US1530928A - Process for making packs for electrical heating units - Google Patents

Description

Patented Mar. 24, 1925.

UNITED STATES PATENT OFFICE.

WILLIAM A. BRAUN, OF DOVER, OHIO, ASSIGNOR T DOVER LIANUFACTURING COM- PANY, A CORPORATION OF OHIO.

PROCESS FOR MAKING PACKS FOB. ELECTRICAL HEATIN G UNITS.

Io Drawing.

To all whom, it may concern:

Be it known that I, 'ILLIAM A. BRAUX, a citizen of the United States of America, and a resident of Dover, in the county of Tuscarawas and State of Ohio, have invented certain new and useful Improvements in Processes for Making Packs for Electrical Heating fnits, of which the following is a specification.

This invention relates to improvements in processes for making packs for electrical heating units and the object thereof is the provision of a dense encasement. for electrical resistance members, having high dielectric and low hygroscopic properties and great thermal conductirity.

In general practice packs are formed in which electrical resistance members are embedded, which are composed of a mixture 0 of various materials and which are 'subjected to great pressure and intense heat in order to effect solidification of the mas The porosity of packs thus formed'is such that their tendency to absorb or become 5 coated with moisture impairs their di-electric property especially during periods of disuse which results in grounding of the electrical current when the resistance members are charged upon resumption of their use.

The present invention contemplates the formation of a tenacious pack in which the (Ii-electric and thermal eomluctivity then-of will be indefinitely preserved. as The objects of the invention are accomplished by the use of materials compounded and applied as hereinafter set forth.

The invention consists in a proce of forming an encasement for electrical resist- 4o ance members utilized in connection with electrical heating units, and by means of which the (Ii-electric property and thermal conductivity of the pack will be enhanced and preserved indefinitely.

In carrying out the invention a pack of usual form is made of a plaster constituted of a mixture of refractory material. clay and boracic acid moistened with water. The components of the plaster are approximate- Application filed January 5, 1923. Serial No. 610,945.

ly in relative proportions as set forth in the following tabulation:

Percent. Refractory material 83 Clay 12 Boracic acid -c 5 The refractory material employed is such as Alundum fines commonly known in the art, or may be such other hard, granular or mlrerulent material of similar character 00 which is possessed of high thermal conductivity and high di-electric properties.

The clay herein used as an agent for holding the pulverulent refractory material suspended in the mixture when the mixture is moistened and in a plastic state, may be of any suitable character, such. for example, as Klingenberg clay, which has been found satisfactory- The boracic acid, when introduced into the mixture, is in powdered form and in the state known as H 130 In preparing the plaster. the ingredients are placed in a pebble mill with water approximately equal in quantity to half of the amountof powder. by weight,:u1d therein is ground and worked into a plastic mass. The composition thus formed is then placed in a suitable mining machine and agitated until used.

The plaster is molded or formed into a pack in a mann r to em ed the resistance wire of the heating clenn-nt so that the resistance wire is completely encased hy the pack. After thus being formed the pack is dried until it becomes hard and is then raised to the normal working temperature of the heating element in which it is used. This heating operation may he carried out by charging the resistance wire initially with electric current of only sullicient strength to heat the resistance wire to its working temperature. When the pack thus heated the l'oracic acid constituent of the mixture of which the pack composed, becomes melted, forming horic oxide (B 0 which saturates the pack during the initial heating thereof so that the granular partitracted.

The constituents of the plaster and their relative proportions, set forth herein as an example of the invention, are subject to such substitutions and variations of proportions as skill in the art affords. and therefore, my invention is extensive thereto. Also other methods of initially heating the pack may be substituted for the particular manner described herein.

\Vhat I claim is 1- 1. The hereindescribcd method of making packs for electrical resistance members consisting of mixing pulvcrulent refractory material, clay and boracic acid substantially in the proportions named herein, forming a plaster by adding water to the mixture, encasing a resistance member in a pack formed of the plaster, drying the pack, and finally reducing the boracic acid content of the pack to boric oxide without melting the refractory material, by initially heating the member only to its working temperature whereby the said member and the particles 1 of material surrounding the member become intimately coated with said oxide.

2. In making a pack of pulverulent rcfractory earthen material for encasing an electrical resistance member, the inclusion of boracic acid with the material of which the pack is formed, charging the resistance member initially after the pack has been formed with electrical current of sutticient strength only to heat the resistance member sufliciently to convert the boracic acid content of the pack into boric oxide and cause an intimate coating thereof to form on the member and the earthen particles of the pack without. melting said member and particles.

3. In making a pack of pulverulent refractory earthen material for encasing an