Patent Publication Number: US-11376653-B2

Title: Feeder system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Russian Patent Application No. 2020112272, filed on Mar. 26, 2020, which application is incorporated herein by reference. 
     The present invention relates to a feeder system for use in metal casting operations utilising casting moulds, and feeder sleeves and breaker cores for use in the feeder system. 
     BACKGROUND 
     In a typical casting process, molten metal is poured into a pre-formed mould cavity which defines the shape of the casting. The casting mould is usually produced by compacting a mixture of sand and binder around a first mould pattern inside a flask, allowing the sand mixture to set and harden, then removing the pattern to leave one half of the moulding cavity. This process is repeated with a second mould pattern which defines the second half of the moulding cavity, and the two halves of the mould (referred to as the cope and drag) are then assembled together to create an entire mould defining the complete mould cavity therein. Although moulds formed in this way may be used multiple times, the mould may eventually fail or the pattern shape may be eroded, at which point the mould is destroyed and the sand recovered and reconditioned for re-use in new moulds. However, with this type of mould, it is difficult to recover the sand and separate it from the binder material at the end of the mould&#39;s useful life. 
     In an alternative casting process, known as the vacuum mould casting process or “V-process”, the mould is created using dry sand which does not contain any binder and the shape of the mould is maintained due to the forces exerted by a vacuum. In the V-process, the mould pattern comprises tiny holes to enable vacuum suction. A first plastic film is drawn over the mould pattern and adhered to the mould pattern by suction. A special flask also equipped with a suction system is placed around the mould pattern and filled with dry sand, which is then compacted. The top side of the flask is covered by a second plastic sealing film and suction is applied through the flask, which causes the first and second plastic films (at the bottom and top, respectively) to adhere to the moulding sand, sealing it within the flask. The vacuum through the pattern is then turned off and the pattern is released, while the vacuum through the flask is continuously applied to keep the sand firm and maintain the shape of the moulding cavity left by the pattern. A cope and drag formed in this way are assembled to form a complete mould cavity, while still applying suction to maintain the shape of the sand, and molten metal is poured into the cavity. Once the metal casting has cooled and solidified, the moulding sand can easily be restored to its original, loose state and recovered for future use by simply turning off the vacuum. 
     In most metal casting processes, the metal will shrink as it solidifies, resulting in shrinkage cavities which in turn result in unacceptable imperfections in the final casting. This is a well-known problem in the casting industry and is addressed by the use of feeder sleeves or risers which are integrated into the mould. Each feeder sleeve provides an additional (usually enclosed) volume or cavity which is in communication with the mould cavity, so that molten metal enters into the feeder sleeve from the mould cavity during casting. During solidification of the casting, molten metal within the feeder sleeve flows back into the mould cavity to compensate for the shrinkage of the casting. After solidification of the casting and removal of the moulding sand, unwanted residual metal from within the feeder sleeve cavity remains attached to the casting and must be removed. In order to facilitate removal of the residual metal, the feeder sleeve cavity may be tapered towards its base (i.e. the end of the feeder sleeve which will be closest to the mould cavity), in a design commonly referred to as a neck down sleeve. When a sharp blow is applied to the residual metal it separates at the weakest point, near to the mould (a process commonly known as “knock off”). A small footprint on the casting is also desirable to allow the positioning of feeder sleeves in areas of the casting where access may be restricted by adjacent features. 
     Although feeder sleeves may be applied directly onto the surface of the casting mould cavity, they are often used in conjunction with a breaker core. A conventional breaker core is simply a plate or disc of refractory material (typically a resin-bonded sand core, a ceramic core or a core of feeder sleeve material) with a hole therethrough, which sits between the mould cavity and the feeder sleeve. The diameter of the hole through the breaker core is designed to be smaller than the diameter of the interior cavity of the feeder sleeve (which need not necessarily be tapered) so that knock off occurs at the breaker core close to the casting surface. More recently developed breaker cores (such as those described in Foseco PCT application nos. WO2016/034872, WO2017/025702 and WO2016/166497) may be in metal tubular form, with a bore therethrough. 
