WHEN Magazine Article- Nov 2012 www.wastehandling.com
This is one of the most overused benefits made by all kinds
of Salespeople, Operators and Manufacturers.
My screens are round and they give me a better
product!
My screens are hexagons and they give me a better product!
My screens are a square and they give me a better product!
I’ve heard it all. And all may be correct. They all may be
wrong also.
So lets figure out what they are really saying.
Here are some facts:
- The same size hole does
not give the same size product in all materials. Green wood is different
than dry wood, logs are different than yard waste, etc. The more moisture
in materials, you will need a larger screen to be able to grind it. Dry
wood requires a smaller screen because you need much more cutting action
on all the pieces for consistency.
- The thicker the screen,
the more baffling effect you will get, which means more fines
- Screens cut on an angle
will give you less fines and more production but also larger material
- A great piece of advice
from Lori Rheinberger of QueenofParts.com,
an Aftermarket Manufacturer: As a rule of thumb, 70% of your material
will be ½ the dimension of your screen size or smaller. So, for example,
with 4 inch screens, 70% of your material should be 2” minus with the
balance being larger than 2”. Good rule to start from when trying to size
a product initially.
Any screen you buy, from the OEM
or Aftermarket Manufacturer, are all design engineered before they are cut, unless
you and your torch are making them in your shop.
On every engineered drawing the actual open hole space
should be shown. That and only that can actually compare 2 screens and how they
compare to the actual product and production versus each other. Because if a
screen doesn’t have the same open area, they are not equal.
What does that mean? With 4” screens, maybe 50% of the
actual screen is open space for material to fall through and the other 50% is
the steel framework making the 4” holes. If you increase to 6”, that open space
may increase to 60%, thus more production and larger product.
But what about using the same
dimension?
For example:
- A round 1 ½” hole measures
an area of 1.77 sq. inches
- A square 1 ½” hole
measures an area of 2.25 sq inches
- That is over 25% more open
space in the square hole
- This means you will get
larger pieces in the square hole and more production.
- Multiply the 25% times
every hole in the screen and you see how much more open space is in the
screen and how your production will increase because of it.
In addition, when the square hole
pattern is layed out on the steel for cutting compared to a round hole, the pattern
lays out much more efficiently creating more holes, which means much more
production because of the extra space created by the extra holes.
So the operator that says, “My
square hole gives me a better product” might be comparing his production to a
round hole screen.
But because the Round hole screen
is smaller and then will have less holes per screen, it will make a finer
product than the square screen, which the other operator may say, “My round
hole gives me a better product” because he has smaller material.
Lastly, the hexagon, which seems
to be the latest greatest in the industry. Layed out for cutting on steel plate
it is probably the most efficient. But be careful, because a 2” hexagon does
not have the same dimension area as a 2” square hole, but just by having more
holes, it will give you more open space and more production. So the operator
that says, “My hexagon hole gives me a better product”, may be comparing his
production to a square hole he used previously. You never know what the
comparisons truly are?
In conclusion, what do we do?
·
Try different screens
·
Ask your supplier for engineered drawings so you
can compare open area of the screens
·
Ask your supplier what customers are buying now
compared to last year or the year before
·
Thinner is better for production quantity and
fines reduction
·
Try to get screens that are angle cut to
increase production and reduce fines
I have some photos posted at www.askthegrinderguy.com for you to
compare and review.
Questions, comments? Dave Whitelaw, grinderguy@askthegrinderguy.com