WO1994023895A1

WO1994023895A1 - Crystalline ice particle mixture for optimum ice blast surface treatment

Info

Publication number: WO1994023895A1
Application number: PCT/US1994/003824
Authority: WO
Inventors: William D. Fraresso; Somyong Visaisouk
Original assignee: Ice Blast International, Inc.
Priority date: 1993-04-20
Filing date: 1994-04-07
Publication date: 1994-10-27
Also published as: CA2121269A1; AU6628094A

Abstract

A crystalline ice particle mixture for use in an ice blast nozzle (30) to achieve optimum surface treatment by air blasting, the ice particle mixture at a surface coating substrate comprises: i) individualized chips (100) having a consistent thickness in a Z dimension and variable length and with in an X and Y dimension. The Z dimension is selected from the range of 0.5 mm to 2 mm for a desired mixture and the X and Y dimensions varying in the range of 2 mm to 10 mm for any desired mixture of the selected Z particle dimension; ii) the ice particle (100) when blasted onto a substrate (90) being at a temperature near the melting point of ice to enable the ice particles to deform on impact against the substrate (90), such lateral plastic displacement of the particles effecting a scrubbing action on a substrate surface; iii) the particle mixture of variable size when blasted against the substrate (90) performs a combination of surface coating rupture and/or surface debris removal to optimize thereby surface treatment.

Description

CRYSTALLINE ICE PARTICLE MIXTURE FOR OPTIMUM ICE BLAST SURFACE TREATMENT

TECHNICAL FIELD

This invention relates to a crystalline ice particle mixture particularly useful in ice blasting of substrate surfaces to achieve optimum surface treatment.

BACKGROUND ART

Particle blasting has been employed for some time to remove material from surface structures. Sand blasting and other types of grit blasting have been used to remove surface finishes from building exteriors, vehicle surfaces, mechanical parts and the like. Sand or grit blasting, however, requires expensive recovery systems to reduce pollution and other environmental hazards. Water can be used in conjunction with the grit blasting procedure to reduce particle losses and consequent harm to the environment.

Although grit blasting is very effective in treating building and vehicle surfaces, great care has to be exercised in treating more sensitive treatment process.

The blasting of ice particles resolves a number of the above problems so that several attempts have been made in providing commercially viable ice blasting equipment. It is appreciated that the blasting of ice particles provides significantly less environmental harm because subsequent to impact the ice particles melt hence assisting in the removal and disposal of abraded material. As a result, there is considerable reduction in dust contributed to the environment. Due to the nature of ice particles, there are several problems associated with blasting the ice particles to achieve sufficient work on the surface to be treated. By their nature, ice particles are not free-flowing. Normally, to provide an accumulation of ice particles during machine shut-down and the like, an inventory of ice particles is accommodated by various mechanical devices interposed between the ice making system and the blast nozzle. However, this results in the ice particles packing and causing plugging problems in the system at various points in the intervening mechanical devices. The variety of mechanical devices normally employed in developing and transporting the ice particles are rotors, augers, classifiers, cyclone separators, metering devices, overflow receivers, surge tanks and the like. All of these components are provided in an attempt to manage the problems associated with ice packing in the system due to the development of ice accumulation. But, by virtue of the provision of these various components, their own interaction can inadvertently result in packing of ice particles at various points in the processing system. Furthermore, the operation of these mechanical components has to be precisely controlled with special precautions to attempt to avoid ice packing in their components and also avoid system clogging. As is appreciated, these problems can be further magnified when ice blast systems are required to operate at distances some 20 to 50 metres from the ice-forming equipment.

U.S. Patent 4,703,590 discloses a particle moulding apparatus suitable for moulding ice particles for blasting purposes. As the ice particles are formed, they are collected in a reservoir at the base of the moulding machine. As the blast system is operated, particles are sucked from the reservoir in the moulding apparatus and transported to the nozzle for purposes of doing work. However, it has been found that the inventory of ice particles within the reservoir of the ice particle making device still causes ice packing and subsequent system clogging, particularly during intermittent blasting operations.

