Abstract:
A heat-reflective protective sleeve includes a substrate ( 10 ) and a sheet of reflective material ( 20 ) fixed on the substrate ( 10 ). The substrate ( 10 ) is elastically deformable from a non-operating position and the sheet ( 20 ) is pleated on the substrate ( 10 ) in the non-operating position.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a thermal protection sheath and its fabrication method. 
     Thermal protection sheaths are routinely used to insulate fluid pipes, for example in automobile vehicles, and in particular in hydraulic circuits, fuel lines, brake fluid lines, cooling fluid lines and conditioned air lines. 
     This kind of thermal protection sheath includes a substrate covered with a reflective material adapted to reflect infrared radiation. 
     The substrate must be sufficiently flexible to adapt to various shapes of pipe and cover them without creasing. 
     A first technique for covering the substrate with a reflective material consists in applying a coating containing particles of aluminum, for example, directly to the outside surface of the substrate. 
     This kind of aluminized coating preserves good flexibility of the substrate of the protective sheath but has limited reflection properties. This is because the binder used to fix the aluminum particles to the surface of the substrate absorbs some thermal radiation and thereby limits the reflective power of the aluminized coating. 
     A second technique consists in fixing a reflective foil, such as aluminum foil or aluminized film, to the outside surface of the substrate. 
     These foils and films improve the thermal protection provided by the sheath but lack flexibility. In particular, the foils tend to tear if the sheath is deformed, and in particular if it is stretched. 
     U.S. Pat. No. 5,660,899 describes a thermal protection sheath comprising a substrate formed by a corrugated plastics material tube covered with a laminated structure glued at all points to the outside surface of the substrate. 
     The laminated structure and the substrate therefore have exactly the same corrugated tube form and the laminated structure and the substrate are in contact over their entire surface. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to propose a flexible and deformable thermal protection sheath having satisfactory heat-reflecting properties. 
     The thermal protection sheath according to the invention includes a substrate and a reflective foil fixed to the substrate, the substrate being elastically deformable from a relaxed configuration. 
     According to the invention the foil is pleated on the substrate in said relaxed configuration. 
     The reflective foil is therefore pleated on the elastic substrate in order not to impede deformation of the thermal protection sheath, which can therefore be fitted without difficulty to pipes of various shapes, and in particular bent pipes. 
     This is because the foil, forming pleats on the substrate, is in contact with the outside surface of the substrate only at certain points and has an external shape different from that of the substrate. 
     The pleated structure of the reflective foil absorbs deformation of the sheath, the reflective foil becoming respectively more pleated or less pleated as the sheath is compressed or stretched. 
     The pleats in the reflective foil on the substrate are advantageously adapted to form reserves of air that further improve the thermal insulation of pipes protected by the sheath. 
     According to one preferred feature of the invention, the substrate has an outside surface provided with openings and the foil is pleated in line with said openings. 
     Accordingly, on elastic deformation of the sheath, the shape of the openings is modified and the reflective foil can be pleated more or pleated less in line with these openings. 
     Preferably, the foil is pleated inside the openings. 
     This further improves the mechanical strength of the thermal protection sheath, the foil forming substantially no pleats projecting on the outside surface of the sheath. The thermal protection sheath therefore has improved resistance to contact wear. 
     In another aspect, the present invention provides a method of fabricating a protection sheath including a substrate and a reflective foil adapted to be fixed to said substrate. 
     According to the invention, the fabrication method includes the following steps:
         elastically stretching the substrate from a relaxed configuration;   fixing the reflective foil to the stretched substrate; and   elastically shrinking the substrate into said relaxed configuration.       

     This fixing the reflective foil directly to the stretched substrate forms the pleats when the substrate shrinks elastically. 
     Thus the elastic properties of the substrate are used to form the pleats in the reflective foil. 
     In accordance with one advantageous feature of the invention the shrinking of the substrate covered with the reflective foil is forced by means of rollers adapted to press said foil onto the substrate. 
     The rollers therefore hold the foil in contact with the outside surface of the substrate even when the latter shrinks, in particular radially. 
     In accordance with a preferred feature of the invention the foil is pleated inside openings in the substrate during the shrinkage step. 
     As previously described, the pleats formed by the foil are formed inside the openings in the substrate and do not project from the thermal protection sheath. 
     According to one advantageous feature of the invention, the substrate includes braided or knitted heat-shrink threads and during the step of shrinking the substrate the sheath is heated to shrink the heat-shrink threads. 
     Thermal shrinkage of the sheath facilitates the formation of pleats in the foil on the substrate. 
