DE69631800T2 - METHOD FOR MAINTAINING BRAKES - Google Patents

Description

brakes made of carbon-carbon composite are due to their Safety, its long life and low weight in planes, like the military planes F-15 and F-16. Today's brake arrangements for aircraft include rotors and stands, those with disc components made of carbon-carbon composite material assembled. It is proven that the wear life extended by carbon brakes can be when the used brakes retrofit method be subjected. The wear life of brakes, the by means of conventional Procedures retrofitted were, is only 50-80 % of new brakes. Although this represents an improvement over the Discarding worn brakes if, however, a retrofit procedure to disposal stands, produces the densified carbon material with a wear life, that of the original brakes more similar is, could significant savings on original parts and repair costs for worn ones Brakes are achieved.

To the compaction process for Carbon-carbon of the prior art include the chemical vapor infiltration (CVI) and infiltration by pitch impregnation or the impregnation with curable Resins at low pressure, resulting in a long process time of the order of magnitude required from 25 to 50 days. Such procedures become traditional for compacting porous Preforms made of carbon for original brake discs made of carbon-carbon composite material as well as to the returner used worn discs. The compression must be slow carried out Be sure to allow the pores on the outside of the brake to be made of carbon not be filled in front of the pores inside the brake made of carbon. If the pores on the outside The brakes are clogged with carbon before the compression of the Interior areas is completed, the interior areas of the brake from carbon insufficiently reached by the precursor.

One Approach to avoid this problem is disclosed in U.S. Patent 4,472,454, issued September 18, 1984 to Houdayer et al., discloses is incorporated herein by reference. According to this patent will be placed the preform in a reaction vessel and with precursor liquid covered. A coil outside of the reaction vessel used for inductive heating of the preform. The preform is heated to a temperature that high enough to the liquid precursor to boil and to the vapor formed at the boiling of the liquid pyrolyze. We posit that the liquid is the exterior of the preform cools, causing a temperature gradient through the thickness of the preform is formed through. The interior of the preform is, as it is not through the boiling liquid chilled becomes warm enough to pyrolyze the steam. In this way The compaction is preferably carried out inside the preform. The entire compaction takes place from the inside to the outside. The Compaction can thus be carried out at a higher speed, without clogging the pores on the outside and thus preventing it the compression inside the preform is to be feared.

This in US 4,472,454 Although the described compaction process shortens the time required to densify a preform, we have discovered several ways to further improve the process.

To the one is desirable in compacting a preform that the induction coil corresponds to the shape of the preform. It is also desirable that the preform is as close as possible to the induction coil located. These requirements are important to a consistent and more efficient heating to reach the preform. A uniform heating is to achieve the desired compression important.

The Adaptation of Houdayer et al. Apparatus to these requirements to fulfill, requires a forming of the coil on the basis of the to be compacted Part. It demands alike a forming of the reaction vessel and the coil at each part. Such a requirement is not desirable, as this is costly and time consuming can be. Furthermore we discovered that the cooling due to the boiling of the liquid, that for generating the desired Temperature gradient is required, does not take place when the reaction vessel too close to the preform. When the walls of the reaction vessel become too Close to the preform, a phenomenon known as "vapor barrier" may occur. at A vapor barrier collects steam at a certain point between the wall of the reactor vessel and the preform and displaced the liquid. This is the heat transfer considerably reduced by convection away from the preform, thereby an overheated one Place formed and the formation of deposits on the outside of the preform is caused. As a result, a part is not compressed evenly is.

The Carbon-carbon composite brakes retrofit method described herein for airplanes significantly reduces the duration of the process, e.g. to 48 hours or less and leads therefore to cheaper Carbon-carbon components. The method is especially for the production of brakes for Aircraft made of carbon and recompressed or re-used of these brakes of interest. In addition, this process leads to the chemical Deposition from the gas phase (CVD) to a densified carbon structure with a density equal to that of one or more original brake components or returnee Brake components similar is that for the use in aircraft are permitted, i. at least 1.85 g / cc, preferably 1.9 g / cc in the deposited carbon matrix, and a suitable CVD microstructure for one Friction material, which is a substantially non-isotropic microstructure represents. Such structural features are required to the frictional wear characteristics to achieve that for Brake components made of carbon are suitable for aircraft.

EP-A-592 239 describes a method and apparatus for compacting of porous Blocks, where the block is heated inductively or by resistance heating in a liquid carbon precursor, for a rapid chemical vapor deposition inside of the block compacting it.

SUMMARY OF THE INVENTION

The Invention provides:

• a) Einsetzen wenigstens einer verschlissenen Bremskomponente aus Kohlenstoff, wobei diese Poren hat, die durch Innenbereiche einschließlich eines geometrischen mittleren Bereichs und einer Außenfläche abgegrenzt werden, in einen flüssigen Kohlenstoffvorläufer, der in einem Reaktor enthalten ist, zum Verdichten einer porösen Struktur, wobei der Reaktor so beschaffen ist, dass er den flüssigen Kohlenstoffvorläufer und mindestens eine interne Induktionsspule enthält, und
• b) induktive Erwärmung der Innenbereiche der verschlissenen Bremskomponente(n) aus Kohlenstoff bis zu einer Temperatur, die oberhalb der Zersetzungstemperatur des flüssigen Kohlenstoffverläufers liegt, wobei die Bildung der Gasphase des flüssigen Kohlenstoffverläufers bewirkt wird, sowie die Infiltration aus der Gasphase in Innenbereiche und Abscheiden pyrolytischen Kohlenstoffs innerhalb der Innenbereiche, bis die verschlissene Bremskomponente aus Kohlenstoff eine Dichte von mindestens 1,85 g/cc und eine nicht isotropische CVD-Mikrostruktur hat, und wobei der induktive Erwärmungsschritt kontinuierlich sein oder durch periodische Abkühlung um mindestens 10 °C unterbrochen werden kann.

