Types of Metal Finishing

Chapter 1: Principle of Metal Finishing

This chapter will discuss what metal finishing is and the processes involved.

What is Metal Finishing?

Metal finishing describes various procedures or processes that can be as simple as buffering to adding a special type of coat to the substrate. Included in the description of metal finishing are a number of cleaning methods, polishing methods as well as other procedures which are meant to improve and enhance the surface of the specific metal product.

Electroplating is used for the finishing process. This process is when an electrical current is used to put metal ions right on the substrate. Although it may look different, the process of plating and finishing are often thought of as being similar.

The plating process is an electronic way of placing metal on a surface that is conductive and is one of the various finishing methods being applied today. The term finishing is very broad and points to a range of processes meant to improve and enhance the physical appearance of the metal product. These different kinds of metal products are available in homes and at work.

Taken underground in its original and raw form, metal is very crude, hard, and unattractive. To make the best use of metal, it needs to be polished, finished, and processed. These methods are done through various processes and procedures. The last stage of metal work is the finishing process.

During this process the metal product goes through different techniques to make it look attractive and much appealing. The process of metal finishing reduces wear greatly on metal products.

Metal finishing also maximizes its electrical conductivity, durability, chemical resistance, electrical resistance, and increases its vulcanization. Although the metal finishing process adds to the aesthetic look of the metal, it also helps in industrial scenarios like resistance to torque and soldering.

A major concern for all metals is their vulnerability to corrosion. The process of finishing greatly reduces chances of corrosion and also serves as a primer when paint is added. Additionally, thorough finishing can minimize cleaning with the aim of removing any defects or deformities. Industries that produce metals have many finishing methods they use to maximize the longevity and durability of their metal products. The finishing process is very important and an essential part of the last steps in making the best quality metal products.

Choosing a Metal Finishing Process or Method

Considering all the factors which are necessary for coming out with a manufacturing decision, it is very important to select a metal finishing procedure that meets the required standards of the end product. All of the metal finishing procedures apply a special treatment to the surface of the metal.

They also apply and make certain adjustments to the surface of the metals by means of a mechanical way. The appropriate procedure to use has to be considered very carefully as each has its advantages.

The process of finishing is the final step in producing the quality appearance and texture for a metal product that fulfills its design as well as giving coverage from rust and tarnishing whilst maximizing the metal product’s strength, thickness, durability, and hardness.

Determining the method of finishing to use can be very crucial to the value of the end product. The first consideration to be taken into account is the cost. The typical costs of the metal finishing process are water, type of coatings, energy expended, various consumables, labor, cleanup, and the amount of waste.

Aside from the costs associated with the task at hand, fixed cost of the maintenance and operation of the equipment being used.one other main factor to be taken into consideration is the type of metal that is to be to be fabricated, which can cover a wide range from stainless steel metals to different types of aluminum. In order to make the end result much more profitable, each of these elements has to be taken into consideration very carefully. Another factor or aspect of the cost decision to note is the amount of time that will be required to finish fabrication.

The process of electroplating can be too slow and consume time while the buffing and polishing can be done instantly. This crucial stage of the finishing process determines the ability to keep up with delivery deadlines and it greatly affects the supply chain.

Chapter 2: Types of Metal Finishing Processes

The process of metal finishing is a very crucial part of metal product production. There are several types of metal finishing such as metal plating, chemical finishing or coating, grinding, buffing, electroplating, and sandblasting. Each process has basic steps with all processes beginning with surface preparation.

Metal finishing processes can include anything from technical processes to buffers. The procedure or method used depends on the requirements of the end product, the structure of the metal, and the use of the product.

Surface Preparation

The key to successful metal finishing is the preparation of the surface to be finished. If improperly prepared, coatings, platings, and other materials will not adhere to the surface. The first step in the preparation process is cleaning the surface of the metal, which can be completed with a variety of chemicals, mineral spirits, or simply wiping the surface with clean dry cloth. A light sanding may be necessary to de-gloss the surface.

Checking the surface of a metal for rust is essential since it will prevent the application of a finish and deteriorate the appearance of the final product. Rust can be removed by sanding, using a wire brush, or a rust removing chemical.

