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WO2004026648A2 - Method for recycling a brake assembly - Google Patents

Method for recycling a brake assembly Download PDF

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Publication number
WO2004026648A2
WO2004026648A2 PCT/US2003/029717 US0329717W WO2004026648A2 WO 2004026648 A2 WO2004026648 A2 WO 2004026648A2 US 0329717 W US0329717 W US 0329717W WO 2004026648 A2 WO2004026648 A2 WO 2004026648A2
Authority
WO
WIPO (PCT)
Prior art keywords
brake shoe
assembly
friction material
temperature
cooling
Prior art date
Application number
PCT/US2003/029717
Other languages
French (fr)
Other versions
WO2004026648A3 (en
Inventor
John J. Carney
Original Assignee
Carney John H
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Carney John H filed Critical Carney John H
Priority to AU2003295334A priority Critical patent/AU2003295334A1/en
Publication of WO2004026648A2 publication Critical patent/WO2004026648A2/en
Publication of WO2004026648A3 publication Critical patent/WO2004026648A3/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
    • B23P11/00—Connecting or disconnecting metal parts or objects by metal-working techniques not otherwise provided for 
    • B23P11/02—Connecting or disconnecting metal parts or objects by metal-working techniques not otherwise provided for  by first expanding and then shrinking or vice versa, e.g. by using pressure fluids; by making force fits
    • B23P11/025—Connecting or disconnecting metal parts or objects by metal-working techniques not otherwise provided for  by first expanding and then shrinking or vice versa, e.g. by using pressure fluids; by making force fits by using heat or cold
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
    • F16D2250/00—Manufacturing; Assembly
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
    • F16D2250/00—Manufacturing; Assembly
    • F16D2250/0092—Tools or machines for producing linings

Definitions

  • the present invention relates generally to a method for recycling a brake shoe to which a friction material is adhesively attached, and in particular to a method for recycling a brake shoe using a cryogenic process to debond the friction material from the brake shoe so that the brake shoe may be reused.
  • Brake shoes are well-known components in automotive brake assemblies used to press a friction material, also known as the brake lining, against a rotating component of a wheel in order to slow the vehicle.
  • a friction material also known as the brake lining
  • the friction material may experience temperatures in excess of 300° C, which can degrade the strength of the friction material and increase its rate of wear.
  • the friction material may experience temperatures in excess of 300° C, which can degrade the strength of the friction material and increase its rate of wear.
  • a method in accordance with the present invention for processing a brake-shoe assembly to separate a brake shoe from a friction material adhesively mounted to the brake shoe so that the brake shoe may be reused.
  • the method comprises the steps of cooling at least a portion of the brake-shoe assembly to a selected temperature, such as a temperature less than
  • cryogenic temperature means any temperature less than -150° C.
  • the time period, the selected temperature, and the rate of cooling may be chosen to cause substantial separation of the brake shoe from the friction material.
  • a separating force may also be applied to the brake-shoe assembly to effect separation of the brake shoe from the friction material in the case that the cooling alone does not cause sufficient separation of the brake shoe from the friction material. The separating force may be applied either simultaneously or subsequently to the cooling step.
  • Figure 1 illustrates a brake assembly comprising a brake shoe and friction
  • Figure 2 illustrates a brake shoe suited for use in a drum brake and having a brake lining mounted thereto;
  • Figure 3 is a flowchart illustrating a method of the present invention.
  • a method for separating a brake shoe 12 from a friction material 14 adhesively mounted to the brake shoe 12 so that the brake shoe 12 may be reused.
  • the method of the present invention may strengthen the brake shoe 12, rendering the reclaimed brake shoe 12 potentially stronger than a new brake shoe of the same type.
  • brake shoe refers to a backing plate for supporting a friction material.
  • brake shoes are formed of a metal, such as steel. The shape and configuration of the brake shoe 12 and the friction material 14 of a particular brake
  • assembly may be selected in accordance with the type of braking system in which the brake shoe 12 and friction material 14 are to be used. For example, with reference to
  • a brake shoe 12 of a brake assembly 10 may be a generally planar piece of metal.
  • the friction material 14 may also be a generally planar structure and have a complementary mating surface for enabling the friction material 14 to be attached or bonded to a planar surface of the brake shoe 12.
  • the friction material 14 may be attached to the brake shoe 12 with an intermediate adhesive layer 16.
  • Such a structure is typically termed a brake pad and is used in disc brakes.
  • the brake shoe and friction material may have some other selected shape and configuration suited for use in a drum brake system, such as depicted in Fig. 2.
