soldering & welding

8/3/2019 Soldering & Welding

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SOLDERING

WELDING



DEFINITIONSDEFINITIONS



SOLDERING

defined as the joining of metals by the fusion

of filler metal between them, at a temperature

below the solidus temperature of the metals

being joined and below 450°C.



BRAZING

Brazing is defined as joining of metals by thefusion of a filler metal between them, at a

temperature below the solidus temperature of metals being joined and above 450°C.



LIQUIDUS TEMPERATURE:

the temperature at which an alloy begins tofreeze on cooling or at which the metal is

completely molten on heating.

SOLIDUS TEMPERATURE:

the temperature at which an alloy becomes

solid on cooling or at which the metal beginsto melt on heating.



WELDING:

The joining of two or more metal parts byapplying heat, pressure or both, with or

without a filler metal, to produce localized

union across the interface through fusion or diffusion.



CAST JOINING

A

nother type of metal joining procedure indentistry. It is the process of combining twocomponents of a fixed partial denture by means of casting molten metal into interlocking region between invested components. This is preferred for

base metal alloys because of technique sensitivity of brazing or soldering these alloys.



SOLDERINGHISTORY

. The old methods of heating metals with coal fires etc. wereno longer practical.



It was discovered that when the vapor fromheated alcohol was ignited over a burning

wick, it burnt with a very concentrated flameof high temperature very suitable for differentheating purposes.



Many different designs emerged using this

technique and these heating tools were

generally called blow pipes. The first known patent is from France and is dated January 7,

1791.



After the Second World War, the propane gas emerged as acleaner and safer fuel for different heating purposes. Theintroduction of propane caused a lot of changes in the blowlamp industry world-wide.



The first appliances used had a metal frame work. The

attachment of axillaries to bring about the different type of

tooth movements required soldering of these parts. Weldingin orthodontics became popular after the arrival of spot

welders. It became popular because of the short time

required, the ease of welding and the absence of elaborate

equipments



Soldering is often used in construction of dental appliances.

Large partial dentures are frequently cast in parts that aresoldered together after carefully fitting them to master cast. Inorthodontics soldering is used for joining wires, bands springsetc



COMPONENTS OF SOLDERED JOINT

Parent metal

Solder/filler metal

Fluxes and Anti fluxes



PARENT METAL The parent metal is the metal or alloy to be joined.

This is also known as a substrate metal or base metal.

Soldering operation is the same for any substrate metal,

but the ease of soldering is not same for any substrate metal.

The composition of parent metal determines-

Melting range

Oxide that forms on the surface during heating

Wettability of the substrate by the molten solder. Soldering should take place below the solidus temperature of the

parent metal.



A low temp soldering is preferred rather than the high tempsoldering for Stainless steel wire to prevent carbide precipitation and to prevent an excessive softening of the wire.So silver solders are generally preferred.



FLUX



FLUX

In Latin flux means ³to flow´.

Purpose of flux is to remove any oxide coating on thesubstrate metal surface when the filler metal is fluid and

ready to flow into place.

They protect the alloy surface from oxidation duringsoldering and dissolve metallic oxides as they are formed.

The resulting solution of oxides or other extraneous matter influx constitutes ³slag´.



CLASSIFICATION OF FLUX

1.According to their primary purpose / activity

Surface protection type: - This type of flux covers themetal surface and prevents access to oxygen, so that nooxides can form.

R educing agent type: - This type reduces any oxides present and exposes clean metal.

Solvent type: -T

his type dissolves any oxides and drivesthem away.

The composition of most commercial fluxes is formulated toaccomplish two or more of these purposes.



2.According to their composition

Borax fluxes

Fluoride fluxes

3. According to the pH of the flux Acidic fluxes ± SiO2

Basic fluxes ± CaO, lime CaCO3 LIMESTONE

Neutral ± Fluorspar (Ca.F2),Borax (Na2B4O2)



BORAX FLUXES

Borax from Persian burah

Also called sodium borate, or sodium tetraborate, or disodium

Tetraborate.