     In the V-process, the feeders are placed on a boss or pin on the mould pattern before the first plastic film is applied to the pattern. Generally, the feeders are placed on the mould pattern as a pre-formed system, with the breaker core attached to the base of the feeder sleeve, e.g. by adhesive. However, bridges of film may sometimes be created between adjacent feeder sleeves. Moreover, any sharp edges at the top of the feeder sleeves may potentially tear the plastic film when it is drawn over the pattern and feeder sleeves. 
     The present invention has been devised with these issues in mind. 
     SUMMARY 
     According to a first aspect of the invention, there is provided a feeder system for metal casting, the feeder system comprising a feeder sleeve mounted on a breaker core. The feeder sleeve has a first end and an opposite second end, a longitudinal axis extending between the first and second ends, and a continuous sidewall extending generally around the longitudinal axis between the first and second ends. The sidewall of the feeder sleeve defines a cavity for receiving molten metal during casting, and the breaker core defines an open bore therethrough for connecting the cavity to the casting. The first end of the feeder sleeve comprises a base portion which is mounted on the breaker core. The second end of the feeder sleeve comprises a planar roof portion and a curved or chamfered portion extending around the periphery of the roof portion, for connecting the sidewall and the roof portion of the feeder sleeve. 
     DETAILED DESCRIPTION 
     Conventional feeder sleeves tend to be squared off at the top, with a substantially 90° corner between the sidewall and the roof portion of the sleeve, resulting in a relatively sharp edge at the top of the sleeve. In the feeder system of the invention, the curved or chamfered portion ameliorates the sharp edge at the top of conventional feeder sleeves and reduces the risk of tearing the plastic film when it is drawn over the pattern during formation of a V-process mould. In embodiments where the feeder sleeve comprises a chamfered portion, this is achieved by effectively creating two edges between the sidewall and the roof portion of the sleeve, each with a corner angle significantly lower than 90°, which are less sharp than a conventional single edge having a corner angle of 90°. In embodiments where the feeder sleeve comprises a curved portion, any hard edges between the sidewall and the roof portion of the sleeve are eliminated entirely. 
     In embodiments, the sidewall of the feeder sleeve is cylindrical. The cross-sectional shape of the cylinder may be generally circular, oval or obround. In some embodiments, the diameter of the cylinder is generally constant from the first end to the second end. In other embodiments, the diameter at the first end of the feeder sleeve may be larger than the diameter at the second end, or vice versa. In some embodiments, the sidewall of the feeder sleeve is generally cylindrical with a frustoconical portion located towards the first end of the feeder sleeve, which tapers towards the breaker core. 
     In embodiments, the base portion at the first end of the feeder sleeve extends substantially perpendicular to the longitudinal axis of the feeder sleeve (i.e. at an angle of about 90° relative to the longitudinal axis of the feeder sleeve). Alternatively, the base portion may be inclined at an angle relative to the longitudinal axis of the feeder sleeve, such that the sidewall on one side of the feeder sleeve is shorter than the sidewall on the opposite side of the feeder sleeve. In embodiments, the base portion extends at an inclination angle of at least 30°, 35°, 40°, 50°, 60°, 70°, 80° or 85° relative to the longitudinal axis of the feeder sleeve. In embodiments, the base portion extends at an inclination angle of no more than 88°, 85°, 80°, 70°, 60°, 50°, 40° or 35° relative to the longitudinal axis of the feeder sleeve. In embodiments, the base portion extends at an inclination angle of 30-88°, 40-85° or 50-80° relative to the longitudinal axis of the feeder sleeve. It will be understood that the breaker core on which the feeder sleeve is mounted will extend in the same direction or at the same inclination angle as the base portion of the feeder sleeve. An inclined base portion and breaker core may be desirable in cases where the feeder system is to be located on an angled section of the casting. 
