Fundamentals
of Mass Finishing
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Mass finishing today is typically done in vibratory finishing
machines, either bowls or tubs. Some of the other processes used are
tumbling
barrels (the old way), centrifugal barrels (commonly known as
Harperizers), and centrifugal disc machines. Education in this "black art" is somewhat
limited since the only University that offers courses in it is SHK (School of Hard
Knocks). For that reason this page was written as an introduction to mass finishing.
The primary uses of Mass Finishing
Deburr
Burnish
Improve surfaces
Clean
Dry
The elements of Mass Finishing
Parts
Equipment
Media
Compound and water
How this works out in real life
Look at your parts and volume
Shop to find the best machine for the job
Make the installation and get it running
Operating tips
Primary uses of Mass
Finishing
Deburr
Deburring is the operation normally thought of in vibratory
finishing. Usually using a mild compound and a ceramic media to deburr the
parts. Most parts are done in a 15 to 30 minute time cycle. As a byproduct of the
deburring, the compound has cleaned the oil or whatever off
of the part and it is now clean.
Burnish
Burnishing, (peening metallic parts to a brilliant luster), can be done with
porcelin media but is usually done with
steel media. Steel media can be had in a number of shapes, but a funny,
flying saucer looking thing, called a balcone is the most popular.
Unlike deburring, when burnishing, compound selection and
metering is critical. You may have to try 4 different burnishing compounds on
aluminum or zinc parts to find the one that makes your parts look the most brilliant,
and once you
get set up and running, if you let it run out of compound for only a few
minutes, your media will turn dull and your parts will look
dull. Remember, when burnishing, your parts will never look better than
your media, so you must keep your media brilliant.
Improve surfaces
With proper media selection, you can change the surface to fit
your requirement. You could use ceramic media to give it a satin finish or
a prepaint finish. You could use steel media to burnish it to a
very shiny surface. Plastic media could be used to give it a smooth
preplate
finish. You can even go the other way and take a smooth part, by using a large media,
and rough it
up. The main thing is to use proper media selection to achieve the surface
finish
you want.
Clean
If you have dirty, oily or greasy parts and need them cleaned, this
can be done in a vibratory finisher. The normal procedure for this would
be to use a machine with internal separation, leaving the gate in the
unload position all the time, dropping the parts in and letting them go
thru one time and then come out of the machine. Because you are trying
to do this in one pass, the larger the outside diameter of the
machine, the better, since all things being equal, more diameter will give
you more time in the machine for the work to be done. If you are using a long radius
machine then it will probably handle steel media which would probably be best for this
application. Then you won't have media wear to worry about which not only costs
money but when it wears down to a size that will lodge in your part, well you know the
rest of that story. If you do use ceramic media for this application go with a
porcelin media that wears very little to minimize media cost and wear/lodging problems,
since the medias only job in this application is to scrub. The compound
is the main force in this job.
If you also want to deburr the part along the way then use conventional
ceramic media. If you use steel media you will still get deburring action
by the media hammering down the burrs. It won't be like being sanded off,
but there won't be any real sharp edges that would cut an assembly person.
Your compound selection, rate and water flow rate will be based on what
you are trying to take off of the part and how effective your compound
is. This job takes a pretty strong compound. Normally this is
done with
cold water because water over 120 degrees can soften the liner and cause
premature wear. If these clean parts need inhibited to keep them
from oxidizing, you can place a spray bar over the screen deck to spray inhibiter on the parts on their way out of the machine.
Dry
The typical use for vibratory finishers in drying is to use ground
corn cob as a media. When the parts come out of the machine used for
finishing, they drop into the machine used for drying and go around one
time and then come out of the dryer. After the cob has dried the part the
cob will continue to polish the part until it comes out.
Elements of Mass
Finishing
Parts
Part size primarily dictates the type of machine you need. Small
parts are generally high volume and you will want a bowl type machine with
internal separation of the parts and the media so you don't have to hand
pick 10,000 parts out of the machine when they get done. If the parts are larger
there won't be many of them in there at a time so you can hand pick the parts faster
than you can use internal separation. If the parts are even larger they may be too
big for the channel width of most bowls and then you would want a tub.
