Ceramic matrix composite airfoil structure with metal shaft

Abstract

The invention discloses a ceramic matrix composite airfoil structure with a metal shaft, belongs to the technical field of composite airfoils, and solves the problem that a traditional metal material is not suitable for preparing an aircraft airfoil structure. The composite airfoil specifically comprises a composite airfoil, an airfoil framework is fixed in the composite airfoil, and a metal shaft is connected to the airfoil framework. The airfoil framework comprises a shaft box, and two sides of the shaft box are respectively connected with two connecting beams; the two turned-over edges on the two sides of the connecting beam are flush with the two side faces of the shaft box, and the two side faces of the shaft box are connected with the composite material wing faces; and the two connecting beams are respectively connected with the two connecting frames. According to the invention, the composite airfoil bears pneumatic pressure, the pneumatic pressure is transmitted to the metal shaft through the airfoil framework, and finally the force is transmitted to the upper surface of the aircraft cabin through the metal shaft, so that the pneumatic pressure borne by the composite airfoil is finally borne by the metal shaft; good mechanical properties are maintained, and high temperature resistance and ablation resistance of a ceramic-based composite material are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of composite wing surfaces, in particular to a ceramic-based composite wing surface structure with a metal shaft. Background Art

[0002] As aircraft develop towards higher flight speeds, the air friction resistance on their wing surfaces increases, which in turn causes the heat generated by the friction between the wing surface and the air to increase. Traditional wing surface structures are made of metal. Although metal wing surface structures have high strength, they cannot withstand the friction temperature between the wing surface and the air under high-speed flight. In high-temperature environments, metal structure wing surfaces have disadvantages such as easy deformation, low high-temperature mechanical properties, and poor ablation resistance. In addition, metal materials have high density and weight, and cannot be lightweight, so they can no longer meet the needs of future aircraft development.

[0003] Continuous fiber reinforced ceramic matrix composites have the advantages of low density, high specific strength and modulus, large damage tolerance, high temperature resistance, oxidation resistance, and corrosion resistance. They have become the research focus of aircraft surface thermal protection systems and will replace some metal materials. As high temperature resistant and ablation resistant functional materials, ceramic matrix composites can replace the high temperature resistant and ablation resistant structures and non-main load-bearing structures of aircraft wing surfaces. The main load-bearing structure of the wing surface still uses a metal structure. In order to maintain the mechanical properties of the metal main load-bearing structure, the temperature of the metal structure needs to be controlled within a lower temperature range.

[0004] As heterogeneous materials, ceramic-based composite materials and metal materials have significant differences in their mechanical and thermophysical properties; therefore, fusing the structures of two different materials together to prepare aircraft wing structures has become a difficult problem in the prior art. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a ceramic-based composite wing surface structure with a metal shaft, which solves the problem that traditional metal materials are not suitable for preparing aircraft wing surface structures due to their heavy weight and poor high-temperature mechanical properties.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A ceramic-based composite wing structure with a metal shaft comprises a composite wing, a wing frame is fixed inside the composite wing, and the wing frame is connected to the metal shaft; the metal shaft is connected to the composite wing through a connecting plate assembly.

[0008] In this scheme, the metal shaft is used as the main load-bearing structure of the wing surface structure, and the composite wing surface is used as a protective structure to protect the metal shaft. This not only maintains the good mechanical properties of the metal shaft, but also has the high temperature resistance and ablation resistance of the ceramic-based composite material.

[0009] Further, the wing frame includes an axle box, and two connecting beams are connected to the two sides of the axle box respectively; two flanges on the two sides of the connecting beam are flush with the two side surfaces of the axle box, and the two flanges of the connecting beam and the two side surfaces of the axle box are connected to the composite wing surface; the two connecting beams are respectively connected to two connecting frames, and the two connecting frames are connected to the two sides of the bottom sealing beam;

[0010] The metal shaft passes through the assembly hole between the composite wing surface and the bottom sealing beam, and is inserted into the shaft box.

