MXPA00011775A - A method and apparatus for extrusion of expanding water holding products such as foodstuff particles or feeding stuff pellets - Google Patents

Abstract

In the extrusion of feed-stuff pellets and relevant consumer products, the extruded products are subject to expansion as a result of the boiling of their water content when the products, after being exposed to high extrusion pressure and a correspondingly high temperature, are discharged to the atmosphere through the extrusion nozzles. Such an expansion is directly aimed at, but it is desirable to be able to control it, which is difficult by adjustment of the ordinary process parameters. With the invention it has been found that the expansion which arises can be controlled in a highly constant manner, i.e. by carrying out the extrusion into a closed chamber in which an over-pressure of a few bar is established in relation to the atmospheric pressure, and which can be regulated. The extrusion products can be continuously discharged from this chamber, or they can be discharged intermittently in portions. The over-pressure moderates the momentary development of steam in the extruded product, and the product is given time to stabilise before being discharged to atmospheric pressure, so that the subsequent further development of steam influences the structure of the product only to a minor degree.

Description

A METHOD AND APPARATUS FOR EXTRUSION OF PRODUCTS OF RETENTION OF EXPANSION WATER AS PARTICLES OF FOOD OR AGGLOMERATED FOOD SUBSTANCES This invention relates to a product extrusion method as specified in the introductory clause of claim 1. In conjunction with the manufacture of extruded products, it is essential that the physical dimensions of the extruded product remain constant to the desired dimensions. This applies to the production of "solid" non-expanded products where expansion is to be avoided, especially in the production of expanded products where the dimensions of the product are greater than the opening (s) of the nozzle, where the aim is to achieve a specific increase in the dimension in relation to the size of the nozzle. The problem arises by itself mainly in the elaboration of expanded products where the expansion is normally aimed at in order to ensure specific characteristics, such as viscosity (fish feed), subsidence characteristics (specifically low feed sinking velocity). fish), characteristics of liquid absorption (fish food), subsidence characteristics (specifically low speed of sinking of fish food), characteristics of liquid absorption (fish food, pet food, food substances), specific low density, constant (pet food, snacks, breakfast products), constant crimp ( fish foods, pet foods, food substances), constant physical form (all products). Ensuring the aforementioned constancy / controllability of the expansion causes major problems with all extrusion systems. The degree of expansion of the extruded product in the extrusion plant depends on conditions such as: Compositions of raw materials. Characteristics / quality of raw materials. Parameters of the extrusion process: * Dosage of the individual ingredients: Mixing of flour. Liquids Steam.

* Cooling / heating of worms / linings. * Speed of rotation of the worm transporter. 5 Configuration of the extruder worm conveyor. Configuration of the extruder nozzle. State of wear of the parts of the process. Especially, the variations in the raw material and the state of wear of the extruder worm conveyor and linings cause variations in production that are difficult to predict. 15 Depending on the conditions that lead to variations in the product, it can be particularly difficult to ensure (via automatic control and regulation of the process, or manually) that the determined products correspond to the product specifications with reasonable tolerance. During the extrusion process, products such as those described above that contain starch raw materials as consequence of a process temperature of 100- A? * MrifataWMÍ ^ Jk ^, ^^ h¿M ^^ Jk 200 ° C, a humidity of 10-35% of H20 and a pressure of 2-80 bar in the extruder worm, will typically gelatinize and convert to a plastic / elastic liquid type shape. In its passage through the arrangement of nozzles of the extruder, the product will move from the pressure of the process (2-80 bar) to atmospheric pressure, which normally takes place the cut of the product in the desired length. The pressure drop through the nozzle plate and the energy content of the product will result in a momentary evaporation of a part of the water content of the product in the opening of the extruder nozzles. The evaporation of water forms steam pockets in the plastic / elastic mass, whereby the product expands. The melting at the temperature caused by the momentary evaporation results in a hardening of the product in a physically and permanently firm form. Normally the expansion of the product stops, when the evaporation vapor pressure in the steam bags achieves an equilibrium in relation to the elasticity of the mass, and / or the further development of the steam flow as a consequence of the energy consumption comprised in the evaporation, resulting in a temperature drop at a temperature corresponding to the boiling point of the mass and / or when all the walls in the vapor pockets explode as a consequence of the internal vapor pressure, and the pressure in the bags normalizes to this mode, whereby the driving force for additional expansion disappears.

