US2364433A

US2364433A - Safety switching arrangement for electrically heated devices

Info

Publication number: US2364433A
Application number: US404451A
Authority: US
Inventors: Frank E Finlayson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1941-07-29
Filing date: 1941-07-29
Publication date: 1944-12-05
Anticipated expiration: 1961-12-05
Also published as: GB557024A

Description

De 5, 1944. F. E. FlNLAYsoN 2,354,433

SAFETY SWITCHING ARRANGEMENT FOR ELECTRICALLY HEATED DEVICES Filed July 29, 1941 Fr-anh E. Fnlayson,

Wwf. wlw b9 His Attcrney.

Furthermore, in such safety switch which Patented Dec. 5, 1944 SAFETY SWITCHIN G ARRANGEMENT FOR ELECTRICALLY HEATED DEVICES Frank E. Finlayson, Ontario, Calif., assignor to General Electric Company, a corporation of New York Application July 29, 1941, Serial No. 404,451

8 Claims.

This invention relates to electric heating devices such as electric ilatirons and more particularly to improved means for automatically disconnecting such devices from the power supply incase the operator neglects to do so.

In the use of electric heating devices, such as electric fiatirons, damage resulting from iire or scorching may occur if the iron is left unattended in the horizontal or ironing position while connected to the power supply. In order to preclude the possibility of such damage it is not uncommon to provide an automatic safety switching arrangement in connection with the handle of the iron whereby the heating circuit is closed when the handle is grasped and automatically opened when it is released. While such arrangements are effective to prevent damage referred to above, they have certain operating disadvantages. For example, during an ironing operation an operator frequently lays the iron aside temporarily while arranging the articles to be i-roned. As a result the handle is grasped and the safety switch operated at frequent intervals and the resulting sparking at the contacts causes undesirable and annoying radio interference. arrangements, since the safety switch shuts oil the heating current each time the iron is temporarily laid aside, the iron has a tendency to cool down to a point where the Yironing operation may be rendered unsatisfactory. Also frequent operationof the safety switch causes the contacts to deteriorate rapidly because of sparking.

An object of my invention is to provide a new and improved control system for an electric heating device.

It is a further object ofrmyminvention to provide a safety switching system operating in conjunction with a handle of an electric heating device, such as an electric atiron, which operates to break the heating circuit at relatively infrequent intervals whereby radio interference resulting from contact sparking is greatly reduced.

Another object of my invention is to provide a is arranged to cooperate with a heat control thermostat of an electrically heated iron inV such a manner that the contacts of the safety switchrarely, if `ayer, are required to break the heating circuit whereby` inexpensive' switch contacts may be utilized and the life of the con'- tacts is greatly extended.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of noveltywhich characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly, according to the illustrated embodiment of my invention, a safety switch, arranged heating circuit. Shutting olf of the heating cur-y rent by the main thermostat permits the safety switch contacts to open and the iron cannot be reenergized, even though the thermostat conta-cts close, until the contacts of the safety switch are again closed by action of the operator. With this arrangement the heating circuit of the iron is broken only by the normal operation of the thermostat contacts which occurs at relatively infrequent intervals whereby radio interference due to contact sparking is greatly reduced.

My invention will be better understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is an elevation view, partly in section, of an electric latiron embodying improved control apparatus constructed in accordance with my invention; Figs. 2 and 3 are partial sectional views showing my improved control apparatus in difterent operating positions; Fig. 4 is a cross-section view of the handle of the atiron shown in Fig. 1 along the line 4-4 looking in the direction of rthe arrows; and Fig. 5 is a diagrammatic showing of the circuit connections of the atlron.

Referring to the drawing, I have shown my invention applied in one form to an electrically heated flatiron having a sole plate I0 that is formed of any suitable material such as cast iron or aluminum. Cast within the sole plate I0 is a sheathed heating element II preferably of the type described in United States patent to C. C. Abbott, 1,367,341, dated February 1, 1921. As shown this heat'ng element comprises a helical resistance heating element I2 mounted in a tubular metallic sheath I3 and supported in spaced relation with reference to the sheath by a compacted layer of insulating material I4 whichpreferably will be of Heating elements of to the desired shape usually formed roughly in the shape of a horseshoe having its terminals I5 at the heel of the iron and its apex at the toe of the iron.