[0011] In this scheme, during the flight of the aircraft, the composite wing surface is subjected to aerodynamic pressure, which is transmitted to the metal shaft through the wing surface frame, and finally the force is transmitted to the aircraft cabin through the metal shaft, so the aerodynamic pressure borne by the composite wing surface is ultimately borne by the metal shaft and the cabin. During the entire force transmission process, the composite wing surface and the metal shaft need to be tightly connected, so the shaft box is designed to ensure full contact between the composite wing surface and the metal shaft; two flanges are designed on both sides of the connecting beam, which can also increase the connection area with the composite wing surface, ensuring that the stress on the composite wing surface is continuously transmitted to the metal shaft and borne by the metal shaft.

[0012] Furthermore, the composite wing surface includes an upper skin and a lower skin, one side of the upper skin and the lower skin is connected to a bottom sealing plate; the upper skin and the lower skin are respectively wrapped around two side surfaces of the axle box, and the inner side of the bottom sealing plate is connected to the bottom sealing beam.

[0013] Furthermore, the connecting plate assembly includes a metal shaft baffle, and the metal shaft passes through an assembly hole in the middle of the metal shaft baffle; the metal shaft baffle is installed in a limiting hole in the middle of the bottom sealing plate; one side of the metal shaft baffle is connected to a heat insulation frame, and the other side of the metal shaft baffle is connected to the bottom sealing beam, and a heat insulation cloth is arranged between the metal shaft baffle and the bottom sealing beam.

[0014] In this solution, a metal shaft baffle is used as a connecting piece to fix the metal shaft on the wing surface frame, and the connection strength is high; a heat-insulating cloth is placed between the metal shaft baffle and the bottom sealing beam to prevent temperature transfer from the composite wing surface to the metal shaft baffle; an insulation frame is added outside the metal shaft baffle to isolate the heat flow in the air, thereby preventing the heat flow in the air from transferring the temperature to the metal shaft baffle during flight.

[0015] Furthermore, a first countersunk bolt hole is opened on the metal shaft baffle, and a first bolt arranged on the first countersunk bolt hole passes through the metal shaft baffle, the heat insulation cloth, the bottom sealing beam and the connecting frame in sequence, and is threadedly connected to the floating support plate nut; a second countersunk bolt hole is opened on the bottom sealing beam, and a second bolt arranged on the second countersunk bolt hole passes through the bottom sealing beam and the connecting frame and is threadedly connected to the floating support plate nut.

[0016] In this solution, the second bolt can connect the bottom sealing beam and the connecting frame into a whole, and the first bolt can connect the metal shaft baffle and the entire wing surface frame into a whole; this design uses a floating support plate nut to achieve the connection of most components, with simple assembly and high connection strength.

[0017] Furthermore, a baffle expansion release gap is left between the metal shaft baffle and the bottom sealing plate; and a bolt expansion release gap is left directly between the first bolt and the bottom sealing beam and the connecting frame.

[0018] In this solution, the composite wing surface expands due to heat during flight of the aircraft. The expansion coefficient of the metal material is greater than the thermal expansion coefficient of the composite material. In order to solve the problem of thermal deformation incompatibility between the metal material and the composite structure, a baffle expansion release gap is designed on both sides of the metal shaft baffle to allow the metal shaft baffle to expand and deform, thereby avoiding the large difference in thermal deformation of the two materials, which leads to stress inside the material when heated.

[0019] Furthermore, the metal shaft includes a solid shaft and a hollow shaft, which are connected in one piece; the solid shaft is passed through an assembly hole between the metal shaft baffle and the bottom sealing beam; the hollow shaft is inserted into the shaft box; the hollow shaft is hollow inside, and a stress relief groove is provided on the side wall of the hollow shaft.

[0020] In this scheme, during the deformation of the composite wing surface under stress, the deformation of the metal structure and the composite structure must be coordinated. The stiffness of the metal shaft is greater than that of the composite wing surface, so the metal shaft may damage the structure of the composite wing surface during the deformation process; therefore, a hollow shaft design is adopted for the end of the metal shaft used for inserting the shaft box, and a stress relief groove is arranged around the hollow shaft, which weakens the stiffness of the metal shaft, and the arc of the cross-section of the front end of the stress relief groove is excessively processed, thereby reducing the stress concentration at the front end of the stress relief groove of the metal shaft.

