Screed plate arrangement and method of attaching a screed plate

Asphalt paving machine includes screed assembly, plurality of lower and upper plate fasteners, and upper and lower screed plates, each having openings, and an electric heater at least partially disposed between the plates. Upper and lower plate fasteners extend into openings of the respective upper and lower screed plates and bores of a frame portion of the screed assembly to couple the plates to the frame portion. The upper plate fasteners couple the upper screed plate to the frame portion independently of the lower screed plate, so the lower plate is displaceable from the upper plate and the frame portion.

TECHNICAL FIELD

The present disclosure relates to asphalt paving machines, and, more particularly, to a screed arrangement and a method of attaching a screed plate to a screed assembly.

BACKGROUND

Laying asphalt paving material on road surfaces entails spreading paving material consisting of an aggregate filled bituminous mixture on a prepared roadbed. The paving material is spread while hot and is then compacted so that a hardened pavement surface is formed upon cooling. Conventional paving machines utilize a heavy assembly termed a “screed” that is drawn behind the paving machine. The screed assembly includes a replaceable screed plate that is constructed of a suitable steel, to spread a smooth even layer of paving material on the prepared roadbed. The weight of the screed assembly aids in compressing the paving material and performing initial compaction of the paving material layer. Screed assemblies can include vibratory mechanisms placed directly on the screed plate or separate vibratory tamper bars connected in tandem with the screed plate to aid in the initial compaction of the paving material.

To facilitate laying of the paving material, the screed plate is typically heated, to a temperature in the range of about 82° to 171° C. (180° to 340° F.). Heating the screed plate assists the paving material in flowing under the screed plate and reduces adhesion of the paving material to the screed plate. If the screed plate is not adequately heated, the bituminous mixture contacting the bottom of the screed plate begins to harden, resulting in buildup of paving material and excessive drag.

Conventional screed plates are commonly heated by fossil fuel powered burners that heat the upper surface of the screed plate by the direct application of flame or hot exhaust gases. The use of fossil fuel burners to heat screed plates has several drawbacks. Combustion of fossil fuels generates smoke that represents a source of environmental pollution, and also poses a poor working environment for the paving workers. Additionally, because the flames or exhaust gases of the burners actually contact the screed surface, warping may result. The contour of the screed plate determines the quality, evenness and smoothness of the paving material that is being laid down. Screed plates are often flexed under extreme tensile loads during use to achieve desired crowning or other surface contours.

One alternate heating system that represents an improvement and which addresses the environmental drawbacks is disclosed in U.S. Pat. RE 36,981 issued Dec. 5, 2000 to Ralph Birtchet and assigned to Universal Screed Inc. Birtchet discloses the use of an elastomeric, electrically powered heating pad assembly positioned on the upper surface of the screed plate with a layer of insulation placed on top of the heating pad assembly. A heavy steel retainer plate assembly is disposed on top of the insulation to hold the heating pad assembly and the insulation in contact with the screed plate. But for the retainer plate assembly, the heating pad assembly and the layer of insulation are loosely positioned on the upper surface of the screed plate, mechanically constrained in their installed positions only by the forward face plate portion and the tail portion of the screed plate, and the side plates. The screed plate is attached directly to the deck plate of the paving machine.

Assembling the screed plate to the paving machine is generally a time consuming process because the screed plate must be precisely oriented relative to the frame. Assembly of the screed plate to the frame typically involves time consuming shimming operations. Inasmuch as the screed plate is a wear component, replacement due to wear may result in considerable downtime, often for days inasmuch as this shimming process must be repeated. Similar delays may result when the screed plate is removed to access the heating assembly for replacement or repair.

SUMMARY

The disclosure describes, in one aspect, an asphalt paving machine comprising a screed assembly, a screed plate assembly, at least two lower plate fasteners, and at least two upper plate fasteners. The screed assembly includes a screed supporting frame portion having at least two first bores and at least two second bores. The screed plate assembly includes at least one lower screed plate having at least two openings, at least one upper screed plate having at least two openings, and at least one electric heater at least partially disposed between the upper and lower screed plates. The lower plate fasteners extend into the at least two openings of the lower screed plate and the at least two first bores of the screed supporting frame portion to couple the lower screed plate to the screed supporting frame portion. The upper plate fasteners extend into the at least two openings of the upper screed plate and the at least two second bores of the screed supporting frame portion to couple the upper screed plate to the screed supporting frame portion independently of the lower screed plat. The lower plate is displaceable from the upper screed plate and the screed supporting frame portion by loosening the at least two lower plate fasteners.

