Blow molding mold for forming hollow double-walled product and blow molding apparatus using such mold

A blow molding mold for making a hollow double-walled product includes male and female mold members movable toward and away from each other. The female mold member has a bottom and has first and second pairs of confronting peripheral wall segments, the wall segments of the second pair being pivotal relative to the bottom between open and closed positions. In one embodiment, the peripheral wall segments of the first pair are fixedly coupled to the bottom. In a different embodiment, the wall segments of the first pair are also pivotal between open and closed positions, and have expansion prevention walls which project outwardly from opposite sides thereof and which, when the wall segments of the first and second pairs are in their closed positions, project outwardly beyond the peripheral wall segments of the second pair.

BACKGROUND OF THE INVENTION 
The present invention relates to a mold for molding a hollow double-walled 
product by supplying a cylindrical parison of synthetic resin extruded by 
the die of an extruder to a position between a pair of male and female 
mold members, moving the mold members toward each other to pinch and seal 
the parison therebetween, and injecting air into the parison, and a blow 
molding apparatus which employs such a mold. 
Various processes for manufacturing hollow double-walled products have been 
developed so far. Examples of such processes are disclosed in Japanese 
Patent Publications No. 46(1971)-14153, 49(1974)-18748, and 
51(1976)-13495. 
However, there are known only few molds used to mold hollow double-walled 
products. There molds are shown in Japanese Patent Publication No. 
49(1974)-41111, Japanese Laid-Open Patent Publication Nos. 60(1986)-67130, 
and 63(1988)-221020. 
According to Japanese Laid-Open Patent Publication No. 60(1986)-67130, a 
mold includes a female mold member having four separate peripheral wall 
segments and a bottom. When air is injected into the parison, the parison 
can be smoothly moved along the inner wall surfaces of the peripheral wall 
segments, so that a double-wall product having a uniform thickness can be 
molded. Double-walled products thus molded are stronger than those 
produced by conventional molds. All of the four peripheral wall segments 
are swingable outwardly, and they are required to swing in timed relation 
to the injection of air into the parison. The mold and a molding apparatus 
using the mold are therefore complex and expensive. Another problem is 
that a product molded by the mold has burrs on all four corners thereof. 
Though the molded product has a sufficient degree of mechanical strength, 
the burrs have to be removed in a subsequent step, and the product needs 
to be improved for its commercial value. 
The mold disclosed in Japanese patent Publication No. 49(1974)-4111 is only 
limited to the fabrication of a product having a body and a lid which 
share a hinge. This mold is therefore less versatile. The hinge of the 
molded product tends to be thin. 
The mold shown in Japanese Laid-Open Patent Publication No. 63(1988)-221020 
also lacks versatility because it is used exclusively to form undercuts on 
molded parts. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a blow molding mold of 
a relatively simple structure which can manufacture a double-walled 
product that has an increased depth and a uniform thickness, and a molding 
apparatus employing such a mold. 
Another object of the Present invention is to provide a blow molding mold 
including peripheral wall segments which will form therebetween no or 
little burrs on a molded product when the peripheral wall segments are 
erected so that the corners of the molded product can easily be treated 
subsequently and neatly be finished for increased commercial value, and 
molded products can be manufactured with a better yield.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Like or corresponding parts are denoted by like or corresponding reference 
characters throughout views. 
FIGS. 1 through 6 show a blow melding apparatus employing a mold according 
to an embodiment of the present invention. As shown in FIGS. 3 and 5, the 
mold comprises a female mold member 10 and a male mold member 20 which are 
fixedly mounted on a pair of support plates 30a, 30b, respectively, of a 
mold clamping device of the blow molding apparatus. 
As shown in FIGS. 1 and 6, the female mold member 10 comprises a bottom 11 
and four peripheral Wall segments 12a, 12b, 12c, 12d, confronting two of 
these peripheral wall segments being operable as a pair. The peripheral 
wall segments 12a, 12b, 12c, 12d are swingable or angularly movable 
outwardly from a closed position in which they form a box as shown in 
FIGS. 4, 5, and 6, about pivot shafts 13a, 13b, 13c, 13d, respectively. 
