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 APPLICATION BULLETIN - NOVEMBER 1995 | BACK TO INDEX  


PDL Microvector Drive cuts costs & increases quality at Kaitaia Mill

 

They dub Wally Harrison the "Fastest operator in the West" for the way he hurls the logs through the Kaitaia mills' band saw. As head rig operator and mill foreman, Wally reckons the new PDL drive makes a real difference to production. "There's been a big improvement since the Microvector was installed, particularly in downtime. We've bumped up our average way beyond what we could do with the old system."


Since we installed a PDL Microvector drive on our log carriage we've made a noticeable impact on production," says Kaitaia Timber Mill Co mill boss, Baden Beard. "PDL Electronics drives were initially introduced to us by Jaymor Industries Ltd, a specialist timber control company and once installed, that one drive has made a noticeable impact on accuracy and productivity. These two factors then add up to increased profitability."

A revolution is occurring right here and now in the timber industry and the new generation of PDL Microvector motor drives looks set to lead the way to the timber mills of the 21st Century where speed and high quality rule the way timber is processed.

The revolution has already arrived as far as Baden Beard is concerned.

"The key to our operation is the log carriage and the time we take to accurately process each log. I would never have predicted that such a simple upgrade would make such a big difference. The Microvector is so inexpensive that a 1% production gain would cover its costs in 3 months. All we needed was to save 90 minutes downtime per month and the Microvector has easily done that."

Profitability hasn't just come from the speed factor alone, but from the fact that the PDL motor drive has brought with it an accuracy that makes every cut of the mill's band saw count.

"The emphasis now in milling is on quality. Under the old system, we would target 52mm and the variation would be from 48 to 56mm. There was no consistency in that, no quality and a lot of unnecessary wastage. We can now cut closely to whatever size we target."

"The result of this accuracy is that we now get less waste, more volume of throughput and less jamming of planers and profilers because we know exactly how to set up the rollers."
The key to the new efficiency lies in the carriage feeding the mill's band saw.

The log carriage in question is a New Zealand-made Edwards brand (made in Tauranga) installed by Kaitaia mill owners the Tanner Group in the early 70s. The critical sizing of the various cuts required of the band saw is controlled by three knees against which the log is clamped. These then shift the log to whatever thickness setting the saw operator decides on by using a Jaymor control system.

The three knees are linked together on a common drive shaft, called a sizing shaft, running the length of the carriage. This shaft is driven via a chain and sprocket system by a 5kW motor on the end of which is a disc brake.

Under the old system, a set works encoder mounted on the central knee relayed distances back to the computer in the operator's box next to the band saw. When the operator programmed another size into the computer, the sizing shaft motor would wind the knees in at full revs and then cut out at a programmable point before the target size. At this point the computer would activate the disc brake on the motor and the knees would brake to a halt at the specified cut width - theoretically.

 

 

Baden Beard won't say if the production successes following installation of PDL's MV3-16 vector drive contributed to his decision to celebrate by buying his brand spanking new XR6, 4 litre Ford Falcon, but he was prepared to give us a hint as to what motivated his spending spree. "I like fast milling systems and I like fast cars. As far as I'm concerned ­ the two go together."


"The trouble was," explains Baden Beard, " the disc brake varied quite a bit in its performance according to whether it was hot or cold, the viscosity of the grease, the wear on the brake pads and so on. There was quite an art in it. We had to actually average all these variables out and try to program them into the system.

"We hadn't been happy with the accuracy of this system for some time so we started looking at the options which of course meant looking at an change to hydraulics or staying with some sort of electrical system. The industry as a whole has always been orientated towards hydraulics so everyone saw that as an answer until Phil Crowther from PDL Electronics stepped in and arranged a meeting with PDL's application engineers and ourselves so we could trial the Microvector option on our own gear. I must admit my initial reaction was that PDL's solution was so inexpensive that it wasn't going to work. But PDL offered to trial the new system on the basis that if we were happy with it we'd buy it and if we weren't they'd pull it out. Well, as you can see, we've still got it and it's working fine!"

The solution worked out by Phil Crowther and PDL's application engineers was to control the sizing shaft motor with a Microvector 3 - 16 drive situated in the operator's cabin.

"The difference is that now, instead of being braked to the programmed size, the system now drives right up to the set point and stops," explains Phil Crowther. "And of course we've completely eliminated the problems with inconsistency you had with the old system."

The Microvector is essentially an addition to the mill's existing automated system designed by Jaymor Industries Ltd, a well-known name in the South Pacific timber milling industry and one of the few specialist timer control companies in the Southern Hemisphere.

"Traditionally, the timber industry has always used hydraulic drives, because that gives us a noise-free drive and either linear or rotary control," explains Jaymor Managing Director Norman Agnew. "but the PDL drives are now so good and so controllable that we're going away from hydraulic drives, especially in rotary applications and using their Microvector drive wherever we can.
"Generally speaking the Microvector drives make the electric solution preferable on economic grounds besides offering greater control than the hydraulics - plus we don't have the waste energy and heat to get rid of and the fact that we can step the motor one pole at a time or even less, is an enormous advantage.

"The Kaitaia mill is basically running as a two speed system, because it's just sitting in the place where the old electric drive was, but the later ones we do a full PID loop on and we're getting some amazing control from them. We're even sending them up to Papua New Guinea and we see them as being a very good drive for the Islands where hydraulics gives a maintenance problem, with infiltration of dirt etc.

"In the later model full PID systems we are about to send up to Papua New Guinea, we'll control the motors totally in a closed loop situation and electrically we're achieving 0.1 of a millimetre in linear motion. With the one at Kaitaia Timber, which is a two speed, they are achieving vastly improved accuracy. We're very pleased with the product and very pleased with the backup and the help we're getting from PDL Electronics.

"We think the PDL Microvectors are a great drive and of course we are great supporters of New Zealand made - because they are a New Zealand drive we are going to support them."

Baden Beard is convinced the new vector system is the wave of the future.

"We're already looking at other applications for the drives in any future upgrade. It's my belief that the vector drive system with its noticeable difference in cost and its accuracy is now a realistic option to hydraulics in the modern saw mill."