FR2598653A1 - Process for manufacturing air chambers for tyres - Google Patents

Abstract

The invention relates to the manufacture of air chambers. It relates to a manufacturing process in which the ends of a tube 6 of a thermoplastic material are cut off by cutters 2a, 2b of a cutting member 1 which simultaneously ensure the heating of the cut face, between 250 and 350 DEG C, for 2 to 4 s. Next, the cutting member 1 and its base 5 are withdrawn and the cut faces are immediately brought into abutment by moving the holding members 3, 4 closer together. Application to the manufacture of air chambers for bicycle tyres.

Description

 The present invention relates generally to a method of manufacturing inner tubes intended for vehicle tires such as bicycles or the like, the inner tubes being formed from a thermoplastic resin.

 Conventional inner tubes for vehicle tires (referred to simply as "inner tubes" hereinafter in this specification) generally have a simple construction since the two ends of a main tube-shaped body, extruded in tubular form, are sleeved at both ends, and a valve is attached. In general, vulcanized natural or synthetic rubber can be used as the material of the inner tube body, however, recent improvements in thermoplastic resins are important enough for Japanese published patent (examined) Nos. 56-39805 to describe a process. manufacturing using a material whose quality is better suited to inner tubes than vulcanized rubber, and the possibilities of using new materials of excellent quality are great in the future.

 A method of manufacturing a conventional inner tube formed from vulcanized rubber is now described briefly. The rubber mixture is extruded in the form of a tube using a extruder, and is cut to a determined length, after a cooling operation. The valve is then glued to the body of the extruded tube and the connection operation is then carried out at the two ends of the body. In the case of the connection operation, the two ends of the tube body are cut simultaneously by heating knives so that the cut faces can be immediately brought into abutment against one another and adhere while being under compression. Finally, the vulcanization operation is carried out. The mechanical resistance of the main body of the tube, the adhesive force existing between the valve and the main body, and the resistance of the part forming the connector are given to the tube by the operation. vulcanization. Thus, the vulcanization operation is very important for obtaining the mechanical strength necessary for the operation of the air chamber.

 The air chamber formed from a thermoplastic resin can be produced by a simpler manufacturing process which does not require the vulcanization operation, even during manufacturing. A conventional method of manufacturing the inner tube formed of a thermoplastic resin is now described briefly. First, the material is extruded in the same way as in the case of vulcanization of a rubber tube, and the cutting operation is carried out after cooling. The valve is bonded to the main body of the extruded tube, by a bonding agent, by high frequency welding or by ultrasonic welding so that the connection operation is carried out. In this connection operation, the two ends of the tube are superimposed on 5 to 10 mm, and are connected by a bonding agent or by high frequency welding.

 In the conventional method of manufacturing the air chamber formed from the aforementioned thermoplastic resin, the rotation of the tire causes jerks during use, given the superposition of the product at the connection part, so that the chambers air of advanced characteristics have drawbacks.

 In addition, the bonding operation by bonding presents dangerous working conditions due to the use of an organic solvent, and is tedious, for example due to the drying time of the bonding agent or dissolution. In addition, the connection operation by high frequency or ultrasonic welding requires significant and tedious work because of the separation necessary so that the adhesive does not settle between the internal face of the upper part of the body and the internal face of its lower part.

 In addition, in the operation of connecting an inner tube of a thermoplastic resin, making a connection simply by depositing a bonding agent and compression, between two cutting faces, is not possible and prevents an end connection because the material does not have bonding properties, and a step of increasing mechanical strength, called vulcanization, is not used as in the case of the connection of a tube formed of a material which can be vulcanized.

 The invention relates to a safe and easy method of manufacturing an air chamber, having a connection part which poses no problems during its implementation and eliminating the drawbacks of the aforementioned known methods.

 More specifically, the method of manufacturing air chambers according to the invention comprises cutting and welding by heating the two end parts of the main body of the tube with a heating knife, then immediately abutting the cut faces, l one against the other, so that they are compressed one against the other, the return of the connection part to the physical conditions prior to the melting operation, after cooling, and the realization of the connection operation.

 Thanks to the connection operation in abutment, the connection part has a construction without overlap, so that the inner tube does not pose problems although the connection can be produced in a safe and easy manner.

Other characteristics and advantages of the invention will be better understood on reading the description which follows of a preferred embodiment, made with reference to the appended drawings in which
Figure 1 is a perspective of the main parts of the connecting device, in an embodiment of the invention;
Figure 2 is an enlarged elevation showing the edge of the cutting tool used in the apparatus of Figure 1
Figure 3 is a section showing how the holding members of the apparatus of Figure 1 ensure the retention of the air chamber; and
Figures 4, 5 and 6 are sections each representing an operating state of the device of Figure 1.

 In the various figures, identical references designate similar elements.

 In a preferred embodiment of the invention, a thermoplastic polyurethane is extruded in the form of a tube 0.65 mm thick and 27 mm wide flat, and the tube is cut to a determined length, after the cooling operation. The valve is bonded by high frequency welding, during the connection operation, as indicated in the description which follows.

