WO2000048816A1

WO2000048816A1 - Extruder housing section

Info

Publication number: WO2000048816A1
Application number: PCT/CH2000/000068
Authority: WO
Inventors: Stefan Rutishauser; Philipp Hanimann; Markus Meyer
Original assignee: Bühler AG
Priority date: 1999-02-15
Filing date: 2000-02-08
Publication date: 2000-08-24
Also published as: AU2275100A; DE19906196A1

Abstract

A section of an extruder housing, comprising an inner border (11) defining an inner space (6) for receiving a worm and partially comprised of at least one inner segment (7) that is made of a friction-resistant material. Each inner segment (7) has a partially circular cross-sectional inner surface. The inner segments (7) are tightened by at least one longitudinal wedge (8) on an outer housing (2). The inner border (11) is made up of partial areas of the inner segments (7) and the longitudinal wedge (8).

Description

Extruder housing section

The invention relates to an extruder housing section according to the preamble of claim 1.

Extruders are used in manufacturing processes in which a starting product, in particular a food or nutrient, is conditioned by means of pressure and / or shear forces as well as heating and / or cooling. For this purpose, an extruder comprises a housing or a casing with an inner edge which encloses an interior with a longitudinal axis. In order to enable heating or cooling, the housing or the jacket wall preferably comprises a line arrangement for a heating or cooling fluid. In the interior, at least one actuator is rotatably arranged about an axis of rotation parallel to the longitudinal axis. Screws or screws are preferably used as the actuating element, which extend radially at least in a part of their circumferential area up to the immediate vicinity of the inner edge and thereby prevent the product from caking on a corresponding area of the inner edge. In the case of extruders with only one actuating member or in the case of single-shaft extruders, the inner edge is circular in cross section, but the inner diameter can change along the longitudinal axis. In the case of extruders with two or more shafts, the cross-section of the inner edge is composed of two or more circular segments, with an actuating member or a screw being assigned to each circular segment.

It has now been shown that the inner edge is exposed to undesirable abrasion, which occurs due to friction over the product or in particular in the start-up phase or in the case of incomplete filling, due to frictional contacts between a screw and the inner edge. The material rubbed off from the inner edge gets into the product as contamination. This is particularly problematic with food or feed. It also increases due to the increasing gap distance between the radial outer edges of the actuators and the inner edge, the risk of caking. Exchanging housing sections with excessively worn inner edges is very complex and costly. Wear-resistant coatings and solid materials usually have a very brittle fracture behavior. Tensile stresses as they arise due to the internal pressure, as well as material stresses due to temperature fluctuations, can destroy the coating or the solid material layer or the housing. In addition, there may be free spaces between the coating and the housing, which lead to poor heat exchange.

The invention is based on the object of finding an extruder housing section which reduces abrasion, ensures good heat exchange and is reliable and simple in construction.

This object is solved by the features of claim 1. The dependent claims describe alternative or advantageous variants.

In the context of the present invention, it was recognized that the inner edge must have both increased friction resistance and high stability and, in order to reduce the risk of cracking, should be under compressive stress in any operating state, if possible. If at least a partial area of the inner edge of the housing is formed by at least one inner segment or bushing extending along the longitudinal axis made of hardened tool steel or another friction-resistant material, increased frictional strength and high stability can be assumed. An inner segment or a bush is assigned to each part-circular cross-sectional area of the inner edge and thus to each shaft or worm. However, because the at least one inner segment must fit tightly against the outer housing of the housing section to ensure good heat transfer and the expansion movements of the outer housing and an inner segment are different, the fastening of the at least one inner segment on the outer housing must be able to absorb high expansion forces. If necessary, the fastening is designed such that it can yield when predetermined limit forces are reached. The fastening device for fastening at least one inner segment or at least one bushing comprises at least one longitudinal wedge which lies along the longitudinal axis with pressing surfaces on lateral clamping surfaces of at least one inner segment. By screwing the at least one longitudinal wedge outwards by means of tensioning screws guided through the outer housing, this transmits a tensioning force with the pressing surfaces to the tensioning surfaces lying thereon. In the tensioned state, the inner surface of the at least one longitudinal wedge adjoins the inner surfaces of the adjacent inner segments essentially continuously as an inner edge. In order to provide a friction-resistant inner edge also in the area of the at least one longitudinal wedge, the longitudinal wedge preferably also consists of hardened tool steel or another friction-resistant material.

The material of the inner segments and especially the longitudinal wedges ensures reduced abrasion. Because only an inner layer made of this material is required, the additional costs associated therewith are so small that they are compensated for by the longer service life of the housing section according to the invention. In addition, only the inner segments can be replaced if necessary. After removing a housing section, only the longitudinal wedges have to be loosened in order to be able to push out the inner segments. It is not necessary to replace entire housing sections. Tightening the inner segments ensures efficient heat exchange and high mechanical safety even with large temperature fluctuations.

