Abstract:
A resinous hose formed by the process for producing a resinous hose, wherein the hose comprises cylindrical portions extending rectilinearly and a bent bellows portion wherein the bellows portion includes a bellows wall having continuous crests and valleys, and a non-bellows wall located on the side diametrically opposite to the bellows wall. The outside diameter of the valleys of the bellows wall is smaller than an outside diameter of the cylindrical portions, and an outside diameter of the non-bellows wall is larger than the outside diameter of the cylindrical portions.

Description:
This is a division of application Ser. No. 09/693,959 filed Oct. 23, 2000 now U.S. Pat. No. 6,447,709. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for producing a resinous hose formed from a thermoplastic resin and having bent portions. 
     2. Description of the Related Art 
     A bendable rubber hose is conventionally used as a radiator hose for an automobile, which is required to be mounted to extend within a narrow engine room. Alternatively, various hoses made from a resin material that is lightweight as compared with the rubber have been proposed. For example, Japanese Patent Application Laid-open No. 7-71663 discloses a radiator hose used by bending a flexible resinous hose having a bellows-shaped unevenness formed thereon into a predetermined shape. 
     However, the conventional radiator hose described in Japanese Patent Application Laid-open No. 7-71663 suffers from the following problem: The resinous hose is arranged in the elastically bent state. For this reason, when the internal pressure of cooling water is applied to the resinous hose, the bent resinous hose is stretched to the original rectilinear shape and hence, the shape of the hose is not stable. 
     Therefore, it is conceived that a resinous hose having the bellows-shaped unevenness formed thereon is plastically deformed into the shape of use, so that the shape at the time of application of the internal pressure is stabilized. To plastically deform the resinous hose having the bellows-shaped unevenness formed thereon into a desired shape, a coil spring may be inserted into the heated resinous hose, or a pressure may be applied to the inside of the resinous hose, thereby applying an external force to the hose to bend the hose, while preventing the hose from being crushed. Then, the hose may be cooled and solidified and thereafter, the coil spring may be withdrawn, or the internal pressure may be removed. Another method is to insert a resinous hose having the bellows-shaped unevenness formed thereon into a die, and then heat the die to form the resinous hose having the desired shape. 
     However, a resinous hose bent by the above methods suffers from the following problem: The steps of producing such hoses are not only complicated and increase the cost, but also when the resinous hose is used in a high-temperature and a high-pressure environment, as is the case with the radiator hose, the pleats of the bellows are stretched by a creep phenomenon, whereby the bent shape is gradually varied. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a resinous hose at a low cost, wherein even if the hose is used in a high-temperature and high-pressure environment, the bent shape thereof can be maintained over a long period of time. 
     To achieve the above object, according to a first aspect and feature of the present invention, there is provided a process for producing a resinous hose formed from a thermoplastic resin having cylindrical portions extending rectilinearly, and a bent bellows portion, the process comprising a first step of forming a cylindrical hose by extrusion, a second step of forming a bellows portion which has pleats each shaped to be differentiated circumferentially, at least at a lengthwise portion of the extruded hose, a third step of heating the hose having the bellows portion formed thereon into a plastic state, and a fourth step of bending the hose by applying a pressure to an inside of the hose heated into the plastic state, thereby stretching the pleats of the bellows portion, and a fifth step of cooling the bent hose. 
     With the above process, the bellows portion which has pleats differentiated circumferentially in shape are formed at least at a lengthwise portion of the extruded hose, and the pressure is applied to the inside of the hose in the heated state to stretch the pleats of the bellows portion, thereby bending the hose. Therefore, any portions of the hose can be bent through any angles in any directions by only changing the positions of the bellows portion, the shapes and the numbers of the pleats and the like. In addition, the bellows portion can be bent only by heating and pressurizing the hose and hence, special equipment is not required, leading to a reduced manufacture cost. Moreover, the pleats of the bellows portion of the completed hose are almost stretched out, whereby the bellows structure is lost. Therefore, even if the hose is exposed to a high temperature and a high pressure, the bent angle of the bellows portion is not varied, and hence, the shape of the hose can be maintained over a long period of time. 
