A method and a device for production of a set of holes

TECHNICAL FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a method for production of a set of holes through a wall by treatment of the wall by forming and/or changing the cross-section of said holes, said holes having as a set a predetermined characteristic, as well as a device for such a production.

"Production of a set of holes" is to be interpreted broadly and covers the formation of a set of holes through a wall by material diverging measures, i.e. by removing material, such as through conventional drilling or by laser burning, or material conserving measures such as displacing material by piercing, changing of the cross-section of already existing holes by increasing the cross-section thereof through diverging and/or conserving machining or material converging measures decreasing the cross- section thereof by for instance partially coating the holes as well as all possible combinations of these types of treatments of the wall for obtaining a set of holes having a predetermined characteristic. Thus, some of the holes may for instance already be there and the production only consist of the formation of additional holes for obtaining said set having a predetermined char- acteristic. "Predetermined characteristic" may for example be a predetermined total cross-section area of said holes or an effective cross-section experienced by a flow through those holes. The characteristic may also be a specific pressure drop for a specific mass flow at a certain feed pressure.

Furthermore, "wall" is also to be interpreted broadly and refers to any "wall-like" element and has not to be a real wall, but it may for instance be a turbine blade in a gas turbine.

The production of a set of holes in the form of effusion cooling holes in a combustor can for a gas turbine will now be described

for illuminating the invention but not in any way limiting the scope thereof. The result of this production has a significant impact on cooling, operating temperature and emissions of the combustor of the gas turbine and the lifetime of downstream components in the turbine. It is known to produce such a set of holes by so-called laser drilling, which means mainly material diverging machining of the wall material by laser beam burning.

It is very important that these holes as a set has a predeter- mined characteristic, such as a predetermined total cross-section area, but also other parameters may be included in said predetermined characteristic, so as to obtain an optimum operation of the combustor and the turbine. This issue is handled by taking the completed part to which said wall belongs to a sepa- rate test stand after it has been removed from the laser machining centre and carrying out measurements thereon. When these measurements show a deviation from said predetermined characteristic of said set of holes correction of for instance the whole combustor assembly flow rate then takes place by for in- stance drilling trimming holes in adjacent parts such as the impingement sleeve.

A number of disadvantages are inherent in this way of proceeding. At least two operations are required with separate fixtures, which slows down the manufacturing process. There will be a significant variation between individual sub-parts having a said wall, since the set of holes of each sub-part will have different characteristics, so that inter-changeability is compromised. Accordingly, one such sub-part may not be replaced by another, since said measurements have not been carried out on a separate such sub-part, but only for the entire combustor assembly. Furthermore, as such sub-parts have to be trimmed and matched, there is an opportunity for mistaken assembly. Since the matching is for the assembly as a whole at a given test con- dition, there will still be flow split variation at conditions away

from this condition, such as those which are experienced in the operation of the gas turbine.

A method of the type defined in the introduction is already known through US patent No. 6 408 610 disclosing a "method of adjusting gas turbine component cooling air flow", in which the production of a set of holes in a wall takes place by coating an area of the wall including existing holes, so that said holes are then partially coated and the cross-section thereof is changed. After this has been done, the component having said set of holes is brought to a pressure flow stand, which is used to flow check the component. It is then checked whether the air flow is within a pre-selected range of desired cooling hole airflows. When this is the case, the component is accepted for use and otherwise it is returned to a chamber for said coating procedure and subjected to further coating, whereupon it is flow checked again in said pressure flow stand. This method solves some of the problems mentioned above, but the production of said set of holes is still time consuming, rather complicated and in some situations not reliable enough.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method and a device of the type defined in the introduction solving the above problems of such methods and devices already known.

With respect to the method this object is according to the invention obtained by providing such a method comprising the steps of arranging for a fluid to flow through said holes at least during the last phase of said production while keeping said wall on the location for said treatment, monitoring said flow through the holes at least during the last phase of said production to monitor the progress of the production of said set of holes, and adapting said treatment to the result of said monitoring for obtaining said set of holes with said predetermined characteristic.

