Patent Publication Number: US-6338615-B1

Title: Pipe switch for two-cylinder thick-material pump

Description:
BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The invention concerns a pipe switch for two-cylinder thick material pumps with a pivot pipe pivotable in front of a two-opening wear plate on the cylinder side, with a wear ring which can be pressed against the wear plate in the rim area of the opening by the hydrostatic pressure present inside the pivot pipe, the wear ring capable of limited axial displacement at the end of the pivot pipe on the cylinder side, the wear ring having a centering portion guided on an axis-parallel centering surface of the pivot pipe as well as a sealing part resting against the wear plate via an abutment surface on the cylinder side, wherein the pivot pipe and the sealing part of the wear ring have opposing annular surfaces which are axially spaced from one another thereby forming an annular gap open towards the inside of the pipe, and with a ring arrangement comprised at least in part of a rubbery elastic material axially spanning the annular gap, the ring arrangement with its respective abutment surfaces lying preferably in a pre-stressed manner against each of the annular surfaces. 
     SUMMARY OF THE INVENTION 
     Tubular branching systems of this kind, which have an automatically hydrostatic adjusting wear ring, are known (DE-A 26 14 895, EP-B 0 656 995). In the annular space there is a rubber elastic ring, which is provided for sealing the gap formed between the centering part and the centering surface and additionally performs a spring function for pressing the sealing part of the wear ring against the wear plate. In practice it has been found that during operation cement deposits form in the area of the radial plane oriented ring surfaces, which despite a material removal in the area of the sealing part and the wear plate could lead to an uncontrolled narrowing of the annular space and to a wearing out of the rubber elastic ring, with a result, that the rubber elastic ring can be pressed out, towards the inside of the pipe, and can be lost. 
     Beginning therewith it is the task of the present invention to improve the known pipe switch of the above-described type in such a manner, that the rubber elastic material of the ring arrangement is not subjected to excessive wear. 
     The inventive solution is based on the concept, that the rubber elastic material is to be protected from the abrasive effect of the cement with suitable means. In order to achieve this, it is proposed in accordance with a first inventive embodiment, that the ring arrangement at least on its surface facing the centering part of the wear ring has an axial ring overlay of a wear retardant material which is stiffer than the rubber elastic material. Preferably the ring overlay is comprised of metal, of a metal or textile fabric, of plastic, or of hard rubber. The ring overlay can be adhered to or vulcanized onto the rubber elastic material. 
     An alternative or advantageous embodiment of the invention envisions that the ring arrangement includes at least two rings of rubber elastic material separated from each other by a hard intermediate ring. The intermediate ring is preferably formed as a metallic ring disk, which has the same inner and outer diameter as the rubber elastic rings. The intermediate ring can be loosely introduced in the ring space between the rubber elastic rings and be provided with multiple through holes separated from each other in angular separation. Preferably the rubber elastic rings are connected to each other via multiple axially parallel pins arranged in angular separation from each other, which pins extend through the through holes in the intermediate ring. 
     According to a preferred embodiment of the invention the rubber elastic rings are vulcanized onto the intermediate ring at their respective contacting surfaces. 
     A further alternative or advantageous embodiment of the invention envisions that the ring arrangement is formed by a rubber elastic ring with a co-axial helical spring vulcanized therein. The helical spring is preferably comprised of spring steel and can be introduced into the rubber elastic ring pretensioned under pressure. In the later case the rubber elastic material is expanded by the helical coil spring in the loose ring arrangement, so that in the assembled condition pretensioned within the annular space a supplemental adjustment means is made available. 
     According to a further alternative or advantageous embodiment of the invention it is proposed that the ring surface adjacent the centering part in a known manner exhibits an annular step formed by a recess facing in the direction of the centering part, undercut with respect to the inside of the pipe, and that a ring seal of elastomeric material separate from the ring arrangement is seated in the annular step. The ring seal has the task of preventing a passage of material through the centering gap, and thereby to minimize the cement deposit on the ring surface facing the centering gap. The ring seal is preferably over-dimensioned with respect to the annular step, which is so dimensioned, that the ring seal is pressed in the annular step under the pretension of the ring arrangement. The ring seal can thereby either exhibit a quadrilateral, in particular, a square cross-section or a round or oval cross-section. Since the inside of the annular step is completely enclosed, it is possible to use therefore a soft elastic material without stiffening. The ring arrangement could in this case be comprised of a one-piece elastomeric ring with a stiffening insert, for example a metal ring. 
     For sealing the ring gap in the centering surface, in accordance with an advantageous or alternative design of the invention a ring notch can be provided in the centering surface of the pivot pipe or in the centering part of the wear ring, for receiving a ring seal for bridging the annular gap between the centering surface and the centering part. 
