The process that was used in the molding of an advanced composite outer by-pass duct planned for the F404 engine is discussed. This duct was developed as a potential replacement for the existing titanium duct in order to reduce both the weight and cost of the duct. The composite duct is now going into the manufacturing technology portion of the program. The duct is fabricated using graphite cloth impregnated with the PMR-15 matrix system

Pratt, R. D.

Wilson, A. J.

English

NASA Technical Reports Server

N86-I1290
FABRICATION PROCESS OF A HIGH TEMPERATURE POLYMER MATRIX ENGINE DUCT
R. D. Pratt and A. J. Wilson
General Electric Company
Aircraft Engine Business Group
The purpose of this paper is to discuss the process that was used in the
moldlng of an advanced composite outer by-pass duct planned for the F404 engine.
This duct was developed as a potentlal replacement for the existing titanium duct
in order to reduce both the weight and cost of the duct. The work was performed
under Contract NAS3-21854 and was funded by both NASA and the Navy.
The composite duct is now completing its development phase and is going into
the manufacturing technology portion of the program under Navy ManTech
sponsorship. The duct is fabricated using graphite cloth impregnated with the
PMRI5 matrix system developed by NASA/Lewls.
The General Electrlc Company has applled advanced polymeric composite
materials in a variety of development Jet engine components for the past decade.
Among these components are fan blades, stator vanes, fan frames, fan ductlng,
cowlings, and shrouds. The matrix resins for composite parts with a service
temperature up to 149°C (300°F), are mostly epoxies. For service temperatures
of 149°C (300OF) to 316°C (600°F) several polylmlde type systems have been
explored. PMRI5 polylmlde resin, developed by NASA/Lewls Research Center, emerged
as the matrix system selected by General Electric for the F404 composite outer
duct. PMRI5 offers several advantages over other polylmlde systems that were tried
in earlier projects. They are:
I) Uniform, high quality material, at competitive costs is available from
several prepreg sources
2) Consistent low void processabillty in a variety of configurations has
been demonstrated
3) The system has excellent physical and mechanical properties even after
exposure to severe engine mission cycle envlromnents
4) Adequate thermal stability.
The concept for making the duct was to vacuum bag-autoclave mold a
cylindrical laminate shell of Graphite/PMR15 (Gr/PMR) on the outside of a steel
mandrel mold. The mandrel mold allows for ease of laying-up the Gr/PMR prepreg and
provides an as-molded surface on the airflow side of the finished part. The
laminate would incorporate various changes in thickness and material orientation as
required for strength, stiffness and configuration.
401
https://ntrs.nasa.gov/search.jsp?R=19860001823 2020-03-23T06:22:46+00:00Z
Sometime after molding, the duct shells would be cut into upper and lower half
cylinders, titanium end flanges riveted into place, axial composite side doublers
added, and all other fittings added to complete the duct. The composite portion of
the duct would weigh approximately 13.6 kg (30 pounds) at assembly. The slightly
tapered cylindrical duct is approximately 76 cm (30 inches) in diameter X 102 cm
(40 inches) in length. From a design standpoint, the composite duct is required to
be fully Interchangeable with the titanium duct it replaces. (see Figure i).
Produclbility was perhaps the prime consideration in the selectlon of
graphite fabric impregnated with PMRI5 as the prepreg form of the Gr/PMRmaterial
for fabricating the F404 composite duct. Fabric could be cut into large easily
handled laminae patterns and readily lald-up on the mold tool. (see Figure 2).
T-300 graphite fiber, produced by Union Carbide, woven into a 24 x 23-8
harness satin fabric was selected as the reinforcement for the duct. This
selection was made in part because of the processing experience and a data base GE
gained in designing and fabricating the Gr/PMR core cowling of the Quiet Clean
Short-Haul Experimental Engines (QCSEE) GE built for NASA/Lewls. T-300 and PMRI5
as a composite was shown to have adequate thermal stability as well as the strength
and modulus of elasticity required for weight efficient duct design.
Allowance for thermal growth of the mold steel and the shrinkage of the
Gr/PMR laminate material was provided for in fabricating an oversize (diameter)
mold tool. Annular Gr/PMR test pieces were molded and then measured precisely to
