EP0925452B9 - Screw rotor set - Google Patents

Abstract

PCT No. PCT/CH97/00279 Sec. 371 Date Feb. 11, 1999 Sec. 102(e) Date Feb. 11, 1999 PCT Filed Jul. 21, 1997 PCT Pub. No. WO98/11351 PCT Pub. Date Mar. 19, 1998Known designs of single-thread screw rotors in single-piece cast iron constructions having wrap angles of >720 degrees with balancing cavities on the face of the screw operate with no unbalance at average rotary frequencies of ( DIFFERENCE 3000 min-1). The use of a pump in processes having sensitive purity and maintenance requirements or working with corrosive substances or where limited space is available and quality is demanded, brings about problems for rotor designing and balancing, which the present invention solves. An uneven mass distribution is accomplished by constructing the rotors with several single parts inside the rotor, by forming cavities and/or by choosing the adequate material, which, combined with the screw length/pitch ratio, cause a static and dynamic balancing. Screw rotors designed as described offer several advantages since they are easy to assemble and have a compact and stable construction. Moreover, they can be used in pumps for the food industry, chemistry, medicine and semi-conductor construction due to the flexibility in material and to the smooth surfaces free from cavities.

Description

The invention relates to measures for balancing a screw rotor set in axially parallel arrangement with opposing external axis engagement as well as with Wrap angles of at least 720 ° in a catchy version.

Center of gravity center distance, end face and wrap angle determine the sizes of the static and dynamic unbalance, which with screws catchy profiles occur;

In the publication Sho 62 (1987) -291486 from Taiko, Japan, one Screw balancing method described: First, static Balancing achieved by fixing the screw length to whole numbers Multiples of the slope. Through cutouts in the screw on both sides, which are hollow or filled with light material is dynamically balanced.

This method of balancing is not feasible when using special materials that cannot be cast. Even with extraordinary Profile geometries, this method has its limits, because on the one hand the wall thicknesses of the Screws cannot be reduced arbitrarily for reasons of stability, on the other hand, an excessive axial expansion of the balancing cavities because of the spiral shape brings significant manufacturing problems; filling the Recesses with light material exacerbate this problem.

Another method of screw balancing is described in Swiss patent application 3487/95 by Busch SA, Switzerland (WO-A-97/21925): the screw length (= 2W ₂ ) is a multiple of the pitch I greater than the 1½ - times the slope (2W ₂ = 5I / 2, 7I / 2, 9I / 2 ...).

To compensate for the remaining static and dynamic imbalance Changes on the outside on passive passive screw parts and / or a or several end balancing cavities and / or external additional masses.

On the one hand, this method offers the possibility of using Special materials or on the other hand leads to reduced balancing cavities, with what an increase in dimensional stability is achieved.

The use of screw rotors for pumping certain media as well as a Desired temperature reduction at the end of the screw required small, smooth, cavern-free screw surfaces that are dirt-repellent and good are to be cleaned. The demands for reduced effort in service, assembly, Spare parts and after small, compact pumps leave the use of external Additional masses become an obstacle.

The invention has for its object to define measures for Balancing of catchy screws with a cavern-free, smooth surface without the Use of external additional masses.

This task is performed with a screw rotor set for screw pumps in axially parallel arrangement with opposing external axis engagement as well as with Wrap angles of at least 720 ° in a catchy version and with smooth, plane-parallel rotor end faces, solved by the fact that each screw rotor from several rigidly connected individual parts with a common one Rotation axis, optionally eccentric centers of gravity and optionally different material densities is formed; that the individual parts inside the rotor an eccentric cavity closed off from the pump chamber, the Form balancing room; that the coordination of the material densities and the Geometry of the individual parts inside the rotor causes the static balancing and affects the dynamic imbalance and that the dynamic balancing at less impact on the static unbalance is achieved by means of arithmetic Determination of the ratio screw length / pitch = a to values, each are slightly smaller than odd multiples of 1/2.

Design options within a given screw geometry lie in the choice of number, shape and material of the individual rotor parts as well as in the Design of the balancing room 3, as characterized in the subclaims.