THE INVENTION It is characterized for all known extrusion systems and for the production of food substances, foods or the like that the nozzle and the cutting system of the extrusion process operate under constant pressure; normally atmospheric pressure possibly light sub-pressure; created by associated suction systems or pneumatic transport systems. To overcome or minimize the expansion control problems specified above it has been found by the present invention that advantageous extrusion can be effected in a pressure chamber on the exit side of the nozzle plate, in which It forms the product, it is cut and it is stabilized to a permanent shape (expansion degree) before it is discharged at atmospheric pressure. By regulating the working temperature of the pressure chamber it is possible to regulate the boiling point for the mass in the mouth of the nozzle arrangement, whereby the development of the vapor caused by the extrusion can be controlled. A corresponding possibility is provided to control the driving force that causes the expansion of the product. According to the invention, the new method will be able to be used for the optimization of the degree of expansion and the capillary structure in products of all known types of extruders (single worm, double worm, dry extruders, cooking extruders with / without preconditioning). The invention will make it possible to use raw materials in the extrusion process which to date have been avoided due to the control problems related to the raw materials. This situation results in smaller needs for (dependence on) scarce resources / expensive ingredients, and the possibility to a greater degree of composing containers (raw material compositions) on a basis of nutritional evaluation / eos to, with less consideration than is put to the performance of the recipient / mat er the premiums from the point of view of expression. According to the invention, the method will make it possible to increase the capacity of the extruders that are assembled with this equipment, since the practical, exploitable capacity of many plants is nowadays restricted by the limit of contollability of the physical form of the product. . The invention, which relates to a method and a complete plant and an aggregate for construction in existing extruders, is illustrated in the drawing, which is a schematic view of an exemplary embodiment of the invention. On the left there is an extruder 2 with a funnel or delivery duct 4 for the material to be formed in the desired granular product, and with an extruder worm 6 for transporting the material towards a nozzle unit 8 with channels 10 of nozzle through which the material is pressed into a chain. In a completely similar way as a picador ^ i¡I? j U ^ i? ? ¡? meat, in front of the nozzle unit 8 there is provided a rotating blade 12 which is driven by a rotor 14, the result being that the chains are continuously cut in the formation 5 of the agglomerates that can simply fall downwards in an arrangement of transportation or collection, adequate. According to the invention, opposite the dispensing end of the nozzle unit 8 is a box element 16 and connects to the edge of the nozzle unit in a hermetic manner, and that it also has a sealing fitting sleeve 18 for the drive shaft of the motor 14. the box member 16 has a part of the bottom in the form of a rotary gate wheel 20 with gate recesses 22, since there is thus also a sealing seal of the box element, which here extends downwards as a discharge channel 24. for the material, which by rotation of the gate holes 22 is made to leave the box part 16. The box part 16 constitutes a pressure chamber in which, as a consequence of the emission of steam from the material that leaves the nozzle unit 8, a certain amount already accumulates BHÜMIMI = ÍÍÍIHÍÍ ^ _¡__ overpressure, which can be controlled by venting through a pressure regulating valve 28 and possibly monitor via a pressure transducer 30. The separate pressure supply can take place via a valve 31 for compressed air or steam, for example in a start phase. Possible condensate will be adsorbed by the agglomerate product, from which it is removed by subsequent, normal drying of the product. The exhaust steam from valve 28 can be used for several heating processes. The increased pressure should serve alone or predominantly for the purpose of increasing the boiling point of the water content of the product during the phase in which it leaves the nozzle unit 8 and precisely with this object in mind it will normally be realistic and suitable to operate within of a pressure range of approximately ^ -6 bar. Below the gate wheel, or in principle still above, a sample taker device 32 can be placed which allows continuous control of the product, including with respect to its specific weight as a function of its degree of expansion. . Naturally, it has also been possible in the known art to be able to carry out a corresponding monitoring with the possibility of adjusting certain parameters of the process in front of the nozzle unit 8, but with the invention, it is possible to work with an additional parameter and extremely important, that is, the pressure in the chamber 16. Precisely this parameter will be able to be controlled with a minimum of time difference between a certain regulation requirement and the execution of the related regulation. It will be obvious that the invention is not limited to the modality shown, since for example a relatively large pressure chamber 16 can be used in which a batch can be accumulated in discharge material, which can then be removed without the use in any special form of discharge gate, but possibly during a short stop of the extruder 2, 6. The method according to the invention can be based on the work of a given process that is carried out with manual, associated adjustment parameters. , which also include the pressure in chamber 16, but the work can also be carried ^ x out naturally with several other degrees of automatic control determined by a given choice of product. It will be appreciated that in this control system a detected change of pressure or temperature in the pressure chamber will account for a very fast activation control parameter. It should be mentioned that a means can be provided within the chamber 16 to prevent the descending agglomerates from packing together in the background, that is, so that they are given better time to stabilize in the free state after their formation, for example, by sliding them in thin layers along a system of inclined plates. It has been found that normally it will be completely sufficient if the pressure chamber is designed to operate at a maximum pressure of 6 bar, that is, it will seldom be advisable to build it to withstand even greater pressures. However, it will understand that the invention, in principle, is not directly limited to any particular maximum pressure. Until a high experience has been achieved, it will be advisable to fix the runs test in order to determine a pressure M ?? Desirable operational m in the pressure chamber for each new product, just as usual to determine the other relevant parameters in this way to have specific product properties as a goal. As an example, it was desired to determine the sinking capacity of fish feed agglomerates based on a certain 22% wheat formula extruded through 3.15 mm holes in nozzle plate. A smaller number of agglomerates under different back pressures were produced and about 25 agglomerates from each group were measured, weighed in bulk and tested for flotation characteristics. The following results are indicated:

