Abstract:
An apparatus for mixing granular inert material with a resin binder in order to form, on a rotating cylindrical mandrel, a tubular manufactured article composed of an inner layer which adheres to the surface of the mandrel, an outer layer and an intermediate layer constituted by a uniform agglomerate obtained from an amalgamation of the granular inert material with the resin binder, comprising at least one mixing line composed of a feeder which is connected to a duct for feeding the granular inert material and a discharge outlet, a mixing device which has an intake port which is suitable to receive the granular inert material from the discharge outlet of the feeder and connections for feeding the resin binder in the mixing device, the mixing device being suitable to form the uniform agglomerate and to apply it onto the inner layer so as to form the intermediate layer.

Description:
[0001]    The present invention relates to an apparatus for mixing granular inert material and resin binder in the production of laminated articles made of composite material, particularly tubular laminated articles. 
       BACKGROUND OF THE INVENTION 
       [0002]    Laminated tubular articles are known which are constituted by a plurality of layers obtained by wrapping structural fibers, mainly glass fibers, impregnated with resin. 
         [0003]    Generally, the inner layer and the outer layer of the laminated article are separated by an intermediate layer constituted by a mixture of resin (binder) and granular inert material (generally sand). 
         [0004]    These articles are produced by wrapping on a rotating mandrel: 
         [0005]    an inner layer, composed of a bundle of structural fibers (generally made of glass) impregnated with resin (binder) by immersion or contact or by gravity or spraying; 
         [0006]    an intermediate layer of granular inert material (generally sand) impregnated with resin (binder) applied by gravity; 
         [0007]    an outer layer, composed of an additional bundle of structural fibers (generally made of glass) impregnated with resin (binder) generally according to the same technology used for the inner layer. 
         [0008]    The above-described technology for manufacturing laminated articles has the severe drawback that it does not allow to control the impregnation and therefore the agglomeration of the granular inert material with the binder. This leads to the risk of forming a nonuniformity in the intermediate layer of the manufactured article which consists of regions predominantly constituted by resin and other regions predominantly constituted by inert material. This is due to the fact that the amalgamation between the inert material and the resin is due substantially to the physical process linked to the surface tension and capillary action of the binder. Since the manufactured article must ensure the characteristics of mechanical strength and impermeability to the liquids conveyed therein even in high-pressure conditions, any damage caused by a region with poor cohesion and with a predominance of inert material is greater than the malfunction that arises from the opposite situation. For this reason, there is a tendency to increase the amount of resin distributed on the sand, with a consequent decrease in the efficiency of the production process and an increase in waste and in the risk of pollution. 
       SUMMARY OF THE INVENTION 
       [0009]    The aim of the present invention is to provide an apparatus which optimizes the process for mixing the granular inert material and the binder in order to ensure the uniformity of the agglomerate and optimize the mixing ratio and accordingly the production parameters. 
         [0010]    Within this aim, an object of the present invention is to provide an apparatus which is capable of modifying the mixing ratios according to the requirements and the external conditions of the production process. 
         [0011]    Another object of the present invention is to provide an apparatus which is simple and therefore cheap to manufacture and which is reliable in operation and capable of offering qualitatively uniform products. 
         [0012]    This aim and these and other objects which will become better apparent hereinafter are achieved with an apparatus for mixing granular inert material with a resin binder in order to form, on a rotating cylindrical mandrel, a tubular manufactured article composed of an inner layer which adheres to the surface of the mandrel, an outer layer and an intermediate layer constituted by a uniform agglomerate obtained from an amalgamation of said granular inert material with said resin binder, characterized in that it comprises at least one mixing line composed of a feeder which is connected to a duct for feeding said granular inert material and a discharge outlet, a mixing device which has an intake port which is suitable to receive said granular inert material from said discharge outlet of said feeder, and connections for feeding said resin binder in said mixing device, said mixing device being suitable to form said uniform agglomerate and to apply it onto said inner layer so as to form said intermediate layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred embodiment thereof, illustrated by way of non-limiting example in the accompanying drawings, wherein: 
           [0014]      FIG. 1  is an axial elevation view of a mixing apparatus associated with a system for producing tubular manufactured articles; 
           [0015]      FIG. 2  is a partially sectional side view, taken along a vertical plane, of the apparatus according to the invention; 
           [0016]      FIG. 3  is a sectional plan view of the apparatus, taken along the line III-III of  FIG. 2 ; 
           [0017]      FIG. 4  is a sectional plan view of the apparatus, taken along the line IV-IV of  FIG. 2 ; 
           [0018]      FIG. 5  is a view of the motor drive assembly of the apparatus according to the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    With reference to the figures, a mixing apparatus is generally designated by the reference numeral  1  and is composed substantially of the pairing of two mixing lines which are capable of providing respective flows of agglomerate composed of inert granular material, generally sand, and intimately mixed with a binder, generally resin. 
