JPH07109162B2 - Wear resistance and grindability for rotary labyrinth seal members Laser engraving Ceramic or metal carbide surface - Google Patents

Description

FIELD OF THE INVENTION This invention relates to gas seals between stationary and rotating members, such as rotary seals in gas turbine engines, and more particularly to gas turbine engines.
A labyrinth type gas seal in a blade tip such as a knife edge.

Background of the Invention Various rotary seals are used in gas turbine engines. Such rotary seals are generally of the type that include a rotating member and another stationary member that cooperates with it across a narrow gap. Such seals are in some cases used between the stationary member and the rotating shaft or drum to maintain a pressure differential within the chamber on each side of the seal. For example, in one type of gas turbine engine, multiple rows of rotor blades extend radially outward from the axis of rotation across the flow path for working medium gas. Adjacent to it, multiple rows of stator vanes extend radially inward from the stator case or shroud across the flow path. In some versions, the stator vanes are cantilevered inward from the stator case. The vanes are positioned to direct the working gas toward or away from adjacent rotor blades. The stator has a sealing surface that orbits the blade tips in each row of blades and in the cantilever stator vane type the rotor encloses the stator vane tips in each stator vane. A surface is provided.

As the gap between the blade or vane tip and the corresponding sealing surface in each row increases, a significant amount of working medium gas escapes around the blade and / or vane tip, reducing aerodynamic efficiency. . In addition, as the gap increases, an additional amount of working medium gas leaks axially around the tip from the downstream end of the blade or rotor to the upstream end.

Therefore, it is desirable to minimize the gap. However, it is also necessary to deal with various dimensional changes that occur during startup, thermal expansion, high speed rotation, and the like. In general,
Under these conditions, some wear of the components occurs, especially during engine startup.

PRIOR ART It is known that a more favorable situation is that the tip or knife edge cuts into the corresponding sealing surface without sustained wear. U.S. Pat.Nos. 4,238,170 and 4,239,4
No. 52 provides a stator or shroud sealing surface with an inner circumferential groove surrounding the blade tip, but this configuration presents alignment difficulties while at the same time thermally induced axial displacement of the blade relative to the stator or shroud. Cannot be absorbed.

Various example rotary seal configurations have been disclosed in the literature where the rotating member creates a passage in a softer, e.g. abradable cooperating member such as a filled honeycomb, porous metal, brittle ceramic, etc. That is, it is formed by cutting, grinding or polishing. It has been found that in some of these configurations an inadequate sealing or gripping action of the cooperating member may occur. In other such configurations, there is a risk of local hot spots or burns on the abradable member. Examples of seals using abradable members are U.S. Pat.No. 3,068,016; 3,481,715; 3,519,282; 3,817,719; 3,
843,278; 3,918,925; 3,964,877; 3,975,165; 4,377,371 and 4,540,336. The abradable seal is designed to cause flake-like delamination or abrasion in the presence of sudden thermal changes and impact loads, causing the blade tip to strike the seal. U.S. Pat.No. 4,377,371 points out that certain materials used as abrasive seals are susceptible to large-scale spalling that progresses rapidly due to the presence of cracks at the seal surface, and the formation of fine microcracks on the seal surface. Disclosed is the glazing of the seal surface by using a laser beam to create the network. AIAA / SAE / ASME 16th Joint Promotion Conference AIAA-80-1
In 193, a paper entitled "Improved Durability Plasma Sprayed Ceramic Coatings for Gas Turbine Engines" submitted by IE Sumner et al., Reports that segmented laser scanning coatings show poor performance.

