CA2267586A1 - Detection of near surface defects by reversed thermography - Google Patents
Detection of near surface defects by reversed thermography Download PDFInfo
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- CA2267586A1 CA2267586A1 CA 2267586 CA2267586A CA2267586A1 CA 2267586 A1 CA2267586 A1 CA 2267586A1 CA 2267586 CA2267586 CA 2267586 CA 2267586 A CA2267586 A CA 2267586A CA 2267586 A1 CA2267586 A1 CA 2267586A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/72—Investigating presence of flaws
Abstract
Disclosed is a method for the detection of near surface defects in components, such as engine block cylinder walls. In a first step, a flow of cold air is applied to an area to be inspected, thereby establishing a heat flow from the inside-out. In a second step, the cooled area is subjected to an inspection by reversed thermography in order to locate any cold spots which would be indicative of defects. The amount of heat extracted by the cold air is a function of the difference in temperature between the air and the surface. In steady-state conditions, that temperature reaches an equilibrium where the cooling rate equals the amount of heat continuously flowing from the hot mass underneath the cooler surface. Where there is a bonding defect, the equilibrium temperature will be lower because heat flow towards the surface is disrupted.
Therefore, defects appear as cold spots, in reversed contrast with traditional thermography.
Therefore, defects appear as cold spots, in reversed contrast with traditional thermography.
Description
DETECTION OF NEAR SURFACE DEFECT'S BY REVERSED THERMOGRAPHY
Field of the invention The present invention relates to a method for the detection of near surface defects by reversed thermography.
The invention also relates to an apparatus for carrying this method which is particularly useful for the inspection of thermal sprayed engine block cylinder wall linings.
Background Thermal spraying is a generic term that encompasses an array of processes used to apply coatings of various high melting point materials (metals, ceramics, etc.) as a spray of droplets heated and propelled by some form of flame or plasma. The coating is built as "splatted" droplets solidify and accumulate on the substrate's surface.
Thermal spraying is extensively used in the aerospace industry and, more recently, has moved into the automobile industry, in particular, for the manufacturing of engine blocks.
Presently, engine blocks are made of cast aluminum with steel sleeves lining the inner surface of the cylinders. The sleeves, a few millimeters th ick, are inserted in the mold prior to the casting of the aluminum. For several years now, auto makers, sometimes in collaboration with thermal spraying equipment manufacturers, have been developing coating processes that would replace the steel inserts. Significant savings in manufacturing costs as well as weight reduction and performance enhancement has fuelled this general trend throughout the industry.
Because it is very thin (.005" to .008"), the wear resistant coating (generally steel) performs better because heat is extracted more. efficiently than through the much thicker sleeve. However, bonding of the coating to the aluminum substrate is critical and bonding defects are generally considered unacceptable. Since an in-service breakdown of the coating leads to failure of the engine, the quality and reliability requirements for these processes are extremely high and it is uncertain if they can be met without some form of inspection method.
There is presently no method of detecting; these defects that could reasonably be used in a production environment. The present Applicant, Tecnar Automation Ltee, became aware of this situation through its contacts with a major car manufacturer on a related matter and the decision was made to pursue this opportunity and develop a suitable method.
Field of the invention The present invention relates to a method for the detection of near surface defects by reversed thermography.
The invention also relates to an apparatus for carrying this method which is particularly useful for the inspection of thermal sprayed engine block cylinder wall linings.
Background Thermal spraying is a generic term that encompasses an array of processes used to apply coatings of various high melting point materials (metals, ceramics, etc.) as a spray of droplets heated and propelled by some form of flame or plasma. The coating is built as "splatted" droplets solidify and accumulate on the substrate's surface.
Thermal spraying is extensively used in the aerospace industry and, more recently, has moved into the automobile industry, in particular, for the manufacturing of engine blocks.
Presently, engine blocks are made of cast aluminum with steel sleeves lining the inner surface of the cylinders. The sleeves, a few millimeters th ick, are inserted in the mold prior to the casting of the aluminum. For several years now, auto makers, sometimes in collaboration with thermal spraying equipment manufacturers, have been developing coating processes that would replace the steel inserts. Significant savings in manufacturing costs as well as weight reduction and performance enhancement has fuelled this general trend throughout the industry.
Because it is very thin (.005" to .008"), the wear resistant coating (generally steel) performs better because heat is extracted more. efficiently than through the much thicker sleeve. However, bonding of the coating to the aluminum substrate is critical and bonding defects are generally considered unacceptable. Since an in-service breakdown of the coating leads to failure of the engine, the quality and reliability requirements for these processes are extremely high and it is uncertain if they can be met without some form of inspection method.
