Finishing (manufacturing technology)
The term plain originates from the field of manufacturing technology . “Finishing” means smoothing the surface of workpieces .
Foundry technology
In the field of foundry technology , coatings are coating materials that are applied to molds and cores in order to smooth the porous molded part surface. Finely ground, refractory to highly refractory materials are used as the base material. The coating layer insulates the substrate and protects against thermal stress from the molten metal.
Textile industry
The size is an impregnation liquid that is applied to textile threads, for example by spraying or dipping, before further processing such as weaving . A sized thread is smoother and more resistant to mechanical stress. Without sizing, a warp thread can easily become brittle due to the constant friction on the weft thread and eventually break.
Natural fibers as well as technical fibers (plastic fibers, carbon fibers , glass fibers ) are coated . Depending on the application, the formulation of the size can vary greatly.
Size for natural fibers
Starch derivative in aqueous solution . Before application, the thread can be moistened to reduce its absorbency so that the size stays on the surface. In the past, sizing was made from wheat flour or glue mixed with water , special chemicals are used in the modern weaving industry . The size is removed with the first wash of a weave. Sizing agents such as PVA , sodium carboxymethyl cellulose (CMC) and PAC are recycled from the liquor after washing in modern textile companies and returned to the production process.
Fiberglass sizing
Glass fibers are drawn from the melt at high speed. The thickness of the fibers is determined by the size of the nozzles and the take-off speed. The hot fibers are cooled by spraying them with water, moistened with size over a dip roller and the individual filaments are then bundled into rovings . The size has several functions: The rovings are bonded by the size binder and thus have sufficient stability against abrasion during transport and against tearing individual fibers or breakage. Since the size usually contains water as a diluent, the rovings must be dried. For this purpose, they are either wound up wet (into so-called cakes ) and then dried, or processed wet and later dried, for example in the production of chopped strands , which are incorporated into thermoplastics for reinforcement .
The type of size binder used depends on the subsequent use of the fibers. There are polymer dispersions of ethylene vinyl acetate , polyester , epoxy resin , polyurethane , as well as natural substances such as starch used. The polymer-based sizing formulations also include other auxiliaries such as antistatic agents , lubricants and adhesion promoters such as silanes . The proportion by weight of size in the dried glass fiber is approx. 0.5%.
In the case of fiberglass-reinforced plastics, the mechanical bond between the plastic matrix and the glass surface is largely brought about by the size, which is therefore the quality-determining factor for the finished composite material . The glass fibers can only absorb mechanical forces from the matrix and give the composite body sufficient strength if there is a sufficient bond. In the case of thermoplastics such. B. polyamide, polyester and epoxy resin sizes are usually used; Polyurethane coatings are common for thermosets .
See also
Individual evidence
- ^ Ulrich Meier-Westhues, Polyurethane / Lacquer, Adhesives and Sealants , Vincentz Network GmbH & Co. KG Verlag Hannover, 2nd edition (2007), ISBN 3-86630-896-5 .