AU1502601A - A process for surface cleaning - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant: SURFACE RESTORATION TECHNOLOGIES PTY LTD Invention Title: A PROCESS FOR SURFACE CLEANING The following statement is a full description of this invention, including the best method of performing it known to me/us: 0 0.

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0000 0 2 A PROCESS FOR SURFACE CLEANING Field of the Invention The present invention relates to a process for cleaning a surface. In one form the invention relates to a process for the projection of airborne particles onto a surface such as timber or stone masonry for the purposes of abrasive cleaning and will primarily be described with reference to this context. It should be appreciated, however, that the invention has broader use in the cleaning and scouring of all manner of surfaces, for example metals, glass or synthetic materials such as plastics, and using any source of gas or compressed gas.

Background Art Methods and apparatus are known in the art for the projection of airborne particles onto a surface for cleaning of that surface. Techniques such as sand blasting can provide removal of surface deposits such as paint, graffiti, rust and the like in order to provide surface or o metal finishing.

20 Apparatus is known in the art to accomplish surface cleaning by dry particle projection in a jet of air onto a surface for example US5718581 and W091/15336. A limited variety of materials are disclosed in the art to act as dry abrasives in order to accomplish surface cleaning when projected in a jet of air onto a surface. In •DE4003324 silica glass pellets of a size less than 250 micrometres are used to clean stone surfaces. In US5718581 and W091/15336 the dry materials used, respectively, are .:oo alumina and silica between 20 and 200 micrometres in size, and sodium bicarbonate (50-1000 micrometre size range with mean size 250-300 micrometre) When using the known apparatus and abrasive materials, the process of surface cleaning can physically damage the appearance and structure of the substrate surface and the cleaning efficiency is limited.

3 Summary of the Invention The present invention in a first aspect provides a process for the abrasive cleaning of a surface including the steps of: dry fluidising organic particulate media using a gas; and directing the fluidised particulate/gas mixture to the surface.

Typically the process operator controls the gas flow rate and pressure and selection of organic media to produce a desired level of cleaning of the surface. When the term particulate is used it refers to any shape of individual or aggregated particles or granules. Many organic materials have the added benefit that they may clean without abrasion.

Typically the surface substrate material is wood, timber, masonry, concrete, stone, metal or fibreglass.

Preferably the organic media has a Moh's hardness of ""less than 5.0 and a particulate diameter size of less than S 20 500 micrometers.

Preferably the organic media includes walnut or apricot shells, grain husks, wheat, rice and/or rice hulls, sugar, seeds, grains and the like or a combination thereof.

Preferably the gas is pressurised and is typically air supplied at a pressure of 10 to 150psi.

*oeIn a second aspect the present invention provides a process for the stagewise abrasive cleaning of a surface including the steps of: dry fluidising non-organic particulate media using a gas; directing the so fluidised non-organic particulate/gas mixture to the surface; followed by the steps of: dry fluidising organic particulate media using a gas; and directing the so fluidised organic particulate/gas 4 mixture to the surface.

Typically the surface substrate material is wood, timber, masonry, concrete, stone, metal or fibreglass.

Preferably the organic media has a Moh's hardness of less than 5.0 and a particulate diameter size of less than 500 micrometers.

Preferably the organic media includes walnut or apricot shells, grain husks, wheat, rice and/or rice hulls, sugar, seeds, grains and the like or a combination thereof.

Preferably the non-organic media of the second aspect includes visy glass and/or limestone abgrit or a combination thereof.

Preferably the gas is pressurised and is typically air supplied at a pressure of 10 to 150psi.

Brief Description of the Drawing Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which Figure 1 shows a schematic flow diagram of a preferred apparatus and process for cleaning a surface in accordance with the present invention.

Modes for Carrying out the Invention Referring to Figure i, a process and apparatus is depicted for the abrasive cleaning of a surface 8 by dry S•fluidising organic particulate media using a pressurised gas to direct the fluidised particulate/gas mixture toward the surface 8. A compressor or compressed air source 10 is arranged to deliver pressurised gas, usually air, via a pressure line 12 to a filter and regulator 14 and thence via a further pressure line 16 into a gun or nozzle delivery device 18. The nozzle typically has an adjustable action mechanism for operator control of the fluidised particulate/gas mixture. The gun or nozzle delivery device 18 is also connected to a reservoir 20 containing dry organic particulate materials via connection hose 22 which 5 facilitates the suction-induced transfer of the feed particulates into the gun delivery device 18. Reservoir can also be connected directly or via a connection hose to pressure line 16 as an alternate means of providing a suction induction of feed particles into the gas stream.