     In embodiments, the breaker core is a conventional plate- or disc-shaped breaker core. Alternatively, the breaker core may comprise a planar base defining a bore therethrough, and an annular raised sidewall extending around the circumference of the base. In embodiments, the raised sidewall has a lower surface, which is attached to or integrally formed with the planar base, and an upper surface opposite to the lower surface, with an inner edge and an oppositely disposed outer edge extending between the upper and lower surfaces. In embodiments, the height of the raised sidewall is at least 1%, 2%, 5%, 10% or 15% of the maximum height of the feeder sleeve, where the height of the raised sidewall is measured from the lower surface to the upper surface and the maximum height of the feeder sleeve is measured from the first end to the second end. In embodiments, the height of the raised sidewall is no more than 15%, 10%, 5%, 2% or 1% of the maximum height of the feeder sleeve. In embodiments, the height of the raised sidewall is 1-15%, 2-10% or 5-10% of the maximum height of the feeder sleeve. It will be understood that, in embodiments where the base portion of the feeder sleeve is inclined relative to the longitudinal axis, the maximum height of the feeder sleeve is the maximum distance between the first and second ends, i.e. where the height of the sidewall of the feeder sleeve is greatest. 
     Providing a breaker core with a raised sidewall enables the feeder system to be applied to the mould pattern in two parts, when desired. In this two-part application process, the breaker core is located on the mould pattern first, then the first plastic film is drawn over the mould pattern and breaker core, and then the feeder sleeve is assembled with the breaker core over the plastic film. This prevents the plastic film from bridging between the feeder sleeves, because the film is not drawn over the sleeves themselves. During casting, the plastic film between the breaker core and feeder sleeve is easily burned away by the molten metal and does not interfere with the casting. 
     In embodiments, the breaker core further comprises a ridge or boss projecting from the upper surface of the raised sidewall in a direction away from the planar base. The boss allows the feeder sleeve to be aligned correctly and mounted securely on the breaker core during assembly of the feeder system. In embodiments, the boss extends completely or partially around the circumference of the inner edge of the raised sidewall. The boss may extend around at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the circumference of the inner edge. The boss may extend around no more than 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% or 10% of the circumference of the inner edge. In embodiments, the boss extends around 25-100% or 25-50% of the circumference of the inner edge. 
     It will be understood that the first end of the feeder sleeve is appropriately configured to be mounted onto the breaker core during assembly of the feeder system. For example, in embodiments where the breaker core comprises a raised sidewall and a boss extending around the inner edge of the raised sidewall, the sidewall of the feeder sleeve may have a thickness which corresponds to the remaining width of the upper surface of the raised sidewall excluding the width of the boss, so that the sidewall of the feeder sleeve fits snugly against the boss. Alternatively, the sidewall at the first end of the feeder sleeve may comprise a cut-out or groove configured to receive the boss on the breaker core. 
     In embodiments, the planar roof portion is centrally located at the second end. Preferably, the roof portion extends perpendicular to the longitudinal axis of the feeder sleeve. 
     In general, the shape of the roof portion may correspond to the cross-sectional shape of the sidewall of the feeder sleeve. For example, in embodiments where the sidewall of the feeder sleeve has a generally circular cross-sectional shape, the roof portion may be generally circular, or in embodiments where the sidewall has a generally obround cross-sectional shape, the roof portion may be generally obround. In embodiments, the roof portion has a minimum diameter which is at least 25%, 30%, 40%, 50%, 60%, 70%, 80% or 85% of the minimum diameter of the sidewall of the feeder sleeve. In embodiments, the roof portion has a minimum diameter which is no more than 90%, 85%, 80%, 70%, 60%, 50%, 40% or 30% of the minimum diameter of the sidewall. In embodiments, the roof portion has a minimum diameter which is 25-90%, 30-80% or 40-70% of the minimum diameter of the sidewall of the feeder sleeve. 
