Introduction - University of Technology, Iraq · Roller burnishing pada fillet poros bertingkat guna memberikan tegangan sisa tekan pada permukaan untuk memperbaiki umur fatigue.

Introduction • Surface Technology outline

Surface

Technology

Surfaces Tribology Surface

Treatment

Fabrication of

Microelectronic devices

Chapter 31 • Integrity • Structure • Texture • Roughness

Chapter 32 • Friction • Wear • Lubrication

Chapter 33

• Burnishing • Hardening • Deposition • Implantation • Coatings • Cleaning

Chapter 34

1. Introduction

• After a component is manufactured, all or parts of its surfaces may have to be processed further or coated in order to impart certain properties and characteristics.

• Surface treatment may be necessary to: { Improve resistance to wear, erosion, and indentation

(slideways in machine tools, wear surfaces of machinery, and shafts, rolls, cams, and gears).

{ Control friction (sliding surfaces on tools, dies, bearings, and machine ways).

{ Reduce adhesion (electrical contacts).

1. Introduction

{ Improve lubrication (surface modification to retain lubricants).

{ Improve corrosion and oxidation resistance (sheet metals for automotive or other outdoor uses, gas turbine components, and medical devices).

{ Improve stiffness and fatigue resistance (bearings and multiple-diameter shafts with fillets).

{ Rebuild surfaces on worn components (worn tools, dies, and machine components).

{ Improve surface roughness (appearance, dimensional accuracy, and frictional characteristics).

{ Impart decorative features, color, or special surface texture.

1. Introduction

• Coating of critical surfaces is among important technological developments.

• Consider, for example, applications where temperatures are high and the environment is hostile, such as turbine blades and other components and surfaces of aerospace structures.

1. Introduction

• In advanced propulsion systems, for example, coatings have important functions. { First, they act as a thermal barrier to reduce the

temperature to which parts are subjected. Engine components are expected to withstand

temperatures as high as 1200 C (2200 F). Temperatures are high because the efficiency of gas

turbines increases with increasing gas temperature. { Second, they protect surfaces from oxidation due to

gases such as hot oxygen, and from hydrogen, used for cooling, which otherwise could form brittle compounds.

1. Introduction

• In addition to these physical and chemical requirements, coatings should also be: { Lightweight, thin, and resistant to damage;

{ have good adhesion; and

{ be easily applied to complex external and internal surfaces.

• Several techniques that are suitable and applicable to certain groups of materials have been developed (see next two Tables).

Metal Treatment

Aluminum Chrome plate; anodic coating, phosphate; chromate conversion coating

Beryllium Anodic coating; chromate conversion coating

Cadmium Phosphate; chromate conversion coating

Die steels Boronizing; ion nitriding; liquid nitriding

High-temperature steels

Diffusion

Magnesium Anodic coating; chromate conversion coating

Mild steel Boronizing; phosphate; carburizing; liquid nitriding; carbonitriding; cyaniding

Molybdenum Chrome plate

Metal Treatment

Nickel- and cobalt-base alloys

Boronizing; diffusion

Refractory metals Boronizing

Stainless steel Vapor deposition; ion nitriding; diffusion; liquid nitriding; nitriding

Steel Vapor deposition; chrome plate; phosphate; ion nitriding; induction hardening; flame hardening; liquid nitriding

Titanium Chrome plate; anodic coating; ion nitriding

Tool steel Boronizing; ion nitriding; diffusion; nitriding; liquid nitriding

Zinc Vapor deposition; anodic coating; phosphate; chromate chemical conversion coating

Sumber: After M. K. Gabel and D. M. Doorman in Wear Control Handbook, New

York, ASME, 1980 p. 248.

1. Introduction

• This lecture describes the methods used to modify the surface structure and its properties in order to impart these desirable characteristics.

• The lecture begins with surface hardening techniques involving mechanical or thermal means and continues with different types of coatings that are applied by various means.

• Some of these techniques are also used in the manufacture of semiconductor devices (next week lecture)

1. Introduction

• Finally, you'll learn about cleaning techniques for manufactured surfaces, particularly lubricant residues, before components are processed further, assembled, and the product is placed in service.

• Environmental consideration: regarding the fluids used and the waste material from various surface treatment processes are among important factors to be considered.

2. MECHANICAL SURFACE TREATMENT AND COATING

2. Mechanical Surface Treatment and Coating

• Several techniques are available for mechanically improving the surface properties of finished components.

• The more common ones are described as follow:

{ Shot peening

{ Roller burnishing and ballizing

{ Explosive hardening

{ Cladding (clad bonding)

{ Mechanical plating

2.1 Shot peening

• In shot peening, the workpiece surface is hit repeatedly with a large number of cast steel, glass, or ceramic shot (small balls), making overlapping indentations on the surface.

• This action causes plastic deformation of surfaces, to depths up to 1.25 mm (0.05 in.), using shot sizes ranging from 0.125 mm to 5 mm (0.005 in. to 0.2 in.) in diameter.

