FI3912760T3

FI3912760T3 - Method for blasting with solid blasting agent

Info

Publication number: FI3912760T3
Application number: FIEP20175859.6T
Authority: FI
Inventors: Bernhard Neukam; Julian Neubacher; Hartmut Kremer; Michael Wimmer
Original assignee: Omya Int Ag
Priority date: 2020-05-20
Filing date: 2020-05-20
Publication date: 2024-01-10
Also published as: HRP20240011T1; PL3912760T3; DK3912760T3; EP3912760A1; HUE065115T2; ES2969079T3; EP3912760B1

Claims

1 20175859.6 METHOD FOR BLASTING WITH SOLID BLASTING AGENT FIELD OF THE INVENTION The present invention relates to a method according to the preamble of independent claim 1 for compressed air blasting using at least one solid blasting agent in order to treat at least one surface, in particular in order to clean the at least one surface from contamination.

STATE OF THE ART By means of compressed air blasting with a solid blasting agent, also known colloquially as “sandblasting”, surfaces can be cleaned from contamination such as rust, old paint, algae and the like, cf., for example, https://de.wikipedia.org/wiki/Sandstrahlen.

According to the state of the art, sand, blast furnace slag and melting chamber slag, glass granulate, corundum, edged cast steel, plastic granulate, nut shells, soda and dry ice can be deployed in a wide variety of fineness levels.

The blasting agent strikes the surface to be treated together with an air jet at a correspondingly high velocity.

Due to the abrasive effect of the striking blasting agent, the substances to be removed are loosened and transported away together with the air jet and the blasting agent.

Recirculation suction systems are often used to partially recover the blasting agent.

Such a method is known from US 2013/029563 A1, which is the closest state of the art.

In some applications, the high aggressiveness or high abrasive effect on the surface to be treated is disadvantageous.

An example of this are facades.

Modern facades are mostly well insulated - this helps to save energy, but causes dew to form on the facade, in particular in the transition period from day to night or vice versa, which in turn promotes biogenic growth.

After just a few years, well-insulated facades become unsightly surfaces on which algae thrive.

Historical buildings, all-wood and part-wood buildings as well as various facade systems also experience significant contamination and superficial weathering over the years, which must be removed periodically and as gently as possible.

While wet cleaning with chemicals causes lasting damage to the floor and facade, dry methods such as the sandblasting are too aggressive.

The problem mentioned is constantly becoming more important, as there is a

2 20175859.6 growing need for surface cleaning, not least due to environmental influences such as soot, nitrogen and sulphur compounds (caused by traffic, industry and house fires), but also bird droppings. The situation is particularly critical in the area of monument protection,

e.g., in the restoration of historical facades, where (“gentle”) methods that preserve the substance as much as possible are required. Finally, energy consumption during surface treatment using known methods is also a point that needs to be improved in line with current trends. OBJECT OF THE INVENTION It is therefore the object of the present invention to provide a method for compressed air blasting using a solid blasting agent that avoids the disadvantages described above. In particular, the cleaning of relatively sensitive surfaces, such as facades, is to be made possible without these surfaces being damaged. This object is achieved by a method for compressed air blasting with the features of claim 1. Advantageous embodiments with useful developments of the invention are specified in the dependent claims. PRESENTATION OF THE INVENTION The core of the present invention is the knowledge that the excessive aggressiveness or excessive abrasive effect on the surface to be treated in known methods can be attributed to excessively high velocities at which the blasting agents are blown onto the surface and ultimately strike there. In known methods, the velocities are in the range of 150 m/s and are necessary so that the compressed air can entrain and transport the blasting agents. In order to achieve lower velocities, lighter blasting agents are therefore provided according to the invention. Accordingly, in a method for compressed air blasting using at least one solid blasting agent in order to treat at least one surface, in particular in order to clean the at least one surface from contamination, it is provided according to the invention that at least one lightweight granulate with lightweight granulate particles is used as the at least one solid blasting agent, wherein the lightweight granulate particles have a hollow and/or foam-like structure. Such lightweight granulates are sufficiently light and have a correspondingly low bulk density, which allows

3 20175859.6 significantly lower velocities of the lightweight granulate particles compared to known blasting agents for compressed air blasting.

