U.S. patent number 3,812,323 [Application Number 05/303,573] was granted by the patent office on 1974-05-21 for electrical heating bands for a feeding system.
This patent grant is currently assigned to Ford Motor Company. Invention is credited to Frank A. Pink.
United States Patent |
3,812,323 |
Pink |
May 21, 1974 |
ELECTRICAL HEATING BANDS FOR A FEEDING SYSTEM
Abstract
Heating bands and cartridge heaters, adapted to be mounted about
cylindrical chambers, manifolds and nozzles conveying heated
plastic from a feeding system to a molding assembly, are arranged
so that spacing between heated elements of the bands can be
increased or decreased depending upon whether one or more of the
elements is energized. The bands are comprised of dual or multiple
wound coils to provide fail-safe operation for the nozzles in the
event one of the coils should be inoperative. A useful method to
achieve the multiple winding is to first generate at least a dual
threaded geometric, and then lay insulated conductors in the
groovings between windings so that strands of independent coils are
in parallel side-by-side relation throughout.
Inventors: |
Pink; Frank A. (Ann Arbor,
MI) |
Assignee: |
Ford Motor Company (Dearborn,
MI)
|
Family
ID: |
23172712 |
Appl.
No.: |
05/303,573 |
Filed: |
November 3, 1972 |
Current U.S.
Class: |
219/535; 219/530;
219/486; 219/521; 219/537 |
Current CPC
Class: |
B29C
45/2737 (20130101); H05B 3/00 (20130101); H05B
3/16 (20130101); B29B 13/022 (20130101); H05B
3/56 (20130101); H05B 3/565 (20130101); B29C
2045/2754 (20130101); B29C 45/78 (20130101) |
Current International
Class: |
B29B
13/02 (20060101); B29C 45/27 (20060101); B29B
13/00 (20060101); H05B 3/58 (20060101); H05B
3/54 (20060101); H05B 3/16 (20060101); H05B
3/00 (20060101); B29C 45/78 (20060101); H05b
003/58 () |
Field of
Search: |
;219/417,421,422,426,430,433,436,441,486,487,521,530,535
;425/378,379 ;222/146HE ;264/102 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Mayewsky; Volodymyr Y.
Attorney, Agent or Firm: Malleck; Joseph W. Zerschling;
Keith L.
Claims
1. In an injection molding machine, having a runnerless molding
assembly and a heated feeding system, said feeding system having
legs of heat conductive material and channel therein for
thermoplastic material and interconnecting an injection means with
a plurality of nozzles of heat conductive material communicating
with the molding assembly, the improvement comprising a heating
apparatus for the nozzles of said feeding system:
a. a plurality of electrical heating strands insulated one from the
other and placed in adjacent side-by-side relation and wound to
form a single layered annular shape while in said side-by-side
relation, said winding surrounding at least one nozzle of said
feeding system,
b. electric circuit means for independently energizing said heating
strands and selectively effective to energize less than all of said
strands at any one time, and
2. The apparatus of claim 1, in which said circuit means is
arranged so that said heating strands within a winding are
energized in independent groups, said groups being arranged so that
strands alternate in the
3. The apparatus as in claim 2, in which each strand extends
substantially throughout the zone of effectiveness of said heating
apparatus so that in the event of failure of one of the groups of
heating strands, at least one
4. An apparatus as in claim 1, in which said heating apparatus
comprises strands arranged in a pattern to form a sleeve with
independent strands interleaved so that each strand traverses the
same zone of the sleeve as the other strands whereby failure of one
strand does not destroy the
5. An apparatus as in claim 3, in which the spacing between
adjacent strands within the winding is no greater than five times
the transverse
6. The apparatus as in claim 1, in which said strands are arranged
in groups independently energized and control means effective to
add to or subtract from those groups being energized to increase or
decrease the spacing between adjacent strands and thereby promote
uniform heating
7. The apparatus as in claim 2, in which the strands are wound in a
helix
8. The apparatus as in claim 2, in which the strands are wound
toroidally
9. The apparatus as in claim 1, in which said circuit means further
comprises control means for independently varying the voltage
applied to said strands, and switch means for providing a staged
heat-up sequence whereby one or more of the strands may be
simultaneously energized at different voltage levels to effect a
desired heating condition.
