GB1592810A - Wear resistent interlocking tile and apparatus comprising same - Google Patents

Description

(54) WEAR RESISTANT INTERLOCKING TILE AND APPARATUS COMPRISING SAME (71) We, MINNESOTA MINING AND MANUFACTURING COMPANY, a corporation organised and existing under the laws of the State of Delaware, United States of America, of 3M Center, St. Paul, Minnesota 55101, United States of America, 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:- This invention relates to a wear and abrasion-resistant tile for use in devices where it may be exposed to abrasion and wear in wet or dry conditions. The tile is particularly adapted for use in wet or dry grinding mills and for conduits where severe abrasion is encountered under any temperature conditions.

Numerous methods have been proposed for combatting problems associated with abrasion of the container in grinding mills and various mixing and pulverizing mills. Particular consideration is here given to dynamic devices such as rotary grinding mills and to static devices such as conduits in which there is motion of more or less abrasive material in suspension in a suitable fluid medium, i.e., gas or liquid.

A constant problem in lining such devices is the selection of a lining material which shows satisfactory wear and abrasion resistance over prolonged time. A particularly desirable refractory for wear resistance because of its hardness is alumina. A problem associated with the use of abrasion-resistant materials such as alumina is that means must be found for applying them in locations where they can be valuable. It is difficult to fabricate large objects of alumina and in use such structures might well be subjected to destructive mechanical action although fully capable of withstanding abrasion.

It has been found that a very useful, wear and abrasion-resistant article for application to flat and curved surfaces is provided by interlocking refractory tile of particular configuration which can be applied in interlocking relationship.

Accordingly in one aspect the present invention provides a refractory abrasion resistant interlocking tile having two adjacent edges convex with tongues and two adjacent edges concave with grooves and a thickness less than any side, each edge being bordered by narrow ledges or shoulders at each surface, the radii of curvature of tongues and grooves being substantially the same and being from one third to two thirds the thickness of the tile with centres of curvature so placed that the arc of the convex edges between ledges or shoulders is greater than the arc of the concave edge between ledges or shoulders.

In another aspect the present invention provides a process for promoting durability of a conduit having portions subject to abrasion from flow of abrasive matter which comprises lining at least a portion of the conduit subject to abrasive forces with refractory abrasion resistant interlocking tile as defined above.

In yet a further aspect the present invention provides a duct consisting essentially of casing, a lining of interlocked abrasion-resistant tile as defined above and expanded intumescent composition between the tile lining and the casing exerting forces thereon respectively centripetally and centrifugally of the tile lining in the casing.

The tiles of the present invention are of the structure shown in Figure 1 with two convex and two mating concave sides forming rotatable tongue and groove joints and a thickness usually less than one quarter the lesser edge length. In the tile shown in Figure 1, it will be seen that small ledges are formed along the convex edges and that the edges of the concave portions also are flattened. These structures are characteristic of the tile herein described and are termed generally herein as ledges or shoulders. They have as one advantage in fabrication that the dies used for compression do not need knife edges and as an advantage for use that the ledges or shoulders of mating sides act as a stop to rotation of one tile with respect to the other. By making the arc of the male edge or tongue greater than that of the female edge or groove, the respective shoulders or ledges are not in contact as is the case with the usual tongue and groove joint thus providing rotatability. The straight line distances between ledges are the chords of the tongues and grooves and the arcs are the distances along the circular pathway or the angle enclosing that part.

The centre of curvature of the tongues and grooves lies in back of the chord, that is on the side away from the tongue within the tile and away from the groove at the other side of the tile. This means that the arcs are always less than 180 .