  • the brake shoe 22 may be provided as a curved metal plate having a specified radius of curvature.
  • the friction material 24 may also be provided as a curved plate having the same radius of curvature as the brake shoe 22 and may be adhered to the brake shoe 22 by an intermediate adhesive layer 26.
  • the friction material 14, 24 typically comprises a material composite capable of withstanding the operating temperatures and dynamic pressures experienced during repeated braking applications.
  • the friction material 14, 24 may comprise asbestos fibers impregnated within a thermosetting resin binder, such as a phenolic resin.
  • the friction material may also comprise fillers, such as rubber, carbon particles, graphite particles, and iron oxide.
  • the friction material 14, 24 may comprise an asbestos-free composite.
  • Such a composite may include components such as sponge iron, sepiolite fibers, acryl fibers, aramid fibers, or other temperature resistant fibers instead of asbestos.
  • Non-asbestos composites may also comprise a thermosetting resin binder, such as a phenolic resin, and suitable fillers.
  • the friction material 14, 24 is typically affixed to the brake shoe 12, 22 using a high temperature adhesive laver 16, 26 which contains phenolic resins.
  • the method includes a cooling step 110 for cooling at least a portion of the combined brake shoe and friction material, i.e., the brake shoe assembly, to a selected temperature.
  • the temperature selected should be sufficiently below room temperature to aid in separation of the friction material 14, 24 from the brake shoe 12, 22.
  • the selected temperature may be a cryogenic temperature, and in particular may be at or below the
  • cooling may be chosen to promote separation of the friction material 14, 24 from the brake shoe 12, 22.
  • it may be desirable to perform the cooling at a relatively high rate of temperature reduction so as to thermally shock the bond between the friction material 14, 24 and the brake shoe 12, 22.
  • the friction material 14, 24 and the brake shoe 12, 22 may contract at different rates due to a difference between the coefficients of thermal expansion for the friction material 14, 24 and the brake shoe 12, 22 or even the bonding or adhesive material 16, 26 therebetween.
  • differential contraction may lead to a mechanical separation of the friction material 14, 24 from the brake shoe 12, 22 or may lead to a weakening of the bond between the
  • One convenient method for performing the cooling step 110 comprises contacting at least a portion of the brake shoe assembly with a coolant. For example, it may be sufficient to contact a component of the brake shoe assembly, such as the brake shoe 12, 22, with the coolant, because that component may have a thermal conductivity
  • One coolant particularly suited for use in the method of the present invention is liquid nitrogen, though other coolants may be used so long as they reduce the temperature of the brake shoe 12, 22, the friction material 14, 24, and/or the adhesive layer 16, 26 sufficiently to aid in separation of the friction material 14, 24 from the brake shoe 12, 22.
  • the volume of coolant brought into contact with the brake shoe assembly should be selected to have sufficient thermal mass to produce the desired decrease in temperature of the brake shoe 12, 22, the friction material 14, 24, and/or the adhesive layer 16, 26. If an insufficient volume of coolant is used, the temperature of the coolant may be raised, resulting in an insufficient degree of cooling to aid in separation of the brake shoe 12, 22 from the friction material 14, 24.
  • the assembly is held at the selected temperature, at step 120, for a time period sufficient to render the brake shoe 12, 22 susceptible to separation from the friction material 14, 24.
  • the cooling step 110 has been performed at a sufficiently high rate and the selected temperature is sufficiently low, the brake shoe 12, 22 and friction material 14, 24 may separate shortly after the selected temperature is reached.
  • the time period of cooling will also be dependent on the size of the brake
  • steps 110 through 130 may be repeated as needed.
  • various parameters may be altered from those used previously, such as the selected temperature, the rate of cooling, or the time period for which the reduced temperature is maintained.
  • a separating force may be applied to the assembly, at step 140, to separate the brake shoe 12, 22 from the friction material 14, 24.
  • Application of the separating force may be performed while the portion of the assembly is maintained at the selected temperature at step 120.
  • the separation force may be applied to the assembly, at step 140, to separate the brake shoe 12, 22 from the friction material 14, 24.
  • the assembly may be returned to room temperature at step 130, at which time the separation force at step 140 may be applied.
  • the separation force may take any form suited to cause separation of the brake shoe 12, 22 and the friction material 14, 24, while maintaining the integrity of the brake shoe 12, 22.
  • a mechanical force may be applied to separate the brake shoe 12, 22 from the friction material 14, 24, such as by striking the brake shoe 12, 22 or friction material 14, 24.
  • the mechanical force may be applied as a shearing force.
  • other forces may be applied to effect separation.
