EXTRUSION HEAD FOR TUBULAR ARTICLES MADE OF PLASTIC MATERIALS

Abstract: An extrusion head for tubular articles made of plastic material comprising a body with at least a first part (2) operatively associated to a flange of an extruder, a central part (3) and a terminal part (4) operatively connected to a spinneret (10) wherein said first part (2) has a plurality of ducts (6) for the passage of the material to be extruded in a fluidic state from the inside of said head (1) to the outside, said conduits (6) communicating with the outside through holes (7) associated to a corresponding number of distribution channels (8) provided in the central part (3) of said body and adjacent to a cylindrical surface of said central part (3), wherein the internal geometry of said distribution channels (8) is such that the fluid pressure distribution along lines (9) separating said channels and said cylindrical surface generates a plurality of fluidic threads, each being of the same flow rate, said fluidic threads creating a tubular homogenous article on the terminal part (4) of said head (1).

Description: "EXTRUSION HEAD FOR TUBULAR ARTICLES MADE OF PLASTIC MATERIALS" The present invention concerns an extrusion head for tubular articles made of plastic materials. The production of tubes through polymers of various kinds is generally carried out by means of hot extrusion of the selected plastic material. In such processes the extrusion head has a critical role, because such a head determines the geometry of hot flows of the material subjected to the extrusion with important final qualitative features of the obtained articles. In order to manufacture tubes and films of plastic material extrusion heads of different kinds are known, which comprise a part associated to an extruder flange, a central part, and a terminal part connected to a spinneret , which causes the molten polymer to fit to the size of the article to be produced. More particularly for polyolefiπs extrusion heads with a spiral distribution of the molten polymer are used, whereas for PVC extrusion heads have generally a spoke pattern wherein the central body has numerous fins connecting the outer part with the inner part: in this case the polymer flow is divided inside the fins and merges again after the said fins. Even if these extrusion heads solve the technical problem, they have some disadvantages. Heads having a spiral distribution have some constructional difficulties due to the machining complexity and manufacturing difficulties for their surface treatments, i.e. chromium plating. Furthermore in these heads the polymer is subjected to a rotational movement which is transferred to the produced tube, and they are unfortunately specific for the kind of treated polymers and require long spinnerets in order to homogenize the material. In case of heads having a spoke pattern there is the drawback of the impossibility of optimizing a head for all possible diameters and thicknesses, hence the memory effect of the polymer flow can not be avoided and on the finished product some stripes of said flow can be seen. Furthermore a qualitative deterioration of the material is obtained and at the end of the treatment the material has chemical-physical features which are lower than it was reasonably expected. The object of the present invention is to avoid the prior art drawbacks. Therefore the subject matter of the present invention is an extrusion head for tubular articles made of plastic material, which, articles, are of simple construction, and efficient operation, because by achieving a perfect flow distribution of the material an optimal mechanical quality of the final product is obtained. Briefly, according to the present invention an extrusion head comprising a body with at least a first part operatively associated to a flange of an extruder, a central part and a terminal part operatively connected to a spinneret for tubular articles made of plastic material has been carried out, wherein said first part has a plurality of conduits for the passage of the material to be extruded in the fluidic state from the inside to the outside of said head, said conduits communicating to the outside through holes associated to a corresponding number of distribution channels provided in the central part of said body and adjacent to a cylindrical surface of said central part, wherein the internal geometry of these distribution channels is such that the fluid pressure distribution along the separation lines between said channels and said cylindrical surface creates a plurality of fluidic threads, each thread having the same flow rate, said fluidic threads being able to generate on the terminal part of said head a homogeneous tubular article. The extrusion head for tubular articles made of plastic material according to the invention is characterized by the features of claim 1. An optimal distribution of the melt with a consequent high qualitative value of the article is advantageously obtained because each distribution channel consists of two branches