EP1305524B1 - Compressor - Google Patents

Abstract

The compressor has two rotors ( 14, 16 ), which are rotatably mounted in a housing ( 10 ) by means of a shaft each, the rotors ( 14, 16 ) rotating without contact with the housing. The rotors ( 14, 16 ) consist of a powder-metallurgical Al-Si alloy, and the housing ( 10 ) consists essentially of aluminum.

Description

The invention relates to a compressor according to the preamble of claim 1.

Compressors generally require cooling in order to dissipate the heat generated during the compression process. On a direct cooling of the rotors and shafts is omitted mostly for cost reasons. The cooling of the rotors is then only indirectly via the flow of fluid and the directly cooled housing.

Because of the direct cooling of the housing, for example by an air flow or a water jacket, and the only indirect cooling of the rotors occurs in operation, a high temperature difference between the housing and rotors. This temperature difference must be taken into account when designing the column. The larger temperature expansion of the rotors is accommodated by enlarged gaps in the cold state. The difference of the gap size in the cold state to the gap size in the operating state, i. at a temperature difference of the order of 100 ° K, is referred to as gap reduction. In order to prevent the rotors from starting up under all circumstances, the gap widths are set for the maximum thermal load resulting from the different pressure ratios and speeds. The consideration of the gap reduction then leads to a dimensioning of the gap widths in the cold state. However, efforts are made to keep the gap as small as possible in order to minimize backflow and maximize volumetric and isentropic efficiency.

These considerations lead in practice to the use of materials with low thermal expansion. The standard material used for housing is cast iron with lamellar graphite and for the rotors cast iron with nodular graphite. The thermal expansion coefficient is in each case α _k = 10.5 ^-6 / K. Using of cast iron for housing and rotors and an outer diameter of the rotors, for example, 100 mm results in the gap reduction, a value of about 0.1 mm. Thus, satisfactory efficiencies can be achieved. On the other hand, the use of a material such as aluminum is out of the question since, because of the thermal expansion more than twice as high, the corresponding gap reduction values would be about 0.24 mm, so that the gap widths would have to be more than twice as high when cold, whereby the gap losses would be increased enormously.

From JP-A-05010282 a compressor is known whose housing is formed of an aluminum alloy and whose rotors are made of resin. In order to avoid a gap reduction in the operation of the compressor as possible, the composition of the resin material is chosen so that it has substantially the same thermal expansion coefficient as the aluminum alloy.

From US-A-4,702,885 a method for producing an aluminum-silicon alloy having improved material properties in terms of heat resistance and wear resistance is known.

The invention provides a compressor which despite the use of aluminum materials has small gap widths and a correspondingly high efficiency. According to the invention, the rotor consists of a powder metallurgically produced, silicon-containing aluminum material and the housing consists essentially of aluminum. Aluminum for the housing is understood to mean essentially pure aluminum or an aluminum alloy with the typical relatively high coefficient of thermal expansion of approximately 23.8 × 10 ^-6 / K. The powder metallurgically produced, silicon-containing aluminum material, however, has a thermal expansion coefficient of only about 16 x 10 ^-6 / K. If, in turn, one starts from a rotor diameter of 100 mm, the result of the material combination according to the invention is a gap reduction at a temperature difference of 100 ° K, which is calculated as follows: $${\mathrm{S}}_{\mathrm{W}\mathrm{A}}=\left({\mathrm{\alpha }}_{\mathrm{k}1}\times \mathrm{\Delta }{\mathrm{T}}_1-{\mathrm{\alpha }}_{\mathrm{k}2}\times \mathrm{\Delta }{\mathrm{T}}_2\right)\times \mathrm{L},$$

With a value of 0.113 mm, the gap reduction is barely larger than the corresponding value when using cast iron for housings and rotors.

The use of aluminum instead of cast iron provides significant advantages, in particular a lower weight, shorter processing times, corrosion resistance, lower production costs.

In the preferred embodiment, an insulating layer is applied to the surfaces of the rotors. Through this insulating layer is the

Heat transfer from the compressed fluid to the rotors reduced. The heat flow is increasingly dissipated via the shaft of the rotor. The reduced heating of the rotors by the insulating layer leads to a lower thermal expansion and therefore allows smaller gap widths, whereby the efficiency is increased.

• Figur 1 schematisch einen geöffneten Klauenverdichter mit Blick auf die Rotoren;
• Figur 2 eine entsprechende Ansicht einer Ausführungsvariante; und
• Figur 3 eine weitere Ausführungsvariante.

Further features and advantages of the invention will become apparent from the following description of two embodiments of the compressor and from the accompanying drawings. In the drawings show:

• Figure 1 shows schematically an open claw compressor with a view of the rotors;
• Figure 2 is a corresponding view of a variant embodiment; and
• Figure 3 shows a further embodiment.

The compressor shown by way of example in Fig. 1 has a housing, generally designated 10, with an inner chamber 12 consisting of two intersecting sub-cylinders of the same size. In the chamber 12, two rotors 14, 16 are accommodated in the form of double-wing Roots. Each rotor 14, 16 is seated on a respective shaft 18, 20. The parallel shafts 18, 20 are synchronized by a (not shown) gear. The rotors 14, 16 run in the interior of the chamber 12 without mutual contact and without contact with the wall of the chamber 12. They roll into each other and thereby form work spaces of variable size, with an internal compression takes place.