Another system which provides for the delivery of ice particles to the blast nozzle is disclosed in U.K. Patent Application 2,171,624. The ice particles are delivered in segments to a venturi restriction for pick up by the high speed air. However, when blasting ceases, the ice particles tend to clog up and pack in their segment portions, resulting in further down time of the system until the clogging is dislocated.

An attempt to overcome these problems is disclosed in PCT International Publication Nos. W090/14927 and W091/04449. The systems which are disclosed in these applications provide for the development of ice, ice crushing, particle sizing, cyclone separation, fluidization and delivery of ice particles to the blast nozzle. As already mentioned, such systems require very precise control and, by virtue of the number of interactive components, defeated the objective in attempting to deal with the accumulation of ice particles and by their nature, packing in the system and causing clogging with consequent significant down¬ time.

Crystalline ice particles are an inexpensive blast medium which lends itself to dust-free surface cleaning and coating removal while at the same time facilitating clean up and waste management. However, with the prior art techniques, the cleaning efficiency or surface treatment is hampered by the structure of the prior art types of ice particles. In the past, it has been thought that the production of ice particles with sharp edges and blasted at very low temperatures to increase the particles' hardness and strength contributed to improved surface treatment effectiveness. It was thought that it would be necessary to incorporate an air cooling unit in order to cool the blast air which is used in projecting particles. However, in accordance with this invention it has been found that the combined features of crystalline ice particles of a prescribed dimension and blasted at a temperature near the melting point of ice significantly in combination enhances coating rupture and surface treatment.

DISCLOSURE OF THE INVENTION

In accordance with an aspect of the invention, a crystalline ice particle mixture is provided for use in an ice blast nozzle to achieve optimum surface treatment by air blasting, the ice particle mixture at a surface comprises: i) individual ice chips having a consistent thickness in a Z dimension and variable length and width in an X and Y dimension. The Z dimension is selected from the range of 0.5 mm to 2 mm for a desired mixture and the X and Y dimensions varying in the range of 2 mm to 10 mm for any desired mixture of the selected Z particle dimension; ii) the ice particle, when blasted onto a substrate being at a temperature near the melting point of ice to enable the ice particles to deform laterally on impact against the substrate; iii) the particle mixture of variable size when blasted against the substrate performs a combination of surface coating rupture and/or surface debris removal to optimize thereby surface treatment. In accordance with another aspect of the invention, a method for ice blasting a substrate surface to remove surface material from the substrate is optimized by the use of the crystalline ice particle mixture in accordance with the above embodiment of the invention, the method comprises air blasting the ice crystalline mixture through a blast nozzle by use of warm blast air to warm the ice particle mixture to the deformable temperature thereof.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the invention are shown in the drawings wherein:

Figure 1 is a perspective view of the ice blasting apparatus in which the ice particle mixture of this invention may be developed.

Figures 2A and 2B schematically demonstrate the work performed by ice particles having internal fractures.

Figures 3A, 3B, 3C, 3D and 3E schematically demonstrate the work performed by the ice particle mixture of this invention in an ice blasting operation.

Figures 4A and 4B schematically demonstrate plastic deformation of the ice particles and the effects of such deformation in the lateral scrubbing of surface coating or surface debris from a substrate surface.

Figure 5 is a perspective view of an exemplary ice particle. Figure 6 is a perspective view of the ice maker and ice fracturing rollers of this invention.

