Blow molding and compression molding of an article

A molding apparatus is provided which is operated to mold an article having a hollow blow molded portion and a substantially solid compression molded portion. A mold is provided which has defined therein at least a first cavity portion and a second cavity portion. A parison is positioned within the mold and blow gas is injected into the interior of the parison to inflate the parison within each of the cavity portions. A compression member is then moved from a retracted position within a recess in the mold to an extended position outside of such recess. The compression member presses a first portion of the parison against the mold interior surface which defines the first cavity portion so as to compression mold a first portion of the parison. Inflation of a second portion of the parison in the second cavity portion accomplishes blow molding of such second parison portion.

This invention relates to an apparatus and method of molding an article 
wherein a portion of the article is blow molded and another portion is 
compression molded. 
Blow molding processes are widely used to form hollow articles from plastic 
materials. Generally, a parison, which is a generally tubular blank of 
molten plastic material, is extruded from a suitable extrusion head and is 
allowed to drop by gravity into the interior of a mold. After upper and 
lower ends of the parison are sealed off by, for example, closing two mold 
parts upon the parison, a compressed gas such as air is injected into the 
parison to pneumatically expand the parison to fit the inside contours of 
the mold. 
It is occasionally desirable to compression mold a portion of an article 
which is being blow molded. Such a need can arise, for example, in hollow 
articles which require an associated high strength, protruding member. 
Prior techniques of combining blow molding and compression molding have 
been used with some success, but improvement would be desirable. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the invention to provide an improved 
apparatus and method for molding an article having at least one hollow 
blow molded portion and a solid compression molded portion. 
The above object is realized by a molding apparatus comprising: extrusion 
means for extruding a molten generally tubular parison having a 
predetermined wall thickness; a mold means for receiving the extruded 
parison, wherein the mold means includes a first interior surface portion 
which defines a first cavity portion and a second interior surface portion 
which defines a second cavity portion, and also including a recess 
generally in alignment with the first cavity portion; a blow means for 
injecting blow gas into the interior of the parison within the mold means 
so as to expand the parison within each of the cavity portions; and a 
compression member which is mounted in the mold means so as to be 
reciprocable between a retracted position in which at least a portion of 
the compression member is disposed within the recess to an extended 
position in which at least part of such compression member portion is 
outside of the recess, wherein in the extended position at least a portion 
of the exterior surface of the compression member is adapted to be closely 
adjacent to the first interior surface portion so as to press only a 
portion of the parison against the first interior surface portion and 
thereby compression mold such a parison portion. 
According to another aspect of the invention, there is provided a molding 
method which comprises: (a) providing a mold as described above; (b) 
positioning a molten generally tubular parison within the mold; (c) 
injecting a blow gas into the interior of the thus positioned parison so 
as to inflate the parison within each of the cavity portions; (d) after 
step (c), moving a compression member from a retracted position to an 
extended position as described above; (e) at least a portion of the 
exterior surface of the compression member being positioned at the 
completion of step (d) or after step (d) so as to press a first portion of 
the parison against the first interior surface portion to thereby 
compression mold the first parison portion; and (f) completing inflation 
of a second portion of the parison in the second cavity portion so as to 
blow mold the second parison portion. 
According to a preferred embodiment of the invention, a plurality of mold 
sections are utilized which are in the open position at the beginning of 
the molding method, and which are moved to their respective closed 
positions at preselected points in the method in order to optimize the 
formation of a complete and well formed article having the desired hollow 
blow molded portion and solid compression molded portion. 
Employing the reciprocable compression member in accordance with the 
invention is particularly advantageous over, for example, a system which 
utilizes a stationary member which cannot be retracted into one of the 
mold sections. By providing the capability of retracting the compression 
member from its extended compression molding position, this helps prevent 
possible tearing or thinning of the parison on the compression member 
during inflation of the parison before compression molding, and also 
provides better extension of the inflated parison into the cavity portion 
associated with compression molding, thereby insuring formation of a 
complete and well formed compression molded portion of the final article.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the invention will now be described with reference to the 
FIGURES. The particular embodiment illustrated and described pertains to 
molding of an article (i.e. container) having a hollow portion with 
compression molded protruding members extending therefrom. A handle is 
blow molded so as to be connected at one end to one protruding member and 
at the other end to the other protruding member. It should be understood 
that this particular embodiment is illustrated and described solely to 
assist an understanding of the invention, and further that the invention 
is applicable to any type and/or shape of article having a blow molded 
portion or portions and a compression molded portion or portions. 
