TASK 70-32-22-250-001
1 . General.
A.This procedure describes the equipment and processes used for eddy current inspection (ECI) of dovetail slot bottoms or similarly-shaped surfaces. Refer to Figure 1.
B.The procedure used for this inspection is similar to the high speed bolt hole inspection (70-32-07). But this procedure requires additional tooling and a complete understanding of the lift-off signals that are continuously displayed during this inspection.
C.The kits that are currently available for slot bottom ECI are given in Step 4. - Subtask 70-32-22-250-003, Equipment Requirements.
D.CF6-80C2 Stage 1 HPT disk with part number 1862M23 was reworked and cannot be inspected by this procedure.
Exceptions to this procedure may be required for specific cases where the procedure or equipment described cannot be used or is not appropriate. Such exceptions should be obtained in writing from GE Aircraft Engines (GEAE).
Figure 1   Typical Inspection Zones - CF6 Slot Bottoms
2 . Applicable Documents.
Subtask 70-32-22-250-001
A.Instruction manuals or other information provided by the equipment manufacturers.
B.Appropriate inspection addendum for the hardware being inspected.
C.FST Procedure 1653, CF6-80C2 Stage 1 HPT Disk Dovetail Slot Bottom ECI.
D.Kit preparation and quality assurance plan, FST Procedure 1925 (applies to the QTC only).
3 . Personnel Requirements.
Subtask 70-32-22-250-002
A.Personnel performing this inspection must be certified in accordance with one of the following:
(1)National Aerospace Standard 410 (NAS 410), which replaces MIL-STD 410
(2)American Society of Nondestructive Testing specification ASNT-TC-1A (ASNT-TC-1A)
(3)Air Transport Association Specification 105 (ATA-105)
(4)Comite Sectoriel Aeronautique Cofrend (COSAC).
(5)A locally approved certification program.
B.Personnel performing this inspection shall receive practical training in the use of this procedure and must demonstrate proficiency in the calibration of the inspection equipment, inspection of the hardware, and evaluation of indications before the authority to accept and reject hardware is delegated.
(1)Personnel who have been trained to do the high speed eddy current bolt hole inspection (70-32-07) must also be trained per this procedure.
(2)Personnel who have been trained to do the CF6-80C2 Stage 1 HPT disk dovetail slot bottom ECI (SB 72-A1026) do not require more training. Training or review is available if desired.
C.Training does not imply that personnel who receive training have met the requirements of inspector certification specified in Step 3.A.
4 . Equipment Requirements.
Subtask 70-32-22-250-003
A.The following equipment is required for this inspection.
NOTE:
Items 4.B. thru 4.D. and item 4.G are not provided by GEAE.
B.Instruments listed in Table 1 are approved for use with this procedure.
 
Kits - Table 1
 
Hardware
Part Number
Slot Bottom ECI Kit
 
CF6-80C2 Stage 1 HPT Disk
1531M84
9392M23
GE-FQAP-448*
 
CF6-6 Stage 1 HPT Disk
9137M40
9687M39
GE-FQAP-478
 
CF6-50 Stage 1 HPT Disk
CF6-50 Stage 1 HPT Disk
CF6-80A Stage 1 HPT Disk
CF6-80C2 Stage 1 HPT Disk
1473M65
9283M55
9362M58
1531M84
9392M23
GE-FQAP-480 or
GE-FQAP-448 plus 448S
 
CF6-6 Stage 2 HPT Disk
9084M52
GE-FQAP-482
 
CF6-50 Stage 2 HPT Disk




CF6-80A Stage 2 HPT Disk**
CF6-80C2 Stage 2 HPT Disk**
9045M35
9264M58
1713M86
1474M49
1814M73
9362M43
9362M43
GE-FQAP-484
 
NOTE:
*Due to slight differences in slot bottom size and tolerances, the fixture contained in GE-FQAP-448 will not always fit CF6-50 or CF6-80A HPT Stage 1 disks. To ensure the ability to inspect CF6-50, CF6-80A, or CF6-80C2 Stage 1 HPT disks, Kit GE-FQAP-480 should be used. As an alternative, Kit GE-FQAP-448 can be used as long as it is used along with GE-FQAP-448S, which is a supplemental kit containing the additional guide fixtures that are included in the GE-FQAP-480 kit.
 
