Rotary injection molding system for suppressing polymer flash

A device and method for flash suppression in a molding with rotation system having a non-rotating mating surface capable of venting gases during the molding process while simultaneously suppressing flash. Flash is directed inwardly and away from the mating surface and contained between a mandrel and mandrel housing in a low pressure reservoir which is completely separate from the mating surface. A cooling fluid is utilized to carry away flash particles from the low pressure reservoir and thereby further prevent contamination of the mating surface.

BACKGROUND OF THE INVENTION 
This invention pertains generally to rotary injection molding systems 
performing plastic parison preforms and more particularly to rotary 
injection molding systems for forming plastic parison preforms which are 
capable of suppressing flash. 
In conventional non-rotating injection molding processes, a plastic 
parison, or preform is formed between a mandrel, or core pin and a molding 
cavity. The parison, or preform, is later blow molded into a finished 
article or reform. To form a mold, elements of the mold must be joined to 
form an enclosure. Assembly of the elements of the enclosure result in the 
formation of a mating interface which is the boundary between the surfaces 
of the elements of the enclosure which mate with one another to form the 
enclosed cavity. 
In conventional non-rotating injection molding systems, the mating 
interface is formed by the mating surfaces of the mandrel and molding 
cavity, which abut with one another when they are joined to form the 
enclosure. The tolerances of the mating surfaces of the non-rotating 
injection molding systems can be made sufficiently precise, i.e., a gap 
space on the order of 0.0005 to 0.001 inches, to allow venting of mold 
gases while simultaneously suppressing the flow of polymer material 
(flash) in the mating interface. Gas venting and suppression of flash is 
achieved in non-rotating injection molding systems for injection pressures 
of polymer on the order of 20,000 psi. Since the mating surfaces of the 
molding cavity and mandrel are static, a seal can be provided by producing 
a clamping force which is greater than the force exerted by the plastic on 
the mating surfaces during the injection cycle. Mating surfaces are 
maintained in a sealed position until the plastic is solidified so as to 
prevent the flow of polymer onto the mating surfaces after disassembly. 
However, in order to produce molded articles of greater strength, it is 
desirable to impart a preferred orientation to long chains of molecules in 
the polymer by rotating or oscillating the mandrel with respect to the 
mold cavity during the formation process, such as disclosed in U.S. Pat. 
No. 3,307,726, the disclosure of which is specifically incorporated herein 
by reference. While molding with rotation produces a superior molded 
article, complications arise in sealing a rotating mating interface to 
prevent the flow of flash material on the mating surfaces. Normal minimal 
tolerances which prevent the flow of flash material into the mating 
interface in a non-rotating objection molding machine are insufficient to 
suppress flash between rotating or oscillating mating surfaces due to 
shear heating of the polymer material by the moving surfaces which reduces 
polymer viscosity. Reduced polymer viscosity in the region of the mating 
interface causes the flow of flash material into the mating interface for 
mating surface tolerances normally utilized in non-rotating injection 
molding systems. Implementation of rotary molding machines in a high 
repetition automated rotary injection molding process has resulted in 
build-up of flash on the mating surfaces. As flash builds up on the mating 
surfaces, the tolerances of the mating interface go out of specification 
and the rotary molding machine must be shut down so that flash can be 
removed. Since clamp pressures imbed the flash material into the mating 
surface, scrapping is normally not effective to completely remove the 
flash material and flash material must consequently be removed using a 
solvent in a time consuming process of washing the mating surfaces. Flash 
problems have prevented implementation of the plastic rotary molding 
machine in a viable high speed, commercially valuable rotary molding 
process. 
Attempts have been made to overcome the problems of flash deposited on the 
rotating mating interfaces, as disclosed in U.S. Pat. Nos. 3,371,387; 
3,389,434; 3,500,503; and 4,083,568; the discloser of which is 
specifically incorporated herein by reference. In general, the above 
referenced patents attempt to overcome the problem of flash forming on 
rotating mating surfaces by providing a flash gap on the order of 0.0002 
to 0.0005 inches, and a low pressure reservoir connected to the flash gap 
for containing flash material emitted by the flash gap. As shown in the 
above referenced patents, and especially U.S. Pat. No. 3,389,434, a flash 
gap is formed in the rotating interface between the mandrel end cavity 
mold directly adjacent the parison. Due to its precise dimensions, the 
flash gap functions as a seal which is capable of emitting flash into the 
low pressure reservoir during peak intervals which occur during the 
molding process. The reservoir operates to collect flash material produced 
between the rotating surfaces of the flash gap. Upon separation of the 
rotating mating surfaces, the flash particles are removed from the 
reservoir by the application of pressurized air. This process is intended 
to eliminate the need to shut down the machine to remove flash particles 
from the reservoir. 
However, several problems exist in implementing the devices in the above 
referenced patents. For example, relatively high clamping pressures are 
still required on the rotating mating interface, even though a low 
pressure reservoir is utilized to prevent flash material from flowing into 
the mating interface. As a consequence of the high clamping pressures 
required between the rotating mating surfaces, the high tolerance required 
for the flash gap, i.e., 0.0002 to 0.0005 inches, are difficult to 
maintain due to the friction and consequent wear generated. Moreover, 
during the process of separation of the mandrel and molding cavity, flash 
particles removed from the reservoir by air pressure become airborne and 
deposit on the mating surfaces. Subsequent joining of the mating surfaces 
causes the previously airborne flash particles to embed in the mating 
interface requiring machine shutdown in the application of a solvent as 
disclosed above, to remove the embedded flash particles to maintain proper 
tolerances. 
OBJECTS OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
rotary molding system. 
It is also an object of the present invention to provide a rotary molding 
system which can be utilized in an automated commercial injection molding 
process. 
Another object of the present invention is to provide a device for flash 
suppression of a parison formed in a rotary molding machine. 
Another object of the present invention is to provide a method of flash 
suppression in a rotary molding machine for forming a parison. 
