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Surface finishing is an essential part of industrial and mechanical parts manufacturing.
The shiny and super smooth metal objects you see are products of surface finishing.
This process improves resilience, corrosion resistance, tensile strength, and removes burrs, defects, and other surface flaws.
Barrel tumbling, also known as barrel finishing, is one of the most popular finishing processes.
The process is suitable for mass finishing relatively small parts. Barrel finishing involves a six or eight-sided barrel, which keeps rotating at a fixed speed.
A mixture of raw metal parts, media, and compounds is in this barrel. The rotating barrel creates friction, rubbing the parts and media against each other.
1. Important Elements of Barrel Tumbling
Three essential elements contribute to a successful barrel tumbling: barrel tumbling equipment, tumbling media, and compound
1.1 Barrel Tumbling Equipment
Barrel tumbling machines mostly come in different affordable designs.
The equipment has different division according to the difference of the vibratory object.
This guide introduce you the Horizontal Octagonal barrel system and the Triple Action Polygonal barrel machines in mass finishing processes today.
1.2 Tumbling Media
Mass finishing processes perform better when parts do not strike against each other.
Add the material to the load to lubricate the process.
Experience has shown that a ratio of three parts media to one part workpiece by volume is generally best for achieving better results.
Although the size and type of material determine the media.
They are usually selected such that they are small enough to pass through breaks, holes, and points, yet large enough not to lodge.
When a large media is used.
Using large media is used, faster action is achieved. If the media is smaller, however, a more refined finish is obtained.
Below are Some Examples of Selected tumble Media
- Porcelain tumbling media: porcelain tumbling media (also called aluminum oxide media) is generally applied in mass finishing processes where an emphasis is laid on deburring and honing. It is more economical and tends to last longer.
- Steel tumbling media: Steel media is always being used where there is the need to burnish or brighten workpieces. They are mild in action, and when used, they do not cause excess wearing of parts.
- Plastic tumbling media: They are excellent for finishing delicate parts in a process that do not involve the excess wearing of work parts.
- Ceramic tumbling media: Regularity in size and shape of the workpiece must be finished to determine if ceramics will work well. Generally, this is used when larger pieces of the workpiece are involved.
1.3 Compound
Addition of compounds in mass finishing processes is geared towards assisting the various actions in achieving the best results.
When compounds are added to mass finishing processes, they produce finer workpieces.
They come in different forms, including liquids and dry powder.
2. Comparison between the Horizontal, Octagonal barrel and the Triple Action Polygonal barrel
2.1 Horizontal, Octagonal Barrel Tumbling Machine
The Horizontal Octagonal barrel system and the Tilting and open-ended barrel designs have several similarities in common.
These two machines may adequately fit into the category of the most commonly used systems.
With the Tilting and open-ended unit, users can adequately monitor their work to make necessary additions if the need arises to varying results.
In contrast, Horizontal barrel systems do not have these features. Instead, they are built with doors which are tightly shot during operation.
Since there is no means for breathing within this system, pressure may develop in them.
These effects mostly occur in operations where the use of acidic media is employed.
The machine is incorporated, therefore with pressure release valves.
These valves must be released before loading or unloading may be done.
2.2 Triple Action Barrel
The Triple Action barrel differs from the Horizontal barrel finishing unit. In this unit, the machine can rotate both horizontally and axially.
This double rotation results in an intense cutting action faster than that obtained with the Horizontal barrel finishing unit. Therefore, it is relatively faster with a shorter cycle time.
3. Wet barrel tumbling and dry barrel tumbling
There are two main types of barrel tumbling processes, namely wet tumbling and dry tumbling. Both methods are cost-effective, require little handling, and finish many parts at the same time
3.1 Wet barrel tumbling
Wet tumbling is the process involves the use of water as a lubricant.
It usually consists of horizontal and oblique barrels made of steel and lined with wood, rubber, neoprene, urethane, PVC or vinyl for better cushioning.
Cushioning increases the life of barrels by reducing the contact between metal parts and barrel surface.
The water often washes out the cutting residue to improve efficiency.
The level of water in the barrel depends on the desired finishing output.
For example, burnishing requires filling the barrel with water up to the level of the load.
As the water level increases, you get a more refined finish and a slower cutting rate.
Sometimes, however, using water can undermine the process’s efficiency as the surface tension makes the parts cling together, especially small and flat metal parts.
Use wet tumbling for the removal of excess stock.
3.2 Dry Barrel Tumbling
Dry tumbling entails using a dry material as a lubricating agent or cleaning compound instead of water.
Use this method for all phases, including polishing.
You can use sand, ceramic parts, wood pegs, and corn cob or walnut shell grit.