NOTE:
**Same part number used on both CF6-80A and CF6-80C2.
C.Probe rotators approved for use with this inspection are listed in Table 2.
D.Probe rotator cables and adapters are listed in Table 2.
 
Eddy Current Instrument Compatibility Chart - Table 2
 
Instrument
Mfr
Rotor
Adapter
Cable
Guide Fixture
 
Elotest B1
Rohmann
HF or STD
ARM-1*
RK-2N
GE-FQAP-302
 
Elotest B2
Rohmann
HF or STD
ARM-1*
RK-2N
GE-FQAP-302
 
Elotest B1V3
Rohmann
HF or STD
ARM-1*
RK-2N
GE-FQAP-302
 
Elotest B300 series
Rohmann
HF
ARM-1*
RK-2N
GE-FQAP-302
 
NDT 19/19e/19ell or Nortec 24
Staveley
19/RA**
SPO-5201
9113660
GE-FQAP-302A
 
Nortec 2000 Series
Staveley
19/RA**
SPO-5201
9122084
GE-FQAP-302A
 
NDT 19/19e/19ell or Nortec 24
Staveley
Spitfire 2000
Not Required
9122091
GE-FQAP-302D
 
Nortec 2000 Series
Staveley
Spitfire 2000
Not Required
9122090
GE-FQAP-302D
 
Phasec 1.1
Hocking
33A022
Not Required
33A023
GE-FQAP-302B
 
Phasec 2s
Hocking
Hocking Mini Rotor PN:33A100
Not Required
33A103
GE-FQAP-302F
 
Phasec 2200
Hocking
33A106
Not Required
33A103
GE-FQAP-302B
 
Deflectoscope SD 2.832 AF 2.833
Forster
HRo 1500
Not Required
Fixed
GE-FQAP-302C
 
Deflectoscope SD 2.832 AF 2.833
Forster
HRo 860T
Not Required
140-639-6
GE-FQAP-302C
 
NOTE:
*R B1 M1 - Approved alternative adapter (GK Engineering).
 
NOTE:
**The Staveley R/A scanner handle might contact the shaft on the Stage 1 HPT disk when positioned for inspection. If this happens, loosen the clamp holding the R/A Scanner in place, and rotate the scanner as far as possible to one side of the guide fixture, then retighten the clamp. This should give adequate clearance between the R/A scanner handle and the shaft, and still keep the eddy current signals in the correct location on the instrument CRT.
E.Guide Fixture and Probe Adapter Kits. One of the following will be required to perform this inspection: GE-FQAP-302, 302A, 302B, or 302C. It is expected that guide fixture kits previously supplied by GEAE will be used for this inspection.
F.Mineral Oil: A small amount of mineral oil or other lubricant may be used to reduce friction for smoother probe rotation, reduced probe and standard wear, and reduce noise. It is important that the lubricant be a relatively inert material to avoid chemical reactions that may affect probe performance or reduce its useful life. The use of mineral oil or other lubricants is not required but is left to the discretion of the user.
G.Cleaning Materials: Approved cleaning materials and solvents should be used to assure part cleanliness before inspection.
H.Table 1 identifies the currently available kits.
CAUTION:
DO NOT USE THE PBH PROBES PROVIDED IN THE SLOT BOTTOM KITS TO INSPECT BOLT HOLES. USE ONLY APPROVED PROBES OR YOU COULD GET INACCURATE RESULTS.
I.Eddy current probes PBH that are in the slot bottom kits are not the same as the SPO 5000 probe that is typically used to inspect bolt holes. PBH probes are not approved for inspecting bolt holes. SPO 5000 probes are not approved for inspection of slot bottoms.
J.Table 3 thru Table 8 list the contents of the slot bottom kits:
 
Eddy Current Inspection Kit GE-FQAP-448: CF6-80C2 Stage 1 HPT Disk - Table 3
 
Part Number
Qty
Description
 
PBH-4040
4
Slot Bottom Probe, 2MHz Bridge Differential
 
MOD 101
1
Calibration Standard - Inco 718 0.310 in. dia hole
 
QT-96-327
1
Calibration Standard Holder
 
JO51338
2
Slot Bottom Probe Guide (nominal)
 
