EFFECT OF ENVIRONMENTAL CONDITIONS OF TWO NATURAL WOOD SEASONING MEDIA

ABSTRACT

The versatility of wood is due to the level of moisture content in wood which determine the performance of wood in service. This performance is as a result of the process used in the drying of the wood species. Wood can be dried through natural and artificial drying method but natural method required little skills and cost in obtaining desirable result. This project was based on the improvement of the natural method of wood drying, in order to reduce the cost of drying wood. Some wood species were selected and used for this project work and the result obtained at the end of the experiment, was presented in this report. Wood exchanges moisture with air; the amount and direction of the exchange (gain or loss) depend on the relative humidity and temperature of the air and the current amount of water in the wood. This moisture relationship has an important influence on wood properties and performance. This paper discussed the physical properties of most interest in the use of wood products. Some physical properties discussed are influenced by species as well as variables like moisture content; other properties tend to be independent of species.

CHAPTER ONE

  Drying, if carried out promptly after conversion of wood, protects timber against primary  decay, fungal stain and attack by certain kinds of insects. Organisms, which cause decay and  stain, generally cannot thrive in timber with moisture content which is below 20%. Several,  though  not  all, insect  pests can live only in  green timber. Dried wood is  less susceptible to  decay than green wood which is above 20% moisture.   Air drying is the drying  of timber by exposing it to the air. The technique of air drying  consists  mainly  of  making  a  stack  of  sawn  timber  (with  the  layers  of  boards  separated  by  stickers) on raised foundations, in a clean, cool, dry and shady place. Rate of drying largely  depends  on  climatic  conditions,  and  on  the  air  movement  (exposure  to  the  wind).  For  successful air drying, a continuous and uniform flow of air throughout the pile of the timber  needs to be arranged (Desch and Dinwoodie, 1996).  The rate of loss of moisture can be controlled by coating the planks with any substance  that  is  relatively  impermeable  to  moisture;  ordinary  mineral  oil  is  usually  quite  effective.  Coating the ends of logs with oil or thick paint, improves their quality upon drying. Wrapping  planks  or  logs  in  materials  which  will  allow  some  movement  of  moisture,  generally  works  very  well  provided  the  wood  is  first  treated  against  fungal  infection  by  coating  in  petrol/gasoline  or  oil.  Mineral  oil  will  generally  not  soak  in  more  than  1–2 mm  below  the  surface and is easily removed by planning when the timber is suitably dry (Rowell, 1983). It  can  be  less  expensive  to  use  this  drying  method  (there  are  still  costs  associated  with  storing the wood, and with the slower process of getting the wood to market), and air drying  often produces a higher quality, more easily workable wood than with kiln drying.   The  drying  rate  of  wood  differs  due  to  the  amount  of  moisture  content  present  in  each  wood cell. Hardwood is said to be more complex than softwood species, due to the types of  different  component  parts  contained  in  the  hardwood  cell  (e.g.  vessel,  lignin,  cellulose  and hemicelluloses)  and  is  discovered  to  require  more  drying  period  (Desch  and  Dinwoodie,  1996).    The  structural  composition  of  wood  and variation  in  the  physical  properties  of  different wood species are the reason for different seasoning period. Each wood species has  different tendency to drying, when exposed to a particular drying phenomenon.   There  are  various  drying  procedures  which  have  been  practiced  over  the  years  and  the  drying  rate  of  these  techniques  differs  from  one  another.  Some  have  been  discovered  to  be  faster than the others during the process of subjecting the wood to drying. It is important to  dry wood before subjecting it to any use, in order to reduce the moisture content (M.C %) of  the wood. An artificial drying technique has been developed and it has been noted to be very  fast  in  drying  wood,  than  the  natural  drying  techniques.  The  disadvantage  of  using  this  method is that the inner layers of the wood fail to dry properly, especially hardwood species  (Innes, 1996). The  cost  of  installation  of  the  equipment  for  the  artificial  drying  techniques  are  very expensive  e.g.  Kiln  dryer.  It  is  a  more  reliable  means  of  drying  techniques  but  when  considering the cost required for installation of the equipment, it will be necessary to exercise  some  caution  before  embarking  on  it,  especially  by  small  firms.  There  is  a  need  for  modifying the natural process of wood seasoning, since it requires little capital.

1.2 STATEMENT OF PROBLEM

The problem with drying of wood artificially is  on the cost for the seasoning. The different  kilns for drying wood are costly to install. There is cost to be incurred during seasoning on  electricity and heat generation etc. There is a need to find another workable and appropriate  way in which we can bring about reduction in the cost required. This can easily be done by  improving the natural means of wood seasoning. An enclosure with black polythene will be  used to speed up the rate of natural drying techniques.

1.3 OBJECTIVES

To determine the drying time of wood in two different media.

To compare the rate of drying of wood in the two media.

1.3 JUSTIFICATION
Due to the problems of cost which can arise from seasoning of wood using artificial  drying  techniques,  it  became  necessary  to  find  a  means  by  which  wood  can  be  properly  seasoned. The major aim is to use a modified natural seasoning method in drying the wood,  which is often at low cost. Since not most of the people or organisations can afford the price  of setting up of equipment for artificial drying method (kiln seasoning), a certain procedures  has  been  developed,  to  mitigate  the  problem  of  cost  as  well  as  uneven  moisture  content  drying.  It  is  essential to  know the  moisture  content  of  wood  in  any  wood  industry before  using it for construction, because too high moisture content cause movement in the wood. If  such wood is used for construction without been seasoned, warping and curling later occur. It  is  therefore  necessary  to  reduce  the  moisture  content  in  wood,  so  as  to  avoid  attack  due  to  fungi and insects.  This  is done to  ensured the satisfactory performance of wood in  use, the  amount of moisture content in wood is generally reduced before wood is put into service by  the  process  of  seasoning  (drying).  The  reasons  for  drying  wood  before  use  can  be  summarized as follows:

1. Most strength properties of wood are  improved by drying.

2. Nailed and screwed joints are stronger in seasoned wood.

3. Glued wood products perform better when assembled from dried wood.

4. Dried wood is better thermal insulating materials than wet wood.

5. Wood is dried to substantially reduce it shipping weight.

6. Dried wood is less susceptible to damage by insects than wet wood.

7. Prior  drying  usually makes  treatment  of  wood  with  preservatives  more  successful.

8. The electrical resistance of dried wood is much greater than that of wet wood.

9. To dry wood to moisture content required for it use, because wood shrinks as its loss moisture.

10. To  increase  dimensional  stability.  Wood  shrinks  across  the  grain  (not  along  the  grain)  when  it  dries.  If  wood  is  cut  to  size  before  it  is  seasoned,  it  will  shrink during drying and thus be undersized in its final form.

11. To reduce or eliminate attack by decay or stain. Wood that is dried below 20  percent moisture content is not susceptible to decay or sap staining.

12. To increase the strength. As wood dries, the stiffness, hardness and strength of  the  wood  increases.  Most  species  of  wood  increase  their  strength   characteristics  by  50 percent  or  more  during  the  process  of  drying  to  15  percent moisture content.
Therefore seasoning of wood is  of greater importance for economical  utilization of wood. In summary, for efficient and economic utilization of all   useable  wood  species,  it  is  very  important  to  dry  the  wood  to  the  moisture  content required in service.

1.4 SCOPE OF THE STUDY

 This study was carried out to determine the moisture content of wood in two media.  The difference in the moisture content of the two media is compared due to the difference in  the climatic conditions of each medium.

Related Project Topics :