The resulting “softness” of the method according to the invention is not only contributed by the reduced exit or impact velocity of the lightweight granulate, but also by the lower mass or density of the blasting agent particles.

It should be noted that the use of lightweight granulate particles also takes into account the problem of energy consumption.

On the one hand, the comparatively lighter blasting material saves significant energy when transporting it to the place of use due to its lower transport weight.

On the other hand, the energy consumption for accelerating and conveying the lightweight granulate particles during actual compressed air blasting is significantly lower than in known methods with known blasting agents.

The treatment of the at least one surface does not necessarily have to be cleaning.

Alternatively or additionally, other effects can also be achieved, for example, a change in the roughness of the surface by forming (also referred to as "surface finishing blasting")

or a change in the property of a layer of material arranged in the area of the surface that includes the surface (also referred to as "solidification blasting").

Either a single type of lightweight granulates or several lightweight granulates of different types together can be used.

In a preferred embodiment of the method according to the invention, it is provided that the at least one lightweight granulate comprises at least one expanded, in particular closed-cell expanded, perlite sand and/or at least one expanded glass and/or at least one glass foam granulate and/or fly ash cenospheres and/or synthetic hollow glass spheres.

These lightweight granulates are sufficiently light.

Ba means of the different lightweight granulates, a large range of diameters smaller than 2 mm, in particular smaller than 500 pm, can further be covered.

Expanded perlite sand (cf., e.g., EP 2697181 B1) and expanded glass (cf., e.g., EP 2708517 B1) prove to be particularly advantageous because their surface properties, in particular closed-cell structure, can be selectively adjusted, which in turn affects the mechanical properties, in particular the compressive strength, of the expanded particles.

It has recently been shown that the bulk density of closed-cell expanded perlite sand can also be selectively adjusted, which represents a further special advantage of this lightweight granulate and enables almost optimal adaptation to different applications.

The compressive strength of the lightweight granulate is proportional to its bulk density.

4 20175859.6

In principle, the density and/or compressive strength of synthetic hollow glass spheres can also be varied but the size range is very limited, in particular to diameters smaller than 125 um.

Moreover, synthetic hollow glass spheres are significantly more expensive than expanded perlite sand.

In accordance with what has been said above, in a preferred embodiment of the method according to the invention, it is provided that the lightweight granulate has a bulk density of less than or equal to 500 g/l, preferably in the range from 30 g/l to 300 g/l, most preferably in the range of 150 g/l to 200 g/l.

Moreover, the surfaces to be treated are protected in that, preferably by choosing the appropriate bulk density, the compressive strength of the lightweight granulate particles is sufficiently small, in particular lower in comparison to known blasting agents.

This means that even if the velocity of the lightweight granulate particles is chosen to be higher than optimal, damage to the surface to be treated can be largely avoided, since in this case the kinetic energy is reduced by destroying the lightweight granulate particles, virtually as security.

Accordingly, in a preferred embodiment of the method according to the invention, it is provided that the lightweight granulate has a compressive strength of less than or equal to 7 N/mm”. In principle, an optimal particle size can be found for every application.

In a preferred embodiment of the method according to the invention it is provided that the lightweight granulate particles have a particle size of less than or egual to 600 pm, preferably a particle size in the range from 100 um to 550 um, most preferably a particle size in the range from 100 um to 400 um.

It has been shown that by this choice a wide range of applications can be covered.

In a preferred embodiment of the method according to the invention it is provided that compressed air with an overpressure in the range from 2 bar to 4 bar, preferably from 2.5 kar to 3.5 bar, is used.

By this choice of the overpressure of the compressed air, sufficiently low velocities can be achieved for the lightweight granulate particles, which are entrained and transported by the compressed air.

This is accompanied by savings in both compressed air and blasting agent, i.e., in lightweight granulate.

In comparison, the overpressure in known methods is in the range of 6 bar.

