Method and apparatus for trimming and finishing the outer edge of a molded record

A method and apparatus is provided for trimming flash from the outer edge of thermoplastic molded records and then finishing the outer edge. A molded record having flash on its outer edge is supported on a turntable and then rotated about its center. The flash and the outer edge of the record immediately adjacent the flash are selectively heated, preferably by using a focused infrared lamp, to a temperature above the glass transition temperature. A cutter is then advanced tangentially through the flash to remove the heat-softened flash from the record. The trimmed outer edge is then finished by bringing a shaped surface into contact with the softened edge and holding it there while rotating the record until the outer edge has the desired finished configuration. The heating is discontinued and the trimmed and finished outer edge is allowed to solidify.

This invention relates to a method and apparatus for trimming flash from 
the outer edge of a molded record and more particularly is concerned with 
an improvement in the finishing of the outer edge. 
BACKGROUND OF THE INVENTION 
Molded records, such as conventional audio records or the more recently 
developed capacitive electronic discs, are manufactured by molding a 
charge of a thermoplastic composition between a pair of metal parts, 
referred to as stampers, which have defined in their molding surfaces a 
mirror image of the pattern desired to be pressed into the molded record. 
It is conventional to use a charge of the thermoplastic composition which 
is somewhat larger than that required to exactly mold the record in order 
to insure that the molded record will not have any voids and that it will 
be of a uniform density. The excess material in the charge is forced out 
from between the stampers during the pressing of the record and forms a 
ring of material around the outer edge of the molded record which is 
referred to as flash. After the record has been pressed it is necessary to 
remove the flash from the outer edge of the record and to finish the outer 
edge to a smooth and precise diameter. 
Removing the flash and finishing the outer edge of records is a source of 
considerable manufacturing problems. One of the major problems which is 
encountered is breakage of the molded records during trimming. This 
typically results in sections of the outer portions of the molded records 
being broken out from the records. Edge cracking is an additional related 
problem. Microcracks are often formed at the outer edge during trimming 
which eventually grow into large cracks which destroy the records. A still 
further problem which is encountered is that the outer edge of the molded 
records is often left in a roughened condition and not sufficiently round 
for proper playback. The above-noted problems and other similar problems 
are especially acute in manufacture of capacitive electronic discs which 
are heavily loaded with conductive carbon particles. 
Many of the manufacturing problems encountered in trimming the flash and 
finishing the outer edge of records can be attributed to brittleness of 
the solidified thermoplastic compositions. It is necessary that the molded 
records be solidified prior to removal from the molding press to prevent 
warp which will distort the information in the recorded area of the 
record. However, as the thermoplastic compositions solidifies, the records 
become relatively brittle and more susceptable to mechanical damage. It 
has been found, for example, that the carbon-filled capacitive electronic 
discs are relatively brittle and prone to breakage, edge cracking and are 
especially difficult to finish. 
Various methods and apparatus have been suggested for trimming flash from 
molded records and for finishing the outer edge of the record. The use of 
opposing rotary cutter wheels has been suggested, but this apparatus has 
not proven satisfactory because the rotary wheels tend to pinch the flash 
and cause a rough, uneven cut. It has also been suggested to use a hot 
knife to trim the flash, but this has proven to be unsatisfactory as it 
requires a separate power source for the knife and the edge tends to be 
distorted. Flusfeder et al. in U.S. Pat. No. 3,412,427, entitled 
"Apparatus For Manufacturing Disc Records," discloses the use of a pair of 
overlapping blades for trimming the flash from records. The apparatus 
which is disclosed is of an overly complex design which makes it difficult 
to consistently obtain satisfactory results in trimming the flash and no 
provision is made for finishing the trimmed edge. Pullen et al. in 
European patent application EP No. 0 044 608 Al, entitled "Improvements 
Relating To Flash Trimming Of Disk Record," discloses the use of a scissor 
type cutter which is brought in on a tangent to trim the flash. No 
provision, however, is made for finishing the trimmed edge. Chambers, et 
al. in U.S. Pat. No. 4,326,325, entitled "Method And Apparatus For 
Deflashing Molded Discs," discloses a dual trimming system in which a 
knife is used to remove the majority of the flash and then a rotary cutter 
is used to remove the remainder of the flash. The Chambers et al. method 
provides somewhat better control of flash removal as compared to the other 
well-known methods, but the outer edge of the disc is left in a 
considerably roughened condition by the rotary cutter. All of the methods 
and apparatus heretofore disclosed, while being marginally acceptable for 
conventional records, were found under production conditions to be 
unsuitable for trimming flash and finishing the outer edge of capacitive 
electronic discs. 
