Abstract:
The invention relates broadly to injection molding machines and more particularly to a novel carriage assembly for use in an injection unit of an injection molding machine.  
     Barrels are conventionally mounted at an end in a carriage of an injection unit. Installation of the barrel in a conventional carriage is difficult and time consuming, and prone to alignment errors.  
     A carriage assembly is disclosed having a first carriage coupler and a second carriage coupler. The first carriage coupler secures a barrel intermediate the ends of the barrel to the carriage. The second carriage coupler retains an end of the barrel in the carriage preventing rotation of the barrel during operation. A barrel alignment member in the carriage provides axial and vertical alignment of the barrel assembly in the carriage assembly during installation of the barrel in the carriage.

Description:
CROSS-REFERENCE TO RELATED COPENDING PATENT APPLICATIONS  
         [0001]    The following patent applications, which are assigned to the assignee of the present invention and filed concurrently herewith, cover subject matter related to the subject matter of the present invention and are incorporated herein by reference:  
                                                             Serial Number   Title                                        Barrel Assembly.           Force Isolating Cradle Assembly.           Injection Unit.                      
 
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention broadly relates to injection molding machines and, in particular to the injection unit of an injection molding machine. Injection molding machines include machines for injecting plastic material, or metal material, or metal material in a thixotropic state.  
           [0004]    2. Summary of the Prior Art  
           [0005]    Operation of an injection molding machine introduces a number of forces, pressures, and stresses on the injection unit. For example, axial carriage force is a force applied to engage the nozzle end of a barrel assembly against a sprue bushing of a mold. This provides a force sealing connection between the nozzle and sprue bushing preventing leakage of melted material during injection. Carriage force is applied and maintained prior to injecting the melt of material.  
           [0006]    Injection force is a force directed along the length of a reciprocating screw located in a bore of a barrel assembly. Injection force results in injecting a melt of material into a mold. There is an axial reactive injection force acting along the length of the barrel assembly as a result of moving a screw forward during the injection stage of a molding process.  
           [0007]    Injection pressure is a pressure required to overcome the resistance to the flow of the melt of material in the nozzle, runner system, and mold cavity. Injection pressure is exerted on the melt in front of the screw tip during the injection stage of a molding process. The accumulator end of a barrel assembly must withstand injection pressure.  
           [0008]    Injection units for molding machines are very well known. For example, the book entitled “Injection Molding machines A User&#39;s Guide 3 rd  Edition” by Johannaber was published in 1994 by Carl Hanser Verlag (ISBN 1-56990-169-4) and contains a detailed description of conventional injection units for plastic injection molding machines in Chapter 3 on pages 38, 39 42, 43, 44, 75, and 76. The reciprocating screw (RS) injection unit includes a barrel assembly which includes a nozzle, barrel head, barrel, axial bore, feed port, heater bands, and thermocouples. A reciprocating screw, which includes a non-return valve, is disposed in the axial bore of the barrel. The axial bore of the barrel includes a metering section and a feeding section. An electric or hydraulic drive operates the screw to feed and meter a melt of material and inject the metered material into a mold. The barrel assembly is fixed and supported, cantilevered, at one end of the barrel by a carriage. Hydraulic or electric actuators connect between the carriage and a frame member or fixed platen of the injection molding system. Operation of the actuators move the barrel assembly towards and away from the stationary platen and provides an axial carriage force through the entire length of the barrel during injection minimizing leakage between the nozzle tip and the sprue bushing. The axial reactive injection force is directed through the entire length of the barrel during injection.  
           [0009]    The book entitled “Injection Molding Operations” produced by Husky Injection Molding Systems Ltd., and printed in Canada, copyright  1980  also contains a description of conventional injection units for plastic injection molding machines on pages  41  through  44 . Again, for the reciprocating screw injection unit, a barrel is supported at a distant end by a carriage, which houses the injection cylinder and a rotational drive. A hydraulic cylinder is connected between the carriage and a stationary platen. In operation of the hydraulic cylinder, the carriage force is applied along the entire length of the barrel. For a two stage injection unit, a barrel is supported at one end by a carriage. The carriage houses the drive. The nozzle of the barrel feeds into a shooting pot which includes an injection piston. The carriage supports another end of the shooting pot. A hydraulic cylinder is connected between the carriage and a stationary platen. In operation of the hydraulic cylinder, the carriage force is applied along the entire length of the shooting pot. The axial reactive injection force is directed through the entire length of the shooting pot during injection.  
           [0010]    U.S. Pat. No. 5,040,589 issued on Aug. 20, 1991 to Bradley et al (assigned to The Dow Chemical Company). The patent describes an injection apparatus for injection molding a thixotropic semi-solid metal alloy. The patent contains a description of an apparatus for processing a metal feedstock into a thixotropic state as the metal is fed into a hopper, located at one end of the barrel, and transported into an accumulation zone located at another end of the barrel. The barrel is constructed of a single piece of material with thick walls. A number of heating zones are defined along the length of the barrel, including sections of the barrel having differing thickness. The feed throat area and zone  4  are relatively thick sections. Zone  3  is a slightly thinner section, and zone  2  is the thinnest section. The barrel is conventionally mounted in the injection unit. A feed throat end of the barrel is mounted in an upright support secured to the frame of an injection unit. A bottom surface of the barrel, intermediate the distant ends of the barrel, rests on a second support also secured to the frame. The carriage force is applied along the entire length of the barrel in operation of the apparatus. All sections of the disclosed barrel must be thick enough to withstand the combination of axial carriage force and axial reactive injection force directed through the entire length of the barrel during injection.  
           [0011]    U.S. Pat. No. 5,983,978 issued on Nov. 16, 1999 to Vining et al (assigned to Thixomat Inc.). The patent describes a thixotropic metal injection molding apparatus. The barrel is formed in two sections to define a high pressure section and a low pressure section. The low pressure section is thinner than the high pressure section. A feed throat end of the barrel is mounted in an upright support of an injection unit. A bottom surface of the barrel, intermediate the distant ends of the barrel, rests on a second support also secured to the frame. The carriage force is applied along the entire length of the barrel in operation of the apparatus. All sections of the disclosed barrel must be thick enough to withstand the combination of axial carriage force and reactive injection force through the entire length of the barrel during injection.  