1. Glatte, kavernenfreie, Prozess- und Service-freundliche Oberfläche:

2. Temperaturreduzierung am Schraubenende durch Oberflächenverkleinerung.

3. Optimierung in der Werkstoffauswahl der Einzelteile mit unterschiedlichen chemischen und mechanischen Beanspruchungen.

4. Einfache Montage, Ersatzteilbeschaffung und - haltung.

5. Kleiner, kompakter, formstabiler Aufbau.

6. Baukastenprinzip durch Kombinationen von Schraubenkörpern mit verschiedenen Rotorachsen.

7. Möglichkeit einer Rotor - Innenkühlung.

The following advantages achieved with the invention are offset by additional expenditure in production:

1. Smooth, cavern-free, process and service-friendly surface:

2. Temperature reduction at the screw end through surface reduction.

3. Optimization of the material selection of the individual parts with different chemical and mechanical stresses.

4. Easy assembly, spare parts procurement and maintenance.

5. Small, compact, dimensionally stable construction.

6. Modular principle by combinations of screw bodies with different rotor axes.

7. Possibility of internal rotor cooling.

Using an embodiment shown in the figures The invention is subsequently explained in more detail:

Fig.1:

Einen Schraubenrotorsatz mit Pilotgetriebe für eine Schraubenpumpe in eingängiger Ausführung nach der Erfindung aus Einzelteilen zusammengesetzt mit exzentrischer innerer Massenkonzentration und mit einem Verhältnis Schraubenlänge/Steigung = 2 W₂/I < 9/2 in einem axialen Schnitt.

Fig.2:

Die Darstellung der spiraligen Stirnprofilschwerpunkt-Ortskurve einer rechtssteigenden Schraube von Fig.1.

Fig.3:

Ein Ausführungsbeispiel eines Rotors des Schraubenrotorsatzes von Fig. 1 in zweiteiliger Ausführung in einer ersten Variante mit flügelförmig gegliedertem Auswuchtraum in einem axialen Schnitt.

Fig.4:

Den Rotor von Fig.3 im Stirnschnitt entsprechend der Linie A-A.

Fig.5:

Die Darstellung der spiraligen Stirnprofilschwerpunkt-Ortskurve sowie strichpunktiert die Ortskurvenäste I, II, III, IV, V der Stirnschnitt-Schwerpunkte des flügelförmig gegliederten Auswuchtraumes von Fig.3, 4.

Fig.6:

Die Stirnschnittgeometrie der ersten Rotorvariante mit Schwerpunkt sowie die maximal zulässige innere Aushöhlung.

Fig.7:

Unterschiedliche Stirnschnittkonturen eines Auswuchtraumes 103, variierend mit der Axialposition W.

Fig.8:

Ein Ausführungsbeispiel eines Rotors des Schraubenrotorsatzes von Fig. 1 in zweiteiliger Ausführung in einer zweiten Variante mit geradem Auswuchtraum in einem axialen Schnitt.

Fig.9:

Den Rotor von Fig.4 im Stirnschnitt entsprechend der Linie B-B.

Fig.10:

Die Darstellung der spiraligen Stirnprofilschwerpunkt-Ortskurve sowie strichpunktiert die Schwerachse des geraden Auswuchtraumes von Fig. 8, 9.

Fig. 11:

Ein Ausführungsbeispiel eines Rotors von Fig. 8 in einer Untervariante mit einseitiger Rotorachse.

Show it:

Fig.1:

A screw rotor set with pilot gear for a screw pump in a single-thread design according to the invention composed of individual parts with an eccentric internal mass concentration and with a screw length / pitch = 2 W ₂ / I <9/2 ratio in an axial section.

Figure 2:

The representation of the spiral front profile center of gravity locus of a right-hand screw of Fig.1.

Figure 3:

An embodiment of a rotor of the screw rotor set of FIG. 1 in a two-part design in a first variant with a wing-shaped balancing space in an axial section.

Figure 4:

The rotor of Figure 3 in the end section along the line AA.