By arranging for said flow through said holes and the monitoring thereof during the production of a set of holes while keeping the wall on the location for said treatment two operations, i.e. pro- duction and checking, are combined in one and no separate fixtures are needed. This shortens the time for the production of said set of holes. The treatment will directly be adapted to the result of the monitoring so that a set of holes with said predetermined characteristic will efficiently and reliably be obtained. Furthermore, combining two operations into one will narrow the necessary tolerance band during production, and an analysis has shown a strong correlation between hardware temperatures and the width of the tolerance band in the case of combustor can cooling flow area.

It is pointed out that it may be arranged for said fluid flow during the entire phase of said production, while the monitoring only takes place during said last phase, which also includes the case of carrying out said monitoring as of a moment in which it is as- sumed that the set of holes has said predetermined characteristic, and when the assumption is correct, the adaption of said treatment will then simply mean that the treatment is stopped. Other combinations of said arranging for the fluid flow and said monitoring thereof are also possible, and the invention also in- eludes the case of intermittently arranging for such a flow and/or monitoring such a flow as long as said wall is kept on the location for said treatment.

According to an embodiment of the invention said treatment is continued until one or more parameters of said flow substantially has assumed a predetermined value. Such parameters may for instance be pressure or mass flowrate of said flow.

According to a further embodiment it is arranged for a fluid to flow through said holes by applying a fluid to said holes with a substantially constant pressure, and said flow is monitored by

measuring the mass flowrate of said fluid through said holes. This way of proceeding is especially suitable when using a liquid, such as water, as said fluid.

According to another embodiment of the invention it is arranged for a fluid to flow through said holes by applying a fluid to said holes with a substantially constant mass flowrate, and said flow is monitored by measuring the pressure by which said fluid is applied to said holes, which advantageously may be carried out when using a gas, such as air, as said fluid.

According to another embodiment of the invention said treatment of the wall comprises material diverging and/or material conserving machining, such as drilling and piercing, respec- tively. It has turned out that it may mostly be arranged for a fluid to flow through said holes during the actual treatment in the form of such machining for facilitating the control of the operation for said production of the set of holes.

According to another embodiment of the invention the pressure by which said fluid is applied to said holes is selected so as to be able to eject possible debris, such as drilling debris, from the holes. This means that said flow being there for ensuring that a set of holes with said predetermined characteristic is obtained is also utilised for removing debris trapped in the holes, so that no extra operation is needed therefor.

According to another embodiment of the invention the mass flowrate by which said fluid is applied to said holes is selected so as to be able to eject possible debris, such as drilling debris, from the holes, which is a suitable way to proceed when using a liquid as said fluid.

According to another embodiment of the invention said fluid is applied to said holes in a pulsating manner so as to eject possible debris, such as drilling debris, from the holes. This is a way

of further improving the debris removing features of said fluid flow.

According to another embodiment of the invention said fluid is applied to said holes in alternating directions so as to eject possible debris, such as drilling debris, from said holes.

According to another embodiment of the invention it is arranged for a fluid to flow through said holes during substantially the en- tire production of said set of holes for removing waste, such as drilling debris, from the holes formed and/or changed.

According to another embodiment of the invention it is arranged for a fluid to flow through said holes only during the last phase of the production of said set of holes, which is advantageous should there be a desire to avoid fluid flow through said holes earlier in the production process for instance to conserve fluid but not limited to this objective.

According to another embodiment of the invention before the step of arranging for a fluid to flow through said holes a de- burring or polishing of sharp edges in at least some of the holes formed or changed is carried out. This further improves the reliability of the method, since that treatment of the sharp edges will give the holes their final shape, and this is particularly advantageous when this is carried out for the majority of the holes before the step of arranging for a fluid to flow through said holes.

According to another embodiment of the invention the method comprises a step of coating at least a portion of an area of said wall including existing said holes. It is then possible to let this coating step be a part of said treatment while partially coating at least some of existing holes for reducing the cross-section thereof. The coating may for example be metal and ceramic

coating, but it also includes application of thermal paint or other paint.