They are based on boric or borate compounds such as boric acid/boric

anhydrate and borax.

It is usually a white powder consisting of soft colorless crystals that dissolveeasily in water.

Borax has a wide variety of uses:-

1. It is a component of many detergents, cosmetics, and enamel glazes.

2. It is also used to make buffer solutions in biochemistry

3. as a fire retardant

4. as an insecticide

5. as a flux in metallurgy6. They act as protective fluxes and reducing fluxes for low stability

oxides such as copper oxide.

- are used for noble metal alloys.



They are available in

Liquid form: Solution of borax/boric acid in water.Indicated for soldering of orthodontic appliances andbridges in which minimum amount of flux isrequired.

Paste form: Formed by mixing borax withpetroleum jelly. Required when fluxes are needed inlarge quantity.

Powder form: Contains a mixture of borax, boricacid, silica flour and finely divided charcoal.Charcoals reducing agent and silica holds moltenflux in surface of hot metal. This is usually used for casting operation.



FLUORIDE FLUXES

Composition:- Potassium fluoride ± 50-60%

Boric acid ± 25-35%

Borax glass - 6-8%

Potassium carbonate ± 8-10%

- the fluoride flux is used with alloys containingbase metals even if a gold/silver solder is used.

- inhalation of fumes should be avoided.



POTASSIUM FLUORIDE

After hydrogen fluoride, KF is the primary source of thefluoride ion for applications in manufacturing and in chemistry.It is an alkali metal halide and occurs naturally as the raremineral carobbiite(potassium-67.30% + fluorine-32.70%)

is a colorless cubic mineral. It is found at Monte Somma,Somma-Vesuvius Complex, Province of Naples, Campania,

Italy. It was discovered in 1956.

Aqueous solutions of KF will etch glass due to the formation of soluble fluorosilicates.



SUPER FLUX

A combination of high melting salts is used asfluxes to combine the good characteristics of eachingredient and create superior flux.

A formula for efficient flux is

Borax glass ± 55 parts

Boric acid ± 35 parts

Silica - 10 parts

.



APPLICATION OF FLUX

Painted on to the substrate metal at the junction of pieces to be joined.

Fused on to the surface of the filler metal strip.

Whatever be the technique used the most important thing to consider

is the amount of flux used.

Too little flux tends to burn off and will be ineffective.

Excess flux remains trapped within filler metal and cause a weakened

joint.

Flux combined with metal oxides forms a glass during soldering process that is

difficult to remove completely.

A two step method for removing residual flux

Blast joint immediately after removal from investment with alumina

abrasive particles followed by boiling in water for about 5 minutes.



ANTI FLUX

Materials used to restrict flow of solder are known as anti flux.

It is applied on the surface of specific area where the solder should flow into.

It is applied before applying flux or solder.

E.g.: Graphite in the form of lead pencil. Disadvantage of graphite is that it can burn off on prolonged heating at hightemperature.

In such cases whiting (CaCO3 in alcohol and water suspension)is used.



FILLER METAL/SOLDER

Qualities of an ideal solder

Ease of flow at relatively low temperature.

Sufficient fluidity to freely flow when melted.

A bility to wet substrate metal.

Strength compatible with that of the structure being joined.

Resistance to tarnish and corrosion.

Acceptable colour to give an inconspicuous joint.

Resistance to pitting during heating.



FLOW TEMPERATURE



FLOW TEMPERATURE

The temperature at which the filler metal wets and flows onthe substrate metal and produces a bond. It is usually higher than the liquidus temperature.

ISO 9333 requires that the flow temperature of the filler

metal should be lower than the solidus temperature of thesubstrate metals. A rule of thumb is that flow temperature of the filler metal should be 56°C (100°F) lower than thesolidus temperature of the substrate metal.

If the flow point of the filler metal is close to or above the

solidus of either substrate alloying can take place. An alloyformed through diffusion can have properties different fromfiller metal and substrate metal.



