US2757588A - Vibrating finishing machine - Google Patents

Description

H- C. POLLITZ VIBRATING FINISHING MACHINE 2 Sheets-Sheet 1 Filed Jan. 13, 1955 INVENTOQ.

Aug, V 1956 H. c. POLLITZ VIBRATING FINISHING MACHINE 2 Sheets-Sheet 2 Filed Jan. 13, 1955 VIBRATING FINISHING MACHINE Harold C. Pollitz, Cedar Rapids, Iowa, assignor to Iowa Manufacturing Company of Cedar Rapids, Iowa, Cedar Rapids, Iowa, a corporation of Iowa Application January 13, 1953, Serial No. 331,041

Claims. (CI. 94-48) The present invention relates to surfacing machinery and particularly to a vibrating finishing machine adapted to spread surfacing material such as bituminous concrete, asphalt, crushed stone, etc., in a layer of controlled thickness having a smooth and uniform surface contour. The machine is specifically designed for handling bituminous concrete and asphalt mixtures and for practicing a novel method of compacting the paving material and smoothing its roadway surface.

It is a primary object of the invention to provide a vibrating finishing machine adapted to lay down a controlled thickness of paving material, with means for effecting adequate compaction of the material through its entire thickness, as well as over its upper surface.

A further important object of the invention is the provision of means for compacting the material of the road surface in such a manner as to not only exclude voids and air pockets within the concrete, but to allow the individual stones of the gravel or aggregate mixture to key themselves together and form themselves into an unusually dense, non-porous, rigid slab capable of withstanding greater loads than a less completely compacted pavement, and less subject to deterioration and the damaging effects of weather and tratfic.

A further object of the invention is to provide a paving machine having means for applying a layer of paving material of unequal thickness, so as to afford any desired crown or other road contour, yet with means for effecting equal and adequate compaction of the material at its thickest points, as well as at its thinner portions. A related object is the provision of means for effecting thorough and adequate compaction of the road surfacing material at th thickest points of the layer of material being applied without causing separation of the asphaltic oils or other bituminous binder material from the aggregate, and without bringing about a tendency toward separation of the fines from the coarser aggregate material.

A further object of the invention is the provision of a vibrating finishing machine wherein the paving material is rapidly and thoroughly compacted throughout the entire thickness of the paving, without tendency toward breaking or crushing the individual stones or pebbles of the aggregate. Obviously, this results in producing a smooth, dense, watertight and wear resistant roadway surface, impervious to weather and capable of sustaining heavy traflic.

A further object is to provide a vibrating finishing machine adapted to lay a smoothly compacted layer of bituminous concrete or the like, wherein the mechanism is so designed and constructed as to be capable of laying the roadway at a greater speed than heretofore believed to be practicable or possible, whereby construction costs may be drastically reduced, and the quality of the finished road greatly improved.

A still further object is the provision of a vibrating finishing machine capable of rapidly laying a sheet of compacted bituminous concrete, for example, yet wherein the construction and relationship of the parts of the nited States Patent 0 machine is such that it is capable of trouble-free operation over a long period of years without need of any unusual care of maintenance.

The foregoing objects are accomplished in the present invention by a unique vibrating finishing machine having features of construction differing considerably from prior art machines of the same general character, so that it is capable of compacting the paving layer applied to the roadway by a method different from the methods heretofore practiced in the art, and having important practical advantages thereover.

In this connection, it may be pointed out that studies of road surfaces laid by the best commercial machines heretofore available have indicated that the bituminous concrete mixtures put down by such machines are not thoroughly compacted throughout the thickness of the concrete layer, even though the surface may be so violently tamped as to cause considerable crushing of the larger particles of the aggregate and consequent defects in the surface. In conventional machines, the compaction is principally at the upper exposed surface of the material, and the underneath portions of the layer are frequently imperfectly compacted, with air pockets or voids which weaken the pavement and render it subject to failure.

The present machine and method avoids such failure by simultaneously subjecting the freshly laid mixture of aggregate and bituminous binder to the effects of heat, pressure and resonant subsurface vibration over a sustained interval of time, so that thorough compaction may take place. In the preferred embodiment of the invention, these results are accomplished by utilizing a relatively large, flat, heated screed activated by a plurality of synchronous electrical vibrators powered by a common electrical source so that they remain in phase with each other at all times, but are individually controlled as to the amplitude or intensity of the vibratory forces which they generate. Thus when individual adjustments have been made, the entire group of vibrators can be further controlled in unison by a master control device. This control is essential for laying variable thicknesses of material, crosswise and lengthwise. Moreover, these vibrators are of such a design that they exert their energy primarily in a vertical direction, and thus avoid losses of energy due to the ineffective lateral components of motion typical of rotary vibrators, for example.

