burr

In engineering, a burr refers to the raised edge on a metal part. It may be present in the form of a fine wire on the edge of a freshly sharpened tool or as a raised portion on a surface, after being struck a blow from an equally hard, or heavy object. More specifically, burrs are generally unwanted material remaining after a machining operation such as grinding, drilling, milling, or turning. When these burrs are removed it is called deburring. However, in the printmaking technique of drypoint, burr, which gives a rich fuzzy quality to the engraved line, is highly desirable - the great problem with the drypoint medium is that the burr rapidly diminishes after as few as ten impressions are printed.
Burr formation in machining accounts for a significant portion of machining costs for manufacturers throughout the world. Drilling burrs, for example, are common when drilling almost any material. The Boeing 747 airplane has approximately 1.3 million holes drilled in it,[citation needed] most of which have to be deburred to some extent. As one could imagine, the cost and time needed to perform these drilling and deburring operations is significant.
In addition to drilling, milling is also a source of burr formation in machining. One good example of unwanted burrs is in the automotive industry where cylinder blocks, pistons and other engine components are cast then milled to a specific dimension. With higher and higher demands placed on accuracy and precision, burr formation is of critical importance because it can affect engine performance, reliability, and durability.
Burrs (sometimes called rotary files) are small cutters used in die grinders, rotary tools or dentist's drills. The name may be considered appropriate when their small sized head (3 mm diameter shaft) is compared to that of a seed of the burr fruit.
To maintain the correct surface speed and cutting conditions they are rotated at the highest speed possible, commensurate with their size and construction. The cutters shown in the image are made from tungsten carbide which allows them to run at higher speeds than similar HSS cutters, yet still maintain their cutting edges.
Burrs (the tools) are also used in CNC machining centers for removing burrs (the small flakes of metal) after a machining process.
These tools usually spin at several thousand RPM. Because the cutting edges are so small, they can be touched when spinning by a finger without cutting the skin, which flexes out of the way. Although it would not be safe to pinch or grip them from two sides. Hard metal or ceramic workpieces cannot flex beyond the cutting edges, so the tools remove material from them. This characteristic makes them suitable for dentistry, as the tool will grind the hard enamel of teeth, yet leaves soft mouth tissues unharmed if the tool should erroneously touch them.
Burr removal after slot milling
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We are producing Rotors for Vane Pump kits. When the slots are milled, big, twisted burrs remain on the rotor's face, where the saw leaves the work. The slots are cut before heat treatment. For the moment we use oil stones for the deburring. Could you, please, recommend another more effective and quicker method? The material is 'Alloy Steel, Reduced Nickel, 0.20% Carbon'. Regards, Despina Rantitsa
Despina Rantitsa
- Havant, Hampshire, UK
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Despina I have to assume a couple things about your part and volume to answer this question. It sounds as if your part is bigger than 12 inches or mm if you are currently using hand stones to deburr. That means that your parts probably weigh at least a pound a piece. Parts of this size can be done in mass finishing equipment, but it must be fairly large to accomodate a number of pieces to make it profitable or cost effective. Another choice is a combustible heat system that will effect only the burr. I am leaning toward a heavy viscous deburring extrudehone system if you can afford it, because it actually duplicates the environment that the part will be working in. Part size and volume are necessary to answer this question properly.
A burl (British bur or burr) is a tree growth in which the grain has grown in a deformed manner. It is commonly found in the form of a rounded outgrowth on a tree trunk or branch that is filled with small knots from dormant buds. Burls are the product of a cambium. A burl results from a tree undergoing some form of stress. It may be environmental or introduced by humans. Most burls grow beneath the ground, attached to the roots as a type of malignancy that is generally not discovered until the tree dies or falls over. Such burls sometimes appear as groups of bulbous protrusions connected by a system of rope-like roots. Almost all burl wood is covered by bark, even if it is underground. Insect infestation and certain types of mold infestation are the most common causes of this condition.
In some tree species, burls can grow to great size. Some of the largest occur in redwoods (Sequoia sempervirens); when moisture is present, these burls can grow new redwood trees. The world's largest and second-largest burls can be found in Port McNeill, British Columbia. One of the largest burls known was found around 1984 in the small town of Tamworth, Australia. It stands 6.4 ft tall, with an odd shape resembling a trombone.
Burls yield a very peculiar and highly figured wood, one prized for its beauty by many; its rarity also adds to its expense. It is sought after by people such as furniture makers, artists, and wood sculptors. There are a number of well-known types of burls (each from a particular species); these are highly valued and used as veneers in furniture, picture frames, household objects, automobile interior paneling and trim, and woodturning. The famous birdseye maple superficially resembles the wood of a burl but is something else entirely. Burl wood is very hard to work in a lathe or with hand tools because its grain is misshapen and not straight.
Some burls are more highly prized than others, including ones originating in rural areas in central Massachusetts, northeast Connecticut, and as far south as Philadelphia. Some types display an explosion of sorts which causes the grain to grow erratically, and it is these burls that the artist prizes over all other types. These spectacular patterns enhance the beauty of wood sculptures, furniture, and other artistic productions. Burls are harvested by a variety of methods. Many redwood trees have them, but there are two things that hinder the harvest of redwood burls, the first being that removing a burl can cause the death of the tree. The second is the sometimes tremendous size of redwood burls; removing them can require the use of heavy equipment, which can be expensive and difficult to get to the tree's location.
Removal of Burrs
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Removing of Burrs
The burrs are rough edges which are generated as a result of the cutting process. It is often called a flash in English. There are the visible burrs as shown in Figure 1 and the invisible burrs, which are confirmed by touching the edge. In order to make an accurate part, it is very important to remove the burrs with a file. We must remove them carefully after the cutting process.
Fig. 1, Visible Burrs