Another object of the present invention is to provide a rotary molding 
machine which essentially eliminates the flash between mating surfaces of 
a rotary molding machine. 
Additional objects, advantages and novel features of the invention are set 
forth in part in the description which follows and will be understood by 
those skilled in the art upon examination of this application, or may be 
learned by practice of the invention. The objects and advantages of the 
invention may be realized and obtained by means of the instrumentalities 
and combinations particularly pointed out in the appended claims. 
SUMMARY OF THE INVENTION 
To achieve the foregoing and other objects and in accordance with the 
purposes of the present invention, as embodied and broadly described 
herein, the apparatus of this invention may comprise a device for 
suppression and removal of flash formed in a rotary molding machine 
comprising: a mandrel; a mandrel housing; a molding cavity adapted to abut 
against the mandrel housing to form a stationary mating interface capable 
of venting gases and suppressing flash from the parison; means for 
coupling the mandrel and the mandrel housing to provide for relative 
rotation between the mandrel and mandrel housing and to form a flash gap 
between the mandrel and the mandrel housing; reservoir means disposed 
between the mandrel and the mandrel housing means for containing flash 
emitted by the aid flash gap; means for removing flash from the reservoir 
means. 
The present invention may also comprise a device for flash suppression of a 
parison formed in a rotary molding machine comprising a mandrel; a mandrel 
housing; means for coupling the mandrel and the mandrel housing to provide 
for relative rotation between the mandrel housing and the mandrel and to 
form a flash gap between said mandrel and the mandrel housing which is 
disposed radially inward from the parison; a molding cavity adapted to 
abut against the mandrel housing to form a stationary mating interface 
between the molding cavity and the mandrel housing, the stationary mating 
interface disposed radially outward from the parison and having machine 
gaps formed therein capable of venting gases and suppressing flash during 
molding; reservoir means disposed between the mandrel and the mandrel 
housing for containing flash emitted by the flash gap; cooling fluid means 
circulated under negative pressure in the reservoir means to solidify and 
carry away flash emitted from the flash gap to prevent the flash from 
depositing on the stationary mating interface. 
The present invention may also comprise a device for suppression, 
collection and removal of flash formed in a rotary molding device 
comprising: a rotating mandrel; a housing; a molding cavity adapted to 
abut against the mandrel housing to form a stationary mating interface 
between the molding cavity and the mandrel housing, the mating interface 
disposed radially outward from the parison and having machined gaps to 
vent gas during molding; means for coupling the rotating mandrel and the 
mandrel housing to form a flash gap between the rotating mandrel and the 
mandrel housing, the flash gap disposed radially inward from the parison; 
reservoir means formed between the rotating mandrel and said mandrel 
housing, said reservoir means disposed radially inward from the parison 
and coupled to the flash gap such that flash emitted by the parison 
through the flash gap is directed away from the mating interface and 
enclosed between the rotating mandrel and the mandrel housing; cooling 
fluid means circulating in the reservoir means under negative pressure to 
solidify the flash emitted by the parison through the flash gap and carry 
away flash particles and other debris in said reservoir to prevent flash 
from depositing on the stationary mating interface; a flash cutter 
disposed in the reservoir for cutting the flash emitted through the flash 
gap into flash particles. 
The present invention may also comprise a method of suppression and removal 
of flash in a rotary molding machine for forming a parison comprising the 
steps of: coupling a mandrel and a mandrel housing to form a flash gap and 
provide for relative rotation between a mandrel and a mandrel housing; 
providing a stationary mating interface between the mandrel housing and a 
molding cavity which is capable of venting gases and suppressing flash 
from the parison; containing flash emitted from the flash gap in a 
reservoir between the mandrel and the mandrel housing; removing flash 
contained in the reservoir using a fluid. 
The present invention may also comprise a device for suppression of flash 
formed in a rotary molding machine comprising: a mandrel; a mandrel 
housing; a molding cavity adapted to abut against the mandrel housing to 
form a stationary mating interface capable of venting gases and 
suppressing flash from the parison; means for coupling the mandrel and the 
mandrel housing to provide for relative rotation between the mandrel and 
the mandrel housing and to form a flash gap between the mandrel and the 
mandrel housing; a reservoir disposed between the mandrel and the mandrel 
housing means and connected to the means for coupling; cooling fluid means 
circulated under negative pressure in the reservoir to solidify polymer in 
the flash gap to form a flash gap seal. 
The advantages of the present invention are that the dimensions of the 
flash gap can be maintained with a high degree of accuracy since rotation 
is provided between the mandrel and mandrel housing so that a non-rotating 
mating interface can be provided between the mandrel and cavity mold which 
is capable of suppressing flash. Just as in the non-rotating molding 
process, the mating interface is also capable of venting gases during the 
molding process while suppressing flash from the parison. 
While the mating interface is disposed radially outward from the parison, 
the flash gap is formed between the rotating mandrel and the mandrel 
housing and is disposed radially inward from the parison. Therefore, flash 
emitted by the flash gap is directed away from the stationary mating 
interface and deposited in a reservoir formed between the mandrel and 
mandrel housing. In this manner, flash particles are directed away from 
the mating interface and contained in a reservoir which is totally 
separate from the mating interface, thereby substantially reducing the 
possibility for contamination. Moreover, a cooling fluid is circulated 
under negative pressure, as disclosed in U.S. Pat. No. 4,091,069 which is 
incorporated herein by reference and forms a part of this disclosure for 
all that it teaches, to remove flash contained in the reservoir further 
reduces the possibility of contamination of the mating surfaces from 
airborne flash particles. Consequently, the present invention results in a 
system which substantially reduces the possibility of contamination from 
the flash and flash particles produced during the molding process of a 
rotary injection molding machine and thereby provides a commercially 
usable rotary injection molding system.

