DE10320073A1 - Strand forming nozzle for viscoelastic materials (outlet widening) - Google Patents

Abstract

The invention relates to a nozzle arrangement 1 for the formation of strands for viscoelastic masses, in particular polymers, dough masses, etc., with a plurality of identical nozzle channels 2 arranged parallel to one another, each of which extends through the nozzle arrangement 1 along the axial conveying direction F of the mass. According to the invention, the outlet area is widened from the inside of the nozzle channel to the outlet opening over a length L¶A¶ along the axial conveying direction F.

Description

The The invention relates to a nozzle arrangement and a method for strand formation for viscoelastic Masses according to the preamble of claim 1 or the preamble of claim 17.

nozzle arrangements for strand formation for viscoelastic Masses, in particular polymers, dough masses, etc., are known per se. As a rule, they are arranged in parallel with several similar nozzle channels equipped, through the nozzle from one inlet opening each one outlet opening each extend, the respective nozzle channels each along the axial conveying direction the mass an inlet area at the upstream end of the nozzle channel and an outlet area at the downstream end of the nozzle channel exhibit. The inlet openings are arranged adjacent to each other.

at the strand formation of viscoelastic materials, e.g. doughs, Polymers, these materials are reshaped. The reshaping, however, requires a flow of the material. At certain points the material also tear. Due to the elastic properties of the viscoelastic Materials occur in deformation and crack formation in one such viscoelastic material also mechanical material tensions that propagate into the formed material. Then this can after reshaping in the reshaped material to further, apparently cause spontaneous deformations. In this context, one often speaks of "shape memory" because it comes from the forming device escaping material with its mechanical material tensions gives the impression of "remembering" a previous form and returning to it want. In the strand formation of pasta or polymers by means of nozzle arrangements this can cause a ripple the one emerging from the individual nozzle channels strands to lead. The On the one hand, tensions arise in the division and distribution of the material on the various nozzle channels and on the other hand with the Elongation of the material entered into the material within the nozzle channels. The due to the division and division of the material in the Material stresses are likely due to their asymmetry in terms of of the strands formed the greatest disruptive influence to have. However, due to the material tensions and the resulting existing trend of strands to change direction in the nozzle channels too an asymmetrical wall friction occur that this material stress in certain circumstances reinforced. However, such strands of viscoelastic materials tend to their exit from the nozzle assembly to the mentioned Crimp.

Furthermore must be relative when forming strands from viscoelastic materials a lot of energy or a high pressure difference on the nozzle arrangement to distribute the material, distribute it on the shaping nozzle channels and finally to press through the shaping nozzle channels, the material is stretched. In other words, the usual shaping nozzle arrangements have viscoelastic materials have a relatively high nozzle resistance for such Materials. This is particularly problematic with dough masses, because here in Contrary to classic polymers like polyesters or rubber - only limited the possibility consists of an at least local, if predominantly only the surface of the Limited temperature increase in the nozzle arrangement their nozzle resistance and reduce the stresses introduced into the material.

The The invention is based, such material stresses the task in viscoelastic materials when they are transformed into material strands minimize as well as the for the strand formation necessary Energy expenditure or the corresponding necessary pressure difference, i.e. the nozzle resistance, to lower.

This object is achieved according to the invention in the nozzle arrangement described at the outset in that the outlet area from the inner area of the nozzle channel to the outlet opening is expanded over a length L _A along the axial conveying direction F.

If a viscoelastic material, e.g. a polymer material or a batter, etc, on the nozzle channel the inventive nozzle assembly occurs, the product stream is divided into several partial streams pressed through the several nozzle channels. In the material occur when entering the nozzle channel and during the Forming tensions in the inlet area. While cutting on cutting edges and / or during a stretch built up in the nozzle channels and then not yet relaxed tensions in the material practically completely relaxed in the widening outlet area. So leave with this nozzle geometry the several small product strands the respective nozzle channels are practically stress-free. The widened outlet area enables one Relaxation of the product in both axial and radial Direction. As a result, corrugations ("shark skin") on the surface of those emerging from the nozzle channels viscoelastic product strands avoided.

