Plastic article or earthenware shaping or treating: apparatus – Female mold and means to shape parison directly by internal... – Including blowing medium supply means
Reexamination Certificate
1999-09-14
2001-08-14
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and means to shape parison directly by internal...
Including blowing medium supply means
Reexamination Certificate
active
06273705
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to blow-pins for use in blow-molding operations. More specifically, the invention pertains to an improved seal assembly for blow pins.
BACKGROUND OF THE INVENTION
So-called blow-pins are utilized to form hollow objects, such as containers, by a process known as blow-molding. A typical blow-pin assembly
10
is illustrated in FIG.
1
. The blow-pin assembly
10
includes a circular body
12
having an outer circumferential surface
12
a.
The body
12
is disposed about a central axis C
1
. The body
12
defines a circular groove
14
proximate the outer circumferential surface
12
a.
The body
12
also defines a central passage
16
. A plurality of through holes
18
are disposed between the groove
14
and the central passage
16
. The through holes
18
place the groove
14
in fluid communication with the central passage
16
.
The blow-pin assembly
10
further includes an O-ring
20
. The O-ring
20
is disposed within the groove
14
, as shown in FIG.
1
. The O-ring
20
is typically formed from an elastic material such as rubber.
The blow-pin assembly
10
is used in conjunction with a thermoplastic parison
22
having a neck portion
22
a
(for clarity, only the neck portion
22
a
is shown in FIG.
1
). The blow-pin assembly is used in conjunction with a hollow mold (not shown). The neck portion
22
a
is positioned over the body outer circumferential surface
12
a
during blow-molding operations. The remaining portion of the parison
22
is positioned within the mold. Pressurized air is directed into the parison
22
by way of the central passage
16
, in the direction denoted by the arrow
24
. The pressurized air causes the parison
22
to expand. The parison
22
expands until it contacts the inner surfaces of the mold. Contact with the inner surfaces restrains the expanding parison
22
, and thereby causes the parison
22
to assume the shape of the mold.
The groove
14
is pressurized during blow-molding operations. More specifically, pressurized air from the central passage
16
pressurizes the groove
14
by way of the through holes
18
. Pressurization of the groove
14
urges the O-ring
20
outward, into the parison neck portion
22
a.
This contact inhibits leakage of air from the pressurized area within the parison
22
. More specifically, the O-ring
20
inhibits leakage of pressurized air between the parison neck portion
22
a
and outer circumferential surface
12
a.
O-rings such as the O-ring
20
have substantial disadvantages when utilized in the above-described application. For example, the elastic material from which the O-ring
20
is formed typically experiences chafing after repeated usage. Such chafing reduces the useful life of the O-ring
20
. This characteristic necessitates frequent replacement of the O-ring
20
when the blow-pin assembly
10
is utilized in high-rate-of-production applications. Frequent replacement of the O-ring
20
increases the operating cost of the blow-pin assembly
10
, and can result in costly interruptions in the production process. Furthermore, O-ring chafing reduces the sealing effectiveness of the O-ring
20
. A reduction in sealing effectiveness can lead to quality-control problems associated with insufficient air pressure within the parison
22
during blow-molding operations.
In light of the above discussion, a need exists for a blow-pin assembly having an improved sealing mechanism. In particular, the sealing mechanism should be more durable than commonly-used seals. The present invention is directed to this goal.
SUMMARY OF THE INVENTION
The present invention provides a blow-pin assembly for use in molding hollow objects from thermoplastic parisons having a neck portion. The molding process is conducted using pressurized air. The blow-pin assembly comprises a circular body having a bottom surface. The body also includes an outer circumferential surface for receiving the neck portion of the parison.
The blow-pin assembly further comprises a ring member that contacts the body bottom surface. The blow-pin assembly also includes an annular seal band. The seal band is retained by the body bottom surface and the ring member proximate the body outer circumferential surface. The seal band is urged into contact with the parison neck portion by the pressurized air. The seal band thus inhibits leakage of the pressurized air between the parison and the blow-pin assembly. The seal band is formed from an abrasion-resistant material such as stainless steel.
In a preferred embodiment of the invention, the body defines a central passage for receiving the pressurized air. The body also defines a first circular recess that adjoins the bottom surface and the outer circumferential surface. Furthermore, the body defines a through hole that extends between the central passage and the first recess. The through hole directs pressurized air from the central passage to the first recess.
The ring member has a top surface that defines a second circular recess. The ring member top surface is fixedly coupled to the body bottom surface so that the first and the second recesses substantially align and form a groove that receives the seal band.
The groove includes a contact surface and the seal band includes first and second contact surfaces. The second contact surface has a substantially identical geometric profile to the contact surface of the groove. The pressurized air from the cental passage urges the first contact surface of the seal band into contact with the parison. The pressurized air from the cental passage also urges the second contact surface of the seal band into surface contact with the contact surface of the groove. The seal band thereby inhibits leakage of pressurized air from both the parison and the groove.
Preferably, the seal band has a substantially V-shaped cross section, and includes a first and a second edge. The groove has a first notch and a second notch that receive the first and the second edges, respectively. This arrangement causes the seal band to be retained in and aligned with the groove.
The seal band has one split line. The blow-pin assembly preferably includes an elastic O-ring. The O-ring is disposed within the groove between the through hole and the seal band. The O-ring is urged against the seal band in response to the pressurized air.
In another preferred embodiment of the invention, the body bottom surface defines a circular recess. The ring member is slidably disposed within the recess so that the ring member is linearly translatable in a first direction in response to the pressurized air. The translation of the ring member in the first direction urges the seal band into the parison neck portion. The seal band thereby inhibits leakage of the pressurized air between the parison and the blow-pin assembly. Preferably, the seal band has a substantially wedge-shaped portion and the ring member has an angled surface that is oblique to the first direction. The wedge-shaped portion slidably engages the angled surface in response to the pressurized air. The engagement of the wedge-shaped portion and the angled surface urges the seal band into the parison neck portion.
Preferably, the bottom surface of the body has a substantially planar portion that is substantially perpendicular to the first direction. The seal band is adapted to abut the substantially planar portion so as to restrain the seal band in the first direction. Furthermore, the seal band preferably has a substantially L-shaped cross-section, and the ring member preferably has a substantially planar surface that is substantially perpendicular to the first direction. The seal band is adapted to abut the substantially planar surface so as to restrain the seal band in a direction substantially opposite the first direction.
An alternative embodiment of the blow-pin assembly comprises a circular body having an outer circumferential surface. The body is centered about a central axis of the blow-pin assembly. The blow-pin assembly also includes a circular gasket having a top surface, an opposing
Crown Cork & Seal Technologies Corporation
Davis Robert
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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