Patent Publication Number: US-6713009-B2

Title: Method and apparatus for molding plastics with elongated metallic cores

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None 
     STATEMENT RE FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     SEQUENCE LISTING 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to molded articles with elongated metallic cores. More particularly the present invention pertains to rotomolded thermoplastic articles, such as window wells and manholes, with integrally molded ladders with rungs that include metallic cores, and both method and apparatus for making. 
     2. Description of the Related Art 
     Window wells serve a purpose that is included in their name. They are a well, or hole in the ground, that is juxtaposed against a window, and that allows light to reach a window. However, when there is human occupancy below grade, it is important to provide a way of escape in the event of fire, or other disaster. 
     Providing larger windows in a lower-level room allows the use of larger window wells, and providing windows that are higher not only allows more sunlight to enter, but also requires larger window wells. 
     As windows and window wells become larger, and particularly higher, they provide an excellent path for emergency egress, in that children and adults may literally step out of the room into the window well and up to safety. 
     However, with deeper window wells, some children, and some adults may not be able to climb out of the window well. To escape a burning building, but to be trapped in a window well, is not a satisfactory way of escaping a fire, and the laws of an increasing number of states are providing requirements for built-in ladders. 
     To meet the need for ladders in window wells, some manufacturers of galvanized steel window wells have riveted-ladders into their window wells, and one manufacturer of molded plastic window wells has molded terraced steps into the window well distal from the window. 
     While both galvanized window wells with ladders and molded plastic window wells have provided useful products, the riveted-ladder window well may fail due to rust, and the terraced-step window well is excessively expensive to manufacture, and does not provide egress that is as safe as that provided by a ladder with rungs that can be grasped by the hands of children and the hands of arthritic adults. 
     BRIEF SUMMARY OF THE INVENTION 
     A wall and ladder structure, which may be in the form of such articles as a window well or a manhole, includes a thermoplastic wall, a plurality of ladder rungs that include both hollow metallic cores that are thermoplastically attached to the wall, and a thermoplastic sleeve that covers each of the metallic cores and that is integral with the thermoplastic wall. 
     The method of making the wall and ladder structure includes: placing a quantity of a thermoplastic inside a mold, heating the mold, rotating the heated mold, disposing at least a portion of a hollow metallic core inside the mold, flowing heated air through the hollow metallic core during at least a portion of time wherein the rotating step is performed, and bonding a layer of the thermoplastic onto the hollow metallic core during at least a portion of the rotating step. 
     The mold apparatus includes an exterior-contour mold, or thermoplastic rotomold, a hollow metallic core, being at least partially disposed inside the mold, that provides a healing passage therein that includes an inlet and that includes an outlet that communicates with furnace air outside the mold, and an air supply port being connected to the inlet. 
     In a first aspect of the present invention, a method for rotomolding a thermoplastic article which comprises placing a quantity of a thermoplastic inside a rotomold, heating the rotomold, and rotating the heated rotomold, the improvement comprises: disposing at least a portion of a metallic core, that includes a heating passage, in the rotomold; flowing heated air through the heating passage during at least a portion of time wherein the rotating step is performed; bonding a layer of the thermoplastic onto the metallic core during at least a portion of the rotating step; the disposing step comprises providing a pair of openings through the rotomold, and clamping the metallic core with respect to the rotomold; and the flowing step comprises communicating the heated air through one of the openings and into the heating passage, and communicating the heated air from the heating passage through the other of the openings to air outside the rotomold. 
     In a second aspect of the present invention, a method for rotomolding a thermoplastic article which comprises placing a quantity of a thermoplastic inside a rotomold, heating the rotomold, and rotating the heated rotomold, the improvement comprises: disposing at least a portion of a metallic core, (hat includes a heating passage, in the rotomold; flowing heated air through the heating passage during at least a portion of time wherein the rotating step is performed: bonding a layer of the thermoplastic onto the metallic core during at least a portion of the rotating step; the disposing step comprises providing first and second openings in the rotomold, inserting first and second clamp bars through respective ones of the openings, and clamping the metallic core between the clamp bars; and the flowing step comprises communicating the heated air into one of the clamp bars and out of another of the clamp bars. 
