AIRCRAFT MAINTENANCE MANUAL - Job Instruction Cards
SURFACE FINISH TREATMENT FOR TITANIUM
1. General
This topic details the requirements and procedures for the cleaning and
surface preparation of titanium and its alloys.
Il also specifies the inspections to be carried out on the process and on the
parts produced.
2. Specifications
This topic classifies the procedures to be used according to the condition
of the parts, for the following methods:
- cleaning without chemical etch,
- pickling with nitrohydrofluoric acid,
- sandblasting,
- mechanical cleaning.
3. Materials and Equipment
A. Materials
- Solvents: Acetone/Careclean AS1 (Mat. No. 11-003E (Ref. 20-31-00)),
- Nitric acid 40-42 Bé,
- Sodium dichromate,
- Hydrofluoric acid 70%,
- Oxide conditioner: Turco 4338 (D9808, F3172, 61102 (Ref. 20-31-00)),
- Wetting agent: Activol 1357 or Turco Form Ti-Etch Additive 200 (D8908,
F3172, 61102 (Ref. 20-31-00)),
- Aluminium oxide sand 180 Mesh or finer,
- Aluminium oxide abrasive paper, 180 Mesh or finer or Scotch Brite Type
A, fine, ultrafine,
- Neutral kraft paper,
- Steel wool (plain steel),
- Stainless steel brushes,
- White gloves, cleaning cloths,
- Pumice 350 Mesh.
CAUTION: THE PRODUCTS USED ARE TOXIC, CORROSIVE AND INFLAMMABLE.
THE USE OF CHLORINATED SOLVENTS IN THE LIQUID OR VAPOUR PHASE IS
PROHIBITED.
WHEN USING CHEMICAL SOLUTIONS ARRANGE THE PARTS SO THAT THEY DO
NOT TOUCH ONE ANOTHER AND ARE NOT IN CONTACT WITH DIFFERENT TYPES
OF METAL, TO PREVENT GALVANIC "PITTING".
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B. Equipment
All tanks with process solutions at either ambient temperatures or
different temperatures, and coated as stated in Table 2 must:
- temperature regulators and thermometers,
- mechanical or air stirring such to obtain a solution with a 5°C (41°F)
change between the hottest and the coldest points during the process,
- deionised drinking water,
- suction.
4. Procedure
A. General cleaning without chemical etching – METHOD I
(Ref. Fig. 1)
B. Cleaning, deoxidation and nitrohydrofluoric acid etching – METHOD II
(Ref. Fig. 2)
C. Abrasive deoxidation – METHOD III
(Ref. Fig. 3)
D. Mechanical cleaning – METHOD IV
(Ref. Fig. 4)
NOTE: The methods to be used are defined in the Table 1 on the ground of
surface contamination, next surface treatment to be applied and
relevant alloys of faying surface.
The Figures 1, 2, 3 and 4 show the different methods.
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ITEM METHOD NOTE
Method I
Cleaning prior to heat treatments
Method III
Preparation for painting or Method II
application of conversion coatings Method III
Removal of surface contaminants
Method I
derived from tools made of low
Method III
fusion point alloys
Preparation of parts before
Methods II, III, IV
welding
Preparation of parts before liquid Method II Smeared surfaces are:
penetrant inspection Parts which have
1) Parts without heat oxides and undergone a reworking
with non-smeared surfaces process able to hide any
---------------------------------- -------------------------------------------- existing defects:
2) Parts with non-tough tough Method II (e.g. sandblasting,
oxides and/or with "smeared" lapping, fitting using
surfaces shavehook, deep-drawing,
---------------------------------- -------------------------------------------- machining)
3) Parts with tough heat oxides Method III
Removal of tough heat oxides Methods III, IV (1) Apply method IV only when
Method III the others have been
" IV found to be inoperative
Removal of graphite and molybdenum
sulphide based separator films or
CTR 72252 followed by pressure washing (3)
lubricants normally used in
machining process
Cleaning of machined parts to
Spray washing or immersion followed by
remove refrigerant or lubricants (2) (3)
alkaline chemical degreasing
which can be emulsified with water
Apply when a specific
Removal of materials for liquid
treatment is not required
penetrant inspection with or Alkaline degreasing
(e.g. preparation for
without tracer
painting) (5)
Use the relevant
Removal of alpha layer Chemical milling specification provided
for by the customer
Preparation for temporary gluing
Manual degreasing with solvent Glue within 4 hours max.
