Method and apparatus for balancing the filling of injection molds

A method of balancing the flow of a molten polymer containing material in a multi-runner injection mold includes the step of providing a mold body having at least one mold cavity and at least two runners. The first runner includes first and second ends and is connected to a source of molten material. The first runner is connected to a second runner. The second runner is connected to the at least one mold cavity. A stream of a molten polymer containing material flows through the first and second runners. The stream is repositioned in a circumferential direction as it flows from the first runner through the second runner while maintaining continuity between laminates of the stream of the molten material in a radial direction. In this way, a balance is provided for the melt temperatures and material properties of the cross branching runners. An apparatus for producing molded products having balanced thermal, material and flow properties includes a device for repositioning a stream of the molten polymer containing material as it flows from a first runner into at least a second downstream runner. If desired, the stream of molten thermoplastic material can be repositioned by approximately 90 degrees.

BACKGROUND OF INVENTION 
This invention relates to a method and apparatus for flowing a stream of 
laminar flowing material into a mold having at least one runner branch, 
branching in at least two directions. More specifically, the present 
invention pertains to a method and apparatus for repositioning the 
non-symmetrical conditions of the flowing material to a desired position 
in a circumferential direction while maintaining continuity between 
laminates from the center through to the perimeter of the runner. 
A conventional mold set for injection or transfer molding of laminar 
flowing polymer containing materials is constructed of high strength 
metals, usually tool steels having a very high compressive yield strength. 
A molded part is formed within a mold cavity. The mold cavity opens and 
closes during each molding cycle along a parting line in order to remove, 
or eject, the molded part. The material producing the molded part is fed 
from a material source to the cavity through a runner system. Often, 
several spaced mold cavities are defined in the mold. These cavities are 
each connected to a material source through a runner. Runners may include 
branches. A branch may occur at the end of a first runner section and 
would intersect at some angle relative to the first runner section. The 
angled branching second runner section may extend in one or more 
directions from its intersection with the first runner section. 
Non-symmetrical conditions are developed in a runner, flowing a stream of 
laminar flowing material, when a runner branch branches in at least two 
direction from the intersection with the first runner section. Branching 
may continue at the end of any number of progressively branching runner 
sections. 
In multi-cavity molds, it is important that the material is delivered to 
each cavity of the mold at the same time and with the same pressure and 
temperature. Any variations in these conditions will result in variations 
in the parts which are produced within these cavities. Such variations can 
include the size, shape or weight of the product as well as the mechanical 
properties and cosmetic appearance of the product. To help assure balanced 
conditions, the length and diameter of the runner feeding each cavity in a 
multi-cavity mold is preferably kept the same. This usually results in the 
runners being laid out in either a radial pattern, a branching "H" 
pattern, or some combination of a radial and a branching "H" pattern. With 
the radial pattern, the melt travels radially outwardly from the material 
source directly feeding a single cavity. Variations of this may branch the 
end of each runner section and feed two or more cavities. With an "H" type 
pattern, the runner is continually split in two directions at the end of a 
given section. In some cases a radial pattern can be placed at the end of 
a branching "H" patterned runner. 
When molding parts using multi-cavity molds, it is important that each 
cavity in the multi-cavity mold produce substantially identical parts. 
This results in consistent part quality and maximum productivity. In order 
to provide such a mold, the cavity dimensions must by nearly identical for 
each of the several cavities and the cooling and delivery of the flowing 
material to each cavity should be substantially the same. It is, 
therefore, standard practice in the design of multi-cavity molds to 
"naturally balance" the runner system in order to help provide the 
required mold filling consistency. In naturally balanced runners, the same 
cross sectional shape and length of runner feeds each cavity. The same 
concept of a natural, or geometrically, balanced runner system may also be 
applied to multiple runner branches which may be feeding a single part at 
multiple locations. 
Most multi-cavity injection or transfer molds are designed with a naturally 
balanced or geometrically balanced runner system in order to minimize 
variations in the material flowing into the cavities during production. 
Despite the geometrical balance, it has often been observed that the 
filling of molds utilizing these naturally balanced runner designs result 
in imbalances. In most case, such imbalances have not been recognized 
until there are more than four cavities in the mold. However, the 
imbalance is actually dependent on the number of branches in the runner 
and can even affect a part molded in a single multi-gated cavity, 
dependent on the layout of the runner system. It has been found that the 
parts formed in some of the cavities, usually those on the inside branches 
closest to the material source, are commonly larger and heavier than are 
the parts formed in the other cavities. 
These flow imbalances have historically been attributed to variations in 
mold temperature and/or mold deflection. Applicant has identified that 
there is a flow-induced cavity filling imbalance which exists in many of 
the most commonly used and accepted "naturally balanced" runner designs 
such as geometrically balanced "H" and modified "H" patterned runners, 
especially those with eight or more cavities. The flow imbalance can be 
created by a non-symmetrical shear distribution within a laminar flowing 
material as it travels through the runner system. Flow imbalance can also 
be created in a runner channel when a laminar flow material has a 
non-symmetrical temperature distribution created either by localized shear 
or differences in temperature between the flowing material and the runner 
wall. Both of these non-symmetrical conditions can result in variations in 
the viscosity of the flowing material and, in some cases, in its 
structure. In most cases, during conventional molding of thermoplastic and 
thermosetting materials, the result is a high sheared hotter, lower 
viscosity material around the inner periphery of the runner channel 
surrounding a relatively low sheared cooler, higher viscosity material in 
the middle of the runner channel. As flow is laminar, when a branch in the 
runner occurs, the high sheared hotter material along the perimeter 
remains in its relative outer position while the inner material is split 
and is now positioned on the opposite side of the flow channel from the 
high sheared hotter material. This side to side variation will create a 
variation between upcoming side to side branching runners, or a mold 
cavity, where the high sheared hotter material will flow to one side and 
the low sheared cooler material will flow to the other side. 
Attention in this regard is directed to the article by Beaumont and Young 
in the Journal of Injection Molding Technology, September 1997, Volume 1, 
No. 3 entitled "Mold Filling Imbalances in Geometrically Balanced Runner 
Systems" (pages 133-143). This article is incorporated herein by reference 
in its entirety. 
The problem has become more evident in recent years as tolerances of molded 
plastic parts have become more demanding and attention to quality has 
increased. The trend toward the use of smaller diameter runners, which it 
was thought would improve the molding process, has compounded the problem. 