           [0012]    There are a number of problems and deficiencies with the known prior art devices. Barrels are costly due to the amount of material required to provide a suitable thickness for withstanding the axial force along the entire length of the barrel. The axial force may be the carriage force, or the reactive injection force, or a combination of these two forces.  
           [0013]    Special materials are required for barrels in use with thixotropic materials and these special materials are very expensive and are difficult to manufacture.  
           [0014]    Thick barrels have a high thermal resistance which affects the efficiency and controllability of heating a material in the axial bore of a barrel.  
           [0015]    Barrels, conventionally mounted in the injection unit, are typically difficult to install and remove. The process of installation and removal within a carriage is time consuming. Installation of the barrel in a carriage is further prone to alignment problems.  
         SUMMARY OF THE INVENTION  
         [0016]    The primary objective of the present invention is to provide an improved barrel assembly for use in an injection molding machine.  
           [0017]    Another primary objective of the present invention is to provide an improved carriage assembly for use in an injection molding machine.  
           [0018]    Another primary objective of the present invention is to provide an improved injection unit for use in an injection molding machine.  
           [0019]    Another primary objective of the present invention is to isolate a portion of a barrel assembly from axial forces.  
           [0020]    An other object of the present invention is to reduce the cost of a barrel assembly.  
           [0021]    Another object of the present invention is to reduce the amount of material required in certain sections of a barrel assembly.  
           [0022]    Another object of the present invention is to reduce the weight of a barrel assembly.  
           [0023]    Another object of the present invention is to reduce the axial stress in a portion of the barrel assembly.  
           [0024]    Another object of the present invention is to reduce the thermal mass in a portion of the barrel assembly.  
           [0025]    Another object of the present invention is to couple and support the barrel intermediate the ends of the barrel for providing more accurate alignment of a nozzle to the sprue bushing.  
           [0026]    Another object of the present invention is to provide a carriage assembly permitting unobstructed access for installing and removing the barrel assembly.  
           [0027]    Another object of the present invention is to provide a carriage assembly with a first coupler for securing the barrel assembly intermediate the ends of the barrel assembly to the cradle assembly.  
           [0028]    Another object of the present invention is to provide a carriage assembly with a second coupler for retaining a portion of the barrel assembly to the cradle assembly.  
           [0029]    Another object of the present invention is to provide a carriage assembly with a barrel support for aligning the barrel within the carriage assembly during installation of the barrel assembly with the carriage assembly.  
           [0030]    The foregoing objects are achieved by providing a barrel assembly for use in an injection molding machine.  
           [0031]    The carriage consists of a cradle member, a mounting surface, and a first carriage coupler. The cradle member has a lengthwise axial opening for receiving a barrel. The mounting surface is for mounting the carriage to an injection unit. The first carriage coupler is aligned with the lengthwise axial opening wherein the first carriage coupler secures the barrel to the carriage intermediate the ends of the barrel.  
           [0032]    As an alternative, the carriage may include a second carriage coupler. The second carriage coupler is aligned with the lengthwise axial opening and the first carriage coupler wherein the second carriage coupler retains the barrel to the carriage intermediate an end of the barrel and the first carriage coupler.  
           [0033]    As an alternative, the carriage may include a barrel alignment member aligned with the lengthwise axial opening wherein the barrel alignment member aligns the barrel with the carriage.  
           [0034]    As an alternative, the carriage may include a second carriage coupler and a barrel alignment member. The second carriage coupler is aligned with the lengthwise axial opening and the first carriage coupler. The barrel alignment member is aligned with the lengthwise axial opening. The second carriage coupler retains the barrel to the carriage intermediate an end of the barrel and the first carriage coupler and the barrel alignment member aligns the barrel with the carriage.  
           [0035]    As an alternative, the first carriage coupler is disposed intermediate a yoke and an end of the cradle member.  
           [0036]    As an alternative, the first carriage coupler comprises an yoke coupler and a cradle coupler. The yoke coupler is disposed on the yoke and the cradle coupler is disposed on the cradle member. The yoke coupler and the cradle coupler engage the barrel for securing the barrel to the carriage.  
           [0037]    As an alternative, the yoke coupler is an engaging surface formed on side of the yoke opposite the cradle coupler.  
           [0038]    In an embodiment of the invention, the engaging surface is a barrel seat formed in a central opening of the yoke.  
           [0039]    As an alternative, cradle coupler comprises a first upright support and a second upright support. The first upright support and the second upright support are separated by an opening for receiving the barrel. The first upright support and the second upright support secure the barrel to the carriage.  
           [0040]    As an alternative, the first upright support includes a first coupling surface and the second upright support includes a second coupling surface wherein the first coupling surface and the second coupling surface engage a coupling surface of the barrel.  
           [0041]    As an alternative, the second carriage coupler includes an engagement member for retaining the barrel.  
           [0042]    As an alternative, the engagement member includes a first coupling member and a second coupling member. The first coupling member and the second coupling member are separated by an opening for receiving the barrel. The first coupling member and the second coupling member retain the barrel to the carriage.  
           [0043]    As an alternative, the first coupling member includes a first coupling surface and the second coupling member includes a second coupling surface.  
           [0044]    In an embodiment of the invention, the first coupling surface and the second coupling surface are a flat recess for engaging a complimentary surface on the barrel.  
           [0045]    In an embodiment of the invention, the first coupling surface and the second coupling surface are grooved for engaging a complimentary surface on the barrel.  
           [0046]    In an embodiment of the invention, the first coupling surface and the second coupling surface are a spline for engaging a complimentary surface on the barrel.  
           [0047]    In an embodiment of the invention, the first coupling surface and the second coupling surface include a slot for engaging a complimentary outwardly projecting member on the barrel.  
           [0048]    In an embodiment of the invention, the first coupling surface and the second coupling surface include an outwardly projecting member for engaging a complimentary slot on the barrel.  
           [0049]    As an alternative, the second carriage coupler includes a retaining plate releasably secured to the cradle member for retaining the barrel in the carriage.  
           [0050]    As an alternative, the barrel alignment member aligns the barrel axially and aligns the barrel vertically in the cradle.  
           [0051]    As an alternative, the barrel alignment member includes a first barrel support member and a second barrel support member. The first barrel support member and the second barrel support member supporting the barrel at a predetermined height in the carriage.  
           [0052]    As an alternative, the first barrel support member includes at least one standoff and the second barrel support member includes at least one standoff.  