It would be highly desirable if a method and apparatus could be provided 
for trimming the flash and finishing the outer edge of records without 
causing breakage, edge cracking and other such problems. 
BRIEF SUMMARY OF THE INVENTION 
A method and apparatus is provided for trimming flash from the outer edge 
of thermoplastic molded records and then finishing the outer edge. A 
molded record having flash on its outer edge is supported on a turntable 
and then rotated about its center. The flash and the outer edge of the 
record immediately adjacent the flash are selectively heated, preferably 
by using a focused infrared lamp, to a temperature above the glass 
transition temperature of the thermoplastic composition. A cutter is then 
advanced tangentially through the flash to remove the heat-softened flash 
from the record. The trimmed outer edge is then finished by bringing a 
shaped surface into contact with the softened edge and holding it there 
while rotating the record until the outer edge has the desired finished 
configuration. The heating is discontinued and the trimmed and finished 
outer edge is allowed to solidify.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1, there is illustrated a molded record 10 which still has attached 
to the outer edge 12 a ring of flash 14 from the molding process. The 
record 10, as illustrated, has a center hole 16, an unrecorded section 18, 
a recorded area 20, in which an information track 22 having the signal 
information defined therein is present, and a protective bead 24 which 
extends to the outer edge 12. The flash 14 is comprised of a relatively 
thin web 26 which extends from the outer edge 12 of the record 10 and a 
substantially thicker, irregularly shaped section 28. The molded record 
10, with the flash 14 still attached, will have the edge cross-sectional 
configuration illustrated in FIG. 2. After the flash 14 is trimmed in 
accordance with the method invention, the cross section of the outer 
portion of the record 10 will have the configuration illustrated in FIG. 
3. 
The method of the present invention is comprised of a number of sequential 
steps. The molded record 10 is received from the pressing operation with 
flash 14 still attached to its outer edge 12. The record 10 is placed on a 
suitable support, then rotated about its center. The record 10 with flash 
14 attached to its outer edge 12 as received from the pressing operation 
should be fully solidified; however, it should preferably still be 
relatively hot in order to facilitate heating the flash 14. The record 10, 
with the flash 14 attached to its outer edge 12, is rotated in a flat 
plane of rotation. As the record 10 is rotated, the flash 14 on the outer 
edge 12 is selectively heated by focusing a heat source directly on the 
flash 14 and outer edge 12 as the record 10 rotates passed the heat 
source. Various heat sources can be utilized, such as RF heaters and the 
like, but it has been found that a highly focused infrared lamp is the 
most preferred heat source in that it is hightly effective, easily 
controlled and relatively inexpensive to purchase and operate. The heat 
source is preferably located immediately before the cutter means 30 used 
to trim the flash 14 so that there will be a minimum loss of heat from the 
flash 14 and outer edge 12 of the record 10 before engaging the cutter 
means 30. The flash 14 and the portion of the record 10 immediately 
adjacent the outer edge 12, as indicated by the dotted lines on FIGS. 2, 
3, 5, 7, 9 and 11, are heated to a temperature above the glass transition 
temperature of the thermoplastic composition used to mold the record 10. 
