Patent Publication Number: US-7219964-B2

Title: Milling machine as well as method for working ground surfaces

Description:
BACKGROUND OF THE INVENTION 
   The invention concerns a milling machine to work ground surfaces, in particular pavements, as well as a process to dispose of dusts and vapors developing during the milling operation on a milling machine. 
   Such milling machines are self-propelled and are also referred to as road milling machines. 
   A front-loading milling machine in accordance is known from DE 102 23 819 A1. The known road milling machines show a self-propelled chassis with a travel drive unit consisting of several wheel units or several crawler track units. The chassis carries a machine frame in which a milling drum is supported transversely to the direction of travel. To achieve the completest possible removal of the milled material, the milling drum is generally enclosed by a housing, the wall of which pointing in the direction of travel is designed as a covering blade with an opening for the milled material. The material processed by the milling drum is accepted by a first transport conveyor, which transfers the processed material at the forward end of the milling machine onto a discharge conveyor, which can be tilted and slewed laterally for transport onto a loading space of a truck. 
   It is already known from DE 102 23 819 A1 and EP 0 971 075 A1 to provide the transport conveyors of a road milling machine with a hood in order to suck off and dispose of the dust developing at the milling drum and beneath the hood of the transport conveyors by means of a ventilator and, where appropriate, a cyclone. 
   In EP 0 971 075 A1, it is proposed to suck off the dust against the direction of the material transport and to dispose of the dust by means of a ventilator and a cyclone at the rear end of the road milling machine. Here, it is of disadvantage that an extraction by suction at the transport conveyors takes place against the direction of transport. The dust-laden air is thereby sucked off towards the rear in the direction of travel and against the actual direction of the material transport, thus requiring a considerable additional expenditure for the equipment of the machine and a distinctly higher ventilator output. The particles separated by means of the ventilator and a downstream cyclone are dropped on the ground surface, thereby contaminating again the ground surface just milled. The cyclone dust separator provided at the rear end can separate only the coarser particles but not the respirable fine dusts, so that the arrangement of the air outlet at the rear end of the road milling machine is arranged too close to the operator&#39;s platform. In this way, the dusts and vapors are blown off at the rear end of the milling machine close to the operator&#39;s platform. In addition, the ventilator transports the dust-laden air so that high wear and tear leads to a short service life of the ventilator. 
   From DE 102 23 819 A1, it is therefore known to divide the channel formed by the hoods on the transport devices and to suck off the air polluted during milling in the direction of the material transport. This provides the advantage that the dusts and vapors are disposed of at a position located considerably farther away from the operator&#39;s platform and dust can only develop during the disposal onto the truck, where the development of dust is unavoidable anyway, and not additionally behind the road milling machine close to the operator&#39;s platform. 
   According to the prior art, the suction device shows an axial-flow fan arranged in a suction channel which, due to the high exposure to dusts and sharp-edged particles, is subject to heavy wear and tear, which ultimately leads to a reduced air output and the development of bearing damages. The fan blades of the axial-flow fan are heavily worn and damaged due to the impact and the deflection of the particles being conveyed at high speed. When larger particles and smaller stones are sucked in, other parts of the ventilator are also damaged mechanically, which in case of a damage to the fan blades frequently results in the occurrence of unbalances leading to bearing damages in continued operation. In case of repair, it is of disadvantage that the ventilator is arranged at a position which is difficult to access and a repair therefore leads to a major break in operation. Finally, due to the transport of the dusts and the sharp-edged particles, the ventilator must be designed in such a way that the clearance between the fan blades and the walls of the ventilator is larger so that the air output and the efficiency of such a ventilator for dust-laden and particle-laden air is lower. 
   A further disadvantage is that although the dusts are blown off at a distant position in relation to the operator&#39;s platform, they are still blown off into the environment so that a pollution of the workplace with dusts and vapors in the vicinity of the operator&#39;s platform, even if reduced, still exists. 
   Starting from this prior art, the task of the invention consists in creating a milling machine of the aforementioned type, as well as a process to dispose of dusts and vapors by means of which dusts and vapors developing during the milling operation and during the transport operation, in particular the respirable dusts, can be sucked off and disposed of with little mechanical expenditure and with higher effectiveness, and the service life of the suction device can be extended considerably at the same time. 
   SUMMARY OF THE INVENTION 
   The invention provides in an advantageous manner that the suction device consists of a suction ventilator, a separator device for solids and a suction channel connected to the rear channel section in the direction of the material transport, that the suction ventilator is arranged downstream of the separator device, and that the separator device disposes of the separated solids either onto the transport device in a forward channel section in the direction of the material transport or into a collecting device and blows off the cleaned air into the open. 
