De Jong, Piet (Prins Willem Alexanderlaan 28, AB 'T Harde, NL-8084, NL)
The invention relates to a method for moulding a raw material, such as meat or dough supplied as a mass, into separate products, comprising the steps of: a) dividing the raw material into portions, b) transporting each portion to a moulding member with at least one mould cavity, c) urging the portion into the at least one mould cavity, and d) removing the products from the mould cavity (or cavities) after moulding thereof. Such a method is generally known and is for instance applied for industrial-scale moulding of (meat) snacks such as hamburgers. In the known method a ground meat mass, also referred to as dough, is divided by a portioning device into portions which are then fed to a moulding apparatus . This moulding apparatus has one or more mould cavities, the form and dimensions of which correspond precisely to those of the desired end product. Each supplied portion is carried into a mould cavity or divided over a number of mould cavities, whereafter the mould cavity (or cavities) is/are closed, for instance by a pressure member. Once the products are fixed in the mould cavity (or cavities) in the desired form, they are removed therefrom, for instance using a reciprocally movable ejecting member, and discharged on a conveyor. A problem of the known method is that the moulded products are not perfectly uniform. Variations can occur in both the form and weight of the products. This is undesirable with a view to the further processing of the products. Weight differences moreover result in.more raw material having to be used as a precaution in order to ensure that the lightest products also have a guaranteed minimum weight, whereby the other products are in fact unnecessarily heavy. Finally, differences in shape detract from the appearance of the products, which are therefore more difficult to sell. The invention therefore has for its object to provide a method of the above described type, wherein these drawbacks do not occur. According to the invention this is achieved in such a method in that at least one of the steps a) to c) takes place under a pressure below atmospheric pressure. By maintaining a pressure below atmospheric during in any case some of the processes, air inclusions possibly present in the raw material are suctioned out, whereby a homogeneous mass is obtained. End products are thus formed which, due to the absence of included air, show practically no variation in either weight or shape. The division of the raw material into portions preferably already takes place under a pressure below atmospheric pressure. The inclusion of air in the raw material is thus prevented from the first stage of the method. When urging of the portions into the mould cavity or cavities) takes place under a pressure below atmospheric, it is ensured that at least during the moulding the material is almost completely free of air inclusions. An optimal filling of the mould cavity (or cavities) is thus achieved, and thereby a uniform and well-defined form of the end products. In order to prevent penetration of air into the portioned material, transporting of the portions advantageously also takes place under a pressure below atmospheric. For an optimal uniformity of the products, it is recommended that during transport thereof to the mould cavity (or cavities) the portion is divided substantially transversely of the direction of transport, wherein this division also takes place under a pressure below atmospheric. The whole process thus takes place at an underpressure. In order to ensure complete extraction of possible air inclusions, and still minimize the effort involved, the pressure below atmospheric can amount to at least 0.5 bar (absolute) . The pressure below atmospheric preferably amounts to between 0.6 and 0.99 bar (absolute), and more preferably to between 0.7 and 0.9 bar (absolute) . The invention further relates to an apparatus for performing the above described method. Such an apparatus, which can be provided in conventional manner with means for dividing a raw material supplied as a mass into portions, means connecting to the portioning means for transporting each portion to a moulding member with at least one mould cavity, means connected to the transporting means and co- acting with the moulding member for urging the portion into the at least one mould cavity, and means co-acting with the moulding member for removing from the mould cavity (or cavities) products moulded thereby, is distinguished according to the invention in that at least a part thereof is connected to a source of underpressure. Preferred embodiments of the apparatus according to the invention are described in the sub-claims 9 to 15. The invention will now be elucidated on the basis of an exemplary embodiment, wherein reference is made to the accompanying drawing, in which: Fig. 1 shows a diagram of the different steps of the method according to the invention, Fig. 2 is schematic representation of the different components of an apparatus according to the invention, and Fig. 3 is a detail view of a mould cavity and a source of underpressure connected thereto as used in the apparatus of fig. 2. An industrial method for moulding products, in particular hamburgers, from a shapeless raw material, such as a ground meat mass or dough, comprises first of all the steps of supplying the mass of raw material (fig. 1, block 1) and dividing the supplied mass of raw material into portions (block 2) . Each portion is then transported (block 3) to a