The pivot shafts 13a, 13b, 13c, 13d are positioned outwardly of and extend 
parallel to the respective side edges cf the bottom 11, and join the 
peripheral wall segments 12a, 12b, 12c, 12d angularly movably to the 
bottom 11. The peripheral wall segments 12a, 12b, 12c, 12d can be 
angularly moved by respective fluid-pressure or hydraulic actuator in the 
form of cylinder units 14a, 14b, 14c, 14d connected between the peripheral 
wall segments 12a, 12b, 12c, 12d and the bottom 11. 
The paired peripheral wall segments 12b, 12d have pairs of parison corner 
expansion prevention walls 15b, 16d, respectively, disposed on their 
opposite sides and extending parallel to the direction in which a parison 
(described later on) will be supplied. The corner expansion prevention 
walls 15b, 15d in each pair project away from each other. In this 
embodiment, the peripheral wall segments 12b, 12d and the corner expansion 
prevention walls 18b, 15d lie substantially flush with each other as 
having substantially two-dimensional (flat) surfaces. 
The male mold member 20 shown in FIGS. 3 and 5 is of a known structure 
comprising a single block or a plurality of blocks. If the male mold 
member 20 is composed of a plurality of blocks, some of the blocks may 
move back and forth when the mold members 10, 20 are clamped. 
The male mold member 20 has a needle-shaped air supply/discharge nozzle 21 
for being inserted into a parison, and a blow injection needle 22. 
However, only the air supply/discharge nozzle 21 may be provided, and the 
blow injection needle 22 may be dispensed with. 
A pair of parison pinching members 41 (FIG. 5) serves to flatten and fuse a 
portion of an extrusion-molded or injection-molded melted parison P 
transversely. 
The blow molding apparatus shown in FIGS. 1 through 6 operates as follows; 
The mold members 10, 20 are first fixedly mounted on the support plates 
30a, 30b, respectively, in confronting relation to each other. At this 
time, the peripheral wall segments 12b, 12d with the corner expansion 
prevention walls 15b, 15d joined thereto are oriented parallel to the 
direction in which the parison P is supplied into the blow molding 
apparatus. More specifically, when the mold members 10, 20 are installed 
on the support plates 30a, 30b with mating faces 16, 26 (FIG. 5) of the 
mold members 10, 20 being directed vertically or obliquely (at an angle 
smaller than 50 to the vertical plane), the peripheral wall segments 12b, 
12d are horizontally spaced from each other and the peripheral wall 
segments 12a, 12c are vertically spaced from each other. 
When a melted tubular parison P is to be supplied from a blow head 40 of an 
extrusion or injection molding machine, the support plates 80a, 80b are 
displaced from each other to space the mold members 10, 20 away from each 
other, and the peripheral wall segments 12a, 12b, 12c, 12d of the female 
mold member 10 are opened, i.e., angularly displaced outwardly in 
horizontal and vertical directions by the respective hydraulic actuators 
14a, 14b, 14c, 14d. At this time, the opposite side edges of the 
vertically spaced peripheral wall segments 12a, 12c are positioned very 
closely to the walls 15b, 15d joined to the horizontally spaced peripheral 
wall segments 12b, 12d. In other words, the wall segments 12b, 12d are 
erected to some extent. 
Then, the parison P is extruded from the blow head 40 into a position 
between the mold members 10, 20. The leading end of the parison P is 
temporarily pinched by the parison pinching members 41 so that the leading 
end of the parison P is scaled off. Then the parison pinching members 41 
are moved away from each other to release the parison P. Air is supplied 
from a second air supply/discharge nozzle 42 (FIG. 5) opening into the 
parison P so that the inner wall surfaces of the parison P will not adhere 
to each other. The parison P as it is extruded is moved along the inner 
surfaces of the peripheral wall segments 12b, 12d and positioned 
therebetween. After the parison P has completely been placed between the 
peripheral wall segments 12b, 12d, the trailing end of the parison P is 
sealed off by the parison pinching members 41. 