Why we need to remove burrs?

(1) In most cases of the machining process, the material is set to a chuck of a lathe or a vice of a milling machine as shown in Figure 2. If the burrs are remained, the material can not be accurately set. And as a consequence, the piece will be mounted at an askew or off center as shown in Figure 3. Also, small amounts of waste can become trapped and as a result can also cause askew or off center work pieces.

Fig. 2, Setting a Material
Fig. 3, If There is a Burr...
(2) If the burrs are not removed, the size of the part can not be accurately measured. It is therefore imperative to remove the burrs before the measurements are taken.
(3) Another reason for removing burrs is that the can cause injury to personal due to sharp edges.
(4) Also if burrs are not removed, they can seriously affect the assembly process of the parts.
Fig. 4, If a Burr is Remained...

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Removiing a Burr using File and a Wooden Surface
It is advisable to use a wooden work surface to aid in the removal of a burr as the timber surface provides a good support while at the same time it does not damage the file if it comes into contact with the timber. Not that the file is "Pushed" along the edge and not "Pulled".
Fig. 5, Using a board to Facilitate the Removal of a Burr

Lathe Process and Removal of a Burr
A burr can also be generated during the lathe process. It can be easy removed by applying a file to the burr on the rotating material. Be careful to not touch the rotating part with your finger.
Fig. 6, Removal of a Burr after Lathe Process

Remove a Burr after Drilling Process
A burr generated during a drilling or tapping process is removed using a bigger drill. A little burr can be easily removed by rotating the drill bit by hand. Larger burrs may need to be removed by mounting the drill bit in a drilling machine.
Fig. 7, Removing a Burr by Hand after Drilling
Electroburr Precision Burr Removal E-mail this company
http://www.electroburr.com
24875 Quarry Rd.
Wellington, OH 44090-9293
Phone: 440-647-2463, 888-338-9650 (toll free)
Fax: 440-647-6598


Precision deburring service utilizing the Burlytic® process, for electrolytic deburring & polishing for high precision instruments & components. Selective & internal deburring, surface finishing & cutting tool honing is available for most hardened & non-hardened metals. This precision deburring & surface polishing is especially suitable for medical & surgical instruments, electronic & other delicate component parts. Additional chemical deburring processes are available, including EdgePrep for removing micro-burrs on tungsten carbide & high speed steel cutting surfaces. A Class 10,000 cleanroom is available for parts that are sensitive to environmental contamination.

