Patent Application
20080292401
The present disclosure relates generally to strategies for inhibiting adhering of asphalt to components of a compactor machine, and relates more particularly to a heated drum compactor machine and method for providing a heated drum.
A wide variety of machines for paving and compacting asphalt have been used for decades. The term “asphalt” is used broadly herein in reference to the class of paving materials consisting of aggregate mixed with one or more viscous materials such as petroleum-derived asphalt, other definitions for “asphalt” notwithstanding. A conventional approach for paving a surface such as a road or parking lot is to distribute hot paving material onto a prepared bed with a paving machine, then follow the paving machine with one or more compactor machines to compact the material to a desired density and obtain an acceptable surface finish. Most commonly, the compacting process is performed with double drum compactors, having a front drum and a back drum, which serve to propel the machine and compact the asphalt to a suitable state via the weight of the compactor, often in cooperation with drum vibrating apparatuses. Completing compaction can often require multiple passes across the asphalt mat with a compactor machine.
Sticky, viscous properties of hot asphalt can cause it to adhere to paving and compacting equipment where relatively cool machine components come into contact with the asphalt. This tendency for hot asphalt to stick to machine surfaces is generally a function of the heat transfer out of the asphalt. The asphalt congeals and increases in viscosity where it is cooled by contact with machine surfaces. The greater a difference in temperature between the asphalt and machine surfaces, the greater the tendency for asphalt to stick. Recognizing this phenomenon, engineers have developed several ways to address asphalt sticking problems over the years.
As asphalt is laid down by a paver, a component of the paver known as a screed is typically used to prepare the asphalt for compacting. Screeds commonly consist of a metallic implement having a surface which slides across a pile of asphalt deposited on a work surface to level and slightly compact the asphalt in anticipation of further working by a compactor. The efficacy of the screed and ultimately quality of the paving job may be affected where asphalt adheres to the screed instead of smoothly slipping past the screed surfaces. In other words, asphalt stuck to the screed can affect the ability of the screed to provide an asphalt mat suitable for finishing with a compactor machine. Irregularities in the asphalt mat laid down in advance of the compactor machine(s) can result in unevenness in the later compacted surface. To address this issue, a screed heater may be employed to heat the back side of the flat plate which slides across the pile of asphalt. Hot fluid circuits, gaseous or liquid fueled burners and electric heaters are used for this purpose. The temperature of the screed surface which contacts asphalt may thereby be increased up to a point at which heat transfer from the asphalt to the screed is reduced or negligible. Accordingly, asphalt has less of a tendency to congeal on the heated screed surface and compromise the planarity and/or uniformity of a finished asphalt mat.
After deposition and working by a paver, the asphalt cools somewhat prior to being compacted. However, the asphalt is still typically hot enough to have sticking problems with components of compactor machines following the paver. Certain compactor designs use tires or belts to compact asphalt, and some of these machines utilize heaters to heat the tires/belts to inhibit adhering of asphalt. The most prevalent known strategy by far, however, is to spray water, detergent or even fuel onto a compacting unit's surface to prevent asphalt from sticking. Such machines also often use a scraper to remove any asphalt that does happen to stick to the drum. While such approaches have a long history of success, there are various reasons why alternatives may be desirable in some situations.
Using the water spray or detergent spray approach requires an extra on-board fluid tank, whereas fuel spray strategies obviously consume excess fuel. Moreover, operating weight of a compactor machine can change due to the consumption of a large volume of fluid carried on board. As an alternative, smaller volumes of water, etc. having less of a proportionate effect on the overall weight of the machine may be used; however, this strategy can require relatively frequent stops to refill the tank and still generally requires a water truck and extra operator on-site.
Further, in conventional fluid spray systems portions of the drum are typically made visible to an operator to allow him or her to inspect the drum for asphalt that does happen to stick. Many drum compactors also utilize noisy vibratory apparatuses to enhance compacting of the asphalt. Noise issues are an increasing problem as some jurisdictions have enacted, or are expected to enact, heightened noise regulations for many types of construction equipment. Exposed drums can permit excessive noise to escape and/or require that such vibratory devices be operated at lower amplitudes than what would otherwise be considered ideal. It will thus be readily apparent that improved strategies for reducing asphalt sticking issues in drum compactors, as well as noise suppression, would be welcomed by the industry.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.
