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Timber drying: top loading

Resources:
Materials
Sector:
Timber and woodworking
Investment cost:
High cost
Payback time:
0.5 - 1.5 Year(s)
Read more
Cost savings:
1 - 3%
Investment cost:
10000 - 30000€
Investment cost for concrete block top loads can be medium to high, investment cost for pneumatic pressure frames is higher
Payback time:
Payback time depends on drying capacity, timber type, and type of top loading method used
Assumptions taken in the presentation of the above performance indicators:

Example calculation done with

  • Kiln capacity approximately 7 000 m3/a
  • Timber price €200/m3

Top loading is an effective method to reduce the twisting of timber during drying. Top loading can be applied using weighted blocks, such as concrete, laid on top of the timber stacks loaded in the kiln, or using pneumatic or hydraulic pressure frames, that are pressed into the top layer during the drying process.

Pneumatic pressure frames require greater investment, but the benefit is that they can adjust the pressure during the drying process. Also, in contrast to concrete block loading, pneumatic pressure frames do not reduce the drying capacity.

Some of the benefits of top-loading can be lost due to the spring back effect after drying. The pressure frames and blocks need to be made from non-corrosive materials to withstand high temperatures and humidity in the drying kiln.

Results

  • Top loading reduces distortion and results in straighter timber with fewer quality problems, which increases its value and reduces material loss
  • Top loading can even help to avoid package collapse during drying
Source

Tarvainen, V. (2005) Measures for improving quality and shape stability of sawn softwood timber during drying and under service conditions, VTT Publications 584, https://www.vtt.fi/inf/pdf/publications/2005/P584.pdf

 

 

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