     Other features and advantages of the invention will become more apparent in the course of the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, which are provided by way of non-limiting example: 
         FIG. 1  is a front view of a thermal protection sheath in accordance with a first embodiment of the invention; 
         FIG. 2A  is a perspective view of a portion of the sheath shown in  FIG. 1 ; 
         FIG. 2B  is a view in cross section of the sheath portion shown in  FIG. 2A ; 
         FIG. 3  is a perspective view of a thermal protection sheath according to a second embodiment of the invention; 
         FIG. 4  is a perspective view of a thermal protection sheath according to a third embodiment of the invention; 
         FIG. 5  is a view in longitudinal section of the thermal protection sheath shown in  FIG. 4 ; 
         FIG. 6  shows a fabrication method according to a first embodiment of the invention; 
         FIG. 7  shows diagrammatically rollers used in the fabrication method according to the invention; 
         FIG. 8  shows a fabrication method according to a second embodiment; and 
         FIG. 9  shows a shrinkage step in a preferred embodiment of the fabrication method according to the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A thermal protection sheath according to a first embodiment of the invention is described first and with reference to  FIGS. 1 ,  2 A and  2 B. 
     The sheath includes a substrate  10  and a reflective foil  20  fixed to the substrate  10 . 
     In this example the substrate is tubular and is formed from knitted threads  13 . 
     Because of the knitted structure of the substrate, the latter has a capacity for elastic expansion in the longitudinal and radial direction. It is therefore elastically deformable, which facilitates fitting it over the pipe to be protected, and can be adapted to diverse pipe shapes. 
     The textile can be knitted directly in tubular form, to form a tubular substrate  10 , or knitted flat and only afterwards rolled to form a tube. 
     Any material can be used for the threads, in particular glass fibers, polyamide fibers or polyester fibers. 
     The substrate  10  is therefore a textile substrate, with openings  12  between the threads  13 . 
     As shown in  FIG. 1 , the substrate  10  has an outside surface provided with openings  12  thanks to the meshes formed by the knitted threads  13 . 
     In accordance with the invention, a reflective foil  20  is fixed to the substrate. The foil  20  forms pleats on the outside surface of the substrate  10  in the rest position shown in FIG.  1 . 
     As shown better in  FIGS. 2A and 2B , the foil is fixed to the fibers  13  of the substrate  10  and is pleated inside the existing openings  12  between the knitted threads  13 . 
     The foil  20  therefore forms small irregular pleats in the openings  12 , disposed in all directions on the outside surface of the substrate  10 . 
     The reflective foil  20  is woven from aluminized glass fibers, for example. It is therefore not elastically deformable in itself, but, thanks to its pleated structure on the substrate  10 , it does not impede elastic deformation thereof, and consequently elastic deformation of the thermal protection sheath. The pleats in the reflective foil  20  prevent the sheath from tearing. 
     When the thermal protection sheath shown in  FIGS. 1 ,  2 A and  2 B is fitted to a fluid pipe, such as a hydraulic pipe, for example, the pleats of the reflective foil  20  in line with the openings  12  in the substrate  10  form reserves or pockets of air on the outside surface of the pipe and therefore improve its thermal insulation relative to surrounding sources of heat. 
     Of course, the substrate  10  could equally be made from various textile materials, and in particular formed from braided threads  13 , as shown in FIG.  3 . 
     The threads used can be monofilament threads or multifilament threads and the braided textile preferably includes a mixture of monofilament threads and multifilament threads to confer on it good mechanical strength combined with great elasticity. 
     In this case, the elastic expansion can be radial, when the braided substrate is compressed longitudinally, or longitudinal, when the braided substrate is stretched longitudinally. 
     A thermal protection sheath according to a third embodiment of the invention is described next with reference to  FIGS. 4 and 5 . 
     In this example, the substrate is in the form of a corrugated plastics material tube  14 . 
     The corrugated plastics material tube can be slit longitudinally before applying the reflective foil  20 . 
     The substrate  14  has an outside surface  11  provided with openings  12  in line with the annular recesses  12  in the corrugated tube  14 . 
     AS shown clearly in  FIG. 5 , a reflective foil  20  fixed to the outside surface  11  of the substrate  14  is pleated opposite the openings  12 , inside the annular recesses  12 . 
     Because of its corrugated structure, the substrate  14  can be stretched elastically in the longitudinal direction. 
     Accordingly, when it is stretched in the lengthwise direction, it is able to deform at the level of the annular recesses  12  in particular because of the pleated structure of the reflective foil  20  inside the annular recesses  12 . 
     In this embodiment, as shown in  FIG. 5 , the pleats formed by the reflective foil  20  inside the annular recesses  12  create reserves or pockets of air  15  on the outside surface  11  of the substrate  10 . These reserves  15  of air further improve the thermal insulation capacity provided by the sheath when fitted to a pipe. 
     The pleats formed in the annular recesses  12  are also irregular in shape and in orientation inside the annular recesses  12 . 
     The various embodiments of the protection sheath can be slit longitudinally to facilitate fitting the sheath to a pipe. It is easier to slit the corrugated substrate longitudinally before applying the reflective foil. 
     The sheath has an inside diameter from 5 mm to 65 mm, for example. 
     A method of fabricating a thermal protection sheath according to the invention is described next, firstly with reference to FIG.  6 . 