It is important that the mating surfaces be of radii of curvature from one third to two thirds, preferably 0.4 to 0.6 and more preferably 0.5 of the thickness of the tile and that the chord and arc on the concave side be less than the chord and arc of the convex side. Both male and female members are made with substantially the same radius of curvature. It is possible to produce useful rotatable joints using radii of curvature more or less than one half the thickness of the tile but the integrity of the joint is compromised outside the range of radii of from one third to two thirds the tile thickness. In all cases the chord of the concave (female) side must be less than that of the convex (male) side to permit rotation or, expressed differently, the height of the tongue must be greater than the depth of the groove. This difference should generally be about 5% or more the thickness of the tile and may be up to 30 /O or more and is preferably 10% to 20% the thickness of the tile. In particularly useful embodiments, the centre of curvature for the convex or male edges will be approximately 1/6 the thickness in back of the ledges or shoulders and of the concave or female edge approximately 1/4 to 1/5 the thickness behind the ledges.

The height of the convex or tongue edge is approximately 1/3 the thickness of the tile and depth of the concave groove side approximately 1/4 to 1/5 the thickness of the tile.

Tiles of the invention may be adhered to a substrate to provide a composite which can be applied to a surface. Such a wear and abrasion-resistant composite covering consists essentially of one ply of flexible composition from 0.2 to 10 mm thick and adhered thereto on one surface refractory abrasion-resistant interlocking tile as defined above. When the substrate is magnetic and the surface is iron or steel adhesion of the composite is accomplished by magnetic force. If greater adhesion is needed than can conveniently be provided by the magnetic force or a nonmagnetic substrate is provided, an adhesive may also be used.

A suitable flexible magnetic sheet material is available commercially in thicknesses of from about 0.8 to 3 mm and in widths up to about 30 cm from Minnesota Mining and Manufacturing Co. under the trade mark Plastiform 8. This material includes a body portion of rubber in which barium ferrite particles are embedded during production of the sheet. It is generally preferred to use material having an alternating type of polarity, particularly with a coating of pressure sensitive adhesive (and low adhesion backing) on one side. Other adhesives may be used rather than pressure sensitive adhesives but in general any adhesive should not become brittle. Tacky and agressive prepolymerized adhesives are therefore preferred over adhesives which polymerize in situ such as epoxy resins.

Alumina of 85% or greater purity is particularly preferred as material for making interlocking tiles of the invention because of its combination of relatively high melting point and greater hardness and hence resistance to wear and abrasion.

Other compositions such as cordierite, mullite, silicon carbide, silicon nitride, alumina-chromia compositions, cermets such as titanium carbide-alumina, and other wear-resistant materials can be used in many applications.

Dimensions of the tile can be varied over considerable ranges depending on the particular application. Individual tiles for lining a tube of circular cross-section should cover an angle of at least 80 and up to 300 as measured from the center of curvature. There will thus be from 12 to 45 tiles in the circumference. Similar criteria can be used for lining elliptical or oval tubes and it is contemplated that tiles of different dimensions can be used together in such situations. Although the tile is shown as flat and essentially square, it will be understood that rectangular shapes generally are useful. Furthermore, it is within the scope of the invention to employ a tile which has a curvature of radius no greater than that of the surface to which applied. Generally one convex edge of each tile will face upstream, i.e., toward the source of flow.

The invention is further described by reference to the drawings wherein Figure 1 shows interlocking tile of the invention Figure 2 shows a cross-section of 2-2 of the tile of Figure 1 Figure 3 shows a grinding mill lined with the composite wear resistant sheet formed from tiles of the invention Figure 4 shows an angled steel sheet covered by composite sheet material formed from tiles of the invention Figure 5 shows a section of 4--4 of the angled steel sheet of Figure 3 Figure 6 shows two interlocking tiles Figure 7 shows diagrammatically one embodiment of the process of the invention for inserting interlocking tiles and intumescent material in a tube Figure 8 shows a tube or duct of circular cross-section lined with interlocking tiles and an expanded intumescent sheet Figure 9 is like Figure 8 for a tube or duct of elliptical cross-section Figure 10 shows a partial section of a tube or duct of Figure 8 provided with means for measuring centrifugal force exerted by the expanded intumescent sheet.

