Since induction melting is independent of the surrounding atmosphere, it is equally valid under vacuum. The melting furnace is entirely contained in a vacuum vessel (typically 10^(-4) torr). The electromangetic stirring, combined with the vacuum, degassed the metal and there is no possibility of oxidation during either the melting or the casting. The inclusions are few in number and are uniformly distributed in the product. Additives can be put in during the melt, without fear of reactions with the atmospher, so that precise repeatability is guaranteed. These features ensure metals and alloys of very high purity, with high resistance to corrosion, fatigue, and temperatura-stress cracking.
(Davies, J., Conduction and Induction Heating, p. 331)
Segregation Induced Cracking:
Segregation induced cracking occurs when low melting point constituents such as phosphorus, zinc, copper and sulphur compounds in the admixture seperate during the weld solidification process. Low melting point components in the molten metal will be forced to the centre of the joint during solidification, since they are the last to solidify and the weld tends to separate as the solidified meatl contracts away from the centre region containing low melting point constituents.
(Bollinghaus, T., Hot Cracking Phenomena in Welds II, p. 116)
Bead Shape Induced Cracking:
This type of centreline cracking is associated with deep penetration processes like Submerged Arc Welding (SAW or method 121) and CO2 shielded Flux Cored Arc Welding (FCAW or method 136). When a weld bead is of a shape where there is more depth than width to the weld cross section, the solidifying grains growing perpendicular to the steel surface intersect in the middle, but do not gain fusion across the joint. To correct for this condition, the individual weld beads must have at least as much width as depth. The total wld configuration, which may have many individual weld beads, can have an overall profile that constitues more depth than width. If multiple passes are used in this situation, and each bead is wider than it is deep, a crack free weld can be made.
(Bollinghaus, T., Hot Cracking Phenomena in Welds II, p. 117)
Masterbatch:
There are three states of aggregation - gaseous, liquid, and solid. Gaseous colorants are not known; consequently either a liquid or a solid color preperation can be chosen for the coloring of plastics. There are two possibilities for a solid color preparation, either a powdery or a granulated form, the latter known as a masterbach.
A masterbach is today the most preferred type of preparation, well documented by the large volume of sales.
A masterbach consists of:
- Polymer as carrier
- Colorants
- Dispersing agent
- If necessary; additives such as stabilizers, nucleating agents, antisatic agents, lubrications, and so forth
(Müller, A., Coloring of Plastics: Fundamentals, colorants, preparations, p. 37,38)
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