There is presently no method of detecting; these defects that could reasonably be used in a production environment. The present Applicant, Tecnar Automation Ltee, became aware of this situation through its contacts with a major car manufacturer on a related matter and the decision was made to pursue this opportunity and develop a suitable method.
l~ns~ection by thermography The basic principle of thexmographic inspection is to establish heat flow conditions through the inspected component and detect disx~zptions in the heat flow pattern caused by potential defects. Some form of infrared (IR) detection device (IR camera for example) measures the surface temperature of the component. Defects perpendicular to the direction of the heat flow will cause the most disruption and therefore will be the easiest to detect.
Since bonding defects in coatings are obviously parallel to the component surface, one must establish heat flow conditions perpendicular to the component surface in order to maximize contrasts caused by these defects. A typical setup will use some form of heat source (generally a laser) to uniformly heat an area of the compoxient surface. If there is no defect, the temperature of the area is uniform. Any defect that restricts the flow of heat from the surface toward the inside of the component will appear ;is a hot spot within the heated area. Figure identified as "prior art" illustrates such a setup.
Of course, the mechanism used to heat the surface must not itself generate IR
radiation that would reflect on the inspected area and blind the IR detector. . A laser is the most convenient heat source from that perspective because its precise color can easily be filtered out of the IR detection device. However, the cost per watt of power can be prohibitive.
Furthermore, safety and limited mean time between failure are also major concerns. Okher heat sources have been used such as joule heating with an electrical current or even a flow of hot air.
Summar of the invention The present invention is based on the discovery that, since engine blocks come out of the coating station at a temperature of aboul: 90 ° C, one could actually use reversed thermography to inspect the coating on cylinder walls.
More specifically, the invention provides a method for the detection of near surface defects in components, including especially but not exclusively engine block cylinder walls, comprising the steps of:
(a) applying a flow of cold air to an area to be inspected, thereby establishing a heat flow from the inside-out, and (b) subjecting the cooled area to an inspection by reversed thexrnography in order to locate any cold spots which would be indicative of defects.
Since bonding defects in coatings are obviously parallel to the component surface, one must establish heat flow conditions perpendicular to the component surface in order to maximize contrasts caused by these defects. A typical setup will use some form of heat source (generally a laser) to uniformly heat an area of the compoxient surface. If there is no defect, the temperature of the area is uniform. Any defect that restricts the flow of heat from the surface toward the inside of the component will appear ;is a hot spot within the heated area. Figure identified as "prior art" illustrates such a setup.
Of course, the mechanism used to heat the surface must not itself generate IR
radiation that would reflect on the inspected area and blind the IR detector. . A laser is the most convenient heat source from that perspective because its precise color can easily be filtered out of the IR detection device. However, the cost per watt of power can be prohibitive.
Furthermore, safety and limited mean time between failure are also major concerns. Okher heat sources have been used such as joule heating with an electrical current or even a flow of hot air.
Summar of the invention The present invention is based on the discovery that, since engine blocks come out of the coating station at a temperature of aboul: 90 ° C, one could actually use reversed thermography to inspect the coating on cylinder walls.
More specifically, the invention provides a method for the detection of near surface defects in components, including especially but not exclusively engine block cylinder walls, comprising the steps of:
(a) applying a flow of cold air to an area to be inspected, thereby establishing a heat flow from the inside-out, and (b) subjecting the cooled area to an inspection by reversed thexrnography in order to locate any cold spots which would be indicative of defects.
As it can be understood, the amount of heat extracted by the cold air is a function of the difference in temperature between the air and the surface. In steady-state conditions, that temperature reaches an equilibrium where the cooling rate equals the amount of heat continuously flowing from the hot mass underneath the cooler surface. Where there is a bonding defect, the equilibrium temperature will be lower because heat flow towards the surface is disrupted. Therefore, defects will appear as cold spots, in reversed contrast with traditional thermography.
The invention also provides an apparah~s for carrying out the above method.
This application comprises:
(a) means for generating a flow of a cold gas;
(b) means for applying the flow of cold gas to a surface area of the component to be inspected, thereby establishing a heat flow from said surface area through said component;
and (c) means for inspecting the cooled area by reversed thermography in order to locate any cold spots that would be indicative of defects.
Brief description of the drawi~s Figure 1 identified as "prior art" is a schematic representation of the detection of bonding defects by laser thermography;
Figure 2 is a schematic representation of tlne detection of bonding defects by the method according to the invention, using air cooled reversed thermography;
Figure 3 is an IR camera image of a cylinder wall surface with defects while cooled with compressed air;
Figure 4 is a curve giving the temperaW re profile along a line running across two defects;
Figure 5 is a schematic representation of an apparatus according to the invention for use to inspect engine block cylinders.
