Mass Finishing Systems: Barrel Tumblers, Vibratory Deburring Machines, and Blasting Equipment
Barrel tumblers work well for jobs requiring heavy burr removal. They are also good for burnishing, rapid radiusing of edges, heavy deburring with or without media and tumbling die-castings to break the parts off the runner. Barrel tumblers are a good choice for very heavy loads that will not run well in a vibratory finisher, such as steel shot for polishing operations, where the media can weigh up to 300 lb per cubic foot. When estimating the capacity required, keep in mind that barrel tumblers run best 50% full. Screened barrels are available for use as a plastic or die-casting deflashing machine. By adding screen doors, parts can be separated.
Wet barrel finishing is a batch system for removing excess material or polishing parts, employing water and other agents to form radii, remove burrs, improve surface appearance, polish and clean. Wet barrel finishing works well for processing metal. Wet barrel finishing equipment may sometimes be used in dry tumbling operations.
Dry barrel finishing is a batch system for mass polishing or removing excess material from plastic or metal parts without liquids by tumbling them in a media and compound mixture. Dry barrel tumblers form radii, deflash, polish and grind. Dry tumbling is valuable for finishing very delicate parts that would be damaged in a wet barrel. A dry system produces a smoother and higher finish. The finished parts have more of a hand-buffed appearance with greater uniformity in the end product - something very difficult to do with hand finishing methods.
Although most methods for barrel finishing employ a wet process, dry tumbling has some definite advantages in particular cases. Some factories are not set up to handle large quantities of water, making wet tumbling impossible. Dry tumbling may be used under such circumstances to eliminate hand finishing.
Vibratory tumble finishing systems produce a cutting action by shaking the processing vessel (the finishing tub) at a high speed, causing the tumbling media and parts to scrub against each other. This scrubbing action precisely abrades the parts to remove burrs. A shaft with rotating eccentric weights mounted on the tub produces the shaking action.
Vibratory deburring machines and finishing systems produce a cutting action that is very thorough. They remove material from pockets and recesses and inside bores, which cannot be done in a barrel tumbler, so they can be used for very delicate or intricate parts. With high speeds and a short stroke, they can also run large bulky parts without damage. Large wing spans and landing struts are routinely run in these systems. Vibratory finishing systems also lend themselves to be automated easily. They can be fully automated for a flow-through operation or used as a basic batch operation. The action is that of a small orbit at a high speed and thus is very powerful, yet causes little stress on the parts.
There are two basic types of blasting equipment. While these systems are traditionally known as sand blasting equipment, all of these types of blasting machines can handle a variety of blast media. The blasting cabinet system is divided into tumble blasters which are a semi-automated, multi-part batch process and the traditional blasting cabinet used by an operator to blast one part at a time. Portable sand blasters come in a variety of sizes and types. The most versatile and valuable portable blasting equipment can blast all types of dry blast media without requiring changes in hardware.
The Tumble Blasters are enclosed cabinet systems that have a rotating basket with a sandblast gun aimed into it. The random tumbling action insures that all parts in the basket are completely sandblasted when the cycle is finished. The process is easy: simply load the barrel, close the door, set the timer, and turn on the dust collector. The barrel slowly turns, gently exposing all parts to the blast stream. When the timer expires, parts are finished and ready for unloading! Tumble blasting systems remove rust and scale, remove hard to reach burrs, produce either bright or dull texture finishes and prepare a surface for bonding.
Sandblast cabinets can perform such operations as scaling and rust removal, deburring, frosting, and surface preparation for coating. Sandblasting cabinets are offered in three styles - standard, split-level and portable. The standard cabinets have door openings on the side as well as a large opening in the front. The split-level style is hinged in the center; the entire top half opens to give access to the work stage, somewhat like a clamshell. This has an advantage when handling large heavy parts. Portable units provide an economical and practical sandblasting option, featuring remote control operation.
There are two basic types of blast systems. The suction machine, also known as a siphon, is most commonly used for light production and general-purpose cleanup. In this type of unit, air passes through the gun, creating a siphon action that sucks up abrasive and delivers it to the nozzle where it is propelled out to the target.
The second type of unit is a direct pressure machine. In this type of unit, the abrasive is held in a pressurized vessel and is pushed from behind, out of the nozzle and onto the target. Air is used to push the abrasive at a much higher flow rate than the suction system. Most jobs will be finished 30 to 50% faster in a pressure blaster. Pressure blasters also have the advantage of allowing much lower pressures to be used for delicate jobs.