US3663799A

US3663799A - Fluoroplastic encapsulated electrical resistance heaters

Info

Publication number: US3663799A
Application number: US79885A
Authority: US
Inventors: Angus H Mcarn
Original assignee: ANGUS H MCARN
Current assignee: ANGUS H MCARN
Priority date: 1970-10-12
Filing date: 1970-10-12
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16

Abstract

An electrical resistance immersion heater in which a resistance heater unit including an attached cold extension is encapsulated in a thin fluoroplastic sheathing. The cold extension and heater are capable of being formed in various shapes, the end of which is enclosed by means of a molded terminal ending.

Description

United States Patent McArn I 1151 3,663,799 1 51 May 16, 1972 541 FLUOROPLASTIC ENCAPSULATED ELECTRICAL RESISTANCE HEATERS [72] Inventor: Angus H. McArn, PO. Box 11127, Pitt- ,sburgh, Pa. 15234 [22] Filed: Oct. 12, 1970 [21] Appl. No.: 79,885

52 u.s.c1 ..219 523,174 75,219/52s, 219/541, 219/544, 219 549, 338/214, 338/274 51 1111.01. ..H05b3/06 5s FieldofSearch ..219/523,528,535,549,552, 219/437, 415, 541, 544; 33s 273-274, 214, 212;

[56] References Cited UNITED, STATES PATENT S 2,982,932 5/1961 Morey, ..219/528X 3,225,321 12/1965 Walter ..219/523 X 3,441,893 4/1969 Gordon et al. ..338/214 X 2,888,547 5/1959 Saper ..219/523 3,045,102 7/1962 Fessenden .....2l9/528 3,097,288 7/1963 Dunlap 219/528 X 3,113,284 12/1963 Van lnth0udt.. ..338/274 3,257,498 6/1966 Kahn 1 74/75 3,356,835 l2/l 967 Watson ..219/549 Primary Examiner-Velodymyr Y. Mayewsky Attorney-Buell, Blenko & Ziesenheim [57] ABSTRACT An electrical resistance immersion heater in which a resistance heater unit including an attached cold extension is encapsulated in a thin fluoroplastic sheathing. The cold extension and heater are capable of being formed in various shapes,

the end of which is enclosed by means of a molded terminalending.

2 Claims, 2 Drawing Figures Patented May 16, 1972 3,663,799

I/VVENTOR. Angus H. McArn gag m HIS ATTORNEYS FLUOROPLASTIC ENCAPSULATED ELECTRICAL RESISTANCE HEATERS My invention relates to electrical heaters and, in particular, to electrical heaters of the immersion type.

Presently, most electrical immersion heater units utilize a coil of resistance wire which can be free standing or wound about a hollow tube or core of mica or other ceramic material; see, e.g., U.S. PatsNo. 1,365,978. The winding of resistance wire is then usually encased in a liquid proof container such as metal, fused quartz, graphite, or glass. A background of the various prior art heaters of the immersion type and their various features by examination of the following non-exhaustive list of US. Patents: U.S. Pat. Nos. 3,476,916; 3,340,382; 3,399,295; 3,107,290; 2,888,547; 274,843; 2,726,316; and 2,727,979.

Substantial advantages have been made in design and fabrication of immersion type heaters, but their use has been greatly limited because of their inability to satisfactorily operate in a variety of different environments such as highly caustic or acidic solutions. Heaters designed to operate in highly corrosive solutions, such as encapsulated glass, fused quartz or graphite heaters, as well as various metal alloys generally include one or more of the following deficiencies: 1) they are extremely fragile, (2) they have limited corrosion resistant parameters, i.e. a limited pH range, etc., (3) they are extremely difficult to fabricate and accordingly, extremely expensive, or (4) they are extremely difficult to clean.

- I have been able to overcome many if not all of the deficiencies found in the prior art immersion type heaters with my present invention. 1 provide an immersion type heater capable of being formed into a number of different configurations for various applications, and which is particularly well adapted for use in highly corrosive solutions. The heater of the present invention is break resistant as well as being adaptable to relatively simple fabrication methods. Moreover, the heater unit is extremely easy to clean.

In general, I provide an immersion heater including a cold extension both of which are tightly encapsulated in an expanded thin fluoroplastic sheathing. Because of the extremely stable carbon-fluoride bond which renders the fluoroplastics chemically inert to a great variety of chemical solutions, the heater is operable in highly corrosive solutions. By the proper application of one or more fluoroplastics to an electrical heater, I am able to provide an extremely flexible and adaptable immersion heater.