Because the extruder sleeves are preferably composed of housing sections or zones, the inner segments and the wedges of the adjoining zones must be pressed tightly against one another in the longitudinal direction. For this purpose, these parts and a radially inner region of the outer housing preferably protrude somewhat in the longitudinal direction over a radially outer region of the outer housing, so that when the outer housing is screwed together, the entire connecting force between these protruding regions is effective and a metallic seal is thereby guaranteed. The drawings explain the extruder housing sections according to the invention using exemplary embodiments. It shows:

Fig. 1 shows a cross section through a housing section of a twin-screw extruder

Fig. 2 shows a longitudinal section through a housing section of a twin-screw extruder

Fig. 3 shows a cross section through a housing section of a twin-screw extruder with only one longitudinal wedge

Fig. 4 shows a longitudinal section through a housing section of a twin-screw extruder, in which the longitudinal wedges are held resiliently by means of disc springs.

Fig. 5 shows a cross section through a housing section of a single-shaft extruder

1 and 2 show a housing section 1 with an outer housing 2, each of which has a flange 3 with bores 4 on its end faces. An inner region 5 of the outer housing 2 projects little beyond the end face of the flange 3. In order to provide an inner space 6 for two screws and the space for inserting two inner segments 7 and two longitudinal wedges 8, four partially overlapping longitudinal bores are formed through the inner housing. In the housing section shown for a twin-screw extruder, the longitudinal axis 9 is arranged in the center, a central plane 10 runs along the longitudinal axis 9 and is oriented such that the two inner segments 7 are arranged in mirror image with respect to this central plane 10 and the longitudinal wedges 8 are each symmetrical with respect to this central plane. The inner segments 7 are designed as tubular segments which are open to one another and each have a segment axis 7a and, with their inner surfaces, form part of the inner boundary 11. The outer sides of the inner segments 7 must fit closely to the corresponding edge regions of the bores. lie to ensure good heat transfer and to keep the inner surface of the inner segments 7 at the desired distance from the screws.

The inner segments 7 are made of friction-resistant material and have a partially circular inner surface in cross section. The longitudinal wedges 8 tighten the inner segments 7 on the outer housing and are preferably also made of a friction-resistant material. In a preferred embodiment, the inner segments 7 and / or the longitudinal wedges 8 are made of hardened tool steel. The areas of the inner edges of the longitudinal wedges 8 essentially continuously adjoin the inner areas of the adjacent inner segments. This provides an inner boundary 11 with only two partial circles in cross section. It goes without saying that for a multi-screw extruder, the number of pitch circles, or inner segments 7 and longitudinal wedges 8, is adapted to the number of screws.

The longitudinal wedges 8 lie along the longitudinal axis 9 with pressing surfaces 12 on lateral clamping surfaces 13 of the inner segments 7 and are preferably screwed outwards by clamping screws 14 which are guided through radial bores of the outer housing 2. The pressing surfaces 12 make clamping forces transferable to the clamping surfaces 13 lying thereon. Since the clamping surfaces 13 of each inner segment lie essentially in the radial planes of this inner segment 13 and the longitudinal wedges 8 can be clamped outwards in the direction of a central plane between the pressing surfaces, tangential clamping forces are transmitted from the longitudinal wedges 8 to the inner segments 7. The longitudinal wedges 8 are designed such that they have the mobility required for clamping in the corresponding bores or on the corresponding clamping surfaces 13.

To accommodate radial expansion of the inner segments 7 due to temperature, the clamping wedges 8 are to be resiliently fastened to the outer housing 2. The suspension is preferably ensured directly by the clamping screws 14, in that they have a length of at least five times the clamping screw diameter. If necessary, however, as shown in FIGS. 3 and 4, spring elements, in particular disc springs 15, between the screw head and its stop surface used on the outer housing 2. The clamping screws are preferably tightened with a predetermined maximum torque.

The end faces of the inner segments 7 and the longitudinal wedges 8 protrude the same distance over the end face of the flange 3 as the inner region 5 of the outer housing 2, so that a metal seal can be achieved between the connected housing sections. The entire connecting force that is achieved between the two flanges is transferred to the somewhat protruding sealing area.

The channel system 16 for the cooling or heating fluid is formed in the outer housing 2. The channel system 16 comprises connection bores 17, connecting channels 18 perpendicular to the longitudinal axis 9 and longitudinal channels 19, which lead from the connecting channels 18 on one end face to the connecting channels 18 on the other end face. The bores for the connecting channels 18 are closed to the outside with plugs. In order to ensure circulation through the longitudinal channels, one connection bore 17 is connected to the connecting channels 18 on one or the other end face. It goes without saying that the channel system 16 can be designed in any way according to the particular extruder insert.

