| 摘要 |
The present invention provides a top frame made from a thermoset foam material. The top frame includes a pair of substantially parallel sides and a pair of substantially parallel ends connected to the sides to form a generally rectangular frame structure. The frame structure has an inner layer and outer surface defining a thickness. The thermoset foam material varies in density along the frame structure thickness such that the density of the thermoset foam material is greatest near the frame structure outer surface to form a hard outer shell.
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