DETAILED DESCRIPTION OF THE INVENTION 
As illustrated in the various figures, the present invention generally 
comprises a system for flash suppression of a parison formed in a rotary 
molding machine having a molding cavity 22 which is adapted to abut 
against a mandrel housing 24 to form a stationary mating interface which 
is capable of venting gases and suppressing flash from a parison 38. Means 
for coupling 28 are provided for coupling the mandrel 26 to mandrel 
housing 24 to provide for relative rotation between mandrel 26 and mandrel 
housing 24 and to form a flash gap 32 between the mandrel 26 and the 
mandrel housing 24. The flash gap 32 is disposed radially inward from the 
stationary mating interface 40 and directs flash emitted by parison 38 in 
a direction away from mating interface 40. A reservoir means 30 is formed 
between mandrel 26 and mandrel housing 24. In several of the embodiments 
disclosed, the reservoir means is disposed radially inward from the 
parison and is coupled to the flash gap such that flash emitted by the 
parison through the flash gap is directed away from the mating interface 
and enclosed between the rotating mandrel and mandrel housing, which is 
totally separate from the mating interface 40 so as to substantially 
reduce the possibility for contamination of the mating interface 40. 
Cooling fluid means 36 is circulated under negative pressure in reservoir 
means 30 and operates to cool and solidify flash emitted from flash gap 
32. Cooling fluid means 36 is circulated and filtered to carry away flash 
particles and any other debris which may accumulate in reservoir 30. Flash 
cutter means 34 is disposed in reservoir 30 and functions to cut flash 
emitted by flash gap 32 into flash particles. 
In operation, mandrel 26 is placed in molding cavity 22 such that mandrel 
housing 24 and molding cavity 22 provide a stationary mating interface 40. 
A polymer is injected through an orifice (not shown) in molding cavity 22 
at very high pressures and temperatures to form a parison 38. Mandrel 26 
is rotated by way of means for coupling 28 to impart a preferred 
orientation to long chains of molecules in the polymer during molding. 
This produces a molded article of greater strength. During the injection 
molding process, flash is emitted through flash gap 32 into a reservoir 
30. A flash cutter 34 cuts the flash into flash particles which are stored 
in a reservoir 30 and carried away by cooling fluid means 36. Cooling 
fluid means 36 also functions to cool and solidify the flash emitted by 
flash gap 32. Since the mating interface 40 is stationary, it is capable 
of venting gases during the molding process while suppressing flash from 
the parison. This was not achievable in prior art molding with rotation 
systems having a rotating mating interface. 
Referring to FIG. 1, an embodiment is illustrated which employs an axial 
flash gap. The mandrel housing 24 comprises housing members 42 and 44 
which are attached. Mandrel housing member 44 is constructed in standard 
split ring fashion and secured directly to mandrel housing member 42 by 
way of an alignment taper 50. Means for coupling the mandrel housing means 
24 to mandrel 26 comprise elements 52, 54, 56, 58, 60 and 62. Elements 52 
and 62 comprise shims which are fabricated in incremental thicknesses to 
adjust the flash gap spacing 32. Elements 54 and 60 comprise bearing races 
for thrust bearing 56 and thrust bearing 58. Thrust bearing 56 which may 
comprise a taper roller, functions to support the thrust load due to 
injection pressure in the molding cavity. Thrust bearing 58 provides a 
pre-load on thrust bearing 56 by proper selection of shim 62. Radial 
bearings 64 and 66 center the mandrel 26 in mandrel housing means 24. If 
thrust bearings 56 and 58 constitute taper rollers, radial bearing 64 and 
66 may be eliminated. Water seal 68 may comprise an O-ring type seal or a 
face type seal. Flash cutter 34 may form a part of mandrel housing 44 or 
may constitute cutter blades which are an insert in mandrel housing member 
44. Wear ring 70 can comprise a carbide or ferrus type metal which is 
brazed to mandrel 26. Molding cavity 22 comprises a neck ring 46 attached 
to injection cavity 48. Neck ring 46 provides a stationary mating 
interface 40 with mandrel housing 44. Neck ring 46 forms the threads on 
parison 38 and is used to strip the finished parison from mandrel 26. 
Cooling fluid means 36 is circulated in reservoir means 30 to remove flash 
particles. Flash gap 32 is formed between wear ring 70, which is mounted 
on the rotating mandrel 26, and the stationary mandrel housing member 44. 
In operation, polymer is injected into the space between injection cavity 
48 and mandrel 26. Trapped air and gases vent out through thin gaps 
machined in neck ring 46 on mating interface 40. Since mating interface 40 
is non-rotating or stationary, i.e., mandrel housing member 44 and neck 
ring 46 are in a stationary relationship to one another, the vent gaps 
machined in neck ring 40 do not flash. Similar mating surfaces between 
members having relative rotation with one another have been found to 
produce flash, as set forth in the prior art. 
The thrust load on mandrel 26 due to injection pressure is sustained by 
thrust bearing 56, bearing race 54 and shim 52. The thrust load is 
transferred through integral bearing race in mandrel 26. Shimmed bearing 
58 is used to preload thrust bearing 56. Radial bearings 64 and 66 
maintain concentricity of mandrel 26 during rotation. The flash gap 
dimension, which is in the range of 0.0002 to 0.0005, is maintained by 
selection of the proper thickness of shim 52. Wear ring 70 on mandrel 26 
provides a wear interface as protection for the gap interface on mandrel 
housing member 44. In the event that wear ring 70 touches mandrel housing 
member 44 while the mandrel 26 is rotating, damage to these close 
tolerance surfaces is minimized. 
During peak pressure intervals in the molding process, polymer flashes 
through flash gap 32 and enters a reservoir 30 which is filled with a 
cooling fluid, such as water or a cooled gas. The cooling fluid is 
circulated under negative pressure to prevent leakage of the cooling fluid 
through flash gap 32 into the molding cavity. Contact with cooling fluid 
freezes off the polymer and stops the flow of flash through flash gap 32. 
