US3316821A

US3316821A - Bituminous paving apparatus

Info

Publication number: US3316821A
Application number: US367102A
Authority: US
Inventors: Donald R Davin
Original assignee: Blaw Knox Co
Current assignee: Blaw Knox Co; White Consolidated Industries Inc
Priority date: 1964-05-13
Filing date: 1964-05-13
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02

Description

Mayz, 9 D. R. DAVIN 3,316,821

BITUMINOUS PAVING APPARATUS Filed May 15, 1964 Donald R. Devil? United States Patent O 3,316,821 BITUMINOUS PAVING APPARATUS Donald R. Davin, Shelbyville, Ill., assignor to Blaw-Knox Company, Pittsburgh, Pa, a corporation of Delaware Filed May 13, 1964, Ser. No. 367,102 1 Claim. (Cl. 94-46) This invention relates to bituminous pavers and particularly to screeds and associated equipment for paving with bituminous concrete. The invention is particularly adapted for use in connection with pa ers having a tractor behind which the screed is towed, the screed resting upon and riding over freshly placed bituminous material.

A common form of bituminous paver employs a selfpropelled tractor having a hopper to receive the bituminous mix and various Spreaders, conveyors and the like to deposit the bituminous mix behind the tractor and across the width of the section which is to be paved. Such tractors customarily include a screed assembly which is towed or carried at the rear of the tractor. Ordinarily, the screed is freely floating. It is pulled by forwardly extending arms which permit the screed to seek a level where it is in equilibrium between the various forces acting upon it, such as its own weight, the upward force of the underlying bituminous material, and the forces applied by the pull arms. A pile of bituminous material is loosely deposited ahead of the screed by the tractor. As the screed advances, it strikes off excess material and carries it forwardly. The screed rides over and the bituminous material not struck off is compacted by the screed into a mat which is ordinarily compacted further by rolling. One form of screed is provided with a sole plate which is in the nature of a large fiatiron. A tamper is provided extending across the width of the screed along the forward edge of the sole plate to compact the bituminous mix and tuck it beneath the sole plate for smoothing.

Such tampers have customarily been vertically positioned and have had a shield in front of them extending forwardly and upwardly to prevent the bituminous material from crawling upwardly upon the tamper and clogging the mechanism.

I have invented new and useful improvements in bituminous paving screed aparatus in which I provide a screed, a sole plate, reciprocating tamper means positioned at an angle to the vertical so that the lower end of the tamper is ahead of its upper end and a curved shield member positioned forwardly of the tamper means. I prefer to mount a tamper at an angle to the vertical for axial reciprocating movement downwardly and forwardly and then upwardly and backwardly. I preferably dispose the tamper with its upwardly end slanted to the rear at an angle of about twenty degrees from the vertical. I preferably mount the tamper with its lower portion in juxtaposition with the forward edge of the sole plate whereby entrance of bituminous material between the sole plate and the tamper is prevented. I prefer to dispose the tamper shield means forwardly of the tamper with the bottom of the tamper and the bottom of the tamper shield in juxtaposition whereby entrance of bituminous material between the tamper and the tamper shield is prevented. I form the shield without any substantial uncurved sections and preferably curve the shield forwardly from a mid-point to the top and bottom edges. The shield thereby extends from its bottom edge upwardly and 'rearwardly to a midpoint whence it extends upwardly and forwardly. I further preferably provide agitator means forwardly of the tamper shield means in position to receive bituminous material which circulates forwardly from the tamper shield means. I prefer to provide screw means disposed forwardly of the screed means in position to receive bituminous material which is pushed upwardly on the shield and forwardly therefrom whereby the bituminous material is remixed and redistributed by the screw means. I further prefer to provide a bevel of chamfer on the lower edge of the tamper whereby the bottom surface of the tamper is of relatively narrow width. I further prefer to dispose the beveled surface so that the upper edge of the beveled surface is forwardly of the bottom edge of the beveled surface. I also prefer to provide screed extension means having the same configuration as the central portion of the screed whereby the screed may conveniently be extended by fixing additional sections thereto.

Other details, objects and advantagesof my invention will become more apparent as the following description of a present preferred embodiment thereof proceeds.

In the accompanying drawings I have illustrated a present preferred embodiment of my invention in which FIGURE 1 is a side view of a bituminous paver embodying my invention;

FIGURE 2 is a view of a portion of the screed shown in FIGURE 1 looking forwardly from behind the paver; and

FIGURE 3 is an end view of the screed structure shown in FIGURE 1, illustrated in greater detail.