           [0053]    As an alternative, the barrel support member includes an insulator disposed intermediate the barrel support member and the barrel for thermally insulating the carriage from the barrel.  
           [0054]    As an alternative, the cradle member includes a frame. The first carriage coupler disposed on the frame and the second carriage coupler disposed on the frame. The first carriage coupler disposed at a distance from the second carriage coupler.  
           [0055]    As an alternative, the cradle member includes a drive mount for mounting a drive assembly. The drive mount disposed on an end of the cradle member. The first carriage coupler and the second carriage coupler and the drive mount are in axial alignment.  
           [0056]    In an embodiment of the invention, the frame is a plurality of tie bars interconnecting the first carriage coupler and the second carriage coupler.  
           [0057]    In an embodiment of the invention, the frame is a first carriage actuator housing and a second carriage actuator housing interconnecting the first carriage coupler and the second carriage coupler.  
           [0058]    In an embodiment of the invention, the first carriage actuator housing is substantially U shaped and the second carriage actuator housing is substantially U shaped The first carriage actuator for housing a first actuator and the second carriage actuator for housing a second actuator.  
           [0059]    In an embodiment of the invention, the first carriage coupler securely clamps the barrel and the second carriage coupler retains an end of the barrel. The second carriage coupler permits axial movement of the barrel with respect to the carriage.  
           [0060]    Further objects and advantages of the present invention will appear hereinbelow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0061]    Embodiments of the present invention will now be described, by way of example only, with reference to the attached figures, wherein  
         [0062]    [0062]FIG. 1 is a diagrammatic side view representation of an injection molding machine illustrating a clamp unit interconnected to an injection unit;  
         [0063]    [0063]FIG. 2 is a perspective view of an injection assembly;  
         [0064]    [0064]FIG. 3 is an exploded perspective view of the injection assembly illustrating a barrel assembly and a carriage assembly;  
         [0065]    [0065]FIG. 4 is a cross sectional view taken along line AA from FIG. 2 illustrating a multi-piece barrel assembly located in the carriage assembly;  
         [0066]    [0066]FIG. 5 is a cross sectional view taken along line AA from FIG. 2 illustrating a nozzle section with a spigot tip;  
         [0067]    [0067]FIG. 6 is a cross sectional view taken along line AA from FIG. 2 illustrating an alternative nozzle section with a semispherical tip;  
         [0068]    [0068]FIG. 7 is a perspective view illustrating an accumulator section of the barrel assembly and a first barrel coupler;  
         [0069]    [0069]FIG. 8 is a cross sectional view taken along line AA from FIG. 2 illustrating an accumulator section of the barrel assembly and a first barrel coupler;  
         [0070]    [0070]FIG. 9 is a cross sectional view taken along line AA from FIG. 2 illustrating a second portion of the barrel assembly;  
         [0071]    [0071]FIG. 10 is a partial perspective view of a second portion of the barrel assembly illustrating a second barrel coupler;  
         [0072]    [0072]FIG. 11 is a top view of cradle member;  
         [0073]    [0073]FIG. 12 is a cross sectional side view of the cradle member taken along line C-C of FIG. 11 illustrating the first cradle coupler, the second carriage coupler, the first barrel support member, and the second barrel support member;  
         [0074]    [0074]FIG. 13 is a front view of the cradle member illustrating the first cradle coupler and the first barrel support member;  
         [0075]    [0075]FIG. 14 is an end view of the cradle member illustrating the drive mount;  
         [0076]    [0076]FIG. 15 is a front view of the yoke;  
         [0077]    [0077]FIG. 16 is a back view of the yoke;  
         [0078]    [0078]FIG. 17 is a cross sectional side view of the yoke taken along line D-D of FIG. 16;  
         [0079]    [0079]FIG. 18 is a partial perspective view of the barrel assembly and carriage assembly illustrating installation of the barrel assembly within the carriage assembly;  
         [0080]    [0080]FIG. 19 is a partial perspective view of the barrel assembly and carriage assembly illustrating the barrel assembly installed in the carriage assembly;  
         [0081]    [0081]FIG. 20 is a top view of the carriage illustrating the relationship between the second barrel coupler and the second cradle coupler;  
         [0082]    [0082]FIG. 21 is a partial top cross sectional view taken along line BB of FIG. 2 illustrating the relationship between the first barrel coupler and the first carriage coupler with a spigot tip nozzle for axial carriage force;  
         [0083]    [0083]FIG. 22 is a top cross sectional view taken along line BB of FIG. 2 illustrating the relationship between the barrel assembly with a spigot tip nozzle and the carriage assembly for axial reactive injection force;  
         [0084]    [0084]FIG. 23 is a partial top cross sectional view taken along line BB of FIG. 2 illustrating the relationship between the first barrel coupler and the first carriage coupler with a semispherical tip nozzle for axial carriage force;  
         [0085]    [0085]FIG. 24 is a top cross sectional view taken along line BB of FIG. 2 illustrating the relationship between the barrel assembly with a semispherical tip nozzle and the carriage assembly for axial reactive injection force;  
         [0086]    [0086]FIG. 25 is a cross sectional view taken along line AA of FIG. 2 illustrating a screw located in the barrel assembly in a first operative position; and  
         [0087]    [0087]FIG. 26 is a cross sectional view taken along line AA of FIG. 2 illustrating a screw located in the barrel assembly in a second operative position.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0088]    An embodiment of the invention is initially described referring to FIG. 1, which illustrates an injection molding machine, generally indicated at  10 . The injection molding machine includes a clamp unit, indicated at  12 , interconnected and secured to an injection unit, indicated at  14 .  
         [0089]    A stationary platen  16  is fixed to a clamp frame member  18  of the clamp unit  12 . A moving platen  20  is operable between an open position and a closed position through an actuator  22 . Those skilled in the art appreciate that the actuator  22  may be either hydraulic, electric, or a combination of hydraulic and electric actuators. A plurality of tie bars  32  extend between the stationary platen  16  and the actuator  22 . A moving half of a mold  24  is mounted on a face of the moving platen  20  and a stationary half of a mold  26  is mounted on a face of the stationary platen  16 .  
         [0090]    The clamp unit  12  of FIG. 1 is a two platen clamp. Alternatively, the clamp unit  12  may be a multi-station clamp unit, for example a stack mold carrier, having more than one moving platen and more than one mold. Alternatively, the clamp unit  12  may be an index clamp unit having a rotating multi-face turret block in place of a moving platen. Alternatively, the clamp unit  12  may be a tandem clamp unit having two molds operated in sequence.  
