Mechanics of the Household / A Course of Study Devoted to Domestic Machinery and Household Mechanical Appliances

by E. S. Keene

The Electric Flat-iron.

—The changes that have been made in domestic appliances by the extended use of electricity have brought many innovations but none are more pronounced than the improvements made in the domestic flat-iron. It was the first of the household heating devices to receive universal recognition and its place as a domestic utility is firmly established.

The relatively high cost of heat as generated through electric energy is in a great measure counterbalanced in the flat-iron by high efficiency in its use. In the electric iron, the heat is developed in the place where it can be used to the greatest advantage, and transmitted to the face of the iron with but very little loss. Because of this direct application the cost of operation is but slightly in excess of the other methods of heating.

The electric flat-iron has now become a part of the equipment of every commercial laundry, where electricity can be obtained at a reasonable rate. The popularity of the electric iron is due to its cleanliness and to the increased amount of work that may be accomplished through its use. Because of the time saved in changing irons and the comfort of the room by reason of its lower temperature, a sufficiently greater amount of work is accomplished to more than compensate for the greater cost of heat.

The electric current is conducted to the flat-iron from the house circuit by wires made into the form of a flexible cord. The cord attaches to the electric-lamp fixture by a screw-plug and connects with the iron by a special attachment piece as indicated at P and R in Fig. 226. Connection is made to an incandescent lamp socket at any convenient place. The only precaution necessary in attaching the iron is to see that the fuse and the wires, which form the circuit, are of size sufficient to transmit the amount of current the iron is rated to use. As explained later, the fuse which is a part of every electric house circuit, and the conducting wires which form the heater circuit, must be sufficient in size to transmit the necessary current without material heating.

Fig. 226.—Electric flat-iron and its attachments.

The cord connects with the socket at P, and the current turned on. It is attached with the iron by a piece R, made of non-conducting and heat-resisting material and arranged to make contact with the heater terminals by two brass plugs that are insulated from the body of the iron and afford easy means of making electric contact. The contact plugs are shown in Fig. 227. To make electric connection, the contact piece is simply pushed over the plugs, where it is held in place by friction. Instructions which accompany a flat-iron when purchased advise that the attachment piece be used in turning off the current. The reason for this is because of the flash that accompanies the break in the circuit when disconnection is made in the socket. This flash is really a small electric arc, that forms as the circuit is broken and which burns away the switch at the point of disconnection. The arc so formed burns away the contact pieces in the switch and it is soon destroyed. The attachment piece will stand this wear more readily than the socket switch and hence is preferable for disconnecting. The irons are frequently provided with a special switch for the service required in the flat-iron.

Fig. 227.—Electric flat-iron showing position of the heating element and contact plugs.

A spiral spring connected to the attachment cord prevents it from kinking when in use and thus breaking the conducting wires. The attachment cord is made of stranded wires to make it flexible. The strands of fine copper wire are made to correspond to the gage numbers by which the various sizes of wire are designated. In use the constant movement of the iron tends to kink the cord and thus breaks the strands. This action is most pronounced at the point where the cord attaches to the iron. For this reason a spiral spring wire encloses the cord for a short distance above the attachment piece. After long usage the cord is apt to break in this vicinity. It may usually be repaired by cutting off the ends of the cords and new connections made in the attachment piece. When the iron is in use the slack portion of the cord is kept from interfering with the work by the coiled wire S, which connects with the cord at any convenient place.

Electric flat-irons are made in a variety of styles and forms, the mechanism of each possessing some particular advantage, but all are provided with the same essential parts, chief of which is the heater with its electric attachment piece. In Fig. 228 is shown very clearly the construction of an example in which attention is called to the points of excellence that are required in a particularly serviceable iron. The form of the heating element which is recognized in the iron is also shown in Fig. 228.

Fig. 228.—Electric flat-iron heating element.

In the figure the heater is made of coils of resistance wire, wound on a suitable frame of mica. The heating element is insulated from the body of the iron with sheets of mica, this being a material that makes an excellent insulator and is not materially affected by the heat to which it is subjected. The resistance wire of which the element is composed is especially prepared to resist the corroding action common to metal when heated in air. The form of the element is such as to permit the least movement of the turns of wire—in their constant heating and cooling—that will allow the different spires to make contact and thus change the resistance. Should the spires of wire come together, the current would be shunted across the contact and the resistance of the element decreased. The effect of such a reduction of resistance would be an increased flow of current and a corresponding increase of heat. In this, as in the electric lamp and all other electric circuits, the current, voltage and resistance follow the conditions of Ohm’s law.

Different sizes of irons will, of course, require different amounts of current. A 6-pound iron, such as is commonly used for household work, will take about 5 amperes of current at 110 volts pressure. The amount of electricity the iron is intended to consume is generally stamped on the nameplate of the manufacturer. This is specified by the number of volts and amperes of current the iron is rated to use. As an example, the iron may be marked, Volts 105-115, Amperes 2-3. This indicates that the iron is intended to be used on circuits that carry electric pressure varying from 105 to 115 volts and that the heater will use from 2 to 3 amperes of current, depending on the voltage.

To estimate the cost of operating such an iron, it is necessary to determine the number of watts of electric energy consumed. The number of watts of energy developed under any condition will be the product of the volts times the amperes. Suppose that in the above example the iron was used on a circuit of 110 volts. Under this condition the current required to keep the iron hot would be 2.5 amperes. The product of these two qualities, 110 × 2.5 is 275 watts. If the cost of electricity is 10 cents per kilowatt-hour (1000 watts) the cost of operating the iron would be

²⁷⁵⁄₁₀₀₀ × 10 cents = 2¾ cents an hour.

Since the electric iron requires a much larger amount of current than is usually required for ordinary lighting, the circuit on which it is used should receive more than passing attention. The wires should be of size amply large to carry without heating the current necessary for its operation. This topic will be discussed later but it is well here to call attention to the necessity for a circuit suited to the required current. If an iron requiring 5 amperes of current is attached to a circuit that is intended to carry only 3 amperes the conducting wires will be overheated and may be the cause of serious results.