A valve 24 can be arranged for manual or automatic control of the flowrate of the dry particulate feed from the reservoir 20. The air filter and regulator 14 can be arranged for manual or automatic adjustment and control of the air flow from the compressor or compressed air source while also facilitating the removal of any moisture from the compressed gas.

The gun or nozzle delivery device 18 typically provides operator control of the direction, velocity and intensity of the flow of the fluidised particulate/gas mixture. In use, the process operator typically makes a considered assessment of the surface to be cleaned and selects a gas flow and pressure combined with a type of abrasive material to suit the cleaning application. A .o 20 considerable degree of operator knowledge is required, as illustrated by the following examples.

Step 1 Materials selection Typically the particle size of the chosen materials is preferably less than 500 micrometres in diameter; even more preferable is a situation where the majority of the particles are less than 250 micrometres in diameter.

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Particles larger in diameter than 500 micrometres are often poorly suspended by a jet of low pressure gas.

For cleaning soft woods such as interior woodwork (skirting boards or window frames), a relatively soft abrasive made of organic materials such as walnut or apricot shell can be used. Apricot shell is softer than walnut shell and can be used in the most delicate applications. These soft abrasives allow removal of one or more layers of paint on such boards without removing the shellac finish of the timber.

6 For cleaning any painted wood or stone surface, use can be made of a relatively harder abrasive substances such as limestone abgrit which removes the paint layers and also any layers of shellac on old timbers.

For cleaning grime or dirt from brick, mortar, sandstone, stone masonry and other non-painted surfaces, the operator can use visy (silica free glass) to clean the surface without defacing the substrate.

For cleaning concrete and fibreglass for cleaning barnacles, molluscs, algae, moss and other buildup on marine structures such as boat hulls, pylons, marine vessels, wharves etc) walnut and apricot shell have been found to be suitable.

Alternative soft organic particulate materials that can be used and which fall within the scope of the invention include grain husks, wheat, rice and/or rice hulls, sugar crystals, seeds, grains and the like.

Generally these soft abrasives function in a similar ""fashion and as substitutes for walnut shell or apricot o* S 20 shell. Generally the selected organic media has a Moh's hardness index of less than 5.0. Combinations of organic material may be used in particular cleaning applications if the situation so requires.

Step 2 Pressure selection When using soft abrasives made of organic materials such as walnut shell for cleaning soft woods or skirting boards, a typical operating air pressure is 95-110psi. In a case when softer apricot shell is used for the same cleaning application, a higher operating air pressure can be used to increase particle velocity to compensate for the softer abrasive nature of the apricot shell. In treating various types of timber, for example western red ochre and cedar, 95psi is a typical pressure for using walnut shell to remove paint layers. However, in treating a softer timber such as oregon wood with a walnut shell abrasive, a pressure of 60psi is preferred, as oregon has an 7 alternating grain made of hard and very soft material.

When using harder, non-organic abrasive substances such as limestone abgrit for cleaning any painted surfaces, a typical operating air pressure is 130-140psi.

For cleaning brick, mortar, sandstone, stone masonry and other non-painted surfaces using the relatively more abrasive visy glass, the pressure range of use is typically 60-140psi depending on the surface, most typically being 120-125psi for stone masonry and brick. However, if a discoloured old brick wall requires cleaning, a low pressure around 60psi is preferred when using such a nonorganic abrasive so as not to damage the substrate mortar or any sandstone bricks, which are relatively soft materials.

More than one abrasive material can be applied sequentially to the substrate surface being cleaned. For example, to clean a dirty sandstone wall, the less expensive and softer limestone abgrit can first be applied and, when a substantial surface cleaning has occurred, the 20 more expensive and harder visy glass abrasive can be utilised at a low pressure to more effectively clean the more resistant remaining coating from the surface without damaging the surface or mortar. If the visy glass was solely used first, rather than after the abgrit, the sandstone surface and the mortar may be damaged during an extended period of cleaning with the relatively harsher abrasive, and the operation can also prove to be more costly in terms of consumable materials. Combinations of non-organic material may be used in particular cleaning 30 applications if the situation so requires. A further and final 'polishing' of the surface can also then be conducted using the relatively softer organic particulate materials such as walnut shell to clean delicate mortar regions or portions of old bricks.

