Q Questions to an expert ti t t Problems related to drying of hardwood Johannes Welling Johannes Welling EDG Seminar in Bled 2009 Johannes Welling
Table of content • Introduction • Why is drying of hardwood so difficult? • Consultancy in drying A public funded service to the industrial clients? • Frequently asked questions – Checking Checking – Casehardening – Discolouration Discolouration • Conclusion and outlook EDG Seminar in Bled 2009 Johannes Welling
Introduction • German situation – 40 million m³ softwood, but only – 10 million m³ hardwood harvested 10 million m³ hardwood harvested • Only small fraction of hardwood converted to high quality products quality products • Main application: furniture, parquet, wall cladding, dec deckings, etc. gs, etc • Hardly no application for constructions • Hardwood mostly visible, softwood often hidden Hardwood mostly visible, softwood often hidden � Quality expectations are high y p g EDG Seminar in Bled 2009 Johannes Welling
WHY IS DRYING OF HARDWOOD SO DIFFICULT? HARDWOOD SO DIFFICULT? Softwood structure • simple s p e • quite homogeneous • very tiny rays very tiny rays • Density difference early/latewood EDG Seminar in Bled 2009 Johannes Welling
WHY IS DRYING OF HARDWOOD SO DIFFICULT? HARDWOOD SO DIFFICULT? Hardwood structure • more complicated o e co p ca ed • Many different cell types • quite inhomogeneous quite inhomogeneous • Wide and high rays • Density difference early/latewood • Density difference early/latewood • built-in weak points EDG Seminar in Bled 2009 Johannes Welling
Consequences • Large vessels act like water pipes, which in some cases are blocked by tylosis • Rays form flaws, in which micro-checks develop easily • Extreme density differences between early and latewood may cause problems y p • High density material dries quite slowly • In high density material steep MC gradients develop I hi h d it t i l t MC di t d l • Steep MC gradients lead to high internal stresses • High extractive content may lead to various types of discolorations EDG Seminar in Bled 2009 Johannes Welling
Consequences • Hardwood Timber is produced and dried in smaller quantities • Differences between the various hardwood species Diff b t th i h d d i are very pronounced • Drying schedules must be adapted to species • Drying schedules must be adapted to species, thickness and quality expectations • Special experience and skills are needed to dry • Special experience and skills are needed to dry hardwood � More problems, more questions EDG Seminar in Bled 2009 Johannes Welling
CONSULTANCY IN DRYING a public funded service a public funded service to the industrial clients? • Only few drying experts available in Europe • Mainly located in universities or research centres Mainly located in universities or research centres • Many experts have retired recently • Positions are not filled again • Positions are not filled again • Whole drying research groups are shut down • Considerable pressure on scientists to find funding • Considerable pressure on scientists to find funding • SMEs not really used to pay for consultancy • Discussion forum not really accepted in Europe • Discussion forum not really accepted in Europe • Language barrier may be one important obstacle EDG Seminar in Bled 2009 Johannes Welling
Frequently asked question and some peculiarities and some peculiarities Checking EDG Seminar in Bled 2009 Johannes Welling
Checking and contract drying • Hardwoods are often dried by contract driers • The drying company does not own the timber • The owner often has carried out a pre-drying • Casehardening or surface checking may be imported into the kiln drying process i t th kil d i • After the kiln drying process, it is almost impossible to determine whether checking o casehardening has to determine whether checking o casehardening has developed during pre-drying or during kiln drying Solution: � check quality before kiln drying !!!! EDG Seminar in Bled 2009 Johannes Welling
Casehardening • Many practitioners do not y p really understand what casehardening is • They are not familiar with application of assessment Stress condition in early drying stage methods methods • They have problems with interpreting the results interpreting the results • They have problems with Stress condition in late drying stage adapting schedules to adapting schedules to avoid strong casehardening EDG Seminar in Bled 2009 Johannes Welling
How to assess casehardening? EDG Seminar in Bled 2009 Johannes Welling
How to assess casehardening? EDG Seminar in Bled 2009 Johannes Welling
Be careful with interpretation! Gap 45 mm 380 mm Gap 45 mm Gap 45 mm 100 mm EDG Seminar in Bled 2009 Johannes Welling
Discolorations • Many different types • Many different reasons • Many different strategies to avoid disclorations • Expert knowledge is necessary • Investigating micro-slices is often necessary • Localisation of coloured substances in the cell tissue is the key to solve the problem i i h k l h bl EDG Seminar in Bled 2009 Johannes Welling
Conclusion and outlook • Questions related to drying defects will continue • Practitioners' expertise on how to avoid problems is diminishing • Knowledge is concentrated in very few experts • Expertise must be translated and become available to practitioners • Practitioners must learn to accept that consultancy services is not for free i i t f f EDG Seminar in Bled 2009 Johannes Welling
Conclusion and outlook • Practitioners should use the EDG discussion forum for getting access to the European knowledge pool in wood drying in wood drying • Record until today – 19 questions posed in 2 years 19 questions posed in 2 years – 29 answers – 5404 views 5404 views � There seems to be some interest � Obviously visitors do not reply to questions � Ob i l i it d t l t ti ?? Any suggestion on how we could change this ?? EDG Seminar in Bled 2009 Johannes Welling
Thank you for listening! Thank you for listening! EDG Seminar in Bled 2009 Johannes Welling
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