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What is "bruising?"
Bruising is a manmade defect in hard maple that is caused in the
sawmill where there is a line bar resaw equipment or certain types
of edger equipment involved. With the installation of all the line
bars by suppliers in our region, we have seen the onset of an epidemic
in bruising that has caused a great deal concern. While we believe
that the benefits of line bar technology far outweigh the problems
they cause in hard maple, we can’t overlook the fact that
line bars are the root cause of bruising and that bruising is a
very concerning issue.
How does it occur?
Bruising occurs as the line bar equipment applies pressure to the
cant while processing, and may happen at any of the following locations:
1) In-feed deck chains, which are in constant motion underneath
the cants as they wait their turn to be processed
2) Cant turners
3) Knurled press feed rollers on the line bar
4) Jump chains located after the line bar
At any one of these stations significant pressure is applied to
the face of the cant, which dents the wood or crushes cells thus
traps moisture in these areas leaving stain in the form of bruising
in the drying process. (our humble, non-scientific theory) The end
result is an odd, splotchy, or dimpled looking, type of stain that
occurs on one face (normally the whitest face) that can be very
clearly distinguished in our lumber at 15/16".
Of the various kinds of bruising, some are more prevalent and significant
than others, either because they either occur more often per thousand
board feet or the stain penetrates deeper into the boards. Or just
plain looks worse than other forms of bruising. (We have identified
four main types of bruising. See the photo at right.)
What has Banks Hardwoods done to address the issue of bruising?
Initially, as bruising began to appear in our lumber, the rough
looking material was cause for concern by our inspectors and for
many of our customers so we began to pull it out of our normal shipments
of #1&2 white maple. Today the percentage of bruising we see
in an average month of production from our supplier base has grown
to approximately 30%. Originally, we began to pull it as a part
of our paint grade, but after tests and experimentation with various
customers and internal product lines here in our own component plants
we have determined that it warranted a better fate. For over a year
we have used the bruised stock internally for our own panels and
mouldings and have been able to monitor the results very closely.
We have experienced little yield loss despite the poor looking lumber
that bruising creates.
How much of a problem is bruising?
It is far less of a problem than normal stain, carmelization, sticker
shadow or block shadow because it comes out during normal processing.
It appears after surfacing to 15/16", but most of it, miraculously,
comes out while being machined to finished thickness. (13/16"
or less) Our studies have shown that when we take .075 - .080"
off the bruised side, 90% of all types of bruising comes out. We
have educated our employees on this issue and have taken measures
to make sure they run the bruising correctly through our machines.
We are now used to dealing with bruising and have developed an internal
awareness as to how to deal with it. This will be important for
our industry to eventually adopt as well.
How have others addressed this problem?
Because we have been pulling most of the bruising we see at the
planer before our customers see it we haven’t heard too much
negative feedback about bruising so we don’t know exactly
how are customers have handled this issue internally or exactly
what they know about it. Also we do not know how our competition
has handled this issue either.
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Rough maple at 15/16".
The same maple samples, finished to 13/16".
Have significant amounts of lumber been wasted because
of this problem?
We realize we are a fairly large supplier of white hard maple to
our industry and we have tried to act responsibly for the benefit
of those who receive our material. We have always tried to hold
high quality standards and in the future it is certainly our goal
to continue to do so. Perhaps in this case we have overreacted.
Fortunately, we’ve had an internal place to go with the material
while we’ve figured it out.
Are you planning on any changes to your policy on bruised
maple?
In the future, to reflect what we feel is a more reasonable solution
to this issue we have adjusted the amount of bruising we are pulling
from our #1&2 white sort now that we have developed a better
understanding of the defect. We are now pulling only the most severe
bruising defects, which through our research have shown to be the
most difficult. Our initial plan is to continue to monitor how that
works in house with our products before we try to reduce the percentage
further. In the meantime we hope to get feedback from our customers
as to what their findings are throughout their systems. Our hope
is that we will all find that while bruising looks bad at 15/16",
it can basically be ignored except for the worst examples.
We also hope to continue to provide feedback to our green suppliers
so that they can be aware of this as an important issue and make
any changes they feel might serve as a partial remedy. Things that
have been discussed have been regulating the pressure of the knurled
press rollers or experimenting with rubberized products instead
of metal in certain areas of the mill equipment. Awareness is the
first step. I doubt there is a perfect solution but there is no
need to go on without a strong focus by all involved so that we
can better understand what we are dealing with.
How can I help?
If anyone who reads this has a better understanding of bruising
or has identified good solutions, or has comments that might be
helpful I would very much appreciate you contacting me by fax or
e-mail.
Thank you.
616-483-2483 or stevebanks@bankshardwoods.com |