The heat generated during operation of the compressor is dissipated essentially by cooling the housing 10. For this purpose, the housing 10 has a plurality of cooling fins, which are flowed around by an air flow. The heated exhaust air is symbolized by arrows in the drawing. The rotors 14, 16 and the shafts 18, 20 are not directly cooled. Part of the heat flow is via the shafts 18, 20 and another part via the fluid flow dissipated. In order to reduce the heating of the rotors 14, 16 during operation, their surface is provided with a thermally insulating coating.

The housing 10 is made of aluminum or an aluminum alloy whose thermal expansion coefficient is about 23.8 × 10 ^-6 / K. The rotors 14, 16 are made of an aluminum material whose thermal expansion coefficient is about 16 x 10 ^-6 / K. This material combination results in a gap reduction, which - based on a rotor diameter of 100 mm - is about 0.113 mm.

• 18,5 bis 21,5 Gew.% Silizium,
• 4,6 bis 5,4 Gew% Eisen,
• 1,8 bis 2,2 Gew.% Nickel
• Rest: Aluminium

The aluminum material of which the rotors 14, 16 are made is produced by powder metallurgy and dispersion-strengthened. The composition of the aluminum material for the rotors is preferably as follows:

• 18.5 to 21.5% by weight of silicon,
• 4.6 to 5.4% by weight of iron,
• 1.8 to 2.2 wt.% Nickel
• Rest: aluminum

The principle underlying the invention is applicable to most types of noncontact rotors compressors, but is particularly applicable to internally compacted two-shaft compressors, e.g. Claw compactor and screw compressor. The invention generally extends to the use of a powder metallurgical Al-Si alloy in rotors of compressors, pumps and rotary engines in combination with an aluminum housing, particularly in machines with non-contacting rotors.

In the embodiment shown in Fig. 2, the housing is composed of an outer body 10a made of aluminum or an aluminum alloy and a ring 10b cast therein. The ring 10b is made of a powder metallurgy, dispersion strengthened Al-Si alloy of the type described in more detail above. The ring forms the boundary of the chamber in which the rotors of the compressor are accommodated. At the interface between Outer body 10a and ring 10b, the two materials are fused together so that an intimate bond between outer body 10a and ring 10b is made. Since the ring 10b is made of a material of substantially greater strength than the material of the outer body 10a, its thermal expansion properties substantially determine the thermal expansion of the housing as a whole. The rotors in this embodiment also consist of an Al-Si alloy of the type described above. The ring is provided with cast-on stiffening ribs 10c directed radially outward. In each corner region of the housing one of these stiffening ribs is arranged.

In this embodiment, a gap reduction of about 0.16 mm can be achieved, again based on a rotor diameter of 100 mm.

In the embodiment shown in Fig. 3, the housing has a bearing cap 22, with two bearings 24, 26 for the shafts 18, 20. On both sides of the bearings 24, 26 in the bearing cap 22, a stiffening rib 28, 30 cast from a dispersion-hardened aluminum alloy. By these stiffening ribs 28, 30 on the one hand, the support of the shafts 18, 20 stiffened, on the other hand, the thermal expansion of the axial distance is reduced.

Claims (14)

1. Compressor comprising a housing and at least one rotor rotatably mounted in the housing by means of a shaft, which rotates without touching the housing, wherein the housing essentially consists of aluminum, and wherein the cooling of the at least one rotor happens indirectly by means of a delivery media flow and via the directly cooled housing, characterized in that the rotor consists of a powder metallurgic Al-Si-alloy comprising a heat strain coefficient of about 16 x 10^{- 6}/K and that the aluminum, of which the housing is made, has a heat strain coefficient of about 23.8 x 10^-6/K.
2. Compressor according to claim 1, characterized in that the Al-Si-alloy is dispersion-hardened.
3. Compressor according to claim 1 or 2, characterized in that the Al-Si-alloy has the following composition:

   18.5 to 21.5 percent in weight silicon,

   4.6 to 5.4 percent in weight iron,

   1.8 to 2.2 percent in weight nickel,

   rest: aluminum.
4. Compressor according to one of claims 1 to 3, characterized in that the housing is cooled by an air flow.
5. Compressor according to one of claims 1 to 4, characterized in that it comprises two rotary pistons, rolling off in each other contact-free.
6. Compressor according to claim 5, characterized in that it works with an inner compression.
7. Compressor according to claim 6, characterized in that the rotary pistons are two-bladed or three-bladed.
8. Compressor according to one of claims 1 to 4, characterized in that it is a screw-type compressor.
9. Compressor according to one of claims 1 to 8, characterized in that an isolating layer is applied to the surface of the rotors.
10. Compressor according to one of the precedent claims, characterized in that the housing has an external body made of aluminum and a ring consisting of a dispersion-hardened powder metallurgic Al-Si-alloy molded therein.
11. Compressor according to claim 10, characterized in that at the interface of the ring and the external body their materials are fused together.
12. Compressor according to claim 10 or 11, characterized in that the ring directly surrounds the rotor.
13. Compressor according to one of the preceding claims, characterized in that the housing has at least one bearing cover provided with cast-in reinforcing ribs made of a dispersion-hardened powder metallurgic Al-Si-alloy.
14. Compressor according to claim 13, characterized in that the reinforcing ribs are arranged on opposing sides of the bearings.

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