CLASSIFICATION OF SOLDERS

l. Soft solders

Hard solders

II. Precious metal solders

Non precious metal solders



SOFT SOLDERS

They are lead- tin eutectic alloy with a low melting point. Sometimes called as plumbers solder. Theyhave low fusion range of about 260°C or less. Softsolders lack corrosion resistance, so they are

impractical for dental use.

HARD SOLDERSHard solders have higher meting temperature &

possess greater hardness and strength. Heating isdone with gas torch or special devices. Two types of hard solders are used in dentistry



Gold solders

Has good tarnish and corrosion resistance

Extensively used for crown and bridge applications.

Composition

Gold ± 45-81 wt %

Silver - 8-30 wt %

Copper -7-20 wt %

Tin or Zinc - 2-4%

Phosphorus - Traces

small amounts of Tin, Zinc and Phosphorus to modify fusiontemperature and flow qualities. They are high fusing with afusion temperature range of 750- 900° C.



Properties of gold solder

1. High resistance to tarnish and

corrosion.

2. Easily flowing

3. High mechanical properties:

Tensile strength- 220-635 Mpa

Surface hardness- 90-200 KHN

Modulus of elasticity- 120,000 Mpa

Proportional Limit- 140-530 Mpa



Silver solders

Used in orthodontic appliances They are low fusing ±fusion temp-600-750°C

Used with stainless steel or other base metal alloys

Resistance to tarnish and corrosion is not as good as goldsolders

But have strength comparable to gold solders



COMPOSITION

Silver -10-80 %

Copper -15-30%

Zinc -4-35%

with small amounts of cadmium, tin and phosphorus.

The formation of silver-copper eutectic is

responsible for the low melting range of silver solder.



HEAT SOUR CE



The most common instrument used as heat source is gas- air or gas- oxygen torch.

The type of torch depends on the type of fuel.

The fuels used are :-

Hydrogen-low heat content, so heating is slow.

Natural gas- heat content is four times that of hydrogen.



Acetylene - high flame temperature, but variation intemperature from one part of the flame to the other part ismore than 100°C. So positioning of the torch is critical. It ischemically unstable gas, decompose to carbon and hydrogen.carbon can get incorporated in to nickel and palladiumalloys.

Propane - is the best choice.Have highest heat content&good flame temperature.

Butane - has similar flame temperature and heat content.Both are readily available. Uniform in quality, virtuallywater free and burn clean.



FLAMEThe flame can be divided in to four zones

- Cold mixing zone (unburned gas)

- Partial combustion zone (oxidizing)

- Reducing zone

- Oxidizing zone (burned gas).

The portion of the flame that is used to heat the soldering assemblyshould be the neutral or slightly reducing part, because this produces themost efficient burning process and most heat.

Improperly adjusted torch or improperly positioned flame can lead tooxidation of the substrate or filler metal and result in a poorly soldered

joint. If unburned portion of flame is used carbon may be introduced to the

substrate or filler.

To prevent oxide formation the flame should not be removed once it has been applied to the joint area until soldering process has been completed.



OVEN (FURNACE) SOLDERING

A furnace with enough wattage to provide heat

required to raise the temperature of the filler

metal to its flow point.

Advantages: Uniform temperature

Close monitoring is possible

Temperature is known

A pplication of vacuum control oxidation



INFRARED SOLDERING

The unit uses light from a 1000 watt Tungstenfilament

quartz- iodine bulb which is mounted at the primaryfocal point of a gold plated elliptical reflector.

The material to be soldered is placed at thereflectors secondary focal point at which thereflected infrared energy of Tungsten light source isfocused.

This is used for high temperature soldering.



TECHNIQUES OF SOLDERING

Investment soldering

Free hand soldering



INVESTMENT SOLDERING Used when very accurate alignment of parts to be

joined is needed. The parts are placed on the master cast with a gap of

at least 1mm.

