EP0865575B2 - Double worm system - Google Patents

Abstract

PCT No. PCT/CH96/00250 Sec. 371 Date Feb. 8, 1999 Sec. 102(e) Date Feb. 8, 1999 PCT Filed Jul. 8, 1996 PCT Pub. No. WO97/21925 PCT Pub. Date Jun. 19, 1997In prior art designs, single-flight cast double worms with angles of contact >720 DEG with large balance hollows at both ends and worm lengths of whole multiples of the pitch operate in the medium rotation speed ranges ( DIFFERENCE 3000 min DIFFERENCE 1) without imbalance. The desired use of special uncastable materials and the manufacturing complexity and the necessary dimensional stability even for extreme profile geometries pose additional problems in balancing which are solved by the present invention. Here, it is possible, by varying the angle of contact of the worm and any balance hollows and/or by altering the contour of the worms in the medium engagement region, to reduce the size of the balance hollows, sometimes to "zero", and with the possible use of additional masses. Besides the advantage of simple raw component manufacture, worms balanced in this way also permit the use of special materials and extreme worm geometries for fitting in pumps used in the chemical, medical and food sectors.

Description

The invention relates to measures for balancing a twin screw set in an axially parallel arrangement with opposite external-axis engagement and with wrap angles of at least 720 ° in a catchy design. Center of gravity distance, face and wrap angle determine the sizes of the static and dynamic imbalance that occur in screws with catchy profiles.

In the disclosure document Sho 62 (1987) -291486 of Taiko, Japan, a method for screw balance is described: First, static balancing is achieved by setting the screw length to integer multiples of the slope. Through two-sided cut-outs in the screw, which are hollow or filled with light material, is dynamically balanced.

This method of balancing is not feasible if special materials are required that can not be cast. Even with unusual profile geometries, this method has its limitations, since on the one hand, the wall thickness of the screws for stability reasons can not be arbitrarily reduced, on the other hand brings too large axial expansion of the balancing cavities because of the spiral shape considerable manufacturing problems.

The invention has for its object to define measures for balancing catchy screws whose geometry is exceptional or their use requires special materials, without much extra effort in production and without jeopardizing the dimensional stability.

This object is achieved in a twin-screw set 1, 2 (Fig.1) in paraxial arrangement with opposite Außenachsigem engagement and wrap angles of at least 720 ° in a catchy embodiment according to the invention that the screw lengths are not fixed to integer multiples of the slope. Preferably, the screw outer contours in the medium inlet region for balancing 3 (Fig.1) are changed.

Design possibilities are given by attaching additional masses 6 (Fig.1) in the outer region, in particular on the pilot transmission and by frontal Anshuchthöhlen 4 (Figure 2), the axial extent is varied for optimization.

1. 1. Leichtere Fertigung und größere Formstabilität im Falle der Anbringung von stirnseitigen Auswuchthöhlen, erreicht durch optimale Dimensionierung von Schraubenumschlingungswinkel, Auswuchthöhlenumschlingungswinkel sowie Auswuchthöhlenquerschnitt.
2. 2. Möglichkeit der Verwendung von Sonderwerkstoffen, die nicht gegossen werden können.
3. 3. Reduzierte Schraubenoberflächen im Ausgangsbereich, was eine Temperaturreduzierung bewirkt.

The advantages achieved by the invention are:

1. 1. Easier manufacturing and greater dimensional stability in the case of the attachment of frontal Auswochthööhlen, achieved by optimizing the dimension of Schraubenumschlingungswinkel, Auswuchtthöhlenumschlingungswinkel and Auswochthöhlenquerschnitt.
2. 2. Possibility of using special materials that can not be cast.
3. 3. Reduced screw surfaces in the exit area, which causes a temperature reduction.

Reference to an embodiment shown in the figures, the invention is explained in more detail below:
Show it :

Fig.1:

A twin screw set for a screw pump in a catchy design according to the invention with wrap angles of 1598 ° and Auswuchtausnehmungen on the screw outer contours in the medium inlet region.

Figure 2:

An embodiment of a twin screw set of Figure 1 with Auswuchtthöhle in front view.

Figure 3:

The representation of the spiral profile centroid locus of a screw profile of Figure 2.