BEST MODES FOR CARRYING OUT THE INVENTION

The ice fracturing system, used to make the crystalline ice particle mixture of this invention, can be used with various types of mobile or stationary ice blasting systems. Alternatively, the system may be sufficiently compact for use in a production line where the unit is mounted adjacent conveyed articles which are to be treated by blasting ice particles onto the conveyed articles. For purposes of describing various aspects of the invention, a mobile ice blast system shall be described. The mobile ice blast system 10 is shown in Figure 1 as mounted on a frame 12 having wheels 14. The frame 12 has an upper cover 16 with an intermediate shelf 18 and a lower shelf 20. The shelves 18 and 20 are connected to the uprights 22 of the frame 12. High pressure air is delivered to the system 10 through high pressure air hose 24. As required, ice particles are delivered through the ice particle delivery hose 26. High pressure air from hose 24 is directed to the blast hose 28. The high pressure air merges with the ice particles in line 26 at the blast nozzle 30. An operator actuated switch 32 is provided on the blast nozzle to effect the desired blasting of ice particles onto a surface to be treated. The ice particle forming system of this invention provides ice particles of a desired size on demand and only when needed at the blast nozzle 30. This avoids any accumulation of ice particles in the ice making/ice fracturing system generally designated 34. The hoses 26 and 28 may extend for considerable distances depending upon the use to which the ice blast system is put. Usually the hoses are of a length in the range of 20 to 100 metres. However, the hose lengths may be shorter, such as in the range of 5 to 20 metres. It is also appreciated that the ice blast system may feed ice particles to a blast nozzle located within less than a metre of the system for purposes of ice blasting devices on a conveyor system or the like.

The ice blast system is controlled by a process controller 36 mounted to control panel 37. When the system is signalled by the operator actuating switch 32, high pressure air is delivered through hose 28 and ice particles are formed for delivery to the blast nozzle 30 via hose 26. The process controller 36 may be programmed to provide a delay of 3 seconds after the switch 32 is actuated and is maintained in the "on" position to avoid false starts due to accidental triggering of the switch. A refrigerated ice maker 38 is provided which directs formed ice flakes and sheets into a deice for transferring ice sheets downwardly. The ice transfer device 40 is in the form of a chute which directs the ice flakes into the ice fracturing unit 42. The ice fracturing unit 42 fractures the ice sheets and flakes into ice particles of a desired size which are transferred by a funnel 42 into the ice particle transport hose 26. The ice fracturing device 44 fractures the ice sheets and ice flakes at the mass flow rate at which the ice sheet and flakes are formed by the ice maker 38. The size of the ice particle forming system 34 is selected to supply in hose 26 a sufficient mass flow rate of ice particles to meet the demands for ice particle blast treatment at the nozzle 30.

Details of the ice maker and ice fracturing unit are discussed further in Figure 6. However, as schematically shown in Figure 1, water is supplied to the ice maker 38 through water line 46. Cooling air, as required, is introduced to the ice maker through air line 48. Refrigerant to cool the ice maker 38 is provided via refrigerant line 50. The motor 52 for rotating the ice making drum is provided on the outside of the ice maker 38. The motor for rotating the ice fracturing rollers of the ice fracturing unit 42 is provided at 54. A refrigeration unit for cooling the ice making device 38 and as well as supplying, as needed, cool air within the ice making device 34 is provided on the system frame 12. The refrigerant unit includes a compressor 56 mounted on shelf 20. The condenser 58 with condenser cooling fans 60 is also mounted on the same shelf. The return line for the refrigerant to the condenser 58 is provided in line 62. Compressed refrigerant is provided in line 64 for delivery to the ice maker 38 and the air chiller 68. Refrigerant is introduced to the chiller 68 through line 70 and retrieved from the chiller 68 through line 72. The refrigerant, as introduced to the ice making device 38 is, as already noted, provided through line 50.

The high pressure supply of air in line 24 is split valve 74 where the majority of high pressure air is directed through line 78 where at coupling 89, feeds high pressure air into line 28. A minor portion of the high pressure air, as regulated by control valve 74, is fed into the dryer 66 through line 82. After the minor portion of air exits the dryer 66 through line 84 the air is chilled in the chiller 68 and exits the chiller through line 86 for coupling to line 48 to supply as needed chilled air to the ice particle forming system 34.

One of the significant advantages of the ice particle forming device 34 of this invention is that the ice particles, as provided at the blast nozzle 30, have minimal internal fracturing. This became apparent upon inspection of the ice particles as they emerge from the blast nozzle 30. It is believed that this additional feature of the ice making unit 34 and hence particle characteristic increases the ability of the blasting system, to perform work on a surface to be treated. As shown in Figure 2A, an ice particle 88 is blasted toward a substrate 90 in a direction of arrow 92. The purpose of the blasting is to remove from the substrate the surface layer of paint 94. With ice particles 88, such as those common to prior forms of ice crushing systems, the particles have internal fracturing indicated by the fine lines 96. This type of particle does minimal work on the surface as theoretically demonstrated in Figure 2B. The outer layer 94 has been impacted by the particle 88. However, due to internal fracturing 96 of the particle, the particle 88 immediately disintegrates into a plurality of subparticles 98 or water droplets with little, if any, work having been done on the coating 94.