Equipment
After you decide that vibratory finishing equipment is what you need, its
time to take a look at the different styles and see what would be best for your job.
Simple bowl type vibratory finisher
If your part doesn't tell you it needs anything special, then the
simplest machine to do the job would be with a bowl type machine without
internal separation. In this operation you just throw the parts in, wait till they are
done, and hand pick them out. Depending on the
manufacturer and the options, this machine can have as few as one moving part. The motor spinning in the center.
Bowl type with internal separation
If your parts are very small there might be hundreds of them in the machine at a
time. It would take too long to hand pick the parts out after every load so you need a
machine with internal separation like the one pictured above. When the parts are
done, the lever on the right lowers a dam into the machine
and then instead of the mass going around and around, it goes up over the screen,
the media falls thru the screen, and the parts walk out of the machine. When the
last part comes out, you move the lever again to raise the dam and put in another load of parts.
Long radius bowl type vibratory finisher with internal
separation
A long radius machine is used when some or all of your parts can be processed
in one revolution. It can be used like a normal machine when that is what you need,
but the fun begins when you have a part that can be processed in one revolution.
You set the gate to the unload position. Now you
are continuously loading parts, they are going around one time, and then coming out,
bypassing the load/unload time.
Depending on your cycle times you can get up to twice as much production out with a
long radius. Good applications for this are cleaning, light deburring, taking the sharp edge
edge off of stampings, getting
that die cast look off of die castings, etc. You can get
7 or 8 minutes pretty easy out of a long radius machine.
Generally speaking, the larger the diameter of the machine, the more minutes you
are going to get. More minutes means more flexability.
On the machine pictured above is the control panel
with timer. This can be used to time your loads during the day, or if you
have long cycle time parts, you could set it to run parts as you leave at
the end of the day to have a load done when you return in the
morning. The little yellow thing to the right of the control panel is the
compound proportioner. Water is piped to it. It sucks compound out of the 55 gallon
barrel placed beneath it and mixes it with water at the rate you
set. Altho not seen in the photo, the flow meter is beside the pump and
you set the compound solution flow with it, marked in gallons per hour. Note
the sediment ring underneath to give sediment
time to settle before going down the drain. On the side is a load chute
to load parts into. Most long radius machines have this to get an extra 30 seconds
or so of run time when in the continuous mode. Long radius machines are great, but
if none of your parts can be run in one revolution then the only benefit is they have a long radius and this gives a shallower angle as the parts come out of the machine. This makes unloading parts much easier. A 20 cu ft long radius is more expensive, uses more electricity,
takes up more floor space and costs more to reline, yet processes the same
amount of parts as a conventional 20 cu ft machine when not being used as a one
revolution machine.
Tub type vibratory finisher
If your parts are very large or very long, then as you can see they
are probably not going to work very well in a bowl. This would be a tub
application. These machines are available in sizes as small as 12" x
12" or as large as the 48" x 144" machine pictured above or as long as 30'
or more. The drive system is more complex than on a bowl. Generally, the
main motor will belt drive some type of variable speed unit which will in turn
belt drive the driveshaft or shafts, with
the larger machines requiring dual shafts or even triple shaft
drives. Each of these shafts will have bearings, couplers, universal
joints, driveshafts between the trunnions or something. Don't let all of
this scare you, just realize that in general, a tub has a more complex drive system than a bowl.
Tub type vibratory finisher with
dividers
If your parts can't stand any part on part
impingement then you must use something like a tub with dividers. On this
particular machine the dividers are movable and removable so that you can
set up as many compartments as you like, or remove them all and run 16'
long parts.