With the arrangement employed in the preferred form of applicants machine, the entire surface of the screed may be supported directly upon the top of the freshly laid bituminous concrete mixture, so that the weight of the screed and its associated parts will bear down on the paving surface, applying a moderate pressure over the entire width of the pavement being laid, and simultaneously vibrating the screed in such a manner that the vibratory energy is not expended on the surface of the material alone, but penetrates entirely through the layer of pavement and even into the soil thereunder. This is best accomplished by utilizing vibrators of comparatively small amplitude, but of frequency considerably higher than ordinarily used, since it has been observed that bituminous concrete mixtures have a natural resonant frequency of vibration at which the entire mass tends to vibrate most readily, and is thus capable of compacting itself most effectively. This resonant frequency of vibration of the mass may vary somewhat according to variable conditions, but excellent results are obtained in most instances by utilization of a series of vibrator units operating in substantially vertical plane and synchronously with each other at a frequency of 3600 impulses per minute. Moreover, this resonant vibration is facilitated in the form of the invention shown herein by j the construction and resilient mounting of the screed,

which is of relatively small mass and, therefore, well adapted to vibrate at such speeds.

It is also to be noted that, as here employed, the screed is of considerable width, such as 18 to 36 inches in actual practice. This sustained period equals the width of the screed divided by the speed of travel. As an example, if the traveling speed is 6 inches per second the material is directly vibrated 3 to 6 seconds. This sustained treatment of the pavement has been found to be of value in allowing sufficient time for the aggregate particles to key themselves together, as the screed is moved thereover, and results in a very dense, firm mat.

A preferred embodiment of the invention is illustrated in the drawings hereof, wherein:

Figure 1 is a side elevation of a road surfacing machine as contemplated by this invention; and

Figure 2 is a detail sectional view taken substantially on the plane of the line 22 of Figure l, with the electrical circuits of the device diagrammatically illustrated thereon.

As illustrated in the present drawings, the machine includes a tractor unit 10 and a hopper 11, both mounted upon a track laying carriage 12 extending between axles 13 and 14 so that the entire tractor unit and its hopper may be self-propelled along the road, as by an internal combustion engine 15, or other prime mover. It is contemplated that the hopper 11 will be periodically filled with a mixture of bituminous concrete or similar material indicated at 16, which will be carried rearwardly through the machine by a central conveyor (not shown) and which will be deposited in the vicinity of a double ended transverse screw conveyor 17 so that it will be spread laterally to cover the width of the roadway surface in front of the screed assembly 18. The screed comprises a relatively thin, substantially flat sheet metal plate 21 which may be 8 or 9 feet, more or less, in length to cover one or more traflic lanes of a typical highway or any substantially flat surface. As shown, it is provided with a short vertical front flange 22 and rear flange 23. The opposite ends of the screed plate are mounted or supported from transverse beams 24 and 25 by riser portions 26 and 27 at the opposite ends of the plate 21, and the risers are bent inwardly at 28 and secured to the cross beams at 29 so that the screed is flexibly mounted and comparatively free to vibrate. Also, the relatively thin sheet metal of the screed plate is of comparatively small mass, so that it is quite capable of vibration at the high frequencies utilized Without material restriction due to either its mass or its mounting facilities. The screed plate maybe heated from its upper side, in a known manner, by oil burners, electrical elements or the like (not shown) and may be adjusted independently at its ends by the two pairs of hand screws 31 and 32, attached to beams 24 and 25 and secured to side arms 33 pivoted to the tractor unit at 34, similar to the old fashioned horse and buggy arrangement. Thus, the entire screed assembly may rest directly upon the surface 35 of the paving material being laid, and the screws 31 and 32 may be set to provide for increasing or decreasing the depth or thickness of the layer. A suitable known crown adjusting device may also be provided, if desired. A mold board 36 is disposed in front of the flange 22 of the screed, but is separately secured to the beams 24 and 25 and end plates 37 so that it is not directly vibrated.

The screed is activated by four vibrators 38, which are of known type and preferably spaced at substantially equidistant points along the forward edge of the screed plate. As shown, each of the vibrators is mounted on a supporting plate 39 at the upper end of a tubular pipe or rod 40 extending down to and welded to the screed plate 21. The vibrators 38 are all of the reciprocating armature type, and in the preferred form of the invention are all powered from a common power source. This may be an alternating current generator, diagrammatically illustrated at 41 in Fi ure 2 of the drawings, and driven by the prime mover 15. The power output may be governed by a control rheostat 42 connected in series and mounted on an instrument panel 43 at any convenient location on the machine (Figure 1). If desired, the frequency of current may also be varied by a governor on the prime mover 15.

The output from the generator 41 passes through a fuse box to a main power contactor 44, the electromagnetic winding 45 of which is connected to the storage battery 46 of the prime mover 15 through a hand operated shut-ofl? switch 47. The switch 47 may be conveniently mounted on the instrument panel 43 and, if desired, the circuit to the power contactor may also extend through a pair of steering clutch limit switches 48 and a traction clutch limit switch 49, so that the operation of the vibrators will be interrupted whenever the machine ceases to advance. The circuit from the power contactor 44 extends to the several vibrators 38 through fuses 51, vibrator switches 52, vibrator control rheostats 53 and dry plate type rectifiers 54. Thus, the alternating current supplied from the generator 41 is converted into a half wave, pulsating, direct current, which is supplied to the windings of the vibrators 38.