In order to maintain the temperature of the iron' Within predetermined limits, I provide a heat control thermostat or thermostatic switch I6 having contacts connected in series circuit relation with the heating element I2 and mov;- able between open and closed positions in accordance with the temperature of the iron in a Well-known manner. While any type of sultable thermostatic switch may be used, I have illustrated one of the type disclosed and claimed in United States Patent 2,152,850 granted May 15, 1939, on the application of J. R. Campbell and assigned to the assignee of the present invention. Briefly, the thermostatic switch I6 described in the above-mentioned Campbell patent comprises a bimetallic element I1 and two similar Z-shaped supporting members I8 the ends of which are secured together and Iastened in good thermal relation to the sole plate I0 by means of a fastening screw 20. Extending outwardly from the upper end of the supporting member I8 are a pair of switch arms 2I and 22 carrying cooperating contacts 23. The

and I9 upper switch arm 2I is resilient in construction and is arranged to bias the contacts 23 to the closed circuit position. The switching member 2I also has a portion 24 extending beyond the contacts 2-3 which is adapted to be engaged by one end of an L-shaped member 25 extending outwardly and upwardly from the free end of the bimetallic member I1. The portion of the bimetallic member I1 having the higher coelcient of expansion is on the lower side so that when the bimetallic member becomes heated to a predetermined temperature its free end moves upwardly whereby the end oi' the L-shaped member 25 engages the outer end 24 of the spring switch arm 2l and opens the contacts 23. The temperature adjustment of the thermostatic switch is effected by means of an adjusting screw 26 mounted in the supporting arm I9. This screw carries at its lower end a button 21 which bears against the resilient supporting member I8. When the screw is adjusted the position of the support and consequently the position of the switch arms 2| and 22 is changed. By adjusting the position of the switch arms 2I and 22 relative to the bimetallic element I1 the temperature setting of the thermostatic switch is changed.

The iron is provided with a cover 30 secured to the sole plate by suitable fastening means not shown. The cover 30 has-a portion 3| extending rearwardly of the sole plate and forming a heel stand for supporting the iron inl an upstanding position. `The iron is provided with a handle 32 which is secured to the upper portion of the cover 30 by means of suitable fastening means, one of which isfshown at 33.

In order to provide means for automatically disconnecting the iron from the power supply when it is left unattended in the horizontal or ironing position, I provide a. safety switch 35 connected in series circuit relation with the heating element I2 and the thermostatic switch IB. The safety switch 35 is mounted on the upper side of the handle 32 and comprises a pair of cooperating contacts 35, one of which is carried on the end of a relatively rigid contact arm 31, while the other contact is carried on the end of a resilient contact arm 38 constructed of bimetallic material for a purpose which will be described in detail below. The

contact arms

31 and 38 together with a leaf spring member 33, the purpose of which will presently appear, are mounted on a at projection 40 extending upwardly from the top surface of the handle 32 by means of a screw 4I. An insulating washer 42 is provided for maintaining the

contact arms

31 and 38 in the proper spaced relation so that the contacts 36 are normally in the disengaged position. Also, an insulating washer 42a is provided for preventing a short circuit between the

contact arms

31 and 38 through the screw 4I.

