GB1595196A

GB1595196A - Solidification of molten material

Info

Publication number: GB1595196A
Application number: GB4176377A
Authority: GB
Original assignee: CARBORUNDUM CO Ltd
Current assignee: CARBORUNDUM CO Ltd
Priority date: 1978-05-26
Filing date: 1978-05-26
Publication date: 1981-08-12
Also published as: JPS5462111A

Description

(54) IMPROVEMENTS IN OR RELATING TO THE SOLIDIFICATION OF MOLTEN MATERIAL (71) We, THE CARBORUNDUM COM PANY LIMITED, a British Company of P.O.

Box 55, Trafford Park, Manchester, M17 1HP, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- The present invention relates to a method and apparatus for cooling and solidifying molten refractory material, such as used for example in the production of abrasive grain exclusively, abrasive and refractory oxide materials.

Recent advances in the field of refractory materials have amply demonstrated the superior properties of both single oxide and mixed oxide materials, for certain applications, when solidified at very fast rates.

These fast rates of solidification, when applied to familiar materials, produce not only a reduction in crystal size resulting in superior strength and impact resistance, but equally important new and novel structures having fracture characteristics and properties which cannot be obtained using conventional methods of slow cooling.

Currently, the methods of achieving rapid cooling and solidification rates rely on exposing the molten refractory material to a large surface area of cold metal. For example, Ball Casting as taught in U.K. patents: 1,409,111/2 (Carborundum), 1,323,282 (Norton), 1,421,174 (Starck), achieve rapid cooling and solidification by pouring the molten material into a bed of loosely packed metal balls confined in a suitable metal outer shell or casing. The basic requirements for this method are: 1) The size and nature of the balls are such as not to melt during pouring of the molten material or during its subsequent solidification.

2) The ball sizes and inter-ball spaces are such as to permit the molten material to penetrate freely and fill the space to a substantial degree.

The best compromise between these two basic requirements varies depending on the melting point and viscosity characteristics of the refractory material being cooled and solidified. Usually ball materials and sizes are chosen to produce the fastest practical cooling rates which impart the optimum desirable properties to the solidified product. For example, steel or cast iron balls would normally be used for alumina or alumina/zirconia alloy abrasives, and the ball diameter would be in the range 2ts to 22" diameter.

Such balls have a high heat capacity and very good thermal conductivity and survive repeated pouring cycles without detriment.

They also do not contaminate the product produced to a degree which is detrimental to its properties or subsequent usage.

Although very successful in many cases in producing materials having desirable properties, ball casting has several disadvantageous features both of a practical and technical nature: 1) In certain cases unidirectional solidification is desirable. This produces crystals, colonies of crystals or mixed crystals having a high degree of orientation which confers desirable anisotropic properties on the substance. Although ball casting can produce such structures to a degree, the threedimensional cooling occurring in the interball space precludes production of such structures throughout the substance.

2) When smaller diameter ball sizes are used to increase the cooling and solidification rate to a maximum, the paths which must be taken by the molten material between the balls are sufficiently tortuous to cause the material to solidify before a sufficiently large proportion of the void space between the balls has been filled. This imposes physical limits on the practical depth and configuration of the ball cast mould design affecting the efficiency of the process.

3) Once filled with molten material the time taken for the mould and contents to cool sufficiently to allow stripping is extremely long. This entails, for practical production rates even on a semi-continuous basis, the handling and re-cycling of very large quantities of balls. This makes necessary the use of heavy, expensive handling equipment.

These three major drawbacks in ball casting are largely overcome in British Patent 1,358,620 (Norton) which teaches the use of a continuous book or plate mould. Two disadvantages with this latter system are its inflexibility in usage and its high capital cost.

The present invention aims to obviate or mitigate the drawbacks encountered with ball casting, and at the same time, to provide distinct advantages regarding flexibility and initial capital cost.

According to a first apsect of the present invention there is proved a method of solidifying a molten refractory material comprising pouring the molten material in to a vessel in which extend a plurality of spaced elongate cooling elements, and allowing the molten material to cool and solidify.

The present invention also provides apparatus for cooling and solidifying molten refractory material comprising a vessel into which the molten material is poured, a plurality of spaced elongate cooling elements extending within said vessel and serving to extract heat from the molten material, and a stripping member through which said elements extend and which is relatively movable along said elements to strip solidified product therefrom.