British Patent Nos. 853314 and 1008526 disclose turbine or compressor blades having ribs at the tips to provide a seal with the rotor or stator shroud, the ribs or cooperating seal surfaces being replaceable when worn. There is. U.S. Pat. No. 4,148,494 discloses a gas turbine blade or vane having abrasive tips comprised of tip-projecting abrasive particles such as Borazon embedded in a nickel or nickel-containing alloy electrodeposited matrix. Abrasive tips of the type described in this patent are difficult to manufacture and are extremely expensive. U.S. Pat. No. 3,339,933 discloses blade teeth coated with bonded alumina, which plunge into a cooperating honeycomb member to form a seal. U.S. Pat.No. 3,537,713 discloses a rotating sleeve having inwardly projecting teeth coated with a hard protective material such as molybdenum or nickel aluminide, which displaces the friction resistant material on a stationary cooperating member. To form alternating protrusions and grooves.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention All of these prior arts lack a cutting ability suitable for cutting into a sealing surface when forming a labyrinth seal, lack wear resistance and corrosion resistance, and produce a high-performance seal. I couldn't. .

OBJECT OF THE INVENTION It is an object of the invention to provide an inexpensive technique for providing teeth, ribs or knife edges coated with a wear resistant coating having excellent cutting ability for cutting into sealing surfaces in rotary seals such as turbines or compressors. Is to establish.

SUMMARY OF THE INVENTION In accordance with the present invention, lasers are provided on chips such as turbine blades, compressor blades, fan blades, impellers, stator vanes, diffusers, shrouds, spoilers, spacers, etc. designed to cooperate with sealing surfaces. A wear resistant ceramic or metal carbide coating having a recess formed therein is formed to provide a laser engraved wear resistant cutting surface that can be cut into the sealing surface.

Here, "laser engraving" refers to a technique of engraving a large number of concave patterns on the surface by laser energy.

Here, the "ceramic or metal carbide coating" is a general term for coatings of general ceramics, hard metals, metal carbides, cemented carbides, ceramics, mixtures of refractory metals and the like, and other wear resistant materials.

In one particular embodiment of the invention, the tip is coated with the laser engraved wear resistant cutting surface of the invention and designed to cut into the sealing surface to provide a labyrinth seal. One or more knife edges, teeth or ribs are formed. The laser engraved surface created by the present invention is wear and corrosion resistant and can be cut into cooperating sealing surfaces with minimal heat generation,
As a result, the deterioration of the physical properties of the covered member or the cooperating sealing member and the risk of warpage due to heat can be minimized.

The cutting ability of the laser engraved surface is believed to be due to the raised land zones acting as a collection of cutting edges, and the recesses between the land zones receive fine cutting debris during cutting and the turbine cools down and chips Is believed to improve cutting performance by releasing it as it retracts from the sealing surface.

Depending on the mode of operation of the laser, the land zone may be part of the original coating material, or it may be melted in the depression and thrown around or pushed into the periphery and along the edge of the depression. It may also consist of material that is deposited above the original surface by the most relocated or deposited material (hereinafter this situation is referred to as redeposition). The redeposited material typically has a different microstructure and properties than the coating body. From the micrographs, it is possible to see the structural and / or morphological changes brought to the ceramic or metal carbide coating surface according to the invention, eg the appearance change of the coating surface after laser treatment.

In the prior art, a ceramic or metal carbide coating was first bonded to the contact surface of a member designed to contact and cut into a member cooperating in the formation of a labyrinth seal, and subsequently laser-engraved to form a plurality of laser-formed recesses. Nothing is found to disclose the inventive concept which involves forming a redeposited material around the resulting recess to provide a uniform cutting surface on the contact surface.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a turbine blade 10 having a knife edge 11 at the tip. Turbine blades 10 are mounted on a rotor 12 and extend towards a stator 13 as a sealing surface. In cold conditions for a new or modified unrun engine as shown in FIG. 1, the knife edge 11 may or may not be in direct contact with the stator 13, while as shown in FIG. The knife edge contacts and cuts into the stator 13 as is accelerated to the design speed. 3rd in design speed
As shown, the knife edge retracts somewhat from the groove 14 cut in the stator. FIG. 4 illustrates the relationship of the knife edge 11 to the sealing surface 13 in a cold engine that has been operated one or more times.

