HEATER MODULE ASSEMBLY FOR AN APPARATUS FOR MELTING AND DISPENSING THERMOPLASTIC MATERIAL

Abstract: Apparatuses for melting and dispensing thermoplastic material in the prior art have slow melting and slow flow velocity of the thermoplastic material. A heater module adapted to be used in an apparatus for melting and dispensing thermoplastic material (24), with other like modules for forming a pre-melt and/or a melting stage (31, 32), for heating the thermoplastic material (24). Each module is of uniform construction and includes an elongated core (35) having a plurality of longitudinally spaced first fins (36) projecting from one side of the core (35) and second fins (37) projecting from the other side of the core (35), but longitudinally uniformly staggered from the first fins (36), so that a plurality of parallel modules adjacent to each other will have the recesses (38, 39) between adjacent fins (36, 37) closed by the opposite fins (37, 36) to form longitudinally staggered vertical holes for the fluid passage of the melted thermoplastic material (24). The staggered vertical holes in the heater modules have increased ratio of the heating surfaces to the opening area and thus reduce the melting time and increase the flow velocity of the thermoplastic material.

Description: Heater Module Assembly For An Apparatus For Melting: And Dispensing Thermoplastic Material This invention relates to apparatus for the melting and dispensing of thermoplastic material, and more particularly to a heater module structure for such apparatus. Background Art Apparatus for melting and dispensing thermoplastic material are known in the art, as evidenced by the following U.S. patents: 2,809,772 eisz October 15, 1957 - 3,377,466 Paulsen April 9, 1968 3,531,023 Mercer September 29, 1970 4,009,974 Scholl March 1, 1977 Disclosure of the ' Invention None of the above patents disclose melting receptacles, chambers or grids assembled from a plurality of heater modules, much less the specific heater module structure contemplated by this invention. It is therefore an object of this invention to provide a plurality of uniform heater modules adapted to be arranged side- by-side to form a heating grid assembly for an entire stage in an apparatus for melting and dispensing thermoplastic material. The heater modules may also be arranged in a plurality of vertical stages, with appropriate heating elements and heat sensing elements to provide progressive melting of the thermoplastic plastic material. More specifically, each, heater module m-ide in accordance with this invention includes an elongated body made of thermally con¬ ductive material, including an elongated core having longitudinally spaced first fins projecting from one side of said, core and longi- tudinally spaced second fins projecting from the opposite side of , said core, the second fins being longitudinally staggered relative to the first fins. Thus, when a second module is laid longitudinally parallel to and adjacent a first " module,, each first fin of the second module spans the corresponding space between each adjacent pair of second fins of the first module to close all vertical spaces between the adjacent first and second fins and to provide longitu¬ dinally staggered vertical holes for the fluid passage of the melted thermplastic material. By placing a plurality of the above heater modules side-J side, an entire grid surface may be built up to form a complete heating stage for rapidly melting the thermoplastic material. Furthermore, where progressive stages are desired, such as in the above recited Mercer patent 3,531,023, an assembly of the above heater modules may be utilized in each stage of the melting apparatus by mounting each, assembled stage within a hopper- type housing having a cross-section of the same shape as, but siightly larger than, the cross-section of the assembled stages. Conventional thermoplastic dispensing elements, such as a dispensing head and hose, may be incorporated below the various stages assembled fuom the heater modules, for dispensing the melted thermoplastic material. By the use of the heater modules made in accordance with this invention, various sizes of heating or grid stages may be con- structed, with one or more vertically arranged stages, with a minimum of assembly time and materials. Brief Description of Drawings FIG. 1 is a front elevation of an apparatus for melting and dispensing thermoplastic material, incorporating the heater modules made in accordance with this invention, and with parts broken away and shown in sections; FIG. 2 is a section taken along the line 2-2 of FIG. 1; FIG. 3 is a section taken along the ' line 3-3 . of FIG. 1; FIG. 4 is an enlarged fragmentary section taken along the line 4-4 of FIG. 3; FIG. 5 is a fragmentary section taken along the line 5-5 of FIG. 4; and FIG. 6 is a fragmentary top perspective view of a plurality of heater modules assembled in a pre— elting stage. Best Mode For Carrying Out The Invention Referring now to the drawings in more detail, the apparatus for melting and dispensing thermoplastic material, or "hot melt applicator," 10 has a base or base plate 11 upon which is supported a conduit block 12 in fluid communication with the bottom wall 13 of a hopper-type housing or heater receptacle 14. Mounted on top of the heater receptacle 14, or forming a vertical extension of the walls thereof, ; is a'*hopper 15 for receiving the thermoplastic material 16 in its solid form. A protective casing or jacket 18 may enclose, and be spaced from, the outer surface of the heating receptacle. As shown, the hopper 15 is integral with the jacket 18. A gear pump 20 is driven by motor 21 through sprocket-chain transmission 22 and the driven shaft 23 to move the molten thermo- plastic material 24 