Repair method for uniformly heating composite structure

• US 6,270,603 B1
• Filed: 06/06/1995
• Issued: 08/07/2001
• Est. Priority Date: 04/09/1991
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Westerman, Everett A., Roll, Phillip E.
• Primary Examiner(s): Aftergut, Jeff H.
• Assistant Examiner(s): Piazza, Gladys
• Application Number:
  US08/468,595
• Time in Patent Office: 2,254 Days
• Field of Search: 156/94, 156/98, 156/323, 425/11, 425/14, 294/020.9, 294/021.1, 244/133
• US Class Current: 156/94
• CPC Class Codes: B29C 2035/0211 resistance heating B29C2035/0811 takes precedence
• CPC Class Codes: B29C 35/02 Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mouldcold vulcanisation B29C35/18 ; vulcanising tyres, presses therefor B29D30/0601
• CPC Class Codes: B29C 65/02 by heating, with or without pressure
• CPC Class Codes: B29C 65/18 using heated tools
• CPC Class Codes: B29C 65/30 Electrical means B29C65/38 takes precedence
• CPC Class Codes: B29C 66/001 Joining in special atmospheres
• CPC Class Codes: B29C 66/002 Removing toxic gases
• CPC Class Codes: B29C 66/1122 Single lap to lap joints, i.e. overlap joints B29C66/45, B29C66/472, B29C66/52272 take precedence
• CPC Class Codes: B29C 66/133 Fin-type joints, the parts to be joined being flexible the parts to be joined being rigid B29C66/1312
• CPC Class Codes: B29C 66/433 Casing-in, i.e. enclosing an element between two sheets by an outlined seam for bookbinding B42C11/06; for packaging B65B; by laminating B32B37/00; enclosing tubular articles between substantially flat elements B29C66/53261
• CPC Class Codes: B29C 66/4332 by folding a sheet over
• CPC Class Codes: B29C 66/45 Joining of substantially the whole surface of the articles methods or apparatus for laminating B32B37/00
• CPC Class Codes: B29C 66/71 characterised by the composition of the plastics material of the parts to be joined welding bar compositions B29C65/125
• CPC Class Codes: B29C 66/721 Fibre-reinforced materials B29C66/729 takes precedence
• CPC Class Codes: B29C 66/7392 characterised by the material of at least one of the parts being a thermoplastic
• CPC Class Codes: B29C 66/7394 characterised by the material of at least one of the parts being a thermoset
• CPC Class Codes: B29C 66/81241 being porous or sintered
• CPC Class Codes: B29C 66/81261 Thermal properties, e.g. thermal conductivity, thermal expansion coefficient
• CPC Class Codes: B29C 66/81455 being a fluid inflatable bag or bladder, a diaphragm or a vacuum bag for applying isostatic pressure inflatable element positioned between the joining tool and a backing-up part B29C66/82421
• CPC Class Codes: B29C 66/81459 being a filled deformable bladder, e.g. bladder filled with oil, with granules or with a meltable solid material B29C66/81455 takes precedence
• CPC Class Codes: B29C 66/82661 : by means of vacuum
• CPC Class Codes: B29C 66/91221 : of the parts to be joined
• CPC Class Codes: B29C 66/91411 : of the parts to be joined, e.g. the joining process taking the temperature of the parts to be joined into account
• CPC Class Codes: B29C 66/91443 : following a temperature-time profile B29C65/38 takes precedence
• CPC Class Codes: B29C 66/91445 : by steps
• CPC Class Codes: B29C 66/91651 : by controlling or regulating the heat generated by Joule heating or induction heating
• CPC Class Codes: B29C 66/919 : characterised by specific temperature, heat or thermal flux values or ranges specific electrical resistance values B29C66/81262
• CPC Class Codes: B29C 66/91921 : in explicit relation to another temperature, e.g. to the softening temperature or softening point, to the thermal degradation temperature or to the ambient temperature
• CPC Class Codes: B29C 66/91951 : in explicit relation to time, e.g. temperature-time diagrams
• CPC Class Codes: B29C 66/92443 : following a pressure-time profile
• CPC Class Codes: B29C 66/92921 : in specific relation to time, e.g. pressure-time diagrams
• CPC Class Codes: B29C 66/961 : involving a feedback loop mechanism, e.g. comparison with a desired value
• CPC Class Codes: B29C 73/12 : Apparatus therefor, e.g. for applying B29C73/30 takes precedence
• CPC Class Codes: B29C 73/32 : using an elastic element, e.g. inflatable bag
• CPC Class Codes: B29C 73/34 : for local heating
• CPC Class Codes: B29K 2063/00 : Use of EP, i.e. epoxy resins or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2071/00 : Use of polyethers , e.g. PEEK, i.e. polyether-etherketone or PEK, i.e. polyetherketone or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2079/085 : Thermoplastic polyimides, e.g. polyesterimides, PEI, i.e. polyetherimides, or polyamideimides; Derivatives thereof
• CPC Class Codes: H05B 3/00 : Ohmic-resistance heating
• CPC Class Codes: H05B 3/28 : heating conductor embedded in insulating material

Abstract

We control the cure temperature within ±15° F. (8° C.) for organic resin matrix composites with a thermal diffusion apparatus which contains a liquid fluid transfer medium to convey heat from an immersed resistance heater to the repair site. Uniform heating of the repair site occurs despite differences in the underlying structure of the repair site, such as the location of underlying spars or other structural features or variations in the skin thickness, because of natural convection within the heat transfer fluid. The fluid transfer medium preferably is a solid, at ambient temperature, but melts at a relatively low, elevated temperature below the cure temperature. We achieve uniform heating that is necessary for suitable repairs to temperatures of at least about 350° F. (177° C.) and simplify monitoring of the repair site temperatures because of the uniform heating we naturally achieve.