Since repeated injection cycles may force more polymer through the flash 
gap 32, a stationary flash cutter 34 is provided. When the build-up of 
flash on rotating mandrel 26 contacts the flash cutter 34, the rotary 
motion of the mandrel 26 allows the blade to slice, shred and chip the 
flash into pieces small enough to be carried away by the cooling fluid. A 
strainer (not shown) in the fluid cooling circulation system removes flash 
pieces. 
FIG. 2 shows an alternative manner of implementing the embodiment 
illustrated in FIG. 1. Element 72 comprises a split ring insert in mandrel 
housing member 44 which is held in position by pre-load thrust bearing 58 
by application of pressure to bearing race 60 and shim 62. This design 
improves dimensional control of flash gap 32 and allows for an easier and 
less expensive replacement of the flash gap surface of split insert 72. 
FIG. 4 illustrates another embodiment utilizing an axial flash gap wherein 
the final flash gap dimension is independent of tolerance build-up in 
bearings, races, etc. As in the embodiment of FIGS. 1 and 2, the flash gap 
dimension is determined by the axial location of the mandrel 26 and 
mandrel housing 24 relative to molding cavity 22. For this reason, the 
embodiments of FIGS. 1, 2 and 4 comprise axial flash gap embodiments. 
As illustrated in FIG. 4, mandrel housing 24 comprises a mandrel housing 
block 74, mandrel housing plate 76, gap insert 78 and attaching means such 
as machine screw 80 and bolt 82. A mandrel plate 84 is attached to mandrel 
26 by way of a split locking collar 86 which positions mandrel plate 84 
axially on mandrel 26 by way of locking plate 88 which is attached to 
mandrel plate 84 using machine screw 90. Split locking collar 86 
incorporates a key (not shown) and core pin keyway (not shown) to transmit 
torque from mandrel 26 to mandrel plate 84 and locking plate 88. Bearing 
race 92 is slip fit into housing plate 76 and secured to prevent rotation 
of bearing race 92 in housing plate 76 by way of pin 94. Spring washer 96 
is disposed between bearing race 92 and housing plate 76. Roller thrust 
bearing 98 is disposed between bearing races 100 and 102. Bearing race 104 
is press fit onto locking plate 88. Taper roller bearing 106 is disposed 
between bearing race 104 and bearing race 92. Radial bearing 108 maintains 
alignment of the core pin. 
In operation, the embodiment of FIG. 4 provides a roller thrust bearing 98 
which supports injection pressure load in a axial direction on mandrel 26. 
Taper roller bearing 106 maintains both axial and radial alignment of 
mandrel 26 during the application of pressure of the molding process. 
Spring washer 96 is used to pre-load thrust bearing 98 and taper roller 
bearing 106 to establish the dimension of flash gap 32. Spring washer 96 
also prevents movement of mandrel 26 into the molding cavity 22 by 
maintaining sufficient pre-load force to resist the hydraulic force 
resulting from injection pressure. The flash gap dimension is determined 
by assembling the mandrel and mandrel housing to the molding cavity and 
fabricating the gap sizing insert 110 to provide the desired flash gap 
dimension. In this manner, final gap dimension of flash gap 32 is 
independent of tolerance build-up in the bearings, races, etc., since 
force applied to mandrel housing 24 is transmitted through thrust bearing 
98 to spring washer 96 which determines the pressure on mandrel 26, 
independently of the pressure applied to mandrel housing 24. In other 
words, the pre-load pressure supplied by spring washer 96 determines the 
flash gap dimension independent of the pressure applied to mandrel housing 
24. 
FIG. 5 discloses an embodiment of the present invention employing a radial 
flash gap. As illustrated in FIG. 5, the mandrel housing comprises gap 
insert 112, mandrel plate 114, and mandrel housing block 116. These 
elements are secured together by bolt 118. Radial bearing 120, as well as 
bearing 132 disposed within bearing races 128 and 130, provide alignment 
of mandrel 26. Bearing 132 also aligns the mandrel 26 and mandrel housing 
24, as well as thrust bearing 122 and associated bearing races 124 and 
126. These elements comprise the means for coupling 28. A hole 138 in gap 
insert 112 transmits flash from low pressure reservoir 30 into secondary 
reservoir 140. Cutter blade 34 cuts flash transmitted through hole 138 
into flash particles. Cooling fluid is passed through secondary low 
pressure reservoir 140 and low pressure reservoir 30 by way of fluid 
access passage 142. Seal 134 is provided to block the flow of cooling 
fluid into the means for coupling 28. Flash gap 32 is disposed in a radial 
direction between gap insert 112 and mandrel 26. The radial flash gap 32 
provides a seal for flash which requires a less critical and more easily 
maintained flash gap dimension. Since flash gap 32 results from the radial 
dimensions of mandrel 26 and gap insert 112, the axial location of the 
mandrel 26 and gap insert 112 have no effect upon the flash gap dimension. 
This constitutes an important difference over the embodiments disclosed in 
FIGS. 1 and 2, since the structure required to maintain axial location and 
provide the tolerances to produce a flash gap in the range of 0.0002 to 
0.0005 inches can be eliminated in a radial flash gap design, such as 
illustrated in FIG. 5. 
In operation, mandrel 26 is inserted into molding cavity 22. Mandrel 
housing 24 and molding cavity 22 provide a stationary mating interface 40 
which is capable of venting gases during the molding process while 
simultaneously suppressing flash. Flash is emitted from parison 38 through 
flash gap 32 into low pressure reservoir 30. A cooling fluid 36 is 
circulated under negative pressure and functions to cool and solidify the 
flash and carry away flash particles by way of fluid access passage 142. 
Flash which does not cool sufficiently and solidify is emitted through 
hole 138 and cut into flash pieces by cutting blade 34. The sheared-off 
polymer flash pieces are carried away by the cooling fluid 36. 
FIG. 3 discloses another embodiment employing a radial flash gap. Mandrel 
housing 24 comprises a gap insert 146 and mandrel housing block 148 with a 
fluid access passage 150 disposed therein. Seal 144 provides a water seal 
between the fluid access passage 150 and means for coupling 128. 
