DE2739286B2 - Silica sand or slag blasting abrasives and process for their manufacture - Google Patents

Description

The sandblasting devices used in sandblasting are designed in such a way that they blow abrasive particles against a surface to be cleaned, whereby the impact is sufficient to effectively remove rust and the like from the surface. As a sandblasting agent Silica sand and slag are mainly used. Silica sand and slag are however brittle and generally have many cracks on the surfaces, so that they will hit the too Break the cleaning surface into fine pieces and generate a significant amount of dust. If " therefore, if the sandblast cleaning is carried out on the open air, 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 is known the crack 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 create a blasting agent 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 w 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

FIG. 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 graphical drawings resulting from comparative experiments according to the present invention and the prior 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 set up in such a way that it supplies the silicon dioxide sand to a metering tank 2 by opening an outlet flap 1 a which is 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 the curing catalyst are thoroughly mixed for about one minute, after which a thermosetting resin is added in a predetermined amount to the Siiysildioxidsand in the mixer 3, while hot air with 80 to 100 ⁰ C from a hot air blower 4 is blown into the mixer and about 5 minutes mixes. As a result, the particles of silicon dioxide sand are coated with a thermosetting resin with a certain thickness, which can be further hardened by further heat treatment.

The amounts of the thermosetting resin and the curing catalyst can vary depending on the properties of the Silica sand is chosen i. 3ei a common silicon dioxide sand used for blasting z. B. 2 parts of thermosetting resin and 1 part of hardening catalyst are used per 100 parts of the silica sand. 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 amount of silicon dioxide sand supplied to the rotary kiln 7 can be varied in accordance with its capacity. At the exit of the rotary kiln 7 there are peripheral outlet openings 8 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 flowing to the entrance of the rotary kiln and finally being discharged into the atmosphere through a suction device 9. It is known that the rotary kiln 7 has toothed rims 11 which are attached several times at suitable locations and that each toothed ring 11 is supported by a pair of rollers 12. As a result, the rotary kiln 7 is rotatably supported on a base 13. At 14 a drive wheel is shown which is mounted on the circumference of the rotary kiln 7 and engages in the gear wheel 16 which is connected to a motor 15. At 17 support rollers are shown which prevent the rotary kiln 7 from inadvertently sliding off in the direction of its inclination. The interior of the rotary kiln 7 is equipped with a plurality of agitator blades 18 which extend from the entrance to the middle of the length of the rotary kiln 7. When rotating the

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. As they lift and drop the sand, the sand comes into contact with the hot gas, making the thermosetting resin coating on the silica sand particles 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. In this connection it should be noted that the in FIG. 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 caused to vibrate by the vibrating device 33, for example by an eccentric moto. Associated with it is an infrared radiator 31, which is attached above. While the silicon dioxide sand, which is fed to the vibratory conveyor 30 by the conveyor belt 6 via the chute 19, as shown in FIG the infrared heater 31 is heated, 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 classifying tower 23. A sieve 25 with the desired sieve size and a vibrating device 26 is provided diagonally below the container 24. Shown at 27 are springs for supporting the screen 25. 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 below and the Siliziutndioxidsand having 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 30 is suitably about 90 seconds. For the selection of any particle sizes of the silicon dioxide sand, several sieves with corresponding 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.

As the curing catalyst, there can be used those of the phosphate type such as aqueous solutions of phosphoric acid (75% concentration) or of the sulfate type, such as an aqueous solution of sulfuric acid (50% concentration), be used. C.

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

(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 test with regard to the penetration depth

Reject. ietes abrasive Penetrating pedicles Common silica sand 95 μΐη Resin-coated with silicon dioxide sand according to the invention 104 μπι Slag (common) 100 μm Slag resin-coated according to the invention 118 μm

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 shows the particle size distribution of a silica sand and a similar silica sand resin-coated according to the invention, measured before and after sandblasting, respectively. The particle size (in mm) was plotted as the abscissa and the percentage as the ordinate. As the curve shows, the particle size distribution of the resin-coated silica sand (the product according to the invention) before use, as shown by curve I, is 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 conventional silica sand, as is shown in curve II, the same particle size distribution makes up 75.4% (6 ⁰ A + 32% + 36.7%), which indicates that there is a relatively large proportion of different particle sizes. If one further examines the particle size distribution of the material after a single use with regard to particle sizes of less than 0.3 mm, which are suitable for reuse, then curve III shows that at the products according to the invention can reuse 68.8%, while with the usual products, as indicated by curve IV, only 39.6% are reusable. It can also be seen that the amount of dust (particles not larger than 0.2 mm), which is detected after a single sandblasting, amounts to 30.1% for the blasting media according to the invention and for the blasting media

of the prior art 38.9%.

4 shows the particle size distribution of slag (conventional type) and the same type of slag, but resin-coated according to the invention, measured in each case before and after a single blasting. The particle size (in mm) before blasting is indicated by curve I 'for the blasting media according to the invention and by curve II' for the uncoated blasting media and the particle size (in mm) after blasting is indicated by curve III ' for the blasting media according to the invention and indicated by curve IV for the usual blasting media. The abscissa indicates the particle size and the ordinate the percentage. This graph shows that particles with a particle size of not less than 0.3 mm after a 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 usual blasting media. It can also be seen that the amount of dust (particles smaller than 0.2 mm) which is detected after a single blasting is 26% with the blasting agent according to the invention, while it is 38.9% with the conventional blasting agent .

From the above experimental results, it is seen that in accordance with Example (I) according to the invention produces the beam means a quantity of dust which is substantially reduced compared to the that, particularly when silica sand by the invention, the amount of dust on i / m of the usual conventional, uncoated abrasives, and Value can be reduced

in can. 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 Has. which is not very different, on the contrary, it is even larger than with conventional blasting media.

Finally, from example (3) it can be seen that the Blasting media according to the invention has fewer cracks than the usual blasting media, so that, as a result, a Greater proportion of the used or irradiated material can be recovered for one re-use.

For this purpose 3 sheets of drawings

Claims (4)

Patent claims: 1. Blasting media made of silicon dioxide sand or Schlakke, characterized in that it is with is provided with a cover made of a thermosetting resin 2. Blasting agent according to claim 1, characterized characterized in that the coating consists of 2 parts of resin and I part hardener consists of 100 parts blasting agent, ι ο 3. A method for producing blasting media from silicon dioxide sand or slag with a coating made from 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 takes place in a rotary kiln. 4. A method for producing blasting media from silicon dioxide 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 with irradiation Infrared rays takes place.