Four Basic Steps for Surface Preparation

• Disassembly – Disassembly is necessary for complex and intricate pieces that have multiple parts. The process of disassembling ensures that all portions of an object will receive finishing.
• Stripping - Stripping is the next step in sanding and can be completed using various chemicals that will remove excess material but not damage the workpiece.
• Polishing – Polishing involves the use of a buffer or polishing wheel. It assists in smoothing irregular surfaces and eliminates any oxidation in the metal surface.
• Cleaning – Cleaning is essential to remove any contaminants that may have adhered to the metal surface and can be completed using mineral spirits, organic solvents, various types of aqueous cleaners, and rinsings.

Plating

Metal plating involves depositing a layer of metal on the substrate of a conductive metal. It is used to coat and protect metals and completed using electroplating or electroless plating. The process of metal plating enhances the properties of the base metal and improves its functionality and appearance.

There are several steps involved in metal plating including pretreatment and preparation, set up, the plating process, and post treatment. The list of metals that are used for plating finishes include zinc, copper, gold, chrome, nickel, and tin, to name a few.

Aside from electroplating and electroless plating, other methods of plating are immersion, carburizing, physical vapor deposition (PVD), and plasma spray coating. Metal plating is an essential part of ensuring that products have an excellent appearance and resistance to wear and tear, corrosion, and rust.

Types of Metals Used for Plating

Metal plating makes a metal stronger and gives it a longer life span. There are several options when it comes to choosing the type of metal that will be applied to a substrate. Additionally, the selection process should include the reasons for applying the metal plating, whether it is for appearance and decorative purposes or for enhanced strength, durability, and solderability.

Chrome Plating - Chrome plating is an electroplating process that involves the use of hexavalent chromium, chromium sulfate, or chromium chloride, which are plated to the substrate.

Hard Chrome Plating - Hard chrome plating is an electroplating process that uses a chromic acid solution to deposit chrome plating with a thickness of 2 microns (µ) up to 250 µ. The types of hard chromes include micro-cracked chromium, micro-porous chromium, porous chromium and crack free chromium.

Nickel Plating - Nickel plating is completed by electroless plating of a nickel phosphorus alloy with the percentage of phosphorus varying between 2% up to 14%. Higher levels of phosphorus increases the hardness and corrosion resistance of the plating.

Teflon (PTFE) Plating - Teflon plating uses the electroless plating process to co-deposit nickel phosphorus and polytetrafluoroethylene (PTFE) on the metal substrate. The plated finish has a dull silver gray appearance with the properties of nickel and the lubricity of PTFE.

Tin Plating - Tin plating involves electrodeposition and hot dipping of tin with brass or copper added to the tin to improve solderability. The properties that tin provides as a coating, aside from solderability, include non-toxicity, ductility, and resistance to corrosion. It is commonly applied to copper and nickel.

Zinc Plating - The process of zinc plating is often referred to as electro-galvanization since zinc is used in the galvanizing of steel. It is applied as part of an electroplating process that gives the substrate resistance to oxidation and corrosion.

Gold Plating - Gold plating is an electroplating process that places a thin layer of gold on silver, steel, or copper. There are different levels of gold plating that depend on the purity of the plated metal and the quality of the base metal.

Conversion Coating

Conversion coating is a surface passivation process that changes the surface of a metal. It produces a metal oxide layer that protects against corrosion, rust, and wear. The conversion coating process uses techniques and processes involving acidic baths or electricity to form a metal oxide coating to protect the substrate from oxygen and corrosion. Examples of conversion coatings are, iridite on aluminum, chromate, phosphate, and black oxide. A special category of conversion coating is anodizing.

With conversion coating, a chemical reaction takes place on the surface of the metal substrate. Unlike plating that places a new layer of metal on the substrate, conversion coating changes the surface layer of a metal. It is often used as preparation for plating or painting.

Conversion coating uses some of the substrate metal to form its coating. During the process, the coating grows into the part and expands as it forms. Conversion coating gets into a part during its formation and gives it greater volume compared to the original metal.

Materials Used for Conversion Coating

Alodine Coating - Alodine coating is a chromate chemical conversion coating that is used to protect aluminum and other metals from corrosion. It creates a base with better adhesion and protects against the loss of electrical conductivity. Alodine coatings have a thickness of 0.00001 inch to 0.00004 inch (0.25 µm to 1 μm).

