METHOD FOR RECOVERING ABRASIVE ELEMENTS CONTAINED IN A RESIN-BONDED MATERIAL AND USE OF SAID ELEMENTS THUS RECOVERED

Abstract

A process for recovery of all or some abrasive elements contained in an abrasive material in which the abrasive elements are dispersed in a resin with at least one phenolic hydroxyl group, the process including steps of: a) bringing the abrasive material into contact with an aqueous nitric solution (S.sub.1), whereby an aqueous nitric solution (S.sub.2) is obtained containing abrasive elements and residue derived from degradation of the resin; then (b) separating the abrasive elements from the aqueous nitric solution (S.sub.2) obtained after step (a). The use of abrasive elements thus recovered particularly to prepare agglomerated abrasives or coated abrasives.

Claims

1) Process for recovery of all or some abrasive elements from an abrasive material in which said abrasive elements are held in a resin with at least one phenolic hydroxyl group, said process including steps of: a) bringing said abrasive material into contact with an aqueous nitric solution (S.sub.1), whereby an aqueous nitric solution (S.sub.2) is obtained containing abrasive elements and residue derived from degradation of said resin; then b) separating the abrasive elements from the aqueous nitric solution (S.sub.2) obtained subsequent to said step (a).

2) Process according to claim 1, characterised in that said resin is a phenoplast.

3) Process according to claim 1, characterised in that said abrasive elements are chosen from the group consisting of alumina, brown corundums, white corundums, violet corundums, zirconia, diamond, silicon carbide, sintered bauxite and mixtures thereof.

4) Process according to claim 1, characterised in that said aqueous nitric solution (S.sub.1) contains at least 20% by mass of nitric acid relative to the total mass of said aqueous nitric solution (S.sub.1).

5) Process according to claim 1, characterised in that said aqueous nitric solution (S.sub.1) also contains sulphuric acid.

6) Process according to claim 5, characterised in that said aqueous nitric solution (S.sub.1)contains at least 30% by mass of sulphuric acid relative to the total mass of said aqueous nitric solution (S.sub.1).

7) Process according to claim 1, characterised in that during step (a), contact is made at a temperature comprised between ambient temperature and 150 C.

8) Process according to claim 1, characterised in that before step (a), a grinding or crushing type treatment is carried out on said abrasive material.

9) Process according to claim 1, characterised in that an additional recycling step is carried out on the nitric acid solution (S.sub.2) obtained after said step (b).

10) Process for preparation of an abrasive material comprising abrasive elements in a binder, said process comprising the following steps of: i) obtaining abrasive elements following a recovery process such as defined in claim 1; ii) bringing the abrasive elements obtained in said step (i) into contact with a binder or a precursor of said binder and mixing the assembly; iii) possibly applying a heat treatment to the mixture obtained after said step (ii).

11) Process for preparation of an abrasive material comprising abrasive elements on a support, said process comprising the following steps of: i) obtaining abrasive elements following a recovery process such as defined in claim 1; ii) depositing abrasive elements obtained after said step (i) on a support with a layer of a first binder; iii) applying a layer of a second binder, identical to or different from said first binder, on the support obtained after said step (ii).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] The single FIGURE shows a diagrammatic representation of the recovery and recycling process according to the present invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

[0086] I. Recovery Process According to the Invention.

[0087] With reference to the single FIGURE, the recovery process according to the invention applied to recycling of abrasive wheels comprises:

[0088] one or several crushing steps, depending on the size of the wheels to be recycled, to obtain fragments smaller than 5 cm;

[0089] an oxidation step with nitric acid at temperatures between ambient temperature and 150 C. with an aqueous solution containing 20 to 98% of nitric acid and 0 to 75% of sulphuric acid; and

[0090] a recycling step of the solvent in the form of nitrogen oxides and a mixture of used acids that can contain organic compounds (resin degradation products) and inorganic compounds (dissolved inorganic fillers).

[0091] II. Examples of the use of a Recovery Process According to the Invention.

[0092] Different types of abrasive materials with a phenol-formaldehyde type resin were recycled using this approach. The abrasive fillers of the different tested materials, the operating conditions and the results of these tests are listed in Table 1 below. Note that compositions in this table are given as a percentage by mass.