A chemical vapor deposition method for recovering one or more carbon brake components for aircraft, comprising the steps of:

• a) inserting at least one worn brake component of carbon, said pores delineated by internal regions including a geometric middle region and an outer surface, into a liquid carbon precursor contained in a reactor for densifying a porous structure, wherein the reactor is such that it contains the liquid carbon precursor and at least one internal induction coil, and
• b) inductive heating of the inner regions of the worn brake component (s) of carbon to a temperature which is above the decomposition temperature of the liquid carbon precursor, causing the formation of the gas phase of the liquid carbon precursor, as well as infiltration of the gas phase into internal regions and pyrolytic deposition Carbon within the interior areas until the worn brake component of carbon has a density of at least 1.85 g / cc and a non-isotropic CVD microstructure, and wherein the inductive heating step may be continuous or interrupted by periodic cooling by at least 10 ° C.

The Invention also presents a method for chemical deposition the gas phase by resistance heating of the brakes made of carbon according to claim 12 ready to return to carbon that has been lost through wear to be trained, and re-cultivation procedures, in which inductive and resistance heating are combined. at some brakes can Such methods of chemical vapor deposition in two to three and a half hours at about 950 to 1100 ° C and atmospheric Pressure with cyclohexane as precursor to be finished. In the rebuilt brake component (s) can in process steps, within 48 hours, preferably 24 hours or less a density of at least 1.85 g / cc and preferably 1.9 g / cc in the deposited matrices and a non-isotropic one CVD microstructure can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The Invention will become apparent from the following detailed description and the better understood in the accompanying drawings. Show it:

1 a sketch of the reactor for compacting preforms;

2A a drawing of a clamping device for holding the preform in the reactor of 1 is used;

2 B a sketchy representation of a coil in the reactor of 1 is used;

3 a drawing of a preform which is heated with an alternative coil assembly;

4 a drawing of a preform which is heated by means of resistance heating;

5 a drawing of a preform, which is heated both inductively and by means of resistance heating;

6 a drawing of a preform which is heated with an alternative coil assembly;

7 a diagram with compaction profiles at different power levels and

8th a representative diagram of the input power to the coil of the reactor vessel as a function of time.

DESCRIPTION THE PREFERRED EMBODIMENT

To the brakes made of carbon for Aircraft suitable for retrofitting include friction disc brakes, the plurality of carbon-carbon rotor disks with a plurality of carbon-carbon stator disks contained in between. Furthermore can worn carbon pressure plates and end plates for brakes again trained become.

With the method according to the invention Any worn carbon surface can be a brake on an airplane again trained become. Suitable brakes for Planes are known to those skilled in the art and include, but are not limited to, those described in U.S. Pat. Nos. 3,934,686, issued January 27 1976 to Stimson et al., 4,613,021, issued September 23, 1986 Lacombe et al., 4,465,165, issued August 14, 1984 to Bok, 4,511,021 issued April 16, 1985 to Grider, 4,804,071 on February 14, 1989 to Schultz et al., 4,982,818, issued on August 8, 1989. January 1991 to Pigford and 5,143,184 issued September 1, 1992 to Snyder et al. which are incorporated herein by reference are.

worn Rotor and stator discs made of carbon thereby again improved be removed from the brake assembly and half of their original Thickness be sanded. The ground discs can by means of the process of chemical vapor deposition for recovery the original one Density and wear properties can be compacted and two ground discs can at reassemble the brakes instead of an original disc be used. The ground discs can optionally also with each other get connected. A technique for joining two worn ones Washers for creating a reconditioned disc is disclosed in US patent No. 4,465,165, issued August 14, 1984 to Pigford. After reconditioning, carbon discs can with protective materials such as those described in U.S. Patent No. 4,837,073, issued June 6, 1989 to McAllister et al Protection against oxidation can be treated.

1 shows a reactor 100 which is suitable for performing a rapid compaction according to the method described in US Pat. No. 4,472,454. If an induction coil, like the coil 104 , used to heat the preform, is the reactor 100 preferably made of non-magnetic materials, such as quartz, glass, aluminum, stainless steel, ceramic, PMC or combinations thereof.

The reactor 100 contains a cavity 102 in which a preform (not shown) is compacted. During operation, the cavity is 102 so far filled with a precursor liquid, that the preform (not shown) is at least covered. The precursor liquid is any liquid that boils and generates vapor that contains chemicals that deposit on the preform (not shown) at a temperature to which the preform (not shown) may be heated. The precursor liquid should also be a non-conductor. The relative dielectric constant of the reagent should be greater than 0.5, more preferably greater than 1, and most preferably greater than 1.5. For depositing carbon on the preform, a hydrocarbon having a suitable boiling point such as cyclopentane, cyclohexene, 1-hexene, gasoline, toluene, methylcyclohexane, cyclohexane, n-hexane or benzene or a combination of these may be used.

Inside the cavity 102 is an induction coil 104 arranged. During operation, the induction coil 104 covered by the precursor liquid and serves to heat the preform (not shown). The sink 104 is made of copper or another highly conductive material that does not react with the precursor liquid even after heating.

The sink 104 is via busbars 106 powered. The busbars 106 are made a highly conductive material, here copper. Preferably, currents of hundreds of amps to thousands of amps are used to provide the required power to heat the preform (not shown). Due to the high amount of electricity, the busbars must 106 have a sufficiently large cross-section to avoid overheating. The busbars 106 can water channels 105 for guiding cooling water through the busbars 106 and through the coil 104 contain.

The busbars 106 are connected to a power supply (not shown). An AC power supply is used. Voltage, current, frequency and shape of the coil 104 are determined by known induction heater design techniques based on the shape and geometry of the preform and the properties of the preform. The voltage is typically in the range of 5 to 750 V. The frequency is in the range of 0.1 kHz to 300 MHz.

The busbars 106 run through the seal 107 in the chamber 102 , Because the chamber 102 during operation contains a precursor liquid, the seal must 107 elastic and also resistant to chemical attack by the precursor liquid. In the event that the reactor 100 made of conductive components, it should also be the busbars 106 electrically from the reactor 100 isolate. For example, silicone rubber can be used to open the reactor 100 through which the busbars 106 happen, seal.

