Patent Publication Number: US-8113737-B2

Title: Device for compacting road paving materials

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device for compacting road paving materials. 
     2. Background 
     Such a device is known from DE 26 00 108 A1. According to this document, a screed upstream of which is arranged a tamper for precompacting the paving material is fastened to the road finisher. During the beginning of a paving operation, it thus occurs that the bituminous mixture in the warm state remains sticking on the cold tamper strip. However, the mixture sticking on the tamper strip leaves behind grooves in the surfacing which can no longer be removed by the following screed and therefore remain on the surface of the roadway covering. To avoid these grooves at the beginning of a paving operation, it is known to heat the tamper strip. The use of a gas burner has been replaced here by an electrical heater which is inserted into an open or closed hollow profile which forms the tamper strip. The electrical heater is then situated in the interior of the tamper strip. 
     EP 0 641 887 B1 discloses a road finisher and tool in the form of a tamper strip for a paving screed. The tamper strip forms a channel between a carrier part and a wear part, in which channel a heating element, in particular a heating bar, is provided. The heating element is an electrical flat-tube heating body which is screened upwardly by a shim. Here, the shim ensures that the heating element is securely clamped such that as large a contact surface as possible results for heat conduction. A disadvantage here is that the heating element frequently breaks. The replacement of a defective heating element leads to undesired downtimes of the road finisher. The maintenance requirement is additionally increased. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to provide a device for compacting road paving materials according to the preamble of claim  1  whose maintenance requirement as a result of defective heating elements is reduced. 
     This object is achieved according to the invention by the features of claim  1 . 
     Accordingly, a tamper strip with an electrical heating element whose fastening takes place by means of clamping by elastic deformation is provided. A statically acting energy accumulator is applied using the elastic change of shape. The energy arising for example from human muscle power when inserting the heating element into the cavity of the tamper strip is thus accumulated in a suitable manner. Here, the energy accumulator element acts according to the invention in the direction of the striking upward and downward movement for bearing the heating element. The heating element is thus supported within the tamper strip over its length and fastened. In a striking tamper, the heating element must be secured against oscillations for purely mechanical reasons. The heating element is therefore protected from vibration. Fastenings by means of screws are not necessary since the spring action is also maintained in the heating state of the heating element. 
     Particular advantages of the self-clamping according to the invention lie in a simple, rapid changeover of the heating element. Thermal stresses over the length of the heating element are avoided and hence the risk of breakage of the heating element is considerably reduced. Furthermore, fewer fastening elements are required, i.e. there is less manufacturing and assembly effort. 
     The heating element is preferably designed as a heating bar in corrugated form or zigzag-shaped form. For fastening, the resilient property of the heating bar is used. This can be automatically clamped in the tamper by means of loaded corrugation. 
     Alternatively, the deformation of a heating bar which is straight in the unloaded state is possible by means of suitable abutments, such as, for example, a corrugated shim, in order to apply the necessary clamping force. 
     Here, the heating element can be designed as a flat-tube heating body or round-tube heating body. According to the invention, it has been found surprisingly that the round-tube heating body maintains the heating capability of the flat-tube heating body. 
     Given the same heating power, the use of a round-tube heating body is more cost-effective than the use of flat-tube heating bodies. 
     It is customary for only one heating filament to be laid within round-tube heating bodies. Preferably, the heating bar is folded over at the end and guided back. This allows the use of only one connection sleeve. This design of the round heating body makes it possible to keep the cavity very small. The round-tube heating bar thus has the same geometric advantages as a flat-tube heating bar. 
     The tamper strip is preferably a horizontally divided construction which has a carrying strip and an impact strip. Preferably provided within the carrying strip is a groove in which the heating element is situated. Following wear of the impact strip, the carrying strip can thus remain on the machine and be further used. The groove is thus not situated in the wearing part. This choice makes it possible to keep the impact strips cost-effective. Here, the impact strips can be of multi-part design and be bridged by means of a cover plate. The connection surfaces are sealed as a result. 
     Further refinements of the invention can be taken from the following description and the subclaims. 
