Abstract:
An extruder includes a container having a main bore for receiving billets, a die and a piston. The container is formed with at least one gas release vent opening into the main bore at a position intermediate between the extruding end of the bore and a midpoint of the bore&#39;s length. Each gas release vent has a valve for allowing selective release of trapped gas. This structure allows venting of gases in such a manner as to allow sequential loading of billets without removal of scrap between them.

Description:
FIELD AND BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to extrusion and, in particular, it concerns an extruder and corresponding method of extrusion which provide venting of gases in such a manner as to allow sequential loading of billets without removal of scrap between them.  
           [0002]    Particular reference will be made below to extrusion presses fed with billets, usually aluminum billets, although it is understood that the invention can be applied to other types of presses also.  
           [0003]    The extrusion presses for billets known at present comprise a fixed cylinder on a fixed base, inside of which cylinder a ram or main piston is movable. A movable cross member is integral with the ram, and usually guided along the base, and carries a stem extending along the extrusion axis. On the same base or another base a fixed cross member is mounted, which carries a die slide, and in the die slide various dies can be interchanged.  
           [0004]    A so-called container having a through chamber for the billet, is movable on the base along the extrusion axis between a working position, in which it is in a sealed or tight manner against a die contained in the die slide, and a rest position, in which it is at a distance from the box which is sufficient for the passage of a shears blade moving transversely to the extrusion axis. The container is moved by cylinders located on the fixed cross member.  
           [0005]    The presses so briefly described operate in the following manner. With the container positioned in an airtight or sealed manner against the die slide complete with a die, a billet at a suitable temperature, which has been carried onto the extrusion axis in any way whatsoever upstream of the container, is first introduced into the container and then pressed against and through the die by means of the stem; the stem moves back at the end of its run and the container is moved away from the die by the cylinders of the container, in such a way that the shears can intervene for separating the produced profile or section from the remaining part of the billet, known as the butt or scrap. The process for removal of the butt typically accounts for wastage of as much as 23% of the raw material, and greatly reduces efficiency of the extrusion cycle.  
           [0006]    The process for preparing a press for extruding a certain quantity of aluminum alloy often leads to air being trapped in the bore of the container, before the alloy being subjected to extrusion pressure. The air is pressurized by the extrusion process and causes serious damage to the finish of the product, in the form of blisters, often accompanied by characteristic noises made by the air when it expands in the atmosphere after passing through orifices.  
           [0007]    A standard cycle for an extrusion process, with the aim of eliminating the problem of trapped air, is called a degassing or “burp” cycle, or pre-pressing cycle. etc. According to this cycle, the aluminum alloy is compacted in the container (positioned against the die) at a pressure equal to or lower than half of the pressure required for extrusion. Such operation is called upsetting of the billet. Then the members which usually are on load during extrusion are released, that is to say, the ram, the stem, the container and the die; in other words, these members are physically moved so as to break the sealed or airtight engagement around the die, allowing air to escape. The cycle which includes degassing is then completed by closing the container once more against the die until a sealed or airtight engagement is obtained, while the main ram reassumes the position for the beginning of the extrusion.  
           [0008]    Various systems have been proposed for improving the degassing cycle such as by provision of a valve in the stem (e.g., U.S. Pat. No. 5,311,761) or maintaining a clearance for gas to escape between the end of the container and the die (e.g., U.S. Pat. No. 5,445,004). None of these systems, however, are effective for avoiding trapping of air between a residue of a prior billet and a newly inserted billet. As a result, there remains major wastage of material and time delay due to the process of removal of the butt as described above between loading of successive billets.  
           [0009]    An alternative approach proposed in order to minimize trapping of gases within the container is to evacuate gases from the container prior to extrusion. Examples of this approach may be found in U.S. Pat. Nos. 5,054,303 and 5,461,899. These vacuum-based implementations, however, are complicated and expensive.  
           [0010]    There is therefore a need for an extruder and corresponding method of extrusion which provide venting of gases in such a manner as to allow sequential loading of billets without removal of scrap between them.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention is an extruder and corresponding method of extrusion.  
           [0012]    According to the teachings of the present invention there is provided, an extruder comprising: (a) a container having a main bore for receiving billets, the main bore having a loading end and an extruding end separated by a length; (b) at least one die associated with the extruding end of the main bore; and (c) a piston deployed for forcing a billet along the main bore towards the extruding end, wherein the container is formed with at least one gas release vent opening into the main bore at a position intermediate between the extruding end and a midpoint of the length, each of the gas release vents being provided with a valve deployable between an open state for allowing release of trapped gas and a closed state for preventing penetration of material from the billets into the at least one gas release vent.  
           [0013]    According to a further feature of the present invention, the at least one gas release vent is implemented as a plurality of gas release vents spaced along at least one line between the extruding end and the midpoint of the length.  