for moulding operations
(1) Method III is applicable to titanium limiting the flow to only sandblasting and alkaline degreasing,
washing and desiccation
(2) Use different washing tanks if of the immersion type
(3) The alkaline solution must preferably be different from that used in the flow of the surface treatments
to prevent pollution
Method to be used
Table 1
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MANUAL DEGREASING WITH SOLVENT
ALKALINE DEGREASING AND WASHING
IMMERSION OF THE PARTS IN SOLUTION No. 1
(REF. TABLE 2)
FINAL WASHING FOR APPROX. 5 MINUTES
IN COLD WATER AND SUBSEQUENTLY (OPTIONAL)
IN HOT WATER (REF. TABLE 2)
COMPLETE DESSICATION WITH FILTERED HOT AIR:
TEMP 55 TO 70°C (131 TO 158°F)
General Cleaning without
Chemical Etching (METHOD I)
Figure 1
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MANUAL DEGREASING WITH SOLVENT
PROTECT VENTS OR AREAS
WITH CRITICAL TOLERANCES
ALKALINE DEGREASING AND WASHING
PARTS WITHOUT HEAT OXIDES PARTS WITH SLIGHT HEAT
DISCOLORATION
IMMERSE IN THE CONDITIONING
SOLUTION OF OXIDES No. 3
(REF. TABLE 2)
WASHING IN WATER FOR 3 MN
TO 5 MN (REF. TABLE 2)
IMMERSE THE PARTS IN THE NITROHYDROFLUORIC
TANK SOLUTION No. 2 (REF. TABLE 2)
WASHING FOR 3 MN TO 5 MN WITH WATER WITH
THE SPECIFICATIONS STATED (REF. TABLE 2)
IMMERSION IN SOLUTION No. 1 OR No. 4 FOR
30 TO 60 SECONDS TO REMOVE ANY SMUT PRESENT
FINAL WASHING FOR 5 MN MINIMUM IN COLD
WATER AND SUBSEQUENTLY (OPTIONAL) WITH HOT
WATER (REF. TABLE 2)
COMPLETE THE DESSICATION WITH FILTERED HOT
AIR – TEMP 55 TO 70°C (131 TO 158°F)
Cleaning, Deoxidisation and
Nitrohydrofluoric Acid Etching (METHOD II)
Figure 2
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MANUAL DEGREASING WITH SOLVENT
SANDBLAST THE PARTS USING ALUMINIUM OXIDE (USED ONLY FOR
TITANIUM) 180 MESH OR FINER WITH WORK PRESSURE NO HIGHER
THAN 30 PSI – SEE NOTES 1, 2 AND 3
WASH THE PARTS FOR 3 MN TO 5 MN WITH COLD WATER
(REF. TABLE 2) REMOVING TRACES OF RESIDUAL ABRASIVE
ALKALINE DEGREASING
IMMERSION OF THE PARTS IN SOLUTION No. 2
(REF. TABLE 2) FOR THE TIME PROVIDED
WASHING FOR 3 MN TO 5 MN WITH WATER (REF. TABLE 2)
IMMERSION IN SOLUTION No. 1 OR No. 4 FOR
30 TO 60 SECONDS TO REMOVE ANY SMUT PRESENT
FINAL WASHING FOR 5 MN MINIMUM IN COLD WATER AND
SUBSEQUENTLY (OPTIONAL) WITH HOT WATER (REF. TABLE 2)
COMPLETE THE DESSICATION WITH FILTERED HOT AIR
TEMP. 55 TO 70°C (131 TO 158°F)
NOTE: 1. When sandblasting titanium, do not use sand which has also been used for
other materials.
2. Sandblasting titanium may cause sparks and parts overheating.
Move the jet at constant speed.
3. Sandblasting fine thicknesses may cause distorted parts and reduced
dimensions.
Work at the specified pressure or even at a lower pressure.
Protect vents and surfaces with close tolerances.