Referring now to FIG. 1, the illustrated apparatus includes the lower 
portion of an extrusion head 10 which is capable of extruding a molten 
generally tubular parison. A blow pin 12, shown in its retracted position, 
is connected to a source of compressed gas, most typically air, and is 
most typically reciprocable between retracted and extended positions by a 
suitable pneumatic drive means (not shown). 
The apparatus further includes a mold, generally indicated at 14, which 
includes separate mold sections 16, 18, 20 and 22. In FIG. 1 the various 
mold sections are shown in their respective open positions. Such mold 
sections have various interior surface portions which together make up the 
total interior surface of mold 14 when closed. The interior surface 
portions define corresponding cavity portions which make up the total mold 
cavity when mold 14 is closed. 
With respect to individual mold sections, mold section 16 has faces 24 and 
26, and interior surface portions 28 and 30 which define cavity portions 
32 and 34, respectively. As shown, cavity portion 34 is directly adjacent 
to and in communication with cavity portion 32 so as to extend outwardly 
from the periphery of cavity portion 32. It can further be seen from FIG. 
1 that cavity portion 34 extends from a lower end, directly adjacent to 
face 24, to its upper end which is offset from face 24. The entirety of 
cavity portion 34 is offset from face 26. Mold section 18 has faces 36 and 
38, and further includes interior surface portion 40 which defines cavity 
portion 42. Mold section 20 has faces 44 and 46, and further includes 
interior surface portion 48 which defines cavity portion 50. Similarly, 
mold section 22 has faces 52 and 54, and further includes interior surface 
portion 56 which defines cavity portion 58. 
It can be seen from FIG. 1 that face 24 matches face 36, face 38 matches 
face 46, face 44 matches face 52, and face 54 matches face 26. The various 
mold sections are closeable upon one another at such matching faces along 
mold closing lines (i.e. parting lines and/or flash lines) as will be 
described and shown in more detail with reference to FIGS. 5-10. 
The apparatus of FIG. 1 is further characterized by: a recess 60 defined in 
mold section 18 so as to be separate from cavity portion 42 and in 
alignment with cavity portion 34; a chamber 62 also defined in mold 
section 18 so as to be separate from cavity portion 42; a compression 
member 64, shown in FIG. 1 as being in its retracted position disposed 
entirely within recess 60 but having its upper face substantially flush 
with face 36 of mold section 18; a piston 66 slidably disposed in chamber 
62; and a shaft 68 connected at its upper end to compression member 64 and 
at its lower end to piston 66. Preferably, compression member 64 and 
piston 66 are of a metallic construction which is most preferably 
dissimilar from the type of metals defining recess 60 and chamber 62. 
Utilizing such dissimilar metals assists in preventing galling with 
respect to metal surfaces in sliding contact with one another. For 
example, if aluminum defines recess 60 one suitable metal for compression 
member 64 would be bronze. It is also preferable that the metal of 
compression member 64 have a high thermal conductivity in order to 
optimize cooling of the compression molded portions of the parison. 
Furthermore, although compression member 64 is shown in FIG. 1 as being in 
its retracted position, compression member 64 as operably connected to 
mold section 18 as described above is reciprocable between such retracted 
position and an extended position, as will be more apparent in subsequent 
FIGURES, along a generally vertical directional line as indicated at 70. A 
compressed fluid source for supplying a suitable hydraulic fluid such as 
oil or water is in fluid communication with chamber 62 by means of 
suitable flexible conduits and passageways in mold section 18 to the upper 
and lower ends of chamber 62. Therefore, piston 66 and associated shaft 68 
and compression member 64 are hydraulically operable. 
Also provided in the apparatus of FIG. 1 are means for moving mold sections 
between respective open and closed positioned, which in the illustrated 
embodiment includes hydraulic cylinders 72, 74, 76 and 78. For clarity of 
illustration, hydraulic supply lines to such hydraulic cylinders are not 
shown in FIG. 1. 