The tile of Figures 1 and 2 has faces (10), convex sides (12) with ledges (16) and concave sides (14) with ledges (18). The mating of two such tiles is shown in Figure 6.

A steel grinding mill (20) having flange (21), shown diagrammatically in Figure 3 with one head (22) broken away, is lined with sheets of magnetic elastomer (23) about 30 cm square bearing about 500 alumina tiles (24) about 1.6 cm square. Mill (20) containing steel balls (26) rotates dry on rollers (27) at about 64 rpm for 216 hours. There is some nicking of thin edges of individual tiles but no evident wear.

The tile is blackened from wear on the steel balls giving finely divided iron which may be partially oxidized. There is no loss of magnetism in the sheet material under the repeated impact of the steel balls. The sheets of tiles are readily stripped away, however, when desired. This is a particularly useful feature in cleaning the mill, particularly if several different materials are to be milled without cross contamination.

In Figures 4 and 5 is shown a wear plate or deflector plate for attachment to the outer surface of an elbow for a conveyor line. It will be seen that steel plate (28) is coated by tiles (24) on a magnetic elastomeric backing. If desired a simple elastomeric backing can be employed to which tiles are adhered and which is then attached to the steel backing by an adhesive. In Figure 5 is shown a much enlarged section of the deflector plate of Figure 4 showing bonding of tiles (24) to magnetic backing (23) by adhesive (25) and further how the magnetic dipoles achieve banding to steel plate (28). In actual experience a plate such as this is found to out-wear a simple steel deflector plate by several times. This results in great conveniences in replacement costs and maintenance expenses. Other uses contemplated include linings for chutes defivering abrasive materials such as coal, cement clinker, ores, gravel, rocks and the like.

Figure 7 shows how tiles are mounted internally by application of centripetal force. Tiles (10) are applied to the surface of a mandrel (32) suitably of cardboard or other flammable material and of slightly larger diameter than the ultimate tile lining. The application may be effected by coating one surface of each tile or the surface of the mandrel with adhesive and placing the tiles in longitudinal and circumferential interlocking relationship. The tiles may also be in a helix around the mandrel so that tiles are aligned longitudinally but offset slightly in the circumference to overlap two tiles in each adjacent longitudinal row. Tiles having holes from concave to convex side may be strung on a wire or cord and wrapped around the mandrel helically. The tiles may also be laid up as two halves of a cylinder which are joined. The tiles may be cemented at some points of contact.

One or more sheets of intumescent sheet material (30) of a thickness of 0.5 to 5 mm is applied around the tiles and maintained in position while the assembly is inserted in tube (40). The total thickness will usually be one half or more the space to be filled. The assembly is next heated to destroy mandrel (32) and to expand the intumescent sheet (30) to intumescent filler (34) which exerts centipetal pressure to tiles (10) and centrifugal pressure on tube (40) and thereby retains tiles (10) securely within tube (40). The same procedure is used to produce the duct as shown in Figure 8 with circular cross-section or with elliptical or oval cross-section as shown in Figure 9.

The intumescent material employed is a sheet material and preferably sheet materials described and claimed in Hatch et al. U.S. Patent 3,916,057 containing unexpanded vermiculite. Other intumescent sheet materials including those comprising organic substances can be used.

It is desirable that after expansion the intumescent sheet material exert a force on the tiles, i.e. centripetally of at least 2 and up to 35 newtons per cm2 to force the tiles into circumferential interlocking relationship. These forces are determined using a conventional Instron Tester to measure the force necessary to force a single tile toward the casing for a distance of 0.75 mm. (The word "Instron" is a Registered Trade Mark). Because of the interlocking of the tiles the measured force on a given tile is estimated to be approximately 150 /, of the actual centripetal force exerted on that tile.

