US3461275A - Infrared quartz heater - Google Patents

Description

1969' R. R. POOLE 3,461,275

' INFRARED QUARTZ HEATER v Filed Jan. 26, 19 68 a Sheets-Shani Aug. 12, 1969 R. R. POOLE 3,461,275

v INFRARED QUARTZ HEATER Filed Jan. 26. 1968' v a Sheets-Sheet z x/ 1 MY Aug. 12, 1969 R. R. POOLE INFRARED QUARTZ HEATER Filed Jan. 26, 1968 United States Patent York Filed Jan. 26, 1968, Ser. No. 700,763 Int. Cl. 11-10% 3/10 US. Cl. 219-553 10 Claims ABSTRACT OF THE DISCLOSURE The quartz heater of the present invention comprises a coiled electrical resistance wire inside a quartz tube and capped at each end by an end cap. The coils may have a variable pitch, to generate less radiant heat energy at the center of the heater than adjacent the end caps. The cemented juncture of the end caps and quartz tube has a metallic filler mesh interposed between the tube and the end cap; the filler mesh is believed to lower the failure rate of the quartz heater. The terminus of resistance wire itself extends through the base of each end cap and is formed into the terminal leads for the quartz heater.

The present invention relates to a high intensity heat radiating unit and more particularly to a quartz heater constructed to withstand the severe environmental stresses imposed by rotary process rolls.

The usual quartz infrared heater consists essentially of a resistance wire heating element, appropriate electrical connections to the heating element and a surrounding quartz envelope or tube. Typically the quartz tube is mounted in ceramic end caps through which the electrical connections pass, the caps serving to mount and attach the heater in the desired position on a structural support.

The art has long since recognized the extent to which quartz heaters of this nature are subject to breakage; the quartz tube is fragile. This problem is particularly severe when thermal cycling (i.e., the heater being turned on and 0d at frequent intervals) is associated with considerable vibration. In point of fact conventional quartz heaters used as the heating element for thin wall rotary process rolls have shown a distressingly short life. The bulk of the failures occur from fracture at the juncture of the quartz envelope with the ceramic end caps and from electric failure due to weakness at the termination structure of the heater wire.

Accordingly, the object of the present invention is to provide an improved high intensity quartz heater of long operating life.

A further object of the present invention is to provide for an improved juncture of the quartz envelope with the end caps in a quartz heater assembly.

Still another object is to provide a quartz heater terminal lead of improved construction.

An additional object is to provide a quartz heater with a simplified yet effective mounting structure,

Further objects and the advantages of the present invention will be apparent from the description thereof which follows.

Reference is now made to the attached drawings wherein:

FIG. 1 is an exploded view of the components of the quartz heater;

FIG. 2 is a side view of the quartz heater during the assembly thereof;

FIG. 3 is a partial section showing the quartz heater in a late stage of assembly.

FIG. 4 is a side view of the quartz heater.

FIG. 5 is a sectional View of the quartz heater shown in FIG. 4.

FIG. 6 is a side view of a dual heater assembly.

3,461,275 Patented Aug. 12, 1969 FIG. 7 is an end view of thin wall rotary process roll with portions broken away.

FIG. 8 is a side section of the precess roll taken along the lines 8-8 in FIG. 7.

' The quartz heater 10 of the present invention is formed from a pair of end caps 12, a quartz tube 14 and a heater element 16 in the form of a coiled resistance wire. Also present is a metal filler mesh 18 of temperature resistant metal, e.g., stainless steel or nickel, which also is highly resistant to oxidation at the elevated operating temperatures of quartz heater 10. A ceramic cement 20 serves as an adhesive to bond the juncture of metallic filler mesh 18, end caps 12 and quartz tube 14 as shown in FIG. 5.

End cap 12 is formed by a circular base 22 and a cylindrical shoulder 24 upstanding therefrom. A circumferential circular groove 26 is provided on shoulder 24 to accommodate a crescent type metallic (e.g., stainless steel) snap ring 28 (shown on FIG. 8), the snap ring 28 being employed in the installation of quartz heater 10 in an overall heater assembly. The base 22 of end cap 12 is provided with a pair of apertures 30 through which the electrical leads to heater element 16 may be passed.

Advantageously the present quartz heater construction uses the heating element wire itself for the high temperature lead wire. As shown in FIG. 2 the resistance wire forming heater element 16 has a coiled central portion 31 and straight or at least noncoiled end portions 32. The end portion 32 is passed through one of the double apertures 30 in the base 22 of end cap 12, then doubled back on itself, the doubled back segment being passed back through end cap 12 by way of the other aperture 30. The terminus of end portion 32 is now looped or hooked around itself (shown in FIG. 2) with loop 34 closely adjacent the coiled central portion 31 of heater element 16. Element 16 is then inserted into end cap 12 so that loop 34 and the coil itself set down into cap 12 adjacent the base 22 thereof (as illustrated in FIG. 5). The doubled back terminal p rtion 32 is now twisted, e.g., five turns per inch, as shown in FIGS. 4, 5 to provide an anchored, integral terminal lead wire 33 for the heating element 16. The lead wire 33 is suitably insulated as by the ceramic fish spine insulators 36 shown on FIG. 6. A terminal 38 may be welded or otherwise secured to the free end of lead wire 33. Desirably two or more quartz heater units can be associated in series by welding or otherwise attaching their lead wires together as at 40, in the double unit structure shown in FIG. 6.

