Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
  • B24C1/003—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods using material which dissolves or changes phase after the treatment, e.g. ice, CO2
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C5/00—Devices or accessories for generating abrasive blasts
  • B24C5/02—Blast guns, e.g. for generating high velocity abrasive fluid jets for cutting materials
  • B24C5/04—Nozzles therefor

Definitions

• This invention concerns a delivery device for cryosandblasting machines and the relative method for surface treatment, in particular in the sector of the historical buildings and artistic and architectural property.
• this invention which is part of the cryosandblasting research project for artistic restoration, proposes a new design of delivery device, able to optimise the spray of CO 2 from a cryosandblasting machine in the form of pellets.
• the innovation to the cryosandblasting system was suggested by the results of tests carried out during the previous stages of the project.
• the aim is, on one hand, to contain the abrasive effect which the cryosandblasting system has been shown to have on some types of stone, and on the other to improve the efficacy of removing the surface deposits from difficult materials for which the use of traditional equipment has not proved to be particularly efficient, with particular reference to the treatments for the restoration of surfaces of historical-artistic interest.
• the invention in question can be applied in the industrial sector which uses CO 2 technology for the treatment or cryosandblasting of surfaces, in particular in the cryosandblasting sector as an innovative method in the treatment of surfaces of historical-artistic interest.
• cryosandblasting is one of the techniques used for the abrasive treatment of surfaces, and it is also known that, in some cases, traditional sandblasting is replaced by so-called cryosandblasting, which instead of sand used solid state CO 2 in the form of pellets .
• cryosandblasting equipment or cryosandblasting machines, which use dry ice require a compressed air generator and a power supply.
• cryosandblasting machine in which the pellets are fed.
• the pellets and the carrier air are pushed into a first conduit, while high output compressed air is conveyed into a second conduit.
• the conduits are connected, at their other end with respect to the machine, to a spray gun, designed to receive the two conduits and to convey the jet towards the surface to be treated.
• a spray gun Inside the gun is a nozzle which joins the two air and CO 2 flows and directs them into the pipe positioned at the exit of the nozzle towards the exterior.
• the nozzle in turn consists of a cylindrical tubular element fitted with a flange with a plurality of axial holes, forming a single body.
• the tubular body and the holes in the flange are arranged, according to known concepts, in a coaxial direction.
• the pressurised gas is emitted in the same direction as the CO 2 pellets, so that they are accelerated with a rectilinear motion in the pipe at the delivery device exit (photo 1), reaching the surface of the material to be treated with a limited collision cross-section (around 2-3 cm with the gun held at a distance of 20-30 cm) .
• photo 1 a rectilinear motion in the pipe at the delivery device exit
• cryosandblasting used in the conventional way did not give the desired results, since during the tests carried out the treated surfaces were damaged due to the excessive violence of the jets emitted.
• This invention proposes to provide a delivery device for cryosandblasting machines and the relative surface treatment method that can eliminate or at least limit the problems described above.
• the invention also proposes to provide a delivery device for cryosandblasting machines and the relative surface treatment method that is easy to produce and carry out in such a way as to be extremely inexpensive to produce and carry out.
• the pressurised gas is emitted in the same direction as the CO 2 pellets, so that they are accelerated with a rectilinear motion in the pipe at the nozzle exit, reaching the surface of the material to be treated with a limited collision cross-section.
• the gas output holes in the new nozzles are inclined so as to form an angle with respect to the output direction axis.
• the dry ice pellets are thus subjected to a lateral acceleration causing the flow to perform a helical motion inside the pipe.
• the collision cross-section of the pellets with the treated material is therefore greater, when used at the same distance, with respect to a traditional nozzle, the angle of incidence also being modified.
• figure 1 represents a schematic view of equipment for cryosandblasting treatment
• figure 2 shows a schematic view of a cryosandblasting gun
• - figure 3 represents a schematic view of a first nozzle according to the invention in which the channels on the flange are inclined at 30° with respect to the output axis
• figure 4 represents a schematic view of a second nozzle according to the invention in which the channels on the flange are inclined at 15° with respect to the output axis
• figure 5 shows a schematic view of a nozzle with holes in line with the axis of the pipe
• - figure 6 shows a schematic view of a delivery device according to the invention
• figure 7 is a schematic view of one of the holes in the flange and its possible inclined axis shapes
• figure 8 shows a schematic view of a gun constructed according to the concepts on which the invention is based
• the delivery device 10 is used together with a cryosandblasting machine according to a scheme indicated in figure 1.
• cryosandblasting equipment therefore consists of a cryosandblasting machine 11, generally on wheels, connected to a power supply and a source of compressed air.