Figure 6 is a side elevational view of an apparatus according to a preferred embodiment of the invention, hereinafter called "cylinder inspection system";
Figure 7 is a schematic perspective view of the head assembly of the system shown in Figure 6;
The invention also provides an apparah~s for carrying out the above method.
This application comprises:
(a) means for generating a flow of a cold gas;
(b) means for applying the flow of cold gas to a surface area of the component to be inspected, thereby establishing a heat flow from said surface area through said component;
and (c) means for inspecting the cooled area by reversed thermography in order to locate any cold spots that would be indicative of defects.
Brief description of the drawi~s Figure 1 identified as "prior art" is a schematic representation of the detection of bonding defects by laser thermography;
Figure 2 is a schematic representation of tlne detection of bonding defects by the method according to the invention, using air cooled reversed thermography;
Figure 3 is an IR camera image of a cylinder wall surface with defects while cooled with compressed air;
Figure 4 is a curve giving the temperaW re profile along a line running across two defects;
Figure 5 is a schematic representation of an apparatus according to the invention for use to inspect engine block cylinders.
Figure 6 is a side elevational view of an apparatus according to a preferred embodiment of the invention, hereinafter called "cylinder inspection system";
Figure 7 is a schematic perspective view of the head assembly of the system shown in Figure 6;
Figure 8 is a top perspective view of parl:ial cross-section of one of the air injectors used in a system shown in Figure 6;
Figure 9 is a top view of a cylinder subj ected to inspection, showing the respective location of the air injectors and mirror of the system shown in Figure 6;
Figure 10 is a block diagramm of the conlTO1 device of the system shown in Figure 6;
and Figure 11 is a typical screen display of a cylinder with defects inspected with the system shown in Figure 6.
Detailed description of the invention As aforesaid, the way bonding defects can be detected by the method according to the invention is schematically illustrated in Figure. 2. As already indicated hereinabove, this method is not restricted to the detection of defects in engine block cylinder walls. As a matter of fact, it can detect any defect whose size, shape and orientation significantly disrupts the heat flowing perpendicularly to the surface of a component.
If such is needed, cold components can be heated prior to inspection. All that is required is that the component be massive enough to act as a "virtually infinite" heat sink (or, in this case, "cold" sink) for as long as it takes to establish steady state heat flow conditions through the inspected layer:In other words, the component has to be much thicker than the inspected layer.
In carrying out the method according to the invention, it is assumed that heat flows in only one direction (inside-out). Of course, heat also flows sideways and can go around a defect, blurring the contrast at the edge of deeper ones. Therefore, the resolution of the method is limited by the depth of potential defects, i.e. the thickness of the inspected layer.
Another factor that contributes to the efficiency of the method according to the invention is the thermal conductivity of the material. If it is high, a physical discontinuity will cause a much greater disruption in the heat flow than if the material is itself a good thermal insulator. Therefore, contrasts in thermal barrier coatings will be lower than in the case of cylinder walls where the steel coating is a fairly good heat conductor and aluminum is an excellent one.
Figure 3 shows images of artificial bonding defects in a test cylinder wall.
The aluminum cylinder was 3" in diameter and 5" long. Wall thickness was 3/8" with a .010" thick steel coating on the inside. For convenience, the ~oylinder was longitudinally cut in two.
An IR camera was aimed toward the inside surface of one of the half cylinders which was then heated with a heat gun (a kind of "industrial" hair dryer) to about 60 ° C. The picture from the IR camera showed a uniformly warm surface.
Figure 9 is a top view of a cylinder subj ected to inspection, showing the respective location of the air injectors and mirror of the system shown in Figure 6;
Figure 10 is a block diagramm of the conlTO1 device of the system shown in Figure 6;
and Figure 11 is a typical screen display of a cylinder with defects inspected with the system shown in Figure 6.
Detailed description of the invention As aforesaid, the way bonding defects can be detected by the method according to the invention is schematically illustrated in Figure. 2. As already indicated hereinabove, this method is not restricted to the detection of defects in engine block cylinder walls. As a matter of fact, it can detect any defect whose size, shape and orientation significantly disrupts the heat flowing perpendicularly to the surface of a component.
If such is needed, cold components can be heated prior to inspection. All that is required is that the component be massive enough to act as a "virtually infinite" heat sink (or, in this case, "cold" sink) for as long as it takes to establish steady state heat flow conditions through the inspected layer:In other words, the component has to be much thicker than the inspected layer.
