■ 10 to 12 g sodium nitrite (accelerator). (The amount of sodium nitrite may need to be adjusted to suit the application; potas- sium nitrite may be used in lieu of sodium nitrite.) For a smaller base quantity of concentrate, use the following measures: ■ 16.5 g powdered zinc ■ 218 ml phosphoric acid (75% to 85% solution) ■ 55 ml distilled water ■ 5 to 6 g sodium nitrite (accelerator). (The amount of sodium nitrite may need to be adjusted to suit the application; potas- sium nitrite may be used in lieu of sodium nitrite.) Procedure. Dissolve the powdered zinc in the phosphoric acid, and then add the distilled water and sodium nitrite. Mix thoroughly and filter through a stainless steel filter screen or paper filter. (Heat and outgassing occur during the acid/zinc mixing and dissolution.) The finished zinc phosphate concentrate then may be mixed in the following phosphating solutions: Solution I (normal): 16 fluid oz concentrate to 6.75 gal of water or 1 fluid oz of concentrate to 54 oz of water Solution II (heavy): 16 fluid oz concentrate to 5 gal of water or 1 fluid oz of concentrate to 40 oz of water Processing temperature is 170 to 180°F (recommended temperature is 175°F). Distilled water will yield the best results, but “soft” tap water is sufficient. Processing time is 3 to 10 minutes. Longer processing times (10 minutes or more) deposit darker-colored and denser coatings and may be necessary for hardened steel parts such as firearm receivers and bolts. The phosphating process is usually self-terminating; chemical action will stop when the part is sufficiently coated. Immediately rinse the phosphated parts in cold running water for 30 seconds. Do not allow the phosphating solution to dry on the phosphated part; otherwise, difficult-to-remove white deposits of zinc salts will form on the parts. The parts then may be dipped into a mild solution of chromic acid and water (1 oz chromic acid to 1 gal of water). Then rinse the parts again in cold running water. Plating Practices and Finishes for Metals 839 Walsh CH13 8/30/05 10:43 PM Page 839 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal Thoroughly dry the parts with compressed or blown hot air. Bake critical parts as outlined herein. Coat the parts with a light oil, an oil-kerosene mix, or WD40 lubri- cant. Then remove or drain excess oil from the parts. The parts now may be assembled or stored for future use. Note: As a safety precaution, hardened and highly stressed parts that have been phosphate treated for 10 minutes or longer should be baked at 300°F for 30 minutes to prevent hydrogen embrittlement. Iron phosphating (reference only). Iron phosphating, also known as coslettizing, uses powdered iron and phosphoric acid in the solution. Accelerator chemicals such as sodium nitrite, potassium nitrate, and potassium nitrite are not normally required for iron phosphating processes. Manganese phosphating (reference only). Manganese phosphating, also called parkerizing, uses powdered iron, manganese phosphate, and phosphoric acid in the solution. Bonderizing. Bonderizing is performed on ferrous metals and alloys in a solution consisting of phosphoric acid, a catalyst, and water. This process is used to impart a rough, tough, frosted surface providing excellent paint adhesion. The phosphated coating is rust resistant. Note: Phosphate coatings are on the general order of 0.0002 in (0.2 mil) thick. All phosphating solutions are used or processed at temperatures of 145 to 200°F. Immediate washing in cold water is recommended after the phosphate coating is applied to prevent white streaks or blemishes from appearing on the surface of the metal or alloy. Phosphate coatings are most applicable for low-, medium-, and high-carbon steels in both the annealed and hardened conditions. Ferrous metal parts that have been highly hardened and some of the higher-alloy steels are more difficult to phosphate coat. On these steels, the phosphate coating will be light gray in color unless the part is immersion-coated for longer periods (10 minutes or longer). Stainless steels and other high-nickel-chromium steels cannot be phosphated. The more iron a ferrous material contains, the thicker and darker will be the phosphate coating. Heavy zinc phosphate coatings are the easiest to apply, with some of the processes requiring only 3 to 5 minutes to complete. Ferrous materials that are case hardened normally cannot be phosphatized. If high-alloy ferrous parts need a 840 Chapter Thirteen Walsh CH13 8/30/05 10:43 PM Page 840 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal heavier or darker coating, they may be processed in phosphating solutions up to double the time normally required, i.e., up to 10 to 15 minutes for the solutions used in the zinc phosphating process detailed in this disclosure. 13.7 Etching Metals The solutions used to etch various metals are often called mordants, and some of the solutions used in the etching processes are as follows. 