Abstract:
An apparatus for melting and dispensing thermoplastic materials such as thermoplastic adhesives referred to as “hot melt” adhesives. More specifically, a one-piece melter tank is suspended from the top of a chassis which also serves as the housing for the entire assembly of the melting and dispensing apparatus.

Description:
This application is a continuation of U.S. Ser. No. 09/334,318, filed on Jun. 16, 1999 now abandoned, which is a continuation of U.S. Ser. No. 08/833,943, filed Apr. 14, 1997 now U.S. Pat. No. 5,919,384, each disclosure of which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an apparatus for melting and dispensing thermoplastic materials such as thermoplastic adhesives referred to as “hot melt” adhesives. More specifically this invention relates to a one piece melter tank which is suspended from a chassis which also serves as the housing for the entire assembly of the melting and dispensing apparatus. 
     BACKGROUND OF THE INVENTION 
     There are many known types of apparatus for converting thermoplastic or so-called “hot melt” materials from a solid state to a molten liquid state. The melted material was maintained in the molten state in the tank in sufficient volume to supply one or more applicators or dispensers. A number of design improvements were made over a period of time to provide greater efficiency of the melt tanks and reduce problems of charring or oxidation of the molten material due to the material being maintained in the molten state for a prolonged period of time. 
     A grid type hot melt applicator was designed to have the capability of melting a very high throughput of thermoplastic material in a very short time so that the molten material was not maintained in a molten state for prolonged periods of time which could result in degradation of the material. A typical grid type applicator is disclosed in U.S. Pat. No. 3,964,645. Other examples are shown in U.S. Pat. Nos. 3,981,416, 4,474,311, 4,667,850, and 4,821,922. Continued efforts to improve melter apparatus has resulted in the present invention. 
     OBJECTS OF THE INVENTION 
     A primary object of this invention is to provide a hot melt unit which is simple to construct and assemble and which can be produced at reduced cost to those devices of greater complexity. 
     Another object of this invention is to provide a low cost tank casting which does not require to of tank flanges which are needed on many of the previous designs. 
     Another object of the invention is to eliminate the need for providing a supporting base beneath the melt tank and manifold. 
     A still further object of this invention is to provide a more versatile pump/drive mounting surface. 
     An even further object of the invention is to provide a simplified one piece melt tank and manifold cast as an integral unit. 
     These and other objects of the invention will become more fully apparent from the description in the following specification and the attached drawings. 
     SUMMARY OF THE INVENTION 
     The combination of a melter tank for thermoplastic material and a supporting chassis comprising: a tank having a bottom and a plurality of sidewalls extending upwardly therefrom, forming an open topped tank, the sidewalls of the tank having upper edge portions extending around the top of the tank, heating means associated with the bottom of the tank, a chassis having a top and at least two sidewalls extending downwardly therefrom, a rigid top insulator panel to rest on the upper edge portions of the tank sidewalls, means connecting the tank to the top of the chassis with the rigid insulator panel clamped between the upper edge portions of the sidewalls and an underside of the top of the chassis to suspend the tank from the chassis. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an entire assembly of a unit of melting apparatus for melting and dispensing thermoplastic material; 
     FIG. 2 is a perspective view of a melt tank of the invention with an integral manifold section cast in one piece with the melt tank; 
     FIG. 3 is a top plan view of the melt tank of FIG. 2; 
     FIG. 4 is a side elevational view of the melt tank of FIG. 3; 
     FIG. 5 is a bottom view of the tank of FIGS. 3 and  4 , with a partial cross-section of the manifold taken on line  5 — 5  of FIG. 4; 
     FIG. 6 is an end view of the melt tank looking at the left end of FIG. 4; 
     FIG. 7 is a plan view of a subassembly of pipes forming a manifold duct system; 
     FIG. 8 is a fragmentary cross-sectional view of a cast manifold duct system with threaded steel nipple inserts; 
     FIG. 9 is a perspective view of a chassis for supporting the melt tank of FIGS. 2 through 6 and showing the melt tank indicated by chain dotted lines mounted within the chassis; and 
     FIG. 10 is a cross sectional side view through the chassis and the melt tank with the melt tank mounted in a suspended position within the chassis. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and in particular to FIG. 1, a complete assembly of a melter unit for melting and dispensing thermoplastic material is indicated generally by the numeral  10 . The unit  10  has a chassis  12  which also functions as a housing for the melt tank which will be shown and described in later drawing figures. A hinged lid  14  is mounted on top of the chassis/housing  12 . A pump assembly  16  driven by an electric motor  18  is mounted on one end of the chassis  12 . A pump cover  19  rests on the top of the chassis  12  and covers the pump  16  and motor  18 . 
     On the opposite end of the chassis  12  is an electrical control box  20  which will not be described in further detail since it is not part of the invention. 
     A manifold access opening  22  is provided on one side of the chassis  12 . Extending from the opening  22  are hose ports  24 , a pressure control  26 , a drain  28 , and a filter unit  30 . 
     Referring now to FIGS. 2 through 6 and in particular to FIG. 2, a melt tank  32  preferably of cast aluminum has an integral manifold portion  34  cast on the bottom of the tank as best seen in FIG. 5. A manifold duct system  35  has a duct  36  which interconnects hose ports  24 , the pressure control  26 , the drain  28  and the filter unit  30  which were previously shown in FIG. 1 as projecting through an access opening  22  in the chassis  12 . 