In one embodiment, the twin screws 1 and 2 (Figure 1) lengths of 4.439 times the slope, which corresponds to a wrap angle of 1598 ° (Figure 3). The front profile 5 (Figure 2) and the slope 1 (Figure 1) determine together with the wall thickness d (Figure 2) most of the contour of the axially mounted Auswuchtthöhlen 4 (Figure 2); the circle 7 (Figure 2) limits this towards the center. In common angular positions of the centers of gravity of solid profile and balancing surface S ₀ , S ₃ (Figure 2), the straight conclusion inevitably results in the balancing surface.

Computationally, the problem is treated as follows:

In a rectangular coordinate system with screw axis as w-axis, and u-axis and v-axis in The center of gravity S ₀ (Figure 3) is positioned on the u-axis in the plane of the central helical cut. The extension of the screw in the w-direction extends symmetrically from -W ₂ ... + W ₂ or in the angular definition of -α ₂ ... + α ₂ , with a relationship α ₂ = (2π / 1) · W ₂ (FIG. II), where 2α ₂ mean the wrap angle of the screw and π = circle number = 3.1415 ....

The areas of the frontal Auswochthöhlen are at -W ₂ ... -W ₁ and + W ₁ ... + W ₂ , which angular positions of -α ₂ ...- α ₁ and + α ₁ ... + α ₂ with α ₁ = (2π / l) · W ₁ (I).

The respective wrap angles of a balancing cavity thus amount to α ₃ = α ₂ -α ₁ (III).

und $${\mathrm{g}}_{\mathrm{3}}\mathrm{=}{\mathrm{g}}_{\mathrm{0}}\mathrm{\cdot }\left({\mathrm{sin\alpha }}_{\mathrm{2}}\mathrm{-}{\mathrm{\alpha }}_{\mathrm{2}}{\mathrm{cos\alpha }}_{\mathrm{2}}\right)\mathrm{/}\left({\mathrm{sin\alpha }}_{\mathrm{2}}\mathrm{-}{\mathrm{sin\alpha }}_{\mathrm{1}}\mathrm{-}{\mathrm{\alpha }}_{\mathrm{2}}{\mathrm{cos\alpha }}_{\mathrm{2}}\mathrm{+}{\mathrm{\alpha }}_{\mathrm{1}}{\mathrm{cos\alpha }}_{\mathrm{1}}\right)$$

wobei g₀ das Produkt aus Vollprofilfläche f₀ und zugehörigem Schwerpunktmittenabstand r₀ (Fig.2) bedeutet, α₂ und α₁ im Bogenmaß einzusetzen sind und g₃ der obenstehenden Definition entspricht.For symmetrical balancing cavities with a constant value g _{3 of} the product of area f ₃ and centroid center distance r ₃ (FIG. 2) (g ₃ = f ₃ · r ₃ = constant (IV)), the requirements for static and dynamic balancing lead to the formulas $${\mathrm{\alpha }}_{}$$$${\mathrm{}}_{\mathrm{2}}\mathrm{\cdot }\sin {\mathrm{\alpha }}_1\mathrm{<figure-callout\; id="2"\; label="cos\; \alpha "\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">cos\; </figure-callout>}{\mathrm{\alpha }}_{}{\mathrm{}}_{\mathrm{2}}\mathrm{=}{\mathrm{\alpha }}_1\mathrm{\cdot }\cos {\mathrm{\alpha }}_1\mathrm{<figure-callout\; id="2"\; label="sin\; \alpha "\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">sin\; </figure-callout>}{\mathrm{\alpha }}_{}{\mathrm{}}_{\mathrm{2}}$$

and $${\mathrm{<figure-callout\; id="3"\; label="G"\; filenames="imgf0003.png"\; state="\{\{state\}\}">G</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{G}}_{\mathrm{0}}\mathrm{\cdot }\left({\mathrm{sin\; .alpha}}_{\mathrm{2}}\mathrm{-}{\mathrm{<figure-callout\; id="2"\; label="\alpha "\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">\alpha </figure-callout>}}_{\mathrm{2}}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">cos</figure-callout>}}_{\mathrm{2}}\right)\mathrm{/}\left({\mathrm{sin\; .alpha}}_{\mathrm{2}}\mathrm{-}{\mathrm{sin\; .alpha}}_{\mathrm{1}}\mathrm{-}{\mathrm{<figure-callout\; id="2"\; label="\alpha "\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">\alpha </figure-callout>}}_{\mathrm{2}}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">cos</figure-callout>}}_{\mathrm{2}}\mathrm{+}{\mathrm{\alpha }}_{\mathrm{1}}{\cos }_{\mathrm{1}}\right)$$

where g _{0 is} the product of solid profile surface f ₀ and associated center of gravity distance r ₀ (Figure 2), α ₂ and α _{1 are to be used} in radians and g ₃ corresponds to the above definition.