• the cryosandblasting machine 11 is designed to be supplied with CO 2 in pellet form which, together with the compressed air, passes through delivery conduits 12 and
• the two conduits 12 and 13 are connected to the couplings 14 and 15 on the rear part of the delivery device 10, which is also attached to a connecting cable 16.
• the delivery device 10 presents the classic shape of a spray gun and consists of a handgrip 17 positioned below a body 18 in which a nozzle 19 is housed.
• the body 18 is equipped with a pipe 20, or barrel, positioned at the exit of the nozzle 19 facing towards the exterior.
• the nozzle 19 presents a cylindrical tubular body 21, to which a flange 22 provided with a plurality of holes 23 is fitted, forming a single body.
• the high output compressed air flows through the holes in the flange 22, while the air carrying the CO 2 passes through the tubular body 21.
• the holes 23 in the flange 22, which according to known solutions are arranged coaxially, are according to the invention arranged with an inclined axis.
• the exit holes for the pressurised gas are inclined respectively at angles of 15° and 30°.
• the inclination of the exit holes 23 in the nozzle allows the dry ice pellets to be subjected to a lateral acceleration causing the flow to perform a helical motion inside the pipe 20.
• the collision cross-section of the pellets with the treated material is therefore greater, when used at the same distance, with respect to a traditional nozzle, the angle of incidence also being modified.
• the exit holes 23 of the nozzle present an average diameter of 7 mm.
• the diameter of the holes 23 is within a range of from 2 to 12 mm. , with a preference for the intermediate sizes.
• the use of a new extruder in the formation process has made it possible to reduce their dimensions, decreasing the diameter to 1.5 mm and the average length to 3 mm.
• the new smaller pellets will be identified with the letter "P", to distinguish them from the larger traditional ones which will instead be identified with the letter "G”.
• the tests were carried out to assess whether the introduction of the above modifications to the cryosandblasting system according to the invention can limit the surface abrasion demonstrated by the original system on some materials such as Vicenza stone, granite, Carrara marble and bricks .
• cleaning tests were also carried out on samples of Carrara marble, botticino limestone and Istria stone.
• the test methods used differ according to the type of stone considered and were also designed on the basis of the results obtained in previous abrasion tests.
• the surface morphology of the various samples was assessed before and after the cryosandblasting tests, using a laser profilometer. This makes it possible to obtain the three-dimensional mapping of the treated part and to calculate the average roughness (Ra) as a characteristic parameter.
• the efficacy of the system in removing surface dirt was, instead, evaluated by macro- and microscopic observation of the samples before and after the treatment.
• the treatment time and the distance between the gun and the surface were also maintained at constant values, respectively 30 seconds and 30 centimetres.
• the list of the granite test pieces and the treatment conditions is shown below.
• the surface profilometric measurements confirm what was observed macroscopically, as can be seen from the following table which shows the average roughness of the various samples before and after the treatment: a net reduction can be observed in average roughness after treatment when changing to smaller pellets, all the other treatment conditions remaining the same.
• the modified gas/pellet nozzles the type with holes inclined at 15° and 30°
• the variation in roughness with respect to before the treatment is even more limited, confirming the lower degree of damage to the sample.
• the test was also carried out on samples of Carrara marble.
• the previous tests performed using the traditional system had shown that, macroscopically, this type of stone can resist the cryosandblasting treatments sufficiently well; the profilometric analyses carried out on the material before and after the treatment had in any case shown a progressive reduction in surface roughness when the CO 2 output and compressed air pressure were decreased, confirming that, even if not visibly apparent, the material is slightly damaged.
• the aim of the tests carried out was to evaluate the modifications to the size of the pellets and to the cryosandblasting spraying system, assessing both the abrasive effect and the cleaning efficacy.
• the Istria stone sample characterised by the presence of stratifications of recrystalized calcite and a compact black surface crust, showed on the other hand a high degree of deterioration due to the breakage of the recrystalization layers, considerably more fragile than the more internal stone matrix.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Containers And Packaging Bodies Having A Special Means To Remove Contents (AREA)
• Pretreatment Of Seeds And Plants (AREA)
• Steroid Compounds (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Catching Or Destruction (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=38372433

Family Applications (1)

Country Status (4)

Families Citing this family (1)

Family Cites Families (7)

• 2006
  • 2006-05-02 IT IT000080A patent/ITVR20060080A1/it unknown
• 2007
  • 2007-04-30 WO PCT/IT2007/000317 patent/WO2007125565A1/fr active Application Filing
  • 2007-04-30 AT AT07736820T patent/ATE546257T1/de active
  • 2007-04-30 EP EP07736820A patent/EP2024137B1/fr not_active Not-in-force

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events