Description
BACKGROUND OF THE INVENTION
This invention relates to the dispensing of viscous material, such
as thermoplastic, and particularly to an apparatus for maintaining
the material in a heated condition while being supplied to a
molding assembly. In the past, radiant heating has been used to
heat flow channels conveying thermoplastic material, the heat being
radiated from coils supplied uniformly with three-phase electrical
power to all coils. Each coil was independently defined but not
independently powered; by that it is meant that each electrical
strand is defined as a single coil wound in either a serpentine or
helical configuration with no other electrical heating strands
interposed between the beginning and ending of such strand.
Premature failure of one of the coils would leave large unheated
zones. This is a particularly troublesome problem in that the
relative value of the heating element itself is small in comparison
to the resulting economic detriment caused by the downtime of a
press worth considerable in excess of the heating element
itself.
One prior art approach to solving the premature failure of a
heating element is to stagger the separate heating elements in
bands and to divide energization of the plurality of electrical
bands in at least two groups, each group having its own separate
power supply. The hope being that in the event of failure of one of
the power supplies or bands there is another group of bands which
can continue to operate. However, it has become apparent through
experience that uniform heating of the viscous material by radiant
means cannot tolerate very wide gaps between the radiant energy
elements without detrimentally effecting the viscous material
itself.
Thus many injection molding shops have attempted to compensate for
the irregular and discontinuous type of heating resulting from an
operational failure in one electrical line, by increasing either
pressure or prolonging the time dwell of the material within the
flow channels. However, the increase in pressure or the increase in
time has lead to many typical types of molding defects as well as
excessive wear and premature failure of the molding assembly.
Still another problem is the inflexibility of varying the spacing
between strands of the radiant heating elements in order to meet
the needs of various stages of the injection molding process. For
example, during the initial heat-up period, the demand for thermal
energy is very high and the closer spacing of the electrical
strands in a specific winding would be desired. Unfortunately, as
certain elevated temperature levels are reached, excessive
operating temperatures occur at the central region of an
independent winding as opposed to the somewhat lower temperatures
occurring at the extremeties of the winding. It has been proposed
in the art that a plurality of consecutive fixed windings should be
arranged to comprise a heating band and at the central region of a
band the windings would be more widely separated and spaced so as
to alleviate this nonuniform condition. However, this sacrifices
uniformity in the rapid-heat up stage.
SUMMARY OF THE INVENTION
The principal object of this invention is to provide a more
effective heating sleeve which may be disposed about one or more
portions of a heated feeding system, the latter being used for
introducing viscous material to the mold of an injection molding
device. The heating sleeve has electrical resistance elements wound
in a pattern with independently energized elements closely
interleaved so that each traverses substantially the same zone as
the other elements whereby failure of at least one of the elements
does not cripple the operating capability of the entire sleeve.
Another object is to provide a unique disposition of independently
energized heating strands coupled with control means for effective
staged heating as well as a capability for selective spacing
between commonly energized strands.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a heated feeding system adapted for
conveying viscous thermoplastic material;
FIG. 2 is a schematic view illustrating a typical power supply
arrangement for the heated feeding system of FIG. 1;
FIG. 3 is one embodiment of one heating sleeve or band adapted for
placement about a portion of the system of FIG. 1; and
FIG. 4 is another embodiment of a heating band adapted for use
similar to the embodiment of FIG. 3.
DETAILED DESCRIPTION
Referring now to the drawings and initially to FIG. 1, a feed
system 10 is illustrated useful in acting as a heated conveyance
for viscous material, such as thermoplastic, to be communicated
between the entrance 9 of a manifold A and the exit portion 8 of
the plurality of nozzles B. The manifold A receives thermoplastic
material from an injection cylinder and delivers the thermoplastic
to six stations at the mouth of a mold cavity of a conventional
molding assembly (not shown). The system 10 of FIG. 1 can be
characterized as runnerless molding in that conventional runners,
usually defined in the molding die block and fed from a single
source, are eliminated; instead, a plurality of heated nozzles
communicate directly with the gate or mouth of the molding die
block. The runnerless molding approach has the advantage of
eliminating scrap losses and time delays due to reclaiming the
scrap.