moulding member which defines one or more mould cavities. At a final stage of this transport, which generally takes place through a relatively narrow conduit, the portion can be divided (block 4) in transverse direction, as seen relative to the direction of transport, so that it is presented uniformly to the moulding member, the working width of which will usually be larger than the diameter of the transport conduit. After reaching the moulding member, the supplied portion is urged with some force into a mould cavity or divided over a number- of mould cavities (block 5) . After a short stay in the mould cavity (or cavities) , each product has assumed its final shape, and can be released from the mould cavity. The moulded products are then discharged (block 7), for instance for the purpose of packing and transport to customers. According to the invention, in any case a part of the above described method takes place under a pressure below atmospheric, therefore an underpressure. Air possibly included in the material can thus be extracted therefrom. Variations in shape and weight of the end products are thus prevented in efficient manner. The urging of the portion of material into the mould cavity (or cavities) (block 5) can for instance take place under a pressure below atmospheric, so that the material therefore completely fills the mould cavity (or cavities) . Because placing of the portion of material into the mould cavity (or cavities) requires only little time, and there is the risk here that not all air can escape from the material, one or more steps prior to the moulding are preferably also already performed under a pressure below atmospheric. For optimum removal of air from the material, the whole method from portioning to the moment of closing the mould cavity (or cavities) takes place under a pressure below atmospheric. The pressure below atmospheric is chosen such that a balance is achieved between the release of included air from the products on the one hand and the effort involved in creating and maintaining the underpressure on the other. It has been found in practice that the use of pressures of less than 0.5 bar (absolute) is not worthwhile. The balance sought can rather be found in a range of pressures between 0.6 and 0.99 bar (absolute), and more particularly between 0.7 and 0.9 bar (absolute) . An apparatus 11 for performing the above described method consists in the shown embodiment of supply means 12, for instance in the form of a feed hopper, and means 13 connecting thereto for dividing into portions the raw material fed by supply means 12 (fig. 2) . These portioning means 13 can for instance comprise a vane pump. Connecting onto portioning means 13 are transporting means 14, for instance in the form of one or more conduits. These transporting means 14 carry the raw material portion by portion to dividing means 15, for instance in the form of a flared housing having therein one or more metering pumps (not shown), again for instance in the form of vane pumps. From these dividing means 15, over practically the whole working width, each portion enters a moulding member 16 defining one or more mould cavities 17. Apparatus 11 further comprises means 18 for urging the portion of material with force into mould cavity (or cavities) 17. Owing to the forced filling of mould cavity (or cavities) 17, the products are moulded therein. After a time mould cavity (or cavities) 17 is/are opened, for instance by displacing the moulding member 16, and the products can be removed therefrom by removing means 19 and be discharged to for instance a conveyor 20. Up to this point the apparatus 11 can in fact be the same as the moulding installation described in the earlier, not yet pre- published Netherlands patent application 1026159 of applicant. According to the present invention a part of apparatus 11 is in any case connected to a source 21 of underpressure. For optimum effect it is important that included air is removed at the earliest possible stage from the raw material. For this purpose the portioning means 13 are thus connected to a source 21 of underpressure. Portioning means 13 can advantageously form part of a so- called vacuum filler as used in sausage production. In the shown embodiment the transporting means 14 and dividing means 15 are also connected to a source of underpressure. Use is made here of a shared source which can for instance be arranged in a housing 22 in which the portioning means 13 are accommodated. The different components of apparatus 11 then of course have to be mutually connected in airtight manner. Finally, the means 18 for urging the portion of material into mould cavity (or cavities) 17 are also connected in the shown embodiment to this source 21 of underpressure. The source 21 of underpressure here in fact forms part of these urging means 18, since the material is partly drawn into mould cavity 17 by the underpressure, which acts on the interior thereof via a conduit 23, a chamber 24 and a large number of small apertures 25 in a wall of each mould cavity 17. Mould cavity 17 is hereby filled optimally, and very well-defined end products are thus obtained. The method and apparatus according to the invention thus enable very uniform products to be moulded from a shapeless raw material mass in relatively simple manner and for a small investment. Although the invention is described above on the basis of an exemplary embodiment, it will be apparent to the skilled person that it can be varied in many ways within the scope of the following claims.