13.7.1 Etching irons, steels, and zinc plate Nitric acid solution. A popular solution for etching irons, steels, and zinc plates consists of a solution of 2 oz 50% nitric acid mixed into 15 oz water. This is a 1:16 solution. Always pour the acid into the water; never pour water into the acid. Pouring water into acid may cause a mixing reaction that could result in acid splashing from the mixing container. The solution is relatively slow acting unless used with a splash-type etching machine. For hand etching, a stronger solution can be used, but the etching cut becomes rough at the edges of the etching action. Solutions as strong as 1:8 can be used: 1 part concentrated nitric acid to 7 parts water by volume. 13.7.2 Etching copper and copper alloys Ferric chloride is often used to etch copper and its alloys. A 40°Bé solution of ferric chloride used at 75 to 80°F etches copper cleanly and not too rapidly so as to produce a rough etched edge. A 40°Bé solution is made by mixing 20 oz ferric chloride (anhydrous) with water to make a final volume of 1 liter (1000 ml). The specific grav- ity of this solution can be from 1.37 to 1.38. The designation 40°Bé (Baumé) is pronounced “40 degrees ‘bow-may’” and is defined with respect to specific gravity by the following equation: With this equation, you may determine the degrees Baumé if you know what specific gravity you want or have, or you may determine the specific gravity required of the solution if you know the degrees Baumé you wish to produce. Specific gravity °Bé = − 145 145 Plating Practices and Finishes for Metals 841 Walsh CH13 8/30/05 10:43 PM Page 841 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal Note: The reaction of ferric chloride produces a great amount of heat when it is dissolved in water. The water temperature should be between 50 and 75°F prior to mixing the ferric chloride solution. Solutions of ferric chloride as low as 300°Bé are used for fast etching of copper and its alloys, while the 40 to 42°Bé solutions are used for etching intaglio printing plates or photogravure work. These solutions also have been used to etch stainless steels. The ferric chloride bath should be contained in a glass, plastic, or wooden tank because the solution is highly corrosive. Do not dispose of these solutions directly into standard drainage systems. The solutions should be diluted in water and neutralized with a base chemical such as sodium bicarbonate. Do not allow the solutions to come into contact with the skin; rubber gloves should be worn at all times during use of these solutions. Printed circuit boards for electronic applications have been pro- duced using ferric chloride solutions for many years. Using the lower °Bé solutions produces a fast and accurate etching action or cut, and the ferric chloride is economical and long lasting. Perchlorate chemicals are also used for etching printed circuit boards. Frank Short’s etching solution. The Frank Short etching solution has been used by printing plate makers and other metalworkers for years and is a slow-acting but very accurate etchant (mordant). The solution may be made as follows: ■ 88 parts by volume distilled water ■ 2 parts by volume potassium chloride ■ 10 parts by volume hydrochloric acid (concentrated) This is a two-part mixture that must be made by mixing two solu- tions and then pouring the two solutions together. Solution 1. Mix 1 oz potassium chloride into 10 oz water at 190 to 200°F Solution 2. Mix 5 oz hydrochloric acid into 34 oz distilled water Then pour solution 1 into solution 2 in a well-ventilated area. Caution: Chlorine gas is evolved when the two solutions are mixed. Allow the solution to sit for 30 minutes to 1 hour before using. Store in a glass bottle with a rubber or glass stopper. The part to be etched is lowered into a shallow glass pan or tank so that the solution covers the part by approximately 1 ⁄2 in. The 842 Chapter Thirteen Walsh CH13 8/30/05 10:43 PM Page 842 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal etching action may be observed directly because the etching solu- tion is clear and transparent. Copper and its alloys, irons and steels, and chromium-plated parts may be etched with this solution. Use adequate ventilation because chlorine gas in small amounts is evolved during the etching action. This solution is often used to check the etching mask for holes prior to fast etching in ferric chloride solutions. A copper part will begin to show a frosting effect a few seconds after immersion in the solution. Holes in the etching mask then may be seen and repaired prior to the final etching. As a final note, titanium heaters are used in etching baths for ferric chloride solutions. 