According to another embodiment of the invention it is arranged for a fluid to flow through said holes during at least a part of said coating step. The flow of fluid may in this way be used for controlling the cross-section area of the holes thus coated, and it may even be controlled so that there will be no coating of the holes and the coating step will then not be a part of said treat- ment for the production of said set of holes. However, in the first case the arranging for a fluid to flow through said holes will influence the result of the changing of the cross-section of the holes by said coating and accordingly itself be a part of said treatment.

According to another embodiment of the invention a set of holes is produced in a wall in a component of a turbomachine. This component may for instance be a combustor can, a guide vane, a turbine blade, a heat shield, a burner or a cooling insert. The method is particularly advantageous for such components with respect to the problems discussed in the introduction of known methods for producing such components.

According to another embodiment of the invention a set of holes is produced in a wall of a component part of a combustor of a gas turbine, and this component part may for instance be a combustor can of a gas turbine, but quite different parts are conceivable, such as a burner. In the case of a can-like shape of said component part this may have any desired cross-section, such as circular and rectangular. However, the component part may just as well be an annular combustor.

According to another embodiment of the invention a set of holes is produced in a wall to be used for impingement cooling by flow of cooling fluid through said holes onto another component.

According to another embodiment of the invention a set of holes is produced through a wall of a member to be cooled by a flow of cooling fluid through said holes. The cooling may for this member be intended to be mainly obtained by the flow through said holes (effusion cooling) or by the passage of the cooling fluid along said wall before passing through said holes while providing a shield against hot fluid (film cooling).

According to another embodiment of the invention a set of holes is produced in a wall for later supply of a component, such as fuel, needed for a combustion in a space at least partially delimited by said wall. This component may for instance be a burner and said space have an arbitrary cross-section.

According to another embodiment of the invention it is arranged for a fluid to flow through said holes by sealing a space on one side of said wall partially delimited by an area of said wall in which said set of holes is intended to be located and said flow is created through said holes by feeding said fluid into said space and through said holes out of said space or by feeding said fluid into said space through said holes. "Feeding" is intended to cover extracting, such as through suction, as well as supplying, such as blowing (in the case of a gas). By sealing a space and carry out said feeding in this way the monitoring of said feed flow for determining whether said set of holes has said predetermined property may be easily and reliably carried out.

With respect to the device the object of the present invention is obtained by providing a device for production of a set of holes through a wall, said holes having as a set a predetermined characteristic, said device comprising an arrangement adapted to subject said wall to a treatment by forming and/or changing the cross-section of said holes, which is further characterized in that it comprises means for supplying a fluid to flow through said holes at least during the last phase of said production with said wall being on the location for said treatment, means adapted to

monitor said flow through the holes at least during the last phase of said production by measuring at least one parameter thereof, means adapted to compare the results of said measurement of said monitoring means with a parameter indicative of said predetermined characteristic, and means adapted to control said arrangement for said treatment of the wall in dependence of the result of said comparison for obtaining said set of holes with said predetermined characteristic.

The function, results and advantages of such a device appear from the description above of the method according to the invention.

According to an embodiment of the invention said control means is adapted to control said arrangement to continue to carry out said treatment until one or more parameters of said flow substantially has assumed a predetermined value, in which these parameters may for instance be the pressure by which the fluid is applied to said holes or the mass flow of the fluid through said holes.

According to an embodiment of the invention the device comprises means for sealing a space on one side of said wall partially delimited by an area of said wall in which said set of holes is intended to be located and including sealing members adapted to sealingly bear against said wall for creating said sealed space, and said supplying means is adapted to create a flow through said holes by feeding said fluid into said space and through said holes out of said space or by feeding said fluid into said space through said holes. Through such a device said set of holes may efficiently and reliably be created in any component having a said wall irrespectively of the shape of said component or wall.

According to a further embodiment of the invention constituting a further development of the embodiment last mentioned said

arrangement is adapted to produce a said set of holes through walls forming an envelope surface of a can-like member, and said sealing means is adapted to create said sealed space by bearing circumferentially against the envelope surface of the can at both ends thereof by sealing members. The space may in this way be created either inside the can-like member by having the sealing members adapted to press against the inner envelope surface of the can-like member or externally thereof by having the sealing members adapted to press against the outer envelope surface of the can-like member.