The busbars 106 For practical reasons, they enter the lower part of the reactor 100 one. If the busbars 106 in the upper part of the reactor chamber 102 would be a poetry even then 107 required. This would not prevent the leakage of liquid, but the escape of vapor from the chamber 102 , The busbars 106 could even by pushing in the shaft 136 in the chamber 102 occur, in which case no special seal is necessary. However, it is desirable to use the busbars 106 as short as possible to reduce power losses at the busbars.

The precursor liquid becomes the reactor 100 through the precursor inlet 108 over the valve 110 fed.

At the beginning is the chamber 102 so far filled with precursor liquid that the preform (not shown) is at least covered. During operation, precursor liquid may be consumed in the deposition reaction or as vapor from the reactor 100 escape. Accordingly, the precursor inlet 108 during operation of the reactor 100 used to replenish the lost precursor liquid.

During a compression process, the dilute liquid may become cloudy. Accordingly, the valve 114 be opened to drain the precursor liquid through a reagent return 112 to the filter 116 to allow what they filtered and back to the reactor 100 is pumped. The filter 116 may be any suitable filter, such as a porous ceramic disk or, more preferably, carbon.

The reagent fluids used here are potentially flammable. Thus, it is preferable that the compression process is performed in an inert atmosphere. For example, nitrogen gas can be used. To get the air out of the cavity 102 blow out the valve 120 opened, which is the influx of nitrogen through the inlet 118 allows. The valve 124 Can be opened to the steam recovery system 130 to empty faster and more efficiently. Once the atmosphere in the chamber 102 replaced by nitrogen, the valve can 128 be opened to nitrogen directly into the ventilation shaft 136 respectively. This nitrogen flow prevents air from entering the cavity 102 penetrates and the valves 120 and 124 can be closed. By closing the valves 120 and 124 the gas flow through the vapor recovery system 130 reduced. So can the vapor recovery system 130 work more effectively.

The vapor recovery system 130 is a system of the type known in the art for the recovery of vaporized liquids. With such a system, the amount of loss incurred in the process and the amount of precursor used can be reduced.

During operation will be in the cavity 102 in close proximity to the coil 104 a brake made of carbon (not shown) is arranged. Exemplary coil types are in 3 . 5 and 6 shown. The carbon brake is preferably mounted in a holding jig that holds the carbon brake firmly in a fixed position relative to the reactor and coil. The exact form of the Spannvor direction results from the shape of the brake made of carbon. Such a tensioning device may be in any convenient manner, such as on a rim 132 , being held.

Depending on the shape of the carbon brake, it may be desirable to use coils of different size or shape. That's why the coil is 104 over the connecting link 134 with the busbars 106 connected. The connecting link 134 is part of the electrical circuit, which also includes the busbars 106 includes. It also contains the water circuit passing through the channels 105 is formed. The connecting link 134 may simply be a metal block, at the mounting points for screws (not shown) the base of the coil 104 with the busbars 106 connect. The connections of the water circuit can be sealed with flexible O-ring seals or in other conventional ways. The material must be resistant to both water and precursor decomposition. Viton or silicone rubber can be used for this purpose. Other mounting arrangements such as slots and grooves or clamps may also be used.

2A shows a drawing of a clamping device 200 for use in connection with the reactor of 1 , The tensioning device 200 contains a ring 202 whose size is so adaptable that he is on the edge 132 ( 1 ) can rest. The screws 203 be through the ring 202 guided. The screws 203 can in the edge 132 ( 1 ) are screwed in to the tensioning device 200 at the reactor 100 ( 1 ) to fix. In an alternative embodiment, the screws 203 only on the edge 132 ( 1 ) rest. This is how the screws serve 203 for adjusting the vertical angle of the tensioning device relative to the edge 132 ( 1 ).

The possibility of adjusting the vertical angle of the tensioning device 200 can be useful if the coil 104 immovable at the reactor 100 ( 1 ) is attached. When the tensioner 200 Holding a brake made of carbon is done with the regulation of the vertical angle of the tensioning device 200 the position of the carbon brake compared to the coil 104 regulated. Since it is preferable to arrange the carbon brake to be concentric with the coil, it is desirable to regulate either the position of the carbon brake or that of the coil.

The tensioning device 200 includes the vertical parts 204A and 204B , A horizontal part 206 extends between the vertical parts 204A and 204B , At the horizontal part 206 is a pillar 208 attached. A carbon brake will attach to the column in any convenient way 208 attached. For example, if the carbon brake is disposed about a spindle, the pin may pass through the spindle into the column 208 be used. Because the horizontal parts 204A and 204B , the vertical part 206 and the pillar 208 in close proximity to the induction coil 104 It is preferred that they be made of a non-magnetic material (with a permeability of about 1). However, they should be made of a material strong enough to support the carbon brake. A glass-epoxy composite can be used. Because the pillar 208 It may be made of a material that is a good thermal insulator and resistant to high temperatures with a carbon-based brake that is heated. The pillar 208 is particularly preferably made of quartz.

To find a suitable relationship between a carbon brake and the coil 104 To ensure it may be desirable to use the coil 104 directly on the clamping device 200 to fix. The sink 104 can then use non-conductive pins 210 at the vertical part 204 be attached.

2 B shows a more detailed view of the coil 104 , The sink 104 optionally consists of a plurality of coil segments 251 . 252 . 253 and 254 , which are electrically connected in parallel. The coil segments 251 - 254 are with the conductive bars 260A and 260B connected. The busbars 106 that the coil 104 power, are with the conductive rods 260A and 260B connected. How out 2 B shows are the busbars 106 in the middle of the conductive bars 260A and 260B connected. Thus, the coil segments 251 - 254 arranged symmetrically around the energy source. Consequently, any voltage drop that may be significant when using high currents is along the length of the coil 104 balanced. This leads to a more uniform heating of a brake made of carbon.