         [0091]    An injection assembly  27  is mounted on a injection unit frame  28  of the injection unit  14 . The frame  28  typically houses the control system, electronics, and power pack. The injection assembly  27  further includes a barrel assembly  30 , a carriage assembly  34  for supporting and securing the barrel assembly  30 , and a drive assembly  36 . The drive rotates a screw to create a melt of material and feed the material forward in the barrel into an accumulation zone. The drive also reciprocates the screw to inject the melt of material into the mold.  
         [0092]    Referring now to FIG. 1 and FIG. 2, the drive assembly  36  is further described. In an embodiment of the invention, the drive assembly includes both hydraulic and electric components. A screw translation drive  38  provides axial movement of the screw (not shown) in the barrel assembly  30 . A screw rotation drive  40  rotates the screw (not shown) within the barrel assembly  30 . The screw translation drive  38  is hydraulic and the screw rotation drive  40  is electric. Alternatively, the drive could be completely hydraulic or completely electric. Activation of the translation drive  38  axially reciprocates the screw without rotation of the screw by the screw rotation drive  40 .  
         [0093]    The barrel assembly  30  is mounted and securely retained within the carriage assembly  34 . The carriage actuator  42  extends between the carriage assembly  34  and the stationary platen (see FIG. 1). Operation of the carriage actuator  42  moves the injection assembly  27  towards and away from the stationary platen for locating the end of a nozzle into contact with a sprue bushing.  
         [0094]    Referring now to FIG. 3, the injection assembly  27  is further described. The carriage assembly  34  includes a cradle member  52 , a yoke  50 , and a drive mount  54  for mounting the drive assembly  36  (see FIGS. 1 and 2).  
         [0095]    The barrel assembly  30  includes a first barrel portion  44 , a first barrel coupler  46 , a second barrel portion  48 , and a second barrel coupler  60 . The first barrel coupler  46  is disposed on the barrel assembly  30  and interlocks with first carriage coupler to secure the barrel assembly  30  in the carriage assembly  34 . The first carriage coupler is formed intermediate the yoke  50  and an end of the cradle member  52  to be described later.  
         [0096]    The location of the first barrel coupler  46  defines a first barrel portion  44  and a second barrel portion  48  of the barrel assembly  30 . The first barrel portion  44  is a section of the barrel that is capable of withstanding injection pressure. The second barrel portion  48  is a section of the barrel that is isolated from axial forces, both the axial carriage force and the axial reactive injection force.  
         [0097]    The second coupler  60  is disposed on the second barrel portion  48  and communicates with a second carriage coupler located at another end of the cradle member  52 , near the drive mount  54 , retaining the second portion  48  of the barrel assembly  30  in the cradle assembly  34 . Alternatively the second coupler  60  may be disposed between the first barrel coupler  46  and an end of the second barrel portion  48 .  
         [0098]    The carriage actuator  42  includes a pair of hydraulic actuators indicated as  56  and  58 . One end of the first carriage actuator  56  connects to one side of the carriage assembly  34  through a conventional fastener such as a pin (not shown) through the openings  51  and  53 . The other end of the first carriage actuator  56  connects to the stationary platen (see FIG. 1). One end of the second carriage actuator  56  connects to a second side of the carriage assembly  34  through another conventional fastener such as a pin (not shown) through the openings  55  and  57 . The other end of the second carriage actuator  58  connects to the stationary platen (not shown).  
         [0099]    Referring now to FIG. 4, a cross sectional view of the barrel assembly  30  is now further described. The barrel assembly  30  is shown mounted within the carriage assembly  34 . The barrel assembly  34  includes the first barrel portion  44  and the second barrel portion  48 . The first barrel coupler  46  is disposed on the barrel assembly  30  and defines the boundary between the first barrel portion and the second barrel portion. The second barrel coupler  60  is disposed at an end on the second barrel portion  48 . In this embodiment, the first barrel coupler  46  is integrally formed on the first barrel section  44  and the second barrel coupler  60  is formed onto the outer surface of the second barrel portion  48 .  
         [0100]    The first barrel portion  44  includes a nozzle  62  and an accumulator  64 . The nozzle  62  is mechanically secured by a plurality of fasteners to an end of the accumulator  64 . The nozzle  62  seals at the joint  66  with the end of the accumulator  64  preventing leakage of melted material. An axial bore of the nozzle  62  aligns with an axial bore of the accumulator  64  permitting a flow of melt during injection. Alternatively, the nozzle  62  is of unitary construction with the barrel assembly  30 .  
         [0101]    The second barrel portion  48  is a feed section and is mechanically secured by a plurality of fasteners to another end of the accumulator  64 . The second barrel portion  48  seals at the joint  68  at the other end of the accumulator  64 . An axial bore of the second barrel portion  48  aligns with the axial bore of the accumulator permitting a flow of melt from the second barrel section  48  to the accumulator  64 . In an alternative embodiment of the invention, the first barrel section  44  and the second barrel section  48  are of unitary construction without the joints  66  and  68 .  
         [0102]    Referring now to FIGS. 5 and 6, two embodiments of a nozzle  62  are described. The nozzle  62  has an elongate cylindrical section  70  extending from a mounting flange  72  to a mold end  86  of the nozzle  62 . The mounting flange  72  is cylindrical and formed integral to the elongate cylindrical section  70 . The mounting flange  72  has a diameter greater than the elongate section  70 . The mounting flange  72  includes a plurality of spaced apart bores  74  for receiving mounting bolts (not shown). The accumulator end  76  of the nozzle  62  includes a spigot seal  78 . The spigot seal  78  is cylindrical and extends outwardly from a side of the flange  72 . The nozzle  62  includes a melt channel made up of a first diameter axial bore  80 , a first concentrator  82 , and a second diameter axial bore  84 . In operation during injection, the melt channel receives the melt from the accumulator through the opening  92 . The melt travels along the melt channel in the nozzle  62  and exits the nozzle at another opening  94  en route to a mold.  