For the purpose of enabling the safety switch 35 to be closed manually when the handle 32 is grasped by the operator and for maintaining the switch closed when the iron is supported on the heel rest in an upstanding or non-ironing position, I provide a pivotally mounted handle lever 43. 'I'he handle lever 43 is pivotally mounted to the cover member 30 by means of a pivot pin 44 which extends through the lever and is supported on an upstanding lug member 45 secured to the cover by the screw 33. As best shown in Fig. 4, the handle lever has a U-shaped cross-section, the inner surfaces of the downwardly extending side walls being arranged to slidably engage the vertical side walls of the handle 32 and to form in conjunction with the handle an enclosed space 45 in which the switch 35 is located. The contour of the lever is so shaped relative to the-handle 32 that a smooth gripping surface is provided which is adapted to be grasped by the operator during the ironing operation. The spring 39 is arranged to engage the upper wall of the handle lever 43 so that the lever is biased upwardly to the position shown in Fig. 1. Extending downwardly from the handle lever is an abutment 46 which is adapted to engage the free end of the contact arm 38. Thus when the handle is grasped by the operator during the ironing operation the lever 43 is depressed against the bias of the spring 39 and the abutment 48 bends the contact arm 38 downwardly so that the contacts 136 of the safety switch are forced into engagement as shown in Fig. 2. It will be noted that the end portion 41 of the handle lever 43 engages an edge 48 of a cutaway portion in the handle 32 to limit the downward movement of the handle. To limit the upward movement of the handle a pin 49 extends through and is mounted in the vertically extending side walls of the handle lever. The pin 49 projects through an elongated slot 50 in the handle 32 and engages the upper edge of the slot to limit the upward movement of the handle lever. The elongated slot permits suiilcient travel of the pin 49 to accommodate the downward movement of the handle lever.

When the iron is supported in the upstanding or non-ironing position on the heel stand 3I there is no danger from iire or scorching and it is desirable to maintain the safety switch Z5 closed in this position independently of any action on the part of the operator so that the iron can be left unattended in this position during initial heating and between ironing periods. To accomplish automatic closure of the safety switch 35 when the iron is in the upstanding position, the pivotally mounted handle lever 43 is provided with an abutment 5I which is adapted to engage the supporting surface when the iron is supported in the upstanding position on the heel stand. In this position the abutment 5I is so located relative to the pivot pin 44 that the weight of the iron causes the handle lever to pivot to the closed circuit position of the safety switch shown in Fig. 2, and hence the safety switch is automatically maintained closed while the iron is in the vertical position.

The circuit connections for the safety switch 35 of the thermostatic switchA I6 and the heating element I2 are best shown in Figs. 1 and 5 of the drawing. 'I'he iron is energized from a suitable source of electric power (not shown), the

power supply conductors

52 and 53 being shown in Fig. 1 as extending inwardly through one wall of the lower portion of the' handle lever 43. The power supply conductor 52 is connected directly to the xed end of the bimetallic contact arm 38 while the other power supply conductor 53 is connected to one of theterminals I5 of the heating element I2. The contact arm'31 of the safety switch is connected by a conductor 54 to one of the contacts 23 of the thermostatic switch I6 while the other of the contacts 23 is connected by a conductor 55 (not shown in Fig. 1) to the other of the terminals I5 of the heating element I2. It will therefore be apparent that the safety switch 35, /the thermostatic switch I 6, and the heating element I2 are connected in series circuit relation with the energizing circuit of the iron.

According to my invention, when the handle lever 43 is depressed and the switch 35 closed by the operator during the ironing operation, means responsive to a flow of current through the heating element of the iron is provided for maintaining the switch 35 in the closed circuit` position independently of the handle lever. Thus, even though the handle lever is released, the switch 35 remains closed until the thermostatic switch I6 opens its contacts to shut off the current to the heating element I2 whereupon the safety switch is permitted to return to its normal open circuit position. In the illustrated embodiment of my invention, this is accomplished by the action of the bimetallic contact arm 38 of the safety switch. When the safety switch 35 is closed by depressing the handle lever 43 the current flowing tothe heating element I2 passes through the bimetallic contact arm 38 and heats it. The bimetallic contact arm comprises an elongated resilient bimetallic bar formed of two metals having different temperature coefficients of expansion such as Invar and steel rigidly secured together lengthwise as by welding. The bimetallic contact arm is arranged with the metal having the higher coeicient of expansion on top so that as the contact arm becomes heated by the passage of current therethrough the contact arm becomes stressed downwardly so as to maintain the contacts 36 of the safety switch 35 in engagement independently of the action of the manually operated handle 43. The contacts of the safety switch will thereafter remain closed until the contacts 23 of the thermostatic switch I6 open on the heat cycle of the thermostat to stop the flow of heating current to the resistance element I2 and to the bimetallic contact arm 38. VAt this time, if the handle lever 43 is in the released position, the contact arm 38 will cool rapidly permitting the contacts to resume the normal open circuit position.

