Method and apparatus for removing coatings and oxides from substrates

A method and apparatus for removing coatings and oxides from substrates that includes a conveyor for moving a substrate in a first direction, at least one nozzle positioned away from the conveyor in position to direct the stream of fluid toward the conveyor and a high pressure fluid supply in fluid commination with the nozzle wherein the pressurized fluid supply is arranged to supply a pressurized fluid to exit the nozzle and direct the fluid at a high velocity to a surface of the substrate for removing a liquid or solid film from the substrate. The method includes providing a pressurized fluid to a stationary nozzle, directing the pressurized fluid from the nozzle in a high velocity fluid stream toward a moving object having a coating and contacting the fluid stream with the object whereby a force of the fluid removes the coating.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to cleaning of materials or parts using
 pressurized water where the nozzle or banks of nozzles are fixed with
 respect to a moving target or product.
 2. Description of the Prior Art
 Surface cleanliness, a key parameter in materials processing and
 manufacturing, significantly affects the quality of a product. Cleaning in
 the manufacturing environment has traditionally been carried out by many
 methods, but these generally break down into two categories: chemical and
 mechanical. Chemical methods have been popular in many industries,
 especially heavy industries, such as primary metals production, because of
 the thoroughness of the cleaning, high quality, high productivity and the
 low cost. Typical chemicals used in such cleaning processes are: water,
 acids, soaps, chlorofluorocarbon (CFC's), chlorinated hydrocarbons,
 aromatic hydrocarbons, and aliphatic hydrocarbons. Mechanical processes
 are typically used where the required surface quality is lower, or
 chemical processes are less convenient or less effective. Typical
 mechanical cleaning methods are: grit blasting, shot blasting, grinding,
 brushing and milling. The use of pressurized water for cleaning is a
 hybrid of the chemical process and the mechanical process. Specifically,
 water is in-itself a solvent and when sprayed at high pressures, it acts
 as an abrasive.
 The chemical cleaning methods, while still quite popular, have been waning
 due to environmental and health concerns. The Clean Air Act Amendments of
 1990, as well as other environmental legislation, have reduced the usage
 of some of the most effective chemicals, such as the volatile organic
 compounds (VOC's) and phosphate based detergents. The effect has been to
 send industry looking for the best alternative technologies. Currently
 used chemical cleaning methods, such as acid pickling of steel, tend to
 generate a vast quantity of waste that must be disposed of or recycled.
 And so, the advantages of superior quality and high productivity for
 chemical methods may soon be lost due to the overwhelming costs of
 environmental control and waste disposal.
 Pressurized water has been used in hot metal production lines.
 Specifically, during reheating of steel slabs and ingots for hot rolling,
 the metal reacts with the oxygen in the air to form a thick oxide scale.
 The scale, formed prior to hot rolling, is referred to as "primary scale".
 This flaky, porous scale is relatively thick and friable. Typically, it is
 0.040-0.050 inches thick. Primary scale is removed prior to hot rolling by
 a pressurized water descaler operating at pressures less than 3500 psi.
 The water exits the nozzles in a fan fashion. The nozzles are positioned
 at a distance, on the order of 6-12 inches, from the surface of the metal.
 Dispensed water contacts the primary scale, which tends to be somewhat
 exfoliated, and lifts it away from the metal. Water is also trapped in
 porous pockets in the scale. At these temperatures, on the order of 1600
 degrees Fahrenheit, steam forms quickly and the scale is also dislodged by
 the rapidly expanding steam.
 During cooling of the hot rolled steel, the oxygen in the air again reacts
 with the metal to form a much thinner and tighter oxide coating. This is
 referred to as "secondary" scale or post hot rolling scale. The secondary
 scale is on the order of 0.005 inches thick or less and is dense and
 uniform in nature. The above-described pressurized water system cannot
 remove the secondary scale. Therefore, abrasion and/or chemical methods
 such as pickling must be used. Pressurized water, i.e., water maintained
 at pressure above 20,000 psi (pounds per square inch) has been used for
 10-20 years in applications, such as rock drilling, stripping paint from
 bridges, metal cutting, cutting of fiber glass circuit boards, and cutting
 of lumber. More recently, pressurized water has been adapted to more
 refined applications, such as robotic stripping of paint from airplanes
 and ships, cleaning electronic circuit boards, CNC machining, cleaning and
 near net shape machining of metal and ceramic parts. In all these
 instances the work piece is held stationary and the nozzle, which supplies
 the high pressure water stream, moves relative to the target.
