Curing apparatus for molding compound

An apparatus for curing a sheet molding compound which comprises at least one pair of molds disposed along a path of transport of the sheet molding compound. The molds defines a cavity therebetween for passage of the sheet molding compound, which has been generally semi- cured and shaped by a shaping apparatus to a predetermined shape, to heat the generally semi-cured sheet molding compound. At least one of the molds is in the form of a movable mold effective to vary a cross-sectional shape of the cavity to follow a thermal expansion and shrinkage which take place in the sheet molding compound during a curing process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a curing apparatus for curing a 
molding compound and, more particularly, to the curing apparatus for 
curing a semi-cured sheet molding compound (such as SMC material or TMC 
material) prepared from unsaturated polyester resin or epoxy resin 
impregnated with reinforcement such as glass fibers, carbon fibers, etc. 
and filler, pigment agent, thickener, inner mold release and an additive 
such as, for example, high temperature curing agent, by heating the sheet 
molding compound after the latter has been shaped by a shaping apparatus 
to a required shape with the fibers oriented in a required direction if 
necessary. 
2. Description of the Prior Art 
The assignee of the present invention has suggested, in JP Laid-open Patent 
Publication No. 5-069450 published Mar. 23, 1993 (or EP-A1-0503554 
published Sep. 16, 1992; U.S. application. Ser. No. 849,662 filed Mar. 10, 
1992; or Taiwan Patent Appln. No. 81101852 filed Mar. 11, 1992), a dry 
material molding method and a dry material of a compound material using a 
semi-cured, fiber-reinforced sheet molding compound such as SMC or TMC 
material for press-molding. 
The molding apparatus referred to above comprises a plurality of rolls in 
combination with either a die mold or a corresponding number of die rolls 
positioned one above the other to define a transport passage therebetween. 
As the semi-cured sheet molding compound is transported through the 
transport passage between the rolls and the die mold or the die rolls, 
either the rolls or the die mold or die rolls, for example, the rolls, are 
moved repeatedly close towards and away from the die mold or die rolls to 
compress the sheet molding compound to a desired thickness so as to shape 
the sheet molding compound and also to orient the reinforcement fibers 
contained therein in a predetermined direction. The pressure applied from 
the rolls to the sheet molding compound to compress the latter is varied 
as the sheet molding compound travels through the transport passage and, 
for this reason, not only is control of the orientation of the 
reinforcement fibers contained in the sheet molding compound possible, but 
it is also possible to orient such reinforcement fibers to thereby avoid 
an arbitrary uneven flow of the material during the molding so that the 
molding compound having a desired or predetermined cross-sectional shape 
can be obtained. 
The suggested molding apparatus includes a shaping apparatus comprising 
rolls and die rolls positioned one above the other for shaping the sheet 
molding compound, containing an additive such as a high temperature curing 
agent, at normal temperatures while the sheet molding compound is in a 
substantially semi-cured state. The molding apparatus also includes a heat 
curing apparatus for curing the shaped sheet molding compound. Thus, the 
suggested molding apparatus is featured in that the shaping and the curing 
are carried out separately but in succession, and the curing apparatus is 
operable merely to perform the curing. 
The molding apparatus disclosed in the above mentioned prior application 
suggests two types of curing apparatus to be installed next to the shaping 
apparatus: 
1) A die in the shaping apparatus is loaded into the curing apparatus while 
the molding compound is retained on the die, and the molding compound is 
cured by heating for a predetermined length of time by means of a heating 
means such as, for example, a heater or hot air device embedded in the 
molding apparatus. 
2) As shown in FIG. 12 of the accompanying drawings and in JP Laid-open 
Patent Publication No. 5-069450 published Mar. 23, 1993 (or EP-A1-0503554 
published Sep. 16, 1992; U.S. appln. Ser. No. 849,662 filed Mar. 10, 1992; 
or Taiwan Patent Appln. No. 81101852 filed Mar. 11, 1992), a curing 
apparatus 4 having a transport passage 5 of a cross-sectional shape 
complemental to that of the sheet molding compound 6 is installed 
preceding a cutting unit 7 and next to a shaping apparatus 3 comprising 
rolls 1 and die rolls 2 positioned one above the other. This curing 
apparatus 4 includes a guide zone 4A, a primary curing zone 4B, a 
secondary curing zone 4C and a third curing zone 4D defined therein in 
this order from an upstream end to a downstream end. Respective portions 
of the transport passage 5 in the guide and primary curing zones 4A and 4B 
are of a size sufficient to provide a clearance relative to an outer 
perimeter of the sheet molding compound defined by the shaping apparatus 
whereas a portion of the transport passage 5 in the third curing zone 4D 
is slightly undersized or slightly oversized relative to the outer 
perimeter of the sheet molding compound so as to accommodate a thermal 
characteristic of the sheet molding compound being treated. 