     In embodiments, the roof portion of the feeder sleeve comprises an open bore therethrough. The bore may be located in the centre of the roof portion. Alternatively, the bore may be offset from the centre of the roof portion. The shape of the bore in the roof section may correspond to the shape of the roof portion. For example, where the roof portion is circular, the bore may also be circular, or where the roof portion is obround, the bore may also be obround. However, the shape of the bore may not necessarily correspond to the shape of the roof portion (for example, where the roof portion is obround, the bore may be circular). The bore may be any size relative to the area of the roof portion. In embodiments, the bore has a minimum diameter which is at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the minimum diameter of the roof portion. In embodiments, the bore has a minimum diameter which is no more than 95%, 90%, 80%, 70%, 60%, 50%, 40% or 30% of the minimum diameter of the roof portion. In embodiments, the minimum diameter of the bore is 20-100% or 40-90% of the minimum diameter of the roof portion. Preferably, the diameter of the bore is less than the diameter of the roof portion, such that some amount of roof portion is present around the entire periphery of the bore, for manufacturing purposes. However, it will be understood that in some embodiments the minimum diameter of the bore may be 100% of the minimum diameter of the roof portion, such that the roof portion consists entirely of the bore. 
     In embodiments where the second end of the feeder sleeve comprises a chamfered portion, the chamfered portion may extend from the sidewall at an angle of at least 10°, 20°, 30°, 40°, 50° or 60° relative to the longitudinal axis of the feeder sleeve. The chamfered portion may extend from the sidewall at an angle of no more than 70°, 60°, 50°, 40°, 30° or 20° relative to the longitudinal axis of the feeder sleeve. In embodiments, the chamfered portion extends from the sidewall at an angle of 10-70°, 20-60° or 30-50° relative to the longitudinal axis of the feeder sleeve. The chamfered portion may extend for a minimum distance, as measured between the sidewall and the roof portion, which is at least 10%, 20%, 30%, 50%, 75%, 100% or 125% of the minimum diameter of the sidewall. The chamfered portion may extend for a minimum distance which is no more than 150%, 125%, 100%, 75%, 50%, 30% or 20% of the minimum diameter of the sidewall. In embodiments, the chamfered portion extends for a minimum distance which is 10-150%, 20-100%, or 20-50% of the minimum diameter of the sidewall. 
     In embodiments where the second end of the feeder sleeve comprises a curved portion, the radius of curvature of the curved portion may be at least 2 mm, 5 mm, 10 mm, 20 mm, 30 mm, 50 mm, 75 mm or 90 mm. The radius of curvature of the curved portion may be no more than 100 mm, 90 mm, 75 mm, 50 mm, 30 mm, 20 mm, 10 mm or 5 mm. In embodiments, the radius of curvature of the curved portion is 2-100 mm, 5-75 mm or 10-50 mm. It will be understood that the exact radius of curvature will depend on the overall dimensions of the feeder sleeve, and may be larger than these values if the feeder is exceptionally large. 
     In embodiments, the feeder sleeve may comprise two or more parts which are fitted together by any suitable means (e.g. adhesive, tongue-and-groove, etc.). One of the parts may comprise the roof portion and the curved or chamfered portion, while another one of the parts may comprise the base portion of the feeder sleeve. 
     According to a second aspect of the present invention, there is provided a feeder system for metal casting, the feeder system comprising a feeder sleeve mounted on a breaker core. The feeder sleeve has a first end and an opposite second end, a longitudinal axis extending between the first and second ends, and a continuous sidewall extending generally around the longitudinal axis between the first and second ends. The sidewall of the feeder sleeve defines a cavity for receiving molten metal during casting. The first end of the feeder sleeve comprises a base portion which is mounted on the breaker core. The breaker core comprises a planar base defining a bore therethrough, and an annular raised sidewall extending around the circumference of the planar base. The raised sidewall has a lower surface, which is attached to or integrally formed with the planar base, and an upper surface opposite to the lower surface. The breaker core further comprises a ridge or boss projecting from the upper surface of the raised sidewall in a direction away from the planar base, which is configured to engage with the base portion of the feeder sleeve. 
