Surface preparation abrasive cleaning

The substrate has to be prepared for cementation. The surface must be clean and free of oxide. Corners and edges are particularly important in diffusion-type coatings sharp edges are usually detrimental. Barrel finishing, ie, tumbling in a barrel with abrasive media, may result in the desired shape. 

Surface preparation is of prime importance, and optimum performance of modern protection coatings can be achieved only if the surface of the steel has been adequately treated. The method of surface preparation depends on the shape and size of the structure or component. Thus it is preferable to blast-clean an openwork steel structure by manual methods, since with this type of structure automatic blast cleaning would lead to excessive impingement of the abrasive on the machine itself. 

Very high standards of surface preparation are necessary, e.g. abrasive blast cleaning to Sa2y, BS7079 Part Al, 1989 for steel components... 

Check surface preparation techniques Use robust metal primer Avoid dissimilar metal contacts upon installation of finished bonded parts Avoid dissimilar metals in abrasion cleaning operation, i.e., steel grit with aluminum... 

Titanium is widely used in aerospace applications that require high strength-to-weight ratios at elevated temperatures. As a result, a number of different prebonding surface preparation processes have been developed for titanium. These generally follow the same sequence as for steel and other major industrial metal substrates degrease, acid-etch or alkaline-clean, rinse and dry, chemical surface treatment, rinse and dry, and finally prime or bond. Mechanical abrasion is generally not recommended for titanium surfaces. 

Alkyd parts are generally very rigid, and the surfaces are hard and stiff. Surface preparation for alkyd parts consists of simple solvent cleaning and mechanical abrasion. Epoxies, urethanes, cyanoacrylates, and thermosetting acrylics are commonly used as structural adhesives. 

The common surface preparation treatment for epoxy resins is to wipe with solvent, mechanical abrasion, and final solvent cleaning. Epoxy parts can be most easily bonded with an epoxy adhesive similar to the material being bonded. Urethanes, cyanoacrylates, and thermosetting acrylics have also been used when certain properties or processing parameters are required. 

For low- to medium-strength bonds, simple mechanical abrasion is a suitable surface preparation if the substrates are cleaned first. This surface preparation has found success in most ABS applications. A silane primer such as Dow Coming A-4094 or General Electric SS-4101 may be used for higher strength.57 For maximum joint strength, a warm chromic acid etch of the ABS substrate is suggested.58... 

Generally only solvent cleaning and abrasion are necessary for surface preparation of polystyrene parts. Methanol and isopropanol are acceptable solvents for solvent cleaning of polystyrene. For maximum bond strength the substrates can be etched with sodium dichromate-sulfuric acid solution at elevated temperature. Table 16.14 shows the results of a study on the durability of joints formed between polystyrene and aluminum with different types of adhesives exposed to different environments. 

One surface preparation method that is unique for composites employs a peel or tear ply.77 Utilization of the peel ply is illustrated in Fig. 16.5. With this technique, a closely woven nylon or polyester cloth is incorporated as the outer layer of the composite during its production layup. This outer ply is then torn or peeled away just before bonding. The tearing or peeling process fractures the resin matrix coating and exposes a clean, fresh, roughened surface for the adhesive. This method is fast and eliminates the need for solvent cleaning and mechanical abrasion. 

Surface preparations must be carefully controlled for reliable production of adhesive-bonded parts. If a chemical surface treatment is required, the process must be monitored for proper sequence, bath temperature, solution concentration, and contaminants. If sand or grit blasting is employed, the abrasive must be changed regularly. An adequate supply of clean wiping cloths for solvent cleaning is also mandatory. Checks should be made to determine if cleaning cloths or solvent containers have become contaminated. 

BS EN ISO 8504-2 2001, BS 7079-D2 2000 Preparation of steel snbsirates before application of paints and related prodncts. Surface preparation methods. Abrasive blast cleaning. 

There are several important steps in this process. Eirstly, the bonding surface should be solvent cleaned to remove all grease and dirt (Degreasing) and then all paint should be removed, taking care not to abrade into the first fibre layer. Paint removal may require a coarser grade of paper than abrasion for surface preparation for bonding (Abrasion treatment), (jrade 150 is approved by some SRMs. Paint strippers are not recommended as they may dissolve the resin in the composite. 

Oily soils must be removed before any other surface preparation is attempted. Otherwise these soils may be spread over the surface. These. soils can also contaminate abrasive cleaning media and tools. Oily soils can be removed faster using liquid cleaners that impinge on... 

Composite abrasive materials, such as Scotch-Brite (3M Company), have proved popular for mechanical surface preparation. These commercial abrasive materials are available in pad and sheet form, and they can conform easily to the shape of a surface. When combined with water flushing, they provide clean, almost oxide-free surfaces. Hand sanding, wire brushing, and other abrasion methods that are highly related to the operator s skill, and patience must be carefully controlled. These processes are a source of inconsistency and should be used only when no other method is possible. 

The cryogenic process uses pelletized carbon dioxide at -73°C as a fluidized abrasive cleaning agent for surface preparation and removal of corrosion and old coatings. Not only does this provide an abrasion mechanism, but certain inorganic salts and organic contaminants can be dissolved with supercritical carbon dioxide. 

Thermoplastics like polymethyl methacrylate (PMMA) or polystyrene should be thoroughly cleaned with a non-solvent such as isopropanol to remove surface contaminants. Abrasion is sometimes necessary to remove all traces of mold release agents. Cyanoacrylates form very strong bonds with many thermoplastics because the monomer swells into the adherend, and when cured, forms an intimate mixture of the plastic and the polycyanoacrylate. Thermosets such as filled phenolics should be treated in the same way as thermoplastics. Rubbers usually require abrasion as well as solvent cleaning to prepare them for bonding. 

---