The semi-cured sheet molding compound such as SMC material is, after having 
been shaped by the shaping apparatus to a desired shape, cured by heating. 
A series of experiments have, however, shown that, as shown in FIG. 11, 
during the curing treatment of the sheet molding compound, the latter 
tends to thermally expand and then shrink and the shrinkage will no longer 
take place after the sheet molding compound has been shrunken a 
predetermined quantity. As shown by solid, dotted and chain lines in the 
graph of FIG. 11, the amount of expansion and that of shrinkage vary with 
the type of the SMC material. In other words, the solid line indicates 
that the maximum amount of thermal expansion is 0.60 mm; the dotted line 
indicates that the maximum amount of thermal expansion is 0.49 mm; and the 
chain line indicates that the maximum amount of thermal expansion is 0.39 
mm. Thus, the amount of thermal expansion is not uniform for all of the 
sheet molding compounds. 
The apparatus suggested under (1) above is used to provide a product having 
predetermined length and cannot therefore be used for curing a long or 
continuous sheet molding compound. 
Also, the apparatus suggested under (2) above cannot be operable where both 
of the coefficient of thermal expansion and the coefficient of thermal 
shrinkage vary since the cross-sectional shape of the transport passage 
through which the sheet molding compound is transported is fixed. 
Accordingly, in the case, for example, where the coefficient of thermal 
expansion is high as compared with the cross-sectional shape of the 
transport passage, an excessive load will act on the sheet molding 
compound, whereas in the case where the coefficient of thermal shrinkage 
is low as compared with the cross-sectional shape of the transport passage 
a molding face defining the transport passage will not contact the sheet 
molding compound resulting in not only an insufficient heating of the 
sheet molding compound, but also a failure to form a smooth exterior 
surface of the eventually cured molding compound. 
SUMMARY OF THE INVENTION 
The present invention has been developed in view of the foregoing problems 
and has for its object to provide an improved curing apparatus for curing 
a continuous sheet molding compound, which apparatus is effective to 
accommodate the thermal expansion and shrinkage of the sheet molding 
compound during the curing process to thereby to accomplish an optimum 
heating and also to provide an authentically excellent surface appearance 
of the eventually cured molding compound. 
To this end, the present invention in one aspect provides an apparatus for 
curing a sheet molding compound which comprises at least one pair of molds 
disposed along a path of transport of the sheet molding compound. The 
molds define a cavity therebetween for passage of the sheet molding 
compound, which has been generally semi-cured and shaped by a shaping 
device to a predetermined shape, to heat the generally semi-cured sheet 
molding compound. At least one of the molds is in the form of a movable 
mold effective to vary a cross-sectional shape of the cavity to follow a 
thermal expansion and shrinkage which take place in the sheet molding 
compound during a curing process. 
According to another aspect of the present invention, the curing apparatus 
comprises at least first, second and third curing zones each including 
upper and lower molds supported one above the other. The first curing zone 
is positioned next to the shaping apparatus to receive the sheet molding 
compound while the second curing zones is positioned intermediate between 
the first and third curing zones. Each of the curing zones has a cavity 
defined between the associated upper and lower molds so that the cavities 
in the first to third curing zones may cooperate to define a transport 
passage in the curing apparatus for continuous transportation of the sheet 
molding compound therethrough. The cavity in the first curing zone is 
preferably tapered towards the cavity in the second curing zone. One of 
the upper and lower molds in the second curing zone is supported for 
movement towards and away from the other of the upper and lower molds in 
the second curing zone. 
The curing of the molding compound may be carried out by heating it by 
means of a heating means in the molds, at normal temperature where a 
normal temperature curing agent is mixed in the molding compound, or by 
radiation with rays of light. All of these techniques may be employed in 
the case where it is desired to cure the molding compound within the molds 
and are conveniently employed where during the curing process the molding 
compound undergoes a change in volume as a result of thermal expansion and 
thermal shrinkage. 
Preferably, the cavity in the first molding zone has entry and exit ends 
adjacent to and remote from the shaping apparatus, respectively, the entry 
end of the cavity in the first molding zone being of a cross-sectional 
shape adjusted to provide a clearance relative to the sheet of molding 
compound, the exit end of the cavity in the first curing zone being of a 
cross-sectional shape substantially similar to or slightly larger than the 
design cross-sectional size of the sheet molding compound. 
The first curing zone is a zone where the curing of the semi-cured sheet 
molding compound is initiated and the extent to which the sheet molding 
compound is expanded thermally is small, for example, about 0.2 mm at the 
entry end of the first curing zone. As described above, the 
cross-sectional shape of the transport passage at the entry end of the 
first curing zone is of a size sufficient to provide the clearance 
relative to the sheet molding compound so that the latter can smoothly be 
introduced into the remaining portion of the transport passage. On the 
other hand, the cross-sectional shape of the transport passage in the 
first curing zone progressively decreases from the entry end towards the 
exit end of the first curing zone to cause the molding face to contact the 
sheet molding compound being cured so that the cross-sectional shape of 
the sheet molding compound may eventually represent substantially that of 
the completely cured molding compound or be slightly larger than the 
completely cured molding compound. 