           [0014]    According to a further feature of the present invention, the at least one gas release vent includes a plurality of gas release vents opening into the main bore substantially along the top of the main bore.  
           [0015]    According to a further feature of the present invention, the at least one gas release vent includes a plurality of gas release vents opening into the main bore at a plurality of different angular positions around the surface of the main bore.  
           [0016]    According to a further feature of the present invention, the main bore has a first internal diameter adjacent to the loading end and a second internal diameter adjacent to the extruding end, the second internal diameter being larger than the first internal diameter.  
           [0017]    According to a further feature of the present invention, the main bore has a first portion extending substantially from the loading end along at least to the midpoint, the first portion being substantially cylindrical with the first internal diameter, and wherein the main bore has a second portion extending substantially from the first portion to the extruding end, the second portion having a gradually increasing internal diameter.  
           [0018]    According to a further feature of the present invention, the second portion has a substantially conical internal surface.  
           [0019]    According to a further feature of the present invention, the substantially conical internal surface has a conical angle of between about 1° and about 10°.  
           [0020]    There is also provided according to the teachings of the present invention, a method of producing an extruded pprofile using an extruder including a container with a main bore, the main bore having a loading end and an extruding end separated by a length, the container being formed with at least one selectively openable gas release vent opening into the main bore at a position intermediate between the extruding end and a midpoint of the length, the method comprising: (a) introducing into the main bore a first billet; (b) forcing the first billet towards the extruding end so as to force material from the billet through a die associated with the extruding end of the bore; (c) while material from the first billet remains within the main bore. introducing a second billet into the main bore; (d) pressing the second billet towards the material from the first billet so as to cause joining of the material from the first billet and the second billet; (e) opening the at least one gas release vent so as to release gas trapped within the main bore; and (f) forcing the second billet towards the extruding end so as to force material from both the first and second billets through the die.  
           [0021]    According to a further feature of the present invention, the opening is performed using a plurality of gas release vents spaced along at least one line between the extruding end and the midpoint of the length.  
           [0022]    According to a further feature of the present invention, the opening is performed using a plurality of gas release vents opening into the main bore substantially along the top of the main bore.  
           [0023]    According to a further feature of the present invention, the opening is performed using a plurality of gas release vents opening into the main bore at a plurality of different angular positions around the surface of the main bore.  
           [0024]    According to a further feature of the present invention, the main bore has a larger internal diameter adjacent to the extruding end than adjacent to the loading end.  
           [0025]    According to a further feature of the present invention, the main bore has a portion of gradually increasing internal diameter from a location between the midpoint and the extruding end extending substantially to the extruding end.  
           [0026]    According to a further feature of the present invention, the second portion has a substantially conical internal surface.  
           [0027]    According to a further feature of the present invention, the substantially conical internal surface has a conical angle of between about 1° and about 10° .  
           [0028]    According to a further feature of the present invention, each billet is prepared prior to introduction into the main bore by removing material from at least a portion of an outer surface of the billet so as to increase smoothness of the billet.  
           [0029]    According to a further feature of the present invention, the billets are aluminum billets. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:  
         [0031]    [0031]FIG. 1 is a schematic partially cut-away side view of an extruder. Constructed and operative according to the teachings of the present invention, after insertion of a first billet into the main bore of the container;  
         [0032]    [0032]FIG. 2 is an enlarged view of the container of FIG. 2;  
         [0033]    [0033]FIG. 3 is a view similar to FIG. 1 after insertion of a second billet; and  
         [0034]    [0034]FIG. 4 is a view similar to FIG. 3 after conjoining of the second billet with material from the fist billet. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    The present invention is an extruder and corresponding method of extrusion.  
         [0036]    The principles and operation of extruders and corresponding methods according to the present invention may be better understood with reference to the drawings and the accompanying description.  
         [0037]    Referring now to the drawings, FIGS.  1 - 4  show an extruder. generally designated  10 , constructed and operative according to the teachings of the present invention. Generally speaking, extruder  10  includes a container  12  having a main bore  14  with a loading end  16  for receiving billets  18 . At least one die  20  associated with an extruding end  22  of main bore  14 , while a piston  24  is deployed for forcing a billet  18  along main bore  14  towards extruding end  22 , all as is known in the art.  
         [0038]    It is a particular feature of extruders according to the present invention that container  12  is formed with at least one gas release vent  26  opening into main bore  14  at a position intermediate between extruding end  22  and a midpoint  28  of the length of bore  14 . Each gas release vent  26  is provided with a valve  30  deployable between an open state for allowing release of trapped gas and a closed state for preventing penetration of material from the billets into the at least one gas release vent.  
         [0039]    In order to maximize the efficiency of gas release, extruder  10  preferably includes multiple gas release vents  26 . Specifically, in the preferred example illustrated here, gas release vents  26  are spaced along one or more lines between the extruding end  22  and midpoint  28 . In some preferred cases, there may be an advantage to positioning vents  26  substantially along the top of main bore  14 . Most preferably, a plurality of gas release vents  26  open into main bore  14  at a plurality of different angular positions around the surface of the bore, for example, with a line of vents  26  as shown along the top and bottom, and similarly along both sides (not shown), of bore  14 .  