  • Such forces may include ultrasonic energy, a magnetic pulse, or any other force which may effect separation. Subjecting the assembly to magnetic pulsing may effect separation by the action of the magnetic field on ferrous materials within the assembly, such as the brake shoe 12, 22. If a particular
  • any of the steps 110 through 140 of Fig. 3 may be repeated at step 150, as necessary until separation is achieved.
  • steps 110 through 150 are principally related to separating the brake shoe 12, 22 from the friction material 14, 24, the method of the present invention may also effect optional strengthening of the brake shoe 12, 22 as part of the process shown in Fig. 3.
  • the selected temperature of step 110 may be a cryogenic temperature suited to promote strengthening of the brake shoe 12, 22.
  • the rate of cooling performed in step 110, the hold time of step 120, and the rate at which the brake shoe 12, 22 is returned to room temperature at step 130 may each be selected to encourage strengthening of the brake shoe 12, 22.
  • Tables 1-5 show the results of experiments in which friction material was sheared from 514 brake shoes under different cooling conditions.
  • Tables 1 - 4 relate to testing of a 514 brake shoe with 9" friction material mounted thereto, and Table 5 relates to testing of a 514 brake shoe with 7" friction material
  • Cohesive failure is the failure of the friction material to hold together when
  • Adhesive failure is the failure of the adhesive to maintain its bond to the brake
  • each sample of friction material was placed on two supports on the ram of a Model P-2100 Press, manufactured by Pasadena Hydraulics Inc., El Monte, CA. These supports spanned a distance of 9.53 cm. A 0.64 cm diameter pin was placed above the midpoint spanned by the friction

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Braking Arrangements (AREA)

Abstract

A method is provided for treating a brake-shoe assembly to facilitate separation of a brake shoe from a friction material, i.e. the brake lining, adhesively mounted to the brake shoe so that the brake shoe may be reused. The method comprises the steps of cooling at least a portion of the brake-shoe assembly to a selected temperature, preferably a cryogenic temperature, and maintaining the cooled portion of the assembly at the selected temperature for a time period sufficient to promote separation of the brake shoe from the friction material. In addition to the cooling, a separating force may be applied to the brake-shoe assembly to effect separation of the brake shoe from the friction material.

Description

METHOD FOR RECYCLING A BRAKE ASSEMBLY
John J. Carney
Field of the Invention
The present invention relates generally to a method for recycling a brake shoe to which a friction material is adhesively attached, and in particular to a method for recycling a brake shoe using a cryogenic process to debond the friction material from the brake shoe so that the brake shoe may be reused.
Background of the Invention
Brake shoes are well-known components in automotive brake assemblies used to press a friction material, also known as the brake lining, against a rotating component of a wheel in order to slow the vehicle. As the friction material is pressed against a rotating wheel component, e.g., a rotor or drum, heat is generated due to the friction between the rotating member and the friction material. Under such conditions, the friction material may experience temperatures in excess of 300° C, which can degrade the strength of the friction material and increase its rate of wear. To render the friction material less susceptible to degradation from the high temperatures, the friction material
typically contains randomly dispersed asbestos fibers which are well suited to high temperature use. However, the high temperatures and mechanical wear of the friction material eventually necessitate replacement of the friction material when it wears beyond a predetermined safety limit. Although only the friction material wears during use, both the friction material and the brake shoe must be replaced unless an economically and environmentally acceptable method is provided for separating the worn friction material
from the brake shoe. Such separation requires debonding of the friction material from the brake shoe, which is typically bonded to the friction material with a high temperature adhesive.
Current separation methods involve heating the brake-shoe/friction-material assembly to over 300° C for a period of time sufficient to decompose the adhesive
between the brake shoe and the friction material. Such methods pose environmental concerns, as a variety of toxic vapors are created by the burning process. The toxic vapors cannot be released into the environment until additional processing steps have been performed to mitigate the vapors. Moreover, along with the decomposition of the adhesive, various components of the friction material are degraded as an unintended consequence of the heating process rendering the friction material friable. A friable material containing asbestos poses severe environmental concerns, as such materials may readily release asbestos particles into the air which are then susceptible to being inhaled. Thus, the current brake shoe separation methods create environmental hazards as well as increased waste disposal costs. In fact, the increased waste disposal cost and environmental mitigation costs are often so great that it eviscerates any potential economic savings. Hence, present methods for reclaiming a brake shoe for reuse are both
economically unfeasible and environmentally undesirable. As a result, the current trend is toward disposal of the brake-shoe/friction-material assembly, rather than reclamation. Yet, disposal of unused brake-shoe/friction-material assemblies may still be environmentally undesirable, since disposal of the brake shoe increases the amount of space used in landfills. Accordingly, it would be desirable to provide a method for separating the brake shoe from the friction material in a manner that would not degrade the structural integrity of the friction material and would permit the reuse of the brake shoe with a minimum of waste disposal issues.
