US3091826A

US3091826A - Hot top seal

Info

Publication number: US3091826A
Application number: US825593A
Authority: US
Inventors: Henry C Bigge
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1959-07-07
Filing date: 1959-07-07
Publication date: 1963-06-04
Anticipated expiration: 1980-06-04

Description

June 4, 1963 c, BIGGE 3,091,826

HOT TOP SEAL Filed July 7, 1959 l I l I! \\\\\\\\\\\\\\\\\\\\\\\\M IN VENTOR ATTORNEY United States Patent 3,091,826 HOT T01 SEAL Henry C. Bigge, Bethlehem, Pa, assignor to Bethlehem Steel Company, a corporation of Pennsylvania Filed July 7, 1959, Ser. No. 325,593 9 Claims. (Cl. 22-147) This invention relates to a hot top for ingot molds. It relates particularly to the seal between the hot top and the ingot mold.

Hot tops of the floating type are well known in the art. In such a design the outside shell of the hot top is of such a diameter that the hot top will extend downwardly into the ingot mold chamber.

Due to irregularities in the hot top shell and the interior wall of the ingot mold a small undesirable but unavoidable space remains between the ingot mold and the hot top. If this space is not sealed, molten metal will work up through this space during the pouring operation and spill over the outside of the ingot mold.

Prior to this invention, attempts were made to prevent this leakage by the use of wiper strips or a single packing material between the hot top and the mold. 'In spite of these precautions leaks could still occur. However, any leak could be stopped before the molten metal spilled over the ingot mold by spraying the leak with Water. This rapid chilling would create a plug of solidified metal to stop the leak. Furthermore, a single packing material under the action of heat frequently bonded so tightly to the hot top and the ingot mold that it was extremely difficult to adjust the hot top during the cooling period of the ingot or to strip the hot top when the ingot had cooled.

With the advent of casting molten metal in a vacuum chamber the problem of leakage between the hot top and the ingot mold becomes acute. The hot top and the ingot mold are totally enclosed in a closed vacuum chamber. Lack of proper visibility into the chamber prevents detection of any leaks that might occur. Even if a leak was detected it would be impossible to take any corrective steps that might be available if one were casting in air, such as chilling the leak with water, because of the surrounding vacuum chamber structure and the vacuum conditions inside the chamber. A leak at the hot top seal would thus go uncontrolled until the pouring operation could be stopped and the cover of the vacuum chamber removed. By then the molten metal would not only overflow and coat the outside of the ingot mold but would coat and possibly burn through the relatively thin wall of the vacuum chamber as well.

Therefore an object of this invention is to provide a sealing arrangement that will prevent the leakage of molten metal through the space between the hot top and ingot mold.

Another object of my invention is to provide a sealing arrangement that will permit the hot top to be stripped after the ingot has cooled.

A further object of my invention is to provide a sealing arrangement having a plurality of layers which not only acts as a safety feature in the event of a failure of one layer but also permits the most eflicient use of the various refractory materials on the market.

A still further object of my invention is to provide a sealing arrangement that can be easily installed regardless of the shape or size of the ingot mold or hot top.

The foregoing objects and the means whereby they are attained will be more fully understood from the following description and claims together with the drawings in which FIGURE 1 is a sectional view of an ingot mold and a floating type hot top enclosed in a vacuum chamber.

See

FIGURE 2 is an enlarged sectional view showing the arrangement of the sealing means.

FIGURE 1 shows an ingot mold and a hot top where 1 is the ingot mold resting on a stool 2. The hot top 3 comprises a metal shell 4 and a refractory brick linking 5. Since the hot top 3 fits inside the ingot mold 1, the hot top is supported by pins or ears 6 which project outwardly from the metal shell 4, and rest on the top flange of the ingot mold or on adjusting blocks, such as shown at 7. Such an arrangement permits the hot top to be adjusted during the cooling period of the ingot. Hold-down rods 8 hold the hot top and the ingot mold together to prevent any upward movement of the hot top during the pouring operation.

For casting the metal in a vacuum the ingot mold l and the hot top 3 are enclosed in a vacuum chamber 14. It is obvious that such a chamber is not needed if the metal does not require vacuum treatment and the ingots are to be cast in air.

The sealing means can be more fully understood by referring to FIGURE 2. A flat metal ring 9 is fastened to hot top shell 4 by bolts or other suitable fastening means It). The ring not only helps to support the refractory brick lining of the hot top but will form a smooth surface with the ingot permitting easier stripping of the hot top after the ingot has cooled. As shown in FIGURE 2, the diameter of the ring is not large enough to seal off the space between the hot top and the ingot mold where the troublesome leakage occur To do so would require extensive machining and fitting of a special ring for each in dividual ingot mold.

The sealing means consists of 3 distinct packing materials paoked in layers. The bottommost layer 11 consists of a fibrous, rope-like, highly refractory material. The fibrous rope-like texture facilitates packing it into the small irregular space and also reduces the thermal conductivity of the material thereby transmitting less heat to the upper layers.

I prefer to use a fibrous rope-like refractory analyzing approximately 50% SiO and 50% A1 0 since such material resists much higher temperatures and the vacuum much better than, for example, the asbestos rope suggested by the prior art.