forming an arc on said cylindrical surface of said central part, where the width and the depth of said branches are at a maximum in proximity of each hole, gradually decreasing away from these holes and vanishing at their tip. The head according to the invention is advantageously used in the production of multilayer articles, because due to the sequential arrangement of a plurality of component parts, said head achieves the production of multilayer tubes with a number of layers corresponding to said plurality of component parts. A further advantageous application of the extrusion head according to the invention is the production of multifilament and short fiber synthetic fibers because the dimensions of said component parts of said head can be designed in order to produce layers of a constant size. The extrusion head according to the present invention is highly versatile because the plastic materials to be used comprise at least those selected from polyolefins, PVC, polycarbonate, methacrylate, EVOH, polystirol, nylon, PET. Further features, advantages and details of the extrusion heads for tubular articles made of plastic material according to the present invention, will be better understood from the following detailed description and from the attached drawings wherein a non limiting preferred embodiment is illustrated by way of example. Figure 1 is a partially sectioned perspective view showing the extrusion head for tubular articles made of plastic material according to the present invention. Figure 2 is a lateral view of the extrusion head shown in Figure 1. Figure 3 is a horizontally sectioned view of the extrusion head according to the present invention. Figure 4 is a schematic view of a plane development of the distribution channels machined on the extrusion head according to the present invention. Figure 5 is a partially sectioned lateral view of the extrusion head shown in Figure 1 when assembled on the extruder. With reference now to the figures of the drawings, the extrusion head 1 for tubular articles comprises a substantially cylindrical body, preferably including a first part 2 which is connected to a flange of an extruder, a central part 3 being adjacent to said first part 2 and a terminal part 4, which connects said head 1 to a spinneret 10. The first part 2 has a central internal duct 5 which allows the passage of the molten polymer from the extruder body to the head. Such a duct 5 splits into a plurality of ducts 6, e.g. three ducts as shown in figure 1 , which lead the polymer in fluidic state from the inside to the outside of the head 1. These conduits 6 communicate with the outside at the beginning of said central part 3 of the head 1 through corresponding holes 7. These holes 7 communicate in turn with a corresponding number of distribution channels 8 abutting to a cylindrical surface of the said part 3 through their own perimetrical curved lines, each channel consisting of two branches 12, which form an arc on said cylindrical surface of the part 3. More precisely the width and the depth of said branches 12 are at the maximum in proximity of each hole 7, gradually decreasing away from these branches and vanishing at their tip; the mathematical rule governing the development has been calculated by imposing particular physical conditions which will be better illustrated hereinafter. The number of distribution channels 8 and as a consequence of ducts 6 will increase with the diameter of head 1 , thus allowing the length of the head to be reduced. Individual thermoregulation devices of the ducts may optionally be provided in order to compensate the flow rate of each duct. The depth, width and the curvature of branches 12, hence their geometry, is determined as above indicated by means of computation, which imposes that the pressure distribution of the fluid along the curved lines 9 of separation between said distribution channels 8 and said cylindrical surface generates a plurality of fluidic threads, each one of the same flow rate. The computation is correlated to the diameter and the width of the instant head, hence there will be different kinds of geometry for each head in a head family. Such a pressure distribution, finally, generates a tube with a substantially constant thickness at every single point on the terminal part 4 downstream to the central part 3. The terminal part 4 as already pointed out is associated to a spinneret 10, which can advantageously be of reduced size due to the optimal geometry of the tube obtained by said terminal part 4. Furthermore also said part 4 can be clearly shorter than the corresponding terminal parts of the prior art heads, because for the above mentioned reason this head does not serve to homogenize the melt. It can be observed that the present head l ean be made of any material and be subjected to various surface treatments e.g chromium plating. During the extrusion in order to produce tubular articles, the plastic material in the molten state travels through the ducts 5,6 and flows into the distribution channels 