Summary of the Invention
To address the above problems, a method in accordance with the present invention is provided for processing a brake-shoe assembly to separate a brake shoe from a friction material adhesively mounted to the brake shoe so that the brake shoe may be reused. The method comprises the steps of cooling at least a portion of the brake-shoe assembly to a selected temperature, such as a temperature less than
-112° C or, alternatively, less than cryogenic temperature, and maintaining the cooled portion of the assembly at the selected temperature for a time period, such as at least 5 seconds or up to three hours, sufficient to promote separation of the brake shoe
from the friction material. Longer time periods can be used for the enhancement of the cryogenic effects on the steel, but separation benefits are not appreciably improved. The term cryogenic temperature as used herein means any temperature less than -150° C. The time period, the selected temperature, and the rate of cooling may be chosen to cause substantial separation of the brake shoe from the friction material. In addition to the cooling, a separating force may also be applied to the brake-shoe assembly to effect separation of the brake shoe from the friction material in the case that the cooling alone does not cause sufficient separation of the brake shoe from the friction material. The separating force may be applied either simultaneously or subsequently to the cooling step. Brief Description of the Drawings
The foregoing summary and the following detailed description of the preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which: Figure 1 illustrates a brake assembly comprising a brake shoe and friction
material bonded thereto;
Figure 2 illustrates a brake shoe suited for use in a drum brake and having a brake lining mounted thereto; and
Figure 3 is a flowchart illustrating a method of the present invention.
Detailed Description of the Invention
In accordance with the present invention, a method is provided for separating a brake shoe 12 from a friction material 14 adhesively mounted to the brake shoe 12 so that the brake shoe 12 may be reused. In addition, the method of the present invention may strengthen the brake shoe 12, rendering the reclaimed brake shoe 12 potentially stronger than a new brake shoe of the same type.
As used herein, the term brake shoe refers to a backing plate for supporting a friction material. Typically, brake shoes are formed of a metal, such as steel. The shape and configuration of the brake shoe 12 and the friction material 14 of a particular brake
assembly may be selected in accordance with the type of braking system in which the brake shoe 12 and friction material 14 are to be used. For example, with reference to
Fig. 1, a brake shoe 12 of a brake assembly 10 may be a generally planar piece of metal. The friction material 14 may also be a generally planar structure and have a complementary mating surface for enabling the friction material 14 to be attached or bonded to a planar surface of the brake shoe 12. The friction material 14 may be attached to the brake shoe 12 with an intermediate adhesive layer 16. Such a structure is typically termed a brake pad and is used in disc brakes. Alternatively, the brake shoe and friction material may have some other selected shape and configuration suited for use in a drum brake system, such as depicted in Fig. 2. In a drum brake system 11, the brake shoe 22 may be provided as a curved metal plate having a specified radius of curvature. The friction material 24 may also be provided as a curved plate having the same radius of curvature as the brake shoe 22 and may be adhered to the brake shoe 22 by an intermediate adhesive layer 26.
The friction material 14, 24 typically comprises a material composite capable of withstanding the operating temperatures and dynamic pressures experienced during repeated braking applications. For example, the friction material 14, 24 may comprise asbestos fibers impregnated within a thermosetting resin binder, such as a phenolic resin. The friction material may also comprise fillers, such as rubber, carbon particles, graphite particles, and iron oxide. Alternatively, the friction material 14, 24 may comprise an asbestos-free composite. Such a composite may include components such as sponge iron, sepiolite fibers, acryl fibers, aramid fibers, or other temperature resistant fibers instead of asbestos. Non-asbestos composites may also comprise a thermosetting resin binder, such as a phenolic resin, and suitable fillers. The friction material 14, 24 is typically affixed to the brake shoe 12, 22 using a high temperature adhesive laver 16, 26 which contains phenolic resins.