In carrying out the method according to the invention, it is assumed that heat flows in only one direction (inside-out). Of course, heat also flows sideways and can go around a defect, blurring the contrast at the edge of deeper ones. Therefore, the resolution of the method is limited by the depth of potential defects, i.e. the thickness of the inspected layer.
Another factor that contributes to the efficiency of the method according to the invention is the thermal conductivity of the material. If it is high, a physical discontinuity will cause a much greater disruption in the heat flow than if the material is itself a good thermal insulator. Therefore, contrasts in thermal barrier coatings will be lower than in the case of cylinder walls where the steel coating is a fairly good heat conductor and aluminum is an excellent one.
Figure 3 shows images of artificial bonding defects in a test cylinder wall.
The aluminum cylinder was 3" in diameter and 5" long. Wall thickness was 3/8" with a .010" thick steel coating on the inside. For convenience, the ~oylinder was longitudinally cut in two.
An IR camera was aimed toward the inside surface of one of the half cylinders which was then heated with a heat gun (a kind of "industrial" hair dryer) to about 60 ° C. The picture from the IR camera showed a uniformly warm surface.
5 Compressed, room temperature air was thc;n blown from a nozzle directly onto an area at the center of the camera's field of view where dc;fects were known to be present. As can be seen in Figure 3, the cone shaped area struck by the compressed air appears as shaded in the IR
image because it is understandably cooler. Near the center, two defects are clearly visible as cold spots within the continuously cooled area. '.Che shape and location of these spots are in perfect agreement with the defect map given by tJhe test cylinder maker.
Figure 4 gives the temperature profile along the faint line marker visible in Figure 3.
As can be seen, the defects are 4 to 6°C cooler than the surrounding area. Considering that the temperature difference between the sample and the compressed air is about 50 ° C, 4 to 6 ° C is a very significant contrast.
Inspection of cylinders In the simple experiment described above, the geometrical complexity of inspecting the inside of a 360° cylindrical surface was circumvented by cutting it in half, thus allowing direct, perpendicular viewing of the interior. For real engine blocks, an optical arrangement has to be designed to allow viewing from the top, such as illustrated by way of example only in Figure 5.
As can be seen, a mirror 1 allows an IR camera 3 located on top of the block to inspect an area 9 inside a cylinder 7. Compressed air should of course be blown via a nozzle 5 onto the same area. The minor 1 and air nozzle 5 are located inside a cylindrical housing that shrouds the remainder of the cylinder's inner surface 7 to prevent IR radiation from that surface to blind the IR camera. The whole assembly pivots 360° ('see the arrow) to scan a complete cylindrical section of the surface. The head is moved up and the process is repeated until the whole cylinder has been covered.
As can be easily understood, the whole process can be automated. A computer can easily collate the various scan results to display an unfolded, continuous image of the whole cylinder which can be processed by image analysis software to signal an operator if the area and density (i.e. intensity of the contrast) of defects exceeds preset thresholds.
image because it is understandably cooler. Near the center, two defects are clearly visible as cold spots within the continuously cooled area. '.Che shape and location of these spots are in perfect agreement with the defect map given by tJhe test cylinder maker.
Figure 4 gives the temperature profile along the faint line marker visible in Figure 3.
As can be seen, the defects are 4 to 6°C cooler than the surrounding area. Considering that the temperature difference between the sample and the compressed air is about 50 ° C, 4 to 6 ° C is a very significant contrast.
Inspection of cylinders In the simple experiment described above, the geometrical complexity of inspecting the inside of a 360° cylindrical surface was circumvented by cutting it in half, thus allowing direct, perpendicular viewing of the interior. For real engine blocks, an optical arrangement has to be designed to allow viewing from the top, such as illustrated by way of example only in Figure 5.
As can be seen, a mirror 1 allows an IR camera 3 located on top of the block to inspect an area 9 inside a cylinder 7. Compressed air should of course be blown via a nozzle 5 onto the same area. The minor 1 and air nozzle 5 are located inside a cylindrical housing that shrouds the remainder of the cylinder's inner surface 7 to prevent IR radiation from that surface to blind the IR camera. The whole assembly pivots 360° ('see the arrow) to scan a complete cylindrical section of the surface. The head is moved up and the process is repeated until the whole cylinder has been covered.
As can be easily understood, the whole process can be automated. A computer can easily collate the various scan results to display an unfolded, continuous image of the whole cylinder which can be processed by image analysis software to signal an operator if the area and density (i.e. intensity of the contrast) of defects exceeds preset thresholds.
zam A complete cylinder inspection system was developed based on the arrangement illustrated in Figure 5. As it can be understood, thc; actual design of the inspection head of the system that was developed is much more comple:~c than the one illustrated in Figure S.
