BACKGROUND OF THE INVENTION 
     .Iadd.This is a reissue of application Ser. No. 06/261,579 and now U.S. Pat. No. 4,387,995. .Iaddend. 
     This invention relates to concrete mixing devices and more particularly to such devices that may be easily transported to a desired location by towing with a vehicle. 
     Several methods for providing mixed concrete are available to the average consumer or small contractor, but none of such methods are entirely satisfactory. Small quantities of concrete may be mixed by hand or in a mixer, but the procedure is difficult, time consuming and expensive. Commercial quantities of ready mix concrete can be obtained by concrete truck, but the cost of delivery is excessive for small applications, and problems arise if not all of the concrete is to be used within a short period of time. 
     Another possible method for an individual to obtain concrete is to rent a trailer specifically designed for carrying mixed concrete. The trailer is filled with the mix, and the individual tows the trailer to the desired location. A major problem with such system is that the concrete tends to separate within a fairly short period of time, and the problem becomes worse if the trailer must be towed for a long distance. Also, if only a portion of the concrete is removed from the trailer for use, the remainder tends to harden before the trailer can be returned, thus creating a difficult and time consuming cleaning problem. 
     U.S. Pat. No. 3,232,586 describes a single wheeled drum that may be used for mixing concrete, but such apparatus is rather complicated and does not offer sufficient flexibility in operation. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a trailer adapted to be towed by a vehicle. A rotatable drum is positioned above the wheels of the trailer and may be raised or lowered into and out of engagement with the wheels. The drum may be also tilted to one side to discharge the contents. A quantity of dry mix is charged into the drum, and the drum, out of contact with the wheels, is towed to the construction site. When concrete is needed at the site, a measured amount of water is added to the mix, the drum is lowered into contact with the trailer wheels, and the drum is rotated by towing the vehicle a short distance. After the desired quantity of concrete has been used, additional water and sand may be added to the drum with additional mixing, such that the remaining concrete does not adhere to the walls of the drum during return of the trailer. 
     The apparatus of the present invention affords numerous advantages, many of which are unique. The apparatus allows relatively small quantities of mixed concrete to delivered at low cost. The concrete may be transported, mixed and used at the convenience of the consumer, without special delivery charges or problems of separation and hardening during transport. Mixing and dispensing of the concrete is simple and less problematic than in conventional systems, and clean-up problems are minimized. Thus, the apparatus of the present invention provides a means for providing small quantities of mixed concrete of high quality at the lowest possible price and at the total convenience of the consumer. 
    
    
     THE DRAWINGS 
     FIG. 1 is a front perspective view of the portable concrete mixing and transport apparatus of the present invention. 
     FIG. 2 is a rear perspective view of the apparatus shown in FIG. 1. 
     FIG. 3 is a vertical sectional view of the apparatus shown in FIG. 1. 
     FIG. 4 is a sectional view taken along line 4--4 of FIG. 3. 
     FIG. 5 is a view similar to FIG. 3 but showing the mixing drum in a raised, towing position. 
     FIG. 6 is a perspective view similar to FIG. 1 but showing the drum in a tilted discharge position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in the various Figures, the apparatus of the present invention generally comprises a trailer 10 upon which a concrete mixing and discharge unit 12 is mounted. The trailer is substantially conventional in nature and comprises a rectangular frame 14 supported upon a pair of axles 16, with four wheels 18 rotatably mounted on the ends of the axles. The trailer also includes the usual drawbar framework 20 terminating in a hitch 22 to enable attachment to a ball joint on the towing vehicle (not shown). 
     A drum 24 is supported over and between the trailer wheels, the axis of said drum being generally parallel to the axis of the axles 16. The drum is generally cylindrical in shape and has closed end walls 26. An access door 28 may be provided in one of the end walls to allow loading of solid and liquid material into the drum. A discharge chute 30 located below a sliding door 32 which is operatively connected to a pivoted handle 34 is provided in the other of the end walls to enable unloading of the mixed concrete when desired. In addition, a door 36 may be provided in the cylindrical body of the drum 24 to facilitate loading of dry materials into the drum from an overhead hopper or conveyor. 
     A pair of upright supports 38 and 40 extend upward from the trailer framework 14 on either side of the drum 24 and, together with the trailer frame, define a rectangular opening into which the drum is received and supported. Spaced longitudinal rollers 42 are mounted near the top of each upright support and are rotatably engageable with the cylindrical surface of the drum, in order to stabilize the drum against excessive longitudinal movement relative to the trailer. 