2.1 Shot peening

• Because the plastic deformation is not uniform throughout the part's thickness, shot peening imparts compressive residual stresses on the surface, thus improving the fatigue life of the component.

• This process is used extensively on shafts, gears, springs, oil-well drilling equipment, and jet-engine parts (such as turbine and compressor blades).

2.2 Roller burnishing

• In roller burnishing, also called surface rolling, the surface of the component is cold worked by a hard and highly polished roller or rollers.

• This process is used on various flat, cylindrical, or conical surfaces (next Figures).

Roller Burnishing Roller burnishing pada fillet poros bertingkat guna

memberikan tegangan sisa tekan pada permukaan untuk

memperbaiki umur fatigue.

Contoh-contoh roller burnishing

pada (a) permukaan konis dan (b)

permukaan datar, serta peralatan

yang digunakan. Sumber:

Sandvik, Inc.


• Roller burnishing improves surface finish by removing scratches, tool marks, and pits.

• Consequently, corrosion resistance is also improved since corrosive products and residues cannot be entrapped.

• Internal cylindrical surfaces are burnished by a similar process, called ballizing or ball burnishing.

• A smooth ball, slightly larger than the bore diameter, is pushed through the length of the hole.

Ballizing (Ball Burnishing)

Diameter bola sedikit lebih besar dibanding

dimater lubang dalam (internal diameter)


• Roller burnishing is used to improve the mechanical properties of surfaces, as well as the shape and surface finish of components.

• It can be used either singly or in combination with other finishing processes, such as grinding, honing, and lapping.

• Soft and ductile, as well as very hard metals, can be roller burnished.

• Typical applications include hydraulic-system components, seals, valves, spindles, and fillets on shafts.

2.3 Explosive hardening • In explosive hardening, surfaces are subjected to

high transient pressures by placing a layer of explosive sheet directly on the workpiece surface and detonating it.

• The contact pressures developed can be as high as 35 GPa (5 x 106 psi), lasting about 2-3 s.

• Large increases in surface hardness can be obtained by this method, with very little change (less than 5 %) in the shape of the component.

• Railroad rail surfaces can be hardened by this method.

2.4 Cladding (clad bonding)

• In cladding, metals are bonded with a thin layer of corrosion-resistant metal by applying pressure with rolls or other means.

• A typical application is cladding of aluminum (Alclad) in which a corrosion-resistant layer of aluminum alloy is clad over pure aluminum.

• Other applications are steels clad with stainless steel or nickel alloys.

• The cladding material may also be applied through dies, as in cladding steel wire with copper, or by explosives.

2.5 Mechanical plating

• In mechanical plating (also called mechanical coating, impact plating, or peen plating), fine metal particles are compacted over the workpiece surfaces by impacting them with spherical glass, ceramic, or porcelain beads.

• The beads are propelled by rotary means.

• The process is used typically for hardened-steel parts for automobiles, with plating thickness usually less than 0.025 mm (0.001 in.).

3. CASE HARDENING AND HARD FACING

3. Case Hardening and Hard Facing

• Surfaces may be hardened by thermal means in order to improve their frictional and wear properties, as well as resistance to indentation, erosion, abrasion, and corrosion.

• The most common methods are described as:

{ Case hardening, and

{ Hard facing

3.1 Case hardening

• Traditional methods of case hardening (carburizing, carbonitriding, cyaniding, nitriding, flame hardening, and induction hardening) were described in Section 4.10 and are summarized in Table 4.1.

• In addition to the common heat sources of gas and electricity, laser beams are also used as a heat source in surface hardening of both metals and ceramics.

Outline of Heat Treatment Processes for Surface Hardening

Process Metals

hardened

Element

added to

surface

Procedure General

Characteristics

Typical

applications

Carburizing Low-carbon steel

(0.2% C), alloy

steels (0.08–

0.2% C)

C Heat steel at 870–950 °C

(1600–1750 °F) in an

atmosphere of

carbonaceous gases (gas

carburizing) or carbon-

containing solids

(pack carburizing). Then

quench.

A hard, high-carbon

surface is produced.

Hardness 55 to 65

HRC. Case depth <

0.5–1.5 mm ( < 0.020 to

0.060 in.). Some

distortion of part during

heat treatment.

Gears, cams,

shafts, bearings,

piston pins,

sprockets, clutch

plates

Carbonitriding Low-carbon steel C and N Heat steel at 700–800 °C

(1300–1600 °F) in an

atmosphere of

carbonaceous gas and

ammonia. Then quench in

oil.

Surface hardness 55 to

62 HRC. Case depth

0.07 to 0.5 mm (0.003

to 0.020 in.). Less

distortion than in

carburizing.

Bolts, nuts, gears

Cyaniding Low-carbon steel

(0.2% C), alloy

steels (0.08–

0.2% C)

C and N Heat steel at 760–845 °C

(1400–1550 °F) in a

molten bath of solutions

of cyanide (e.g., 30%

sodium cyanide) and

other salts.

Surface hardness up to

65 HRC. Case depth

0.025 to 0.25 mm

(0.001 to 0.010 in.).

Some distortion.