In operation, flash passes through flash gap 32 into reservoir 30 where it 
is cooled and solidified by a cooling fluid 36. The flash is then cut into 
pieces by cutting blade 34 and carried away by cooling fluid 36 in fluid 
access passage 150. Fluid access passage 150 provides an inlet, an outlet 
and a circular path around cutting blade 34. 
FIG. 6 discloses another embodiment employing an axial flash gap. Mandrel 
housing 24 comprises a gap plate 160, a mandrel housing plate 162, and a 
mandrel housing block 164. The mandrel housing 24 forms a stationary 
mating interface 40 between the mandrel housing 24 and molding cavity 22. 
Mandrel 26 rotates in mandrel housing 24 by way of a plurality of bearings 
comprising tapered roller bearing 218, tapered roller bearing 250, thrust 
bearings 214 and 252, thrust bearings 212 and 254, radial bearings 208, 
256 and thrust washer 196. Mandrel 26 is coupled to a mandrel driver 224 
by a spline 223. A gap 221 is provided between mandrel driver 224 and 
mandrel 223 to provide clearance during rotation. An O-ring seal 226 is 
disposed between mandrel driver 224 and mandrel 26 to provide a water seal 
for water circulating in mandrel 26. Mandrel 26 is coupled to rotor 202 by 
split locking collar 204, drive pin 230 is inset into mandrel 26 and rotor 
202 to prevent slipping of the rotor whenever mandrel 26 is rotated. Rotor 
202 is coupled to locking plate 200 by way of bolts 228 which provides a 
preload force to hold split locking collar 204 in place. Drive pin 206 is 
disposed between rotor 202 and locking plate 200 and is formed of a 
hardened steel sufficient to withstand sheer forces. Drive pin 234 couples 
mandrel housing block 164 and mandrel housing plate 162. Drive pin 234 is 
made of a hardened steel to prevent rotation between mandrel housing plate 
162 and mandrel housing block 164. Flash cutter 34 is coupled to locking 
plate 200 by drive pin 244 disposed in opening 246 of flash cutter 34. 
Spring washers 198, 199, are disposed between cutter 34 and locking plate 
200 to provide a preload force on locking plate 34 in the axial direction. 
Bolt 232 locks mandrel housing 162 to gap plate 160 in conjunction with 
drive pin 210. Snap ring 192 is disposed to hold pin 234 in place. 
Fluid inlet opening 166 is coupled to fluid channel 168 which is in turn 
connected to annular fluid channel 170. Annular fluid channel 170 forms an 
annulus in mandrel housing block 164. Fluid channel 172 in mandrel housing 
plate 162 couples to annular fluid channel 170, fluid channel 176 and 
fluid channel 174. Fluid channel 174 couples to annular fluid channel 175 
formed in mandrel housing plate 162. Annular fluid channel 170 and annular 
channel 188 are coupled together by fluid channel 177 formed in gap plate 
160. Annular fluid channel 188 is coupled to annular fluid channel 189 by 
various openings formed in flash cutter 34, as illustrated in FIGS. 8 and 
9. 
FIG. 7 discloses a perspective end view of the flash cutter 34 of FIG. 6 
from an end adjacent to spring washers 198 and 199. FIG. 8 discloses a 
perspective end view of flash cutter 34 of FIGS. 6 and 7 viewed from the 
opposite end from that shown in FIG. 7. As schematically illustrated in 
FIGS. 7 and 8, fluid from annular fluid channel 188 is channeled between 
flash cutter 34 and locking plate 200 and flows through gaps 270, 274 and 
276, formed in flash cutter 34. Fluid then flows through openings 278, 280 
and 282 around mandrel 26. 
Fluid emitted by openings 278, 280 and 282 passes through openings 284, 286 
and 288 of the flash cutter into annular fluid channel 189, as illustrated 
in FIG. 6. Fluid from annular fluid channel 189 passes through fluid 
channel 236 to annular fluid channel 186. Fluid from annular fluid channel 
186 passes through fluid channel 187 to annular fluid channel 238. Fluid 
from annular fluid channel 238 passes through fluid channel 240 and exits 
through fluid outlet opening 242. 
In operation, mandrel 26 is inserted in molding cavity 22 such that mandrel 
housing 24 abuts against molding cavity 22 to form a stationary mating 
interface 40 which has milled slots 262 capable of venting gases while 
simultaneously suppressing flash from the parison during the molding 
process. Flash gap 32 has a gap spacing on the order of 0.0002 to 0.0005 
inches. The flash gap is connected to a reservoir 30 which is coupled to 
annular fluid channel 189 which flushes away flash pieces produced by 
flash cutter 34 in reservoir 30. Fluid is circulated under negative 
pressure between fluid inlet opening 166 and fluid outlet opening 242. The 
fluid circulates through fluid channel 168, annular fluid channel 170, 
fluid channel 172, fluid channel 174, annular fluid channel 175, fluid 
channel 177 into annular fluid channel 188. Fluid then circulates down 
along the back side of flash cutter 34 through openings 270, 274, 276 into 
openings 278, 280 and 282 formed around the surface of mandrel 26, as 
shown in FIGS. 6 and 7. Fluid then passes into openings 284, 286 and 288 
as shown in FIG. 9, which couple directly to annular fluid channel 189 and 
reservoir 30, as shown in FIGS. 6 and 7. Flash particles are removed from 
reservoir 30 by the fluid which passes through fluid channel 236, annular 
fluid channel 186, fluid channel 187, annular fluid channel 238 and fluid 
channel 240 into fluid outlet opening 242. The fluid is circulated under 
negative pressure such as disclosed in the above referenced U.S. Pat. No. 