7447
10
Scotch Brite Cleaning Pads
 
0121-4
125 ml
Light Mineral Oil
 
03-006
1
Squeeze Bottle - 125 ml
 
2901A319
2
#43 Drill Bit for use with #4-40 Tap
 
2636A41
2
Hand Tap #4-40 plug
 
92196A108
4
#4-40 x 3/8 in. long Socket Head Cap Screws
 
Q404
1
Black Action Marker Size 33
 
1419
1
Platt Case
 
N/A
1
Kit Label
 
N/A
1
Kit Certification Package
 
Eddy Current Inspection Kit GE-FQAP-448-S: CF6-50, CF6-80A, and CF6-80C2 Stage 1 HPT Disks - Table 4
 
Part Number
Qty
Description
 
JO51338-002
1
Slot Bottom Probe Guide (0.002 in. under nominal)
 
JO51338-004
1
Slot Bottom Probe Guide (0.004 in. under nominal)
 
Eddy Current Inspection Kit GE-FQAP-478: CF6-6 Stage 1 HPT Disk - Table 5
 
Part Number
Qty
Description
 
PBH-4042
4
Slot Bottom Probe, 2MHz Bridge Differential
 
MOD 103
1
Calibration Standard - Inco 718 0.610 in. dia hole
 
QT-96-327
1
Calibration Standard Holder
 
JO52485
1
Slot Bottom Probe Guide (nominal)
 
JO52485-002
1
Slot Bottom Probe Guide (0.002 in. under nominal)
 
JO52485-004
1
Slot Bottom Probe Guide (0.004 in. under nominal)
 
7447
10
Scotch Brite Cleaning Pads
 
0121-4
125 ml
Light Mineral Oil
 
03-006
1
Squeeze Bottle - 125 ml
 
Q404
1
Black Action Marker Size 33
 
1419
1
Platt Case
 
N/A
1
Kit Label
 
N/A
1
Kit Certification Package
 
Eddy Current Inspection Kit GE-FQAP-480: CF6-50, CF6-80A, and CF6-80C2 Stage 1 HPT Disk - Table 6
 
Part Number
Qty
Description
 
PBH-4040
4
Slot Bottom Probe, 2MHz Bridge Differential
 
MOD 101
1
Calibration Standard - Inco 718 0.310 in. dia hole
 
QT-96-327
1
Calibration Standard Holder
 
JO51338
1
Slot Bottom Probe Guide (nominal)
 
JO51338-002
1
Slot Bottom Probe Guide (0.002 in. under nominal)
 
JO51338-004
1
Slot Bottom Probe Guide (0.004 in. under nominal)
 
7447
10
Scotch Brite Cleaning Pads
 
0121-4
125 ml
Light Mineral Oil
 
03-006
1
Squeeze Bottle - 125 ml
 
Q404
1
Black Action Marker Size 33
 
1419
1
Platt Case
 
N/A
1
Kit Label
 
N/A
1
Kit Certification Package
 
Eddy Current Inspection Kit GE-FQAP-482: CF6-6 Stage 2 HPT Disk - Table 7
 
Part Number
Qty
Description
 
PBH-4047
4
Slot Bottom Probe, 2MHz Bridge Differential
 
MOD 104
1
Calibration Standard - Inco 718 0.554 in. dia hole
 
QT-96-327
1
Calibration Standard Holder
 
JO52463D
1
Slot Bottom Probe Guide (nominal)
 
JO52463D-002
1
Slot Bottom Probe Guide (0.002 in. under nominal)
 
JO52463D8-004
1
Slot Bottom Probe Guide (0.004 in. under nominal)
 
5490
1
Roll of Teflon Tape
 
7447
10
Scotch Brite Cleaning Pads
 
0121-4
125 ml
Light Mineral Oil
 
03-006
1
Squeeze Bottle - 125 ml
 
Q404
1
Black Action Marker Size 33
 
1419
1
Platt Case
 
N/A
1
Kit Label
 
N/A
1
Kit Certification Package
 
Eddy Current Inspection Kit GE-FQAP-484: CF6-50, CF6-80A, and CF6-80C2 Stage 2 HPT Disk - Table 8
 
Part Number
Qty
Description
 
PBH-4043
4
Slot Bottom Probe, 2MHz Bridge Differential
 
MOD 101
1
Calibration Standard - Inco 718 0.310 in. dia hole
 
QT-96-327
1
Calibration Standard Holder
 
JO52279
1
Slot Bottom Probe Guide (nominal)
 
JO52279-002
1
Slot Bottom Probe Guide (0.002 in. under nominal)
 