     According to a second aspect and feature of the present invention, in addition to the first feature, the bellows portion of the hose formed in the second step includes a bellows wall having continuous crests and valleys, and a non-bellows wall located on the side diametrically opposite to the bellows wall. Additionally, in the second step, a portion of the cylindrical hose formed in the first step is displaced radially inwards to form the valleys on the bellows wall, and a portion of the cylindrical hose is displaced radially outwards to form the non-bellows wall. 
     With the above feature, a portion of the cylindrical hose is displaced radially inwards to form the valleys of the bellows wall, and a portion of the cylindrical hose is displaced radially outwards to form the non-bellows wall in the second step. Therefore, the decrease in thickness of the bellows wall that may be thinned during the formation can be suppressed to the minimum, and the thickness of the non-bellows wall that may be thickened during the formation can be positively decreased, whereby the thickness of the bellows portion of the entire hose can be uniform over the entire region. Thus, durability can be enhanced without increasing the weight of the hose and without decreasing the sectional area of a flow path. 
     According to a third aspect and feature of the present invention, there is provided a resinous hose formed in the second step of a process for producing a resinous hose according to the first feature, wherein the bellows portion includes a bellows wall having continuous crests and valleys, and a non-bellows wall located on the side diametrically opposite to the bellows wall, the outside diameter of the valleys of the bellows wall being smaller than the outside diameter of the cylindrical portions, and the outside diameter of the non-bellows wall being larger than the outside diameter of the cylindrical portions. 
     With the above feature, the outside diameter of the valleys of the bellows wall is smaller than the outside diameter of the cylindrical portions, and the outside diameter of the non-bellows wall is larger than the outside diameter of the cylindrical portions. Therefore, the decrease in thickness of the bellows wall that may be thinned during the formation can be suppressed to the minimum, and the thickness of the non-bellows wall that may be thickened during the formation can be positively decreased, whereby the thickness of the bellows portion of the hose can be uniform over the entire region. Thus, the durability can be enhanced without increasing the weight of the hose and without decreasing the sectional area of a flow path. 
     The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A to  7  show embodiments of the present invention, wherein 
     FIG. 1A is a side view of a completed resinous hose; 
     FIG. 1B is a view taken in the direction of an arrow  1 B in FIG. 1A; 
     FIG. 2 is a side view of the resinous hose before being bent; 
     FIG. 3 is a sectional view taken along a line  3 — 3  in FIG. 2; 
     FIG. 4 is a sectional view taken along a line  4 — 4  in FIG. 2; 
     FIG. 5 is a sectional view taken along a line  5 — 5  in FIG. 2; 
     FIGS. 6A to  6 H are views showing steps of producing the resinous hose; and 
     FIG. 7 is a longitudinal sectional view of a resinous hose before being bent according to a second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will now be described with reference to FIGS. 1A to  6 H. 
     As shown in FIGS. 1A and 1B, a hose H made of a thermoplastic resin and used as a radiator hose for an automobile includes first, second, third and fourth cylindrical portions  11 ,  12 ,  13  and  14  any of which is formed into a cylindrical shape, a first bellows portion  15  provided between the first and second cylindrical portions  11  and  12 , a second bellows portion  16  provided between the second and third cylindrical portions  12  and  13 , and a third bellows portion  17  provided between the third and fourth cylindrical portions  13  and  14 . The first, second and third cylindrical portions  11 ,  12  and  13  are bent on the same plane at the first and second bellows portions  15  and  16 , and the fourth cylindrical portion  14  is bent at the third bellows portion  17  so as to extend out from the plane. 
     FIGS. 2 to  5  show the shape of a hose H at a stage before bending of the first to third bellows portions  15  to  17 . The first to third bellows portions  15  to  17  each of which is formed into the bellows-shape having three, five and two pleats  15   a ,  16   a  and  17   a , respectively. Each of the pleats  15   a ,  16   a  and  17   a  includes a large-diameter crest  18  and a small-diameter valley  19 . The small-diameter valley  19  has the same cross section as cross sections of the first to fourth cylindrical portions  11  to  14  and has a center O commonly with the first to fourth cylindrical portions  11  to  14 . The large-diameter crest  18  has a center O′ of its cross section, which is eccentric by ε to the center O of the cross section of the valley  19 . 