The middle layer 12 is a non-porous heat setting plastic refractory. The non-porosity is needed to stop any metal leaking through the bottom layer and the bond strength developed by this material must not be so great as to prevent the stripping of the hot top.

Several refractories could be used for this layer. I prefer to use a fireclay base material analyzing approximately MgO. However any fireclay base refractory analyzing from 5080% MgO would work almost as well. Mullite and Sillimanite resist high temperatures well y enough and are non-porous so they can also be used for the middle layer.

The topmost layer 13 serves a dual function. First, it acts as a protective cap to prevent erosion by any hot metal spilling over the top of the hot top. In vacuum casting this is quite important since the pouring stream is in the shape of a wide conical stream of many droplets due to the action of the vacuum. Some of these droplets may fall outside the hot top and land on the seal area. For this reason, the top layer should be very dense and highly refractory to prevent any erosion by the hot metal.

Secondly, the top layer serves as a hold-down means for the lower layers. When the hot top is completely filled the static head of the metal will tend to push upwards against the packing at the hot top seal. Therefore the top layer should also bond tightly to the ingot mold and the hot top to resist this static head. This layer is relatively thin so that this bonding action does not prevent the stripping of the hot top when the ingot has cooled.

Since this layer will'be farthest from the hot metal the tight bond should form at a relatively low temperature. I have found that by using a plastic refractory analyzing approximately 95% MgO, 2% SiO 1% CaO, 1% Cr O 0.5% Fe O 0.5% A1 the bond will set up at a temperature of around 1800 degrees Fahrenheit. By using such a material I avoid the uncertainty that insufiicient heat from the molten metal will reach this material to set up the bond. Because of the low temperature at which the bonddevelops, I am able to use gas jets to set up this bond before starting a pour.

Each layer should be securely rammed or vibrated into place around the circumference of the hot top before placing the next layer on top.

As an example of my invention I have used 5" of the bottom layerll, topped by 8" of layer 12 which is then capped with 5" of layer 13 in a 62" diameter ingot mold. The top surface of layer 13 is flush with the top of the ingot mold. I

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In combination, an ingot mold, a hot top adapted to extend downwardly into the mold, and a seal between said ingot mold and said hot top, said seal comprising a bottom layer of fibrous refractory, a middle layer of plastic refractory and a top layer of another plastic refractory.

2. In combination, an ingot mold, a hot top adapted to extend downwardly into the mold, and a seal between said ingot mold and said hot top, said seal comprising a bottom layer of fibrous rope-like refractory material, a middle layer of a dense non-porous plastic refractory, and a top layer of a very dense plastic refractory with a high bond strength.

3. In combination, an ingot mold, a hot top adapted to extend downwardly into the mold, and a seal between said ingot mold and said hot top, said seal comprising a bottom layer of fibrous rope-like refractory material, a middle 'layer of a dense non-porous plastic refiactory, and a top layer of a very dense plastic refractory with a high bond strength, said bond strength being developed at a relatively low temperature.

4. In combination, an ingot mold, a hot top adapted to extend downwardly into the mold, said mold and said hot top being enclosed in a surrounding vacuum chamber, and

a seal between said ingot mold and said hot top, said 4 seal comprising a bot-tom layer of fibrous refractory, a middle layer of plastic refractory and a top layer of another plastic refractory.

5. In combination, an ingot mold, a hot top adapted to extend downwardly into the mold, said mold and said hot top being enclosed in a surrounding vacuum chamber, and a seal between said ingot mold and said hot top, said seal comprising a bottom layer of a fibrous rope-like refrac tory material, a middle layer of a dense non-porous plastic refractory, and a top layer of a very dense plastic refractory with a high bond strength.

6. 'In combination, an ingot mold, a hot top adapted to extend downwardly into the mold, said mold and said hot top being enclosed in a surrounding vacuum chamber, and a seal between said ingot mold and said hot top, said seal comprising a bottom layer of a fibrous rope-like refractory material, a middle layer of a dense non-porous plastic re fractory, and a top layer of a very dense plastic refractory with a high bond strength, said bond strength being developed at a relatively low temperature.

7. A method of packing the space between the exterior wall of a floating hot top and the interior wall of an ingot mold, said method comprising packing a bottom layer of fibrous refractory, a middle layer of plastic refractory and a top layer of another plastic refractory into said space.

8. A method of packing the space between the exterior wall of a floating hot top and the interior wall of an ingot mold, said .method comprising first packing a layer of fibrous rope-like refractory material into said space, packing a second layer of dense non-porous plastic refractory on top of said first layer, and capping both layers with a third layer of a very dense plastic refractory having a high bond strength.

9. A method of packing the space between the exterior wall of a floating hot top and the interior wall of an ingot mold, said method comprising first packing a layer of fibrous rope-like refractory material into said space, packing a second layer of dense non-porous plastic refractory on top of said first layer, and capping both layers with a third layer of a very dense plastic refractory having a high bond strength, said bond strength being developed at 'a relatively low temperature.

7 References Cited in the file of this patent Kaufiman Dec. 9, 1958

Claims

1. IN COMBINATION, AN INGOT MOLD, A HOT TOP ADAPTED TO EXTEND DOWNWARDLY INTO THE MOLD, AND A SEAL BETWEEN SAID INGOT MOLD AND SAID HOT TOP, SAID SEAL COMPRISING A BOT-