SUMMARY OF THE INVENTION 
     The present invention relates, generally, to the shirring of thin walled tubular casings and the like and, more particularly, to an improved shirring mandrel. 
     It is well known in the art, as for example Ives U.S. Pat. No. 3,112,517, to introduce compressed air into the unshirred portion of the casing to inflate the same, whereby it may be more easily carried over the mandrel. 
     It has also been found that spraying the inner surface of the casing, immediately prior to shirring, with a humidifying agent, such as water, results in a shirred casing strand having superior mechanical properties. 
     Implemation of preshirring inflation and humidification has been hindered by the problems of providing for different flow rates for the air and water, and of maintaining uninterrupted fluid flows during doffing, when a severed strand of shirred casing is passed along the entire length of the shirring mandrel and transferred to a receiving mandrel. 
     It is therefore a primary object of the present invention to provide an improved shirring mandrel adapted for preshirring introduction of an inflating medium and a humidifying agent into the casing and more particularly, to introduce these fluids at different flow rates, and without interruption. 
     It is a further object to provide an improved shirring mandrel, adapted as described above, which may be employed with existing shirring machinery with a minimum of modification thereto. 
     With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following description, the claims, and the several views illustrated in the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view of the improved shirring mandrel of the present invention. 
     FIG. 2 is a cross-sectional view taken substantially along line 2--2 of FIG. 1. 
     FIG. 3 is a cross-sectional view taken substantially along line 3--3 of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The mandrel of the present invention comprises a body 1, means for separately conveying two fluids through the body 1, and means for maintaining an uninterrupted flow of both of the fluids during passage of a portion of casing along the entire length of the body 1. 
     As shown in the drawings, the body 1 is a substantially cylindrical hollow member, having outer dimensions identical with those of conventional mandrel, and including first and second body portions 1a and 1c respectively, and a relatively short intermediate body portion 1b therebetween. 
     The fluid conveying means includes first and second fluid passageways 2 and 3 respectively, formed in the body 1. In the first and second body portions 1a and 1c, the passageways 2 and 3 are concentricly positioned, the first passageway 2 being outermost in the first body portion 1 a, while the second passageway 3 is outermost in the second body portion 1c. In the intermediate body portion 1b, the passageways 2 and 3 are eccentric, serving to achieve the crossover between the innermost and outermost positions. Outlets 21 and 22, communicating with the first and second passageways 2 and 3 respectively, are formed in the downstream end of the body 1, and are configured to produce spray discharges on the interior surface of casing material being shirred on the mandrel. 
     The flow maintaining means includes first and second valve means 4 and 5 respectively, formed in the first and second body portions 1a and 1c, the first valve means 4 being located in the first body portion 1a, and the second valve means 5 straddling the intermediate body portion 1b. Each of the valve means 4 and 5 includes paired first and second self-closing valves 4a, 4b and 5a, 5b respectively, arranged such that one of each pair of valves communicates with the first passageway 2 and the other communicates with the second passageway 3. The valve means 4 and 5 are adapted for alternating flow as will be described hereinafter. 
     Each of the valves 4a, 4b, 5a and 5b comprises a port 6 formed in the body 1. The ports 6 are resiliently sealed by cylindrical, hollow, elastomeric flaps 7 concentric with the body 1. As best seen in FIG. 1, the flaps 7 include wall portions 7a, underlying the ports 6 which taper inwardly in the direction of flow through the passageways 2 and 3. The wall portions 7a are deflectable to nonsealing positions upon applications of external pressure thereagainst. 
     Mounted radially inwardly of the flaps 7 are rigid, cylindrical supports 13 which limit the deflection of the flap wall portions 7a and prevent eversion or dislodgment of the flaps 7. Support vents 13a are formed in the supports 13, radially inwardly and slightly axially offset from the ports 6 and provide for communication between the ports 6 and the passageways 2 and 3. 
     The mandrel is alternately supported by one of the openable upstream and downstream clamps 8 and 9 respectively. The clamps 8 and 9 are provided with fluid conduits 8a and 8b, 9a and 9b respectively for supplying fluids to the mandrel. Valve means (not shown) are included in the conduits 8a, 8b, 9a and 9b, whereby flow is permitted through a clamp which is gripping the mandrel, and ceases when the clamp opens. 
     In use, casing is shirred on the downstream end of the mandrel by means well known in the art. Initially, the upstream clamp 8 is closed about the mandrel, while the downstream clamp 9 is open (FIG. 1). After a suitable length of casing has been shirred on the mandrel, a predetermined length thereof is severed from the following casing. The severed strand is urged upstream along the mandrel, past the downstream clamp 9, to a position between the clamps 8 and 9. The upstream clamp 8 is now opened, while the downstream clamp 9 is closed. As the upstream clamp 8 opens, the flaps 7 of the valves 4a and 4b reassume their undeflected position sealing the ports 6 of the first valve means 4, while the closing of the downstream clamp 9 results in external fluid pressure being applied to the flaps 7 of valves 5a and 5b, causing a deflection thereof and permitting fluid to flow through the ports 6 of the second valve means 5. The severed strand may now be slid along the remaining length of the mandrel and removed at the upstream end thereof. It is to be noted that continuous fluid flow are maintained during this operation and that shirring is not interrupted. 
     Pins 10 are provided on the clamps 8 and 9 for mating with recesses 11 in the mandrel body 1. The mandrel is thus interlocked at all times with whichever of the clamps 8 and 9 is in the closed, supporting position, displacement of the mandrel thereby being prevented. 
     As is apparent from the drawings and the description, the formation of the passageways 2 and 3 and placement of the valve means 4 and 5 is accomplished by positioning a number of members in the interior of the hollow body 1 and sealing them thereagainst with conventional O-ring type seals. 
     While the preferred arrangement of the parts and method of application has been shown in illustrating the invention, it is to be clearly understood that various changes in details may be made without departing from the scope and spirit of the claims appeded thereto.
An improved mandrel for use in a shirring machine, having two axially oriented substantially concentric fluid passageways formed therein equipped with two pairs of self-closing valves whereby two fluids may be separately introduced into the passageways for injection into the interior of casing material being shirred thereon. The valve pairs are adapted to be used alternately, whereby a strand of shirred casing may be passed along the entire length of the mandrel without interrupting the fluid flows.