Advantageously, the outlet area is from the inner area of the nozzle channel to the outlet opening over a length L _A along the axial conveyor Direction F expanded like a bell, wherein preferably the widening angle of the widened widening along the axial conveying direction, which is measured between the axial conveying direction and the inner wall of the channel outlet region, increases continuously. In particular, the increase in the widening angle along the axial conveying direction can increase continuously, for example the widening angle increasing from 0 ° in the interior of the nozzle to 90 ° at the downstream end of the nozzle body. Here, the widening in longitudinal section can follow, for example, an arc of a circle whose radius of curvature R _{A is} greater than the radius R _{K of} the interior of the nozzle channel. This curved, widened outlet area replaces the edge of conventional outlet openings by a curved, continuous transition from a vertical tangent in the interior of the nozzle channel to a tangent, which in an extreme case is horizontal, at the downstream end of the outlet area.

In a special embodiment, the inner wall of the nozzle channel in the outlet area can have a higher surface roughness than the rest of the inner wall of the nozzle channel over a length L _R along the axial conveying direction. As a result, the surface of the product can be specifically influenced by the choice of the roughness and / or the material of the roughened area.

The axial length L _{R of} the rough region is therefore preferably less than the axial length L _{A of} the outlet widening, less than the axial length L _{E of} the inlet widening and less than the axial length L _{S of} the cutting edges.

However, it is also advantageous to provide a plurality of successive roughened areas over large axial partial areas of the nozzle channels, each of which fulfills the condition v _F > L _R / T _RELAX . In this way, the interplay of wall adhesion and wall gliding (sticking / sliding effect) can be influenced. The periodicity or the spatial frequency of the rough axial wall sections of length L _R and the flow velocity allow more wall breaks to be triggered per unit of time, ie the alternating relatively rough and relatively smooth wall sections result in a higher-frequency adhesion / Forced sliding effect. This has the advantage that no such high material tensions can build up and thus there are little or no cracks on the product.

at an advantageous embodiment is between two at the upstream end of the nozzle body adjacent inlet openings one parallel to the axial conveying direction F extending partition arranged on its upstream End has a cutting edge.

If a viscoelastic material, e.g. a polymer material or a dough mass, etc., impinges on the nozzle arrangement according to the invention the one in the housing along the conveying direction F zoom out Product stream divided into several partial streams one of which flows through one of the several nozzle channels. By the sharp cutting edges become the product flow brought up to the nozzle arrangement cut into several partial streams as soon as it entered the several nozzle channels. Because each of the cutting edges only has a very small area of attack for the product represents a very large force locally on the cutting edge on the impinging viscoelastic product. Along the cutting edges This creates a locally concentrated shear force, which is the product divided. But before the viscoelastic approach to the cutting edges If the product tears off at the cutting edges, it deforms until Reaching its breaking stress and elongation at break, whereby in potential energy is stored in the viscoelastic material, which is passed on to the several partial streams. Overall, however, are those in the division and distribution of the viscoelastic material by means of cutting edges on the several Nozzle channels in the material registered voltages significantly lower than a conventional one Nozzle arrangement without sharp cutting edges, so that even when distributing the nozzle arrangement according to the invention brought up viscoelastic material on multiple strands has much less content in the shape memory of the viscoelastic material, causing the tendency to deform of product strands (Crimp, etc) when exiting the nozzle channels as well the nozzle resistance is significantly reduced. These positive effects are particularly pronounced with pasta nozzle arrangements.

Preferably is the upstream of the inlet area of each of the neighboring ones Inlet openings arranged Area completely parallel to the axial conveying direction surrounding partition walls, whose upstream end is designed as a cutting edge is. As a result, the material entering the respective nozzle channels is cut practically everywhere, where it still has to be cut up, so that extremely little tension in the material can be entered.

The cutting edges can form an angle other than 90 ° to the axial conveying direction of the material. For example, they can run at an angle of approximately 30 to 60 ° to the material's direction of conveyance. However, an acute angle is preferred. This is because the more acute the angle to the conveying direction, the greater the length L _S, measured along the conveying direction, of the region in which the material is cut in the radial direction perpendicular to the conveying direction, for example from the outside radially radially inwards. The radially outwardly flowing areas of the material are then cut, for example, first, while the radially inwardly flowing areas of the material are cut later. Then, however, the radially outer areas already had time to reduce their stresses that were entered into the material during cutting. Through the cutting process, a total of fewer tensions are thus introduced into the material distributed over the nozzle channels than would be the case with cutting edges running at right angles to the direction of flow (simple "cutter" principle).

