Processing of VESTOSINT® PA 12 powders
THE RIGHT PROCESSING TECHNIQUE FOR EACH APPLICATION
When it comes to producing the thermoplastic matrix of a fiber composite material or applying a metal coating, requirements will differ. This is why a variety of processes are used to apply VESTOSINT® to workpieces.
- Fluidized-bed coating is used primarily for wire products.
- The minicoat process is used primarily for small technical articles.
- Repair work is executed mainly with the flame-spray process.
- The scattering process is particularly suited to fabrication of large-scale fabrics.
- The spray process is used especially for the production of strips.
- Composites with high fiber volumes can be produced with the suspension process.
Fluidized-bed coating has been used in powder coating since 1952. It is the most cost-effective method for plastic-coating preheated, primarily metallic objects. The technology combines the fluidized-bed and dipping processes.
Requiring minimal tooling, the technique achieves layer thicknesses of 250 to 500 micrometers; even layers of one to two millimeters are possible. In this process, heated steel production parts of any shape are dipped for a few seconds in fluidized VESTOSINT® powder. The powder sinters to the surface of the piece and fuses into a smooth surface, thanks to its residual heat.
A fluidized-bed coating pan consists of the powder container and the air receiver, separated by a porous fluidizing bottom. Oil- and dust-free air flows into the air receiver and passes through the fluidizing bottom in the form of fine bubbles. It transforms the sintering powder to a fluidized state, which resembles a boiling liquid. The fluidized-bed coating powder has a particle size distribution ranging from 30 to 250 microns, and is adjusted so as not to produce dust. Depending on the desired coating thickness, the pieces are heated to 230–450°C and dipped for 2–10 seconds.
The process works without solvent. Materials that change their shape, lose their properties or generate gases during the above-described procedure cannot be coated.
Key applications for fluidized-bed coating with VESTOSINT® include the coating of
- Wire products of all kinds (e.g., dishwasher racks and refrigerator shelves) - Industrial components (e.g., springs, rollers, drive shafts, valve handles, handrails)
The principle of minicoating is similar to that of fluidized-bed coating. Hot (small) parts are dropped into a fluidized VESTOSINT® powder pan. (The powder is flooded with air or changed into a liquid-like state through ultrasound.) As the parts fall, the powder sinters to the metallic surface.
The objects are then conveyed out of the VESTOSINT® container in a vibrating trough and the surface is further smoothed, no matter the shape of the articles being coated.
The main fields of application for minicoating include the coating of clips for the undergarment industry, and component coating for the electrical and automotive industries.
Flame spraying, developed at the beginning of the last century, is one of many types of thermal spraying processes. In this process, the combustion of a gas/oxygen mixture generates the thermal energy to melt the powder and warm the surface of the substrate. A carrier gas—normally compressed air—serves as the medium for transporting the melted particles to the substrate surface. The advantages of this process include low investment costs and the option of coating large parts on site, without an oven.
In addition to classical application processes, VESTOSINT® powders may also be processed in the flame-spray process. By this method, the powder is fed into a flame spray gun where it is surrounded and melted by a circular flame. It is then applied to the surface to be coated.
Since the process can be used anywhere, it is particularly favored for repair work, as well as coating pipe bushings, tanks and similar objects.
Different manufacturing processes are used depending on the type of composite required.
Because of the round shape of VESTOSINT® particles, they have outstanding flow properties. This is why they can be applied extremely well in the scattering process and then melted in a downstream oven. The use of calendars ensures intensive impregnation of the filaments or fabric. This process is particularly suitable for fabrics with large surface areas. Two passes through the scattering station allow for double-sided coating.
As with electrostatic powder coating, the powder is sprayed with a spray gun onto strips that have been widened into individual filaments in the coating space. By heating to temperatures above the melting point, a bond is obtained between the reinforcing fiber and the VESTOSINT® powder. This process is particularly suitable for strips.
Another method for manufacturing composites is impregnation with an aqueous VESTOSINT® suspension. In this case, very fine powders can be used, making high fiber volume contents achievable.