Claims

1. A method for obtaining substantially uniform temperatures in the repair of damaged areas in a repair site using a resin composite for field repair of aerospace structure despite the fact that the repair site includes one or more underlying spars or other structural features and despite variations in the thickness of the substrate at the repair site, comprising the steps of:

(a) preparing a repair site including laying up an organic matrix resin, fiber-reinforced patch over the damaged area, the matrix resin having an elevated cure temperature;

(b) covering the repair site, including the patch and underlying spars or structural features, with a thermal diffusion apparatus, the apparatus including a temperature-sensitive, phase change heat transfer medium contained within a flexible bladder capable of conforming to the contour of the repair site and an electrical resistance heater immersed in the heat transfer medium;

(c) powering the heater to increase the temperature of the repair site along a heating profile and changing the phase of the heat transfer medium from solid to liquid to promote convective and conductive heat transfer between the heater and the repair site; and

(d) monitoring the temperature at the repair site and controlling the power supplied to the heater in response to the measured temperature of the repair site, including maintaining the temperature relatively constant at the cure temperature of the matrix resin for a sufficient time to promote the cure.

2. The method of claim 1 wherein the cure temperature is controlled within ±

15°

F. (8°

C.) of a set point.

3. The method of claim 1 wherein the heating profile includes a heating cycle where the temperature of the repair site increases slowly from ambient to the cure temperature at a rate to avoid thermal shock to the repair site.

4. The method of claim 3 wherein the heating profile also includes a cooling cycle following the cure where the temperature of the repair site decreases slowly from the cure temperature to ambient at a rate to avoid thermal shock to the repair site.

5. The method of claim 4 wherein the heating rate and the cooling rate are both about 1-5°

F. (0.5-2.5°

C.)/minute.

6. The method of claim 2 wherein the set point is at least about 350°

F. (177°

C.).

7. The method of claim 1 further comprising the step of sealing the repair site with a vacuum bag that encloses the thermal diffusion apparatus.

8. The method of claim 4 wherein the cure temperature is controlled within ±

15°

F. (8°

C.) of a set point.

9. The method of claim 1 wherein the thermal diffusion apparatus includes thermal insulation on the flexible bladder not in contact with the repair site.

10. A method for obtaining substantially uniform temperatures in the repair of damaged areas in a repair site using a resin composite for field repair of aerospace structure despite the fact that the repair site includes one or more underlying spars or other structural features and despite variations in the thickness of the substrate at the repair site, comprising the steps of:

(a) preparing a repair site including laying up an organic matrix resin, fiber-reinforced patch over the damaged area, the matrix resin having an elevated cure temperature;

(b) covering the repair site, including the patch and underlying spars or structural features, with a thermal diffusion apparatus, the apparatus including a temperature-sensitive, phase change heat transfer medium contained within a flexible bladder capable of conforming to the contour of the repair site and an electrical resistance heater immersed in the heat transfer medium;

(c) powering the heater to increase the temperature of the repair site along a heating profile and changing the phase of the heat transfer medium from solid to liquid to promote convective and conductive heat transfer between the heater and the repair site; and

(d) monitoring the temperature at the repair site and controlling the power supplied to the heater in response to the measured temperature of the repair site, including maintaining the temperature relatively constant at the cure temperature of the matrix resin for a sufficient time to promote the cure

wherein the heat transfer medium is beeswax.

11. The method of claim 10 wherein the cure temperature is controlled within ±

15°

F. (8°

C.) of a set point.

12. The method of claim 10 wherein the heating profile includes a heating cycle where the temperature of the repair site increases slowly from ambient to the cure temperature at a rate to avoid thermal shock to the repair site.

13. The method of claim 12 wherein the heating profile also includes a cooling cycle following the cure where the temperature of the repair site decreases slowly from the cure temperature to ambient at a rate to avoid thermal shock to the repair site.

14. The method of claim 13 wherein the heating rate and the cooling rate are both about 1-5°

F. (0.5-2.5°

C.)/minute.

15. The method of claim 11 wherein the set point is at least about 350°

F. (177°

C.).

16. The method of claim 10 further comprising the step of sealing the repair site with a vacuum bag that encloses the thermal diffusion apparatus.

17. The method of claim 16 wherein the cure temperature is controlled within ±

15°

F. (8°

C.) of a set point.

18. The method of claim 10 wherein the thermal diffusion apparatus includes thermal insulation on the flexible bladder not in contact with the repair site.