

In the outer surface 10 of the metal shaft 8 are preferably provided unevennesses in the form of grooves 11 or the like, which grooves 11 extend over a helical line round the shaft 8 over a distance which, in the longitudinal direction X-X' of the shaft 8, is smaller than or equal to the length of this rotor 9 and which grooves 11 enclose an angle with the longitudinal direction of the shaft 8.

As is represented in figure 3, preferably two or more grooves 11 are provided in the shaft which extend for example crosswise in a helical line round the rotor 9.

It is clear that the grooves 11 can also be provided according to another pattern in the shaft 8, for example as two helical lines in one and the same direction but with a different pitch.

These grooves 11 preferably have a depth which corresponds to 1.5 to 5% of the diameter of the shaft 8, such that a tongue and groove joint can be formed so to say between the shaft 8 and the rotor 9.

According to the invention, a sealing 12 is provided between the shaft 8 and the rotor 9 which, in this case, is formed of an 0-ring made of an elastic synthetic material, such as rubber or the like.

Preferably, the above-mentioned elastic synthetic material of the sealing 12 is an elastomer, such as vulcanized rubber.

Of course, also a thermoplastic elastomer can be used to form the sealing 12.

The sealing 12 is hereby provided on one of the far ends 13, 14 at or near the rotor 9, in particular preferably on the far end 13 of the rotor 9 which corresponds to the high-pressure side on the outlet 7 of the screw-type compressor 1.

Moreover, the sealing 12 is preferably embedded in the composite material of the rotor 9, as the rotor 9 is cast round the shaft 8 and round the sealing 12.

It should be noted that the rotor 9 is preferably at least partly connected to the metal shaft 8, such that a rotation of the rotor 9 in relation to the shaft 8 is avoided.

Providing the above-mentioned unevennesses in the form of grooves 11 or the like is advantageous in that the contact surface between the composite material of the rotor 9 and the shaft 8 is relatively large, as a result of which a good adhesion of the composite material to the shaft 8 is obtained.

Of course, it is also possible to provide unevennesses in the shaft 8 by means of sandblasting, pelting, providing corrugations, etching unevennesses or by means of a combination of the above-mentioned techniques with grooves 11 and/or the like.

The composite material is preferably a polymer resin on the basis of a vinyl ester with fillers .

As a polymer resin can also be applied a two-component polyurethane which is obtained by polymerizing an isocyanate with a polyol, such as for example a polyurethane of a methyl diphenyl di-isocyanate with a polyol.

Also a polymer resin on the basis of a di-isocyanate and an epoxy compound may possibly be used as polymer resin.

The working and use of the above-described water-injected screw-type compressor 1 is simple and as follows.

By driving the screws 2, 3, air or another gas is sucked in via the inlet 5 and forced out at a high pressure via the outlet 6, while water is being injected in appropriate amounts in the rotor chamber via the openings 7. Intensive research has proven that the sealing 12 which is provided according to the invention results in a considerably longer life of the screws 2, 3 compared with known screws.

A method for manufacturing the rotor according to the invention mainly consists in providing a sealing 12 on the metal shaft 8 which is provided with unevennesses in the form of grooves 11, in a place which corresponds to the place where the far end 13, 14 of the rotor 9 is provided.

Next, the shaft 8 is placed in a mould together with the sealing 12, and the composite material is cast round the shaft 8 and round the sealing 12, which composite material, after it has cured, forms the rotor 9 to be realised, such that the sealing 12 is embedded in the composite material of the rotor 9.

Figure 4 represents a variant in which the sealing 12 is made in the form of a ring-shaped collar which has been vulcanized on the shaft 8 and subsequently has been cast in the rotor 9 together with the latter, which collar has a Y-shaped cross section.

Figure 5 represents another variant in which the sealing 12 is formed of a layer of elastic plastic extending over a distance F between the composite material of the rotor 9 and the metal shaft 8.

The distance D may hereby vary as a function of the material which has been selected for the shaft 8, the rotor 9 and the sealing 12, and also as a function of the capacity of the screw-type compressor 1 in which the screw 2, 3 is applied.