As shown in Figure 6, this inspection system comprised an inspection head 21 and a camera 3 mounted on a turntable 23 to provide roW tion for the scans. A
vertical slide 25 moved the turntable/camera/head assembly from a bottom scan position to a top scan position within the cylinder, as well as to a completely retracted position out of the engine block being inspected. The centerline of the engine block cylinder is identified by letter "A" . The assembly also comprised an assembly line conveyor 27 to move the engine block when the head 21 and camera 3 were in retracted position to align the nc;xt cylinder for inspection or to bring a new block for inspection. Of course, movements of the conveyor were coordinated with the inspection sequence.
As shown in Figure 7, the inspection head 21 comprised a top plate 29, a bottom plate 31 and two side plates (not shown) in the back for stiffening the assembly and hiding the rest of the cylinder's inner surface from the camera.. The assembly 21 also comprises two air injectors 11, 11' fixed to the bottom plate 31 on which the mirror 1 was also mounted. The top plate 29 had a view-port 33 through which the camera had access to the mirror 1. The top plate was thick enough to house the air ducts that feed the injectors. All elements of the head except the minor surface were coated with IR absorbing black paint.
The air injectors 11, 11' were designed to focus the flow onto a narrow vertical strip along the full length of the cylinder portion viewed through the mirror. The air injectors were also designed to minimize obstruction of the camera lens aperture and allow for a maximum of IR radiation to be collected.
As is better shown in Figure 8, each air injiector 11, 11' comprised an aluminium body 13 closed by a steel cover 15 with a gasket 17 in between. The air injector 11 defined a square cavity 19 which series as a manifold into which compressed air is brought from the top. The compressed air escaped through a series of 50, 10 mm long, 1 mni2 small nozzles 21. Because of its aspect ratio, each nozzle 21 maximized air velocity in the longitudinal direction, thus producing an air jet that remains fairly well collimated up to about 10 mm away. Disposing 50 of those along a line therefore produced an air jet i.n the shape of a blade.
This principle is well known to manufacturers of air nozzles for various industrial applications such as cleaning, stripping debris off a conveyor belt, etc.
As shown in Figure 6, this inspection system comprised an inspection head 21 and a camera 3 mounted on a turntable 23 to provide roW tion for the scans. A
vertical slide 25 moved the turntable/camera/head assembly from a bottom scan position to a top scan position within the cylinder, as well as to a completely retracted position out of the engine block being inspected. The centerline of the engine block cylinder is identified by letter "A" . The assembly also comprised an assembly line conveyor 27 to move the engine block when the head 21 and camera 3 were in retracted position to align the nc;xt cylinder for inspection or to bring a new block for inspection. Of course, movements of the conveyor were coordinated with the inspection sequence.
As shown in Figure 7, the inspection head 21 comprised a top plate 29, a bottom plate 31 and two side plates (not shown) in the back for stiffening the assembly and hiding the rest of the cylinder's inner surface from the camera.. The assembly 21 also comprises two air injectors 11, 11' fixed to the bottom plate 31 on which the mirror 1 was also mounted. The top plate 29 had a view-port 33 through which the camera had access to the mirror 1. The top plate was thick enough to house the air ducts that feed the injectors. All elements of the head except the minor surface were coated with IR absorbing black paint.
The air injectors 11, 11' were designed to focus the flow onto a narrow vertical strip along the full length of the cylinder portion viewed through the mirror. The air injectors were also designed to minimize obstruction of the camera lens aperture and allow for a maximum of IR radiation to be collected.
As is better shown in Figure 8, each air injiector 11, 11' comprised an aluminium body 13 closed by a steel cover 15 with a gasket 17 in between. The air injector 11 defined a square cavity 19 which series as a manifold into which compressed air is brought from the top. The compressed air escaped through a series of 50, 10 mm long, 1 mni2 small nozzles 21. Because of its aspect ratio, each nozzle 21 maximized air velocity in the longitudinal direction, thus producing an air jet that remains fairly well collimated up to about 10 mm away. Disposing 50 of those along a line therefore produced an air jet i.n the shape of a blade.
This principle is well known to manufacturers of air nozzles for various industrial applications such as cleaning, stripping debris off a conveyor belt, etc.
In the system that was developed, two such air injectors 11, 11' were used. As is better shown in Figure 9, the two air injectors 11, 11' lhereinafter called "clockwise injector" and "counter-clockwise injector", respectively, were positioned within the cylinder 7 to be inspected so as to inject air at an angle of 45° toward a same spot.
