Vibratory machines and barrel tumblers are both mass finishing technologies that render a refined finish to massive volumes of parts in a short span of time. Both methods are capable of preparing metal parts for coating, and both are widely used for polishing, deburring, burnishing, de-scaling, de-flashing, and radiusing. However, there are several differences between these two equipment choices in terms of operating processes, uses, media, and so on.
What is vibratory finishing? — Vibratory finishing involves placing parts, media, and compounds into a vibratory tub or bowl. This machinery then applies force to the parts, an action that leads to the media and the parts to rub and grind against each other, the effect of which is to deburr or polish the parts.
This type of finishing also is widely used for mass finishing applications such as cleaning, descaling, polishing, and surface preparation. The results of this type of deburring cannot be achieved with manual labor, which is why vibratory equipment configurations such as batch tubs, round bowls, or through-feed machines are selected by high-volume manufacturers.
What is barrel finishing? — Barrel or tumble finishing involves placing parts, abrasive media, and the compounds in a barrel with water. The rotation of the barrel leads to the tumbling of the media mass and parts. This causes friction, which results in the abrading of the parts in the mass, and the quick and efficient deburring of the part’s surfaces.
Typically, deburring barrels come in the form of batch-type processing machines. However, in-line batch processing and single-pass processing equipment also can be found.
The difference between barrel tumbling and vibratory finishing lies in the way that the machines create the necessary degree of friction between the parts and media that is required to eliminate imperfections from those metal parts.
Now let’s have a look at some of the parameters involved to understand both methods better and use them appropriately.
Media preferences — In a vibratory finishing system it is common to use ceramic or preformed plastic media. Ceramic media has a higher density and can be used effectively to polish and/or grind hard metals, such as stainless steel. This option also includes porcelain, made from pure aluminum oxide, making it suitable for finer grinding and achieving a high-gloss finish.
Plastic media typically comes with a polyester base, but it also may be formaldehyde- or urea-based. This is the media typically used for softer metals, such as zinc and brass. Ceramic and plastic media generally are combined with abrasives such as silica, aluminum oxide, and zirconium at the time of finishing.
Plastic pellets can be used for cushioning in barrel tumblers only. They’re not suitable for use in vibratory tumblers: They spread around the barrel to absorb impact between the rocks in the tumbler. In turn, this helps reduce chipping and bruising of stones such as quartz and obsidian. Plastic pellets can be reused several times in the same-size grit.
Cutting action — The vibratory tumbler tends to move at a very high speed while the barrel tumbler grinds at an applied force, which is typically higher. The cutting action in the barrel tumbler is limited to the slide area (around 25% of the total load). In the vibratory tumbler, however, the entire load is cut with each pulse (around 1,800 times a minute). This is the reason that cycle times in a vibratory tumbler are shorter than the barrel tumbler.
In a vibratory finishing systems, the parts being processed will move to a very small extent in relation to each other. In the barrel finishing system, the parts move all over the barrel, which can lead to the formation of a bigger radii in the barrel tumbler, but smaller compared to a vibratory tumbler. Parts in barrel tumbling can form a one-eight radius while removing little material from the flat sections.
The vibratory tumbler will handle large chunky media to produce a considerable radius, but it will remove a sufficient amount of material from the flat sections, thanks to its scrubbing action.
With regard to the finish quality, vibratory finishing systems produce an even and a smooth finish due to the moving of the parts. A vibratory tumbler will cut inside a piece, deburring every area the media can reach. Fragile parts are safe in such a system because the load moves as a single unit. The scope for tearing action or imbalance in force that can garble parts is minimum to none.
Also, larger parts and large-size media will initiate a faster cutting action. Their weight, however, will not influence the cutting action. After all, plastic media is much lighter than ceramic media and still results in a good cut.
With barrel finishing systems, you’ll achieve an uneven surface with rounded-off corners. Barrel tumbling is especially favorable when it comes to brute stock removal. Parts with heavy radii and foundry castings are best run in a barrel tumbler as its peening action works the tougher parts. Apart from this, hardened and polished steel shot is used to impart a sheen to the parts. This media can be used in a vibratory machine, but it is best to use the barrel tumbler for a denser and glossy surface.
Toughness — Barrel tumbling action is more aggressive than that of vibratory finishing, which is why this method is ideal for finishing smaller and harder metal pieces that need serious finishing treatment. The effects of the process can be adjusted according to the equipment and finishing media being used. However, barrel tumbling is best suited for tougher mass metal finishing tasks.
Shakeout Systems — Vibratory drums are ideal for no-bake, brass, and other foundry applications that necessitate the decrease or removal of damage to casting surfaces. Some benefits of the non-rotating and enclosed design are better dust collection and air system attachments, the option to add peripheral add-ons (such as water addition), and for connecting support equipment to the drum.
Rotary drums can offer an economical approach to processing castings in all types of foundries. However, the lifting and dropping of castings may damage the products and escalate scrap rates. Rotary drums are frequently found in ductile-iron foundries, where they help to restrict the extent of manual labor needed to de-gate castings and decrease the problem of entangled castings and sprue.
Cost — Vibratory systems and equipment are significantly more expensive due to the significant space requirements. Barrel tumbling systems, on the other hand, cost less but they will take longer to complete the same job. This is because they wear out tumbling media at a much slower pace compared to vibratory systems.
Both vibratory and barrel finishing systems come with their own benefits and limitations. It is best to know which aspects of each one works best for an optimal and efficient finishing job in a specific application. The above distinctions should help foundries and diecasters to understand better these systems and how they are used.
Vernon Glick is a marketing executive active in the manufacturing sector. Contact him at [email protected]