Due to the presence of the clearance at the entry end of the first curing 
zone, the sheet molding compound is cured by radiation heat in the case of 
the use of a heating means and, as the clearance decreases, the sheet 
molding compound is sufficiently heated in contact with the molding face. 
As hereinbefore discussed, other than the use of the heating means, curing 
at normal temperature or the use of any other heating means may be 
employed to facilitate the curing. 
The second curing zone is a zone where the thermal expansion of the sheet 
molding compound reaches a maximum thermal expansion followed by a thermal 
shrinkage. In this second curing zone, the sheet molding compound has 
attained a rigidity and, therefore, when the sheet molding compound 
contacts the molds while having been thermally expanded, a friction is 
developed therebetween to an extent that the sheet molding compound is no 
longer moved merely relying on a force with which the sheet molding 
compound is transported. Therefore, in the second curing zone, one of the 
upper and lower molds is supported for movement relative to the other of 
the upper and lower molds so that the movable mold can be displaced 
relative to the fixed mold to accommodate the thermal expansion of the 
sheet molding compound, allowing the sheet molding compound to slidingly 
contact the molding face of the movable mold at all times. 
Preferably, the movable mold in the second curing zone is urged under a low 
or null pressure towards the cavity in the second curing zone so that the 
movable mold can be displaced in accordance with a change in volume of the 
molding compound material without substantially applying any pressure to 
the sheet molding compound to keep the sheet molding compound in sliding 
contact with the molding face of the movable mold. The molding face of the 
movable mold does preferably contact one of the opposite surfaces of the 
sheet molding compound which eventually provides an exterior surface, so 
that the one of the surfaces of the sheet molding compound can be smoothed 
to provide the authentically excellent surface appearance. 
Preferably, the fixed mold in the second curing zone includes a plurality 
of juxtaposed support rollers, top line portions of the juxtaposed support 
rollers lying in a common plane along which the sheet molding compound 
moves. These support rollers may be elastically yieldably supported by 
means of a corresponding number of elastic elements. With this system, the 
friction developed between the sheet molding compound and the fixed mold 
can be minimized, and this is particularly true where the elastic elements 
are employed to elastically yieldably support the support rollers. 
A portion of the curing apparatus adjacent the exit end of the second 
curing zone is the third curing zone in which the sheet molding compound 
having been thermally shrunken no longer undergoes any change in shape and 
is maintained at a substantially constant shape. Therefore, the upper and 
lower molds in this third curing zone are adjusted so that the cavity in 
the third curing zone represents a uniform cross-sectional shape over the 
length thereof while providing a slight clearance relative to the 
substantially cured sheet molding compound being slid through the cavity 
in the third curing zone. 
It is to be noted that the use of the third curing zone is not always 
essential and the second curing zone may extend to the exit opening of the 
curing apparatus. 
Preferably, a heating means may be embedded in any one of the upper and 
lower molds in any one of the first to third curing zones, in combination 
with a temperature control means for controlling the heating means so that 
the sheet molding compound being transported through the transport passage 
can be cured in a controlled manner. 
The sheet molding compound which may be employed in the practice of the 
present invention may be a SMC (sheet molding compound) material which 
contains fiber reinforced resins and which is prepared by mixing a 
resinous compound, comprising unsaturated polyester resin or epoxy resin 
mixed with additives such as filler material, thickener, release agent, 
dyes and others. The compound is impregnated with reinforcement fibers 
such as chopped strands, and then the fiber reinforced resinous compound 
is sandwiched between polyethylene sheets to provide a laminar sheet and 
is finally the laminar sheet is heated to a maturing temperature (e.g., 
40.degree. C.) to increase the viscosity of the resinous compound to 
thereby render it non-viscous. 
The curing apparatus of the present invention is conveniently used in 
association with the shaping apparatus disclosed in the previously 
mentioned publication. 
As hereinbefore indicated, in the curing apparatus of the present 
invention, since the cavity in the first curing zone is so adjusted as to 
have a cross-sectional shape sufficient to provide a clearance relative to 
the sheet molding compound, the latter can be smoothly introduced into the 
transport passage in the curing apparatus. Also, since the clearance can 
be progressively decreased, the heating by radiation can be followed by 
contact heating and, therefore, the sheet molding compound can be 
sufficiently cured by heating. 