Claims (10)

1. CLAIMS 1. A method to extrude products that by the heat associated with the process are expanded by the internal boiling of water by the release of pressure after the product passes through the extrusion nozzles, characterized in effecting the extrusion in a closed chamber and maintaining a controlled pressure thereon to effectively control the temperature of the internal boiling, this pressure being preferably 1 / 2-6 bar.
2. 2. A method according to claim 1, whereby an overpressure in the pressure chamber is controlled mainly by a controlled exit of steam originating from the extruded products.
3. 3. A method according to claim 1, whereby the extrusion is carried out continuously and the products are commonly discharged by means of a gate arrangement or alternatively, the extrusion is carried out discontinuously and the products are discharged in the form of lots starting from the pressure chamber.
4. 4. The extrusion plant, especially for the manufacture of these products, which by the heat associated with the process are expanded by the internal boiling of the water by the release of pressure after the product passes through the extrusion nozzles, for example , food or food substances, since the plant comprises a middle nozzle unit for pressing the material of the product through the nozzles, characterized in that on the discharge side of the nozzle unit, there is a closed chamber for temporary reception of the products directed from the nozzle unit, the closed chamber is connected with a pressure regulating means to maintain an adjustable, desirable pressure in this chamber.
5. The plant according to claim 4, characterized in that the pressure regulating means comprises mainly a controlled exhaust valve for the moderation of the pressure build-up which is already caused by the emission of steam from the extruded product.
6. The plant according to claim 5, characterized in that the pressure regulating means further comprises a pressure control valve for supplying compressed air to the pressure chamber.
7. 7. The plant according to the indication 4, characterized in that the pressure regulation means is arranged to maintain a pressure of 1 / 2-6 bar in the pressure chamber.
8. The plant according to claim 4, characterized in that the closed chamber is arranged for continuous operation, since it is provided with a gate arrangement for continuous discharge of the extruded products.
9. The plant according to claim 4, characterized in that the closed chamber is arranged for intermittent operation, that is, for the successive discharge of a large, accumulated portion of extruded products by simple opening to the atmosphere.
10. 10. Unit for accumulation of an extrusion plant, characterized in that it comprises a chamber part for mounting in a closed adjustment manner on the discharge side of the nozzle equipment in the formation of a plant according to claim 4, part of the plant that includes an exhaust valve for the steam and a means to release the products from the same. SUMMARY OF THE INVENTION In the extrusion of agglomerates of food substances and relevant consumer products, the extruded products are subjected to expansion as a result of the boiling of their water content when the products, after which they are exposed to a high extrusion pressure and at a correspondingly high temperature, they are discharged into the atmosphere through the extrusion nozzles. This expansion is directly sought, but it is desirable that it be able to control it, which is difficult due to the adjustment of the ordinary process parameters. With the invention it has been found that the originating expansion can be controlled in a highly constant manner, that is, by extruding in a closed chamber in which an overpressure of a few bars is established relative to the pressure atmospheric and that can be regulated. Extrusion products can be continuously discharged from this camera, or they are discharged intermittently in portions. The overpressure moderates the momentary development of steam in the extruded product and the product is given time to stabilize before it is discharged at atmospheric pressure, so that the additional, subsequent development of steam influences the structure of the product only at a minor degree.