In order to achieve a more uniform heating, each coil segment can optionally have a different length. Since the coil segments 252 and 253 closer to the power tap of the busbars 106 For example, they can be made with a longer length than the coil segments 251 and 254, by B. get more windings. The size of the coil segments 252 and 253 can also be such that the resistance in the circuit of the busbars 106 through any coil segregation mente 251 - 254 is identical.

The sink 104 Optionally, it may be designed to have a nonuniform winding density along its length to compensate for gravity effects during the process. Thus, vapor generated by the boiling precursor liquid rises upward along the carbon brake. It is possible that both the amount and the speed of the steam at the upper end of the brake are higher in carbon than at the lower end. Thus, the heat transfer from the carbon brake at the top may be different from that at the bottom. To counteract this, it is possible to use a coil 104 to construct, which allows for a different heating at the upper end of the carbon brake. For example, the winding density of the coil at the upper end may be lower or the distance between the coil and the carbon brake may be lower at the upper end.

3 shows the ratio of a preform 302 to a coil 304 within a reactor 300 , The preform 302 is in the middle of the coil 304 and both are in a precursor liquid 308 immersed.

For applications with induction heating the coil is generally shaped to be heated Part corresponds. The diameter of the coil can be smaller, where the diameter of the part is smaller. Alternatively, the winding density the coil in the areas increased in which the one to be heated Item further away from the spool.

The sink 304 can be shaped to fit the preform 302 equivalent. Alternatively, a second coil, coil 306 , in the preform 302 be used. The current flow through each coil should be such that the magnetic flux generated by each coil is in the preform 302 is in phase. Preferably, both coils 304 and 306 connected to the same power supply to ensure the in-phase of the currents through the coils. The arrangement in 3 is of course only useful for hollow preforms. With the two coils 304 and 306 is the magnetic flux in the entire preform 302 uniform. Areas of the preform 302 further from the coil 304 are removed and therefore not effective from the coil 304 are heated, are closer to the coil 306 and are heated more effectively by her. In this way, a uniform heating of the preform can be achieved without the special construction of a coil for each preform.

4 shows an alternative method of heating a preform 402 , In this case, the preform has 402 the shape of a staff or a pole. The preform 402 is between the electrodes 404 clamped. The preform 402 is clamped in any convenient manner, so that good electrical and mechanical connections are provided.

The electrodes 404 are made of any material that can carry the current required to densify the part without substantial heating or reaction with the precursor liquid.

In this case, the electrodes are 404 Made from 1.9 cm (three quarter inch) copper rods, with slots 406 are provided. In the gap around the preform 402 are washers made of copper 408 arranged. The washers 408 are with bolts 410 at the threaded ends 412 the electrodes 404 screwed into the preform 402 pressed.

During operation, the preform becomes 402 in a precursor liquid 414 brought in. The electrodes 404 are connected to a power supply (not shown) that conducts current through the preform 402 which provides the preform 402 heated. When the resistance of the preform is low, for example, when the preform is made of carbon fibers or other fibers held together by charred resin, a high power supply is preferred. The amount of electricity required depends on the cross-sectional area of the preform 402 and its specific resistance. The current should be sufficient, however, part of the preform 402 about the pyrolysis temperature of the precursor liquid 414 to warm out. While currents on the order of 1,000 amps are likely to be required, the precise amount of current can also be determined empirically based on preform temperature measurements. DC is preferred, but AC can also be used. It may be necessary to reduce the current during the compaction of the preform 402 to change. With increasing compaction of the preform 402 The resistance is likely to decrease, requiring an increase in current to maintain a steady warming. For this reason, it may be preferable to use a pyrometer with which the temperature of the preform unun is broken or measured at periodic intervals, after which either the voltage of the power supply is adjusted to preserve the desired current, or the current is adjusted directly.

The device in 4 is particularly suitable for compacting preforms whose shape has a uniform cross-section, such as bars or rods or tubes of uniform diameter and wall thickness, flat plates or other shapes with a uniform cross-sectional area at right angles to the direction of current flow. Such preforms may have the finished shape or "net shape". Alternatively, slices or other shapes may be cut after compression from the bar, bar, flat plates or other shapes. In this way, parts with non-uniform cross-section can be compacted. Alternatively, several parts can be cut from a compacted part, so that in fact the simultaneous compression of several parts in a reactor with only one power supply unit is possible.

4 shows the preform 402 aligned horizontally in the reactor vessel. Any orientation can be used. 5 shows an alternative configuration for compacting a preform 502 , The preform 502 is inside an induction coil 504 appropriate. The ends of the preform 502 are on electrodes 506 connected. After connection to a suitable power supply as described above, the coil provides 504 Induction heat for the preform 502 and the electrodes 506 facilitate resistance heating.

The preform 502 contains a concave area 508 , Preforms having concave areas or areas of different cross-sections are generally undesirable for uniform heating by resistance heating because the current density and thus the heating in the concave areas is higher. Concave areas are also not conducive to uniform heating by means of induction heating because concave areas without special coil construction are not heated as well as the surrounding areas. However, the use of both resistance heating and induction heating provides for more uniform heating since overheated areas associated with resistance heating are more likely to be compensated by the cold spots of induction heating. Accordingly, it is possible to use the preform 502 evenly and without special coil construction, the contour of the preform 502 corresponds to warm.

The Combination of resistance and induction heating is also to that effect advantageous that they better control the heating of the Preform allows. In order to best compact the preform, it is desirable that the center of the preform is initially at a temperature above the pyrolysis temperature of the precursor liquid heated becomes. It creates a temperature gradient, due to the cooling effect the precursor liquid decreases from the center of the preform to its periphery. at this temperature distribution occurs the deposition of compacting Material preferably in the middle of the preform. With progressive Compaction it is desirable that the areas of the preform that are radially from the center to Outside run, gradually exceed the pyrolysis temperature. Resistance heating generated Heat practically evenly over the across the cross section, with only second order differences due to the resistivity changed by the temperature gradient occur. As the precursor liquid the exterior of the Preform cools, The resulting temperature profile is the warmest in the middle and the coolest on the edge. Furthermore he falls Resistance at some preforms with increasing temperature, so electricity, and thus additional heat generation on the hotter Concentrate inner sections of the preform. This temperature distribution is particularly suitable for the beginning of the compression cycle.