     As discussed above in relation to the first aspect, providing a breaker core with a raised sidewall enables the feeder sleeve to be assembled on the breaker core after the first plastic film has been drawn over the mould pattern, preventing the creation of plastic film bridges between adjacent feeder sleeves. 
     In embodiments, the second end of the feeder sleeve comprises a planar roof portion and a curved or chamfered portion extending around the periphery of the roof portion, for connecting the sidewall and the roof portion of the feeder sleeve. Alternatively, the second end of the feeder sleeve may comprise only a planar roof portion, connected directly to the sidewall at a 90° angle. 
     The invention also resides in a feeder sleeve and a breaker core for use in the feeder system according to embodiments of the first and second aspects. 
     According to a third aspect of the invention, there is provided a feeder sleeve for use in metal casting, the feeder sleeve comprising a first end and an opposite second end, a longitudinal axis extending between the first and second ends, and a continuous sidewall extending generally around the longitudinal axis between the first and second ends, the sidewall defining a cavity for receiving molten metal during casting, the first end of the feeder sleeve being configured for mounting on a breaker core, and the second end of the feeder sleeve comprising a planar roof portion and a curved or chamfered portion extending around the periphery of the roof portion, for connecting the sidewall and the roof portion of the feeder sleeve. 
     According to a fourth aspect of the invention, there is provided a breaker core for use in metal casting, the breaker core comprising a planar base defining a bore therethrough and an annular raised sidewall extending around the circumference of the planar base, the raised sidewall comprising a lower surface, which is attached to or integrally formed with the planar base, and an upper surface opposite to the lower surface, the breaker core further comprising a ridge or boss projecting from the upper surface of the raised sidewall in a direction away from the planar base, the ridge or boss being configured to engage with the base portion of a feeder sleeve. 
     The features described above in relation to embodiments of the first aspect may apply equally to embodiments of the second, third and fourth aspects. All combinations of the aspects of the present invention are considered, except where there is any technical incompatibility. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
         FIGS. 1-3  are schematic views of a feeder system according to an embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of the feeder system shown in  FIGS. 1-3 ; 
         FIGS. 5-7  are schematic views of a feeder system according to a different embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of the feeder system shown in  FIGS. 5-7 ; 
         FIG. 9  is a schematic view of a feeder system in accordance with a further embodiment of the present invention; 
         FIG. 10  is a plan view of the feeder system shown in  FIG. 9 ; 
         FIG. 11  is a schematic view of an embodiment of a breaker core for use with embodiments of the feeder system of the invention; and 
         FIG. 12  is a schematic view of another embodiment of a breaker core for use with embodiments of the feeder system of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1-4 , there is shown a feeder system  100  comprising a feeder sleeve  10  mounted on a breaker core  11 . The feeder sleeve  10  has a first end  12  and an opposite second end  13 , with a longitudinal axis A extending between the first and second ends  12 , 13 . A continuous sidewall  14  extends generally around the longitudinal axis A in the shape of a cylinder, defining a cavity therein for receiving molten metal. The diameter D 1  of the sidewall  14  is constant from the first end  12  of the feeder sleeve  10  to the second end  13 . 
     The second end  13  of the feeder sleeve  10  comprises a centrally located, planar roof portion  16  which extends perpendicular to the longitudinal axis A. The second end  13  also comprises a curved portion  15  connecting the sidewall  14  and the roof portion  16  of the feeder sleeve. The radius of curvature of the curved portion  15  is 28.5 mm. The roof portion  16  is circular and has a centrally located bore  17  extending therethrough, which is also generally circular in cross-section. The diameter D 2  of the roof portion  16  is 50% of the diameter D 1  of the sidewall of the feeder sleeve, and the diameter D 3  of the bore  17  is less than the diameter D 2  of the roof portion  16 , such that a part of the roof portion  16  extends around the entire periphery of the bore  17 . 