     In this example, the substrate  10  is a braided textile tube. Of course, an analogous fabrication process can be used for a different substrate, and in particular a substrate in the form of a corrugated tube  14 , preferably slit-longitudinally, or a knitted textile substrate. 
     The fabrication method includes firstly a step of elastically stretching the substrate  10  from a relaxed configuration. 
     Here the braided substrate  10  is elastically stretched in the radial direction. 
     The substrate  10  can be stretched elastically along a continuous line by passing the substrate over a cylindrical mandrel whose diameter is greater than the inside diameter of the substrate  10  in the relaxed configuration. 
     In the case of a knitted structure, as shown in  FIGS. 1 ,  2 A and  2 B, the substrate  10  is elastically stretched in the longitudinal and radial directions to increase its length and its radius. 
     In a second step of the fabrication process the reflective foil  20  is fixed to the stretched substrate  10 . 
     In this embodiment, the reflective foil  20  is laminated onto the substrate  10  in the lengthwise direction of the substrate  10 . 
     In this example two strips of reflective material  20  are fixed to two opposite faces of the expanded substrate  10 . 
     As shown in  FIG. 7 , rollers  21  with a concave profile  21   a  are adapted to apply a strip of reflective material to a respective half-circumference of the expanded substrate  10 . 
       FIG. 6  shows a small area  20   a  of overlap providing a perfect joint between the two strips of reflective material  20  on the substrate  10 . 
     Of course, a different number of strips and rollers  21  for applying them to the substrate  10  could be used, in particular four rollers disposed in quadrature about the tubular substrate  10  and in pairs in two transverse planes offset lengthwise of the tubular substrate  10 . 
     As shown in  FIG. 8 , when fixing the reflective foil  20  to the stretched substrate  10 , the foil  20  could equally be applied in a helix around the substrate  10 . 
     The reflective foil  20  is fixed to the substrate  10  by means of an adhesive. 
     In the conventional way, that adhesive can be a thermoplastic or thermosetting glue or a pressure-sensitive adhesive. 
     Hot air jets or heated rollers  21  can be used if the adhesive must be heated to glue the reflective foil  20  to the substrate  10 . 
     A double-sided adhesive can be applied to the reflective foil  20  before fixing it to the substrate  10 . Alternatively, a double-sided adhesive can be applied directly during lamination of the reflective foil  20  to the substrate  10 , between the foil  20  and the substrate  10 . 
     The substrate  10  then shrinks elastically into its relaxed configuration on leaving the mandrel used during stretching it and fixing the reflective foil  20 . 
     The elastic shrinkage can be unforced and obtained simply by the elastic return of the stretched substrate to its relaxed configuration. 
     As shown in  FIG. 9 , the elastic shrinkage of the substrate  10  covered with the reflective foil  20  can be forced by means of rollers  22   a ,  22   b  adapted to press the foil  20  onto the substrate  10 . 
     In this embodiment, two pairs of rollers  22   a  and  22   b  are used, disposed along the path of the thermal protection sheath after leaving the mandrel. 
     The rollers  22   a  and  22   b  have a semicircular concave profile similar to that of the rollers  21  used for fixing the foil  20  and shown in FIG.  7 . 
     The radius of the semicircular profile of the rollers  22   a  and  22   b  decreases in the direction in which the thermal protection sheath moves on leaving the mandrel to accommodate radial shrinkage of the elastic substrate  10 . 
     Furthermore, the speed of the rollers  22   a  that are on the upstream side relative to the direction of movement of the thermal protection sheath on leaving the mandrel is higher than the speed of the downstream rollers  22   b.    
     The speed ratio provides some lengthwise shrinkage of the substrate  10  on leaving the mandrel. 
     The rollers  22   a  and  22   b  therefore facilitate elastic shrinkage of the substrate  10  and adhesion of the reflective foil  20  to the substrate  10 . 
     Also, the foil  20  is introduced into and pleated inside the openings in the substrate during this shrinkage step so that the pleats formed do not project from the substrate  10  but instead lie inside the openings  12 . 
     If the substrate includes braided or knitted heat-shrink threads, during the step of shrinking the substrate  10  the sheath can preferably be heated to shrink the heat-shrink threads. 
     The rollers  22   a  and  22   b  used during this shrinkage step can therefore be heated. 
     The invention provides a thermal protection sheath having a good capacity for elastic stretching limited only by elastic stretching of the substrate  10  itself or unpleating of the reflective foil  20 . 
     Of course, many modifications can be made to the embodiment described above without departing from the scope of the invention. 
     In particular, the substrate can be stretched longitudinally and/or radially during the stretching step. 
     Also, during elastic shrinkage of the substrate, the thermal protection sheath could travel over a path defined by rods curved in all directions in space to ensure uniform shrinkage of the substrate  10  and uniform pleating of the reflective foil  20 . 
     The number of rollers  22   a ,  22   b  used when shrinking the sheath can be less than or greater than the two pairs of rollers  22   a ,  22   b  described in the above embodiment. 
     The reflective foil used can be a foil made from any synthetic polymer that is metallized and in particular chromium-plated.