Thereafter, one or both of the support plates 30a, 30b are moved to 
displace the mold members 10, 20 toward each other until the parison P is 
lightly sandwiched between a projecting face 27 of the mold member 20 and 
an inner surface of the bottom 11 of the mold member 10 and the parison P 
is pierced by the air supply/discharge nozzle 21 on the mold member 20. 
The mold members 10, 20 are further moved toward each other to flatten the 
parison P. When the parison P is flattened to a desired size, the mold 
members 10, 20 are stopped temporarily. 
While regulating the air pressure in the parison P, the hydraulic actuators 
14a, 14b, 14c, 14d are simultaneously operated to erect the peripheral 
wall segments 12a, 12b, 12c, 12d slowly. During this time, the layer of 
the parison P which faces the female mold member 10 is brought into 
contact with the inner surfaces of the bottom 11 and the peripheral wall 
segments 12a, 12b, 12c, 12d. The parison P may also contact with the 
corner expansion prevention walls 15b, 15d. 
As the peripheral wall segments 12a, 12b, 12c, 12d are progressively 
erected with respect to the bottom 11, the layer of the parison P which 
faces the male mold member 20 is also brought into wilder contact with a 
main wall surface 28 of the mold member 20. The peripheral wall segments 
12a, 12b, 12c, 12d are finally pressed against each other along their 
adjacent edges, and also against the adjoining side edges of the bottom 
11. 
Portions of the parison P which are positioned along the adjacent edges of 
the peripheral wall segments 12a, 12b, 12c, 12d are borne by the corner 
expansion prevention walls 15b, 16d fully or substantially fully against 
outward expansion. These portions of the parison P may be wrinkled along 
the edges of the peripheral wall segments 12a, 12b, 12c, 12d, projecting 
into the parison P or increasing the wall thickness of the parison P. 
Since the parison P is not pinched between the adjacent peripheral wall 
segments 12a, 12b, 12c, 12d, no burr is formed on the parison P by these 
peripheral wall segments. 
Then, the support plates 30a, 30b age further moved toward each other to 
press the mating surfaces 16, 26 against each other. Any excessive parison 
layer then forms burrs between these mating surfaces 16, 26. 
Remaining air between the parison P and the mold members 10, 20 is removed, 
and air under pressure is injected from the air supply/discharge nozzle 21 
or the blow in needle 22 to inflate the parison P along the inner surfaces 
of the mold members 10, 20. Thereafter, the mold members 10, 20 with the 
parison P therebetween are cooled, the mold members 10, 20 are separated 
away from each other, and the peripheral wall segments 12a, 12b, 12c, 12d 
are opened or angularly moved outwardly by the respective hydraulic 
actuators 14a, 14b, 14c, 14d, after which the molded product is removed 
from the mold members 10, 20. 
The molded product of a double-walled construction has burrs on its edge 
around the open end thereof. Therefore, such burrs are removed. If any 
burrs are present on the corner edges between side panels of the product 
and the edges between the bottom panel and side panels thereof, such burrs 
are also removed. After the molded product has been deburred, it is 
presented as a finished product. 
In another blow molding process, the parison P may be supplied between the 
mold members 10, 20 in a direction across the peripheral segments 12b, 
12d, i.e., the corner expansion prevention walls 15b, 16d joined thereto, 
and the support plates 30a, 30b may be vertically movable toward and away 
from each other. In this blow molding process, the support plate 30a lied 
horizontally as shown in FIG. 4. Mere specifically, the parison P is 
horizontally supplied toward the mold members 10, 20, and then over one of 
the peripheral wall segments 12b, 12d which are open and along the inner 
surfaces of the bottom 11 and the peripheral wall segments 12b, 12d. 
Thereafter, the blow molding process is carried out as described above. 
FIGS. 7 and 8 show a female mold member according le another embodiment of 
the present invention. The female mold member 10 shown in FIGS. 7 and 8 
differs from the female mold member 10 shown in FIG. 2 in that corner 
expansion prevention walls 15b, 15d have partly conical or inwardly 
concave inner surfaces, the inner edges of which lie substantially with 
the inner surfaces of the peripheral wall segments 12b, 12d. In a blow 
molding process, the peripheral wall segments 12b, 12d are tilted more 
outwardly than those illustrated in FIG. 1. 
