EP1671036B1

EP1671036B1 - Inlet hopper construction for a twin-screw pump

Info

Publication number: EP1671036B1
Application number: EP03818493A
Authority: EP
Inventors: Knud Simonsen
Original assignee: CFS Slagelse AS
Current assignee: GEA Food Solutions Denmark AS
Priority date: 2003-09-10
Filing date: 2003-09-10
Publication date: 2007-07-25
Anticipated expiration: 2023-09-10
Also published as: BR0318499A; DE60315201D1; ATE368183T1; WO2005024238A1; CN1839264A; NO20061192L; EP1671036A1; AU2003258494A1; DK1671036T3; ES2290559T3; DE60315201T2

Abstract

An inlet hopper construction for a twin-screw pump comprises two mutually engaging feed screws (1,1'), said feed screws (1,1') being positioned at the bottom of the inlet hopper (3) for feeding the material towards the twin-screw pump, and two mutually engaging pump screws (2,2') aligned co-axially with the feed screws (1,1') and positioned in a pump casing with close clearances with said casing (4) and between the mutually engaging flights and grooves. The inlet hopper (3) is formed with a close fitting with the bottom part of the feed screws (1,1') and a widening out (5) along the outer sides of the feed screws (1,1') in order to allow the material in the hopper (3) to enter into the grooves of the feed screws (1,1') from the sides as well as from the top.

Description

TECHNICAL FIELD

The present invention relates to an inlet hopper construction for a twin-screw pump of the kind set forth in the preamble of claim 1.

BACKGROUND ART

In inlet hopper constructions for twin-screw pumps of this kind it is known to provide the feed screws in the bottom part of the hopper with a close fitting between the screws and the bottom of the inlet hopper by having a cylindrical bottom formation with approximately same radius of curvature as the radius of the feed screws and having this cylindrical formation extending to approximately half way up along the sides of the feed screws, where a mainly planar extension is forming the rest of the hopper construction. A hopper construction of this kind is e.g. known from US-4,566,640 and US-4,685,628 .

DISCLOSURE OF THE INVENTION

It is the object of the present invention to provide an inlet hopper construction of the kind referred to above, with which it is possible to improve the filling of the feed screws and consequently the filling of the pump screws, and this object is achieved with an inlet hopper construction for a twin-screw pump of said kind, which according to the present invention also comprises the features set forth in the characterising clause of claim 1. With this arrangement, the material from the hopper is able to fill the feed screw grooves from the sides as well as from the top of said feed screws, whereby the filling of the feed screws and consequently the pump screws is increased compared to the constructions in accordance with the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed part of the present description, the invention will be explained in more detail with reference to the exemplary embodiment of an inlet hopper construction for a twin-screw pump according to the invention shown in the drawings, in which