     In a third aspect of the present invention, mold apparatus for rotationally molding thermoplastic articles comprises: a thermoplastic rotomold; a hollow metallic core being disposed in the rotomold; and means for flowing hot air through the hollow metallic core. 
     In a third aspect of the present invention, mold apparatus for rotationally molding thermoplastic articles comprises: a rotomold having a pair of openings therethrough; an elongated metallic core having a heating passage therein, ends and being at least partially disposed inside the rotomold; a clamp bar that includes a longitudinal passage and that extends through the openings to clamp the ends of the metallic core with respect to the rotomold such that the longitudinal passage is in communication with the heating passage; and a hot air passage that includes an inlet port, the heating passage, the longitudinal passage and a transverse passage that communicates air from one of the openings into the heating passage and from the heating passage through another of the openings to air outside the rotomold. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a top view of a rotomolded wall and ladder structure, or rotomolded window well, showing an outwardly-extending top flange, showing, by breaking out a portion of the top flange, one of two outwardly-extending side flanges that are used to attach the window well to a building structure, showing a partial bottom, and showing a top view of one of the ladder rungs; 
     FIG. 2 is a side elevation of a rotomolded wall and ladder structure, or rotomolded window well, taken substantially as shown by view line  2 — 2  of FIG. 1, showing the outwardly-extending top flange, showing four bracing ribs that are horizontally-disposed and inwardly-extending, showing a bottom flange that depends downwardly from a partial bottom, and showing, by phantom line, a bottom that is cut from the window well after molding; 
     FIG. 3 is an inside elevation of the rotomolded window well of FIGS. 1 and 2, taken substantially as shown by view line  3 — 3  of FIG. 1, showing the rungs of the ladder positioned in respective ones of the bracing ribs, and also showing the flange that extends downwardly from the partial bottom; 
     FIG. 4 is a partial cross section of the rotomolded window well of FIGS. 1-3, taken substantially as shown by section line  4 — 4  of FIG. 3, showing one of the ladder rungs molded into the wall, and showing one of the hollow metallic cores molded inside the ladder rung; 
     FIG. 5 is an enlarged and partial cross section of the window well of FIGS. 1-4 and a portion that is molded between two window wells that are molded top-to-top, and then removed to provide an outwardly-extending flange for both window wells; 
     FIG. 6 is a top view of a manhole that includes two halves that are each much the same as the window well of FIGS. 1-5, but when bolted together, they form a manhole for laddered human access to and from a lower level; 
     FIG. 7 is a top view of a manhole similar to that of FIG. 6, except the two halves of FIG. 6 are molded integrally in FIG. 7; and 
     FIG. 8 is an enlarged and partial cross section of the mold for rotomolding the window well of FIGS. 1-3, the manhole of FIG. 6, and the manhole of FIG. 7, taken substantially the same as FIG. 4, showing one of the elongated hollow metallic cores clamped into the mold by a tubular clamp bar and a clamp plate, and showing a nozzle in the clamp plate that injects hot air through the tubular clamp bar and the hollow metallic core. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1-3, a rotomolded plastic wall and ladder structure, or rotomolded plastic window well,  10  includes a curved thermoplastic wall  12  having a height  14 , and a ladder  16  that includes a plurality of ladder rungs  18  that are vertically spaced, as shown. Each of the ladder rungs  18  includes a hollow elongated metallic core, or tubular metallic core,  20 , and a thermoplastic sleeve  22  as shown in FIG.  4 . 
     The thermoplastic sleeve  22  is molded onto a respective one of the hollow metallic cores  20 , and the thermoplastic sleeve  22  is molded integrally with the thermoplastic wall  12 . 