The disclosure also describes, in one aspect, a screed plate assembly for attachment to a screed supporting frame portion of an asphalt paving machine. The screed supporting frame portion has at least two first bores and at least two second bores. The screed plate assembly includes at least one lower screed plate having at least two openings, at least one upper screed plate having at least two openings, at least one electric heater at least partially disposed between the upper and lower screed plates, at least two lower plate fasteners adapted to extend into the at least two openings of the lower screed plate and the at least two first bores of the screed supporting frame portion to couple the lower screed plate to the screed supporting frame portion, and at least two upper plate fasteners adapted to extend into the at least two openings of the upper screed plate and the at least two second bores of the screed supporting frame portion to couple the upper screed plate to the screed supporting frame portion independently of the lower screed plate. The lower plate is displaceable from the upper screed plate and the screed supporting frame portion by loosening the at least two lower plate fasteners.

The disclosure describes in another aspect a method of attaching a screed plate assembly to a screed assembly of an asphalt paving machine, wherein the screed assembly includes a screed supporting frame portion. The method includes providing at least two first bores and at least two second bores in the screed supporting frame portion, providing a screed plate assembly including at least one lower screed plate having at least two openings, at least one upper screed plate having at least two openings, and at least one electric heater disposed between the upper and lower screed plates, extending at least two upper plate fasteners into the at least two openings of the upper screed plate and the at least two second bores of the screed supporting frame portion to secure the upper screed plate to the screed supporting frame portion, and extending at least two lower plate fasteners into the at least two openings of the lower screed plate and the at least two first bores of the screed supporting frame portion to secure the lower screed plate to the screed supporting frame portion, the at least two upper plate fasteners securing the upper screed plate to the screed supporting frame portion independently of the lower screed plate.

DETAILED DESCRIPTION

This disclosure relates to a design and mounting arrangement for coupling a screed plate to a screed assembly12of an asphalt paving machine10, as shown inFIG. 1. The asphalt paving machine10is supported by a propelling arrangement14that is driven by an engine16in a conventional manner.

The screed assembly12is pivotally connected behind the asphalt paving machine10by tow arms18. The screed assembly12may be any of a number of configurations such as a fixed width screed or a multiple section screed that includes extensions. As shown inFIG. 2, the screed assembly12may be provided with a main screed section20with a left and a right screed section22,24. The left and right screed sections22,24are hingably connected to one another along a longitudinal centerline26so that various operations, such as crowning, can be performed. A screed extension28is provided behind and adjacent to each of the left and right screed sections22,24, although the screed extensions28may be positioned in front of the main screed section20. The screed extensions28are slidably movable, such as by actuators (not shown), so that varying widths of paving material can be laid. The screed assembly12may also include a tamper bar arrangement29positioned forward of the main screed section20, as shown inFIGS. 1 and 2, and/or a vibratory mechanism21positioned above the left and right screed sections22,24and the screed extensions28to aid in the initial compaction of the paving material being laid down.

Turning toFIGS. 3-5, each of the screed sections22,24,28includes at least one screed plate assembly30that is removably connected to and supported by a screed supporting frame portion32. The ends of the screed plate assembly30and screed supporting frame portion32may be reinforced by end plates34.

The screed plate assembly30includes an upper screed plate36and a lower screed plate38, both of which are coupled to the screed supporting frame portion32. The lower screed plate38is an elongated largely flat metal plate having an upper surface40and a lower surface42positioned between a leading edge44and the trailing edge46. In the illustrated embodiment, the upper screed plate36is likewise a largely flat structure, although it may be of an alternate configuration so long as the upper and lower screed plates36,38are coupled to the screed supporting frame portion32as described herein.

According to a feature of the disclosed screed plate assembly30, the upper screed plate36is coupled to the screed supporting frame portion32independently of the lower screed plate38. In this way, as illustrated inFIGS. 4 and 5, the lower screed plate38may be displaced from the screed supporting frame portion32for service, repair, or replacement, while the upper screed plate36remains in position on the screed supporting frame portion32. For the purposes of this disclosure, the term “displaced” shall include both completely removing the lower screed plate38from the screed supporting frame portion32, and merely spacing the lower screed plate38from the upper screed plate36and the screed supporting frame portion32, as shown, for example, inFIGS. 5 and 4, respectively.

The upper screed plate36is coupled to the screed supporting frame portion32by at least two connectors50,52, and the lower screed plate38is coupled to the screed supporting frame portion32by at least two connectors54,56. While any appropriate connecting arrangement may be utilized, in the illustrated embodiment, the screed supporting frame portion32includes a plurality of bores60,62,64,66through which connectors50,52,54,56from the upper and lower screed plates36,38extend. More specifically, connectors50,52extend from the upper screed plate36through first bores60,62in the screed supporting frame portion32, and connectors54,56from the lower screed plate38extend through the second bores64,66of the screed supporting frame portion32.

The connectors50,52,54,56may be of any appropriate design. By way of example only, the connectors50,52,54,56may be threaded fasteners, as illustrated, which are received by locking nuts68. It will be appreciated that the connectors50,52,54,56may extend through openings70,72in the upper and lower screed plates36,38, or they may be otherwise secured to the upper and lower screed plates36,38. For example, they may be secured in openings70,72in the form of recesses in the upper and lower screed plates36,38. In this way, the term “openings” is intended to include both bores that extend completely through the upper and lower screed plates36,38, as well as recesses that extend only partway through the thickness of the upper and lower screed plates36,38.