The mirror 1 was positioned between the injectors. Preliminary tests have shown that up to that angle of 45°, the cooling effect of the air jet is almost as good as when it was aimed straight at the surface (0°). This allows the least amount of obstruction of the camc;ra leans aperture, as previously mentioned.
For the same reason, the body 13 of each injector 11, 11' containing the manifold was located on the exterior side of the injection holes.
The reason why two air injectors 11, 11' were used, is as follows. A complete inspection sequence requires two scans, one for thc; bottomp art of the cylinder wall and one for the top part. For the second scan, the head rotates in the reverse direction from the first one.
This reduces twisting of all the cables connecting; to the inspection head without the need for a "cable untwisting" reverse rotation between the two scans. Since better contrasts were obtained when the inspection head rotated in the direction of the flow, it was found that two injectors were actually required, one for the clockwise scan and one for the counter-clockwise one.
As aforesaid, Figure 7 also shows the 4:i°mirror 1. As is illustrated, the mirror was wider at the top where it was the most distant from the inspected area than at the bottom, where it was very close to it. Again, this was made to exploit the full aperture of the camera lens, i.e.
every part of the inspected area "accesses" the whole aperture of the lens.
Figure 10 is a block diagramm of the central device of the inspection system that was developed and tested. As is shown, the developed system was controlled by a PC
type computer which captured the camera's video signal throu~;h a frame-grabber card (also called "video"
card) located in one of the computer's expansion slots and which also drove the vertical and rotational axis stepper motors through a stepper motor controller connected to the computer's printer port.
Figure 11 illustrates a typical screen display that was obtained after inspection of a cylinder with the system shown in Figures 6 to 10. The complete thermal image of the cylinder's inner surface was displayed. Darker areas are regions where the cooling effect of the air jet was most effective in reducing surface temperature, indicating inferior heat transfer properties that may be caused by delamination or other forms of sub-surface defects.
The top and bottom scans produced the top and bottom part of the image which were seamlessly morphed together to display the whole cylinder at once. Each half image was obtained by juxtaposing data from a single vertical line captured about 600 times during the 360° rotation of the head. Within the field of view of the camera, this line was chosen as the centerline of the area cooled by the air injectors. Since the frame grabber card acquired 60 images/s from which 60 lines/s were extracted, each scan took approximately 10 seconds, and therefore a complete inspection, a little over 20 seconds.
The software saved all cylinder images as it automatically sequenced through inspection of the whole engine block. Various standard image analysis criteria such as severity, size or density of defects could be adjusted to provide a simple "passed" or "failed" signal to the operator.
"Failed" blocks were diverted out of the .assembly line for closer examination by QC
personal later on who could recall individual cylinder images form these blocks and make the final decision to scrap or process them.
Of course, modifications could easily be made to the method and apparatus disclosed hereinabove and illustrated in the accompanying drawings without departing from the scope of the present invention.
The mirror 1 was positioned between the injectors. Preliminary tests have shown that up to that angle of 45°, the cooling effect of the air jet is almost as good as when it was aimed straight at the surface (0°). This allows the least amount of obstruction of the camc;ra leans aperture, as previously mentioned.
For the same reason, the body 13 of each injector 11, 11' containing the manifold was located on the exterior side of the injection holes.
The reason why two air injectors 11, 11' were used, is as follows. A complete inspection sequence requires two scans, one for thc; bottomp art of the cylinder wall and one for the top part. For the second scan, the head rotates in the reverse direction from the first one.
This reduces twisting of all the cables connecting; to the inspection head without the need for a "cable untwisting" reverse rotation between the two scans. Since better contrasts were obtained when the inspection head rotated in the direction of the flow, it was found that two injectors were actually required, one for the clockwise scan and one for the counter-clockwise one.
As aforesaid, Figure 7 also shows the 4:i°mirror 1. As is illustrated, the mirror was wider at the top where it was the most distant from the inspected area than at the bottom, where it was very close to it. Again, this was made to exploit the full aperture of the camera lens, i.e.
every part of the inspected area "accesses" the whole aperture of the lens.
Figure 10 is a block diagramm of the central device of the inspection system that was developed and tested. As is shown, the developed system was controlled by a PC
type computer which captured the camera's video signal throu~;h a frame-grabber card (also called "video"
card) located in one of the computer's expansion slots and which also drove the vertical and rotational axis stepper motors through a stepper motor controller connected to the computer's printer port.
