Ram-Based Methods for Forming Thermoplastic Article Having Smooth Edges
AssigneeConverter Manufacturing, LLC
InventorMillard F. WALLACE
Life of this patent
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Abstract
The disclosure relates to forming shaped thermoplastic articles having smooth peripheries. Many thermoplastic articles have sharp edges formed upon molding or cutting the article from a feedstock sheet. Such sharp edges can damage thin plastic films or flesh which they contact, and smoothing the edges is desirable. Described herein are methods of forming a smooth periphery for such sharp-edged articles by rolling over the sharp edge. The smoothing operation is performed by forming a deflectable flange including a bend region separated from the potentially sharp peripheral edge by a spacer, deflecting a portion of the deflectable flange, and softening at least one bent portion of the deflectable flange to yield a smooth periphery upon cooling.
Claims30
A method of making a tray-shaped article having a smooth periphery, the method comprising
- impinging a formed thermoplastic sheet against a ram,
- the sheet having a shape comprising a tray-shaped body having a concave compartment with a rim, the inner extent of the rim enclosing the compartment and the outer extent of the rim bearing a spacer completely around its periphery, the spacer including the entire peripheral edge of the sheet, the compartment and the spacer extending away from the same face of the rim, and
- the ram having an upper surface shaped
- to engage the entire peripheral edge of the sheet as the sheet is impinged against the ram and
- to urge the spacer inwardly toward the compartment as the sheet is increasingly impinged against the ram;
- heating at least the peripheral edge of the sheet to at least the glass transition temperature of the thermoplastic as the peripheral edge contacts the upper surface of the ram;
- further impinging the sheet against the ram, so that the spacer is urged inwardly toward the compartment at least until the peripheral edge of the sheet is entirely within the outer extent of the rim;
- and
- cooling the peripheral edge of the sheet while it remains entirely within the outer extent of the rim to yield the tray-shaped article having a smooth periphery.
A method of making a tray-shaped article having a smooth periphery, the method comprising
- impinging a formed thermoplastic sheet against a ram,
- the sheet having a shape comprising a tray-shaped body having a concave compartment with a deflectable flange completely surrounding the compartment, the deflectable flange comprising
- an extension that extends peripherally about the entire periphery of the compartment,
- a bend region having a smooth contour extending peripherally about the entire periphery of the extension, and
- a spacer, including the peripheral edge of the sheet, extending peripherally about the entire periphery of the bend region and being connected at an approximately right angle with the extension by the bend region;
- the ram having an upper surface shaped
- to engage the entire peripheral edge of the sheet as the sheet is impinged against the ram and
- to urge the spacer inwardly toward the compartment as the sheet is increasingly impinged against the ram;
- heating at least one of the peripheral edge of the sheet, the spacer, the bend region, and the extension to at least the glass transition temperature of the thermoplastic as the peripheral edge contacts the upper surface of the ram;
- further impinging the sheet against the ram, so that the spacer is urged inwardly toward the compartment at least until the peripheral edge of the sheet is entirely within the outer extent of the rim;
- and
- cooling the sheet while the peripheral edge thereof remains entirely within the outer extent of the deflectable flange to yield the tray-shaped article having a smooth periphery.
Dependencies are inferred from the claim text.