Bolts, nuts, screws,

small gears


Process Metals hardened Element

added to

surface

Procedure General

Characteristics

Typical

applications

Nitriding Steels (1% Al,

1.5% Cr, 0.3% Mo),

alloy steels (Cr,

Mo), stainless

steels, high-speed

tool steels

N Heat steel at 500–600

°C (925–1100 °F) in an

atmosphere of ammonia

gas or mixtures of

molten cyanide salts. No

further treatment.

Surface hardness up

to 1100 HV. Case

depth 0.1 to 0.6 mm

(0.005 to 0.030 in.)

and 0.02 to 0.07 mm

(0.001

to 0.003 in.) for high

speed steel.

Gears, shafts,

sprockets, valves,

cutters, boring

bars, fuel-injection

pump parts

Flame hardening Medium-carbon

steels, cast irons

None Surface is heated with

an oxyacetylene torch,

then quenched with

water spray or other

quenching methods.

Surface hardness 50

to 60 HRC. Case

depth 0.7 to 6 mm

(0.030 to 0.25 in.).

Little distortion.

Gear and sprocket

teeth, axles,

crankshafts, piston

rods, lathe beds

and centers

Induction

hardening

Same as above None Metal part is placed in

copper induction coils

and is heated by high

frequency current, then

quenched.

Same as above Same as above

3.1 Case hardening

• Case hardening, as well as some of the other surface-treatment processes, induce residual stresses on surfaces.

• The formation of martensite in case hardening causes compressive residual stresses on surfaces.

• Such stresses are desirable because they improve the fatigue life of components by delaying the initiation of fatigue cracks.

3.2 Hard facing

• In hard facing, a relatively thick layer, edge, or point of wear-resistant hard metal is deposited on the surface by any of the welding techniques described in Chapters 27 and 28.

• A number of layers are usually deposited (weld overlay).

• Hard coatings of tungsten carbide and chromium and molybdenum carbides can also be deposited using an electric arc (spark hardening).

3.2 Hard facing

• Hard-facing alloys are available as electrodes, rod, wire, and powder.

• Typical applications for hard facing are valve seats, oil-well drilling tools, and dies for hot metalworking.

• Worn parts are also hard faced for extended use.

5. VAPOR DEPOSITION

5. Vapor Deposition

• Vapor deposition is a process in which the substrate (workpiece surface) is subjected to chemical reactions by gases that contain chemical compounds of the materials to be deposited.

• The coating thickness is usually a few m, which is much less than the thicknesses provided by the techniques described in the previous Sections.

5. Vapor Deposition

• The deposited materials may consist of:

{ metals,

{ alloys,

{ carbides,

{ nitrides,

{ borides,

{ ceramics, or

{ various oxides.

5. Vapor Deposition

• The substrate may be:

{ metal,

{ plastic,

{ glass, or

{ paper.

5. Vapor Deposition

• Typical applications are coating:

{ cutting tools,

{ drills,

{ reamers,

{ milling cutters,

{ punches,

{ dies, and

{ wear surfaces.

5. Vapor Deposition

• There are two major deposition processes:

{ physical vapor deposition and

{ chemical vapor deposition.

• These techniques allow effective control of:

{ coating composition,

{ thickness, and

{ porosity.

5.1 Physical vapor deposition • The three basic types of physical vapor

deposition (PVD) processes are: { vacuum or arc evaporation (PV/ARC), { sputtering, and { ion plating.

• These processes are carried out in a high vacuum at temperatures in the range of 200-500 C (400-900 F).

• In physical vapor deposition, the particles to be deposited are carried physically to the workpiece, rather than by chemical reactions as in chemical vapor deposition.

5.1 Physical vapor deposition

• In vacuum evaporation, the metal to be deposited is evaporated at high temperatures in a vacuum and is deposited on the substrate, which is usually at room temperature or slightly higher.

• Uniform coatings can be obtained on complex shapes.

― Vacuum evaporation.


• In PV/ARC, which was developed recently, the coating material (cathode) is evaporated by a number of arc evaporators (three are shown in next Figure), using highly localized electric arcs.


Physical Deposition

Ilustrasi skematik proses physical deposition. Sumber: Cutting Tool

Engineering.

1

2

3


• The arcs produce a highly reactive plasma consisting of ionized vapor of the coating material.

• The vapor condenses on the substrate (anode) and coats it.

• Applications for this process may be: { functional (oxidation-resistant coatings for high

temperature applications, electronics, and optics)

{ or decorative (hardware, appliances, and jewelry).



• In sputtering, an electric field ionizes an inert gas (usually argon).

• The positive ions bombard the coating material (cathode) and cause sputtering (ejecting) of its atoms.

• These atoms then condense on the workpiece, which is heated to improve bonding (next Figure).

― Sputtering


Ilustrasi skematik proses sputtering. Sumber: ASM International

― Sputtering


• In reactive sputtering, the inert gas is replaced by a reactive gas, such as oxygen, in which case the atoms are oxidized and the oxides are deposited.

• Carbides and nitrides are also deposited by reactive sputtering.

