US2848589A - Electric flat iron with a thermo-switch - Google Patents

Description

Aug. 19, 1958 J. CARLSEN ELECTRIC FLAT IRON WITH A THERMO-SWITCH Filed April 1, 1957 ATTORNEY United States 2,848,589 ELECTRIC FLAT IRON WITH A THERMO-SWK'ICH John Carlson, Lyngby, Denmark Application April 1, 1957, Serial No. 649,767

Claims priority, application Denmark April 7, 1956 3 Qlaims. (Cl. 219-25) This invention relates to an electric fiat iron constructed with a thermoswitch comprising two elements that are subjected to different thermal expansion when the fiat iron is heated.

The thermo-switch of such flat irons is as a rule based on the employment of a bimetallic strip, which at one end is attached to the bottom of the flat iron in good heat conducting connection therewith, so that the temperatureof the bimetallic strip increases with that of the bottom of the fiat iron, whereby the bimetallic strip assumes a curved shape, and a contact mounted at the free end of the bimetallic strip is disengaged from a stationary contact.

The detailed construction of the bimetallic switch may be varied in many ways and switches may also be used, in which the two elements subjected to different thermal expansion are not combined to a strip, but mounted individually. However, all these constructions have in common that they receive heat from the bottom of the flat iron only in one point or a few points. Consequently, the temperature of the bimetallic strip or the thermo-switch as a whole will follow the variations of the temperature of the bottom of the flat iron only with some delay. This delay must be taken into account when adjusting and calibrating the thermo-switch. If, however, this adjustment and calibration is performed on the basis of the quasi-stationary condition, in which the thermo-switch intermittently closes and breaks, the heating circuit of the fiat iron during the carrying out of the ironing operation, it may occur that when starting from cold condition, the temperature of the bottom of the flat iron may exceed the adjusted temperature very considerably before the thermo-switch operates to break the circuit whereby the articles to be ironed may sometimes be spoiled.

It is the object of the present invention to provide a simple construction of a flat iron with a thermo-switch by which this drawback is eliminated.

With this object in view the essential feature of the invention resides in the fact that one of the elements of the thermo-switch is constituted by the bottom of the flat iron. Hereby the thermal delay of the thermo-switch is completely eliminated, and also when starting up the flat iron from cold condition the interruption will take place exactly at the moment, when the temperature of the flat iron has reached the adjusted temperature. It has been found that the longitudinal expansions'of a flat iron of normal size are suflicient for being converted into a contact movement of suitable size, particularly when the fiat iron consists of a material with a relatively high coemcient of thermal expansion such as aluminum. In order to have the largest possible expansion available, the whole or practically the whole length of the bottom of the flat iron should preferably be used as an element of the thermo-switch, and for the same reason the other element should preferably consist of a material having a very low coefficient of thermal expansion, such as Invar.

This is also desirable in order to avoid the anticipating ice effect that would occur if a material were used having a higher coefficient of thermal expansion.

Preferably, the temperature responsive elements of the thermo-switch and the contact controlled thereby should be connected with each other in such a manner that the movement is transmitted at a stepped up ratio from said elements to said contacts. This can be obtained by means of suitable leverage or by constructing the temperature responsive element of the thermo-switch not constituted by the bottom of the fiat iron in the form of a strip attached to the bottom of the flat iron at both ends thereof and carrying or being coupled to one contact of the contact set at an intermediate point of its length.

The invention will now be described in further detail with reference to the accompanying drawings, in which Fig. 1 shows a longitudinal section through the bottom of a fiat iron according to the invention with a thermo-switch mounted thereon, according to one embodiment of the invention, and

Fig. 2 a plan view of same.

In the drawing, 1 is the bottom of the fiat iron, which at its front end has a portion of increased height 2, from which an edge portion 3 of increased height extends along the sides and to the rear end of the fiat iron. A bracket 4 is attached to the portion 2 of increased height and carries two rigid arms 5 extending across the bottom of the flat iron at some distance therefrom and carrying a bracket 6 at their rear ends. On the bracket 6a cam '7 is rotatably mounted, which has anaxial cam surface and is manually adjustable for the purpose of adjusting the temperature of the bottom of the flat iron at which the current supply to the fiat iron is to be interrupted. The cam surface of the cam 7 is engaged by a nose 8 of an arm 9 rotatably mounted on the bracket 4. The arm 9 in turn carries a rotatably mounted arm 10, to which one end of a rod or wire 12 of Invar is attached below the axis of rotation 11. The said rod or wire 12 extends the Whole way to the rear edge of the fiat iron where it is attached by means of a nut 13 and a locking nut 14 to a plate 15 extending across a notch 1'6 in the rear edge portion of the bottom of the flat iron. The arm 10 is drivably engaged with a contact 17, which is resiliently mounted on the bracket 6 and cooperates with another contact 18 which is also resiliently mounted on the bracket 6.

The electric circuit of the fiat iron extends through a conductor 19 via the contact set 17, 18 to another conductor 20 and from there to the heating element 21 of the flat iron.

When current is supplied to the flat iron, the bottom of the latter will increase in length owing to the thermal expansion, while the Invar element 12 maintains its length practically unchanged. Thereby the Invar element 12 will tend to turn the arm 10 in the anti-clockwise direction, whereby the electric circuit of the flat iron is interrupted when the bottom of the flat iron has assumed a certain temperature. The temperature, at which the interruption takes place, can be adjusted by turning the cam 7, whereby the arm 9 is rotated about its axis and thereby displaces the axis of rotation 11 of the arm 10.

I claim:

1. An electric flat iron comprising in combination a thermo-switch with two contacts; a first element of a high coefiicient of expansion forming the bottom of said iron; a second element of a low coefiicient of expansion in the shape of an elongated strip, mounted with its onefirst terminal to the one-first end of said iron; 21 step-up leverage means, responsive to variations in expansion of said two elements, including a first pivoted arm, inter posed between one-second end of said first element and the adjacent second terminal of said second element, said leverage means including a second arm pivotally mounted on said first arm for opening and closing said contacts automatically in response to variation in expansion of said two elements in excess of pre-set temperature limits and manually operated means to pre-set the automatic opening and closing of said contacts in response to predetermined temperatures, said manually operated means mounted to controllably displace the free end of said second arm.

2. An electric flat iron having a thermo-switch included in the electric circuit thereof, comprising a first arm which is mounted for rotational adjustment about a fixed axis substantially parallel to the bottom of the fiat iron, a second arm pivotably connected With said first arm for rotation relative thereto about an axis spaced from said fixed axis, and an elongated element having a co-efficient of thermal expansion different from that of the bottom of the flat iron connected between a point of said second arm spaced from said second axis and a remote point of the body of the fiat iron, said second arm forming an operating arm of said thermo-switch.

3. An electric fiat iron as claimed in claim 2, in which said first arm is rotatably mounted in a bracket and has a portion extending substantially longitudinally of the flat iron, said bracket being constructed with a support located below the free end of said extending portion, a cam member being rotatably mounted on said support in a position such as to engage said free end of said 10 first arm.

References Cited in the file of this patent UNITED STATES PATENTS 15 2,052,662 Roehl et a1. Sept. 1, 1936 2,686,240 Reichold July 6, 1937 2,184,270 Campbell Dec. 26, 1939 2,201,115 Reingruber et a]. May 14, 1940 2,461,561 McLelland et al. Feb. 15, 1949 20 2,797,292 Polivka June 25, 1957

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