I have found that `by properly designing the bimetallic contact arm 38 of the safety switch the contacts can be made to stay closed in about fifteen seconds maximum time after manual closing of the switch by depressing the handle lever, and upon deenergizing of the heatingcirtacts 36 of cuit, as by opening of the contacts of the thermostatic switch when the handle lever 43 is in the released position, the contacts of the safety switch will open in about twenty seconds maximum time. The factors influencing the design of the bimetallic contact arm include the resistance and dimensions of the bimetallic material and the amount of heating current drawn by the resistance element I2. The contact opening temperature of the safety switch should be well above the maximum ambient temperature under all operating conditions to insure the opening thereof when the handle lever is released and the thermostatic switch contacts open to deenergize the heating circuit.

In operation, let it be assumed that theiron is cold and connected to the power supply. As shown in Fig. 1 the contacts ofthe thermostatlc switch will be closed but the contacts of the safety switch 35 will be open due to the fact that the spring member 39 biases the handle lever 43 to the released position. If now the handle lever 43 is depressed eitherby the action of the operator in grasping the handle or by placing the iron in the upstanding non-ironing position in which it is supported by the heel stand 3| and the abutment 5I, the safety switch 35 will be actuated to the closed position as shown in Fig. 2. The closure of the safety switch completes the energizing circuit to the heating element I2 whereupon itcommences to heat the sole plate I0. It will be observed that the current owing through the heating element I2 also flows through the bimetallic contact arm 38 since they are connected in series circuit relation. This causes the contact arm 38 to become heated locally whereby it becomes stressed downwardly and acts to keep the contacts 36 closed independently of the pressure exerted by the abutment 46 of the handle lever. When the sole plate reaches the predetermined temperature corresponding to the control point for which the thermcstatic switch I6 is set, the free end of the bimetallic bar I1 moves upwardly and engages the end portion 24 of the contact arm 2| and opens the contacts 23 to deenergize the heating element I2. Thereafter the contacts 23 of the thermostatic switch cyclicly open and close to maintain the temperature of the sole plate within predetermined limits in a well-known manner.

Now let it be assumed that the operator releases the handle lever 43 and leaves the iron in the horizontal ironing position where it may do damage if it is not disconnected from the power supply. Let it also be assumed that at the time the operator releases the handle lever the contacts 23 of the thermostatic switch IB are in the closed or low temperature position, the thermostat being on the heating portion of the heating cycle. As soon as the operator releases the handle the spring 39 will force the handle lever 43 upwardly to the released position. The conthe safety switch 35, instead of opening at the time the handle lever is released and breaking the circuit to the heating element I2, remain closed due to the fact that the bimetallic contact arm 38 has been heated locally and is stressed downwardly by the action of the heating current flowing therethrough. Therefore, the abutment 46 moves out of contact with the free end of the contact arm 38 as shown in Fig. 3 of the drawing. When the temperature of the iron reaches the maximum temperature of the thermostat heat cycle, the thermostat contacts 23 move to the'open or high temperature posi- 4 tion to interrupt the fiow of current to the heating element l2 and also through the bimetallic contact arm 38. After a short interval of time the bimetallic contact arm 38 cools and moves upwardly causing disengagement of the contacts 36 of the safety switch 35, the safety switch returning to the position shown in Fig. 1 of the drawing. The safety switch now being opened the heating element l2 cannot be reenergized even though the contacts 23 of the thermostatic switch I6 reclose when the temperature of the iron fails below the contact closing value and the iron therefore cools down to room temperature or until such a time as the operator again grasps the handle and depresses the handle lever 43 to reclose the safety switch 35.

If the handle lever 43 should be released by the operator at a time during the thermostat heat cycle when the contacts 23 are in the open or high temperature position, the contacts of the safety switch will open immediately without time delay since there will be no heating current flowing through the bimetallic contact arm 38 to heat it and cause it to bend downwardly and maintain the contacts 36 in engagement. However, the fact that the contacts of the safety switch open immediately under this condition is immaterial since no current flow will be broken by the contacts and therefore there will be no troublesome sparking.