It is preferable, however, to limit the temperature to which the flash 14 
is heated to below the flow point of the thermoplastic composition in 
order to permit a controlled removal of the flash 14 during trimming. If 
the temperature of the flash is below the glass transition temperature, 
the molded record 10 will be brittle and tend to break and edge crack will 
occur during trimming. If the temperature of the thermoplastic composition 
is raised significantly above the glass transition temperature, for 
example, to the flow point of the thermoplastic composition, the flash 14 
will not be removed smoothly and the outer protective bead 24 will tend to 
be drawn and distorted during trimming. It is important that the heating 
of the outer edge 12 be limited to the portion of the area which is 
immediately adjacent the flash 14 in order to prevent warping of the 
entire record 10. To limit the amount of heating of the outer edge 12, the 
heat source is precisely focused on the flash 14 and outer edge 12 of the 
record 10. 
The flash 14 is trimmed from the record 10 preferably by tangentially 
advancing a cutter means 30 through the heated flash 14. The flash 14 can 
be removed over the course of only approximately one revolution of the 
record 10 by rapidly advancing the cutter means 30 through the entire 
width of the flash 14 to a point on the outer edge 12 of the record 10. 
However, in practice it has been found preferable to remove the flash 14 
over a series of revolutions in that it provides more precise trimming and 
lessens the danger of breakage and edge cracking. As illustrated in FIGS. 
4 to 11, in the preferred method of this invention, the thick irregular 
shaped section 28 of the flash 14 is initially removed by first plunging 
the cutter means 30 rapidly through the irregular shaped section 28 and 
then rotating the record 10 about one full revolution. As illustrated in 
FIGS. 4 and 5 which show the trimming at point A on FIG. 1, the irregular 
shaped section 28 of the flash 14 is removed during the first revolution. 
Thereafter in subsequent revolutions, the cutter means 30 is advanced more 
slowly in the tangential direction so as to remove the thin web 26 of the 
remaining flash 14 in a number of revolutions as shown in FIGS. 6 through 
9. In FIGS. 6 and 7, the relationship of the cutter means 30 and the flash 
14 at point B on FIG. 1 is shown in detail. The cutter means 30 is 
advancing through the flash 14 to about the mid-point of the thin web 26 
of the flash 14. In FIGS. 8 and 9, the relationship of the cutter means 30 
to the flash 14 at point C in FIG. 1 is shown in detail. The cutter means 
30 is shown as it tangentially approaches and meets the other edge 12 of 
the record 10. 
The gradual removal of the flash 14 over a plurality of revolutions has 
several advantages. One of the more important advantages is that the 
removal of the thick irregular section 28 of the flash 14 in the initial 
rotation allows the thin web 26 of the flash 14 to be exposed directly to 
a heat source focused in the plane of rotation. The remaining thin web 26 
of the flash 14 being closer to the heat source and being substantially 
thinner than the protective bead 24 can be rapidly and selectively heated 
to the glass transition temperature while the protective bead 24, being 
more massive and preferably being cooled by heat sinks, will remain in a 
hardened condition except for the portion of the outer edge 12 immediately 
adjacent the flash 14. 
In FIGS. 10 and 11 there is shown in greater detail the finishing of outer 
edge 12 of the record 10 which occurs at point D on FIG. 1. As shown in 
FIGS. 10 and 11, the cutter means 30, which has a flat rearward surface 
32, is advanced through a tangent point on the outer edge 12 of the record 
10. The flat back surface 32 of the cutter means 30 is brought into 
sliding contact with the outer edge 12 of the record 10 as is best shown 
in FIG. 11. The outer edge 12 of the record 10, being in a softened 
condition as a result of being heated to and maintained above its glass 
transition temperature, is effectively shaped in a finished configuration 
by the flat back surface 32 of the cutter means 30, the flat back surface 
32 in effect being a shaping tool. During the finishing step, the rough 
edge produced during trimming and imperfections, such as rough spots and 
strings of plastic extending from the outer edge 12, are corrected to 
provide a smooth outer surface. The heating of the outer edge 12 and the 
shaping and finishing are continued until the desired smoothness and 
roundness is obtained. Once the shaping and finishing of the outer edge 12 
is completed, he cutter means 30 is disengaged from the outer edge 12 and 
the heating is discontinued. The thermoplastic composition at the outer 
edge 12 is then allowed to cool below its glass transition temperature and 
solidify in the desired configuration. 