         [0103]    In a first embodiment of the nozzle  62 , the mold end  86  includes a spigot tip  88 . The spigot tip  88  is cylindrical and extends into a complimentary cylindrical bore in a sprue bushing (not shown) for tight sealing engagement between the mold end  86  of the nozzle  64  and the sprue bushing during injection of a melt of material. In operation, the spigot tip  88  is in sliding sealing engagement with the complimentary cylindrical bore in the sprue bushing. The spigot tip  88  is permitted to move with respect to the sprue bushing.  
         [0104]    In a second embodiment of the nozzle  62 , the mold end  86  includes a convex semispherical tip  90 . The semispherical tip  90  engages a complimentary concave semispherical opening in a sprue bushing (not shown) for tight sealing engagement between the mold end  86  of the nozzle  64  and the sprue bush during injection of a melt of material. In operation, the semispherical tip  90  is in force sealing engagement with the complimentary concave semispherical opening in the sprue bushing.  
         [0105]    Referring now to FIGS. 7 and 8, an accumulator section, generally indicated as  64  is described. The accumulator includes an elongate section  104 , and a first barrel coupler  46 . In an embodiment of the invention, the coupler  46  includes an axial force linkage member, indicated as  96 , and a thermal isolator, indicated as  98 . Alternatively, the coupler  46  may include a linkage insulator  99  which is an axial force linkage member  96  integrated with a thermal isolator  98 . An axial melt channel extends through the accumulator  64 . The axial melt channel includes a first accumulator diameter bore  112 , a second concentrator  110 , and a second diameter bore  116 . The first accumulator diameter bore  112  aligns and connects with the first diameter bore  80  of the nozzle  62 . The second diameter bore  116  aligns and connects with an axial bore  147  of the second barrel portion  48  (not shown). The volume defined by the second diameter bore  116  (which defines an accumulation zone) determines the maximum available shot size for injection into a mold.  
         [0106]    The accumulator  64  is substantially cylindrical with a suitable wall thickness (between the outer surface of the elongate section  104  and the melt channel) to withstand high pressure due to injection and reactive injection force. In an embodiment of the invention, the wall thickness of the accumulator  64  must also withstand axial carriage force.  
         [0107]    The nozzle  62  connects to an end wall  118  of the accumulator  64  through the flange  72  of the nozzle  62 . The end wall  118  of the accumulator  64  includes a plurality of threaded bores  108 . The flange  72  of the nozzle  62  includes a corresponding plurality of bores  74 . Bolts interconnect the nozzle  62  to the accumulator  64  by the bores  74  and threaded bores  108 . The bore  114  in the accumulator  64  is of complimentary diameter to tightly receive the spigot  78  of the nozzle for sealing engagement between the nozzle  62  and the accumulator  64 . Alternatively, a seal may be installed to prevent leakage between the nozzle  62  and the accumulator  64 . Heater bands are conventionally secured to an outer surface of the accumulator  64  and the side  126  of the coupler  46 .  
         [0108]    In an embodiment of the invention, the coupler  46  is integrally formed on an end of the accumulator  64 . Alternatively, the coupler  46  may be a separate component retained or secured to the accumulator  46 . For example, the coupler  46  may be welded to the outer surface of the accumulator  64 , or threaded to the accumulator  64 . Those skilled in the art will appreciate that any retained or secured connection must be designed to withstand axial forces.  
         [0109]    In an embodiment of the invention, the coupler  46  includes an axial force linkage member  96 . For the embodiment illustrated, the axial force linkage member  96  is a pair of outwardly extending members integrally formed on the first end wall  120  of the coupler  46 . Alternatively, the axial force linkage member  96  may be a plurality of outwardly extending members, or a plurality of standoff posts, or a cylindrical ring member that may be integral or separate from the coupler  46 . In another embodiment of the invention, the coupler  46  includes a pair of axial force linkage members ( 150 ,  96 , see FIG. 21 and FIG. 23) disposed on the first end wall  120  and the second wall  124  of the coupler  46 .  
         [0110]    Those skilled in the art will appreciate that the cross sectional area of the force linkage member  96  of the coupler  46  is such to withstand the required axial forces. In addition, placement of the axial force linkage member  96  is such to provide an even symmetrical load distribution.  
         [0111]    Alternatively, the coupler  46  may include a second axial force linkage member (or linkage insulator) located on a second end wall  124  of the coupler  46 .  
         [0112]    In an embodiment of the invention, the axial force linkage member  96  includes a thermal isolator, generally indicated as  98 . For the embodiment illustrated, the thermal isolator  98  is integrally formed on an end of the axial force linkage member  96 . By minimizing the cross sectional area of the linkage member  96  for contact with a first carriage coupler (not shown) in the cradle member  52 . In operation, the thermal isolator reduces the conductive heat transfer from the hot accumulator  64  and the coupler  46  to the cradle member  52  and the yoke  50 . Alternatively, the thermal isolator may be separate from the axial force linkage member  96 , or may be a coating, or may be a different material for reducing the conductive heat transfer. The thermal isolator is disposed intermediate all contacting surfaces between the first barrel coupler  46  and the first carriage coupler. Those skilled in the art will appreciate that the thermal isolator is such to withstand the required axial forces.  
         [0113]    The nozzle  62  and the accumulator  64  together form the first barrel portion  44  of the barrel assembly. The first barrel portion  44  optionally includes a liner or protective coating to protect the melt channel from abrasive and corrosive materials.  
         [0114]    Referring now to FIGS. 9 and 10 , a second barrel portion  48  is described. The second barrel portion  48  shown is a feed section of the barrel assembly  30  and includes an axial bore  147 , a first opening  146 , a second opening  134 , and a feed throat  140 . Material enters the second portion  48  through the feed throat  140 . A screw (not shown) disposed in the axial bore  128  conveys the material forward in the axial bore  147  towards accumulator  64 .  
         [0115]    The second barrel portion  48  is substantially cylindrical with a suitable wall thickness (between the outer surface of the elongate barrel and the axial bore  147  acting as a melt channel) to withstand pressure developed due to compacting and sheering the feed material. Axial forces are not directed through the second barrel portion  48 .  
         [0116]    The second barrel portion  48  optionally includes a liner  138  installed within an outer barrel  142  to protect the barrel from abrasive and corrosive materials.  
         [0117]    The opening  146  permits the installation and removal of a screw (not shown) within the axial bore  147 .  