     The wall  12  includes first and second ends,  24 A and  24 B, a concave inner surface  26  upon which the ladder rungs  18  are disposed, a pair of attaching flanges  28  that extend outwardly from respective ones of the ends,  24 A and  24 B, an outwardly-extending top flange  30 , an integrally-molded partial bottom  32  that extends inwardly of the curved wall  12 , and a downward flange  38  that depends from the bottom  32 . 
     The wall and ladder structure  10  further includes a plurality of bracing ribs  40  that are horizontally-disposed and inwardly-extending, and that increase the structural integrity of the structure  10 . The ladder rungs  18  are disposed vertically within respective ones of the ribs  40 . 
     Preferably, two of the wall and ladder structures  10  are molded with the outwardly-extending top flanges  30  proximal to each other, and with a U-shaped portion  42 , of FIG. 5, connecting the top flanges  30 . After molding, the two wall and ladder structures  10  are separated by cutting at lines  44 , thereby leaving the outwardly-extending top flanges  30 . 
     Referring now to FIG. 6, a manhole or plastic wall and ladder structure  50  includes two identical manhole halves  52  that are attached to each other by any suitable means, such as the attaching flanges  28  of the window well  10  of FIGS. 1-3, thereby providing a continuous outer wall  54  that provides an enclosed passageway  56  inside the continuous outer wall  54 . As shown in FIG. 6, preferably, the manhole halves  52  are not perfectly semicircular, but are shaped, as shown, to nest together for shipping. 
     Referring now to FIG. 7, a manhole or plastic wall and ladder structure  58  includes a continuous outer wall  60 , an enclosed passageway  62 , and at least one ladder  16 . 
     As shown in FIGS. 6 and 7, two of the ladders  16  of FIGS. 1-4 are included in one manhole,  50  or  58 . However, as will be seen as the tooling is discussed, with only minor modification to the tooling, one of the manhole halves  52  could be molded without the ladder  16 , so that the manhole  50  would have only one ladder  16 . In like manner, the manhole  58  could be molded with only one ladder  16 . 
     Referring now to FIGS. 6 and 7, the manholes  50  and  58  may be stacked to provide manholes of greater height, not shown, by any suitable means, such as providing bottom flanges, not shown, that are similar, or the same as, the top flanges  30  of FIG. 2, and bolting the two flanges together. 
     Referring now to FIG. 8, mold apparatus  70  for rotationally molding thermoplastic articles, such as the window well  10 , the manhole  50 , or the manhole  58 , includes an exterior-contour mold, or thermoplastic rotomold,  72 , a plurality of the metallic cores  20  of FIG. 4, each of which includes a heating passage  74  therethrough, an inlet port  78  that is connected to a nozzle fitting  80  having a nozzle  82 , but that may have an air-to-air heat exchanger  84  interposed between the inlet port  78  and the nozzle fitting  80 , a venturi throat  86  that is a part of a clamp bar passage or longitudinal passage  88  that extends through a tubular clamp bar  90 , a clamp plate  92  that is pivotally attached by means of a pivot anchor  94 , and a guide sleeve  96  for the clamp bar  90  that includes an opening  98 . 
     As shown in FIG. 8, the clamp bars  90  each include a pilot portion  102  that pilotingly engages the heating passage  74  of one of the cores  20 , the clamp bars  90  each include a clamping face  104  that clampingly engages an end  106  of one of the cores  20 , and the clamp plate  92  includes a clamp foot  108  that clampingly engages the clamp bar  90  and that provides a transverse passage  110  between the clamp bar  90  and the clamp plate  92 . 
     Another clamp bar  90  with another clamp bar passage  88  and another pilot portion  102 , another clamp plate  92  with another pivot anchor  94 , and another guide sleeve  96  with another opening  98 , not shown, same as those shown, are provided for another end, not shown, of the hollow metallic cores  20 . 
