Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ARTICLE FORMING PROCESS, AND PRODUCT
TECHNICAL FIELD
This invention is directed to a process for manufactur-
ing a thermoplastic container, and to containers obtained by
way of the process.
BACKGROUND ART
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In the manufacture of thermoplastic ware such as con-
tainers, the use of multi axis molds enables precise die cast-
ing of quite complex shapes. However, the fineness of section
that may be cast, and the complexity of the form selected is
constrained by flow limitations of the plastic medium, at
economic production rates.
As a consequence, certain desireable features of the
article in manufacture may not be readily or economically
provided by existing processes.
DISCLOSURE OF INVENTION
In accordance with the present invention certain modi-
fications to a molded article are obtained by providing a pre-
determined thermal gradient to selected portions of the
article, applying a deforming force to the selected portion of
the article, and deforming the article in a first direction to
a predetermined extent sufficient to achieve the desired modi-
fication of form in a second direction.
In the case of a hollow container produced by molding,
the preferred method includes interrupting the molding cycle
prematurely, before the article is cooled to the point of
rigidity in all its parts, removing it from the mold, and
applying a mechanical force in deforming relation thereto, to
p~roduce a desired extent of deformation at a required loca-
tion, where plastic flow may be achieved.
In the case of a drinking glass of substantially cylin-
drlcal form, establishment of a thermal gradient within the
mold enables safe removal of the molded glass in a solidified,
partially non-set condition.
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The desired thermal gradient is more readily achieved
at a portion of the container where a change in section
fac:Llitates the establishment of the thermal gradient.
In one embodiment the molded container is removed from
the mold while still in a plastic condition adjacent the
bottom of the container section, where a section of greater
mass exists. The application of an axial deforming force then
produces deformation both axially and laterally.
The application of an axial compressive force is
readily achieved, leading to a shortening of the overall
height of the container, and the generation of a protruberant
ring in the still-plastic segment adjacent the bottom of the
container.
Control of the thermal state of the article, and the
extent and rate of the deforming force may be such that the
generation of residual stresses is substantially avoided, and
visible evidence of flow lines is also absent.
In one embodiment of a drinking glass in accordance
with the invention, the provision of a local annular ring
ad~acent the base serves to lower the centre of gravity of the
glass, and provides a locating ring which greatly facilitates
secure handling of the glass while distinguishing it in
~ appearance. The rings also serve to protect the highly
; finished upper surfaces of the glasses when crated for
shipment, by serving as abuttments that ensure separation of
the highly finished surfaces and prevents them from contacting
each other.
In the case of a wine glass form of container, the
local protruberance may be located in the stem, adiacent the
lower surface of the bowl of the glass.
In the case of a larger container, in the form of a
jug, the protruberance also is located adjacent the base, to
provide a matching appearance with that of a form of drinking
glass, to which the process also is applied.
.~ The subiect process may be used with a range of
; plastics materials, including acrylics, which normally
demonstrate certain molding flow limitations that may preclude
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direct in~ection molding of the desired end product.
In carrying out the process, the duration of the
molding cycle is shortened, such that a semi-plastic condition
still exists at the desired location, adjacent a major section
of the article, upon removal from the mold; preferably after
rapidly removing the sprue and the flash, the article is
placed in a press and a deforming load applied thereagainst,
to shorten the article while causing it to bulge outwardly at
a predetermined location, so as to form the desired locating
ring.
A simple press, having an air cylinder to apply a
predetermined load, with predetermined axial and lateral
deformations has been found satisfactory.
The present invention thus provides a process for
deforming a thermoplastic container to provide a permanent
deformation in the shape thereof at a first portion, and in a
first direction, comprising the steps of:
establishing a thermal gradient along the shape in a
second direction normal to the desired first direction, to
establish the temperature of the first portion in the plastic
flow regime;
applying a deforming force to the container in the
second direction, to produce substantially stress free
deformation of the shape in the first portion and in the first
direction, and cooling the container to a temperature below
the plastic flow regime.
In the preferred embodiment the container shape
comprises a hollow section, having a non-uniform cross
section, constituting a local heat sink therefor.
In carrying out the process as described, the step of
establishing a thermal gradient consists of molding the
container within a mold, and removing the container from the
mold, to establish the desired temperature and thermal
gradient.
The above disclosed process has been carried out on a
container comprising a substantially cylindrical drinking
glass, having a thickened bottom portion, the deforming force
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being applied axially of the drinking glass, producing the
first deformation as substantially a radial outward deflection
adjacent the thicker bottom portion.
The process generally includes the step of severing at
least a portion of a riser or sprue from the molded glass.
The process can provide a decorative molded
thermoplastic container having a body portion comprising an
open topped hollow container, with a thickened section forming
the bottom of the container, and a unitary thickened,
outwardly protruding annular ring located adjacent the
thickened section, and integral with the container.
In a preferred embodiment of the container, the
thermoplastic is an acrylic resin.
It will be understood, however, that other resins may
also be used.
In the case of a molded plastic drinking glass the form
of the hollow container is symmetrical.
In the case of a jug, having a handle, the form of the
container is asymmetrical.
In the case of the jug or a drinking glass embodiment
the container annular ring is located above the container
bottom.
In the case of a wine glass type of embodiment of the
container the annular ring may be located below the container
bottom, to form a part of the stem of the "glass".
BRIEF DESCRIPTION OF DRAWINGS
Certain embodiments of the invention are described by
way of illustration, without limitation of the invention
thereto, reference being made to the accompanying drawings,
wherein:
Figure 1 is an elevational view, in partial section of
a drinking glass prior to completion of the process;
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`: Figure 2 is an elevational view of a drinking glass
after carrying out the process in accordance with the present
~ invention;
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Figure 3 is an elevational view showing a press appar-
atus used in carrying out the process according to the inven-
tion.
BEST MODE OF CARRYING OUT THE INVENTION
Referring to Figures 1 and 2, a thermoplastic drinking
glass 10 of substantially cylindrical form has a base portion
12 thicker in section than the wall portion 13.
After subjecting the glass 10 to the presently disclos-
ed process there is produced a glass 14 of reduced height,
having an annular protruberant ring portion 16 adjacent the
base thereof.
Referring to Figure 3, a press arrangement 20 has an
air cylinder 22 and a platen 24, beneath which a glass 14 or
like article may be positioned.
In the preferred embodiment an injection molded thermo-
plastic article is removed somewhat prematurely from its mold,
wherein the rim portion is fully and permanently solidified,
while a portion of greater section is still in a plastic or
semi-plastic state, such that the desired deformation zone is
at such temperature that it can flow with substantially no
residual stress to mar or weaken the ensuing product.
In the case of a molded acrylic embodiment, the melt
temperature is normally in the 400 to 450F range, and the
mold generally operates at about 110 to 130F. On premature
removal of the molded article, before final solidification
takes place in the mold, into an ambient room temperature of
say 75F, the rate of cooling may increase. However, the mass
of the article and its rate of cooling may be such that inter-
mediate operations, such as the trimming of flash, and docking
of the sprue may be readily carried out prior to mounting the
article into the press, and carrying out the required deforma-
tions.
It will be understood that the subject process may be
carried out in a range of sizes and styles of container.
INDUSTRIAL APPLICABILITY
Widespread commercial use.
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