It is also advantageous if the inlet area of the nozzle channels is widened from the inner area to the inlet opening opposite to the axial conveying direction F along a length L _E , the widening angle of the inlet widening measured between the axial conveying direction and the inner wall of the channel inlet area in the range from 5 ° to 45 °, but preferably in the range of 8 ° to 25 °. It is particularly simple in terms of manufacturing technology if the widening angle from the inner region to the inlet opening is constant, ie if there is a cone-like inlet widening. Thus, even with relatively high conveying speeds of the material, a "gentle" expansion, that is sufficiently slow for the viscoelastic material, can be achieved by the nozzle arrangement, that is to say that the relaxation time of the viscoelastic material is smaller than the time taken for the material to expand in the inlet widening.

Conveniently, is the nozzle arrangement designed so that the nozzle channel along its entire length a circular Cross section. The boundary conditions are the same everywhere on the walls, what a uniform, if possible leads to symmetrical elongation.

A compact design of the nozzle arrangement is characterized in that the axial length of the channel inlet area between 50% and 80% of the total length of the nozzle channel is.

The interior walls of the nozzle channel consist of Teflon or similar at least in some areas Material to ensure the adherence of the viscoelastic material to the interior walls and to minimize sliding friction on it.

In the process for strand formation for the viscoelastic masses mentioned, in particular polymers, dough masses, etc., using the nozzle arrangement described above, the viscoelastic mass is pressed through it by means of a pressure gradient Δp between the upstream end and the downstream end of the nozzle arrangement. According to the invention, the pressure drop Δp is selected such that the flow velocity v _{F of} the viscoelastic mass along the conveying direction F in a respective axial partial region of the nozzle arrangement in which at least part of the material deformation required for the strand formation takes place, the condition v _F < L / T _{RELAX is} fulfilled, where T _{RELAX is} the relaxation time of the viscoelastic mass and L (= L _S , L _E , L _A ) is the axial length of the respective axial partial area of the nozzle arrangement.

This ensures that in the individual forming steps of the viscoelastic material necessary for strand formation, such as cutting along a length L _S at the cutting edges, stretching along a length L _{E of} the inlet widening and the final relaxation along the length L _A of Spout widening, the material always has enough time to relax, so that when it emerges at the end of the nozzle arrangement according to the invention, the material has practically no tension.

In order to make optimal use of the roughened axial partial area mentioned above, in the method according to the invention the flow velocity v _{F of} the viscoelastic mass along the conveying direction F is matched with the length L _{R of} the roughened axial partial area of the nozzle arrangement such that the condition v _F > L _R / T _{RELAX is} fulfilled, where T _{RELAX is} the relaxation time of the viscoelastic mass and L _{R is} the axial length of the roughened partial area. As already mentioned above, this allows the surface of the product to be specifically influenced by the choice of the roughness and / or the material of the roughened area.

Further Advantages, features and possible uses of the invention result not to be construed restrictively from the following description preferred embodiments based on the drawing, whereby:

1 is a sectional view through a nozzle arrangement according to the invention along the axial product conveying direction F;

2 a plan view of the inventive nozzle arrangement of 1 along the product conveying direction F;

3 is a sectional view through a nozzle channel according to the invention along the axial product conveying direction F;

4 is a sectional view through a further nozzle duct according to the invention along the axial product conveying direction F;

5 a sectional view through a Dü is the prior art vertical channel along the axial product conveying direction F; and

6 a sectional view through another nozzle channel of the prior art along the axial product conveying direction F.

1 is a sectional view through a nozzle arrangement according to the invention specially designed for dough for noodle production 1 along the axial product conveying direction F. The total of four nozzle channels 2 having nozzle arrangement 1 (please refer 2 ) is in a cylindrical housing 7 accommodated. An inlet opening 3 is located at the upstream end of each nozzle channel 2 , and an outlet opening 4 is located at the downstream end of each nozzle channel 2 , Which is at the inlet opening 3 subsequent inlet area 2a every nozzle channel 2 is widened like a cone during the outlet area 2c is cylindrical. The expansion angle α (see 3 ) is about 10-20 °. At the upstream end of the nozzle arrangement 1 there are four partitions 5 (please refer 2 ) that run parallel to the axial conveying direction F and the area upstream from the inlet openings 3 divide into four sections, each upstream from an inlet opening 3 are located. The edges of the partition walls pointing opposite to the axial conveying direction F. 5 are each as an inclined cutting edge 5a formed from the inner wall of the housing 7 extends both radially inwards and in the conveying direction F.

