US2024856A - Electric flatiron - Google Patents

Description

Dec. 17, 1935.` M. H. GRAHAM ELECTRIC FLATIRN Filed June l5, 1934 ib mmm"` 172/ (zz fg 29 |||||||Ill`l /NvE/voz Maur/ce H. Gra/vam By Z/s ryogsys Patented Dec.` 17, 1935 4UNITED STATES PATENT OFFICE ELECTRIC FLATIBON Maurice H. Graham, St. Louis Park, Minn.

Application June 15, 1934, Serial No. 730,745

' 'l Claims. (Cl. 21S-25) My present invention relates to electrically heated ilatirons and, generally stated, the invention consists of the novel devices, combinations of devices and arrangement of parts hereinafter 5 described and dened in the claims. The accurate regulation of heat in an'electrically heated fiatiron involves problems that are peculiar to flatiron structures. The sole plate of the fiatiron, in use, will be subjected to various different heat-absorbing conditions, sometimes to delicate materials such as laces, chiffons and the like, which absorb heat very slowly, and sometimes to damp blankets andthe like, which absorb heat very rapidly. vIn practice and in accordance with underwriters rules and regulations, one thousand watts is about the limit which can be supplied to an electrical iiatiron or to any other current-utilizing device over the ordinary wires of a house installation.

Experience has shown that cast iron is the best metal for use in the sole plate of an electrically heated ilatiron. By experiment I have found that for the greatest accuracy of heat control, the switch actuator should-be incorporated in the sole plate and should be of a metal that has a lower co-emcient of expansion and a slower rate'of heat exchange than the cast iron sole plate. I have further found that the emciency of the iron kwill be increased by incorporating the electric heating element also in the sole plate of the flatiron. The problem has been yto find a metal for use as a switch actuator which will not only have a lower co eilicient of expansion than cast iron, but will maintain a constant or even rate of expansion and contraction at the high temperatures at which flatirons should be maintained in use.

Cast iron has been found to be the best for the sole plate of a fiatiron. I have obtained substantially perfect results by making the switch actuator in the form of a metal alloy bar or rod closely embedded in the groove or slot in the sole plate and made of a nickel-steel alloy, to wit: an alloy consisting of 42% nickel 45 and 58% steel. The co-eilicient of expansion of cast iron is .059, and that of the nickel-steel alloy .026. When thus made, the sole plate will have more vthan twice the expansion of the nickel-steel actuator bar. Moreover, the cast iron of the sole plate will absorb and radiate heat faster than the nickel-steel actuator bar, which action,`together with the fact that the actuator is embedded in the sole plate, give an ideal action that will hereinafter more fully 05 appear.

The proportions of nickel and steel in the above alloy are of great importance. A nickelsteel alloy consisting of 36% nickel and 64% steel is a metal known as invar metal." This invar metal, as is well known, expands and con- 5 tracts .very slightly intemperatures below 350 degrees F., but at temperatures above 350 degrees F., it expands very rapidly and unevenly so that it cannot be relied upon vfor accurate control of a tiatiron, the temperature of which 10 should be around 500 degrees F. At 500 de-v grees F., invar and cast iron have substantially the same co-eilicients of expansion. However, the 42% nickel-58% steel alloy has an even rate of expansion and contraction at all tem- 15 peratures below 650 degrees F.

By experiment I have found that the nickel employed in the nickelrsteel alloy for the Switch actuator must not be less than 40% or more than 5o%. The above 42%-58% nickel-steel zo alloy in the form of a bar is not fragile, has good strength and when embedded in the sole plate as stated, has been found to give a switch control that is almost perfect in-its accuracy. As a further important characteristic this nickel- 25 steel alloy, in respect to cast iron, has a slower rate of heat exchange, that is, will not cool as rapidly or absorb heat as rapidly as cast iron.

The invention above outlined is illustrated in the accompanying drawing, wherein like chara0 acters indicate like parts throughout the several views.