Conversely, the induction coil causes 504 greater heat generation near the periphery of the preform. The amount of heat generated falls at the penetration depth to 14% of the maximum value. The penetration depth is again a function of the frequency and decreases inversely proportional to the square root of the frequency. By appropriate selection of a frequency using known techniques familiar to those skilled in the art of induction heating, the induction coil can 504 generate more heat in the periphery of the preform. This heat distribution is desirable at the end of the compression cycle. Accordingly, desirable results can be achieved by having the preform 502 heated first by means of resistance heating and then the current through the coil 504 is increased. If desired, the current through the electrodes 506 be reduced at the same time.

A similar heat distribution during the compression cycle can also be achieved by a protruding induction coil. The frequency of the power supply is initially set to achieve a penetration of about one quarter to one third of the diameter of the preform. Taking into account the heat transfer from the preform, this penetration depth results in a maximum heat concentration in the middle of the preform. Ideally, the power supply of the coil is set so that the preform is heated just above the pyrolysis temperature of the precursor liquid while the precursor liquid cools the remainder of the preform below the pyrolysis temperature. With increasing densification of the center of the preform, the frequency of the power supply may be increased to heat the preform to a temperature somewhat above the pyrolysis temperature in regions that are slightly out of center. The power supply of the coil can also be reduced somewhat to ensure that the remainder of the preform remains below the pyrolysis temperature of the precursor liquid. Such adjustments can be made until the preform is fully densified. The exact rate of change of frequency and power depends on the shape and composition of the preform, and may be subject to change. U. be determined empirically.

Even If an induction coil is used without resistance heating, desirable Results can be achieved by the power supply the induction coil is increased with the progress of the compression cycle.

7 Figure 3 shows three curves that help to understand how to achieve more complete compaction with increasing power supply during the compaction cycle. 7 shows the curves 702 . 704 and 706 , each representing the density of a densified preform as a function of the distance to the center of the thickness of the preform. The curve 702 was created with relatively low input power. The density shows a maximum at the midline. This compaction pattern is the result of heating the center to a temperature high enough to provide pyrolysis of the precursor liquid. The outside of the preform is cooled so that no pyrolysis and associated deposition reactions occur. The curve 706 was created with relatively high input power. The maximum density occurs in the periphery because the periphery is heated to a temperature high enough to provide pyrolysis of the precursor liquid. Pyrolysis causes deposits that prevent infiltration of the precursors into the center of the preform. The curve 704 was created with a medium power and shows a maximum density between the midline and the periphery.

To improve compaction, it is desirable to use a power P _o at the beginning, such as that used to generate the curve 702 has been used. At the end of the compression cycle, it will be preferable to use a power P _f as used to generate the curve 706 has been used. In between, it is expedient to use a power which corresponds to a curve 704 leads. 8th shows a curve with desirable input powers versus time P (t) during the compression cycle. Initially, the power is set to P _o . At the end of the compression cycle at time T _f , the power equals P _f . During the compression cycle the power is increased. How out 8th it is evident that the power is proportionally increased by the power n at the moment t. This is a desirable ratio because the chemical reaction that causes the deposits increases with increasing temperature. This will take less time to compact the outside of the preform. The other portions of the preform are also densified to some degree during interior compaction. As a result, the peripheral portions of the preform compress much faster than the interior, and less time is required to compact the outer portions of the preform.

The values μ, P _o , P _f , T _f and n depend on such factors as the size and geometry of the preform and the particular precursor liquid used. These values can be calculated theoretically. Due to the complicated nature of the phenomena in question, it may be preferable to determine the appropriate values preferably empirically. Here, multiple series of experiments that are periodically interrupted to observe the preform and measure its density may be required to determine the appropriate pitch. It has been observed that values for n ranging between 1 and 5 are satisfactory for one or more carbon brake components as described herein. However, other values may be desirable for other geometries.

It should be noted that 8th shows a continuous change in performance. However, the performance can be increased in individual steps. The same pattern of different input power can also be used regardless of the method of heating the preform. In addition, the curve of 8th in that the power is applied continuously. As described below, it may be useful to pulse the applied power periodically between a "on" state and an "off" or lower level state. If a pulsed energy source is used, set the curve in 8th the power is in the "on" state.

Another way to control the deposition is the regulation of the pressure in the reactor chamber. Initially, it is desirable to cool the periphery of the preform so that deposition occurs substantially internally. The cooling takes place by boiling or evaporation and convection of the precursor liquid and by radiant heat transfer. When the center of the preform is compacted, less peripheral cooling is desirable so that the densification of the exterior of the preform is rapid. To reduce the cooling, the pressure in the reactor chamber can be changed. For example, the pressure can be released simply by closing the ventilation duct 136 increase.

As described above, it is desirable the compaction preferably occurs inside the preform. Refer to the process control techniques described above to the control of a compaction process by control the warming of the preform. It is also possible to vapor diffusion in to control the preform.

If more steam gets into the interior of the preform or the Steam concentration increases inside the preform, the occurs Compression preferably in the interior of the preform.

One way to increase the concentration of materials that form a deposit inside the preform is by pulsating heating of the preform. Pulsing the heating allows out-diffusion of byproducts generated during the formation of a vapor phase deposit from the preform when no heating occurs or heating is reduced. For example, when cyclohexane is used as the precursor liquid, H _{2 is} produced as a by-product. If the power supply to the coil (using induction heating) or the preform power supply (using resistance heating) is interrupted periodically for a period of time sufficient to allow H _{2 to} diffuse out of the preform, the resumption may occur Warming more cyclohexane vapor diffuse into the preform. The concentration of cyclohexane vapor is then higher because H _{2 has} escaped.