 Work has been carried out by Dr. David Summers at the University of
 Missouri to develop efficient nozzles for hand-held wands. These hand-held
 systems have been used at pressures up to 60,000 psi and a flow rate of
 1-2 gpm (gallons per minute). Work has also been carried out by the NASA
 Marshal Space Flight Center (MSFC) where ultra high pressure water has
 been adopted to robotically move the high pressure nozzle over a
 stationary object (a reusable rocket booster) to remove left over fuel.
 Similarly, the Air Force has been testing a robotic system to remove paint
 from airplanes. MSFC has also been experimenting with the injection of a
 solid abrasive into the high pressure stream to increase the efficiency of
 the process. The abrasive currently used is made of baking soda (sodium
 bicarbonate) and the process leaves solids that must be disposed of. A
 problem with abrasive type system is that the abrasive must be disposed of
 offsite. This is a costly endeavor.
 It is an object of the present invention to provide an improved cleaning
 method for materials processing with increased productivity.
 It is further an object of the present invention to provide a substrate
 cleaning method that is faster than the prior state of the art, results in
 a more uniform surface quality than the prior state of the art and
 minimizes waste.
 SUMMARY OF THE INVENTION
 One aspect of the present invention utilizes a high pressure slurry of ice
 and water directed toward a moving substrate to clean a surface of the
 substrate. The present invention omits the use of chemicals, thereby
 significantly reducing the risk to the environment. Further, the present
 invention provides various advantages over traditional chemical cleaning
 methods, such as simplification of the process, improvement in efficiency,
 improved surface quality, improvement of the work environment and reduced
 energy costs. The present invention provides an advantage over current
 high pressure cleaning systems utilizing solid abrasive injection by using
 ice particles in the cleaning fluid as the abrasive. Furthermore, the
 present invention eliminates the need to dispose of or recycle the
 leftover solids of the chemical cleaning solution. The prior art systems
 include leftover solids are often mixed with hazardous waste and,
 subsequently, must be treated as a hazardous waste.
 Another aspect of the present invention is a pressurized water cleaning
 method for materials processing and manufacturing, that includes the steps
 of:
 (a) conveying or moving a product having a surface through a set of fixed
 nozzles or spray headers; and
 (b) directing a pressurized stream of cleaning fluid toward the surface of
 the product. Preferably, the cleaning fluid is water. The stream may
 include ice particles. Preferably, the pressurized stream is in the range
 of 10,000 psi (pounds per square inch) to 120,000 psi. By pressurized
 stream it is meant that the supply of pressurized liquid to a nozzle prior
 to the liquid exiting the nozzle in a stream at approximately atmospheric
 pressure.
 The moving product may be in the form of a strip, sheet, rod, wire, bar or
 filament. The materials may be carbon steel, stainless steel, titanium,
 brass, copper, bronze, Inconel, aluminum, glass, kevlar, polymer,
 fiberglass, or foam. Essentially, the process may be used on all materials
 and materials systems where the surface layers are required to be removed.
 This could apply to oils and greases on any substrate, surface oxides on
 metallic substrates, and protective coatings on metals, paints, polymers
 or ceramics. Generally, the present invention can be used where an
 undesirable coating or film, solid or liquid, needs to be removed from a
 substrate.
 The present invention is also an arrangement for cleaning materials that
 includes a conveyor for transporting a product or target material having a
 surface and a set of nozzles or spray header positioned to direct a high
 pressure stream of cleaning fluid toward the product surface as the
 product is positioned on the conveyor. Preferably, the product travels at
 a speed of ten (10) feet per minute (fpm) to five hundred (500) feet per
 minute (fpm). Preferably, the cleaning fluid flows at a volumetric flow
 rate of one (1) gallon per minute to fifty (50) gallons per minute per
 nozzle and more preferably one gallon per minute to twenty (20) gallons
 per minute. A set of spray headers are positioned above and below the
 target material or product to clean the respective surfaces. The spray
 headers are configured to direct pressurized cleaning fluid onto the
 surface of the product. A nozzle or a set of nozzles are coupled to the
 spray headers to deliver a stream of pressurized cleaning fluid towards
 the respective surfaces. The nozzles may be single or multiple orifice
 nozzles and may supply a cylindrical stream or a fanned stream of cleaning
 fluid. The nozzles may be fixed, but preferably the nozzles rotate about a
 longitudinal axis of the nozzle.