According to another embodiment of the invention said arrangement is adapted to produce a said set of holes through walls forming an envelope surface of a can-like member, the de- vice also comprises holding means adapted to hold said can-like member fixed in place during said treatment by the action of inflatable members upon said can-like member, and said holding means comprises means adapted to inflate said inflatable members and let gas out thereof for holding and releasing, respec- tively, said can-like member. By using this type of inflatable members as holding means an accurate geometrical location of said can-like member with an adequate resistance to machining forces may be obtained without damaging the can-like member and facilitating quick and easy fixing and releasing of the can- like member.

According to another embodiment of the invention said sealing members of said sealing means are formed by said inflatable members adapted to circumferentially press against the enve- lope surface of said can-like member when inflated. By combining the inflatable members of the holding means and the sealing members the design and the operation of the device is simplified.

According to another embodiment of the invention said inflatable members have leakage holes opening into said sealed space,

and said supplying means is adapted to also act as said inflating means. This design combining the supplying means and the holding means simplifies the device by only requiring one supply line for both holding (fixing) said can-like member and supplying said fluid flow for monitoring the progress of the production of said set of holes.

Further advantages as well as advantageous features of the invention appear from the following description and the other de- pendent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a spe- cific description of embodiments of the invention cited as examples.

In the drawings:

Fig 1 is a schematic cross-section view through a part of a known gas turbine having components during the manufacture of which the method and the device according to the present invention may be applied,

Fig 2 is a sketch very schematically illustrating a device according to a first embodiment of the invention, and

Fig 3 is a view corresponding to that of fig 2 of a device according to a second embodiment of the invention.

DETAILED DESCRI PTION OF EMBODIMENTS OF THE INVENTION

A known gas turbine as used in for instance a power plant is schematically illustrated in fig 1 . The gas turbine has an air inlet

1 at one end followed by a compressor 2 for compressing the air

from said inlet. Combustors 3 having a can-like shell are distributed around the turbine shaft 4. Fuel is introduced into the respective combustor at 5 and is there mixed with a part of said air from the air inlet 1 for the combustion. Hot gases resulting from the combustion are driving the turbine blades 6 of the turbine part of the gas turbine and guided through guide vanes 7. Parts of the gas turbine may be provided with a set of holes having as a set a predetermined characteristic, such as a predetermined total cross-section area. These holes may be ap- plied for different reasons, such as for cooling. Thus, cooling air may for instance be introduced as a layer along the interior walls of each combustor can and escape through such holes for protecting the wall of the combustor can through so-called effusion cooling. Similar holes may be arranged for use for film cooling in for instance some or all turbine blades 6 and/or guide vanes 7. A set of holes may also be arranged in an impingement sleeve very schematically indicated at 8 used for so-called impingement cooling of the outer walls of the combustors 3.

A device and a method for production of a said set of holes will now be described with reference to fig 2. It is illustrated how a combustor can 9 having a substantially circular cross-section is provided with a set of holes 10 having a predetermined characteristic by a device according to a first embodiment of the inven- tion. This device comprises an arrangement 1 1 in the form of a laser beam for treatment of the wall 12 of the combustor can 9 by substantially material diverging machining in the form of laser burning, so-called laser drilling. The device further comprises means for sealing a space 13 inside the combustor can partially delimited by an area of the wall 12 in which said set of holes is intended to be located. This sealing means comprises inflatable tyre-like members 14, 15 arranged at both ends of the combustor can 9 and adapted to circumferentially press against the inner envelope surface thereof when inflated as shown in fig 2. The sealing means also comprises means 16 for supplying compressed air to said inflatable members. The inflatable members

14, 15 and the means 16 for supplying compressed air also constitutes a holding means adapted to hold said can-like member fixed in place during said treatment. The combustor can 9 is in this way fixed on a machine table 17 by being pressed down thereonto by said inflatable members. Release of the combustor can may easily be achieved by letting the air out of said inflatable members.