The paver comprises a. tractor 1 propelled by an engine 2, through appropriate power transmissions. An operator seat 3, a steering wheel 4, and other controls are placed rearwardly of the engine in position for the operator to observe the paving action while operating the payer. Tractor 1 is supported by a rear wheel 5 upon each side of the tractor and front wheel 6 on each side of the tractor. Each rear wheel includes a pneumatic tire mounted upon a steel rim fixed to a driven axle. From wheels 6 have solid or semi-pneumatic tires and are connected to steering wheel 4 through a linkage so that they can be turned. to one side or the other by the operator, thereby steering the tractor. A material receiving hopper 7 is provided at the forward end of the tractor and has sides 8 formed of steel plates. Hopper 7 is filled from trucks which deliver bituminous paving mix to the job site from a batch plant and dump it into hopper 7. Conveyors are provided within the tractor body and act to move bituminous mix from hopper 7 rearwardly and deposit the mix just ahead of a screw conveyor 9 which extends transversely across the rear of the tractor in front of the screed structure. Screw conveyor 9 is mounted on brackets 10 which are fastened to the tractor frame. Conveyor 9 is driven by engine 2 through clutches and has one half reverse threaded on the other half so that rotation of conveyor 9 urges material from the center of the paver toward the two sides of the paver. Each half is under separate control of the operator so that either or both halves of conveyor 9 may be operated at any given time. p

A screed pull arm 11 is fitted on each side of the tractor. A stud 12 extends from each pull arm 11 and is in front of a vertical beam 13 mounted on each side of the tractor at a forward point near the hopper. A roller bearing 14 is fitted upon stud 12 so that the arm may conveniently be moved up and down despite forces developed by a rearward pull upon arm 11. a

A stud extends outwardly from pull arm it behind vertical beam 13.

Studs

12 and 15 thereby resist substantial forward and back movement by pull arm 11. A clevis 16 is pivoted to pull arm 11 at its forward end and is connected to a piston rod 17 of hydraulic cylinder '18. Cylinder 18 is in turn connected by a rod 19 to the frame of tractor 1. Hydraulic fluid is supplied under pressure to the top and bottom of each cylinder 18, to enable the forward end of each pull arm to be moved up and down. Each pull arm 11 extends rearwardly of the tractor and terminates in a downward extension 24). Each end of the screed is pivoted at a pivot point 21 to the downward extension of one of the pull arms. The screed comprises a box-like screed body 22 having a sole plate 23 mounted to its lower face. An upwardly extending bracket 24 is welded to the screed body at each end and is pivoted to the pull arm at pivot point 21. A platform 25 extends rearwardly from the screed body on each side to'enable a workman to stand upon it and ride with the paver.

Each bracket 24 terminates in fitting 26 having a bushing 27 at its upper end. A shaft 28 is rotatably mounted in bushing 27 and is rotated by a crank 29, connected to one end of shaft 28; A toothed wheel 30 is also fitted to shaft 28 and crank 29 and has teeth 31 and slots 32 around its circumference. A detent 33 is pivotally mova ble up and down and may be dropped into one of slots 32 to lock shaft 28 in any given position. Shaft 28 is connected through a universal joint 34 to one end of a turnbuckle assembly 35. The other end of the turnbuckle 36 is connected to the inner face of pull arm 11.

A longitudinal tamper 37 is mounted upon the forward side of the screed for reciprocating movement. Tamper 37 is positioned at a slope to the vertical with its lower end forward of its upper end. The tamper is preferably positioned at an angle of about 20 from the vertical. It is mounted for reciprocating up and down movement along its axis. Since it is at a slope, it moves alternately downwardly and forwardly and then upwardly and rearwardly. A tamper drive shaft 38 is rotatably mounted in a pillow block 39 and cap 40 fitted at the top of the'screed. Shaft 38 carries eccentrics upon which a crank connected to the upper end of tamper 37 is journaled. Such details of construction are well known and for purposes of simplicity are not illustrated or described herein.

The lower end of tamper 37 has a chamfer 41 so that the bottom surface of the tamper is relatively thin. The angle of chamfer 41 is at a somewhat larger angle to the tamper than the angle of the tamper to the vertical. The upper edge of chamfer 41 is thereby forward of the lower edge of chamfer 41.

r A tamper shield 43 is positioned forwardly of the tamper and fastened to the screed by brackets 44. Shield 43 has a lower section 45 which is adjacent to the lower portion of tamper 37. From its lowermost edge the tamper shield extends upwardly and rearwardly until it reaches a mid-point 46 of the tamper shield whence the tamper shield extends upwardly and forwardly.

