April 2012 Archives

Barrel polishing automated and is used on generally small sized precision machine parts and complex shaped parts by placing them in rotary barrels or vibrating barrels with polishing agents and compounds. Since the efficiency is high, it is becoming popular in light of automation and labor saving needs.

The rotary barrel polishing rotates the polishing agents and work pieces inside a tumbling barrel. As shown on [Fig.1], the top layer of the subject parts fall against the direction of the rotation creating a slide layer. This slide layer recirculates and polishes the entire batch uniformly.

The amount of polishing varies depending on barrel rpm sue to changes in slide layer formulation. For normal polishing, 30~40rpm is appropriate, and 15~20 rpm for gloss finishing. Generally, when the barrel DIA is D [m] and barrel fill ratio is 55%, the polishing condition relationship is said to be shown as in [Table 1].

[Table 1] Barrel rpm and polishing condition

There are horizontal type and triple type of rotary barrel polishing. The triple type was supposedly named after the effects of the sides. [Fig.2] shows the flow of barrel contents, and [Fig.3] external appearances of the both.

The base surface to be buffed needs to be processed with paper buffs such as emery cloth with abrasives, and oil based polishing agents are used with loose buffs and sisal buffs for the finishing and gloss finishing. The oil based polishing agents are comprised of minute abrasive particles dispersed in greases such as stearic acid. The stearic acid which is in solid form at room temperature melts with heat generated by pressing it against buffs and the abrasives adhere to the buffs. The stearic acid also reduces the friction when polishing and lowers the heat. Oil based polishing agents are shown in [Table 1].

[Table 1] Types of oil based polishing agents

Buff polishing can be processed with simple machinery and tools but also is highly dependent on human hand processes and induces high costs. Therefore, automating of buff polishing is performed. For the automated buffing processes, water or oil based liquid polishing agents are used since the solid oil based polishing compounds do not yield high efficiency. The liquid agents can be sprayed onto the surfaces to be buffed to supply proper amounts.

An example of an automated buffing machine is shown in [Fig.1]

Buff polishing is indispensable in obtaining mirror finishes. In general, the term buff polishing encompasses a wide range of polishing methods from the paper finishing mentioned before to flatten a rough surfaces to obtaining mirror finishing. Various polishing methods and obtained finishes are shown in Table 1 below.

[Table 1] Types of buff polishing methods and finishes

Buff polishing begins with selecting the shape and the material. The buff materials are mainly classified into cotton and hemp linen (sisal), and shapes are classified as follows. (see [Fig.1])

1. Paper buff
   Circular canvas cloth are stacked and sawn together and polishing material is adhesive fixed. Mainly used for rough polishing.
2. Loose buff
   Circular calico cloth are stacked and only the center is sawn. The centrifugal force of rotating generates elasticity.
3. Bias buff
   Cloth is cut along fold lines and creases are stacked into round shape. The cloth ends do not fray.
4. Pocket buff
   Folds are made deep and circular sawn together. Air pockets promote Heat radiation and good abrasive retention.

[Fig.1] From left: Loose buff, Paper buff, Bias buff