The parts are fastened with sticky wax before

placing soldering investment. Anti flux is applied to confine the flow of solder.

The investment is preheated to eliminate moisture.

Flux can be applied before or after heat treatment.

Soldering is carried out with reducing flame at 750-870°C.

The investment is cooled 5 min before quenching.

Flux will cool to a glass which is removed by

pickling.



FREE HAND SOLDERING

Free hand soldering is used for soldering

orthodontic appliances.

Orthodontic torches can be placed on a benchso that both hands can be used to hold the

parts in position.



Hydroflame

Oxyhydrogen generator- H2O- H2/O2

Burns gas ² high H2 content-Reducing flame



SOLDER JOINT GAP

If the gap is too great the strength will be

controlled by the strength of the filler.

If the gap is narrow the strength will belimited by the flux inclusions& porosities by

the incomplete flow of the filler, metal.



STEPS IN SOLDERING

Cleaning and preparing the surfaces to be joined Assembling the parts to be joined

Preparation and fluxing of the gap surfaces betweenthe gaps

Maintaining the proper position of the parts during procedure.

Control of proper temperature

Control of time to ensure adequate flow of thesolder& complete filling of the solder joint



ORTHODONTIC SOLDERING

In orthodontic applications low temperature soldering is usedto prevent carbide precipitation and to prevent excessivesoftening of the wire.

Low fusing silver solders are used with a solderingtemperature range of 620-655°C.

Fluoride fluxes are used for orthodontic stainless steel andother base metal alloys.

Free hand soldering technique is employed with a needle likenon luminous gas air flame is used.



The work should be held 3mm beyond the tip of the bluecone in the reducing zone of the flame.

Soldering should be observed in a shadow, against a black back ground, so that the temperature can be judged by thecolor of the work. The color should never exceed a dull red.

Flux must cover all the areas to be joined before heat isapplied.

As soon as the flux fuses solder is added and heating iscontinued until metal flows around the joint. The work isthen removed from the heat and quenched in water .



SOLDERING APPLICATIONS IN

ORTHODONTICS

Wire to wire

Tubes can be soldered to the bridge of the Adams clasp.

Attachment of springs to arch wire. When soldering anauxiliary spring to arch wire, the solder must be a gold onewith a melting point below 800°C.

Soldering lingual arch or palatal arch: to hold the arch duringsoldering position it on the model and place a blob of wet pumice over the middle portion of the model. Water isimmediately soaked on to the cast leaving dried pumice whichis firm enough to secure the arch during soldering.(F.G.Thompson, JCO 1969 A pril)



study was conducted to compare and evaluate the

tensile strength of silver soldered joints of stainless

steel and cobalt - chromium orthodontic wires with

band material.

findings of the study were suggestive that all three

wires may be used for preparing silver soldered joints

irrespective of the quality of the wire.

Dua R & Nandlal B-1996

SOLDERING FAILURES



SOLDERING FAILURESAre due to:

Failure to clean the parts to be joined

Improper fluxing

Poor flow of solder

Over heating of the solder can lead to pitted joint of low strength

Besides porosities and brittleness from oxides, gases, or foreign matter resulting from the soldering procedures as factors for increasing theincidences of failure of soldered joints.

Creep, corrosion, stress corrosion cracking, corrosion-fatigue, and

corrosion-erosion.

Gas embitterment can also be generated by gases formed fromelectrochemical processes. Hydrogen embitterment from corrosion is avery well-known phenomenon that occurs with some material-solutioncombinations and at temperatures comparable to physiologic conditions.



CORROSION OF SOLDERED JOINTS

A consideration of the composition of silver solders reveals that anymaterial containing up to about 20 percent zinc and 20 to 30 percentcopper with additions in some cases of low cadmium and tin cannotremain inactive to physiologic solutions.

Weak corrosion-prone micro structural phases composed mainly of copper and zinc has been shown to occur within the solder itself. It is

known that corrosion occurs when an electrolyte comes into contact witha soldered joint.

