GB796554A - Improvements in snap-action electric switch mechanisms, particularly for electric iron thermostats - Google Patents

Abstract

796,554. Thermal switches. THOMPSON & CO. (SUNBURY), Ltd., R. E., and MACANDREW, J. F. Jan. 28, 1957 [Jan. 26, 1956], No. 2614/56. Class 38 (5). A snap-action switch comprises a leaf-spring 1 carrying a contact 3 and a trifurcated leafspring 2 carrying a contact 4, the springs 1 and 2 being anchored to a common support 5 and the central tongue 11 of the spring 2 being held compressed in the direction of its length by engagement of its free end with an abutment 12 carried by a further leaf-spring 13. In the form shown, a button 9 on a bimetallic strip 7 bears on the spring 1 and an insulating pin 18 forming part of an adjusting screw 17 bears on the abutment 12. Upward movement of the bimetallic strip 7 causes corresponding movement of the spring 1 and, through engagement of the contacts 3, 4, of the spring 2 until the compound spring member 2, 11, 13 snaps over-centre and opens the contacts. When the bimetallic strip 7 cools and returns to its original position, the spring 1 follows it and a stop 15 mounted on a bracket 16 attached to the spring pushes the compound spring member 2, 11, 13 over-centre again to reclose the contacts. In an alternative form (not shown), the spring assembly 1, 2, 13 is inverted so that the button 9 on the bimetallic strip bears on the abutment 12 and the insulating pin 18 bears on the spring 1. Upward movement of the bimetallic strip thus directly causes the compound spring member 2, 11, 13 to snap over-centre and the contacts 3, 4 to open. The spring 13 may also be replaced by a bimetallic strip. The stop 15 may be replaced by a contact which co-operates with an additional contact on the spring 2 so that these contacts are closed when the contacts 3, 4 are open and vice versa. The switch is suitable for use in an electric iron.