[0021] Furthermore, a heat-resistant layer is provided between the hollow shaft and the shaft box, and the heat-resistant layer is wound around the hollow shaft.

[0022] In this solution, when assembling the hollow shaft, the end wrapped with the heat-resistant layer is directly inserted into the shaft box. This design can not only prevent heat transfer between the hollow shaft and the shaft box, thus playing a role of heat insulation, but also fill the gap between the two, so that the metal shaft and the composite wing surface fit tightly, so that the force can be better transmitted from the composite wing surface to the metal shaft, ensuring a more stable connection between the two.

[0023] Furthermore, a step is provided at the connection position between the solid shaft and the hollow shaft, and a thermal insulation pad is also provided on the contact surface between the step and the thermal insulation cloth.

[0024] In this solution, the metal shaft is separated from the wing frame structure by a thermal insulation pad, thereby preventing heat transfer between the two.

[0025] Furthermore, the materials of the heat insulating cloth, the heat barrier layer and the heat insulating pad are all quartz cloth.

[0026] The beneficial effects of the present invention are:

[0027] In the ceramic-based composite wing structure with a metal shaft provided by the present invention, the metal shaft is used as the main load-bearing structure. During flight, the composite wing bears aerodynamic pressure, and transmits the aerodynamic pressure to the wing frame, and then the wing frame transmits the aerodynamic pressure to the metal shaft and is borne by the metal shaft, so that the entire wing structure has a high load-bearing capacity. In the wing frame, the shaft box wraps the metal shaft, and connecting beams with turns are arranged on both sides of the shaft box. The upper skin and the lower skin of the composite wing are wrapped on the flanges of the shaft box and the connecting beam, so that the composite wing and the metal shaft are assembled, and the contact area between the composite wing and the metal shaft after assembly is large, and the connection is tighter. The heat-resistant layer is wound on the metal shaft, which can delay the heat generated by the friction of the composite wing surface with air to be transferred to the metal shaft, so that the metal shaft maintains good mechanical properties during the flight of the aircraft.

[0028] In the ceramic-based composite wing surface structure with a metal shaft provided by the present invention, a composite wing surface and a metal shaft are designed, and thermal insulation is achieved between the metal shaft and the composite wing surface by a combination of thermal insulation material and a thermal insulation gap, thereby blocking heat transfer between the two, solving the problems of stiffness matching and thermal matching between the metal shaft and the composite wing surface, and enabling the metal shaft to maintain good mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of a ceramic-based composite wing structure with a metal shaft according to the present invention;

[0030] Figure 2 An exploded view of a ceramic-based composite wing structure with a metal shaft according to the present invention;

[0031] Figure 3 An exploded view of the wing surface skeleton and the ceramic matrix composite wing surface of the present invention;

[0032] Figure 4 An exploded view of the connecting plate assembly of the present invention;

[0033] Figure 5 It is a partial cross-sectional schematic diagram of the connection plate assembly of the present invention;

[0034] Figure 6 It is a schematic diagram of the structure of the metal shaft of the present invention;

[0035] Figure 7 It is a schematic diagram of the structure inside the metal shaft of the present invention.

[0036] Reference numerals:

[0037] 1. Metal shaft; 11. Solid shaft; 12. Hollow shaft; 13. Stress relief groove; 2. Wing frame; 21. Connecting beam; 22. Shaft box; 23. Connecting frame; 24. Bottom sealing beam; 25. Heat-resistant layer; 3. Connecting plate assembly; 31. Metal shaft baffle; 311. Baffle expansion release gap; 32. Insulation frame; 33. Insulation cloth; 34. Insulation pad; 4. Composite wing; 41. Upper skin; 42. Lower skin; 43. Bottom sealing plate; 5. Floating support plate nut; 51. First bolt; 511. Bolt expansion release gap; 52. Second bolt; DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. The specific implementation of the present invention is described below to facilitate the understanding of the present invention by those skilled in the art, but it should be clear that the present invention is not limited to the scope of the specific implementation. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