The centrifugal force can be measured in a specially built tube similar to the one of Figure 8 but with a series of plungers built into the casing as shown in Figure 10. It will be seen that the two shown are staggered so that only one is shown in section. Each device consists essentially of a large hexagonal nut (50) welded to casing (40) with plug (52) having central hole (54) in which is loosely fitted plunger (60) with foot (62) fitting into a hole in casing (40). The several devices are assembled before refractory tiles (10) are inserted so that the surface of foot (62) is substantially flush with the inner surface of casing (40) and rests against the face of plug (52). The expanded intumescent mat (34) exerts centrifugal pressure against plunger feet (62) and casing (40). The force necessary to move plunger (62) against mat (34) for a distance of 0.75 mm is measured as the centrifugal force.

The tubes employed will usually be metal such as steel and of at least 5 cm diameter and preferably at least 10 cm and upwards to 100 cm and more. Larger tubes can be lined using larger tiles in order to remain within the chord angles noted. The ratio of minor to major axis of elliptical or oval tubes should be greater than 0.3 because of the difficulty of achieving uniform centripetal force.

Alumina tiles as shown in Figure l approximately 15.5 mm on a side are formed by firing alumina bodies in conventional procedures. These tiles are used in the grinding mill as described above. They are also mounted in mild steel tubing (e.g., stovepipe) about 13.5 cm long by 12.5 cm in internal diameter having 0.09 cm wall thickness as follows: A circular cylindrical self-supporting mandrel of light cardboard about 13.5 cm long and 10.7 cm in diameter is covered with double-coated pressure sensitive adhesive tapes and tiles are adhered to the mandrel. Twenty-two interlocking tiles encircle the circumference of the mandrel in a row to give an exterior diameter of 11.68 cm. Nine such rows of interlocking tiles are assembled to complete the cylinder; so that the individual tiles are arranged in longitudinal rows. The cylinder is inserted into a stove pipe as described above. The average gap between the tiled cylinder and the pipe is 4.2 mm. Intumescent sheet material, as described in U.S.

3,916,057 and about 3.6 mm thick, is carefully wrapped around the tiled cylindrical mandrel as a mat and the resulting assembly into the pipe.

The entire assembled unit is placed in a furnace and heated to 6500C to expand the intumescent mat. The expansion of the mat exerts an inward i.e.

centripetal, force on the interlocking tiles and an outward, i.e. centrifugal, force against the pipe thereby securely holding the tiles in place. During the heating at 650"C, the cardboard mandrel and the tape are destroyed leaving the tiles as the exposed inner surface. The integrity of the mounting is determined by the following test. A 2270 gm hammer on 43.2 cm radius pivot arm is mounted so that it swings in an arc and strikes the side of the tile lined pipe. The force exerted by the expanded intumescent sheet material is proportional to the thickness of the mat for a given composition. Mats of 0.234 cm, 0.269 cm and 0.363 cm are prepared according to the description given in U.S. 3,916,057 and ducts lined with tiles are prepared as above using the three thicknesses of intumescent sheet material. The force exerted on the tiles is predetermined to be about 2, 4 and 8 newtons per cm2 respectively.

Impact tests are run by varying the vertical height to which the hammer is raised and allowed to swing through its natural arc. The results of such tests are tabulated below: TABLE I Thickness Pressure Drop Height Sample (cm.) (newtons/cm2) (cm.) Results 1 0.234 2.1 14 Tile loosens 17 Tile drops out 2 0.269 4.1 31 Tile loosens 31 Pipe deforms 3 0.363 8.3 38 No effect 41 Pipe deformed Thus, it is established that interlocking tiles held in place by an intumescent mat expanded to yield a pressure of at least 2 newtons per square centimeter or more having useful integrity.

Several tests are conducted by the above described procedure for determining centifugal and centripetal forces using the tile described above in a steel casing about 12.5 cm in diameter fitted with five of the test plungers as shown in Figure 10 the foot of each being 0.71 cm2. Twenty-two rows of tiles are required and agap of about 4.0 mm is formed between the tiles and casing. Intumescent sheets of various uncalendered and calendered or compressed thickness are used so that various ranges of pressures are developed. The test pieces are prepared and fired as described above and forces measured on an Instron Tester as set forth above. The data are tabulated in Table II.