     The duct system  35  can either be machined into the manifold portion  34 , or made with cast in place cored ducts and porting, or the duct system can be preformed as a subassembly of steel pipe or other suitable metal in a configuration similar to that shown in FIG.  7  and the subassembly can then be positioned in a mold (not shown)in which the melt tank is formed and the duct system can be cast in place within the manifold portion  34  at the same time the entire melt tank is cast. 
     If the duct system  35  uses standard cored porting in which the duct and ports are cast in place around, for example, a sand core, then internally threaded steel insert nipples  24   a,    26   a    28   a  and  30   a  as shown in FIG. 8 are needed to provide stronger threaded openings than would be provided by the cast material of the tank manifold  34 . 
     The preferred method of forming the manifold duct system  35  is to preform a subassembly of steel pipes as shown in FIG. 7 wherein a duct  36  connects ports  24 ,  26 ,  28  and  30  all of which are brazed or welded together to form the subassembly  35 . All the ports are internally threaded in the same manner as the steel nipple inserts  24   a,    26   a,    28   a,  and  30   a  shown in FIG.  8 . 
     Using a preformed subassembly of steel pipes provides a duct system which is better able to contain the high pressure of melted liquid being pumped through the duct system and such steel pipe duct system compensates for any porosity in the tank material in manifold portion  34 . 
     Regardless of which method is used for forming the duct system  35 , it is important to have internally threaded steel nipples in the outlet ports to provide a positive seal with any components which may screwed into the port without the need for any O-ring seals. 
     Referring again to FIG. 2, the tank  32  which is of substantially rectangular shape has end walls  38  and  40  and sidewalls  42  and  44 . 
     A bottom  46  is inclined diagonally across the tank  44  at an angle with respect to a horizontal plane to permit drainage of molten material in the tank from the highest corner of the bottom to the lowest corner of the bottom which is indicated in FIG. 3 by a triangular low area  48  which also contains a circular pump recess  50 . The recess  50  functions as a sump or collection recess from which a pump withdraws molten material as will be explained later in further detail. 
     As shown in FIGS. 2 and 3, a series of fins or ribs  52  extend vertically upward from the bottom  46  and are inclined at angles to direct the flow of molten material toward the low area  48  and the pump recess  50 . As shown in FIG. 3, a sinusoidal pattern of electrical resistance heating wires  54  are embedded inside the tank bottom  46 . These wires are connected electrically in a know manner (not shown) to an electrical power source in the control box  20 . During the melting operation the wires  54  heat the tank bottom  46  and the heat passes through the fins  52  to provide heat transfer to the material in the tank. 
     A cast in place mounting tab  56  each having a slot  58  is positioned on each corner of the tank  32 . 
     The chassis  12  is shown in detail in FIG. 9 as a substantially rectangular box shaped member having sidewalls  60  and  62  formed integrally with a top  64  from heavy gauge sheet metal. A separate end wall  66  is attached to one end of the chassis and the opposite end is closed by the control box  20  shown in FIG.  1 . 
     The top  64  has an access opening  68  which provides communication with the melt tank  32  and which is covered by the lid  14  shown in FIG. 1. A pump access hole  70  is also provided in the top  64  of the chassis  12  to receive the pump assembly  16  and to permit it to extend downwardly into the tank  32  as shown in FIG.  10 . 
     A fixed nut  72  i s attached to the chassis top  64  near each corner thereof in a position to be in alignment with one of the four mounting tabs  56  on the tank  32 . Each tab  56  receives a bolt  74  extending through one of the slots  58  and screwing into one of the nuts  72 . A plurality of “Belleville washers”  76  are positioned on each bolt  74  between the bolt head and the bottom of the respective mounting tab  56  when the bolt  74  is threaded into one of the nuts  72  and is tightened against the tab  56 . The washers  76  compensate for expansion and contraction of the bolts  74  due to changes in temperature of the bolts. 
     As best seen in FIG. 10, the melt tank  32  when mounted in a suspended position from the chassis top  64  clamps a rigid insulation panel  78  between the top edge  33  of the tank  32  and the chassis top  64 . The sidewalls  60  and  62  and ends of the chassis can be lined with flexible insulation panels  80 . 
     The chassis  12  has a removable bottom  82  and four resilient foot pads  84  located at each corner to serve as vibration dampers. 
     The pump assembly  16  is mounted in the opening  70  by means of a drive mount  86  attached to the chassis top  64 . The pump  16  extends downwardly to near the bottom of the pump recess  50 . In operation the pump  16  draws in molten material from the recess  50  and passes it through a drop tube (not shown) into the manifold portion  34  where it passes through the filter unit  30  and then to the duct  36  and to hose ports  24 . The operation of the pump  16  will not be described in further detail since the pump does not form part of the invention. For purposes of illustration a “Gerotor” type pump is shown which uses intermeshing gears to move the molten material from the recess  50  into the manifold portion  34 , however other types of pumps can also serve this function. 
     It should be understood that certain variations can be made in the structural details of the melt tank and the chassis and these as well as other modifications can be made in the device shown herein without departing from the scope of the invention.