Figure 5:

The representation of the spiral front profile center of gravity locus as well as dash-dotted lines of the locus branches I, II, III, IV, V of the front cut center of gravity of the wing-shaped balanced balancing area of Fig. 3, 4.

Figure 6:

The face cut geometry of the first rotor variant with the center of gravity as well as the maximum permissible internal cavity.

Figure 7:

Different end cut contours of a balancing room 103, varying with the axial position W.

Figure 8:

An embodiment of a rotor of the screw rotor set of FIG. 1 in a two-part design in a second variant with a straight balancing space in an axial section.

Figure 9:

The rotor of Figure 4 in the end section along the line BB.

Figure 10:

The representation of the spiral front profile center of gravity locus and dash-dotted line the center of gravity of the straight balancing area of Fig. 8, 9th

Fig. 11:

An embodiment of a rotor of FIG. 8 in a sub-variant with a rotor axis on one side.

In one embodiment, the screw rotors 101; 201 (Fig. 3, 4; 8, 9) each consisting of two parts, a cylindrical screw body and one coaxial rotor axis formed. The screw body 104; 204 (Fig.3; 8) is with a screw thread of approx. 9/2 loops as well as with a coaxial Provide central bore. Within the screw body 104; 204 is the Central bore 106; 206 (Fig. 3; 8) expanded to an eccentric cavity, Balancing room 103; 203 (Fig. 3; 8). In the central bore 106; 206 of Screw body 104; 204 is the rotor axis 105; 205 (Fig.3; 8) by press fits fixes and closes the balancing room 103; 203 to the outside. On interlocking area ensures the torque transmission between Rotor axis 105; 205 and screw body 104; 204. From manufacturing and Strength reasons are screw body 104; 204 and rotor axis 105; 205 out different metallic materials.

A in the rotor axis 105; 205 provided channel 107; 207 (Fig.3; 8) is used Ventilation or cooling of the balancing chamber 103; 203 from one against that Pump medium sealed point out; present embodiment shows a Central bore on the suction side with cross bore in the area of the Balancing room for ventilation.

Mathematical treatment:

In a right-angled coordinate system u, v, w, the following relationships generally apply to an arbitrarily shaped body of homogeneous density when rotated around the w axis and having an extent p ≤ w ≤ q

p, q =

Integrationsgrenzen   [ cm ]

P_u, P_v =

Kraftkomponenten   [ g ]

M_u,w, M_v,w =

Momentkomponenten   [ gcm ]

ω =

2π/T = Drehzahl   [Rad/sec]

π =

Kreiszahl = 3,1415....

T =

Umlaufzeit   [ sec ]

τ =

γ/b   [ g sec² / cm⁴]

γ =

Spez. Gewicht   [g/cm³]

b =

Erdbeschleunigung = 981   [cm/sec²]

g <w> =

f <w>. r<w>   [ cm³ ]

f <w> =

Stirnschnittfläche als Funktion von w   [ cm² ]

r <w> =

Schwerpunktmittenabstand als Funktion von w   [ cm ]

 <w> =

Schwerpunktpositionswinkel als Funktion von w   [ Rad ]

It means:

p, q =

Integration limits [cm]

P _u , P _v =

Force components [g]

M _{u, w} , M _{v, w} =

Moment components [gcm]

ω =

2π / T = speed [wheel / sec]

π =

Circle number = 3.1415 ....

T =

Orbital period [sec]

τ =

γ / b [g sec ² / cm ⁴ ]

γ =

Specific weight [g / cm ³ ]

b =

Acceleration due to gravity = 981 [cm / sec ² ]

g <w> =

f <w>. r <w> [cm ³ ]

f <w> =

Face cut area as a function of w [cm ² ]

r <w> =

Center of gravity center distance as a function of w [cm]

 <w> =

Center of gravity position as a function of w [Rad]

For a screw body in the u, v, w system (Fig. 2) with a middle face cut in the uv plane and center of gravity So the middle face cut on the u axis as well as with constant pitch l, constant face surface fo and constant center of gravity center distance r ₀ follows in particular g <w> = g 0 = f 0 · r 0 = const. f <w> = α = (2π / l) · W