         [0040]    Valves  30  may be of any type suited to the operational conditions (temperature and pressure) within bore  14 . Typically, a small displacement valve of the type used in internal combustion engines is suitable. The displacement required to efficiently allow escape of pressurized trapped gases is typically of the order of about a millimeter or less. Actuation of valves  30  is typically achieved via a small actuator rod (not shown) passing along the bore of each vent  26  and spring-biased to return to its closed position. Opening of valves  30  may be performed simultaneously or sequentially, initiated automatically or manually, by any suitable control mechanism as will be clear to one ordinarily skilled in the art. Details of a control mechanism do not constitute part of the claimed invention and will not be described here.  
         [0041]    According to a further preferred feature of the present invention, main bore  14  has a first internal diameter  32  adjacent to loading end  16  and a second internal diameter  34  adjacent to extruding end  22 , where second internal diameter  34  is larger than first internal diameter  32 . Specifically, a first portion  36  of main bore  14 , extending substantially from loading end  16  along at least to midpoint  28 , is preferably substantially cylindrical, while a second portion  38 . extending substantially from the first portion to extruding end  22 , preferably exhibits a gradually increasing internal diameter. This region of increasing diameter is preferably limited to the third of bore  14  proximal to extruding end  22 , and most preferably lies within the quarter of the length nearest extruding end  22 . Most preferably, second portion  38  has a substantially conical internal surface with a conical angle (defined as the inclination relative to a central axis of symmetry) of between about 1° and about 10°, and preferably no more than about 5°. The presence of portion  38  with a gradually increasing diameter has been found to be highly effective at localizing trapped gases within that region, thereby facilitating their efficient release via vents  26 .  
         [0042]    Turning now to the operation of extruder  10  and the corresponding method of the present invention, a first billet  18  is first introduced into main bore  14  as shown in FIGS. 1 and 2. Extrusion then proceeds in a conventional manner, typically with a “burp cycle” which may optionally also include opening of valves  30  if required, followed by extrusion with piston  24  driving material from billet  18  through die  20  to produce an extruded article  40 . Then, at the end of a required length of extrusion when a relatively small portion of the first billet material is left, piston  24  is withdrawn and a second billet  18 ′ is introduced into main bore  14  (FIG. 3). This is done without the conventional step of opening the container and cutting away the butt of first billet  18 . The second billet  18 ′ is then pressed towards the material from the first billet  18  so as to cause conglomeration of the material from the first billet and the second billet. This typically occurs at pressures lower than the extrusion pressure, such as, for example, the conditions used for upsetting of the billet as mentioned above. At this stage, valves  30  are opened so as to release trapped gas via vents  26 . Optionally, the container may also be opened very slightly in the same manner as during a normal “burping cycle” to additionally release any gases which may have become trapped at the end of bore  14 . Extrusion then proceeds as before with piston  24  forcing material from both the first and second billets through the die. The loading, pressing, gas release and extruding steps may then be repeated again and again without requiring opening of the container or disposal of residual material until the end of the extrusion session.  
         [0043]    According to a further preferred feature of the method of the present invention, each billet is prepared prior to introduction into the main bore by removing material from at least a portion of an outer surface of the billet so as to increase smoothness of the billet. This preparation serves a double purpose. Firstly, smoothing of the billet facilitates passage of gases along spaces between the billet and internal surfaces of bore  14 . thereby avoiding the formation of isolated gas pockets which might not reach vents  26 . Additionally, “scalping” of the billets removes a large proportion of oxides and other impurities which are typically present in surface layers of billets. This enhances the quality and uniformity of the extruded product.  
         [0044]    Devices and methods for billet scalping per se are well known in the art and will not be dealt with here in detail. Most preferably. conventional metal cutting techniques such as milling techniques may be used to remove an outer layer of a substantially cylindrical billet to provide a high quality highly cylindrical billet. The total quantity removed is typically no more than about 5%, and more preferably no more than about 2%, of the total material of the billet. ensuring that the wastage is clearly outweighed by the much larger savings in raw materials resulting from the use of the “butt” of each billet.  
         [0045]    It will be noted that this extruder and the extrusion method facilitated thereby offer numerous profound advantages when compared to conventional techniques. Firstly, huge savings in both time and raw materials are afforded by enabling use of residual material from a previous billet conglomerated with a subsequent billet without the problems of trapped gases. Additionally, since the remainder of a billet is not discarded, the operator has much greater flexibility to choose at what point to stop the extrusion for loading a new billet. This allows stops to be planned at the end of required lengths of extruded products, thereby further reducing wastage.  
         [0046]    It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the spirit and the scope of the present invention.