• Very thin polymer coatings can be deposited on metal and polymeric substrates with a reactive gas, causing polymerization of the plasma.

― Sputtering


• Radio-frequency (RF) sputtering is used for nonconductive materials such as electrical insulators and semiconductor devices.

― Sputtering


• Ion plating is a generic term describing the combined processes of sputtering and vacuum evaporation.

• An electric field causes a glow discharge, generating a plasma (next Figure).

• The vaporized atoms in this process are only partially ionized.

― Ion Plating


Ilustrasi skematik perlengkapan pelapisan ion. Sumber: ASM International.

― Ion Plating

5.2 Chemical vapor deposition • Chemical vapor deposition (CVD) is a

thermochemical process.

Ilustrasi skematik proses chemical vapor deposition.

5.2 Chemical vapor deposition

• In a typical application, such as coating cutting tools with titanium nitride (TiN), the tools are placed on a graphite tray and heated to 950-1050 C (1740-1920 F) at atmospheric pressure in an inert atmosphere.

• Titanium tetrachloride TiCl4 (a vapor), hydrogen, and nitrogen are then introduced into the chamber.

• The chemical reactions form titanium nitride on the tool surfaces.


• For coating with titanium carbide, methane is substituted for the gases.

• Chemical vapor deposition coatings are usually thicker than those obtained from PVD.

• A typical cycle for CVD is long, consisting of

{ 3 hours of heating,

{ 4 hours of coating, and

{ 6 - 8 hours of cooling to room temperature.


• The thickness of the coating depends on: { the flow rates of the gases used,

{ time, and

{ temperature.

• The CVD process is also used for producing diamond coatings (see Section 13) without using any binders, unlike polycrystalline diamond films which use 1 to 10 % binder materials.

6. ION IMPLANTATION

6. Ion Implantation

• In ion implantation, ions (charged atoms) are introduced into the surface of the workpiece material.

• The ions are accelerated in a vacuum to such an extent that they penetrate the substrate to a depth of a few m.

• Ion implantation (not to be confused with ion plating) modifies surface properties by increasing surface hardness and improving friction, wear, and corrosion resistance.

6. Ion Implantation

• This process can be controlled accurately, and the surface can be masked to prevent ion implantation in unwanted places.

• Ion implantation is particularly effective on materials such as aluminum, titanium, stainless steels, tool and die steels, carbides, and chromium coatings.

• Typical applications include cutting and forming tools, dies and molds, and metal prostheses such as artificial hips and knees.

6. Ion Implantation

• When used in specific applications, such as semiconductors (next week lecture), this process is called doping (meaning alloying with small amounts of various elements).

7. DIFFUSION COATING

7. Diffusion Coating

• Diffusion coating is a process in which an alloying element is diffused into the surface of the substrate, thus altering its properties.

• Such elements can be supplied in solid, liquid, or gaseous states.

• This process acquires different names, depending on the diffused element, as you can see in Table 4.1, which describes diffusion processes such as carburizing, nitriding, and boronizing.


Process Metals

hardened

Element

added to

surface

Procedure General

Characteristics

Typical

applications

Carburizing Low-carbon

steel (0.2%

C), alloy

steels (0.08–

0.2% C) C

Heat steel at 870–950 °C

(1600–1750 °F) in an

atmosphere of

carbonaceous gases (gas

carburizing) or carbon-

containing solids

(pack carburizing). Then

quench.

A hard, high-carbon

surface is produced.

Hardness 55 to 65

HRC. Case depth <

0.5–1.5 mm ( < 0.020 to

0.060 in.). Some

distortion of part during

heat treatment.

Gears, cams,

shafts, bearings,

piston pins,

sprockets, clutch

plates

Nitriding Steels (1% Al,

1.5% Cr, 0.3%

Mo), alloy

steels (Cr,

Mo), stainless

steels, high-

speed tool

steels

N

Heat steel at 500–600 °C

(925–1100 °F) in an

atmosphere of ammonia

gas or mixtures of molten

cyanide salts. No further

treatment.

Surface hardness up to

1100 HV. Case depth

0.1 to 0.6 mm (0.005 to

0.030 in.) and 0.02 to

0.07 mm (0.001

to 0.003 in.) for high

speed steel.

Gears, shafts,

sprockets, valves,

cutters, boring

bars, fuel-injection

pump parts

Boronizing Steels

B

Part is heated using

boron-containing gas or

solid in contact with part.

Extremely hard and

wear resistant surface.

Case depth 0.025–

0.075 mm (0.001–

0.003 in.).

Tool and die steels

8. ELECTROPLATING, ELECTROLESS PLATING, AND ELECTROFORMING

8. Electroplating, Electroless Plating, and Electroforming

• Plating, as in other coating processes, imparts:

{ resistance to wear and corrosion,

{ high electrical conductivity,

{ better appearance and reflectivity, and

{ similar desirable properties.

8.1 Electroplating

• In electroplating, the workpiece (cathode) is plated with a different metal (anode), while both are suspended in a bath containing a water-base electrolyte solution.