At some stage during formation of lead wires from end portions 32, the filler mesh 18 and quartz tube should, of course, be placed around heater element 16 and inside end caps 12. FIGS. 2 and 3 illustrating the relationship of these component parts during assembly of quartz heater 10. A preferred assembly technique is to form completely a twisted lead wire 33 at one end, cement the tube, mesh and cap together at that end, then repeat the assembly operation at the other end, i.e.,

(1) !Place the components in proper juxtaposition.

(2) Form the doubled back, looped resistance wire end (as shown in FIG. 3).

(3) Set quartz tube 14 and filler mesh into end cap 12, then twist the exposed end portion 32 and cement.

(4) Add insulators 36, and weld on terminal 38. Desirably the completed quartz heater 10 has the axis line of apertures 30 of one end cap 12 disposed at a right angle to the axis line of the apertures of the other end cap.

In any event a conventional adhesive ceramic heat resistant cement 20 is placed at the juncture of quartz tube 14, filler mesh 18, and cap 12, then set, e.g., by heating at F. for about six hours to adhesively bond together the end cap, the filler mesh and the quartz tube.

The low failure rate of present quartz heater structure seems attributable to several features. Allusion has already been made to use of the heating element wire itself as the terminal leads. This feature is desirable, aside from any saving in cost by elimination of the several pieces of hardware otherwise used to affix separate lead wires to the heater element. The integral character of the terminal lead permits a more compact heater construction and avoids possibility of burnout at the juncture of the lead wire to the heating element wire. Another feature of construction significant for low failure rate is the metal filler mesh 18. Presence of metal filler mesh 18 seems to reduce the incidence of fracture of the quartz tube where it enters an end cap. It is theorized that submitting the quartz heater to extensive vibration causes breakdown of the ceramic cement joining the quartz tube and end cap, with loss of cement particles. Thereafter vibration causes the quartz tube to move separately from the end cap, which in turn causes the tube surface to craze; eventually the tube fractures. The mesh of filler 18 acts to trap the adhesive cement in the mesh openings, and seems also to absorb some of the vibrational energy thereby preventing breakup of the cement and subsequent tube fracture.

Filler mesh 18 may be of several forms such as woven wire, knitted wire or expandes metal, the lattermost being preferred. Thus a sheet of expanded (or woven) wire mesh cut to proper size is rolled into a tubular piece of appropriate diameter without overlapped ends. The height of the tubular piece is sufficient for filler mesh piece 18 to extend beyond end cap 12 (e.g., 0.25 inch) as shown in the drawing.

Repeated allusion has been made to use of the present quartz heater structure for the heating elements of thin walled process rolls. Such a structure is illustrated in FIGS. 7 and 8 wherein a rotary thin walled process roll 100 is radiantly heated by multiple quartz heaters mounted in a heater assembly support 102. Support 102 comprises a hollow cylinder 104 carrying a heat insulator 106. A plurality of spiders 108 secure cylinder 104 to a cylindrical sleeve 110 surrounding a supporting shaft 112. Shaft 112 is of course supported at one or both ends independently of rotating process roll 100 and of the roll drive mechanism. There the heating assembly 102 as a whole is disposed in a stationary position inside rotating process roll 100. Present on the cylinder 104 at or adjacent its terminal ends are rings 114. The spacing between rings 114 corresponds closely to the overall length of quartz heaters 10 so that the heaters may be mounted therein. The terminals 38 of one polarity from each quartz heater 10 extend to a bolted connection on one electrode connector 130 at apertures 134. The terminals of opposite polarity connect to electrode connector 128, as is shown in FIGS. 7, 8. The electrodes 122 themselves are spaced apart inside shaft 112 by bushings 124 and an end bushing 126. The central electrode 122 is joined at 132 to connector 130 while the outside electrodes are joined to connector 128.

The heater assembly actually illustrated in FIGS. 7, 8 is for a twelve pack, using six heater pairs 120, each pair being formed as shown in FIG. 6. Six pairs of apertures 116 are provided in the rings 114 on cylinder 104. Insertion of the quartz heaters 10 on the heater assembly support is relatively facile, since the end caps 12 fit closely inside the apertures 116. The heaters are slipped into apertures 116, then retaining crescent rings 28 are placed in the groove 26 (one at each end cap) to lock the quartz heater 10 in place. These ring retainers 28 are to restrain longitudinal movement of heater 10 in either direction. The fit of quartz heater 10 in apertures 116 is suflicient to prevent disengagement from rings 114, whether heater 10 is hot or cold, allowing for the differential thermal expansion and contraction characteristics of support 102 and heater assembly 10. Pairing heaters 10 in a series connection as shown in FIG. 6 permits all of the electrical connections to the heater assembly to be at whichever end may be most convenient to the power supply.

