TY - BOOK
T1 - Measures for improving quality and shape stability of sawn softwoof timber during drying and under service conditions
T2 - Best Practice Manual to improve straightness of sawn timber
A2 - Tarvainen, Veikko
N1 - Project code: R1SU00884
PY - 2005
Y1 - 2005
N2 - In the EU funded STRAIGHT project, different processing
methods (drying, sorting, conditioning and
re-engineering) were investigated in order to minimise
the distortion of sawn softwood timber. This Best
Practice Manual summarises the main outcome from the
study and was primarily written for industry. This manual
describes the methods studied, and the advantages and
disadvantages they bring to the sawmilling process and
end uses of sawn timber. The methods for improving
straightness are ranked according to a distortion
acceptance percentage measured over the central 2000 mm
portion of structural batten, when straightness is the
main criteria (twist 4 mm / 100 mm, bow 4 mm, spring 3 mm
& cup 2 mm / 100 mm). Other important criteria included
in each assessment is extra drying and handling costs,
the impact of using different methods on other factors of
quality and the improvement in the saleability of
material from normal sawmill production.
The methods studied were a) pre-sorting of logs according
to the angle of spiral grain, b) twisting small diameter
logs during sawing to counteract natural direction of
twist, c) re-engineering boxed-pith battens using green
gluing (splitting battens along their length and
re-engineering whilst "green"), d) twisting the drying
load in the opposite direction to natural twist (the
support sections on the kiln wagon were angled to
counteract the normal direction of twist), e) top-loading
of the kiln, f) oscillating drying schedules to introduce
mechano-sorptive creep to reduce twist, g)
high-temperature drying and finally, h) new conditioning
techniques where dried, twisted timber was re-stacked and
stickered on angled supports to promote opposite twisting
during special conditioning.
It was found that the best straightening results were
achieved by the re-engineering and green gluing of
boxed-pith battens before drying. The most cost-effective
method of improving straightness of timber was
top-loading. How cost-effective the opposite twisting
will be depends on the practical solutions to be
developed. The main disadvantage of top-loading and
counter-wise twisting during drying was the amount of
"spring back" which occurs when timber is subjected to
gradual changes in environmental conditions. These
methods of drying are deemed suitable if the timber is
kept under pressure or used soon after drying or
re-engineered so that the spring-back effect is reduced.
AB - In the EU funded STRAIGHT project, different processing
methods (drying, sorting, conditioning and
re-engineering) were investigated in order to minimise
the distortion of sawn softwood timber. This Best
Practice Manual summarises the main outcome from the
study and was primarily written for industry. This manual
describes the methods studied, and the advantages and
disadvantages they bring to the sawmilling process and
end uses of sawn timber. The methods for improving
straightness are ranked according to a distortion
acceptance percentage measured over the central 2000 mm
portion of structural batten, when straightness is the
main criteria (twist 4 mm / 100 mm, bow 4 mm, spring 3 mm
& cup 2 mm / 100 mm). Other important criteria included
in each assessment is extra drying and handling costs,
the impact of using different methods on other factors of
quality and the improvement in the saleability of
material from normal sawmill production.
The methods studied were a) pre-sorting of logs according
to the angle of spiral grain, b) twisting small diameter
logs during sawing to counteract natural direction of
twist, c) re-engineering boxed-pith battens using green
gluing (splitting battens along their length and
re-engineering whilst "green"), d) twisting the drying
load in the opposite direction to natural twist (the
support sections on the kiln wagon were angled to
counteract the normal direction of twist), e) top-loading
of the kiln, f) oscillating drying schedules to introduce
mechano-sorptive creep to reduce twist, g)
high-temperature drying and finally, h) new conditioning
techniques where dried, twisted timber was re-stacked and
stickered on angled supports to promote opposite twisting
during special conditioning.
It was found that the best straightening results were
achieved by the re-engineering and green gluing of
boxed-pith battens before drying. The most cost-effective
method of improving straightness of timber was
top-loading. How cost-effective the opposite twisting
will be depends on the practical solutions to be
developed. The main disadvantage of top-loading and
counter-wise twisting during drying was the amount of
"spring back" which occurs when timber is subjected to
gradual changes in environmental conditions. These
methods of drying are deemed suitable if the timber is
kept under pressure or used soon after drying or
re-engineered so that the spring-back effect is reduced.
KW - dimensional stability
KW - distortion
KW - straightness
KW - sawn timber
KW - quality improvement
KW - drying
KW - service conditions
KW - Best Practice Manual
KW - recommendations
KW - sorting
M3 - Report
SN - 951-38-6679-3
T3 - VTT Publications
BT - Measures for improving quality and shape stability of sawn softwoof timber during drying and under service conditions
PB - VTT Technical Research Centre of Finland
CY - Espoo
ER -