It will be seen that my improved safety switching arrangement functions to disconnect automatically the iron from the power supply in case it is left unattended in the horizontal. ironing position. It will be observed that with my improved control system the contacts of the safety switch do not interrupt the energizing circuit of the heating element I2 except in a relatively -rare case when the handle lever is initially depressed and then released after a very short interval so that the bimetallic contact arm 35 does not have a chance to heat sufficiently to maintain the contacts of the safety switch closed. This rarely occurs, however, since, as] pointed out above, the bimetallic contact arm may be designed so that it needs to be closed not over fifteen seconds to heat sufficiently to stay closed and the times when an operator initially grasps and releases the handle in less than this period are rare. Therefore since the contacts of the safety switch are not required to break the load circuit there is no sparking so that these contacts may be of inexpensive construction and they will operate a long time without deterioration.

Furthermore, it will be noted that regardless of the frequency of the operation of the handle lever 43 by the operator, except for the rare occasion noted above, the energizing circuit of the heating element I2 will be broken only at such times as the contacts of the thermostatic switch move to the open circuit position incident to the normal operation of the thermostat. I'herefore, radio interference resulting from sparking contacts is reduced to a minimum.

The time delay feature of providing means f or keeping the contacts of the safety switch closed after the handle lever is released until the main thermostat switch opens its contacts provides an additional advantage that when the operator temporarily releases the handle while arranging articles to be ironed, the heating current is not immediately cut off so that there is no tendency for the iron to cool down during these temporary idle periods.

While I have shown and described particular embodiments of my invention, it will occur to those skilled in the art that various changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A safety control system for an electric heating device having a heating element, a circuit for energizing said heating element and an operating handle adapted to be grasped by an operator when said device is being used, said system comprising a thermostatic switch responsive to the temperature of said heating element for controlling said circuit, said thermostatic switch having a high temperature position and a low temperature position, a normally open safety switch connected in series with said circuit, a manually operated member for effecting closure of said safety switch to render said thermostatic switch effctive for controlling said circuit, said manually operable member being arranged to be actuated by the operator when said handle is grasped, means dependent on the flow of current in said circuit when said thermostatic switch is in the low temperature position for maintaining said safety switch closed after said manually operated member is released, said last mentioned means becoming ineffective when said thermostat moves to the high temperature position whereby said safety switch opens precluding further control of said circuit by said thermostatic switch until said safety switch is again manually closed by the operator. i

2. A safety control system for an electric heating device having a heating element, a circuit for energizing said heating element, and an operating handle adapted to be grasped by an operator l when said device is being used, said system comprising a thermostatic switch movable between open and closed positions in accordance with the temperature of said element, a safety switch biased to an open position, said switches being connected in series with said circuit, manually operated means for closing said safety switch, said manually operated means being arranged to be actuated by the operator when said handle is grasped, means responsive t0 the ow of current in said circuit when both of said switches are in the closed circuit position for maintaining said safety switch closed after the manually operated means is released, said thermostatic switch moving to the open circuit position when the temperature of said heating element rises above a predetermined value thereby deenergizing said circuit whereby said safety switch moves to the open circuit position precluding further energizatic-n of vsaid circuit by said thermostatic switch until said safety switch is manually reclosed by the operator.

3. In combination, an electric iron having a handle, a heating element for said iron, an energizing circuit for said heating element, a thermostatic switch responsive to the temperature of said iron for interrupting said circuit when said temperature reaches a predetermined high value and for reclosing said circuit when said temperature falls to a predetermined low value, a normally open safety switch connected in series with said circuit, manually operated means adapted to be actuated when said handle is grasped for closing said safety switch, a bimetallic member arranged to maintain said safety switch closed when heated, and means for locally heating said bimetallic member in accordance with the current flowing in said circuit, said means being rendered ineifectiveresponsively to the operation of said thermostatic switch in interrupting said circuit when said temperature reaches said predetermined high value so that said bimetallic member is permitted to cool, said member cooling at such a rate that it releases its holding force on said safety switch prior to the closure of said circuit by said thermostatic switch in response to the cooling of said iron to said predetermined low temperature.

