REINFORCED FLEXIBLE HOSE, AND METHOD AND WORKING HEAD FOR THE PRODUCTION THEREOF

Abstract: A reinforced flexible hose comprises a reinforcement element (2) made of a relatively rigid plastic material, such as rigid PVC, totally immersed into one tubular layer (3) made of a plastic material containing plastifying substances, such as flexible PVC. The reinforcement element (2) is a spirally shaped plastic thread ribbon with its minimum diameter longer than the inner diameter of the tubular layer wherein it is immersed and it is coated with a film (4) made of a relatively thin plastic material forming a barrier against plastifying substances contained in the tubular layered (3) material, in such a way that any migration of these plastifying substances is always prevented, along with the consequent embrittlement and cracking phenomena involving the reinforcement element (2). The material making up the film (4) is chosen to be such that it steadily adheres both to the flexible layer (3) and to the rigid reinforcement element (2). The basic material making up the film (4) is preferably chosen in the group comprising polyamides, polyesters, polyurethane, polyketone, polyethylene copolymers and nitrile rubber.

Description: REINFORCED FLEXIBLE HOSE, AND METHOD AND WORKING HEAD FOR THE PRODUCTION THEREOF Field of the invention The present invention relates to a flexible hose made of a reinforced plastic material, which is particularly suitable for suction and transport of liquids and gases, as well as powders and solid material suspensions. In particular, the present invention relates to a reinforced hose having an inner reinforcement generally shaped as a helicoidal spiral, which hose, in consideration of its peculiar shape, is commonly named spiral type hose. Further features of the present invention relate to a method for the production of a hose as well as of a working or extrusion head of the hose. Background of the invention Reinforced flexible hoses are known, and these essentially comprise an inside reinforcement element made of a relatively stiff or rigid generally spirally shaped material. The reinforcement element is immersed in a support layer or a main tubular wall made of a relatively flexible material. The basic materials of which the different parts of the hose are made have a high price/quality ratio. For instance, the spiral can be made of rigid PVC, whereas the tubular layer can be made of flexible PVC. For that purpose, PVC can be additioned with suitable plastifying substances that are useful for increasing the flexibility related properties of the basic plastic material. A problem arising from said known materials is that the plastifying substances additioned to the PVC tend to migrate towards the rigid PVC. This tendency to migrate is particularly enhanced and critical when the percentages of plastifying substances is relatively low, namely in the 5% range, and such that they cause PVC to become brittle, along with the risk that the reinforcement spiral cracks and eventually breaks. This may give rise to local mechanical failures of the hose that inevitably lead to a decrease in the degree of sealing of the hose, therefore a loss of positive or negative pressure internally thereof. This is particularly true when the hose undergoes even negligible stresses, strains, shears and compressions. In technical jargon this phenomenon is called "cracking". In order to try and solve the problem posed by cracking, a number of solutions were put forward in the past, among which for example the employment of plastifiers that do not exhibit any migration phenomenon. A further solution is that of replacing the flexible plastic material with other materials that do not contain any plastifiers, such as PUR (polyurethane) or other plastic materials that do not become brittle as rigid PVC typically does. However, the above mentioned solutions proved to be disadvantageous from an economical point of view, and little suitable for their employment in the production of hoses pertaining to the law range of the market. Summary of the invention A primary object of the present invention is to provide a reinforced flexible hose provided with a new type of spirally shaped rigid reinforcement that exhibits an enhanced resistance to the cracking phenomenon and that features a remarkable durability in time even when subjected to permanent mechanical stresses, strains and shears such as expansions, shocks and compressions. A further particular object of the present invention is that of conceiving a hose of the above indicated type that has a relatively simple structure that is also easy to produce and whose production leads to reduction in cost with its structural features remaining the same. The above objects are accomplished according to claim 1 by a reinforced flexible hose, particularly suitable for the suction and transport of liquids and gases, which comprises a reinforcement member made of a relatively rigid plastic material that is fully immersed into a tubular wall made of a plastic material containing plastifiers, characterised in that said reinforcement member is homogeneously coated by a film made of a suitable plastic material which defines a barrier against migration of the plastifying substances from said tubular wall towards said reinforcement member. Suitably, the reinforcement member is in the form of a thread wound to form a substantially helicoidal spiral. The spiral has a minimum diameter that is longer than the inner diameter of said tubular support wall. The basic material the tubular support wall is made of is the same basic material the reinforcement material is made of, PVC for example, with the addition of suitable plastifying substances. The