8 through the holes 7. At this point the pressure drop created by the geometry of the distribution channels generates a plurality of fluidic threads with the same flow rate on the perimetrical lines 9 of said channels 8 and these fluidic threads hence produce a perfectly homogeneous tubular article on the terminal part 4. The above illustrated technical solution can be used treating different plastic material such as polyolefins, PVC, polycarbonate, methacrylate, EVOH, polystyrene, nylon, PET achieving optimal results, because the results obtained with this head are independent from the used polymer. The head 1 according to the present invention can also be advantageously used in order to produce multilayer tubes: this solution is becoming more and more requested by the market for enviromental reasons related to the declining use of materials which are not reusable and to the use of recycled materials. In such a case the component parts 2, 3, 4 of the head body are repeated once for each layer to be carried out. More particularly, the first part 2, being a structure made of single channels, easily solves the main problem of the multilayer heads, i.e. the intersection of flows of different polymers. The central part 3 is repeated several times on the cylindrical bodies which will be mounted coaxially one inside the other, on the internal parts of which distribution channels calculated on basis of the desired final thickness will be carried out. The terminal part 4 allows the various layers to be overlapped and the dimensions of the final article to be obtained according to the desired diameters and thicknesses. An alternative use of the head for multilayer tubular articles consists of its application in the field of multifilament or short synthetic fibers: in this case such a multilayer head is used as to obtain single layers of constant thickness. This kind of head combined to a particular prior art spinneret allows a clear improvement in the spreading the denier values of singles roves, a better temperature distribution on said head and an increase of the cooling capacity with consequent increase of productivity to be obtained. Numerous variations, modifications, arrangements, integrations, variants and substitutions of course can be made to the previously described preferred illustrative and non-limiting embodiment without departing from the scope of the present invention as determined by the appended claims.

Claims: CLAIMS 1. An extrusion head for tubular articles made of plastic material comprising a body with at least a first part (2) operatively associated to a flange of an extruder, a central part (3) and a terminal part (4) operatively connected to a spinneret (10) characterized in that said first part (2) has a plurality of ducts (6) for the passage of the material to be extruded in a fluidic state from the inside of said head (1 ) to the outside, said ducts (6) communicating with the outside through holes (7) associated to a corresponding number of distribution channels (8) provided in the central part (3) of said body and adjacent to a cylindrical surface of said central part (3), wherein the inner geometry of said distribution channels (8) is such that the fluid pressure distribution along lines (9) separating said channels and said cylindrical surface generates a plurality of fluidic threads, each being of the same flow rate, said fluidic threads creating a tubular homogenous article on the terminal part (4) of said head (1 ) . 2. The extrusion head for tubular article made of plastic material according to claim 1 , characterized in that each of said distribution channels (8) comprises two branches (12), forming an arc on said cylindrical surface of said central part (3). 3. The extrusion head for tubular articles made of plastic material according to claim 2, characterized in that the width and the depth of said branches (12) are at a maximum in proximity of each hole (7), gradually decreasing away from branches and vanishing at their tip. 4. The extrusion head for tubular articles made of plastic material according to claim 1 , characterized in that said head (1 ) is provided with a sequential plurality of its own component parts (2,3,4) allowing multilayer tubes with a number of layers corresponding to said plurality of component parts to be obtained. 5. The extrusion head for tubular articles made of plastic material according to claim 4, characterized in that the dimensions of the component parts (2,3,4) of said head are designed in order to obtain layers of constant size so as to allow multifilament and short synthetic fibers to be obtained. 6. The extrusion head for tubular articles made of plastic material according to claim 1 , characterized in that said plastic materials comprise those selected from polyolefins, polycarbonate, methacrylate, EVOH, polystyrene, nylon, PET.

Inventors: LUPI CAMILLO, LUPI, CAMILLO
Applicants: LUPI CAMILLO, TECNOMATIC SPA, LUPI, CAMILLO, TECNOMATIC S.P.A.
Application year: 2001
Main classification: B29C47
IPC codes: B29C47