US1158972A - Electric furnace. - Google Patents

Description

i. A. BOECK.

` ELECTRIC FURNAC. APPLICANON FILED NOLQI T911.

1,1 58.972. Patented Nov. 2, 191.5.

UNITED sTATEs PATENT oEEroE.

PERCY A. BOECK, OF WORCESTER, MASSACHUSETTS, ASSIGNOR TO NORTON COMPANY, E WORCESTER, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Nov. 2, 1915.

Application filed November 2, 1911. Serial No. 658.092.

I'o all whom 'it may concern.'

Be it known that I, PERCY A. BoECK, a

.citizen of 'the United States, residing at Worcester, in the county of lVorcester and State ofMassachusetts, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification.

This invention relates to electric resistance furnaces, or analogous constructions such as electric heaters', rheostats or the like, the objects of the invention being the provision of an improved construction of this stood that the principles are equally appli-l cable to the construction of other types of electric furnaces or electricf furnace elements, as for example muffle or Crucible furnaces, heating or resistance elements, and the like. Y

In the drawings, the gureis a central longitudinal section, the central portion being broken away.

l represents a tube or core of highlyrefractory material of high thermal conductivity, this tube constituting the support for the resistance element. As illustrated the tube l is provided with an external helical groove 2, in which the resister 3 is coiled. The resister may comprise a wire of nickelchromium alloy, platinum, or other suitable material, and is preferably formed, before being wound upon the core or support, into a continuous coil or helix, which is then wound in the groove 2 in the manner indicated. This construction presents the particular advantagesthat the length of the resister can be increased to any necessary' extent, while at the same time the liability of breakage is minimized. The support l should be of a material which in addition to the necessary refractory character ossesses high thermal conductivity. Suitable materials for the purpose are previously molten alumina grains bonded by fritting together or by the use of a small proportion of a ceramic or basic bond; and silicid of carbon, bonded by re-crystallization or otherwise. l

The core, with the resistance element wound thereon. is filled and covered with a substantial layer of refractory cement el, and the whole is covered by a casing 6, which may be of iron. Between the refractory cement 4 and the casing 6 is a filling 5, preferably consisting of pounded magnesia and constituting an electrical and thermal insulator. As illustrated by way of example, the refractory covering L is formed with end flanges 4a which support the casing 6 and retain the filling 5. The terminals 3a of the resister 3 extend outwardly through apertures 7 in the casing 6 in position for connection to the external circuit.

8 represents a removable cover, which may consist of the same material as the core 1. It is to be understood that the details of construction above described are illustrative only.

The refractory cementA or composition 4 which covers the resistance element 3 is composed of grains of previously molten alumina, in conjunction with a relatively small proportion, say'5 to l5 per cent. or somewhat more, of a suitable bond, as for example a plastic clay, or lime or magnesia. A composition of this character presents very important technical advantages for chemically inactive with respect to the resister and preserves the wire from corrosion; and by reason of its high thermal conductivity, greatly exceeding that of porcelain, lire-clay or the like, it conducts the heat rapidly from the resister, thereby preventing general or localized overheating and consequent injury. At the same time it aids in the even distribution of heat throughout the core. Furthermore, by reason of the high specific heat of the cement it is adapted to serve as a heat accumulator or equalizer, preventing unduly large fluctuations of the interior temperature when articles are introduced `into or removed from the furnace, or when the covers are removed. It will be understood that a cement of this character may be used in connection with any desired type or core or support and resister.

use in this connection: in particular it is .In a furnace or heater constructed as herein described, the distribution of the resister is such as to provide a substantially even temperature-Within the chamber, While at the Same time the coils or turns of the resister are rmly held. The Walls in contact with the resister may be made very thin, and their thermal conductivity i's such as practically to avoid danger of cracking or checking during rapid changes of temperature.

I claim: p n

1. In an electric furnace, a furnace chamber having Walls'of refractory material, a

resistance element surrounding said Wall,

and a heat-distributing and heat-equalizing envelop comprising4 prevlously molten alumina, sald envelop incloslng the resistance element and Serving to prevent general or local overheating thereof. y

2. In an electric furnace, a furnace charnber having Walls of refractory material, a resistance element surrounding said Wall, a heat-distributing and heat-equalizing envelop comprising previously molten alumina, said envelop inclosing the resistance element and serving to prevent general or local overheating thereof, and a heat-insulating pack ing surrounding said envelop. A

In testimony whereof I aliX my signature in presence of two Witnesses.

PERCY A. BOECK.

f Witnesses: i V

ALDUS C. HIGGINS, EARLS: C. MORSE.

Images