Patent Publication Number: US-8113738-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 increased. The heating capacity is further determined by the contact heat. 
     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 heating element is low-maintenance and has a good heating capacity. 
     This object is achieved according to the invention by the features of claim  1 . 
     Accordingly, a tamper strip with an electrical heating element is provided whose heating element as a round-tube heating body is particularly robust and can be easily handled by the connection to a connecting block. The heat distribution is improved by the arrangement of the bars. By virtue of its length and deformability, the round-tube heating body looks better than a flat-tube heating body. Finally, it is possible for a round-tube heating body for the cavity in the tamper strip to be dimensioned to be smaller such that the heat losses through convection can be kept low. 
     The round-tube heating body can be fastened by means of clamping by a holder plate or by elastic deformation. In the case of clamping by elastic deformation, a statically acting energy accumulator can be 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 preferably 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. 
     The round-tube heating body 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 round-tube heating body 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. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the appended 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 G-G according to  FIG. 7 . 
     
    
    
     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 smooths 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  FIGS. 2 and 3 , 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 . The heating element  12  is formed by a round-tube heating body whose heating filament  20  is at least folded over once at a free end of the round-tube heating body to form two bars  33 ,  34  arranged adjacently to one another. According to  FIG. 2 , the two bars  33 ,  34  are next to one another. According to  FIG. 3 , the two bars  33 ,  34  lie above one another. 
     According to  FIG. 2 , in order to clamp the heating element  12 , a holding strip  31  is provided which by means of screws  32  presses the heating element  12  onto a bottom  26  of the cavity  11  such that said heating element lies in a play-free manner in the cavity  11 . 
     According to  FIG. 3 , 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 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. 2  and  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 . 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 . 
     According to the second exemplary embodiment shown in  FIG. 3  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 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  FIG. 3 , the bending points are situated in a plane. However, this is not absolutely necessary. 
       FIG. 6  shows the insertion of a heating element  12  according to  FIG. 3  in the cavity  11  of the tamper strip  9 . 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. 7 ,  8 . 
     As shown in  FIG. 3 , the heating element  12  is 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  33 ,  34  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  as a round-tube heating body has a good bending property. 
     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. For example, the carrying strips  23  can have a projecting pedestal  30  on its top side for component reinforcement. The tamper  8  is fastened to the drive  10  for example via arms  28 ,  29  on the tamper strip  9 . 
     According to  FIG. 2 , the cavity  11  is formed in a tamper strip  9  in which the carrying strip  23  is formed in one piece with the impact strip  24 . The cavity  11  can then be formed, for example, by a core drilling. 
       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. 
     According to  FIG. 7  and  FIG. 8 , 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  27  is an additional, preferably nonheated element of corrugated or bent shape which clamps the heating element  12 .