     The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  shows a schematic side view of a road finisher, 
         FIG. 1   b  schematically shows a sectional representation of a screed, 
         FIG. 2  schematically shows in section a tamper strip according to a first exemplary embodiment, 
         FIG. 3  schematically shows in section a tamper strip according to a second exemplary embodiment, 
         FIG. 4  schematically shows in section a tamper strip according to a third exemplary embodiment, 
         FIG. 5  schematically shows a section A-A according to  FIG. 4 , 
         FIG. 6  schematically shows a section according to  FIG. 4  when inserting the heating element, 
         FIG. 7  schematically shows in section a tamper strip according to a fourth exemplary embodiment, 
         FIG. 8  schematically shows a section C-C according to  FIG. 7 , 
         FIG. 9  schematically shows in section a tamper strip according to a fifth exemplary embodiment, 
         FIG. 10  schematically shows a section D-D according to  FIG. 9 , 
         FIG. 11  schematically shows in section a tamper strip according to a sixth exemplary embodiment, 
         FIG. 12  schematically shows a section E-E according to  FIG. 11 , 
         FIG. 13  schematically shows in section a tamper strip according to a seventh exemplary embodiment, 
         FIG. 14  schematically shows a section F-F according to  FIG. 13 , 
         FIG. 15  schematically shows in section a tamper strip according to an eighth exemplary embodiment, 
         FIG. 16  schematically shows a section G-G according to  FIG. 15 , 
         FIG. 17  schematically shows in section a tamper strip according to a ninth exemplary embodiment, 
         FIG. 18  schematically shows a section H-H according to  FIG. 17 . 
     
    
    
     DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     The road finisher  1  according to  FIG. 1   a  comprises a chassis  2 , a drive unit  3 , a material bunker  4  situated at the front in the direction of travel and a distribution auger  5  situated behind. Lateral arms  6  are used to tow a screed  7  which lays paving material which is transported rearwardly from the material bunker  4  and distributed by the distribution auger  5 . The screed  7  is preferably a vibrating screed which smoothes and compacts. At least one tamper  8 , as is represented in  FIG. 1   b , is arranged at the side of the paving screed  7  situated at the front in the direction of travel F. According to  FIG. 1   b , two tampers  8  are arranged behind one another. This is accordingly a double tamper screed. Furthermore, a tamper  8  can also be arranged downstream of the screed  7 . The screed  7  can have a fixed working width or be laterally extendable as an extension screed for larger working widths. The tamper  8  arranged in front of the screed  7  in the direction of travel F operates as a precompacting element. 
       FIGS. 1   a  and  1   b  thus show a device for compacting road paving materials, comprising a screed  7  which is fastened to a road finisher  1  and extends transversely to the working direction of the finisher  1 , and a tamper  8  which is arranged upstream of said screed. The tamper  8  described below can preferably additionally or alternatively be arranged downstream of the screed  7 . 
     The tamper  8  has a tamper strip  9  which can be driven to perform a striking upward and downward movement. A drive  10  is provided for driving the tamper strip  9 . 
     As shown in  FIG. 2 , the interior of the tamper strip  9  is equipped with an electrical heater in the form of a bar-shaped heating element  12  which can be clamped in a cavity  11  of the tamper strip  9 . The cavity  11  forms an enclosed space for the heating element  12 . In order to clamp the heating element  12 , a spring accumulator which bears the heating element  12  in the direction of the striking upward and downward movement S is provided. The spring accumulator achieves clamping by elastic deformation. The spring accumulator clamps the heating element  12  along the cavity  11  in such a way that the heating element  12  lies in a stabilized or play-free manner in the cavity  11 . The thermal expansion of the heating element  12  in the direction of a free end  13  is provided for. The clamping according to the invention of the heating element  12  by bracing without articulation avoids breakages of the heating element  12 . The cavity  11  can have a round or angular cross section; it can be formed by a core drilling or it can be designed as a closed groove. 