Earlier, use sand with smooth stones for metal parts.
However, the trend has recently shifted towards using an organic material such as corn cob or walnut shell grit to better retain dirt and even oils.
For finishing plastic parts, you need to use softer materials such as wood peg.
4. Parameters Contributing to Successful Mass Finishing
4.1 Barrel Load
If better results are required, barrel load height should not be less than 45% or more than 60% of the entire barrel capacity.
At a load height of 50%, optimum finishing results are achieved. While more action and more flawed finish are obtained between 40 and 45%.
4.2 Speed
Select the right media and complementing compounds and place the parts in the barrel.
These barrels rotate at a speed of between 20 to 40 RPM.
This will go on for some time, depending on the desired result.
Depending on the barrel size and capacity and items to be placed in it, while also making considerations on the types of workpieces and schedule, the RPM is selected to suit whatever purpose as is required.
When a barrel systems need to run on just the right amount of speed, it creates the necessary friction between parts.
Achieve faster action by increasing the speed but may lead to poor finishing.
Slower speed, however, may produce more refined finishing, however with extended cycle time.
A standard for rotational speed has been in use in Japan for many years. We calculate with the following equation:
N=D/K1/2
N = speed of barrel (rpm), D = diameter of the barrel (m or ft), and K = a proportionality constant. The value of K differs depending on the finish. When D is given in meters:
- Brilliant finishes (K = 8)
- Lustrous finishes (K = 15–20)
- Medium finishing (K = 20–25)
- Rough finishing (K = 25–30)
4.3 Slide and Slope
As the barrel rotates, workpieces consequently collide with themselves, the media and compound. Depending on the desired results, we choose the right rotation speed. If the rate is too fast, the system may be damaged or become ineffective. On the other hand, when the pace is slower, parts may not be damaged but may lead to a more protracted process cycle.
4.4 Use the Right Cleaning Compound
As is the case with any finishing process, barrel tumbling also requires careful use of cleaning compound. Usually, the media to parts ratio is three to one by volume. If you are finishing fragile or large items, use more media for better protection and higher productivity.
You can use Aluminum oxide for deburring and honing if the parts have irregular shape and size. On the other hand, you can use steel burnishing balls and shapes only for burnishing and brightening. Steel burnishing balls will not remove light burrs. But, you can add a finishing compound to get high-quality finishing.
Preformed plastic media is probably the best for finishing aluminum, die-cast, and delicate parts. You can use ceramic media if retaining the size and shape of the components is necessary. However, it wears faster than aluminum oxide.
5. Key Benefits of Barrel Tumbling
Most manufacturers tend to use barrel finishing owing to their unique benefits. The excellent news is barrel tumbling methods are becoming increasingly sophisticated. So, the benefits will continue to grow.
5.1 Better Consistency
When it comes to mass finishing, maintaining consistency is key to a better output.
All mass-finished parts should exhibit the same level of brightness, smoothness, appearance, and other mechanical properties.
This is why manufacturers prefer using barrel tumbling. Compared to hand polishing, it offers a higher level of uniform finishing results.
5.2 Less Time-Consuming
Barrel finishing is one of the fastest finishing processes out there. Usually, a typical barrel tumbling requires just six to 24 hours, depending on the desired finish, parts, and media.
You don’t need to monitor the process continuously. You have to set the parameters such as load volume and time of the cycle and relax just before the process begins. There’s little handling required during the process.
5.3 High Adaptability
The third biggest benefit of barrel tumbling is its adaptability. You can calibrate a tumbling machine as per your desired specifications.
Whether you want to remove oils or finish intricate parts with hard-to-reach areas, barrel tumbling is the right choice.
You can also use a variety of finishing media and additives to get the desired level of finish.
This is why you can process anything, from large metal parts to small and fragile items.
5.4 Finishing at Scale
Barrel tumbling is perhaps the best way of finishing a vast quantity of parts in a short time.
With little handling required, you can process multiple batches at a time having thousands of components.
For longer runs, you can run the system overnight. Plus, you don’t have to worry about the consistency and quality of the finish.
5.5 Other Benefits
It is cost-effective than hand finishing techniques. Barrel tumbling increases the toughness and strength of the parts. Tumbling provides a certain amount of stress relief. You can also blend forgings and castings using this process.
6. Conclusion
Outlined above is the most basic description of the different barrel mass finishing process. Since its inception, barrel tumbling has incorporated many other essential practices and techniques.
Manufacturers are in search of a cost-effective, efficient, and consistent finishing processes. This is where barrel tumbling comes in.
Hopefully, understanding these various benefits and the basics of barrel finishing will help you use this process more efficiently. Feel free to tell us about your customized barrel tumbling requirements in your comments.