JO52279-004
1
Slot Bottom Probe Guide (0.004 in. under nominal)
 
7447
10
Scotch Brite Cleaning Pads
 
0121-4
125 ml
Light Mineral Oil
 
03-006
1
Squeeze Bottle - 125 ml
 
Q404
1
Black Action Marker Size 33
 
1419
1
Platt Case
 
N/A
1
Kit Label
 
N/A
1
Kit Certification Package
5 . Pre-inspection Part Preparation.
Subtask 70-32-22-250-004
A.Clean all the slot bottoms using strips of Scotch Brite. Refer to Figure 2. The parts will have been previously cleaned in preparation for FPI. Using the Scotch Brite to further clean the slot bottoms will reduce eddy current noise and allow the probe to run smoother.
(1)After cleaning with Scotch Brite, clean all slot bottoms using a soft cotton or paper towel and an approved solvent.
B.Locate the serial number on the end of one of the dovetail posts and mark the first slot bottom clockwise (aft looking forward) from that post as slot bottom #1. Refer to Figure 3.
C.Number the slot bottoms clockwise (aft looking forward).
Figure 2   Cleaning Slot Bottoms Using the Edge of a Piece of Scotch Brite
Figure 3   Slot Bottom Marking
6 . Initial Equipment Set-up.
Subtask 70-32-22-250-005
A.Select the appropriate inspection kit for the hardware to be inspected.
CAUTION:
DO NOT WEDGE OR SHIM A LOOSE FITTING PROBE. THE WEDGE OR SHIM COULD WORK LOOSE DURING INSPECTION, RESULTING IN A LOSS OF INSPECTION SENSITIVITY.
B.Insert the eddy current probe into the calibration standard hole to check the probe fit. It is necessary that the probe contacts the surface of the hole but there should be no interference or binding. Significant probe drag may slow or stop the probe rotor. If the probe is too loose or too tight, try another probe from the same kit.
C.If using a probe with a solid ball, as in kit GE-FQAP-482 (no split), apply Teflon tape to the inside surface of the hole in the calibration standard.
(1)Remove the probe from the probe rotator.
(2)Apply a piece of tape to the surface of the hole opposite the EDM notch. Refer to Figure 4. After each piece is put in place, smooth it out using a pen, pencil, or other suitable cylindrical object.
(a)The EDM notch location is at the bottom of the hole, where the hole diameter is engraved. Refer to Figure 4.
(3)Test the fit by inserting the probe into the hole. If a small amount of friction can be felt all the way through the hole, the fit is correct.
(4)If no resistance can be felt, add another piece of tape.
(5)If the probe can support itself in the hole, then the fit is too tight and one piece of tape should be removed.
D.Install the probe rotator into the guide fixture. Refer to Figure 5.
(1)The Staveley R/A scanner handle might contact the shaft on the Stage 1 HPT disk when positioned for inspection. If this happens, loosen the clamp holding the R/A Scanner in place, and rotate the scanner as far as possible to one side of the guide fixture, then retighten the clamp. This should give adequate clearance between the R/A scanner handle and the shaft, and still keep the eddy current signals in the correct location on the instrument CRT.
E.Insert the probe and probe adapter (if necessary) into the probe rotator.
F.Visually check that the probe is positioned correctly within the guide fixture. It should be almost even with the bottom of the guide fixture shoe, but it should not stick out beyond the bottom of the guide fixture shoe. It may be necessary to loosen the clamps, which hold the probe rotator in place, and to reposition the probe rotator. Refer to Figure 5.
G.If the probe cannot be positioned per Step 6.D., it will be necessary to move the probe rotator within the guide fixture. Some guide fixtures have additional sets of threaded holes that are used to attach the clamp that holds the probe rotator in place. Move the clamp to the other holes and try to position the probe as described in Step 6.D.
H.If the probe cannot be correctly positioned, modify the guide fixture by drilling and tapping holes so that the clamp can be attached in such a way to allow for the correct positioning of the probe.
(1)If the correct tap is not available for the screws installed in the guide fixture, it is acceptable to use locally available screws as required.
I.Once the probe is in the correct axial position within the guide fixture, connect the cable from the probe rotator to the eddy current instrument.
Figure 4   Typical Calibration Standard
Figure 5   Probe Rotator, Guide Fixture, and Probe
7 . Equipment Calibration.
Subtask 70-32-22-250-006
A.Adjust the eddy current instrument to the initial settings as specified in Table 9 thru Table 20.
 
