Summary
• Dutch research and development has resulted in a wireless, hand held means of grading.
• Its performance is comparable to a larger, mechanical grader.
• An in-line system has also been developed and measure 30 boards per minute.

A collaborative venture between the University of Delft in the Netherlands and the Dutch company Brookhuis Micro Electronics has resulted in cheaper, more compact technology for timber grading to current and upcoming EU standards.

Machine grading generally works by measuring the straightness of sawn timber in an unloaded condition and the deflection caused by a standard load applied by the machine, then computing the stiffness through a comparison of the two values. Usually automatic-ally, that value is then compared with values set by the current standard and the appropriate grade is printed directly on to the timber.

Such equipment provides a means of meeting the rules, including the latest EU Directive which will make it obligatory for rectangular cross-section structural timber as tested to EN 14081 to be CE?marked (see below), but it also tends to take up a lot of floor space and is not cheap.

The Brookhuis solution uses a laptop, a printer and wireless communication – and it’s hand held.

The new electronic Mobile Timber Grader (MTG), which calculates stiffness, natural frequency and strength to a range of international standards, is simply held against the cut end of a piece of timber and displays all the relevant measurements on an LCD screen. It also wirelessly transmits the information to the database on the PC from which labels can then be generated.

How it works

The MTG works by identifying the frequencies generated by a small impact on the timber and comparing those data with standard data for the species being tested to determine its strength and other characteristics.

The hand held unit has a small hammer on one side and a receiver on the other. The hammer hits the wood, sending a known force through the wood and the wave returning from the timber is recorded by the receiver. This is then sent by Bluetooth to the PC which analyses the result, calculates the modulus of elasticity and allots a strength grade based on the timber dimensions and species. The timber is then marked, either by hand or with a label printed by the system, with the grade and the data is stored.

Following the successful launch of the MTG as a mobile unit, an in-line version of the technology has also been developed. Measuring up to 30 boards per minute, the system can be combined with a moisture meter and a density meter. By adding exact parameters in the computer model, the yields improve even further, and Brookhuis says that payback of the additional investment can be achieved over two years.

Quality assurance and training

MTG user Evan Buytendijk, a timber industry consultant in the Netherlands, advises timber merchants, sawmills or companies using timber, on their internal quality assurance systems to meet ISO 9001 or CE-marking requirements and also carries out inspections of structural timber for clients, usually when there is a claim or dispute.

“The main reason we use the MTG is the independent measurement and registration of each piece of timber,” said Mr Buytendijk. “Using the MTG is faster and simpler and the data can be incorporated directly into a report.”

He also uses the tool for training people to grade structural timber.

“The big difference between visual grading and grading using the MTG is the reduced level of knowledge necessary,” he said. “The only important visual aspects are according to table 1 of EN 14081. And of course the yield of, for example C24, is higher by machine grading then by visual grading.”

Better yield

Brookhuis claims the MTG’s performance is comparable to that of much larger and more expensive mechanical graders. The company’s tests also found that it gives up to 30% better yield and grading results than visual strength grading and can grade timber up to C40 or D70.

The UK price depends on the timber species licences bought, but the approximate cost, including training, is around £10,000.

Experience at several companies making routine use of the MTG shows that staff usually learn hos to use it after some brief initial training and a few days’ practice.

The MTG is approved to the standards of EN 14081-4 and, as soon as it has been integrated into the quality assurance system of the user, says Brookhuis, it can be certified as a standard procedure. n

• Compulsory CE?marking of structural timber according to EN 14081-1, which was due to come into effect on September 1, has been postponed for three years to September 1, 2012.

John Kissock, chairman of the UK Timber Grading Committee, points out that any company carrying out grading must operate a factory production control system approved by a notified body. In the UK these bodies are BM TRADA, CATG and BSI.