Also, in the second curing zone in which the sheet molding compound has 
gained a sufficient rigidity and the amount of change in volume resulting 
from the thermal expansion and shrinkage of the sheet molding compound is 
large, the movable mold is displaced to accommodate the thermal expansion 
and shrinkage of the sheet molding compound and, therefore, no excessive 
frictional force is developed between it and the molds, allowing a smooth 
transport of the sheet molding compound. Also, since no excessive load is 
imposed on the sheet molding compound during the thermal expansion taking 
place, the orientation of the reinforcement fibers in the sheet molding 
compound can be maintained as given ideally during the shaping process. In 
other words, during curing of the sheet molding compound by heating, the 
orientation of the reinforcement fibers is not damaged.

DETAILED DESCRIPTION OF THE EMBODIMENT 
Referring first to FIG. 1, a curing apparatus embodying the present 
invention is shown in the form of a curing apparatus 10 and installed in 
any known molding apparatus, such as shown in FIG. 12, at a curing site 
downstream of a shaping apparatus 3 and upstream of a cutting unit 7 with 
respect to the direction in which a continuous sheet molding compound 6 of 
a generally rectangular cross-section is transported therethrough. The 
shaping apparatus 3 of a type employed in the prior art molding apparatus 
shown in FIG. 12, includes a lower group of juxtaposed rolls 1 and a upper 
group of juxtaposed die rolls 2, the upper and lower groups of the rolls 1 
and 2 being positioned one above the other so as to define a transport 
passage through which the sheet molding compound 6 is transported towards 
the curing apparatus 10. 
The curing apparatus 10 has a guide passage 21 having a cross-sectional 
shape complemental to that of the sheet molding compound 6 defined therein 
with one end thereof communicated with the transport passage in the 
shaping apparatus 3. This curing apparatus 10 has first, second and third 
curing zones Z1, Z2 and Z3 defined therein in the order from an upstream 
side towards a downstream side thereof. An upstream portion of the guide 
passage 21 encompassed by the first curing zone Z1 is of a size sufficient 
to provide a clearance around a cross-sectional size of the rectangular 
cross-sectioned sheet molding compound 6, while a downstream portion of 
the guide passage 21 encompassed by the third curing zone Z3 is of a size 
either substantially equal to or slightly oversized relative to the 
cross-sectional size of the sheet molding compound depending on a thermal 
characteristic of the sheet molding compound 6. 
The shaping apparatus 3 so far shown in FIG. 1 is of a four-stage rolling 
design wherein the upper group of the four rolls 1 and the lower group of 
the four die rolls 2 are employed in paired fashion. The lower die rolls 1 
are drivingly coupled with a common drive mechanism while the upper rolls 
2 are rotatably supported. The lower and upper groups of the rolls 1 and 2 
are so arranged that the distance of spacing S between the lower and upper 
groups of the rolls 1 and 2 progressively decreases from a first shaping 
stage towards a final shaping stage conforming to the direction of 
transport of the sheet molding compound 6. 
The sheet molding compound 6 is preferably in the form of an SMC material 
which is a semi-cured molding material of unsaturated polyester resin 
impregnated with reinforcement fibers. As this sheet molding compound 6 is 
transported through the transport passage in the shaping apparatus 3, the 
sheet molding compound 6 is stepwisely compressed by the rolls 1 and 2 at 
normal temperatures so as to represent a predetermined cross-sectional 
shape (e.g., complemental to the shape of a generally U-sectioned cavity 
12A in a mold assembly as shown in FIG. 3). 
The curing apparatus 10 has an entry end X and an exit end Y defined 
adjacent the shaping apparatus 3 and the cutting unit 7, respectively, and 
also has the first, second and third curing zones Z1, Z2 and Z3 as 
described above. This curing apparatus 10 includes upper and lower molds 
13 and 14, 15 and 16, or 17 and 18 in each of the upstream, intermediate 
and downstream portions thereof, which molds are closely positioned 
relative to each other in a direction conforming to the direction of 
transport of the sheet molding compound The guide passage 12 extends from 
the entry end X to the exit end Y of the curing apparatus 10 and is 
delimited between the upper molds 13, 15 and 17 and the lower molds 14, 16 
and 18. 
In the curing apparatus 10 shown in FIG. 2, the upper and lower molds 13 
and 14 in the first curing zone Z1 and the upper and lower molds 17 and 18 
in the third curing zone Z3 are fixed in position, whereas in the second 
curing zone Z2 the upper mold 15 is supported for movement close towards 
and away from the lower mold 16 which is fixed in position. 
More specifically, as shown in FIGS. 2 to 9, all of the upper and lower 
molds forming the curing apparatus 10 are housed within a mold enclosure 
(or mold housing) 20 made of heat insulating material. A portion of the 
mold enclosure 20 adjacent the entry end X is formed with an entry opening 
21 while a portion of the mold enclosure 20 adjacent the exit end Y is 
formed with an exit opening 22, the entry and exit openings 21 and 22 
leading to and from the guide passage 12, respectively. 