Referring now to Figure 3, a method in accordance with the present invention for removing a friction material 14, 24 from a brake shoe 12, 22 is illustrated. The method includes a cooling step 110 for cooling at least a portion of the combined brake shoe and friction material, i.e., the brake shoe assembly, to a selected temperature. The temperature selected should be sufficiently below room temperature to aid in separation of the friction material 14, 24 from the brake shoe 12, 22. For example, the selected temperature may be a cryogenic temperature, and in particular may be at or below the
condensation temperature of liquid nitrogen (LN2), -196° C. In addition, the rate of
cooling may be chosen to promote separation of the friction material 14, 24 from the brake shoe 12, 22. For example, it may be desirable to perform the cooling at a relatively high rate of temperature reduction so as to thermally shock the bond between the friction material 14, 24 and the brake shoe 12, 22. Accordingly, the friction material 14, 24 and the brake shoe 12, 22 may contract at different rates due to a difference between the coefficients of thermal expansion for the friction material 14, 24 and the brake shoe 12, 22 or even the bonding or adhesive material 16, 26 therebetween. Such differential contraction may lead to a mechanical separation of the friction material 14, 24 from the brake shoe 12, 22 or may lead to a weakening of the bond between the
friction material 14, 24 and the brake shoe 12, 22.
One convenient method for performing the cooling step 110 comprises contacting at least a portion of the brake shoe assembly with a coolant. For example, it may be sufficient to contact a component of the brake shoe assembly, such as the brake shoe 12, 22, with the coolant, because that component may have a thermal conductivity
sufficient to transmit the cooling effect of the coolant to the adhesive layer 16, 26. The brake shoe 12, 22, being formed of a metal, has a relatively high thermal conductivity, and is therefore suited to transmit the lower temperature from the coolant to the adhesive layer 16, 26. Alternatively, it may be desirable to submerge the assembly within the coolant to a depth sufficient to place the adhesive layer 16, 26 within the coolant. In certain instances, it may even be desirable to submerge the entire brake shoe assembly into the coolant. Submerging the adhesive layer 16, 26 within the coolant may decrease the amount of time required for the adhesive layer 16, 26 to reach the selected temperature, and therefore, may decrease the overall time required to promote separation of the brake shoe 12, 22 from the friction material 14, 24.
One coolant particularly suited for use in the method of the present invention is liquid nitrogen, though other coolants may be used so long as they reduce the temperature of the brake shoe 12, 22, the friction material 14, 24, and/or the adhesive layer 16, 26 sufficiently to aid in separation of the friction material 14, 24 from the brake shoe 12, 22. The volume of coolant brought into contact with the brake shoe assembly should be selected to have sufficient thermal mass to produce the desired decrease in temperature of the brake shoe 12, 22, the friction material 14, 24, and/or the adhesive layer 16, 26. If an insufficient volume of coolant is used, the temperature of the coolant may be raised, resulting in an insufficient degree of cooling to aid in separation of the brake shoe 12, 22 from the friction material 14, 24.
Once the desired portion of the brake shoe assembly is cooled to the selected temperature in step 110, the assembly is held at the selected temperature, at step 120, for a time period sufficient to render the brake shoe 12, 22 susceptible to separation from the friction material 14, 24. In the case where the cooling step 110 has been performed at a sufficiently high rate and the selected temperature is sufficiently low, the brake shoe 12, 22 and friction material 14, 24 may separate shortly after the selected temperature is reached. The time period of cooling will also be dependent on the size of the brake
shoe assembly being cooled. In the event that the brake shoe 12, 22 has not separated from the friction material 14, 24 after maintaining the portion of the brake shoe assembly at the selected
temperature, additional, optional steps may be performed in order to facilitate the separation of the brake shoe 12, 22 from the friction material 14, 24. For example, as shown in Fig. 3, at optional step 130, the assembly may be heated at a rate sufficiently fast so as to thermally shock the assembly and cause separation between the brake shoe 12, 22 and the friction material 14, 24. Should this provide insufficient to separate the brake shoe 12, 22 from the friction material 14, 24, steps 110 through 130 may be repeated as needed. Upon repetition of the steps 110 through 130, various parameters may be altered from those used previously, such as the selected temperature, the rate of cooling, or the time period for which the reduced temperature is maintained.
Alternatively, or additionally, a separating force may be applied to the assembly, at step 140, to separate the brake shoe 12, 22 from the friction material 14, 24. Application of the separating force may be performed while the portion of the assembly is maintained at the selected temperature at step 120. Alternatively, the separation force
may be applied after such step 120.
For example, after step 120, the assembly may be returned to room temperature at step 130, at which time the separation force at step 140 may be applied. The separation force may take any form suited to cause separation of the brake shoe 12, 22 and the friction material 14, 24, while maintaining the integrity of the brake shoe 12, 22.