4,091,069 the disclosure of which is specifically incorporated herein by 
reference, to insure that the fluid does not pass through flash gap 32 
into the molding cavity. The fluid functions to flush out reservoir 30 and 
remove flash particles so that they do not become airborne and interfere 
with stationary mating surface 40. The fluid can comprise water, a polymer 
solvent or any other desired fluid. In addition to flushing out the flash 
pieces, the fluid also functions to freeze off the polymer so that it can 
be chipped away by flash cutter 34. 
Additionally, the flash seal may be formed from the polymer in this 
embodiment and all the embodiments disclosed herein. In this case, the 
polymer fills flash gap 34 and at least a portion of reservoir 30 and is 
solidified by the cooling fluid so that the polymer ceases to flow through 
the flash gap. A rotary flash seal is therefore formed by the polymer 
material. 
A series of O-rings 178, 180, 182, 184, 248, and 179 are disposed 
throughout the device that isolate the fluid channels described above. The 
O-rings also function to isolate the bearings to prevent oil or grease 
from traveling into the fluid channels. This allows a recirculating 
lubrication system to be employed in the device wherein oil is circulated 
around the bearings during operation. If a recirculating system is not 
employed, the bearings can be prepacked in grease. In this case, the 
O-ring seals function to prevent loss of the lubricating material during 
operation. Spring washers 198 and 199 function to preload flash cutter 34 
in an axial direction against thrust washer 196. A gap is machined between 
flash cutter 34 and gap plate 160 adjacent reservoir 30. The gap is 
machined to ensure that the cutter sheers off polymer emitted into 
reservoir 30. 
Locking plate 200 functions to provide a surface for spring washers 198 and 
199 to apply a predetermined force on cutter 34 and also functions as a 
bearing retainer to insure that core pin 26 remains straight in molding 
cavity 22. Radial bearing 208, together with tapered bearing 220 allow the 
core pin to rotate in mandrel housing 24 while minimizing radial 
deflection of mandrel 26. A typical problem in rotary molding devices are 
that during the process of injection molding, injection pressures are so 
high that they cause the mandrel 26 to be deflected. Close tolerances are 
needed in the radial bearings since any play in the radial bearings will 
cause the mandrel 26 to shift to one side causing a non-concentric mold. 
When this occurs, wall thickness of the finished article will be thicker 
on one side than the other. Bearings 220, 250, 208 and 256 have 
sufficiently tight tolerances to prevent deflection of the pin during the 
high pressures of the injection molding process. Tapered bearings 220 and 
250 are bearings which function to take up both axial and radial forces. 
By proper machining of rotor 202, a preload force can be placed on races 
216 and 258 in a direction towards mandrel drive 224 to tighten up 
bearings 220 and 250 and thereby eliminate any play in the bearing. 
Tolerances of 0.0004 to 0.0006 are provided in radial bearings 208 and 256 
to minimize deflection of mandrel 26. Tapered bearings 220 and 250 totally 
eliminate play because of the tapered shape of the bearings and races. 
Bearings 214 and 252 comprise large thrust bearings which are capable of 
withstanding core pin injection pressures on the order of 20,000 to 30,000 
psi which are typically encountered in the rotary injection molding 
process. The entire force placed on the core pin is supported by thrust 
bearings 214 and 252. The size of thrust bearings 214 and 252 set the 
location of rotor 202. Thrust bearings 212 and 254 function as preload 
bearings. Mandrel housing block 164 is threaded to match threads 211 of 
mandrel housing plate 162. Mandrel housing plate 162 and mandrel housing 
block 164 are assembled by screwing these units together to preload thrust 
bearings 212 and 254 against rotor 202. This preloads the whole system 
back against mandrel housing block 164 through thrust bearings 214 and 
252. That holds rotor 202 in a set position. 
The rotor 202 is coupled to mandrel 26 by split locking collar 204. Split 
locking collar 204 is a very close tolerance machine part which fits into 
a notch in mandrel 26. The tolerances of the notch in locking split collar 
204 are so close that split locking collar 204 is packed in dry ice to 
shrink the split locking collar 204 to provide sufficient clearance for 
assembly. This provides a tight fit of rotor 202 with mandrel 26 so as to 
eliminate axial play of mandrel 26. Rotor 202 is bolted to locking plate 
200 by a bolt 228 with a preload force designed so that there is little 
clearance between the final position of locking plate 200 and split 
locking collar 204 on rotor 202. When these elements are clamped together 
in this manner, they become one solid unit that cannot shift on mandrel 
26. Also, drive pin 230 is placed in a recess on mandrel 26 which matches 
a similar recess on rotor 202 to take up any rotary torque between these 
items. 
A predetermined, preload force is applied between mandrel housing block 164 
and mandrel housing plate 162 by screwing these items together on threads 
211. When this predetermined force is reached, pin 13 is inserted through 
one of a series of holes in mandrel housing plate 162 which is aligned 
with one of a series of slots, such as slot 235 formed in mandrel housing 
block 164. Slots 235 in mandrel housing block 164 are formed every 
16.degree. around the circumference of mandrel housing block 164 while 
holes, such as hole 237, are formed in mandrel housing plate 162 every 
15.degree.. In this manner, a hole 237 in a slot 235 will align for every 
1.degree. of rotation of these items so that a pin can be inserted to 
obtain a desired preload force for every 1.degree. of rotation between 
mandrel housing plate 162 and mandrel housing block 164. The threads 
between mandrel housing plate 162 and mandrel housing block 164 are 
buttress type threads which are capable of withstanding high pressures 
generated by the injection molding process. One degree of rotation 
produces an axial displacement of approximately 0.00014 inches. Snap ring 
192 is provided to hold pin 234 in place. Snap ring 92 can be quickly and 
easily removed for removal of pin 234 to quickly disassemble the unit. The 
entire cartridge can then be removed and a new cartridge inserted and 
thereby minimize down time in a high speed automated process. 
Mandrel 26 fits into a mandrel driver 224 by a spline between the two. 