In the preferred method of this invention, as described above, the shaping 
tool which is used is formed as an integral part of the cutter means 30 in 
that it allows one moving part to conduct two functions, namely, to remove 
the flash 14 and finish the outer edge 12. It is possible, however, to use 
a separate tool for trimming the flash 14 and another for finishing the 
outer edge 12. The forming surface of the shaping tool, whether it is an 
integral part of the cutter means 30 or a separate tool, can be of various 
selected shapes so as to impart a given desired configuration to the outer 
edge 12 of the record 10. 
Apparatus 34 for practicing the method of this invention is schematically 
illustrated in FIGS. 12 and 13. The apparatus 34 includes a support means 
36 for holding and rotating a record 10 about its center. The support 
means 36 has a lower turntable 38 which is connected to a drive motor 40 
for rotating the lower turntable 38. An upper turntable 42 is also 
provided which moves vertically, as indicated by the arrow 46, into and 
out of engagement with the lower turntable 38 so as to permit loading of a 
record 10 and thereafter cause the record 10 to rotate. The upper and 
lower turntables 38, 42 are of diameter so as to extend to and engage the 
protective bead 24 of a record 10 positioned between them. The upper and 
lower turntables 38, 42 are made of a good heat conductor, such as 
aluminum, so as to act as heat sinks to prevent excessive amounts of heat 
from being transferred to the recorded area 20 of a record 10 held between 
the turntables 38, 42. 
A cutter 48 is located adjacent the turntables 38, 42 for trimming of flash 
14 from a record 10 held between the turntables 38, 42. The cutter 48 
illustrated in FIGS. 12 through 14 for use in this invention is a single 
blade unheated knife having a leading cutting edge 50. Other types of 
cutters can likewise be used, such as guillotine cutters, scissors 
cutters, and the like, but for reasons to be explained below, the single 
blade cutter 48 is the most preferred type of cutter for use with the 
apparatus 34 of this invention. 
The cutter 48 is moveably mounted on a guide means 52 which is positioned 
adjacent the turntables 38, 42. As best illustrated in FIGS. 12 and 13, 
the cutter means 48 is mounted on a slide 54 which in turn is guided by a 
set of rails 56. Other types of guidance systems can be used for directing 
the cutter means 48. The guide means 50 is specifically designed so as to 
advance the cutter 48 at a predetermined rate in a path which is 
tangential to the outer edge 12 of the record 10. The speed of advancement 
can be selected to removal all of the flash 14 in the course of about one 
revolution. Preferably, however, the guide means 50 is programmed to 
advance the cutter 48 rapidly as, for example, in a plunge cut through 
thick section 28 of the flash 14 and then to remove the thick section 28 
during one revolution of the record 10. The cutter 48 is then advanced at 
a slower rate to remove the remaining thin web 26 of the flash 14 over 
several additional revolutions. 
A further essential part of the apparatus 34 of this invention is a heating 
means 58 positioned adjacent to the support means 36. The heating means 58 
includes a heat source 60 and support structure 62 for positioning the 
heat source 60. The heat source 60 should be capable of being focused at a 
relatively small area and of rapidly heating material presented in the 
area. More specifically, the heat source 60 should be capable of being 
focused on the flash 14 and outer edge 12 of a record 10 held by the 
support means 36, and heating the flash 14 to a temperature above its 
glass transition temperature as the record 10 is rotated past the heat 
source 60. It is preferable in order to have as uniform a heating as 
possible, that the heat source 60 be located in the plane of rotation of 
the record 10 as indicated by the dotted line on FIG. 13. The heat source 
60 can be of various types, but preferably is an infrared lamp. The 
heating means 58 is positioned as close as possible to the cutter 48 so 
that the cutter 48 so that the cutter 48 is able to trim the flash 14 
before it cools down. 