As said, in the method according to the invention, sufficiently low velocities of the lightweight granulate particles can be achieved during compressed air blasting, which are significantly lower than in known methods.

Accordingly, in a preferred embodiment of

20175859.6 the method according to the invention, it is provided that the lightweight granulate particles have a velocity in the range from 90 m/s to 130 m/s, preferably from 99 m/s to 121 m/s.

According to the invention, it is provided that at least the lightweight granulate 5 particles are suctioned off and recycled after they have struck the at least one surface.

This means that at least a large part of the lightweight granulate particles can be reused, in particular if the bulk density is chosen correctly, which protects the environment and saves costs.

After the lightweight granulate particles have struck the surface, a material stream is generally suctioned off.

In addition to air, this material stream can, optimally, predominantly comprise undestroyed lightweight granulate particles, i.e., lightweight granulate particles that have not been destroyed upon impact.

Further, the material stream can optimally comprise only a few crushed lightweight granulate particles, i.e., lightweight granulate particles that have been destroyed due to the impact on the surface.

Finally, the material stream can also comprise material that has been removed (by the lightweight granulate particles), for example, contamination particles detached from the surface.

Due to the relatively low velocities of the lightweight granulate particles, the proportion of undestroyed lightweight granulate particles in the material stream can be kept very high, which makes recycling economical.

In addition, as mentioned above, the compressive strength of the lightweight granulate can be selected or adjusted accordingly, so that the proportion of undestroyed, recyclable lightweight granulate particles is further increased.

Depending on the sensitivity of the surface to be treated, in particular to be cleaned, the lightweight granulate, in particular with regard to its density, should preferably be chosen so that a maximum of 10%, preferably a maximum of 5%, of the lightweight granulate particles are destroyed during the compressed air blasting in order to achieve a good recycling rate while ensuring treatment success.

It has been shown that lightweight granulate particles made from closed-cell expanded perlite sand are particularly suitable for recycling, as they can be specifically matched to the surface to be treated, particularly with regard to compressive strength and bulk density, so that during compressed air blasting or treating the surface only an extremely small proportion of the lightweight granulate particles is destroyed.

6 20175859.6

In a particularly preferred embodiment of the method according to the invention, it is provided that recycling is carried out by means of at least one cyclone, wherein crushed lightweight granulate particles are separated as waste by means of at least one downstream filter.

This means that the material stream is separated in the cyclone essentially into a first fraction with the crushed lightweight granulate particles - in particular pure gas with the crushed lightweight granulate particles - and a second fraction with the undestroyed lightweight granulate particles and, optionally, the removed material.

For reuse, the lightweight granulate particles from the second fraction can be processed or other substances (in particular removed material) can be separated from the second fraction, for example, using a sieve.

The filter is arranged downstream of the cyclone, particularly on its clean gas side.

It should be noted that in the case of perlite sands, the crushed lightweight granulate particles or the crushed perlite sand particles can be further used, for example,

as a fertilizer, which represents a further advantage of using perlite sands in the method according to the invention.

In addition, the material can be disposed of practically anywhere as non-hazardous waste.

Analogous to what was said above, in a device for compressed air blasting using at least one solid blasting agent in order to treat at least one surface, in particular to clean the at least one surface from contamination, it is optionally provided that the device is configured to perform a method according to the invention.

To ensure sufficiently low velocities of the lightweight granulate particles, analogous to what was said above, in a preferred embodiment of the device it is provided that at least one overpressure means, in particular at least one compressor, is provided to provide compressed air with an overpressure in the range from 2 bar to 4 bar, preferably from 2.5 bar to 3.5 bar, in order to use the compressed air to accelerate the lightweight granulate particles to a velocity in the range of 90 m/s to 130 m/s, preferably from 99 m/s to 121 m/s.

Of course, other known overpressure means, such as compressed air reservoirs,

can also be provided alternatively or additionally.

At the velocity, the lightweight granulate particles together with the compressed air typically emerge from a nozzle in the direction of the surface to be treated and subsequently strike the surface at essentially this or approximately this velocity.