The device further comprises means in the form of compressed air supplying means 18 for supplying a fluid to flow through said holes at least during the last phase of said production of the set of holes. In this case the fluid is air and is fed to the interior of the sealed space 13 for escaping through the holes 10. Another alternative would be to suck air from the exterior and into the space 13 through said holes 10. The device also comprises means schematically indicated at 19 adapted to monitor said fluid through the holes at least during the last phase of said production by measuring at least one parameter thereof, such as the pressure of the air inside said space 13. It is for instance possible to supply a fixed mass flow, preferably after a certain portion of the holes have been drilled, and then stop drilling when the pressure measured by the monitoring means 19 has changed to a correct fixed value. The mass flow may for a gas be established by measuring pressure differences and for a Nq- uid by measuring the velocity of the liquid. Thus, 19 may stand for more than one sensor arranged on separate locations. The device comprises for this sake means 20 adapted to compare the results of said measurement of said monitoring means with a parameter indicative of said predetermined characteristic as well as means 21 adapted to control the arrangement 1 1 for said treatment of the wall in dependence of the result of this comparison for obtaining a set of holes with said predetermined characteristic.

The supplying means 18 may be adapted to supply said fluid to the space 13 and by that the holes in a pulsating manner so as to eject possible debris, such as drilling debris, from the holes.

The method for production of a set of holes having a predetermined property may through the use of this device be altered in many different ways as appear from the above discussion of the method according to the invention. One advantageous way to proceed is to drill so-called trimming holes, i.e. holes being less critical for the proper function of the set of holes for the later intended use thereof, during said last phase of the production of said set of holes. These holes may primarily be located close to the ends of the combustor can 9 as indicated by the holes 22 and 23. Sufficient cooling during the later use of the combustor can is in this way ensured where the component are most sensitive, whereas the number of holes in the end regions is not critical and may be adapted to the result of said comparison.

It is shown how a shield 24 is arranged for preventing the laser beams from damaging the fixture part 25 therebehind interconnecting the inflatable members 14, 15.

The air connections to the inflatable members and said space are preferably flexible, so that the machine table 17 can trav- erse/swivel past a fixed laser head of the arrangement 1 1 . Moreover, leaving the supply of fluid to said space flowing as the "holding fluid" is removed would pre-release or eject the can 9 for even easier handling.

Fig 3 schematically illustrates a device according to a second embodiment of the invention differing from that according to fig 2 only with respect to the holding means and the means for supplying fluid to flow through said set of holes, why only these parts will be further described here and the other parts have been provided with the same reference numerals as used for the embodiment according to fig 2. Said supplying means and hold-

ing means are here combined in one member 16' adapted to supply compressed air to the inflatable members 14, 15. However, these members are provided with leakage holes 26, 27 through holes in the structure 25 holding said inflatable mem- bers. These holes 26, 27 allow a flow of fluid into the space 13 and out thereof through the holes 10 of said set of holes under production. The holes 26, 27 have to be dimensioned to ensure a higher holding pressure inside the inflatable members than the pressure resulting inside the space 13. The supply of fluid for said flow through the holes 10 and for holding the combustor can fixed in place and sealing the inner space thereof is in this way combined, which results in a simplified construction, i.e. a cheaper tooling fixture. The device according to this embodiment only works in blow-mode, with pressure and not mass flow control and imposes continuous operation throughout the machining through the arrangement 1 1 . The leakage holes 26, 27 are in fact applied through a member connected to the inflatable members and enclosing a volume together therewith. The expression "said inflatable members having leakage holes" does accordingly in this context also include such an arrangement of the leakage holes as shown in fig 3. "Inflatable" is in this disclosure to be interpreted to not only include inflating a member by a gas but also by a liquid for creating a volume change of said member.

The invention is of course not in any way restricted to the embodiments described above, but many possibilities to modifications thereof would be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims.

As already mentioned, a set of holes may according to the invention be produced in the most different components for having various function in the later use of the respective component.

The number of holes in said set of holes may be arbitrary, which also apply to the pattern and size of said holes, and said set of holes may very well include holes of different sizes and shapes. The holes may for instance have a square or conical shape.