         [0118]    The second end wall  136  of the second portion  48  connects to the coupler side of the accumulator  64  through the flange  130 . The end wall  120  of the coupler  46  includes a plurality of threaded bores  102 . The flange  130  of the second portion  48  includes a corresponding plurality of bores  132 . Bolts interconnect the second portion  48  to the coupler  46  by the bores  132  and thread bores  102 . The bore  100  in the coupler  46  is of complimentary diameter to tightly receive the cylindrical connector  128  of the second portion  48  for sealing engagement between the coupler  46  and the second portion  48 . The bore  122  in the coupler  46  is of complimentary diameter to receive the flange  130 . Alternatively, a seal may be installed to prevent leakage between the first portion and the second portion  48 . The second diameter bore  116  of the accumulator  64  axially aligns with the axial bore  147  of the second portion  48 .  
         [0119]    A second barrel coupler  60  is formed on an end of the second portion  48 . The second barrel coupler  60  includes at least one engagement member, indicated as  153  for complimentary engagement with a cradle engagement member for preventing rotational movement of the barrel assembly  30  during operational rotation of the screw (not shown). Heater bands are conventionally secured to an outer surface of the second barrel portion  48 .  
         [0120]    In the embodiment illustrated, the engagement member  153  is a flat recess machined on the outer surface of the barrel. Alternatively, the engagement member  153  may be an outwardly projecting member, or a groove, or a slot, or splined. Optionally, another recess  155  engages a removal plate (not shown) for preventing the barrel assembly from tipping forward when released from the cradle assembly and aligning the second barrel section vertically with the drive assembly.  
         [0121]    In an application of the machine where the melt of material is a metal in a thixotropic state, for example, magnesium, the nozzle  62  may be made from DIN  2888  or DIN  2999 . The accumulator  44  and first barrel coupler  68  (including the axial force isolator) may be made from Inconel  718  with a Stellite  12  liner. The second portion  48  may be also made from Inconel  718  with a Stellite  12  liner.  
         [0122]    In an application of the machine where the melt of material is plastic, the nozzle  62  may be made from SAE 4140 steel with an H 13  tip. The accumulator  44  and first barrel coupler  68  (including the axial force isolator) may be made from 4140 with a cast liner. The second portion  48  may be made from 4140 with a cast liner.  
         [0123]    The nozzle  62 , accumulator  44 , first barrel coupler  68 , and second portion  48  may be machined from a billet of material, or alternatively, they may be formed by a hot isostatic pressing (HIP) process and then machined.  
         [0124]    Referring now to FIGS. 3 and 11, the cradle member  52  of the carriage assembly  34  is further described. The cradle member  52  is substantially rectangular as shown in the top view of FIG. 11. A first cradle coupler  178  if formed on one end of the cradle member  52 . A drive mount  54  is formed on a second end of the cradle member  52 . The drive mount  54  includes an axial bore to connect the drive assembly to an end of a screw located in an axial bore of a barrel (not shown). The first cradle coupler  178  and the drive mount  54  are aligned about a longitudinal axis of the cradle member  52 .  
         [0125]    The first cradle coupler  178  and the drive mount  54  are interconnected by a first carriage actuator housing  170  and a second carriage actuator housing  172 .  
         [0126]    The first carriage housing  170  forms a lengthwise U-shaped rectangular channel for housing a first carriage actuator  56 . The first carriage housing  170  includes a support web  180  located near an end of the first carriage housing  170  and extends between an upper carriage member  182  and a lower carriage member  184 . An upright wall member  192  connects the upper carriage member  182  and the lower carriage member  184 .  
         [0127]    The second carriage housing  172  forms a second lengthwise U-shaped rectangular channel for housing a second carriage actuator  58 . The second carriage housing  172  includes a support web  186  located near an end of the second carriage housing  172  and extends between an upper carriage member  188  and a lower carriage member  190 . A second upright wall member  194  connects the upper carriage member  188  and the lower carriage member  190 .  
         [0128]    The cradle member  52  has a lengthwise axial opening  176  extending from the first end  174  of the cradle member  52  to the drive mount  54 . This opening provides clear unobstructed access for inserting and removing a barrel assembly (see FIG. 3) within the cradle member  52 .  
         [0129]    Referring now to FIG. 11 and FIG. 12, the first cradle coupler  178  and the second carriage coupler  148  are further described.  
         [0130]    The cradle member  52  includes a second support  206  that extends between the upright wall members ( 192 ,  194 ) at the first end  174  of the cradle member  52 . In an embodiment of the invention, a first cradle coupler  148  includes a first coupling member  208  and a second coupling member  210 . The first and second coupling members ( 208 ,  210 ) extend outwardly from the upright wall members ( 190 ,  192 ). The first coupling member  208  includes a first coupling surface  212  and the second coupling member  210  includes a second coupling surface  214 . The first cradle coupler  178  forms an opening about the longitudinal axis to receive the first barrel coupler  46 . In an embodiment of the invention, the first coupling surface  212  and the second coupling surface  214  engage the axial force linkage member  96  the barrel coupler  60 . Alternatively, the first coupling surface  212  and the second coupling surface  214  engage the thermal isolator  98 . A pair of support gussets  216  extend between a back surface of the first and second coupling members ( 208 ,  210 ) and the upright wall members ( 192 ,  194 ).  
         [0131]    The cradle member  52  also includes a first support  196  that extends between the upright wall members ( 192 ,  194 ) and the drive mount  54 . The first support  196  is T shaped. In an embodiment of the invention, the second carriage coupler  148  includes a first coupler member  198  and a second coupler member  200 . The first and second coupler members ( 198 ,  200 ) extend upwardly from an upper surface first support  196  and outwardly from the upright wall members ( 192 ,  194 ). The second carriage coupler  148  forms a opening about the longitudinal axis to receive the second barrel coupler  60 . A first coupling surface  202  and a second coupling surface  204  engage complimentary surfaces ( 153 ) of the second barrel coupler  60 .  
         [0132]    A first barrel support member  218  is formed on an upper surface of the second support  206 . The first barrel support member  218  includes a first upright standoff  222  and a second upright standoff  224 . The standoffs ( 222 ,  224 ) are of a height above the upper surface of the second support  206  to engage an outer surface of the barrel assembly  30  for locating the first barrel coupler  46  with respect to the first cradle coupler  178 .  