For example, a mechanical force may be applied to separate the brake shoe 12, 22 from the friction material 14, 24, such as by striking the brake shoe 12, 22 or friction material 14, 24. The mechanical force may be applied as a shearing force. Alternatively, other forces may be applied to effect separation. Such forces may include ultrasonic energy, a magnetic pulse, or any other force which may effect separation. Subjecting the assembly to magnetic pulsing may effect separation by the action of the magnetic field on ferrous materials within the assembly, such as the brake shoe 12, 22. If a particular
force is insufficient to separate the brake shoe 12, 22 from the friction material 14, 24, any of the steps 110 through 140 of Fig. 3 may be repeated at step 150, as necessary until separation is achieved.
While steps 110 through 150 are principally related to separating the brake shoe 12, 22 from the friction material 14, 24, the method of the present invention may also effect optional strengthening of the brake shoe 12, 22 as part of the process shown in Fig. 3. As such, it is possible to perform steps 110 through 140 in a manner so as to both effect separation of the brake shoe 12, 22 from the friction material 14, 24, as well as strengthen the brake shoe 12, 22. In particular, the selected temperature of step 110 may be a cryogenic temperature suited to promote strengthening of the brake shoe 12, 22. In addition, the rate of cooling performed in step 110, the hold time of step 120, and the rate at which the brake shoe 12, 22 is returned to room temperature at step 130 may each be selected to encourage strengthening of the brake shoe 12, 22. " Further, it may be desirable at step 130 to elevate the brake shoe 12, 22 to a temperature higher than room temperature after completion of the maintaining step 120 in order to strengthen the brake shoe 12, 22. Further features of the invention shall be made apparent in the following examples. EXAMPLES
The data provided in Tables 1-5 below show the results of experiments in which friction material was sheared from 514 brake shoes under different cooling conditions. Tables 1 - 4 relate to testing of a 514 brake shoe with 9" friction material mounted thereto, and Table 5 relates to testing of a 514 brake shoe with 7" friction material
mounted thereto. The procedure used in performing the experiments first involved
applying a particular temperature treatment to the bonded friction material and brake
shoe. After the temperature treatment was complete the friction material was sheared
from the brake shoe using a machine configured to perform an axial shear test. The load
required to shear the friction material from the brake shoe was recorded from the
machine's pressure gauge. The surface of the brake shoe to which the friction material
had been bonded was visually inspected to estimate the cohesive failure of the friction
material and the adhesive failure of the bond between the friction material and the brake
shoe. Cohesive failure is the failure of the friction material to hold together when
sheared. Adhesive failure is the failure of the adhesive to maintain its bond to the brake
shoe. Thus, a brake shoe to which no friction material adheres after shearing is deemed
to exhibit 100% adhesive failure and 0% cohesive failure. A brake shoe to which a layer
of friction material remains over the entire surface of the brake shoe is deemed to exhibit
0% adhesive failure and 100% cohesive failure.
Referring now to the data in Table 1, the baseline condition is shown, where the
brake shoe and friction material were not cooled, and the friction material was sheared
from the brake shoe at room temperature. The data show that the average load required
to shear the friction material from the brake shoe was 4733 psi and that on average 50%
adhesive failure resulted, indicating that 50% of the surface of the brake shoe to which
the friction material had been bonded still had a layer of friction material bonded thereto
after shearing.
Figure imgf000012_0001
Table 1 No cooling, sheared at 21° C
The effects of immersing the brake shoe and friction material into liquid nitrogen and returning the brake shoe and friction material to room temperature prior to shearing are presented in Table 2. The brake shoe and friction material were submerged in 7.8 1 of liquid nitrogen for ten seconds. The brake shoe and friction material were removed from the liquid nitrogen and allowed to return to room temperature prior to shearing the friction material from the brake shoe. The data show that the average load required to shear the friction material from the brake shoe was 3200 psi and that on average 77% adhesive failure resulted, indicating that 77% of the surface of the brake shoe to which the friction material had been bonded was free from any friction material after shearing. Thus, cooling to liquid nitrogen temperature and shearing at room temperature required less shearing force and promoted greater adhesive failure than the baseline condition presented in Table 1.
Figure imgf000013_0001
Table 2 Immersed in LN2, Sheared at 21° C
Figure imgf000013_0002
Immersed in LN2, Sheared at Approx. LN2 Temperature
The effects of immersing the brake shoe and friction material into liquid nitrogen and shearing at liquid nitrogen temperature are presented in Table 3. The brake shoe and friction material were submerged in 7.8 1 of liquid nitrogen for ten seconds. The brake shoe and friction material were removed from the liquid nitrogen and sheared within ten seconds after removal from the liquid nitrogen. The data show that the average load required to shear the friction material from the brake shoe was 2533 psi and that on average 90% adhesive failure resulted, indicating that 90% of the surface of the brake shoe to which the friction material had been bonded was free from any friction material after shearing. Thus, cooling to liquid nitrogen temperature and shearing at liquid nitrogen temperature required less shearing force and resulted in improved removal of the friction material from the brake shoe than the conditions presented in Tables 1 and 2.