Torque is transmitted through the spline to rotate the mandrel 26 which in 
turn rotates rotor 202, locking plate 200 and flash cutter 34. The spline 
is used in a production tool to enable an operator to quickly change 
entire unit as a cartridge if some problem develops. A gap 221 is provided 
between mandrel housing 24 and mandrel driver 224 to prevent contact of 
these elements. An O-ring seal 226 is provided between mandrel 26 and 
mandrel driver 224 to seal cooling fluid which is circulated through 
mandrel 26. 
The spline also allows some misalignment between mandrel housing 24 and 
mandrel driver 224. The drive system for mandrel driver 224 has its own 
bearings and since it is difficult to align more than two bearings on a 
shaft, a spline allows for some misalignment so that tight tolerances 
between the drive system of mandrel driver 224 and mandrel housing 24 are 
not required. 
As stated previously, it is desirable to provide a flash gap having a 
dimension ranging from 0.0002 to 0.0005 inches between mandrel 26 and gap 
plate 160. Grinding of the surface of mandrel housing plate 162 which 
abuts against preloaded thrust bearings 212 and 254 provides a larger 
flash gap 32. If a smaller gap is desired, a ring shim can be inserted 
between gap plate 160 and mandrel housing plate 162 at a location where 
drive pin 210 and bolt 232 couple gap plate 160 and mandrel housing plate 
162. This moves gap plate 160 in a direction towards molding cavity 22 and 
produces a smaller flash gap 32. 
FIG. 9 discloses another embodiment of the present invention utilizing an 
axial gap. The embodiment illustrated in FIG. 9 is the same as the 
embodiment illustrated in FIG. 6 with the exception that the embodiment of 
FIG. 9 provides for adjustment of the flash gap 32. Since adjustment is 
provided by dividing the rotor 202 of FIG. 6 into two elements, i.e. rotor 
element 280 and rotor element 282. Rotor elements 280 and 282 are coupled 
together by buttressed threads which are designed to withstand large 
forces in the axial direction. Rotation of rotor elements 280 and 282 
causes an axial displacement of 0.00014 inches per each degree of axial 
rotation. Adjustment of flash gap 32 is provided by rotating rotor 
elements 280 and 282 with respect to one another until the desired flash 
gap is achieved. At that point, a locking pin 284 is inserted in one of a 
series of slots in rotor element 280 and 282 which align with one another. 
The slots in rotor element 280 are disposed every 15.degree. around its 
circumference. Similar slots are formed in rotor element 282 every 
16.degree. around its circumference on a matching surface with rotor 
element 280. Consequently, a pair of slots aligns for each degree of 
rotation of rotor elements 280 and 282 with respect to each other so that 
locking pin 284 can be inserted in a pair of aligned slots for each degree 
of rotation. In this manner, the flash gap 32 can be adjusted without any 
machining of the parts. By measuring the dimensions of flash gap 32, it 
can be determined how many degrees of rotation are required to provide a 
desired flash gap dimension since each degree of rotation either adds or 
subtracts approximately 0.00014 inches to the gap. This design is 
extremely useful in a production situation since it provides a means for 
easily adjusting a gap in a quick and simple manner without machining. 
In order to achieve a high tolerance gap 32, threads 278 are preloaded to 
eliminate movement upon application of pressure to mandrel 26 during the 
injection molding process. Locking pin 284 is pressed into a ring 286 
which abuts against preload ring 288. Bolt 290 is tightened in locking 
plate 292 to force rotor element 280 towards the rear of the housing. 
Force is transmitted through ring 286 to rotor element 282 to apply a 
force in the forward axial direction against rotor element 282 and provide 
a preload force to threads 278 to eliminate any movement between rotor 
elements 280 and 282 when force is applied to mandrel 26 during the 
injection molding process. In this manner, preloading of threads 278 
ensures high tolerances for the gap dimension of flash gap 32. The amount 
of preload applied to threads 278 is determined by the torque applied to 
the series of bolts 290. 
FIG. 10 illustrates another embodiment of the invention, also shown 
partially in FIG. 11, wherein the flash gap 32 is an axial flash gap. In 
this embodiment the mandrel housing 24 comprises a main housing block 310 
having a central bore therein for receiving the mandrel 26. A first 
sealing plate 312 is fixedly attached in a cut out portion on one face of 
housing block 310 and is fixedly secured thereto by conventional fastening 
means 314, such as bolts or the like. The first sealing plate 312 has a 
central bore 313 therein which is positioned in coaxial alignment with the 
central bore 311 in the mandrel housing block 310. A second sealing plate 
316 is mounted in a cut out portion on an opposite side of the housing 
block from plate 312. Plate 316 has a central bore 317 therein positioned 
in coaxial alignment with the bore in the housing block 310. A third 
housing plate 318 is mounted with one planar face surface thereof in 
abutting engagement with an outer planar surface of plate 316. Both plate 
316 and 318 are fixedly secured to one another and to housing block 310 by 
conventional fastening means 320, such as bolts. An axially extending 
cylindrical cavity 319 coaxial with bores 311, 313 and 317 is cut into the 
face surface of housing plate 318 on the face positioned adjacent to 
housing plate 316. This cylindrical cavity 319 receives and encompasses a 
portion of the mandrel 26 and defines a reservoir means 30 for receiving 
and discharging flash particles. A cylindrical bore 32 is positioned 
coaxially with cylindrical cavity 319 and extends through plate 318. 
Housing block 310 comprises a fluid inlet opening 330 in one face thereof 
which is connected to a fluid inlet passage 332 within the block which 
communicates with reservoir means 30 through an inlet bore 333 in plate 
316. A fluid outlet passage 334 in fluid communication with a fluid outlet 
opening 336 in another face of housing block 310 communicates with 
reservoir 30 through a fluid outlet bore 335 in plate 316. 