     In order to guarantee a reliable sealing of the ring space over a long operating time, it is proposed in accordance with a further advantageous or alternative embodiment of the invention to have a tensioning mechanism provided between the pivot pipe and wear ring, with which the pretensioning of the ring arrangement can be adjusted. The tensioning mechanism preferably includes at least two, more preferably three tensioning screws distributed about the circumference of the pivot pipe and displaceable axially parallel with respect to the pivot pipe, each tensioning screw engaging respectively in an axis-parallel oriented thread of the wear ring. The tensioning screws are preferably formed as set screws guided with their shaft respectively in a rim open axial guide of the pivot pipe and their head is supported against a shoulder bordering against the axial guide. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following the invention will be described in greater detail on the basis of an illustrative embodiment represented in schematic manner in the drawings. There is shown 
     FIG. 1 a thick material pump with C-shaped pivot pipe in partial sectional diagrammatic perspective representation; 
     FIG. 2 an enlarged section from the pipe switch with internally centered wear ring in sectional representation; 
     FIG. 3 an embodiment of a pipe switch deviating from FIG. 2 with externally centered wear ring in untensioned (upper) and pretensioned (lower) condition of the rubber elastic ring arrangement in sectional representation; 
     FIG. 4 an embodiment of a pipe switch deviating from FIG.  2  and FIG. 3 with internal centered wear ring and supplemental quadrilateral (upper) and round (lower) seal ring in sectional representation; 
     FIG. 5 a further deviating embodiment of a pipe switch with tensioning mechanism for the ring arrangement in sectional cut-through representation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The thick material pump shown in FIG. 1 is comprised essentially of two conveyance cylinders  10 , of which the end openings  12  open into a material supply container  14  and alternatingly during the pressure stroke (arrow  16 ) are in communication with a conveyance line  20  via a pipe switch  18  and during the suction stroke (arrow  22 ) are open to the material supply container  14  with suctioning of material. The conveyance cylinders  10  are operated reciprocally, in counter-stroke, via a hydraulic drive cylinder  24 . For this purpose the conveyor pistons  26  are connected via a common piston rod  28  with the piston  30  of the drive cylinder  24 . In the area between the conveyor cylinders  10  and the drive cylinders  24  there is a water box  32  through which the piston rods  28  extend. 
     The end openings  12  of the conveyor cylinders  10  are covered by a glasses-shaped wear plate  34 . On the inner side of the material supply container  14  the pivot pipe  36  of the pipe switch  18 , which in the illustrative embodiment is C-shaped, is pivotable back and forth about a horizontal axis in front of the glasses shaped wear plate  34 , with its friction ring  38  carried inside, such that its cylinder facing opening  40  alternatingly is positioned before the one of the openings  12  of the conveyor cylinders  10  while exposing the other opening  12  to the inner side of the material container  14 . For the pressure tight connection between the pivot pipe  36  and the wear plate  34  there is on the cylindrical centering surface  42  of the pivot pipe  36  the wear ring  38  mounted with its centering part  46  axially displaceable. The operation of the pivot pipe  36  occurs via hydraulic means  48  controllable via a switch lever  50 . 
     As can be seen from FIG. 2 through 4, the wear ring  38  beside the centering part  46  has a sealing part  54  lying with its cylinder side surface  52  against the wear plate  34 . The pivot pipe  36  and the sealing part  54  of the wear ring  38  are besides this provided with opposing radial ring surfaces  56 ,  58  separated axially from each other and open to the pipe internal annular space  59 . The annular space  59  is bridged over axially by a ring arrangement  60 , which with its respective end faces  62 ,  64  lies against one of the annular surfaces  56 ,  58  under pretension. On the end face facing the centering part  46  of the wear ring  38  an axial ring overlay  80  is vulcanized onto the ring arrangement  60 , which is comprised of a material which, in comparison to the rubber elastic material, is stiffer and more wear resistant, such as for example metal, textile weave, plastic or hard rubber. The abutment surface  82  on the wear ring  38  limits the axial movement of the wear ring  38  on the pivot pipe  36 . 
     In the illustrative embodiment shown in FIG. 2 the ring arrangement  60  includes three rubber elastic rings  66 ,  68 ,  70 , which are pairwise separated from each other via loosely introduced metallic intermediate rings  72 ,  74 , and which can be connected with each other via angularly separated pins  76 . The intermediate rings  72 ,  74  exhibit through-holes  78  in angular separation from each other, through which a part of the pin  76  extends. The axial ring overlay  80  is provided on the end surface of the rubber elastic ring  66  facing the centering part  46  of the wear ring  38 . 
     In the illustrative embodiment according to FIG. 3 the ring arrangement  60  is formed by a one-piece rubber elastic ring  84 , in which a helical spring  86  of spring steel is co-axially vulcanized in. The helical spring can be embedded in the rubber elastic material of the ring  84  either untensioned or pre-tensioned under pressure. In the later case, in the case of wear, at least a part of the pre-tension of the coil spring  86  is available for adjustment of the wear ring  38 . Besides this the coil spring  86  insures that the ring arrangement  60  even in the case of low shore hardness of the rubber elastic material exhibits a sufficient circumferential stability, which would prevent a driving out or unseating of the ring arrangement  60  into the internal space of the pipe. In the illustrative embodiment according to FIG. 3 the wear ring  38  is guided with its centering part  46  on an outer centering surface  42  of the pivot pipe  36 . In accordance therewith in this case the wear reducing axial ring overlay  80  is situated upon the surface  64  of the ring arrangement  60  facing the ring surface  58 . In the operating condition the wear ring  38  is so tensioned against the wear plate  34  via the pivot pipe  36 , that the gap width X between the wear ring  38  and the pivot pipe  36  in the area of the abutment  82  is reduced from 4 mm to 0.5-1 mm. The pre-tension stroke of 3-3.5 mm is converted to a transverse expansion of the rubber elastic component of the ring arrangement  60  towards the pipe inside, which is shown in the lower part of FIG. 3 as a bulge. 