Typical flow thru installation (sometimes called
a continuous)
In a flow thru, parts are dropped in on the
far end and pass thru the machine one time and then come out. Unlike a
bowl, where you can run the part for whatever amount of time you want and
then unload it, on a flow thru you only get a certain amount of time. This
is usually from 6 to 20 minutes depending on the machine. The longer the
machine, the more minutes. With a bowl you lose time loading and
unloading. With a flow thru it is continuously processing. This
makes for a very high output machine. Flow thrus
are also very complicated machines. Imagine how many moving parts there
are to this thing. Generally, the
main motor will belt drive some type of variable speed unit which will in turn
belt drive the driveshaft or shafts, with
the larger machines requiring dual shaft
drives. Each of these shafts will have bearings, couplers, universal
joints, driveshafts between the trunnions or something. Then there is the screener
with motor, belt, vibe unit of some
type and normally fiberglass springs. Then there is the elevator with motor,
gearbox, chain drive, belt and many bearings. If you buy one of these
things, the production manager may love you, but the maintanence man will hate your
guts. Illustrated is a normal
oscillating screener to separate the parts from the media. In
addition to having a big wide screen deck to separate parts from
the media, you can also have a media classifier underneath the primary
screen to classify the media when it gets down to a size that can lodge in
your part. This is a big deal if you have media lodging
problems. Some good applications for a flow thru are die castings,
stampings and powdered metal parts. The amount of time a flow thru gives is
a good match for what
these parts need. Very few flow thrus are capable of handling steel media
so if your parts need this keep it in mind. On some applications people are
trying to replace flow
thrus with multi-passes and racetracks.
Typical multi-pass machine
The object here is to try to
get more minutes of process time in one pass like a flow thru, but with the
simplicity of a bowl. The channels
on these are normally not wider than 8" so they are for smaller
parts. Altho you can load it heavily and process a lot of parts, you
can also drop a part in every 10 or 15 seconds and it will never catch up to
the part in front of it, as it approaches the unload ramp, and ding it up like they
can do in any other kind of
machine. Another strange and neat thing
they do is that the part stays in the same amount of time whether there is
1 part in the machine or 500. So if you are running a
stamping press and there are normally 100 parts in the machine at a time
as you are running continuously and suddenly the press stops for what ever
reason, the parts come out in the same amount of time. Whereas in a flow
thru, since it is gravity fed and dependent on total load, it loses its
feed as no new parts are coming in.
Oval type finisher (sometimes called a race
track)
Ovals are another means to simulate a flow thru, but with a simpler
machine. The run length of the channel can be made long enough to give
several minutes in a one pass thru operation. Notice
how there is plenty of room for an extended screen deck to
make for good parts/media separation. There is also room for a media
classifier. So there we have all of the good features of a small flow thru
with a machine that has more like the simplicity of a bowl.
If you need to run your parts 10 minutes in one revolution an oval might be
the cheapest way to do it. And most ovals have a gate so you can use it as a
conventional machine when you need to, a feature not found on flow thrus and
multipasses. These machines won't yet replace the largest of the flow thrus but
development is ongoing.
Cob Dryer
This is a vibratory finisher used as a cob dryer. Altho parts can be
brought from anywhere and thrown in, it is normal to have the parts come right out of the vibratory finisher, as on the left in this photo, and fall into the load chute of the cob
dryer on the right, then go one revolution in the cob dryer and come
out. If the part has any blind holes, it won't work well with cob. The cob
sticks in the holes and won't come out unattended. Normally, cob
dryers don't have a lining or a gate.
Combo style machine
This is what is called a combo machine. Combos are neat. It is a normal vibratory
finisher on the inside, but when you raise the gate to unload, the parts (after being separated from the media)
fall into a cob dryer ring on the outside that acts like
a stand alone dryer. The part goes around the cob ring one revolution and then comes
out. If your parts are not too friendly, or you are running a large
volume of parts, your cob may get wet. In that case you will need to heat
the cob by some means. This particular machine uses heat
lamps. Those are the three things you see hanging over the
outside ring.