The upper screed plate36may include openings74that allow for passage of the connectors54,56extending from the lower screed plate38toward the screed supporting frame portion32. The openings74may be of any appropriate design. For example, the openings74may be generally round or they may be slots (not shown) that extend from the sides surfaces76of the upper screed plate36to accommodate passage of the connectors54,56.

Each screed plate assembly30is heated by a screed heating arrangement80. The screed heating arrangement80includes at least one electric heater82positioned to heat at least the lower screed plate38. A greater number electric heaters82may be provided for each screed plate assembly30, as shown, for example, inFIGS. 3-5. The length and number of each electric heater82varies depending on the length the screed plate assembly30for each screed section22,24,28.

Each electric heater82is connected to an electric power supply88, shown inFIG. 1. One suitable electric power supply88for the practice of the present invention is an electric generator90, with the output connections of the electrical generator90being connected to the leads86of a corresponding electric heater82. The electrical generator90is operatively connected to the engine16of the asphalt paving machine10, such as by direct connection or powered by a hydraulic motor (not shown). The generator90may be either an AC or DC generator such as a 12 or 24 volt DC or 110 or 240 AC generator.

Any appropriate design of electric heater82may be utilized. The electric heater82in the illustrated embodiment is configured as a thin, elongate sheet or ribbon and formed from a resistive conductor, e.g., a thin conductive wire or ribbon. It will be appreciated, however, that alternate designs of electric heaters82may be utilized, such as, electric heaters82that present a broader profile. A resistive conductor within each electric heater82terminates with a set of leads86or electrical conductors that protrude from the electric heater82.

In the illustrated embodiment, the electric heater82is sandwiched between the upper and lower screed plates36,38. Consequently, displacing the lower screed plate38from the upper screed plate36and the screed supporting frame portion32, as shown inFIGS. 4 and 5, provides access to the electric heater82for repair or replacement. Depending upon the design of the electric heater82and the upper and lower screed plates36,38, the electric heater82may be slid out from between the upper and lower screed plates36,38, and a new or repaired electric heater82slid back into position.

The upper and lower screed plates36,38may be made of any appropriate material. By way of example only, the lower screed plate38may be constructed of a high wear steel, while the upper screed plate36may be formed of steel, a ferrous material, or composite insulating material. For example, the upper screed plate36may be formed of a material which assists in conducting heat from the electric heater82to the lower screed plate38to enhance heating of the lower screed plate38. Alternatively or additionally, the upper screed plate36may be formed of a material that provides an insulative effect, which may minimize heat loss from the electric heater82and the lower screed plate38.

Returning toFIG. 3, respective layers of insulation material (not illustrated) may be positioned to cover each electric heater82to reduce loss of heat from the heater82and more effectively transfer the heat to the lower screed plate38. If desired, such a layer of insulation material may be secured in place by any appropriate means, such as, for example, a plurality of straps (not illustrated). In the illustrated embodiment, for example, a channel92is formed between the screed supporting frame portion32and the upper screed plate36which may receive such insulation. Alternatively or additionally, an insulation blanket (not illustrated) may be provided along the top surface of the screed supporting frame portion32.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to screed plate assemblies30and their attachment to asphalt paving machines10. The screed plate assembly30including upper and lower screed plates36,38may reduce the time associated with repair or replacement of the lower screed plate38or the electric heater82. In some embodiments, when the lower screed plate38is displaced from the upper screed plate36and the screed supporting frame portion32, the electric heater82may be simply slid out from between the upper and lower screed plates36,38. A replacement electric heater82may then be slid back into position before the lower screed plate38is again moved toward the upper screed plate36and the screed supporting frame portion32.

Maintaining the mounted upper screed plate36in position while displacing the lower screed plate38from the upper screed plate36and the screed supporting frame portion32may reduce or eliminate entirely the time associated with calibrating attachment of the screed plate assembly30to the screed supporting frame portion32, that is, the screed plate assembly30generally will not require the complete shimming process typically associated with mounting of a screed plate assembly30.

Placement of the electric heater82between the upper and lower screed plates36,38may enhance efficiency of the heating arrangement80. Heating of the lower screed plate38may be improved by way of enhanced conduction of heat from the electric heater82to the lower screed plate38, or by enhancing the consistency of heat transmitted to the lower surface42of the lower screed plate38.

In some embodiments, placement of the electric heater82between the upper and lower screed plates36,38may leave the upper surface of the upper screed plate36for placement of additional insulating blankets, or mounting a vibration pod directly to the screed plate assembly30.

During operation of the asphalt paving machine10, the electric heater82flexes with the screed plate assembly30as the paving machine10traverses the road bed were asphalt paving material is being laid. When a thin design of the electric heater82is utilized, the placement of the electric heater82between the upper and lower screed plates36,38may act to minimize stresses on the electric heater82.