The Heat only needs for a relatively short period of time to be interrupted. The length of the period depends on the size of the preform and the compaction stage. The outward diffusion of the by-products from the middle of a thick preform may take longer than that from the Edge areas. Consequently, it may be desirable to heat Beginning of the compression cycle while the interior of the preform is compacted to interrupt for longer periods of time. The heating should preferably for a period of 0.01 seconds to 10 minutes, more preferably 0.01 second to 3 minutes, interrupted. The heating should be interrupted at intervals whose length is inversely proportional to the production rate of the by-products is and preferably between about 0.01 seconds to 3 minutes.

The Interruption of heating also has the further advantage of being more durable end products arise. The durability of the compacted part is based on Part on the durability of the deposited material. The durability The deposited material, in turn, is characterized by its microstructure certainly. With increasing deposition of the material grow the crystalline Areas. However, a part is more permanent when all these areas stay small. When the heating is interrupted long enough so that the part to a temperature cooling down which allows re-nucleation for crystallization, does this to smaller areas. There are such areas as small, the smaller than the diameter of the fibers making up the preform is manufactured, typically below 5 microns.

The Heat should be applied to the preform until the area is up grown the desired size is. Here are times of about 0.1 second to 5 minutes typical. The heating should be long enough be interrupted to the preform below the temperature for the renewed Germination for cool the crystallization allow. Here, times of 0.01 seconds to 10 seconds are typical. Since the deposition is exponentially dependent on the temperature, can be a cooling as little as 10 to 200 ° C for a renewed Germination for the crystallization suffice.

The Control of grain size is included the production of friction material as used in brakes also important. Smaller areas can give a different coefficient of friction to lead as larger areas. The control of the size of the areas allows thus producing materials with the desired Coefficient of friction.

It should be noted that the pulses do not require a constant duty cycle or must occur within constant time intervals. How out 8th As can be seen, the power level during change the compression cycle. The pulse characteristic may change with the power level.

An alternative way of increasing the deposition of material inside the preform is the use of pressure waves in the liquid precursor. These waves are visible in the gas phase as density waves forcing precursors into the part and pulling off byproducts. In the system described above, pressure waves exist in the liquid due to the generation and concentration of beads associated with the boiling of the liquid precursor. The magnitude of the waves can be increased by cooling either the precursor liquid or the exterior of the reaction vessel. In 1 can the filter 116 For example, include a cooling section for cooling the liquid. Alternatively, the reactor 100 be surrounded by a water jacket or other cooling device.

One alternative approach for generating pressure waves in the precursor liquid is the insertion of one or more transducers into the precursor fluid. In this case, an acoustic or ultrasonic transducer can be used become. The transducer can be pulsed to cause waves in the precursor fluid to create. It can also be a mechanical agitation or stir either the preform or the runner liquid.

6 shows an alternative coil arrangement, which is preferred for compacting and Wiederertüchtigen of brake discs. Here is a disk-shaped preform 602 between disc coils 604 arranged. The disc coils 604 provide more efficient heating in the middle of some preforms, such as the preform 602 as a coil, for example, like the coil 304 ( 3 ) is trained. Disc coils are also useful for full thickness high resistivity preforms and for heating preforms having edges along the axis of a coil such as a coil 104 ( 1 ).

6 shows disc coils 604 with uniform spacing between the windings. In some cases, a non-uniform spacing may be desirable. When the preform 602 for example, a disk having a hole in the middle, the winding density can be increased in the area just between the outside of the preform and the outside of the hole in the center of the preform. Preferably, construction techniques traditionally used in induction heating systems are used.

6 shows the preform 602 on a net 610 rests. The network 610 or a similar support structure holds the preform 602 while allowing the precursor liquid 608 the bottom of the preform 602 can reach. In general, preforms for carbon-carbon composites are made from fibers held together by resin or tar. The resin or tar is then heated to a high temperature to convert it to carbon. The carbon is still porous and still needs to be compacted. However, the preform is generally relatively stiff and there are many preform bearing capabilities. According to the invention, instead of the preform 602 provided a worn brake component made of carbon.

The preform out 6 is called a dry preform because it is not held together by charred resin or tar. A type of dry preform is a "needled" preform made by stacking fiber layers and piercing the stack with barbed needles. The needles pull the fibers through the layers, holding the layers together. The preform thus produced is less stiff and must u. U. on its entire length on a structure, such as a frame or net 610 , rest.

dry Preforms also have a higher one resistivity as a preform made by resin or Tar is held together, so a higher frequency for efficient Heat these materials is required. With incipient compaction the preform must have the frequency u. U. reduced to that To compensate for the drop in resistivity. Similar Adjustments may be necessary for resistance heating. The current must u. U. increased to compensate for the falling resistance.

Some preforms require very high frequencies for efficient induction heating. In this case, the resistance heating described here can be used. Alternatively, the high frequency energy may be generated by a microwave source rather than an induction coil. When microwaves are used, the reactor vessel should be made of a material which reflects the microwave energy and be shaped as a cavity, as used in microwave ovens. If necessary, the openings in the reactor vessel must be less than one quarter of the wavelength of Fre or be covered with a conductive network whose openings are smaller than a quarter of the wavelength. Frequencies in the range of 300 MHz to 300 GHz, more preferably frequencies in the range of 915 MHz to 2.45 GHz can be used.

In conjunction with the induction coils described here, flux concentrators can also be used. 6 shows, for example, a disc coil that generates a symmetrical field pattern. Flux concentrators such as ferrite beads or the commercially available Fluxtrol product sold by Fluxtrol Company may be used. For example, the flux concentrator may be attached to the exterior of the coil away from the preform to direct more of the generated flow to the preform.

EXAMPLE 1

The Brakes on an F-16 aircraft were removed and worn out Rotor discs are ground from carbon, so each rotor disc resulted in a half-thickness rotor. It was the rotors around round discs of carbon-carbon with a diameter of 12 inches (30.5 cm) during the the operation of the aircraft for the duration of a normal life cycle have been used for braking.

Three rotors (disc 2 . 3 and 4 ) were separately compacted under process conditions that meet the rotor disk conditions described below 3 were similar. Each rotor was immersed in cyclohexane in a reactor separate from the one in 1 and 6 kind shown was. At the end of the compression, the total density of the rotor was approximately equal to that of the original carbon brake rotor.