TABLE-US-00001 TABLE 1 Examples of recycled materials, operating conditions and performances. Loss of mass Solvent (%) composition Mass of Mass of (complement to recovered Abrasive added Solvent Reaction 100% in the form material M Depolymerisation material (M) material M volume temperature of water) (g) yield Brown 10.01 g 60 mL 130 C. under 68% HNO.sub.3 33% 99.9% corundum reflux - 2 h 6.71 g Brown 10.14 g 18 mL 130 C. under 68% HNO.sub.3 27% 69% corundum reflux - 2 h 7.36 g Brown 10.01 g 30 mL 130 C. under 68% HNO.sub.3 32% 91% corundum reflux - 2 h 6.77 g Brown 9.97 g 46 mL 130 C. under 68% HNO.sub.3 34% 99.9% corundum reflux - 2 h 6.58 g Brown 10.60 g 60 mL 130 C. under 68% HNO.sub.3 33% 99.8% corundum reflux - 5 h 7.05 g Brown 9.95 g 60 mL 130 C. under 68% HNO.sub.3 29% 99.2% corundum reflux - 2 h 7.08 g Brown 10.40 g 55 mL 130 C. under 34% HNO.sub.3 20% 40% corundum reflux - 2 h 8.29 g Brown 10.04 g 60 mL 130 C. under 23% HNO.sub.3 28% 75% corundum reflux - 2 h 33% H.sub.2SO.sub.4 7.27 g Brown 972 g 3500 mL 90 C. 68% HNO.sub.3 27% 99.9% corundum 710 g Sintered bauxite 13.02 g 53 mL 130 C. under 68% HNO.sub.3 24% reflux Mixture of solgel 515 g 750 mL 77 C. 68% HNO.sub.3 15% 99.9% alumina, alumina balls and violet corundum Sol - gel 0.98 kg 1250 mL 80-85 C. 68% HNO.sub.3 39% 99.9% alumina Cold-pressed 9.48 g 30 mL 130 C. under 68% HNO.sub.3 11% 99.93% sol gel reflux alumina Sintered alumina 14.96 g 40 mL 130 C. under 68% HNO.sub.3 33% reflux Violet corundums 146 g 500 mL 90 C. 68% HNO.sub.3 45% 99.86% 80.6 g

[0093] III. Comparison of Performances of Products Fabricated from New Grains and Grains Recycled using the Process According to the Invention.

[0094] Comparative cutting tests were performed to quantify the impact of recycling on cutting properties of abrasive grains.

[0095] Thus, ten cutting disks were fabricated based on brown corundums. Five were put to one side, the other five were recycled using the process according to the invention.

[0096] The composition of collected/recycled corundum grains were firstly compared with non-recycled grains (Table 2).

[0097] The recycled grains were then used to make five disks, using the same method as for the first disks. The ten disks were then used for cutting tests on stainless steel parts, and the results of these tests are given in Table 3 below.

TABLE-US-00002 TABLE 2 Composition of brown corundums that have and have not been recycled Name Original corundum grains Recycled corundum grains Al.sub.2O.sub.3 97.6 98.0 SiO.sub.2 0.49 0.31 Fe.sub.2O.sub.3 0.20 0.16 TiO.sub.2 1.60 1.48 CaO 0.05 0.00 MgO 0.00 0.00 K.sub.2O 0.00 0.00 Na.sub.2O 0.00 0.00 P.sub.2O.sub.5 0.01 0.01 Cr.sub.2O.sub.3 0.00 0.00 MnO 0.00 0.00 ZrO.sub.2 0.16 0.15 C 0.18 0.07 S 0.04 0.04 LOI 0.10 0.06 sum [% by 100.00 100.00 mass]

TABLE-US-00003 TABLE 3 Results of comparative cutting tests Recycled abrasive Disks New abrasive elements elements Initial diameter (mm) 176.88 176.76 Final diameter (mm) 173.73 173.88 Wear (mm) 3.15 2.88 Wear area (cm.sup.2) 8.67 7.95 Cutting area (cm.sup.2) 3.13 3.13 Number of cuts 20 20 Total cut area (cm.sup.2) 62.52 62.52 G-Ratio 7.30 7.26 Feed rate (cm.sup.2/s) 1.12 1.12 Power (mA) 17.12 17.73 Performance (%) 100.0 99.4

[0098] FX analyses show that there is no significant difference in the composition between grains recycled using the method according to the invention and grains that have not been recycled.

[0099] Furthermore, comparative cutting tests show that performances of cutting disks fabricated from recycled corundum grains are similar to performances of grains fabricated from new corundums, and particularly the difference in G-ratios, defined as the ratio between the volume removed to the abrasive volume used is less than 1%.

REFERENCES

[0100] [1] Patent application U.S. 2003/032384 in the name of Noritake Co., Limited published on Feb. 23, 2003;

[0101] [2] International application WO 96/20070 in the name of Schleifmittel-Werk Karl-Seiffert GmbH & Co. published on Jul. 4, 1996;

[0102] [3] International application WO 2011/092021 in the name of Gottfried Wilhem Leibniz Universitat Hannover published on Aug. 4, 2011;