| 摘要 |
A spring coil (11) has an open-ended terminal convolution (11b, 11c) which is connected to the body (11a) of the coil through a gradient arm (20) which can be varied in length in manufacture to alter the spring compression and firmness. Offset portions (12, 13, 14) are formed on each terminal convolution with a major straight part (13a) which is outwardly spaced from minor straight parts (13c) for a three point engagement for the offset portion to a border wire (18). The offset portions (12, 14) have inside (25a) and outside (25b) shoulders adjacent their ends, with the pitch of joing cross-helicals (17) chosen so that a cross-helical simultaneously engages the outside shoulders of a pair of overlapped offset portions (12, 14). The spring rows are further arranged across the width of the mattress, with the columns extending along the length. Cross-helicals (28) can then be used across portions of the width for extra firmness for the entire mattress, or for selected areas, such as the middle third. |
