WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
79.03 Zinc dust, powders and flakes. 7903.10 - Zinc dust 7903.90 - Other The heading covers : (I) Zinc dust as defined by Subheading Note f (c to this Chapter is obtained by condensation of zinc vapour which is produced either direct y in a zinc ore reduction o eration or by the treatment of zinc-bearing materials by boilin . These products must not e confused with the flue dusts, variously known as " zinc ue dust ', " zinc oxide flue dust " or "zinc baghouse flue dust " which are classified in heading 26.20. % (2) Zinc powders as defined in Note 8 (b) to Section XV and zinc flakes. The provisions of the Explanatory Note to heading 74.06 apply, mutatis rnutandis, to this heading. Zinc dust, powders and flakes are mainly used to coat other metals by metallic cementation (sherardisation), in the manufacture of paints, as chemical reducing agents, etc. The heading also excludes : (a) Zinc dust, powders or flakes,pre ared as colours, paints or the like (e.g., made u with other colouring matter or put up as suspensions, &sPersions or pastes, with a binder or solvent) ( apter 32). & (b) Zinc pellets (heading 79.01).
Zinc and articles thereof Note. 1.- In this Chapter the following expressions have the meanings hereby assigned to them : (a) Bars and rods Rolled, extruded, drawn or forged products, not in coils, which have a uniform solid cross-section along their whole length in the shape of circles, ovals, rectangles (including s uares), equilateral trian les or regular convex polygons (includin " flattened circles " and '' mddified rectan les '' of $ich two opposite sides are convex arcs, k e other two sides being straight, of equal f e n d and parallel). Products with a rectangular (including s m e ) , triangular or poly onal cross-sectlon may have corners rounded along theu whole length. ~ j thickness e of such pro8ucts which have a rectangular (including " modified rectangular ") cross-section exceeds one-tenth of the width. The expression also covers cast or sintered products, of the same forms and dimensions, which have been subsequently worked after production (otherwise than by simple trimming or de-scaling), rovided that they have not thereby assumed the character of articles or products of other fmdings. Rolled, extruded, drawn, forged or formed products, coiled or not, of a uniform cross-section along their whole length, which do not conform to any of the definitions of bars, rods, wire, plates, sheets, strip, foil, tubes or ipes. The expression also covers cast or sintered products, of the same form, whch have been sugsequently worked after production (otherwise than by simple trimming or de-scaling), provided that they have not thereby assumed the character of articles or products of other headings. (c) Wire RoIled, extruded or (d) Plates, sheets, strip and foil Flat-surfaced products (other than the unwrought products of heading ,79,01), coiled or not, of solid rectangular t t h e r than s m e ) cross-sechon with or wthout rounded corners (including " modifie rectan es " w h ~ htwo opposite aides are convex arc, the other two sides being straight, of equal ength and parallel) of a uniform thickness, which are : P 01 - of rectangular (including square) shape with a thickness not exceeding one-tenth of the width, - of a shape other than rectangular or square, of any size, provided that they do not assume the character of articles or products of other headings. Heading 79.05 applies, inter alia, to plates, sheets, strip and foil with patterns (for example, grooves, ribs, chequers, tears, buttons, lozenges) and to such products which have been perforated, corrugated, polished or coated, provided that they do not thereby assume the character of artlcles or products of other headings. (e) Tubes and pipes Hollow products, coiled or not, which have a uniform cross-section with only one enclosed void along their whole length in the shape of circles, ovals, rectangles (including squares), equilateral triangles or regular convex polygons, and which have a uniform wall thickness. Products with a rectangular (including square), equilateral triangular or regular convex polygonal cross-section, which may have corners rounded along their whole length, are also to be considered as tubes and pipes provided the inner and outer cross-sections are concentric and have the same form and onentation. Tubes and ipes of the fore oing cross-sections may be olished, coated, bent, threaded, drilled, waiste ,expanded, cone-s aped or fitted wth flanges, co lars or rings. a P % Subheading Note. 1.