[0039] like Figure 1 and Figure 2 As shown, this embodiment provides a ceramic-based composite wing structure with a metal shaft, which integrates the metal material and the ceramic-based composite material to achieve both high temperature resistance and high load-bearing performance; and performs a heat insulation design between the metal material and the ceramic-based composite material to avoid the mismatch between the mechanical properties and the thermophysical properties of the dissimilar materials; it specifically includes:

[0040] Metal shaft 1, airfoil skeleton 2, connecting plate assembly 3 and composite airfoil 4;

[0041] Among them, a wing frame 2 is fixed inside the composite wing surface 4, and a metal shaft 1 is connected to the wing frame 2; the metal shaft 1 is the main load-bearing structure of the wing structure, and the composite wing surface 4 is used as a protective structure to protect the metal shaft 1; the metal shaft 1 is connected to the composite wing surface 4 through a connecting plate assembly 3. During the flight of the aircraft, the composite wing surface 4 is subjected to aerodynamic pressure, which is transmitted to the metal shaft 1 through the wing frame 2, and finally the force is transmitted to the aircraft cabin through the metal shaft 1, so the aerodynamic pressure borne by the composite wing surface 4 is finally borne by the metal shaft 1 and the cabin.

[0042] like Figure 3As shown, the wing frame 2 includes an axle box 22, two connecting beams 21, two connecting frames 23 and a bottom sealing beam 24; two connecting beams 21 are connected to the two sides of the axle box 22; two flanges on both sides of the connecting beam 21 are flush with the two sides of the axle box 22, and the two flanges of the connecting beam 21 and the two sides of the axle box 22 are connected to the composite wing 4; the two connecting beams 21 are connected to the two connecting frames 23 respectively, and the two connecting frames 23 are connected to the two sides of the bottom sealing beam 24; the metal shaft 1 passes through the assembly hole between the composite wing 4 and the bottom sealing beam 24, and is plugged into the inside of the axle box 22. In the process of transmitting the aerodynamic pressure to the metal shaft 1, the composite wing 4 and the metal shaft 1 need to be tightly connected, so the design of the axle box 22 ensures that the composite wing 4 and the metal shaft 1 are fully in contact; the two flanges on both sides of the connecting beam 21 can also increase the connection area with the composite wing 4, ensuring that the stress on the composite wing 4 is continuously transmitted to the metal shaft 1.

[0043] The composite wing surface 4 includes an upper skin 41 and a lower skin 42 , and a bottom sealing plate 43 is connected to one side of the upper skin 41 and the lower skin 42 ; the upper skin 41 and the lower skin 42 are respectively wrapped around the two side surfaces of the shaft box 22 , and the inner side of the bottom sealing plate 43 is connected to the bottom sealing beam 24 .

[0044] like Figure 4 As shown, the connecting plate assembly 3 includes a metal shaft baffle 31, a heat insulation frame 32 and a heat insulation cloth 33; the metal shaft 1 passes through the assembly hole in the middle of the metal shaft baffle 31; the metal shaft baffle 31 is installed in the middle limit hole of the bottom sealing plate 43; one side of the metal shaft baffle 31 is connected to the heat insulation frame 32, and the other side of the metal shaft baffle 31 is connected to the bottom sealing beam 24, and a heat insulation cloth 33 is arranged between the metal shaft baffle 31 and the bottom sealing beam 24, and the heat insulation cloth 33 is used to prevent the transfer of temperature and prevent the temperature from being transferred from the composite wing surface 4 to the metal shaft baffle 31; the heat insulation frame 32 is added outside the metal shaft baffle 31 to isolate the heat flow in the air and prevent the heat flow in the air from transferring the temperature to the metal shaft baffle 31 during flight.

[0045] A first countersunk bolt hole is provided on the metal shaft baffle 31. A first bolt 51 provided on the first countersunk bolt hole passes through the metal shaft baffle 31, the heat insulation cloth 33, the bottom sealing beam 24 and the connecting frame 23 in sequence, and is threadedly connected to the floating support plate nut 5; the first bolt 51 can connect the metal shaft baffle 31 and the entire wing frame 2 as a whole. A second countersunk bolt hole is provided on the bottom sealing beam 24. A second bolt 52 provided on the second countersunk bolt hole passes through the bottom sealing beam 24 and the connecting frame 23 and is threadedly connected to the floating support plate nut 5; the second bolt 52 can connect the bottom sealing beam 24 and the connecting frame 23 as a whole.