establish the final sizing of the mold. The mold tool was made with an axlal
spindle supported at each end with frames mounted to an all steel cart. This
allowed for a convenient working height, rotating the mold during the lay-up, and
mobility to and from the autoclave. (see Figure 3).
An assembly fixture was designed and built for positioning the end flanges
to the composite duct shell. This fixture allows for match drilling the holes for
rivets used in assembling the titanium end flanges to the duct body. A drill
fixture for the axial split line doublers was also made.
The Gr/PMR materials was received in rolls as uncured prepreg with a colored
po1_vethylene separator film on one side. The PMRI5 contains a certain amount of
free methanol, as received, which gives the material tack and drape in the prepreg
form. In preparing the prepreg laminae for the duct, a second ply of polyethylene
separator film of another color was applied to the exposed side of the material as
it was unrolled for cutting. The Gr/PMR, now having polyethylene on both sides,
could be cut into laminae patterns and handled without losing its tack and drape
from evaporation of the methanol. The different color polyethylene film sides
provided an easy means for retaining identity of the symmetrical laminae patterns
with off-axls orientations. Laminae kits were then prepared for the duct lay-up,
according to the engineering design.
Teflon mold release was _pplled to the mold tool prior to applying the first
ply of laminae. It was necessary to add additional methanol to the mold side of
this first ply after the polyethylene separator film was removed, so that the
material would have sufficient tack to adhere to the mold surfacc during the
preforming operation.
402
The Gr/PMR material, as received, can be debulked to about 406 to 432
microns (16 to 17 mils) prior to molding. Debulking is necessary to eliminate the
potential for wrinkling the material during auto-clave molding.
After the final ply was layed-up a spiral wrap of heat shrinkable Dacron
fabric tape, known as Ceconlte, was then applied and shrunk tightly into place.
The Ceconlte fabric was used over the preform to permit venting of the volatiles
produced when the preform was imidized. The preform was imidlzed in an air
circulating oven according to the following schedule:
o Room temperature to 77°C at i/2°C/min
o Hold 77°C for 60 minutes
o Raise to 135°C at i/2°C/mln
o Remove immediately from the oven to room temperature.
This schedule does not complete the Imldizatlon of the PMRI5 system.
After imldlzatlon to 135°C, the preform was stripped of the Ceconlte and
release fabric and then recovered with porous release fabric and two plies of
knlt-flberglass cloth breather. Four-lnch wide strips of heavy tooling glass cloth
were added parallel to the axis of the tool and overlapped two inches with each
adjacent piece. The assembly was held tightly to the preform with a spiral wrap of
glass cloth tape. A steel sash chain was wrapped into the glass cloth at each end
of the preform to act as a 'header' for the venting of the vacuum bag to be
applied. Kapton H film from DuPont was used as the vacuum bag. The bag was sealed
with a high temperature sealant and checked for leaks by pulling a vacuum. The
assembly was double bagged for insurance against loss in the autoclave with another
ply of Kapton H. It was separated from the inner bag with a ply of style 1581
glass cloth breather and then checked for leaks with vacuum.
The entire assembly was moved into the autoclave and rechecked for leaks in
the vacuum bags using the vacuum system in the autoclave. The assembly was
autoclave molded according to the following schedule:
o
o
apply 13 kPa of vacuum
raise temperature to 204°C at 3.5°C/mln
o hold 204°C for 15 minutes, then apply full vacuum
raise temperature to 238°C at 2/3°C/min then apply 1277 kPa
autoclave pressure and continue 1277 kPa and full vacuum throughout
o raise temperature to 252°C in 30 minutes
o hold 252°C for 30 minutes
o
o
raise temperature to 307°C at l°C/mln
hold 307oc/1277 kPa and full vacuum for 180 minutes
403
release the vacuum and pressure slowly (to prevent buckling) before
lowering temperature
o cycle complete - post cure later
The duct shells were easily removed from the mandrel tool after debagging. After a
thorough visual inspection the duct shells were inspected by ultrasonlc thru
transmission with a 'C' scan readout. The 'C' scan indicates apparent defects as
varying shades of grey on electro sensitive record paper. The grey scale is
proportional to the attenuation of the ultrasonic signal and can be adjusted so as