With respect to individual hydraulic cylinders, hydraulic cylinder 72 is 
adapted to move mold section 16 downward from an open position to a closed 
position or upward from a closed position to an open position along a 
generally vertical directional line as indicated at 80. Hydraulic cylinder 
78 is similarly adapted to move mold section 22 along a vertical 
directional line as indicated at 82. In the illustrated embodiment and as 
shown, directional lines 80 and 82 are generally parallel and are further 
parallel to directional line 70 along which compression member 60 is 
reciprocable. Hydraulic cylinder 74 is adapted to move mold section 18 
along a horizontal directional line as indicated at 84 between open and 
closed positions. Hydraulic cylinder 76 is similarly adapted to move mold 
section 20 along a horizontal directional line as indicated at 86 between 
open and closed positions. Note that directional lines 84 and 86 are 
parallel and generally perpendicular to directional lines 70, 80 and 82. 
Of course, the various hydraulic cylinders could be connected to the mold 
sections differently from that illustrated. For example, such hydraulic 
cylinders could be connected to the mold sections in a manner which would 
permit closure of mold sections 16 and 22 upon mold sections 18 and 20, 
respectively, by upward movement of mold sections 18 and 20 rather than 
downward movement of mold sections 16 and 22. 
Referring now to FIG. 2, there is shown another cross sectional view of the 
apparatus of FIG. 1 which shows mold section 16 and associated cavity 
portions 32 and 34. As shown, cavity portion 34 is positioned on one side 
of mold section 16, and a substantially identical cavity portion 88 is 
positioned on the other side of mold section 16 so as to also be directly 
adjacent to and in communication with cavity portion 32. An additional 
cavity portion 90, as depicted by broken lines and as indicated at 90, 
extends between cavity portion 34 and 88. FIG. 2 also shows mold section 
18 and associated cavity portion 42. An additional cavity portion 92 is 
depicted by broken lines and is indicated at 92. Cavity portions 90 and 92 
cooperate to form a cavity for blow molding a handle extending between 
cavity portions 34 and 88 as will become more apparent in subsequent 
FIGURES. Compression member 64 and associated shaft and piston are shown 
in broken lines as being directly beneath and in alignment with cavity 
portion 34. A substantially identical compression member 94, also having 
an associated shaft and piston, is positioned on the opposite side of mold 
section 18 beneath and in alignment with cavity portion 88. 
Referring now to FIG. 3, there is shown another view of mold section 16 
having cavity portions 32, 34, 88 and 90 defined therein. Also shown in 
FIG. 3 is face 24 of mold section 16. 
Referring now to FIG. 4, there is shown another view of mold section 18 
having cavity portions 42 and 92 defined therein. Also shown in FIG. 4 are 
compression members 64 and 94 which are the same shape as and clearly 
mateable with cavity portions 34 and 88. 
Although not shown, it is preferable to have an additional blow means, such 
as a blow needle, for injecting blow gas into cavity portions 90 and 92, 
since blow gas is prevented from reaching these cavity portions during 
compression molding within cavity portions 34 and 88, as will become more 
apparent below. 
An embodiment of a method in accordance with the invention using the 
apparatus of FIG. 1 will now be described with reference to FIGS. 5-10. 
Referring to FIG. 5, mold 14 is shown with its respective mold sections 16, 
18, 20 and 22 in their open positions. Blow pin 12, however, has been 
moved from its retracted position as shown in FIG. 1 to its extended 
position, after which a molten generally tubular parison 96 is extruded 
from extruder head 10 so as to drop by gravity to a position within mold 
14 between the various mold sections as illustrated. Also as shown by the 
broken away portion of parison 96, parison 96 is hollow and has a wall 98 
of predetermined thickness which is suitable for compression molding of a 
portion of the parison within cavity portion 34 by compression member 64, 
as will be described further below. Compression member 64 is shown in FIG. 
5 as being in its retracted position at this point of the method. 