 A refrigeration system may be provided to generate small ice particles in
 the cleaning fluid prior to exiting the spray headers. The ice particles
 in combination with water exiting the nozzle form an ice water mixture
 where the ice acts as an abrasive when it contacts the product surface.
 Preferably, ice is injected into the cleaning fluid when necessary.
 A fluid pump is in fluid communication with the spray headers to supply
 ultra high pressure cleaning fluid to the headers. The pressures supplied
 by the pump may be in the range of 10,000 psi to 120,000 psi. Preferably,
 the flow rate generated by the pump may be between one (1) and fifty (50)
 gpm and the spray headers have a maximum width of eighty (80) inches. The
 conveyance speeds may range from ten (10) feet per minute (fpm) to five
 hundred (500) fpm.
 The present invention is believed to be particularly well suited to clean
 oxides, especially secondary scale, from metal substrates, such as steel,
 copper alloys, aluminum, and titanium alloys. It is also believed to be
 well suited to remove protective coatings such as paint or zinc from a
 coiled substrate. The present invention is applicable for cleaning any
 type of films, such as grease or paint from metal or nonmetallic
 substrates.
 More specifically, the present invention is a material cleaning system that
 includes a conveyor for moving a substrate in a first direction and at
 least one nozzle positioned away from the substrate. A pressurized fluid
 supply is in fluid communication with the nozzle. The nozzle is arranged
 so that the pressurized fluid exits the nozzle and is directed to a
 surface of the substrate for removing a liquid or a solid film from the
 substrate. Preferably, the pressure of the fluid prior to exiting the
 nozzle is on the order of 10,000 psi to 120,000 psi and, more preferably,
 40,000 psi to 60,000 psi. Preferably, a plurality of nozzles are provided
 with a header and arranged over the conveying arrangement. Preferably, a
 reel system is used to convey the substrate in close proximity to the
 nozzles. Alternatively, any type of conveying system may be used, for
 example, rotary tables, rotating spindles, reel-to-reel take up, etc. The
 pressurized fluid is accomplished through a crank type pump, a piston
 pump, or any other pump capable of generating the necessary pressures and
 volumes.
 In another embodiment of the present invention, a pressurized mixture of
 ice and water can be provided to the nozzles. A high velocity stream of
 the mixture contacts a surface of the substrate, thus removing a film
 coating on the substrate.
 The present invention is also a method for removing a coating on a
 substrate that includes the steps of:
 (a) providing a pressurized fluid to a stationary nozzle, which may be
 multi-ported and rotate or oscillate about an axis;
 (b) directing the pressurized fluid from the nozzle in a high velocity
 fluid stream towards a moving object having a surface coating; and
 (c) contacting the fluid stream with the object, whereby a force of the
 fluid removes the coating. Preferably, the fluid is water. More
 preferably, the fluid is a mixture that includes an abrasive. Most
 preferably, the mixture is made up of ice and water.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 is a schematic showing a cleaning system 10 made in accordance with
 the present invention. Specifically, the cleaning system 10 includes a
 pressurized supply of water 12 in fluid communication with a conduit 14.
 The conduit 14 is in fluid communication with a plurality of nozzles 16.
 The nozzles 16 are arranged so that the pressurized fluid (preferably
 water) exits the nozzles in a high velocity stream 18 to contact a
 substrate 20 having a coating, such as an oxide coating or grease coating
 on a substrate of metal or non-metallic material, such as plastic.
 FIG. 2 shows the cleaning system shown in FIG. 1 in more detail. A water
 supply 22 is in fluid communication with a conduit 24. The conduit 24 is
 in fluid communication with a high pressure (HP) pump 26. The high
 pressure pump 26 is in fluid communication with a conduit 28. The conduit
 28 is in fluid communication with a spray header 30 containing a plurality
 of nozzles 32. The nozzles are arranged so that the pressurized fluid
 exits the nozzles at a high velocity stream 34 to contact a moving
 substrate 36 having a coating.