to show the extent of the laminates void content in the range level chosen. The
design called for a maximum allowable void content of three (3) percent. The 'C'
scan grey scale was adjusted to show a near black readout for this level of voids.
The duct shells used were proven to contain less than three percent voids and no
delaminations. A more thorough ultrasonic survey was also made by measuring the
actual attenuation of the ultrasonic signal at grid locations marked on the ducts.
Precise void content values were calculated and recorded for these locations. (see
Figure 4).
The extensive hardware to be attached to the ducts at engine assembly
required adding embossments to the duct shell in order to have spatial location
identical to that on the titanium ducting to be replaced. These embossments along
wlth areas requiring added stiffness or strength and the axial split llne doublers,
all made of Gr/PMRI5, were then lald up on the duct shells. They were molded and
bonded into position in several vacuum bag-autoclave cycles. These secondary
laminations were not oven imidized separate from the autoclave as were the duct
shells as it was necessary to hold the position of the various laminae for
embossments, stiffeners and doublers with a vacuum bag. The operations used to add
these secondary laminations were:
Mark the position of the buildup areas on the duct shell from precise
mylar overlays
Prepare the surface for bonding using a chlorothene solvent wlpe before
and after a light grlt blast
o Prepare the prepreg kits for the buildups
Apply one ply of Style 120 glass cloth/PMR15 to the area (50% resin
PBW). This material serves as an adhesive
Apply the buildup plies to the duct shell and dampen them with methanol,
If required, to 'tack' them into position
o Apply Teflon release fabric over the laminae
o Apply glass fabric bleader and breather
o Double envelope bag with Kapton film.
The secondary laminations were autoclave molded as follows:
o Apply 13.6 kPa of vacuum
404
o Raise temperature to 71°C at 0.83°C/mln
o Hold 71°C for 60 minutes
o Raise temperature to i16°C at O.42°C/mln
o Apply full vacuum
o Raise temperature to 249°C @ 1.2°C/mln
o Apply 1277 kPa autoclave pressure
o Hold 249°C for 30 minutes
o Raise Temperature to 307°C at 1.2°C/mln
O Hold 307°C wlth full vacuum and 1277 kPa pressure for 180 minutes.
Wlth all the secondary laminations completed, the duct was ready for
machining and assembly to the end flanges. The sequence of events were:
o Trim the duct and the axial doublers to dimension
o Match drill the axial doublers wlth the duct shell for the bolting
o Cut the duct shell into upper and lower halves
o Using the assembly fixture, match drill and rivet the titanium end
flanges to the duct shell
o Complete all other machining of the embossments and mounting areas for
the hardware assembly
o Final ultrasonic inspection
o Seal coat wlth Skybond 703 polylmlde resin
o Assemble and bond inserts
o Post cure
o Install studs
o Pa rc ma rki ng
o, Final inspection
The composite duct subjected to static load testing, exceeded requirements.
The composite duct installed on a factory engine is sill1 In test and performing
well. The manufacturing technology portion of the program is now underway to ready
the composite duct for production.
405
OF POOR QUALITY
GE F404 Composite Duct Program
All BosSes T300 Graphite Fsbrlc/PMR 15 Resin Barrel Ti 6.4 End Flanges
/ Attached to Barrel
and Build-Ups p/ with A286 RivetsT30OIPMR 15
Ti 6-4
Actustor Post
TI 6-4
Nut Channels
Inco 718 Bolts,
A286 Nuts
"1_ Ti 6-4 Studs
• And Fittings
[] Composite 70%
[] Titanium 25%
[] Steel 5%
Figure 1
F404 Composite
Duct Ply
Arrangement
Warp
Ply _A To Axis4
1 36 ° O°
2 51 ° -45 °
3 24 ° 0 °
4 39 ° +45 °
5 54 ° -45 °
6 42 ° +45 °
7 30 ° -45"
8 45 ° + 45 °
9 60 ° 00
10 33 ° -45 °
11 48 ° 0°
4.Partial Plies In Edge All 7
Areas Butt Joined C Full Body
Plies\/
1.5cm
11
Figure 2
J
406
F404 Composite Duct Mold
Figure 3
F404 Duct SIN 80003
Void Content Determined from the Attenuation
of the Thru Transmission Ultrasonics
Degrees am CCW from Aft end
Dist. from TOp_. 40" 100" Ply 120" 153" BOI__ 240" 2/10" Ply 300"
Alt End 0* Build Up 180 °-- Build Up
5cm 1.5% 1.5% 1.5% 1.5% 1.5% 1.S% 1.5% 1.5%
25cm 1.6% 1.5% 1.S% 2.5% 2.0% 1.5% 1.5% 1.5%
46crn 1.5% 1.5% 1.5% 3.0% 2.5% 1.5% 1.5% 1.5%
66cm 1.6% 1.6% 1.5% 2.0% 3.5% 3.5% 2.0% 1.5% 1.5%
86cm 1.5% 1.5% 1.5% 2.0% 5.0% 4.0% 2.0% 1.5% 1.5%
104cm 1.5% 1.5% 1.5% 1.6% 1.5% 1.6% 1.6% 1.5%
Figure 4
407


Fabrication process of a high temperature polymer matrix engine duct

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server