In one aspect, the present disclosure provides a compactor machine having a frame, a front compacting element and a back compacting element mounted to the frame. At least one of the compacting elements includes a compactor drum having an outer surface configured for compacting asphalt. The compactor machine further includes a heating system configured to heat the outer surface, the heating system having at least one heating element and a control device configured to control an output of the at least one heating element to the outer surface.
In another aspect, the present disclosure provides a method for providing a heated compactor drum for a compactor machine. The method includes mounting at least one heating element to a compactor machine having a front compacting element and a back compacting element, at least one of the compacting elements comprising a compactor drum. The method further includes coupling a control device with the at least one heating element to enable controlling an output of the at least one heating element to an outer surface of the compactor drum.
In still another aspect, the present disclosure provides a compactor machine having a frame and at least one compactor drum mounted to the frame, the at least one compactor drum having an outer surface configured for compacting asphalt. The compactor machine further includes a heating system configured to heat the outer surface, the heating system having at least one heating element and a control device configured to control an output of the at least one heating element to the outer surface. The compactor machine further includes an electrical power source mounted on the compactor machine, the at least one heating element including at least one electrically powered heating element coupled with the electrical power source.
Referring to
It should be appreciated, however, that compactor machine 10 is illustrative only as depicted in
Each of compactor drums 14 and 16 may include an outer surface, shown via reference numeral 34 on drum 16, configured for compacting asphalt. Outer surface 34 may consist of a cylindrical, smooth metallic drum surface comprising the exterior of a shell of drum 16. As compactor machine 10 is passed across an asphalt mat to compact it, outer surface 34, and the corresponding outer surface of drum 14, will roll against an asphalt mat laid by a paver. As a result, the asphalt of the mat will increase in density and develop a relatively smooth surface finish. As mentioned above, heating system 29 may be used to heat drum 16, in particular outer surface 34, prior to and/or during the compacting process.
Control device 30 may be used to control heating system 29 during increasing the temperature of outer surface 34 from an ambient temperature to a higher temperature sufficient to inhibit adhering of asphalt thereto. Control device 30 may also be used in controlling a temperature of outer surface 34 once heated to keep outer surface 34 at a desired temperature or within a desired temperature range. It has been discovered that where a drum outer surface has a temperature within a range of about 20° F. of an asphalt temperature, asphalt will not typically substantially adhere to the drum outer surface. Depending upon the particular project, different types of asphalt mixtures having different properties may be laid and subsequently compacted at different optimal temperatures. Thus, the actual temperature or temperature range at which drum 16 is maintained may depend upon the chosen asphalt type. Moreover, control device 30 might include a plurality of temperature set points corresponding to different types of asphalt. In still further embodiments, control device 30 might be programmable with different user-entered temperature settings. While much of the present description emphasizes apparatus and method associated with a single drum, it should be appreciated that the present description is similarly applicable to design and heating system control for a second drum, such as drum 14. In most embodiments, where double drum compactors such as compactor 10 are used each of the drums may be heated and temperature controlled in the manner described herein. Control device 30 might thus be configured to control heating of each of drums 14 and 16 via one or more heating systems such as heating system 29.
Compactor machine 10 of
Heating system 29 may be thermostatically controlled, hence, control device 30 may comprise a thermostatic control device. To this end, a temperature sensor 32 may be positioned within enclosure 17 and oriented such that a temperature of outer surface 34 may be sensed as surface 34 is rotated past temperature sensor 32. Temperature sensor 32 may comprise a non-contact temperature sensor spaced from outer surface 34 which operates by directly sensing a temperature of outer surface 34, for instance by sensing infrared radiation. Alternatively, temperature sensor 32 might actually contact outer surface 34, or it might be used to indirectly determine temperature of outer surface 34, for example by sensing a temperature of air within enclosure 17. In still other embodiments, temperature sensor 32 or another temperature sensor might sense an asphalt temperature and output signals indicative of asphalt temperature for use by control device 30 in controlling a temperature of outer surface 34.