A first precision roller bearing 338 is positioned at one axial end of bore 
311 in block 310 and a second precision roller bearing 340 is positioned 
in the opposite axial end of bore 311. Both roller bearings 338, 340 
engage an enlarged diameter mandrel portion 342 which extends through the 
housing block bore 311. A conventional annular packing 344 is provided 
between the two roller bearings. The bearings are isolated by a first 
O-ring 346 mounted in a groove portion of the bore 313 in mandrel sealing 
plate 312 and a second O-ring 348 mounted in a groove portion of the bore 
317 of second mandrel sealing plate 316. 
A mandrel flange portion 350 is positioned outside of the mandrel housing 
24 at the end of the mandrel distal the molding cavity 22. The flange 
portion 350 has an outer radial surface 352 which accepts thrust loading 
from a thrust bearing 390 portion of a conventional rotational drive means 
392. The thrust bearing 390 is received in annular torque transmitting 
relationship about a smaller diameter connecting portion 354 of the 
mandrel 26. 
Mandrel axially extending groove portions 360, 362, 364, etc. are provided 
in equally circumferentially space relationship at one end of the mandrel 
enlarged diameter portion 342. The groove portions 360, 362, 364, etc. 
define mandrel cutter portions 361, 363, 365, etc. In one preferred 
embodiment, the mandrel groove portions comprise an axially length of 
between 0.12 inches and 0.25 inches and comprise a circumferential width 
of between 0.12 inches and 0.25 inches. A flash gap defining mandrel 
portion 370 is positioned axially next adjacent the grooved end of mandrel 
enlarged diameter portion 342. The flash gap defining portion 370 has a 
diameter smaller than that of enlarged portion 342 and slightly larger 
than that of the adjacent parison receiving mandrel portion 372. The 
interior surface 380 of mandrel housing plate 318 bore 321 is positioned 
in spaced radially opposite relationship with mandrel portion 370, and 
thus mandrel portion 370 and mandrel housing surface 380 define an axial 
gap 32 therebetween. An inwardly positioned radially extending surface 384 
of housing plate 318 which intersects bore surface 380 is positioned a 
sufficient axial distance from the terminal end surface of cutter portions 
361, 363, 365, etc. so as to prevent abrasive contact therewith. 
Typical operating parameters and dimensions for the apparatus illustrated 
in FIGS. 10 and 11 may be as follows: 
1. The small diameter portion 372 of the mandrel has a diameter between 
0.90 inches and 0.75 inches and an axial length between 7.00 inches and 
3.50 inches. 
2. The ratio of diameters of the mandrel small diameter portion 372 to the 
mandrel intermediate diameter portion 370 is between 1.0 and 1.25. 
3. The ratio of diameters of the small diameter portion 372 and the 
enlarged diameter portion 342 is between 1.5 and 2.5. 
4. The axial distance between the flash gap 32 and the radially extending 
terminal surface of said mandrel enlarged diameter portion 342 is between 
0.02 inches and 0.06 inches. 
5. The axial length of the flash gap 32 is between 18 inches and 0.25 
inches. 
6. The average radial dimension of the flash gap 32 is between 0.0002 
inches and 0.0008 inches. 
7. The forming pressure of the parison 38 forming material is between 
15,000 psi and 20,000 psi. 
8. The average parison 38 wall thickness is between 0.06 inches and 0.160 
inches. 
9. During formation of the parison 38, the mandrel 26 rotates at an average 
speed of between 200 rpm and 350 rpm. 
10. The molecular weight MC (the weight average molecular weight) of the 
material forming the parison 38 at injection temperature is between 35,000 
and 400,000, which includes substantially all forms of polystyrene. 
In operation, mandrel 26 is inserted into the molding cavity 22. Mandrel 
housing 24 and molding cavity 22 provide a stationary mating interface 40 
which is capable of venting gases during the molding process while 
simultaneously supressing flash. Mandrel 26 is maintained in relatively 
fixed radial position relative mandrel housing 24 by precision roller 
bearings 338, 340. A precise flash gap distance is provided by accurate 
machining of mandrel surface 370 and mandrel housing plate bore surface 
380. The axial position of mandrel 26 within housing 24 and molding cavity 
22 is determined by the axial position of thrust bearing 390 which is 
coupled to mandrel end portion 354 in abutting engagement with radial 
surface 352. Mandrel cutter portions 361, 363, 365, etc. cut any flash 
transmitted through flash gap 32 into small flash particles which are 
carried away by fluid 36 flowing through reservoir 30. The fluid 36 may 
comprise pressurized air, water under negative pressure or other fluids. 
The present invention, therefore, provides a system which substantially 
reduces the possibility of contamination from flash particles produced 
during a molding process of a rotary injection molding machine and thereby 
provides a commercially usable rotary injection molding system. This is 
accomplished by using a non-rotating mating interface which is capable of 
venting gases produced during the molding process while simultaneously 
suppressing flash. Rotation of the mandrel is provided between a mandrel 
housing and the mandrel so that the non-rotating mating interface can be 
provided between the mandrel housing and cavity mold. A flash gap is 
consequently formed between the rotating mandrel and mandrel housing so 
that flash particles are directed away from the mating interface and 
contained in a reservoir which is totally separate from the mating 
interface. A cooling fluid is also utilized to remove the flash particles 
contained in the reservoir to thereby substantially reduce the possibility 
for contamination of the mating interface by flash and flash particles and 
to allow the rotary molding system to maintain proper tolerances and 
thereby provide a commercially usable rotary injection molding system. 
The foregoing description of the invention has been presented for purposes 
of illustration and description. It is not intended to be exhaustive or to 
limit the invention to the precise form disclosed, and other modifications 
and variations may be possible in light of the above teachings. For 
example, the flash gap may be disposed along any portion of the parison 
lip as long as flash is directed away from the mating interface and 
contained in a reservoir which is physically separated from the mating 
interface. The embodiment was chosen and described in order to best 
explain the principles of the invention and practical application of the 
invention to thereby enable others skilled in the art to best utilize the 
invention in various embodiments and various modifications as are suited 
to the particular use contemplated. It is intended that the appended 
claims be construed to include other alternative embodiments of the 
invention except insofar as limited by the prior art.