Abstract:
An extrusion machine having a barrel containing a bore formed of three lobes, designed to receive a liner whose outer face is also formed of three lobes and which has two secant bores which have parallel axes and are adapted to receive two screws.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an extrusion machine barrel, as well as a liner for such an extrusion machine barrel. 
     The invention applies particularly to extruders which have at least two screws, and more generally to extrusion machines in which mixing, kneading, comminuting, reaction, drawing-out, baking and in particular shearing effects are introduced by passing through the barrel a substance that is carried along by the rotation of the screws. 
     BACKGROUND OF THE INVENTION 
     In general, an extrusion machine comprises a barrel of elongate shape equipped with a bore extending along the entire length of the said barrel and in which there is a liner that envelops the screws. 
     When the extrusion machine comprises two parallel-axis screws, the liner comprises two parallel-axis cylindrical bores in which the screws are placed, and these screws may or may not intermesh. 
     The screws are fitted on their periphery with, in particular, helically-wound flights which carry in a downstream direction the substance which is introduced via an upstream end of the barrel. 
     The substance is thus carried along as far as the downstream end of the barrel, which may be fitted with an extrusion die or alternatively simply have an outlet orifice if the substance is not to be subjected to an extrusion operation. 
     In order to vary the treatment to be carried out as the substance progresses along the barrel, the screws generally consist of successive regions which have flights of different shape or pitch or which comprise specific treatment members. 
     Until now, the bore in the barrel was obtained by making two secant drillings which form two longitudinal ribs where they intersect and by machining these longitudinal ribs to obtain a flat surface between the two drillings so as to produce a bore formed of two half lobes joined by flat portions. 
     This technique therefore requires a number of machining tools, particularly a boring machine for the drillings and a milling machine to produce the flat surfaces. 
     Furthermore, it is necessary when performing the stage of grinding the bore of the barrel, to use special-purpose tools of special shape, given that this bore is formed of a series of curved portions and flat portions. 
     These various operations and the change of tooling for each of these operations significantly increases the cost of the barrel and the time taken to machine the bore in the barrel. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to overcome these drawbacks by providing an extrusion machine barrel which is easier to machine and allows a reduction in manufacturing lead time. 
     The subject of the invention is a barrel of an extrusion machine comprising a bore having three lubes and begin intended to take a liner in which at least two parallel-axis screws are rotated. 
     According to other features of the invention: 
     the lobes of the bore are formed by three secant drillings, the axes of which are mutually parallel and lie in the same plane as the main axis of the barrel, the axis of one of the drillings lying on the main axis and the axes of the other two drillings being located on either side of and equidistant from this main axis, 
     the first drilling is made on the main axis of the barrel and the second and third drillings are made one on each side of and secant with the first drilling, the diameters of these drillings being roughly equal, 
     the first drilling is made on one side of and at a given distance from the main axis of the barrel the second drilling is made on the other side of the main axis and the same distance away from the main axis of the barrel and the third drilling is made on this main axis, the drillings being secant and the diameters of the drillings being roughly equal, 
     the axes of the drillings arranged on either side of the drilling that lies on the main axis of the barrel lie inside the circumference delimited by the drilling that is arranged on the main axis, 
     the axes of the drillings that are arranged on either side of the drilling that lies on the main axis of the barrel lie on the circumference delimited by the drilling that is arranged on the main axis, 
     the axes of the drillings arranged on either side of the drilling that is arranged on the main axis of the barrel lie outside the circumference delimited by the drilling that is arranged on the main axis, 
     the drillings are made by a boring machine or a drilling machine. 
     Another subject of the invention is an extrusion machine barrel liner in which at least two parallel-axis screws are rotated, the outer face of the liner being formed by three lobes and comprising two parallel-axis secant bores. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will become clear through the description which will follow, given with reference to the appended drawings, in which: 
     FIG. 1 is a schematic perspective view of a section in accordance with the invention, 
     FIGS. 2 to  4  are views in cross section showing various stages of a first method of machining the bore inside the barrel, 
     FIGS. 5 to  7  are views in cross section showing the various stages of a second method of machining the bore inside the barrel. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 1 schematically shows a section of a barrel  1  of a parallel-axis twin-screw extrusion machine in which mixing, kneading, comminuting, reaction, drawing-out, baking and in particular shearing effects are produced by passing through this barrel  1  a substance that is carried along by the rotation of the screws. 
     The barrel  1  is of elongate shape and of any desired external cross section, for example of circular, oval, square or rectangular external cross section. 
     This barrel  1  is made up of a solid body  2  comprising a bore  3  extending along the entire length of the barrel  1  and intended to take a liner  4  which has two parallel-axis secant bores  5  and  6  in which two screws not shown, are placed. 