FIG. 5 illustrates a turbine blade 20 having a tip 21, which is again mounted on the rotor 12 and extends towards the stator 13 as a sealing surface. In cold conditions for a new or modified and unrun engine as shown in FIG. 5, the tip 21 may or may not be in direct contact with the stator 13 while the turbine as shown in FIG. As it accelerates to design speed, the tip contacts and cuts into the stator 13. At design speed, the tip retracts somewhat from the groove 22 cut in the stator, as shown in FIG. FIG. 8 illustrates the relationship of the tip 21 to the sealing surface 13 in a cold engine that has been operated one or more times.

Ceramic or metal carbide coatings 15 and 23 are formed on the surfaces of knife edge 11 and tip 21, respectively. The coating is coated and laser engraved in the manner described below to create a laser-formed depression as described below. Any suitable ceramic or metal carbide coating may be applied to knife edge 11 or tip 21. For example, tungsten carbide and alloys and / or mixtures of tungsten carbide with cobalt, nickel, chromium, iron and the like and mixtures of these metals can be used. In addition, titanium carbide, tungsten-titanium carbide and chromium carbide are also useful. Carbides such as those mentioned above may be used alone or mixed or alloyed with cobalt, chromium, tungsten, nickel, iron or other suitable metals. Examples of the ceramic coating include alumina, a mixture of alumina and titania, chromia, a mixture of chromia and alumina, zirconia mixed with magnesia, and the like. By way of example, the following coating composition manufactured and sold by the Applicant is a preferred example that may be used to provide the coatings 15 and 23: LC1B 65 wt% chromium carbide (92 wt% chromium, 8 wt% %carbon)
And coating containing 35% by weight nichrome (80% by weight nickel and 20% by weight chromium) LCO-17 10% by weight alumina and 90% by weight cobalt alloy (54% by weight C
o, 25 wt% Cr, 10 wt% Ta, 7.5 wt% Al, 0.8 wt% Y, 0.7
Coating containing Lwt1N-40 82 wt% W, 14 wt% Co and 4 wt% C UCAR 24-K titanium nitride coating LZ-4B 8 wt% magnesia And a mixture containing magnesia-stabilized zirconia containing 92 wt% zirconia LTB-8 LCO-22 coated on top of LCO-35 coating and further coated on LZ-4B ceramic or metal carbide coating is a detonation gun process or The metal surface of the knife edge 11 and the tip 21 is coated by a thermal spray method such as a plasma coating process. Explosive gun processes are well known and are described in U.S. Patent Nos. 2,714,563, 4,173,685 and 4,51.
It is described in detail in No. 9,840. In this method, oxygen, acetylene, and nitrogen are delivered to the barrel of the gun along with a coating material charge, such as ceramic, metal carbide or metal powder. The gas mixture is ignited and the resulting blast wave accelerates the powder to about 2400 ft (731.5 m) / sec while simultaneously heating it near or above its melting point.
The maximum free combustion temperature of the oxygen-acetylene mixture under constant pressure conditions occurs at about 45% acetylene and about 3140.
℃. However, under conditions such as explosion where combustion takes place in a substantially constant volume, the temperature is probably above 4200 ° C, so most materials can be melted by this process.

The barrel is aimed at the substrate and powder at a temperature at, near, or above the melting point is deposited on the substrate. The barrel is flushed with nitrogen after each explosion. This cycle is repeated about 4 to 8 times per second and each spray powder is about 25 mm.
This results in the deposition of circular coatings that are a few microns thick in diameter. The entire coating is produced by a number of overlapping circular coatings, each circular coating consisting of a number of overlapping thin lenticular or elongated tabular grains corresponding to individual powder particles. The overlapping circles are tightly controlled to produce a relatively smooth coating.