     When the hose H is viewed axially, the pleats  15   a ,  16   a  and  17   a  of the first to third bellows portions  15  to  17  disappear on generating lines a, b and c parallel to the axis of the hose H, respectively. Each of these portions is a non-bellows wall  31  of the hose H. The unevenness of the corrugated shape of each of the pleats  15   a ,  16   a  and  17   a  is the largest at diametrically opposite portions of the hose H with respect to the generating lines a, b and c. Each of these portions is a bellows wall  32  of the hose H. Two of the generating lines a and b lie on the same straight line, but the other one generating line c lies at a location displaced through a circumferential angle of 45° from the two generating lines a and b. 
     In the present embodiment, the smallest thickness of the hose H is 1.0 mm, and the inside diameter of the valley  19  of the hose H (the inside diameters of the first to fourth cylindrical portions  11  to  14 ) is 30 mm. A difference between the diameters of the crest  18  and the valley  19  of the hose H is 3.5 mm, and the pitch between the adjacent pleats  15   a ,  16   a ,  17   a  is 6.3 mm. 
     Steps of producing the hose H will be described with reference to FIGS. 6A to  6 H. 
     First, as shown in FIG. 6A, a cylindrical hose H as a blank is formed by an extrusion using a thermoplastic resin such as TPO (an olefinic thermoplastic elastomer) and PA (a polyamide) as a starting material. 
     Then, as shown in FIG. 6B, pleats  15   a ,  16   a  and  17   a  of first to third bellows portions  15  to  17  are formed in the hose H by a corrugator  23  including a pair of die groups  21  and  22 . Each of the die groups  21  and  22  is comprised of a large number of block-shaped dies  21   a ,  22   a —connected together in an endless fashion. The dies  21   a ,  22   a —of both the die groups  21  and  22  have molding surface portions for forming the pleats  15   a ,  16   a  and  17   a  on opposed surfaces. The hose H formed by the extrusion and having a high temperature is clamped between the dies  21   a  and  22   a  of the revolved die groups  21  and  22  and drawn by suction to become into close contact with the molding surface portions of the dies  21   a  and  22   a , whereby the pleats  15   a ,  16   a  and  17   a  are formed to produce a continuous hose H having a shape as shown in FIG.  6 C. 
     Subsequently, as shown in FIG. 6D, the continuous hose H is cut at a predetermined length having first to fourth cylindrical portions  11  to  14  and first to third bellows portions  15  to  17 . As shown in FIG. 6E, female couplers  24 ,  24  are fixed to opposite ends of the cut hose H by adhering or welding, and a male coupler  25  as a blind plug is coupled to one of the female couplers  24 . The female coupler  24  and the male coupler  25  are known and coupled together into a liquid-tight state by only pushing them to each other, and the coupling of these couplers is released by pushing a button (not shown) mounted on the female coupler  24 . 
     Then, as shown in FIG. 6F, water containing 50% of a coolant incorporated therein is poured into the hose H through the other female coupler  24  (i.e., the coupler  24  to which the male coupler  25  is not coupled) such that the water occupies about two third of the internal volume of the hose H. Thereafter, as shown in FIG. 6G, the male coupler  25  as the blind plug is coupled to the other female coupler  24 , thereby encapsulating the water in the hose H. 
     Subsequently, as shown in FIG. 6H, the hose H in which the water is encapsulated is placed into a thermostatic chamber  26  and heated at 120° C. for 2 hours. This causes the water in the hose H to be heated into vapor, thereby increasing the internal pressure in the hose H, for example, to 2×10 5  Pa. Therefore, the pleats  15   a ,  16   a  and  17   a  of the hose H brought into a plastic state under the influence of a high temperature are stretched out under the action of the internal pressure. At this time, the unevenness of the corrugated shape of each of the pleats  15   a ,  16   a  and  17   a  is non-uniform in circumferential direction of the hose H. Therefore, in locations on the generating lines a, b and c where the pleats  15   a ,  16   a  and  17   a  don&#39;t exist, the hose H is little stretched axially. On the other hand, in locations opposite to the generating lines a, b and c where the unevenness of the corrugated shape is high, the hose H is stretched axially to the largest extent. As a result, the first to third bellows portions  15  to  17  of the hose H are bent through a predetermined angle with the generating lines a, b and c being on an inner side, whereby the hose H having a desired bent-shape is formed. When this hose H is removed out of the thermostatic chamber  26  and cooled down to ambient temperature lower than a plastic temperature, the shape of the hose H is stabilized in the predetermined bent-shape. 