Attention is also directed to the article by Beaumont, Young and Jaworski 
entitled "Solving Mold Filling Imbalances in Multi-Cavity Injection Molds" 
found in the Journal of Injection Molding Technology, June 1998, Volume 2, 
No. 2, pages 47-58. This article is also incorporated herein by reference 
in its entirety. 
The imbalance found in a multi-cavity mold can be significant, resulting in 
mass-volume, flow-rate variations between the cavities of as high as 19--1 
in extreme cases. The magnitude of the imbalance is material-dependent as 
is the sensitivity of the imbalance to process. A variety of different 
types of thermoplastics, including amorphous and semi-crystalline 
engineering and commodity resins, have been shown to exhibit significant 
mold filling imbalances in branching runner molds. 
While the majority of the description herein will refer to thermoplastic 
materials, it should be recognized that imbalanced conditions can occur in 
any mold with a branching runner, branching in at least two directions, in 
which a variety or types of fluid can flow. Such imbalances occur for any 
fluid exhibiting a) laminar flow and b) viscosity which is affected by 
shear rate (as with a non-Newtonian fluid) and/or by temperature c) 
characteristics where variations in shear or flow velocity across a flow 
channel will create variations in the materials characteristics. Both of 
these characteristics are typical of thermoplastics, thermosetting 
materials and many of today's powdered metal and powdered ceramic molding 
materials. A polymer carrier is often employed with powdered metals and 
powdered ceramics. It is the polymer which gives such powdered metal or 
powdered ceramic materials the same characteristics as plastic materials 
exhibit in regards to viscosity effects and laminar flow. 
The traditional methods of balancing flow in multi-cavity molds by 
restricting high flow runner branches or gates, cannot be expected to 
provide both a pressure and a thermal balance in the flowing material. 
Even if a pressure balance can be achieved, a melt temperature variation 
between the several cavities remains. Additionally the balance achieved by 
this means is very sensitive to material and process changes. 
The ability of this invention to control the position of the asymmetric 
material conditions not only can be used to balance flow in runner 
branches but can be used to control the asymmetric material conditions 
flowing into a part forming mold cavity. Many of the properties of the 
molded part can be influenced by conditions of the melt from which it is 
formed. Some of these include how the molded part will shrink, warp, its 
mechanical properties and its appearance. With an understanding that a 
part might warp as a result of temperature variations, the asymmetric 
temperature across the laminar flowing material entering the cavity, 
through a runner and gate, could be positioned to control this warpage. 
With thermoplastic materials which will commonly warp towards a hot side 
of a mold, the asymmetric laminar flowing material could be positioned 
such that the hotter melt entering the cavity be placed along the cooler 
mold half. This could potentially offset the mold temperature variations. 
A similar principle could be applied to address effects of part geometry 
on warpage or some other need to control distribution of other material 
properties which might be affected by the shear and temperature 
variations. 
Flow diverters have been used to change the flow patterns in laminar 
flowing material. One known device of this type is illustrated in U.S. 
Pat. No. 5,683,731 of Deardurff et al. This device contains a central flow 
channel and a plurality of diverters. The device is positioned in a melt 
stream. Melt from some portion of the inner laminates of the melt stream 
is fed into a central flow channel and melt from some portion of the outer 
laminates of the melt stream is fed into a plurality of diverters which 
are adjacent to the central flow channel. The melts from the two flow 
paths are later recombined such that the material from each of these flow 
regions is distributed equally between the plurality of flow channels. 
However, in Deardurff et al., the inner and outer laminates of the flow 
channel are separated and recombined. This results in a more complicated 
and expensive device than what is necessary. Moreover, Dearduff's device 
would not be practical in a runner system which solidifies and is ejected 
from the molding process during each cycle as the device would become 
molded into the runner and ejected from the mold. Therefore, Deardurff's 
devise is limited to hot runner, or non solidifying runner, applications 
where the plastic in the runner does not solidify and is not ejected from 
the mold. 
In addition, Deardurff's device is relatively complex and requires 
consideration of the relative sizes and shapes of the central flow channel 
and the diverter. The sizes and shapes of these channels will dictate a) 
how much of the outer laminates will be repositioned relative to the 
central flow channel b) where they will be positioned and c) their 
distribution relative to each other. Also, any changes in material or 
process may alter the distribution of the melt between the central and 
diverter channels. Furthermore, Deardurff's device accomplishes its 
objective by selectively diverting some portion of the outer laminates and 
distributing them among a plurality of channels. The disadvantage of this 
design is that it can only selectively rearrange the melt across the flow 
channel in two distinct inner and outer regions. This limits the 
contribution of this devise as the variation across a melt channel is 
continuous and complicated by the fact that the change in the materials 
conditions across the flow channel are not normally linear. Achieving a 
continuous redistribution of melt is not possible with a device which 
selectively separates the laminates into two distinct regions, namely the 
inner and outer regions. 
Other known diverters are equally disadvantageous. None of these devices is 
capable of repositioning the laminates in a melt in a circumferential 
direction while maintaining continuity between the laminates in a radial 
direction. 
Additionally, the division of the flow channel into a multitude of flow 
channels, i.e. the central channel and the several diverter channels in 
the known devices creates a potentially significant pressure loss--as 
pressure drop is approximately a function of the radius of a round flow 
channel to its fourth power--due to the resultant smaller channels. The 
alternative is to significantly increase the cross section of all the flow 
channels in order to alleviate the high pressure loss resulting from the 
smaller flow channels which significantly complicates the construction of 
such a mold. 
Accordingly, it has been considered desirable to develop a new and improved 
process and apparatus for controlling flow in runners which would overcome 
the foregoing shortcomings and others while providing better and more 
advantages overall results. 
BRIEF SUMMARY OF THE INVENTION 
In accordance with the present invention, a new method and a new mold 
structure are provided for controlling mold filling. Mold filling is 
controlled in a mold having at least one runner which branches in two 
directions by controlling the position of non-symmetrical conditions of 
concentric laminates which occur across the flow path of a stream of 
laminar flowing material. 
More particularly, in accordance with the method and mold structure of this 
invention, a mold body is provided having at least one mold cavity and a 
runner having at least one branch which branches in two directions. The 
runner includes at least a first runner section which intersects a second 
runner section. In some applications of this invention another portion of 
the runner branches in two directions and the second runner section 
branches in one direction, while in other applications it is the second 
runner which branches in two directions. 