Another important element of the apparatus 34 of this invention is a 
shaping means for finishing the outer edge 12 of the trimmed record 10. 
There are two types of shaping means which are preferably used with the 
apparatus 34 of this invention. One type of shaping means is formed as an 
integral part of the cutter 48. More particularly, the back surface 64 of 
a single blade cutter 48 is shaped to finish the outer edge 12 of a record 
10. The most simple and perhaps the most useful shaping tool is formed by 
using a flat planar rear surface of a single blade cutter 48 to shape the 
outer edge 12. This is shown in operation in FIGS. 10 and 11 wherein the 
outer edge 12 of the record 10 is finished with a flat surface 32. 
Alternatively, the back surface 66 of a single blade cutter 68 can be 
shaped in the desired configuration or a shaped insert 70 can be secured 
to the cutter 68 so as to form an integral part of the cutter 68 as shown 
in FIG. 15. 
An alternate embodiment which can be used with single blade cutters 48, but 
preferably is used with scissor cutters or the like, includes a separate 
shaping means 72 positioned adjacent the support means 36. The separate 
shaping means 72 has an edge shaping tool 74 whose position which is 
controlled with, for example, an air cylinder 76. The shaping tool 74 
mounted in the separate shaping means 72 can have various configurations 
similar to shaping tools formed as part of the cutter blade 68. The 
shaping tool 74 can be planar to form a flat on the outer edge 12 or can 
have a shaped surface such as a concave forming groove 78 as shown in FIG. 
16. 
In operation, a record 10 having flash 14 attached to its outer edge 12 is 
positioned on the lower turntable 38 so as to be centered. The upper 
turntable 42 is then brought into contact with the record 10 so as to hold 
the record 10 about its protective bead 24. The motor 40 is used to rotate 
the turntables 38, 42 and thus the record 10 about its center. The heat 
source 60 is actuated and focused on the flash 14 in the plane of 
rotation. As the record 10 is rotated, the flash 14 will be heated above 
its glass transition temperature. Once this point is reached, a cutter, 
preferably a single blade cutter 48, is advanced in a tangential path 
toward a point on the outer edge 12 of the record 10. The cutter is 
preferably rapidly plunged through the thick section 28 of the flash 14 
and then held in position while the record 10 is rotated until the thick 
section 28 of the flash 14 is removed, this being about one revolution of 
the record 10. Thereafter, the cutter is advanced slowly in a tangential 
path so as to remove the remaining thin web 26 of flash 14 in a series of 
revolutions of the record 10. After the leading edge of the cutter has 
passed through the tangent point, the advance of the cutter is stopped or 
slowed considerably so the outer edge 12 of the record 10 rotates against 
the back surface 64 of the cutter which if it has a predetermined shape 
corresponding to the edge configuration desired to be imparted to the 
outer edge 12 of the record 10. Alternatively, the cutter, after reaching 
the tangent point, can be retracted to its starting position and a 
separate shaping tool 72 brought into contact with the outer edge 12. The 
record 10 is rotated with the shaping tool 72 in contact with the heated 
outer edge 12 until the outer edge 12 is finished in the desired 
configuration. 
After the outer edge 12 has been finished in the desired configuration to 
the required smoothness, the shaping tool, whether it be part of the 
cutter or a separate tool 72, is disengaged and the heating of the outer 
edge 12 is discontinued. The outer edge 12 of the record 10 is allowed to 
cool to a temperature below the glass transition temperature. The upper 
turntable 42 is then separated from the lower turntable 38 and the 
trimmed, finished record is removed. 
The method and apparatus of this invention has been found to produce 
finished records having an outer edge quality not heretofore obtainable 
using the prior art conventional methods. In addition, the problems of 
breakage and edge cracking due to trimming have been eliminated.