   The invention enables a simple design which does not require the setup of a road milling machine to be basically modified, so that existing road milling machines can also be retrofitted. Given that the suction ventilator of the suction device is arranged behind the separator device, the suction ventilator is operated on the pure-air side, so that the suction ventilator has a longer service life. The invention enables not only a significantly longer service life of the suction ventilator, but also a significant improvement of the air quality in the vicinity of the operator&#39;s platform. The pure air is blown off directly into the open. By separating the solids by means of the separator device, the percentage of respirable dusts is reduced to a considerable extent, so that the workplace conditions are considerably improved. The separated solids can be disposed of either onto the transport device in the forward channel section or into a collecting device. 
   Such a collecting device can, for example, consist of an air-permeable dust bag which can be removed during breaks in operation of the road milling machine in order to dispose of the separated solids. 
   It is preferably provided that the separator device consists of a filtering device and that the filter cake forming in the filtering device can be disposed of onto the transport device in the forward channel section or into the collecting device. The use of a filtering device has the advantage that it provides a high efficiency with regard to the respirable dusts and that the separated solids can be compacted to a filter cake which can be disposed of more easily without dusts being able to develop again to a considerable extent during the disposal. In principle, it is also possible to compact the filter cake even further with binding agents, for instance, a hydrous mist so that no dusts at all can develop during the disposal. 
   The filter cake can be removed automatically by the filtering device in predetermined time intervals or at a predetermined drop in pressure. It is also possible to clean the filtering device during breaks in operation only, for example, when replacing cutting tools, provided that the filter capacity is dimensioned accordingly. A further opportunity to remove the filter cake from the filtering device arises at each exchange of the truck traveling in front of the road milling and the short break in operation associated therewith. 
   For cleaning purposes, the filtering device is then charged with, for example, a vibration or a pulsed counter pressure. 
   One preferred embodiment provides that the forward channel section is separated from the rear channel section by means of separating media in order to largely block any air current without impeding the transport of the milled material. By separating the channel into a forward and a rear channel section, it is ensured that the dust-laden air, which is sucked off via the suction channel in the direction of the material transport, is sucked off from the rear dust-laden channel section only and that no air current can arise in the forward channel section against the direction of the material transport. The division is effected by means of separating media which, on the one hand, do not impede the transport of the milled material and, on the other hand, prevent an air current against the direction of the material transport. 
   It is preferably intended that the transport device shows at least one transport conveyor with a conveyor belt and that sealing media for the channel consist of hoods sealing against the conveyor belt and against the housing of the transport conveyor. Together with the conveyor belt and together with the housing of the transport conveyor respectively, the hoods thus form an enclosed channel so that the milled material passes through the transport device entirely enclosed in its circumference. In this way, no dusts or vapors can escape along the channel to the outside. Minor gaps in the course of the channel are irrelevant, because the channel is under negative pressure so that polluted air cannot escape at possible leaks but, at the most, air is sucked in. 
   A second forward transport device can accept the milled material at a transfer point at the end of the first rear transport device. The transfer point between the first and the second transport device is sealed in its circumference by means of flexible sealing media which are fastened to at least one of the transport devices. In this manner, a continuous channel is formed which includes both transport devices. 
   The separating medium can consist of a flexible flap which seals the rear channel section of the transport device against any entry of air against the direction of the material transport. In doing so, the negative pressure in the rear channel section reinforces the sealing by sucking the flap onto the conveyor belt. 
   In the following, embodiments of the invention are explained in more detail with reference to the drawings: 
   With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a first embodiment of the invention in a front-loading road milling machine. 
       FIG. 2  is a top view of the filtering device resting on the forward transport device. 
       FIG. 3  is a view of the filtering device on the rear frontal end. 
       FIG. 4  is a view on the forward frontal end of the rear transport conveyor. 
       FIG. 5  is an enlarged illustration of a first embodiment of the suction device. 
       FIG. 6  is an enlarged illustration of a second embodiment of the suction device. 
       FIG. 7  is a cross section of the transport device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A road milling machine  1  to work pavements is shown in  FIG. 1  in the embodiment of a front-loading road milling machine. It is understood that the invention is also applicable to different milling machines that are provided with at least one transport device  14 ,  18 . 
