Mass finishing
Encyclopedia
Mass finishing is a group of manufacturing
processes that allow large quantities of parts to be simultaneously finished. The goal of this type of finishing is to burnish
, deburr, clean, radius, de-flash, descale, remove rust
, polish, brighten, surface harden, prepare parts for further finishing, or break off die cast runners. The two main types of mass finishing are tumble finishing, also known as barrel finishing, and vibratory finishing
. Both involve the use of a cyclical action to create grinding contact between surfaces. Sometimes the workpieces are finished against each other; however, usually a finishing medium is used. Mass finishing can be performed dry or wet; wet processes have liquid lubricant
s, cleaners, or abrasive
s, while dry processes do not. Cycle times can be as short as 10 minutes for nonferrous workpieces or as long as 2 hours for hardened steel
.
Mass finishing processes can be configured as either batch systems, in which batches of workpieces are added, run, and removed before the next batch is run, or as continuous systems, in which the workpieces enter at one end and leave at the other end in the finished state. They may also be sequenced, which involves running the workpieces through multiple different mass finishing processes; usually, the finish becomes progressively finer. Due to the random action of the processes, mass finishing is as much an art as it is a science.
Cut: Media which cut can remove burrs and can smooth surfaces. As a carrier of abrasive grain, the large medium pieces effectively increase the impact force of the abrasive on the metal part to be cut, thereby improving the efficiency of the abrasive. Cutting media develop dull, matte
surfaces.
Luster: Some grades of medium are designed to promote luster on the surface of metal parts. These products are generally non-abrasive or have a very low degree of abrasiveness. They deburr by peening
, rather than actually removing the burr. Media selection, therefore, will control the degree of surface luster, making the part bright and shiny or developing a very matte, dull surface characterized by a completely random scratch pattern, or anything in between.
Part separation: A very important function of the medium is to separate parts during the deburring, cutting, surface improving or burnishing operations. The media:parts volume ratio is normally used to control the amount of part-on-part contact which will occur in a vibratory or tumble finishing operation. At low ratios, considerable part-on-part contact occurs, while at higher ratios part-on-part contact is limited.
Surface scrubbing: Media have the unique ability to scrub surfaces and physically assist compounds in their cleaning function. Both abrasive and non-abrasive media are effective in this. They can remove organic soils, scale, and other inorganic residues.
Media come in a wide range of materials in order to fulfill various needs.
Aluminum media: Aluminium
media are typically cast part
s and are available in a wide variety of shapes and sizes. Aluminum scrubs parts and can work in conjunction with cleaning compounds to clean parts. Since aluminum is fairly nonabrasive it tends to remove surface impurities without affecting the part's surface qualities. Its cost is typically higher than other cast media. Wear rates are lower than ceramic
but higher than steel media.
Preformed ceramic media: Ceramic media are manufactured by mixing clay-like materials and water with abrasives, forming the mud into shapes, drying the shapes, and firing them at high temperatures to vitrify the binder. Many of these binders are porcelain
-like in nature. Variability in these products occur both with the type of binder used, firing temperatures, the amount, size and type of abrasive grains they contain, and their uniformity of firing. This type of media today is the general workhorse of mass finishing systems and is the type of medium generally used, because of its availability in a variety of shapes and sizes, low cost, and low wear rate.
Preformed resin-bonded media: Plastic or resin
-bonded media utilize a wider range of abrasive types and sizes than preformed ceramics. The most popular grades are those using quartz
as an abrasive. Aluminum oxide, silicon carbide
and other abrasives are also used. Usually, low-cost polyester
resins are employed as the binder and the various shapes are produced by casting. Resin bonded media is good for preparing a metal surface for plating
.
Steel: Case hardened, stress-relieved steel preformed shapes are available in a variety of sizes and configurations. Balls, balls with flat spots, ovoids (footballs), diagonally cut wire similar to angle-cut cylinders, ball cones and cones (both of which are different than the general concept of cones) and pins are the most commonly used. Steel media weigh approximately 300 pounds per cubic foot and are expensive for initial installation, but, because of their minimal attrition rate and extreme cleanliness, are being more widely used for light deburring applications and cleaning. Compounds are available to keep steel burnishing media clean and bright for extended periods.
Synthetic random-shaped media: The most popular synthetic random media is fused
aluminum oxide, which is available in a number of grades. The more loosely bound, coarse-grained materials are characterized by fast cut and high depreciation rates. Because of the dark color of fused aluminum oxide, the soil generated by this material is excessive in many applications. Fine-grained fused aluminum oxide is generally employed for burnishing and in this respect is unexcelled in many applications with the possible exception of steel. Where some light cutting is required, fine-grained aluminum oxide can develop a better luster on stainless steels and other hard surfaces than can be achieved with steel burnishing media.