TABLE II Run 1 2 3(b) 4 5 6 Thickness of Intumescent sheet (mm) Uncalendered 2.84 3.43 3.99 2.67 3.63 4.09 Calendered 1.91 3.30(a) 3.56 (e) 2.74 3.40 Free expansion - 80 96 100 155 161 Weight of 555 cm2 piece in g. 80.7 90.6 ' 122.9 80 104.5 127.5 Bulk density after expansion in g/cm3 0.36 0.41 0.55 0.36 0.47 0.57 Centrifugal force (c) in newtons/cm2 15.8 30.0 22.5 16.5 34.7 48.1 Centripetal force (d) in newtons/cm2 5.2 25.8 12.5 9.7 32.1 32.1 Ratio of centrifugal to centripetal force 3.04 1.16 1.80 1.70 1.08 1.49 (a) Compated with roller rather than calendered.

(b) Aqueous treatment after placement of tile and sheet material before expansion. One plunger stuck.

(c) Average of five measurements except Run 4.

(d) Average of five measurements, assuming movement of tile affects 6.5 cm2.

(e) Not calendered.

WHAT WE CLAIM IS: 1. A refractory abrasion resistant interlocking tile having two adjacent edges convex with tongues and two adjacent edges concave with grooves and a thickness less than any side, each edge being bordered by narrow ledges or shoulders at each surface, the radii of curvature of tongues and grooves being substantially the same and being from one third to two thirds the thickness of the tile with centers of curvature so placed that the arc of the convex edges between ledges or shoulders is greater than the arc of the concave edge between ledges or shoulders.

2. A refractory abrasion resistance interlocking tile as claimed in Claim I, wherein the height of convex edges above adjacent ledges or shoulders is substantially one third the thickness of the tile and the depth of concave edges below adjacent ledges or shoulders is substantially one fourth to one fifth the thickness of the tile.

3. A wear and abrasion-resistant composite covering consisting essentially of one ply of flexible composition from 0.2 to 10 mm thick and adhered thereto on one surface refractory abrasion-resistant interlocking tile as defined in Claim I.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE I Thickness Pressure Drop Height Sample (cm.) (newtons/cm2) (cm.) Results

1 0.234 2.1 14 Tile loosens

17 Tile drops out

2 0.269 4.1 31 Tile loosens

31 Pipe deforms

3 0.363 8.3 38 No effect

41 Pipe deformed Thus, it is established that interlocking tiles held in place by an intumescent mat expanded to yield a pressure of at least 2 newtons per square centimeter or more having useful integrity.

Several tests are conducted by the above described procedure for determining centifugal and centripetal forces using the tile described above in a steel casing about 12.5 cm in diameter fitted with five of the test plungers as shown in Figure 10 the foot of each being 0.71 cm2. Twenty-two rows of tiles are required and agap of about 4.0 mm is formed between the tiles and casing. Intumescent sheets of various uncalendered and calendered or compressed thickness are used so that various ranges of pressures are developed. The test pieces are prepared and fired as described above and forces measured on an Instron Tester as set forth above. The data are tabulated in Table II.

TABLE II Run 1 2 3(b) 4 5 6 Thickness of Intumescent sheet (mm) Uncalendered 2.84 3.43 3.99 2.67 3.63 4.09 Calendered 1.91 3.30(a) 3.56 (e) 2.74 3.40 Free expansion - 80 96 100 155 161 Weight of 555 cm2 piece in g. 80.7 90.6 ' 122.9 80 104.5 127.5 Bulk density after expansion in g/cm3 0.36 0.41 0.55 0.36 0.47 0.57 Centrifugal force (c) in newtons/cm2 15.8 30.0 22.5 16.5 34.7 48.1 Centripetal force (d) in newtons/cm2 5.2 25.8 12.5 9.7 32.1 32.1 Ratio of centrifugal to centripetal force 3.04 1.16 1.80 1.70 1.08 1.49 (a) Compated with roller rather than calendered.