[0046] like Figure 5As shown, a baffle expansion release gap 311 is left between the metal shaft baffle 31 and the bottom sealing plate 43; a bolt expansion release gap 511 is directly left between the first bolt 51 and the bottom sealing beam 24 and the connecting frame 23. During the flight of the aircraft, the composite wing surface 4 is heated and expanded. The expansion coefficient of the metal material is greater than the thermal expansion coefficient of the composite material. In order to solve the problem of thermal deformation mismatch between the metal material and the composite material structure, baffle expansion release gaps 311 are designed on both sides of the metal shaft baffle 31 to allow the metal shaft baffle 31 to expand and deform, thereby avoiding the large difference in thermal deformation between the two materials, which causes stress inside the material when heated.

[0047] like Figure 6 As shown, the metal shaft 1 includes a solid shaft 11 and a hollow shaft 12, and the solid shaft 11 and the hollow shaft 12 are connected in an integral manner; the solid shaft 11 is inserted into the assembly hole between the metal shaft baffle 31 and the bottom sealing beam 24; the hollow shaft 12 is inserted into the shaft box 22; Figure 7 As shown, the hollow shaft 12 is hollow inside, and a stress release groove 13 is opened on the side wall of the hollow shaft 12; in the process of deformation of the composite wing surface 4 under stress, the coordination of the deformation of the metal structure and the composite structure must be ensured, and the stiffness of the metal shaft 1 is greater than that of the composite wing surface 4, so the metal shaft 1 may damage the structure of the composite wing surface 4 during the deformation process; therefore, the end of the metal shaft 1 used to insert the shaft box 22 adopts a hollow shaft 12 design, and a stress release groove 13 is set around the hollow shaft 12, which weakens the stiffness of the metal shaft 1, and the arc of the front end cross section of the stress release groove 13 is excessively processed, thereby reducing the stress concentration at the front end of the stress release groove 13 of the metal shaft 1.

[0048] A heat-resistant layer 25 is provided between the hollow shaft 12 and the shaft box 22, and the heat-resistant layer 25 is wrapped around the hollow shaft 12; when assembling the hollow shaft 12, the end wrapped with the heat-resistant layer 25 is directly inserted into the shaft box 22. This design can not only prevent the heat transfer between the hollow shaft 12 and the shaft box 22, and play a role in heat insulation; it can also fill the gap between the two, so that the metal shaft 1 and the composite wing surface 4 fit closely, so that the force can be better transmitted from the composite wing surface 4 to the metal shaft 1, ensuring that the connection between the two is more stable.

[0049] A step is provided at the connection position between the solid shaft 11 and the hollow shaft 12, and a heat insulation pad 34 is also provided on the contact surface between the step and the heat insulation cloth 33; the heat insulation pad 34 separates the metal shaft 1 from the wing frame 2 structure, thereby preventing heat transfer between the two.

[0050] The heat insulating cloth 33 , the heat barrier layer 25 and the heat insulating pad 34 are all made of quartz cloth.

[0051] The airfoil skeleton 2 and the composite airfoil 4 are both made of ceramic-based composite materials.

[0052] In this embodiment, all ceramic matrix composite components are prepared through two-dimensional fiber reinforced preform laying, shaping, sewing, fiber interface layer preparation, ceramic matrix chemical vapor deposition and other process links. After the mechanical properties of the prepared parts meet the requirements, all ceramic matrix composite components are connected together through an online integrated assembly process. Finally, in order to ensure the reliability of the connection, the assembled composite wing surface is subjected to ceramic matrix chemical vapor deposition to improve the interface connection performance of each structural part, and finally the thermal insulation component and the metal shaft 1 are installed.

[0053] Those skilled in the art will appreciate that the embodiments herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the invention.

Claims

1. A ceramic matrix composite wing structure with a metal shaft, characterized in that: It comprises a composite wing surface (4), wherein a wing surface frame (2) is fixed inside the composite wing surface (4), and a metal shaft (1) is connected to the wing surface frame (2); the metal shaft (1) is connected to the composite wing surface (4) via a connecting plate assembly (3).

