Platform-Top and Convolute-Coil Types.
The convolute-coil or platform-top springs are similar to the open-coil type except that additional features are added to provide a firmer resting surface for the mattress. In the platform type, the open spaces in the top of the spring are partly covered by flexible metal bands running both the length and breadth of the springs. The convolute coils have several extra turns of wire as each coil approaches the top of its spiral. When slightly compressed these turns flatten out in the same plane, providing a broader supporting area. The platform-top and convolute-coil springs are designed specifically as a foundation for inner-spring mattresses. If an inner-spring mattress is used with an ordinary open-coil spring the smaller springs of the mattress are likely to force their way down into or between the larger spring coils, with a resultant premature breakdown of the mattress. The platform-top and convolute-coil types close up the open spaces and eliminate this hazard.
Better grade springs, whether of open-or closed-coil type, usually are of double-deck construction. Between the top and bottom of the frame there is a center wire with supporting bands running both the length and breadth of the springs. This support makes possible the use of a longer coil, which acts as a double spring. The lower half of the coil is more tightly wound and is stiffer for the support of the sleeper's weight. The upper half then contributes the resilience. Another mark of a good spring is the use of two or more steel braces, known as stabilizers, which prevent sidesway and border sagging.
Box Springs.
Box springs consist of spiral springs attached to a foundation, usually of wood, and cushioned with a layer of upholstery. The coils are larger and heavier than the usual open-coil springs. The entire unit is enclosed in a box-like frame and covered with ticking. Box springs originally were designed to give much resiliency so that they could be used with solid-filled mattresses of hair or cotton. Most box springs today, however, are constructed with the firm tops which are necessary for use with inner-spring mattresses.
Each coil in the box spring is set into a slat of wood or steel. The coils are held upright by being tied one to another, to the border, and to the foundation. The borders usually are of wire or rattan. In the better types, the springs are hand-tied with a special twine. A wire-tied-spring unit is used in the cheaper models.
Box springs usually are sold with covers which match certain mattresses in the same price range. This permits the sale of mattress and box springs as a single unit.
SUGGESTIONS FOR THE SALESPERSON
Figure 28.—Box-spring construction.