Media
Media Composition
For general deburring this will probably be a preform shape ceramic with
aluminum oxide abrasive impregnated. Random shape aluminum oxide or novaculite might be used. For burnishing, a case hardened steel formed
media would probably be used, but a porcelin could be used if your machine
can't handle the weight of steel media. Plastic media might be used on aluminum parts and for very fine finishes or preplate finishes.
Media size and shape
After your composition is selected you must look at what size and shape
media to use. You want to select your media to give the best finish,
without lodging, with longest life. First, decide on what shape would be
best to keep from lodging, then see how big of a size you can use and
still keep a good finish. Big media is cheaper than small media, big
media lasts longer than small media, big media cuts faster than small
media, but big media doesn't give as fine a finish as small media. So use
the largest media that gives you a finish that you can live with.
Media to parts ratio
Last you must decide what media to parts ratio to use. What you are
trying to do here is to maximize the amount to parts processed with out
suffering part on part impingement. Some examples of media to parts ratios
are:
1:1 Equal volume of media and parts, this can only be used when part
on part impingement is not a problem because with this small amount of
media they will be hitting each other alot.
4:1 Probably average ratio. Delicate parts may get dinged up at this
ratio, but most are safe. If you are running a bowl type machine with
internal separation this ratio gives plenty of media to push the parts
out.
10:1 10 times as much media as parts. This gives more media in the machine so there will be less part on part impingement.
Compound and water
Altho some people still use dry powder compounds, most people today
use a liquid flow thru system for the compound and
water because this setup is easier to handle and leaves less room for operator error.
In this setup, compound and water are mixed, usually by a
proportioner but can be done manually, and continuously fed
into the machine. The drains are open and continuously
drain. Regardless of what you are doing with your machine, solution
flow thru the machine will be about 1 gallon per cubic foot per hour, unless
you are doing massive dirt or grease removal.
Compound usage averages about 1 ounce per cubic ft per hour. Compound
selection depends on the job to be done. Deburring is fairly simple and
most compounds will give good results. Burnishing is more difficult and
you might have to try several different compounds to achieve the color you
want, especially on aluminum and zinc. Degreasing is going to take a pretty strong
formulation to cut the
grease. Inhibiting is usually pretty easy, depending on your climate and
how long you need to protect the parts.
How this works out in real
life
Look at your parts and volume
Calculate how many parts per hour that you need to run, how long it will take to
run them, the media to parts ratio that the parts need and how many parts will fit
in a cubic foot to come up with the size and type of machine you need.
Example:
You know that you need 40,000 parts per week.
Your shop runs 40 hours per week, so you need 1,000 parts per hour.
You know from the sample tests that the part will be done in 15 minutes.
You calculate it will take 15 minutes to load and unload.
So we now know that the machine must hold 500 parts per load.
The part doesn't get beat up too easily so we will go with 4:1 media ratio.
You measure your parts and 500 of them are 4 cubic feet.
You now know that you need a 20 cubic foot machine.
Shop to find the best machine for the job
Look at the available machines. Always think about keeping it as simple as
possible,
without giving up the capabilites you need.
If you are buying a bowl type machine and you can do without internal
separation, then buy without it. You're machine will be much cheaper and simpler.
Automatic recirculating oil lubrication generally isn't needed on machines of
10 HP or less so why put up with all of the additional complexity. Just get
manual grease lube. Keep it simple.
A low working height will make it easier to gets parts in and out.
Where will you get parts and technical help on this machine?
Buy a good name brand machine from a guy you can trust to help you
along. Don't buy a no-name machine from some shyster, who has no idea what
it is or does, and couldn't set it up to test run it for you if he had to.
Remember, you make your money by getting parts out the door, not by saving 50 cents
on a machine.
Make the installation and get running
If you have a choice on voltage, go 460 volt instead of 230. This will cut
your amperage draw in half. Take a look at the different compound proportioners
available, some can run 5 machines as easily as one. Think about using a sediment tank
if possible, to keep from running the sludge down the drain.
If you can buy your compound in totes,
it should be cheaper, the freight should be less and you won't have the drums to
dispose of when they get empty.