(b) Aqueous treatment after placement of tile and sheet material before expansion. One plunger stuck.

(c) Average of five measurements except Run 4.

(d) Average of five measurements, assuming movement of tile affects 6.5 cm2.

(e) Not calendered.

WHAT WE CLAIM IS: 1. A refractory abrasion resistant interlocking tile having two adjacent edges convex with tongues and two adjacent edges concave with grooves and a thickness less than any side, each edge being bordered by narrow ledges or shoulders at each surface, the radii of curvature of tongues and grooves being substantially the same and being from one third to two thirds the thickness of the tile with centers of curvature so placed that the arc of the convex edges between ledges or shoulders is greater than the arc of the concave edge between ledges or shoulders.

2. A refractory abrasion resistance interlocking tile as claimed in Claim I, wherein the height of convex edges above adjacent ledges or shoulders is substantially one third the thickness of the tile and the depth of concave edges below adjacent ledges or shoulders is substantially one fourth to one fifth the thickness of the tile.

3. A wear and abrasion-resistant composite covering consisting essentially of one ply of flexible composition from 0.2 to 10 mm thick and adhered thereto on one surface refractory abrasion-resistant interlocking tile as defined in Claim I.

4. Wear and abrasion-resistant composite covering as claimed in Claim 3.

wherein the flexible composition includes magnetic particles providing magnetic lines of force at the exposed surfaces of the composition.

5. A wear and abrasion-resistant composite covering as claimed in claim I or 2.

wherein the height of convex edges above adjacent ledges or shoulders of the refractory abrasion resistant interlocking tile is substantially about one third the thickness of the tile and the depth of concave edges below adjacent ledges or shoulders is substantially one fourth lo one fifth the thickness of the tile.

6. A process for promoting durability of a conduit having portions subject to abrasion from flow of abrasive matter which comprises lining at least a portion of the conduit subject to abrasive forces with refractory abrasion resistant interlocking tile as defined in Claim 1.

7. A process for promoting durability of a conduit having portions subject to abrasion from flow of abrasive matter which comprises lining at least a portion of the conduit subject to abrasive forces with a composite covering of elastomeric backing and refractory abrasion-resistant interlocking tile adhered to the backing as defined in Claim 3.

8. A process for promoting durability to abrasion of the inner surS.lce of a hollow tube of round to elliptic cross-section comprising (A) providing the tube internally with a first laver of insulative sheet I:rterinl which expands to form a resilient mat on heating and a second layer of intrlocking refractory abrasion resistant tile as defined in Claim I temporarily positioned inward of the first layer, clearances between the tube and the first and second layers s being sufficiently large to permit relative movement between the tube and the second layer and not being greater than the expanded thickness of the insulative sheet material, and (B) heating the tube under condition of substantially uniform circumferential heat distribution with the first and second layers in position whereby expansion of the insulative sheet material is effected substantially uniformly so that force is exerted centripetally of the tube on the interlocking tile sufficient to hold the tile in securely interlocked relationship within the tube.

9. A process as claimed in Claim X, wherein at least said second layer is applied externally to a mandrel of destructible composition and the assembly is inserted into the tube.

10. A process as claimed in Claim 8 or 9 wherein clearance between tube, intumescent sheet material and tile are selected in consideration of expansion potential of the sheet material such that a force is exerted centripetally on the tile layer of at least 2 newtons per cm2.

11. A duct consisting essentially' of casing. a lining of interlocked abrasionresistant tile as defined in Claim I and expanded intumescent composition between the tile lining and the casing exerting forces thereon respectively centripetally and centrifugally of the tile lining in the casing.

12. Refractory abrasion resistant interlocking tiles substantially os herein described with reference to the accompanying drawings.

13. A process substantially as herein described for promoting the durability of a conduit.

14. A duct substantially as herein described.