     The first end  12  of the feeder sleeve  10  is mounted on the breaker core  11 , and is inclined at an angle α of 70° relative to the longitudinal axis, such that the sidewall  14  is shorter on one side of the feeder sleeve  10  than on the opposite side. The breaker core  11  comprises a planar base  110  and a raised sidewall  111  extending around the circumference of the planar base  110  (best seen in  FIG. 4 ). The planar base  110  is generally circular and comprises a centrally located bore  112  extending therethrough. The raised sidewall  111  has a lower surface  113  which is in communication and integrally formed with the planar base  110 , and an upper surface  114  opposite to the planar base  110 , with an inner edge  115  and an oppositely disposed outer edge  116  extending between the lower and upper surfaces  113 ,  114 . The height H 2  of the raised sidewall  111 , as measured from the lower surface  113  to the upper surface  114 , is 6.25%% of the maximum height H 1  of the feeder sleeve  10 , as measured from the first end  12  to the second end  13  where the height of the sidewall  14  is greatest. 
     The breaker core  11  further comprises a boss  117  projecting from the inner edge side of the upper surface  114  of the raised sidewall  111 . The boss  117  extends around 25% of the circumference of the inner edge  115 . The base of the sidewall  14  of the feeder sleeve  10  has a thickness T 1  which corresponds to the remaining area of the upper surface  114  of the raised sidewall  111  excluding the boss  117 , such that the base of the sidewall  14  abuts against the boss  117 . 
     Referring to  FIGS. 5-8 , there is shown another embodiment of a feeder system  200  according to the present invention. The feeder system  200  comprises a feeder sleeve  20  mounted on a breaker core  21 . The feeder sleeve  20  has a first end  22  and an opposite second end  23 , with a longitudinal axis B extending between the first and second ends  22 , 23 . A continuous sidewall  24  extends generally around the longitudinal axis B, generally in the shape of a cylinder defining a cavity therein for receiving molten metal. The diameter of the sidewall  24  is slightly smaller at the second end  23  of the feeder sleeve  20  than at the first end  22 , such that the sidewall  24  has a minimum diameter D 4  at the second end  23  of the feeder sleeve. 
     The second end  23  of the feeder sleeve  20  comprises a centrally located, planar roof portion  26  which extends perpendicular to the longitudinal axis B. The second end  23  also comprises a chamfered portion  25  connecting the sidewall  24  and the roof portion  26  of the feeder sleeve. The chamfered portion  25  is inclined at an angle β of 50° relative to the longitudinal axis B and extends for a distance W 1  equal to 24% of the minimum diameter D 4  of the sidewall  24 . The roof portion  26  is circular and has a centrally located bore  27  extending therethrough, which is also generally circular in cross-section. The diameter D 5  of the roof portion  26  is 63% of the minimum diameter D 4  of the sidewall of the feeder sleeve, and the diameter D 6  of the bore  27  is less than the diameter D 5  of the roof portion  26 , such that a part of the roof portion  26  extends around the entire periphery of the bore  27 . 
     The first end  22  of the feeder sleeve  20  is mounted on the breaker core  21 . The first end  22  of the feeder sleeve  20  extends perpendicular to the longitudinal axis B, such that the sidewall  24  has a uniform height. The breaker core  21  comprises a planar base  210  and a raised sidewall  211  extending around the circumference of the planar base  210  (best seen in  FIG. 8 ). The planar base  210  is generally circular and comprises a centrally located bore  212  extending therethrough. The raised sidewall  211  has a lower surface  213  which is in communication and integrally formed with the planar base  210 , and an upper surface  214  opposite to the planar base  210 , with an inner edge  215  and an oppositely disposed outer edge  216  extending between the lower and upper surfaces  213 ,  214 . The height H 4  of the raised sidewall  211 , as measured from the lower surface  213  to the upper surface  214 , is 6% of the height H 3  of the feeder sleeve  20 , as measured from the first end  22  to the second end  23 . 
