DE2739286C3 - Silica sand or slag blasting abrasives and process for their manufacture - Google Patents

Description

Rotary furnace 7 and when hot air is blown in, after silicon dioxide sand has been fed via conveyor belt 6 to rotary furnace 7 through a chute 19, the silicon dioxide sand is repeatedly exposed to the action of the agitator blades 18.By these lift the sand and let it fall again, the sand comes in Contact with the hot gas, whereby the coating of thermosetting resin on the particles of silica sand becomes insoluble and infusible. The silicon dioxide sand flowing over the agitator blades 18 inside the rotary kiln is conveyed by rotation and inclined arrangement of the rotary kiln 7 to its exit, where the sand finally flows out through the outlet openings 8. 2 vibratory conveyor 30 shown instead of the rotary kiln 7, which is shown in FIG. 1 can be used as a circulating and conveying device. The vibratory conveyor 30 is supported on springs 32 and is made to vibrate by the vibrating device 33, for example by an eccentric motor. Associated with it is an infrared radiator 31, which is attached above. 1 is fed and vibrated and transported on the vibratory conveyor 30, it is heated by the infrared heater 31 and the thermosetting resin coating becomes insoluble and infusible. Returning to FIG. 1, the silicon dioxide sand particles that come from the rotary kiln 7 are collected in a chute at the lower end 20 of a bucket elevator. The particles collected in this way are then conveyed with the bucket elevator 21, which is operated by the motor 22, into a container 24 which is located in a classification tower 23. A sieve 25 with the desired sieve size and a vibrating device 26 is provided diagonally below the container 24. At 27 springs for supporting the screen 25 are shown. The particles which pass the vibrating screen 25 are then fed to a conveying tank by means of a conveyor 28. At 29, a vacuum cleaner is known, which serves to suck cold air that flows into the Klassierturm 23 from the bottom and the silica sand, which has a temperature of about 110 ⁰ C on leaving the rotary kiln 7 and the swing conveyor 30, to about 80 ° to 50 ⁰ C cools. The time which the silicon dioxide sand needs to pass through the rotary kiln 7 or the vibratory conveyor 10 is suitably about 90 seconds. For the choice of any desired particle size of the silicon dioxide sand, several sieves with appropriate mesh sizes are available, which are used as required.

The thermosetting resins suitable for the invention include phenolic resins, urea resins, melamine resins, Polyester resins and alkyd resins. Resins which are commercially available under Name urea-furfuryl alcohol-formaldehyde resin and phenol-furfuryl alcohol-formaldehyde resin.

Curing catalysts which can be used are those of the phosphate type, such as aqueous'- 'et · ... gen of phosphoric acid (75% concentration) or of the sulfate type, such as an aqueous solution of sulfuric acid (50% concentration), be used.

The properties of the blasting agent according to the invention during blasting are shown below in examples shown, in comparison to a blasting sand of the usual type

(1) Result of the comparative experiment on the amount of dust

Blasting media used

Common silica sand

Silica sand resin coated according to the invention

Slag (common)

Slag resin coated according to

the invention

Amount of dust 361 mg / m ³

22 mg / m ³

13.2 mg / m ³

11.3 mg / m ³

The above result was achieved by measuring the amount of dust (in mg) per 1 m ³ at a distance of 11 m behind the test point at which the abrasive was blasted against the surface to be cleaned.

(2) Result of the comparative experiment with regard to the depth of penetration

Blasting media used Indentation depth Common silica sand 95 μΐη Resin-coated with silicon dioxide sand according to the invention 104 μΐη Slag (common) ΙΟΟμηι Slag resin-coated according to the invention 118μΐη

The above result was obtained by taking the average of twice blasting against one calculated cleaning surface.

(3) Result of the comparative experiment with regard to the particle size distribution

In Fig. 3 is the distribution of the particle size of a Silica sand and a similar silica sand which was resin-coated according to the invention, is shown, measuring before and after sandblasting. The particle size (in mm) was as The abscissa and the percentage are plotted as the ordinate. As the curve shows, the particle size distribution is the resin-coated silica sand (the product according to the invention) before use, as shown by curve I, such that the particle size range of 1.1 mm to 0.6 mm is 93.2% (13% + 54% + 26.2%). This proves that the particles are very uniform in size, while in the case of ordinary silica sand, as shown in curve II, the same particle size distribution 75.4% (6% + 32% + 36.7%), which indicates that a relatively large proportion of different particle sizes is present. One further examines the particle size distribution of the material after single use with regard to particle sizes of less than 0.3 mm, which is for a Reuse are suitable, so curve III shows that one in the invention 68.8% reuse of products, while common products, as indicated by curve IV only 39.6% are reusable. It can also be seen that the amount of dust (particles that are not are greater than 0.2 mm), which is determined after a single sandblasting, in the inventive Blasting media makes up 30.1% and the blasting media

of the prior art 38.9%.

In Fig. 4 the particle size distribution of slag (common type) and the same type of slag, but resin coated according to the invention, shown, measured in each case before and after one time Rays. The particle size (in mm) before blasting is given by curve! ' for the abrasives according to Invention indicated and by the curve II 'for the uncoated abrasives and the particle size (in mm) after the blasting is indicated by the curve III 'for the blasting media according to the invention and by the Curve IV shown for the usual abrasives. The abscissa gives the particle size and the ordinate the Percentage on. This graph shows that particles with a particle size of not less than 0.3 mm after single blasting, which can be reused, 73.5% (3% + 9.5% + 22.6% + 17.1%) make up for the blasting media according to the invention, and 60.5% (2.1% + 6.1% + 15.8% + 18.4%) for the common abrasives. It can also be seen that the amount of dust (particles smaller than 0.2 mm) that one finds after a single blasting, in which the blasting agent according to the invention accounts for 26%, while it amounts to 38.9% with the usual blasting media.

