IE46667B1

IE46667B1 - Extrusion head

Info

Publication number: IE46667B1
Application number: IE427/78A
Authority: IE
Original assignee: Diepal
Priority date: 1977-03-16
Filing date: 1978-03-01
Publication date: 1983-08-24
Also published as: BR7801588A; NL178558C; IT1093333B; CH624604A5; CA1108368A; DK116378A; ATA179078A; YU55078A; MX144912A; AR213475A1; SE7803009L; JPS53142585A; JPS619010B2; ES234508U; PT67730A; NO780911L; FI63161C; IE780427L; GB1600783A; AU3415378A

Abstract

The extrusion adapter includes a breaker plate (16) placed between the tip (17) of the extruder screws and the pressure-equalising chamber (18). The downstream side of this breaker plate, coming before the pressure-equalising chamber, has a plane face whereas the upstream side has a recess which has the shape of a cone whose apex (opening) angle is the same as that of the tip of the screws. This breaker plate is formed by two series of parallel-axis channels (20). This extrusion adapter is intended especially for equipping a line for manufacturing products in the form of sheet (strip) by the cooking-extrusion-expansion process, in particular for the manufacture of food products.

Description

The invention,relates to an extrusion head intended more particularly, but not exclusively, for equipping apparatus for the manufacture of products in strip form, by the extrusion-expansion baking process.

Extrusion assemblies currently used for carrying out 'ι this process are known; they generally comprise a feed hopper equipped with a mixer and a metering pump, which introduces the mixture of the constituents into a heated barrel equipped with a device comprising one or two rotating screws and terminating in one or more nozzles which are characteristic of the shape which it is desired to impart to the finished product.

Xn these assemblies, the pressure imparted to the doughy product in the screws of the extruder, further increased by progressive reduction in the pitch of the screw from where the mixture of the constituents enters to where it leaves, imparts to the doughy material pushed by the screw or the two screws a rotary movement in the chamber located between the conical tips of the or each screw and the adjacent front wall of the extruder. This rotary movement results, at the outlet of the extrusion nozzle, in a relatively disordered distribution of the dough over its entire cross-section.

Thus in the case where the extruded product is to be manufactured in the form of a strip, by virtue of its having been extruded through a slot, it is found that the edge portions of this strip are thinner and that there are surface irregularities which persist after cooling and interfere both with the appearance of the finished product and with the achievement of satisfactory packaging, because of the lack of planarity of the slabs obtained after the strip has been cut.

Many extruders have, in a position between the tip of the extrusion screw and the chamber preceding the nozzle, a perforated element which acts as a flow breaker plate and is intended to increase both the shearing action and the back pressure. Such flow breaker plates are described, for example, in U.S. Patent No. 2,543,679 (issued February 27, 1951 to Jurian W. Van Riper), U.S. Patent No. 3,018,807 (issued January 30, 1962 to James W. Clinefelter), U.S. Patent No. 3,054,677 (issued September 18, 1962 to William R. Graham Jr., and Benjamin Grogg), U.S. Patent No. 3,284,848 (issued November 15, 1966 to Richard M. Rice), and U.S. Patent No. 3,462,277 (issued August 19, 1969 to Robert R. Reinhart), as well as in British Patent Specification No. 1,213,455 (issued to Plasticizers Limited).

The perforations of these flow breaker plates are either distributed over the entire surface of the plate or arranged uniformly completely around one or more concentric circles, or arranged aligned relative to one another. However, these flow breaker plates employed alone do not make it possible to achieve perfect equalisation of the speed of the dough; to achieve this result it is still necessary to modify the shape of either the pressure chamber which precedes the flow breaker plate or the chamber located between this plate and the extrusion nozzle. Λ device described in French Patent No. 1,250,844 (issued to Diversey France) makes it possible to render the flow of dough uniform by means of plano-concave or plano-convex perforated lens-shaped bodies. Because of the concavity or convexity of the compensator described in this patent, the perforations form passages of differing lengths, depending on their position relative to the axis of the screw, and.the strands of dough passing through each of these perforations thus undergo different pressure losses.