More

7 20175859.6 precisely, the lightweight granulate particles emerge from the nozzle at an exit velocity (to which they are accelerated by the compressed air) and strike the surface at an impact velocity.

How much the impact velocity differs from the exit velocity essentially depends on the distance between the nozzle and the surface, wherein the velocity of the lightweight granulate particles decreases as the distance increases due to air resistance.

In order to make the recycling described above possible in principle, in a preferred embodiment of the device it is provided that at least one suction head is provided in order to suction off at least the lightweight granulate particles after they have struck the at least one surface.

That means, the suction head serves to suction off the material stream mentioned above, which includes at least the lightweight granulate particles.

In order to recover undestroyed lightweight granulate particles from the material stream so that they can be used again for compressed air blasting, analogous to what was said above, in a particularly preferred embodiment of the device it is provided that at least one cyclone arranged downstream of the at least one suction head and at least one filter arranged downstream of the at least one cyclone are provided to recycle the lightweight granulate particles and to separate crushed lightweight granulate particles as waste.

According to what has been said above, for example, a sieve can be provided in order to separate other substances (in particular removed material) from the fraction provided by the cyclone which contains the lightweight granulate particles not crushed

Analogous to what was said above, a system comprising the device and the at least one lightweight granulate is optionally provided.

Analogous to what was said above, in a preferred embodiment of the system it is provided that the at least one lightweight granulate comprises at least one expanded, in particular closed-cell expanded, perlite sand and/or at least one expanded glass and/or at least one glass foam granulate and/or fly ash cenospheres and/or synthetic hollow glass spheres.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be explained in more detail using an exemplary embodiment.

The drawings are exemplary and are intended to demonstrate the idea of the invention, but are in no way intended to restrict or even exhaustively represent it.

It shows:

8 20175859.6

Fig. 1 a flow diagram of an embodiment of a method according to the invention

Fig. 2 a detailed view of a suction head of Fig. 1

Fig. 3 a detailed view of a material stream of Fig. 2 MODES FOR CARRYING OUT THE INVENTION

Fig. 1 shows a flow diagram of an embodiment of a method according to the invention for compressed air blasting using at least one solid blasting agent in order to treat at least one surface 2, in particular in order to clean the at least one surface 2 from contamination 3 (cf., Fig. 2), wherein at least one lightweight granulate with lightweight granulate particles is used as the at least one solid blasting agent, wherein the lightweight granulate particles have a hollow and/or foam-like structure. In the exemplary embodiment shown, the lightweight granulate particles are closed-cell expanded perlite sand particles 1. Analogously, Fig. 1 illustrates an embodiment of a device for compressed air blasting using at least one solid blasting agent in order to treat the at least one surface 2, in particular in order to clean the at least one surface 2 from contamination 3, wherein the device is configured to perform the method according to the invention. Alternatively,

Fig. 1 illustrates an embodiment of a system comprising the device as well as the lightweight material granules with closed-cell expanded perlite sand particles 1. The expanded perlite sand particles 1 are fed to an injector 13 from a blasting agent container 12. The perlite sand particles 1 are mixed with compressed air 7 in the injector

13. The compressed air 7 is generated by means of a compressor 8, which sucks in air 18 from the environment, and, in the exemplary embodiment shown, has an overpressure of only approximately 3 bar. Due to the low density of the perlite sand particles 1, this overpressure is sufficient for the perlite sand particles 1 to be entrained by the compressed air 7 and transported to a nozzle 14 within a supply line 19. In the exemplary embodiment depicted, the bulk density of the expanded perlite sand particles 1 is less than or equal to 500 g/l. Not only does the compressed air 7 emerge from the nozzle 14, but the perlite sand particles 1 also emerge, wherein the perlite sand particles 1 have a - comparatively low - (exit) velocity of approximately 110 m/s. The perlite sand particles 1 subsequently hit the

9 20175859.6 surface 2 to be cleaned from contamination 3, wherein the nozzle 14 is directed towards the surface 2. Due to the relatively small distance between nozzle 14 and surface 2, an impact velocity at which the perlite sand particles 1 strike the surface 2 is only insignificantly lower than the exit velocity.