Initial Control Settings for Rohmann Elotest B1 - Table 9
 
Function
Setting
 
Frequency
2.0 MHz
 
Gain
72 dB
 
X Axis Gain
0 dB
 
Y Axis Gain
0 dB
 
Preamplifier
Max value possible
 
Bandwidth
HF
 
Phase
0°
 
Dot Position
0/0
 
Filter Type
BP (Band Pass)
 
Filter Frequency
1 kHz
 
Initial Control Settings for Rohmann Elotest B1V3 and B1V4 - Table 10
 
Function
Setting
 
Frequency
2.0 MHz
 
Bandwidth
HF (V3 only)
 
Gain
72/72 dB
 
Preamplifier
Max Value Possible
 
Y-Spread
0
 
X-Spread
0
 
Phase
250°
 
Filter: High Pass
400 Hz
 
Filter: Low Pass
1 kHz
 
Initial Control Settings for Rohmann Elotest B2 - Table 11
 
Function
Setting
 
Sweep: Display (switch)
X-Y
 
Sweep: Fine
N/A
 
Sweep: Coarse
N/A
 
HP Filter: Hz
40
 
HP Filter: Range
X10
 
HP Filter: BP
0
 
HP Filter: Switch
On
 
Sensitivity: Y x2
0
 
Sensitivity: dB
20
 
Phase
4.0
 
Freq: Switch
Display
 
Freq: Fine
Adjust as needed to obtain 2000 kHz
 
Freq: Range
5
 
Filter
HF
 
LPF
1 kHz
 
Driver Circuit
-12
 
Receiver Pre-amp
30 dB
 
Initial Control Settings for Rohmann Elotest B300 Series - Table 12
 
Function
Setting
 
Frequency:
Amplitude:
2.0 MHz
100%
 
Preamplifier:
Main Amplifier:
Spread Y:
Max Value Possible
30dB
0.0dB
 
Phase:
Low Pass:
High Pass:
330°
1KHz
400 Hz
 
Dot Position Y:
Dot Position X:
0.0%
0.0%
 
Rotor Speed:
2500 rpm
 
NOTE:
The Rohmann Elotest B300 series eddy current instrument is only approved for use with the Rohmann HF series rotor.
 
Initial Control Settings for Forster Defectoscope SD 2.832 - Table 13
 
Function
Setting
 
Power (1/0)
1 (On)
 
Filter (TP/HP)
400
 
Sensitivity
50 dB
 
Frequency
200 kHz (use exp button)
 
Phase
184
 
1p
1
 
U1
0
 
Yo (Y position)
50
 
Xo (X position)
0
 
Intense
As needed
 
X/Y (dB spread)
0
 
Store Time
1
 
Display
Impedance Mode (TR)
 
Signal Display
Off (0)
 
X1, X10 Switch
X10
 
I/O Switch On Motor
As Desired
 
Initial Control Settings for Forster Defectoscope SD 2.833 - Table 14
 
Function
Setting
 
Drive
25 Ohms
 
Att.
0 dB
 
Freq.
2 MHz
 
Phase
218
 
Gain
76 dB
 
Y Spread
0 dB
 
X Spread
0 dB
 
HP (filter)
400 Hz
 
LP (filter)
1 kHz
 
Time
0.1 s
 
Initial Control Settings for Hocking 2200 - Table 15
 
Function
Setting
 
Drive
0 dB 2.0 V
 
RPM
3000
 
Display
XY
 
Persist
0.1 S
 
CH 1 Freq.
2 MHz
 
CH 1 Gain
52 dB
 
CH 1 X:Y
0.0 dB
 
Angle
294
 
Low Pass Filter
1500 Hz
 
High Pass Filter
500 Hz
 
IMP Gain
+20 dB
 
X-Pos 1
0
 
Y-Pos 1
0
 
Initial Control Settings for Hocking Phasec 1.1 - Table 16
 
Function
Setting
 
Frequency
2.0 MHz
 
Gain
46 dB
 
Phase
64
 
Store
---
 
Hi-Pass (filter)
400
 
Lo-Pass (filter)
1500
 
I/P
---
 
Horizontal Position
0
 
Vertical Position
0
 
V/H Ratio
1:1
 
Sweep
Off
 
RPM
1500
 
Initial Control Settings for Staveley Nortec 19ell - Table 17
 
Function
Setting
 
Frequency
2000 kHz
 
Gain (horiz and vert)
80.000
 
Position
128 (50%)
 
