US2259242A - Process for making heating elements - Google Patents

Description

Oct. 14, 194 1. E. K. CLARK 2,259,242

PROCESS FOR MAKING HEATING ELEMENTS Filed Feb. 18, 1939 2 Sheets-Sheet l WITNESSES: INVENTOR 560 K. C/ar/f.

ATTORNEY 41 Patented Oct. l4, 3941 Earl K. Clark, Mansfield inghouse Electric'& East Pittsburgh, Pa. vania Ohio, assignor to West- Manufacturing Company, a corporation of Pennsyl- Application February 18, 1939, Serial No. 257,167

2 Claims.

My invention relates to electric heaters and more particularly to methods of making a preformed ceramically insulated heater for a flatiron or the'like.

The general process of compacting a cementitious or refractory insulating material about an electrical resistor is well known to the art. However, due to the application of considerable pressure upon the insulating material during the process, it has been practically impossible to produce an unsheathed heater in which the resistor is formed from a helical coil. This difflculty has been caused by the coil shifting under the compactin'g pressure. Further, it has been practically impossible to get a uniform distribution of the insulating material inside the coil. In addition, the difliculties of getting the insulating material within a coiled resistor are considerably increased with a heating element formed in an elliptical helical manner, especially so, when the long axis 01' the helix is mounted in a vertical position.

It is, therefore, an object of my invention to provide a method of making a heating element having an ellipticallycoiled resistor and a uniformly compacted cementitious insulating material located within and about such coil.

A further object of my invention is to provide a method of making a preformed ceramical- 1y insulated heater for flatirons, or the like, which eliminates the necessity of handling cement in the vicinity of the finished and polished iron sole plate.

A further object of my invention is to provide a method of producing a heating element having a ceramic insulating material pressed around a coiled resistor without distorting such resistor.

Another object of my invention is to provide method of producing a ceramically insulated heater in which the resistor is mechanically retained within the insulationso as to he centraliy located therein and which will not shift its peeltion'upon applying the final compacting pressure.

' Still another object of my invention is to provide an efficient, economical method of producing a ceramically insulated gore-formed fi tiron heater and of measuring the quantity 1nsulating material required.

'Qther objects of invention will either pointed out specifically in the course of the following description of a method of forming a device embodying my invention, or will be apparent from such description. A

the accompanying drawings:

plate in which a heating element embodying my invention is located.

Fig. 2 is a partial elevational and sectional view of an illustrative press for making the heating element embodying my invention;

Fig. 3 is a perspective view of the heating elewith insulating material l8, compacting the inbody portion, a

Figure 1 a perspective view of a z'iatircn sale sulating material, invertin structure and placing additional insulating material upon the outer side of the resistor, and finally compacting the whole heating element.

More specifically, the die structure l3 comprises, in this instance, a first stripper plate or holding device i l, main forming dies 29 and 22,

a second stripper plate 24 and a pressure die 2G which is adapted to be inserted between the forming dies 20 and 22 and within. the slot it.

The first stripper plate it comprises a main plurality of upwardly extending bosses 28 and an upwardly extending holding portion 30. 1e upwardly extending bosses 28 cooperate with recessed portions 3! the main forming dies 28 and 22, so as to pcsition and retain such forming dies in a given fixed location and an upwardly extending holding portion 30. The upwardly extending holding portion 3t is substantially the same shape as one-half of the heating element in to he formed and is adapted to extend upwardly between the main forming dies 28 and 22 within theslct 36 formed therebetween. The forming dies .20 and 22 are thus retained in a given position and. in conjunction with holding portion Si), determine the configuration of the heating element to be formed. In this in stance, the slot therebetween is approximately the same shape as the slot 53 the flat-iron scieplate 55.

The upwardly plate H has a grooved slot 32 located substantially in the middle of the upper surface thereof. The grooved slot 32 is substantially the same Width as the external minor axis of the elliptically coiled resistor 2 and has a depth substantially one-half the external major axis of holding portion 38 of the stripper such resistor.- The groove 32 is thus capable of retaining the resistor I! in a vertical position at substantially the middle of the slot l6 and permits only substantially the upper half of the resistor to be exposed for a purpose hereinafter described. However, it is to be understood that the resistor B? may be retained within the die structure by any other suitable holding device.