2. The ceramic matrix composite wing structure with a metal shaft according to claim 1, characterized in that: The wing surface skeleton (2) comprises an axle box (22), and two connecting beams (21) are respectively connected to two sides of the axle box (22); two flanges on both sides of the connecting beam (21) are flush with two side surfaces of the axle box (22), and the two flanges of the connecting beam (21) and the two side surfaces of the axle box (22) are both connected to the composite wing surface (4); the two connecting beams (21) are respectively connected to two connecting frames (23), and the two connecting frames (23) are connected to two sides of the bottom sealing beam (24); The metal shaft (1) passes through the assembly hole between the composite material wing surface (4) and the bottom sealing beam (24), and is inserted into the interior of the shaft box (22).

3. The ceramic matrix composite wing structure with a metal shaft according to claim 2, characterized in that: The composite wing surface (4) comprises an upper skin (41) and a lower skin (42), and one side of the upper skin (41) and the lower skin (42) is connected to a bottom sealing plate (43); the upper skin (41) and the lower skin (42) are respectively wrapped around two side surfaces of the axle box (22), and the inner side of the bottom sealing plate (43) is connected to the bottom sealing beam (24).

4. The ceramic matrix composite wing structure with a metal shaft according to claim 3, characterized in that: The connecting plate assembly (3) comprises a metal shaft baffle (31), the metal shaft (1) passes through an assembly hole in the middle of the metal shaft baffle (31); the metal shaft baffle (31) is installed in a limiting hole in the middle of the bottom sealing plate (43); one side of the metal shaft baffle (31) is connected to a heat insulation frame (32), the other side of the metal shaft baffle (31) is connected to the bottom sealing beam (24), and a heat insulation cloth (33) is arranged between the metal shaft baffle (31) and the bottom sealing beam (24).

5. The ceramic matrix composite wing structure with a metal shaft according to claim 4, characterized in that: A first countersunk bolt hole is formed on the metal shaft baffle (31), and a first bolt (51) arranged on the first countersunk bolt hole passes through the metal shaft baffle (31), the heat insulation cloth (33), the bottom sealing beam (24) and the connecting frame (23) in sequence, and is threadedly connected to the floating support plate nut (5); A second countersunk bolt hole is provided on the bottom sealing beam (24), and a second bolt (52) arranged on the second countersunk bolt hole penetrates the bottom sealing beam (24) and the connecting frame (23) and is threadedly connected to the floating support plate nut (5).

6. The ceramic matrix composite wing structure with a metal shaft according to claim 5, characterized in that: A baffle expansion release gap (311) is left between the metal shaft baffle (31) and the bottom sealing plate (43); A bolt expansion release gap (511) is directly left between the first bolt (51), the bottom sealing beam (24) and the connecting frame (23).

7. The ceramic matrix composite wing structure with a metal shaft according to claim 4, characterized in that: The metal shaft (1) comprises a solid shaft (11) and a hollow shaft (12), wherein the solid shaft (11) and the hollow shaft (12) are connected in one piece; the solid shaft (11) is inserted into an assembly hole between the metal shaft baffle (31) and the bottom sealing beam (24); the hollow shaft (12) is inserted into the shaft box (22); the hollow shaft (12) is hollow inside, and a stress release groove (13) is provided on the side wall of the hollow shaft (12).

8. The ceramic matrix composite wing structure with a metal shaft according to claim 7, characterized in that: A heat-resistance layer (25) is provided between the hollow shaft (12) and the shaft box (22), and the heat-resistance layer (25) is wound around the hollow shaft (12).

9. The ceramic matrix composite wing structure with a metal shaft according to claim 8, characterized in that: A step is provided at the connection position between the solid shaft (11) and the hollow shaft (12), and a heat insulation pad (34) is also provided on the contact surface between the step and the heat insulation cloth (33).

10. The ceramic matrix composite wing structure with a metal shaft according to claim 9, characterized in that: The heat insulating cloth (33), the heat-resistance layer (25) and the heat insulating pad (34) are all made of quartz cloth.

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