Process rolls such as the roll shown in FIGS. 7 and 8 have relatively rigid heating requirements. The present quartz heater construction and heater assembly are particularly well adapted to heat thin wall rotary process rolls. For example they may be employed as the roll heating elements in the system disclosed by copending application Ser. No. 475,206 of John H. Troll, filed July 26, l965, now Patent No. 3,369,106, issued Feb. 13, 1968. Alluded to in that application is the desirability of controlling the axial thermal profile of the process roll. Inescapably, a process roll such as roll 100 loses more heat by radiation and convection adjacent the roll ends (end effect) than from the mid regions of the roll. A particular advantage of the present quartz heater construction is the possibility therein for providing a non-uniform heat output from the heater by appropriate construction of heater element 16.

As illustrated in the drawing, heater element 16 is a coiled resistance wire. Normally the coiled central portion 31 has coils of uniform pitch throughout, with the adjacent convolutions being closely spaced so as to provide maximum (uniform) output per running inch of heater element. For installation of quartz heater 10 in process rolls, however, such a resistance wire is relatively disadvantageous because end elfects create an axial temperature differential along the roll; the roll is hotter in the center than adjacent either end. However, if the resistance wire of heater element 16 is constructed with a variable pitch in coiled central portion 31, the nonuniformity of heat output from the wire coil can be predetermined so as to flatten out the temperature differential along the roll. Thus, in one preferred embodiment heater element 16 is constructed with the coil convolutions in the middle 17 of central portion 31 spaced farther apart than the coils adjacent straight ends 32 of the heater element 16. Thereby, the temperature profile of process roll 100 is flattened out. Still other pitch variations can provide special heating effects. Thus quartz heater 10 may be built to emit 50% of its radiation from of the heater length and 50% from the remaining While particular embodiments of the invention have been illustrated and described, it will be obvious that changes and modifications may be made without departing from the invention and it is intended to cover in the appended claims all such modifications and equivalents as fall within the true spirit and scope of this invention.

What is claimed is:

1. A quartz heater comprising a quartz tube, a ceramic end cap at each end of said tube, and a resistance heating element inside said tube with the terminal leads thereof extending out through said caps and a cylindrical metal filler mesh interposed between the quartz tube and the end cap at the juncture of the tube and cap, the juncture of tube, filter mesh and cap being adhesively bonded by a heat resistant ceramic cement.

2. The heater of claim 1, wherein the metal filler mesh is a piece of rolled, expanded metal.

3. The heater of claim 1, wherein the lead wires thereto are formed from the heater element.

4. The apparatus of claim 1, wherein said coiled resistance wire has a predetermined nonuniform pitch whereby the energy emitted by said heater varies axially thereof.

5. A quartz heater comprising a quartz tube, a ceramic end cap at each end of said tube and secured thereto, and a resistance heating element inside said tube with the terminal leads thereof extending out through said caps, each cap having a pair of apertures in the base thereof, the resistance heating element being a coiled resistance wire with noncoiled terminal end portions thereon, the noncoiled end portion passing out from the cap through one base aperture thereof and doubling back in through the other base aperture thereof with the doubled back wire end portion outside the cap being twisted, said exposed twisted wire end portions being said terminal leads.

6. The apparatus of claim 5, wherein the doubled back end portion of said resistance wire terminates in a loop hooked around said resistance wire inside the cap.

7. The apparatus of claim 5, wherein the said coiled resistance wire has a predetermined nonuniform pitch whereby the energy emitted by said heater varies axially 5 thereof.

8. The apparatus of claim 5, wherein a cylindrical metal filler mesh is interposed between the quartz tube and the end cap at the juncture of the tube and cap, the juncture of tube, filter mesh and cap being adhesively bonded by a heat resistant ceramic cement. 9. The apparatus of claim 1, wherein each end cap has a circular groove on the periphery thereof, said grooves being adapted to placement therein of a retainer ring for ultimate installation.

10. The apparatus of claim 7, wherein the mount for said quartz heater comprises a cylindrical support means having apertured ring members around the periphery thereof adjacent each end, the apertures on each ring being aligned, said quartz heater end caps fitting into a pair of aligned apertures and retainable therein by place ment of a retaining ring in the circular groove of each end cap.

References Cited UNITED STATES PATENTS 1,110,532 9/1914 Byce 338-218 2,535,268 12/1'950 Coats 219553 X 2,596,837 5/1952 Calvert 219-553 X 2,690,491 9/1954 Calvert 338-236 2,957,154 10/1960 Strokes 219-553 X 3,345,448 10/1967 Malkin 1325 VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R.

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