   The road milling machine  1  serves to mill off ground surfaces, in particular pavements made of asphalt, concrete or the like. The road milling machine  1  shows a chassis with, for example, four crawler track units  4  which carries the machine frame  2 . It is understood that the crawler track units may be substituted wholly or in part by wheeled units. A milling drum  8 , which extends transversely to the direction of travel, is supported in the machine frame  2 . The milling depth is preferably set by means of the height adjustment of the crawler track units  4 . The road milling machine  1  depicted in  FIG. 1  is also referred to as front-loading road milling machine, since it conveys the milled material to the front in the direction of travel onto a transport vehicle  10 . In front of the milling drum  8  in the direction of travel, a first transport device  14  consisting of a transport conveyor with a conveyor belt  15  is arranged in a duct  9  of the machine frame  2 , which runs in the machine frame  2  at an inclination. The first transport device  14  transports the milled material  3  on the conveyor belt  15  to a second transport device  18  which preferably also shows a conveyor belt  19 . The second transport device  18  is adjustable in height by means of an adjustable inclination and can additionally be slewed sideways by, for instance, ±30°, so that transport vehicles  10  standing next to the lane of the road milling machine can also be loaded. Alternatively to the conveyor belts  15 ,  19 , the use of conveyor augers arranged in a duct is also possible. 
   To achieve the completest possible transport of the milled material, the milling drum  8  is generally enclosed by a drum housing  58 , the wall of which pointing in the direction of travel is designed as a blade  52  with an opening  56  for the milled material. 
   The milling drum  8  is provided with cutting tools arranged in the shape of a helix, which are arranged in such a manner that the milled material  3  is transported to the opening  56  in the blade  52 . At the rear end of the drum housing  58  in the direction of travel, a wall  60  of the drum housing  58  is provided, which closes off tightly with the milled ground surface and levels the milled ground surface so that no fragments of the milled material  3  remain on the milled ground surface. With its lower edge, the wall  60  is pressed against the ground surface hydraulically in order to achieve the best possible sealing. 
   At the machine frame  2 , a conveyor protection and support device referred to as conveyor shoe  50  is fastened in a guide in a height-adjustable manner. The conveyor shoe  50  receives the rear end of the first transport device  14 . The opening  56  of the drum housing  58  forms a first transfer point  5  at which the milled material is transferred by the milling drum  8  onto the first transport device  14 . 
   In the embodiment of  FIG. 1 , the operator&#39;s platform is located above the milling drum  8 , but as is usual with road milling machines, it can also be arranged in the rear or the forward area of the machine frame  2 . 
     FIGS. 5 and 6  show in detail the first transport device  14 . 
   The transport device  14  is fastened in a preferably centrally arranged duct  9  of the machine frame  2  and can easily be detached from the conveyor shoe  50  for maintenance purposes and be removed through the duct  9 . 
   The transport device  14  with the conveyor belt  15  shows a hood  22  which, jointly with the carrying side  15   a  of the conveyor belt  15 , forms a channel section  16   a  of a channel  16  which extends from the drum housing  58  to the end of the second transport device  18 . As can be seen in detail in the cross section of  FIG. 7 , the hood  22  of the first transport device  14  is fastened to the frame of the first transport device  14  by means of hood supports  44 . Elastic lips  46  can be fastened at the hood supports  44  on both sides of the transport conveyor and can touch the carrying side  15   a  of the conveyor belt  15  in the peripheral area over the entire length of the carrying side  15   a.    
   In the same way, the second transport device  18  can also be provided with a hood  26 . In this way, the entire channel  16  can be sealed off dust-proof and gas-proof against the environment, even though the sealing of the forward channel section  16   b  is actually only required in case a perceptible development of dust in the forward channel section  16   b  is detectable at all. 
   In the upper area of the hood  22  close to the discharge end but at a distance to the discharge end, the hood  22  of the first transport device  14  shows at least one connection  23 ,  23   a ,  23   b  to which at least one suction channel  24  can be connected. In the embodiment of  FIG. 1 , the suction channel  24  is formed by two suction hoses  24   a ,  24   b  which lead from the connections  23   a ,  23   b  to the inlet side of a filter housing of a filtering device  25 , which is preferably fastened on top of the hood  26  of the forward transport device  18  in the area of the forward channel section  16   b . The filtering device  25  preferably consists of several, for instance, ten filter cartridges  31  which are preferably paralleled to form one large filter surface. The suction ventilator  28  is arranged on the outlet side, i.e. on the pure-air side, and is thus charged with pure air only. Because the suction ventilator  28  is operated behind the filtering device  25 , bearing damages and damages to the fan blades and additional ventilator elements are prevented in an advantageous manner, and in comparison to the prior art, a considerably longer service life of the suction device  20  is achieved. Because a filter cake can form in the filtering device  25 , it is further possible to not only remove the vapors developing during the milling operation from the area of the operator&#39;s platform, but to bind them within the filter cake forming in the filtering device  25 . As a result, not only the dust load but also the pollution of the respirable air with vapors is reduced to a considerable extent by the suction device  20 , so that the workplace conditions can be improved to a considerable extent. An exhaust air connection  29  allows the cleaned exhaust air to be blown off directly into the open. Alternatively, the pure air can be blown off at the forward end of the filtering device  25  or at the forward end of the forward transport device  18 . The suction ventilator  28  enables a high ventilator output, thus generating a correspondingly high negative pressure in the rear channel section  16   a  and in the drum housing  58  enclosing the milling drum  8 . The dusts and vapors developing during the milling operation are, therefore, sucked off reliably and with high efficiency via the suction channel  24 ,  24   a ,  24   b.    