The vertically extending slot it formed between the forming dies 28 and 22 is substantially the same width and approximately the same shape as that desired of the finished heater iii. However, the vertical height of such slot is considerably greater than that of the height of the finished heater it. In this instance, the height of the slot i6 is of such value as to permit it to be used as a measuring device for the insulating material to be placed therein, substantially as hereinafter described.

The second or other stripper plate 2 3, located at the bottom of the die structure in Figs. 6 and 7, is substantially the same shape as the first stripper plate or holding device it and has a plurality of bosses 2Q which cooperate within corresponding apertures 33 within the dies 25 and 22, and a holding portion 36.

The holding portion 3% of the second stripper plate '25 portion 3B of the lower stripper plate 53. However, holding portion 3 3 of plate 2 3 is substantially as long as the distance the pressure die 28 extends into the slot it during the first compacting operation. Accordingly, it is obvious that after the pressure die 26 has compacted the first portion of cementitious insulating material placed within the slot it, the upper stripper plate 25 may be located upon the forming dies 20 and 22 with the holding portion 3 3 contactin the flat upper surface of the compacted insulating material, substantially as hereinafter described.

The pressure plate die 28 of the die structure i3 has a downwardly extending die portion 36: which is substantially the same shape as the slot i6 soas to freely extend therein as the die is forced downwardly.

The die structure it may be operatively associated with a pressure applying device or press 38 which is illustratively shown in Fig. 2. The press 38 includes a base plate 69 and a vertically moving pressure-applying member 52. The pressure device or press 38 is adapted to supply a relatively large pressure to the cementitious insulating material located within the slot it by means of the pressure die 26 which is rigidly attached to the vertically moving member 42. The

base plate in has an undercut or depressed portion 4| which is substantially the same shape as the stripper plates M and 2 1. This portion Bi thus permits the plates it and 25 to be accurately centered thereon with respect to the pressure die 26.

The cementitious refractory ceramic insulating heater I is constructed in accordance with my invention substantially as follows: the die structure I3 is operatively associated with the pressure device 38 by having the pressure die 26 attached to the vertically moving member 42 and by having the first stripper plate M located and centered upon the base plate 40 within the depressed portion M. The main forming dies and'22 are then positioned upon the first plate l4, whereupon the vertically extending slot {6 is located therein (see Fig. 2). The elliptically coiled resistor i2 is then positioned within the is somewhat shorter than the holding groove 32 upon the holding portion 30 of the holding device I4 in the slot Hi. The resistor I2 is thus positioned at substantially the midpoint of the slot it with the main axis thereof located in a vertical position. The cementitious ceramic insulating material I8 is then put in and just fills the slot [6, the slot it thus acting as a measuring device. In other words, the insulating material i8 is located within the slot it so as to just fill such slot (see Fig. i). Inasmuch as the insulating material is substantially in a powdered form it is obvious that such material will be evenly disposed within the loosely coiled resistor and aboutthe upper portion thereof.. The pressure device 38 is then actuated so that the moving member 52 thereof will force the pressure die 2% downwardly. The die portions 35 thereof will then enter into the slot i8, engaging the insulating material It and preliminarily compacting it into a-relatively solid mass. Inasmuch as the insulating material is evenly distributed within and around the upper portion of the resistor 52, it is obvious that the pressure applied to the insulating material it will then evenly compact it to a uniformly dense mass within the resistor l2 and about the upper portion thereof (see Fig. 5).

The grooved slot 32 located in the holding portion 30 of the first holding device it being substantially the same shape as the lower half of the resistor i2, retains the resistor in a fixed vertical position, during the compacting step, insuring a uniform distribution of the compacted insulating material entirely within the coils of the resistor and limits the amount of insulating material being located about the outer surface of the coil.