Due to the low velocity of the perlite sand particles 1, the surface 2 is not damaged.

At the same time, the contamination 3 can still be removed.

In the exemplary embodiment shown, the perlite sand particles 1 have a particle size of less than or equal to 600 um, which proves to be favourable for a wide range of applications.

In principle, depending on the application or depending on the sensitivity of the surface 2 to be treated, in particular based on empirical values, an optimal combination of bulk density and particle size/granulation can be selected.

In complex tests, particularly good results were achieved for cleaning of surfaces 2 on facades for a bulk density of the perlite sand particles 1 of approx. 150 g/l and a grain size of 150 um to 550 um or for a bulk density of approx. 200 g/l and a grain size of 100 um to 400 um.

As the bulk density decreases, the compressive strength of the perlite sand particles 1 also decreases.

In the exemplary embodiment shown, the compressive strength of the perlite sand particles 1 is less than or equal to 7 N/mm”. This ensures that even at higher velocities of the perlite sand particles 1, the surface 2 is not damaged, since in this case the kinetic energy is reduced by destroying the perlite sand particles 1 upon impact on the surface 2.

In the exemplary embodiment shown, the nozzle 14 is arranged within a suction head 9. During compressed air blasting, the suction head 9 is brought up to the surface 2 to be cleaned and can touch it with an edge, so that a cavity is delimited by the suction head 9 and the surface 2, in which cavity the treatment or cleaning process takes place.

The suction head 9 initially prevents the perlite sand particles 1 from being lost after their impact on the surface 2. Instead, these "used" perlite sand particles 1 are suctioned off from the suction head 9 through a suction-off line 20 opening into the suction head 9 by means of a fan 10.

As said, the perlite sand particles 1 striking the surface 2 remove or strip contamination 3 from the surface 2, so that removed material 22 is created.

This removed material 22 is suctioned off together with the “used” perlite sand particles 1. This means that a material stream 17, which, in addition to air, includes the “used” perlite sand

10 20175859.6 particles 1 and the removed material 22, is suctioned off through the suction-off line 20.

In the detailed view of Fig. 3 it can be seen that the material stream 17 contains not only undestroyed perlite sand particles 1, but also a certain, typically not completely unavoidable, proportion of perlite sand particles 6, which were crushed upon impact with the surface 2 and form correspondingly very small, very light particles that typically enclose no or only a small void volume.

In order to recover undestroyed perlite sand particles 1 for further use in compressed air blasting, the material stream 17 is first fed via the suction-off line 20 to a centrifugal separator in the form of a cyclone 4. On the clean gas side of the cyclone 4,

exhaust air 21 escapes together with the crushed perlite sand particles 6, wherein the latter are separated in a filter 5 arranged downstream of the cyclone 4 and then reach a waste container 15.

Due to their mass, the cyclone 4 separates the undestroyed perlite sand particles 1 and the removed material 22 from the exhaust air 21 together with the crushed perlite sand particles 6. By means of a downstream sieve 11, the undestroyed perlite sand particles 1 are separated from the typically significantly larger removed material 22. The removed material 22 is then also fed to the waste container 15.

The undestroyed perlite sand particles 1, on the other hand, are ready to be fed again to the injector 13 and reach the blasting agent container 12, which supplies the injector 13 with perlite sand particles 1.

In order to ensure that the injector 13 is always supplied with a sufficient number of perlite sand particles 1, a container 16 with fresh expanded perlite sand is further provided.

If necessary, perlite sand particles 1 can also be supplied to the blasting agent container 12 from this container 16.

REFERENCE NUMERAL LIST

1 Expanded perlite sand particles

2 Surface

3 Contamination

4 Cyclone

5 Filter

6 Crushed perlite sand particles

11 20175859.6 7 Compressed air 8 Compressor 9 Suction head 10 Fan 11 Sieve

12 Blasting agent container 13 Injector 14 — Nozzle 15 Waste container

16 Container with fresh expanded perlite sand 17 — Material stream 18 — Sucked-in air 19 — Supply line 20 — Suction-off line

21 — Exhaust air 22 — Removed material