| 摘要 |
The thermoplastic shade material (3), cut to shape, is applied to the block (6). Top (1) and bottom (2) stiffening rings lie in prepared rebates. After heat-softening upper and lower shades edges, a frame supporting a circular membrane with a central opening descends over the block, while a vacuum is established between it, the block and the supporting table, to compress the lower shade edge round the corresponding ring. Optionally, a double membrane, expanding to enclose a toroidal space (30), is used. Air pressures both inside (52) and below (51) the toroid are varied to bend the shade edge around the ring. Similar techniques, e.g. using a continuous membrane, are used to finish the upper shade edge. |