From the above test results it can be seen that according to Example (1) the blasting agent according to the invention produces an amount of dust that is significantly reduced compared to that of conventional, uncoated blasting media, and that in particular with silicon dioxide sand by the invention the amount of dust can be reduced to Vh of the usual value. This means that the invention Pollution is reduced and that working conditions are remarkably improved.

From example (2) it can be seen that a blasting agent coated with resin according to the invention has a penetration depth which is not very different, on the contrary, it is even larger than with conventional blasting media.

From example (3) it can be seen that the abrasive according to the invention has fewer cracks than the usual blasting media, so that as a result a larger proportion of the used or irradiated Material can be recovered for reuse.

For this purpose 3 sheets of drawings

Claims (4)

Patent claims: 1. Blasting media made of silicon dioxide sand or slag, characterized in that it is coated with a thermoset resin is provided. 2. Blasting agent according to claim 1, characterized in that the coating consists of 2 parts of resin and 1 part hardener to 100 parts blasting abrasive 3. Process for producing abrasive from silica sand or slag with a coating of a thermosetting resin according to claims 1 or 2 by mixing the blasting agent with the resin and subsequent curing, characterized in that the curing in takes place in a rotary kiln. 4. Process for producing abrasive from silica sand or slag with a coating of a thermosetting resin according to claims 1 or 2 by mixing the blasting agent with the resin and subsequent curing, characterized in that the curing on a vibratory conveyor under irradiation with infrared rays. The sandblasting devices used in sandblasting are designed to contain abrasive particles Blow against a surface to be cleaned, the impact being sufficient to remove rust and the like from the Effectively remove surface. Silica sand and slag are mainly used as sandblasting agents used. However, silica sand and slag are brittle and generally have many cracks on them Surfaces, so that they break into fine pieces when they hit the surface to be cleaned and generate a significant amount of dust. If you therefore do sandblasting in the open air makes, the entire environment is affected and the environment is polluted. Another one a significant problem is the health of workers who inhale such dust. From US-PS 31 55 466 it is known to reduce the cracking and brittleness of blasting media made from slag avoid by superficially sintering the slag particles. Such a method can of course Do not use on silica sand. The object of the invention is to ichaffen a blasting agent that is based on silicon dioxide sand or Slag has an increased strength when used. According to the invention, this is achieved in that the blasting agent is coated with a thermosetting coating, which has been made insoluble and infusible, is coated, thereby increasing the strength of the abrasive material, which may be silica sand or slag is increased. Especially with silica sand, which many Has cracks, the resin penetrates into the innermost points of these cracks and thereby increases the impact strength of silica sand. When blasting the blasting agent according to the invention against the surface to be cleaned, the through the Impact generated heat is absorbed and the coating of the thermoset resin continues hardened, which increases the cleaning effect even more will. F i g. 1 is a schematic view of an apparatus for producing blasting material according to a Embodiment of the invention. Fig. 2 is a schematic view of another Embodiment of the invention. 3 and 4 show particle size distributions in COMPARATIVE GRAPHIC DRAWINGS RESULTING FROM COMPARATIVE EXPERIMENTS IN ACCORDANCE WITH THE PRESENT INVENTION and the state of the art. The invention is explained below for silicon dioxide sand, it is in the same way for a Blasting abrasives made from slag can be used. Referring to FIG. 1, a material tank 1 containing silicon dioxide sand is arranged to supply the silicon dioxide sand to a metering tank 2 by opening an outlet flap 1 a attached to the lower part of the material tank 1. After a predetermined amount of silicon dioxide sand has been metered into the metering tank 2, the sand is fed to the mixer 3 arranged below the metering tank. In the mixer 3, a curing catalyst is also added in a predetermined proportion to a thermosetting resin which will be described later, and the silica sand and the curing catalyst are thoroughly mixed for about one minute, after which a thermosetting resin in a predetermined amount is added to the silica sand in the mixer 3 is added while hot air with 80 to 100 ⁰ C from a hot air blower 4 is blown into the mixer and mixed for about 5 minutes. As a result, the particles of silica sand are coated with a thermosetting resin with a certain thickness, which can be further hardened by a further heat treatment. The amounts of the thermosetting resin and the curing catalyst can vary depending on the properties of the Silica sand can be chosen. A common silica sand used for blasting will be z. B. 2 parts of thermosetting resin and 1 part of curing catalyst per 100 parts of the silica sand used. When using slag, similar proportions can be used. The silicon dioxide sand is then placed in the container 5 and flows from there onto a conveyor belt .6. which leads to a rotary kiln 7. With this arrangement, the supplied amount of Silicon dioxide sand to the rotary kiln 7 vary according to its capacity. At the exit of the rotary kiln 7 circumferential outlet openings 8 are provided at suitable intervals. At this end of the rotary kiln 7 hot gas or heated air of about 300 ° C is blown through a nozzle 10, the hot gas for Entrance of the rotary kiln flows and is finally let through a suction 9 into the atmosphere. It it is known that the rotary kiln has 7 ring gears 11 which are attached several times at suitable locations and that each ring gear 11 by a pair of rollers 12 is supported. As a result, the rotary kiln 7 is rotatably supported on a base 13. At 14 becomes a drive wheel shown, which is mounted on the circumference of the rotary kiln 7 and engages the gear 16, which with a Motor 15 is connected. At 17, support rollers are shown which prevent the rotary kiln 7 from accidentally moving into To slide in the direction of its tendency. The rotary kiln 7 is inside with a plurality of agitator blades 18, the extend from the entrance to the middle of the length of the rotary kiln 7, equipped. When rotating the