Referring to the drawing:

Fig. i is a vertical section taken longitudinally through the major axis of an electric fiatiron 35. embodying my invention and illustrating a very desirable form thereof, some parts being shown in full;

Fig. 2 is a vertical section of the iron shown in Fig. 1, with the handle, casing and certain 4e other parts removed, and some parts broken away; and

Fig. 3 is a fragmentary section taken on the line 3-3 of Fig. 2.

Referring to the drawing, the numeral 0 in- 45 dicates the sole plate of a atiron which is of cast iron; and the numerals I0, I: and l2 indicate, respectively, the metal anchoring plate, the sheet metal shell or cover and the handle of the fiatiron. The said parts 0 and il are 50 shown as rigidly but detachably connected by screws i3 and the said elements I0, il and l2 are shown as rigidly but detachably connected by screws I4. For the highest eillciency, the electrical heating element, which is formed by 56 manifold wire coils I5, is embedded in the sole plate 9. Preferably, this embedding'of.. the coils I5 is accomplished ina-manner' 'disclosed' and claimed in my pending application, Serial No.

705,716, filed January 8, 1934, entitled "Elecare two manifold coils I5, the terminals of which are indicated at |5a and I5b. l

On the heel of the shell or cover IIV are the usual circuit lead terminals |8, to which theV socket ot an electric supply cable is adapted to be connected in the well-known manner.

A'Ihe supply circuit to they heating coils I5 includes an electric switch which may take various forms but which, as illustrated in these views, Figs. l, 2 and 3, includes contact points I9 and 20 carried by the up-turned prongs of a U-shaped spring switch 2|, the lower portion of which is anchored to the sole` plate 9 by ak short cross bar 22 which, in turn, is rigidly butA detachably secured to thesole plate by` screws 23 `or the like. lThe contact point I9 is electrically connected by a flexible metal ribbon 24` to one of the terminals |5a of the heating coil, and the other of said terminals |5a will,

by a wire, not shown, be connected to the other lead terminal I8, to wit: the lead terminal to which the ribbon 25 is not connected. The said lead terminals 8, of course, are insulated the `one from the other. The coil terminals |5b are electrically connected by a suitable conductor indicated in Fig. 2 at 26. Therearprong of the spring support 2| is Yadapted to be variably set; and this, as` shown, is accomplishedby a lpressure screw .21 that worksthrougha post 28 anchored to the heel or rear portion of the sole plate.

The switch actuator used in the iron illustrated in the drawing is shown as in the form of a at bar 29, made of the nickel-steel. alloy above described. This actuator barv is incorporated in the sole plate and is quite closely tted into a longitudinal groove 30 formed at thelongitudinal axis of the sole plate and extended at its rear portionintoa small well or y depression 3| in which the lower portion of th switch 2| is shown as mounted.

At its rear end, switch actuator bar 29 is shown as provided with an upwardly and rearwardly projecting nger l32 that works through. a per' foration inthe front arm ofthe switch 2| and has a projecting lug that exerts a forward pull y on the front arm of the switch 2| in the switchcontact points I3 andj 2|| inengagement thereby 'closing'.,lthfe'llliit through 'the electrical heating elexnei'ts of theiiatiron, providingof course, that there isa supply of current to the terminals 8. Whenrheat is applied to the sole plate 5 from the electrical heating coils, the sole plate will, with the materials above indicated, expand Y more than twice as fast as the actuator bar 29, and hence will exert a forward pullwon the bar 29; and at some certain temperaturef'the bar 29, acting on the front arm ofthe switch 2|, will separate the contacts I9 and 20, thereby automatically cutting off the supply kof `current to the heating elements. f