Black Oxide Coating - Black oxide is a conversion coating that gives parts a matte black appearance and is applied using an electrochemical or chemical treatment process. It forms from a reaction with a part that has been immersed in an alkaline aqueous salt solution at 285o F (140o C). Reaction between iron in the metal and the oxide bath forms a compound known as magnetite. A black oxide coating improves a parts appearance, reduces light reflection, and enhances dimensional stability.

Electroplating

Electroplating or electrodeposition uses electric current to dissolve metal and place its ions on the surface of a workpiece. The four basic components of electroplating are an anode, cathode, solution, and power source. The anode is a positively charged electrode that forms the plating. The cathode is the substrate to be plated and acts as a negatively charged electrode.

The solution is electrolytic and contains metal salts, such as copper sulfate, to facilitate the flow of electricity in the electroplating process. Electric current is added by a power source that applies electrical current to the anode. When the anode and cathode are placed in the solution and DC current is supplied, the metal oxidizes and allows metal atoms to dissolve in the solution. Ions from the metal move to the negatively charged substrate.

Electropolishing

Electropolishing, like electroplating, uses an electrical current and chemicals to polish metal parts. It removes material from the surface of a metal with a 0.0002 accuracy. Electropolishing improves the surface finish of metals, removes tiny, minute imperfections, and deburrs and deeply cleans metal surfaces to the microscopic level.

Parts to be treated are lowered into a tank filled with an electrolyte solution of phosphoric and sulfuric acid. Metal plates that line the tank serve as cathodes for running a positive DC electric current through the tank to remove a small amount of metal from metal pieces. Treated parts have a clean, smooth, passivated surface and are rinsed several times to remove any residual electrolyte solution.

Electropolishing is a passivation process that removes free iron from a metal surface and gets below the metal skin and levels the peaks and valleys of the surface. It has proven to be a more effective passivation process than traditional passivation.

Hot Dipped Galvanizing

Hot dipped galvanizing is used to coat steel by lowering it into a molten zinc bath. The three basic steps of the process are surface preparation, galvanizing, and inspection. The critical step in the process is surface preparation, which involves degreasing, pickling, and fluxing where pickling is an acidic bath while fluxing removes oxides and coatings. Without proper surface preparation, the zinc will not adhere to the surface of the steel.

Once properly prepared, the steel is dipped into a molten zinc bath of approximately 98% zinc at 830° F. The steel is placed in the zinc bath such that the coating can reach every portion of the steel.

Metalized Sprayed Coating

Metalized sprayed coatings, also known as thermal spray coating, is a method for providing corrosion protection. It involves spraying heated metals that are heated electrically or using a flame and applying them to various types of surfaces from concrete to steel. Metalized coatings can be applied in any environmental conditions. Once the metal is applied to a surface, it instantly cures.

The process of metalized sprayed coating is favored over other coating processes, such as epoxy, due to its durability and extremely long service life. Structures that have been metalized have resistance to the effects of impact and ultraviolet rays. The metals that are most commonly used as metalized sprayed coatings are zinc, aluminum, and alloys of those metals.

Anodizing Process

The name or term anodizing is defined or usually described as the conversion coating that is applied to the aluminum metal. Anodizing gives a description of the conversion coating process that is applied to magnesium, titanium, niobium, or the tantalum parts in particular. A major distinguishing factor between anodizing and the general conversion coating processes is that anodizing is generated by both electric current and chemical conversion at the metal surface.

The current applied drives the layer anodizing to be able to form in a much thicker and faster way than it would by means of a chemical reaction only. One other interesting factor of anodizing is that the process leaves tiny microscopic pores in the coating. These pores can be filled with dyes to make a range of part colors.

Painting Process

The process of painting is applying a substrate of a liquid organic coating. These substrates can be wood, plastic, metal, ceramic, paper, foam, or metals. The paint being applied varies from solvent based to solids paints considering of course UV curing liquids.

As a result the paint can be a liquid because of numerous carriers like water or solvents to a two part epoxy paint. This paint is cured by cross linking than drying by evaporation of the carrier. Various spraying methods can be used to apply the paint and a few are described briefly below:

Electrophoretic Painting Process

The E-coat painting process is defined as a cross between plating and painting. This is a method where a metal part is dipped in a water based solution and that contains a paint emulsion. Afterwards there is an electric voltage introduced to the part. This causes condensation of the paint emulsion.