         [0020]    The two flows of agglomerate are deposited between two layers  2 ,  3  ( FIG. 1 ) of structural fibers, generally glass fibers, impregnated with a binder, generally resin, and are wrapped in a helical arrangement on a cylindrical mandrel  4  which rotates about a horizontal axis A in the direction B, so as to form a tubular manufactured article of which the layer  2  constitutes the internal lining, the layer  3  constitutes the outer wrapping and the agglomerate, provided by the mixing apparatus, constitutes the intermediate layer, which is designed to stiffen the tubular manufactured article and which, in the example described here, is assumed to be provided by superimposing a pair of layers  5 ,  6 , each of which is dispensed by a mixing line. The structure of the mandrel  4  and the means for its movement referenced here are assumed to be of a type known in the background art and are not described hereinafter for the sake of conciseness in description. In particular, it is assumed that the mandrel is actuated with a rotary motion about the axis A combined with an advancement motion in the direction B, such that the advancement stroke performed at each turn of the mandrel is equal to the pitch of the helical wrapping with which the layers are applied in order to provide the complete surface covering of the mandrel. 
         [0021]    The apparatus  1  is composed ( FIG. 4 ) of a frame which comprises two mutually parallel walls  7 ,  8 , which are stiffened by a horizontal connecting surface  9 . In the opposite lateral portions of the walls  7 ,  8  there are respective circular openings, through which two tubular elements  10 ,  11  are guided which are mutually parallel and are fixed to the walls  7 ,  8 . The tubular elements  10 ,  11  constitute the jackets of two screw feeders  12 ,  13  for feeding the granular inert material which contributes to the formation of the intermediate layer  5 . The inert material is unloaded into the feeders  12 ,  13  through respective distribution tubes  14 ,  15  ( FIG. 5 ) which branch out in a fork-like arrangement from a common feeder pipe  16  which is connected to a container of the granular inert material. 
         [0022]    The jackets  10 ,  11  of the feeders are provided in a lower region with discharge openings  17 ,  18 , through which the granular inert material, fed from above through the tubes  14 ,  15  and pushed by screw feeders  19 ,  20  of the feeders  12 ,  13 , is conveyed toward intake ports  21 ,  22  of two underlying mixing devices  23 ,  24  ( FIGS. 2 ,  3 ), in which the mixing with a binder is performed and the amalgamation of the agglomerate intended to form on the mandrel  4  the intermediate layer  5 ,  6  of the manufactured article is completed. 
         [0023]    For the actuation of the two screw feeders  12 ,  13 , the shafts  25 ,  26  have respective portions whose diameter is smaller than the one on which the screw feeders  19 ,  20  are wound, said screw feeders lying outside the jackets  10 ,  11  and being connected to a motor drive assembly, generally designated by the reference numeral  27  ( FIG. 4 ). Said assembly comprises a box-like structure  28 , which is composed of a pair of walls  29 ,  30  which are rigidly coupled at right angles to the wall  7  and to the front edges of which two plates  31 ,  32  which are parallel to the wall  7 , are rigidly coupled. The plates  31 ,  32  are joined by a flange  33  which cantilevers out from the plate  32  and supports, with a rib  34 , an elongated plate  35 , hereinafter referenced as strip, which is flat and parallel with respect to the plate  31 . 
         [0024]    Two supports  36 ,  37  ( FIGS. 4 ,  5 ) are fixed to the plate  31  and to the strip  35 , and respective bearings for rotary support of the shaft  25  of the screw feeder  19  are arranged therein. 
         [0025]    A friction clutch system  38  is arranged on the portion of the shaft  25  that lies outside the jacket  10 , and a pulley  39  is functionally associated therewith and is provided with a peripheral set of teeth on which a toothed belt  40  meshes. The friction clutch system  38  comprises pneumatically-actuated elements in order to allow the rotary coupling and uncoupling of the pulley  39  from the shaft  25  when the screw feeder  19  is to be actuated or respectively stopped. 
         [0026]    The belt  40  is closed in a loop around a second pulley  41 , which is keyed to the output shaft  26   a  of a gearmotor  42  which is coupled by means of a flange, in a cantilever arrangement, to the wall  30 . The actuation of the gearmotor produces the direct actuation of the screw feeder  20  and the rotary actuation of the screw feeder  19  by means of the transmission composed of the pulley  41 , the belt  40 , the pulley  39  and the friction clutch system  38 . A belt tensioning roller  43  ( FIG. 4  at  5 ) is conveniently fixed to the plate  32  in a cantilever arrangement, avoids the skipping of the belt  40  and thus ensures a uniform dosage of the inert material toward the mixing devices  23 ,  24 . 
         [0027]    The mixing devices  23 ,  24  are constructively similar to the above-described feeders  12 ,  13 . As more clearly shown by  FIG. 3 , the reference numerals  44 ,  45  designate the cylindrical jackets, in which the screw feeders  46 ,  47  rotate which are arranged below the feeders  12 ,  13  and run parallel to them. The jackets  44 ,  45 , downstream of the wall  8 , are provided with connections  48 ,  49  ( FIGS. 1 ,  2 ), through which the binder and any catalysts to be mixed with the granular inert material conveyed by the feeders  12 ,  13  are introduced in the jackets. 
