Bowl vs. Tub Vibratory Machine
What should a shop keep in mind when purchasing its first vibratory machine for general finishing and deburring?
Q. We are a sub-contract manufacturing company that machines a variety of parts of different sizes, alloys and quantities. We are considering purchasing our first vibratory machine for general finishing and deburring. Can you explain how these systems work and whether we should purchase a bowl- or tub-type machine? —K.B.
A. The vibratory finishing process can burnish (brighten), provide uniform finishes, clean, deburr, radius, stress-relieve and refine the surfaces of your parts.
The energy of both the bowl and tub vibratory machines is generated by an electric motor rotating an eccentric weighted shaft between 1,200 and 2,700 rpm.
This shaft is attached vertically to a bowl machine and horizontally to a tub machine.
The machines can have adjustable amplitude (power setting) by shaft weight adjustment and variable-speed motor settings. The shaft generates the vibrating energy to the machine; the machine transfers its energy through the media to the part.
Although it’s best to review parts and production rates before making a machine type and size recommendation, I recommend the bowl vibratory machine more often than the tub. The bowl has a more stable and precise process with more flexibility. The bowl vibratory systems can be set up for part unload, rinse, inhibit, part drying and media classification.
Here is a summary of both bowl and tub vibratory machines that may help you determine what is right for you:
Bowl Vibratory Equipment
Bowl vibratory machines are comprised of a donut-shaped U-channel. The bowl can have various channel sizes and overall diameters. It is suspended by springs that are attached to a round base. The eccentric shaft is mounted vertically through the center column of the bowl. The bowl can be driven by an external drive motor attached to the base running the center shaft by a V-belt drive. A bowl can also be driven by an integral drive motor where the weighted eccentric shaft is built within the motor and mounted together in the center column.
- Internal part unloading and media separation.
- Less part-to-part damage.
- Secondary operations such as media classification, part rinse and drying can be integrated.
- Can be built for batch or continuous automation.
- Restrictive on long parts.
- Higher capital investment.
Tub Vibratory Equipment
Tub vibratory systems are comprised of a rectangular U-shaped tub. The tub can have various channel diameters and channel lengths. It is mounted and suspended on springs attached to the base of the machine. The motor and rotating shaft are generally located within the base. The shaft is attached to the bottom of the tub and run by a V-belt drive from the motor that is attached to the base.
- Long part processing.
- Easily divided, for running large parts that cannot touch or different media at one time.
- Smaller systems are inexpensive and portable.
- Large systems can be built for continuous in-line automated operations.
- Manual part unloading.
- Small flat parts stick to the tub side walls.
- Parts migrate to the drive end of the tub decreasing media-to- part ratio which can increases part- on-part damage.
Choice of equipment, media and compounds has a major impact on your finishing applications.
Consider these five variables to determine what fits your application.
Surface finish types for commercially supplied stainless steel sheet are detailed in various standards. ASTM A480-12 and EN10088-2 are two; BS 1449-2 (1983) is still available, although no longer active. These standards are very similar in that they define eight grades of surface finish for stainless steel. Grade 7 is “buff polished,” while the highest polish—the so-called mirror polish—is designated Grade 8