GB1571239A - Abrasive materials and a method of producing such materials - Google Patents

Description

(54) ABRASIVE MATERIALS AND A METHOD OF PRODUCING SUCH MATERIALS (71) We, NOJIMAGUMI COMPANY LIMITED, a Japanese Company of 604-1, Nojimahikinoura, Hokutan cho, Tsuna gun, Hyogo Prefecture, Japan, 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 abrasive materials and to a method of producing such materials.

Abrasive materials are used in sand blasting processes for removing rust and the like from surfaces. The most common abrasive materials used in sand blasting are silica sand and slag but a disadvantage of such materials is that they are brittle, and generally when particles of the materials strike a surface to be cleaned, they break into smaller particles and produce dust and consequent pollution of the atmosphere.

According to the present invention there is provided a coated abrasive material, wherein the material is selected from silica sand or slag, and the coating which directly overlies said material is a thermosetting resin selected from a phenolic resin, a urea resin, a melamine resin, a polyester resin or an alkyd resin, each including a setting catalyst which coating is rendered substantially insoluble and unmeltable.

According to a further feature of the invention there is provided a method of producing a coated abrasive material comprising the steps of: adding a thermosetting resin selected from a phenolic resin, a urea resin, a melamine resin, a polyester resin or an aralkyd resin each including a setting catalyst therefor, to an abrasive material selected from silica sand or slag; admixing the resultant product in the presence of heated air thereby to coat said material with said resin, and subsequently reheating and stirring said heated mixture so as to render the thermosetting resin coated on the material insoluble and unmeltable.

Abrasive materials coated with a thermosetting resin which has been rendered insoluble and unmeltable in accordance with the present invention have increased strength. Thus, particuarly in the case of silica sand the particles of which have many cracks and fissures, the resin penetrates the material thereby increasing impact resistance of the silica sand and reducing the production of dust when using the material for sand blasting.

Furthermore, the presence of the thermosetting resin coating which has been rendered insoluble and unmeltable increases the efficiency of blast cleaning when an abrasive material according to the invention is used. More particularly, when the abrasive material is blown against a surface to be cleaned, the material will increase in temperature due to heat generated by the impact. In the case of abrasive material in accordance with the present invention, the insoluble and unmeltable thermosetting resin coating is such that it is not melted or solubilized by the heat of impact but sets further and thereby improves the efficiency of the blast cleaning operation.

Following is a description by way of example only and with reference to the accompanying drawings of one method of carrying the invention into effect.

In the drawings: Figure 1 is a schematic view of apparatus for producing abrasive materials according to one embodiment of the invention; Figure 2 is a schematic view of one aspect of another embodiment of the invention; and Figures 3 and 4 are particle size distribution- comparison test graphs showing the data of comparative tests between the present invention and the prior art.

Referring now to Figure 1 of the drawings, a tank 1 containing silica sand and/or slag is adapted in this instance to supply sand to a measuring tank 2, by opening an outlet damper la disposed in the lower region of the tank 1. After a predetermined amount of sand has been measured by the tank 2, it is dumped into a mixer 3 disposed below the tank. Also charged into the mixer 3 is a setting catalyst in predetermined proportion to a thermosetting resin and the sand and setting catalyst are uniformly mixed for about one minute, whereupon a thermosetting resin in predetermined proportion to the sand is charged into the mixer 3 and, while blowing hot air at 8e-100"C from a hot air blower 4 into the mixer, the resin and sand are mixed for about five minutes.In consequence, the particles of sand are provided with a thermosetting resin coating of predetermined thickness formed on their surfaces and such coatings are dried and set by the action of heat.

