1. Field of the Invention
The present invention relates generally to a method of producing a reinforced rubber hose, and more particularly to a method suitable for producing a relatively short reinforced rubber hose with an optimum strength, by utilizing a plastic mandrel.
2. Discussion of the Prior Art
According to a known method, relatively short reinforced rubber hoses such as fuel hoses and Freon hoses for motor vehicles are produced usually in the manner described below.
Initially, a relatively long rubber or plastic mandrel reinforced by a core and having a length of about 100-130 m is prepared. On the outer surface of this long mandrel, there is extruded an unvulcanized inner rubber tube. A tubular reinforcing layer such as a fiber layer is formed on the outer surface of the inner rubber tube, and an unvulcanized outer rubber tube is extruded on the outer surface of the tubular reinforcing layer. Then, the unvulcanized inner and outer rubber tubes on the long mandrel are vulcanized in a known manner, whereby a long rubber hose is formed on the long mandrel. The long mandrel is removed from the prepared long rubber hose, by utilizing a hydraulic pressure, and the long rubber hose is cut into short rubber hoses having a desired length (usually, 100-300 mm).
On the other hand, the removed long mandrel is returned to the first step for extruding the unvulcanized inner rubber tube thereon, so that each portion or length of the mandrel is used repeatedly.
In the prior method described above wherein the long mandrel is reclaimed as it is, the prepared long rubber hose is subjected to an excessively high hydraulic pressure generated by a suitable hydraulic device, in order to remove the long mandrel from the long rubber hose. To withstand such a high hydraulic pressure, the rubber hose is reinforced to a larger extent than practically required. For instance, a Freon hose reinforced by a polyester layer and having an outside diameter of 24 mm has a nominal operating pressure of 30 kg/cm.sup.2, and is designed to withstand up to 180 kg/cm.sup.2. However, this Freon hose should be reinforced so as to withstand a hydraulic pressure of 230 kg/cm.sup.2 applied upon removal of the mandrel from the hose. Thus, the hose should be reinforced more than required in practical use.
Further, the long mandrel repeatedly used as it is tends to be expanded due to heat during vulcanization of the unvulcanized rubber tubes, whereby the outside diameter of the long mandrel is likely to increase. Also, the mandrel tends to be damaged during the repeated use. Hence, the long mandrel should be regularly checked for an undesirable increase in its outside diameter and its surface condition, in order to prevent a variation of the inside diameter of the produced rubber hose from the nominal value. Moreover, the conventional method requires a space for storing long mandrels for replacing the consumed mandrel.