Preferably the elongate elements, which should be of a metal having a suitable heat capacity and melting point, are mutually parallel and are arranged in rows, which may be staggered. Furthermore, the elongate elements preferably have rounded edges and, for optimum results, the curvature of said edges is chosen depending on the fusion point of the molten refractory material. Generally the higher the radius of curvature the better the result.

The invention is particularly applicable to the cooling and so idification of oxide materials, such as a binary oxide co-fusion, particularly on alumina zirconia alloy, which may be used as abrasive products. The invention will be further described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a vertical sectional view of one embodiment of apparatus in accordance with the invention Fig. 2 is a plan view of the apparatus of Fig. 1; Fig. 3 is a plan of a further embodiment of apparatus in accordance with the invention; and Figs. 4 to 9 show various arrangements and cross-sectional forms of elongate elements which may be used in accordance with the invention.

Referring to Fig. 1, a first embodiment of apparatus in accordance with the invention comprises an open-topped mould vessel 1 into which the molten refractory material may be poured, and a plurality of vertically disposed rods 2 of circular section extending within the mould 1.

The mould 1 is rectangular in plan view (see Fig. 2) and has four vertical walls 3 which rest on a honeycomb ejection plate or stripping member 4 which itself rests on a base plate 5 of which the lower ends of the rods 2 are firmly located. The walls 3 are clamped together so as to confine the pour to the inter-rod cavities. The base plate 5 is clamped in position by means of clamps 6 and is provided with a plurality of jacking holes 7 which are overlaid by the peripheral edge faces of the ejection plate 4. The ejection plate 4 has apertures 4a which locate over the rods 2 and is used to facilitate the removal of solidified material in the manner to be described.

The rods 2 are of mild steel and are arranged in staggered rows (see Fig. 2) in a manner such that the rods are in hexagonal configuration (see also Fig; 4). The rods 2 terminate approximately 4 to 2tt below the top of the walls 3 so as to allow for a small amount of overpour during filling of the mould 1. Each of the rods 2 is rounded at its upper end thus eliminating sharp edges which might melt during the pouring operation. Additionally, as shown in Fig. 1, the rods 2 are of constant cross-section throughout their length but, if desired, the rods may be slightly tapered so as to be of slightly narrower cross-section at their upper ends than at their lower ends. It will of course be appreciated that the holes 4a of the ejection plate 4 are of such size as just to clear the maximum rod diameter.

The dimensions of the illustrated apparatus may of course be varied to suit particular applications but, in one example of suitable apparatus, the pouring cavity of the mould 1 is 12" square by 10' deep, the rods are of 1" diameter and the inter rod spacing 8 (see Fig. 2) is 3/us". Depending on the specific gravity of the material with which such an apparatus is filled, typically it will hold from 3 to 70 lb of final product.

In operation a series of the above described apparatus would be conveyed past the pouring orifice of a furnace and filled in sequence. Once an individual mould 1 has been filled, solidification of the melt takes place very quickly due to extraction of heat by the rods 2. The large contraction of the bulk is relieved by fracture occurring in the material between the rods 2, resulting in a zonal crack or fracture system throughout the solidified mass. There is a net contraction locally which generates a clearance to facilitate stripping between the solidified product and the rods 2.

Solidification usually occurs within one minute. After this period ejection of the solidified product can be made at a suitable time period to suit the production rate. Typically this would be within ten minutes from the time the pour was made. The solidified but still very hot material is recovered from the mould by removing the walls 3 and jacking the ejection plate 4 away from the clamped base plate 5 by means of jacks (not shown) locating the jacking holes 7. If desired, the moulds 1 can be left to cool completely.

Under normal conditions of hot stripping, once the product has been ejected the apparatus is water cooled leaving just sufficient heat capacity in it to evaporate quickly any residual water. The mould 1 can then be re-assembled very rapidly and retuned to the furnace for re-filling.

Occasionally material of a very low viscosity may partially enter the clearance gap between the rods 2 and holes 4a in the ejection plate 4. Stripping is made more difficult when this occurs. The problem can be eliminated by covering the ejection plate 4 with a 1/32N to 411 layer of powder of the same composition as the material to be cooled. This powder may be obtained from unwanted fines generated during crushing.

Experience has shown that in the case of certain abrasive grains, the properties obtained using the above apparatus are intermediate between ball cast and plate cast grains, but usually far nearer the plate cast grains in crystalline characteristics and physical/mechanical properties.