The present invention provides an extrusion head for a screw extruder, said head comprising a nozzle having at least one extrusion orifice symmetrical (as hereinafter defined) about a single axis of the nozzle orifice or an axis common to the nozzle orifices; a diffuser plate disposed so as to be placed between the nozzle and the tip of the screw of an extruder in which the head is to be mounted; and a pressure equalisation chamber between the diffuser plate and the nozzle; wherein the side of the diffuser plate nearer said pressure equalisation chamber has a planar face and the opposite side presents a conical recess whose taper angle is intended to conform to that of the tip of the extruder screw of said extruder, and wherein the diffuser plate is provided by two sets of axially parallel ducts which are all situated at the same distance from the said axis of symmetry and are disposed symmetrically with respect to a median plane (as hereinafter defined) of said nozzle which includes said axis of symmetry, along two opposed circular arcs having the same radius.

Symmetry of the extrusion orifice(s) of the nozzle, as used herein, is intended to denote that in the case of a single nozzle orifice the axis of symmetry passes - 5 through the centre of area of that orifice, and that in the case of a multiple orifice nozzle the axis of symmetry is such that it passes through a point of symmetry of the centres of area of the various orifices. The term median plane of the nozzle is intended to denote a plane which includes the axis of symmetry and has the area of the orifice or the centres of area of the various orifices symmetrical thereabout.

This diffuser plate fulfils two specific purposes: On the one hand, it arrests the rotary movement imparted to the doughy product by the extruder screw and converts it to a linear translational movement towards the nozzle orifice or orifices and, on the other hand, by virtue of the arrangement of the channels all located on separate axis of the same circle, maintains constant the linear speed imparted to the strands of dough passing through these channels which channels are all located in zones of equal pressure. After having passed through the channels, these strands of dough merge together again in the chamber located downstream of the diffuser grid, and give a sheet of homogeneous dough which, after extrusion, results in a uniform product.

In order to avoid the presence of a zone where the product could stagnate in the pressure equalising chamber, the diffuser plate advantageously has a central channel located along the axis of the extrusion no22le.

In the case where two nozzle orifices are located at the end of each screw, said two sets of parallel channels are all located at the same distance from the axis of symmetry passing between the two nozzle orifices and are arranged symmetrically relative to the said plane of symmetry.

Because of this arrangement the central channel of the diffuser plat'e, which serves to avoid the stagnation of the doughy product which could lead to blocking of the 1 I nozzle orifice, is omitted because a dead zone will form immediately downstream of the centre of the diffuser plate and this dead zone will be devoid of doughy product and will thus not present any danger of stagnation of the dough.

Hence, at the extruder outlet, a strip of curved cross-section but of uniform thickness across its entire cross-section is obtained, and this strip does not need to be spread by means of a conical metal piece, as is generally the case in conventional extrusion devices, more especially where these devices comprise an annular nozzle orifice or a nozzle orifice in the shape of a sector of a ring.

The extrusion nozzle orifice or orifices located downstream from the diffuser plate will advantageously have the shape of one or more slots.

In the particular case of nozzle orifices in the form of a slot, a curved cross-section strip devoid of longitudinal streaks or surface irregularity will be obtained by virtue of the diffuser plate. In order to ensure that this strip is of uniform thickness over its entire cross-section, it is advantageous to make the nozzle orifice in the form of a slot which has lateral enlargements. This avoids a loss of pressure and a slowing down of the dough flow at the two ends of the nozzle slot, which would lead to a thinning of the edges of the extruded product.

The extrusion nozzle orifices can also have other shapes such as a semi-circular shape, a cruciform shape, a lozenge shape, in which the axis of symmetry of such a nozzle orifice will pass through the centre of area of the orifice. 6 6 61 - 7 The components which constitute the extrusion head are in the form of one block, regardless of whether they are made in one piece or assembled by welding.

The extrusion head may advantageously and alternatively consist of two separate symmetrical components assembled by means of a sleeve and detachable fixing straps. This arrangement greatly facilitates the cleaning of the head and more especially of the nozzle orifice.

The diffuser plate occupies a fixed position in the extrusion head but is not permanently fixed thereto; instead, it is detachably fixed thereto by means of straps.

The extruder in which the extrusion head according to the invention is incorporated may advantageously include, downstream from the nozzle, one or more tension control bars which control the tension in the extruded product and are adjustable and pivotable about a common axis or different axes, for example by being mounted on a pivot shaft or shafts.