 FIG. 3 in accordance with this invention shows a cleaning system spray
 header 38 with a plurality of nozzles 40 arranged so that the pressurized
 fluid (preferably water) exits the nozzles as a high velocity stream 42 to
 contact a substrate 44 that is being moved by a conveying system 46.
 FIG. 4 shows another embodiment of the present invention and includes a
 water supply 48 in fluid communication with a conduit 50. The conduit 50
 is in fluid communication with a high pressure pump 52, such as the pumps
 previously described. The pump is in fluid communication with a conduit
 58. A system for making an ice slurry or mixture 54 is provided. This
 system 54 includes a refrigeration unit and a pump, such as a screw pump.
 The system to make an ice slurry 54 is in fluid communication with the
 conduit 58, through a conduit 56. The conduit 58 is in fluid communication
 with a branching conduit 60 having an upper portion and a lower portion.
 The lower portion of the branching conduit 60 is in fluid communication
 with a bottom spray header 62 and an upper spray header 62'. The spray
 headers are provided with a plurality of nozzles for directing the
 cleaning fluid toward a substrate. A coiler 66 is positioned on one side
 of the spray headers 62 and 62' and an uncoiler 68 is positioned on
 another side of the spray headers 62 and 62'. A substrate 70, such as a
 metal strip, is wound around the coiler 66 and uncoiler 68. The metal
 strip 70 includes a film, such as grease or oxides, on its outer surfaces
 71 and 73. The nozzles of the spray headers 62 and 62' direct the high
 pressure water with ice mixture toward the metal strip or substrate 70 for
 removal of the coating. The pressurized water exits as a high velocity
 stream and then contacts the moving metal strip 70. Contact of the high
 velocity water and ice mixture causes the coating to be removed.
 FIG. 5 shows the mechanics of the removal of a coating from a substrate in
 more detail. Specifically, FIG. 5 shows a substrate 80, such as the metal
 strip 70, shown in FIG. 4, having a coating 82, such as an oxide coating
 or grease coating. A high velocity fluid stream 84 is directed at the
 substrate 80 at a contact point 86. The stream 84 contacts the substrate
 surface 88 at an angle .alpha.. The substrate 80 travels in a direction X
 opposite the direction of the liquid stream 84. The liquid stream can be a
 mixture of ice and water. After the liquid stream 84 contacts the
 substrate surface 88 and the coating 82, coating particles 90 are carried
 away by the stream 84, thereby exposing the surface of the base material.
 Preferably, water is used as the cleaning solution. The pressures of the
 water supplied by the pump preferably are in the range of 10,000 psi to
 120,000 psi and, more particularly, 40,000 to 60,000 psi. Preferably, the
 flow rate of the pump may be between one (1) and fifty (50) gallons per
 minute and more preferably between twelve (12) and twenty (20) gallons per
 minute. Preferably, the spray headers have a maximum width of 80 inches so
 that a standard steel strip can be cleaned. The high pressure fluid, i.e.,
 water, can be accomplished through a crank type pump, a piston pump, or
 any other pump capable of generating the necessary pressures and flow
 rates. One type of pump that can attain these high pressures is Model
 D1500-40 manufactured by New Jet Technologies of Seattle, Wash.
 An important aspect of the present invention is that the substrate is
 conveyed by conveyors relative to the nozzles. FIG. 3 shows a plurality of
 driven rollers 46 as the conveyor. Other types of conveying arrangements
 can be used, such as a reel system as shown in FIG. 4 or rotary tables,
 rotating spindles, reel-to-reel take up, etc.
 The nozzles for directing the liquid toward the moving substrate are
 specifically designed for high pressure fluid applications. Nozzles can
 direct the high pressure fluid in a straight high velocity line or a
 fanned stream. The nozzles may be fixed to the header or not rotate or
 they may rotate about a longitudinal axis of the nozzle, as shown in FIG.
 3.
 The present invention is believed to be well suited to clean oxides from
 metal substrates, such as steel, copper alloys, aluminum and titanium
 alloys. It is also believed to be well suited to remove protective
 coatings, such as paint or zinc from a sheet or a coiled substrate.
 Furthermore, it is believed that the present invention is well suited for
 removing greases and other organic coatings on a substrate, such as steel.