     As shown in  FIG. 3 , exchanging the heating element  12  is additionally noticeably simpler if it is fastened only to the end side of the tamper  8  via a connecting block  14 . There is no need to loosen clamping screws which previously had to be freed from paving materials. The standstill of the machine for exchanging the heating element  12  is therefore considerably shortened. The heating element  12  is electrically connected via the connecting block  14  to a power source, for which purpose a connection cable  19  is provided. The connecting block  14  is fastened to the tamper strip  9 . 
     The heating element  12  is preferably designed as a corrugated, bent or zigzag-shaped heating bar whose elastic change in shape forms the spring accumulator. The heating element  12  is seated elastically prestressed in the cavity  11  of the tamper strip  9 . The cavity  11 , which extends along the tamper strip  9 , thus has dimensions, in particular in terms of height and width, which define the elastic deformation of the heating element  12  and hence the prestress (cf.  FIG. 6 ). The elastic change of shape of the heating element  12  is used, for which purpose the thickness of the corrugation or the zigzag shape of the heating bar with respect to the cavity  11  is selected.  FIG. 6  shows for example the energy arising from human muscle power (when inserting the heating element  12 ) for building up the statically acting spring accumulator while using the elastic change of shape. The independent clamping of heating bars as heating elements  12  is not dependent on the tube shape. The heating element  12  can be formed by a flat-tube heating body, a round-tube heating body or a cartridge heating bar. 
     According to  FIG. 2 , the heating element  12  is designed as a flat-tube heating body. According to  FIG. 3 , the heating element  12  is designed as a round-tube heating body. The number of corrugations of the bending points  15 ,  16 ,  17 ,  18  can vary. However, at least one bending point is required. The axis of the bending can vary. According to  FIGS. 2 and 3 , the bending points are situated in a plane. However, this is not absolutely necessary as will also be stated below with reference to  FIGS. 7 to 18 . 
     In addition to the stepped shape of the bending points, a spiral form can also be selected. Any departure from the straight shape allows clamping in the cavity  11  as long as the spatial extent of the heating element  12  prior to the insertion into the cavity  11  is larger than the available space of the cavity  11  following the insertion, i.e. the formation of a spring accumulator.  FIG. 6  shows the insertion of a heating element  12  in the cavity  11  of the tamper strip  9 . 
     On the other hand, the cavity  11  can also be spatially curved. Here, an originally straight heating bar as heating element  12  is brought into a curved shape by means of the mounting operation, with the result of independent clamping. The curvature of the heating bar about an axis can also be combined with a cavity which is curved in another axis. Finally, the resilient clamping action can also be separated from the actual heating element  12 . Here, use is made of an additional, nonheated shim of corrugated or bent shape in order to clamp the heating element  12 , as is represented in  FIGS. 15 ,  16 . 
     As shown in  FIG. 3 , the heating element  12  is preferably designed as a round-tube heating bar. This round-tube heating bar has only one heating filament  20  whose free end  13  is folded over and guided back. The start  21  and end  22  of the one heating filament  20  are connected and fastened to the one connecting block  14 . By using a round-tube heating bar with a folded-over heating filament  20 , the cavity  11  can be designed to be small. The thus reduced convection provides a large saving potential of heat loss to the benefit of heat conduction and heat radiation. The heating filament  20  transfers heat to the tamper strip  9 , with the contact to the tamper strip  9  no longer being paramount as in the case of flat-tube heating bodies. The folded-over heating filament  20  forms a heating assembly with two bars of the heating filament  20  of a round-tube heating body arranged above or next to one another, said bars being connected in a common connecting block  14  to an electrical supply line  19 . 
     The four bending points  15 ,  16 ,  17 ,  18  provided according to  FIG. 3  are chosen such that the heating element  12  builds up enough spring stress in order to be sufficiently firmly clamped in the tamper strip  9  during the operation of the tamper  8 . The heating element  12  preferably has a good bending property so that it allows an elastic deformation of its own. 