Plasma techniques for coating knife edges are traditionally practiced in U.S. Pat.Nos. 3,016,447, 3,914,573, 3,
958,097, 4,173,685 and 4,519,840. In plasma coating technology, plasma torches comprising a copper anode and a tungsten cathode are commonly used. A gas such as argon or nitrogen or a mixture of these with hydrogen or helium is injected around the cathode and through the anode which acts as a throttling nozzle. A direct current arc, normally ignited by a high frequency discharge, is maintained between the electrodes. The arc current and voltage used will depend on the anode / cathode design, gas flow rate and gas composition. The working voltage varies in the range of about 5-80 kW depending on the torch type and operating parameters.

A gas plasma is generated by the arc, which is a free electron,
It contains ionized atoms and few neutral atoms and undissociated diatomic molecules when nitrogen or hydrogen is used. Plasma gas velocities using most conventional torches are subsonic, but supersonic velocities are possible using convergent or unwidened nozzles with critical exit angles. Plasma temperature should exceed 50,000 ° F (27,760 ° C). Ceramic coating powder or metal carbide coating powder is introduced into the plasma stream. The coating powder melts in the plasma and impinges on the substrate. The plasma coating method uses much higher temperatures than the explosive gun method (D-gun method) and is a continuous method. On the other hand, the explosive gun method is intermittent and discontinuous.

The coating thickness applied by either the plasma method or the D-gun method is 0.5-100 mils (0.013-2.54 mm),
It can preferably range from 2 to 15 mils (0.051 to 0.381 mm).

Following deposition of the coating on the knife edge or other cutting surface, the resulting ceramic or metal carbide coating bonded onto the knife edge or other surface provides a more uniform surface for subsequent laser engraving application. Therefore, it can be ground with a diamond wheel. Other than dimensional control of the coated surface, no grinding step is usually required for the parts described herein.

Ceramic or metal carbide coatings use pulsed lasers in solid form such as YAG or gas form such as CO ₂ to create laser-formed depressions and land zones of appropriate pattern and depth on the coating surface. Laser engraved. The depth of the laser-formed recess is measured from the bottom of the recess to the top of the land surrounding it, ranging from a few microns or less to 120-140 microns (3.05-3.56 mm) or more, eg 2-200 microns. (0.051-5.08m
m), preferably in the range of 20 to 100 microns (0.508 to 2.54 mm). Average diameter is 1.0-12 mils (0.025
4 to 0.305mm), preferably 2.5 to 10 mils (0.064 to 0.254m)
m) range. The average diameter and depth of each depression is
It is controlled by the energy amount of the laser pulse and the pulse length. The spacing between the laser-formed depressions is controlled by the laser burning rate and the relative momentum between the laser surface and the coated surface. The number of laser-formed depressions per linear inch (2.54 cm) typically ranges from 80 to 800, preferably 100 to 400.

A wide variety of laser machines can be used to form indentations in ceramic or metal carbide coatings. In general,
Lasers are available that can provide a very wide range of Joule heat / pulses, pulse times and operating frequencies. Therefore, there is no problem in selecting the appropriate laser and operating conditions to create the surface morphology described herein.

The surface of the ceramic or metal carbide coating after laser engraving shows a group of land zones and (a) slight evaporation of material and in some cases (b) melting of additional material when the coating is impinged by a laser pulse. It includes indentations in the form of micro depressions or cells formed by movement and repositioning (reattachment). It was found that the redeposited material, if present, was significantly different than the original coating. In general, it is denser and less porous than the original material, and has a different atomic structure, such as alumina that appears as separate phases in the intact coating, but forms a single phase after modification by laser treatment. It may have a titania mixture. The land zone, whether the original coating material or a redeposited material formed as a ridge around each depression, constitutes a micro-cutting edge, which is an abrasive material or honeycomb structure bound to the stator surface. It has suitable grinding performance for cutting in. The thickness of the redeposited material may range from 10 to 40%, preferably 20 to 30% of the total recess depth as measured from the surface of the original coating. The depressions occupy 10 to 90% of the surface area, preferably 50 to 90%. The corresponding preferred land area is 10-50%.

The depressions are formed in a random pattern in the ceramic or metal carbide coating. The average center-to-center distance between the depressions is substantially constant.

