US3185565A

US3185565A - Method and apparatus for safe operation of vacuum chambers

Info

Publication number: US3185565A
Application number: US238222A
Authority: US
Inventors: Kendrick C Taylor
Original assignee: Pennsalt Chemical Corp
Current assignee: Pennwalt Corp
Priority date: 1962-11-16
Filing date: 1962-11-16
Publication date: 1965-05-25
Anticipated expiration: 1982-05-25
Also published as: ES293556A1; LU44770A1

Description

y 25, 1965 K. c. TAYLOR 3,185,565

METHOD AND APPARATUS FOR SAFE OPERATION OF VACUUM CHAMBERS Filed Nov. 16, 1962 2 Sheets-Sheet 1 INVENTOR. KIND/PICK C. TAYLOR BY MW 5W ATTORNEY 25, 1 K. c. TAYLCR 3,185,565

METHOD AND APPARATUS FOR SAFE OPERATION OF VACUUM CHAMBERS Filed Nov. 16, 1962 2 Sheets-Sheet 2 INVENTOR. KIND/PICK C. TAYLOR BY MZK 5W XTTOR/VEV 3,185,565 METHOD AND APPARATUS FOR SAFE OPERA- TION F VACUUM CHAMBERS Kendrick C. Taylor, Oreland, Pa., assignor, by mesne assignments, to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 16, 1962, Ser. No. 238,222 7 Claims. (CI. 75-93) In general, this invention relates to a new and improved safety device for vacuum furnaces and, more particularly, to apparatus for preventing explosions in large vacuum furnaces due to the accumulation of explosive gases in the top thereof.

In large induction melting vacuum furnaces and other types of steel degassing furnaces, it has been advantageous to fabricate or design the vacuum envelope within such a furnace in a manner so that substantial volumes of explosive gas mixtures accumulate at the top thereof. This design is most desirable from material handling aspects in order to afford easy and ready access to the furnace crucible, internal ladle, or ingot mold by an overhead crane. The design calls for placing the vacuum pump equipment at the base of the furnace as theelements mentioned above weigh from to 200 tons each and, therefore, must be handled with extremely large equipment.

, The problem of explosive gases rising to the top of a at reduced pressure conditions and offer a substantial hazard to personnel. A ladle within the furnace has been known to lift one foot due to these explosions.

Normal engineering techniques to overcome this problem would call for mounting the evacuation manifolds of the vacuum pump adjacent to the top of the chamber in order to remove the explosive mixture as it develops. A further technique would be to vacuum break the vessel with an inert gas such as nitrogen.

However, these methods have considerable disadvantages. It is extremely awkward to'place the exhaust manifolds high on the furnace as they get in the way of the overhead cranes and other structure in the steel mill and additionally require long vacuum conduits which are costly to fabricate.

Vacuum breaking is inadequate since explosions have occurred in the duration of the technique.

In order to avoid and overcome the foregoing and other difficulties of the prior art practices, it is the general object of this invention to provide new and improved safety apparatus for furnaces.

Another object ofthis invention is to provide a new and improved safety device for vacuum furnaces which eliminates large explosions due to gases collected at the top of the furnace.

Another object of this invention is to provide a new and improved safety device for vacuum furnaces which is inexpensive to install and operate.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a cross sectional view of a vacuum furnace utilizing apparatus built in accordance with the principles of the present invention.

FIGURE 2 is a cross sectional view of a stream degassing vacuum furnace utilizing safety apparatus built in accordance with the principles of the present invention.

In FIGURE 1, there is shown an induction heating vacuum furnace generally designated by the numeral 10.

The furnace 10 consists of a large cylindrical housing 12 which is placed in a suitable depression in the floor 14 of a steel mill. A cover 16 is provided which may be removed for access to the housing 12 and may be utilized when in place to vacuum seal the furnace 10.

The furnace 10 has a steel outer surface 18 and a refractory inner surface 20. A vacuum pump 22 is con- 'nected to the interior of the housing 12 through a conduit 24. t The vacuum pump 22 is located at the bottom of the housing 12 near the floor of the steel mill for the reasons stated previously.

Within the housing 12, there is placed a rotatable induction heating ladle 26 manufactured from a non-mag netic material 28 through which are placed induction heating coils 30 which may be suitable energized from a source not shown. The inner surface of the induction mounted upon a support 36 and is adapted to be rotated about an axle 38 by suitable means not shown. The

ladle 26 has been shown in phantom in its pivoted position. In this position, the ladle has been indicated with prime numerals.

In operation, the top 16 is first removed from the housing 12 and metal placed within the crucible 32. The top 16 is then returned to place and the vacuum pump 22 evacuates the housing 1-2. The metal within the crucible 32 is then induction heated through the coils 30.

When the metal is induction heated, its surface is vacuum degassed by the vacuum within the housing 12. After heating, the ladle 26 is pivoted to the position shown in phantom and the metal poured from the spout 34;.

A splash guard 35 is provided so that the metal poured from the ladle 26' will flow in a smooth stream into a waiting ingot mold 37 mounted on a rotatable table 40.

When the molten metal pours from the spout '34 into the mold 37, it is stream degassed by the vacuum pump 22.

The table 40 supports a number of molds 37 which are to be filled from the metal within the ladle 26.

The table 40 is adapted to be driven by a motor 42 located in a space 44 below the housing 12. The motor drives the table 46 through two

bevel gears

46 and 48 connected through a shaft 52 to the motor 42. A suitable support bearing '50 is provided to maintain the shaft 52 in its vertical position while allowing rotation thereof.

The top cover 16 has spaced electrodes 54, 56 and '53 placed therethrough so that the tips of the electrodes are disposed within the oven 10. The electrodes 5'4, 56 and 58 are connected through a suitable conductor 60 to a timing switch 62 in series with the source of electrical energy 64.