     It should be noted that if the hose H is previously heated in a heating oven before it is placed into the thermostatic chamber  26 , thereby previously rising the temperature of the water in the hose, the time of treatment of the hose in the thermostatic chamber  26  can be shortened. 
     The male coupler  25  is removed from the female coupler  24 , whereby the hose H is completed. When the hose H is connected at its opposite ends to a radiator and an engine of an automobile, the operation for mounting the hose H can be finished simply by coupling the female couplers  24 ,  24  at the opposite ends of the hose H to male coupler  25 ,  25  previously mounted to the radiator and the engine. 
     The bending angles of the first to third bellows portions  15  to  17  of the hose H are determined automatically by the number of the pleats  15   a ,  16   a  and  17   a . For example, the hose H of the present embodiment is bent through about 12° per one pleat  15   a ,  16   a ,  17   a  and hence, the bending angle of the first bellows portion  15  having the three pleats  15   a  is about 36°; the bending angle of the second bellows portion  16  having the five pleats  16   a  is about 60°; and the bending angle of the third bellows portion  17  having the two pleats  17   a  is about 24°. 
     In the first to third bellows portions  15  to  17  of the completed hose H, the pleats  15   a ,  16   a  and  17   a  have been almost stretched out and as a result, the bellows structure has been lost. Therefore, even if the hose H is exposed to a high temperature and a high pressure of cooling water when it is used as a radiator hose, the pleats  15   a ,  16   a  and  17   a  cannot be stretched and hence, the bending angles of the first to third bellows portions  15  to  17  cannot be varied over a long period of time. In the embodiment, even if a state at a temperature 120° C. and an internal pressure of 1.25×10 5  Pa is continued for 200 hours, the change in contour of the hose H is little observed. In addition, even if the hose H is stored in ambient temperature over a long period of time, the change in contour of the hose H is little observed. 
     By changing only the positions, shapes and numbers of the bellows-shaped pleats  15   a ,  16   a  and  17   a  which are previously formed in the hose H, any portions of the hose H can be bent through any angles in any directions. Moreover, only by heating the hose H in the thermostatic chamber  26 , the pleats  15   a ,  16   a  and  17   a  are stretched automatically, whereby the hose H is bent. Therefore, special equipment is not required, leading to a reduction in cost. 
     A second embodiment of the present invention will now be described with reference to FIG.  7 . 
     FIG. 7 shows a longitudinal sectional view of a hose H having first, second and third bellows portions  15 ,  16  and  17  formed by a corrugator  23 . The outside diameter of cylindrical portions  11  to  14  having a lengthwise constant circular sectional shape is a given value R 0 , and the thickness of the cylindrical portions  11  to  14  is also a given value t 0 . On the other hand, each of the first, second and third bellows portions  15 ,  16  and  17  includes a bellows wall  32  where crests  18  and valleys  19  are continuous, and a flat non-bellows wall  31 . The outside diameters of the hose H about its center at the bellows wall  32  and the non-bellows wall  31  are different from each other. More specifically, the outside diameter R 1  of the valley  19  of the bellows wall  32  is set smaller than the outside diameter R 0  of the cylindrical portions  11  to  14  (R 1 &lt;R 0 ), and the outside diameter R 2  of the non-bellows wall  31  is set larger than the outside diameter R 0  of the cylindrical portions  11  to  14  (R 2 &gt;R 0 ). 
     In the first embodiment shown in FIG. 2, both of the outside diameter R 1  of the valley  19  of the bellows wall  32  and the outside diameter R 2  of the non-bellows wall  31  are equal to the outside diameter R 0  of the cylindrical portions  11  to  14 . In this case, the bellows wall  32  is stretched during formation of the first to third bellows portions  15  to  17  to have a decreased thickness thereof and on the other hand, the non-bellows wall  31  is not stretched with the thickness thereof being not decreased. Therefore, the thickness of the bellows wall  32  is smaller, and the non-bellows wall  31  is larger. When the first to third bellows portions  15  to  17  are non-uniform in thickness in the circumferential direction in the above manner, the strength of the bellows wall  32  having the smallest thickness is reduced and as a result, the durability of the entire hose H is reduced. If the thickness of the entire hose H is increased in order to prevent the above state, the following problems occur: the thickness of the non-bellows wall  31  becomes excessively large, resulting in an increased weight; and when the outside diameter of the hose H is uniform, the sectional area of a flow path is decreased. 