Figure 11 illustrates a typical screen display that was obtained after inspection of a cylinder with the system shown in Figures 6 to 10. The complete thermal image of the cylinder's inner surface was displayed. Darker areas are regions where the cooling effect of the air jet was most effective in reducing surface temperature, indicating inferior heat transfer properties that may be caused by delamination or other forms of sub-surface defects.
The top and bottom scans produced the top and bottom part of the image which were seamlessly morphed together to display the whole cylinder at once. Each half image was obtained by juxtaposing data from a single vertical line captured about 600 times during the 360° rotation of the head. Within the field of view of the camera, this line was chosen as the centerline of the area cooled by the air injectors. Since the frame grabber card acquired 60 images/s from which 60 lines/s were extracted, each scan took approximately 10 seconds, and therefore a complete inspection, a little over 20 seconds.
The software saved all cylinder images as it automatically sequenced through inspection of the whole engine block. Various standard image analysis criteria such as severity, size or density of defects could be adjusted to provide a simple "passed" or "failed" signal to the operator.
"Failed" blocks were diverted out of the .assembly line for closer examination by QC
personal later on who could recall individual cylinder images form these blocks and make the final decision to scrap or process them.
Of course, modifications could easily be made to the method and apparatus disclosed hereinabove and illustrated in the accompanying drawings without departing from the scope of the present invention.
Claims (14)
1. A method for the detection of near surface defects in a component, comprising the steps of:
(a) applying a flow of a cold gas to a surface area of the component to be inspected, thereby establishing a heat flow from said surface area through said component; and (b) subjecting the cooled surface area to an inspection by reversed thermography in order to locate any cold spots that would be indicative of defects.
(a) applying a flow of a cold gas to a surface area of the component to be inspected, thereby establishing a heat flow from said surface area through said component; and (b) subjecting the cooled surface area to an inspection by reversed thermography in order to locate any cold spots that would be indicative of defects.
2. The method of claim 1, wherein the gas used in step (a) is air and the inspection of step (b) is carried out with an infrared camera.
3. The method of claim 2, comprising the additional steps of:
preheating the component prior to carrying out steps (a) and (b); and using compressed air at room temperature for carrying out step (a).
preheating the component prior to carrying out steps (a) and (b); and using compressed air at room temperature for carrying out step (a).
4. The method of claim 2, wherein the component is an engine block cylinder.
5. The method of claim 3, wherein the component is an engine block cylinder.
6. An apparatus for the detection of near surface defects in a component, comprising:
(a) means for generating a flow of a cold gas;
(b) means for applying the flow of cold gas to a surface area of the component to be inspected, thereby establishing a heat flow from said surface area through said component; and (c) means for inspecting the cooled surface area by reversed thermography in order to locate any cold spots that would be indicative of defects.
(a) means for generating a flow of a cold gas;
(b) means for applying the flow of cold gas to a surface area of the component to be inspected, thereby establishing a heat flow from said surface area through said component; and (c) means for inspecting the cooled surface area by reversed thermography in order to locate any cold spots that would be indicative of defects.
7. The apparatus of claim 6, wherein:
the means (a) for generating the flow of cold gas is an air compressor;
the means (b) for applying the flow of cold gas is an air nozzle connected to the air compressor; and the means (c) for inspecting the cooled surface area is an infra-red camera.
the means (a) for generating the flow of cold gas is an air compressor;
the means (b) for applying the flow of cold gas is an air nozzle connected to the air compressor; and the means (c) for inspecting the cooled surface area is an infra-red camera.
8. The apparatus of claim 7, further comprising:
(d) means for preheating the component prior to carrying out the detection, whereby air at room temperature can be used as said cold gas.
(d) means for preheating the component prior to carrying out the detection, whereby air at room temperature can be used as said cold gas.
9. The apparatus of claim 7 for use when the surface area to be inspected is in a cavity within the component, wherein said apparatus further comprises:
a mirror sized to be inserted into the cavity and oriented to allow the infra-red camera to inspect the cooled surface area from outside of said cavity;
a housing for shrouding non-inspected areas of the cavity while the surface area to be inspected is subjected to the said inspection; and means for moving said mirror, air nozzle and housing within the cavity to inspect a plurality of said surface areas.
a mirror sized to be inserted into the cavity and oriented to allow the infra-red camera to inspect the cooled surface area from outside of said cavity;
a housing for shrouding non-inspected areas of the cavity while the surface area to be inspected is subjected to the said inspection; and means for moving said mirror, air nozzle and housing within the cavity to inspect a plurality of said surface areas.