FIG. 9 fragmentarily shows a female mold member in accordance with still 
another embodiment of the present invention. The female mold member shown 
in FIG. 9 is substantially the same as the female mold member shown in 
FIGS. 7 and 8 except that each of corner expansion prevention walls 15b, 
15d has a number of air outlet holes 19 defined therethrough and extending 
between its inner and outer surfaces. The air outlet holes 19 are 
connected to a pressurized air source 50 through a control valve 61. While 
the peripheral wall segments 12a, 12b, 12c, 12d are being tilted inwardly 
from an outwardly open position until adjacent ones of the peripheral wall 
segments 12a, 12b, 12c, 12d are pressed against each other, warm air 
supplied from the pressurized air source 50 is injected through the air 
outlet holes 19 into the female mold member. When the air is thus 
supplied, the layers, near the walls 15b, 15d, of the parison placed in 
the female mold member are kept out of contact with the walls 15 b, 15d by 
the dynamic pressure and layer of the supplied air, and hence will not 
form burrs thereon. 
With the foregoing embodiments, since the peripheral wall segments of the 
female mold member are pivotally tiltable outwardly with respect to the 
bottom, the parison can be supplied between the male and female mold 
members with the peripheral wall segments opened outwardly. In operation, 
the parison as it is supplied is first brought into contact with the 
bottom and then held by the female mold member so as to face the male mold 
member. When the peripheral wall segments are lifted with respect to the 
bottom, they are brought into contact with the parison through a greater 
area of contact. Even when the peripheral wall segments are opened 
outwardly, gaps or spaces therebetween are closed by the corner expansion 
prevention surfaces. The air outlet holes 19 are connected to a 
pressurized air source 50 through a control valve 51. While the peripheral 
wall segments 12a, 12b, 12c, 12d are being tilted inwardly from an 
outwardly open position until adjacent ones of the peripheral wall 
segments 12a, 12b, 12c, 12d are pressed against each other, warm air 
supplied from the pressurized air source 50 is injected through the air 
outlet holes 19 into the female mold member. When the air is thus 
supplied, the layers, near the walls 15b, 15d of the parison placed in the 
female mold member are kept out of contact with the walls 15b, 15d by the 
dynamic pressure and layer of the supplied air, and hence will not form 
butts thereon. 
With the foregoing embodiments, since the peripheral wall segments of the 
female mold member are pivotally tiltable outwardly with respect to the 
bottom, the parison can be supplied between the male and female mold 
members with the peripheral wall segments opened outwardly. In operation, 
the parison as it is supplied is first brought into contact with the 
bottom and then held by the female mold member so as to face the male mold 
member. When the peripheral wall segments are lifted with respect to the 
bottom, they are brought into contact with the parison through a greater 
area of contact. Even when the peripheral wall segments are opened 
outwardly, gaps or spaces therebetween are closed by the corner expansion 
prevention walls which thus prevent the parison from being expanded 
between these corner expansion prevention walls. When the peripheral wall 
segments are fully erected with respect to the bottom, the corner 
expansion prevention walls hold the corresponding parison layers, reducing 
burrs on the parison. Alternatively, by regulating the air pressure in the 
parison, any burrs are prevented from being formed on the molded product 
at its corners and edges except the open end thereof. 
The edges between the peripheral walls or panels of the molded product are 
rendered strong since they arc thick or wrinkled inwardly. The edges and 
corners of the molded product are not reduced in thickness but the molded 
product has a substantially uniform wall thickness. Inasmuch as few burrs 
are formed on the product, the process of deburring the product is 
simplified and the material can be utilized efficiently. 
The female mold member shown in FIGS. 1 through 6 can easily be 
manufactured since the corner expansion prevention walls are simple in 
configuration. 