2 is a top view of the nozzle assembly according to the invention 1 of 1 along the product conveying direction F (see 1 ). You can see the four nozzle channels 2 with their respective conical inflow area 2a as well as that of the cylindrical housing 7 radially inwardly extending partitions 5 covering the area above the nozzle arrangement 1 divided into four sections. The four sharp cutting edges 5a extend diagonally opposite to the conveying direction F.

If so, as in 1 schematically indicated with the flow profile V (r), a viscoelastic material, such as a polymer material or a dough mass, etc., on the nozzle arrangement according to the invention 1 strikes, that is in the housing 7 Product stream led along the conveying direction F is divided into four partial streams, one of which flows through one of the four nozzle channels 2 flows. Through the sharp cutting edges 5a the nozzle assembly 1 Product flow introduced before entering the four nozzle channels 2 cut into four streams. Because each of the cutting edges 5a only a very small contact surface on the product opposite to the conveying direction F acts on the cutting edge 5a locally a very large force on the cutting edge 5a impinging viscoelastic product. Along the cutting edges 5a there is a locally concentrated shear force that breaks up the product. But before that to the cutting edges 5a If the viscoelastic product tears off at the cutting edge, it deforms until it reaches its breaking stress, whereby potential energy is stored in the viscoelastic material, which is passed on to the four partial flows and leads to partial relaxation in these four partial flows before further deformation or Reshaping of the viscoelastic material in the four product sub-streams takes place when the material enters the respective nozzle channels 2 entry. Here, too, occur in the material as it enters the nozzle channels 2 and during the forming in the respective inlet areas 2a Tensions on. However, these are less than at the cutting edges 5a and do not lead to product demolition.

Compared to conventional nozzle arrangements without cutting edges and without a conical widening with an expansion angle according to the invention of approximately 10-20 °, the design of the cutting edges according to the invention reduces 5a of the partitions 5 and the lead-in areas 2a of the nozzle channels 2 the extent of that in the nozzle arrangement according to the invention 1 conveyed tensions and formed in the material formed as well as the flow resistance of the nozzle arrangement 1 ,

In the nozzle arrangement according to the invention 1 namely, the transformation of a large to four small product strands associated with the build-up of material stresses takes place essentially in two steps. In a first step, the large product strand at the cutting edges 5a cut into four small strands. In a second step, the four partial strands are then in the conical inlet areas 2a stretched. Immediately after the first step (cutting on the cutting edges 5a ) and before the second step (stretching in the inlet area 2a ) there is at least partial relaxation (stress reduction, reduction of potential energy) in the material while it is on the partition walls 5 slides. If the product is in the conical inlet areas 2a is stretched, material tensions also build up, whereupon in the subsequent cylindrical outlet areas 2c again an at least partial relaxation takes place. The viscoelastic material, which is divided into four small product strands, leaves the outlet openings practically stress-free 4 of the nozzle channels 2 , so that there are no noteworthy deformations (eg ripples) of the four emerging product strands. Because of the cutting edges, a product is torn off at much lower product shear forces, too the flow resistance of the nozzle arrangement according to the invention 1 significantly reduced.

The nozzle arrangement according to the invention 1 thus enables operation with a lower pressure difference than conventional nozzle arrangements, ie a lower pressure drop in the product along the nozzle arrangement 1 and with a practically complete "deletion" of the shape memory in the emerging partial strands of the product.

3 is a sectional view through a nozzle channel according to the invention also specially designed for dough for noodle production 2 along the axial product conveying direction F. This nozzle channel 2 can replace the in 1 nozzle channels shown 2 be used. Instead of the cylindrical outlet area 2c of the nozzle channel 2 the 1 closes here downstream of the inlet area 2a initially a relatively short cylindrical interior 2 B and then a bell-shaped expanded area 2c on. This run-out area 2c replaces the edge of the outlet opening 4 (please refer 1 ) by a curved continuous transition from a vertical tangent in the interior 2 B of the nozzle channel 2 to a horizontal tangent at the downstream end of the outlet area 2c , The radius of curvature R _{A of} the outlet widening increases towards the outlet opening 4 continuously, ie there is a bell-like widening with the outlet opening 4 decreasing curvature.