After parison 96 is extruded and positioned within mold 14 as described 
above, hydraulic cylinders 74 and 76 are activated so as to move mold 
sections 18 and 20 generally horizontally toward one another. As shown in 
FIG. 6, mold sections 18 and 20 accordingly close upon one another at 
their respective matching faces along parting line 100 so that cavity 
portions 42 and 50 are directly adjacent to and in communication with one 
another. Since mold sections 18 and 20 are respectively connected to mold 
sections 16 and 22 by hydraulic cylinders 72 and 78, mold sections 16 and 
22 are also caused to move generally horizontally toward one another and 
close at their respective matching faces along parting line 102 so that 
cavity portions 32 and 58 are directly adjacent to and in communication 
with one another. Both of parting lines 100 and 102 can be seen in the 
illustrated embodiment to be generally vertically oriented. Closure of the 
above described mold sections along parting lines 100 and 102 causes pinch 
off areas of mold sections 16 and 22, as indicated at 104, to sealingly 
pinch an upper end of parison 96. In addition, pinch off areas of mold 
sections 18 and 20, as indicated at 106, sealingly pinch a lower end of 
parison 96 therebetween and around blow pin 12. Of course, although not 
shown, a suitable opening is provided through mold sections 18 and 20 for 
blow pin 12. Finally in FIG. 6, it is shown that compression member 64 is 
still in its retracted position. 
At the same time as or shortly after closure of the mold sections shown in 
FIG. 6, a first blow gas injection stage preferably begins, hereinafter 
referred to as the "preblow" stage, in which a blow gas such as air is 
injected from blow pin 12 into the interior of parison 96 so as to expand 
the parison within each of cavity portions 32, 34, 42, 50 and 58 as shown 
in FIG. 7. In addition and as shown, parison 96 also expands into open 
areas between cavity portion 34 and compression member 64 and between the 
horizontally extending faces of the various mold sections. A preferred 
pressure range for the preblow stage is about 5 to about 15 psi. As shown, 
compression member 64 is still preferably in the retracted position in the 
illustrated embodiment. 
After the preblow stage is allowed to continue for a short period of time 
of, for example, about 0.5 to about 2 seconds, the blow gas pressure is 
elevated to a higher level of preferably about 15 to about 30 psi to begin 
what is hereinafter referred to as the "low pressure" stage. According to 
the illustrated embodiment, it is preferred that at the beginning of the 
low pressure stage or shortly thereafter compression member 64 is moved to 
its extended position as shown in FIG. 8. In such an extended position, 
compression member 64 is shown as being entirely outside of recess 60. 
However, a portion of compression member 64 could be allowed to stay 
within recess 60 if desired. It can also be seen from FIG. 8 that parison 
96 has further expanded as compared to FIG. 7. 
After the low pressure stage is allowed to continue for a predetermined 
period of time, such as for example about 2 to about 5 seconds, hydraulic 
cylinders 72 and 78 are activated to move respective mold sections 16 and 
22 in a generally downward direction. As shown in FIG. 9, the uppermost 
end of parison 96 outside of the various mold sections is caused to tear 
away from extrusion head 10, and mold sections 16 and 22 are caused to 
close upon mold sections 18 and 20, respectively, at horizontally disposed 
matching faces along flash lines 108 and 110. This brings cavity portions 
32 and 58 directly adjacent to and in communication with cavity portions 
42 and 50, respectively. Flash lines 108 and 110 can be seen to be 
substantially continuous and lie in a generally horizontal plane so as to 
be perpendicular to substantially continuous parting lines 100 and 102 
which lie in a generally vertical plane. Closing of the various mold 
sections along flash lines 108 and 110 causes formation of an outwardly 
extending rib as indicated at 112 via compression molding between the 
horizontally disposed matching faces of the various mold sections. 
More importantly, closure of the mold sections as described immediately 
above causes compression member 64 as maintained in its extended position 
to be closely adjacent to interior surface portion 30. As described 
previously with reference to FIG. 1, interior surface portion 30 defines 
cavity portion 34. Compression member 64 accordingly presses a first 
portion of parison 96 against interior surface portion 30 so as to 
compression mold such first portion of parison 96. This forms a strong, 
substantially solid protruding member, as indicated at 114 which is at 
least partially offset from flash line 108 and entirely offset from 
parting line 102. 