This pivotable tension bar, which is located on the end of a drying tunnel at which the heating element of the drying tunnel is disposed, makes it possible to work the extruded strip by raising its side edges and thus ensures perfect uniformity of the product obtained after toasting.

The pivotable tension bars are preferably arranged so that they are staggered one behind the other and are above one another.

Generally, the apparatus of this invention may be used for making any toasted panification product by the extrusion-expansion baking process. These products may for example be special loaves, bread rolls, or toasted slices.

In order that the present invention may be better understood the following description is given, merely by way of example, witlj reference to the accompanying schematic drawings in which:Figure 1 is a schematic view of a manufacturing line which is equipped with the extrusion head of this invention and with a tension bar, is especially suitable for the manufacture of bread slices or toast by the baking-extrusionexpansion process; r Figure 2 is a longitudinal section of an embodiment of the extrusion head according to the invention, which can be fitted onto the end of the extruder; Figure 3 is a front elevation along the arrow A of Figure 2; Figure 4 is a rear elevation along the arrow B of Figure 2; Figures 5, 6 and 7'show another embodiment of the extrusion head according to the invention; Figure 8 is a longitudinal section of an extrusion head according to the invention, in the case where two nozzles are arranged at the end of each screw; Figure 9 is a rear elevation along the arrow C of Figure 8; Figure IO is a front elevation along the arrow D of ,/ ft Figure 8; Figure 11 is a schematic longitudinal section of the 25 end of the extruder, of the type equipped with two heads as illustrated in Figure 8; and Figure 12 is a diagram of the pressure of the flow of dough as a function of the distance from the centre.

The manufacturing line shown in Figure 1 is of the conventional type comprising a metering screw 2, an extruder 3 of the co-rotating twin-screw type, of which at least one of the two screws is equipped with the - 9 extrusion head 4 according to the present invention. The extruder further includes two pivotable tension bars 5 and 6, a drying tunnel 8, a pair of sheeting rollers 9, a rotating knife cutting device 12, a toasting tunnel 13 and packaging devices 14 of a known type which are not shown in detail in the Figure.

Figures 2, 3 and 4 show details of one form of extrusion head 4 in accordance with the invention, and Figure 2 shows the head 4 fitted onto the end of the extruder 3.

The head comprises, upstream from the extrusion nozzle 15, a diffuser plate 16 located in an intermediate position between the tip of one of the screws 17 of the extruder 3 and a pressure equalising chamber 18.

This plate 16 has two sets of channels 20 arranged symmetrically relative to the median plane of the extrusion nozzle 15 all with their axes parallel, and all located at the same distance from the axis of symmetry of the nozzle 15, along circular arcs shown in Figure 4.

Furthermore the diffuser plate 16 has a central channel 19 located along the axis of the extrusion nozzle 15.

Figures 8, 9, 10 and 11 show details of an alternative embodiment of extrusion head 25 which can be fitted onto the end of a co-rotating twin-screw extruder, where two nozzles are located at the end of each extruder screw.

This head comprises, upstream from the two extrusion nozzles 26 and 27, a diffuser plate 29 located in an intermediate position between the tip of one of the two screws 28 of the co-rotating twin-screw extruder and a pressure equalising chamber 31. This diffuser plate 29 has two series of channels 32 arranged symmetrically relative to the plane of symmetry of two nozzle slots 26 1 - 10 and 27 of the nozzle 15 all with their axe;; parallel, and all located at the same distance Irom the axi;; οΓ symmetry common to the two nozzle slots (i.e. the central axis in the horizontal plane of symmetry of the nozzle 15), along circular arcs shown in Figure 9.

In contrast to the plate shown in Figures 2, 3 and 4, this plate does not have a central channel located along the axis of symmetry of the nozzle orifice.

In fact, in the head illustrated in Figures 2 to 4, the presence of this central channel was necessary in order to avoid creating, opposite the single no22le slot, a stagnation zone in the pressure equalising chamber, and thereby to avoid a possible blockage of the nozzle slot by an accumulation of doughy product resulting from this stag15 nation. By contrast, the head of Figures 8, 9, 10 and 11 has the end of each co-rotating screw of the extruder equipped with at least two extrusion orifices. Two dead zones 33a, 33b (Figure 11) form in the pressure equalising chambers 31a, 31b, at the centre of the diffuser plates 29a, 29b, but these dead zones will be occupied by just liberated air previously entrained by the screws, instead of being occupied by dough, so no stagnation whatsoever of the /i doughy material can take place.