The source 64 may be a DC. battery as shown or an alternating current source. The cover 16 is grounded. As

many electrodes

54, 56 and 58 may be provided as desired.

The timer 62 is operative to periodically connect the

electrodes

54, 56 and 58 to the source 64. Source 64 preferably provides more than 600 volts although discharge may occur as low as 3 30 volts. Discharge occurs between the tips of the

electrodes

54, 56 and 58 and the grounded furnace 10.

When discharge occurs, it ignites those mixtures which have accumulated within the cover 16 to forcefully explode them. The timer is operative to cycle from 40 seconds to 3 minutes depending upon the particular conditions in the furnace 10.

Since the gases are ignited at such close intervals, only a small amount is exploded each time the electrodes are energized. Thus, only small ineffective explosions occur and the danger of large accumulations of hydrogen and carbon monoxide has been eliminated.

The products of the combustion of the hydrogen and carbon monoxide are water and carbon dioxide which will, by reason of their specific gravity, drop to the bottom of the furnace 18 to be withdrawn by the vacuum pump 22.

FIGURE 2 relates to a second embodiment of the present invention in which the same principles as discussed above are utilized with a stream degassing vacuum chamber. In this embodiment, a vacuum chamber 68 is shown having a bottom housing 70 and a cover 72. A vacuum pump 74 is utilized to withdraw gases from the chamber 68. A stand 76 is mounted on the bottom of the housing 70 to receive an empty ladle 78 therein. The ladle 78 is supported on the stand 76 by

trunnions

80 and 82.

The cover 72 has a funnel aperture 84 over which is mounted on a support 98 a second ladle 86. The ladle 85 has molten metal 90 therein which is to be transferred to the ladle 78 in the vacuum chamber 68.

A valve stem 92 is provided in the ladle 86 in communication with a valve opening 94. Reciprocation of the valve stem 92 allows molten metal to flow through the opening 94. Cylindrical supports 96 and 98 are utilized to align and separate the ladle 86 and the cover 72 respectively. A diaphragm 100 is provided between the cylindrical supports 96 and 98 to maintain the vacuum in the chamber 68. When the molten metal passes through the opening 94, it breaks the diaphragm 1G0 and molten metal will pass through the funnel 84 into the ladle 78. A conduit 102 is provided in the cover 72 to direct a gas at the molten stream as it passes into the ladle 78 if desired. The molten metal as it passes into the ladle 78 is stream degassed.

Four

electrodes

104, 106, 108 and 110 are provided in the cover 72 for the purposes discussed with respect to FIGURE 1. The

electrodes

104, 106, 108 and 110 are connected through a conductor 112 to a timing circuit and a suitable source of electrical energy. The electrodes, when energized, are operative to explode small accumulations of gases rising into the interior of the cover portion 72.

It can easily be understood that the objects of the present invention have been accomplished by the provision of new and improved safety apparatus for vacuum chambers, furnaces and the like which is operative to prevent large explosions due to accumulated light gases in the cover of the chamber or furnace. In place of the large explosion, periodic small explosions which cannot be harmful are set off by suitable electrical apparatus provided in the cover of the chamber or furnace.

This equipment can be installed on existing vacuum chambers and furnaces as well as new installations. The apparatus has eliminated the need for costly and awkward vacuum conduits near the top of the furnace, and has avoided inadequate vacuum breaking procedures.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

1 claim:

1. Safety apparatus for vacuum chambers comprising ignition means for periodically igniting gases at predetermined intervals in the top of a vacuum chamber, and control means for periodically operating said ignition means at said predetermined intervals to prevent large accumulations of light explosive gases in the top of the vacuum chamber.

2. The safety apparatus of claim 1 wherein said ignition means includes electrical discharge means adapted when connected to a source of electrical potential to create a spark discharge, and said control means includes timing means for periodically connecting at said predetermined intervals said electrical discharge means to a source of electrical potential.

3. Safety apparatus for vacuum chambers comprising a vacuum chamber having a circular cross section at least ten feet in diameter, support means in said vacuum chamber for supporting a bath of molten metal, vacuum means located at the base of said vacuum chamber for evacuating gases accumulated within said chamber, and ignition means for periodically igniting at predetermined intervals accumulated gases not withdrawn from said chamber by said vacuum means in the top of said vacuum chamber above the molten bath supported on said support.

4. Safety apparatus for vacuum chambers comprising a vacuum chamber having a bottom housing and a top cover, a support within said housing for supporting a bath of molten material, vacuum means for evacuating gases accumulated within said chamber, said vacuum means being in communication with said vacuum chamber adjacent the bottom of said housing, and ignition means mounted on the cover of said housing for periodically igniting at predetermined intervals accumulated gases in the top of said vacuum chamber not withdrawn from said chamber by said vacuum means.

5. The safety apparatus of claim 4 wherein said ignition means include electrodes passing through the cover and mounted thereon, and said ignition means further including a timing means for periodically connecting said electrodes to a source of electrical potential at said predetermined intervals.

6. The safety apparatus of claim 5 wherein said ignition means includes a source of electrical potential, said source of electrical potential having a voltage greater than 330 volts.

7. A method comprising the steps of generating a bath of molten metal, evolving light combustible gases from the molten metal, causing said gas to rise above said bath, and periodically igniting above said bath at predetermined intervals said light combustible gases evolving from said molten bath.

References Cited by the Examiner UNITED STATES PATENTS 2,492,947 1/50 Bellstedt 23-277 2,986,641 5/61 Michels 2321OX MORRIS O. WOLK, Primary Examiner. JAMES H. TAYMAN, JR., Examiner.