Angle
00
 
Filter High Pass
400
 
Filter Low Pass
WB
 
SP 02 (probe drive)
Mid
 
SP 04 (persist)
Off
 
SP 05 (auto erase)
Sweep Erase On
 
SP 07 (CRT erase)
1 S
 
SP 19 (HPF pole)
2 Pole
 
SP 22 (scan RPM)
1500
 
Continuous Null
Off
 
Null
As Required
 
F1/F2 (frequency)
Frequency 1
 
C/F (Course/Fine)
Fine
 
Initial Control Settings for Staveley Nortec 19/19e* - Table 18
 
Function
Setting
 
Frequency
2000 kHz
 
Gain (horiz and vert)
75.000
 
Position
128 (50%)
 
Angle
00
 
Filter High Pass
200
 
Filter Low Pass
500
 
SP 02 (probe drive)
Mid
 
SP 04 (persist)
Off
 
SP 05 (auto erase)
Sweep Erase On
 
SP 07 (CRT erase) for XY Display
1 S
 
SP 07 (CRT erase) for Sweep Display
Off
 
Continuous Null
Off
 
Null
As Required
 
F1/F2 (frequency)
Frequency 1
 
C/F (Course/Fine)
Fine
 
NOTE:
NDT 19 must be Serial Number 347 or higher.
 
