Metal Joining PDF

Metal Joining Dr.Wayel Huraib  Soft Tissue Considerations Welding : Metal Joining and Dental Lasers The term welding is used if two pieces of similar metal are joined together without the addition of another metal that is, the metal pieces are he...

Metal Joining Dr.Wayel Huraib  Soft Tissue Considerations Welding : Metal Joining and Dental Lasers The term welding is used if two pieces of similar metal are joined together without the addition of another metal that is, the metal pieces are heated to a high enough temperature so they join together by melting and owing. Dr.Wayel Huraib fl  TERMS AND DEFINITIONS Metal Joining and Dental Lasers Brazing And Soldering : The words soldering and brazing are used if two pieces of metal are joined by means of a third metal called as ller. Dr.Wayel Huraib fi  REQUIRMENTS 1- It should melt at temperatures below the solidus temperature of the Metal Joining and Dental Lasers parent metal. 2- When melted, it should wet and ow freely over the parent metal. 3- Its color should match that of metal being joined. Dr.Wayel Huraib fl  REQUIRMENTS Metal Joining 4- It should be resistant to tarnish and and Dental Lasers corrosion. 5- It should resist pitting during heating and application. Dr.Wayel Huraib  TYPES OF SOlDERS OR BRAZING MATERIAlS SOFT SOlDERS : Metal Joining and Dental Lasers Soft solders have low melting range of about 260 °C. They can be applied by simple means like hot soldering iron. They lack corrosion resistance and so are not suitable for dental use. Dr.Wayel Huraib  TYPES OF SOlDERS OR BRAZING MATERIAlS HARD SOlDERS : Metal Joining These have a higher melting and Dental Lasers temperature and greater strength and hardness. They are melted with the help of gas blowtorches or occasionally in an electric furnace. Hard solders are more commonly used in dentistry. Dr.Wayel Huraib  APPlICATIONS OF SOlDERING 1- For soldering various types of wires Metal Joining and Dental Lasers in orthodontics. 2- In pedodontics, to construct various types of space maintainers. 3- In removable partial prosthodontics for soldering of clasps. Dr.Wayel Huraib  APPlICATIONS OF SOlDERING 1- For joining of various components of xed partial prostheses Metal Joining and Dental Lasers 2- Repair of perforations in crowns and bridges. 3-To develop contact points in crowns. 4- For cutting and rejoining an ill- tting distorted bridge. Dr.Wayel Huraib fi fi  APPlICATIONS OF SOlDERING Dr.Wayel Huraib  PROPERTIES OF DENTAL BRAZING MATERIAlS FUSION TEMPERATURE : The fusion temperature of the solder should be at least 50 °C lower than the parent metal. Gold solders – 690 to 870 °C Silver solders – 620 to 700 °C Dr.Wayel Huraib  PROPERTIES OF DENTAL BRAZING MATERIAlS FlOW : A good ow and wetting (low wetting angle) of the parent metal by the solder is essential to produce a good bond. Dr.Wayel Huraib fl  PROPERTIES OF DENTAL BRAZING MATERIAlS FlOW : Factors a ecting ow 1. Melting range Solders with short melting ranges have better ow. 2. Composition of parent metal Gold and silver based alloys have better ow than nickel based alloys. 3. Oxides Presence of an oxide layer on the parent metal reduces the ow. Dr.Wayel Huraib 4. Surface tension of solder. fl ff fl fl fl  PROPERTIES OF DENTAL BRAZING MATERIAlS COlOR : The color of gold solders varies from deep yellow to light yellow to white. In practice, most dental solders are able to produce an inconspicuous joint. Dr.Wayel Huraib  PROPERTIES OF DENTAL BRAZING MATERIAlS TARNISH AND CORROSION RESISTANCE : Tarnish resistance increases as the gold content increases. However, lower neness gold alloys also perform well clinically without any serious tendency to discolor. Silver solders have reduced tarnish resistance when compared to gold alloy solders. Dr.Wayel Huraib fi  PROPERTIES OF DENTAL BRAZING MATERIAlS MECHANICAl PROPERTIES : Gold solders have adequate strength and hardness and are comparable to dental cast gold alloys having a similar gold content. Silver solders also have adequate strength and are similar to the gold solders. Dr.Wayel Huraib  STEPS IN SOlDERIN PROCE ْRE 1. Selection of solder. 2. Cleaning and polishing of components. 3. Assembly of the prosthesis in soldering investment. 4. Application of ux. Dr.Wayel Huraib fl Dْ  STEPS IN SOlDERIN PROCE ْRE 5. Preheating the bridge assembly. 6. Placement of solder. 7. Application of hot gas ame to joint and solder. 8. Cooling of assembly followed by quenching in water fl Dْ  TECHNICAL CONSIDERATIONS FOR SUCCESSFUL SOlDERING Cleanliness Metal should be free of oxides. Gap between parts. Selection of solder Proper color, fusion temperature and ow. Temperature. Time. fl  ADVANTAGES AND DISADVANTAGES Advantages : 1. Low cost. 2. Relative e ectiveness. ff  ADVANTAGES AND DISADVANTAGES Disadvantages : 1. Problems such as oxidation of the parts joined by weld. 2. Joint porosity and overheating of the union during the welding process can promote small structural defects and failure of the rehabilitation treatment.