     The cylindrical surface of the drum has one or more ring-shaped flanges 44 extending outwardly from the drum surface. A pair of closely spaced, laterally opposed rollers 46, are mounted in aligned positions on each of the upright supports 38 and 40. The flange 44 of the drum projects between the pairs of laterally opposed rollers 46, which define a low friction guideway to prevent lateral shifting of drum along its axis relative to the trailer, while allowing the drum to rotate about its axis. The rollers 42 and 46 thereby prevent longitudinal and lateral shifting of the drum while allowing the drum to rotate. 
     Means are provided to raise and lower the drum 24 out of and into contact with the wheels or tires 18 of the trailer, and to tilt the drum into a discharge position. 
     FIGS. 1 through 4 show the drum 24 in the lowered or mixing position wherein the cylindrical surface of the drum rests upon each of the wheels or tires 18 of the trailer. In the lowered position, it may be seen that if the trailer is moved forward or rearward, rotation of the wheels will cause the drum to rotate in the opposite direction of the wheels. In this connection, it will be noted that the distance between adjacent wheels is substantially less than the diameter of the drum, such that the drum is substantially supported on the wheels. 
     As shown in FIGS. 3 and 4, agitating bars or vanes are provided in the interior of the drum to assist mixing of the concrete. Preferably, a pair of x-shaped supports 50 are secured in the ends of the drum, and the legs of the supports carry a plurality of spaced v-shaped agitating bars 52 extending parallel to the axis of the drum. The agitating bars 52 rotate with the drum and agitate the concrete mix that would otherwise tend to settle and accumulate at the bottom of the drum. 
     As shown in the Figures, the means for raising and lowering the drum 24 relative to the trailer comprises a curved strap 54 extending between the upright supports 38 and 40 and beneath the drum, said strap having a sufficiently side surface to support the drum in a stable fashion as shown. The respective ends of the strap are attached to a forward rigid cross-bar 48 on one end and to a rearward rigid cross-bar 49 on the other end. One cross-bar 49 is pivotally connected at 56 with a hook or similar structure on one of the upright supports 40; the other cross-bar 48 is hooked over or otherwise pivotally connected at 58 (FIG. 3) to the movable car 60 of a jack. As shown, the jack is conventional in nature and includes a lever bar 64 connected into the car 60, which includes an internal ratchet mechanism for climbing up a toothed upright support 66 when the handle is pivoted up and down. In the alternative, a hydraulic jack, cylinder or other suitable lifting mechanism may be employed. 
     When the drum 24 is in a raised position and is spaced away from the tires of the trailer, one end of the drum may be tilted down into a discharge position, as shown in FIG. 6. This can be accomplished by virtue of the pivotal connections 56 and 58 between the cross-bars 48 and 49 and the upright supports 38 and 40. If desired, the strap 54 may be positioned slightly off center away from the discharge side of the drum to facilitate manual tilting of the drum into the discharge position. 
     The apparatus also includes means to cradle the drum in a stable raised position, which is the position used during transport to and from the construction site. As shown in FIG. 5, a pair of cradles 70 are pivotally mounted on opposite sides of the trailer frame 14 beneath the drum. The cradles 70 each have an upper curved recessed wall 72 corresponding to the curvature of the drum, and a lower portion hinged to the frame. When not in use, the cradles are folded inwardly so as not to be in contact with the drum when in a lowered or tilted position. In addition, a flexible line or chain 74 may be strapped over the drum when resting on the cradle for added support. 
     The operation of the apparatus of the present invention may now be understood. The drum 24 is first loaded with a quantity of dry concrete mix such as cement and sand. The apparatus is placed in the travel position with the drum raised and the hitch 22 is attached to a vehicle for towing to the desired location. 
     Upon arrival at the construction site, the drum 24 is lifted slightly and the cradles are folded inwardly. The drum 24 is then lowered onto the tires 18 in the mixing position as shown in FIGS. 1 through 3. A quantity of water is then added to the mix, which is sufficient to form concrete of the proper consistency. Although not shown, the apparatus may be provided with a self-contained water tank to provide a supply of water in remote locations. 
     After addition of water, the concrete is mixed by towing the apparatus slowly over a short distance, which causes the drum to rotate. When the necessary amount of mixing has been attained, the jack 64 is operated to raise the drum, and the drum is then tilted toward the discharge end 26. The mixed concrete is then discharged as needed. 
     After the desired amount of concrete has been used, additional water may be added and the drum rotated in order to clean the drum and prevent any remaining concrete from adhering to and hardening on the interior surfaces of the drum.
A portable concrete mixing and transport device comprises a trailer having wheels and a drum supported above the wheels, said drum being movable into and out of engagement with the wheels. Concrete mix carried in the drum is agitated by pulling the trailer with the drum in contact with the wheels, causing the drum to rotate. The drum may be tilted to allow pouring of the mix. The device allows for convenient and inexpensive transport and mixing of small quantities of concrete.