   In the area of the first transfer point  5 , i.e. at the lower end of the hood  22  and at the opening  56  of the drum housing  58  or the conveyor shoe  50  respectively, flexible rubber mats can seal off the transfer point  5  in its circumference. Minor leaks of the drum housing  58  or between the channel  16  and the drum housing  58  respectively are irrelevant, because due to the negative pressure no polluted air can escape but, at the most, air from the environment is sucked in. As can best be seen from  FIG. 4 , flexible flaps  36  are provided as separating media between the first and the second channel section  16   a ,  16   b  at the upper end of the hood  22  which, on the one hand, allow the milled material  3  on the conveyor belt  15  to pass and, on the other hand, prevent an air current against the transport direction of the first transport device  14 . If only a single transport conveyor is provided, the separating media are, for example, positioned in the middle of the single transport device. 
   In order to seal the rear channel section  16   a  in the best possible way at its upper end, the flaps  36  are provided with slits. Several flaps  36  are preferably arranged behind one another to achieve an improved air sealing between the channel sections  16   a ,  16   b  ( FIG. 5 ). 
   It is understood that the separating media inside the channel  16 , which preferably consist of flaps  36 , can also be arranged at a different position, for example, behind the second transfer point  7  in the direction of the material transport in the area of the second transport device  18 . In this case, the suction channels  24   a ,  24   b  of the suction device  20  are connected to the hood  26  of the second transport device  18  upstream of the separating media in the direction of the material transport, preferably close to the separating media. The rear channel section  16   a  thus ends at the separating media which are arranged downstream of the transfer point  7  in the direction of the material transport. 
   As can best be seen from  FIG. 7 , the conveyor belt  15  is guided via support rollers  62 ,  64 , whereby the carrying side  15   a  forms an essentially U-shaped trough in that the support rollers  64  are tilted correspondingly. The lower support roller  62  supports the return side  15   b  of the conveyor belt  15 . As can be seen from  FIGS. 3 and 4 , ribs  17  are provided on the surface of the conveyor belt  15  which improve the conveyance of the milled material  3  on the conveyor belt  15 . 
   At the upper end of the transport device  14 , the milled material  3  is transferred into a receiving bin  35  of the second transport device  18  at the second transfer point  7 , whereby the milled material  3  is conveyed to the discharge end via the conveyor belt  19  and disposed of onto the transport vehicle  10 . The filter cake of the filtering device  25  can, for example, also be disposed of into this receiving bin  35  via a flap  37  in the filter housing  33  ( FIG. 5 ). Alternatively, the filter cake can be filled into a collecting device  39  consisting of a dust-collecting bag ( FIG. 6 ) which is fastened to an opening of the filter housing  33 . With this embodiment, a flap  37  in the bottom of the filter housing  33  can also be provided as and when required. 
   The transition point at the transfer point  7  is enclosed by sealing media consisting of flexible mats  30  so that the first transport device  14  and the second transport device  18  form a channel  16  which is continuous in the direction of the material transport and sealed in its circumference. 
   The filtering device  25  illustrated in  FIGS. 2 and 3 , which consists of several filter cartridges  31 , is cleaned in time intervals which can be selected by the operating personnel, for example, during breaks in operation, such as the exchange of the truck  10  traveling ahead or the replacement of cutting tools, upon manual command, for example, by vibration or by charge with a pressure impulse, in counter flow direction. In doing so, the filter cake sitting on the filter cartridges  31  is removed. The filter cake can, of course, also be cleaned automatically depending on the drop in pressure developing with the prolonged operating period of the filtering device  25  or after predetermined time intervals. Due to the inclination of the bottom of the filter housing  33 , the filter cake removed from the filter cartridges  31  can slide to the rear end of the filter housing  33  where it can, for example, be disposed of via a flap  37  and the receiving bin  35  onto the forward transport device  18 . In doing so, it is also possible to additionally compact the filter cake by means of a spray and to increase the cohesion of the separated particles by the spray. The filter cake is placed onto the forward transport device  18  behind the separating media in an advantageous manner. 
   As can be seen from  FIG. 2 , the suction hoses  24   a ,  24   b  of the suction channel  24  enter the filter housing  33  from two opposite sides. Thereby, the filter cartridges  31  are charged from the outside with the dust-laden and vapor-laden air. 
   Although a preferred embodiment of the invention has been specifically illustrated and described herein, it is to be understood that minor variations may be made in the apparatus without departing from the spirit and scope of the invention, as defined by the appended claims.