TABLE 1 Process conditions: Compression of brake rotor disc 3 made of carbon

The surface temperature the brake rotor disc was made of carbon during the compression cycles at about Estimated 800-1,100 ° C. It It was generally observed that heating to an internal temperature from 950 to 1,100 ° C over one Period of 2.0 to 3.5 hours in cyclohexane was sufficient to worn To restore brake components made of carbon with a density, at least equal to an original part or a conventional one Way again Brake component made of carbon of the same size, density and composition which is used in aircraft operation.

To The compaction became samples of the compacted rotors of a 2-hour post-reheat treatment under argon atmosphere at temperatures of 1,800, 2,100 and 2,400 ° C exposed.

test samples on a smaller scale (Outer diameter 1.25 inches, inside diameter 0.85 inches) were from solid points machined in each rotor and machined on the inside and outside outer edge the test specimens became one before the wear and friction test Antioxidant paint applied.

EXAMPLE 2

• Drehzahl der Proben:116 kg (257 Ibs)
• Bei max. Drehzahl an der Scheibe anliegende Normalkraft: 31.500 U/min
• Druck an der Scheibenoberfläche: 24 atm (390 psi)

To simulate wear and performance during landing conditions of an F-16 aircraft (with a landing speed of 210 knots), the following parameters were set on an experimental apparatus used at Composite Testing and Analysis, University of Michigan:

• Speed of samples: 116 kg (257 lbs)
• At max. Speed at the disc applied normal force: 31,500 U / min
• Pressure at the disk surface: 24 atm (390 psi)

• Max. Geschwindigkeit der Bremsoberfläche: 53,7 m/s (2114 in/s)
• Max. Berührungsdruck zwischen Bremsscheiben: 24 atm (390 psi)
• Max. Temperatur der Bremsobertläche bei Geschwindigkeit Null: 815 °C

These parameters yielded a model that simulated the following maximum conditions encountered during the landing of an F-16 aircraft:

• Max. Braking surface speed: 53.7 m / s (2114 in / s)
• Max. Contact pressure between brake discs: 24 atm (390 psi)
• Max. Brake surface temperature at zero speed: 815 ° C

rotor samples were tested in 10 cycles and wear measurements performed. The calculation of the coefficients of friction was based on of data only during the last five Cycles were determined to determine the effect of surface defects excluded. The results shown below are compared to data the brakes worn out with new brakes and control samples were collected. The "worn" brake samples represent conventional wiederertüchtigte worn brakes, d. H. to become two worn discs ground and used instead of an original brake disc.

TABLE 2 Wear results after ten braking cycles

Coefficient of friction everyone sample

The results show that when a worn brake for a half thickness F-16 aircraft is subjected to the reconditioning process of the present invention, the wear and friction characteristics of the brake are significantly improved. In these tests, the use of the retreading process, even without reheat treatment, resulted in wear characteristics that matched or even exceeded those of a new or traditionally rebuilt brake, without endangering it the coefficient of friction.

The wear data from Table 2 show that the samples in a 3-hour compression cycle were processed, showed 25% less average wear as the samples of new brakes. The data from Table 2 also shows the results of reheating treatment of samples. These data, although limited, suggest that if the brakes after re-conditioning high temperatures Both the wear characteristics and the friction coefficient are exposed of the material changed become. The data of the pair of reheated samples with reheating treatment at 2,100 ° C show 56% less wear same average friction value as the samples of new brakes.

To the Wiederertüchtigen worn brakes can also other than the process conditions mentioned here by way of example can be used and the practitioner can choose appropriate conditions changes brake components, device size and construction, liquid carbon precursor and process conditions to take into account. The process conditions can also be adapted to the simultaneous processing of several Carbon brake components with or without the use of a susceptor to enable. It only applies to the requirement that the conditions be a microstructure of the carbon-carbon composite resulting from a coefficient of friction, wear characteristics and Thermal properties is characteristic of the operation of brakes for Aircraft are sufficient and that the process of chemical deposition must be completed quickly from the gas phase, d. H. within less than 48 hours, preferably less than 24 hours.

Accordingly, the Invention limited only by the scope of the appended claims.

Claims (23)