During a molding cycle a stream of laminar flowing material is flowed in 
the runner. The laminar flowing material has non-symmetrical conditions 
which occur in a direction across its path downstream of a branch in the 
runner where the first runner section intersects the second runner 
section. In accordance with this invention, these non-symmetrical 
conditions are repositioned to a desired position in a circumferential 
direction around the center of the path of the runner, while continuity is 
maintained between the laminates from about the center through to the 
perimeter of the runner. 
More particularly, in accordance with one aspect of this invention, the 
non-symmetrical conditions of the laminar flowing material are 
repositioned by a laminate repositioner which is located in at least a 
portion of the runner. The laminate repositioner has a structure which 
determines both the amount and the direction of circumferential 
repositioning of the non-symmetrical conditions which occur. 
In accordance with another aspect of this invention, the first runner 
section intersects the second runner section at an angle, and the laminate 
repositioner includes the intersection between these runner sections. The 
second runner section may branch at this intersection in one direction or 
it may branch in two directions through extensions in a first direction 
and in a second direction from the intersection by the first runner 
section. The first runner section may intersect the second runner section 
at a 90 degree angle or at any other angle which causes the desired 
repositioning of the non-symmetrical conditions. When branching extensions 
of the second runner section are not in a straight line with one another, 
the first runner section intersects each of them at an angle other than 90 
degrees. This angle is also chosen to affect the amount of repositioning 
of the non-symmetrical conditions of the laminar flowing material. 
In many applications of this invention, the runner includes a third runner 
section which is intersected by an end of the second runner section 
located in the first direction. The runner also includes a fourth runner 
section which is intersected by an end of the second runner located in the 
second direction. The laminate repositioner repositions the 
non-symmetrical conditions of the laminar flowing material to a position, 
in a circumferential direction about the center of the path of the second 
runner, which is substantially symmetrical from side-to-side relative to 
the third runner section and the fourth runner section. As a result, the 
normal imbalance of flow through the third runner section and the fourth 
runner section is significantly improved. 
In still other applications of this invention, the repositioning of the 
non-symmetrical conditions is to a position, in a circumferential 
direction around the center of the path of the second runner section, 
which causes the non-symmetrical conditions to be distributed in a desired 
manner within the mold cavity. For certain applications of this invention 
it is advantageous to reposition the non-symmetrical conditions of the 
laminate flowing material approximately 90 degrees. For other applications 
of this invention it is advantageous to reposition the non-symmetrical 
conditions at some other angle to obtain the desired fill of one or more 
mold cavities. 
In one embodiment of this invention the laminate repositioner uses at least 
one length of runner having a spiraling circumference with a non-circular 
cross sectional shape, which is progressively repositioned along each 
length of runner, to reposition the non-symmetrical conditions of the 
laminar flowing material. In another embodiment of this invention the 
laminate repositioner includes, in the runner, a dividing member having a 
spiraling shape which divides the cross section of the runner 
substantially in half along a radial direction. In either embodiment the 
amount of repositioning of the non-symmetrical conditions is at an angle 
of less than 180 degrees. 
This invention can be used with many types of molds. Certain embodiments of 
this invention are particularly useful with molds of a type in which the 
laminate flowing material solidifies in the runner of the mold during each 
molding cycle and thereafter is removed from the runner prior to the 
completion of the molding cycle. One such embodiment of this invention can 
be applied to a mold of this type which has a pair of mold plates and a 
parting line between these plates which opens and closes during a normal 
molding cycle. The laminate repositioner includes a first runner section 
of the runner and a second runner section of the runner which are located 
along the parting line, with the first runner section intersecting the 
second runner section at an angle. The intersection occurs at an area on 
the periphery of the second runner section at which the centerline of the 
second runner section and the centerline of the intersecting first runner 
section are at different elevations from one another. At the area of 
intersection the laminar flowing material flows in a direction between the 
different elevations of these centerlines which is not the same direction 
as the flow in either the first runner section or the second runner 
section. 
In this embodiment of this invention, the amount of change in elevation 
between the first runner section and the second runner section can be 
selected to affect the amount of repositioning of the non-symmetrical 
conditions which occurs. Alternatively, the angle of the direction of flow 
of the laminar flowing material between the centerlines of the first and 
second runner sections can be selected to affect the amount of 
repositioning of the non-symmetrical conditions. Another alternative is to 
choose the angle of intersection of the first runner section with the 
second runner section to affect the amount of repositioning of the 
non-symmetrical conditions. The structure of this laminate repositioner 
can take many forms, some of which are shown and described below. 
This invention does not reside in any one of the features of the method and 
mold structure disclosed above which are more fully discussed in the 
Description of the Preferred Embodiment and claimed below. Rather, this 
invention is distinguished from the period art by its combination of 
structural features which make up a unique method and mold structure. 
Important features of this invention are shown and described below to 
illustrate the best mode contemplated to date of carrying out this 
invention. 
Those skilled in the art will realize that this invention is capable of 
embodiments which are different from those shown and that the details of 
the method and mold structure can be changed in various manners without 
departing from the scope of this invention. Accordingly, the drawings and 
description are to be regarded as illustrative in nature and are not to 
restrict the scope of the invention. Additionally, the claims are to be 
regarded as including such equivalent methods and mold structures as do 
not depart from the nature and scope of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While this invention is generally related to a means for improving the 
balance between runner branches in a multi-cavity mold by rearranging the 
non-symmetrical conditions of a laminar flowing material in the runner of 
a mold to provide symmetry to a downstream branch, the means for 
rearranging a melt can also be employed to control the non-symmetrical 
conditions entering a mold cavity through a branching runner and thereby 
control the molded parts final characteristics. The runners can either be 
hot runners or cold runners. 
During molding, where cavities in a mold are fed by a conventionally 
geometrically balanced H-type, or modified H-type branching runner, a 
separation of the high shear and low shear laminar flowing material will 
occur. This has been described above. However, such variation can take 
place in runners which exhibit patterns other than the H pattern, such as 
, for example, a radial pattern or combinations of radial and H patterns. 