Advantages The advantages of the invention over the prior art are 8 many. The method of the invention concerns only a dry surface treatment process which is important when dealing with older timber and interior surfaces in homes or heritage buildings which cannot withstand moisture. Some abrasives from the prior art such as sodium bicarbonate are only suitable as abrasives when suspended or partially solubilised in water. Known surface cleaning techniques involving dry blasting particles onto a surface by means of pressurised air operate at typical pressures of 30-150psi.

Wet blasting processes normally operate with pressurised stream pressures typically up to an order of magnitude higher than this, which is unsuitable for many delicate surfaces.

The present invention does not utilise common industrial purpose harsh 'sand-blasting' abrasives such as garnet, beach sand or ilmenite, which are both damaging to sensitive substrates and dangerous where they contain other fine particulates. Sources of garnet frequently contain fine arsenic or lead particles and beach sand contains fine S 20 silica. Airborne fine silica is a known cause of lung disease in humans. For such materials to be used as surface abrasives, the process must be wet to control the dust so generated.

The superiority of a gentle and adjustable surface cleaning process means that the interiors of heritage buildings may be restored without resorting to removing glass from window panes or damaging the delicate surfaces of old timbers. The process can be conducted in multiple cleaning stages using various combinations of steps involving different abrasives (both organic and nonorganic), gas pressures and gas flows to achieve the desired effect.

In preferred embodiments, a dry surface cleaning process can provide improved rates of cleaning of delicate wooden or stone surfaces at a lower cost without the water damage associated with prior art, while preserving the 9 physical structure and appearance of the substrate material surface.

It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms a part of the common general knowledge in the art, in Australia or any other country.

Whilst the invention has been described with reference to a number of preferred embodiments it should be appreciated that the invention can be embodied in many other forms.

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Claims (14)

1. A process for the abrasive cleaning of a surface including the steps of: dry fluidising organic particulate media using a gas; and directing the fluidised particulate/gas mixture to the surface.

2. A process as claimed in claim 1 wherein the surface substrate material is wood, timber, masonry, concrete, stone, metal or fibreglass.

3. A process as claimed in claim 1 or claim 2 wherein the organic media has a Moh's hardness of less than and a particulate diameter of less than 500 micrometers.

4. A process as claimed in claim 3 wherein the organic media includes walnut or apricot shells, grain husks, wheat, rice and/or rice hulls, sugar, seeds, grains and the like or a combination thereof.

A process as claimed in any one of the preceding S 20 claims wherein the gas is pressurised and is supplied at a pressure of 10 to 150psi.

6. A process as claimed in any one of the preceding claims wherein the gas is air.

A process for the stagewise abrasive cleaning of a surface including the steps of: dry fluidising non-organic particulate media using a gas; directing the so fluidised non-organic ~particulate/gas mixture to the surface; a followed by the steps of: dry fluidising organic particulate media using a gas; and directing the so fluidised organic particulate/gas mixture to the surface.

8. A process as claimed in claim 7 wherein the surface substrate material is wood, timber, masonry, concrete, 11 stone, metal or fibreglass.

9. A process as claimed in claim 7 or claim 8 wherein the organic media has a Moh's hardness of less than and a particulate diameter of less than 500 micrometers.

A process as claimed in claim 9 wherein the organic media includes walnut or apricot shells, grain husks, wheat, rice and/or rice hulls, sugar, seeds, grains and the like or a combination thereof.

11. A process as claimed in any one of claims 7 to wherein the non-organic media includes visy glass and/or limestone abgrit or a combination thereof.

12. A process as claimed in any one of claims 7 to 11 wherein the gas is pressurised and is supplied at a pressure of 10 to 150psi.

13. A process as claimed in any one of claims 7 to 12 wherein the gas is air.

14. A process for the abrasive cleaning of a surface as herein described with reference to the accompanying 20 drawings and examples. oeooi •Dated this 17th day of January 2001 SURFACE RESTORATION TECHNOLOGIES PTY LTD By its Patent Attorneys GIFTHA GRIFFITH HACK ae o