Claims
- 1. A process for forming a foam thermoplastic article having dense surfaces and a porous less dense inner structure comprising the steps of:
- (a) dry blending a mixture of a thermoplastic powder and a chemical blowing agent in sufficient quantity to make said article;
- (b) compressing said blend into a briquette having green strength;
- (c) heating said briquette to a temperature in the range from about the alpha transition temperature to less than the melt forming temperature of said powder and the activation temperature of said blowing agent;
- (d) maintaining said temperature for a period sufficient to soften and sinter said briquette; and
- (e) forging said briquette within said temperature range with sufficient heat to activate said blowing agent, and with substantial plug flow deformation to obtain substantial fusion of the powder forming said article while providing said dense surfaces.
- 2. The process of claim 1 wherein the blowing agent is selected so as to be activated at a temperature greater than that experienced in steps (c) and (d).
- 3. The process of claim 1 wherein the blowing agent is selected so as to be activated at a temperature less than melt forming temperature of said powder.
- 4. The process of claim 3 wherein the blowing agent is selected so as to be activated at about the forging temperature necessary to obtain substantial fusion of said powder as set forth in step (e).
CROSS-REFERENCE TO RELATED APPLICATION
This application is a division of application Ser. No. 736,628, filed Oct. 28, 1976, now U.S. Pat. No. 4,323,531, which is a continuation of application Ser. No. 484,498, filed July 1, 1974, now abandoned, which in turn was a division of application Ser. No. 215,632 filed Jan. 5, 1972, now abandoned, which itself was a continuation-in-part of application Ser. No. 119,669, filed Mar. 1, 1971, now abandoned.
US Referenced Citations (4)
Divisions (2)
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Number |
Date |
Country |
Parent |
736628 |
Oct 1976 |
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Parent |
215632 |
Jan 1972 |
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Continuations (1)
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Number |
Date |
Country |
Parent |
484498 |
Jul 1974 |
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Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
119669 |
Mar 1971 |
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