Conversely, as demonstrated in Figures 3A to 3E, ice particles 100, as preferably made by the apparatus and process of Figures 1 and 6 do not include extensive internal fracturing. Instead, the particles tend to be relatively clear compared to particles such as 88 made by prior forms of ice crushing devices. The particles 100 are blasted towards the substrate 90 in the direction of arrow 102 to perform work on the exterior coating 94. As shown in Figure 3B, the particle 100, because it was not internally fractured, commences compression of the coating 94 where there may be some yielding in the substrate 90 as well. As shown in Figure 3C, the continued momentum of the particle 100 causes continued and perhaps further compression in the coating 94 to form a compressed region 104 beneath the ice particle 100. During this continued compression of the coating 104 there is a deformation in the particle 100 as indicated by arrows 101 and 103. This lateral deformation in the particles is similar to a materials science type of plastic flow in a solid particle while the particle retains its integrity without disintegrating into smaller sub- particles. However, with ice particles, this sudden plastic-like flow of the particle mass causes a phase change in the particle from ice to liquid. Hence, the continued momentum causes the particle to deform laterally, so that as the particle exerts a compressive force on the coating 94 it as well exerts a lateral shear force to the coating 94. During this deformation of the particle 100 it becomes liquid by virtue of a phase change and thereby leaves the surface coating 94 in the form of water droplets. As the water moves away from the compressed region, the surface coating 94 in the compressed region 104 rebounds to the extent shown in Figure 3D. Such rebound of the surface coating establishes a tensile force in region 104 where this tensile force overcomes the adhesive attractive force of the coating to the substrate. In overcoming the adhesive attractive force of the coating to the substrate 90, the coating commences to lift away from the substrate and develops a slight space 105 between the coating and the substrate 90. The tensile force in the region 104 lifting the coating from the substrate 90 does so without causing substrate damage. Assuming sufficient tensile force has been developed in the coating in region 104, the coating ruptures as shown at 104 of Figure 3E where the coating has ruptured into individual particles 107. This principle of coating rupture is particularly useful in removing hard materials such as paints, urethanes, adhesives, thin film plastics and the like.

The force required to effect coating separation is much lower than the damage threshold of most substrates because coating separation is a result of the tensile force overcoming the adhesive force of the coating/substrate system whereas substrate damage is the result of the impact force overcoming a much higher cohesive force. For this reason, ice particles can be used to remove coatings with little or no damage to the substrate. Furthermore, the phase change produces a water mist which assists in the containment of blast debris such as dust and small particulate. Also, because the ice particles are small, the developed moisture is in turn of a reduced amount so that clean up in the area of spray is minimal. This is particularly useful for requirement in ice blasting on a continuous operation in an enclosed system.

The ice blasting system involving the ice particle mixture of this invention may also be used for the removal of surface dust, grease, rust or other contaminants which may constitute a softer type of coating compared to the harder coatings 9 of Figure 3A to 3E by a mechanism to be discussed with respect to Figures 4A and 4B. In Figure 4A, the ice particle 100 in deforming in the direction of arrows 109 and 111 due to continued momentum in the direction of arrow 113 physically scrubs the surface 115 as it exerts a lateral shear force on the surface of the substrate 90. This scrubbing and lateral shear force loosen the soft surface film or deposit 97 from the surface where the deposit is subsequently flushed away by the water resulting from the phase change of ice particle 100. Hence, the particle mixture of this invention is very effective in the removal of grease films and the like from the surfaces.