The amounts of said thermosetting resin and setting catalyst may be suitably changed according to the properties of the silica sand or slag used. As an example.

in the case of No. 4 silica sand specified in the Japanese Industrial Standards (JIS), 2 parts of thermosetting resin and 1 part of setting catalyst are used with respect to 100 parts of No. 4 silica sand. As for slag, proportions similar to those described may be used. By the process described above, the particles of silica sand or slag are coated with said thermosetting resin independently without the particles sticking to each other to form a lump or lumps. In this case, since hot air is supplied during the mixing, the thermosetting resin undergoes a chemical change which renders it insoluble and unmeltable to some extent. When slag is used, however, the resin on the particles of slag becomes viscous like glue and the viscous condition of the resin lasts longer than in the case of silica sand, making it somewhat difficult to achieve the thermal setting thereof.Thus, in order to make the thermal setting complete and also, in the case of silica sand, to cause the resin, which has penetrated even to the innermost areas of cracks peculiar to silica sand, to thermally set completely, the silica sand of slag mixed and resin-coated in the preceding process is heat treated again.

More particularly, the stirred silica sand (or slag, reference hereinafter being made to silica sand) is charged into a hopper 5 and then the treated silica sand flowing out of the bottom of said hopper 5 is received on a conveyor 6 for transport to a rotary kiln 7. This arrangement for receiving the silica sand from the mixer 3 and then transporting it by the conveyor 6 is intended to adjust the rate of supply of silica sand to the rotary kiln 7 according to the capacity of the latter. On the exit side of the rotary kiln 7, outlet ports 8 suitably spaced apart are formed in the outer peripheral surface of the rotary kiln 7 and hot gas at about 300"C is blown into the rotary kiln 7 from the exit of the latter, said hot gas traveling toward the entrance ofthe rotary kiln and being finally expelled into the atmosphere by an exhaust fan 9.

As for said hot gas, air heated by waste gas resulting from combustion of kerosene or the like is used and is blown into the rotary kiln 7 by a nozzle 10. As is known in the art, the rotary kiln 7 has annular rails 11 mounted thereon at a plurality of suitable places and each annular rail 11 is supported by a pair of rollers 12. In this way, the rotary kiln 7 is rotatably supported on a support base 13. Designated at 14 is a driven gear wheel fixed on the outer peripheral surface of the rotary kiln 7 and meshing with a drive gear wheel 16 secured to a motor 15, whereby the rotary kiln 7 is rotated around its own axis in one direction. Designated at 17 are support rollers each abutting against the lateral surface of the associated annular rail 11. While each support roller 17 is shown located above the associated support rollers 12 for simplicity of illustration only, actually it is located between and above the level of the associated support rollers 17. The support rollers 17 serve to prevent the rotary kiln 7 from inadvertently sliding in the direction of inclination thereof. The rotary kiln 7 is internally provided with a plurality of stirring vanes 18 extending from the entance to the middle of the length of the rotary kiln 7.Accordingly, with the rotary kiln 7 being rotated around its own axis and with heated air being blown thereinto, if silica sand transported by the conveyor 6 is supplied to the rotary kiln 7 through a chute 19, the silica sand is repeatedly subjected to the action of the stirring vanes 18 scooping it and then dropping it with the rotation of the rotary kiln 7 around its own axis and during this action it comes in contact with the hot gas, whereby the thermosetting resin coatings on the particles of silica sand undergo a final thermosetting chemical change to be rendered insoluble and unmeltable. The silica sand urged on by the stirring vanes 18 flows inside the rotary kiln while being shaken or vibrated until it reachesthe exit side of the rotary kiln 7 and finally flows out through the outlet ports 8.In this connection, it is to be noted that a vibration conveyor 30 shown in Fig. 2 may be used as the heating and stirring means in place of the rotary kiln 7 shown in Fig. 1. More particularly. the vibration conveyor 30 supported by springs 32 and adapted to be vibrated by vibration means 33 such as an eccentric motor is associated with infrared ray radiating devices 31 located thereabove, so that while the silica sand supplied to the conveyor 30 from the conveyor 6 through the chute 19 shown in Fig. 1 is being vibrated and transported by the conveyor 30, it is heated by the infrared ray radiating devices 31 so as to render the thermosetting resin coatings insoluble and unmeltable. Referring back to Fig. 1, the silica sand particles which have been discharged from the rotary kiln 7 are collected at the lower end of a bucket lifter 21 by a chute 20.The particles thus collected are then lifted by the bucket lifter 21 operated by a motor 22 and are supplied into a hopper 24 disposed in a sorting tower 23. Disposed inclined below hopper 24 is a wire screen 25 having the required mesh, and vibrating means 26 is provided for vibrating the wire screen 25. Designated at 27 are springs for supporting the wire screen 25. Of the silica sand particles flowing down the hopper 24 onto the wire screen 25, only those having particle sizes below a certain limit are allowed to pass through the wire screen 25 under the action of the vibrations imparted thereto while the others having sizes above said limit flow down in said wire screen 25 and are discharged into the outside of the system. Those passing through the wire screen 25 are then transported by a conveyor 28 to a product storage tank.Designated at 29 is an exhaust fan serving to discharge cool air which is being admitted into the sorting tower 23 from below, whereby the silica sand which was at about 110"C when leaving the rotary kiln 7 or vibration conveyor 30 is cooled to about 8050 C. The time required for the silica sand to pass through the rotary kiln 7 or vibration conveyor 30 is suitably about 1 minute and 30 seconds. If the mesh size of the wire screen 25 is changed, the particle size of silica sand which can be sorted will differ. Thus, it is convenient to prepare a plurality of wire screens having different mesh sizes so that they may be selectively used.