Figure imgf000014_0001
hnmersed in LN2 Three Times, Sheared at 21° C
The effects of immersing the brake shoe and friction material into liquid nitrogen multiple times and shearing at room temperature are presented in Table 4. The brake shoe and friction material were submerged in 7.8 1 of liquid nitrogen for ten seconds. Upon removal the brake shoe and friction material were allowed to return to ambient room temperature. This process of cooling and returning to room temperature was repeated two more times for a total of three repetitions. The data show that the average load required to shear the friction material from the brake shoe was 133 psi and
that on average 45% adhesive failure resulted, indicating that 45% of the surface of the brake shoe to which the friction material had been bonded was free from any friction material after shearing. Thus, this temperature treatment of the brake shoes necessitated greater shearing force and resulted in poorer removal of the friction material from the brake shoe than the treatments presented in Tables 1 - 3. These trends amorig the data
in Tables 1-4 for 9" friction material are substantially replicated for 7" friction material, as presented by the data in Table 5.
Figure imgf000015_0001
Table 5 The effects of cooling a friction material to -196° C on the strength of the friction material are illustrated by the data of Table 6. Flat strips of U.S.A. 70 friction material were tested. U.S.A. 70 consists of 58 percent asbestos, 3% barytes, 1% hexo,
3% coal, 5% graphite, and 5% friction modifiers. The strips were 0.64 cm thick, 5 cm wide, and 14.6 cm long. After optional cooling of the sample, each sample of friction material was placed on two supports on the ram of a Model P-2100 Press, manufactured by Pasadena Hydraulics Inc., El Monte, CA. These supports spanned a distance of 9.53 cm. A 0.64 cm diameter pin was placed above the midpoint spanned by the friction
material, and the ram was raised to drive the friction material into the pin with sufficient force to break the friction material. The force necessary to break the friction material was recorded. To test the effect of cooling on the friction material strength, the friction material to be tested was submerged in 7.8 1 of liquid nitrogen for ten seconds. The cooled friction material was removed from the liquid nitrogen, placed in the press, and tested within ten seconds after removal from the liquid nitrogen. As seen by the data in
Table 6 the friction material cooled to -196° C required a greater force to break than the untreated, un-cooled materials.
Figure imgf000016_0001
Table 6
These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the
claims.

Claims

ClaimsWhat is claimed is:
1. A method for treating a brake assembly to separate a brake shoe from a friction material adhesively mounted thereto, comprising the steps of: a) cooling at least a portion of the assembly to a selected cryogenic temperature; b) maintaining the portion of the "assembly at the selected cryogenic temperature for a time period sufficient to promote separation of the brake shoe from the friction material; and c) applying a separating force to the assembly to separate the brake shoe from the friction material.
2. The method according to claim 1, wherein the adhesive comprises a phenolic resin.
3. The method according to claim 1 , wherein the step of cooling comprises cooling the brake shoe and the friction material.
4. The method according to claim 1 , wherein the step of cooling comprises cooling the brake shoe to the selected temperature.
5. The method according to claim 1, wherein the step of maintaining the portion of the assembly at the selected temperature comprises maintaining the brake shoe at the selected temperature for a time period sufficient to increase the strength of the brake shoe.
r
6. The method according to claim 1, comprising the step of elevating the temperature of the portion of the assembly above the selected cryogenic temperature, after the maintaining step, at a rate sufficient to increase the strength of the brake shoe.
7. The method according to claim 1, wherein the step of applying a separating force comprises applying at least one of ultrasonic energy, thermal shock, magnetic pulse, or mechanical force.
8. The method according to claim 1, wherein the step of applying a separating force comprises applying a shearing force to shear the brake shoe from the friction material.
9. The method according to claim 1 , wherein the step of cooling comprises the step of contacting the portion of the assembly with a cryogenic coolant.
10. The method according to claim 9, wherein the portion of the assembly includes the brake shoe.
11. The method according to claim 9, wherein the cryogenic coolant comprises a liquefied gas.
12. The method according to claim 11, wherein the liquefied gas comprises liquid nitrogen.
13. The method according to claim 1 , wherein the time period is up to three hours.
14. The method according to claim 1 , wherein the time period-is at least five seconds.
15. The method according to claim 1, wherein the selected temperature is less than -150 degrees Celsius.
16. The method according to claim 1, wherein the step of applying the separating force is performed after the step of maintaining the portion of the assembly at the selected temperature.