Wherever the liquid can reach the metal surface, a part can be painted inside and out. The voltage applied causes a limitation on the coating thickness. The areas with a high voltage become insulators as a coating is built enabling areas with low voltage to build up. Because the exterior is wholly insulated by the coating, the inside can be coated. A rinse tank then takes away all the residual emulsion from the part. It recycles it by ultrafiltration back to the paint tank.

Powder Coating Process

The process of powder coating is the same as the painting process except that the paint is a dry powder and not a liquid. The powder adheres to the parts because of electrostatic charging happening to powder and the grounding of the parts.

Substrates that can endure the heat of powder curing and those that can be grounded electrically in order to enhance attachment of the charged particle can be used. During the heat application is when the powder flows and performs curing. There are several benefits of powder coating over general paints and these are:

• There is powder recovery for reuse.
• There is no VOC that is generated meaning no VOC destruction is needed.
• This process can be more durable than paints.

However, there are also some drawbacks of powder coating over paints and these are that they can have much less leveling in comparison to paint and also because of the higher temperature needed. Curing is more energy intensive compared to paint drying.

Drying and Curing

Curing and drying operations are very energy intensive operations in the powder coating process. The drying and curing operations are bonded with convection ovens. Using convection heating is costly and very slow if the parts are heavy and large. This is because the evaporation or curing will be greatly dependent on the part temperature. The part must be hot enough for the part surface to dry or for curing of the powder coat. Large amounts of air volumes need to be exhausted and heated from the convection oven to dry or cure the parts effectively.

One other good side of heating using infrared is found in the powder coat curing. The continuous and rapid heating of the part surface will give better powder flow as well as minimum chance of dirt defects or dust. The reason being the little air flow that is available to deposit particles rather than convection heating.

A point to note, using infrared curing for the liquid paints has a much helpful effect because infrared light does not heat the paint but the part surface leading the paint to dry from the inside out. As often in convection curing, here the paint doesn’t trap water or solvent inside the paint or neither does it skin over, progressing to the paint surface.

Metal Grinding

Metal grinding processes finishes off all the rough edges, smooths welds, deburrs, creates very sharp edges, and can generate unique effects. Two common types of grinding are stationary or handheld grinding machines with industrial grinding wheels.

The main principle behind grinding is the use of attrition, friction, or compression in order to smoothen the metal surface. The smoothness of the surface that is finished is usually determined by the type of grinder being used. Numerous grinding methods can be adopted to come up with the shape, size, and features of the end product.

There is a wide range of methods of grinding like electrochemical, centerless, cylindrical, surface to mention only a few. It is crucial to decide the right method for the types of metal and end product when using these grinding methods.

Tumbling

Tumbling finishing, or barrel tumbling, involves placing parts, a media, and various compounds in a barrel and rotating the barrel to round corners, deburr, grind, descale, burnish, and polish parts in bulk. The tumbling process creates friction between the parts, media, and compounds. The two types of tumbling are wet and dry with wet tumbling used to remove excess material while dry tumbling is used for multiple finishing applications.

The nature of different parts and metals necessitates the use of a tumbling finishing method that will produce the highest quality and best finish. Vibratory tumbling creates smooth and polished surfaces for fragile and delicate parts. It combines the energy of an abrasive and water with a rapidly vibrating machine.

Dry tumbling uses a vibratory bowl cleaner with an electric motor mounted on the bottom and a media. As the bowl vibrates, parts rub against the media, each other, and the sides of the bowl. The media for dry tumbling is normally corn cob or walnut shells. Corn cob media, which is also used for sand blasting, produces a high gloss finish and takes a long time. Walnut shell media is more aggressive than corn cob media but produces a satin like finish.

Alkaline Cleaning

Alkaline cleaning is also a finishing process. Initially the alkaline cleaning tanks are put in line and then the bulk of the dirt load is taken. The main purpose of the tanks is to remove wax, grease, oils, particulates, and light oxides on the part surfaces.