It has been previously stated that the vibrators are of the reciprocating armature type, so mounted that their output energy is expended in substantially a vertical direction, so it is delivered to the screed plate 21 with the greatest degree of effectiveness, and achieves the greatest possible depth penetration into the road surfacing material. It is also to be observed that the several vibrators of the device all function in synchronism, since they are energized by the same power source, yet the amplitude or intensity of the vibrators may be individually controlled by manipulation of the four separate vibrator control rheostats 53. Simultaneous control of the amplitude of all of the vibrators may be accomplished by adjustment of the generator control rheostat 42. With this arrangement, it is entirely practicable to adjust the individual vibrators so that when a crowned road surface is being laid, for example, the vibrators above the thickest portion of the roadway exert the most violent vibration, with those at the thinner portions vibrating with progressively less intensity. This avoids separation of the fine particles or bituminous binder in the thin portions of the roadway while maintaining an adequate power output to insure deep penetration and thorough subsurface compaction at even the thickest portions.

From the foregoing it should be apparent that the present machine and method for compacting a bituminous concrete surface makes use of the fact that cohesive aggregate materials have a natural or resonant period of vibration at which the individual particles of the aggregate have been found to move most easily, and key themselves together with greatest facility. Moreover, the provision of a screed as here disclosed is of advantage in accomplishing this, in that it provides a physical structure capable of vibrating at the resonant frequency of the materials being handled. The screed is also sufliciently wide so that the materials under it are held in a heated and compressed state for an appreciable period of time, and thus vibrated at their resonant frequency long enough so that the individual particles of the aggregate have adequate time to key themselves into an unusually dense, solid surface. In addition to this, the present mechanism makes use of an arrangement wherein the energy expended by the vibrators may be precisely controlled across the entire roadway, so as to be expended where most eflective to accomplish the desired degree of compaction.

Having thus described my invention, what I claim as new and desire to secure by United States Letters Patent is:

1. In a paving machine, a support, a screed having a vertically flexible screed plate suspended from said support, a plurality of vibrators connected to said plate at points spaced apart lengthwise thereof effective for imparting vertical vibration to lengthwise areas of said plate, means for varying simultaneously and to the same extent the intensity of vibration of said vibrators during operation thereof, and supplemental means for selectively varying the intensity of said vibrators individually during operation thereof, said vibrators providing means whereby said areas of said plate may be vibrated at the same intensity or at different intensities optionally during continued operation of said vibrators.

2. In a paving machine, a support, a screed having a vertically flexible screed plate suspended from said sup port, said plate being flat and substantially oblong in plan and of considerable width relative to its length, a plurality of vibrators connected to said plate at points spaced apart lengthwise thereof effective for imparting vertical vibration in the same directions to lengthwise areas of said plate, and means for varying the intensity of vibration of said vibrators either simultaneously to the same extent or individually to different extents during continued operation thereof, whereby said areas of said plate may be vibrated at the same intensity or at different intensities optionally during continued operation of said vibrators.

3. In a paving machine, a support, a screed having a vertically flexible screed plate suspended from said support, said plate being flat and substantially oblong in plan and of considerable width relative to its length, a plurality of electromagnetic vibrators disposed above said plate spaced apart lengthwise thereof and respectively comprising a rod connected at its lower end to said plate adjacent the leading edge thereof and effective for imparting vertical vibration to a lengthwise area of said plate, and means for varying the intensity of vibration of said vibrators either simultaneously to the same extent or individually to different extents during operation thereof, whereby the lengthwise areas of said plate corresponding to said rods may be vibrated at the same intensity or at different intensities optionally during continued operation of said vibrators.

4. In a screed for compacting and finishing road surfacing material, a substantially oblong flat and vertically flexible screed plate, a plurality of vibrators connected to said plate at points spaced apart lengthwise thereof effective for imparting vertical vibration in the same directions to lengthwise areas of said plate, and means for varying the intensity of vibration of said vibrators either simultaneously to the same extent or individually to different extents during operation thereof, whereby said areas of said plate may be vibrated at the same intensity or at different intensities optionally during continued operation of said vibrators.

5. In a screed for compacting and finishing road surfacing material, a substantially oblong flat and vertically flexible screed plate, a plurality of electromagnetic vibrators disposed above said plate spaced apart lengthwise thereof and respectively comprising a rod connected at its lower end to said plate effective for imparting vertical vibration to a lengthwise area thereof, and means for varying the intensity of vibration of said vibrators either simultaneously to the same extent or individually to different extents during operation thereof, whereby the lengthwise areas of said plate corresponding to said rods may be vibrated at the same itnensity or at different intensities optionally during continued operation of said vibrators.

References Cited in the file of this patent UNITED STATES PATENTS Re. 19,816 Wurzbach Jan. 7, 1936 1,926,193 Clark Sept. 12, 1933 1,943,076 Jackson Jan. 9, 1934 2,042,156 McCrery May 26, 1936 2,310,185 Weyandt Feb. 2, 1943 2,333,041 Poulter Oct. 26, 1943 2,351,592 Barber June 30, 1944 2,597,221 Barber May 20, 1952 2,644,379 Lowe July 7, 1953

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