The ice blasting system involving the ice particle mixture of this invention may also be used for the removal of surface dust, grease, rust or other contaminants as demonstrated in Figure 4B. The depression of Figure 4B is intended to show a deep pore or the like in a metal casting. Ice blasting has been found to be particularly useful in this regard. The ice particle 100 in deforming in the direction of arrows 115 and 117 due to continued momentum in the direction of arrow 119 exerts lateral sheer force to the surface 121 of the substrate 90. This sheer force removes surface debris 123 from the surface where the surface debris is carried away by the water droplets resulting from the phase change of the ice particle 100 to water. Hence, the particle mixture of this invention is very effective in the removal of grease and the like from the surfaces.

It has been found that a range of particle size is important in the optimum function of this invention. The ice particles in the selected size range provide discreet impacts which are capable of removing surface coatings, removing surface contaminants, deburring of machine castings, decontamination of radioactive surfaces and the like. The particles are of a size which impact the surface, deform laterally to allow thereby the coating to rebound and develop a tensile stress in the coating so that it ruptures to provide openings for further ice blast particles to continue surface removal. It is desired to use particles within the defined range of 2 mm to 10 mm because it has been found that particles of this size range develop a relatively short impact loading time in compressing the substrate coating and the like so that the coating may rebound due to a developing tensile force overcoming the adhesive forces of the coating to the substrate surface. The crystalline ice particles of this invention within the defined size range are capable of developing the much shorter impact loading times. Larger particles of the prior art, particles of the prior art which include internal fractures and high pressure water blast or the like are all less effective than blasting the crystalline ice particle composition of this invention.

With high pressure water blast, the loading time is not discreet; that is, there is no rebound time for the coating which is one reason that the ice particle composition of this invention optimized the efficiency of the ice blast system in surface treatment. This effect may be further optimized by blasting the particles at the substrate surface essentially perpendicular to the plane of the surface where it has been found that in the use of crystalline ice mixture of this invention the impact force may be substantially higher before damage is caused to the substrate than with solid particle blasting media such as sand or plastic particles.

It has been found that the particle mixture having a range of particle sizes from 2 to 10 mm performs a variety of functions in surface treatment to optimize surface coating removal. The larger particles tend to have longer contact time for physical scrubbing and clear away debris and other surface contaminants whereas the smaller particles are more effective in lifting the substrate coating and the like because the very short contact time before phase change occurs which tends to generate maximum tensile force in the coating. This type of action is very difficult to achieve with larger particles; that is, particles larger than 10 mm because of a prolonged deformation action and particle integrity, nor with particles much less than 2 mm because of the lack of momentum in applying a compressive force to the surface substrate. The use of the particle range also increases the chances of having an earlier effect on surface treatment removal to optimize surface coating removals and the like.

It is, therefore, understood that the particles as they relate to a preferred embodiment of this invention have a structure essentially that as shown in Figure 5. The particle 100 has dimensions in either the X or Y direction in the range of 2 mm to 10 mm. In this particular embodiment, the X and Y directions are almost the same but it is appreciated that either direction may be considerably larger than the other. The thickness of the particle is in the Z dimension which may range from 0.5 mm to 2 mm with a preferred thickness being in the range of 1 mm.

An additional aspect in optimizing the work performed by the ice particle mixture is the use of warm blast air through hose 28 that leads to the blast nozzle 30 of Figure 1. This warmer is such to warm the particles as they arrive at the nozzle 30 from the cooler delivery hose 26, to a temperature near the ice particles' melting temperature. The ice particles are preferably in a temperature in the range of 0°C to -5°C. This temperature range provides very effective lateral sheer and scrubbing action on the surface because the momentum of the particles is sufficient to cause deformation in the particles as they move laterally during their phase change from a solid to a liquid. Hence, the temperature of the blast air and hose 28 is sufficient to effect this warming action but is not sufficiently warm to cause the particles to melt when blasted through the nozzle 30. It has been found that blast air temperatures in the range of 140°F to 160°F that is in the range of 60°C to 70°C are most effective.

It has also been found that the size range for the particles in the X and Y dimension being in the range of 6 to 10 mm is very effective for cleaning substrate surfaces to remove a film or layer of grime or oil based material. On the other hand, ice particle chips having a smaller dimension in the range of 2 mm to 4 mm is very effective for removing adherent surface coatings from the substrate, that is where the majority of the particles in the mixture have that size range.