It is not always the case that the high sheared hotter material, which is 
normally near the outer laminates of the flow channel, ends up in cavities 
which are fed by the outer branching runners which are closest to the 
point of injection. The final point of destination relative to the point 
of injection is dependent on runner layout. FIG. 1 illustrates a-runner 
layout where the normally high sheared hotter laminar flowing material 
ends up in the outer cavities and the normally low sheared cooler material 
ends up in the inner cavities. More specifically, in FIG. 1, the laminar 
flowing material initially travels in a mold 10 along a first runner 
section 12. At the end of the first runner section, the material takes a 
90 degree turn and splits in opposite directions as it flows into a second 
runner section 14. At the first end of the-second runner section 14, the 
laminar flowing material flows into a first tertiary runner 16 which feeds 
a first mold cavity 18 and a second mold cavity 20. At the second end of 
the second runner section, the laminar flowing material flows into a 
second tertiary runner 22 which feeds a third cavity 24 and a fourth 
cavity 26. The layout illustrated in FIG. 1 is such that the high sheared 
hotter laminar flowing material is expected to end up in cavities 18 and 
26 which are further from the point of injection than are cavities 20 and 
24 as this is the path of the high shear material developed around the 
perimeter of the first runner section 12. 
Another type of conventional runner layout is illustrated in FIG. 2. This 
runner layout 30 includes a first runner section 32 which feeds a second 
runner section 34. One end of the second runner section feeds a first 
tertiary runner 36 which in turn feeds a pair of fourth order runners 38 
and 40. The first fourth order runner 38 feeds first and second mold 
cavities 42 and 44. The second fourth order runner 40 feeds third and 
fourth mold cavities 46 and 48. At the other end of the second runner 
section 34, it feeds a second tertiary runner 50 which in turn feeds 
another pair of fourth order runners 52 and 54. A third fourth order 
runner 52 feeds fifth and sixth mold cavities 56 and 58. A fourth order 
runner 54 feeds seventh and eighth mold cavities 60 and 62. 
In each of these cases, the designer is striving to keep the runner lengths 
and diameters feeding each cavity substantially the same. The diameters of 
the runners may change along their lengths but the change needs to be 
consistent in each of the branches feeding the cavities. This construction 
provides a geometrical balance to the runner system. 
During laminar flow, the laminar flowing material flowing near the 
stationary runner walls experiences an increased shear versus that portion 
of the laminar flowing material which is traveling in the midstream of the 
runner channel. During the thermoplastic injection molding process, 
frictional heating occurs just inside of a thin frozen layer formed as the 
plastic touches the cold runner surfaces. In thermosetting material, not 
only does frictional heating occur but the mold is generally hotter than 
the material introduced into the mold. This tends to compound the thermal 
variation that is created within these outer high friction laminates and 
the innermost laminates or portions of the laminar flowing material. 
The result of this frictional heating is a relatively high temperature 
layer which is created near the outermost perimeter of the runner channel. 
When the melt comes to the end of a runner branch, it is split in two 
directions. Due to the nature of the laminar flow, the high sheared hotter 
material traveling along the outer laminates will maintain its position to 
a significant extent along the outer region of the flow channel. This will 
result in the high sheared hotter material from a first runner section 
flowing along the inside edge of a second runner section which branches in 
two directions. With the branch of the second runner section that goes to 
the right, the high sheared hotter outer laminate on the right side of the 
first runner channel section will flow along the wall of the right side of 
the new branch. The cooler low sheared center laminate will go to the 
opposite left side of the new right turning runner branch. The opposite 
will happen in the left branch of this second runner section where the 
high sheared hotter outer laminate of the left side of the first runner 
section will flow along the wall on the left side of the new branch. The 
low sheared cooler center laminate will flow to the opposite right edge of 
the new left turning runner channel. The result will be that one half of 
the two branching second runner sections will be hotter than will the 
other half. 
If at the end of this left and right branching runner section, the melt 
enters a cavity, the high sheared material will continue into the cavity 
and proceed along one side and the low sheared material will proceed into 
the cavity along the other side. This side to side variation in material 
conditions may result in undesirable characteristics in the molded part. 
At the end of this second left and right branching runner section, if the 
runner is again split, i.e. as in FIG. 1 and 2, the high sheared hotter 
material follows the branch on its side and the low sheared cooler 
material follows the branch on its side. The result is that the material 
traveling down each of these further runner branches will be of a 
different temperature and shear history. This material may then enter 
directly into one or more cavities or may continue to be split as in FIG. 
2. Each time the flow is split at a new runner branch, the high sheared 
hotter material follows the inside edge of the new runner branch. The 
result is that the laminar flowing material approaching and entering the 
center most cavities fed from the high sheared hotter outer laminates of 
the first runner section of a mold with this type of runner system has a 
hotter melt temperature than the temperature of the material entering the 
outermost mold cavities fed from the low sheared cooler inner laminates of 
the first runner system. With reference now to FIG. 2, mold cavities which 
would receive the relatively low sheared cooler temperature material would 
be mold cavities 42, 44, 46, 56, 58, and 60. The mold cavities which would 
receive the relatively high sheared hotter material would be mold cavities 
48 and 62. These mold cavities are in the path of high shear melt 
developed in the first runner section 32. Such variations in temperature 
will result in variations in the final molded product which might include 
size, weight and mechanical properties. As the variation in material 
conditions can be nearly continuous across the runners path, it can be 
expected that each time a runner branches, the melt conditions feeding 
each of the branches will be different. Therefore it can be expected that 
there is also a variation between cavities 42,44 and 46 and between 
cavities 56, 58 and 60. The mold will have four different sets of molded 
parts. The four sets being molded with like material will be 48 and 62, 46 
and 60, 44 and 58, 42 and 56. 
In the conditions described above, it is assumed that frictional heating 
dominates over any cooling of the melt provided by the walls of the mold. 
With materials like most moldable plastic materials the resulting 
variation in temperature is compounded by the shear thinning which is 
occurring in these outer high friction regions due to the non-Newtonian 
characteristics of plastic materials. Such non-Newtonian characteristics 
will also affect viscosity of the melt across the channel. In some cases 
where frictional heating is not the dominating parameter, as might occur 
with large runner diameters and slow flow rates, the opposite condition 
could occur where the outer laminates are cooler than the inner laminates. 
In either case, there is a likelihood of a variation in melt temperatures, 
viscosity and/or the flow conditions across the runner channel. All of 
these variations will be carried on into a part forming mold cavity, or 
into downstream runner branches as described above which will eventually 
feed into a part forming mold cavity. 