- In this Chapter the following expressionshave the meanings hereby assigned to them : (a) Zinc, not alloyed Metal containing by weight at least 97.5 % of zinc. (b) Zinc alloys Metallic substances in which zinc predominates by weight over each of the other elements, provided that the total content by weight of such other elements exceeds 2.5 %. (c) Zinc dust Dust obtained b condensation of zinc vapour, consisting of spherical particles which are finer than zinc pow e n . At least 80 % by weight of the particles ass throu h a sieve with 63 micrometres (microns) mesh. It must contain at least 85 /o by welg t of metalf;IC zinc. d f~ GENERAL This Chapter covers zinc and zinc alloys, and certain articles thereof. Zinc is mainly extracted from the sulphide ore (zinc blende or sphalerite), thou the carbonate and silicate ores (smithsonite, hernimorphite, etc.) are also used (see the Exp anatory Note to heading 26.08). k" In either case, the ore is first concentrated and is then roasted or calcined to produce zinc oxide (in the case of the sulphide and carbonate ores or water-free zinc silicate (in the case of silicate ores). Zinc is extrac.ted fiom these by t h e m reduction or (except in the case of silicate ores) electrolysis. I' (I) Thermal reduction is effected by heating the oxide or silicate with coke in closed retorts. The temperature is sufficient to vayorise the zinc which distils over into condensers where most of the metal is collected as ' spelter ". This impure zinc may be used directly for galvanising, or may be refined by vmous methods. Some impure metal is also deposited in the retort extensions as a very fine powder known as zinc dust or blue powder. A modem modification of the process is based on the continuous reduction of zinc oxide and distillation of zinc in vertical retorts. This process gives very pure metal suitable for making die-casting alloys. (II) Electrolysis. The zinc oxide is dissolved in dilute sulphuric acid. This solution of zinc sulphate is carefully purified to remove cadmium, iron, copper, etc., and is then electrolysed to produce a very pure zinc. Zinc is also obtained by resmelting zinc waste and scrap. Zinc is a bluish-white metal which can be rolled, drawn, stam ed, extruded, etc., at suitable cast. It is resistant to atmosp eric corrosion and is therefore tern eratures, and it can use in building and to form protective coverings for other metals, especially iron and steel galvanising, electro-deposition, sherardising, painting or spraying). % B Zinc is also used in the manufacture of alloys; many of these (e.g., brass), contain a predominance of other metals, but the following are the rincipal zinc alloys which may fall in this Chapter under the provisions of Note 5 to Section : & (1) Zinc-aluminium alloys, usually with added cop er or magnesium used for die-castin , especially for automobile parts (carburettor bo 'es, radiator grilles, dash-boards, etcfj cycle parts (pedals, d a m cases, etc.), radio parts, refrigerator parts, etc. Alloys of thl same metals are use to produce sheets stronger than ordinary zinc, press-tools, and as cathodic protection anodes (sacrificial anodes) for protecting pipelines, condensers, etc., against corrosion. d" !i (2) Zinc-cop er alloys (button metal alloys), for casting, stamping, etc. See Subheading and 1 (b) concerning the distrnction between zinc and mnc alloys. Notes I Pa) The Chapter covers : (A) Spelter and unwrought zinc, and waste and scrap (headings 79.01 and 79.02). (B) Zinc dust, powders and flakes (heading 79.03). (C) Products enerally obtained by rolling, drawing or extruding the unwrought zinc of heading 78.01 @eadi.ngs79.04 and 79.05). (D) Tubes, pipes and fittings and the other articles of the residual heading 79.07 which covers all other zinc articles other than those covered by Note 1 to Section XV or included in Chapter 82 or 83 or those more specifically covered elsewhere in the Nomenclature. Products and articles of zinc may be subjected to various treatments to improve the properties or a pearance of the metal, etc. These treatments are general1 those referred to at the end of the 8eneral Explanatory Note to Chapter 72, and do not affect t e classification of the goods. i' The classification of composite articles is explained in the General Explanatory Note to Section XV.