Particles of the size of Figure 5 having the characteristics as required with respect to Figure 3 can be made by the ice fracturing unit as shown in more detail in Figure 6. The ice fracturing system is capable of fracturing ice sheets and flakes made by the ice making unit where the ice particles of the desired internal characteristics and size range. The ice making unit 38 contains a water bath 110 in which a chilled rotatable drum 112 is immersed. The refrigerant which enters line 50 passes through the central tube 114 to chill the body portion 116 of the drum. The motor 52 rotates the drum at a constant circumferential velocity in the direction of arrow 118. As the drum rotates in the direction of arrow 118, a thin film of water 120 is picked up on the surface of the drum. Due to the continuous chilling of the drum 112 by refrigerant in line 50, the sheet of water 120 commences to freeze and is essentially frozen by the time the sheet reaches the upper circumferential position of the drum. Doctor blade 126, as mounted on angled support 128 contacts the surface 130 of the drum to lift the freshly formed sheet of ice from the drum surface along the doctor blade 126 as shown in dot at 127. The sheet of ice 132 formed on the surface 130 of the drum develops cracks 134 to form sheet portions which become ice flakes 136 or small ice sheets when lifted by the doctor blade 126.

Chilled air or normal compressed air may be introduced through air inlet 48 which directs the air to an air manifold 138. The air manifold has a plurality of holes 140 directing blasts of air in the direction of arrow 142 onto the surface of the doctor blade 126 and over the support 128. The air blast assists in moving the flakes and sheets of ice 136 along the surface 128 and into the chute 40, as shown in Figure 1 where the ice travels downwardly in the direction of arrow 144.

The ice fracturing rollers 146 and 148 are located below the ice making unit 38. The ice fracturing unit 42 has the ice fracturing rollers 146 and 148 positioned so as to provide a nip region 150 which extends horizontally of the ice fracturing unit 42. The ice sheets and flakes 136 are then directed into the nip 150 where the ice fracturing rollers 146 and 148 fracture such ice flakes and sheets into the desired ice particles 100. The rollers 146 and 148 are operated at a rate to process at least the flow rate of the ice sheets and flakes at which they are generated by the ice making unit 38. As a result, there is no accumulation of ice sheet or flakes above the ice fracturing unit 42 and when refrigerant is removed from the roller 112 of the ice making unit, there is an almost immediate cessation in the making of the ice sheet. The air blast provided by nozzles 140 clear any remaining ice particles from the support surface 128; hence, all ice above the ice fracturing unit 142 is quickly processed without any accumulation above the ice fracturing unit during shutdown or dwell periods when blasting is stopped. The ice fracturing rollers 146 and 148 are counter-rotated in the direction of arrow 152. The rollers are mounted on shafts 154 and 156 and mounted in a support block with appropriate bearings 158. The support block 158 has elongated apertures 160 and 162, where aperture 162 permits relative movement between the rollers toward and away from each other to provide for adjustment in the extent to which the rollers intermesh. The purpose of this adjustment is to provide one way in which the size of the ice particles is varied. The particle sizing can also be varied by altering depth of fracturing projections on the rollers. The rollers are driven by respective gear trains comprising gears 164 and 166 keyed to the rollers 146 and 148. The gears are designed and mounted in a manner to permit this lateral adjustment between the rollers 146 and 148. The shaft 154 is driven by the motor 54 to effect the desired synchronized rotation of the rollers 146 and 148 through use of gears 164 and 166. The synchronized rotation of the rollers 146 and 148 is such to always ensure a processing of the ice sheet and flakes. The rate of rotation may be varied depending upon the mass flow rate of ice generated by the ice making unit 38. The gears 164 and 166 are keyed to the rollers 146 and 148 to ensure that the fracturing spikes on the rollers are properly intermeshed to avoid damaging of the spike edges. This ensures that the rollers always function at peak efficiency to provide the ice particles 100 of a desired and consistent sizing with minimal, if any, internal fracturing of the ice particles. It is appreciated that other forms of drive systems for the rollers 146 and 148 may be provided, although for purposes of illustration and for simplicity in construction, the first and second gear trains 164 and 166 are the preferred form of drive devices which as noted are appropriately keyed to the shafts 154 and 156 to fix the relative rotational synchronized meshed position for the counter-rotating ice fracturing rollers 146 and 148.