4. In combination, an electric iron having a handle, a heating element for said iron, a circuit for energizing said heating element, a thermostatic switch responsive to the temperature of said iron for interrupting said circuit when said temperature reaches a predetermined high value and for reclosing said circuit when said temperature falls to a predetermined low value, a normally open safety switch connected in series with said circuit, manually operated means adapted to be actuated when said handle is grasped for closing said safety switch, a bimetallic member operatively associated with said safety switch and movable to a position to maintain said safety switch closed when locally heated, said bimetallic member being arranged to be traversed and heated by the current flowing in said circuit so that when said thermostatic switch attains a predetermined high temperature to interrupt said circuit said bimetallic member cools and at such a rate that it releases its holding force on said safety switch prior to the reclosure of said circuit by said thermostatic switch responsively to the cooling of said iron to said predetermined low temperature.

5. In an electric heating device, a heating element, a circuit for supplying current to said heating element and a handle for operating said device, a normally open switch for controlling the ow of current in said circuit, closing means for closing said switch when said handle is grasped by the operator and for releasing said switch when said handle is released, means dependent upon a flow of current in said circuit for holding said switch closed independently of said closing means, means responsive to the temperature of said device for opening said circuit when said temperature rises to a predetermined high value and for reclosing said circuit when said temperature falls to a predetermined low value, and when said handle is released said means dependent upon current iiow functioning responsively to the operation of said temperature responsive means in opening said circuit always to release its holding effect on said switch prior to the operation of said temperature responsive means to reclose said circuit when said temperature falls to said .predetermined low valut` 6. In an electric heating device, a heating element, a circuit for supplying current to said heating element and an operating handle that is grasped by the operator when said device is being used, a thermostatic switch responsive to the temperature of said device for interrupting said circuit when saidtemperature reaches a predetermined high value and thereafter for reclosing said circuit when said temperature falls to a predetermined low value, a normally open safety switch connected to control said circuit, manually-operated means operable to a position to operate said safety switch to close said circuit when said handle is grasped by the operator and to a position to release said safety switch when said handle is released, and timing means dependent upon a Iiow of current in said circuit :for holding said safety switch to hold said circuit closed independently of said manually-operated means so that the safety switch holds said circuit closed after said manually-operated means releases it until said thermostatic switch opens to deenergize said circuit, whereupon said timing means functions to release its holding eiect on said safety switch in a timed interval, said timing means being set to always release its said holding effect prior to the reclosure of said circuit by said thermostatic switch due to said temperature falling to said predetermined low value.

7. A safety control system for an electric fiatiron having a heating element, a circuit for energizing said heating element, and an operating handle adapted to be grasped by an operator when said iron is being used, said system comprising a thermostat having two control positions connected to control the flow of current to said element, a normally open switch for controlling,r said circuit, manually operated means for closing said switch, said manually operated means being arranged to 'be actuated by an operator when said handle is grasped and means responsive to a condition iniiuenced by the position of said thermostat for maintaining said switch in a closed position independently of said manually operated means when said thermostat is in one of said positions, said last mentioned means becoming ineffective when said thermostat moves to the other of lvsaid positions whereby said switch automatically opens to deenergize said circuit if said manually operated means has been released by the operator.

8. In combination, an electric iron having a handle, a heating element for said iron, an energizing circuit for said heating element, a thermostatc switch responsive to the temperature of said iron for interrupting said circuit when said temperature reaches a predetermined high Value and for reclosing said circuit when said temperature falls to a predetermined low Value, a safety switch connected to control said circuit, manually-operated means adapted to be actuated when said handle is grasped for operating said safety switch to a position to close said circuit, a temperature responsive member arranged when heated to maintain said safety switch in said position, and heating means for locally heating said temperature responsive member in accordance with the current flowing in said circuit, said heating means being rendered ineffective responsively to the operation of said thermostatic switch in interrupting said circuit when said temperature reaches said predetermined high value so that said temperature responsive member is permitted to cool, said member cooling at such a rate that it releases its holding force on said safety switch prior to the closure of said circuit by said thermostatic switch in response to the cooling of said iron to said predetermined low temperature.

FRANK E. FINLAYSON.