Because of the symmetrical expansion of - W ₂ ... + W ₂ corresponding to position angles of -α ₂ .... + α ₂ it also follows: p = -W 2 q = + W 2 W 2 = α 2 · (I / 2π)

For the unbalanced screw (= full screw), the following immediately follows from the symmetry: P V =  M u, w = 

The remaining components are determined as follows:

From (1), (5), (6), (6a), (7), (8) =>

From (3), (5), (6), (6a), (7), (8) =>

τ₀ =

γ₀/b   [g sec²/cm⁴]

γ₀ =

Spez. Gewicht des Schraubenkörpers   [g/cm³]

I =

Steigung   [cm ]

r₀ =

Schwerpunktmittenabstand der Vollschraubenstirnfläche   [cm]

f₀ =

Stirnfläche der Vollschraube   [cm²]

α₂ =

1/2 Schraubenumschlingungswinkel   [Rad ]

I und g₀ sind durch die Schraubengeometrie fixiert; ω ist eine rein betriebsabhängige Größe mit ω > ; τ₀ ist werkstoffabhängig und somit bedingt variabel mit τ₀ > ; Hauptvariable ist der Umschlingungswinkel = 2 α₂.It means:

τ ₀ =

γ ₀ / b [g sec ² / cm ⁴ ]

γ ₀ =

Specific weight of the screw body [g / cm ³ ]

I =

Slope [cm]

r ₀ =

Center of gravity of the solid screw face [cm]

f ₀ =

Face of solid screw [cm ² ]

α ₂ =

1/2 screw wrap angle [wheel]

I and g ₀ are fixed by the screw geometry; ω is a purely operational variable with ω>; τ ₀ depends on the material and is therefore conditionally variable with τ ₀ >; The main variable is the wrap angle = 2 α ₂ .

By varying α ₂ alone, however, P _u =  and M _{v, w} =  cannot be achieved simultaneously (static and dynamic balancing). In the present patent application, eccentric mass concentration is formed inside the screw without external additional masses and without frontal balancing caverns.

In the embodiment described here, the rotor axis has no influence on the unbalance; the balancing chamber is formed inside the solid screw and it alone provides compensation for static and dynamic imbalance; thus the problem here is reduced to pure design without the influence of the material data, ie the static and dynamic values of the solid screw and the balancing chamber have to be matched in such a way that the following 4 equations are fulfilled:

The index " ₃ " indicates the affiliation to the balancing room.

In a first variant (FIGS. 3, 4) of the exemplary embodiment, the required Pitch depth t (Fig. 3) is relatively large, corresponding to a relatively small core diameter c (Fig.3). The effective balancing space 103 here consists of three axially aligned equidistantly arranged, congruent, spiral wings 108 (Fig.4), which the Follow the course of the screw thread parallel to the distance. 5 shows dash-dotted lines 5 potential wing positions I-V; in the variant described here, only the middle positions II, III, IV, equipped (rough coordination).

In a balancing space 103 formed in this way, the static value becomes strong, the dynamic value changes little, by varying the wing size and shape. In the case of the unbalanced screw, changing the screw length (= 2 W ₂ ) in the vicinity of odd multiples of half the pitch leads to strong dynamic and weak static changes.

The area f ₀ and the center of gravity position r ₀ , ϕ _s can first be determined from the given screw face contour (FIG. 6) using known methods. You get

From this => g ₀ = f ₀ · r ₀ = 261.636 [cm ³ ].

With (also given) pitch I = 6.936 [cm], for the solid screw with variation of α ₂ from (1b) and (3b), numerical values are obtained, which are shown in Table 1.

The shape of the balancing space can be determined from the conditions (2b), (4b), (1b), (3b) are not necessarily derived; rather, it is necessary to have a geometry First of all, to determine the 4 key data, then the geometry to correct, redefine the 4 key data etc., until (2b), (4b), (1b), (3b) are met with sufficient accuracy.