Process of deburring moldings made from granular material
Document Type and Number:
United States Patent 4560586


Abstract:
A process for the deburring of bonded moldings of granular material, for example, casting sand cores, by coating them in the same operation with a surface layer. The moldings are circulated within an annular vibrator together with an abrasive body medium which contains a powdered coating agent, the medium being preferably deflocculated by an approximately 50% proportion of hard-foam bodies.





Huzhou Finishing Co., Ltd is a member of King¡¯s Ceramics & chemcicals Co.,Ltd.(KCC), the largest ceramic grinding media, polishing media and deburring media producer in Asia.
Our plant is located in the east coastal part of China, only 150Kms far away from Shanghai seaport which is the largest seaport in China. Easy-access high way makes it only with 1.5 hours driving from Shanghai hub to our plant.
As a leading supplier in providing solutions for surface finishing and polishing, we have the annual capacity of 10,000tons polishing media over 5,000 sets of machines and 500 tons of polishing compounds. We produce more than 6,000 different types of polishing media for various applications, the materials ranging from ceramic, alumina, brown corundum, white corundum, wood chips, corn, resins boneded, green silicon carbide with different shapes such as triangle media, ball media, tri-star media, oblique triangle media, cylinders media, cone media, four-star shape media, elliptical media, grain media, fan media, cubic media, pyramid media, etc. The complete line of polishing media makes us in a strong position to satisfy our customers needs fully.
Accession number;00A0887894 Title;Burr Removal Process Using Arc Discharge. Author;KUSUMOTO KAZUOMI(Gunma Univ., Fac. of Eng.) SOUMA TATSUNORI(Gunma Univ.) Journal Title;Nihon Kikai Gakkai Kanto Shibu Burokku Godo Koenkai Koen Ronbunshu
Journal Code:L4051A
ISSN:
VOL.2000;NO.;PAGE.217-218(2000) Figure&Table&Reference;FIG.6 Pub. Country;Japan Language;Japanese Abstract;This study deals with a removal process of edge burrs for thin mild-steel plate by arc discharge. It has been carried out to remove burrs for SS400 workpiece of 2.3mm thick under various processing conditions, such as arc currents and tracking speeds of workpiece. The characteristics of this process are discussed for pencil type, chisel type and new chisel type electrodes, respectively. It is shown that processing parameters increase with an increase in arc current and a decrease in processing speed. Moreover, newly-developed chisel type electrode has a long usage life and can bebattle of the burr: New strategies and new tricks, The
Manufacturing Engineering , Feb 1996 by Gillespie, LaRoux K
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When deburring costs become a serious problem, most companies call several equipment vendors asking for a magic process that removes burrs cheaply, quickly, and without affecting the part or other processes. Effectiveness of this approach is poor. The "solution" developed often creates more problems than it solves. A more practical approach is a program that defines the kinds of burrs a part has and evaluates the production process to see which burrs might be prevented or modified. Then, if deburring is still needed, consider part quality, cost of labor and new equipment, and the ease with which the deburring operation will blend in with the existing product flow.
More Articles of Interest
• Why we need standards for burrs
• Inspecting for burrs
• Micromachining to millionths
• Down Under burr removal
• Fighting the battle of the burr