Natural random-shaped media: River rock, granite
, quartz
, limestone
, emery
and other naturally occurring abrasive materials are also used in vibratory and tumble finishing applications. In general, these media are not very efficient in vibratory equipment because of their high attrition rates.
Cobmeal, walnut-shell flour, and related materials: These are used for drying applications because of the natural ability of these materials to absorb water from metal surfaces. These can also be blended with abrasives and used for fine-polishing applications in vibratory, barrel, or spindle finishing equipment.
Other: Shoe pegs, leather, carpet tacks, and many other solid materials have been used at one time or another in tumble or vibratory finishing for certain applications.
. They may be liquids or dry powders. They are usually broken up into four types: deburring and finishing, burnishing, cleaning, and water stabilizing.
Deburring and finishing: These compounds are mainly designed to suspend the small particles created when deburring and abrading parts. They are also designed to keep workpieces clean and inhibit corrosion.
Burnishing: Burnishing compounds are designed to enhance brightness and to develop certain colors after mass finishing.
Cleaning: These compounds are usually dilute acid
s or soap
s designed to remove soil, grease, or oil from the incoming parts. They also provide corrosion resistance for ferrous and non-ferrous parts.
Water stabilizers: These are used in conjunction with water to maintain a consistent water hardness and level of metal ions. This helps ensure consistent results from batch to batch.
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...
processes that allow large quantities of parts to be simultaneously finished. The goal of this type of finishing is to burnish
Burnishing (metalworking)
Burnishing is the plastic deformation of a surface due to sliding contact with another object. Visually, burnishing smears the texture of a rough surface and makes it shinier...
, deburr, clean, radius, de-flash, descale, remove rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...
, polish, brighten, surface harden, prepare parts for further finishing, or break off die cast runners. The two main types of mass finishing are tumble finishing, also known as barrel finishing, and vibratory finishing
Vibratory finishing
Vibratory finishing is a type of mass finishing manufacturing process used to deburr, radius, descale, burnish, clean, and brighten a large number of relatively small workpieces....
. Both involve the use of a cyclical action to create grinding contact between surfaces. Sometimes the workpieces are finished against each other; however, usually a finishing medium is used. Mass finishing can be performed dry or wet; wet processes have liquid lubricant
Lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...
s, cleaners, or abrasive
Abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away...
s, while dry processes do not. Cycle times can be as short as 10 minutes for nonferrous workpieces or as long as 2 hours for hardened steel
Hardened steel
The term hardened steel is often used for a medium or high carbon steel that has been given the heat treatments of quenching followed by tempering. The quenching results in the formation of metastable martensite, the fraction of which is reduced to the desired amount during tempering. This is the...
.
Mass finishing processes can be configured as either batch systems, in which batches of workpieces are added, run, and removed before the next batch is run, or as continuous systems, in which the workpieces enter at one end and leave at the other end in the finished state. They may also be sequenced, which involves running the workpieces through multiple different mass finishing processes; usually, the finish becomes progressively finer. Due to the random action of the processes, mass finishing is as much an art as it is a science.
Media
Media are designed for four things:Cut: Media which cut can remove burrs and can smooth surfaces. As a carrier of abrasive grain, the large medium pieces effectively increase the impact force of the abrasive on the metal part to be cut, thereby improving the efficiency of the abrasive. Cutting media develop dull, matte
Matte
Matte may refer to:In film:* Matte , filmmaking and video production technology* Matte painting, a process of creating sets used in film and video* Matte box, a camera accessory for controlling lens glare...
surfaces.
Luster: Some grades of medium are designed to promote luster on the surface of metal parts. These products are generally non-abrasive or have a very low degree of abrasiveness. They deburr by peening
Peening
Peening is the process of working a metal's surface to improve its material properties, usually by mechanical means such as hammer blows or by blasting with shot . Peening is normally a cold work process...
, rather than actually removing the burr. Media selection, therefore, will control the degree of surface luster, making the part bright and shiny or developing a very matte, dull surface characterized by a completely random scratch pattern, or anything in between.
Part separation: A very important function of the medium is to separate parts during the deburring, cutting, surface improving or burnishing operations. The media:parts volume ratio is normally used to control the amount of part-on-part contact which will occur in a vibratory or tumble finishing operation. At low ratios, considerable part-on-part contact occurs, while at higher ratios part-on-part contact is limited.
Surface scrubbing: Media have the unique ability to scrub surfaces and physically assist compounds in their cleaning function. Both abrasive and non-abrasive media are effective in this. They can remove organic soils, scale, and other inorganic residues.