• Although the plating process involves a number of reactions, basically the metal ions from the anode are discharged under the potential from the external source of electricity, combine with the ions in the solution, and are deposited on the cathode.

8.1 Electroplating

(a) Ilustrasi skematik proses electroplating. (b) Contoh-contoh part hasil proses

electroplating. Sumber: Courtesy of BFG Engineering

(a)

8.1 Electroplating

• All metals can be electroplated, with thicknesses ranging from a few atomic layers to a maximum of about 0.05 mm (0.002 in.).

• Complex shapes may have varying plating thicknesses.

• Some design guidelines for electroplating are shown in the next Figure.

Petunjuk Electroplating

(a) Ilustrasi skematik pelapisan yang tidak merata (exaggerated) pada komponen chasis

electroplating. (b) Petunjuk desain untuk electroplating. Perhatikan bahwa sudut tajam

luar maupun dalam harus dihindarkan untuk kesamaan ketebalan lapisan. Sumber: ASM

International.

8.1 Electroplating • Chemical cleaning and degreasing and thorough rinsing of the workpiece prior to plating are essential.

• The parts are placed on racks or in a barrel (bulk plating) and lowered into the plating bath.

• Common plating materials are chromium, nickel, cadmium, copper, zinc and tin.

• Chromium plating is carried out by first plating the metal with copper, then with nickel, and finally with chromium.

• Hard chromium plating is done directly on the base metal and has a hardness up to 70 HRC.

8.1 Electroplating

• This method is used to improve wear and corrosion resistance of tools, valve stems, hydraulic shafts, and diesel- and aircraft engine cylinder liners-and also for rebuilding worn parts.

• Typical electroplating applications are copper plating aluminum wire and phenolic boards for printed circuits, chrome plating hardware, tin plating copper electrical terminals for ease of soldering, and components requiring resistance to wear and corrosion and good appearance.

8.1 Electroplating

• Because they do not develop oxide films, noble metals (such as gold, silver, .and platinum) are important electroplating materials for the electronics and jewelry industries.

• Plastics such as ABS, polypropylene, polysulfone, polycarbonate, polyester, and nylon also can be electroplated.

8.1 Electroplating

• Because they are not electrically conductive, plastics must be preplated by such processes as electroless nickel plating (see Section 8.2).

• Parts to be coated may be simple or complex, and size is not a limitation.

8.2 Electroless plating

• Electroless plating is carried out by chemical reactions, without the use of an external source of electricity.

• The most common application utilizes nickel, although copper is also used.

• In electroless nickel plating, nickel chloride (a metallic salt) is reduced with sodium hypophosphite as the reducing agent-to nickel metal, which is then deposited on the workpiece.


• The hardness of nickel plating ranges between 425 HV and 575 HV, and can be heat treated to 1000 HV.

• The coating has excellent wear and corrosion resistance.

• Cavities, recesses, and the inner surfaces of tubes can be plated successfully.

• This process can also be used with nonconductive materials, such as plastics and ceramics.


• Electroless plating is more expensive than electroplating.

• However, unlike electroplating, the coating thickness in electroless plating is uniform (see Fig. 33.8).

8.3 Electroforming

• A variation of electroplating is electroforming, which actually is a metal fabricating process.

• Metal is electrodeposited on a mandrel (also called mold or matrix), which is then removed.

• Thus the coating itself becomes the product. • Simple and complex shapes can be produced by

electroforming, with wall thicknesses as small as 0.025 mm (0.001 in.).

• Parts may weigh from a few grams to as much as 270 kg (600 lb).

8.3 Electroforming a) Contoh urutan dalam proses

electroforming. (1) Mandrel

dipilih dengan ukuran nominal

yang tepat, (2) Mandrel

kemudian dimesin sesuai

dengan geometri yang

diinginkan (dalam hal ini

bellows). (3) Logam yang

diinginkan kemudian di

lapiskan (secara electroplating)

ke permukaan mandrel. (4)

Material yang telah dilapis

kemudian ditrim jika

diperlukan. (5) Mandrel

kemudian dibuang chemical

machining.

8.3 Electroforming

(b) Beberapa contoh part yang dibuat dengan

electroforming. Sumber: Courtesy of Servometer, LLC.

8.3 Electroforming

• Mandrels are made from a variety of metallic (such as zinc or aluminum) or nonmetallic materials, which can be made electrically conductive with proper coatings.

• Mandrels should be physically removable without damaging the electroformed part.

• They may also be made of low-melting alloys, wax, or plastics, which can be melted away or dissolved with suitable chemicals.

8.3 Electroforming

• The electroforming process is particularly suitable for low production quantities or intricate parts (such as molds, dies, waveguides, nozzles, and bellows) made of nickel, copper, gold, and silver.

• It is also suitable for aerospace, electronics, and electro optics applications.

• Production rates can be increased with multiple mandrels.

10. CONVERSION COATING

10. Conversion coating

• Conversion coating, also called chemical reaction priming, is a coating that forms on metal surfaces as a result of chemical or electrochemical reactions.

• Various metals, particularly steel, aluminum, and zinc, can be conversion coated.