plastic material of which the film is made of is chosen among materials that are compatible both with said reinforcement material and with that of said tubular wall so that a mutual adhesion of these elements is promoted. Preferably, the basic material the barrier film is made of is chosen in the group consisting of polyamides, polyesters, polyurethanes, polyketones, polyethylene copolymers or nitrile rubber. A further object of the present invention is to conceive an extrusion device that allows an easy and cost effective production of the hose according to the invention on a continuous basis and by means of a single coextrusion operation involving all components of said hose. The above object is accomplished by the production of an extrusion head for the production of a reinforced flexible hose according to the invention, which comprises a first conduit for the introduction of plastic material for the manufacturing of a relatively rigid reinforcement member, a second conduit for the introduction of another plastic material containing plastifying substances bound to form a relatively flexible tubular layer or wall, an outlet nozzle communicating with said first and said second inlet ducts for the coextrusion of a plastic material strip formed by said tubular layer where said reinforcement member is immersed, means for the continuous deposition of said strip on a substantially rectilinear mandrel so that said substantially tubular wall of the hose is formed wherein said reinforcement member is immersed, characterised by providing a third injection conduit suitable for the coextrusion of a plastic material film onto said reinforcement member so that it forms a barrier against migration of the plastifying substances from said tubular wall to said reinforcement material. A further object of the present invention is to provide a method for the production of the hoses according to the invention, said method making it possible to produce them in a cost effective way. This object is accomplished by means of a method for the production of a reinforced flexible hose according to the invention that comprises the following steps according to claim 10: a) heating a first plastic material bound to form a relatively rigid reinforcement member, and a second plastic material containing plastifiers bound to form a relatively flexible support layer, up to taking them to a fluid or pasty state; b) coextruding said materials in a pasty state through an outlet nozzle in order to form a strip having a suitable cross-section and an indefinite length, said strip comprising said support layer wherein said reinforcement member is immersed, c) continuously depositing said strip in a plastic state onto a substantially rectilinear rotating mandrel, along a spirally shaped path having mutually contacting spires so that the substantially tubular and reinforced wall of the hose is formed; d) keeping said strip on the mandrel for the time necessary for molecular adhesion of the extruded materials to take place, for forming the outside hose wall; e) cooling the strip down to ambient temperature to form the finished hose, characterised in that it comprises a step f) wherein a film is coextruded, said film being made of a third plastic material forming a barrier against migration of said plastifiers from said tubular wall to said reinforcement member. The hose obtained by means of the above method protects the material making up the rigid reinforcement material against migration of plastifying substances so that the embrittlement phenomenon is eliminated. Brief description of the drawings Further features and advantages of the present invention will be more apparent from the following description of a preferred but not exclusive embodiment of a reinforced flexible hose according to the invention illustrated by way of not limiting example in the attached table of drawings wherein: Fig. 1 is a partially sectional perspective view of a segment of a reinforced flexible hose according to the invention, Fig. 2 illustrates the section of a detail of the hose wall shown in Fig. 1 ; Fig. 3 illustrates a sectional view of an extrusion head for the production of the hose shown in Fig. 1 ; Fig. 4 illustrates a perspective view of a production step of the hose shown in Fig. 1 at an intermediate production step; Fig. 5 illustrates a front view of the extrusion head shown in Fig. 3; Figs. 6, 7, 8 illustrate differently shaped sections of the strip of coextruded plastic material making up the hose according to the invention. Description of a preferred form of embodiment With reference to figures 1 and 2 a flexible hose is illustrated, generally indicated by reference numeral 1 , comprising a reinforcement element 2 made of a plastic material, such as substantially rigid PVC, on which a supporting layer 3 is laid of a plastic material, of the PVC type and containing plastifying substances, such that it exhibits a certain flexibility which is more or less enhanced according to the requirements of the final product. Preferably, reinforcement member 2 is substantially shaped as a thread wound to form a helicoidal spiral whereas support layer 3 is coextruded between the coils of reinforcement element 2 so as to form the tubular wall of hose 1 . A peculiar feature of the invention resides in that the reinforcement element 2 is coated with a film 4 made of a suitable plastic material. The basic material of which film 4 is made is chosen to be such that it forms a barrier that prevents migration of the plastifiers contained in the plastic material of layer 3 towards reinforcement member 2. Advantageously, the plastic material used for layer 3 coating the rigid spiral is chosen to be such that it results to be