Abstract:
Auxiliary end heating devices on an elongated, heated hot melt distribution manifold body assist in maintaining uniform temperatures throughout all portions and passageways of the manifold body. The heating devices preferably take the form of thick film electrical resistive heaters of plate-like construction. The end heaters are on their own control circuit separate and apart from the circuit for other heaters for remaining portions of the manifold body. Special isolating slots are formed in lower corners of the manifold body between supporting standoffs and overhead melt passageways in the manifold body.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to injection molding manifolds and, more particularly, to ways of managing heat distribution throughout the manifold in an effort to achieve uniform temperatures of all melt channels or passages, even those near the ends of the manifold.  
         BACKGROUND AND SUMMARY  
         [0002]    Elongated manifold blocks typically have a central inlet passage that delivers hot melt from an extruder or other source into the center of the block and then splits it into a main runner that delivers the melt to a series of injection nozzles spaced along the length of the manifold body. While various means are typically utilized to keep the body hot so that the melt flows properly at all times, the opposite ends of the manifold are typically exposed to ambient air. Consequently, passages associated with the endmost nozzles are difficult to maintain at the same high temperatures as other passages in the body. Moreover, structures utilized to support the manifold often function as heat sinks to draw off disproportionate amounts of heat in end portions of the body and compound the problem.  
           [0003]    The present invention addresses this problem by providing a way of supplying auxiliary heat specifically to opposite end portions of the manifold body in addition to that which is supplied to the body as a whole. Furthermore, the temperature in at least one of the end portions is sensed separately from the rest of the body to control the auxiliary supply of heat separately from the main supply, with a view to establishing a uniform temperature throughout the entire body if at all possible.  
           [0004]    In a preferred form of the invention, each auxiliary source of heat is a generally flat electrical resistance type heater applied to each end surface of the manifold body. Preferably, the heater covers the entire exposed surface of the end of the body. In addition, in order to reduce the amount of heat drawn off by supports at the corners of the body, a pair of isolating slots extend transversely through the entire body and are located generally between each support and the melt passages in the upper and inboard regions of the body. In a preferred form, each isolating slot is generally L-shaped, having a vertical leg that is shorter than the horizontal leg and with the horizontal leg extending inwardly toward the center of the body from the bottom of the vertical leg.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a front elevational view of a distribution manifold assembly for an injection molding machine constructed in accordance with the principles of the present invention;  
         [0006]    [0006]FIG. 2 is a slightly enlarged, fragmentary cross-sectional view thereof taken substantially along line  2 - 2  of FIG. 1; and  
         [0007]    [0007]FIG. 3 is a slightly enlarged fragmentary cross-sectional view thereof taken substantially along line  3 - 3  of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0008]    The present invention is susceptible of embodiment in many different forms. While the drawings illustrate and the specification describes certain preferred embodiments of the invention, it is to be understood that such disclosure is by way of example only. There is no intent to limit the principles of the present invention to the particular disclosed embodiments.  
         [0009]    The distribution manifold assembly  10  includes an elongated parallelepiped metallic manifold body  12  preferably constructed from 4140 alloy steel. Body  12  is supported by a pair of end supports or standoffs  14  and  16  and by a center support  18 , all of which are preferably constructed from a low thermal conductivity material such as 304 stainless steel. Underlying the supports  14 ,  16  and  18  is a horizontal support plate  20  that is preferably constructed of a high carbon alloy steel.  
         [0010]    Secured to the front face of body  12  is a sprue bushing  22  that is adapted to be connected to the outlet of an extruder or other source of hot melt for the purpose of supplying such molten plastic material to manifold assembly  10 . Sprue bushing  22  has a through passage  24  that delivers melt to an upwardly inclined inlet passage  26  in body  12 . Inlet passage  26 , in turn, intersects with a main, longitudinally extending runner passage  28  that extends essentially the full length of body  12  in opposite directions from central inlet passage  26 . Main runner  28  is capped at its opposite ends by a pair of plugs  30  and  32 . A series of branch passages  34  intersect with main runner  28  along the length thereof and lead to corresponding injection nozzles  36 . Preferably, nozzles  36  may take the form of the nozzles disclosed and claimed in co-pending application Ser. No. 10/272,974, filed Oct. 16, 2002 in the name of Brian R. Lefebure titled “Injection Molding Nozzle.” Said application is hereby incorporated by reference into the present specification.  
         [0011]    Manifold body  12  is provided with heating mechanism broadly denoted by the numeral  38  for keeping body  12  at a high enough temperature that plastic material within the various internal passages of body  12  remains molten at all times. In part such heating mechanism  38  takes the form of four electrical resistance type heating rods or elements  40  that extend along the length of body  12  and are situated at each of the four corners thereof as viewed from the end or in transverse cross-section. Elements  40  may, for example, take the form of rods available from Watlow Electric Manufacturing Company of St. Louis, Mo. and are secured in place in a well-known manner. Opposite ends of elements  40  project outwardly beyond manifold body  12  and into corresponding upright receivers  42  and  44  wherein elements  40  are electrically connected with various circuitry and the like. A sensor in the nature of a thermocouple  46  received within body  12  generally near the mid-portion thereof above main runner  28  is connected in the same electrical circuit as heating elements  40  for the purpose of controlling operation of elements  40 . Thermocouple  46  is operable to sense when the temperature within the surrounding region of manifold body  12  drops to a predetermined level so as to cause heating elements  40  to be activated as necessary to maintain the predetermined temperature. Although a wide variety of sensors may be utilized for carrying out this function, one acceptable sensor is a standard thermocouple available from Watlow Electric Manufacturing Company of St. Louis, Mo.  