Expressed in percentages in relation to the length of the rotor 9, the distance D preferably varies between 50 and less than 10%.

Also the thickness of the above-mentioned layer may vary and it is preferably restricted to a thickness which is smaller than the depth of the grooves 11 which are provided in the outer surface 10 of the shaft 8, such that this layer follows the relief of the outer surface 10 of the shaft 8 over its entire thickness, as is represented in more detail in figure 6.

In this variant, the sealing 12 is preferably made of an elastic plastic which preferably adheres to the metal of the shaft 8 in a chemical manner and which preferably also adheres in a chemical manner to the composite material of the rotor 9.

An advantage of the above-described variant is that, when the distance D is relatively large, the sealing 12 may serve so to say as a buffer for the differential expansion between the metal shaft 8 and the rotor 9 in a composite material, when the latter expand and/or shrink over different distances and at different speeds under the influence of temperature variations.

A method for realising a screw 2, 3 according to the above- described variant consists in applying the material of the sealing 12 in a liquid state round the shaft 8 and in placing the shaft 8 together with the sealing 12 in a mould and in subsequently, before the sealing 12 has cured, casting the composite material of the rotor 9 round the shaft 8 and the sealing 12.

When a natural or synthetic rubber is used for manufacturing the sealing 12, the latter can be vulcanised when it is cast round the shaft 8, after which, while this vulcanised rubber is cooling down or after it has cooled, the rotor 9 is cast round the shaft 8 and the sealing.

If the sealing 12 is made of a thermoplastic elastomer, the composite material is preferably cast round the shaft 8 before the material has cooled to its elastic condition.

Preferably, an elastic material is chosen for the sealing 12 whose shrinkage while cooling or curing is smaller than the shrinkage of the composite material of the rotor 9 while curing, such that, after the screw 2, 3 has been formed, the sealing 12 is put under strain.

Such a material selection offers as an additional advantage that, when the thickness of the layer forming the sealing 12 is smaller than the depth of the grooves 11, the composite material of the rotor 9 at the height of the grooves 11, while curing, pushes against the sealing 12 in different directions, which results in a good physical bond between the rotor 9 and the sealing 12.

According to another variant which is not represented in the figures, the sealing 12 can also be made of a polymer resin which is either or not identical to the polymer resin which is applied for manufacturing the rotor 9, whereby, in order to form the sealing 12, fillers and/or additives which are either or not different are used.

As is represented in figure 7, two or more sealings 12 can be provided as well between the shaft 8 and the rotor 9, in particular one in the vicinity of both far ends 13, 14 of the rotor 9, which may be particularly advantageous if the screw 2, 3 is applied in a screw-type compressor 1 which serves as a high pressure stage and which, as a consequence, is exposed to relatively high pressures both on its inlet side and on its outlet side.

It should be noted that, if one or several sealings 12 extend over a relatively large distance between the rotor 9 and the shaft 8, this sealing or these sealings 12 must be made of a dimensionally stable material which allows for a good bond, both with the shaft 8 and with the rotor 9, so as to avoid any play in the connection between the shaft 8 and the rotor 9.

The sealing 12 can also be obtained by means of a coating on the basis of for example a two-component paint system, whereby the above-mentioned coating extends over a part of or over the entire length of the shaft 8.

In the above-mentioned coating may be either or not mixed an amount of composite material, as a result of which the bond of this coating with the composite material may be improved.

Although in the above-described variants, both screws 2 and 3 of the screw-type compressor 1 are provided with the above-mentioned sealing or sealings 12, it is also possible to provide only one of the screws 2 or 3 with one or several sealings 12.

It is also possible to provide additional layers between the sealing 12 and the shaft 8 and/or between the sealing 12 and the composite material of the rotor 9, made of an adhesion material which makes it possible to bond the sealing 12 either or not in a chemical manner with the shaft 8 and/or the composite material of the rotor 9, whereby these adhesion materials also have to form a watertight layer then.

