Dental Soldering, Welding and Brazing.pptx

How often do you solder? Have you ever asked yourself how important soldering is in the overall context of dental laboratory work – and which requirements are essential to achieve a successful soldering result? If you have, then you may find this background information insightful. Come with us on a journey through the past, present and future of the (dental) soldering technique!

1. Dental Soldering, Welding and Brazing Dr. Abhidha Tripathi MDS First Year

2. Definition Ideal requirements Types of Solders Composition Properties Flux and Antiflux Techniques Welding Cast Joining References Contents

3. Definition Metal joining operations are usually divided into four categories: welding, brazing, soldering and cast-joining. WELDING : 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 flowing. 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 filler.

4. Definition Soldering operation at or above 450 degree C is generally termed brazing. Most dental soldering procedures are actually brazing but the names are used interchangeably in dentistry. Brazing is defined as a joining by the fusion of filler metals between them at a temperature below the solidus temperature of metals being joined and above 450 degree C.

5. It should melt at temperatures below the solidus temperature of the parent metal. When melted, it should be wet and flow freely over the parent metal. Its color should match that of metal being joined. It should be resistant to tarnish and corrosion. It should resist pitting during heating and application. IDEAL REQUIREMENTS OF A BRAZING MATERIAL (DENTAL SOLDER )

6. The Soldering Process

7. For soldering to be successful basic practical steps should be followed: The   surface  of the alloy should be  free from dirt  and oxides. If using soldering investment use the smallest amount possible. This will maintain the proper position of the parts during the procedure. Place flux  in the joint to be soldered. Select  a suitable  solder  which melts 50°C-100°C below the melting point of the components. Heat  the  components  evenly by either using the reducing zone of the flame or a furnace. When the flame is evenly  cherry red ,  apply the solder . The Soldering Process

8. The  parts  being joined are not melted during soldering but  must be thoroughly wettable  by liquefied solder. The careful and skillful use of the soldering torch flame is important to a high quality soldered joint. A well-defined, not-too-large pointed flame is advisable for the final heating of solder in a localized area, but a larger, less well defined flame of the “brush” type may be used for the initial heating. The  operation should be completed in the shortest time  possible to avoid oxidation of the base metal ingredients of the alloys involved and to prevent damage to the microstructures of the alloys. The Soldering Process

9. They may be divided into two major groups: 1. Soft solders 2. Hard solders 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, e.g., lead-tin alloys (plumbers solders). HARD SOLDERS These have a higher melting 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. They are also used for industrial purposes and in the jewelry trade, e.g., gold solders and silver. TYPES OF SOLDERS OR BRAZING MATERIAL

10. Soldering is often used in construction of dental appliances. Components of solder joint Parent metal Flux Antiflux Solder/ filler metal Composition

11. The parent metal is the metal or alloy to be joined. It is also known as substrate metal or base metal. The composition of parent metal determines : Melting range Oxide that forms on the surface during heating Wettability of the substrate by the molten metal Parent Flux

12. The Latin word ‘flux’ means flow. For a solder to wet and flow properly, the parent metal must be free of oxides. This is accomplished with the help of a flux. FUNCTION OF FLUX To remove any oxide coating on the parent metal. To protect the metal surface from oxidation during soldering. Fluxes

13. TYPES Fluxes may be divided into three activity types. Protective - This type covers the metal surface and prevents access to oxygen so no oxide can form. Reducing - This reduces any oxide present to free metal and oxygen. Solvent - This type dissolves any oxide present and carries it away. Most fluxes are usually combination of two or more of the above. Fluxes

14. COMMONLY USED DENTAL FLUXES Boric and borate compounds Used with noble metal alloys. They act as protective and reducing fluxes. 2. Fluoride fluxes Fluoride fluxes like potassium fluorides are used on base metal alloys and are usually combined with borates. They help to dissolve the more stable chromium, nickel and cobalt oxides. Fluoride fluxes should be used carefully around porcelain as it can attack the porcelain. Note: Excess flux should be avoided as it can get entrapped within the filler metal and result in a weak joint.

15. The flow can be controlled by use of an antiflux material. Solder will not flow into an area where antiflux has been applied. It is applied before the flux or solder is appalied . Examples of antiflux are graphite (soft lead pencil), rouge (iron oxide) or whiting (calcium carbonate) in an alcohol and water suspension. ANTIFLUX

16. The heat source is a very important part of brazing. In dentistry, two heat sources may be used: 1. Flame 2. Oven HEAT SOURCE

17. The most commonly used heat source is a gas-air or gas-oxygen torch. The flame must provide enough heat not only to melt the filler metal but also to compensate for heat loss to the surroundings. Thus, the flame should not only have a high temperature but also a high heat content. FLAME BRAZING OR SOLDERING

18. The Various Gases Used are Hydrogen : It has the lowest heat content and therefore heating would be slow. It is not indicated for soldering of large FPDs. Natural gas : It has a temperature of 2680°C and heat content is four times that of hydrogen. However, normally available gas is nonuniform in composition and frequently contains water vapor.

19. The most commonly used heat source is a gas-air or gas-oxygen torch. The flame must provide enough heat not only to melt the filler metal but also to compensate for heat loss to the surroundings. Thus, the flame should not only have a high temperature but also a high heat content. FLAME BRAZING OR SOLDERING

20. Torch Soldering

21. Acetylene : It has the highest flame temperature and a higher heat content than H2 or natural gas. Temperature from one part of its flame to another may vary by more than 100°C. Therefore, positioning the torch is critical and proper part of the flame should be used. It is chemically unstable and decomposes readily to carbon and hydrogen. The carbon may get incorporated into the Ni and Pd alloys, and hydrogen may be absorbed by the Pd alloys.