Examples will be described below. The following notations and abbreviations indicate the following: D-Gun coating method Ceramic or metal carbide powder is loaded into the barrel with nitrogen, oxygen and acetylene and exploded to about 6000 °.
Explosive gun method of coating a ceramic or metal carbide coating on a substrate by generating a temperature of F (3316 ° C), melting the ceramic or metal carbide powder and spraying it toward the substrate Plasma coating method Ceramic or metal carbide A technique for continuously coating a substrate with a ceramic or metal carbide coating by injecting a powder into a plasma of an ionized gas formed by establishing an electric arc across an inert gas, particularly argon. Ceramic or metal carbide powder
Continuously delivered to plasma with operating temperature as high as 50000 ° F (27760 ° C). The powder is heated in a plasma and accelerated with an expanding gas and directed to a substrate. Here, the powder cools, congeals and binds to the substrate.

Screen size Average number of indentations per unit linear inch (2.54 cm) LW1N-40 Coating containing 82 wt% W, 14 wt% Co and 4 wt% C Example 8 Rotating members of a rotary labyrinth seal Knife edge seal specimen, knife edge 60 mesh Al ₂ O
Prepared for coating by grit blasting with ₃ . Al ₂ O ₃ grit is 5 inches (1
(2.7 cm) at a projection distance of 15 psi (14.5 kg / cm ² ) through a pressure projector using a 1/4 inch (6.35 mm) inner diameter Al ₂ O ₃ nozzle aimed at the knife edge.
A total of about 32 seconds was projected at a flow rate of 2.1 Ib (953 g) / minute.
The surface of the knife edge after grit blasting is 105 Ra
It had a roughness of. Knife edge coupon, gas composition of 28% acetylene, 28% oxygen and 44% nitrogen, 11ft ³ (0.31
0.005 ~ LW1N-40 coated by using an explosive gun operating with a gas flow rate of m ³ ) / min and a powder feed rate of 54 g / min
A coating thickness of 0.008 inches (0.13 to 0.20 mm) was provided.

Six of the coated knife edge seal coupons were treated by laser engraving both sides with the laser beam perpendicular to the knife edge surface. The laser conditions are
It was intended to provide a laser-formed recess diameter in the range of 0.010-0.006 inch (0.25-0.15 mm), which corresponds to a screen size of 100-140. In addition, laser engraving
It was performed under conditions set to give a recess depth of 50-70 microns. The laser was operated at a power of 59 W, a pulse duration of 145 μs and a frequency of 1000 Hz. The amount of energy per pulse was about 0.059 Joule. The indentations formed had a depth of 50 μm and had an average screen size of 130 indentations per inch (2.54 cm). Therefore, the average diameter of the depressions is 0.0077 inches (0.20 mm) (1/13
It was 0). Therefore, in this case, the depression is about 79
Land area will account for the remaining 21%.

After engraving, also by scanning electron microscopy (SEM) by metallographic techniques to confirm the actual depth and diameter of the recesses, to check for the presence and absence of redeposited material and to inspect the overall condition of the engraving. Was used for macro and micro structural analysis. The average pit depth from the original coating surface to the bottom of the pit was found to be 45.6 μm and the average pit depth from the top surface of the redeposited material to the bottom of the pit was 73.6 μm. The average thickness of the redeposited material was measured as 23.8 μm. A Zeiss metallurgical microscope was used for depth and thickness measurements.

Under microscope observation, a substantially uniform distribution of laser-formed depressions and the presence of redeposited material along each depression was observed under 120 × magnification with an indium replica, as shown in FIG. In addition, the original coating was seen between the individual indentation rows. Observation of the individual indentation morphology at 560 times magnification shown in Figure 10 showed the presence of redeposited material along the perimeter of the laser engraved indentation and the presence of the original coating around it.