     In the conventional way, the screws consist of successive regions which have flights of different shape or pitch or which comprise specific treatment members. 
     These screws carry along in the downstream direction the substance which is introduced via an upstream end of the barrel  1 . 
     As depicted in FIG. 1, the bore  3  formed in the barrel  1  is made up of three lobes, A, B, C, respectively. 
     The liner  4  has an external profile that corresponds to the profile of the bore  3 . 
     Thus, the liner  4  has an external face that is formed of three lobes. 
     In general, the method of machining the bore  3  in the barrel  1  consists in making, in succession, three secant drillings, the axes of which are mutually parallel and lie in the same plane as the main axis of the barrel  1 , the axis of one of the drillings lying on the main axis and the axes of the other two drillings lying one on each side of and equidistant from this main axis, and in performing an operation of grinding these drillings. 
     A first method of machining the bore  3  in the barrel will now be described with reference to FIGS. 2 to  4 . 
     First of all, as depicted in FIG. 2, a first drilling  10 , the axis a of which lies on the main axis of the barrel  1  is made. 
     Next, and as depicted in FIG. 3, a second drilling  11  secant with the first drilling  10  and of a diameter roughly equal to the diameter of this first drilling  10  is made on one side of the first drilling  10 . 
     The axis b of the second drilling  11  is parallel to the axis a of the first drilling  10 . 
     Finally, and as depicted in FIG. 4, a third drilling  12  secant with the first drilling  10  and of a diameter roughly equal to the diameters of the first drilling  10  and of the second drilling  11  is made on the other side of the first drilling  10  with respect to the second drilling  11 . 
     The axis c of the third drilling  12  is parallel to the axes a and b of the first drilling  10  and of the second drilling  11 , respectively. 
     The axes a, b and c of the drillings  10 ,  11  and  12  lie in the same plane. 
     Furthermore, the axes b and c of the second  11  and of the third  12  drillings respectively, are equidistant from the axis a of the first drilling  10 . 
     According to a first embodiment depicted in FIG. 4, the axes b and c of the second drilling  11  and of the third drilling  12 , respectively, lie inside the circumference delimited by the first drilling  10 . 
     According to two other embodiments, the axes b and c of the second drilling  11  and of the third drilling  12 , respectively, may lie on or outside the circumference delimited by the first drilling  10 . 
     A second method of machining the bore  3  in the barrel  1  will be described with reference to FIGS. 5 to  7 . 
     In this case, and as depicted in FIG. 5, a first drilling  20  is made on one side of and at a given distance from the main axis of the barrel  1 . 
     The axis a′ of this first drilling  20  is parallel to the main axis of the barrel  1 . 
     Next, and as depicted in FIG. 6, a second drilling  21  is made on the other side of and the same distance away from the main axis of the barrel  1  with respect to the first drilling  20 . 
     The second drilling  21  is secant with the first drilling  20  and the axis b′ of this second drilling  21  is parallel to the axis a′ of the first drilling  20  and to the main axis of the barrel  1 . 
     Finally, and as depicted in FIG. 7, a third drilling  22  is made on the main axis of the barrel  1 , the axis c′ of this third drilling  22  being parallel to the axes a′ and b′ of the first drilling  20  and of the second drilling  21 , respectively. 
     The axes a′, b′ and c′ of the drillings  20 ,  21  and  22  lie in the same plane and the diameters of the said drillings  20 ,  21  and  22  are roughly equal. 
     According to a first embodiment depicted in FIG. 7, the axes a′ and b′ of the first drilling  20  and of the second drilling  21 , respectively, lie inside the circumference delimited by the third drilling  22 . 
     According to two other alternative forms, the axes a′ and b′ of the first drilling  20  and of the second drilling  21 , respectively, may lie on the circumference delimited by the third drilling  22  or outside this circumference. 
     The drillings  10 ,  11 ,  12  and  20 ,  21 ,  22  are made solely by means of one tool, for example of the boring machine or drilling machine type, commonly used in the field of machining. 
     These drillings  10 ,  11 ,  12  and  20 ,  21 ,  22  form the three lobes A, B and C of the bore  3  of the barrel  1 . 
     Once the drillings  10 ,  11  and  12  or  20 ,  21  and  22  have been completed, a grinding stage is performed using a tool of a conventional shape commonly employed in the grinding of a cylindrical bore. 
     The external profile of the liner  4  is produced, for example, using a grinding machine commonly used in the field of machining. 
     With such a barrel, the number of operations needed to produce the bore is reduced, as thus is the machining time, and this machining employs only tools which are commonly used, thus making it possible to reduce the cost of manufacturing the barrel.