Table of Contents
22.4.3 Cleaning/washing fluids
At aeroengines cleaning/washing fluids are applied for different purposes. Are those
approved from the OEM for the particular use and is the application sufficient,
specified problems can be prevented with acceptable safety. Of especial importance is the washing of the compressor, it is discussed in
Cleaning agents and similar media are also locally very limited used, especially for external application. They serve for:
- rust removal,
- corrosion protection and
- removal of coke and soot.
Also the contact with media, which are not directly planned for the use at the aeroengine, is possible. Such media are used for the air fuselage/airframe. Concerned are:
- cleaning agents,
- solvents and
- paint removers.
The approval of new media takes place according to the specifications of the responsible authority and the OEM. It applies as well to the deterioration of materials (Fig. "Washing and cleaning media") and functions of the part/component as also to health risks and environment aspects.
Fig. "Washing and cleaning media": This summary schall sensitise the practitioner. It shows possible problems of the
application of cleaning agents.
„A“ Contamination of cabin air (Ill. 19.2-9 and Fig. "Survey of cockpit crew"): Concerned are media which are transported by the vent air. Odour nuisance and naturally annoyance of the feeling of the crew and the passengers must be avoided.
„B” Corrosion at components of aeroengines can be triggered directly by an unsuitable medium. But the medium can also with the deterioration of protecting coatings (e.g., paints/lacquers) or the removal of a protecting oil film stimulate corrosion indirectly.
„C, D“ Deterioration or temporary change of the properties of plastics. Especially in the region of the fan, in modern aeroengines most different plastics like resins and elastomeres are used. For example in rub/rub in coatings and sound absorbers. To the lasting deteriorations count drop in strength, embrittlement, crack formation and delamination. A temporary change is swelling. It causes dimensional changes. drop in strength and separation. This is especially true for elastomeres as rub in coatings for blade tips and labyrinths (Fig. "Operation behaviour of elastomers by swelling").
„E” Disturbance of the function of aeroengine components: Safety relevant functions are based for example on sliding/anti friction coatings. Are the properties of these disturbed or the coatings solubilized and leached, this can lead as far as the failure of an aeroengine. To this, two examples:
The anti friction layer/coating on blade roots in the region of the fan and compressor shall not only prevent wear/fretting. The load/stress at the contact surface of the blade root is increased, especially for titanium alloys of fan blades, with the rise of the friction. Simultaneously fretting reduces the fatigue strength dangerously (volume 2, Ill. 6.1-8 and Bild 6.1-15.1).
It is potential dangerous, if a lubricant is used at joints/hinges with spherical bearings (hardened steels) of actuating systems, like they are applied at variable compressor guide vanes (Fig. "Environmental influences of lubricants") and thrust reverser actuation systems (Fig. "Beware unsuitable lubricants") which can be washed out or changed. The result can be corrosion with stiffness up to blocking/jamming (Fig. "Approved lubrication media"). Occurs wear with markedly increase of the clearence, this can trigger malfunctions (e.g., compressor surge concerned by compressor guide vanes) and/or overload of weakened bearing cross sections (Lit. 22.4-16).
„F“ Abrasive deterioration can be rather expected from dry cleaning media (chapter 19.2.3) like shells (nuts, rice). These are used for the cleaning of compressor blading from tenacious deposits. Endangered are surfaces of plastics, paints/lacquers and light metal alloys. To these belong guide vanes in the booster region, directly behind the fan.
„G, H” Reactions with other auxilary media can change the functionality of the components. So the acting of MoS2 containing lubricants can lead, togather with water based wash media (Ill. 22.4-1), to corrosion and to clamping/jamming of friction bearings from annealed steel.