The lower molds 14, 16 and 18 of the curing apparatus 10 are fixed to the 
mold enclosure 20. However, the upper molds 13 and 17 paired respectively 
with the lower molds 14 and 18 are fixed to associated upper mold holders 
23 and 25 fixedly secured to the mold enclosure 20 while the upper mold 15 
paired with the lower mold 16 is supported by an upper mold holder 24, 
fixedly secured to the mold enclosure 20, for movement up and down, that 
is, in a direction towards and away from the associated lower mold 
As best shown in FIGS. 3 and 4, the first curing zone Z1 includes the upper 
mold 13 fixedly connected to the upper mold holder 23. This upper mold 13 
cooperates with the lower mold 14 to define a generally U-sectioned cavity 
12A as best shown in FIG. 3, the cavity 12A having a size uniform over the 
entire length thereof from an entry end a to an exit end b thereof since 
the upper and lower molds 13 and 14 are fixed in position. 
As best shown in FIG. 4, over the length of the upper mold 13 from the 
entry end a to the exit end b, the upper mold 13 has a molding face 13a 
which is inclined towards a mating molding face 14a of the lower mold 14 
so as to progressively decrease the clearance between it and the sheet 
molding compound 6 being transported. This can be accomplished by using 
the upper mold 13 having a thickness progressively increasing from the 
entry end a towards the exit end b as best shown in FIG. 4. 
The cross-sectional shape of a portion of the cavity 12A adjacent the entry 
end a is so chosen as to have a size larger than the cross-section of the 
sheet molding compound which has been shaped by the shaping apparatus 3, 
so that a sufficient clearance can be created. Therefore, the 
semi-hardened sheet molding compound 6 shaped by the shaping apparatus 3 
can smoothly be inserted into the cavity 12A with no difficulty. 
On the other hand, the cross-sectional shape of another portion of the 
cavity 12A adjacent the exit end b is so chosen as to be substantially 
equal to or slightly larger than a design cross-sectional size of the 
sheet molding compound 6 so that the sheet molding compound 6 approaches 
the molding faces 13a and 14a. 
Each of the upper and lower molds 13 and 14 and the upper mold holder 23 
has a plurality of sheath heaters 26 embedded therein and spaced a 
predetermined distance from each other. These sheath heaters 26 are used 
to heat the upper and lower molds 13 and 14 and the upper mold holder 23 
to a predetermined temperature. It is, however, to be noted that, in place 
of electric heaters such as the sheath heaters 26, any suitable heating 
means such as a heating jacket for circulating a pressurized steam or 
heated oil therethrough may be employed. 
As best shown in FIGS. 5 to 7, in the second curing zone Z2, while the 
lower mold 16 is fixed to the mold enclosure 20, the upper mold 15 is not 
fixed to the upper mold holder 24, but is secured to lower ends of 
respective support rods 27 so that the upper mold 15 can be selectively 
lowered and elevated relative to the associated lower mold 16 and in a 
direction towards and away from the upper mold holder 24. Each of the 
support rods 27 slidably extends through bearing holes 24a and 20d formed 
in the upper mold holder 24 and an upper wall 20c of the mold enclosure 
20, respectively. An upper end of each support rod 27 protruding outwardly 
from the upper wall of the mold enclosure 20 further extends slidably 
through a bearing hole 28a defined in a support plate 28 and is integrally 
formed with a radially outwardly extending collar 27a. A bearing 31 of 
each support rod 27 below the support plate 28 and situated within the 
bearing hole 20d in the upper wall 20c of the mold enclosure 20 is also 
formed with a radially outwardly extending collar 27b. 
Each support rod 27 has a pair of balancing coil springs 29 and 30 mounted 
therearound. The balancing coil spring 29 is interposed between the collar 
27b in the bearing 31 situated within the bearing hole 20d in the upper 
wall 20c of the mold enclosure 20 and an undersurface of the support plate 
28, while the balancing coil spring 30 is interposed between the collar 
27a at the upper end of the respective support rod 27 and an upper surface 
of the support plate 28. The balancing coil spring 30 is operable to urge 
the respective support rod 27 upwardly together with the upper mold 15, 
whereas the balancing coil spring 29 is operable to urge the respective 
support rod 27 downwardly together with the upper mold 15. The balancing 
coil springs 29 and 30 are so counterbalanced that the upper mold 15 can 
be cushioned up and down together with the support rods 27 relative to the 
support plate 28 and, at the same time, movable in a direction towards and 
away from the associated lower mold 16. 
With the support rods 27 retained by the balancing coil springs 29 and 30 
in the-manner described above, the upper mold 15 secured to the lower ends 
of the support rods 27 is normally biased towards the associated lower 
mold 16 under a low pressure (for example, 4,900 Pa in the illustrated 
embodiment). In other words, the balancing coil springs 29 and 30 are so 
chosen as to exert a low pressure of, for example, 4,900 Pa with which the 
upper mold 15 can be biased towards the associated lower mold 16. 