through the conduit block 12 into the heated dispensing head 25. Hose 26 conveys the hot thermoplastic material 24 from the dispensing head 25, preferably through a nozzle 27, to a point of discharge. The controls for the apparatus 10 are mounted in the control housing 29 on the outside of the jacket 18. A plurality of heater modules 30, made in accordance with this invention, are assembled within the heating receptacle 14 to provide an upper, or pre-melt, stage 31 and a lower, melting, or progressive melting stage 32. Each module 30 includes an elongated body 34 of thermally con¬ ductive material. Each elongated body 34 includes an elongated substantially rectangular core 35 of substantial height or depth having a plurality of first and second fins 36 and 37 projecting from opposite sides of the core 35. Each of the first and second fins 36 and 37 is a substantially uniform, rectangular cross-section. Moreover, the first fins 36 and the second fins 37 are_uniformly longitudinally spaced apart to form recesses 38 and 39, respectively, of uniform longitudinal dimensions equal to the longitudinal dimen¬ sion of each of the fins 36 and 37. Moreover, the second fins 37 are longitudinally staggered relative to the first fins 36 so that a fin 37 is in lateral alignment with a first recess 38, while each first fin 36 is in lateral alignment with a corresponding second recess 39. As best disclosed in FIGS. 3 and 6, a heating stage is built up by assembly of a plurality of modules 30 longitudinally parallel and adjacent to each other, with the first fins 36 of the second module 30' (FIG. 6) opposite and aligned with a second recess 39 in the first module 30, such that the lateral outer vertical face of the fin 36 closes the recess 39. In a similar manner, the outer vertical face of each fin 37 closes an opposing recess 38. Thus, the closed recesses 38 and 39 form longitudinally staggered verti¬ cal holes, each* hole having a rectangular cross-section, completely enclosed laterally and longitudinally, but vertically vide a fluid passage for the molten thermoplastic material 24. Each module body 34 is heated by a plurality of heating elements 40, such as cartridges or calrod elements received in heating element holes 41 formed in the core 34. One or more of the modules 30, 30' may be provided with a well 42 in its core 34 for receiving a thermal sensing element 43. The heating elements 40 may be connected by electrical leads or wires 44 through an electrical conduit 45 to a heater control device 46. In order to provide space for the heater wires 44, the upper portion of the core 34 may be relieved to form a chamber 47, the upper portion of which may be closed by a cap 48, secured by screws 46. Each group of parallel modules 30. in each stage 31 and 32 may be held in assembled position by the ganging bars 50 at each end of the module 30. The ganging bars 50 may be connected together by the vertical connecting bars 41 and suspended from the upper edge of the hopper 15 by the hanger bars 52. The method of supporting the assembled modules 30 by the hanger bars 52 prevents any fastener members from penetrating the walls of the heater receptacle 14, to eliminate leakage of the very hot molten thermoplastic material 24. The thermal sensing elements 43 for each heating stage 31 and 32 are connected to separate and independent theπnostatic controls, so that the pre-melt stage 31 may be heated to and maintained at a lower temperature than the progressive melt or melting stage 32, as described in the prior U.S. Mercer patent 3,531,023. In the preferred form of the invention, each longitudinal body 34 is made of a monolithic, thermally conductive material, including the core 34 and the fins 36 and 37. The module construction 30 and 30' provides substantial exter¬ ior heat transfer surface by virtue of a plurality of longitudinally spaced vertical fins 36 and 37 projecting from opposite sides of the core 34. Industrial Applicability The function and operation of the apparatus 10 is substantially the same as that of the apparatus described in the prior Mercer patent 3,513,023. By prefabricating a plurality of the uniformly constructed modules 30 and 30', thermoplastic melting devices and apparatus_, . —^=:_^-. may be easily and very quickly and economically assembled, regard¬ less of the number of vertical stages required, and regardless of the transverse size and capacity of the apparatus desired. It has been found ih the actual operation of an apparatus 10 incorporating only a pre-melt stage assembled from the modules 30 that the capacity of the molten thermoplastic material flow was dramatically increased from approximately 136 kilograms per hour to from 363 to 545 kilograms per hour. The top walls 56 and 57 of the respective fins 36 and 37 are sloped, so that they decline laterally from the core 34 to facili¬ tate drainage of the molten thermoplastic material 24 downward into, the corresponding vertical holes 38 and 39, to prevent unwanted accumulation of the thermoplastic material on top of the modules 30 and 30'. It is also within the scope of this invention to provide hori¬ zontal holes in the core 34 to receive heating elements, such as heating elements 40, longitudinally horizontally within the core 34. The monolithic thermally conductive material incorporated in each of the modules may be of an aluminum alloy, such as aluminum alloy No. 202413 or aluminum alloy 6061T6. It has been found that a pre-melt stage 31 or progressive melting stage 32 has been designed which affords a greater ratio of heating surface to the opening areas for the thermoplastic material, thereby reducing the melting time and increasing the flew velocity of the thermoplastic material 24 through the respective melting stages 31 and 32, respectively.

