Friday, January 6, 2012

Hey Grinder Guy, will a screen help me reduce cost in my mulch operation?

Original Post November 1, 2011

            It sounds like you are struggling with operational costs vs. sales prices like most everyone these days.
In short yes, but it does create other issues. Screening will make your mulch perfectly consistant, but can make it look bad too. For example, I recently purchased a $5 bag and a $2 bag of colored mulch from my local home improvement store. The $5 bag was very nicely colored and had a good size and texture except I pulled out about a half dozen pieces that were 10”-18” long. Are you kidding me? This is what I get for $5 a bag? The $2 bag was colored about the same but the product looked awful. This mulch was obviously screened to remove the fines, but it looked as if they removed everything 1 1/2” and minus so it made the product look very rough. But I guess that’s what you get for $2 these days.
            I have seen many mulch companies that have started screening their products to remove the fines, mostly for bagged materials to save on colorant usage and bag weight. Some just drop out fines while others scalp the overs also.
This causes several issues you will need to deal with:
·         The overs are easily recycled back to the grinder
·         The fines must be dealt with. Some sites send them for fuel while others use them for soil amendment. Find an outlet before you start screening.
·         While removing the weight, you are also removing some volume. You will need to increase your raw materials which will increase your cost per yard.
·         Your trucking costs inbound will increase because of the greater volume of  raw materials and your outbound trucking will increase because the weight of the fines is greater than the mulch itself so the truckload quantities will be smaller.
·         Different materials make different sizes after the grinding process, so you may need to mix materials or change screen sizes on the screener

So what is the answer?
Just dropping out the fines is a quick fix
If you have an abundance of materials and have a lucrative market for the fines, then that is fine. If not, MAKE LESS FINES!
The number one mistake operations make is that they keep everything the same and drop in a screener, so you end up with the same costs, wear etc., plus you added a screener. You are screening to make the perfect product, so use the screener to make your product size and not the grinder. Increase the grinder screen size. If you use a 1 ½” to make your mulch, then try a 3” screen to feed into the screener and keep increasing the screen size until the finished product size starts looking too rough. This will reduce your fines, fuel usage and wear, and then recycle the overs back to the grinder.

What screener?
·         Trommels work better than flat decks because of shear screen volume but nothing works better than a star screen for easy adjustability in product size without changing screens.
·         Match the screener to your finished product production rate. Matching the grinder production rate, especially after increasing screen sizes, will overload every other component downstream, unless you are only stockpiling.

Fines screen sizes will be anywhere from ¼” to ¾” depending on your product, but don’t drop out too many fines. The overs can usually be scalped with 1 ½” or 2”. The star screen adjustability makes it “push buttoningly” simple to change the product size on the fly.

In conclusion, if you couple the grinder to a screener you are now starting to automate the process. Whether you are grinding whole trees or regrinding, you can now load at a specific rate while reducing engine load and fuel usage and extending the life of your engine and grinder.
Combine those savings with your savings from increasing the grinder screen size which increased your grinder wear parts life, and now it makes CENTS to screen your mulch.

Have a question, we’ll try and answer, grinderguy@askthegrinderguy.com

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