     The embodiment according to FIG. 4 is different from the embodiment according to FIG. 2 above all therein, that the centering part  46  adjacent ring surface  56  includes an annular step  88  formed by a recess facing in the direction of the centering part  46 , undercut with respect to the pipe inside, in which a ring seal  90 ,  90 ′ of an elastomeric material separate from the ring arrangement  60  is seated. In the example shown in the upper part of FIG. 4, the ring seal  90  exhibits a quadrilateral cross-section, while the ring seal  90 ′ in the lower part of FIG. 4 is formed as an O-ring. In both cases the ring seal  90 ,  90 ′ is so over-dimensioned with respect to the axial recess of the annular step  88  that under the pre-tension of the ring arrangement  60  it is completely pressed into the annular step  88 . In the upper part of FIG. 4 the unpresssed condition is shown with a gap width X of 3 mm and in the lower part in the compressed condition with a gap width X of 0.5-1 mm. The pre-tensioned stroke in the case of the wear of the sealing part  54  of the wear ring  38  and the wear plate  34  is available as adjustment stroke. Also in the illustrative embodiment according to FIG. 4 a wear reducing ring overlay  80  is provided on the centering part  46  facing surface  62  of the ring arrangement  60 , which however is not necessary because of the supplemental sealing rings  90 ,  90 ′. 
     In the illustrative embodiment shown in FIG. 5, the ring arrangement  60  includes two rubber elastic rings  66 ,  68  between which a metallic intermediate ring  73  formed as a ring disk is provided. The rubber elastic rings  66 ,  68  are vulcanized onto the intermediate ring  73  on their surfaces facing the intermediate ring  73 . The metallic intermediate ring  73  and the adjacent rubber elastic rings  66 ,  68  exhibit the same inner and outer radius. Further, a radially outwardly open annular tee-slot  92  is provided in the centering part  46  of the wear ring  38 , wherein a ring seal  94  is introduced in the annular gap between the centering part  46  and the centering surface  42  of the pivot pipe  36  in a bridging manner. In order to insure that the pre-tension in the area of the ring arrangement remains maintained during increasing wear in the area of the cylinder side surface  52  of the wear ring  38 , a supplemental tensioning mechanism  96  is provided positioned between the pivot pipe  36  and the wear ring  38 . The tensioning mechanism  96  includes multiple, preferably three, tensioning screws  98  distributed positioned about the circumference of the pivot pipe, which with their tips  100  engage in an axially-parallel oriented threading  102  of the wear ring, with their shaft  104  extending through a radial edge open axial guide  106  of the pivot pipe  36  and with their from outside accessible head  108  lie against the radial guide  106  bordering pivot pipe associated shoulder  110 . With the tensioning mechanism  98  a minimal pre-tension of the ring arrangement can be adjusted, so that no material to be conveyed can penetrate into the annular space  59  from the inside of the pipe. The ring seal  98  insures on the other hand therefore, that the annular space  59  is also sufficiently sealed with respect to the external situated material supply container. 
     In summary the following is to be concluded: The present invention relates to a pipe switch for a dual-cylinder thick-liquid pump, wherein said system comprises a pivoting pivot pipe  36  located in the front of a glasses-like wear plate  34  on the cylinder side as well as a wear ring  38  which is capable of limited axial displacement at the end of the pivot pipe  36  on the cylinder side. The ring can be pressed against the wear plate  34  by the hydrostatic pressure existing inside said pivot pipe. The wear ring  38  has a centering portion  46  guided on an axis-parallel centering surface  42  of the pivot pipe  36  as well as a sealing part  54  resting against the wear plate  34  through an abutment surface  52  on the cylinder side. The pivot pipe  36  and the sealing part  54  of the wear ring  38  have annular surfaces  56 ,  58  which face each other and which are axially spaced from one another by an annular gap  59  opened towards the inside of the pipe. An annular system  60  exhibiting at least a rubber elasticity is further provided, wherein said system axially covers the annular gap  59  and has its abutment surfaces  62 ,  64  resting in a prestressed manner against each of the annular surfaces  56 ,  58 . In order to allow for an automatic anti-wear readjustment of the wear ring, the annular system  60  has an axial annular support  80  provided on its abutment surface  62  which faces the centering portion  46  of the wear ring  38 , wherein said support  80  is made of a wear-resistant material which is more rigid than the rubber-elastic material.