Accordingly, when the sheet molding compound 6 being passed between the 
upper and lower molds 15 and 16 undergoes a thermal expansion, the upper 
mold 15 can be shifted upwardly together with the support rods 27 to such 
a position as shown in FIG. 6 to thereby accommodate the thermal expansion 
of the sheet molding compound 6. The balancing coil spring 30 may be of a 
type having a relatively large diameter and also having a spring constant 
of 1.58 kgf/mm and the balancing coil spring 29 may be of a type having a 
relatively small diameter and also having a spring constant of 1.31 
kgf/mm, the spring constant of the system of these springs being 2.89 
kgf/mm. 
Since each movable mold is supported by the above two systems and Since the 
spring constant of each movable mold is 5.78 kgf/mm (=2.89.times.2) and 
the area of projection surface of each movable mold is (75 mm.times.300 
mm), a 1 mm displacement results in a pressure of 0.025 kgf/cm.sup.2 
[=(5.78.times.1.0)/(7.5.times.30)] or 2,520 Pa. 
It is to be noted that the above described biasing means may not be always 
limited to double springs, but any means effective to permit the upper 
mold 15 to move up or down in response to expansion or .contraction of the 
sheet molding compound 6 may be employed. In a normal state, however, a 
gap 33 as shown in FIG. 5 is formed between an upper face of the upper 
mold 15 and the upper mold holder 24 to accommodate a stroke of movement 
of the upper mold 15 so that the cross-section of a cavity 12B formed 
between molding faces 15a and 16a of the respective upper and lower molds 
15 and 16 varied. 
As best shown in FIG. 7, the upper mold 15 in the second curing zone Z2 has 
a cross-sectional shape uniform over the entire length thereof from an 
entry end b' to an exit end c and, therefore, the cavity 12B formed 
between the molding faces 15a and 16a of the upper and lower molds 15 and 
16 has a cross-sectional shape similarly uniform over the entire length 
thereof from the entry end b' to the exit end c. It is to be noted that, 
where the length of the second curing zone Z2 in a direction conforming to 
the direction of transport of the sheet molding compound 6 is small, a one 
point support system for the support of the upper mold 15, that is, the 
use of a single support rod 27 at a location intermediate of the length of 
the upper mold 15, may be sufficient. On the contrary thereto, where the 
second curing zone Z2 has a substantial length, two or more support rods 
27 may be employed. 
The lower mold 16 is formed with a generally U-sectioned rectangular recess 
16b for accommodating a plurality of juxtaposed support rollers 35 as 
shown in FIGS. 5 to 7 with their longitudinal axes lying perpendicular to 
the lengthwise direction of the lower mold 16. The support rollers 35 are 
accommodated within the recess 16b with springs 34 interposed between the 
bottom of the recess 16b and the support rollers 5, the springs 34 being 
so chosen as to permit respective top points on the support rollers 35 to 
lie on the molding face 16a. Accordingly, as the sheet molding compound 6 
being passed through the cavity 12B undergoes a thermal expansion, the 
support rollers 35 are displaced downwardly against the associated springs 
34 to accommodate the thermal expansion of the sheet molding compound 6. 
It is to be noted that, in the illustrated embodiment, the lower mold 16 
has been shown and described as formed with the-single rectangular recess 
16b for accommodating the juxtaposed support rollers 35. However, the 
lower mold 16 may be formed with a plurality of recesses, one for each 
support roller 35. Alternatively, the support rollers 35 may be 
substantially embedded in the lower mold 16 with their top portions 
exposed outwardly so as to lie on the molding face 16a. It is also to be 
noted that the position where the support rollers 35 are installed and/or 
the number of the support rollers 35 may be chosen in consideration of the 
magnitude of displacement at a location where the thermal expansion of the 
sheet molding compound 6 is maximized and the length of time over which 
the maximum thermal expansion of the sheet molding compound 6 is retained. 
It is again pointed out that, although the support rollers 35 may not 
always be supported on the springs 34, friction can be 
considerably-reduced when the support rollers 35 are supported on the 
springs 34. 
Even in the second curing zone Z2, each of the upper and lower molds 15 and 
16 and the upper mold holder 24 has a plurality of sheath heaters 26 
embedded therein and spaced a predetermined distance from each other for 
heating the upper and lower molds 15 and 16 and the upper mold holder 24 
to a predetermined temperature. 
As best shown in FIGS. 8 and 9, in the third curing zone Z3, and upper mold 
17 is fixed to the upper mold holder 25 in a manner similar to the upper 
mold 13 in the first curing zone Z1. This upper mold 17 in the third 
curing zone Z3 has a shape uniform over the length thereof from an entry 
end c' to an exit end d and, hence, a cavity 12C defined between 
respective molding faces 17a and 18a of the upper and lower molds 17 and 
18 has a shape uniform over the length thereof. The cross-section of the 
cavity 12C lying in a plane transverse to the lengthwise direction thereof 
is so chosen as to be substantially equal to or slightly larger than the 
design cross-section of the substantially completely cured sheet molding 
compound 6 to thereby allow the latter to move through the cavity 12C 
while slidingly contacting the molding faces 17a and 18a. It is to be 
noted that sliding contact between the cured sheet molding compound 6 and 
the molding faces 17a and 18a may not always be essential. 
