Metals galling

H. E. Boyer and T. L. Gall, eds.. Metal Handbook, Desk Edition, American Society for Metals, Metals Park, Ohio, 1985, pp. 4—11. 

Carbon—graphite materials do not gall or weld even when mbbed under excessive load and speed. Early carbon materials contained metal fillers to provide strength and high thermal conductivity, but these desirable properties can now be obtained ia tme carboa—graphite materials that completely eliminate the galling teadeacy and other disadvantages of metals. 

To protect clamping system, use dissimilar metals to prevent galling on threaded fasteners... 

To combat this problem, soft materials such as Babbitt are used when it is known that a bearing will be exposed to abrasive materials. Babbitt metal embeds hard particles, which protects the shaft against abrasion. When harder materials are used in the presence of abrasives, scoring and galling occurs as a result of abrasives caught between the journal and bearing. 

When two metals in intimate contact are subjected to vibration, a dark powder forms at the areas of contact. The effect is referred to as fretting corrosion though it is due to wear rather than true corrosive attack. The galling effect between nickel and steel ensures good resistance to fretting corrosion and lubricated nickel against steel is a very satisfactory combination used widely in industry for components assembled by press-fitting. 

In addition, the extreme hardness of the metal, its low coefficient of friction and its non-galling property, combined with its corrosion resistance, make it particularly valuable as a coating where resistance to wear and abrasion are important. Thick deposits applied for this purpose are referred to as hard chromium to distinguish them from the thin decorative deposits. 

Eisch, Behrooz and Galle give compelling evidence for the intervention of radical species in the desulphonylation of certain acetylenic or aryl sulphones with metal alkyls having a lower oxidation potential at the anionic carbon. The primary evidence presented by these workers is that the reaction of 5-hexenylmagnesium chloride outlined in equation (85) gives a mixture of desulphonylation products, in accord with the known behaviour of the 5-hexenyl radical, in which the cyclopentylmethyl radical is also formed. 

Many dyes that have no chemical affinity to fibrous substrates can be attached to such substrates by intermediary (go-between) substances known as mordants. These are either inorganic or organic substances that react chemically with the fibers as well as with the dyes and thus link the dyes to the fibers. Mordants are traditionally classified into two main classes, acid and metallic mordants. The acid mordants are organic substances that contain tannins (see Textbox 64) as for example, gall nuts and sumac. The metallic mordants are inorganic substances, mostly mineral oxides and salts that include metal atoms in their composition. Table 94 lists mordants of both these types, which have been used since antiquity. 

Unless otherwise specified, the need for hard-facing and the specific hard-facing material for each application is determined by the vendor and described in the proposal. Alternatives to hard -facing may include opening running clearances f.7.4) or the use of non-galling materials, such as Nitronic 60, Waukesha 88, or non-metallic materials, depending on the corrosiveness of the pumped liquid. 

Hatchett fused the ore with potassium carbonate. When he took up the melt with boiling water, a brown residue remained. When nitric acid was added to the yellow filtrate, a copious white precipitate was thrown down. The preceding experiments shew, said he, that the ore which has been analyzed consists of iron combined with an unknown substance and that the latter constitutes more than three fourths of the whole. This substance is proved to be of a metallic nature by the coloured precipitates which it forms with prussiate of potash and with tincture of galls by the effects which zinc produces when immersed in the acid solutions and by the colour which it communicates. .. to concrete phosphoric acid, when melted with it. . . . He mentioned that it retained oxygen tenaciously and that the oxide was acidic. Although the specimen Hatchett analyzed was very small, he hoped to get more soon from a gentleman now in England (Mr. Smith, Secretary to the American Philosophical Society). This was evidently Thomas P. Smith, who died in 1802 (53). 

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