Q Questions to an expert ti t t Problems related to drying of - - PowerPoint PPT Presentation

Q ti t t Questions to an expert Problems related to drying

• f hardwood

Johannes Welling Johannes Welling

Johannes Welling EDG Seminar in Bled 2009

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

Johannes Welling EDG Seminar in Bled 2009

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,

deckings, etc. dec gs, etc

• Hardly no application for constructions
• Hardwood mostly visible, softwood often hidden

Hardwood mostly visible, softwood often hidden Quality expectations are high

Johannes Welling EDG Seminar in Bled 2009

y p g

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

Johannes Welling EDG Seminar in Bled 2009

WHY IS DRYING OF HARDWOOD SO DIFFICULT? HARDWOOD SO DIFFICULT?

Hardwood structure

• more complicated
• 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

Johannes Welling EDG Seminar in Bled 2009

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

I hi h d it t i l t MC di t d l

• In high density material steep MC gradients develop
• Steep MC gradients lead to high internal stresses
• High extractive content may lead to various types of

discolorations

Johannes Welling EDG Seminar in Bled 2009

Consequences

• Hardwood Timber is produced and dried in smaller

quantities Diff b t th i h d d i

• Differences between the various hardwood species

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

Johannes Welling EDG Seminar in Bled 2009

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

Johannes Welling EDG Seminar in Bled 2009

Frequently asked question and some peculiarities and some peculiarities

Checking

Johannes Welling EDG Seminar in Bled 2009

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

i t th kil d i into the kiln drying process

• 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 !!!!

Johannes Welling EDG Seminar in Bled 2009

Casehardening

• Many practitioners do not

y p really understand what casehardening is

• They are not familiar with

application of assessment methods

Stress condition in early drying stage

methods

• They have problems with

interpreting the results interpreting the results

• They have problems with

adapting schedules to

Stress condition in late drying stage

adapting schedules to avoid strong casehardening

Johannes Welling EDG Seminar in Bled 2009

How to assess casehardening?

Johannes Welling EDG Seminar in Bled 2009

How to assess casehardening?

Johannes Welling EDG Seminar in Bled 2009

Be careful with interpretation!

380 mm Gap 45 mm Gap 45 mm Gap 45 mm 100 mm Johannes Welling EDG Seminar in Bled 2009

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

i i h k l h bl tissue is the key to solve the problem

Johannes Welling EDG Seminar in Bled 2009

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

i i t f f services is not for free

Johannes Welling EDG Seminar in Bled 2009

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 Ob i l i it d t l t ti Obviously visitors do not reply to questions ?? Any suggestion on how we could change this ??

Johannes Welling EDG Seminar in Bled 2009

Thank you for listening! Thank you for listening!

Johannes Welling EDG Seminar in Bled 2009