The curing of the sheet molding compound (SMC material) 6 by heating it 
within the curing apparatus 10 of the above described construction will 
now be described. 
Referring to FIG. 1, a substantially semi-cured SMC sheet 6 having a 
predetermined thickness is transported in between the rolls 1 and the die 
rolls 2 of the shaping apparatus 3. As the SMC sheet 6 is transported 
through the shaping apparatus 3, the SMC sheet 6 is stepwisely compressed 
to a generally U-shaped cross-section having a predetermined thickness and 
is subsequently supplied continuously into the curing apparatus 10 best 
shown in FIG. 2. 
The SMC sheet 6 entering the entry opening 21 of the curing apparatus 10 is 
first passed through the first curing zone Z1. Since the cross-section of 
the cavity 12A is chosen to be larger than the cross-section of the SMC 
sheet 6 so as to provide a clearance, the SMC sheet 6 can be smoothly 
supplied into the cavity 12A between the upper and lower molds 13 and 14. 
Since the clearance exists at the entry side of the cavity 12A, the SMC 
sheet 6 is heated by radiation. However, as the SMC sheet 6 being 
transported through the cavity 12A approaches the exit end b of the first 
curing zone Z1, the clearance decreases and, therefore, the SMC sheet 6 
slidingly contacts the molding faces 13a and 14a wherefor heat is directly 
conducted from the molds to the SMC sheet 6 to heat the latter. Due to the 
heating within the first curing zone Z1, the SMC sheet 6 is cured and, by 
the time it reaches the exit end b, the SMC sheet 6 comes has attained a 
rigidity. 
The SMC sheet 6 having passed through the cavity 12A in the first curing 
zone Z1 subsequently enters the second curing zone Z2 in which the SMC 
sheet 6 is heated for a predetermined length of time.. As the SMC sheet 6 
is heated in the second curing zone Z2, the SMC sheet 6 undergoes a 
thermal expansion as shown in FIG. 11 and then comes to slidingly contact 
the respective molding faces 15a and 16a of the upper and lower molds 15 
and 16. Since the molding face 16a of the lower mold 16 is fixed in 
position while the upper mold 15 is movable, the thermal expansion of the 
SMC sheet 6 having a sufficient rigidity causes the upper mold 15 to shift 
upwardly against the balancing coil springs 29 and 30 to accommodate such 
thermal expansion. 
While the upper mold 15 shifts upwardly as the thermal expansion of the SMC 
sheet 6 progresses, the upper mold reaches an upwardly shifted limit when 
the thermal expansion of the SMC sheet 6 attains a peak, followed by 
shrinkage of the SMC sheet 6. As the SMC sheet 6 shrinks, the upper mold 
having reached the upwardly shifted limit is shifted downwardly by the 
effect of the composite spring force of the balancing coil springs 29 and 
30 to allow the upper mold 15 to follow the shrinkage of the SMC sheet 6. 
It is to be noted that, since the SMC sheet 6 is continuously transported 
through the cavity 12B between the upper and lower molds 15 and 16, the 
thermal expansion of the SMC sheet 6 is greatest at a location spaced a 
predetermined distance inwardly from the entry end and, as the SMC sheet 6 
is moved past such location, thermal shrinkage takes place in the SMC 
sheet 6, with the thermal expansion and shrinkage consequently being 
depicted by respective curves similar to each other. Accordingly, the 
amount of displacement of the upper mold 15 displaceable with a change in 
volume of the SMC sheet 6 is substantially constant at the same location, 
allowing the upper mold 15 to be maintained as though retained at a 
constant position. 
Since the SMC sheet 6 has been shaped by the shaping apparatus 3 to the 
predetermined shape, application of a pressure to the SMC sheet 6 in the 
curing apparatus is not desirable. However, in the curing apparatus 10 
embodying the present invention, the movable upper mold 15 is biased by an 
extremely low pressure, or a null pressure, created by the balancing coil 
springs 29 and 30 and, therefore, the movable upper mold 15 can move in 
accordance with a change in volume of the SMC sheet 6 without imposing any 
excessive load thereon. In other words, the movable upper mold 15 can, 
while constantly slidingly contacting the SMC sheet 6, move up and down 
repeatedly to follow the volumetric change of the SMC sheet 6. 
One of the opposite surface of the SMC sheet 6 which contacts the molding 
face 15a of the upper mold 15 provides an excellent surface appearance of 
a final product obtained from the completely cured SMC sheet 6 and, 
therefore, the surface can be made smooth by allowing the SMC sheet 6 to 
slidingly contact the molding face 15a of the movable upper mold 15 at all 
times. 
