TASK 70-22-80-160-801
1 . General.
A.Cleanliness requirements exist to reduce or eliminate contamination events where a mainshaft engine or gearbox bearing ingests hard particles and fails, or where contamination starves an engine bearing or component of oil due to blockage of the supply stream orifice. When properly applied, cleanliness involves masking of debris traps and hard-to-clean areas during repair activities, cleaning the part adequately, and protecting the part, especially after it is cleaned. If hard particles are ingested by bearings, the bearing surfaces may be damaged and fail prematurely. If the particles are large and are present in the oil supply circuit, this can lead to blockage of an orifice, resulting in oil starvation of a bearing, a gear mesh or a component.
B.The primary causes for hard particle contamination in a Service Shop environment are:
(1)Inadequate cleaning processes after repair.
(2)Inadequate masking during grit blast operations or dry grind/blend operations.
(3)Inadequate part protection after cleaning.
(4)No cleaning step after all wet manufacturing/repair processes (machining procedures like turning, milling, etc.).
(5)Rework or repair of part after cleaning or at assembly without recleaning.
(6)Transfer of hard particles from assembly tooling.
(7)Deposition of hard particles through air currents after the part is clean or during assembly activities.
(8)Deposition of hard particles through assembly aids.
(9)Transfer of hard particles from protection or packaging materials.
C.This practice defines the requirements and process steps involved in performing cleanliness inspections to minimize risk of bearing damage and premature failure due to hard particle contamination.
D.Definitions.
(1)Air Curtain - Physical barriers, portable or permanent, or the flow of forced air that creates an air separation between adjoining areas within a shop environment.
(2)Alternate Process Completion - A repetition of the cleanliness inspection without any preceding cleaning operation. It is recommended that this method be chosen when the exceedance of the Table 1 weight requirement after the initial cleanliness inspection is 0.3 mg or less.
(3)Cleanliness - The maximum allowable quantifiable debris as measured gravimetrically (weight limit).
(4)Hard Particle - Abrasive materials such as aluminum oxide, silicon carbide, and other oxides, carbides, and nitrides.
(5)Hard Particle Source (HPS) - Any abrasive operation and any location where abrasive media is either used or stored.
(6)Process Completion - A repetition of the part final cleaning operation to correct conditions that caused the failure of a cleanliness inspection.
2 . Equipment.
Subtask 70-22-80-160-001
A.Recommended cleanliness check equipment:
(1)A device to provide forced impingement of the flushing solution.
(2)Filter holder.
(3)Fritted glass base and rubber stopper.
(4)Holding clamp.
(5)250 ml minimum funnel.
(6)1.85 inch (47 mm) diameter, 3.0 micron absolute membrane filter made of a compatible material with the flushing solution that is being used.
(7)Vacuum flask.
(8)Vacuum pump or aspirator with a pull range that includes 26 inches Hg.
(9)Petri dishes.
(10)Forceps with non-serrated tips.
(11)Balance scale with a ± 0.1 mg tolerance.
(12)A drying oven with a temperature range that includes 130°F (54°C).
(13)Automatic particle counter that is capable of analyzing to AS4059 particle size categories. Hiac/Royco 8011 is one of the commercially available equipments, which meets requirement above. Available from Hach Company. Refer to the List of Suppliers in Step 4 of 70-80-00.
(14)Bench top ultrasonic cleaner machine with generator has frequency 40-80 kHz range.
(15)Soft bristle brushes.
(16)Single use, powder free gloves.
3 . Materials.
Subtask 70-22-80-160-002
 
Consumable Product
No.
 