     As shown in FIG. 8, the nozzle fitting  80  is threadingly inserted into the clamp plate  92 , and a clamp device  112 , which may be a manually actuated clamp, is provided to selectively allow the clamp plate  92  to be pivoted outwardly, thereby allowing the pilot portion  102  to be removed from the cores  20 , to allow the clamp bar  90  to be removed from the sleeve  96 , and to provide a releasably longitudinal clamping force on the ends  106  of the cores  20 . 
     Although two of the clamp plates  92  are used, one for each end of one of the hollow metallic cores  20 , the nozzle fittings  80  are used at only one end  106  of the cores  20 , since hot air exits at another end  106  opposite to the end  106  wherein hot air is jetted into the heating passage  74  provided by the hollow metallic cores  20 . Although not shown, one of the clamp plates  92  may be used for more than one of the cores  20 . 
     As hot air is jetted into the venturi throat  86  by the nozzle  82 , furnace air is drawn into the venturi throat  86  through the transverse passage  110 , flows through the longitudinal passage  88 , flows through the heating passage  74  provided by one of the hollow metallic cores  20 , flows through another longitudinal passage  88  in another clamp bar  90 , not shown, and out of another transverse passage  110 , not shown, into furnace air. 
     With regard to the air-to-air heat exchanger  84 , preferably at least 15.2 meters (50 feet) of 12.7 millimeter (0.50 inch) copper tubing is formed into a coil and is used to preheat compressed air that is supplied to the inlet port  78  before the compressed air is jetted into the venturi throat  86  by the nozzle  82 . 
     Preferably, the thermoplastic rotomold  72  is made from sheets of aluminum and/or molded aluminum. However, preferably, the clamp bars  90  are made from a brass or bronze material that has a coefficient of heat transfer that is greater than that of aluminum, thereby optimizing heat transfer into the cores  20 . However, for cores  20  with a L/D (length/diameter) ratio greater than eight, heat transfer through the clamp bars  90  is not sufficient to achieve satisfactory molding without flowing hot air through the cores  20 , as taught herein. 
     The method of the invention comprises: placing a quantity of a thermoplastic inside a mold, heating the mold, rotating the heated mold, disposing at least a portion of a hollow metallic core in the mold, flowing heated air through the hollow metallic core during at least a portion of time wherein the rotating step is performed, and bonding a layer of the thermoplastic onto the hollow metallic core during at least a portion of the rotating step. 
     The method of the invention may additionally include: compressing air, heating the compressed air, discharging compressed air through a nozzle, pulling mold-furnace air through a venturi throat, providing a pair of openings through the mold, communicating the heated air in through one of the openings and out through the other of the openings, disposing a clamp bar through one of the openings, pressing the clamp bar against the hollow metallic core, providing a releasable longitudinal clamping force against an end of the hollow metallic core, communicating the heated air through one of the openings and into the hollow metallic core, and/or communicating the heated air from the hollow metallic core through the other of the openings to furnace air outside the mold. 
     The method of the invention may additionally include: providing first and second openings in the mold, inserting first and second clamp bars through respective ones of the openings, inserting first and second pilot portions of the clamp bars into respective ends of the hollow metallic core, and releasably clamping ends of the hollow metallic core between the clamp bars, communicating the heated air into one of the clamp bars and out of another of the clamp bars, using a hollow metallic core that has insufficient draft for successfully pulling the core from the thermoplastic article and leaving the core in the thermoplastic article subsequent to the bonding step, and/or using a hollow metallic core that includes sufficient draft for successfully pulling the core from the thermoplastic article and withdrawing the core from the thermoplastic article subsequent to the bonding step. 
     While specific apparatus and method have been disclosed in the preceding description, and while numbers have been inserted into the claims parenthetically, it should be understood that these specifics have been given for the purpose of disclosing the principles of the present invention, and that many variations thereof will become apparent to those who are versed in the art. Therefore, the scope of the present invention is to be determined by claims included herein without any limitation by numbers parenthetically inserted in the claims.