If so, as in 1 described, a viscoelastic material, such as a polymer material or a dough, etc., on the nozzle channel 2 the nozzle arrangement according to the invention 1 strikes, the product flow divided into four partial flows is through the four nozzle channels 2 pressed (see 1 and 2 ). As in 1 also occur in the material when entering the nozzle channel 2 and during forming in the lead-in area 2a Tensions on. During the first step (cutting on the cutting edges 5a ) and / or during the second step (stretching in the inlet area 2a ) built up and not yet relaxed tensions in the material also become the widening outlet area 2c practically completely relaxed. This means that even with this nozzle geometry, the four small product strands leave the nozzle channels practically stress-free 2 , A particular advantage of the expanded outlet area 2c but now consists in the fact that it enables the product to relax both in the axial and in the radial direction. This can cause corrugations ("shark skin") on the surface of the nozzle channels 2 Avoid emerging viscoelastic product strands, such as those with a sharp-edged outlet opening 4 at a cylindrical outlet area 2c (please refer 1 ) practically always occur.

The axial length of the in 1 and in 3 shown relaxation areas, essentially by the axial length L _{S of} the cutting edge 5a and the axial length L _{A of} the outlet area 2c are formed and the maximum flow velocity v _{F of} the viscoelastic mass along the product conveying direction F is preferably adapted to the relaxation time T _{RELAX of} the product material such that the material has enough time to pass through the respective relaxation areas in order to reduce the stresses built up in it beforehand, ie V _F × T _RELAX <L _S or V _F × T _RELAX <L _A.

If the nozzle channels 2 with the conical inlet area 2a and the bell-like outlet area 2c the 3 in the with cutting edges 5a equipped nozzle arrangement 1 are used, this not only enables a lower pressure drop in the product along the nozzle arrangement 1 and a practically complete "deletion" of the volume shape memory in the emerging partial strands of the product, but also a "deletion" of the surface shape memory of these product strands.

Another advantage of the bell-like outlet area 2c The nozzle channels is that there is a smooth transition from the inside of the nozzle channels 2 present flow with a parabolic velocity profile to the outside of the nozzle channels 2 existing "flow" with a constant speed profile, ie the moving strand allows. This can cause cracking on the surface of the nozzle channels 2 emerging strands can be prevented.

4 is a sectional view through a further nozzle channel according to the invention, also specially designed for dough for noodle production 2 along the axial product conveying direction F. The is at the inlet opening 3 subsequent inlet area 2a of the nozzle channel 2 is widened like a bell during the discharge area 2c is cylindrical. The radius of curvature R _{E of} the inlet widening is at the inlet opening 3 smallest and increases with increasing depth of penetration along the nozzle channel 2 to to tangentially into the cylindrical outlet area 2c proceed.

Similar to the bell-like outlet area, the bell-shaped inlet area carries 2a to a gentle treatment of the product. Abrupt changes in speed, which usually lead to cracks in the product, are avoided by the gentle acceleration of the product in the bell-shaped inflow area 2a , so that here too a smooth transition from a flow with a constant speed profile upstream of the nozzle channels 2 to a current with parabolic speed profile inside the nozzle channels 2 he follows.

5 is a sectional view through a nozzle channel 2 of the prior art along the axial product conveying direction F. The nozzle channel is from its inlet opening 3 up to its outlet opening 4 designed as a cylinder with a constant radius R _K.

6 is a sectional view through another nozzle channel 2 of the prior art along the axial product conveying direction F. The inlet area 2a has a much larger expansion angle α than the invention and has a much shorter length L _E than in the invention.