compatible and chemically similar to the PVC making up the two hose members so as to promote the molecular adhesion phenomena and to avoid separation of the layers. Such a material is extruded at relatively high temperatures and it will result to be suitable for making up film 4 having an extremely reduced thickness, in the micron range for example. As a not limiting example, the basic material forming film 4 can be chosen in the group consisting of synthetic resins of the polyamide, polyester, polyurethane, polyketone, polyethylene copolymer, nitrile rubber types. The thus produced flexible hose 1 will exhibit anti-cracking properties suitable for remarkably increase resistance and durability of the hose in comparison with the hoses found in the prior art. Advantageously, the materials making up the several components of the hose can be coloured or pigmented with different colours, shades and hues so as to yield to the widest variety of aesthetic effects. Thus, is can be possible to produce ranges or series of easily distinguishable products on account of their colours. Hose 1 can advantageously be produced by means of a coextrusion process of the several above listed plastic components by means of an extrusion head illustrated in detail in Fig. 3. In the form of embodiment shown, the extrusion head, overall indicated with reference numeral 5, comprises two sections 6, 7 mutually joined by means of screws, and joined to a supporting plate or frame 8. Section 6 is provided with at least two inlet channels 9, 10 for respective plastic materials at the fluid or pasty state. In particular, channel 9 fulfils the function of feeding a plastic material of the PVC type for example that is bound to form reinforcement member 2, whereas channel 10 fulfills the function of feeding PVC containing plastifying substances for example bound to form the flexible support layer 3. Channels 9, 1 0 converge towards a coextrusion chamber that leads outside through an outlet channel or nozzle 1 2 through which a plastic material strip or ribbon is extruded. As shown in Fig. 4, strip S still in its pasty state is laid and wound onto a substantially rectilinear rotating mandrel M, following a spirally shaped path, to form the continuous outside surface of hose 1 . Thanks to the affinity and compatibility of the extruded thermoplastic materials, a molecular adhesion take space between them during extrusion, which guarantees homogeneity and sealing of the outside surface. According to the invention, head 5 is provided with a third channel 1 1 , obtained from section 6 for example, for the deposition of a film 4 made of a suitable plastic material onto reinforcement member 2. Said film is suitable to form a barrier that prevents migration of the plastifying substances contained in the support layer 3 towards the reinforcement member 2. Similarly channel 1 1 converges towards nozzle 1 2 in such a way that film 4 results to be homogeneously coextruded onto reinforcement member 2 completely wrapping it. Obviously the diameter and the geometry of channels 9, 10, 1 1 may be sized in such a way that the desired thicknesses and dimension can be obtained. Moreover, nozzle 1 2 may be formed so as to obtain a predetermined geometry for strip S, said geometry being suitable for forming tubular wall 3 of the hose. As shown in detail in Fig. 5 depicting a front view of head, the movable connection between sections 6, 7 of the head by means of screws 13 makes it possible to perform the quick replacement of section 7 with another section wherein an outlet channel or nozzle 1 2 presents a cross section that is different from the first one. Some examples of said cross sections are schematically shown in Figs. 6, 7, 8. Thus strips of materials having a variety of cross sections can be extruded, which cross sections making it possible to produce hoses 1 having different outside surfaces. The method according to the present invention for the production of hose 1 employing the above described extrusion head may comprise the following steps. Extruded thermoplastic materials are firstly heated up to reach their fluid or pasty state, and they are fed along ducts 9, 10, 1 1 of section 6 of extrusion head 5 up to nozzle 1 2, through which they are coextruded to form a strip S having a suitable cross section and having an indefinite length. A peculiar feature of the method according to the invention is that strip S comprises reinforcement member 2 immersed in the tube like wall 3 with the interposition and coextrusion of film 4, which fulfills the function of forming a barrier that prevents migration of the plastifiers from the material of which wall 3 is made towards member 2. Strip S is wound to form a coil onto a mandrel M rotating following the direction shown by arrow R and with the coils mutually contacting, when it is still in its pasty state. Strip S is kept on mandrel M for the time necessary for the film 4 material to molecularly adhere both to reinforcement material 2 and to the material making up layer 3. With this process the outside surface of tube 1 thus forms and it is then cooled to ambient temperature. From reading the above description it is clear that the hose, the extrusion head and the method according to the present invention fulfills their objects and aims, and it is specifically highlighted that the hose produced according to the invention is not subject to any embrittlement phenomena. Moreover it is worth emphasising that its production is simple and cost effective. The instant application is based upon Italian patent application VI99A000142, filed on 8 July 1 999, the disclosure of which is hereby expressly incorporated by reference thereto, and the priority of which is hereby claimed.