A cost-effective deburring technique is a function of acceptable deburring quality, numbers of parts involved, how fast a part can be deburred, floor space available, and environmental and safety issues.
Define Your Terms
Before starting on a burr-removal program, it's important to know exactly what a burr is and what type of edge conditions are wanted. As quality expectations increase, clear standards are becoming more important. For example, some manufacturers and researchers call the microscopic slivers left on ground surfaces "burrs." One company reportedly checks for burrs with instruments at 400X magnification.
The specification "parts must be burr-free" is meaningless without some reference to inspection approaches. Should your test for burrs involve unaided visual inspection, or tests using a 10X, 40X, or 100X microscope? Without clearly written burr and edge-finishing standards more scrap will continue to be generated.
The lack of uniform standards creates three problems:
1. No clear definition of a burr causes many parts to be unnecessarily rejected or, unfortunately, passed.
2. Not knowing the kind of edge needed causes overzealous deburring that wastes money.
3. Constantly changing, undocumented standards within a plant means specifications change with the product and workforce.
To help remedy this situation, the World-Wide Burr Technology Committee's Standard (WBTC STD-1.1995Draft) for burrs and edge finishing provides technical definitions for burr-related words. Another draft, WBTC-STD-13.1995 provides a comprehensive overview standard for specifying edge conditions caused by a variety of cutting situations. Manufacturers using these definitions have consistent product specifications. Test magnification levels are defined, and terms are explicit. If nothing else, these two standards provide models from which companies can generate in-house specifications.
Part Design
The first line of defense against burrs is to prevent their occurrence or at least minimize their negative influence. Various set up, machining, and process control tricks have been used for years, but only recently has an effort been made to systematize their applications.
The Consortium on Deburring and Edge Finishing (CODEF), led by Dr. David Dornfeld of the University of California, Berkeley, looks at ways to eliminate or minimize burr formation by evaluating part design and manufacturing process. The work primarily defines geometry conditions that do not produce burrs or produce smaller burrs. A secondary effort is to put burrs where they can be easily removed.
Here are a few anti-burr basics:
*Several different kinds of burrs can be produced by a single face-milling cut. Conversely, changing feeds and speeds affect each burr differently. For example, burrs get thicker and higher when the angle of the cutting tooth and the side of the workpiece exceed 90 deg. By controlling the angle at which the tool exits the workpiece, this burr can be made smaller and easier to remove A side burr gets smaller when the cutter-to-edge angle is 60 deg. or less.
*For a complex part, determining optimum part setup angles and optimum part geometry requires computer analysis. CODEF has a prototype software program that optimizes design for burr removal. Eventually, this work will lead to concurrent engineering, so that part design and process parameters stress easy burr removal.
*A burr's location may make it difficult to remove. Computer simulation of the manufacturing processes may make it possible to eliminate such complex geometries in the design before they create burrs.
*Increasing drill feed rate significantly increases burr height (length) as well as thickness.
*For most processes, burr thickness is the most important variable in removal. Except for small burrs, burr height usually has little to do with the economics of the removal process. It is therefore critical to know how thickness increases with a given process and how removal efforts are influenced by thickness.
*To prevent burrs from forming on a part, a nontraditional machining process is required such as electrochemical machining or a special press which pushes stock back into the sheet before it tears from the sheet. In this instance of push-back blanking, the half-sheared blank is put in a second press which pushes the half-sheared piece back into the blank in such a manner that the part breaks free of the blank.
used at high processing speed and great current. (author abst.)


Centrifugal Deburring And Finishing Machine



Gala Equipments offers centrifugal deburring and finishing system. It is a proven technique for deburring and fine finishing of components in ultra short time which cannot be finished in vibratory finishing machine, rotary barrel or by any other conventional method. For example, removal of milling burrs from gears and lock components, deburring and bright finishing of thin or sticky products, removal of shearing and file marks from the components, etc, can be done in centrifugal finishing machine in 30 minutes time. Also critical applications like descaling and fine finishing of the textile spinning rings. Areas of application are textile rings; watch, electrical and electronic components; zipper components; surgical needles and its allied components; gears, magnetic ferrites and automobile lock components; pen nibs, jewellery, etc; and, all other types of small and delicate ferrous and non-ferrous components.

The present invention provides a hobbing machine. The hobbing machine includes a clamp fixture adapted to retain a gear blank. A motor is operatively connected to the clamp fixture and is configured to rotate the clamp fixture and the gear blank together at a predetermined speed. A rotatable cutter is translatable into engagement with the gear blank and is configured to cut the gear blank and thereby produce a plurality of gear teeth. A de-burring tool is translatable into engagement with the gear blank and is configured to remove burrs from the gear blank as the gear teeth are being cut. A motorized spindle is operatively connected to the de-burring tool, and is configured to power and rotate the de-burring tool at a predefined speed to optimize the removal of the burrs.


METAL PARTS FINISHING MACHINES
Electro chemical deburring machines , Electro chemical machining machines ,
Thermal Deburring Machines , Die Polishing Machines.