In the embodiment shown in Figures 2, 3 and 4, the constituent parts Of the extrusion head are in the form of one block, regardless of whether they are made in one piece or assembled by welding.

The diffuser plate occupies a fixed position in the extrusion head 4, but it is not integral with this head since it is instead fixed thereto by straps or any other fixing means. - 11 In another embodiment shown in Figures 5, 6 and 7, the extrusion head 4 consists of two separate components held together by a sleeve and detachable fixing straps 22. This embodiment greatly facilitates cleaning of the head and especially of the nozzle 15. The plate 16 again occupies a fixed position in the extrusion head, but is not integral therewith.

In all the embodiments, the whole of the apparatus, from the mixer to the extruder outlet, is heated by induction (Foucault current) so as to reach the appropriate temperatures for the mixture to be extruded.

The pulverulent constituents of the mixture to be extruded are mixed in a milling mixer (not shown) before being introduced into the metering screw 2 of the extruder 3; at the same time the amount of water required is supplied by means of a metering pump (not shown). Malaxating discs (not shown) are located, in a manner which is in itself known, upstream from the screws of the extruder 3 and permit good mixing of the pulverulent products and the water, and thus ensure uniform hydration of the combined constituents of the product to be extruded.

The pitch of the screw of the extruder decreases, again in a manner which is in itself known, from the inlet towards the outlet of the apparatus, so as gradually to increase the pressure on the product to be extruded. Counter-threads (threads having a converse pitch and with flights broken) of a conventional type (not shown) are located downstream from the screws and upstream from the pressure equalisation chamber of the extruder, so as to avoid stagnation of the products, which would cause irregularities in the extruded product. 6 667 - 12 The stream of dough or other similar material is forced, by the rotary movement imparted to it by the screw 17 or by the two co-rotating extruder screws 28a and 28b, into the space located between the male cone which forms the end of the or each screw and a female cone of the diffuser plate 16, 29a_or 29b. In the case shown in Figure 11, this space constitutes for each screw the compression chamber 30a, 30b respectively.

The tips of the screws thus impart a certain pressure to the doughy product in the region of this compression chamber, the isobaric curves being concentric circles centered on the axis of the respective screw.

The plot of pressure as a function of the radial distance, shown in Figure 12, enables this phenomenon to be better understood.

The channels of the diffuser plates 29a, 29b, located at I, J, K and L all receive a doughy product which is at a pressure of about 150 bars. Since the path lengths travelled by the strands of dough which pass through these channels are identical, the pressure losses are also identical for these four strands. At 1^, J^, and L·^, these strands are subjected to the same pressure and thus have the same speed. On leaving the channels of the plate, all the strands I, J, K and L again merge together and pass through the respective nozzle slots 26a, 27a, 26b and 27b, resulting in the production of perfectly flat strips which exhibit neither longitudinal streaks, nor surface irregularities, nor sag.

The rotary movement imparted to the dough by the screws is thus arrested and converted to a linear movement, and the linear speed imparted to each strand of dough issuing from the channels of the diffuser grid is the same for all the strands. 6 6 6 7 - 13 The particular arrangement of the nozzle slots furthermore makes it possible to guarantee that the strip extruded from nozzle 26a, 26b, 27a_ or 27b has a uniform thickness over its entire width. As can in fact be seen from the nozzles shown in Figure 10, the slots which form the two nozzle slots 26 and 27 are provided with lateral enlargements 34 and 35. This arrangement makes it possible to avoid a localized pressure loss and a slowing down of the dough flow at the two ends of the nozzle slot, which would otherwise result in thinning of the edges of the extruded dough.

In fact the nozzle extrusion slot, for example the nozzle slot 27, receives the strands of dough issuing from the ten channels 32 arranged in an arc of a circle across the upper part of the diffuser plate shown in Figure 9.