• Oxides that naturally form on their surfaces are a form of conversion coating.

• Phosphates, chromates, and oxalates are used to produce these coatings.


• They are used for purposes such as corrosion protection, prepainting, and decorative finish.

• An important application is in conversion coating of workpieces as a lubricant carrier in cold forming operations (see Section 12).

• The two common methods of coating are immersion and spraying.

• The equipment involved depends on the method of application, the type of product, and considerations of quality.


• As the name implies, coloring involves processes that alter the color of metals, alloys, and ceramics.

• It is caused by the conversion of surfaces (by chemical, electrochemical, or thermal processes) into chemical compounds, such as oxides, chromates, and phosphates.

• An example is blackening of iron and steels, a process that involves solutions of hot caustic soda, resulting in chemical reactions that produce a lustrous, black oxide film on surfaces.

11. HOT DIPPING

11. Hot Dipping

• In hot dipping, the workpiece, usually steel or iron, is dipped into a bath of molten metal, such as:

{ zinc (for galvanized-steel sheet and plumbing supplies),

{ tin (far tinplate and tin cans for food containers), aluminum (aluminizing), and

{ terne (lead alloyed with 10 to 20 % tin).

11. Hot Dipping

• Hot-dipped coatings on discrete parts or sheet metal provide long-term corrosion resistance to galvanized pipe, plumbing supplies, and many other products.

• A typical continuous hot-dipped galvanizing line for steel sheet is shown in the next Figure.

Pencelupan Panas Flowline untuk

galvanizing dengan

pencelupan panas

kontinyu lembaran baja.

Peralatan las (kiri atas)

digunakan untuk

mengelas ujung ujung

gulungan agar aliran

material kontinyu.

Sumber: American Iron

and Steel Institute.

11. Hot Dipping

• The rolled sheet is first cleaned electrolytically and scrubbed by brushing.

• The sheet is then annealed in a continuous furnace with controlled atmosphere and temperature and dipped in molten zinc at about 450 C (840 F ) .

• The thickness of the zinc coating is controlled by a wiping action from a stream of air or steam, called air knife (similar to air-drying cars in car washes).

11. Hot Dipping

• The coating thickness is usually given in terms of coating weight per unit surface area of the sheet, typically 150-900 g/m2 (0.5-3 oz/ft2).

• Service life depends on the thickness of the zinc coating and the environment to which it is exposed.

• Various precoated sheet steels are used extensively in automobile bodies.

• Proper draining to remove excess coating materials is an important consideration.

12. PORCELAIN ENAMELING, CERAMIC COATING, AND ORGANIC COATINGS

12. Porcelain Enameling, Ceramic Coating, and Organic Coatings

• Metals may be coated with a variety of glassy (vitreous) coatings to provide corrosion and electrical resistance and for service at elevated temperatures.

• These coatings are usually classified as porcelain enamels and generally include enamels and ceramics.

• The word enamel is also used for glossy paints, indicating a smooth, hard coating.


• Porcelain enamels are glassy inorganic coatings consisting of various metal oxides.

• A fully developed art by the Middle Ages, enameling involves fusing the coating material on the substrate by heating them both to 425-1000 C (800-1800 F) to liquefy the oxides.

• Depending on their composition, enamels have varying resistances to alkali, acids, detergents, cleansers, and water-and come in different colors.


• Typical applications for porcelain enameling are:

{ household appliances,

{ plumbing fixtures,

{ chemical processing equipment,

{ signs,

{ cookware, and

{ jewelry.


• Porcelain enamels are also used as protective coatings on jet-engine components.

• The coating may be applied by dipping, spraying, or electro-deposition, and thicknesses are usually 0.05-0.6 mm (0.002-0.025 in.).

• Metals that are coated are typically steels, cast iron, and aluminum.

• Glasses are used as lining for chemical resistance, and the thickness is much greater than in enameling.


• Glazing is the application of glassy coatings on ceramic wares to give them decorative finishes and to make them impervious to moisture.

• Ceramic coatings such as aluminum oxide or zirconium oxide are applied, with the use of binders, to the substrate at room temperature.

• Such coatings act as thermal barriers and have been applied (generally by thermal spraying techniques) to hot extrusion dies, turbine


• Metal surfaces may be coated or precoated with a variety of organic coatings, films, and laminates to improve appearance, eye appeal, and corrosion resistance.

• Coatings are applied to the coil stock on continuous lines, with thicknesses generally of 0.0025-0.2 mm (0.0001 -0.008 in.).

• Such coatings have a wide range of properties: flexibility, durability, hardness, resistance to abrasion and chemicals, color, texture, and gloss.


• Coated sheet metal is subsequently formed into various products, such as:

{ TV cabinets,

{ appliance housings,

{ paneling,

{ shelving,

{ residential building siding,

{ gutters, and

{ metal furniture.


• More critical applications involve, for example, naval aircraft which are subjected to high humidity, rain, seawater, pollutants (such as from ship exhaust stacks), aviation fuel, deicing fluids, battery acid, and which are also impacted by particles such as dust, gavel, stones, and deicing salts.