VOHRAS INTERNATIONAL
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Electrochemical Deburring Machines

PROBLEM AREA ?
Have you Problems in the following Areas?
Deburring after machining?
Large quantities to be deburred?
Deburring problems at hole penetrations?
Burr which is not easily accessible?
Rounding work in addition to deburring?
Provision of slots or contours in addition to deburring?

Engineers over the years have been confronted by the problem of the efficient removal of burrs and sharp edges from various facets on components, and with the rapid increase in automatic machining cycles some components are absorbing more time on burr removal than the machining content.
Deburring has been described as the corrective treatment of components having had burrs created by other machining processes.
Today, the majority of deburring is still performed by means of hand tools, although the introduction of methods such as rotating and vibratory barrels, metallic paste, thermal deburring and ultrasonics to name but a few, are bringing consistency to the product.
Electro Chemical Deburring is one of the most efficient methods being utilised today, especially on internal features where conventional methods are extremely difficult and arduous.
Electro Chemical Deburring and Static Machining is ideally suited to both batch and flow production, where set time cycles are essential. The typical time cycles for deburring are between 5 seconds and 30 seconds, and static machining seldom involves .
Please let us have your Drawings as well samples so that we could forward the same to the Manufacturers for a suitable machine and trial results if possible. We can also offer you Re Furbished machines. Looking forward for your valued querries.




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Burrs are the unwanted portion of metal which remain at the edges of components after machining. Debutting is therefore essential which is commonly done by filling on by using deburring machine tools. Filing off burr is time consuming and it also does not give smooth edge; whereas burr removal using deburring machine tool is not always possible or economical. Deburrin hand tools offer fast , efficient and economical solution for burr removal.

Barrel Finishing Guide

Producing good surface finishes using barrel finishing depends on the right selection and use of tumblers, abrasives, lubricating agents, carrying agents and polishing agents.
Barrel finishing, also known as barrel tumbling, is a surface improving operation in which a mixture of parts, media and compounds are placed in a six- or eight-sided barrel and rotated at a predetermined speed for the purpose of rounding corners, deburring, grinding, descaling, deflashing, improving surface finish, burnishing, polishing and radiusing parts in bulk. It works by tumbling parts in a rotating barrel, thus creating friction by tumbling parts against each other and against other materials, such as media and compounds.

Tumbling Highlights
• Parts can be finished less expensively than by hand.
• Many parts can be processed at one time.
• Requires very little handling.
• Parts are tougher and stronger after tumbling.
• Tumbling provides a certain amount of stress relief.
• Forgings and castings can be blended.
• Machine parts and stampings can be deburred and burnished to a high finish.
• On long runs, the systems can run overnight.
• Careful and proper machining of your parts will save tumbling time.
There are two types of barrel finishing: wet tumbling and dry tumbling. Wet tumbling is used almost exclusively for removal of excess stock. Dry tumbling is used for all phases, including polishing.

Wet Tumbling
Horizontal and oblique barrels are commonly used in wet tumbling. The horizontal barrel is generally octagonal or hexagonal in shape. Though the oblique barrel is easier to load and unload, the horizontal is preferred because of its larger capacity and better tumbling action.

Barrels are made of steel, often with linings of wood, rubber, neoprene, urethane, PVC or vinyl. The lining cushions the impact of the tumbling parts against the barrel, thus prolonging the life of the barrel. The most popular barrel dimensions vary in diameter (18" to 36") and in length (18" to 42"). Usually, the diameter is smaller than the length. Horizontal barrel speeds vary from 20 to 38 RPM, depending on the barrel size and the items to be tumbled. Fragile parts, for example, require slower speeds to prevent possible damage.

After a barrel is filled up to about half of its capacity with parts and media, water is added to within three to five inches below the load. This can be varied either way. The lower the water level, the faster the cut. The more water used, the finer the finish and the slower the cutting rate. For burnishing, the water should be about level with the load.

The compound is put into the barrel last. Depending upon the amount of material to be removed from the parts, tumbling will take anywhere from 6 to 24 hours. Very light plastic parts require adding smooth ceramic or hardwood media in a dry process to increase the load weight.