To provide a consistent melt to each of the cavities fed by branching 
runners such as is illustrated in FIGS. 1 and 2, the laminar flowing 
material may be repositioned in a circumferential direction, while 
maintaining continuity between the laminates in a radial direction. The 
rotation of all the laminates, without separation, provides the best 
assurance that continuous variations which exist through a runners cross 
section are all affected by the circumferential repositioning. The present 
invention provides for repositioning all of the fluid laminates in a 
runner in a circumferential direction which is perpendicular to the 
direction of flow. Such repositioning is relative to the approximate 
center through to the perimeter of the stream of laminar flowing material 
without requiring the physical separation or repositioning of the relative 
positions of the laminates--i.e., the laminates from the central region do 
not move to the outer region of the cross section of the flow channel and 
vice versa, nor do limited selected regions of outer or inner laminates 
require specific repositioning through specially balanced channels. 
Instead, the present invention strategically repositions the locations of 
all the laminates across the flow channel such that when they are split at 
a-downstream branch in the runner, the melt conditions between the two 
branches are more balanced. When so repositioned, the viscosity and 
thermal variation will not be from the left side to the right side of a 
runner channel, but rather will be from the top to the bottom of the 
runner channel. When the repositioned melt in a runner channel now feeds a 
further left and right branching runner each of the right and left 
branching runner sections will receive nearly equal top to bottom melt 
variations. The amount of repositioning can vary dependent on the required 
positioning of the flow laminates to achieve the objective of balancing 
the melt conditions in a branching runner system or to strategically place 
the melt laminates within a part forming mold cavity. 
Several embodiments of a means for repositioning the flow of a laminar 
flowing material according to the present invention will be disclosed 
hereinafter. 
When a laminar flowing material flowing through a runner channel changes 
direction, the material will remain substantially in its relative position 
across its flow path, i.e. circumferential positioning of melt laminates 
will remain substantially the same relative to a plane common to both 
runner sections. Changes in the relative circumferential position of flow 
laminates between a first and second runner section is accomplished 
through a number of embodiments of the present invention by causing the 
material to flow through compound directional changes combining three flow 
directions where no more than two of the three flow directions can be 
described on a common plane, i.e. the angle between a first and second 
flow direction will be on a different plane than the angle between the 
second and third flow direction. Thereby, though the circumferential 
positioning remains the same along a given directional change, the 
compound angles along different planes causes the flowing material 
entering the first directional change to become circumferential 
repositioned relative to the material exiting the second directional 
change. With reference now to FIG. 3, a mold used with a solidifying 
runner including a first mold half 70 and a second mold half 72 is there 
illustrated. Defined in the first mold half is a first runner section 74. 
Defined in a second mold half is a second runner section 76 which is 
intersected on it periphery by one end of a first runner section 74 which 
is at a different elevation and extends at an angle which is approximately 
perpendicular thereto. In this embodiment, the laminar flowing material 
travels along the first runner section 74. At the point at which the first 
runner section would normally branch, within the same mold half 70 into a 
second runner section, the first runner channel is terminated. At least a 
portion of the branching or second runner section is defined at a 
different elevation in the second mold half 72 at its intersection with 
the first runner section and can either entirely or partially overlap the 
end of the first runner. The melt is repositioned in the runner by 
diverting the flow of the melt in a direction approximately normal to the 
longitudinal axes of the primary and secondary runners. 
At the end of the first runner section channel 74, the melt is diverted 
upwardly, in a direction approximately normal or perpendicular to the 
molds parting line. After traveling a short distance in this perpendicular 
direction, the melt enters the secondary runner 76. The second runner 
section 76 extends in a direction approximately perpendicular to the first 
runner section The flow geometry of FIG. 3 will result in the hotter outer 
laminate being located adjacent the bottom of the secondary runner 76 and 
the cooler inner laminate being located adjacent the top of the secondary 
runner. 
Having the melt travel approximately normal or perpendicular to the plane 
of the mold parting line prior to entering the intersecting branching 
runner, effectively rolls the melt entering the secondary runner 
approximately 90 degrees relative to its previous position in the primary 
runner. 
Another way of describing FIG. 3 is that as the end of the first runner 
section terminates at a different elevation from the intersecting portion 
of the second runner section, the laminar flowing material is forced to 
flow in a direction between the differences in elevation of the flow 
center lines of the first runner section 74 and second runner sections 76 
at the intersection of the second runner section 76. The second runner 
section, which is at an angle to the first runner section, extends along 
the parting line of the mold and may extend in one or two directions from 
the intersection. The elevation differences of the two intersecting runner 
sections causes the laminar flowing material to flow along the direction 
of the elevation change between 74 and 76 which is a direction that is not 
common to either of the intersecting runner sections 74 or 76 and creates 
a third flow direction and a second directional change. The resultant 
compound directional changes combine three flow directions where no more 
than two of the three flow directions can be described on a common plane. 
As the material flowing in the direction of the elevation change between 
74 and 76 changes angle at the beginning of the second runner section 76, 
the high shear material which would have been traveling along the sides of 
the runner section 74 will be positioned substantially along the bottom of 
the branching runner section 76 if it is proceeding in two directions, or 
on the top and bottom of the branching runner section 76 if it is 
proceeding in one direction. Material flowing along the top and bottom of 
runner section 74 will become positioned substantially along the sides of 
runner section 76 whether it is branching in one or two directions. The 
effect is that the material proceeding down runner section 76 from the 
intersection will be repositioned circumferentially relative to its 
original position in the first runner section 74. 
A flow direction between the flow center lines of the runner sections 74 
and 76 which causes the melt to travel approximately 90 degrees relative 
to the flow directions of both 74 and 76, which are also at 90 degrees to 
one another, will result in an approximate 90 degree repositioning in the 
circumferential direction of the laminar flowing material in the second 
runner section 76 relative to its previous position in the first runner 
section 74. However, in some cases, it may be desirable to reposition the 
melt in a circumferential direction by some other amount. This would 
include the cases where a mold's runner may include more than two branches 
or where a traditional sprue feeding a primary runner in a mold may be 
used. This could be accomplished in various ways. With reference now to 
FIG. 4, at the end of a first runner section 80 in a first mold half 82, 
the intersection of the channels could be constructed at some other angle 
than perpendicular to the plane of the mold's parting line causing the 
melt flowing through this junction to flow at some angle other than 
approximately 90 degrees to the flow directions of the first runner 
section. To this end, FIG. 4 shows an end wall 84 having an acute angle 
rather than a substantially perpendicular wall ending the channel. At 
least a portion of the second runner section 86 is positioned in a second 
mold half 88 where its flow center line is at a different elevation than, 
and where it is intersected on its periphery by, the first runner section 
80 and at least a portion of end wall 84. 