Equation (V) provides at least one solution for α ₁ for any helix angle 2α ₂ (with α ₂ >2π); The dimensions of the balancing cavity follow from α ₁ and α ₂ : From (III) the wrap angle and from (VI) the desired cross-section g ₃ .

d.h. für eine Schraubenlänge der 4-fachen Steigung $${\mathrm{wird\hspace{1em}dort\hspace{1em}g}}_3=g_0\cdot 4/7.$$

For manufacturing reasons, the wrap angle α _{3 of} the balancing cavity should be as small as possible; In the case of several solutions for α _1, therefore, the largest value is used with α ₁ <α ₂ . Exact investigations show that the most unfavorable conditions occur at screw lengths of integer multiples of the pitch, for 2W ₂ = 2L, 3L, 4L, 5L ... K · L, according to the embodiment according to the above publication: The balancing belt angle there is α ₃ = π , the dynamic characteristic g ₃ reaches a maximum, which requires a maximum balancing cavity: $${\mathrm{<figure-callout\; id="3"\; label="G"\; filenames="imgf0003.png"\; state="\{\{state\}\}">G</figure-callout>}}_{\mathrm{3}\mathrm{.}}\mathrm{Max}\mathrm{=}{\mathrm{G}}_{\mathrm{0}}\mathrm{\cdot }\mathrm{k}\mathrm{/}\left(\mathrm{2}\mathrm{k}\mathrm{-}\mathrm{1}\right)$$

ie for a screw length of 4-fold pitch $${\mathrm{will\; there\; <figure-callout\; id="3"\; label="g"\; filenames="imgf0003.png"\; state="\{\{state\}\}">g</figure-callout>}}_3=G_0\cdot 4/\mathrm{7th}$$

For the execution of the invention described here, screws with wrap angles of 2α ₂ = 5π, 7π, 9π ... corresponding to screw lengths of 2W ₂ = 5 * I / 2, 7 * I / 2, 9 * I / 2 are selected.

The balancing belt angles are then also α ₃ = π, but the dynamic characteristic value g ₃ reaches a minimum here, which means a minimum balancing cavity: $${\mathrm{<figure-callout\; id="3"\; label="G"\; filenames="imgf0003.png"\; state="\{\{state\}\}">G</figure-callout>}}_{\mathrm{3}}.\min \mathrm{=}{\mathrm{G}}_{\mathrm{0}}\mathrm{/}\mathrm{2}$$

Reinforcing ribs at the end of the balancing cavities lead to asymmetrical conditions, which are partially absorbed by correction of the wrap angles 2α ₂ , α ₃ .

As a further measure for balancing the screws 1, 2 are changed to the passive Außenkonturteil on the suction side. The passive area 3 (Figure 1) extends in both screws on all parts that are required neither to form the first suction-side working cell nor to maintain stability. This external balancing can be used alternatively or in combination with one or more frontal Auswochtthöhlen.

In a sub-variant, external balancing additional masses 6 (FIG. 1) are used in the region of the pilot transmission.

Claims (7)

1. Twin screw system for a screw pump in axis-parallel arrangement, with counter-running outer axis engagement, and with angles of contact of at least 720°, in single flight design, characterised in that the screw lengths are not integer multiples of the pitch and that frontal balancing hollows (4) are provided in the medium intake area.
2. Twin screw system according to claim 1, characterised in that the screw length is greater by an integer multiple of the pitch than 1½ times the pitch.
3. Twin screw system according to claim 1 or 2, characterised in that the screw outer contours are modified in the medium inlet area, wherein the screw outer contours are modified at the passive outer contour parts on the suction side.
4. Twin screw system according to any of claims 1 to 3, characterised in that at least one end of the screw is provided with an inner balancing hollow (4).
5. Twin screw system according to claim 4, characterised in that both screw ends are provided with a balancing hollow (4).
6. Twin screw system according to claim 4 or 5, characterised in that the winding angles of the balancing hollows can be varied for optimum adaptation.
7. Twin screw system according to any of claims 3 to 6, characterised in that additional masses (6) are applied in the outer area, at the pilot gear.

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