Note: Descriptions are shown in the official language in which they were submitted.
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HOT MELT DISPENSER~
Background of the Invention
This in~ention relates to the art of hot melt
p~mping and dispensing apparatus, and pertains more parti-
cularly to an improved heater construction for such appa-
5 ratus.
The prior art describes a number of hot meltdispensers which liquefy and dispense plastic materials
which are normally solid or semi-solid at room temperature,
and which materials become sufficiently plastic or liquid
at elevated temperatures to permit dispensing directly
from the shipping container or barrel. Commonly, such
devices include an arrangement for lowering a combined
heating element and pump directly into the open end of
the shipping container forliquefying or melting the
plastic material in the region directly below a heated
platen for delivery by pump of the heated and liquified
material to a remote location. Such apparatus is shown,
for example, in the United States patents of Von Haase,
2,522,652 of 1960; Hooker, 3,031,106 of lg62t Weitzel,
2~ 3,113,705 of 1963; Skonberg, 3,282,469 of 1966; Van Riper,
Jr. et al, 3,412,903 of 1968; and McCreary, 3,637,111
o~ 1972.
Commonly, the dispensing apparatus includes a
heated follower plate assembly which supports a pair of
gaskets about its periphery, which carries, supports or
incorporates a pump, and which carries, supports or
- incorporates a heater or heater segments on the bottom
thereof exposed directly to the plastic material within
the container, for liquefying- the plastic material which
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is exposed directly to ~he heater, and for delivery of such
plastic material through suitable passageways to the inlet
of a pump. Either a platform may be provided by means of
which the container is elevated or a mechanism may be pro-
vided by meansiof which the plat~ assembly is lowered intothe container.
Commonly, such heating assemblies are provided with
heating elements which present flat heated surfaces to the
plastic material to be melted. While such apparatus has proven
to be highly useful with material which is readily elevated to
a flowable temperature, and where the demand for such material
is relatively low, such heating elements have proven to be less
than fully effective when applied to material which requires a
higher melt temperature or when applied to installations where
greater flow rates are required, or both.
Hot melt materials which are dispensed by the appa-
ratus of this invention are an extension of the thermoplastic
family of products. Commonly, higher melt index polymers are
being used in blendsO These materials comprise a series of
families including bu*yl rubber, meltable rubbers, and the
"low end" of common polymers such as polyethylene; acrylics,
polypropylene, polyesters, and polyamides. Melt temperatures
can range anywhere from the ambient up through 500 F or more,
with the bulk of applications being in the 250 F to 350 F
range. However, there are many materials which move more
readily by the addition of temperature even though they, in
themselves, are not considered in the hot melt family of
products. In other words, warming the product decreases its
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viscosity and allows it to be handled more readily. A product
which, as an example, would be impossible to pump at 60F., may
very well be the type o product that when elevated to the
temperature of 90F. or so would be a pumpable material.
Characteristics of the p~ped material range from a
sharp melting product through those products which essentially
only change in viscosity having no sharply defined transition
temperature between the "solid" and molten phases. Chemists
blend in many types of additional compounds to provide tackiness,
providing a series of compounds which are considered pressure
sensitive. They behave much like the equivalent materials in
the rubber based families which require the elimination of
solvent for their inherent pressure sensitive characteristics.
Viscosities c~n range anywhere from light syrup through
the butyl family which can be handled at temperatures which
permit, for example, extruding a bead which retains its circular
cross-section as it cools.
Summary of the Invention
One aspect of the invention provides a hot melt pumping
and dispensing apparatus in which a platen carrying a pump and
a plastic material heater is lowered into a barrel of hot melt
material for melting and dispensing the same from the barrel,
the improvement in heater construction comprising a plurality
of sector-shaped heater segments arranged in a circle on said
platen and defining at the common apex a pump inlet opening,
each of said heater segments having a body, a heater element
in said body, and a plurality of depending heat conducting
projections extending downwardly from said body and terminating
substantially at a common plane, said projections defining
therebetween flow passages providing for material flow into said
inlet, said projections being proportioned to extend into said
material in advance of said body to preheat and soften said
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material for liquefaction by said body.
A further aspect of the invention provides a hot
melt pumping and dispensing apparatus in which a platen carrying
a pump and a plastic material heater is lowered into a barrel
of hot melt material for melting and dispensing the same from
the barrel, the improvement in heater construction comprising a
heater body means defining a central pump inlet opening, and
a plurality of integral depending heat conducting projections
extending downwardly from said body means~ said projections
defining therebetween flow passages providing for material flow
into said inlet, said projections being proportioned to extend
into said material in advance of said body means to preheat and
soften said material.