Solvent, General
C04-002  
 
Isopropyl Alcohol
C04-035  
 
Aqueous Cleaner Solution
No.
Operating Temperature
 
Triton X-100
S1209
Ambient Temperature
 
Extreme Simple Green Aircraft & Precision Cleaner
S1210
Ambient Temperature
4 . Process Guidelines.
Subtask 70-22-80-160-003
A.For parts that have internal cavities, the cleanliness inspection method must be capable of addressing all part surfaces, and must not be affected by air pockets that may be trapped in cavities.
B.Materials used for part protection must be stored and managed in a manner to minimize the risk of contamination of the materials.
C.After cleaning of tubes and hoses, part protection must include the capping of tube openings. Plugs or caps must be sufficiently tight to remain in place during normal handling, but must not distort or damage the tube or fitting.
D.Any fixtures required for performing the cleanliness inspection test must be cleaned prior to each use.
E.If the part has internal passages, reverse flushing must be performed during the cleanliness inspection test.
F.Whenever parts are stored for an extended period of time they must be covered or protected.
G.When handling parts, single use powder free gloves must be worn.
H.If drying a part in an oven, the surface that the part contacts must be either cleaned prior to drying the part, or a clean single use barrier must be put between the part and oven surface.
I.Cleanliness inspection flushing solution must be filtered through a 1.2 microns or finer filter prior to use.
NOTE:
A cost effective method of pre-filtering flushing solution is to install a 1.2 microns or finer inline cartridge filter in the supply hose.
J.It is recommended that the nearest hard particle source be a minimum of 100 feet from where the cleanliness inspection test is going to be performed.
K.It is recommended that the cleanliness inspection area be isolated by walls or air curtains from areas where abrasive operations are performed.
L.It is recommended that air handling systems for the cleanliness inspection area have air filtration to a level of 30 microns or less.
M.It is recommended that table tops or work surfaces be cleaned prior to each use or have a clean single use protective cover applied prior to each use.
N.It is recommended that the soft bristle brushes be cleaned prior to each use.
5 . Procedure.
Subtask 70-22-80-160-004
A.Debris Collection for Analysis by Weight.
(1)Collect debris with one of the following methods:
(a)Weigh a new, clean, and dried 3.0 micron or finer absolute membrane filter (that is compatible with the flushing solution) to the nearest 0.1 mg. Record this value as Wnew. Drying time for a new, clean filter is 10 minutes minimum at 120 to 140°F (49 to 60°C).
(b)Set-up the filter vacuum system and insert the new, clean, and dried membrane filter.
(c)Flush the part thoroughly with the flushing solution to cover all internal and external surfaces of the part, or the zoned areas of the part specified in the repair procedure.
(d)For tubes and hoses, the flushing solution must comprise of either 65-85% of their internal volume, or at least 100 ml. The tube or hose openings must be sealed, and the flushing solution agitated vigorously for at least 30 seconds. For tubes or hoses with less than 100 ml volume, agitation is not required.
(e)Using a clean and soft bristle brush, lightly brush across all accessible debris trap area surfaces (i.e. pockets, threads, grooves, slots, holes, cavities, etc.).
(f)Repeat flushing as noted in Subtask 70-22-80-160-004, paragraph 5.A.(1)(c), to include all brushed surfaces.
(g)Collect all of the flushing solution from Subtask 70-22-80-160-004, paragraph 5.A.(1)(c) and paragraph 5.A.(1)(f), and pass it through the membrane filter using the vacuum system.
(h)Flush the inside surfaces of the collection container with additional clean flushing solution. Perform this flushing with the collection container at an angle above the funnel so that the flushing solution flows from the surfaces of the collection container directly into the funnel. Assure that all of the flushing solution passes through the membrane filter.
NOTE:
If using aqueous solution, do an additional rinse with at least 0.05 gallon (200 ml) of clean deionized water to eliminate wetting agent residue on the filter.
(i)When the collection container flushing is complete, perform a final flush of the sides of the funnel using additional clean flushing solution.
(j)Remove the filter membrane using a forceps as follows:
1For solvent flushing solution, dry the filter in an oven at a temperature of 120 to 140°F (49 to 60°C) for 45 minutes minimum.
2For aqueous flushing solution dry the filter in an oven at a temperature of 180 to 200°F (82 to 93°C) until the part reaches the oven temperature and all traces of surface water are removed.
(2)An alternative test sample collection method may be used for parts which allow complete immersion within an ultrasonic cleaner, excluding bearings and assemblies containing bearings. Collect debris by immersion as follows:
(a)Immerse the cleaned part into a clean ultrasonic bath solution which has been filtered through a 1.2 microns or finer absolute filter. Parts can be suspended in the ultrasonic bath in a beaker or other approved container that holds enough solution to fully submerge the part.
(b)Parts being cleaned must be suspended in the tank so that there is no metal-to-metal contact between the parts and any tank or transducer surface.
(c)A maximum ultrasonic process time must be established and controlled. The minimum process time is 5 minutes. The ultrasonic cleaner must be turned on for a period of 5 minutes minimum. The orientation of the part must be changed a minimum of one time during the cleaning period.
(d)Thoroughly flush all surfaces of the part (external and internal) with additional filtered bath solution into the ultrasonic bath or other appropriate container.
(e)Utilize the entire bath solution in which the part was immersed, including the flushing solution in other container if used, for the test sample.
B.Debris Collection for Analysis by Automatic Particle Counting.
(1)Collect all flushing solution obtained by flushing or immersion with ultrasonic bath in another clean container.
C.Rinsing the Parts which are Processed with Aqueous Solutions.
(1)Rinse the part and hardware with deionized, distilled, or demineralized water by pressurized water jet and immersion at room temperature.
(2)Optional Procedure. Rinse the part and hardware in hot water at 120 to 150°F (49 and 66°C) to help faster drying.
D.Drying the Parts which are Processed with Aqueous Solutions.
(1)Flash dry the part as follows:
(a)Keep the part submerged until it reaches a temperature sufficient to apply flash drying.
NOTE:
The time required will vary with part size, water temperature and tank size. Proper flash drying is indicated by seeing the water on the surface of a part start to "flash" or "whisk" off as the part is being removed from the hot water tank.
(b)Remove the part from the water. The part will flash dry as soon as it is removed from the water. Use repositioning, suction, blotting with a clean, absorbent material, or by blowing off with an oil and water filtered shop air gun to remove excess water.
(2)You can substitute drying the part in an air re-circulating oven for the dwell time in the hot water as follows:
(a)Remove the part from the water. You can remove excess water by repositioning, suction, blotting with a clean lint-free cloth, or blowing the water off with an oil and water filtered shop air gun.
(b)Move the part to the oven and dry at 200°F ±25°F (93°C ±14°C) until the part reaches the oven temperature and all traces of surface water are removed.
E.Analysis of Debris.
(1)Analyze the debris by one of the following two methods:
(a)Analysis of Debris by Weight.
1Weigh the dried filter membrane to the nearest 0.1 mg, and record this value as WP.
2Calculate the debris weight as: Wdebris = Wp - Wnew.
3Determine the conformance of the debris weight to the requirements of Table 1 for the specified class.
 
