EP0995879B1 - Twin feed screw rotors - Google Patents

Description

The invention relates to twin screw rotors for installation in positive displacement machines for compressible media, especially pumps, which Rotors catchy executed with varying pitch and intended are, in paraxial, opposite external engagement with wrap angles of at least 720 ° and in an enclosure an axial chamber sequence to form without blast hole connections, wherein the end profile of a Kernkreisbogen, a cycloid-shaped hollow flank, an outer circle arc and another flank (see WO 97/21926).

The patent DE 87685 shows a Schraubenräderkapselwerk designated machine in which the screw rotors with variable pitch are formed. The machine is both a motor and a pump usable. To - when operating as an engine - the increase in the volume of Arbeitskammem in addition to boosting the relaxing medium the rotors are optionally conical.

In the patent DE 609405 is an air chiller with compressor and expander described, the two screw pairs with variable Have slope and flight depth. The envelope surfaces of the rotors are conical educated.

Both of the aforementioned machines have the disadvantage that they conical cylinders require, whereby the rotors on one side only and can be expanded. This increases the effort in the assembly and Dismantling of the machines, especially during maintenance and cleaning work is very disadvantageous.

The patent application EP 0697523 relates to a screw displacement machine, in which the intermeshing rotors unequal, as "male" and "female" designated screw profiles, so-called S.R.M. profiles with continuous slope change. The forehead profile is varied so that the tooth head angle or the length of the outer circle arc a monotonically growing function in dependence from the wrap angle. Such profiles have the disadvantage that a good foreclosure of the axial sequence of working cells because of the remaining Blasloches is not possible. The vacuum losses caused by the blow hole have efficiency losses result, so with such a Machine at least at low and medium speeds no good inner Compaction is possible.

The published patent application DE 19530662 discloses a screw suction pump with externally meshing screw elements, at the slope the screw members continuously from their inlet end to their outlet end decreases to cause the compression of the gas to be dispensed. The shape of the teeth of the screw rotor exhibits an epitrochoidal and / or Archimedean curve. This machine has the disadvantage that the achievable internal compression rate in the geometric relationships shown moderate. In addition, the missing forehead profile variation fixes that anyway not good compression ratio and leads because of the reduction in depth the gap between the screw outer diameter and the housing for Screw end towards an increased leak rate.

The laid-open specification DE 4445958 describes a screw compressor with counter-rotating, external-meshing screw elements. The thread helices of the screw elements are from an axial End to the second axial end away from it continuously smaller. As Profile is proposed a rectangular or trapezoidal profile. A disadvantage of such Profile geometries is that they only work lossless enough, when the flight depth in relation to the diameter is small, as stated in the above Publication is executed. Such a machine thus has a big one Construction volume and a big weight. It is another disadvantage of such Profile geometries that require extremely high pitch changes are when a satisfactory internal compression rate is to be achieved. How in the mentioned DE 19530662 also fixed here the missing Stirnprofilvariation this shortcoming and this leads to an increased leakage rate due to reduction the depth of the gap between screw outside diameter and housing towards the end of the screw.

Other publications, such as SE 85331, DE 2434782 and DE 2434784 relate to internal-axis screw machines with non-constant Slope of the screws or varying forehead profiles. These machines all have the disadvantage that the construction cost is high and that in In any case, also on the intake side dynamic seals are needed.

There are also some publications, for example DE 2934065, DE 2944714, DE 3332707 and AU 261792, which two-shaft compressor with describe screw-like rotors. There are the rotors and in some Cases also the housing of axially successively arranged profile discs composed of different thickness and / or contour and cause such internal compression. All machines with screw-type rotors have the disadvantage that their efficiency over that of machines is reduced with helical rotors, because by the stepped Construction of dead spaces and vortex zones arise. Furthermore, in screw-like Rotors to expect problems in terms of shape consistency, as they to warm up during operation.

Based on this prior art, the invention is the Task to propose twin screw rotors, which the above have not mentioned disadvantages.