Figure 1 schematically shows a cross section of an inlet hopper construction in accordance with a preferred embodiment of the present invention with feed screws mounted therein,
Figure 2 schematically shows the construction in Figure 1 for indicating the different radii of the feed screws and the cylindrical formation of the bottom of the hopper construction,
Figure 3 shows the construction of Figures 1 and 2 in a longitudinal cross section, and
Figures 4a and 4b schematically shows combined feed screws and pump screws for use in the hopper construction in accordance with the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The inlet hopper construction shown in Figures 1-3 for a twin-screw pump comprises two mutually engaging feed screws 1,1' positioned at the bottom of the inlet hopper 3 for feeding the material from the hopper 3 toward the twin-screw pump. The twin-screw pump comprises two mutually engaging pump screws 2,2', preferably with constant pitch, as shown in Figures 4a and 4b, which in the embodiment shown are positioned on a shaft common with the shaft of the feed screws 1,1', and thus aligned co-axially with the feed screws. Furthermore, the twin-screw pump comprises a pump casing 4 (not shown in detail) and the pump screws 2,2' are positioned in the casing 4 with close clearances between the casing 4 and between the mutually engaging flights and grooves of the pump screws 2,2'. The function of the twin-screw pump is as known from the prior art and it should not be necessary here to explain this function in detail. In the embodiment shown in the drawings, the twin-screw pump has its pumping screws 2,2' extending out of the casing 4 in order to prevent the twin-screw pump from being "over-filled".
In certain applications, in which the twin-screw pump is used for dosing material, e.g. for filling sausages, it is of major importance that the pump screws 2,2' are completely filled with material from the hopper 3. In traditional constructions, e.g. as known from the above-mentioned US-4,566,640 , the filling of the pumping screws 2,2' will normally only reach 80%-85%, especially in connection with certain high viscosity or lumpy material. The result of such insufficient filling is a reduced precision of the dosing of material out of the twin-screw pump. In order to increase the above filling percentage, the present invention prescribes the provision of a widening out 5 along the outer sides of the feed screws 1,1', which allows the material in the hopper 3 to enter into the grooves of the feed screws 1,1' from the sides as well as from the top. In the embodiment shown in the figures, the widening out 5 along the outer sides of the feed screws 1,1' are formed as a cylindrical formation of the bottom with a radius R+X, which is larger than the outer radius R of the feed screws 1,1', and the inlet hopper 3 is formed with a close fitting with the bottom part of the feed screws 1,1' by having the centre for the cylindrical formation of the bottom part positioned at a distance Y above the centre for the feed screws 1,1', where Y ≤ X.
As an alternative, the position of the centre for the cylindrical formation of the bottom part can be positioned at a distance Y in a direction deviating from vertical by an angle α and with the same restrictions between X and Y as mentioned above. The angle α is preferably between 0° (as shown in Figure 2) and 30°. In a preferred embodiment, the value of X is between 10 and 50% of R and the value of Y is X - δ, where δ is between 0 and 5% of R.
It will be evident for a man skilled in the art that other formations than the cylindrical formation of the bottom part can provide a similar widening out 5 along the outer sides of the feed screws 1,1' and that the dimensioning of the widening out naturally will depend on the material to be fed towards the twin-screw pump, i.e. the viscosity, granularity, and other parameters for the pumped material.
As shown in Figure 3, the hopper construction 3 is provided with a conically narrowing transition part 6 between the widening out bottom part 5 and the pump casing 4. This conical narrowing transition part 6 provides a further increased filling of the feed screws 1,1', when the material in the hopper 3 is transported towards the pump screws 2,2' and the pump casing 4. Preferably, the conical narrowing transition part 6 is formed as a combination of two truncated cones, thus providing a smooth transition from the two cylindrical hopper bottom parts with radius R+X to the two cylindrical pump casings 4 with radius R. In the embodiment shown, the cone angle, i.e. the top angle of the cone is approximately 30°. Other angles are naturally possible, but this angle should preferably be kept below 50°.
As shown in Figures 1-3, the bottom part of the hopper construction 3 is provided with axially extending rails 7 in order to guide the material axially along the feed screws 1,1' during the rotational movement of said feed screws 1,1'.
Preferably, the screws 1,2 and 1',2', respectively, are rotating in opposite directions and in such directions that the movement direction of the feed screws 1,1' along the outer sides of the hopper 3 is in the direction of the bottom of the inlet hopper 3. Such a rotational direction will improve the function of the widening out 5 along the outer sides of the feed screws 1,1' for improved filling of the feed screws 1,1' and accordingly, the pump screws 2,2'.
In the embodiment shown, the radius R for the feed screws 1,1' and the pump screws 2,2' is constant and identical, but for a man skilled in the art it will be evident that other formations of the feed screws and the pump screws can be envisaged.
In the embodiment shown in the drawings, the feed screws 1,1' are formed with relatively narrow flights and relatively broad grooves, which is especially suitable in connection with high viscosity and/or lumpy material. However, the feed screws 1,1' can be formed in other ways, e.g. identical to the pump screws 2,2', said last possibility being an advantage in connection with materials of low viscosity.
Experiments have shown that with a construction corresponding to the above described preferred embodiment, the filling of the pump screws 2,2' can be increased from 85%, as measured on a traditional construction, to approximately 98-99%, as measured with the preferred embodiment.
Above, the invention has been described in connection with a preferred embodiment and it will be evident for a man skilled in the art that many modifications can be made without departing from the scope of the appended claims.

Claims

Inlet hopper construction for a twin-screw pump comprising two mutually engaging feed screws (1,1'), said feed screws (1,1') being positioned at the bottom of the inlet hopper (3) for feeding the material towards the twin-screw pump,
two mutually engaging pump screws (2,2') aligned co-axially with the feed screws (1,1') and positioned in a pump casing with close clearances with said casing (4) and between the mutually engaging flights and grooves, said inlet hopper (3) being formed with a close fitting with the bottom part of the feed screws (1,1') and a widening out (5) along the outer sides of the feed screws (1,1') in order to allow the material in the hopper (3) to enter into the grooves of the feed screws (1,1') from the sides as well as from the top, characterised by the widening out (5) along the outer sides of the feed screws (1,1') being formed as a cylindrical formation of the bottom with a radius (R + X) which is larger than the outer radius (R) of the feed screws (1,1').
Inlet hopper construction in accordance with claim 1, characterised by the distance Y (Y ≤ X) between the centre of the feed screws (1,1') and the centre for the cylindrical formation of the bottom part, whereby there is provided a close fitting between the bottom part of the feed screws (1,1') and the inlet hopper (3) bottom section.
Inlet hopper construction in accordance with claim 2, characterised by comprising an angle α between the vertical direction and the line between the centres for the feed screws (1,1') and the centres for the cylindrical parts of the bottom of the hopper (3), where 0° ≤ α ≤ 30°.
Inlet hopper construction in accordance with any of the preceding claims, characterised by choosing X = 10-50% of R and choosing Y = X - 6, where 0 < δ ≤ 5% of R.
Inlet hopper construction in accordance with any of the preceding claims, characterised by further comprising a conically narrowing transition part (6) between the widening out bottom part and the pump casing.
Inlet hopper construction in accordance with claim 5, characterised by the conical narrowing transition part (6) being formed as a combination of two truncated cones.
Inlet hopper construction in accordance with claim 6, characterised by the cone angle γ of the conically narrowing transition part (6) being 10-50°, preferably 25-35°, and more preferred equal to 30°.
Inlet hopper construction in accordance with any of the preceding claims, characterised by the rotational direction of the two mutually engaging feed screws (1,1') being such that the movement direction of said feed screws (1,1') along the outer sides is in the direction of the bottom of the inlet hopper (3).
Inlet hopper construction in accordance with any of the preceding claims, characterised by the feed screws (1,1') and the pump screws (2,2') having the same diameter (2R).
Inlet hopper construction in accordance with any of the preceding claims, characterised by comprising axially extending rails (7) in the bottom of the hopper construction for guiding the material axially along the feed screws (1, 1').