On the other hand, as the SMC sheet 6 undergoes the thermal expansion 
within the second curing zone Z2, a frictional force is developed between 
the molding face 16a of the lower mold 16 and the SMC sheet 6 then 
slidingly contacts the molding face 16a. This frictional force may hamper 
a smooth movement of the SMC sheet 6 through the cavity 12B. Because of 
this, the plural support rollers 35 are accommodated within the recess 16b 
in the lower mold 16 along the molding face 16a so that the top portions 
of these support rollers 35 can contact the lower surface of the SMC sheet 
8 in a line contact fashion to thereby minimize the generation of the 
frictional force and, hence, to facilitate a smooth movement of the SMC 
sheet 8 through the cavity 12B. Accordingly, the SMC sheet 8 can be 
smoothly moved through the cavity 12B in the second curing zone Z2 as it 
is pushed from the shaping apparatus 3. 
When the amount of thermal shrinkage of the SMC sheet 6 attains a 
predetermined value subsequent to the thermal shrinkage thereof, little 
change in volume occurs in the SMC sheet 6. At this time, the SMC sheet 6 
emerges outwardly from the second curing zone Z2 and enters the third 
curing zone Z3 as shown in FIGS. 8 and 9. 
As hereinbefore described, the cavity 12C in the third curing zone Z3 has a 
uniform cross-sectional shape from the entry end c' to the exit end d. 
During the continuous passage of the SMC sheet 6 through the cavity 12C in 
the third curing zone Z3, the opposite surfaces of the SMC sheet 6 which 
then no longer undergo a change in volume are held in sliding contact with 
the respective molding faces 17a and 18a of the upper and lower molds 17 
and 18 to receive heat from the sheath heaters 26. By so doing, the SMC 
sheet 6 is completely cured as it emerges outwardly from the exit end d of 
the cavity 12C in the third curing zone Z3, that is, the exit opening 22 
of the curing apparatus 10. 
From the foregoing description of the preferred embodiment of the present 
invention, it has now become clear that, in the curing apparatus for 
curing the continuous sheet molding compound such as SMC material shaped 
by the shaping apparatus, at least one of the molds at which the sheet 
molding compound undergoes a change in volume as a result of cyclic 
thermal expansion and shrinkage is employed in the form of a movable mold 
to accommodate such characteristic of the sheet molding compound, and thus 
the possibility of application of an excessive load to the sheet molding 
compound can be eliminated advantageously. Therefore, without destroying 
the predetermined shape of the sheet molding compound defined by the 
shaping apparatus installed at a stage preceding the curing apparatus, the 
reinforcement fibers contained in the sheet molding compound can be 
ideally maintained as oriented. 
Also, it is possible to allow the molding face of the movable mold to 
slidingly contact the surface of the sheet molding compound at all times 
and, therefore, where such surface of the sheet molding compound is used 
as an excellent surface appearance of the eventually obtained product, an 
authentically excellent surface appearance can be obtained. 
Moreover, since at the entry side of the curing apparatus the 
cross-sectional shape of the cavity is so designed as to be larger than 
the cross-section of the sheet molding compound to provide a sufficient 
clearance, the sheet molding compound can smoothly be transported 
therethrough as it is pushed. Yet, in the second curing zone at which the 
sheet molding compound attains a sufficient rigidity and also undergoes 
the maximum thermal expansion, one of the molds is supported for movement 
towards and away from the other of the molds and employs a plurality of 
support rollers and, therefore, the friction between the sheet molding 
compound and any one of the molds can advantageously be reduced to 
facilitate a smooth movement of the sheet molding compound as it is 
pushed. 
Although the present invention has been described in connection with the 
preferred embodiments thereof with reference to the accompanying drawings, 
it is to be noted that various changes and modifications will be apparent 
to those skilled in the art. For example, although in the foregoing 
embodiment of the present invention the upper molds 13 and 17 in the first 
and third curing zones Z1 and Z3 have been shown and described as fixed in 
position, they may be supported for movement in a direction towards and 
away from the associated lower molds 14 and 18 in a manner similar to the 
upper mold 15 in the second curing zone Z2 as shown in FIG. 10, and they 
may optionally be provided with support rollers mounted in the lower molds 
14 and 18 in a manner similar to those in the lower mold 16 in the second 
curing zone Z2. 
Also, the use of the support rollers 35 in the second curing zone Z2 is not 
always essential in the practice of the present invention. 
A mechanism for movably supporting the upper mold in the second zone Z2 is 
not limited to the type wherein the balancing coil springs 29 and 30 are 
employed as shown and described, and any suitable mechanism capable of 
allowing the upper mold in the second curing zone Z2 to follow the 
volumetric change of the sheet molding compound may be employed. 
Accordingly, such changes and modifications are to be understood as 
included within the scope of the present invention as defined by the 
appended claims, unless they depart therefrom.