As has already been mentioned, these strands, all issuing at the same speed from the channels 32, merge together again in the pressure equalising chamber 31 before being extruded through the nozzle slot 26. When they pass through the nozzle slot, these ten strands all have an identical coefficient of friction with the upper and lower walls of the nozzle slot, if, in contrast, this nozzle slot had a uniform depth, the two strands of dough located in the outer lateral positions would additionally undergo friction against the end walls of the nozzle slot and a pressure drop, and slowing down at the two ends, would this occur .

It is to avoid this disadvantage that the passage of the strands located in the outer lateral positions is assisted by equipping the two ends of each nozzle slot 26, (Figure 10) with lateral enlargements 34 and 35, which ensure that the two strands in the outer lateral positions 6 6 6^ - 14 have a passage cross-section larger than that of the other strands.

The next operations subsequent to the extrusion are shown schematically in Figure 1. The extruded dough next issues through the nozzle 15 in the form of a continuous strip 24 which is still doughy and is curved upwardly convex as viewed in transverse cross-section. It then passes under the tension bar 6 and is immediately taken up by the conveyor belt of the drying tunnel 8 while the pivotable tension bar 5 is in the low position (shown in broken lines in Figure 1). The bar 5 is then raised, by pivoting it on shaft 6 to bring it to an operating position close to the vertical, this operating position being capable of variation in accordance with the desired tension which will itself depend on the plasticity of the doughy strip.

The strip 24 then follows the path shown in solid lines in Figure 1.

Where it is not considered necessary to subject the strip to any tension whatsoever on leaving the extrusion head 4, the tension bars 5, 6 will be pivoted so as to bring them into a position level with shaft 7.

After passing through the infra-red heated drying tunnel 8, the strip passes between the two sheeting rollers 9 and is then cut into slabs of the desired size by the rotating knife 12. The cut slabs then pass through the toasting tunnel 13. Finally, they are cooled on the conveyor belt, by the action of a stream of cold air, before being conditioned and packaged in the conventional manner.

Claims

1. An extrusion head for a screw extruder, said head comprising a nozzle having at least one extrusion orifice symmetrical (as hereinbefore defined) about a single axis of the nozzle orifice or an axis common to the nozzle orifices; a diffuser plate disposed so as to be placed between the nozzle and the tip of the screw of an extruder in which the head is to be mounted; and a pressure equalisation chamber between the diffuser plate and the nozzle; wherein the side of the diffuser plate nearer said pressure equalisation chamber has a planar face and the opposite side presents a conical recess whose taper angle is intended to conform to that of the tip of the extruder screw of said extruder, and wherein the diffuser plate is provided by two sets of axially parallel ducts which are all situated at the same distance from the said axis of symmetry and are disposed symmetrically with respect to a median plane (as hereinbefore defined) of said nozzle which includes said axis of symmetry, along two opposed circular arcs having the same radius.

2. An extrusion head according to claim 1, wherein the diffuser plate has a central channel located along said axis of symmetry of the extrusion nozzle.

3. An extrusion head according to claim 1, wherein said nozzle has two extrusion orifices and said median plane is the plane of symmetry passing between the two extrusion nozzle orifices.

4. An extrusion head according to any one of claims 1 to 3, wherein the or each extrusion orifice is in the form of a slot.

5. An extrusion head according to any one of claims 1 to 3, wherein the or each extrusion orifice has a semicircular, cruciform or lozenge shape in cross section. - 16

6. An extrusion head substantially as hereinbefore described with reference to, and as illustrated in. Figures 2 to 4, 5 to

7. , 8 to 10 or Figure 11 of the accompanying drawings. : 5 7. An extrusion apparatus incorporating an extrusion head according to any one of claims 1 to 6, and including: heating means downstream from the nozzle; and between the nozzle and the heating means, a tension-inducing guide comprising one or more tension bars which are pivotable 10 about one or more axes.

8. An extrusion apparatus according to claim 7, wherein the tension-indueing guide comprises two pivotable tension bars arranged staggered one behind the other along the direction of extrudate movement and one above the 15 other.

9. . A process for the manufacture of foodstuff products comprising extruding doughy material using the apparatus of any one of claims 1 to 8.

10. A process according to claim 9, wherein the 20 foodstuff product comprises special bread loaves or toasted flat panification products, obtained by expansion and baking after the extrusion step.