In this instance, the horizontal plane of the top face of holding portion 38, which determines the lowermost point of the insulating material it prior to and during the first compacting step is positioned at substantially the mid-point of the vertical or major axis of the resistor 82 (see Figs. 5 and 6). In addition, the material is located within the coils of the resistor i2. However, the insulating material placed upon and within the resistor during the first step of production need not completely fill the resistor, and the dividing line need not be positioned exactly as described so long as the compacted material is capable of retaining the coil in a fixed position during the remaining steps of the process.

The pressure die 26, by reason of the movable action of the moving member i2 is then removed from the main forming dies 20 and 22. The second stripper plate 24 is then located or positioned upon the main forming dies 29 and 22 with the holding portion 35 extending into the slot It and resting upon the upper surface of the compacted insulating material i8. The die structure 83 including the second and first stripper plates 24 and it, respectively, and the main forming dies 20 and 22 is then reversed or inverted so that th upper strip or plate 2t will be located at the bottom of the main forming dies 28 and 22. The upper or second stripper plate will then be positioned within the depressed portion 6i so as to'again center the slot is with respect to die 26.

The lower or first stripper plate it, which is now on top, is then removed, leaving the now upper portion of the slot l8 open (illustrated as 5a in Figs. 6 and 7). Additional insulating material I8 is then positioned within and just filling the exposed portion of the slot it, which therein; but when at this stage is located again acts as a measuring device for the amount of insulating material'required. The loose. uncompacted cementitious refractory insulating material Ila is then located upon the previously compacted insulating material I. and about the now upper or remaining portion of the resistor i2. However, inasmuch as the inner space of the coil II has been previously substantially filled and compacted with insulating material, thenewly added insulating material Ila cannot extend the coil II has been only partially filled the additional or second portion of insulating material will fill the remaining space within such coil. The vertically moving pressure applying member 42 is then moved downwardly, causing the die portion 36 of the pressure die member ftto extend into the slot i and compact the additional insulating material Ila (see Fig. 7).

The final compacting pressure in the step just described is substantially greater than the preliminary compacting pressure in the step previously described, inasmuch as the resistor I! was already firmly positioned within the compacted material I8 and will not move with respect to the outer edge thereof even though a relatively high pressure is applied. Accordingly, it follows, that the final pressure application may be of such value as to safely and satisfactorily.

compact the insulating material into a solid homogeneous mass about and within the helically coiled resistor.

It is to be understood that the coiled resistor may be of any desired shape other than the preferred elliptical section used herein. it is to be understood that the insulating material used in thefirst compacting step is to be located within as well as about the coils of such resistor so as to allow the resistor to be retained in a given fixed position .while the initial pressure or compacting step'is effected. v

After having had sufiicient pressure applied thereto, the main forming dies II and .22 are removed from the second stripper plate 24, which at the bottom. The heating unit it may then be moved fromthe holding given fixed position, the insulating material isevenly distributed throughout the heater, and

However,

because of the even distribution of insulating material, afin'al compacting pressure may be applied which will form a solid homogeneous insulating mass about and within the resistor without causing the resistor to shift therein.

It therefore follows that by using the two-step compacting process embodying my invention in which the resistor is centered and held in position until firmly embedded in the first portion of insulating material, such element, after having the second portion of insulating material placed thereon, may be subjected to a second pressure substantially greater than the first without causing the resistor to shift its-position, In other words the process embodying my invention provides a method for centering and holding the resistor within the insulating material and elimihating electrical insulating faults in the final product.

Various modifications may be made in the method of forming the device embodying my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations imposed by the prior art and the appended claims.

-I claim as my invention:

1. The method of making an electrical heating element in which the resistor; is in the form of a helical coil, which comprises encompassing a portion of the helical coil below a horizontal longitudinal plane therethrough to hold the coil in place, placing uncompacted insulating material within the entire coil but around only the unencompassed portion of the coil above said plane, compacting the insulating material around said unencompassed portion of the coil, inverting the coil and freeing the encompassed portion thereof, placing uncompacted insulating material around the freed and now upper portion, and compacting the additional insulating material.

2. The method of making a heating element inadditional material.

. EARL K. CLARK shall be placed thereon as are

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