     In the second embodiment, however, the amount of bellows wall  32  stretched during the formation can be decreased, whereby the decrease in thickness of the bellows wall  32  can be suppressed to the minimum, because the outside diameter R 1  of the valley  19  of the bellows wall  32  is set smaller than the outside diameter R 0  of the cylindrical portions  11  to  14 . In addition, the non-bellows wall  31  can be positively stretched during the formation, whereby the thickness t 2  of the non-bellows wall  31  can be decreased, because the outside diameter R 2  of the non-bellows wall  31  is set larger than the outside diameter R 0  of the cylindrical portions  11  to  14 . As a result, the difference between the thickness t 1  of the bellows wall  32  and the thickness t 2  of the non-bellows wall  31  after the formation can be decreased, whereby the durability of the entire hose H can be enhanced without increasing the thickness of the entire hose H that causes an increase in weight and a decrease in sectional area of the flow path. 
     When the hose H having a thickness t 0  of 2.5 mm and made by extruding the polyamide  12  and TPO (thermoplastic olefin) into a cylindrical two-layer configuration is formed into the same shape as in the first embodiment in FIG. 2, the smallest thickness t 1  of the bellows wall  32  is 1.0 mm, and the smallest thickness t 2  of the non-bellows wall  31  is 2.5 mm and thus, the difference between the smallest thickness t 1  and the smallest thickness t 2  reaches 1.5 mm. On the other hand, when the hose H is formed into the same shape as in the second embodiment in FIG. 7, the smallest thickness t 1  of the bellows wall  32  is increased to 1.5 mm, and the smallest thickness t 2  of the non-bellows wall  31  is decreased to 2.0 mm and thus, the difference between the smallest thickness t 1  and the smallest thickness t 2  is also decreased to 0.5 mm. 
     A coolant liquid was encapsulated in an amount of 50% into each of the hose H in the first embodiment and the hose H in the second embodiment, and these hoses H were subjected to a durability test at a temperature of 130° C. and an internal pressure of 0.2 Mpa. The result showed that the hose H in the first embodiment was broken in 200 hours, and the hose H in the second embodiment was broken in 260 hours. 
     The shapes and the numbers of the bellows-shaped pleats  15   a ,  16   a  and  17   a  are not limited to those in the embodiments and may be changed properly. In short, if the height and the shape of the unevenness of the pleats  15   a ,  16   a  and  17   a  of the hose are varied in the circumferential direction, or the pleats  15   a ,  16   a  and  17   a  are formed at only a circumferential portion of the hose H, a difference can be generated in axially stretched amount among circumferential portions of the hose H to bend the hose H. 
     In the embodiments, the hose H containing water filled therein has been placed into the thermostatic chamber  26 , where it has been heated and pressurized simultaneously by the high-temperature and high-pressure vapor generated from the water. Alternatively, for example, the heating of the hose H may be carried out by a heater or the like, and the pressurization of the hose H may be carried out by the supplying of compressed air or by another means. Therefore, third and fourth steps of the present invention may be carried out simultaneously or in sequence. 
     The hose H according to the present invention can be also utilized in any application other than a radiator hose for an automobile. 
     In the embodiments, the female couplers  24 ,  24  have been mounted at the opposite ends of the hose H, but these female couplers  24 ,  24  are not necessarily required. 
     The material for the hose H is not limited to TPO (thermoplastic olefin) and TPAE (thermoplastic polyamide), and any other thermoplastic resins can be used alone or in the form of a plurality of layers. 
     The outside diameter of the crest  18  of the bellows wall  32  has not been defined in the second embodiment, but its value is suitable to be as large as equal to the outside diameter R 2  of the non-bellows wall  31 . The difference (R 0 −R 1 ) between the outside diameter R 1  of the valley  19  of the bellows wall  32  and the outside diameter R 0  of the cylindrical portions  11  to  14  is also suitable to be as large as equal to the difference (R 2 −R 0 ) between the outside diameter R 2  of the non-bellows wall  31  and the outside diameter R 0  of the cylindrical portions  11  to  14 . 
     Although the embodiments of the present invention have been described in detail, it will be understood that the present invention is not limited to the above-described embodiments, and various modifications in design may be made without departing from the spirit and scope of the invention defined in claims.