Claims: CLAIMS I . Reinforced flexible hose (1 ) particularly suitable for the suction and transport of liquids and gases, comprising at least one reinforcement member (2) made of a relatively rigid plastic material that is completely immersed in a substantially tubular supporting wall (3) made of a plastic material containing plastifying substances, characterised in that said at least one reinforcement member (2) is homogeneously coated with a film (4) made of a suitable plastic material defining a barrier preventing migration of said plastifying substances from said support wall (3) towards said reinforcement member (2). 2. Reinforced flexible hose according to claim 1 , characterised in that said at least one reinforcement member (2) is substantially thread shaped and it is wound to form a substantially helicoidal spiral having a minimum diameter that is longer than the inner diameter of said support wall (3). 3. Reinforced flexible hose according to claim 1 , characterised in that the basic material forming said tubular support wall (3) is made of the same basic material of which is made said reinforcement member (2) with the addition of suitable plastifying substances. 4. Reinforced flexible hose according to claim 3, characterised in that said basic plastic material is PVC. 5. Reinforced flexible hose according to claim 1 , characterised in that the plastic material of which said film (4) is made is chosen amongst the materials that are compatible both with the material forming said reinforcement member (2) and with the material forming the tubular wall (3) so as to promote the mutual adhesion between said elements. 6. Reinforced flexible hose according to claim 5, characterised in that the basic material forming said film (4) is chosen in the group consisting of polyamides, polyesters, polyurethanes, polyketones, polyethylene copolymers or nitrile rubber. 7. Reinforced flexible hose according to one or more of the preceding claims, characterised in that one or more plastic materials forming said reinforcement member (2), said tubular wall (3) and said film (4) are coloured and pigmented with different colours, shades and hues in comparison with those of the other plastic materials. 8. Extrusion head for the proconduition of a reinforced flexible hose 1 according to one or more of claims 1 to 7, comprising a first conduit (9) for the introduction of a plastic material for the production of a relatively rigid reinforcement member (2), a second conduit (10) for the introduction of another plastic material containing plastifying substances adapted to form a relatively flexible tubular layer or wall (3), an outlet nozzle (1 2) communicating with said first and second introduction conduits (9, 10) for the coextrusion of a plastic material strip (S) formed with said tubular layer (3) in which said reinforcement member (2) is immersed, means for the continuous deposition of said strip (S) onto a substantially rectilinear mandrel (M) in such a way that it forms said substantially tubular wall (3) wherein said reinforcement member (2) is immersed, characterised in that a third introduction conduit (1 1 ) is provided for the coextrusion of a plastic material film (4) onto said reinforcement element (2) so as to form a barrier that prevents migration of plastifying substances from said tubular wall (3) to said reinforcement member (2). 9. Extrusion head according to claim 8, characterised in that it comprises two sections (6, 7) movably coupled in order to change shape and section of said outlet nozzle (1 2) so as to vary the geometry of the strip (S) of coextruded material. 10. Method for the production of a reinforced flexible hose according to anyone of claims 1 to 7, comprising the following steps: a) heating a first plastic material bound to form a relatively rigid reinforcement member, and a second plastic material containing plastifiers adapted to form a relatively flexible support layer (3), up to bringing them to the pasty state; b) coextrusion of said pasty materials through an outlet nozzle (1 2) to form a strip (S) with a suitable cross section and an indefinite length, comprising said support layer (4) wherein said reinforcement member (2) is immersed; c) continuous laying of said strip (S) at the plastic state onto a substantially rectilinear rotating mandrel (M), along a spirally shaped path having its coils mutually contacting so as to define the substantially tubular and reinforced hose wall; d) keeping said strip (S) on the mandrel for the time necessary to obtain a molecular adhesion of the extrusion materials to form the outside surface of the hose (1 ); e) cooling the strip (S) down to ambient temperature for forming the finished hose (1 ), characterised in that it comprises a coextrusion step f) of a third plastic material onto said reinforcement member (2), said third plastic material forming a barrier against migration of said plastifiers from said tubular wall (3). 1 1 . Method according to claim 10, characterised in that said film (4) is homogeneously deposited onto the outside surface of said reinforcement member (2).

Inventors: MEZZALIRA RINALDO, MEZZALIRA, RINALDO
Applicants: FITT SPA, MEZZALIRA RINALDO, FITT S.P.A., MEZZALIRA, RINALDO
Application year: 2000
Main classification: F16L11
IPC codes: B29C47, B29C53, F16L11