Erdem Özdemir - 030070307 - 8th Week Definitions - Part 2

Bright Dipping (Pickling)

Surface Cleaning
New- Better Definition

Pickling in solutions containing 4 to 15 vol %5 Sulfuric acid or -40 to 90 vol% hydrochloric acid is used for the removal of oxides formed on the surface of copper-base materials during mill processing and fabricating operations. The sul­furic acid solution is used to remove black cop­per oxide sealc on brass extrusions, forgings. and machinal parts; oxide on copper tubing, forgings. and machined parts; and light anneal­ing scale or tarnish. The hydrochloric acid solu­tion is primarily used for finishing, but is also used to remove scale and tarnish from brass forgings and machined parts, and oxide on cop­per forgings and machined parts. Conditions for pickling copper-base metals with sulfuric acid and hydrochloric acid are shown in Table I. Sometimes no additional surface preparation is necessary to produce the uniformity of appear­ance required for further finishing of copper; however, heavily sealed material may need a bright dip or color dip after pickling.

Except for bright annealed material, copper alloys must he pickled after each annealing treatment, completely descaled, and bright dipped to produce a natural surface color and luster suitable for other finishing treatments such as electroplating or painting. Scale dip and bright dip solutions arc given in Table 2. Bright dips for copper-base materials consist of sulfuric and nitiric acids in varying proportions with a small amount of water and hydrochloric acid. Proprietary pickle and bright dips, using sulfuric acid and stabilized hydrogen peroxide, are also available. Whereas the conventional brighi dips use highly concentrated acids, this sulfuric acid-hydrogci) peroxide bath is dilute and reduces worker safety hazards.

(Copper and Copper Alloys, 2001, Joseph R. Davis, ASM International. Handbook Committee, P320)

Previous

Bright dipping is used to produce highly reflective surfaces on non-ferrous metals, particularly copper and brass. To bright up copper, it is first dipped in sulphuric acid which acts to oxidize the surface. It is followed by a dip in nitric acid to dissolve the newly formed oxide on copper. By this process, the microscopic hills and valleys on the metal surface are leveled off, increasing the reflectivity of the metal. Bright dip is followed by thorough rinsing and wiped dry to avoid tarnishing. Proprietary solutions are available for various non-ferrous metals. Bright dipping is the most effective process of removing oxides from non-ferrous metals and gives a highly reflective surface which is necessary to have before plating the surfaces. A very thin layer of plating on a bright dipped surface will make the surface more attractive.

(Kaushish, J.P., Manufacturing Process,Eastern Economy Edition, pg.543)

 Direct Driven Presses

Forging Process
New Definition

Direct-driven presses usually employ hy­draulic oil or water emulsion as ihc working me­dium. In earlier vertical press designs, al the start of the downstroke the upper ram falls under gravity and oil is drawn from the reservoir into the ram cylinder through the suction of this fall. When the ram contacts the workpiece. the valve between the nun cylinder and the reservoir is closed and the pump builds up pressure in the ram cylinder. This mode of operation results in relatively long dwell times prior to the start of deformation. As illustrated in Fig. 11.1(b), dur­ing the downstroke in modern direct-driven presses a residual pressure is maintained in the return cylinders or in the return line by means of a pressure relief valve. Thus, the upper ram is forced down against pressure and the dwell inherent in the free fall is eliminated. When the pressure stroke is completed, i.e.. when the up­per ram reaches a predetermined position, or when the pressure reaches a certain value, the oil pressure on the ram cylinder is released and diverted to lift the ram.

(Cold And Hot Forging: Fundamentals And Applications, 2004, Taylan Altan, Gracious Ngaile, Gangshu Shen, P 116)

There is no previous definition