The feeding system here particularly comprises the manifold A
having an H configuration with the legs 12 and 13 of the H
interconnected by a cross member 11. The manifold is formed of a
heat-conductive material such as low carbon steel and contains a
central channel 14 (see FIG. 2) in each of the legs and member,
effective to convey the viscous material from the entrance 9 to the
various nozzles B. The legs and cross member each are maintained in
a heated condition by means D having resistance elements 28 and 29
insulated at 7 embedded in the walls thereof and independently
energized. The elements 28 and 29 are continuous and extend
throughout the side walls of the manifold; the elements are sized
to impart a considerable quantity of heat.
Each of the nozzles B (here six in number; 5, 15, 16, 17, 18 and
19) comprise a cylindrical body of heat conductive material having
a central channel 20 defined therein adapted to communicate with
the riser 6 leading from the channel 14. Each nozzle has a flat
exit face 21 adapted to mate with the complimentary surface of a
molding assembly for maintaining a tight seal therebetween.
The improved heating apparatus herein comprises a plurality of
heating sleeves or bands, 22, 23, 24, 25, 26 and 27 adapted to be
mounted as a group on one and each of the nozzles; the bands are
arranged at spaced locations along the axis of the nozzle for
imparting radiant heat to the nozzle and thence to the viscous
material to maintain a selected temperature in material. Each
sleeve or band (see FIG. 3) has at least two electrically
conductive strands 31 and 32 wound to form a single layered
configuration having the independent strands 31 and 32 interleaved
and in side-by-side relationship throughout the configuration.
Circuit means E is connected to the extremeties of the strands 31a,
31b, 32a, 32b so as to selectively and independently energize each
of said strands. Each strand extends substantially throughout the
entire zone of heating to be affected by each sleeve on each
nozzle. It is important that the spacing 33 between adjacent
independent strands be no greater than about five times the
transverse dimension of a strand.
Circuit means E is here preferably shown to comprise two
independent circuits, circuit 40 being commonly connected to
certain strands in all of the bands and circuit 41 being commonly
connected to other strands in all of the bands. In the event of
failure of one of the circuits, the failed circuit can be shut down
leaving the other strands operable in each of the heating sleeves
to maintain uniform heating unattainable by the prior art.
To enable the heated feeding system to provide a staged heat-up
sequence, the circuit means E has a variable voltage control
connected in each circuit for selectively allowing for initially
ultra-high voltage to obtain a rapid heat input and at controlled
points the voltage can be reduced to maintain uniform temperature
levels. In addition, each heating sleeve may be arranged with
several strands acting in groups, each group commonly energized
with strands of each group interleaved in sequence. For example,
group one may have strands one and four, group two has strands two
and five, and group three has strands three and six. When wound,
the strands are arranged in side-by-side relation and in the
sequence of one-two-three-four-five-six. Thus spacing between
heated strands may be varied. If all groups are energized, a
condition may be reached when excessive heat is generated in the
central region of the sleeve. To correct this, one of the groups
may be deenergized or reduced in current to equal a larger unheated
air space between remaining energized groups. Alternatively, one of
the groups may be relatively short and located only at the central
region of the sleeve; thus deenergization of this one group will
have a more direct effect on only the central region.
Various winding arrangements can also be achieved within the
framework of this invention. In FIG. 3, the interleaved strands are
wound in a helical pattern about the axis 34 of the sleeve. In FIG.
4, the strand group is wound in a toroidal pattern about the axis
34.
A method for fabricating the winding of a sleeve comprises:
a. Providing a double (or multiple) threaded geometric generation
on the periphery of a fixture; continuous adjacent grooves will
result as provided by the threads;
b. Insert an independent continuous insulated electrical conductor
in each groove of the generation;
c. Bind the winding in the configuration thus assumed in the
generation by such means as a suitable supporting wrap 35 having
one location 36 where the extremeties of the conductors may extend
through and beyond for connection to a power source;
d. Collapse the fixture and remove from the winding without
disturbing the winding configuration.
As alternative embodiments to the heating bands illustrated in
FIGS. 3 and 4, the inventive winding can be utilized in cartridge
heaters adapted to be immersed within the viscous plastic rather
than surround a chamber, manifold or nozzle as previously
disclosed.
* * * * *