10. The apparatus of claim 9, wherein the component is an engine block cylinder.
11. The apparatus of claim 8 for use when the surface area to be inspected is in a cavity within the component, wherein said apparatus further comprises:
a mirror sized to be inserted into the cavity and oriented to allow the infra-red camera to inspect the cooled surface area from outside of said cavity;
a housing for shrouding non-inspected areas of the cavity while the surface area to be inspected is subjected to the said inspection; and means for moving said mirror, air nozzle and housing within the cavity to inspect a plurality of said surface areas.
a mirror sized to be inserted into the cavity and oriented to allow the infra-red camera to inspect the cooled surface area from outside of said cavity;
a housing for shrouding non-inspected areas of the cavity while the surface area to be inspected is subjected to the said inspection; and means for moving said mirror, air nozzle and housing within the cavity to inspect a plurality of said surface areas.
12. The apparatus of claim 11, wherein the component is an engine block cylinder.
13. The apparatus of claim 7, further comprising:
means for collecting scan results from the infrared camera;
means for displaying an unfolded, continuous image of the surface area subjected to said inspection; and means for processing the collected scan results by image analysis and for giving a signal if a detected defect exceeds a preset threshold of area and/or density.
means for collecting scan results from the infrared camera;
means for displaying an unfolded, continuous image of the surface area subjected to said inspection; and means for processing the collected scan results by image analysis and for giving a signal if a detected defect exceeds a preset threshold of area and/or density.
14. The apparatus of claim 11, further comprising:
means for collecting scan results from the infrared camera;
means for displaying an unfolded, continuous image of the surface area subjected to said inspection; and means for processing the collected scan results by image analysis and for giving a signal if a detected defect exceeds a preset threshold of area and/or density.
means for collecting scan results from the infrared camera;
means for displaying an unfolded, continuous image of the surface area subjected to said inspection; and means for processing the collected scan results by image analysis and for giving a signal if a detected defect exceeds a preset threshold of area and/or density.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2267586 CA2267586A1 (en) | 1998-04-16 | 1999-04-13 | Detection of near surface defects by reversed thermography |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2231524 CA2231524A1 (en) | 1998-04-16 | 1998-04-16 | Detection of near surface defects by reversed thermography |
| CA2.231.524 | 1998-04-16 | ||
| CA 2267586 CA2267586A1 (en) | 1998-04-16 | 1999-04-13 | Detection of near surface defects by reversed thermography |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2267586A1 true CA2267586A1 (en) | 1999-10-16 |
Family
ID=29712970
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2267586 Abandoned CA2267586A1 (en) | 1998-04-16 | 1999-04-13 | Detection of near surface defects by reversed thermography |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2267586A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2444796A3 (en) * | 2007-08-08 | 2012-12-19 | Semi-Conductor Devices - An Elbit Systems - Rafael Partnership | Thermography based system and method for detecting counterfeit drugs. |
| US9008408B2 (en) | 2009-02-05 | 2015-04-14 | D.I.R. Technologies (Detection Ir) Ltd. | Method and system for determining the quality of pharmaceutical products |
| WO2019173958A1 (en) * | 2018-03-13 | 2019-09-19 | 大连理工大学 | Detection method for hollowing of exterior wall decorative surface layer |
| CN115931873A (en) * | 2022-12-06 | 2023-04-07 | 秦皇岛艾科晟科技有限公司 | Production line for machining surface of cover machine and detection process of production line |
-
1999
- 1999-04-13 CA CA 2267586 patent/CA2267586A1/en not_active Abandoned
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2444796A3 (en) * | 2007-08-08 | 2012-12-19 | Semi-Conductor Devices - An Elbit Systems - Rafael Partnership | Thermography based system and method for detecting counterfeit drugs. |
| US8586928B2 (en) | 2007-08-08 | 2013-11-19 | Semi-Conductor Devices—An Elbit Systems-Rafael Partnership | Thermography based system and method for detecting counterfeit drugs |
| US9008408B2 (en) | 2009-02-05 | 2015-04-14 | D.I.R. Technologies (Detection Ir) Ltd. | Method and system for determining the quality of pharmaceutical products |
| WO2019173958A1 (en) * | 2018-03-13 | 2019-09-19 | 大连理工大学 | Detection method for hollowing of exterior wall decorative surface layer |
| US11367171B2 (en) | 2018-03-13 | 2022-06-21 | Dalian University Of Technology | Method for detecting hollowing of exterior wall finish layer |
| CN115931873A (en) * | 2022-12-06 | 2023-04-07 | 秦皇岛艾科晟科技有限公司 | Production line for machining surface of cover machine and detection process of production line |
| CN115931873B (en) * | 2022-12-06 | 2024-03-22 | 秦皇岛艾科晟科技有限公司 | Cover machine surface detection production line and detection process thereof |
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