The common theme one often hears these days in U.S. manufacturing tends to involve
so-called “lean manufacturing.” In today’s economic environment
it is imperative that we—as manufacturers—re-examine all aspects of
our manufacturing practices in order to maintain their competitive advantage.
When it comes to buffing and polishing, the area most often looked at for improvement
usually involves buffing media, meaning buffing wheels and buffing compounds.
After all, if you can find an everlasting buff and a compound that allows you
to polish your parts in 50% of your current cycle time, you’ve cut your
costs tremendously. But we all know it’s not that easy.
One area that is often overlooked is the application of compounds to buffing
wheels. While it may seem like a small piece of your buffing operation, it is
perhaps one of the most important step. Buffing compounds can be broken up into
two types: solid bar compound and liquid buffing compound.
Solid Bar Compound
Typically, solid bar compound is used in manual or semi-automatic buffing operations.
Usually, a simple motor-driven buffing jack is used. However, this method is
sometimes used on buffing wheels as large as one-meter wide, usually in the
cutlery industry. The operator presses a bar of compound onto the rotating buffing
wheel for a short interval. Once the buff is loaded with compound, the operator
then buffs the workpiece. Often, the operator must load the buff with compound
many times during the operation, depending on the size of the piece or the finish
requirements.
While this method may at first seem inexpensive—since no application system
is needed—it actually has many disadvantages.
First, it is unsafe. While it is difficult to put a dollar amount on the cost
of an injury, it more than outweighs the relatively small investment of an automatic
bar application system. Second, it can lead to inconsistent finishing results
due to its subjective nature of application. Third, the time spent by the operator
loading the buffing wheel with compound is essentially machine idle time.
In comes the automatic bar feeder. These devices come in various configurations.
They can range from simple cylindrical tubes with a pneumatically activated
bladder that clamps the bar and uses pressure from above or gravity to feed
the bar compound into the buff, to more complex systems such as the device
shown
in the box on the right.
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A
simple cylindrical tube with a pneumatically activated
bladder
that clamps the bar and uses pressure
from above or gravity to feed the bar compound into the
buff (as shown on the left) or a more complex system such
as the device shown on the right.
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This system uses pneumatic clamps to hold the bar in place while in contact
with the buffing wheel. It also uses a pneumatic cylinder to index the bar into
position in increments of 0.004-0.008 inch.
Regardless of the type of bar feeder one chooses to use, the advantages are
tremendous. It goes without saying that this is obviously safer than a manual
application. The operator will apply a consistent amount of compound with each
application, leading to more consistent finishing results. The biggest payoff
however will be productivity, since the operator can now use all of his time
at the buffing station for buffing and not applying compound. Depending on cycle
times and amount of compound applied, productivity could easily be enhanced
by 50% and up. That is real savings!
Liquid Buffing Compound
Liquid buffing compound is most often applied using a spraying system that uses
either low-pressure atomizing spray guns or, more recently, high-pressure airless
spray guns.
Low-pressure systems are perhaps the simplest and least expensive systems to
operate. They consist of a compound source that is pumped using a drum-style
pump, diaphragm pump or, in some cases, a pressure pot. The buffing compound
is pumped to the spray gun at a typical pressure of 80-400 psi, depending on
the type of delivery system used. The spray gun is activated via a solenoid
valve that is triggered either using a footswitch or a timer. Once the spray
gun is activated, air pressure is introduced to the spray gun and is used to
atomize the buffing compound as it exits the gun. This forms a “mist”
that is sprayed onto the buffing wheel or directly to the actual part being
buffed.
Low-pressure spray guns operate relatively trouble free due to the relatively
small number of parts contained inside the gun, as well as the low pressure
at which compound travels through the gun. Consequently, maintenance costs and
downtime of these guns are relatively low.
While a low-pressure system is sometimes the preferred method, such as on extrusion
and sheet buffing, there are some disadvantages of these systems.