It is also understood that the particle size, particularly in the Z dimension can be varied by altering the speed at which the motor 52 rotates the chilled drum 112. It is understood that the faster the motor 52 rotates the drum to provide a higher circumferential velocity the thinner the film of water 120 is picked up on the surface of the drum. As a result, the thinner film of water forms a thinner sheet of ice to be fractured by the fracturing rollers. Depending upon the desired Z dimension for the ice particle chips, one can select a motor speed which can vary the thickness of the chip within the desired range 0.5 mm to 2 mm. As noted for most applications, the preferred thickness for the ice particle chips is in the range of 1 mm. Normally, by trial and error, the speed of the motor 52 can be adjusted or selected depending upon the type of motor to provide particles having this desired thickness.

It is understood that in accordance with this invention, the ice particle mixture is particularly useful with ice blast systems which may involve hose lengths of 1 to 2 m, perhaps through to 100 m in length. It has been found that for most applications, incoming air is provided at 150 to 350 scfm at a pressure in range of 60 to 250 psig. With these operating parameters, it has been found that the mass flow rate of ice is preferably in the range of 120 lbs. per hour to 300 lbs. per hour. The ice fracturing unit as shown in Figure 6 is quite capable of handling mass flow rates of this magnitude where the particle sizing is consistently provided within the range of 2 mm to 10 mm.

Although preferred embodiments of the invention are described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

Claims

WE CLAIM;

1. A crystalline ice particle mixture for use in an ice blast nozzle to achieve optimum surface treatment by air blasting said ice particle mixture at a substrate surface, said mixture comprising: i) individual ice chips having a consistent thickness in a Z dimension and variable length and width in an X and Y dimension, said Z dimension being selected from the range of 0.5 mm to 2 mm for a desired mixture and said X and Y dimensions varying in the range of 2 mm to 10 mm for any desired mixture of said selected Z particle dimension, ii) said ice particle, when blasted onto a substrate, being at a temperature near the melting point of ice to enable said ice particles to deform laterally on impact against said substrate, iii) said particle mixture of variable size when blasted against a substrate performing a combination of surface coating rupture and/or surface debris removal to optimize thereby surface treatment.

2. A crystalline ice particle mixture of claim 1, wherein said Z particle dimension is about 1 mm.

3. A crystalline ice particle mixture of claim 1 wherein the majority of said particles having an

X-Y dimension in the range of 2 mm to 4 mm for removing adherent surface coatings from said substrate.

4. A crystalline ice particle mixture of claim 1 wherein the majority of said particles have an X-Y dimension in the range of 6 mm to 10 mm for cleaning substrate surfaces to loosen surface deposit or to remove a film or layer of grim or oil based material.

5. A crystalline ice particle mixture of claim 1 wherein said chips have irregular shape to enhance thereby rupture of surface coating on said substrate.

6. A crystalline ice particle mixture of claim 1, wherein said ice particles are at a temperature within the range of 0°C to -5°C when blasted at said substrate.

7. A crystalline ice particle mixture of claim 1, wherein said ice particles go through a phase change during plastic deformation of said particles whereby the developed water carries away debris removed from the substrate.

8. A method for ice blasting a substrate surface to remove surface material from said substrate, said ice blast removal method being optimized by use of a crystalline ice particle mixture of claim 1, said method comprising air blasting said ice crystalline mixture through a blast nozzle by use of warm blast air to warm said ice particle mixture to said deformable temperature.

9. A method of claim 8 wherein said selected range of ice particle size in the X and Y dimensions provides on impact against the substrate an impact loading time during which a compressive force is exerted on said substrate and which is sufficiently brief to permit a subsequent maximum tensile force to develop in a coating on said substrate, said tensile force in said coating overcoming adhesive forces of said coating to said substrate to rupture thereby said coating.

10. A method of claim 9 wherein during phase change of said impacting ice particle undergoing deformation, said ice particle imparts a lateral scrubbing action on said substrate.