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SLP evolves in response to market demand
Wood-Mizer developed the Small Log Processing (SLP) line to provide an efficient and economical way to process small logs while achieving good productivity and high yield of sawn boards.
SLP lines are designed to customers' requirements from a choice of twin and single vertical bandsaws, multi-head horizontal bandsaws, and associated log handling and conveying systems. The addition of a Wood-Mizer edger or multirip offers customers the ability to add further value and productivity.
These lines have been installed for customers around the world since they were introduced in 2007, and are used for cutting a variety of species and in a range of environments. Wood-Mizer has always encouraged feedback from all customers, so that the technical design team can enhance the performance of machinery and blades to meet the changing needs of sawmillers. For the SLP line, this has led to a number of innovations.
One of these is the 'Spiky Chain' system for feeding logs through the TVS twin vertical bandsaw. This was initially developed in order to increase productivity. With the standard 'dogged' feed chain there will always be gaps between logs, as each one has to pause on the deck until the next dog (usually spaced about 170mm apart) on the chain arrives to feed the log through the sawblades.
"The Spiky system is a continuous spiked feed chain with overhead spiked rollers before the saw", said Roman Frontczak, technical director at Wood-Mizer Industries. "These grip the log as soon as it is positioned on the special 'V'-shaped loading table, which means logs can be fed butt to butt with no gaps between them. Depending on the length of logs, the Spiky feed can increase productivity by 10-20%.
"A second factor behind the development of the new system was to assist with short logs that are not straight - 'banana shaped' - as well as logs that have significant taper. In these situations the Spiky feed not only maintains productivity but also a good quality of cut, because the grip of the lower chain together with the grip of the overhead wheel ensure that the log is very well controlled as it is moved through the bandsaw blades".
The force of a blade driving down through the side of a log exerts a 'turning' pressure on the log. The standard dogged feed has an overhead roller after the saw to prevent this, but if the log is 'banana shaped' or excessively tapered it will be unbalanced on the bed and there is increased risk that the log will turn. However, this cannot happen with the Spiky system.
Originally, the controls for the TVS as well as the standard dogged feed system were mounted on the TVS itself. With the development of the Spiky feed, all controls were placed on a remote operator console, which can be placed in the best position for the operator at the head of the line. This is particularly important when the Spiky feed is used because the operator is further away from the TVS - logs have to fit under the top spiked wheels and are loaded further back, rather than close to the bandsaw as is the case with the dogged chain.
Along with the Spiky chain, a new laser alignment system was developed to help the operator adjust the position of the vertical bandsaw blades on the TVS to achieve the best cut for each log. 'Green' lasers are now available (rather than 'red'), which are more durable and also more visible in daylight. The lasers have been designed so that they are easy for customers to mount on the head.
Another change made in response to customer feedback is a slight redesign of the TVS feed table for the Spiky chain system. A central leg previously supported the table, but users reported that this made it awkward to clear away sawdust that falls from the blades between the two heads. The solution from the Wood-Mizer design team was to remove this leg, and support the Spiky feed table by fixing it directly to the TVS frame. It might sound like a small change, but for SLP operators this makes it much easier to keep the area around the bandsaw clear of sawdust.
In response to the actual experience of SLP users, modifications have also been made to the blade tensioning system on the SVS single head and TVS twin head vertical bandsaws.
"We have replaced the original manual screw with a hydraulic pump system operated by a lever", said Roman Frontczak. "This provides better control, making it easier and quicker to tension the blades since the operator reads a pressure gauge rather than judging the position of a sliding pointer against a vertical scale.
"In addition, safety is improved because there is a cut-off valve that senses if there is a fall in pressure - which would occur, for example, if a blade breaks - and automatically stops the main motor for the bandsaws and the feed system. The motor cannot then be restarted until the tension is reapplied".
Both the SVS and TVS have magnetic linear devices which feed precise positioning information to the Setworks controller. Previously the linear strips were exposed, and there was a risk that in environments of high temperature and humidity the strips could distort, or they could be contaminated with sawdust, which from some species of timber can be chemically aggressive or highly abrasive. A re-design means that the linear strips are now installed inside a housing so that they are protected from the environment.
After logs have been sawn through the TVS and SVS, they are conveyed to the HR500 multi-head horizontal resaws for cutting into multiple boards of the desired thickness in a single pass. Depending on user requirements, the HR500 can have from one to six resaws.
A further development for the HR500 is the option of heavy-duty top rollers for better control of cants that are very short or badly curved - which can be a particular issue with rubberwood.
"If a log is curved there is a lot of tension inside the wood", said Roman Frontczak, "and in order to achieve straight, accurate cutting it is necessary to keep the cant firmly pressed down onto the feed bed so the tension does not cause the wood to spring up between each head as successive boards are cut.
"As standard, each HR500 head has a single top roller of 200mm or 300mm diameter, which is suitable for many applications. However, for short cants with lots of tension, such as rubberwood, the heavy-duty option has two rollers for each head, one either side. This means that cants are held down onto the bed before and after the sawblade".
A new valve system for the blade lubrication system on the HR500s has been introduced and is now supplied as standard. All heads are linked to a central lubricant supply - rather than needing a container on each head - and the manual valves have been replaced with an automatic system that opens when the heads are working and shuts off when they stop.
All these developments and options represent an evolution of the successful SLP line in direct response to the operational experience and needs of customers. However, this does not represent a 'final stage' since Wood-Mizer actively encourages feedback and will always be ready to make further innovations to address particular issues and applications - because above all the company wants customers to have successful and profitable businesses.
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This article was published in the 'Wood-Mizer Today' company newsletter.
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