Whatever you do, don't try to reinvent the wheel. Life is too short to
do everything the hard way. Alexander Graham
Bell invented the telephone for a reason. It was so you could call
somebody when your vibrator is not running right. If you need some
help, call the guy you bought the machine from, call the compound
supplier,
call the media salesman, call your momma, call someone.
Operating Tips
Compounds
For a starting point, mix your compound 1 ounce to a gallon of water.
Start with a solution flow of 1 gallon per cubic foot per hour.
Use the least amount of compound that you can.
The mildest compound that will do the job is best.
Just about anything will work deburring clean steel parts.
Burnishing zinc takes a different compound from burnishing aluminum.
Burnishing in one revolution sounds easy, but seldom is.
Some compounds are slipperier than others and make it hard to unload.
Alkaline compounds provide some rust inhibiting.
Suds kill action.
Some compounds suds up more than others.
Water kills action.
Make sure your drains are working well.
Know your compound ph.
Keep liquid compounds from freezing.
Don't forget, some compounds are strong and can cause great pain.
Soft water works better than hard water and doesn't spot as bad.
Have your MSDS handy in case the Feds drop in.
Media
Big or heavy media cuts faster than small or light media.
Small media gives a finer finish than big media.
The more abrasive the media the faster it wears out.
The more abrasive the media the greater the wear on the liner.
Steel media solves the sludge problem.
Balcones are the benchmark steel media.
Balcones roll and unload better than other steel media.
If your machine can't handle steel media, try polishing spheres.
Plastic media is often used on aluminum parts or for a pre-plate finish.
Sometimes plastic media can be used with water as compound.
Sometimes aluminum oxide media screws up later brazing of your parts.
Weight and lead angle for bowls
Shaft rotation is opposite desired media direction of travel.
The bottom weight leads the top weight as the shaft rotates.
Lead angle is the angle between the top and bottom weights.
90 degrees is a good starting lead angle.
More lead angle increases forward speed.
More top weight increases forward speed.
120 degrees gives maximum action.
Adding bottom weight increases roll.
Decreasing weight on one end can act as increasing the other.
Adding more weight anywhere will increase action in general.
More total load in the machine requires more weights.
The least amount of weight that will do the job is best.
You generally have nearly twice as many weights on bottom as on top.
If the machine jumps up and down that is usually too many total weights.
Machines
Ultramatic makes a nice flow thru package.
Rotofinish has the best burnishing reputation.
Almco makes good tubs.
Sweco has quality second to none.
Ultramatic makes the best very large tubs.
Combos (bowls with a cob ring on the outside) are neat.
To be a burnisher the machine would have to handle steel media.
To handle steel media it will have to have more horsepower.
To handle more power the machine needs to be built stronger.
If it doesn't have 1/2 HP per cu ft it probably won't handle steel media.
A machine can run batch with less horsepower.
In theory a soft liner is better for burnishing than a hard liner.
Anybody can make a good small burnisher.
A curved outer wall prevents light flat parts from dancing there.
A gate hinged at the bottom prevents trapping parts unseen.
Rotofinish gate clearing is neat to prevent trapping parts.
Recirculating oil lube isn't needed on machines of 10 HP or less.
Only use a flow thru if you can't get the minutes you need in a bowl.
Flow thru's are a hassle but nothing will throw more parts on the floor.
A benefit to flow thru's is the media classification that you get as a plus.
Multipasses and racetracs are trying to replace some flow thrus.
General operating tips
Don't think you know it all, if you need help, call someone that knows.
Take care of your machine as if it costs money to replace it.
Don't try to run a part more than 75% the width of the tub.
Devcon can be used to patch bad places in your lining.
Be good to your environment.
Cob meal dryers work awfully good on some parts.
If your machine has an oil cooler, run the water thru it before using it for compound.
Don't let your steel media rust.
Constantly ride your maintenance people to take care of your machines.
Just about the time you think you know it all about vibratory
finishing, along comes a part you thought would be easy and it makes a fool out of you.
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