2015年7月18日土曜日

Kenneth J. Anusavice 著 「Phillips Science of Dental Materials」Eleventh Edition  Saunders刊  pp.608-609より抜粋

Soldering of Dental Alloys

Substrate Metal for Soldering

Metal-joining operations are usually divided into three categories: brazing, soldering, and welding. The definitions seem remarkably similar. The primary difference between soldering and brazing requires a heating temperature above 450 °C (840 °F) but below the solidus temperature of the substrate metal(s) the difference between these two processes and welding is that welding may no require a filler metal and the metal surfaces to joined will fuse locally.
For dental applications the term soldering is commonly used to describe the build-up of contact area of joining of two metal parts such as components of a fixed partial denture or an intraoral appliance.

The soldering process involves the substrate metal(s) to be joined, a filler metal (usually called solder), a flux, and a heat source. 
All are equally important, and the role of each must be taken into consideration to solder metal components successfully.
Some of the terms and definitions listed in the key term section are modified versions of those provided in the Metals Handbook, Desk Edition (1992). The terms and definitions that follow serve as a reference to differentiate among brazing, soldering, and welding. Because the liquidus temperature of the filler metal is the only difference between the terms brazing and soldering, the term soldering is used subsequently as a general term to describe both processes.

 The substrate metal, sometimes known as the basis metal, is the original pure metal or alloy that is prepared for joining to another substrate metal or alloy. 
Before casting became the popular method of producing metal prosthetic structures, many appliances were constructed by forming shapes from wrought plate and wire and then soldering these pieces together to produce the required configuration. 
Dental casting alloys that can be soldered or welded include gold-based, silver-based, palladium-based, nickel-based, cobalt-based, and titanium-based alloys, as well as commercially pure titanium. Note that principles for soldering or welding are the same for any any substrate metal. Thus the individual who performs the soldering or welding procedure for cleaning the surfaces to allow intimate contact with molten filler metal, the most compatible filler metal to be used, and the heating temperature that will ensure adequate flow of filler metal or fusion of adjacent surfaces if weldering is performed. The composition of the substrate metal determines its melting range. As previously noted, the the soldering should take place below the solidus temperature of the substrate metal(s). The composition of the substrate metal determines the oxide that forms on surface during heating, and, if used, a flux must be able to reduce this oxide, inhibit further oxidation, or facilitate its removal. The composition and cleanliness of the substrate metal and the temperature to which it is heated determine the wettability of the substrate by the molten solder alloy. The solder chosen must wet the metal at as low a contact angle as possible to ensure wetting of the joint area. To prevent flow onto adjacent areas, an antiflux such as rouge mixed with chloroform can be painted on the areas before heating the assembly.

 The manufacture or supplier is responsible for providing explicit instruction for eliminating the oxide layer during the joining process. The instructions for every alloy should also include a recommendation for the appropriate filler metal (solder) and flux. For alloys that will be bonded to porcelain, this recommendation should include filler metals for both prefiring (presolder) and postfiring (postsolder), and appropriate flux for the substrate alloy. As stated earlier in this chapter, the technical term for joining metals before firing of the veneering ceramic layers is presoldering (or prebrazing), and the technical term for joining metals after the veneering process is postsoldering (or postbrazing).
Phillips' Science of Dental Materials

ISBN-10: 0721693873
ISBN-13: 978-0721693873

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