Alternately, and with reference now to FIG. 5, a first runner section 90 is 
illustrated as being positioned in a first mold half 92 and at least a 
portion of a second runner section 94 is illustrated as being located in a 
second mold half 96 at a different elevation than, and is intersected on 
it periphery by, the first runner section. FIG. 5 shows an embodiment in 
which at least a portion of the second runner section partially overlaps 
the first runner section. This partial overlap will cause the flowing 
material to flow in a direction other than 90 degrees when it flows 
between the different elevations of the first and second runner sections. 
With reference now to FIG. 6, a first runner section 100 is illustrated to 
be in the same mold half as at least a portion of the second runner 
section 104. In order to create the required additional flow direction at 
the angled intersection between the first and second runner sections a 
flow diverter 106, in conjunction with a first runner section extension 
102 of runner section 100, causes the flowing material in runner section 
100 to be positioned at a different elevation prior to where it intersects 
the second runner section 104 at its periphery. By this means the creation 
of the same additional flow direction described for FIG. 3 is provided at 
the intersection of first and second runner sections which are an angle to 
one another. 
It is apparent from FIG. 6 that like FIG. 3 an approximately 90 degree 
repositioning in the circumferential direction of the of the laminar 
flowing material is accomplished because the flow diverter 106 causes the 
melt to be positioned in the first runner section extension 102, which is 
fully above the height, or cross section, of the second runner section 
104. The melt thereby will travel approximately 90 degrees relative to the 
flow direction of both the first runner section extension 102 and second 
runner sections 104 while the two resultant directional changes can not be 
described on a same plane. The result is that the laminar flowing material 
in the second runner section will become repositioned in a circumferential 
direction by approximately 90 degree relative to its original position in 
the first runner section extension. As long as the first runner section 
extension and the first runner section are defined along the same parting 
line and are flowing in the same axial direction, the laminate positions 
in the circumferential direction for both will remain the same as they 
change elevation. 
The sole purpose of the first runner section extension is to raise the 
centerline of the first runner section to a different elevation as the 
intersecting second runner section. Therefore it is considered a portion 
of the first runner section. 
With reference now to FIG. 7, an embodiment is disclosed in which there is 
less than a 90 degree repositioning of the melt in a circumferential 
direction. In this embodiment, a first runner section 110 communicates 
with a first runner section extension 112 which in turn communicates with 
a second runner section 114 which is at a different elevation than the 
first runner extension 112. However, in this embodiment, a diverter 116 
which is defined in the material of the mold half between the first runner 
section 110 and the second runner section 114 does not cause the material 
in the first runner extension 112 to be elevated to a position which is 
fully above the height, or cross section, of the second runner section 
114. This construction results in the laminar flowing material flowing at 
some angle less than 90 degrees as it flows from the first runner section 
extension 112 into the second runner section. This will result in the 
laminar flowing material being circumferentially repositioned in the 
second runner section by some angle less than 90 degrees relative to its 
original position in the first runner section extension channel. Thereby 
the height of the diverter controls the angle of the direction of flow of 
material between the two elevations. 
With reference now to FIG. 8, an embodiment of the invention is shown in 
which a first runner section 120 is defined in a bottom half 122 of the 
mold and a first runner section extension 124 is defined in a top half 125 
of the mold. At least a portion of the second runner section 126 is 
defined in the bottom half mold 122 where it is intersected on its 
periphery by the first runner section extension and at a different 
elevation to the first runner extension. FIG. 6 and FIG. 8 are very 
similar except for the cross sectional shape of the runner in FIG. 6 is 
trapezoidal with non radiused corners whereas in FIG. 8 the bottom of the 
runner is radiused. This has little effect on the performance of the 
invention. The diverter 128, as illustrated, will cause the laminar 
flowing material to be positioned in the first runner section extension 
124 at a height which is fully above the cross sectional height of the 
second runner section 126. The material flowing from 124 to 126 will 
therefore travel approximately 90 degrees relative to flow direction of 
both the first runner section extension and the second runner section 
resulting in a circumferential repositioning in the second runner section 
of the stream of laminar flowing material of approximately 90 degrees 
relative to its previous position in the first runner section extension. 
By reducing the height of the diverter 128, the angle of the direction of 
flow of material between the two elevations of the intersecting runners is 
reduced which reduces the relative circumferential position of the flowing 
material in the second runner section relative to its original position in 
the first runner section. 
With reference now to FIG. 9, another embodiment of the present invention 
is there illustrated. In this embodiment, a first runner section 130 is 
defined partially in a bottom mold half 132 and partially in a top mold 
half 134. A first runner section extension 135 is defined only in the top 
mold half 134. At least a portion of a second runner section 136 is 
defined only in the bottom mold half 132 at where it is intersected on its 
periphery by the first runner section extension and at a different 
elevation to the first runner section extension. A diverter 138 is 
positioned to cause the laminar flowing material to be positioned in the 
first runner section extension 135. As a portion of the first runner 
section 130 is already in the top mold half, the diverter 138 in FIG. 9 
does not need to be as tall as diverter 128 in FIG. 8 in order to position 
the laminar flowing material at an elevation which is above the full 
height of the cross section of the second runner section. Despite the 
reduced height of the diverter in FIG. 9, an approximate 90 degree 
rotation is still achieved as the flow direction from the first runner 
section extension 135 to the angled second runner section 136 is 
approximately 90 degrees relative to the flow direction of both first 
runner section extension 124 and the second runner section 136. 
By progressively reducing the height of the diverters in FIG. 6-9, the 
angle of the direction of flow of material between the two elevations of 
the intersecting runners is decreased. This reduced angle will reduce the 
relative circumferential repositioning of the laminar flowing material in 
the second runner section relative to it previous position in the first 
runner section. The same principle can be applied to the designs in FIG. 