• For aluminum structures, organic coatings have consisted typically of an epoxy primer and a polyurethane topcoat, with a lifetime of four to six years.

• Primer performance is very important for coating durability; consequently much research is being conducted to develop improved coating materials.

Example: Ceramic coatings for high temperature applications

• Characteristics such as wear resistance and thermal and electrical insulation, particularly at elevated temperatures, can be imparted on products by ceramic coatings rather than imparting these properties to the base metals or materials themselves.

• Selecting materials with such bulk properties can be expensive or may not meet the structural strength requirements in a particular application.


• Thus, for example, a wear-resistance component does not have to be made completely from a wear-resistant material, since the properties of only a thin layer on the component's surface are relevant for wear.

• Consequently, coatings have important applications.

• The table below shows various ceramic coatings and typical applications at elevated temperatures.

Lapisan keramik untuk aplikasi suhu tinggi

Property Type of ceramic Application

Wear resistance Chromium oxide Aluminum oxide Aluminum titania

Pumps, turbine shafts, seals, compressor rods for the petroleum industry; plastics extruder barrels; extrusion dies

Thermal insulation Zirconium oxide (yttria stabilized) Zirconium oxide (calcia stabilized) Magnesium zirconate

Fan blades, compressor blades, and seals for gas turbines; valves, pistons, and combustion heads for automotive engines

Electrical insulation Magnesium aluminate Aluminum oxide

Induction coils, brazing fixtures, general electrical applications


• These coatings may be applied either singly or in layers, as is done in multiple-layer coated cutting tools.

Multiphase Coatings

Multiphase coatings diatas karbida

tungsten. Tiga lapisan oksida

aluminium dipisahkan oleh lapisan

sangat tipis Titanium Nitrit. Sisipan

dengan jumlah lapisan sebanyak tiga

belas lapis telah dibuat. Ketebalan

lapisan biasanya berkisar antara 2

sampai 10 μm. Source: Courtesy of

Kennametal, Inc., and Manufacturing

Engineering Magazine, Society of

Manufacturing Engineers.

13. DIAMOND COATING

13. Diamond Coating

• The properties of diamond that are relevant to manufacturing engineering were described in Section 8.7.

• Important advances have been made in diamond coating of metals, glass, ceramics, and plastics, using various chemical and plasma-assisted vapor deposition processes and ion-beam enhanced deposition

Type General Characteristics

Diamond Hardest substance known; available as single crystal or

polycrystalline form; used as cutting tools and abrasives

and as dies for fine wire drawing.

13. Diamond Coating

• Techniques have also been developed to produce free-standing diamond films on the order of 1 mm (0.040 in.) thick and up to 125 mm (5 in.) in diameter, including smooth and optically clear diamond film (unlike the hazy gray diamond film formerly produced).

13. Diamond Coating

• Development of these techniques, combined with important properties of diamond such as:

{ hardness,

{ wear resistance,

{ high thermal conductivity, and

{ transparency to ultraviolet light and microwave frequencies,

have enabled the production of various aerospace and electronic parts and components.

13. Diamond Coating • Examples of diamond-coated products are:

{ scratchproof windows (such as for aircraft and missile sensors to protect against sandstorms), sunglasses,

{ cutting tools (such as drills and end mills),

{ calipers,

{ surgical knives,

{ razors,

{ electronic and infrared heat seekers and sensors,

{ light-emitting diodes,

{ diamond-coated speakers for stereo systems,

{ turbine blades, and

{ fuel-injection nozzles.

13. Diamond Coating

• Studies are continuing on growing diamond films on crystalline copper substrate by implantation of carbon ions.

• An important application is in making computer chips.

• Diamond can be doped to form p- and n-type ends on semiconductors to make transistors (next lecture), and its high thermal conductivity allows closer packing of chips than silicon or gallium-arsenide chips, thus significantly increasing the speed of

14. PAINTING

14. Painting

• Because of its decorative and functional properties (such as environmental protection), low cost, relative ease of application, and the range of available colors, paint is widely used as a surface coating.

• Engineering applications of painting range from all types of machinery to automobile bodies.

14. Painting

• Paints are classified as:

{ enamels, which produce a smooth coat and dry with a glossy or semiglossy appearance;

{ lacquers, which form a film by evaporation of a solvent; and

{ water-basepaints, which are easily applied, but have a porous surface, absorb water, and are not as easily cleaned as other paints.

14. Painting • Paints are now available with good resistance

to abrasion, fading, and temperature extremes; they are easy to apply and dry quickly.

• Selection of a particular paint depends on specific requirements.

• Among these are resistance to mechanical actions (abrasion, marring, impact, and flexing) or to chemical actions (acids, solvents, detergents, alkalis, fuels, staining, and general environmental attack).

• Common methods of applying paint are

Pengecatan

Metoda aplikasi pengecatan: (a) dip coating, (b) flow coating, dan (c) electrostatic spraying.

Sumber: Society of Manufacturing Engineers.

14. Painting

• In electrocoating or electrostatic spraying, paint particles are charged electrostatically and are attracted to the workpiece surfaces, producing a uniformly adherent coating.