The temperature at which the contacts I9 and 20 will be separated and the ciment cut offvin the iron, may be varied by forward and rearward adjustmentsv of the rear arm of the switch` 2 I, and which adjustment is, as shown, accomplished by adjustments of the screw 21. 20 Assume that the adjustment of the screw 21 is such that under the relative rapid expansion of the sole plate and the relativelyslower exf pansion of the bar 29, the latter, acting on. the switchv2|,`will separate the contact points 25 |9 and 20 when the temperature of they sole plate reaches 500 degrees F. 'I'he instant that the circuit is .thus broken by the separation of thel contacts I9 and 20, the temperature ofthe sole'` plate of the atiron and Vall other Vparts 80 ofthe atiron, for thatmatter, willcommence 1 to recede, but the temperature of the sole plate will decrease more rapidly than that of the actuator` bar `29, and there will be a lag in the lowering of temperature and hence` the con- $5 traction ofthe bar 29 inrecspecttothe lowering of temperature andV contraction of the vsole plate., The bar `29 tends to maintain, for a short interval, the length that is assumed at the' instant of breaking of thekcircuit, and while the 40 sole plate is -rnaking its initial contraction. i This permits the initial contraction ofthe sole plate to again close the switch, thereby again turning on the current as soon' as the sole plate of thel atiron has beeny very slightly 45 reduced, to wit: from 500 degrees F. to approximately 498.degrees F. l

When the current has been again turned on, and heat kapplied to the iron, there will be alag in the heat absorption and an expansion of the 50 switch actuator bar 29 inrespect to the rapidity of the heat-absorption and expansion of the sole plate, so that when the temperatureof the sole plate has been but slightly raised, to wit:`r back to the predetermined desired temperature `as- 55 sumed to'be'500 degrees F.. the circuit will be again opened andthe currentv to the vheating element cut off. In actual experiments with atirons having Va switch actuator made of a material of a higher co-eillcientl of expansion 00` than the sole plate, it has been` found that the v lag will then be in the sole platefand that this v lag worksagainst accuracy of control, so thaty there will be a drop or variation in temperature of the sole plate of approximatelyl degrees F., 05 depending somewhat on the character ofthe work being ironed, but always of such material variation-as to destroyv accuracy of control.

The eiilciency of the scheme above described, requires the switch actuator to be embedded or 70 incorporated inthe sole plate so that it is subject to direct heat. exchange with the sole plate and isl subjected to the same temperatures; and the accuracy ofthe-control is improved by having direct contact .between the switch actuator 16 and the sole plate. Moreover, the emciency of the flatiron is further improved by embedding the electrical heating element in the sole plate so that the three elements, to wit: the sole plate, the electrical heating element and the switch actuator, are incorporated substantially as a unit.

In the above description of the structure illustrated, the desired temperature is assumed to be 500 degrees F., but this predetermined tcmperature may obviously be varied by varying the position of the rear contact point I9 in respect to the contact point 20 through the adjustment of the screw 21 which acts on the rear arm of the spring switch member 2|.

What I claim is:

1. In an electric iron having a heating element and a supply circuit for said heating element including a switch; a sole plate, and a metallic switch actuator associated with said sole plate and having a substantially different coeiilcient of expansion tromthat of vthe sole plate, said actuator being a nickel-steel alloy in which the nickel is in a proportion oi from forty to mty percent o1 the total metal in the alloy, whereby said switch is operated by the di'erential expansion and contraction oi said sole plate and actuator.

2. The structure dened in claim 1, in which said actuator is in the form of a bar, one end of which actuates said switch and the other end oi' which reacts against the sole plate at a point remote from said switch.

3. 'Ihe structure defined in' claim 1. in which said switch is at the heel end of said sole plate and said actuator is in the form of a bar that acts upon said switch at its rear end and the front end of which reacts against the front toe end of said sole plate.

4. The structure defined in claim 1, in which said switch actuator and said heating element are incorporated in said sole plate.

5. In an electric iron having a heating element and a supply circuit for said heating element including a switch; a sole plate, and a metallic switch actuator associated with said sole plate and having a substantially different coemcient o! expansion i'rom that o! the sole 15 plate, said actuator being a nickey steel alloy in which the nickel is in a proportion of approximately 42% of the alloy, whereby said switch is operated by the dierential expansion and contraction of said sole plate .and actuator.

6. 'I'he structure defined in claim 5, in which said actuator is in the form of a bar incorporated in said sole plate.

7. I'he structure dened in claim 5, in which said switch actuator is m the :om of a bar m- 25 corporated in said sole plate adjacent the longitudinal center thereof, land in1whicl1 said actuator is connected at one en d to said switch and at its other end to the sole plate.

MAURICE H.. GRAHAM;

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