The limit for the expansion of the balancing room is due to a stability-related Given minimum wall thickness. Because of the varying spatial curvature of the Screw surface is a determination of the boundary line in the face cut only Computationally possible: face cut contour and slope I deliver the for each point Screw surface a normal vector, the amount of the minimum wall thickness is equated. The end point of the vector is then in a fixed plane (w = constant) screwed and delivers a point of the boundary line. With one specifically IT program developed for this, the sub-programs of which are profile-specific Contained formulas, the curve data were shown in dash-dot lines in FIG Boundary line calculated for a wall thickness of 0.7 [cm].

Because of the complex tortuous form, functions g ₃ <w> and  ₃ <w> that can be realized can only be represented mathematically in an extremely complex manner with additional problems in the subsequent integration ((1b) ... (4b)); an approximation method with the summation of finitely many small partial amounts via an EDP program leads to the goal more quickly:

For this purpose, the balancing space is arranged axially one after the other in staggered fashion Split slices of the same thickness ΔW. The front contour of each disc is separate defined by many individual points and saved in this way.

A computer program then calculates the values g _n and  _n for each slice and stores them in field data memories.

Another EDP program retrieves these values and forms the integral values by adding them up:

The pane front cut contour is now being constructed in the middle area of the wing optimally extended to the limit line (dash-dotted in Fig. 6) and the Center of gravity positions of solid screw and balancing chamber to cover brought 108 (Fig.4),

The middle area extends over a (initially) variable number of m of the same Disks, the end areas each have 5 disks of decreasing contours (Fig.7). At ΔW = 0.108 [cm] and variation of m one obtains for the 3-winged Balancing room the values shown in Table 2.

A good approximation is given by values α ₂ = 806.8 ... 806.9 [<°] and m = 10. A subsequent fine adjustment is made by making corrections to the disc geometry. The calculated value of the screw length / pitch relation here is 2 W ₂ / I = a = 4.4825 <9/2.

In a second variant (FIGS. 8, 9) of the exemplary embodiment, the required one Gait t (Fig. 8) relatively small, corresponding to a relatively large core diameter c (Fig.8). The effective balancing space 203 (FIG. 8) runs in a straight line, axially parallel with constant cross section (Fig. 9) eccentrically within the Screw core area, axially mediated (Fig. 10).

P_u/ω²τ₀ =

g₀·(I/π)·sinα₂
α₂ = 14,0662   [ Rad ]
I = 5,390   [ cm ]
g₀ = 150,374   [ cm³ ]

P_u/ω²τ₀ =

257,347   [ cm⁴ ]

A balancing chamber 203 designed in this way has no influence on the dynamic unbalance. In the arithmetic treatment, the exact value a _o = screw length / pitch near 9/2 loops is first determined with the aid of (3a), for which the dynamic unbalance of the screw is also "zero". This value a _o is independent of the profile. Some values for different wraps are shown in Tab. 3. From this follows directly (1a) the (profile-dependent) value of the static imbalance of the screw:

P _u / ω ² τ ₀ =

g ₀ · (I / π) · sinα ₂
α ₂ = 14.0662 [wheel]
I = 5.390 [cm]
g ₀ = 150.374 [cm ³ ]

P _u / ω ² τ ₀ =

257.347 [cm ⁴ ]

The value of balancing space 203 is equated to this value by adjusting the cross-section and length:
e = 2.85 [cm] d = 1.6 [cm] => j = 20.3 [cm]

In a sub-variant (FIG. 11) of the second variant, the screw rotor 302 flying on the rotor axis coaxially attached to the screw body on one side stored. The eccentric balancing chamber 303 is from the axisless end face of the Screw rotor accessible via a large coaxial bore and can therefore open several types can be manufactured. Form screw body and rotor axis preferably a one-piece unit, the coaxial bore on the rotor face side is optionally closed by a plug 309. Special proportions of the Screw body, i.a. due to the one-sided storage, lead to the same Calculation of deviating proportions e, d, j of balancing space 303.