• Unlike conventional spraying, in which as much as 70 % of the paint may be lost, in electrostatic spraying the loss can be as low as 10 %.

• However, deep recesses and corners are difficult to coat by this method.

15. SURFACE TEXTURING

15. Surface Texturing

• As seen throughout the preceding lectures, each manufacturing process, such as casting, forging, powder metallurgy, injection molding, machining, grinding, polishing, electrical-discharge machining, grit blasting, and wire brushing, produces a certain surface texture and appearance.

• Obviously some of these processes can be used to modify the surface produced by a previous process; for example, grinding some surfaces of a cast part.

15. Surface Texturing • However, manufactured surfaces can further

be modified by secondary operations for technical, functional, optical, or aesthetic reasons.

• Called surface texturing, these additional processes generally consist of:

a.etching, using chemicals or sputtering techniques,

b.electric arcs, and

c. atomic oxygen, which reacts with surfaces and produces fine conelike surface textures.

• The possible adverse effects of any of these processes on material properties and

16. CLEANING SURFACES

16. Cleaning surfaces

• We have stressed the importance of surfaces and the influence of deposited or adsorbed layers of various elements and contaminants on surfaces.

• A clean surface can have both beneficial and detrimental effects.

16. Cleaning surfaces • Although an unclean surface may reduce the

tendency for adhesion and galling, in general cleanliness is essential for more effective application of metalworking fluids, coating and painting, adhesive bonding, welding, brazing, soldering, reliable functioning of manufactured parts in machinery, food and beverage containers, storage, and assembly operations.

• Cleaning involves removal of solid, semisolid, or liquid contaminants from a surface, and it is an important part of manufacturing

16. Cleaning surfaces • The word clean, or the degree of cleanliness of

a surface, is somewhat difficult to define.

• How, for example, would you test the cleanliness of a fork or dinner plate?

• Two simple and common tests are based on:

{ Wiping with a clean cloth and observing any residues on the cloth, as we all have done at one time or another.

{ Observing whether water continuously coats the surface. If water collects as individual droplets, the surface is not clean (water break test). Test this phenomenon yourself by wetting dinner plates that have been cleaned to varying degrees.


• The type of cleaning process required depends on the type of contaminants to be removed.

• Contaminants, also called soils, may consist of rust, scale, chips and other metallic and nonmetallic debris, metalworking fluids, solid lubricants, pigments, polishing and lapping compounds, and general environmental elements.

16. Cleaning surfaces • Cleaning processes. Basically there are two types

of cleaning methods: mechanical and chemical.

• Mechanical cleaning methods consist of physically disturbing the contaminants, as with wire or fiber brushing, dry or wet abrasive blasting, tumbling, and steam jets.

• Many of these processes are particularly effective in removing rust, scale, and other solid contaminants.

• Ultrasonic cleaning may also be placed in this category.


• Chemical cleaning usually involves the removal of oil and grease from surfaces.

• It consists of one or more of the following processes:

{ Solution. The soil dissolves in the cleaning solution.

{ Saponification. A chemical reaction that converts animal or vegetable oils into a soap that is soluble in water.

{ Emulsification. The cleaning solution reacts with the soil or lubricant deposits and forms an emulsion. The soil and the emulsifier then become


{ Dispersion. The concentration of soil on the surface is decreased by surface-active materials in the cleaning solution.

{ Aggregation. Lubricants are removed from the surface by various agents in the cleaner and collect as large dirt particles.

16. Cleaning surfaces • Some common cleaning fluids are used in

conjunction with electrochemical processes for more effective cleaning.

• These fluids include:

{ Alkaline solutions are a complex combination of water-soluble chemicals. They are the least expensive and most widely used in manufacturing operations. Small parts may be cleaned in rotating drums or barrels. Most parts are cleaned on continuous conveyors by spraying them with the solution and then rinsing them with water.

{ Emulsions generally consist of kerosene and oil in water and various types of emulsifiers.


{ The most common solvents are petroleum solvents, chlorinated hydrocarbons and mineral spirits. Solvents are generally used for short runs; fire and toxicity are major hazards.

{ Parts are subjected to hot vapors of chlorinated solvents to remove oil, greases, and wax. The solvent is boiled in a container and then condensed. The process is simple and the cleaned parts are dry.

{ Various acids, salts, and organic compound mixtures are effective in cleaning parts covered with heavy paste or oily deposits and rust.


• Cleaning discrete parts having complex shapes can be difficult.

• Design engineers should be aware of this difficulty and provide alternative designs, such as avoiding deep blind holes, making several smaller components instead of one large component that may be difficult to clean, and providing appropriate drain holes in the part to be cleaned.


• The proper treatment and disposal of cleaning fluids, as well as the various fluids and waste materials from the processes described in this chapter, are among important considerations for environmentally safe manufacturing operations.

Introduction - University of Technology, Iraq · Roller burnishing pada fillet poros bertingkat guna memberikan tegangan sisa tekan pada permukaan untuk memperbaiki umur fatigue.

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