Media come in a wide range of materials in order to fulfill various needs.
Aluminum media: Aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
media are typically cast part
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
s and are available in a wide variety of shapes and sizes. Aluminum scrubs parts and can work in conjunction with cleaning compounds to clean parts. Since aluminum is fairly nonabrasive it tends to remove surface impurities without affecting the part's surface qualities. Its cost is typically higher than other cast media. Wear rates are lower than ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
but higher than steel media.
Preformed ceramic media: Ceramic media are manufactured by mixing clay-like materials and water with abrasives, forming the mud into shapes, drying the shapes, and firing them at high temperatures to vitrify the binder. Many of these binders are porcelain
Porcelain
Porcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
-like in nature. Variability in these products occur both with the type of binder used, firing temperatures, the amount, size and type of abrasive grains they contain, and their uniformity of firing. This type of media today is the general workhorse of mass finishing systems and is the type of medium generally used, because of its availability in a variety of shapes and sizes, low cost, and low wear rate.
Preformed resin-bonded media: Plastic or resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
-bonded media utilize a wider range of abrasive types and sizes than preformed ceramics. The most popular grades are those using quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
as an abrasive. Aluminum oxide, silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
and other abrasives are also used. Usually, low-cost polyester
Polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
resins are employed as the binder and the various shapes are produced by casting. Resin bonded media is good for preparing a metal surface for plating
Plating
Plating is a surface covering in which a metal is deposited on a conductive surface. Plating has been done for hundreds of years, but it is also critical for modern technology...
.
Steel: Case hardened, stress-relieved steel preformed shapes are available in a variety of sizes and configurations. Balls, balls with flat spots, ovoids (footballs), diagonally cut wire similar to angle-cut cylinders, ball cones and cones (both of which are different than the general concept of cones) and pins are the most commonly used. Steel media weigh approximately 300 pounds per cubic foot and are expensive for initial installation, but, because of their minimal attrition rate and extreme cleanliness, are being more widely used for light deburring applications and cleaning. Compounds are available to keep steel burnishing media clean and bright for extended periods.
Synthetic random-shaped media: The most popular synthetic random media is fused
Melting
Melting, or fusion, is a physical process that results in the phase change of a substance from a solid to a liquid. The internal energy of a substance is increased, typically by the application of heat or pressure, resulting in a rise of its temperature to the melting point, at which the rigid...
aluminum oxide, which is available in a number of grades. The more loosely bound, coarse-grained materials are characterized by fast cut and high depreciation rates. Because of the dark color of fused aluminum oxide, the soil generated by this material is excessive in many applications. Fine-grained fused aluminum oxide is generally employed for burnishing and in this respect is unexcelled in many applications with the possible exception of steel. Where some light cutting is required, fine-grained aluminum oxide can develop a better luster on stainless steels and other hard surfaces than can be achieved with steel burnishing media.
Natural random-shaped media: River rock, granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
, emery
Emery (mineral)
Emery is a very hard rock type used to make abrasive powder. It largely consists of the mineral corundum , mixed with other species such as the iron-bearing spinels hercynite and magnetite, and also rutile...
and other naturally occurring abrasive materials are also used in vibratory and tumble finishing applications. In general, these media are not very efficient in vibratory equipment because of their high attrition rates.
Cobmeal, walnut-shell flour, and related materials: These are used for drying applications because of the natural ability of these materials to absorb water from metal surfaces. These can also be blended with abrasives and used for fine-polishing applications in vibratory, barrel, or spindle finishing equipment.
Other: Shoe pegs, leather, carpet tacks, and many other solid materials have been used at one time or another in tumble or vibratory finishing for certain applications.
Compounds
Compounds are added to mass finishing processes to assist in deburring, burnishing, cutting, cleaning, descaling, and inhibiting corrosionCorrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
. They may be liquids or dry powders. They are usually broken up into four types: deburring and finishing, burnishing, cleaning, and water stabilizing.
Deburring and finishing: These compounds are mainly designed to suspend the small particles created when deburring and abrading parts. They are also designed to keep workpieces clean and inhibit corrosion.
Burnishing: Burnishing compounds are designed to enhance brightness and to develop certain colors after mass finishing.
Cleaning: These compounds are usually dilute acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
s or soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...
s designed to remove soil, grease, or oil from the incoming parts. They also provide corrosion resistance for ferrous and non-ferrous parts.
Water stabilizers: These are used in conjunction with water to maintain a consistent water hardness and level of metal ions. This helps ensure consistent results from batch to batch.