22. Propane : It is the best choice. It has the highest heat content (2385 Btu) and a good flame temperature (2850°C). Butane : It is more readily available and is similar to propane. Both propane and butane are uniform in quality and water-free.

23. An electric furnace with heating coils may be used for brazing. The furnace also provides heated surroundings, so less heat is lost to other parts of the fixed partial denture and the atmosphere. OVEN BRAZING (FURNACE BRAZING)

24. Two techniques of dental soldering are employed to assemble dental appliances: A. FREE HAND SOLDERING : In free hand soldering the parts are assembled and held in contact manually while the heat and solder are applied. B. INVESTMENT SOLDERING : In investment soldering, the parts to be joined are mounted in a soldering type of investment. The hardened investment holds it in position while the heat and solder are applied. TECHNIQUE OF SOLDERING

25. Selection of solder Cleaning and polishing of components Assembly of the prosthesis in soldering investment Application of flux Preheating the bridge assembly Placement of solder Application of hot gas flame to joint and solder Cooling of assembly followed by quenching in water STEPS IN SOLDERING PROCEDURE

26. Cleanliness—Metal should be free of oxides Gap between parts Selection of solder—Proper color , fusion temperature, and flow Flux-type and amount  Flame—Neutral or reducing in nature Temperature Time TECHNICAL CONSIDERATIONS FOR SUCCESSFUL SOLDERING

27. The liquid solder is drawn into the joint through capillary action. Therefore, an optimum gap is necessary for proper flow, strength of the joint and to avoid distortion of the assembly. Gap width ranging from 0.13 to 0.3 have been suggested. If the gap is too narrow, strength is limited due to — Porosity caused by incomplete flow — Flux inclusion If the gap is too great — The joint strength will be the strength of the solder. — There is a tendency for the parts to draw together as the solder solidifies. Gap between parts

28. Flame The flame has multiple zones . The portion of the flame that is used should be neutral or slightly reducing. An improperly adjusted or positioned flame can lead to oxidation and/or carbon inclusion. Once the flame has been applied to the joint area, it should be removed until brazing is complete. Due to its reducing nature, the flame gives protection from oxidation.

29. Temperature The temperature used should be the minimum required to complete the brazing operation. Prior to the placement of the solder, the parent metal is heated till it is hot enough to melt the filler metal as soon as it touches. A lower temperature will not allow the filler to wet the parent metal. A higher temperature increases the possibility of diffusion between parent and filler metal.

30. Time The flame is held until the filler metal has flowed completely into the connection and a moment longer to allow the flux or oxide to separate from the fluid solder. Insufficient time increases chances of incomplete filling of joint and possibility of flux inclusion in the joint. Excessive time increases possibility of diffusion. Both conditions cause a weaker joint

31. Applications Of Soldering Assemble long span fixed partial dentures. Joining wrought wire clasps arms to cast partial dentures framework. Joining precision attachments. 4. Joining sections of metal superstructure for implant supported restorations etc. To overcome distortion in multiunit cast fixed prostheses,. Repair of perforated crown and bridges. Develop contacts points in crown. Cutting and rejoining of ill fitted distorted bridge.

32. The term welding is used if two pieces of similar metal are joined together without the addition of another metal. It is usually used to join flat structures such as bands and brackets. WELDING

33. INDICATIONS In orthodontics to join flat structures like bands and brackets. In pedodontics, to weld bands and other appliances. In prosthodontics, to join wrought wire clasps and repair of broken metal partial dentures.

34. Cold welding is done by hammering or pressure. An example of cold welding is the gold foil filling. Hot welding uses heat of sufficient intensity to melt the metals being joined. The heat source is usually an Oxyacetlyene flame or high amperage electricity.

35. Basically two methods are followed : Fusion welding : where the parts are melted and joined but pressure is ot applied. E.g : Gas welding, Laser welding Pressure welding : where parts are heated and pressed but not melted. E.g : Spot welding.

36. Spot welding Pressure welding Laser welding Laser micro welding Methods

37. The two clean metal surfaces to be welded are placed together under pressure. Two ends of wire or band to be welded are placed between two copper electrodes of welder and pressed together When switch is pressed large current passes through the wires or band on the copper electrode. Combined heat and pressure fuses the metal pieces at that point. Spot welding

38. This is also called cold welding and does not require heat application. Gold foil is welded by pressure or cold welding Two layers of gold foil are joined by application of pressure at room temperature. 2. Pressure welding

39. LASER welding is stronger than solder joints of comparable size. The laser micro welder is high power industrial laser capable of delivering 20J/pulse for maximum of 6 mili seconds at a wire. Used for orthodontic appliances such as space maintainers, retention devices etc. 3. LASER Welding

40. Spot welding maybe used as method of fusing Stainless steel strip for making bands Securing attachments to the bands Attaching springs to a rigid bow wire, or to bands It is used more in the construction of fixed prosthesis Application of Spot Welding

41. Ryge G: Dental soldering procedures. Dent Clin North Am1958;2:747-757 [2]. American Dental Association: Dentists’ Desk Reference:Materials , Instruments and Equipment (ed 2). Chicago, ADA,1983, pp. 261-268 [3]. JM Ney Company: Ney Basic Cast Restorations. Bloomfield,CT , Ney, 1984, pp 86-91 [4]. Shillingburg HT, Hobo S, Whitsett LD, et al: Fundamentals ofFixed Prosthodontics (ed 3). Chicago, Quintessence, 1997,pp. 509- 534 [7]. Rosenstiel SF, Land MF, Fujimoto J: Contemporary FixedProsthodontics (ed 4). St. Louis, Mosby/Elsevier, 2006,pp. 843-866 References