Six laser engraving knife edge coupons were tested at ambient temperature conditions. In this test, the knife edge is 950 ft (2
Rotated at an edge speed of 89.6m) / sec and 0.002
It was plunged into the arcuate sealing surface at a rate of inch (0.01 mm) / sec. This resulted in a 0.06 inch (0.15 mm) groove in the 30 second test and a 0.030 inch (0.08 mm) groove in the 15 second test on the sealing surface.

EFFECTS OF THE INVENTION By forming a large number of recesses by laser on a coating surface having high corrosion resistance and wear resistance such as ceramics, an excellent grinding action is exhibited, and it has succeeded in establishing a seal forming technology superior to conventional ones. This can be cut into the cooperating sealing surface with minimal heat generation, thus minimizing the risk of physical deterioration of the covered or cooperating sealing member and warpage due to heat. It is limited. The recess between the land zones is
Improves cutting performance by receiving fine cutting debris during cutting and releasing it as the turbine cools and the tip retracts from the sealing surface. In this way, we succeeded in creating a high quality rotary seal.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing the relative position of a turbine blade having a knife edge and a sealing surface for a cold state of a new engine. FIG. 2 is a partial cross-sectional view showing the relative position of a turbine blade having a knife edge and a sealing surface as the engine is accelerated toward a design speed. FIG. 3 is a partial cross-sectional view showing the relative position of a turbine blade having a knife edge and a sealing surface when the engine is operating at a design speed. FIG. 4 is a partial cross-sectional view showing the relative position of the turbine blade having the knife edge and the sealing surface when the engine becomes cold. FIGS. 5, 6, 7, and 8 are partial cross-sectional views sequentially showing the relative positions of the turbine blade having the tip and the sealing surface in a state corresponding to the first to fourth aspects. FIG. 9 is a 120 × magnification photomicrograph showing the grain structure of a laser-formed surface produced in accordance with the present invention. FIG. 10 is a 560 × photomicrograph showing the grain structure of the individual depressions in FIG. 10, 20: Turbine blade 11: Knife edge 12: Rotor 13: Sealing surface (stator) 14, 22: Groove 15, 23: Coating 21: Tip

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-252689 (JP, A) JP-A-59-224221 (JP, A) JP-A-55-58342 (JP, A) JP-B-49- 13810 (JP, B1)

Claims (7)

[Claims] 1. A first member and a second member, the first member including at least one sealing tooth having a tip cooperating with the second member, the tip comprising a ceramic or metal carbide bonded thereto. In a rotating gas seal provided with a coating, thereby blocking gas flow between the first member and the second member, the coating made of ceramic or metal carbide has a plurality of laser-formed recesses, and A rotating gas seal, characterized in that it provides a wear resistant cutting surface that can be cut into the second member. 2. A turbine or compressor blade comprising a tip surface adapted to cooperate with a sealing surface to form a seal, the tip surface being provided with a coating of ceramic or metal carbide. Or a turbine or compressor blade, wherein the coating of metal carbide has a plurality of laser-formed recesses and provides a wear resistant cutting surface that can be cut into the second member. 3. A coating formed on the tip with at least one knife edge projecting in the direction of movement of the tip with respect to a second member, the surface of the knife edge comprising a ceramic or metal carbide bonded thereto and the coating. A seal or turbine or compressor blade according to claim 1 or 2 having a plurality of laser-formed recesses formed in the surface of the seal. 4. A seal or turbine or compressor blade according to any one of claims 1 to 3, wherein the coating thickness prior to forming the laser-formed depression is 0.5-100 mils (0.0127-2.54 mm). . 5. A seal or turbine or compressor blade according to any one of claims 1 to 4, wherein the depressions are formed in a chaotic pattern with substantially uniform spacing between adjacent depressions. . 6. The screen of the laser-formed recess is 3 per cm.
A seal or turbine or compressor blade according to any one of claims 1 to 5 in the range of 1 to 315 indentations (80 to 800 indentations per linear inch). 7. A laser-formed recess as claimed in 50-90% of the surface and a land zone between the recesses as the remaining 50-10% of the surface, as claimed in any one of claims 1-6. Seals or turbine or compressor blades.