17. The method according to claim 1, wherein the step of applying the separating force is performed simultaneously with the step of maintaining the portion of the assembly at the selected temperature.
18. A method for treating a brake assembly to separate a brake shoe from a friction material adhesively mounted thereto, comprising the steps of: a) cooling at least a portion of the assembly to a selected temperature; b) maintaining the portion of the assembly at the selected temperature for a time period sufficient to promote separation of the brake shoe from the friction material; and c) applying a separating force to the assembly to separate the brake shoe from the friction material.
19. The method according to claim 18, wherein the adhesive comprises a phenolic resin.
20. The method according to claim 18, wherein the step of cooling comprises cooling the brake shoe and the friction material.
21. The method according to claim 18, wherein the step of cooling comprises cooling the brake shoe to the selected temperature.
22. The method according to claim 18, wherein the step of maintaining the portion of the assembly at the selected temperature comprises maintaining the brake shoe at the selected temperature for a time period sufficient to increase the strength of the brake shoe.
23. The method according to claim 18 , comprising the step of elevating the temperature of the portion of the assembly above the selected temperature, after the maintaining step, at a rate sufficient to increase the strength of the brake shoe.
24. The method according to claim 18, wherein -the step of applying a separating force comprises applying at least one of ultrasonic energy, thermal shock, magnetic pulse, or mechanical force.
25. The method according to claim 18, wherein the step of applying a separating force comprises applying a shearing force to shear the brake shoe from the friction material.
26. The method according to claim 18, wherein the step of cooling comprises the step of contacting the portion of the assembly with a cryogenic coolant.
27. The method according to claim 26, wherein the portion of the assembly includes the brake shoe.
28. The method according to claim 26, wherein the cryogenic coolant comprises a liquefied gas.
29. The method according to claim 28, wherein the liquefied gas comprises liquid nitrogen.
30. The method according to claim 18, wherein the time period is up to three hours.
31. The method according to claim 18, wherein the time period is at least five seconds.
32. The method according to claim 18, wherein the selected temperature is less than -112 degrees Celsius.
33. The method according to claim 18, wherein the step of applying the separating force is performed after the step of maintaining the portion of the assembly at the selected temperature.
34. The method according to claim 18, wherein the step of applying the separating force is performed simultaneously with the step of maintaining the portion of the assembly at the selected temperature.
35. A method for treating a brake assembly to separate a brake shoe from a friction material adhesively mounted thereto, comprising the steps of cooling at least a portion of the assembly to a selected cryogenic temperature, and maintaining the portion of the assembly at the selected cryogenic temperature for a time period sufficient to promote separation of the brake shoe from the friction material.
36. The method according to claim 35, comprising the step of raising the temperature of the cooled portion of the assembly to a selected release temperature at a rate sufficient to separate the brake shoe from the friction material.
37. The method according to claim 35, wherein the step of cooling comprises cooling the selected portion of the assembly at a rate sufficient to substantially separate the brake shoe from the friction material.
38. The method according to claim 35, wherein the adhesive comprises a phenolic resin.
39. The method according to claim 35, wherein the step of cooling comprises cooling the brake shoe and the friction material.
40. The method according to claim 35, wherein the step of cooling comprises cooling the brake shoe to the selected temperature.
41. The method according to claim 35, wherein the step of maintaining the portion of the assembly at the selected temperature comprises maintaining the brake shoe at the selected temperature for a time period sufficient to increase the strength of the brake shoe.
42. The method according to claim 35, comprising the step of elevating the temperature of the portion of the assembly above the selected temperature after the maintaining step.
43. The method according to claim 42, wherein the step of elevating temperature comprises elevating the temperature at a rate sufficient to increase the strength of the brake shoe.
44. The method according to claim 35, wherein the step of cooling comprises the step of contacting the portion of the assembly with a cryogenic coolant.
45. The method according to claim 44, wherein the portion of the assembly includes the brake shoe.
46. The method according to claim 44, wherein the cryogenic coolant comprises a liquefied gas.
47. The method according to claim 46, wherein the liquefied gas comprises liquid nitrogen.
48. The method according to claim 35 , wherein the time period is up to three hours.
49. The method according to claim 35, wherein the time period is at least five seconds.
50. The method according to claim 35, wherein the selected temperature is less than -150 degrees Celsius.
PCT/US2003/029717 2002-09-19 2003-09-18 Method for recycling a brake assembly WO2004026648A2 (en)

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