In order to ensure that the inner edges 11 of two adjoining housing sections 1 connect exactly to one another, alignment bores 20, into which alignment bolts (not shown) can be inserted, are optionally provided on the end faces of the housing sections 1.

In Fig. 2, three additional holes 21 are drawn, which extend through the outer housing 2 and the longitudinal wedge 8 to the interior 6 and are optionally used for receiving a sensor or as a feed opening for a product additive or a conditioning fluid such as water or steam. Unused additional bores 21 are closed with plugs.

3 shows an embodiment with two inner segments 7 and only one longitudinal wedge 8. The pressing surfaces 12 of the longitudinal wedge 8 press against one of the lateral clamping surfaces 13 of the inner segments 7. The other two lateral clamping surfaces 13 abut each other. The stop of the clamping screw 14 is spring-loaded with a plate spring 15.

5 shows a housing section for a single-shaft extruder. Only an inner segment 7 and a longitudinal wedge 8 are used. Because the segment axis 7a and the longitudinal axis 9 now coincide, no tangential clamping forces could be transmitted to radial clamping surfaces 13 with a longitudinal wedge 8 which can be screwed outwards. The longitudinal wedge would then rather have to be pressed inwards for tensioning, which is less advantageous. In the example shown, the clamping surfaces 13 and the pressing surfaces 12 lying against them are aligned in such a way that the desired clamping of the inner segment can be achieved by clamping the longitudinal wedge 8 outwards. For this purpose, the two pressing surfaces 12 diverge somewhat radially inwards.

It goes without saying that the inner segments and longitudinal wedges can also be used in housing sections with changes in cross section. The shape of these insert parts must be adapted to the respective cross-sectional changes.

Claims

claims

1. extruder housing section with an inner edge (11) which encloses an interior (6) for receiving at least one screw and extends along a longitudinal axis (9), characterized in that to provide a friction-resistant inner edge (11) on the inside of a The outer housing (2) has at least one inner segment (7) made of friction-resistant material with a cross-sectionally inner surface and at least one longitudinal wedge (8), the at least one longitudinal wedge (8) and the at least one inner segment (7) on the outer housing (2). tight.

2. Extruder housing section according to claim 1, characterized in that the at least one inner segment (7) and / or the at least one longitudinal wedge (8) consists of hardened tool steel.

3. Extruder housing section according to claim 1 or 2, characterized in that the inner surface of the at least one longitudinal wedge (8) connects essentially continuously as an inner edge to the inner surfaces of the adjacent inner segment regions.

4. Extruder housing section according to one of claims 1 to 3, characterized in that the at least one longitudinal wedge (8) along the longitudinal axis (9) with pressing surfaces (12) bears against lateral clamping surfaces (13) of at least one inner segment (7) and can preferably be screwed outwards by means of clamping screws (14) guided through the outer housing (2), the pressing surfaces (12) making clamping forces transferable to the clamping surfaces (13) lying thereon.

5. Extruder housing section according to claim 4, characterized in that at least two inner segments (7) are arranged as tubular segments, each with a segment axis and at least two longitudinal wedges (8), preferably at least two inner segments (7) are arranged in mirror image with respect to a central plane (10) running along the longitudinal axis (9) and the longitudinal wedges (8) are each symmetrical with respect to a central plane (10).

6. extruder housing section according to claim 5, characterized in that the longitudinal wedges (8) on the inner segments (7) make tangential clamping forces achievable, preferably by the clamping surfaces (13) of each inner segment (7) substantially in the radial planes of this inner segment (7) lie and the longitudinal wedges (8) can be stretched outwards in the direction of a central plane (10) between the pressing surfaces (12).

7. extruder housing section according to one of claims 4 to 6, characterized in that the clamping wedges (8) are resiliently attached to the outer housing (2), the suspension optionally by means of spring elements, in particular disc springs (15), but preferably directly Clamping screws (14) with a length of at least five times the clamping screw diameter is guaranteed.

8. Extruder housing section according to one of claims 1 to 7, characterized in that a longitudinal bore is provided in the inner housing for receiving each inner segment and each longitudinal wedge.

9. extruder housing section according to one of claims 1 to 7, characterized in that the outer housing (2) comprises a flange (3) for connecting adjoining housing sections and preferably an inner region (5) of the outer housing and the at least one inner segment (7) and the at least one longitudinal wedge (8) protrude slightly beyond the end face of the flange, so that a metal seal can be achieved between the connected housing sections.