After a run, the parts and the barrel should be rinsed thoroughly with fresh water. Parts are then removed and dried by one of several methods, such as tumbling with corn cob grit, sitting under heat lamps or spinning dry. Rinsing media after it has been used can prevent contamination or undesirable results if reused later.

Most mass finishing methods employ the use of water to lubricate and carry away the cutting residue. Without water, the parts would be scratched and black from embedded abrasives. When combined with our compounds, the water not only carries the abrasives and keeps the media clean, but also acts as a cushion to help protect the parts.

However, there are times when water can be a hindrance, such as when processing thin, flat parts (where the water surface tension makes the parts cling together) or when trying to polish or smooth a plastic part (that can absorb the water and become too soft to resist scratching or deformation). There are also polishing operations on jewelry that are limited to the smoothness of the shine that is produced when the media is too heavy and hard. So, how do we run parts safely without the help of water?

Dry Tumbling
For dry tumbling, the horizontal octagonal barrel is used almost exclusively. This barrel sometimes has a metal skin, and a hardwood lining which can be replaced when necessary. A barrel that is 30" in diameter by either 36" or 42" in length is considered standard. For versatility, these barrels may be divided into two compartments. Dry barrels are often double-decked so that one barrel is above the other, although both are set in the same frame. This saves floor space, especially when operating multiple barrels. Barrel speeds in dry tumbling are generally kept at 28 to 32 RPM.

Over the years, several techniques have been developed. In the earliest tumbling operations, water was not used. Sand was used with smooth stones. The sand not only aided the cutting, but also provided an extraordinary amount of surface area to carry the dirty residue. This avoided having the residue embedded into the surface of the parts. Thus, if something is provided to carry the dirt instead of water, parts can be run successfully.

The addition of an organic material such as corn cob grit or walnut shell grit proves more absorbent than sand, therefore carrying more dirt and even oils. Organic materials are also very good carriers of abrasives.

Plastics require a soft media, such as wood pegs, to avoid damage. However, a soft media does not cut much. Adding corn cob grit treated with pumice to the load greatly speeds up cutting. Pumice is silica that is a volcanic ash product. It is a friable, very sharp, long crystal. Because it is soft, it will fracture into smaller sharp crystals even under the light load of wood media. Harder abrasives will not fracture and, therefore, will stop cutting when they get dull. Hence, pumice is the abrasive of choice for dry cutting.

Self-tumbling metal parts with ceramic or plastic media will work very well with pumice added as an abrasive and with corn cob grit added to absorb the dirt.

Extremely high, bright finishes can be achieved by using wood pegs or walnut shells treated with a wax and an abrasive. The abrasive used should be one micron or less in size. There are ready-made polishing creams for this type of work, such as Metaglos and Microlyte. Metal parts can be finished in a tumbling barrel overnight, or in an hour or less in a high-energy machine. Most wire eyeglass frames and quite a bit of gold jewelry are polished in this process.

Plastic parts, such as buttons and plastic eyeglass frames, are usually run with wood pegs or sometimes extra large corn cob grit. If given time and careful handling, plastic parts can be polished to a finish that approaches hand buffing. Since the media is comparatively light, it takes a 10 to 15 hour run to get results. Since there is no burnishing effect, the whole job is done by the abrasives. A plastic eyeglass frame must go through three to four steps (progressively finer) and it could take one day for each step. Still, compared to hand polishing, mass finishing is a lot more economical.

Although the barrel-finishing cycle described here will suffice in the majority of cases, some simple deflashing operations, as is often done with plastic compression molded parts, can be performed by just tumbling the parts against each other in a screened barrel that will permit the scrap to fall out. This type of operation does not usually require media. The action of part against part will remove the flash while the holes in the barrel will permit the waste to escape, keeping the parts clean. Vinyl molded parts cannot be deflashed this way because the flash will bend rather than break. Freezing the vinyl can overcome this. Tumbling with dry ice in either liquid or solid form will do the job in a standard wet barrel.