Initial Control Settings for Staveley Nortec 24 - Table 19
 
Function
Setting
 
Frequency
2 MHz
 
H Gain
80.0
 
V Gain
80.0
 
Angle
355
 
HP Filt
400
 
LP Filt
WB
 
HPF Pole
2 Pole
 
Display
60.000
 
Sweep
Off
 
V Pos
50%
 
H Pos
50%
 
Screen
---
 
Persist
Off
 
Swp Ers
On
 
Disp Ers
1 S
 
Grat
On
 
Sweep
Off
 
Scan RPM
1500
 
Initial Control Settings for Staveley Nortec 2000 Series - Table 20
 
Function
Setting
 
Frequency
2.0 MHz
 
Angle
195°
 
H Gain
68.0 dB
 
V Gain
68.0 dB
 
Probe Drive
Mid
 
HP Filt
400
 
LP Filt
1000
 
Sweep
Off
 
V Pos
50%
 
H Pos
50%
 
Persist
Off
 
Swp Ers
As Required
 
Disp Ers
As Required
 
Graticule
On
 
Scan RPM
1500
B.Apply a very small amount of mineral oil to the tip of the probe.
C.Place the guide fixture on the calibration standard, center it over the calibration hole and translate the probe carefully into the hole.
NOTE:
If using a probe with a solid ball (no split), refer to Step 6.C.
D.With the probe coil positioned well into the hole but away from the EDM notch (as shown in Figure 4), null the instrument.
NOTE:
If using a solid probe, align the eddy current probe coil with the EDM notch and lower the probe into the hole until the coil just disappears (and is above the notch). Null the instrument. This step is necessary to avoid nulling in air.
E.Turn on the probe rotator and slowly translate the probe through the hole until the EDM notch is located and a signal is displayed on the eddy current instrument. Refer to Figure 6.
F.Scan the length of the EDM notch and observe the response on the CRT. There will be two separate indications from the EDM notch. One will be at the top of the notch and one will be at the bottom of the notch.
G.Hold the rotor at the position where the largest notch signal response is obtained.
H.Adjust the instrument phase (rotation) control to orient the notch signal vertical. Refer to Figure 6.
I.Adjust the gain control to produce a notch signal with vertical peak to peak amplitude of 4 major screen divisions.
J.If the instrument gain adjustments are in 1 dB steps, it may not be possible to achieve a notch signal amplitude of exactly 4 major screen divisions. If the exact calibration amplitude cannot be obtained, use the next higher gain setting.
K.Translate the rotor to scan the entire length of the notch to ensure that the calibration was performed at the location of the largest notch signal amplitude.
L.Switch the instrument display to the sweep mode (x/t) and again translate the probe rotator to scan the entire length of the notch and verify that a 4 division peak to peak response is obtained from the EDM notch. All inspections will be performed in the sweep mode.
M.If the notch is displayed at the left or right edges of the instrument display, reposition the guide fixture on the calibration standard by moving it 90°.
N.It is very important to verify that the probe rotator is positioned within the guide fixture so that the slot bottom indications will be seen in the approximate center of the screen of the eddy current instrument. If necessary, adjust the probe rotator position as described in the following steps.
(1)With the probe still rotating, move the rotator and guide fixture assembly away from the calibration standard and carefully insert a small metal object (such as a small screwdriver) between the probe and guide fixture shoe as shown in Figure 7.
(2)The displayed signal should be in the center of the instrument display. If the signal is not in the center of the instrument display, turn off the probe rotator, loosen the clamps holding it in place, and rotate the probe rotator within the guide fixture. Then secure the clamps and repeat Steps 7.N.(1) and (2). until the display signal is in the center of the instrument display.
O.Record the instrument calibration settings on the inspection data sheet in Figure 8 (Form 1653-1).
Figure 6   Instrument Display - Typical Calibration
Figure 7   Adjustment of Probe Rotator within the Guide Fixture
Figure 8   Eddy Current Inspection - Slot Bottoms - Form 1653-1
8 . Hardware Inspection.
Subtask 70-32-22-250-007
A.Install the slot bottom fixture on the forward side of the dovetails as shown in Figure 1. The five holes in the fixture should line up with slot bottoms 1 thru 5. Refer to Figure 9 and Figure 10.
(1)Some slot bottom fixtures (such as part number J052463D in Kit GE-FQAP-482) have been designed for use with probes that have a solid ball (no split).
(2)To be sure of probe contact with the slot bottom all the way through the scan, the holes on the forward side of the fixture are intentionally offset in the radial direction. This creates an intentional misalignment, so that the probe stays against the slot bottom.
B.Place a reference mark on the dovetail post that is between the last slot bottom and the #1 slot bottom. Refer to Figure 10. This mark will be used to help keep track of where the fixture has been placed and what slot bottoms have been inspected.
C.The slot bottom fixture should seat on the forward embossments and the aft side of the fixture should be approximately even with the aft corners of the slot bottoms. Refer to Figure 9.
D.Place the guide fixture and the rotor on the slot bottom fixture as shown in Figure 11. The guide fixture should always be positioned as if it is sitting on the embossments, not on the dovetails.
E.Carefully center the probe over the hole in the fixture, manually rotate the probe so that the coil is facing the slot bottom, and push the rotor down until the probe coil is well into the slot bottom.
F.Null the eddy current instrument.
G.Move the probe out of the hole and turn on the rotor.
H.Inspect the #1 slot bottom by slowly translating the probe into the hole in the slot bottom fixture and all the way down through the slot bottom until it comes out on the aft side of the disk. Scan the slot bottom a second time by slowly translating the probe back up through the slot bottom and out of the hole in the fixture.
(1)As the probe first enters the slot bottom, signals will appear to the left and right sides of the center of the instrument display (refer to Figure 12), and they will change shape as the probe enters the slot bottom, then remain relatively constant until the probe exits the slot bottom. These are lift off signals and are caused by the rotating coil entering and exiting the slot bottom. If there are any defects, the signals will occur between the lift off signals. Refer to Figure 12.