The thermosetting resins available for the present invention include phenolic resin, urea resin, melamine resin, polyester resin, and alkyd resin. As an example, such resin is prepared by deriving furfural from pentose which is extracted from the stalks of cone or kaoliang, adding hydrogen to said furfural to provide furfuryl alcohol, and denaturing the latter with a phenol. Generally, mention may be made of those resins which are commercially available under the name of urea-furfuryl alcohol formaldehyde resin and of phenol furfuryl alcohol formaldehyde resin.

As for setting catalysts, it is desirable to use phosphate type catalysts such as an aqueous solution of phosphoric acid (75 concentration) or sulfuric type catalysts such as an aqueous solution of sulfuric acid (50% concentration).

The effects of abrasive materials prepared according to the present invention used for blast cleaning are shown below by way of example in comparison with conventional abrasive materials for blast cleaning.

(1) Result of Comparative Test for Amount of Dust Abrasive Material Used Amount ofDust No. 4 silica sand (JIS, conventional) 361 mg/m3 No. 4 silica sand resin-coated according to the invention 22 mg/m3 Slag (conventional) 13.2 mg/m3 Slag resin-coated according to the invention 11.3 mg-m3 The above result was obtained by measuring the amount of dust (in mg) per I m3 at a location 11 m downstream of the site for tests where an abrasive material was blown against a surface to be cleaned.

(2) Result of Comparative Test For Depth of Indentations Abrasive Material Used Depth of Indentations No. 4 silica sand (JIS, conventional) 95,u EL No, 4 silica sand resin-coated according to the invention 104cm Slag (conventional) 100,a Slag resin-coated according to the invention 118 The above result was obtained by calculating the average of two blasting operations against a surface to be cleaned.

(3) Result of Comparative Test for Particle Size Distribution Fig. 3 shows the distribution of particle sizes of No. 4 silica sand (JIS, conventional) and No. 4 silica sand resin-coated according to the invention as measured before and after each material is blasted once, the particle size (in mm) being plotted as abscissa and the percentage as ordinate. According to this graph, it is seen that the distribution of particle sizes of No. 4 silica sand resin-coated (the present invention article) before use, as indicated by curve I, is such that the particle size range of 1.1 mm to 0.6 mm covers 93.2% (13% + 54% + 26.2%), demonstrating that the particles are very uniform in size, whereas in the case of No.