These objects are achieved according to the invention in that the slope is not monotonous and as a dependent variable of the wrap angle is defined that the slope in a first portion of the suction end of the screw increases and after about one wrap reaches a maximum value that the slope in one to the first subarea subsequent second portion decreases and about one wrap reaches a minimum value before the pressure end of the screw and that the Gradient in a subsequent to the second portion third portion is substantially constant.

Particular embodiments of the invention are in the dependent Claims circumscribed.

Figur 1

ein Paar miteinander in Eingriff stehende Schraubenrotoren,

Figur 2

den rechtsgängigen Rotor,

Figur 3

den linksgängigen Rotor,

Figur 4

einen Stirnschnitt eines Schraubenrotors mit variierendem Profil,

Figur 5

die Abwicklung der Referenzspirale eines erfindungsgemässen Rotors,

Figur 6

den Steigungsverlauf der Abwicklung gemäss Figur 4,

Figur 7

den Verlauf des Arbeitskammerquerschnitts bei einer Maschine ohne und mit Profilvariation,

Figur 8a bis 8c

Gehäuse-, Rotor-, und Arbeitskammerquerschnitt eines mit erfindungsgemässen Rotoren ausgestatteten Verdichters und

Figur 9a bis 9p

Stirnschnitte durch ein Rotorenpaar, welche die Entwicklung des Arbeitskammerquerschnitts gemäss Figur 7 veranschaulichen.

The invention will be described in more detail below with reference to embodiments shown in the drawings. It shows

FIG. 1

a pair of intermeshing screw rotors,

FIG. 2

the right-hand rotor,

FIG. 3

the left-handed rotor,

FIG. 4

a front section of a screw rotor with varying profile,

FIG. 5

the development of the reference spiral of a rotor according to the invention,

FIG. 6

the gradient course of the development according to FIG. 4,

FIG. 7

the course of the working chamber cross-section in a machine without and with profile variation,

FIGS. 8a to 8c

Housing, rotor, and working chamber cross-section of a compressor equipped with rotors according to the invention and

FIGS. 9a to 9p

End sections through a pair of rotors, which illustrate the development of the working chamber cross-section according to Figure 7.

FIG. 1 shows an exemplary embodiment of a pair of screw rotors 1 and 2 which stand together in an axially parallel external engagement. FIGS. 2 and 3 show each of the rotors 1 and 2 according to FIG. 1 separately. It can be clearly seen in these figures that the outer shell and the core are cylindrical and thus the flight depth is constant over the screw length. In FIG. 3, the mass Δw ₁ and Δw _{3 show} that the pitch of the screw varies along the axis, but that the height h of the helical outer cylindrical rotor surface remains constant, whereby leakage losses between rotor and housing inner wall against the pressure side, as at Some of the above-mentioned machines according to the prior art occur in an undesirable manner, be avoided. The reference numeral 7 designates the reference spiral in this figure, which will be discussed in more detail later, and 8 is the second limiting spiral of the outer cylindrical rotor surface.

FIG. 4 shows a rotor in a section at right angles to the rotor axis. The resulting end profile has a Kemkreisbogen 3 with a constant over the entire screw length radius Rb, which - in a clockwise direction - after a sector angle γ in a cycloid-shaped hollow flank 4 passes. The geometry of the hollow flank 4 is unchanged over the entire screw length. At the hollow flank 4 closes at point B at an acute angle an outer circle arc 5 with a constant over the entire screw length radius Ra, which passes to a sector angle γ at point C in a further edge 6. The variation of the front profile contour along the screw axis is based on a change in the sector angle γ and on a change in the geometry of the further flank 6. The variation of the sector angle γ along the screw axis is preferably at least spatially approximately equidistant course of a reference spiral formed by the outermost points of the hollow flank B _α (7 in FIG. 3) and the second limiting spiral (points C) (8 in FIG. 3) of the outer cylindrical rotor surface.