The silver solders react readily to chemical attack.

The breakdown reaction between silver-soldered stainless steel joints is

an electrochemical process with no initial evidence of gross macroscopiccorrosion.

After a time, many silver-soldered joints exhibit a change in appearancesuch as darkening to resemble a tarnished, corroded surface.



BIOCOMPATIBILITY

Si lv i a Sisti ni - 2008 ±

Traditional silver soldering is toxic for osteoblastdifferentiation, fibroblast viability, and keratinocytegrowth

For Cadmium-containing solders, because of Cadmium'stoxicity, a continual appraisal must be made regardingCadmium's fate biologically. The release of Cadmium fromdental alloys has been the subject of several reports.

Even in the case of such nontoxic elements as Zinc, Copper,Tin, and Silver, the introduction of higher concentrations of these elements via soluble corrosion products can alter their

behaviour



It is believed that possible allergies to nontoxic metals released fromdental alloys may be formed.

Metabolic and bacteriologic participation can also occur in response tocorroded metallic agents. Furthermore, the penetration and staining of hard dental tissues due to the release of metallic ions from solders or any biomaterial are definitely to be avoided.

Laboratory tests indicate that silver-soldered stainless steel joints degradein a saliva substitute and other prepared solutions.

Corrosion products containing oxides, hydroxides, and chlorides of zinc,copper, tin, and cadmium can be easily identified. Silver is also attacked

Besides the oral physiologic fluids, additional chemical agents containedin mouth rinses and in toothpastes for oral antiseptic, need carefulappraisal for resistance to the degradation and corrosion of dental

materials.

Many commercial mouth rinses contain active chlorides and additionalcomponents. The chlorides are notorious for their depassivationtendencies of metallic materials.

NE ER SILVER SOLDERS



NEWER SILVER SOLDERS

For joining stainless steel, additional alloys with improved corrosion resistance

classifications of silver soldering alloys (referred to here as brazing alloys),

includingBAg-18 and BAg-21 (American Welding Society), can be used very

effectively.

These silver soldering alloys have silver contents at about the same level as the

solder products presently employed, but they have slightly higher copper contents, with additions of up to about 10 percent tin for wetting stainless steels

and up to about 3 percent nickel for immunity to crevice corrosion.

The important fact is that both cadmium and zinc are removed from these alloys.

The soldering (brazing) temperature range is between 700 and 900°C, in some

instances about 200°C higher than the presently employed products.

Because of the non-free-flowing characteristics of these proposed soldering

alloys for dental applications, familiarization with their properties and handling

characteristics is advisable.



WELDING

Welding is the process by which the surfaces of metals are joined by mixing, with or without the useof heat.

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 usuallyan oxyacetylene flame or high amperage electricity.



TYPES OF WELDING

SPOT WELDING

PR E SSUR E WELDING

LAS E R WELDING

P LASM A WELDING



LASER WELDING

crystals of yttrium aluminum

garnet (YAG) doped with

neodymium(Nd) are mainlyused to emit laser beams

(Nd:YAGlaser)



Jens Johannes BOCK- 2008

The use of additional filling material in

TIG- and laser welding improved themechanical behavior of orthodontic wire

joint configuration and can be

recommended for achieving higher fracture strength



PLASMAWELDING



PR ESSUR EWELDING



SPOTWELDER

THEORY



THEORY Orthodontic spot welders employ the electrode

technique and are used instead of soldering in caseswhere the heating cycle must be very short, in order to prevent changes in the physical properties of thecomponents being joined.

Orthodontic welding is achieved by passing a largeamount of current for a very short duration through anarea of high resistance. Heat is generated of amagnitude great enough to cause melting at theinterface in contact.

Copper electrode - Low resistence



In spot welding the following three properties

of the metal are favorable:

A comparatively low melting point

(approximately 1370° C.),

high electric resistance,

And low conductivity of heat.