3-5 where reducing the elevation difference between the intersecting 
runners, changes the direction of flow of material between the two 
elevations, which will control the relative rotation of the flowing 
material. Additionally, by reversing the position of the overlapping 
runner sections along the parting line at their intersection, the 
direction of the of the circumferential repositioning of the laminar 
flowing material in all of the embodiments of the present invention as 
described in FIGS. 3-9. 
Though the descriptions for FIGS. 3 through 9 above have been specific as 
to the location of the runners being along the parting line of a mold, 
these same methods could be used in a mold with non solidifying runners 
where the runners would not be on a mold parting line. 
While in the previous embodiments, the second runner sections are all shown 
as being disposed approximately perpendicular to the first runner section, 
this need not always be the case. FIG. 10 illustrates a mold in which a 
first runner section 142 communicates with a pair of branching runners 144 
and 146 that are disposed at an angle other than a 90 degree angle to the 
first runner section 142. When the elevation difference between the first 
and second runner sections, of the construction shown in FIG. 3-9, is 
included at the intersection of the angled branching runners, a rotation 
in the laminar flowing material will occur. However, by changing the angle 
between the intersecting first and second runner sections from 90 degrees 
at the point of their intersection and elevation change, the repositioning 
of the laminar flowing material in a circumferential direction into the 
branching runner sections can be controlled. 
With reference now to FIG. 11, a cavity half 150 according to a preferred 
embodiment of the present invention is there illustrated. Partially 
defined in this cavity half is a first runner section 152. The first 
runner section communicates with a second runner section 154 that is also 
partially defined in the cavity half 150. 
FIG. 12 illustrates a core half 156 which is adapted to be mounted on the 
cavity half. Defined in the core half is another portion 158 of the first 
runner section and another portion 160 of the second runner section. Also 
defined in the core half is a protrusion 162 which fits into an indented 
section 164 of the first runner section 152 defined in the cavity half 
150. In this way, a somewhat arching first runner section channel is 
defined by the core half and the cavity half. The flow of laminar flowing 
material will be such that the laminar flowing material will flow in an 
arc along the first runner section and approach the second runner section 
from below and in a direction approximately normal to both the 
longitudinal axis of the second runner section and to the longitudinal 
axis of the beginning of the first runner section. This construction 
provides a more distinct control of the direction of flow of material from 
the first runner section into the second runner section while still 
providing for the compound directional changes between a first runner 
section and a second runner section required to achieve the relative 
repositioning of the laminar flowing material a circumferential direction. 
With reference now to FIG. 13, another preferred embodiment of the present 
invention is there illustrated. In this embodiment, a first runner section 
170 is shown as communicating with the second runner section 172. The 
longitudinal axis of the second runner section is oriented approximately 
normal to the longitudinal axis of the first runner section. Located at 
the intersection of the runners is a flow diverter in the form of a pin 
174. As is illustrated in FIG. 14, the pin does not extend the entire 
height of the second runner section. Moreover, the diameter of the pin is 
smaller than is the diameter of either the first runner section or the 
second runner section. The height of the pin and the diameter of the pin 
are suitably controlled to adjust the flow of the laminar flowing material 
around the pin in such a way as to create an elevation change in a portion 
of the laminar flowing material at the junction of the runner sections and 
thereby creating the compound directional changes of the melt stream 
flowing from a first to second runner section creating the relative 
circumferential repositioning of the laminar flowing material. While a pin 
174 is illustrated as the flow diverter, it should be appreciated that 
flow diverters having other shapes than a pin could also be employed. For 
example, flow diverters having the shape of an arrowhead or a hexagon 
could also be employed. Also, flow diverters with varying cross sections 
can be employed. 
In other words, a means is provided for diverting the flow of the laminar 
flowing material through the use of an insert or pin which can be placed 
at the intersection of a pair of runners where it is desirable to 
reposition the melt. This allows an additional means for a repositioning 
to occur in a typical runner configuration in which the runners are all 
located in the same plane. As is evident from FIG. 14, one mold half 176 
of the mold body contains both the first runner section 170 and the second 
runner section 172. The pin 174 can be detachably mounted to the mold half 
176 at the intersection of the first and second runners sections. In this 
way, when a different type of thermoplastic is flowing through the 
runners, a pin with a different height, a different diameter or a 
different cross section may be used. 
The present invention is advantageous even in a situation where there are 
four cavities using the runner layout as illustrated in FIG. 1, or even 
less. In each instance, the melt delivered to each cavity will still be 
balanced even though there may be thermal variations within the melt 
entering each cavity. What is important to recognize is that the thermal 
variations in the melt will exist within each cavity and not between the 
several cavities. If it is desirable that the material entering a cavity 
be the same from side to side, the melt could be repositioned as it is 
split in the runner immediately prior to approaching a particular cavity. 
The embodiments of the present invention provided in the descriptions of 
FIGS. 3 through 14 describe the runner to be along a parting line. These 
methods provide for a runner which solidifies during normal molding 
cycles. By defining the runners along a molds parting line, the runner can 
be removed through conventional means between parting lines during every 
molding cycle by opening the parting line. 
The impact of the imbalance of the flow is most dramatic when producing 
high precision products. As a result, many companies requiring high 
precision plastic products must limit the number of cavities in a mold in 
order to produce product in each of the cavities with the required high 
tolerances. However, with the balanced system provided by the invention 
herein, a mold with a larger number of cavities may be used and higher 
yields can thus be obtained. Therefore, the present invention can 
significantly reduces product costs in the molding process. 
With reference now to FIG. 15, another form of a laminar flow rotation 
devise 179 is there illustrated. This construction includes a runner 
dividing member having a spiraling shape and includes a first side 180, a 
second side 182, a first side edge 184 and a second side edge 186. The 
runner dividing member is positioned in a runner 190 as illustrated in 
FIG. 16. The runner dividing member has a leading edge 192 and forms a 
pair of spiraling surfaces 194 and 196 over which the laminar flowing 
material flows. The runner dividing member also has a trailing edge 198. 
The runner dividing member of FIG. 15, spirals 90 degrees between the 
leading edge 192 and the trailing edge 198. This will result in a rotation 
in the circumferential direction of the laminar flowing material flowing 
along it. The runner dividing member of FIGS. 15 and 16 is particularly 
useful in a non solidifying runner type system in which the laminar 
flowing material in the runner does not solidify between cycles and is not 
ejected between molding cycles. The runner dividing member 179 would 
normally be positioned in a runner after non-symmetrical conditions in the 
laminar flowing material has been developed and prior to where the 
repositioning in a circumferential direction is desired. 