Process for re-aging a worn Brake component made of carbon for an aircraft, wherein the component Has pores through interior areas including a geometrically middle area and an outer surface demarcated The procedure includes the following steps: Provide a reactor containing a liquid Carbon precursor and at least one internal induction coil; Insert the worn Braking component of carbon in the liquid carbon precursor, the contained in the reactor; Inductive heating of the interior of the worn brake component made of carbon up to a temperature which is above the decomposition temperature of the liquid carbon precursor, as well as infiltration of the vapor into interior areas and pyrolytic deposition Carbon inside the interior until the worn Brake component made of carbon has a density of at least 1.85 g / cc and has a non-isotropic CVD microstructure, and in which the inductive heating step be continuous or interrupted by periodic cooling by at least 10 ° C. can be. The method of claim 1, wherein the inductive heating step as long as the worn brake component of carbon persists has a density of at least 1.9 g / cc. The method of claim 1, wherein the reactor is attached to a Capacitor for compressing the vaporized liquid carbon precursor and for the return of the liquid Carbon precursor coupled into the reactor. The method of claim 1, wherein the method additionally comprises Step of warming the re-trained Brake component made of carbon to a temperature of about 1500 up to 2400 ° C after completion of the chemical vapor deposition. The method of claim 1, wherein the worn Brake component made of carbon by heating over a period of 2.0 to 3.5 hours to an internal temperature of 950 to 1100 ° C and a outside temperature from 800 to 1110 ° C in cyclohexane completely wiederertüchtigt becomes. The method of claim 1, further comprising the steps of: a) adjusting an initial frequency and a power supply of the induction coil, wherein the initial frequency and the power cause sufficient heat to be achieved in a geometrically central region of the worn carbon brake component that is sufficient , to the Pyrolysis of the vapor and the deposition preferably in the pores trigger, which are located in the geometrically middle region of the worn brake component made of carbon; b) supplying an initial amount of energy to the induction coil at the initial frequency sufficient to heat the geometrically centered region of the worn brake component to a temperature sufficient to compress the geometric center region without concomitantly compressing other interior regions and the exterior surface of the worn brake component Carbon is sufficient; c) upon compression of the geometric mean region of the worn carbon brake component, supplying energy to the induction coil at one or more frequency settings, wherein the amount of energy and frequency adjustment cause a sufficient amount of heat to be stored in the interior areas of the worn carbon brake component to initiate the pyrolysis of the vapor and the deposition preferentially in the pores located in the interior regions of the worn brake component of carbon adjacent to the geometric center region; and d) adjusting the amount of energy supplied to the induction coil at one or more frequency settings, the amount of energy and frequency adjustment causing the interior regions of the worn brake component to be outwardly of and radially outward of the geometric center region a thickness of the worn brake component made of carbon are gradually compressed. The method of claim 1, wherein the step of chemical deposition at a pressure of one-half to four atmospheres carried out becomes. The method of claim 1, wherein the liquid carbon precursor is at least a liquid C5 to C9 hydrocarbon. The method of claim 8 wherein the liquid carbon precursor is selected from a group which is cyclopentane, hexene, cyclohexene, 1-hexene, cyclohexene, gasoline, Methylcyclohexane, benzene and toluene, or a combination of these includes. The method of claim 1, wherein the coefficient of friction the returnee Braking component of carbon is at least 0.27. The method of claim 1, wherein the worn Braking component is selected from carbon from a group, the carbon rotors, carbon stands, carbon end plates and carbon pressure plates. Process for re-aging a worn Brake component made of carbon for an aircraft, wherein the component Has pores that range from interiors including at least one geometric delimited in the middle area and an outer area and the method comprises the following steps: Provide a reactor containing a liquid Carbon precursor and at least one set of electrodes with connectors to an electrical contact with the worn brake component made of carbon, and the at least one energy source for the electrical heating the worn brake component of carbon provides; Deploy the worn brake component of carbon in the liquid carbon precursor, the contained in the reactor, the supply of a sufficient amount of electricity to the worn brake component made of carbon, around the interior areas the worn brake component made of carbon by resistance heating on a temperature above the decomposition temperature of the liquid carbon precursor heat and thereby the formation of a vapor from the liquid carbon precursor as well the infiltration of the vapor into the interior and the deposition pyrolytic carbon within the interior, until the worn brake component made of carbon has a density of at least 1.85 g / c.c. and a non-isotropic CVD microstructure of at least 1.85 g / c.c. Has,  the step of feeding a sufficient amount of electricity is continuous or interrupted gets out to the interior areas of the worn brake component Carbon at least 10 ° C to cool periodically. The method of claim 12, wherein the resistance heating step as long as the worn brake component of carbon persists a density of at least 1.9 g / c.c. Has. The process of claim 12, wherein the reactor is connected to a condenser for compressing the vaporized liquid carbon precursor and returning the liquid carbon precursor to the reactor is coupled. The method of claim 12, wherein the method additionally the step of warming the returnee Brake component made of carbon to a temperature of about 1500 up to 2400 ° C after completion of the chemical deposition. The method of claim 12, wherein the worn Brake component made of carbon by heating over a period of 2.0 to 3.5 hours to an internal temperature of 950 to 1100 ° C and a outside temperature from 800 to 1100 ° C in cyclohexane completely wiederertüchtigt becomes. The method of claim 12, wherein the method additionally the steps contains: a) Setting an initial Power to a set of electrodes, with the initial Power supply causes a sufficient amount of heat in the indoor areas the worn brake component is accumulated from carbon, to pyrolysis of the vapor and the deposition preferably in the pores trigger, located in the interior of the worn brake component made of carbon including the geometric middle area; and to trip someone the amount of electrical current supplied to the set of electrodes around the interior of the worn brake component made of carbon from the geometrically middle region of the worn brake component made of plastic outward gradually compress in the radial direction. The method of claim 12, wherein the step of chemical deposition at a pressure of one-half to four atmospheres carried out becomes. The method of claim 12, wherein the liquid carbon precursor is at least a liquid Contains C5 to C9 hydrocarbons. The method of claim 19, wherein the liquid carbon precursor is selected from a group that includes cyclopentane, hexene, cyclohexene, 1-hexene, cyclohexane, gasoline, methylcyclohexane, benzene and toluene, or a combination of these. The method of claim 12, wherein the coefficient of friction the returnee Braking component of carbon is at least 0.27. The method of claim 12, wherein the whole or a part of the carbon brake component is warmed up with means, the induction heating means and the resistance heaters include. The method of claim 22, further comprising the steps of: a) adjusting an initial frequency and a power supply of an induction coil, wherein the initial frequency and power cause sufficient heat to be stored in a geometrically central region of the worn carbon brake component Achieve temperature sufficient to generate the steam by pyrolysis and preferably deposit carbon in the pores, which are located in the geometrically middle region of the worn brake component made of carbon; b) supplying an initial amount of current to the induction coil at the initial frequency sufficient to compress the geometrically centered region of the worn carbon braking component without concomitantly compressing other interior regions and the exterior surface of the worn carbon brake component; c) after densification of the geometric mean region of the worn carbon brake component, supplying an amount of energy to the induction coil at one or more frequency settings, the amount of energy and frequency adjustment causing sufficient heat to be stored in the interior areas of the worn carbon brake component in order to trigger the pyrolysis of the vapor and the deposition preferably in the pores, which are located in the interior of the worn brake component made of carbon adjacent to the geometrically middle region; d) supplying electrical current to the worn brake component of carbon through the electrodes to heat the worn brake component of carbon by resistance heating; and e) adjusting the amount of electrical current and the amount of energy supplied to the induction coil at one or more frequency settings, wherein the amount of electrical current and amount of energy and frequency adjustment cause the interior regions of the worn brake component to be of geometric geometric mean Range out to the outside in the radial direction and through a Thickness of the worn brake component can be compressed from carbon.