Molten metals, printing with

When a casting is to have a hollow section, a core must be incorporated into the mould. Cores can be made from metal or more commonly from sand, made separately in a core box, and inserted into the mould after the pattern is removed and before the mould is closed. They are located and supported in the mould in a seating formed by the core prints on the pattern. The core must be strong enough to support itself and withstand the flow of molten metal, and in some cases it may be necessary to reinforce it with wires to give added strength. The more complex cores are produced from CO sand. 

The next phase will address eliminating lead from board finishes—the protective coatings applied to termination pads on printed wiring boards to protect metal conductors from degradation (e.g., oxidation, corrosion) and remain solder-wettable. Finishes are applied in a number of ways, including dipping into a molten metal bath (e.g., tin, solder), electroless plating, etc. Alternative finishes must, of course, be compatible with the lead-free alloy selected in Step 1. 

Base Metal Finishes. The low cost of base metal finishes obviates selective coating. Electro deposition is used for 0.5—5 p.m thick coatings of tin and tin—lead alloy, usually about 50 wt % Sn, 50 wt % Pb, on electronic connector contacts, on contacts at the edges of printed circuit boards, and on terminals. Sheet copper alloys that have been coated with tin—lead alloy are widely used for contacts that are stamped and then formed into the desired shapes, such as pins having a closed end and sockets. Aluminum connectors that have utility—industrial appHcations are more thickly coated, and hot-dipping in molten tin is common. 

Solder masks (solder resists) are protective polymer coatings used on printed circuit boards (PCB s) to prevent solder bridging between conductors during soldering (1-3). The selective application of the solder mask limits the amount of conductor area in contact with the molten solder, minimizing solder usage and slowing the rate of conductor metal contamination in the solder pot. 

Screen printing Ag-Pd electrodes. The cost of the electrode materials is a big concern. In fact, the noble metals account for more than half the cost price of MLCCs. Alternative nonprecious metals such as copper and nickel have been used. A different approach to reducing the cost of metallization is the fugitive electrode process. The electrodes are made of carbon, which is removed during sintering in air. The remaining cavities are then pressure infiltrated with either molten lead or a tin-lead alloy to produce the electrodes. 

Type metal was an alloy with low melting point that was utilized to make the type for printing. The composition may be 81% lead, 15.5% antimony and 3.5% tin. The molten alloy expands on solidification and thus fills the moulds very well. This gives the type sharp edges. The technique has entirely been replaced by new printing methods. 

In-mold decoration is commonly used in the automotive sector to achieve special effects (wood grain, brushed metal look, etc.) on interiors and exteriors. The dominant incumbent is laminated film in which the decorative effects are back printed behind the surface layer. Typically, these films are thermoformed off-line and placed in an injection or compression mold that is subsequently filled with molten substrate polymer. 

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