Further according to the illustrated embodiment, it is preferred that at a 
time of about 0 to about 5 seconds after closure of the various mold 
sections as shown in FIG. 9 and compression molding of protruding member 
114, the blow gas pressure is elevated further to a pressure of preferably 
about 50 to about 100 psi. This begins a third blow gas injection stage 
hereinafter referred to as the "high pressure" stage. It is in this stage 
that inflation of parison 96 is completed so as to blow mold second, 
third, fourth and fifth portions of parison 96 within cavity portions 32, 
42, 50 and 58, respectively, as shown in FIG. 10. The high pressure stage 
is typically carried out for about 1 to about 3 minutes, after which the 
various mold sections are opened and the molded article removed from the 
mold. 
Referring now to FIG. 11, the article as molded in accordance with the 
illustrated embodiment is shown. The article comprises a hollow blow 
molded portion 116 having the outwardly extending rib 112, two compression 
molded protruding members as indicated at 114 and 118, and a generally 
cylindrical handle 120 extending between the compression molded protruding 
members 114 and 118. 
Referring now to FIG. 12, there is shown a cross sectional view of a 
portion of the article of FIG. 11 which more clearly shows the structure 
of blow molded hollow portion 116 and compression molded protruding member 
114. 
An example will now be described to further illustrate the invention, but 
should not be construed to limit the invention in any manner. 
Articles substantially as shown in FIGS. 11 and 12 were molded using an 
apparatus substantially similar to the apparatus of FIGS. 1-4, except that 
the apparatus of this example was adapted to compression mold only one 
protruding member in accordance with the invention whereas the other 
protruding member was blow molded into a hollow form. The steps employed 
in the molding method were substantially like those described previously 
and shown in FIGS. 5-10. The articles were molded with MARLEX HXM 50100-2 
(high density polyethylene) using a shaped die adapted to extrude a 
parison 9 inches in diameter having a wall thickness of 300 mil. Air was 
used as the blow gas at the following pressures: preblow of 12 psi, low 
pressure blow of 18 psi, and high pressure blow of 90 psi. The extrusion 
head temperature was set at about 400.degree. F. 
Seven runs were made. In each run, the timing of various events with 
respect to a preselected zero time are set forth in Table I. 
TABLE I 
______________________________________ 
Time 
Event (secs.) 
______________________________________ 
Start of parison extrusion -9.8 
End of parison extrusion 0 
Start closing mold section 16 upon section 22 and 
0 
mold section 18 upon section 20 
Mold section 16 closed upon section 22 and 
8.3 
mold section 18 closed upon section 20 
Preblow starts 8.3 
Start upward movement of compression member 64 
9.0 
Stop upward movement of compression 
9.2 
member 64 so as to reach extended position 
Preblow ends and low pressure blow starts 
9.2 
Start closing mold section 16 upon section 18 and 
12.4 
mold section 22 upon section 20 
Mold section 16 closed upon section 18 and 
15.9 
mold section 22 closed upon section 20 
Low pressure blow stops and high pressure 
16.8 
blow starts 
High pressure blow ends 105.0 
Mold sections start to open 
117.0 
______________________________________ 
Of the seven articles produced by the seven runs of this example, the 
protruding member of four of such articles was completely and well formed. 
In three articles, the protruding member was completely formed except for 
a part of only the end portion of the protruding member as indicated at 
122 in FIGS. 11 and 12. End 122 is shown as vertically extending in FIG. 
12. It is believed that this could have been prevented by further delaying 
extension of the compression member 64. 
The above results in accordance with the invention compare very favorably 
with control runs which were carried out by maintaining compression member 
64 in the extended position throughout the molding cycle. Such control 
runs consistently produced incomplete protruding members, most of which 
were only about half formed. 
Obviously many modifications and variations of the present invention are 
possible in light of the above teachings. For example, a different 
sequence of blow gas injection stages could be utilized, such as only one 
or two stages. Another possible variation could involve delay of the 
extension of the compression member 64 until complete closure of the mold, 
whereby compression molding of the associated protruding member would 
occur upon compression member 64 reaching its extended position. It is 
therefore to be understood that within the scope of the appended claims 
the invention may be practiced otherwise than as specifically described.