Cleanliness Class Matrix - Table 1
 
SPM Cleanliness Class
Total Debris Weight (mg)
 
A
1
 
B
2
 
C
3
 
D
4
 
E
5
 
F
7
 
G
8
 
H
See Note
 
NOTE:
The debris weight requirement of Class H will be given in applicable service document.
4If the debris weight does not conform to the requirements of Table 1, the part must be subjected to either Process Completion and a repeated Cleanliness Inspection or Alternate Process Completion.
(b)Analysis of Debris by Automatic Particle Counting Equipment.
1Use automatic particle counting equipment to analyze the debris in the flushing solution provided the flushing and debris collection procedure meets or exceeds the requirements of Subtask 70-22-80-160-004, paragraph 5.B.
2Agitate the solution in order to suspend the particles in the solution. Immediately drain the 100 ml solution sample into a clean sample bottle for use in the automatic particle counting equipment.
3Determine the conformance of the debris particle count to the requirements of Table 2 for the specified class.
 
Alternate Hardware Cleanliness - Table 2
 
SPM Cleanliness Class
Maximum Number of Particles, by Size, per 100 ml of Flushing Solution
 
0 to < 0.001 in. (0 to < 0.025 mm)
0.001 to < 0.002 in. (0.025 to < 0.05 mm)
0.002 to 0.004 in. (0.05 to 0.1 mm)
> 0.004 in. (0.1 mm)
 
A
Counting not required
612
106
0
 
B
1,220
212
0
 
C
2,450
424
0
 
D
4,900
848
0
 
E
9,800
1,700
0
 
F
19,600
3,390
0
 
G
39,200
6,780
0
 
H
Not Applicable
Not Applicable
Not Applicable
Not Applicable
4If the debris particle count does not conform to the requirements of Table 2, the part must be subjected to either Process Completion and a repeated Cleanliness Inspection or Alternate Process Completion.
F.For parts requiring preservation, coat parts with preservation oil specified by the service document. The preservation oil must be filtered through a 10-25 micron filter prior to use.
G.Immediately after the cleanliness inspection, and part preservation if necessary, parts or assemblies must be suitably packaged to prevent corrosion or contamination.
H.After bagging, mark or label the bag as “CLEANLINESS CRITICAL PART. DO NOT OPEN UNTIL READY TO INSTALL.”
6 . Quality Assurance Checks.
Subtask 70-22-80-160-005
A.Insure that flushing solutions and preservation oils have been filtered prior to use.