Abrasive Deoxidisation (METHOD III)
Figure 3
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MANUAL DEGREASING OF THE AREA TO DEOXIDISE
WITH SOLVENT
DEOXIDISE THE PARTS BY MANUAL OR MECHANICAL
BRUSHING USING THE BRUSHES OR VIA LOCALISED
DEGREASING OR BY RUBBING THE AREA WITH
350 MESH PUMICE WHICH IS DRY OR DAMPENED
WITH WATER CONTAINING LESS THAN 6 PPM
CHLORINE
IF APPLICABLE, DRY THE AREA WITH A JET OF
DRY AIR.
RUB THE AREA WITH CLEAN CLOTHS SOAKED IN
CARECLEAN AS1
Mechanical Cleaning (METHOD IV)
Figure 4
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SOLUTION CHEMICAL COMPONENT TANK QUANTITY CONTROLS WORK PARAMETERS
COATING PER 100 LITRES G/LITRE
No. 1 INHIBITED NITRIC ACID 20 l (5.284 G) 280 to 310 Temp. 57 to 63°C
NITRIC ACID ------------------ AISI 316 ------------------ ----------- (134.6 to 145.4°F)
SODIUM DICHROMATE 2/3 kg 21 to 25 Immersion time 20 mn to
(4.41/6.61 lb) 40 mn
No.2 NITRIC ACID 45 l (11.89 g) 560 to 670
NITROHYDROF- ------------------- ------------------ -----------
LUORIC ACID HYDROFLUORIC ACID 4.0 l (1.06 g) QTY. NECESSARY Room Temp. +35°C
TO MAINTAIN (95°F)
ETCHING SPEED
MAX.100 Immersion time
KOROSEAL
------------------- ------------------ -----------
WETTING AGENT 0.20 l (0.05 g) 35 to 45 a) normally 1 to
or
ACTIVOL 1357 or DYNE/CM 3 minutes
TURCO TI ETCH ------------------ AT ROOM
PVC
ADDITIVE 200 1.5 g (23.15 g) TEMPERATURE b) etching for smeared
------------------- ------------------ ----------- surfaces for
or
IRON - 5 g/l max. inspection with
------------------- ------------------ ----------- dry penetrants.
CARBON-
TITANIUM - 10 g/l max.
BRICK
------------------- ------------------ ----------- When necessary,
ETCHING SPEED nominally remove 0.05 mm
ON Ti6AL4V (0.0002 in.) based on
0.0025 to the etchning speed value
0.035 supplied by the
INCHES/HOUR Laboratory.
No. 3 OXIDE TURCO 4338 MILD 25 kg (55.12 lb) 240 to 299 Temp. 88°C (176°F) to
CONDITIONER ------------------- STEEL OR ------------------ ----------- BOILING
CARBON
BRICK Time 30 mn minimum
No. 4 NITRIC NITRIC ACID AISI 316 48 l (12.68 g) 665 to 735 Temp. 49 to 54°C
ACID SOLUTION (120.2 to 129.2°F)
Time 20 to 40 minutes
WASHING WATERS WATER PVC INTERMEDIATE WASHES
pH 5 to 9 CHLORINE
30 ppm max.
TDS 750 ppm max.
------------------
FINAL COLD AND/OR
HOT WASHES T (55 to
70°C (131 to 158°F)
– pH 5 to 9
CHLORINE 6 ppm max
– TDS 100 ppm max
Solutions
Table 2
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5. Controls
A. Process control
The processed parts, as visually inspected, must be free from oil, grease,
fingerprints, foreign metal contamination, and oxides.
Cetermine the H2 content, which shall not exceed 20 ppm with a Ti6A14V test
piece (annealed and cleaned with a method other than sandblasting) immersed
for the appropriate time to remove 0.001 inches/surface.
The hydrogen content must be determined using ASTM E 146 or an equivalent
method.
Determine, when in use and as necessary, the etching speed of the solution
using test pieces of annealed TI6A14V of dimensions 2.5" to 3" per surface
and thickness 0.015 to 0.050", with an immersion time of 15 ± 0.5 minutes.
Etching speed, inches/surface/hour
based on a time of 15 minutes = 2 x weight loss x original thickness
initial weight
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