With regards to the detergent additives in tanks, they could build up oil emulsions, surface oil, suspended solids and sludge forming at the tank bottom. Considering the acids, the chemicals for cleaning are taken in during the process of removing contaminants as well as preventing their redeposition.

Bath Chemistry Control

Initially, there is a need for a method or procedure in order to monitor the alkaline cleaning strength of the bath. It may be as complicated as moving a sample out for chemical verification or very simple as measuring the pH value. The cleaning supplier of the chemicals can either test certain procedures to monitor or provide the test kits or can correct the cleaning chemistry as it ages.

Surface Oils

To remove surface oils, a combination of surface sparging to a weir and using many oil skimmers available today can be used to remove the building up oil from the weir. Precaution should be taken on dead zones on the surface of the tank.

This is where oils build up and be redeposited as the parts move out of the tank. A well-constructed sparger will drive a layer of surface water across the tank as well as over the weir. Various methods can then be brought in such as disk skimmer, belt simmer, and concentrator vanes.

Removing Particulates

All the heavy particles which are found on the tank bottom can be removed by method of bag filtration or any other simple filtration procedure. The removal of heavy solids is very important especially when the cleaning tank consists of ultrasonic transducers on the tank bottom. A dirt layer on top of the ultrasonic transducers greatly minimizes the efficient action of the ultrasonic cleaning. The parts which are heavily soiled may need a dual filter system and this dual filter system caters for switching as the alternate side gets loaded, this allows the filter change-outs on the fly.

Emulsions and Suspended Solids

Emulsified oils and suspended solids are other oils that need to be considered. They are very hard to remove by normal filtration processes. A method that often breaks the oil emulsions is called ultrafiltration and afterward it removes the solids that are suspended without shaking the cleaning chemistry that is active. The ultrafiltration process type highly depends on the pH value of the cleaning chemistry and the bath’s temperature. Capable filters polymers on removing the emulsion oils and suspending solids but cannot endure high temperatures or extreme pH values. There are some commercially available systems of ultrafiltration which are capable of handling pH ranges from 0 to 14 and high temperatures of up to 158°F.

Media Blasting

Media blasting involves the use of various types of materials to remove debris, dirt, and particles from the surface of a metal. Although commonly referred to as sand blasting, sand is not the only material used to clean encrusted surfaces. Each project requires the selection of the correct media to fit the conditions and type of metal.

In many cases, when a product has been media blasted, it does not require any more finishing, which helps save time and money. Of the different finishing methods, media blasting is the fastest, a factor that increases efficiency and productivity.

Types of Media Used for Media Blasting

Different types of abrasive materials are used in the media blasting process, including aluminum oxide, silica sand, crushed glass, nut shells, silicon carbide, corn cob grit, plastic abrasives, and glass beads.

• Glass Beads - Media blasting with glass beads provides a satin like finish and has a variety of uses. Glass beads are environmentally friendly, recyclable, and chemically inert.
• Aluminum Oxide - Aluminum oxide is an aggressive blasting material that is lightweight, cost effective, and recyclable.
• Plastic Abrasive - Plastic abrasives are ideal for the removal of surface material without cutting into the metal. It is a soft media that works well on hard metals for surface finishing.
• Silicon Carbide - Silicon carbide is the hardest of the various types of media and is used for extremely challenging surface finishes. It is used for lapping, glass etching, and blast cutting.
• Steel Shot - Steel shot is used for a variety of purposes due to its toughness and recyclability. It can remove contaminants, texture a surface, or be used for peening applications for hardening a surface.
• Nut Shells - Nut shells, or walnut shells, abrasives are made from crushed nuts. It is the hardest of the soft abrasives and is used when harsher abrasives may harm the surface of a metal. Nut shell abrasives are used for polishing and cleaning fiberglass, wood, plastic, and stone.
• Corn Cob Grit - Corn cob grit is made from the woody ring on a corn cob. It is a softer abrasive that can be used to clean, deburr, burnish, and de-flash metals. Industries that use corn cob grit include jewelry manufacturing, cutlery, engine parts, and fiberglass. Additionally, corn cob grit can be used to remove graffiti from concrete, wood, brick, and stone.
• Crushed Glass - Crushed glass abrasives are made from recycled glass. The different shapes of the glass pieces provide angular shapes for surface cleaning with a uniform profile for low particle embedment. It is used for cleaning, restoration, and scale removal as well as enhancing the appearance of discolored surfaces. Unlike many of the other abrasive materials, crushed glass is a single use abrasive that is not recyclable.
• Micro Sand Blasting - Micro sand blasting combines air with an abrasive to produce a focused stream. The fine nozzle of micro sand blasting, that is 0.25mm up to 1.25 mm (0.009 in up to 0.048 in), applies a stream of abrasive to a small section of a large workpiece.