Parts
The number of parts which will fit safely into a barrel will be determined by the barrel size, size of the part, the part's fragility, shape and weight and the end result desired.

Parts usually account for 1/3 of the total barrel load. The amount of parts that can be put into the barrel in relation to the amount of media is a compromise between maximum economy and maximum finish. Good surfaces will not be obtained if there are too many parts in the barrel. On the other hand, stock removal will be slowed down if there are too few parts in the barrel. The fewer parts there are in the barrel, the better the finish. The more parts there are in the barrel, the more economical.

As a general rule, simple shapes, such as balls and squares, can be barrel-finished with little fear of damage. Assuming that two parts are of a similar size, it is possible to process more of a simple shape than an intricate one. This is also true when considering weight, since larger quantities of lighter items as opposed to heavier items can be barrel finished in one operation.

Barrel Load
Barrel load heights (parts and media) should not be less than 45% or more than 60% of capacity. Load heights between 40% and 45% produce more action but a poorer finish. The optimum load height is 50%, with approximately three parts media to one of parts to keep parts from impinging. On large or fragile parts, the ratio may have to increase to as much as 6:1. As the load height increases, the action is slowed. Raising the load height may be used to soften the action; lowering the height speeds up cutting but can cause a coarser finish. However, it is at times possible to tumble very large parts if the barrel is overloaded to 80% with additional media and run at a slower speed.

Carrying Agents
The purpose of abrasive operations is to remove tool marks and flash, to smooth rough surfaces and to form radii. In dry tumbling, it is advisable to use a carrying agent in addition to abrasive powders.

A carrying agent, by acting as a buffer between the parts, will prevent them from damaging each other and produce smoother surfaces. The carrying agent will also carry the abrasive into recesses that would not be reached otherwise. Carrying agents include corn cob grit, walnut shell grit and wood pegs.

The majority of abrasive operations are carried out with wood pegs, since corn cob grit and walnut shell grit are too light to create sufficient friction. All carrying agents should be of a size which makes part separation easy and which will not lodge in any holes or crevices. Therefore, carrying agents come in a variety of sizes.

Media
Media is any material that is added to the load of parts to act as a cushion, keeping the parts from hitting one another, and act as a carrier for the compound. Normally media is used in a ratio of three parts media to one part parts by volume. Using more media and fewer parts per load can protect large or fragile parts.

In barrel finishing, the size and type of media depends on the material, size and holes in the part. The media should be small enough to freely pass through holes, recesses and prongs, or large enough not to lodge. The larger the media is, the faster the cut; the smaller the media is, the finer the cut.
• Wood pegs are usually used in "dry tumbling", but denser or coarser media, such as walnut shell or corn cob grit, can be used for faster cutting action if the finish is not important.
• Aluminum oxide is used for deburring and honing where irregular shape and size is not important. Aluminum oxide is economical and long lasting.
• Preformed plastic media is a lightweight, resilient media, excellent for finishing aluminum, die-cast and delicate parts. It will give little or no impingement on parts.
• Preformed ceramic media is an abrasive media used where regularity in size and shape are important. It cuts faster than aluminum oxide, but also wears faster.
• Steel burnishing balls and shapes are used only in burnishing and brightening. They will not remove metal, but will dull light burrs. Very high finishes can be obtained with the addition of a burnishing compound. Use three to five parts of media to one part of work pieces by volume for general ferrous work (3:1 for steel, 5:1 for magnesium or aluminum). By increasing the ratio or the media, the finish will be finer. Do not use or mix steel burnishing shot with abrasive media.
• In self-tumbling (tumbling the parts without media), only deburring or burnishing compounds and water are used. If the parts are not too delicate or intricate in shape and the burrs are fully exposed, self-tumbling is possible. It is economical, because more parts can be loaded in the barrel. An additional benefit is that there is not a separation problem.
Compounds
An abrasive compound is the next consideration. This is the additive that determines the type of operation that will be performed. If the media is treated with a cutting compound, there will be a grinding action; with a polishing cream, a smooth luster will appear. Do not mix acidic compounds with alkaline compounds, since undesirable pressure may result in the barrel.