The female mold member shown in FIGS. 7 and 9 is advantageous in that the 
peripheral wall segments with the corner expansion prevention walls joined 
thereto can also be opened largely in the outward direction, and when the 
peripheral wall segments are opened, they are interconnected by the corner 
expansion prevention walls to prevent the parson from being overly 
expanded at the corners. Moreover, the peripheral wall segments are 
tiltable through a larger angle to form a molded product of a deeper 
double-walled construction. The peripheral wall segments may have 
substantially uniform surfaces, and may be attached to the support plate 
in an angular position which is 90.degree. different from that shown tn 
FIGS. 2 and 3. 
With the embodiment shown in FIG. 9, the corners of the parison are 
supported by the dynamic pressure or layer of air supplied from the air 
outlet holes, making the parison free of burrs. As the air outlet holes 
are connected to the pressurized air source through the control valve, the 
pressure of air to be supplied from the air outlet holes can be adjusted 
to a suitable level depending on the thickness, material, and shape of a 
parison to be introduced into the blow molding apparatus. 
FIG. 10 shows a female mold member according to yet another embodiment of 
the present invention. The female mold member 110 comprises four 
peripheral wall segments 114 and a bottom 115, and has a box-shaped recess 
defined thereby. 
The peripheral wall segments 114 include upper and lower movable wall 
segments 114a, 114b and laterally spaced fixed side wall segments 114c, 
114d. The upper and lower wall segments 114a, 114b have proximal portions 
116 (FIG. 11) pivotally supported on the bottom 115 by first pivot shafts 
117 located outwardly of edges of the bottom 115. The upper and lower wall 
segments 114a, 114b are angularly movable between an open position in 
which they are angularly displaced outwardly and a closed position in 
which they are erected in the vicinity of the other fixed side wall 
segments 114c, 114d, thereby forming a female mold. The side wall segments 
114c, 114d are fixed perpendicularly to the bottom 115. 
As shown in FIG. 11, a blow molding apparatus which incorporates the female 
mold member shown in FIG. 10 includes a male mold member 111. The female 
and male mold members 110, 111 jointly constitute a blow molding mold A. 
The blow molding apparatus B also includes a pair of support plates 132, 
133 on which the male and female mold members 111, 110 are mounted. The 
support plates 132, 133 are horizontally movable toward and away from each 
other by a mold clamping device (not shown). 
Fluid-pressure or Hydraulic actuators comprise hydraulic cylinders 118 
having ends pivotally supported on the support plate 133 by second pivot 
shafts 119 which are located outwardly of the pivot shafts 117 and extend 
parallel thereto. The hydraulic cylinders 118 have piston rods 120 
pivotally connected at distal ends thereof to intermediate portions of the 
upper and lower wall segments 114a, 114b by third pivot shafts 121 
extending parallel to the first and second pivot shafts 117, 119. The 
hydraulic actuators operate to angularly move the upper and lower wall 
segments 114a, 114b between an open position in which they lie 
substantially parallel to the bottom 115, i.e., the support plate 133, and 
a closed position in which they are erected substantially perpendicularly 
to the bottom 115, i.e., the support plate 133, thereby forming a female 
mold. 
The ends of the hydraulic cylinders 118 may be connected to the bottom 115, 
by the pivot shafts 119. 
The male mold member 111 is of a shape complementary to the female mold 
member 110, and comprises a hollow prismatic peripheral wall 122 which is 
rectangular in shape when viewed in plan, and an inner surface forming 
block 123 movably disposed in the hollow peripheral wall 122 and movable 
toward and away from the bottom 115 of the female mold member 110. The 
peripheral wall 122 has an upper surface 126 engageable with the lip ends 
126 of the peripheral wall segments 114 of the female mold member 110. 
When the upper surface 126 engages the tip ends 126 of the peripheral wall 
segments 111, they sever a parison P and confine the severed parison P 
between the mold member 110, 111. The inner surface forming block 123 has 
a projecting surface 127 lying parallel to the inner surface 131 of the 
bottom 115. 
The inner surface forming block 123 has a pointed tube (not shown) 
projecting from the center of the surface 127, the pointed tube having an 
air outlet hole (not shown) connected to an air cylinder of a pressure 
regulating device. 
The inner surface forming block 123 and the peripheral wall 122 have air 
suction holes (not shown) opening at the surfaces 125, 127 and 
communicating with a vacuum pump (not shown). The air suction holes in the 
inner surface forming block 123 are positioned on opposite sides of the 
air outlet hole. 
