Drop solder

Between 1979 and 1989 there was a virtual elimination of the use of lead-soldered food cans, with a concomitant drop in lead levels in food. Average daily intakes of lead for adults, based on an analysis of 27 market basket samples taken nationwide for a 1980-1982 Total Diet Study, were as follows (Gartrell etal. 1986b) ... 

The tube-in-tube or multitube-in-tube heat exchangers are useful in small Linde lique-fiers or in the final Joule-Thomson stage of any liquefier. The performance of Linde-type exchangers is easy to calculate, and their realization is simple. In the examples shown in Fig. 5.12 (a)-(c), the tubes are concentric and the outer wall contributes appreciably to the pressure drop in the outer stream without contributing to the heat transfer. Usually, the smaller inner tube is used for the high-pressure stream and the low-pressure stream flows through the outer annular space. The tubes in Fig. 5.12 (d) and (e) are solder bonded while that in (f) is flattened and twisted before insertion into an outer tube. 

Accidental installation in a human eye of one drop of a 50% zinc chloride solution caused immediate and severe pain, which persisted despite immediate irrigation with water. The corneal epithelium was burned, and corneal vascularization followed. After many weeks, areas of opacification and vascularization remained in the cornea. Zinc chloride has caused ulceration of the fingers, hands, and forearms of workers who used it as flux in soldering. ... 

Use of Zinc Chloride in Soldering. Glean two copper wire ends with emery paper and place them on a sheet of asbestos so that they are in contact with each other. Put 1-2 g of metallic tin on the asbestos sheet. Heat an electrical soldering iron until it acquires a dark red glow, touch the tin with it, and transfer the drop of molten tin to the place of contact of the copper wires. What do you observe Did the tin solder the ends of the wires ... 

Examination of the Solder from the Tin.—The solder to be examined is that found in the inner part of the tin. It is either cut from the tin and then melted or heated by means of a bunsen flame until it drops into an unglazed porcelain crucible, in which it is fused to a homogeneous button. In this the lead is determined by one of the following method ... 

Continue heating until the top piece appears to drop down. This indicates that the solder has begun to melt. A bright seam of metal can be seen around the edges. This means that the solder has flowed. 

When the solder has flowed, remove the heat, grasp the piece with tweezers, and drop it into the pickle solution to clean it. Remove the soldered piece with copper tongs and rinse with water. 

The wetting balance technique is a variant of the maximum pull (or detachment) method used to measure liquid-vapour surface tensions (Keene 1993). It is nowadays widely employed in the electronics industry to quantify wetting of solders, but has also been used for wetting studies in metal/ceramic systems (Naidich and Chuvashov 1983b, Nakae et al. 1989, Rivollet et al. 1990). As compared to the sessile drop method which needs planar substrates, solids of various geometry can be studied by this technique. 

In these experiments the silver vessel which contained the substance to be examined had, of course, to be filled with hydrogen instead of with air, in order to facilitate equalization of temperature. To this end there was a little silver capillary in the cover which was rapidly closed airtight with a drop of solder after filling with hydrogen. The glass vessel containing the calorimeter had also to be filled initially with hydrogen, at about 1 cm. pressure, which was pumped off after the temperature of the calorimeter had fallen sufficiently low. 

Sometimes the lever spring will not remain in place, but will slip out. To remedy the evil, take a common Berdan cartridge primer, or any other kind will do. only take one that has been used or has had the priming removed, put inside it a drop of solder, ing acid and a bit of solder, enough to fill it when melted. Hold it over the lamp until the wider fuses. When it has coded, wet the charger with a touch of the add just where the bend of the spring comes, and there place the primer with the solder next the wet place. Hold it in position with a bent piece of wire or a strip of steel bent like a loop. Hold over the lamp, with the primer downward, until the solder is melted. Replace the spring, axKl it will be found that it will remain firmly in its place. 

Two other effects due to surface tension are the capillary rise of liquids in small tubes and porous wicks (without which kerosene lanterns or copper sweat-solder fittings wouid not work at all) and the tendency of jets of liquid to break up into drops (asj from a garden hose or diesel fuel injector). Surface tension effects are very important in systems involving large surface areas, such as emulsions (mayonnaise, cold cream, water-based paints) and multiphase flow through porous media (oil fields). We discuss the effects in Chap. 17 see also Refs. 4 and 5. 

T. Schiesser, E. Menard, T. Smith, and X Akin, Microdynamic solder pump drop on demand eutectic SnPb solder dispensing device. Proceedings, Surface Mount International, San Jose, CA, 1994, 501-509. 

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