     The breaker core  21  further comprises a boss  217  projecting from the inner edge side of the upper surface  214  of the raised sidewall  211 . The boss  217  extends around the entire circumference of the inner edge  215 . The base of the sidewall  24  of the feeder sleeve  20  has a thickness T 2  which corresponds to the remaining area of the upper surface  214  of the raised sidewall  211  excluding the boss  217 , such that the base of the sidewall  24  abuts against the boss  217 . 
     Referring to  FIGS. 9-10 , there is shown a further embodiment of a feeder system  300  according to the present invention. The feeder system  300  comprises a feeder sleeve  30  mounted on a breaker core  31 . The feeder sleeve  30  has a first end  32  and an opposite second end  33 , with a longitudinal axis (not shown) extending between the first and second ends  32 , 33 . A continuous sidewall  34  extends generally around the longitudinal axis with an obround cross-sectional shape, defining a cavity therein for receiving molten metal. 
     The first end  32  of the feeder sleeve  30  is mounted on the breaker core  31 . The first end  32  of the feeder sleeve  30  extends perpendicular to the longitudinal axis, such that the sidewall  34  has a uniform height. The breaker core  31  comprises a planar base (not shown) and a raised sidewall  311  extending around the circumference of the planar base. The planar base is generally obround and comprises a centrally located bore extending therethrough (not shown). 
     The second end  33  of the feeder sleeve  30  comprises a centrally located, planar roof portion  36  which extends perpendicular to the longitudinal axis. The second end  33  also comprises a curved portion  35  connecting the sidewall  34  and the roof portion  36  of the feeder sleeve  30 . The roof portion  36  is obround and has a centrally located bore  37  extending therethrough, which is also obround in cross-section. 
     As shown in  FIG. 10 , the sidewall  34  has a minimum diameter D 7  between the long sides of the obround cross-section and a maximum diameter D 8  between the short sides of the obround cross-section. The obround roof portion  36  also has a minimum diameter D 9  between the long sides and a maximum diameter D 10  between the short sides. The minimum D 9  diameter of the roof portion  36  is around 40% of the minimum diameter D 7  of the sidewall  34 . The diameter of the bore  37  is less than the diameter of the roof portion  36 , such that part of the roof portion  36  extends around the entire periphery of the bore  37 . 
     Referring to  FIG. 11 , there is shown an embodiment of a breaker core  400  for use in a feeder system according to embodiments of the present invention. The breaker core  400  comprises a planar base  410  and a raised sidewall  411  extending around the circumference of the planar base  410 . The planar base  410  is generally circular and comprises a centrally located bore  412  extending therethrough. The raised sidewall  411  has a lower surface (not shown) which is in communication and integrally formed with the planar base  410 , and an upper surface  414  opposite to the planar base  410 , with an inner edge  415  and an oppositely disposed outer edge  416  extending between the lower and upper surfaces  413 ,  414 . The breaker core  400  further comprises a boss  417  projecting from the inner edge side of the upper surface  414  of the raised sidewall  411 . The boss  417  extends around approximately 25% of the circumference of the inner edge  215 . 
     Referring to  FIG. 12 , there is shown another embodiment of a breaker core  500  for use in a feeder system according to embodiments of the present invention. The breaker core  500  comprises substantially the same features as the breaker core  400  shown in  FIG. 11 , except that the planar base  510  is obround rather than circular and the boss  517  extends around the entire circumference of the inner edge side of the upper surface  514 . The bore  512  extending through the planar base  510  is also obround in cross-section.