The present invention concerns a worm squeezer for extraction of plant and fruit juices from e.g. medical plants, fruit and berries and oil plants. When extracting plant juices and oils it is essential both to extract as much as possible of the liquid and to conserve therein substances which are desirable for taste and nutrition. It is therefore important that squeezing takes place at high pressure but with little heat development. Low heat development is essential, among others in order to prevent the protein of the plant from coagulating and so follow the plant fibres as wastes instead of being retrieved in the plant juice and in order that the fat shall not become rancid and destroyed.

In conventional plant juice extraction machines juice and oils are squeezed out by means of a high pressure against a comparatively small surface, e.g. thereby that the material is conveyed by a screw against a restriction washer under high axial pressure. The plant juice is often removed in radial direction. This brings with it poor efficiency and quality due to high local friction heat, low contact time for the plant material to the liquid releasing surface and thereby that only a minor part of the material will be contacted with the surface. The efficiency is also reduced thereby that the juice and oil is retained by capillary forces.

The present invention is for a worm squeezer for extraction of plant and fruit juices and oil, whereby the above mentioned drawbacks are avoided. Thus a worm squeezer according to the invention gives high radial pressure and a rapid exchange of the outwardly exposed material.

A worm squeezer according to the invention has a housing with an inner circular cylindrical volume, wherein there is a worm screw. The housing has openings as required for supply of plant

material and feeding out of the remains after extraction. The screw is correspondingly designed with a feeding section and a squeezing or extraction section. Essential for the invention is the design of the screw threads in the extraction part of the screw and the adaption of the screw to the housing in this section.

In order to achieve the above mentioned objectives of the worm squeezer the pressure on the plant material in the extraction section shall be low in axial direction and high in radial direction. The axial pressure causes transport of the plant material and heat due to friction. The radial pressure causes the desired extraction of juices from the plant material. The plant juices are removed from the squeezer in the usual way, e.g. thereby that the housing of the squeezer is sufficiently perforated or comprises channels. It is also desirable that the extraction pressure can be varied in order to adapt the worm squeezer to different raw materials.

The invention will below be described more in detail with reference to the enclosed figures.

Figure 1 shows the housing of the squeezer in cross section and a squeezing worm therein.

Figure 2 shows a cross section of the squeezing worm and the housing at right angle to its central axis.

The worm squeezer shown in figure 1 has a housing 1 with an inner space primarily in the shape of a right angled circular cylinder, wherein is placed a worm 3. The housing has a feed opening 2 for feeding of plant raw material. The worm has a thread 4 with a constant outer diameter along the entire length of the worm. The desired features of the worm squeezer are obtained also by variation of the diameter of the central core of the worm 5. The worm can be rotated and also displaced in its lengthwise direction but the arrangements therefore are of

conventional kind and not shown in the figure.

From the figure can be seen that the worm can be said to be divided into a feeding section and an extraction section. The diameter of the central core 5 of the worm is essentially smaller in the feed in section than in the extraction section. Furthermore, the core diameter and the pitch of thread in the feed in section are preferably constant and the worm here works like a simple feeder screw. The length of the feed in section of the worm is large enough so that the opening of the hopper always is above the feed in section of the worm independent of how this has been displaced in its lengthwise direction. In the extraction section the diameter of the core as well the pitch of the worm thread 4 varies. Seen from the feed in section the core diameter increases and the thread pitch decreases. In both cases the change is preferably continuous and most preferably linearly continuous. Furthermore, the core is so designed that its outer surface between the threads always is parallel with the axis of the worm and thus also with the inner cylindrical surface of the housing. By this design of the worm one obtains the desired conditions during extraction. The design of the worm also brings with it that the material rotates in the threads, as has been marked with bent arrows in figure 1. Hereby is achieved that new material all the time is exposed to the worm and to the housing, whereby locally higher temperatures due to friction are avoided and a high degree of extraction of juices and oil is obtained.

In order to reduce the risks that the material rotates with the worm, the inside of the cylinder may have grooves 6 or bars 7. In a most preferred embodiment of the invention the housing is made as shown in figure 2. The housing comprises three circular bent overlapping plates each forming one third of the inside of the housing. The number of plates may vary with different embodiments but is mostly between two and six. The plates are enclosed in burst collar bands not shown in the figures. By the overlapping one obtains edges corresponding to the above

mentioned bars. This embodiment has turned out to give very good results and a long life as wear is concerned. The plates have a number of radial slits to let out the extracted plant juice.

Between the outside of the worm threads and the cylindrical housing there is a slit. The size of this slit may vary due to the squeezed material and its properties, e.g. concerning the risk for rotation with the worm. Furthermore, the worm is arranged to be displaceable in axial direction in order to make possible to vary the final extraction pressure which can be reduced thereby that the extraction section of the worm more or less is pushed outside the housing. This displacement may take place either to a fixed position or be variable depending upon the actual pressure in the squeezer.