aluminum cleaning ?

[Tree top pilot 13]

The manual I have states to use PPG 533 cleaning agent that is phosphoric acid based...no mention of water dilution prior to use or rinsing it off. Another option is to use Dow 1205 that is made up from Toluene, Methyl ethyl ketone, and Dipropylene glycol monomethyl ether-a plasticizing agent. I have also read that the Highlander manual states that acetone or MEK as being good to use before the 2 previously mentioned products. These will only have a degreasing action. Is it going to be a problem not removing the oxide layer or keeping it off before bonding the ribs using acetone or MEK?

I did see someone mention that without alodine , you would only get 30%-40% bond strength. So what gives here? Lost in the debates of what to do....and not getting anything built in the process. What did you guys use or do? Abrading the surface with aluminum oxide based products like red scotch bite and emory cloth from 3M seems to be counter productive in getting rid of the oxide layer to be bonded....or is the acid supposed to remedy this problem?

Thanks in advance..sorry to be a PITB...I just want to do this right - the first round

Edited 15 Jan 2012 by Tree top pilot

[Tree top pilot 13]

Copied from the interweb from an aerospace company deposition of structural docs sent to me from a friend in the industry....

Basic principles for long-lasting bonds in critical structures involving composites and aluminum.

The basic principles for long-lasting bonds are well filleted joints and resistant oxides. A large number of pretreatment processes have been developed for aluminium.

Some of the most common (and some of the more unusual) are presented here. Choice is determined by the environment where the aluminium is to be used, likely stresses and costs.

Full details of the processes and any risks to the work environment should, of course, be obtained before starting any form of treatment.

The main purpose of priming prior to the bonding of aluminium is to fill (seal) the surface when high-viscosity and/or fast setting adhesives are to be used.

Priming becomes more important where the aluminium is to be used in a corrosive environment and no surface treatment that improves corrosion resistance (e.g. anodising) is contemplated. Primer also “impregnates†and strengthens porous oxides, e.g. after chromating.

Requirement specification

It is advisable to draw up a requirement specification for the properties of the final bond and the use-related aspects of the adhesive. This helps crystallise the demands really being placed on the adhesive. It also makes it easier to specify exactly what is required to the adhesive manufacturer.

Pretreatment operations in bonding

Process

Result

Use (max.)

Cleanung/ degreasing

Minimum requiement for ensuring a clean and defi ned bonding surface.

For moderately stressd joints in dry surroundings.

Fine grinding/blast cleaning

Removes weak surface layers e/g/ oxides. Safer than degreasing.

Highly stressed joints in dry environments. Unstressed joints in fresh water.

Boiling water for 5 - 10 min. after pickling

Gives resistant, but moderately

strong oxides.

Lightly stressed joints using

flexible adhesives in humid,

corrosive environments.

Phosphating/

chromating

Corrosion resistant, but weak,

porous oxides.

Lightly stressed joints using elastic

or very low-viscosity adhesives in

corrosive environments.

Hydrochloric acid

at 20°C for

30 seconds

Quick, can impart a dark-colouring

to the aluminium surface.

Moderately stressed joints, even

in corrosive surroundings. Relatively

uncommon process.

Etching in

chrome/

sulphuric acid

Thin, strong oxides. Long used

in the American aero-industry.

Highly stressed joints outdoors.

However, cannot withstand strongly

corrosive environments.

Anodising in

sulphuric acid

Thick very resistant oxide.

Lightly stressed joints in corrosive

environments. Best with elastic

adhesives.

Anodising in

chromic acid

chromic acid Medium-thick, strong oxide.

Used in the European aero-industry

since the 40’s.

Highly stressed joints, even in

corrosive environments

Anodising in

phosphoric acid

Porous, very resistant oxide. Is used

together with low-viscosity primer.

Optimum pretreatment for highly

stressed joints in corrosive

environments.

Hope this helps and not offending to anyone...I will be using phosphoric acid method...Like to know all I can about the methods and reasons why......

[dholly 718]

None of my Avid Mk-IV, KF3 and KF4-1200 manuals recommended a phosphoric acid cleaning agent, but there are so many Avid and Kitfox wings built without it, I think that it is safe to say it's not necessary. Of course, you do have to be very careful not to touch the sanded areas or get oily finger residue on any parts to be epoxied. FWIW, here's what I did on mine: (clean with MEK > clean with Acetone > crosshatch sand with #220 grit > blow off dust with compressed air > clean with MEK > clean with Acetone > clean/degrease with Naptha > apply Scotch-Weld Degreaser > Hysol ribs).