The blow molding mold A and the blow molding apparatus B operate as 
follows: The female and male mold members 110, 111 are installed 
respectively on the support plates 133, 132 with the surface 127 of the 
inner surface forming block 123 confronting the inner surface 128 of the 
bottom 115 parallel thereto in spaced-apart relationship. At this time, 
the upper and lower wall segments 114a, 114b are angularly displaced or 
open widely outwardly as shown in FIG. 11. 
Then, a melted tubular parison P is supplied from the blow head E of an 
extrusion or injection molding machine into a position between the male 
and female mold members 111, 110 spaced from each other, i.e., between the 
fixed wall segments 114c, 114d. Thereafter, the upper and lower ends of 
parison P are gripped respectively by two pairs of gripper jaws (not 
shown) located remotely from the mold members 110, 111, while at the same 
time air is injected from air supply/discharge nozzles on the gripper jaws 
into the parison P to preliminarily expand the parison P. 
The support plates 132, 133 are moved toward each other until the upper 
surface 127 of the inner surface forming block 123 comes in contact with 
the outer surface of a layer (which will be an inner wall of the molded 
product) of the parison P, whereupon the parison P is slightly shaped. 
Then, the actuator, preferably a hydraulic cylinder, of the mold clamping 
device is operated to move the inner surface forming block 128 toward the 
female mold member 110 for thereby deforming the layer of the parison P 
along the outer profile of the block 123. 
At the same time, the opposite layer (which will be an outer wall of the 
molded product) of the parison P which has been preliminary expanded is 
contained by the bottom 116 of the female mold member 110. Thereafter, the 
hydraulic cylinders 118 are operated to extend the piston rods 120 to 
angularly move the upper and lower wall segments 114a, 114b from the open 
position inwardly toward the closed position. As the upper and lower wall 
segments 114a, 114b are thus angularly moved, the opposite layer of the 
parison P is partly brought into contact with the inner surface of the 
bottom 115 and the upper and lower wall segments 114a, 114b. The mold 
member 110, 111 are further moved toward each other to deform the other 
layer of the parison P which has been held against the female mold member 
110. The upper and lower wall segments 114a, 114b are displaced closely to 
the bottom 115 and the adjacent side wall segments 114c, 114c along the 
edges thereof, thus forming the female mold against which the opposite 
layer of the parison P is deformed without being locally extended, as 
shown in FIGS. 13 and 14. 
Any excessive layers or portions of the parison P project from its edges 
and form burrs near the upper and tower corners of the molded product. In 
order to prevent the pressure in the parison P from rising due to the 
operation of the mold members, air in the parison P may be removed by the 
air supply/discharge nozzles. 
Subsequently, the support plates 132, 133 are moved slowly toward each 
other until the lip ends of the peripheral wall segments of the female 
mold member 110 engage the peripheral wall 122 of the male member 111. 
Therefore, the mold A is clamped to confine the parison P between the mold 
members 110, 111, as shown in FIG. 15. The portions of the parison P which 
project out of the mold A are then cut off. The center of the inner layer 
of the parison P thus confined between the mold members 110, 111 is 
pierced by the pointed tube on the male mold member 111, and air is 
supplied into or discharged from the parison P through the tube to 
regulate the air pressure in the parison P with the pressure regulating 
device. At the same time, the vacuum pump is operated to discharge air 
from a space parison P and the mold A through the air suction holes in the 
male mold member 111. The inner and outer layers of the parison P are thus 
deformed along the inner surfaces of the mold members 110, 111. The 
parison P is cooled and solidified by cooling water flowing through 
cooling water passages (not shown) defined in the mold members 110, 111, 
whereupon a hollow double-walled product of a desired shape is molded as 
shown in FIG. 16. 
The molded product can be removed from the blow molding apparatus B by the 
process which is a reversal of the aforesaid process. 