1

nozzle assembly

2

nozzle channel

2a

intake area of the nozzle channel

2 B

interior of the nozzle channel

2c

discharge area of the nozzle channel

3

Inlet opening of the nozzle channel

4

Outlet opening of the nozzle channel

5

partition wall

5a

cutting edge

7

casing

F

conveying direction

L _S

axial Expansion of the cutting edge

L _E

axial Expansion of the inlet widening

L _A

axial Extension of the outlet widening

R _K

radius of curvature of the nozzle channel cross section

R _E

radius of curvature the enema widening

R _A

radius of curvature the spout widening

v _F

flow rate of the viscoelastic material

α

expansion angle

Claims (18)

Nozzle arrangement for strand formation for viscoelastic masses, in particular polymers, dough masses, etc., with at least one nozzle channel extending through the nozzle from an inlet opening to an outlet opening, which along the axial conveying direction of the mass through the nozzle has an inlet region at the upstream end of the nozzle channel, an inner region in the Has inside the nozzle and an outlet area at the downstream end of the nozzle channel, characterized in that the outlet area is widened from the inside of the nozzle channel to the outlet opening over a length L _A along the axial conveying direction F. nozzle assembly according to claim 1, characterized in that between the axial conveying direction and the expansion angle measured on the inner wall of the channel outlet area the widening of the outlet increases continuously along the axial conveying direction. nozzle assembly according to claim 1 or 2, characterized in that the increase of the widening angle increases continuously along the axial conveying direction. nozzle assembly according to claim 3, characterized in that the widening angle from 0 ° in Inside the nozzle up to 90 ° am downstream end of the nozzle body increases. nozzle assembly according to claim 4, characterized in that the expansion in longitudinal section follows an arc. Nozzle arrangement according to claim 5, characterized in that the radius of curvature R _{A of} the circular arc of the widening is greater than the radius R _{K of} the interior of the nozzle channel. Nozzle arrangement according to one of the preceding claims, characterized in that the inner wall of the nozzle channel in the outlet area has a higher surface roughness than the rest of the inner wall of the nozzle channel over a length L _R along the axial conveying direction. Nozzle arrangement according to claim 7, characterized in that the axial length L _{R of} the rough area is less than the axial length L _{A of} the outlet and less than the axial length L _{E of} the inlet. nozzle assembly according to one of the preceding claims, characterized in that they have several mutually parallel nozzle channels of the same type with each other adjacent inlet openings and that at the upstream end of the nozzle body between two adjacent ones inlet openings one parallel to the axial conveying direction F extending partition is arranged on its upstream End has a cutting edge. nozzle assembly according to claim 9, characterized in that the upstream arranged from the inlet area of each of the adjacent inlet openings Area completely parallel to the axial conveying direction extending partitions surround is formed, the upstream end of each as a cutting edge is. nozzle assembly according to claim 9 or 10, characterized in that the cutting edges one different from 90 ° Angle to the axial conveying direction Form F. Nozzle arrangement according to one of the preceding Henden claims, characterized in that the inlet area is widened conically from the inner area to the inlet opening opposite to the axial conveying direction F along a length L _E , the widening angle of the inlet widening measured between the axial conveying direction and the inner wall of the channel inlet area in the range from 5 ° to 45 °, in particular in the range from 8 ° to 25 °. nozzle assembly according to claim 12, characterized in that the widening angle from Inside area to the inlet opening is constant. nozzle assembly according to claim 12 or 13, characterized in that the nozzle channel along its entire length a circular cross section Has. nozzle assembly according to one of the preceding claims, characterized in that the axial length of the duct inlet area between 50% and 80% of the total length of the Nozzle channel is. nozzle assembly according to one of the preceding claims, characterized in that the inner walls of the nozzle channel consist of Teflon at least in some areas. A method for strand formation for viscoelastic masses, in particular polymers, dough masses, etc., using a nozzle arrangement according to one of Claims 1 to 16, in which the viscoelastic mass is pressed through it by means of a pressure gradient Δp between the upstream end and the downstream end of the nozzle arrangement characterized in that the pressure drop Δp is chosen such that the flow velocity v _{F of} the viscoelastic mass along the conveying direction F in the interior of a nozzle channel fulfills the condition v _F <L _A / T _RELAX , where T _{RELAX is} the relaxation time of the viscoelastic mass and L _A the axial length of the outlet widening is. A method according to claim 17, characterized in that the flow velocity v _{F of} the viscoelastic mass along the conveying direction F in the interior of a nozzle channel fulfills the condition v _F > L _R / T _RELAX , T _RELAX the relaxation time of the viscoelastic mass and L _R the axial length of the rough area.