  The process of micro sand blasting is used for areas as small as 1.3 mm by 2 mm (0.051 in by 0.08 in) and is widely used for cleaning small workpieces such as medical instruments. Small minute imperfections on an instrument can radically affect an instrument’s performance. Blasting it with a soft abrasive removes built up residue without damaging the instrument.

Wet Media Blasting

Wet media blasting, known as vapor blasting or vapor honing, involves the use of an abrasive, a liquid, and compressed air to change a surface finish with water as the liquid to provide a smoother and consistent results. Any type of blasting media can be used with wet media blasting with the choice of media strongly influencing the success of the blasting process.

The concept of wet media blasting is to increase the safety of the blasting process for the material and the operator. Water diffuses and eliminates any dust produced by the blasting process and adds mass to the particles to make them more effective.

Brushed Metal

Brushed metal provides friction to the work material diminishing all imperfections while it creates a textured grain that leaves a smooth exterior finish. Fine bristle brushes or an abrasive belt are utilized in this process leaving a surface that is non-reflective and dull.

The configuration and direction of the grain can be determined by the positioning of the abrasive and its type. Brushing metals removes some of their luster and gives them a distinctive look. Different brushed finishes can be produced by using stainless steel that is power driven, wire wheel brushes brush back sander heads, nylon discs, and different types of abrasive cloth.

Phosphating Process

The phosphating process is typically classified as a conversion coating process. This is because the process includes the removal of metal as part of the reaction. It differentiates from processes such as black oxide or anodizing in that the phosphate coating reaction is a precipitation reaction. The last or final surface is a layer of crystals of phosphate sticking to the metal surface.

For coatings that use paint and powder, there are two primary functions of a phosphate. Initially, the applied coating offers better paint and powder coating adhesion. This is due to the organic behavior of phosphate crystals that anchor sites and secondly, the phosphate layer behaves like a barrier for corrosion in case there is scratching of the organic coating. When testing for rust creep, the rust creep is much minimized when there is phosphate under the powder coat layer or paint layer in comparison to no conversion layer under on organic coating.

The Phosphate can be used as a standalone coating for such purposes like lubricity in parts making. Common phosphating chemistries are the zinc phosphate, iron phosphate, and the manganese phosphate. The other phosphating chemistries like Plaforizing are not traditional in their chemistry and in their application because they are single step .they are organo-phosphate meaning they can react with both the metal surface and the organic contaminants

Passivation

Passivation mainly applies to stainless steel. It is a treatment used to protect metal from corroding by making the metal passive in regard to its environment. Passive films are made of a combination of metal and oxygen to form a passive oxide layer. Passivation allows corrosion to occur on the surface of steel or stainless steel to form a tight bound with the metal.

The bond between the metal and the corrosive layer creates a seal that keeps the corrosion from progressing beyond the top layer to other layers of the metal. A metal is passivated when its surface is covered with a layer of corrosion. If a metal with passivation is scratched or damaged, it naturally heals by molecules from the next layer.

The effectiveness of passivation is dependent on the elements that are used since not all oxides are protective. Porous oxides allow oxygen to get through and do not form a seal causing the metal beneath the first layer to corrode.

Part Drying

The various processes under part drying include:

Water Spotting

An easy way to avoid water spotting is using deionized water in the final rinse process. Water spots are usually caused by minerals in normal water. They can be removed by removing the minerals. Another method that will reduce water spots is the air blow off procedure aimed at removing the droplets of water before they have time to dry. This procedure is dependent on part orientation and geometry on the racks. If the air fails to reach specific areas on the parts because of the geometry or if parts block one another then spotting can still happen in such areas.