         [0028]    The two mixers  23 ,  24  are significantly longer than the feeders  12 ,  13  in order to ensure a suitable homogeneous amalgamation of the agglomerate that forms the intermediate layer  5 ,  6 . The jackets  44 ,  45 , in a manner similar to the jackets  10 ,  11 , are supported in the walls  7 ,  8  and are connected thereto by way of fixing means  50 ,  51  of any type, capable of allowing quick disassembly of the screw feeders and to perform inspections and the necessary mixer cleaning operations. 
         [0029]    At the discharge outlets of the jackets  44  and  45  there are two respective bending elements  52 ,  53  ( FIGS. 1 ,  2 ,  3 ) for guiding and wrapping ribbons  54  unwound from respective reels  55 . The ribbons  54  are made of permeable material, for example fabric, non-woven fabric and the like, in order to be able to be impregnated by the binder and facilitate the adhesion of the agglomerate to the layers  2  and  3  of the manufactured article. Each bending element  52 ,  53  is constituted by a sort of funnel-shaped chute, which has a nozzle  56  for expelling the agglomerate, which is aligned with the axis of the respective screw feeder  46 ,  47 . The bending elements  52 ,  53  are intended to accompany and longitudinally bend upward the lateral edges of the ribbons  54 , which are made to slide by traction below them, so as to wrap them around the agglomerate that exits from the nozzles  56  of the two mixers  23 ,  24 . 
         [0030]    In a manner similar to the feeders  12 ,  13 , the shafts  57 ,  58  of the screw feeders  46 ,  47  also have reduced-diameter portions connected to a motor drive assembly designated by the reference numeral  59  ( FIG. 3 ). The shaft  57  can rotate, by means of bearings, in supports  60 ,  61  which are fixed to the plate  31  and to a second strip  62 , which is coplanar and arranged below the strip  35 . A friction clutch system  63  is arranged on the shaft  57  and a toothed pulley  64  is functionally associated therewith and is engaged by a toothed belt  65 . The friction clutch system  63  is similar to the one that actuates the friction clutch system  38  of the feeder  12  described above, i.e., it comprises a pneumatically-actuated element to allow the coupling and uncoupling of the pulley  64  with respect to the shaft  57  and therefore of the screw feeder  46 . The belt  65  is closed in a loop around a second pulley  66  and tensioned by means of a belt tensioning roller  67  ( FIG. 5 ), which is fixed in a cantilever fashion on the plate  32 . The pulley  66  is keyed onto an output shaft  68  of a gearmotor  69 , which is flanged in a cantilever fashion to the wall  30  of the frame  28 . The shaft  68  is connected to the shaft  58  of the screw feeder  47  and is supported in a bearing which is accommodated in a support  70  which is fixed to the strip  62  which is coplanar to the strip  35 . 
         [0031]    The operation of the apparatus according to the invention, albeit entirely evident from the provided description, is as follows. The granular inert material, fed from the tube  16  and from the branches  14 ,  15  through the discharge outlets  17 ,  18  and the intake ports  21 ,  22 , is conveyed into the feeders  12 ,  13  and then transferred by the screw feeders  19 ,  20 , with a regular flow, into the mixers  23 ,  24 , where it receives the addition of the resin binder and the catalysts fed through the connections  48 ,  49 . 
         [0032]    The mixing action performed by the screw feeders  46 ,  47 , as the agglomerate advances toward the output nozzles  56 , forms an increasingly homogeneous amalgamation. As the agglomerate exits from the nozzles  56 , it is wrapped by the ribbons  54  guided under the bending elements  52 ,  53  and contoured and closed in a tube-like configuration so as to form two cylindrical beads of agglomerate having a pasty consistency, which by depositing on the cylindrical surface of the mandrel, due to the axial translational motion of the latter, wrap with a continuous tension around the mandrel, forming a layer  5 ,  6  which covers uniformly the previously applied layer  2 . 
         [0033]    As can be seen, the described apparatus therefore achieves the proposed aim and objects. In particular, by adjusting the speed of the gearmotors  42 ,  69 , it allows to control the flow of inert material and agglomerate. At the same time, by controlling the flows of binder and of any catalysts by means of a traditional pumping system, it is possible to optimize the percentages of the components of the agglomerate, reducing the excesses of binder which would otherwise be lost or poorly used and ensuring constancy of the characteristics. 
         [0034]    An important prerogative of the described apparatus is provided by the friction clutch systems  38 ,  63 , which allow to activate or deactivate the feeder  12  and respectively the mixer  23  so as to provide one or two beads of agglomerate and obtain a single- or double-thickness intermediate layer  5 ,  6 . 
         [0035]    Another important advantage of the described apparatus is that it can be installed at different levels with respect to the level of the mandrel  4 , particularly above it, thus allowing the simple deposition of the agglomerate directly on the mandrel and its distribution by means of spatulas or other devices capable of leveling its irregularities. 
         [0036]    The disclosures in European Patent Application No. 08425073.7 from which this application claims priority are incorporated herein by reference.