Screw rotors with profile geometries of both variants of the described embodiment according to the in Fig.3, 4, 6, 7; 8, 9 reproduced proportions were theoretically founded and computer-aided calculated and realized for 1 length unit (LE) = 1cm and successfully tested. α ₂
[<°] P _u / ω ² τ ₀
[cm ⁴ ] M _{v, w} / ω ² τ ₀
[cm ⁵ ] 807.4 577.045 229.381 807.3 576.998 213.715 807.2 576.950 198.053 807.1 576.900 182.394 807.0 576.848 166.739 806.9 576.794 151.087 806.8 576.739 135.438 806.7 576.682 119.793 806.6 576.623 104.151 m P _u / ω ² τ ₀
[cm ⁴ ] M _{v, w} / ω ² τ ₀
[cm ⁵ ] P _v / ω ² τ ₀
[cm ⁴ ] M _{u, w} / ω ² τ ₀
[cm ⁵ ] 13 641.926 231.623 -3.902 3,970 12 619.980 199.530 -4.081 3,574 11 596.549 170.234 -4.251 3,192 10 571.692 143.681 -4.410 2,824 9 545.467 119.803 -4.559 2.473 8th 517.937 98.519 -4.697 2,140 7 489.169 79.735 - 4,824 1.827 Relationships screw length / pitch = a _o = 2W ₂ / I with a straight balancing chamber with a constant cross-section. a _o = 2W ₂ / I = 2 α ₂ / 2π 2,459 3,471 4,477 5,481 6,484 7,486 odd multiples of ½ 2.5 2.7 2.9 2.11 2.13 2.15 Etc ...

Claims (9)

1. Screw rotor set for screw pumps in an axially parallel arrangement engaging in opposite directions in the external axes and with wrap angles of at least 720° in a single-thread construction, and with smooth plane-parallel rotor end faces, characterized in that each screw rotor (1, 2; 101, 102; 201, 202; 301, 302) consists of several individual parts fixed rigidly together with a common axis of rotation, optionally eccentric centre of gravity positions and optionally different material densities; the individual parts inside the rotor form an eccentric cavity separable from the pump chamber, the balancing cavity (3; 103; 203; 303); adjustment of the material densities and the geometry of the individual parts inside the rotor cause static balancing and affect dynamic unbalance, and dynamic balancing is achieved with little effect on static unbalance by calculated determination of the screw length/pitch ratio = a at values which are somewhat smaller than uneven multiples of ½.
2. Screw rotor set as per claim 1, characterized in that each screw rotor (1, 2; 101, 102; 201, 202) consists of a cylindrical screw body (104; 204) and a coaxial rotor shaft (105; 205), which form an eccentric cavity, the balancing cavity (103; 203) inside the screw body.
3. Screw rotor set as per claim 1, characterized in that each screw rotor (1, 2) consists of a cylindrical screw body and a coaxial rotor shaft with a cross-section bearing-mounted eccentrically inside the screw body and that the screw body and rotor shaft are made of materials of different densities.
4. Screw rotor set as per claims 2 and 3, characterized in that each screw rotor (1, 2) consists of a cylindrical screw body and a coaxial rotor shaft with a cross-section mounted eccentrically inside the screw body and that the screw body and rotor shaft are made of materials of different densities and form an eccentric hollow cavity, the balancing cavity (3) inside the screw body.
5. Screw rotor set as per claim 1, characterized in that each screw rotor (1, 2; 301, 302) consists of a cylindrical screw body (304) with a rotor shaft applied coaxially on one side and that the screw body has an eccentric hollow cavity, the balancing cavity (303) on the inside, whose access on the shaft-free end face of the rotor can be sealed optionally with a plug (309).
6. Screw rotor set as per claim 2 or 4, characterized in that the balancing cavity (103) has several wing-type extensions on the side (108), which follow the screw thread with parallel centreline.
7. Screw rotor set as per claim 2 or 4 or 5, as an alternative to claim 6, characterized in that the balancing cavity (203) runs axially in a straight line with constant cross-section, so that the effect on the dynamic unbalance is equal to «zero».
8. Screw rotor set as per claim 2 or 4 or 6 or 7, characterized in that the balancing cavity (103; 203) is ventilated or cooled by means of a channel (107; 207) arranged in the rotor shaft.
9. Screw pump with a screw rotor set as per one or more of claims 1 to 8.

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