Timber Processing Technology Advances with Hydraulics

Agricultural fence posts are increasingly being produced by UK timber mills using a debarker newly-developed by Technorton in Ludlow, who have redefined the hydraulic technology at the heart of the machine.

Key to the hydraulics is a 12-section spool valve, designed especially for the debarker by Hydraulic Projects (Hy-Pro). The valve incorporates manual, solenoid, flow divider and flow control sections enabling the machine to be driven from a single pump. Another innovation is the use of a micro PLC (programmable logic controller) to sequence the various hydraulic axes during operation.

Technorton originally concentrated on making mobile forestry equipment, but a few years ago saw a developing need in the market for a static debarker. The primary objective was to automate much of the process so that productivity could be taken to new levels for the timer processing industries. To maintain the reliability over time, high reliability of the debarker and its hydraulics were necessary and this lead to the idea of simplifying the systems design and specifying top quality robust components throughout.

“Manual debarkers are fairly simple devices. The bark is removed by adjustable knives mounted on a cast iron spinning disc. The wood is held against and rotated past the disc by a feed roller and pressure wheel mechanism,” explains Technorton’s Carl Barters. “Automating this constitutes a couple of axes, but we also have to look at the infeed, output and handling of the peelings. This all adds up to a dozen or so axes.”

The designers had several ideas about how to proceed, most of which focussed on rationalising the hydraulics layout into an optimum design that met requirements for performance, reliability and manufacturability. Realising that specialist expertise was required they contacted Hydraulic Projects in Dawlish, Devon and effectively fused the two companies’ design teams into one.

“We wanted to offer the market a flexible machine that could be configured in different ways so that it would suit individual situations. This had ramifications on the hydraulic systems design, but Hy-Pro took the brief in their stride and developed a bespoke 12-section valve for us.”

It was decided to drive the main cutting disc directly by an electric motor, as this was obviously the most energy efficient way. However every other axis is hydraulically driven. The feed roll and pressure wheel have of necessity to be powerful and of variable output, yet simple and compact. To achieve the rapid responsiveness required for high speed operations hydraulics was the only viable option.

Likewise, the power required for the materials handling on the infeed suggested a hydraulic solution. This section of the machine includes an infeed drag conveyor, a singulator to separate one post from the next and a kicker to present it to the debarking section. The conveyor has of necessity to be variable speed, and here it was decided to use a Control Techniques’

electronic inverter drive in conjunction with the hydraulic power pack driving a number of Comer hydraulic motors.

After debarking the posts are transferred, again using hydraulic handling technology to a stacker ready for final processing. The bark peelings are blown laterally into a hopper, and most timber mill operators chip this for use in soil conditioners.

“Hy-Pro developed a valve block that mixes manual and solenoid-operated spools,” says Barters. “This allows us to configure each machine to precisely meet each clients specifications. As users are becoming more confident with high productivity debarking, there is a tendency to automat all the valves. For this reason we fit a Siemens Logo micro controller, which despite its tiny size has the I/O capacity to control all the axes.”

Technorton built the first debarker in this range two years ago for a mill in Southern Ireland, which reports that at 50 tonnes or 3000 posts per day it is now approaching 1.5 million posts total production. The machine has proved 100 per cent reliable and the mill has decided to double production by adding a second unit.