The runner dividing member 179 is positioned in the melt flow channel such 
that it divides the flow into two halves. The trailing edge 198, or exit 
end of the runner dividing member is twisted in a spiral by some angle in 
relation to the leading edge. The melt approaching the runner dividing 
member will be split into two "D" shaped flow paths. The spiraling runner 
dividing member will cause the melt to be moved in a circumferential 
direction. The divided "D" shaped flows are recombined at the trailing 
edge 198 of the runner dividing member. The relative positions of the 
laminates to each other will remain the same. Only their position along 
the circumference of the flow channel will have been changed. In the 
disclosed embodiment, the two halves of the melt are repositioned by 
approximately 90 degrees. However, for the non solidifying runner system, 
the runner dividing member can reposition the laminar flowing material by 
less than 90 degrees, such as, e.g., 70 degrees or more than 90 degrees, 
such as, e.g., 110 degrees or even 150 degrees, if that is desired. 
The runner dividing member 179 can be employed at an intersection between 
two runners. However, it would normally be positioned downstream from a 
branch where the non-desirable melt variations have been created. 
With reference now to FIG. 17, a set of flow channels is there illustrated. 
In this embodiment, a first runner section 200 splits into first and 
second runner sections 202 and 204. The geometry of the flow path is such, 
however, that the substantially circular diameter of the first runner 
section leads to non-circular beginning portions of the second runner 
sections. The spiraling circumference of the noncircular flow paths at the 
outset of the second runner causes a repositioning in a circumferential 
direction of the laminar flowing material which flows from the first 
runner section to each of the second runner sections. The laminar flowing 
material is repositioned by about 90 degrees. It is apparent that in this 
embodiment, the runners 200, 202 and 204 are defined by mating channel 
halves in a pair of mold cavity halves 210 and 212. It is also apparent 
from FIG. 17 that a vertically extending wall 214 defines the end of the 
first runner section 200 and splits the flow of laminar flowing material 
into the pair of second runner sections 202 and 204. The non-circular 
shape of the beginning of the second runner sections 202 and 204 causes a 
repositioning of the laminar flowing material in a radial circumferential 
direction while maintaining continuity between the laminates of laminar 
flowing material in a radial direction. While the inlets to the second 
runner sections 202 and 204 are non-circular, once the repositioning has 
taken place, the second runner sections can assume a circular cross 
section which can then be maintained. With reference now to FIG. 18, a top 
elevational view is there illustrated of the design shown in FIG. 17. With 
reference now to FIG. 19, a view of the spiraling circumferential design 
of FIG. 17 is there shown as a flow channel. The inlet end of the first 
runner section 200 is shown feeding the two second runner sections 202 and 
204. 
It should be apparent that the spiraling circumference of the non-circular 
runner section causes the repositioning in a circumferential direction of 
the laminar flowing material and where space is available could be 
positioned downstream from the junction with the first runner section. It 
should also be understood that the non circular cross sectional shape 
could take any form where the spiraling shape will cause a spiraling 
effect on the melt flowing through it. 
It should be apparent that the instant invention is useful not only in 
situations where there is a multi-cavity mold, but also in situations 
where there is a many branched runner system which feeds a single central 
mold cavity. 
With reference now to FIG. 20, another type of conventional mold is there 
illustrated. This mold 230 is a single cavity multi-runner mold for 
manufacturing a circular object. The mold includes a first runner section 
232, a second runner sections 234 and a pair of tertiary runners 236 and 
238 which lead to several gates of a mold cavity 240. FIG. 20 also 
illustrates the path of a high shear laminar flowing material 246 and a 
low shear laminar flowing material 248 which flow into the mold cavity 
240. Without the presence of a means for repositioning the laminar flowing 
material as it flows through the several runners--such as the means 
disclosed herein--the circular object being molded will have differing 
properties depending upon which half, roughly, of the product is examined. 
The magnitude of the flow imbalance is dependent upon which type of 
thermoplastic material is being molded and the process. Engineering 
resins, such as PMMA, 33% glass filled /6, PBT and ABS showed the 
greatest sensitivity to flow imbalance. Polyolefins proved to be the least 
susceptible to flow imbalances of the materials tested. 
With reference now also to FIG. 21, a two cavity mold 250 is there 
illustrated with a simple runner system. In this embodiment, flow 
imbalances in the mold occurs because of the non-symmetrical parts which 
are being molded in the two mold cavities 252 and 254. As a result of the 
non-symmetrical mold cavities, laminar flowing material would be subject 
to differential filling of the two mold cavities 252 and 254 as it flows 
from a first runner section 256 into a second runner sections 258. Thus, 
in the absence of a means for repositioning the laminar flowing material, 
a first high shear layer of material 260 is outwardly oriented in the 
first mold cavity 252 and forms the left side of the molded part. A second 
high shear layer of material 262 is outwardly oriented in a second mold 
cavity 254, however forming the opposite right side of the like molded 
part. A first low shear material 264 is inwardly positioned in the first 
cavity 252 forming the right side of the molded part. A second low shear 
material 266 is inwardly positioned in the second mold cavity 254 however 
forming the opposite left side of the like molded part. The result is the 
two sides of the parts formed in the two cavities will be formed 
differently. This same condition could be developed in a four cavity mold 
where a second set of cavities and runners would be fed by the same first 
runner section. 
Finally, with reference now to FIG. 22, two spiraling flow runner dividing 
members 280 and 282, such as those illustrated, e.g. in FIGS. 15 and 16, 
can be positioned in a second runner section 284 in a non solidifying 
runner arrangement downstream from a first runner section 286 thereof. In 
this way, the laminar flowing material which flows in opposite directions 
in the second runner section 284 is rotated by the two spiraling diverters 
as it flows either directly into one or more mold cavities or into 
respective tertiary runners. One can employ more than the pair of 
spiraling diverters 280 and 282 illustrated in FIGS. 22. 
The invention has been described with reference to several preferred 
embodiments. Obviously, modifications and alterations will occur to others 
upon the reading and understanding of the preceding specification. It is 
intended that the invention be construed as including all such alterations 
and modifications insofar as they come within the scope of the appended 
claims or the equivalents thereof.