         [0133]    A second barrel support member  220  is formed on an upper surface of the first support  196 . The second barrel support member  220  includes a first upright standoff  226  and a second upright standoff  228 . The standoffs ( 226 ,  228 ) are of a height about the upper surface of the second first support  196  to engage an outer surface of the barrel assembly  30  for locating the second barrel coupler  60  with respect to the second carriage coupler  148 .  
         [0134]    The first barrel support member  218  and the second barrel support member  220  form a barrel alignment member and axially align the barrel assembly  30  when housed in the cradle member  34 . The cradle member  52  may include additional barrel support members.  
         [0135]    Referring now to FIG. 13, the first end  174  and first cradle coupler  178  of the cradle member  52  are described. A yoke mounting surface  230  extends between the first carriage housing  170  and the second carriage housing  172 . The yoke mounting surface  230  includes a number of threaded bores for receiving bolts to secure the yoke  50  to the cradle member  52 . The first upright standoff  222  and the second upright standoff  224  are spaced apart a distance to securely support an outer surface of the barrel assembly  30 . The cross sectional area of the first coupling surface  212  and the second coupling surface  214  is selected to withstand and distribute axial carriage force to the first barrel coupler  46 . The first barrel coupler  46  fits into the barrel coupler opening, generally indicated as  232 .  
         [0136]    Referring now to FIG. 14, the drive mount  54  of the cradle member  52  is further described. The drive mount  54  includes a mounting surface  234  for mounting a drive assembly  36 . A number of thread bores  236  are provided to receive bolts for mounting the drive assembly  36  to the drive mount  54 . A opening  238  is provided to connect the drive assembly  36  to an end of a screw mounted in a barrel (not shown).  
         [0137]    Referring now to FIGS. 15, 16, and  17 , the yoke  50  is further described. The yoke  50  is rectangular having a front face  240 , a back face  242 , a left side  244 , a right side  246 , top and bottom. The yoke  50  is of suitable thickness to withstand axial carriage force. The yoke  50  includes a number of openings  248  for receiving bolts to secure the yoke  50  to the yoke mounting surface  230  of the cradle member  52 . The central axial bore  250  has a first diameter for receiving the barrel assembly  30  and a second diameter for receiving the barrel coupler  46 . The coupling surface of the yoke  50  engages the second axial force linkage member  150 . In an embodiment of the invention, the coupling surface is a barrel seat  252  formed between the first diameter and the second diameter. The barrel seat  254  has a cross sectional area to withstand and distribute axial carriage force.  
         [0138]    In an embodiment of the invention, the first carriage coupler  152  is formed by the yoke  50  and the first cradle coupler  178  of the cradle member  34 .  
         [0139]    The yoke  50  includes a pair of yoke supports ( 254 , 258 ). A first yoke support  254  is mounted on a side of the yoke  50 . A second yoke support  258  is mounted on another side of the yoke  50 , opposite the first yoke support  254 . The yoke supports are axially aligned. The first yoke support  254  includes a supporting surface  256  and the second yoke support  258  includes a supporting surface  260 . The supporting surfaces ( 256 ,  260 ) engage complimentary surfaces of the first carriage actuator  56  and the second carriage actuator  58  for supporting the yoke  50  during assembly of the carriage assembly  34 .  
         [0140]    In an embodiment of the invention, the yoke is plate steel A36 and the cradle assembly is cast from A536. Alternatively, the cradle assembly may be a pair of couplers interconnected by tie bars.  
         [0141]    In an alternative embodiment of the invention, the first carriage coupler is interconnected to the second carriage coupler by a plurality of tie bars. In another alternative embodiment of the invention, the first carriage coupler is interconnected to the second carriage coupler by frame member.  
         [0142]    Installation of the barrel assembly  30  in the carriage assembly  52  is described with reference to FIGS. 18 and 19. The cradle member  52  is mounted on the frame  28  of the injection unit  14  for axial movement of the injection assembly with respect to the injection unit frame  28  (not shown). The carriage actuator  42  is mounted in the cradle member  52  and connected to a stationary member, for example the stationary platen  16  of the injection molding machine  10 . The carriage actuator  42  is operated to move the cradle member  52  away from the stationary platen  16  (see FIG. 18). The yoke  50  is placed on the carriage actuator  42  away from the first end  174  of the cradle member  52 . The supporting surface  256  engages one actuator and the supporting surface  260  engages the other actuator.  
         [0143]    The barrel assembly  30  is lowered into the opening of the cradle member  34 . The first barrel coupler  46  is aligned with the first cradle coupler  178 . The second barrel coupler  60  is aligned with the second carriage coupler  148 . The barrel assembly  30  is lowered until the barrel assembly  30  engages the first barrel support member  218  and the second barrel support member  200 . The barrel support members ( 218 ,  200 ) align the barrel assembly  30  in the cradle member  34 .  
         [0144]    A rectangular retaining plate  262  (see FIG. 19) engages the support surface  155  of the second barrel coupler  60  for retaining the barrel assembly  30  vertically in the cradle member  52 . The plate  262  is secured by conventional bolts to the first and second coupler member ( 200 ,  198 ). A lower surface of the plate  262  engages the support surface  155  permitting axial movement of the barrel assembly  30  in the carriage assembly  34 .  
         [0145]    The yoke  50  is moved towards the first end  174  of the cradle member  52  and secured to the first end  174  of the cradle member  52  by a number of bolts. A number of alignment pins and openings are provided between the yoke  50  and the yoke mounting surface  230  for aligning the yoke  50  to the cradle assembly  34 . The first barrel coupler  46  is effectively secured and clamped to the carriage assembly. The reciprocating screw (located within the axial bore of the barrel assembly) is then connected to the drive assembly  36   
         [0146]    Those skilled in the art will appreciate that removal of the barrel assembly  30  from the carriage assembly  52  is the reverse operation of mounting.  
         [0147]    Referring now to FIG. 20, the barrel assembly  30  and second barrel coupler  60  are shown mounted in the carriage assembly  34  as a top view without the yoke  50 .  
         [0148]    The second barrel coupler  60  engages the second carriage coupler  148 , retaining the second barrel portion  48  of the barrel assembly  30  to the cradle member  52 . The second barrel coupler  60  and the second carriage coupler  148  prevent the barrel assembly  30  from rotating about the longitudinal axis during rotational operation of the screw (not shown). The second barrel coupler  60  and the second carriage coupler  148  permit axial longitudinal movement of the second barrel portion  48  effectively isolating the second barrel portion from axial forces.  