Turning to
Turning now to
Referring to
Referring to the drawings generally, similar to conventional paving practice, compactor machine 10, and possibly a plurality of such machines, may follow a paver distributing asphalt onto a work surface such as a prepared road bed or the like. Prior to beginning to compact asphalt, it may be desirable to preheat compactor drums 14 and 16. The following description focuses primarily on drum 16, however, it should be understood to refer also to heating/controlling temperature of drum 14, as well as the other embodiments described herein, except as otherwise noted. Preheating may take place prior to driving compactor 10 onto asphalt, while loaded on a transfer machine, etc. In one preheating strategy, engine 20 may be started and used to power generator 22 such that electrical power is available to heating elements 36. Once control device 30 is activated, which may take place upon turning an ignition key for compactor 10, thermostat 40 will receive inputs from temperature sensor 32 corresponding to a temperature of outer surface 34 of drum 16. Thermostat 40 will typically be configured to turn relay 42 on, if it is not already on, when signals from temperature sensor 32 indicate that outer surface 34 is below a desired temperature or temperature range considered appropriate for inhibiting sticking of asphalt.
With power available from generator 22, heating elements 36 may begin to radiate heat energy toward outer surface 34, reflective elements 38 reflecting heat energy that might otherwise be wasted back toward outer surface 34. In the embodiments of
Once compactor machine is ready to begin compacting asphalt, it will typically be driven onto the asphalt mat. During operation, drums 14 and 16 will tend to be heated via contact with the hot asphalt, reducing a need for heating via heating elements 36. Drums 14 and 16 will tend to lose a certain amount of heat to ambient, even with enclosures 15 and 17 and, hence, supplemental heating with heating system 29 may often take place. As described above, temperature sensor 32 may continuously or intermittently output signals indicative of a temperature of outer surface 34. Control device 30 may control supplying of electrical power to heating elements 36 in response to an output of temperature sensor 32, thereby maintaining a temperature of outer surface 34 at or close to a desired temperature considered appropriate for inhibiting adhering of asphalt. The embodiments shown in
The present disclosure thus provides an altogether new strategy for inhibiting adhering of asphalt to compactor drums. Earlier approaches to this problem in drum compactors utilized bulky, heavy, unwieldy and sometimes ineffective means for inhibiting sticking and removing asphalt. While it has been known for some time to use electric heaters in the context of pneumatic compactor machines, such strategies are not applicable to the differing materials, properties and use of drum compactors, and typically require an operator's best guess as to how long to heat the tires, how often to apply supplemental heat, and when the tires are sufficiently heated. This can result in a risk of damaged tires, wasted energy and compromised compaction quality, as well as requiring operator monitoring and activity. The present disclosure offers a far more elegant and effective approach in the context of drum compactors in that a control strategy useful for both preheating drums and maintaining drum temperature is possible rather than simply relying on an operator's best guess.
The present strategy provides the additional advantage over earlier strategies in that an operator does not need to monitor the compactor drum surfaces to assure that asphalt does not stick. Since asphalt does not stick to the drum surfaces at all or only negligibly with the present approach, the overall quality of the finished paved surface can be improved over earlier paving strategies without requiring close monitoring to ensure nothing is going wrong. The foregoing features together also make a truly autonomous compactor machine much more practicable than with earlier designs, as all or substantially all of the machine systems may be electrically powered and do not require operator interaction. It is contemplated that engine 20 may comprise a diesel engine configured to run continuously at an optimal speed, providing power for motor(s) 21, steering actuator(s) 23 and heating system 29. Vibratory apparatus 160 may also be electrically powered. Remote control of one or more machines, or automated path planning by a computer, may be used to substantially improve performance and efficiency of a paving operation.
Yet another advantage afforded by the present disclosure is the increased heat retention and noise suppression made possible by substantially enclosing the drums, as shown in
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modification might be made to the presently disclosed embodiments without departing from the full and fair scope of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.