The preferred form of heater construction includes a
plurality of individually cast, direct-heated segments which
are positioned on the support platen or plate generally in a
circular arrangement, and which define the pump inlet opening
at a common apex.
One of the difficultiPs in normally applying heat
to hot melt materials is of applying heaters above the product,
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with the usual arrangements requiring the heat be transferred
through a variety of surfaces into the final product to be
heated. By using cast-in heaters formed in segments, it is
possible to change any one of the segments in the event of
a failure. Also, the radial gaps between the segments can
be controlled to provide flow passageways for transferring
material which is already molten into a centrally-located
pump. Also, the relatively axially thick heater segments
assures that the heat is transferred from the heater elements
to the material, increasing the life of the electric elements.
Each of the cast heater segments is preferably
formed with a plurality of depending, heat-conducting pro-
jections which terminate at a common plane. The projections
precede the main heater body into the material and provide
a greatly increased area for dissipation of heat, so that
the material underlying the heater bodies is preheated and
softened. The projections serve to remove heat ~rom the
body of the heaters directly into the material or product.
The projections further define therebetween a multitude
of flow passages which provide for the flow of melted plastic
material in~ardly into the pump inlet.
In the preferred embodiment, the projections are
formed as solid, vertically~extending substantially cylin-
drical members, each of the same dimensions, and arranged
- 25 in equally spaced relationship from each other on each of
the heater segments. They are formed with axial lengths
which substan~ially exceed their diameters, and are also
formed as an integral portion of the main body o~ the
heater.
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It is accordingly an important object of the inven-
tion to provide a hot melt pumping and dispensing apparatus
incluaing an improved heater construction.
Another important object of the invention is to
~5 provide hot melt pumping apparatus in which a heater is formed
as a plurality of arcuate segments arranged in a circle and
defining at a common apex a heater inlet passage.
A further object of the invention is to provide
a heater, as outlined above, formed with a plurality of de-
pending heat conducting projections which extend downwardly
from the heater body and into the plastic material in advance
of the body, for preheating and softening hot melt material
within a container or the like.
These and other objects and advantages of the inven-
tion will be apparent from the following description, the
accompanying drawings, and the appended claims.
Brief Description of the Drawings
Fig. 1 is an elevational view of hot melt pumping
and dispensing apparatus in accordance with this invention;
Fig~ 2 is an enlarged vertical cross section through
a platen showing the heater elements in elevation, with a
portion thereof being broken away;
Fig. 3 is a bottom plan view of one of the heater
segments; and
Fig. 4 is a top plan view thereof.
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iC~6~!357
.
Description of the Preferred Embodiment
-
Referring first to Fig. 1, the improved hot melt
dispensing apparatus according to this invention includes a
base plate 10 on which are supported a plurality of uprights,
including a pair of upright support cylinders 12 and 14. The
base 10 supports a barrel 15 of hot melt material to be dis-
pensed by the apparatus of this invention.
The cylinders 12 and 14 are supported at their upper
ends at a transfer support 16. Also, a control box 20 may be
supported on the base 10 and support 16 for including the
electrical and temperature-monitoring controls of the dis-
pensing apparatus.
, - A pair of cylinder rods 22 and 24 extend upwardly
respectively from the cylinders 12 and 14. The rods are joined
and connected at their ~tops by a crosshead 25. The crosshead
25 also supports a pump drive motor 26 and a right angle drive
gear box 27.
The crosshead 25 further supports a depending tube
30. A follower plate assembly indicated generally at 32 in
Fig. 1 is carried by the tube 30, and is shown in the raised
or eleva~ed position prior to entering the barrel 15. Air under
pressure may be admitted into the cylinders 12 and 14 to cause
the rods 22 and 24 to extend and lift the crosshead,25 and the
associated structure supported thereon to an elevated or raised
position, as shown in Fig. 1. Similarly, air under pressure
may be applied to the opposite ends of the cylinders 12 and 14
to cause the ~ollower plate assembly 32 to be lowered into the
barrel with a predetermined force'or pressure against material
in the barrel 15.
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Referring to Fig. 2, the follower plate assembly 32
is shown as including a generally cylindrical bottom plate 40
on which is mounted a cylindrical body 42, which supports a
cover plate 43. The body 42 is formed with a pair of pexipheral
grooves which respectively support a pair of hollow elastomer
seals 45. The seals 45 engage the in~ide walls of the barrel 15
and provide a fluid-tight seal therewith. The support tube 30
is joined to the assembly 32 by a flange 46 and an annular
spacer 47. The spacer 47 preferably receives a gear-type
positive displacement cartrid~e type pump 48. The pump 48 is
directly driven by the motor 26 and the drive 27 through a
drive shaft 50 within the tube 30, as coupled by a universal
joint 52.