         [0149]    Referring now to FIG. 21, a partial view of the barrel assembly  30  is shown mounted in the carriage assembly  34  as a partial cross sectional view taken along line BB of FIG. 2.  
         [0150]    The barrel assembly  30  is housed and secured in the carriage assembly  34 . In an embodiment of the invention, the thermal isolator and the first axial force linkage member  96  engages a surface of the first carriage coupler  152 . A ring shaped second axial force linkage member  150  is located on a other side of the coupler  46 . A thermal isolator surface of the second axial force linkage member  150  engages an inner surface (barrel seat) of the yoke  50 . The yoke  50  is located at the front of the carriage assembly  34 . The yoke  50  is bolted to a forward section of the carriage assembly  34  to securely clamp the first barrel coupler  46 .  
         [0151]    The clamping force to secure the barrel assembly  30  with the carriage assembly  34  is provided between the yoke  50  and the carriage assembly  34 . The clamping force is directed through the second axial force linkage member  150  (including a thermal isolator), the first barrel coupler  46 , and the first axial force linkage member  96  (including a thermal isolator).  
         [0152]    In operation, there are two different applications where axial carriage force is directed through the barrel coupler  46 . When the nozzle  62  includes a spigot tip  88  (see FIG. 5), the yoke includes a first carriage stop  156  and a second carriage stop  158  (alternatively, a single carriage stop). The first and second stop are mounted by bolts to a front face of the yoke  50 . The first and second stop extend outwardly from the front face of the yoke  50  to engage a surface of the stationary platen. The length of the first and second stop is such to permit a length of the spigot tip  88  to enter into the sprue bushing. Operation of the carriage actuator  42  moves the carriage assembly  34  and barrel assembly  30  towards the stationary platen  16  (see FIG. 1) until the first and second stop engage the stationary platen  16  preventing further forward movement. The carriage actuator  42  is further operated to create the axial carriage force. The axial carriage force is directed through the first carriage actuator  56  and the second carriage actuator  58  to the carriage assembly  34 . The carriage assembly  34  further directs the axial carriage force through the first carriage coupler  152  to the first axial force linkage member  96 , the first barrel coupler  46 , the second axial force linkage member  150 , the yoke  50 , and the first and second stops. This isolates the second barrel portion  48  from axial carriage force.  
         [0153]    Referring now to FIG. 22, axial injection force is described. During the injection phase, the screw translation drive  38  is operated to move the screw forward in the barrel assembly  30 . An injection force is directed from the translation drive  38  to the reciprocating screw body  164 , and to the melt of material located in front of the reciprocating screw. A reactive injection force is directed back through the accumulator  64 , to the first barrel coupler  46 , (including linkage members) to the first cradle coupler  152 , to the first and second carriage actuator housings ( 170 ,  172 ), to the drive mount  54 , and to the screw translation drive assembly  30 . The second barrel portion is isolated from the axial reactive injection force.  
         [0154]    Referring now to FIG. 23, when the nozzle  62  includes a semispherical tip  90  (see FIG. 6), the first stop  156  and the second stop  158  are not required. Operation of the carriage actuator  42  moves the carriage assembly  34  and barrel assembly  30  towards the stationary platen  16  unit the semispherical tip  90  engages the sprue bushing. The carriage actuator  42  is further operated to create the axial carriage force. The axial carriage force is directed through the first carriage actuator  56  and the second carriage actuator  58  to the carriage assembly  34 . The carriage assembly  34  further directs the axial carriage force through the first carriage coupler  152  to the first axial force linkage member  96 , the first barrel coupler  46 , the accumulator  64 , and the nozzle  62 . The first barrel portion distributes axial carriage force and the second barrel portion is isolated from axial carriage force.  
         [0155]    Referring now to FIG. 24, axial injection force is described. During the injection phase, the screw translation drive  38  is operated to move the screw forward in the barrel assembly  30 . An injection force is directed from the translation drive  38  to the reciprocating screw body  164 , and to the melt of material located in front of the reciprocating screw. A first reactive injection force is directed back through the accumulator  64 , to the first barrel coupler  46 , (including linkage members) to the first cradle coupler  152 , to the first and second carriage actuator housings ( 170 ,  172 ), to the drive mount  54 , and to the screw translation drive assembly  30 . A second reactive injection force is directed back through the nozzle  62  to the accumulator  64 , to the first barrel coupler  46 , (including linkage members) to the first cradle coupler  152 , to the first and second carriage actuator housings ( 170 ,  172 ), to the drive mount  54 , and to the screw translation drive assembly  30 . The second barrel portion is isolated from the axial reactive injection force.  
         [0156]    Referring now to FIGS. 25 and 26, operation of a screw in a the barrel assembly is described. The barrel assembly, including the nozzle  62 , accumulator  64 , first barrel coupler  46 , second barrel portion  48 , and second barrel coupler  60  is secured and retained respectively in the carriage assembly  34  as previously described. A screw is located within the axial bore of the accumulator and the second barrel portion. The screw includes a screw tip  160 , a check valve  162 , and a reciprocating screw body  164 . The screw is reciprocatable between an injected position (see FIG. 13) and a maximum shot position (see FIG. 14).  
         [0157]    In operation, the screw starts at the injected position. Feed material enters the axial bore of the barrel assembly through the feed port. The material is melted and conveyed forward along the screw body  164  towards the screw tip  160 . As a shot of material develops in front of the screw tip  160  in the accumulation zone of the accumulator  64 , the screw moves aft until an appropriate shot volume is received in the accumulator zone. Then, the screw is advanced forward injecting the shot of melt into a mold. The check valve  162  permits the melt to move forward, but not backward of the check valve. In operation, the check valve reciprocates only within the axial bore of the accumulator  64 .  
         [0158]    In an embodiment of the invention, the barrel assembly is formed by a single unitary construction. In another embodiment, the barrel assembly is a first section connected to a second section. In another embodiment, the first section is a nozzle connected to an accumulator. In another embodiment, the first section is nozzle connected to a barrel head which is connected to an accumulator.  
         [0159]    It is to be understood by persons skilled in the art that the invention is not limited to the illustrations described herein, which are deemed to illustrate the best modes of carrying out the invention, and which are susceptible to modification of form, size, arrangement of parts and details of operation. The invention is intended to encompass all such modifications, which are within its spirit and scope as defined by the claims.