HOW TO PERFORM THE VOLUMETRIC SHRINKAGE TEST OF TIMBER (IS : 1708 ( Part 3) – 1986) ?

VOLUMETRIC SHRINKAGE TEST OF TIMBER

This test is performed to determine the amount of volumetric  shrinkage happen in timber when it moves from wet to dry condition. Volumetric shrinkage tells how much a wood species will shrink, but it doesn’t indicate the direction of the shrinkage. The two primary planes or surfaces of wood where shrinkage takes place are across the radial plane, and across the tangential plane, corresponding to radial shrinkage, and tangential shrinkage; these two values, when combined, should roughly add up to the volumetric shrinkage.

OBJECTIVE

To determine the volumetric shrinkage of timber.

APPARATUS :

• Weighing Balance : 0-10 kg.

• Oven : maintain a temperature of  105- 110°C

PREPARATION OF SAMPLE :

The specimens of timber are prepared with  5 × 5  × 15  cm or 2 × 2  × 6  cm sizes.

PROCEDURE :

• The specimen is weighed initially (usually green) and the volume determined.

• A suitable vessel, half filled with water, is kept on the pan of a weighing balance and weighed.

• The specimen is then completely dipped in water by means of a needle and  weighed again. The difference of the two readings is volume of the specimen.

• The specimen is taken out of the water, wiped with dry cloth, end-coated by immersion in hot paraffin, allowed to air-season under room conditions and weighed periodically until moisture content of about 12 per cent is reached. The volume is determined again.

• The specimen is then kept in an oven at 103° 2°C until an approximately constant weight is reached.

•  After oven-drying, the specimen is again weighed and, while still warm, is immersed in hot paraffin wax bath,care being taken to remove it quickly to ensure only a thin coating.

• The volume of the paraffin-coated specimen is determined by immersion as before.

CALCULATION :

Volumetric shrinkage form initial condition to required dry condition =

Moisture Content =

Oven Dry Specific Gravity =

where 

W1 and V1 = Initial weight and initial volume

Wr and Vr = Weight and volume at the initial required dry condition at r per cent moisture content.

W0 and V0 = Final weight and final volume