There are supported on the lower surface of the
plate 40 a plurality of essentially identical sector-shaped
heater segments 60 as shown in Figs. 3 and 4. Each heater
segment 60 is formed with a curved outer peripheral wall 62,
generally radially extending sides 64 and a truncated apex
65. Each heater segment 60 is preferably formed of cast
aluminum and incorporates a cast-in heating element 68 as-
shown in broken view in Fig. 2. The electrical terminals 69
extend upwardly through access openings 70 formed in the
follower plate. Bolts 72 extend downwardly through the
follower plate into the body of the heater segments 60 for
securing the segments in underlying relation to the bottom
plate 40.
The individual heater segments 60 are arranged
side-by-side in a circle on the plate 40, and define at a
common apex formed by the truncated surfaces 65 at a central
pump inlet opening 75 as shown in Fig. 2. Narrow radial flow
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passages 76 are defined between the adjacent walls 64 of the
heater segments. In the embodiment shown, six heater segments
60 are employed as subtending an approximate arc of 30. ~ow-
ever, it is within the scope of this invention to arrange the
heater into a fewer or greater number of sector-shaped heaters.
The lower heat conducting surfaces of the heater
segments 60 are preferably formed with a pluralit~ of depending,
integral heat conducting projections 80. In the embodiment
shown, the projections 80 are all the same diameter, and are
generally cylindrical in shape, but may be formed as tapered
cones with about a 1-1/2 taper wider at their bases when
ioined with the segments 60 than at their tips 82. The tips
of the projections preferably terminate at a common plane and
are ar~anged in a regular grid or pattern as shown in Fig. 3
to define therebetween a multitude of flow passages. The
generally cylindrical pin-shaped projections provide a heating
area which is greatly increased over ~he planar area which
would otherwise be presented to the plastic material and may
extend a depth of approximately 2", for example, below the
surface of the heater body itself. The pins or projections 80
thus precede the main bodies of the segments ~0 and extend
into the plastic material in advance to preheat and soften
the plastic material for flow therebetween and flow through
the radial passages 76 into the central inlet ~pace 75 and from
there into the inlet of the pump 48. The pump outlet opens
into a fitting 90 to which a tube 92 (Fig. 1) is attached fox
delivery of the hot melt material to a remote location.
The segmented heater construction of the present
invention has been found substantiallyto increase the capacity
of the dispensing apparatus. For example, when a follower plate
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assembly 32 of 22" in diameter is provided by this invention
with 738 pins 2" long, a heating surface of approximately
2,400 square inches is formed. The employment of the pins
provides a seven to eight times increase in effective area
over that of a simple or flat annular heating plate of the
same diameter. A 27,000 watt heater constructed according
to this invention can provide a flow rate for example, of
10 gallons per minute. However, the flow rate is, itself,
a function of many factors including the specific heat of
the material and the ability of the material to conduct energy.
Preferably, the projections 80 are each formed of the same
diameter and are arranged in sustantially equal spacing from
each other and for an axial length which substantially exceeds
their diameter.
While the preferred embodiment as shown and des-
cribed herein incorporates a plurality of generally cylindrically
shaped depending pins 82, it is to be understood that in the
broader aspects of the invention, the pins may be eliminated
and suitable heating channels or grooves formed in place
thereof, or a flat lower surface may be provided for the seg-
ments 60. The individual segments 60 permit ease of maintenance
by removal and replacement of any one segment which has become
inoperative. Further, by controlling the arcuate widths of
the segments, the capacity of the radial channels or passages
76 may be controlled or varied, and the depth of such passages
also be varied, to accommodate a quantity of the liquefied
material for delivery to the inlet of the pump ~8. It will
also be noted that the principal body of the heater seyment 60
is relatively deep, as shown in Fig. 2, providing a mass of
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aluminum for conduction of heat from the heating element 68
for the protection of the heatirlg element. The increased
surface such as provided by the pins 82 assures constant
direction of energy flow from the element into the underlying
material within the barrel 15.
While the form of apparatus herein describe con-
stitutes a preferred embodiment of this invention, it is
to be understood that the invention is not limited to this
precise form of apparatus, and that changes may be made
therein without departing from the scope of the invention.