der Abwicklung w betrachtet. Dieser Wert w' ist die dynamische Steigung der oben erwähnten Referenzspirale. Man sieht in dieser Figur, dass die Steigung bei α=0 mit dem Wert L₀ / 2π beginnt, wobei L₀ eine der mittleren Steigungshöhe entsprechende Konstante ist. In einem ersten Teilbereich T₁ nimmt w' zu und erreicht bei α=2π den Maximalwert (1+A)·L₀ / 2π, wobei A der Amplitudenmoderator ist. Im zweiten Teilbereich T₂, der sich von 2π bis 6π erstreckt, nimmt die Steigung ab und erreicht bei α=6π den Minimalwert (1+A)·L₀ / 2π, den sie im dritten Teilbereich T₃ bis zum Ende der Schraube beibehält.FIG. 5 shows in a diagram the development w of the reference spiral mentioned in connection with FIG. 4 as a function of the wrap angle α. For comparison, a straight line g and corresponding sections P ₀ , 2P _0, etc. of the development of a spiral with a constant pitch are shown. The course of the slope is more clearly recognizable when the first derivative shown in Figure 6

the settlement w considered. This value w 'is the dynamic slope of the above-mentioned reference spiral. It can be seen in this figure that the slope at α = 0 starts with the value L ₀ / 2π, where L _{0 is} a constant corresponding to the mean slope height. In a first subregion T ₁ , w 'increases and, at α = 2π, reaches the maximum value (1 + A) * L ₀ / 2π, where A is the amplitude moderator. In the second subregion T ₂ , which extends from 2π to 6π, the slope decreases and reaches at α = 6π the minimum value (1 + A) · L ₀ / 2π, which it retains in the third subregion T ₃ to the end of the screw ,

FIG. 7 shows the chamber cross-section F as a function of the wrap angle α, wherein the curve F _o shown by a solid line shows the chamber cross-section without profile variation and the dashed curve F _{m shows} the chamber cross-section with profile variation.

In Figure 8a the cross section is shown of the invention for receiving twin screw rotors certain housing, Figure 8b shows one of the representation of Figure 4 corresponding section through the rotors and in figure 8c the chamber cross-section F _o is shown hatched.

In FIGS. 9a to 9p, the development of the working chamber cross section is shown in end sections represented as a function of the wrap angle. The latter is indicated in the figures in degrees.

Claims (3)

1. Twin screw rotors for installation in displacement machines for compressible media, which rotors are designed single-threaded with varying pitch and are intended to be in axis-parallel, opposed, outside engagement with angles of contact of at least 720°, and to form in a housing an axial sequence of chambers without blow-hole connections, the end profile comprising a core arc of a circle (3), a cycloidal hollow flank (4), an outer arc of a circle (5) and a further flank (6), characterised in that the pitch does not run monotone and is defined as a variable dependent upon the angle of contact, in that the pitch in a first section (T₁) increases from the suction-side screw end, and reaches a maximal value after approximately one turn, in that the pitch in a second section (T₂), adjacent to the first section, decreases and reaches a minimal value at approximately one turn before the delivery side screw end, and in that the pitch in a third section (T₃), adjacent to the second section, is substantially constant.
2. Twin screw rotors according to claim 1, characterised in that the end profile contours along the screw axis vary in that the sector angle (γ) of the core arc of a circle (3) and outer arc of a circle (5) change and in that the geometry of the further flank (6) changes, the core circle radius (Rb), the outer circle radius (Ra) and the geometry of the hollow flank being constant, and the outermost points of the hollow flank forming the reference spiral (7) for definition of the pitch course.
3. Twin screw rotors according to claim 2, characterised in that the variation of the sector angle (γ) of the core arc of a circle (3) and outer arc of a circle (5) along the screw axis is determined by a spatially at least almost equidistant course of the reference spiral (7) and of the second demarcation spiral (8) of the outer, cylindrical rotor surface.

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