         [0012]    In conventional manifold assemblies the branch passages associated with the endmost nozzles present the biggest challenge for maintaining the desired heat level because in conventional manifold assemblies opposite ends of the manifold body are exposed to ambient air. For the sake of illustration, the branch passages of manifold body  12  have been labeled  34   a  through  34   f  with the two endmost branches being branches  34   a  and  34   f.  If manifold body  12  were a conventional body, branches  34   a  and  34   f  would be the branches most subject to heat loss.  
         [0013]    However, in accordance with the present invention, heating mechanism  38  includes a pair of auxiliary end heating devices  48  and  50  applied to opposite ends of body  12  for the purpose of maintaining branches  34   a  and  34   f,  as well as their adjacent portions of main runner  28 , at substantially the same temperature level as all other passages within body  12 . In a preferred embodiment, each end heating device  48 ,  50  takes the form of a generally flat electrical resistance type heater such as that available from Watlow Electric Manufacturing Company of St. Louis, Mo. as a thick film heater having a 300 or 400 series stainless steel substrate. Preferably, each heating device  48 , 50  is attached to the flat, corresponding end surface  52  or  54  of body  12  by suitable fasteners such as screws  56 . As illustrated in FIG. 3, each end heating device  48 ,  50  overlies and covers virtually the entire surface area of the corresponding end surface  52  or  54 . Preferably, as illustrated with respect to heating device  50  in FIG. 3, each heating device  48 ,  50  is designed to produce three different levels or zones of heat output from the top to the bottom of the device, namely zones A, B and C. Zone A in the top one-third of the device produces the lowest heat output, while zone B in the middle one-third produces the highest output. Zone C in the lower third produces an intermediate range of heat output.  
         [0014]    Each heating device  48 ,  50  has a pair of leads  58  and  60  connected to corresponding terminals  62  and  64  that connect electrically with heating elements of the devices. Leads  58  and  60  are connected in an electrical circuit that is separate and apart from that for heating elements  40  and sensor  46  so that devices  48  and  50  are not controlled by sensor  46 . Instead, devices  48  and  50  are controlled by a separate sensor  66  that is preferably the same type of thermocouple as sensor  46 . In a preferred embodiment, only one of such sensors  66  is utilized to control both devices  48 ,  50 .  
         [0015]    In a preferred form of the invention the sensor  66  is located in an end portion of manifold body  12  so as to be in the most advantageous position for detecting temperature variations in that critical region of the body. For purposes of the present invention, an end portion of body  12  is defined as that portion of the body that extends from the center line of the next-to-the-last branch passage in the body to the corresponding end surface of the body. Thus, in the present embodiment, manifold body  12  has two end portions  12   a  and  12   b.  End portion  12   a  extends from the center line  68  of inboard nozzle  36   b  and branch passage  34   b  outwardly to end surface  52 , and end portion  12   b  extends from center line  70  of inboard nozzle  36   e  and branch passage  34   e  outwardly to end surface  54 . In the illustrated embodiment, the sensor  66  is located in end portion  12   b,  preferably slightly outboard of the central axis  72  of endmost nozzle  36   f  and endmost branch passage  34   f.    
         [0016]    To further control and manage heat distribution and loss within manifold body  12 , each end portion  12   a  and  12   b  is provided with its own isolating slot  74  or  76  that passes entirely transversely through body  12  generally between the corresponding standoff  14  or  16  and the overhead melt passageways  28  and  34 . Each slot is generally L-shaped, having a relatively short vertical leg  78  and a longer horizontal leg  80 . Horizontal leg  80  intersects vertical leg  78  at the lower end of leg  78 , while vertical leg  78  intersects horizontal leg  80  at the outer end of horizontal leg  80 . Vertical leg  78  is entirely disposed outboard of the axis  72  associated with endmost nozzle  36   f  and endmost branch passageway  34   f.  Horizontal leg  80  is spaced a short distance above the lower two heating elements  40  of manifold body  12 .  
         [0017]    Operation  
         [0018]    Operation and use of manifold assembly  10  should be apparent from the foregoing description. With the auxiliary end heaters  48  and  50  in place, the end branch passages  34   a  and  34   f  are no longer exposed to heat loss to the degree suffered by prior art manifolds. Instead, end portions  12   a  and  12   b  of manifold body  12  can be maintained at substantially the same temperature level as the remaining portion of the manifold body with the result that much better melt flow characteristics can be obtained. Moreover, by having end heating devices  48 ,  50  under the control of their own sensor  66 , rather than relying upon the sensor  46  used for the central region of the manifold body, precise temperature control can be obtained exactly where heat loss is most likely to occur.  
         [0019]    The isolating slots  74  and  76  immediately above each of the standoffs  14 ,  16  serve as a way of breaking the drain of heat that otherwise occurs from the passageways in end regions of the body due to the standoffs  14 ,  16  acting as heat sinks. Slots  74 , 76  perform their function without significantly weakening the structural integrity of the manifold body in these areas.  
         [0020]    The inventor(s) hereby state(s) his/their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his/their invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.