Drying Process

Finishing processes necessitate the use of water and compounds to create the desired finish on a part. Since the presence of water can lead to problems in manufacturing, it is essential that parts be dried prior to being moved on for further processing. Although not as complex as finishing methods, the choice of drying process has to be carefully considered to ensure the workpiece is completely dry.

There are several types of machines used to dry parts, which are divided by their drying medium or the use of hot air. Workpieces with simple shapes and surfaces can be dried quickly at high speeds and lower temperatures. Complex workpieces with undercuts, internal passages, and intricate shapes require longer drying times and longer stays in drying equipment at higher temperatures.

There are many types of after finishing dryers, which include rotary vibratory, belt, drum, and centrifugal. Drying media includes maizorb made from crushed corn cobs. It is the most common form of drying media with granule sizes of 0.002 in to 0.2 in (0.5 mm to 5 mm). During the drying process, the media may need to be replaced every few days when residual contaminants, like oil, are present.

Rotary vibratory dryers and drum dryers use a drying media for drying small to medium sized parts. Belt dryers and drying centrifuges use hot air for drying. Very small workpieces that are too small for other drying methods are dried using a drying centrifuge. Belt dryers are used to dry large complex parts to avoid media getting trapped in parts.

Hot Final Rinse

As with the other factors regarding metal finishing, rinsing is a crucial process that requires careful planning to ensure the proper results. Its purpose is to remove and dilute surface films and contaminants to diminish part failure. Rinsing uses a medium to wash the surface to condition and prepare a part for its next process.

Water is used in the rinsing process and requires that the process be highly efficient to make the best use of the water supply. Four factors to consider when addressing a rinsing process are water purity, mechanical action, length of time of rinsing, and the temperature of the water.

The most readily available water supply is from city or well water. Although they provide easy access, they may contain chlorides or sulfates that initiate the corrosion process. The best type of water is deionized (DI) or reverse osmosis filtered water (RO) that have impurities removed. The rinsing process is enhanced by the use of agitation to place the water in closer contact with the part being treated. Additionally, the water should be heated to 75o F to 85o F (24o C to 29o C) to make the rinsing process more effective.

Air Drying

There are two air drying categories that can be used independently or in conjunction with each other.

High Velocity Air – its main purpose is to remove the water from the parts rather than dry it.

Heated Air– Heated blowers blow.

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Chapter 3: Applications and Advantages of Metal Finishing

This chapter will discuss the applications and benefits of metal finishing.

Applications of Metal Finishing

There are numerous applications of metal finished products in many industries. In manufacturing, finished metals are used for materials that have a high sensitivity to oxidation. The coatings applied help prevent any chemical reaction from happening.

In the automotive industry, metal finished products are used to protect the internal part of the combustion engine from high temperatures. In the aerospace industry metal finished products are also used to prevent corrosion and wear inside the engine blocks.

For industrial uses finished metal is also of great significance since machines are much prone to corrosion, wear and tear as well as other factors that may lead them to deformation quickly.

There is a vast range of household applications for metal furnished products as they play an important role as decorative material. Metal finishing has such a big impact that this process is often used in preserving the life of metals.

Advantages of Metal Finishing

There are numerous advantages of using finished metals such as resistance to wear and tear. Another factor is that finishing can aid in the adjustment of mechanical properties. The metal finished products are much less likely to corrode. There is also preservation of the aesthetic properties.

Various types of materials come with many different microstructures. Metal finished products can work with low and high atmospheric pressure. Some have different scales of porosity through the thickness. The metal finished products also can be decorative and endure high temperatures. The processes of making them are cost effective. They are also used for biomedical applications. Another benefit is they have a high adhesion quality and are available in complex geometries.

Disadvantages of Metal Finishing

Metal finished products also come with some drawbacks. Each of the metal finished products has its own operation range, because of the mechanical properties of the different coating or finishing material that is used. As a result, the efficiency differs from one metal product to the other in areas with different pressure and temperature conditions. The industrial sector requires very high vacuum or corrosion resistance metals with a high melting point and great tensile strength.

Conclusion

The metal finishing products come in different shapes and sizes. They have impacted the industrial sector where much corrosion, wear and tear of metals do happen. Metal finishing applications are so broad with the available technology. Machines can operate smoothly for quite a long period of time because of these finishing techniques.

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