Presses – Methods
Reexamination Certificate
2000-08-21
2001-11-13
Vo, Peter (Department: 3721)
Presses
Methods
C100S282000, C100S264000, C425S398000
Reexamination Certificate
active
06314873
ABSTRACT:
TECHNICAL FIELD
The present invention relates to thermal presses and methods for fabricating plastic articles from a web of thermoplastic material. More particularly, the present invention relates to a drive assembly and methods for moving a platen in thermal presses.
BACKGROUND OF THE INVENTION
Thermal presses often form a web of thermoplastic material into yogurt cups, drinking cups, and other types of plastic articles.
FIG. 1
is a schematic illustration of a system for forming a continuous web of a thermoplastic material and fabricating finished articles from the web. At the beginning of the process, finely divided pieces of the thermoplastic material are transferred from a bin
20
through an extruder
22
, a polishing roll assembly
24
, and a rubber roll assembly
25
to transform the finely divided pieces into a continuous web of the thermoplastic material. The web, for example, is generally a continuous sheet having a width of approximately 2-6 feet and a thickness of approximately 0.005 to 0.500 inches. The web moves from the roll assemblies
24
and
25
to a heat tunnel
26
that heats the web to a point at which the material can be physically deformed and still retain a desired shape. The web then moves from the heat tunnel
26
to a thermal press
28
.
The thermal press
28
generally uses two complementary molds, such as a plug and a die, to form a section of the web into the finished article. typical thermal press has a plug platen, a platen drive assembly to raise and lower the plug platen, and a plug assembly attached to the plug platen. The plug assembly typically includes a separate final-drive motor coupled to the plug to move the plug along a drive axis independently from the movement of the platen, and the plug assembly may also include a press plate having an opening aligned with the plug to allow the plug to pass through the press plate. The thermal press also generally includes a separate die platen coupled to the platen drive assembly.
The thermal press
28
drives the plug into the die to form the finished article from the web. In operation, the plug and die assemblies are initially positioned on opposite sides of the web. The platen drive assembly drives the plug platen and die platen toward one another until the press plates press against opposing sides of the web. The final-drive mechanism then drives the plug through the opening in the press plate and into the web. As the plug travels into the die, the web stretches to conform to the shape of the plug and die. A vacuum is also typically drawn in the die and pressurized “form air” is typically blown from the plug to more accurately shape a portion of the web to conform to the shape of the plug and die. After the web is formed into the finished article, a positive air pressure passes through the plug to separate the finished article from the plug. The finished article is then cooled to a point at which it will retain its shape. In a typical application, several plugs are coupled to the final-drive motor and several dies are aligned with the plugs such that a plurality of plugs simultaneously pass into a corresponding plurality of dies to form a plurality of finished articles.
One manufacturing concern related to thermal presses is that the rim of the finished articles may not be formed accurately. The rim of a finished article is formed by the press plates as the platen drive assembly presses the press plates against opposing sides of the web. Conventional thermal presses, however, may not consistently apply the necessary pressure to shape the thermoplastic web in the rim region of the finished articles. As a result, one problem with conventional thermal presses is that they may not consistently produce rims having the desired wall thickness or shape.
Another manufacturing concern of fabricating articles from thermoplastic materials is that the walls of the finished articles may not be formed accurately. For example, the wall thickness of the finished articles may not be uniform or within a desired range. The wall thickness of a finished article is a function of many factors, including the consistency of the vacuum drawn in the dies and the form air from the plugs. If the vacuum in a die or the pressure of the form air is not sufficient, the wall thickness or the shape of the finished article may not accurately conform to the shape of the die. Many conventional thermal presses may not provide a consistent vacuum in the dies or sufficient form air pressure from the plugs because leaks may form between the press plates and the web at the rim of a finished article. Such leaking at the rim is particularly problematic when the press plates do not apply sufficient pressure against the web. Therefore, many conventional thermal presses may not accurately form the walls and the rims of the finished articles.
SUMMARY OF THE INVENTION
The present invention is directed toward thermal presses and methods for forming a portion of a thermoplastic web into a finished article. In one embodiment, a thermal press includes a primary frame, a drive shaft rotatably attached to the frame, and a first arm projecting away from the drive shaft. The drive shaft can extend from one side of the frame to another to rotate about its longitudinal axis, and the drive shaft can have a load area spaced apart from the primary frame. The first arm projects from the drive shaft at the load area, and the first arm is connected to the drive shaft to rotate with the drive shaft. The first arm includes a connecting point configured to pivotally attach the first arm to a second link that is rotatably attached to a first forming assembly. The rotation of the drive shaft rotates the first arm and the second link to move the first forming assembly along a travel path between an engaged position and a disengaged position. In the engaged position, the first forming assembly presses the web against a second forming assembly to shape a portion of the web and form the rim of the finished article. As the first and second forming assemblies press against the web, a load force is exerted at the load area on the drive shaft. In the disengaged position, the first and second forming assemblies are spaced apart from the web.
The thermal press also includes a counter-force assembly that can have a counteracting element and a support element. When the drive shaft rotates the first arm to position the first forming assembly in the engaged position, one embodiment of the counteracting element is configured to engage the support element and act either directly or indirectly against the first arm and/or the drive shaft at the load area. The counteracting element and the support element act together to exert a counteracting force at the load area that opposes the load force when the first and second forming assemblies press against the web. In several embodiments of the invention, the counter-force assembly accordingly inhibits or prevents deflection of the drive shaft under the load force. Thermal press, therefore, can consistently apply sufficient force against the web between the first and second forming assemblies to accurately form a rim and a wall of a finished article.
In one particular embodiment, the counteracting element is a second arm having a first section at the load area on the drive shaft and a second section projecting away from the drive shaft opposite from the first arm. The first and second arms of this embodiment define a first link. In one aspect of this embodiment, the first and second arms are integral components of the first link. In an alternative aspect of this embodiment, the first and second arms are separate components that are attached to one another proximate to the drive shaft at the load area. Additionally, the support element can be a flange or block having a surface aligned with the second section of the second arm and spaced apart from the drive shaft to engage the second section of the second arm when the first forming assembly enters the engaged position. Thus, as the first forming assembly enters the engaged position, t
Lee Myron G.
Nagy Edward A.
Huynh Louis K.
Stratton Ballew PLLC
Vo Peter
LandOfFree
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