13.7.3 Etching aluminum and aluminum alloys Most aluminum alloys can be etched using sodium hydroxide solu- tions of varying strengths. Sodium hydroxide is commonly called caustic soda or lye and is a low-cost chemical. Sodium hydroxide is very corrosive or caustic and is poisonous. When aluminums are etched using sodium hydroxide solutions, one of the reaction products is hydrogen gas, which is highly explosive when mixed with normal air. Proper venting must be employed when using this process for etching aluminum alloys. The etching action is relatively rapid, especially if the sodium hydroxide solution is above 1:16 (1 part sodium hydroxide to 15 parts water). Strong solutions produce a violent foaming reaction and substantial amounts of hydrogen gas. Conversion formulas for chemical solutions. Figure 13.18 shows the conversion formulas for solutions having concentrations expressed in various ways. 13.8 Anodizing Anodizing is a process of oxidation produced in an electrolytic bath. Aluminum and its alloys are most commonly anodized, although the anodizing process may be performed on magnesium, zinc, and titanium. This section will cover the anodize coatings and processes for aluminum and its alloys only. The anodic coating, being alu- minum oxide, is extremely hard and abrasive, especially aluminum hardcoat anodized surfaces. The classifications for aluminum and aluminum alloy anodic coatings are as follows. Plating Practices and Finishes for Metals 843 Walsh CH13 8/30/05 10:43 PM Page 843 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal Figure 13.18 Solution conversion equations. (Source: Handbook of Chemistry and Physics, 50th ed., Chemical Rubber Publishing Company, Cleveland, Ohio.) 844 Walsh CH13 8/30/05 10:43 PM Page 844 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal Classifications Type I. Chromic acid anodizing, conventional coatings produced from chromic acid baths. Shall not be applied to alloys containing over 5% copper or over 7% silicon or when alloying elements exceed 7.5%. Type IB. Chromic acid anodizing, low-voltage process, 20 V. Heat- treatable alloys, such as T4, T6, etc., should be tempered prior to anodizing. Type II. Sulfuric acid anodizing, conventional coatings produced from sulfuric acid baths. Heat-treatable alloys, such as T4, T6, etc., should be tempered prior to anodizing. Type III. Hard anodic coatings (hardcoat). Shall not be applied to alloys containing over 5% copper or over 8% silicon unless agreed on by the supplier. Heat-treatable alloys, such as T4, T6, etc., should be tempered. Classes Class 1. Nondyed, natural, including dichromate sealing Class 2. Dyed Standard specifications for anodized aluminum and aluminum alloys ASTM B244, Thickness of Anodic Coatings, Measurement of ANSI/ASTM B137, Weight of Coatings on Anodized Aluminum, Measurement of ASTM B117, Method of Salt Spray (Fog) Testing Sealing anodized aluminum and aluminum alloys. All types of anodiz- ing must be sealed using any of the following methods after the electrolytic anodized coating is applied: ■ Immersion in an aqueous solution of 5% sodium dichromate (15 min at 90 to 100°C) ■ Immersion in deionized water (15 min at 100°C) ■ Immersion in an aqueous solution of nickel or cobalt acetate (100°C for 15 min) ■ Teflon impregnation processes (for sealing and lubricity) Plating Practices and Finishes for Metals 845 Walsh CH13 8/30/05 10:43 PM Page 845 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal Anodic coating design data Radii of curvature on anodized parts Nominal coating thickness, in Radius of curvature (outside/inside), in 0.001 approx. 0.032 0.002 approx. 0.062 0.003 approx. 0.093 0.004 approx. 0.125 Thickness ranges of anodic coatings on aluminum and aluminum alloys Coating type Thickness range, in I and IB 0.00002 to 0.0003 II 0.00007 to 0.0010 III 0.0005 to 0.0045 Minimum thickness (typical) of anodic coatings on aluminum and alloys. See Fig. 13.19 for minimum typical anodic coating thicknesses on various aluminum alloys per type. Maximum thicknesses of anodic coatings on various aluminum alloys. Figure 13.20 shows the maximum attainable thicknesses of anodic coatings on selected aluminum alloys. Design notes for anodized parts 1. A 2-mil hardcoat anodic coating (0.002 in) will penetrate the part 0.001 in and protrude from the part 0.001 in. A 1.000-in-diameter part that is anodized 2 mils (0.002 in) will have a finished diame- ter of 1.002 in. Half the coating is inside the part, and half is on the outside. 2. Avoid blind holes in parts. 3. Avoid hollow weldments (drill 0.250-in-diameter weep holes in the part). 4. Avoid steel inserts. 5. Avoid sharp corners (see radii chart above). 