Compound use is typically quite high with a low-pressure system because of the
air turbulence created by the rotating buffing wheel. Compound exiting the gun
at a relatively low pressure simply cannot penetrate the wind barrier surrounding
the buffing wheel, leading to a large amount of compound throw-off. In most
cases, a majority of the buffing compound ends up on the machinery or shop walls
and not on the buffing wheel where it belongs. Challenges also arise when trying
to cover wide buffs. Even when using large-angle spray nozzles, the compound
simply can’t penetrate the air curtain surrounding the buffing wheel. This
calls for either a gun-mover (usually a pneumatically operated device which
traverses the gun across the full width of the buffing wheel) or more spray
guns.
High Pressure Systems are used more in recent years due to their many advantages.
There are two types of common high-pressure spray gun systems.
The first type applies liquid compound through an airless spray gun via a complete
high-pressure system. This consists of a high-pressure spray gun, a high-pressure
pumping system and high-pressure manifolds, hoses and fittings.
The advantage of this system is that the high pressure by which the compound
leaves the spray gun allows the compound to penetrate the air turbulence around
the buffing wheel. These types of guns can generate pressures up to 4,000 psi.
Another advantage of these guns is the ability to control the spray time using
a timer or other device. These guns tend to be compact, making them easy to
mount in confined areas, especially on complex automated systems. In some cases
they are easily changed over due to the mounting mechanism that uses a simple
manifold mounting plate and only a few screws.
While the compound savings can be substantial, it is important to recognize
that these systems do have their drawbacks. Due to the high pressures inside
the gun, significant wear and tear is inevitable on the spray gun. In addition,
the high-pressure pumps that feed the compound to the gun must periodically
be re-built due to the pressurized pumping of the abrasive buffing compound.
It also needs to be noted that all hoses, fittings, and manifolds must be able
to withstand these extremely high pressures that are present throughout the
system.
The second type of high-pressure spray gun is the “high/low” spray
gun. These systems use normal shop compressed air (70-100 psi). Through a specially
designed chamber, the spray gun internally multiplies the spray pressure from
ratios of 14:1 to 20:1. This means that incoming air pressure of 100 psi would
result in spraying pressures up to 2,000 psi, which is more than enough to penetrate
the wind barrier of the rotating buffing wheel.
The major difference of this type of spray gun when compared to either a low-pressure
gun or a true high-pressure gun is the amount of compound dispensed during each
cycle. The compound cavity inside the gun determines the volume of compound
dispensed with each cycle. This can be an advantage, as it will dispense a precisely
measured amount of compound with each shot, allowing for some control over your
process. However this can also be a disadvantage, especially in applications
that require large amounts of buffing compound, as the gun body will not have
time to refill in between spraying cycles.
Other advantages to this type of spray gun include significant compound savings,
low compressed air use, and more consistent finishing results. As with any system
using abrasive compounds at high-pressures, wear and tear on the spray gun is
evident and replacement parts and maintenance will contribute to the total cost
of ownership. Studies have shown, however, that this expense is far outweighed
by compound savings.
Which Method To Choose? Unfortunately, there is no clear-cut answer.
If an operation is currently buffing and polishing in a manually oriented environment,
it certainly should look at automatic solid bar compound feeders, or perhaps
consider evaluating a liquid compound system as an alternate. Manual application
of bar compounds is simply unsafe and unproductive.
Those who are currently using a liquid compound system might want to re-evaluate
their current system and perhaps consider alternatives. For instance, it is
quite simple to connect a low-pressure spray gun system to one compound source
and connect a high-pressure spraying system to another compound source. Analyze
factors such as: compound use, replacement parts costs, downtime, and finish
quality over a period of three to six months. Compound savings may outweigh
the cost of replacement parts and maintenance. It’s also possible that
the volume of production or application simply can’t justify a particular
system.
Often I ask customers why they are using their current method of compound application.
Many times the response is “because this is the way we have always done
it.” While there is no “perfect system” in the world of buffing
compound application, there are alternatives. Take a look—you might be
surprised what you’ve been missing out on.