4 silica sand (conventional article) indicated by curve II, the same particle size range covers 75.4% (6% + 32.7% + 36.7%), showing that there is a relatively large amount of variation in particle size. Further, when the particle size distribution of the material after being used once is investigated as to particle sizes of not less than 0.3 mm capable of being re-used, it is seen that in the case of the present invention article indicated by curve III, 68.8% is re-usable, whereas in the conventional article indicated by curve IV, only 39.6% is re-usable. It is also seen that the amount of dust (particles of not more than 0.2 mm) found after single blasting is 30.1% with the present invention article and 38.9 with the conventional article.

Fig. 4 shows the distribution of particle sizes of slag (conventional article) and the same kind of slag resin-coated according to the present invention as measured before and after each material is blasted once. The particle size (in mm) before said blasting is indicated by curve I' for the present invention article and by curve II' for the conventional article and the particle size (in mm) after said blasting is indicated by curves III' for the present inventive article and by curve IV' for the conventional article. The abscissa indicates the particle size and the ordinate indicates the percentage.According to this graph, it is seen that the particle sizes of not less that 0.3 mm after single blasting which are capable of being re-used cover 73.5% (3 Ó + 9.5% + 22.6% + 17.1%) with the present inventive article and 60.5% (2.1 Ó + 6.1% + 15.8% + 18.4%) with the conventional article. It is also seen that the amount of dust (particles of not more than 0.2 mm) found after single blasting is 26% with the present invention whereas it is 38.9% with the conventional article.

From the comparative test results described above, it is seen that as shown in the item (1) the abrasive materials resin-coated according to the invention provide a rate of production of dust which is much less than that of the conventional articles and that particularly in the case of silica sand the invention is capable of reducing it to about 1/14 of the conventional value. This means that the invention prevents environmental pollution and contributes much to the improvement of working environmental conditions.

As is clear from the item (2), the abrasive materials resin-coated according to the invention provide as indentation depth which is not very different from or, rather, greater than that provided by the conventional articles, demonstrating that the invention improves the blast cleaning effect . Further, as is clear from the item (3), the abrasive materials according to the invention retain fewer cracks than the conventional articles, so that a correspondingly greater proportion of used or blasted material can be recovered for re-use by installing an abrasive material recovering device, thus contributing much to the reduction of cost.

WHAT WE CLAIM IS: 1. A coated abrasive material, wherein the material is selected from silica sand or slag, and the coating which directly overlies said material is a thermosetting material selected from a phenolic resin, a urea resin, a melamine resin, a polyester resin or an alkyd resin, each including a setting catalyst which coating is rendered substantially insoluble and unmeltable.

2. A coated material according to claim 1 wherein the coating comprises two parts by weight of thermosetting resin, and one part by weight of setting catalyst with respect to one hundred parts by weight of a silica sand.

3. A coated material according to either of claims 1 or 2 wherein the thermosetting resin is selected from a phenolic resin or a urea resin.

4. A coated material according to claim 3 wherein the resin is a ureafurfuryl alcohol formaldehyde resin or a phenol furfuryl alcohol formaldehyde resin.

5. A coated material according to any preceding claim wherein the setting catalyst is selected from a phosphate or sulfate type catalyst.

6. A method of producing a coated abrasive material comprising the steps of: adding a thermosetting resin selected from a phenolic resin, a urea resin, a melamine resin, a polyester resin or an alkyl resin each including a setting catalyst therefor, to an abrasive material selected from silica sand or slag; admixing the resultant product in the presence of heated air thereby to coat said material with said resin and subsequently reheating and stirring said heated mixture so as to render the thermosetting resin coating on the material insoluble and unmeltable.

7. A method according to claim 6 wherein two parts by weight of the thermosetting resin and one part by weight of the setting catalyst are added to 100 parts by weight of a silica sand.

8. A method according to either of claims 6 or 7 wherein the thermosetting resin is selected from a phenolic resin as a urea resin.

9. A method according to claim 8 wherein the resin is a urea furfuryl alcohol formaldehyde resin or a phenol furfuryl alcohol formaldehyde resin.

10 A method according to any one of claims 6 to 9 wherein the setting catalyst is selected from a phosphate or sulfate type catalyst.