Claims: Claims 1. A heater module assembly adapted to be used in an appara¬ tus for melting and dispensing thermoplastic material, comprising: (a) at least first and second heater modules (30, 30'), (b) each of said heater modules comprising an elongated body (34) of thermally conductive material including an elongated core (35) having longitudinal, transverse, and vertical dimensions, and first and second sides, (c) each of said bodies (34) including longitudinally spaced, vertically disposed, first fins (36) projecting laterally from the first side of each of said correspond¬ ing cores (35), each first fin (36) having exposed heat transfer surfaces and defining a substantially vertical first recess (38) between each pair of adjacent first fins (36), (d) each of said bodies (34) further including longitudi¬ nally spaced, vertically disposed, second fins (37) pro¬ jecting laterally from the second side of each of said cores (35), each second fin (37) having exposed heat transfer surfaces and defining a substantially vertical second recess (39) between each pair of adjacent second fins (37), (e) said first and second heater modules (30, 30'), being arranged so that said corresponding elongated bodies (34) are substantially parallel and adjacent to each other, (f) each first fin (36) of said first body (34) spanning a second recess (39) of said second body (34), and each second fin (37) of said second body (34) spanning a first recess (38) of said first body (34) , so that each of said first recesses (38) on said first body and each of said second recesses (39) on said second body are closed by opposing corresponding fins to form longitudinally stag¬ gered substantially vertical holes through which thermo¬ plastic material is adapted to flow, (g) each of said first fins (36) on said first body having substantially the same longitudinal dimension as a corres¬ ponding second recess (39) on said second body and each of said second fins (37) on said second body having substantially the same longitudinal dimension as a corres- _• " •'" *•** ponding first recess (38) on said first body, and (h) heating means (40) within said bodies (34) for heat¬ ing the exposed heat transfer surfaces of said first and second fins (36,37). 2. The invention according to claim 1 in which each of said first and second fins (36,37) and each of said first and second recesses (38,39) have uniform rectangular cross-sections. 3. The invention according to claim 1 in which said heater module assembly is mounted within a hopper-type housing (14) whose cross-section is substantially the same as, but slightly larger than, the cross-section of said assembly to provide a space between at least one wall of said hopper-type housing (14) and the adjacent vertical surface of said assembly to permit vertical flow of the thermoplastic material between said assembly and said wall of said housing, and means (12) at the bottom of said hopper- type housing for discharging the melted thermoplastic material. - 4. The invention according to claim 3 in which said! heater module assembly constitutes an upper, pre-melting stage (31), and further comprising a second heater module assembly constituting a lower melting stage (32) below said upper stage (31) . 5. The invention according to claim 4 in which the holes in said upper stage (31) are substantially vertically aligned with the holes in said lower stage (32) . 6. The invention according to claim 1 in which each of said first and second fins (36,37) have top walls which decline later¬ ally away from the cores (35) of said corresponding first and second bodies (34).

Inventors: MERCER D
Applicants: MERCER CORP
Application year: 1980
Main classification: F27B14
IPC codes: B05C5, B29B13, F27B14, F27D23