6. Avoid heavy to thin cross sections on the part. 7. Allow for the anodic coating in your design tolerances on the part. 846 Chapter Thirteen Walsh CH13 8/30/05 10:43 PM Page 846 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal Anodic coating specifications Name Hardcoat anodize Chromic anodize Sulfuric anodize Army/Navy Mil-A-8625, Ty-3 Mil-A-8625, Ty-1 Mil-A-8625, Ty-2 G.E. AMS-2468D AMS-2470H AMS-2471D Boeing Code-302 Code-300 Code-301 IBM 41-207 41-204 41-203 Grumman G-9031 9030B G-9032 Hardcoat anodize processes ■ Martin ■ Alumilite ■ Alpha ■ Mae Plating Practices and Finishes for Metals 847 Figure 13.19 Anodic coating thickness. Walsh CH13 8/30/05 10:43 PM Page 847 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal ■ Sanford ■ Boeing ■ Scionic ■ Hardas ■ Imperv-X 848 Chapter Thirteen Figure 13.20 Maximum anodic coating thickness. Walsh CH13 8/30/05 10:43 PM Page 848 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plating Practices and Finishes for Metal [...]... Source: McGraw-Hill Machining and Metalworking Handbook Chapter 14 Fastening and Joining Techniques and Hardware 14.1 Bolts, Screws, Nuts, and Washers Bolts and screws are the most commonly used types of fastening devices The thread on a bolt or screw may be compared with an inclined plane wrapped around a cylinder, thus assuming the form of one of the basic machines Many different thread-form standards... manufacturer’s literature The wet-film thickness required for a specific dry-film thickness is found by dividing the desired dry-film thickness by the percentage of solids by volume of the coating to be used (Wet-film thickness is measured during application by a wet-film thickness gauge.) A fast and accurate estimate of wet-film thickness required to obtain a specified dry-film thickness and theoretical coverage... Systems: American Standard Њ and Metric (60Њ V) The international standard screw threads consist of the unified inch series and the metric series The metric series is standardized into the M and MJ profiles The unified series is designated as UN (unified national) Another unified profile is designated as UNR, which has a rounded root on the external thread The metric profile MJ also has a rounded root on the... both the internal and external threads Both the UNR and MJ profiles are used for applications requiring high fatigue strength; they are also employed in aerospace applications A constant-pitch unified series is also standardized and consists of 4, 6, 8, 12, 16, 20, 28, and 32 threads per inch These are used for sizes over 1 in in diameter, and 8UN, 12UN, and 16UN are the Downloaded from Digital Engineering... 14.20 Both number and letter size drills are indicated with their decimal equivalents The standard limits of size for both American and unified national series screw threads are fully covered in Table 14.1 The four sections of the table are extracted from National Bureau of Standards Handbook H-28 and are in general agreement with current American National Standards Institute (ANSI) standards The table... and thread-forming screws Types AB, A, B, BF, and C are thread-forming, whereas types D, F, G, T, BF, and BT are thread-cutting or self-tapping Type U is a spiral screw type that is driven or press-fit into the appropriately sized hole All thread forms shown are 60° V thread Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies... American standard socket-head shoulder screws and socket-head cap screws Fastening and Joining Techniques and Hardware 863 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Walsh CH14 8/31/05 4:00 PM Page 864 Fastening and Joining... Chapter Thirteen Figure 13. 21 Wet-film to dry-film paint-finish nomograph of the part owing to the electrostatic attraction Two types of powders are used: thermoplastics and cross-linked thermosets Following the spraying operation, the coated part is passed through a furnace to melt (thermoplastic) or cure (thermoset) the powder The parts being coated often are hung from a closed-loop overhead conveyor... finish must be directed to the proper paint manufacturer if high-quality results are expected High-quality paints and correct base-metal preparation techniques are expensive and require the proper equipment and facilities There are many government regulations in force Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies... 0.25 0-2 0UNC-2B Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Walsh CH14 8/31/05 4:00 PM Page 870 Fastening and Joining Techniques and Hardware 870 Chapter Fourteen Thread fit classes Unified thread series and interference-fit . website. Source: McGraw-Hill Machining and Metalworking Handbook Figure 14.1 Dimensions for American standard bolts. 856 Walsh CH14 8/31/05 4:00 PM Page 856 Downloaded from Digital Engineering Library. specifications Name Hardcoat anodize Chromic anodize Sulfuric anodize Army/Navy Mil-A-8625, Ty-3 Mil-A-8625, Ty-1 Mil-A-8625, Ty-2 G.E. AMS-246 8D AMS-2470H AMS-247 1D Boeing Code-302 Code-300 Code-301 IBM 4 1-2 07. be directed to the proper paint manufacturer if high-quality results are expected. High-quality paints and correct base-metal preparation techniques are expensive and require the proper equip- ment