Fig. 3 shows a plan view of a further embodiment of apparatus in accordance with the invention which comprises an open-topped mould 20 having a plurality of horizontally disposed circular section rods 21 extending therein. The rods 21 are arranged in two clusters with the rods of each cluster being arranged in aligned rows (see also Fig. 5). The mould 20 comprises front and rear walls 22 and two side walls 23 through each of which extends one of the rod clusters. The rods 21 of each cluster are firmly located in respective plates 24 which are each associated with hydraulic rams 25 which are operable to withdraw the rods 21 from the mould 20 through the side walls 23.

In use, the mould 20 is filled with molten material which is then allowed to cool and solidify as previously. The solidifed material may be recovered by operating the rams 24 to withdraw the rods 21 from the mould 20 thus leaving the solidified material which may then be removed from the mould 20.

It is found that the aligned rows of rods 21 allow better penetration by the molten material than is obtained with staggered rows: It is however possible to use staggered assemblies of horizontal rods with satisfactory results depending on the viscosity of the melt, size of rod and cavity dimensions.

Figs. 4 to 9 illustrate a typical range of rod cross-sectional shapes and packing configurations which can be used at a wide variety of cross-sectional sizes and rod lengths. Figs.

4 and 5 relate to circular section rods and respectively illustrate portions of assemblies of such rods in staggered and aligned rows, as described previously with reference to Figs. 1 and 3. In the arrangement of Fig. 4, each rod is at the apex of a regular hexagon defined with five other rods (i.e. a hexagonal arrangement) whereas, in Fig. 6, each rod is at the corner of a square defined with three other rods (i.e. a cubic arrangement).

Fig. 6 illustrates square sectioned rods in cubic arrangement. The rods of Fig. 6 have rounded edges to prevent melting.

Fig. 7 illustrates triangular sectioned rods in hexagonal arrangement. The rods once again have rounded edges to prevent melting.

Figs. 8 and 9 both relate to rods of rectangular section with rounded ends and respectively illustrate such rods in hexagonal and cubic arrangement (i.e. staggered and aligned rows respectively).

WHAT WE CLAIM IS: 1. A method of solidifying a molten refractory material comprising pouring the molten material into a vessel in which extend a plurality of spaced elongate cooling elements, and allowing the molten material to cool and solidify.

2. A method as claimed in claim 1 wherein the molten refractory material is an oxide material.

3. A method as claimed in claim 2 wherein the oxide material is a binary oxide co-fusion.

4. A method as claimed in claim 3 wherein the binary oxide co-fusion is of alumina and zirconia.

5. A method as claimed in any one of claims 1 to 4 wherein the elongate cooling elements are mutually parallel.

6. A method as claimed in claim 5 wherein the elongate cooling elements are in aligned rows.

7. A method as claimed in claim 5 wherein the elongate cooling elements are in staggered rows.

8. A method as claimed in any one of claims 1 to 7 wherein the elongate cooling elements are of circular section.

9. A method as claimed in any one of claims 1 to 7 wherein the elongate cooling elements have rounded edges.

10. A method as claimed in claim 9 wherein the elongate cooling elements are of square cross-section with rounded corners.

11. A method as claimed in claim 9 wherein the elongate cooling elements are of triangular cross-section with rounded

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Claims

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time period to suit the production rate. Typically this would be within ten minutes from the time the pour was made. The solidified but still very hot material is recovered from the mould by removing the walls 3 and jacking the ejection plate 4 away from the clamped base plate 5 by means of jacks (not shown) locating the jacking holes 7. If desired, the moulds 1 can be left to cool completely.

Under normal conditions of hot stripping, once the product has been ejected the apparatus is water cooled leaving just sufficient heat capacity in it to evaporate quickly any residual water. The mould 1 can then be re-assembled very rapidly and retuned to the furnace for re-filling.

Occasionally material of a very low viscosity may partially enter the clearance gap between the rods 2 and holes 4a in the ejection plate 4. Stripping is made more difficult when this occurs. The problem can be eliminated by covering the ejection plate 4 with a 1/32N to 411 layer of powder of the same composition as the material to be cooled. This powder may be obtained from unwanted fines generated during crushing.

Experience has shown that in the case of certain abrasive grains, the properties obtained using the above apparatus are intermediate between ball cast and plate cast grains, but usually far nearer the plate cast grains in crystalline characteristics and physical/mechanical properties.

Fig. 3 shows a plan view of a further embodiment of apparatus in accordance with the invention which comprises an open-topped mould 20 having a plurality of horizontally disposed circular section rods 21 extending therein. The rods 21 are arranged in two clusters with the rods of each cluster being arranged in aligned rows (see also Fig. 5). The mould 20 comprises front and rear walls 22 and two side walls 23 through each of which extends one of the rod clusters. The rods 21 of each cluster are firmly located in respective plates 24 which are each associated with hydraulic rams 25 which are operable to withdraw the rods 21 from the mould 20 through the side walls 23.