11. A method according to any one of claims 6 to 10 wherein the admixture of the resultant products is effected while air at a temperature of 80" to 100"C. is passed over said product.

12. A method according to any one of claims 6 to 11 wherein the subsequent reheating step is performed in a rotary kiln by blowing a hot gas thereinto over said heated mixture.

13. A method according to claim 12 wherein said hot gas is blown into the kiln at a temperature of about 300"C.

14. A method according to either of claims 12 or 13 wherein the hot gas is air.

15. A method according to any one of claims 6 to 11 wherein the subsequent reheating step is performed in a vibration conveyor irradiated with infra-red radiation.

16. A method according to any one of claims 6 to 15 wherein the final coated abrasive material is air cooled prior to storage.

17. An abrasive material according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

18. A method of producing a coated material substantially as hereinbefore described and as illustrated in the accompanying drawings.

19. A method of blast cleaning an article which comprises utilizing a material according to any one of claims 1 to 5.

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

Claims (19)

**WARNING** start of CLMS field may overlap end of DESC **. recovering device, thus contributing much to the reduction of cost. WHAT WE CLAIM IS:

1. A coated abrasive material, wherein the material is selected from silica sand or slag, and the coating which directly overlies said material is a thermosetting material selected from a phenolic resin, a urea resin, a melamine resin, a polyester resin or an alkyd resin, each including a setting catalyst which coating is rendered substantially insoluble and unmeltable.

2. A coated material according to claim 1 wherein the coating comprises two parts by weight of thermosetting resin, and one part by weight of setting catalyst with respect to one hundred parts by weight of a silica sand.

3. A coated material according to either of claims 1 or 2 wherein the thermosetting resin is selected from a phenolic resin or a urea resin.

4. A coated material according to claim 3 wherein the resin is a ureafurfuryl alcohol formaldehyde resin or a phenol furfuryl alcohol formaldehyde resin.

5. A coated material according to any preceding claim wherein the setting catalyst is selected from a phosphate or sulfate type catalyst.

6. A method of producing a coated abrasive material comprising the steps of: adding a thermosetting resin selected from a phenolic resin, a urea resin, a melamine resin, a polyester resin or an alkyl resin each including a setting catalyst therefor, to an abrasive material selected from silica sand or slag; admixing the resultant product in the presence of heated air thereby to coat said material with said resin and subsequently reheating and stirring said heated mixture so as to render the thermosetting resin coating on the material insoluble and unmeltable.

7. A method according to claim 6 wherein two parts by weight of the thermosetting resin and one part by weight of the setting catalyst are added to 100 parts by weight of a silica sand.

8. A method according to either of claims 6 or 7 wherein the thermosetting resin is selected from a phenolic resin as a urea resin.

9. A method according to claim 8 wherein the resin is a urea furfuryl alcohol formaldehyde resin or a phenol furfuryl alcohol formaldehyde resin.

10 A method according to any one of claims 6 to 9 wherein the setting catalyst is selected from a phosphate or sulfate type catalyst.

11. A method according to any one of claims 6 to 10 wherein the admixture of the resultant products is effected while air at a temperature of 80" to 100"C. is passed over said product.

12. A method according to any one of claims 6 to 11 wherein the subsequent reheating step is performed in a rotary kiln by blowing a hot gas thereinto over said heated mixture.

13. A method according to claim 12 wherein said hot gas is blown into the kiln at a temperature of about 300"C.

14. A method according to either of claims 12 or 13 wherein the hot gas is air.

15. A method according to any one of claims 6 to 11 wherein the subsequent reheating step is performed in a vibration conveyor irradiated with infra-red radiation.

16. A method according to any one of claims 6 to 15 wherein the final coated abrasive material is air cooled prior to storage.

17. An abrasive material according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

18. A method of producing a coated material substantially as hereinbefore described and as illustrated in the accompanying drawings.

19. A method of blast cleaning an article which comprises utilizing a material according to any one of claims 1 to 5.