 Figure 1 is a perspective view showing the essential part of a connection device, according to an embodiment of the invention which comprises a heating member 1 intended to move vertically with a heating device, and a sensor intended to be used for temperature regulation and arranged inside, a cutting member 2 or knife being mounted on each side of the heating member 1. The cutting member 2 is mounted with a certain inclination relative to the direction A of movement so that the space between the cutting blades 2a and 2b can be precisely adjusted by vertical displacement of the mounting position. The face of the edge of the cutting member 2 which is opposite to the heating member 1, is polished and forms a right angle with respect to the main body of the tube, that is to say that this face and the direction A of displacement are parallel, so that the cutting faces can be heated and melted uniformly after the cutting operation of the main body of the tube. Although the angle formed by the edge of the cutting member 2 is advantageously as acute as possible so that the quality of cutting is good, the face forming the angle a is polished in a plane making an angle of 15 to 200 with the face placed on the side of the heating member 1 as shown in FIG. 2, because an angle that is too small reduces the conduction of the heat coming from the heating member 1. The temperature of the edge of the heating member 2 section is adjusted so that it keeps a determined value between 250 and 350 C. The upper support member 3 is intended to open or close vertically relative to the lower support member 4 so that the body main 6 can be firmly tightened and retained horizontally between the support members 3 and 4. In addition, the members 3 and 4 are intended to move to the right and to the left in the directions B and C. A support base 5 is intended to move vertically, that is to say in the direction D. L 'cutter member 2 and the support members 3 and 4 are intended to ensure the positioning operation, by displacement relative to the support base 5 constituting a reference.

 Figure 3 is a section on which the main body 6 of the tube is clamped and held in the support members 3 and 4, from above and from below. The main body 6 is held horizontally by the upper holding member 3. The lower retaining member 4 is machined so that it has a suitable shape so that the body 6 can be completely housed in the retaining member 4.

 The connection operation by implementing the device is now described with reference to FIGS. 1 and 4 to 6.

 First, as shown in Figure 1, the two end parts of the body 6 of the tube are held by the holding members 3 and 4. At this time, it is preferable that the end of the body 6 is cut over a distance as small as possible so that the tube is not wasted. The tube should be cut over 10 to 20 mm so that the cut pieces cannot stick to the cutting member 2 and can be expelled by blowing air.

 The heating element 2 is moved downward, in the direction of arrow A as indicated in FIG. 4, so that the two end parts of the body 6 are cut by the element 2. Simultaneously, the appliance remains in the position shown in Figure 4 so that the cut face is heated and melted. The space between the holding members 3 and 4 and the edge of the cutting member 2 then becomes the length of the cut and melted part. The length of this part, as well as the holding time, i.e. heating time, the melting time and the temperature of the edge of the cutting member are important parameters for the adjustment of the various operating conditions. In the embodiment considered, the corresponding space, that is to say the length of the molten section, is preferably between 0.3 and 0.7 mm, and the holding time, that is ie heating and melting, is between 2 and 4 s.

 The cut pieces of the body 6 are expelled by compressed air. As shown in Figure 5, the support members 3 and 4 are open to the right and to the left, in direction B, so that the melted and cut face of the body 6 is spaced from the cutting member 2.

The heating member 1 is then immediately returned to its initial position and the support base 5 is moved in the direction D. As also shown in FIG. 5, the right and left support members 3 and 4 are properly placed abutted against each other by displacement in direction C so that they cooperate by compression. These operations must be carried out quickly so that the cut and melted faces of the body 6 cannot cool.

 After cooling for 3 to 10 s in the compressed state, the holding members 3 and 4 are opened vertically so that the connected tube is extracted. At this time, the face of the upper holding member 3, at the level of the connection part of the body 6, is connected to the face of the lower support 4 by a burr of the connection part. A powder is applied beforehand as a lubricant from the surface to the internal face of the main body 6 so that sticking is avoided. A surface lubricant, such as a liquid, especially silicone or the like, has detrimental effects on the fitting. On the other hand, intangible starch or calcium carbonate powders, having a granular diameter of 5 to 50 μm which are generally used in the dusting industry, are very suitable.

 In the embodiment described, the two end parts of the tube are cut then heated and melted by the cutting faces of the heated cutting member, and the melted faces are immediately brought into abutment against each other so that the tube formed of a thermoplastic resin can be connected very easily to itself, under safe circumstances and during a simple operation.

 In addition, in the embodiment considered, the material used is a thermoplastic polyurethane, subjected to a temperature of 250 to 3500C by the cutting member, for 2 to 4 s of heating and melting, the length of tube which undergoes the cutting and melting being from 0.3 to 0.7 mm. Air chambers of all sizes, using many types of thermoplastic resins, can be manufactured by adjusting the operating conditions.

 The foregoing description indicates that the inner tube can be made safely, simply and easily with a thermoplastic resin by end fitting. The air chamber of high characteristics, does not disturb the operation by its connection part and can be produced at a low cost, during a small number of steps.

 Of course, various modifications can be made by those skilled in the art to the methods which have just been described only by way of nonlimiting examples without departing from the scope of the invention.

Claims (5)

 1. A method of manufacturing inner tubes for vehicle tires, characterized in that it comprises the simultaneous cutting, with heating cutters (2a, 2b), of the two end parts of a tubular main body formed of a thermoplastic resin, so that the cut faces of this body are heated and melted by the cutting members, then the connection by immediate end-to-end arrangement of the cut and melted faces 11 one against the other.  2. Method according to claim 1, characterized in that it comprises moving the cutting member (2a, 2b) in a direction perpendicular to the body of the tube at the time of the tube cutting operation.  3. Method according to claim 1, characterized in that the cutting member (2a, 2b) has a face parallel to the cutting plane of the main body and another face which makes an angle of 15 to 200 with the first face.  4. Method according to claim 1, characterized in that the thermoplastic resin is a thermoplastic polyurethane, the temperature of the cutting edge of the cutting member is adjusted between 250 and 3500C, and the heating time of the face of the cut body by the cutting member is between 2 and 4 s.  5. Method according to claim 1, characterized in that it further comprises the spreading of an impalpable powder of a surface lubricant on the internal face of the part of the body of the tube which must be cut.