STATIC LOCAL-E TESTING
The measurement of the local-E in a static testing machine is the standard method for the measurement of this property.
Therefore the static local-E sets the standard by which we can judge the accuracy of the dynamic local-E measured by the grading machine.
The Figure below illustrates the principle of three point, centrally loaded on the wide face, static testing. This loading arrangement best simulates the measurements taken in the grading machine. Local-E can also be estimated using other loading arrangements such as four point bending on the wide face if the timber is relatively defect free and the effects of knots on local-E are small. The four point bending approach works best in clear timber.
There are commercially available, dead weight, three and four point testing machines designed to measure the static local-E at the mill. These machines are similar in operation to a laboratory universal testing machine where the timber is loaded over a set span, ie the grading machine test span, and the deflection is measured with a device situated under the timber at span centre. Dead weight testers are normally used in the mill to reduce the overall cost and to simplify calibration procedures.
The static local-E of timber is determined in this type of machine from the force applied, the resulting deflection reading and the timber size. This type of machine has one drawback when we try to test timber with unequal overhanging ends. In this situation, if the unequal overhang is large enough, the local-E can be erroneous. To overcome this dead weights are added to the shorter end to "balance" the overhang. Tadpole provides the necessary tools for the operator to determine the static local-E with the correct "balance" weights and to record the results.
In the Tadpole control system we measure the static local-E of special control sticks called calibration sticks. Calibration sticks are normally made from production material and are used to determine how accurately the grading machine can measure local-E at production speeds. The calibration sticks are passed at specific times during production. Calibration sticks are also called 'control planks'.
We also measure the static local-E of production samples and compare this to the dynamic local-E to determine how accurately the production itself is being graded.
© 2008 Wood Technology Australia Pty Ltd