 Also, the present invention is believed to be well suited for the removal
 of similar coatings on non-metallic material, such as plastic.
 Preferably, the present invention utilizes an intermediate pressure of
 water or liquid higher. By definition intermediate pressures are 5,000
 psi-20,000 psi, very high pressures of water 20,000 psi-60,000 psi, and
 ultra high pressures at greater than 60,000 psi. The present invention can
 operate at all of these pressure ranges and preferably 5,000 psi-120,000
 psi. Preferably, the present invention is used to remove scale from rolled
 metal and most preferably secondary scale, which is a metal oxide,
 although the present invention can also be used to remove primary scale.
 Preferably, the water exits a rotating or oscillating nozzle as shown in
 FIG. 6. FIG. 6 shows a nozzle 100 which is in fluid communication with the
 spray header 62, in a high pressure source of water shown in FIG. 4. The
 nozzle 100 is adapted to rotate about an axis 102 so that a stream of
 water 104 contacts an area of a substrate, such as steel, 106 to remove an
 oxide coating, such as a secondary coating. Preferably, the water pressure
 supplied to the nozzle is in the range of 5,000-120,000 psi; the angle of
 attack .alpha. as shown in FIG. 6 is between 90.degree. and 75.degree. as
 measured from the surface of the substrate 106 where the stream of water
 104 contacts the substrate 106 or 0.degree.-15.degree. as measured from a
 vertical axis normal to the surface of the substrate 106 where the stream
 of water 104 contacts the substrate 106; the volume of water flowing
 through the nozzle is between 1-20 gallons per minute (GPM), preferably
 6-20 gallons per minute (GPM); and the velocity of water exiting the
 nozzle is on the order of two thousand feet per second or more at a stream
 diameter between 0.03 inches and 0.065 inches. One such nozzle is provided
 as the ultra high pressure (UHP) GUN, Model # UPSG-40 manufactured by
 Underpressure Systems, Inc. in which the stream of water exits at 3,000
 feet per second and the pressure of the pressurized water is on the order
 of 60,000 psi. The substrate moves in the horizontal direction 108
 relative to the nozzle 100 and the nozzle rotates about axis 102 relative
 to the substrate 106. Preferably, the nozzle rotates or oscillates at
 50-5,000 RPM (revolutions per minute). Preferably, the nozzle 100 includes
 a plurality of ports, of which only one is shown in FIGS. 6 and 7, and
 oscillates or rotates about the axis 102 wherein a high velocity water
 stream 104 exits from each of the ports, so that each of the fluid streams
 contact the object, whereby the force of the fluid from each of the fluid
 streams removes the coating on the substrate 106.
 FIG. 7 shows the nozzle 100 having a stream of high velocity water 104. The
 water stream 104 has three zones: zone one 110 is known as the coherent
 where the water stream has the highest energy; zone two 112 is known as
 the unstable zone, where the water stream begins the fade out and lose
 energy; and zone three 114, the dispersion zone, where the water stream
 104 breaks into droplets and has the least amount of energy. In the case
 of primary scale, the waterdrop forms of zone three 114 will suffice to
 remove the scale. However, dispersion will not remove secondary scale.
 Therefore, the nozzle tip 116 must be positioned close to the substrate so
 that the water stream 104 contacts the substrate in the unstable zone,
 i.e., metastable zone, or within the coherent zone. Preferably, the nozzle
 tip 116 is positioned between 1/2-2 inches away from the substrate
 surface, which based upon the above-identified parameters, results in a
 water stream that is either in the coherent zone 110 or unstable zone 112
 but not in the dispersion zone 114. The coherent zone occurs within a
 distance X, from the nozzle tip 116; the unstable zone occurs between a
 distance X.sub.1 and X.sub.2 from the nozzle tip 116; and the dispersion
 zone occurs a distance greater than a distance X.sub.2. These distances
 X.sub.1, X.sub.2, and X.sub.3 are defined by various factors, such as the
 initial water stream diameter and the supply pressure of the water to the
 nozzle.
 Although the present invention has been described in detail in connection
 with the discussed embodiments, various modifications may be made by one
 of ordinary skill in the art without departing from the spirit and scope
 of the present invention. Therefore, the scope of the present invention
 should be determined by the attached claims.