The present invention is by no means restricted to the above- described embodiments represented in the accompanying drawings; on the contrary, such a screw according to the invention for a water-injected screw-type compressor may be realised according to different variants while still remaining within the scope of the invention.

Claims

Claims .

1.- Improved screw of a water-injected screw-type compressor which mainly consists of a metal shaft around which has been cast a rotor made of a composite material, characterised in that at or near at least one far end (13-14) of the rotor (9) has been provided a sealing (12) between the rotor (9) and the shaft (8) .

2.- Improved screw according to claim 1, characterised in that the rotor (9) is at least partly in direct contact with the shaft (8) .

3,- Improved screw according to claim 1, characterised in that the sealing (12) is formed of an 0-ring which is provided round the shaft (8) and which is embedded in the composite material of the rotor (9) .

4.- Improved screw according to claim 1, characterised in that the sealing (12) is formed of a layer of an elastic synthetic material which is provided round the shaft (8) and which is embedded in the composite material of the rotor (9) .

5. Improved screw according to claim 1, characterised in that the sealing (12) is formed of a ring-shaped collar with a Y-shaped cross section.

6.- Improved screw according to claim 1, characterised in that the sealing (12) is formed of a layer of a polymer resin which is provided round the shaft (8) and which is embedded in the composite material of the rotor (9) .

7.- Improved screw according to claim 6, characterised in that in the polymer resin of the above-mentioned sealing (12) are provided fillers and/or additives.

8,- Improved screw according to any one of claims 3 to 7, characterised in that the rotor (9) is cast round the shaft (8) and in that the sealing (12) is embedded in the rotor (9) as the composite material of the rotor (9) is cast round the shaft (8) and round the sealing (12) .

9.- Improved screw according to claim 4 or 1, characterised in that the above-mentioned layer of the sealing (12) is formed of a material which bonds with the shaft (8) as well as with the rotor (9) .

10.- Improved screw according to claim 9, characterised in that the sealing (12) is formed of a material which bonds as a result of a chemical reaction with the material of the shaft (8) and/or the material of the rotor (9) .

11.- Improved screw according to claim 1, characterised in that the sealing (12) is formed of an elastomer.

12.- Improved screw according to claim 11, characterised in that the sealing (12) is formed of vulcanized rubber.

13.- Improved screw according to claims 1 or 2, characterised in that the sealing (12) extends over at least a part of the rotor (9) .

14.- Improved screw according to claim 13, characterised in that the sealing (12) extends over at least 10% of the length of the rotor (9) .

15.- Improved screw according to claim 13, characterised in that the sealing (12) extends over at least 30% of the length of the rotor (9) .

16.- Improved screw according to claim 13, characterised in that the sealing (12) extends as of one of the far ends (13- 14) of the rotor (9) .

17.- Improved screw according to claim 1, characterised in that the sealing (12) consists of a coating which is provided round the shaft (8) .

18.- Improved screw according to claim 17, characterised in that the above-mentioned coating extends over the entire length of the shaft (8) .

19.- Improved screw according to claim 1, characterised in that the shaft (8) is provided with grooves (11) at the connection between the rotor (9) and the shaft (8) .

20,- Improved screw according to claim 19, characterised in that the grooves (11) enclose an angle with the longitudinal direction X-X' of the shaft (8) .

21.- Method for forming a screw according to any one of the preceding claims, consisting of a metal shaft and a rotor, characterised in that it consists in providing at least one sealing (12) round the shaft (8), in putting the shaft (8) in a mould together with the sealing (12) and in casting a composite material in the mould so as to form the rotor (9) as the composite material cures.

22.- Method according to claim 21, characterised in that the composite material is cast round the shaft (8) and the sealings (12) while the sealing (12) has not cured completely.

23.- Method according to claim 21, characterised in that the materials for the sealing (12) and the rotor (9) are selected such that the shrinkage of the composite material of the rotor

(9) is larger while curing than the shrinkage of the material out of which the sealing (12) is made.