As shown in FIG. 17, burrs are formed on the upper and lower corners of the 
outer layer of the molded product the corners being reinforced by the 
burrs. In order to form such burrs, burr-forming gaps may be disposed on 
the mating edges of the wall segments 114a, 114b, 114c, 114d. The burrs 
thus formed by the burr-forming gaps will serve as reinforcing ribs on the 
outer corners of the formed product. 
Depending on the shape of a molded product to be produced, the mold members 
110, 111 of the mold A shown in FIGS. 11 through 15 may be arranged so 
that they are vertically movable toward and away from each other. 
With the embodiment shown in FIGS. 10 through 17, the melted parison which 
has been injection- or extrusion- molded is supplied between and gripped 
by the male and female mold members, and air is injected into the gripped 
parison to cause the inner and outer layers of the parison to be shaped 
along the inner surfaces of the male and female mold members. The parison 
is expanded in one direction and formed into a molded double-walled 
product. The female mold member is of a box-shaped structure comprising 
peripheral wall segments and a bottom. The upper and lower peripheral wall 
segments spaced along the direction in which the parison is supplied are 
pivotally supported on the bottom outwardly of edges thereof by pivot 
shafts parallel to these edges, and angularly movable from a position in 
which they are open outwardly to a position in which they are located 
closely to the bottom and the other adjacent peripheral wall segments, 
thus forming a female mold. The other peripheral wall segments are fixed 
to the bottom. 
After one layer (which will be an outer layer of the molded product) has 
been brought into contact with the inner surface of the bottom, the inner 
surfaces of the upper and lower peripheral wall segments which have been 
open outwardly are turned inwardly into contact with the layer of the 
parison to deform the parison in a manner to hold the parison from its 
upper and lower ends. When the parison is thus deformed, the layer thereof 
is brought into contact with the inner surfaces of the upper and lower 
peripheral wall segments through a successively wider area of contact upon 
inwardly turning movement of the upper and lower peripheral wall segments. 
Therefore, after the parison has contacted the female mold member, it is 
not locally extended, and the upper and lower walls of the molded product 
are smoothly shaped into a uniform thickness substantially along the inner 
surfaces of the female mold which is gradually assembled by the upper and 
lower peripheral wall segments. 
Since the female mold is assembled upon contact of the edges of the upper 
and lower wall segments with those of the bottom and the adjacent side 
wall segments, the layer of the parison is gradually shaped along the 
inner surfaces of the female mold. Any excessive portions of the parison 
are gathered toward these edges, and will remain attached to the molded 
product as burrs at the upper and lower corners thereof. The burrs thus 
formed can effectively be utilized as reinforcing members for the upper 
and lower corners of the molded product. The product thus molded has a 
deep configuration. 
Because the upper and lower wall segments are openable widely outwardly, 
when they are opened outwardly, the inner surfaces of the bottom and side 
wall segments can be cleaned to remove burr debris which has been cut off 
by the bottom and side wall segments. 
If the female mold member is used in combination with the male mold member 
with the movable inner surface forming block, a deeper hollow 
double-walled product which is not thin at the corners can be molded. 
The male and female mold members are horizontally movable toward and away 
from each other, and the female mold member includes four peripheral wall 
segments. Where only the upper and lower wall segments are angularly 
movable between the open and closed positions, the mold members can form a 
deep container in the shape of a rectangular parallelepiped. 
In the blow molding apparatus, the male and female mold members are 
detachably mounted on the support plates of the mold clamping device and 
the upper and lower wall segments are connected to the support plates by 
the actuators. The blow molding apparatus of such a construction can mold 
a neatly shaped hollow double-walled product with their upper and lower 
corners reinforced with burrs. 
The actuators comprise fluid-pressure or hydraulic cylinders for angularly 
moving the upper and lower wall segments between the open position in 
which they are substantially parallel to the support plates and the closed 
or erected position in which they are substantially perpendicular to the 
support plates. The upper and lower wall segments can be angularly moved 
easily under forces from the actuators. With the upper and lower wall 
segments in the open position, the melted parison supplied from the 
injection or extrusion molding machine can be delivered into a position 
between the fixed side wall segments of the female mold member. 
Although certain preferred embodiments have been shown and described, it 
should be understood that many changes and modifications may be made 
therein without departing from the scope of the appended claims.