(a)On some hardware, such as the CF6-6 Stage 1 and 2 HPT disks, there could be a total of four signals which are not indications and will be displayed throughout the length of the slot bottom. The outer signals are from the dovetail fir trees, and the inner signals are the lift off signals. If there are any defects, the indications will appear in the center of the screen display, between the lift off signals. Refer to Figure 13.
(2)On average, the peak to peak amplitude of the lift off signals will be 1-4 divisions, but this will be different from one slot to another, and can at times exceed full screen height.
(3)It is important that the position of the guide fixture (shown in Figure 11) be maintained throughout the inspection so that indications will appear between the lift off signals. If the guide fixture were positioned so that it was outside of the holes on the slot bottom fixture, the indications would occur outside of the lift off signals and might not be as easily observed.
(4)The translation speed should be relatively slow - approximately two-tenths of an inch per second (0.2 in/sec) or less. At this speed, the inspection of one slot bottom (which is one inch deep), should take at least five seconds in each direction.
I.As the probe is scanned down and then back up through the slot bottom, watch the instrument display for any indication between the liftoff signals EQUALING or EXCEEDING 3 divisions peak to peak. Refer to Figure 12.
(1)Cracking can occur anywhere within the slot bottom, including at the corners. It is important to watch the instrument display as the probe enters and exits the slot bottom, as well as during the entire scan.
J.If an indication that equals or exceeds 3 major divisions peak to peak is observed, verify that it is repeatable, and then mark an X on the dovetail posts on each side of the slot bottom that was rejected.
K.Record the indication amplitude and slot bottom number on the Inspection Data Sheet on Figure 8 (Form 1653-1).
L.Move to the next slot bottom and repeat the inspection.
M.Continue the inspection until all five slot bottoms covered by the fixture have been inspected.
N.At the completion of the fifth slot bottom, make another mark on the dovetail post just past the last slot bottom that was inspected. Refer to Figure 10.
(1)Two dovetail posts are now marked.
(2)The slot bottoms between these marks have been inspected.
O.Remove the bottom fixture.
P.If rejectable indications were observed, perform an inspection per Step 10. - Subtask 70-32-22-250-009, Indication Evaluation/Reject Criteria.
Q.Place the slot bottom inspection fixture in the next set of slot bottoms to be inspected. The last dovetail post marked should be just outside of the fixture.
R.Inspect the next five slot bottoms. Do not mark the last dovetail until all five slots covered by the slot bottom fixture have been inspected.
S.Repeat this procedure until all slot bottoms have been inspected.
T.Write the inspection results on the Inspection Data Sheet in Figure 8 (Form 1653-1).
Figure 9   Slot Bottom Fixture Seated on Forward Embossments
Figure 10   Dovetail Post Marking During Inspection
Figure 11   Guide Fixture, Probe Rotator, and Probe in Position for Inspection
Figure 12   Typical Screen Displays - Liftoff Signals and Indications
Figure 13   Typical CRT Display for CF6-6 Stage 1 and Stage 2 HPT Disk Dovetail Slot Bottoms
9 . Post Inspection Calibration Check.
Subtask 70-32-22-250-008
A.A calibration check shall be performed upon the completion of each inspection, at least every hour, whenever any system component or the inspector is changed, or any time the inspector suspects a change may have occurred in the inspection system.
B.Return the guide fixture to the calibration standard. Center the fixture over the calibration hole, and move the probe carefully into the hole.
C.With the probe well into the hole and the coil away from the EDM notch, null the instrument.
D.Scan the length of the EDM notch and hold the rotor at the position where the largest notch signal response is obtained.
E.If the notch response obtained is 4 major screen divisions, plus or minus one-half of a major division, the test is acceptable.
F.If the notch response has decreased by more than one-half major screen division, the system must be re-calibrated and any hardware inspected since the last acceptable calibration must be re-inspected.
G.If the notch response has increased by more than one-half major screen division, the system must be re-calibrated prior to the inspection of any additional hardware.
(1)Hardware inspected and determined to be rejectable since the last acceptable calibration should be re-inspected.
(2)Hardware inspected and determined to be acceptable since the last acceptable calibration need not be re-inspected.
10 . Indication Evaluation/Rejection Criteria.
Subtask 70-32-22-250-009
A.Evaluate any slot bottom that had indications that EQUAL or EXCEED 3 major divisions peak to peak.
B.Perform a calibration check as described in Step 9. - Subtask 70-32-22-250-008, Post Inspection Calibration Check.
C.Repeat the inspection of the slot bottom to relocate the indication and confirm that it exceeds the evaluation and rejection threshold requirements.
D.If the indication is confirmed, clean the slot bottom using very fine Scotch Brite or an approved equivalent.
E.Visually inspect the slot bottom under the white light. Clean as required, to remove any remaining dirt or foreign material. Write on the Inspection Data Sheet ( Figure 8) any significant physical conditions such as scratches, nicks, and raised metal that are observed in the slot bottoms or on the forward or aft corners of the slot bottoms.
F.Clean the slot bottom with a clean paper or cotton towel.
G.Repeat the inspection of the slot bottom after cleaning. If the indication amplitude has reduced, repeat the cleaning process as necessary until the indication is removed or the amplitude of the eddy current indication is reduced to an acceptable amplitude.
H.If the indication cannot be reduced in amplitude to less than 3 divisions peak-to-peak, or increases in amplitude as a result of the cleaning process, the hardware shall be considered rejected and unserviceable.
I.Record all inspection information and inspection results on the Inspection Data Sheet in Figure 8 (Form 1653-1).