FOUNDED in Brisbane over 100 years ago, the family owned company Moxon Timbers sources domestic timber and flooring both nationally and internationally for the building industry. Their range of timber products includes Australian cypress, jarrah, spotted gum and teak, as well as exotic, hard-to-find species. Imported European Baltic pine for structural use has become a significant part of the business since the late 1990s. Moxon also provides oak products to prize-winning wine makers from a number of countries.
Moxon’s production and sales manager, Brian Spillane, approached MPA Engineering to improve their timber stress-grading machine, by introducing the latest control technology.
Designed in the early 1970s, the machine controls were outdated, with some requiring manual operation. The gearbox had to be adjusted manually from inside the machine, making it a cumbersome way to vary the speed. It also required some additional safety features - which workplaces are now providing to ensure operator safety.
In consultation with the client, David Daymond, an MPA engineering control systems engineer, designed, programmed and installed a new system, using a Siemens S7200 224 PLC, Siemens MM440 variable speed drive, Siemens OP3 operator panel, SMC Pneumatics, CMG motor/gearbox and SICK safety relays (UE43-2s).
Raymond ensured the functionality of all mechanical specifications and the drive features, and interpreted the original grading algorithm to suit the new control system - with a view to making its performance even better than the original.
To set parameters for bending limits - which define grades and their associated bending pressure - the operator panel was installed, making it easy to calibrate the process.
Using a reference bar and by pressing a button on the operator panel, the bending sensors on the machine are readily reset to zero.
With fewer manual adjustments required by the operator and with a turn of the dial, the timber stress-grading machine can process timber at between 30 and 80 metres per minute. Statistical data from each batch of timber can also be collated in a timely manner.
For example, batch quantities with averages are collected, and the speed can then be read and adjusted accurately on a dial, with the runtime recorded in hours, as well as kilometres, thereby assisting in maintenance requirements.
According to Spillane, “the upgrade has improved the functionality and accuracy of the machine to the point where we now have repeatability that was previously thought unattainable”.
Grading timber: how is it done?
• To ascertain the grade of a length of timber, it is passed through a timber stress-grading machine.
• As it moves through the machine, a cylinder applies pressure over a 915 mm span and measures deflection at intervals of 150 mm.
• Paint colours representing the various grades are applied at each measurement interval, and the length of timber is given a final colour grade at the end of the process.
• The graded timber is segregated and stacked in packs of the various grades.