Other advantages and features of my invention will become apparent from a perusal of the following detailed specification taken in connection with the following drawings:

FIG. 1 is an elevation in partial section of the immersion heater, cold extension and molded junction; and

FIG. 2 is a plan view of a shallow tank immersion heater design.

Referring to FIG. 1, immersion heater comprises an electrical resistance heater unit 12. Heater 12 can be a commercially available unit and as such usually includes a resistive coil 13 having a pair of leads l5 and 16. Heater 12 also includes a casing 17 generally comprising a deformable light metal or similar material.

Leads

15 and 16 are connected through a cold extension 21 to a molded juncture or terminal for con-. nection with an outside power source by means of

wires

26 and 27 respectively. The outside power source may also be connected with a thermo couple or other thermostatic device for temperature regulation of the solution in which the heater is placed and which does not comprise a part of this invention.

To each end of heater 12 is a fixed a cold extension 21 usually comprising a hollow metal tube having a length sufficient for formation into any desired configuration. The cold extension is mounted or affixed to the cold end 22 of the heater 12 by any suitable metallurgical or mechanical means. By utilization of standard heaters, it is, therefore, possible to design and fabricate a very large number of sizes and configurations of immersion heaters by selection of varying sizes of cold extensions. The cold extension is filled with an insulating material 23 such as an epoxy or a magnesium oxide.

The heater and cold extension are then encapsulated with a sheathing of expanded fluoroplastic 20. The thin fluoroplastic coating, e.g., fluorinated ethylene propylene is preferably placed over both extensions and the heater as single piece to provide a fluid-tight barrier. The sheathing is tightly drawn against heater unit to maximize heat transfer. The heater including the cold extensions, with the fluoroplastic sheathing is then formed intothe desired configuration, e.g., F IG. 2.

At the ends of the cold extension, FIG. 2,

wires

26 and 27 are connected with a pair of leads going to a source of current, or alternatively, lead directly to connection with power source. This connection is then included within or, alternatively, the wires pass through terminal 25 which is molded to seal the cold extension as well as the connection or wires. Terminal 25 provides, therefore, a seal against fluid and is useful in supporting the entire unit on the edge of fluid tank, etc.

The temperature of the resisting unit 12 must be maintained below the maximum continuous operating temperature of the fluoroplastic. Accordingly, the heat flux of the unit 10 is a function of the heat transfer rate of the fluoroplastic covering. For example, the heat transfer rate of fluorinated ethylene propylene (FEP) is approximately 6(10) call(sec)(cm )(c/cm). This is equivalent to 35.2 (10) watts/(in)(F./in). Accordingly, for an 0.015 inch thick sheath of FEP, the temperature drop would be approximately 4.25 F./w./in and operating at 30 wlin a temperature gradient of 127 F. would be established. Thus, based on the heat transfer of F .E.P., a 0.015 inch sheathed immersion heater 10 with heater unit 12 operating at 450 F. maximum continuous temperature would be capable of maintaining a solution at approximately 323 F.

Experiments have confirmed the heat transfer rates and establish the operability of these heaters. Heaters with an 0.012 inch thick FEP sheathing were operated for a continuous period of 562 hours with a solution temperature of l-l90 F. Other heaters of varying sizes sheathing thickness have been operated for over 6 months without any failure. These heaters are extremely resistant to corrosion failures and are easy to clean. For example, 20 w/in heaters having 0.020 inch F E? sheath have continuously operated F. H SO for over 280 hours without any failure.

While I have shown a presently preferred embodiment of my invention, it may otherwise be described as set forth in the following claims.

I claim:

1. An electrical resistance immersion heater comprising an electrical resistance heating means including a deformable thin metallic housing therefor; a pair of cold extensions one attached to each end of said housing and adapted to carry electrical wire therethrough to connect said resistance means with a power source; at least one molded terminal at which each cold extension terminates; and an outer fluoroplastic sheathing tightly covering said housing and said cold extension in direct contact therewith whereby the housing and extension are rendered fluid resistant, said sheathing being from between about 0.012 and 0.020 inches in thickness.

2. An electrical resistance immersion heater as set forth in claim 1 wherein said pair of cold extensions, one at each end of said housing come together in a contiguous relationship.