A heater 49 is provided to preheat the screed box before the screed is placed into service. A fan 5%) delivers air to the heater and then forces the heated air into and through the screed and sole plate. A handrail 51 is mounted on the screed, and a turnbuckle linkage 52 is installed to maintain longitudinal stiffness of the screed.

Screed extensions

53, 54 and 55 are provided to lengthen the screed thereby increasing the width being paved. The extensions are conveniently comprised of sole plates 23', 23", 23" and box sections 22', 22", and 22", respectively. Corresponding extensions are fitted to screw conveyor 9 to extend it concurrently with the screed. A lifting cable 56 extends over a sheave 57. One end of cable 56 is attached to pull arm 11 and the other end to a winch controlled by the operator.

When the paver is in operation, bituminous mix is delivered to hopper 7, and the tractor moves forward. While it is advancing, bituminous mix is delivered in front of screw conveyor 9 by the internal conveyors. Screw conveyor 9 is operated to keep an adequate quantity of the mix distributed across the front of the screed. The conveyors are operated to keep an excess quantity of bituminous mix piled up in front of the screed. As the paver advances, the screed strikes off the excess bituminous material. The material which is not struck off is tamped down by tamper 37 as it passes over the bituminous material and reciprocates between the tamper shield and wear plate 43 at the forward edge of sole plate 23. The tamped material is further compacted and smoothed by the sliding motion of sole plate 23 as it passes over the material. The excess material which is struck off is necessarily carried forwardly in front of the screed. As the screed advances, the excess material in front of tamper shield 43 is forced upwardly by the slope of the tamper shield until the material reaches the midpoint do of the shield. Thereafter the excess is forced upwardly by the pressure of excess mix from below, but by reason of the shape of the tamper shield, the mix is forced upwardly and forwardly from mid-point 46 until it falls from the upper portion 47 of the tamper shield onto screw conveyor 9. The mix tends to become compacted by the pressures in being struck off. As the excess mix falls back into screw conveyor 9;, it is broken up and remixed, thereby being restored to a live condition. In this manner there is a continuous movement of excess bituminous mixture ahead of the screed. The excess material is constantly being worked until it is tamped under the sole plate and smoothed down into the furnished mat. There are no places in which excess mix accumulates and becomes compacted until a large lump breaks free.

Use of the invention enables bituminous paving to be laid at substantially higher speeds than has been possible heretofore with screeds having tamper shields which extend only forwardly or which have substantial planar sections in them. A notable problem has been the laying of mixes formed of fine aggregates, sometimes known as sheet asphalt, without tearing the finished mat. Since the customary practice is to lay a base course of large aggregate and to reduce the size of the aggregate as each succesive course is laid, the problem of tearing of the final course makes the problem most pronounced where it cannot be obviated by a later course. The exact speed at which a course of sheet asphalt can be laid without tearing depends upon many things such as the mix used, the weight of the screed, and its unit pressure. When these factors are alike, the maximum speed which can be reached without tearing is quickly established by trial and error.

By way of comparison, a paver having a conventional screed heretofore typifying good design was used on a particular asphaltic mix of fine aggregate. That paver reached a maximum speed of about twenty feet per minute without tearing the mat. When, however, a paver having a screed of like weight and size but embodying the invention was used on the same mix, paving speeds of up to seventy three feet per minute were successfully maintained.

While I have illustrated and described a present preferred embodiment of my invention, it is to be understood that i do not limit myself thereto, and that my invention may be otherwise variously practiced within the scope of the following claim.

I claim:

Bituminous paving apparatus comprising a screed having sole plate means for smoothing bituminous material into a mat, a transversely extending tamper positoned at the forward edge of the sole plate means and arranged for up and down axial reciprocating motion, said tamper having its upper end rearwardly of its lower end, a tamper shield positioned forwardly of the tamper and initially sloping upwardly and rearwardly from its lowermost portion at substantially the same angle to the vertical as the tamper, sloping upwardly and rearwardly to a mid-point and thence upwardly and forwardly to the uppermost portion of the tamper shield, and bituminous material agitating and distributing means positioned forwardly of the tamper sheld in position to agitate and redistribute bituminous mix struck oif by the screed.

References Cited by the Examiner UNITED STATES PATENTS Barber 94-46 Barber 94-46 Mentes 94-46 Widelo 94--46 Schrimper 94-46 CHARLES E. OCONNELL, Primary Examiner. 10 N. C. BYERS, Assistant Examiner.