VARIABLES A ND THEIR APPLICATION

Welding of stainless steel depends on the

proper use of each of the following three

variables: 1. The current flowing through the circuit.

2. The time during which the current is

allowed to flow. 3. The mechanical pressure applied at the

welding head.

The improper application of these variables can result in either



The improper application of these variables can result in either over- or under welding

UNDE

R WE

LDING - Insufficient current

- The current passed for an insufficient amount of time

- Pressure applied inadequate in approximation.

OVER WELDING - Yield weak a joint as under welding.

- Progressive corrosion.

This occurs when chromium is precipitated at the grain boundaries of each crystal. This process is known as weld

decay.

A satisfactory welded joint is one which is strong, has notundergone oxidation (blackening), and has not been over compressed during fusion.



CLINICAL APPLICATION The use of the spot welder in orthodontics is so common that it

is almost a reflex.

1.The welding surfaces should be clean of all debris materialsand oxides.

2.The surface of each electrode must be smooth, flat, and perpendicular to its long axis. When the electrodes aretogether, they should be in total contact. If not, they should befiled until total contact is achieved. Sparking and localized

over welding will result if interface contact is not uniform.

3.Adjust the welder to settings recommended by themanufacturer .



4. Select the proper electrode for the thickness or shape of the

material to be welded.A

broad electrode should be used for thin material and a narrow one for thick material. This willallow sufficient heat to reach the weld area, but not over weldor oxidize the weldmates.

If too narrow an electrode is used in welding a bracket (thick)to a band (thin), localized over welding will occur in the thinmaterial and under welding in the thick material

Proper electrode selection² a broad electrode for thin materialin conjunction with a narrow electrode for the thicker

material² will result in an even distribution of the weldnugget



5.Insert the weldmates between the electrodes, close themtogether, and depress the weld button.

If sparking is observed, localized over welding has occurred.The electrodes should be checked for size and/or contact. If

black areas are seen at the points where the electrodescontacted the weldmates, over welding has occurred.

(JCO-Volume, 1976 Feb Orthodontic welding-Robert E.Binder. DMD)



A CHECK LIST FOR SUCCESSFUL

WELDING

Mount the electrodes correctly in the welder andadjust with parallel, precision filing to eliminategaps.

Weld together only wires of the same material.

Place the thinner wire in the groove of the lower electrode.

Use 1540 Newtons of pressure.

Set the voltage according to the operatinginstructions.

Use a single electrical impulse.

CONCLUSION



CONCLUSION

The choice of solder material has extreme importance in determining the properties of the soldered joints.

Soldering is still a useful and needed procedure for the joining of metallic parts. The choice of whether free-hand or investment, torch or oven, or preor post ceramic soldering techniques are used, as well as variations in gap

distance and high- or low-fusing soldering alloys, is in many instances upto the discretion of the orthodontist and technician.

The breakage of soldered components is one of the pitfalls associated withthis joining procedure. Even though following guidelines shouldtheoretically prevent them from occurring, solder failures are not rare.

Sestini. et al.13 (2006) found a good tolerance of electrical

resistance and laser welding, while traditional silver solder

was toxic for osteoblast differentiation, fibroblast viability

and keratinocyte growth.



Spot welding is suitable only when the thickness of the band or flangemore or less corresponds to that of the sheet to which it is to be welded,and should not be used to join auxiliary springs and arch wires. One kindof electrode is ample for spot welding in the construction of orthodonticappliances.

In the final analysis, however, the combination of techniques which offer optimum mechanical, physical, and chemical properties or offer thedesired property with the most favorable must be selected.



REFERENCES Phillip¶s science of dental materials- Anusavice

dental materials ±A programmed review of selected topics-W.J.O¶Brien

Dental Materials ±C

raig.

removable appliances ± PC Adams

American journal of orthodontics 1937 may

American journal of orthodontics 1982 February

journal of clinical orthodontics 1969 April

journal of clinical orthodontics 1969 November



THANK YOU

soldering & welding

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