In use, the mould 20 is filled with molten material which is then allowed to cool and solidify as previously. The solidifed material may be recovered by operating the rams 24 to withdraw the rods 21 from the mould 20 thus leaving the solidified material which may then be removed from the mould 20.

It is found that the aligned rows of rods 21 allow better penetration by the molten material than is obtained with staggered rows: It is however possible to use staggered assemblies of horizontal rods with satisfactory results depending on the viscosity of the melt, size of rod and cavity dimensions.

Figs. 4 to 9 illustrate a typical range of rod cross-sectional shapes and packing configurations which can be used at a wide variety of cross-sectional sizes and rod lengths. Figs.

4 and 5 relate to circular section rods and respectively illustrate portions of assemblies of such rods in staggered and aligned rows, as described previously with reference to Figs. 1 and 3. In the arrangement of Fig. 4, each rod is at the apex of a regular hexagon defined with five other rods (i.e. a hexagonal arrangement) whereas, in Fig. 6, each rod is at the corner of a square defined with three other rods (i.e. a cubic arrangement).

Fig. 6 illustrates square sectioned rods in cubic arrangement. The rods of Fig. 6 have rounded edges to prevent melting.

Fig. 7 illustrates triangular sectioned rods in hexagonal arrangement. The rods once again have rounded edges to prevent melting.

Figs. 8 and 9 both relate to rods of rectangular section with rounded ends and respectively illustrate such rods in hexagonal and cubic arrangement (i.e. staggered and aligned rows respectively).

WHAT WE CLAIM IS: 1. A method of solidifying a molten refractory material comprising pouring the molten material into a vessel in which extend a plurality of spaced elongate cooling elements, and allowing the molten material to cool and solidify.
2. A method as claimed in claim 1 wherein the molten refractory material is an oxide material.
3. A method as claimed in claim 2 wherein the oxide material is a binary oxide co-fusion.
4. A method as claimed in claim 3 wherein the binary oxide co-fusion is of alumina and zirconia.
5. A method as claimed in any one of claims 1 to 4 wherein the elongate cooling elements are mutually parallel.
6. A method as claimed in claim 5 wherein the elongate cooling elements are in aligned rows.
7. A method as claimed in claim 5 wherein the elongate cooling elements are in staggered rows.
8. A method as claimed in any one of claims 1 to 7 wherein the elongate cooling elements are of circular section.
9. A method as claimed in any one of claims 1 to 7 wherein the elongate cooling elements have rounded edges.
10. A method as claimed in claim 9 wherein the elongate cooling elements are of square cross-section with rounded corners.
11. A method as claimed in claim 9 wherein the elongate cooling elements are of triangular cross-section with rounded

apices.
12. A method as claimed in any of claims 1 to 11 wherein the elongate cooling elements are vertical.
13. A method as claimed in any one of claims 1 to 11 wherein the elongate cooling elements are horizontal.
14. A method as claimed in any one of claims 1 to 13 wherein the elongate cooling elements are of mild steel.
15. Apparatus for cooling and solidifying molten refractory material comprising a vessel into which the molten material is poured, a plurality of spaced elongate cooling elements extending within said vessel and serving to extract heat from the molten material, and a stripping member through which said elements extend and which is relatively movable along said elements to strip solidified product therefrom.
16. Apparatus as claimed in claim 15 wherein the stripping member forms a wall of the vessel.
17. Apparatus as claimed in claim 12 wherein a ram is provided for moving the cooling elements through the stripping member.
18. Apparatus as claimed in claim 12 wherein two horizontal arrangements of cooling elements are provided with the elements of each arrangement locating through a respective stripping member forming a wall of the vessel.
19. Apparatus as claimed in claim 15 wherein the cooling elements are vertical, the stripping member is located on a clamped member supporting the elements, and the walls of the vessel are removable and are located on the stripping member.
20. Apparatus as claimed in claim 19 wherein the member supporting the elements is provided with apertures through which jacks may operate to raise the stripping member.
21. Method of solidifying a molten refractory material substantially as hereinbefore described with reference to Figs. 1 and 2 or any one of Figs. 3 to 9 of the accompanying drawings.
22. Apparatus for solidifying molten refractory material substantially as hereinbefore described with reference to Figs. 1 and 2 or any one of Figs. 3 to 9 of the accompanying drawings.