Cutting & Pre-Polishing (Dry Tumbling)
Our Dry Abrasive Cream and Dry Cutting Cream produce smooth cutting without caking on parts or clogging recesses. This abrasive compound must be removed from the barrel after each run of 16 to 24 hours because the pumice in the cream breaks down after approximately 20 hours of running time. If it is not removed, the broken down compound will dirty the plastic and barrel and retard the action of any new compound introduced. Automatic removal of the compound can be achieved by running the barrel with a screen door.

There will be times when a pumice and compound mixture should not be used since it will clog holes or recesses in the parts. In such a situation, Shynolyte Pre-Polishing Cream can be applied directly to wood pegs.

Although the abrasive process creates a smooth surface, the surface will not be smooth enough to take a polish and further abrasive operations are necessary.

Polishing (Dry Tumbling)
This is the most critical operation in the finishing of plastic parts. Should the surface of the plastic parts be too rough, a satisfactory finish cannot be obtained.

As a general rule, a cream is used as the polishing agent and applied directly to wood pegs. Finishing creams consist of waxes and/or abrasives. The drawback of a cream made with waxes is that the wax is removed during handling, thus eliminating the polish. It is wise to polish with a combination cream of wax and abrasives, such as our Microlyte Polishing Cream or our Metaglos Polishing Cream for metals. Waxes can be mixed with an abrasive, serving as a lubricant while receiving some protection during handling.

Plastic parts should be relatively clean before going into the barrel for polishing. Enough cream should be placed in the barrel or the wood pegs will scratch the parts. The wood pegs must be watched for cream and dirt build-up. When there is an excessive build-up, the plastic parts scrape the cream and dirt from the pegs, creating a powder. This powder then nullifies any lubricating agents and the pegs scratch the plastic parts. Placing too many parts in the barrel will also produce this condition as well as cause damage from parts colliding against other parts.

Speed
The RPM of the barrel is very important. Speeds that are too slow will not create enough friction between parts. The best results can be achieved at 28 to 30 RPM, depending on the work to be done and the size of the barrel. Greater speeds will result in a faster action, but a poorer finish. Slower speeds will take longer to do the job, but will be safer for large or delicate parts. When deburring parts, it is best to start at a low RPM to cut the burr instead of rolling it over. The RPM can be increased when this danger has passed. For burnishing, a higher RPM can be used.

Small barrels require faster speeds to equal the same amount of surface feet per minute as larger barrels. Faster speeds may be desirable for deburring parts, but these faster speeds may overcome the force of gravity and interrupt the constant even slide zone within the barrel, causing part impingement, pitting, or damage to the parts being processed. Instead of the parts tumbling, they may become airborne and get pounded or showered with heavy particles, causing impact damage. Where the part surface finish is not important and shorter cycle times are more desirable, this may be an acceptable process, but it is not the best use of the equipment. Continued use at a high RPM will shorten the life of the media by breaking it up faster or it may affect the inner walls or liner of the work chamber.

Slide and Slope
The standard barrel system’s efficiency to deburr or polish depends on the ability of the parts and media to slide down a slope created by gravity. If the slope is broken up by too fast of a speed, the parts may become airborne causing part damage and/or the barrel system to become ineffective. Too slow a speed does not hurt the parts, but makes the cycle time longer. When faster speeds are desirable, there should be a greater quantity of water and chemical compound in the barrel to give more cohesion to the mass; this will also soften or buffer the impact or hammering effect of the media on the parts.

If the barrel is turning too fast, the desired sliding action will be adversely affected. Parts will be carried toward the top of the barrel and dropped. This can damage the plastics. The slide of the workload depends on the diameter of the barrel, the RPM of the barrel, the height of the load level and the height of the water level. With a 60% load level and a water level one inch below load level, the greatest slide is obtained at about 150 surface feet per minute (SFPM). At the beginning of the tumbling cycle, a low SFPM will avoid the rolling over of some burrs. The SFPM can be raised after ten or fifteen minutes. A low SFPM will also help protect delicate parts. Too much SFPM will cause the load to fly around in the barrel and create impinging and pitting.