     According to  FIG. 3 , the tamper strip  9  preferably comprises a carrying strip  23  and an impact strip  24 . The tamper strip  9  is thus divided horizontally. In order to form the cavity  11  in an enclosed space of the tamper strip  9 , the carrying strip  23  preferably contains a groove  25  in which the heating element  12  is situated. The groove  25  is closed via a top surface  26  of the impact strip  24  to form the cavity  11 . After wearing of the impact strip  24 , the carrying strip  23  can remain on the finisher  1  and be further used. The groove  25  can thus be made in a nonwearing part. 
     The impact strip  24  can be composed of a plurality of impact strip segments. The impact strip  24  can for example have at least two impact strip segments arranged behind one another. The impact strip segments can be bridged by a cover plate. The cover plate can then form the top surface  26  for delimiting the cavity  11 . 
     Furthermore, the impact strip  24  is preferably designed as a thin-walled profile. The carrying strip  23  can be adapted as carrying body to the use conditions. The tamper  8  is fastened to the drive  10  for example via arms  28 ,  29  on the tamper strip  9 . 
     The following exemplary embodiments in the schematic drawings of  FIG. 4  to  FIG. 18  show the electrical heating element  12  in the cavity  11  of the tamper strip  9 . The respective fastening by clamping must ensure on the one hand that the heating element  12  is sufficiently fixed with respect to the vibrations which occur; on the other hand, the relative movement between the heating element  12  and the cavity  11  which results from the thermal expansion of the heating element  12  must be possible. 
       FIG. 4  and  FIG. 5  show the tamper strip  9  according to  FIG. 3  with two bars of the heating filament  20  of a round-tube heating body which are arranged above one another. The cavity  11  is closed at the end face of the tamper strip  9  by the connecting block  14 . As shown in  FIG. 6 , the heating element  12  is more greatly bent before installation than in the mounted state. During the mounting operation, for example through the application of human muscle power, the heating element  12  is pushed laterally into the groove  25  between the carrying strip  23  and impact strip  24 . In the meantime, the heating element  12  deforms elastically and if appropriate proportionally plastically into a prestressed form to such an extent that it fills the groove  25 . The proportion of the elastic deformation causes the clamping. The length of the cavity  11  is dimensioned in such a way that the heating element  12  can expand toward the free end by a sliding movement. As shown in  FIG. 5 , the heating element  12  in the closed system of the cavity  11  is completely enveloped by the tamper strip. No direct contact between the heating element  12  as round-tube heating body and impact strip  24  is required. The surface temperature of the round-tube heating body is increased in comparison to a flat-tube heating body with contact. The round-tube heating body is suitable for this higher temperature. The proportion of the heat flow from the reduced contact heat transfer of the round-tube heating body is therefore in particular divided between heat radiation and convection as heat transfer types. 
       FIG. 7  and  FIG. 8  show an exemplary embodiment of a heating element  12  with a round-tube heating body which differs from  FIG. 4  in that the corrugation or bending is designed to be shorter. 
       FIG. 9  and  FIG. 10  show an exemplary embodiment of a heating element  12  with a round-tube heating body which is clamped transversely to the impact direction and in which the heating filament  20  is horizontally corrugated or bent. One bending point  18  is represented. The heating filament  20  lies in the manner of a snake on the top surface  26  of the impact strip  24 . 
       FIG. 11  and  FIG. 12  show an exemplary embodiment with two bars of the heating filament  20  which are arranged next to one another. Here too, the spring accumulator bears the heating element  12  in the impact direction S. 
       FIG. 13  and  FIG. 14  show an exemplary embodiment of a heating element  12  with a round-tube heating body which is clamped transversely to the impact direction, comparable to  FIG. 9  and  FIG. 10 . The two bars of the heating filament  20  here lie above one another and not next to one another. 
     According to  FIG. 15  and  FIG. 16 , the spring accumulator provided is a corrugated or bent shim  27  whose elastic change of shape forms the spring accumulator. Here, the resilient clamping action is separated from the actual heating element  12 . The shim is an additional, preferably nonheated element of corrugated or bent shape which clamps the heating element  12 . 
     According to  FIGS. 17 and 18 , instead of a stepped shape, a spiral shape of the heating filament  20  is provided.