What happens when fine and extremely fine wood dust and lubricant come into contact? Glue-bonding is a sure-fire outcome. The function of wood processing machines can degrade materially. For the development of a glue-dispensing system on edge-gluing machines, a mid-sized company is therefore counting on lubricant-free and maintenance-free lead screw units with anti-backlash nuts, which ensures clearance-free operation of the adjustment unit and therefore precision glue dispensing for the life of the machine.
"Furniture product variety continues to increase, and consumer demands are becoming increasingly varied. For these reasons, our customers are demanding the best possible production flexibility", explains the mechanical engineering technician and design department manager at Brandt Kantentechnik GmbH in Lemgo, Ralf Garnjost. This may involve demanding shop fitting work, one-off production for customized needs, living and bedroom furniture or functional office furnishings: the specialist for edge technology, a member of the globally active Homag Group, provides a solution to match any requirements profile. "Our construction-kit system with customized machines for any customer needs and machining tasks ranges from the simple entry-level machine for mom and pop woodshops to highly automated edge gluing machines", Ralf Garnjost summarizes.
The product range of the company, which was founded in 1955, addresses any trend for customer needs and machining tasks.
The center of attention of the machine development activities is on practical and profitable solutions that guarantee the best possible production results to customers world-wide. The Lemgo based production facility employs nearly 280 employees; this is in addition to facilities in the Czech Republic, Poland and China. With an export share of nearly 80% and customers in over 90 countries, the edge specialist is among the globally leading suppliers.
The latest development is the QA 45 glue dispensing system, which is available as an option starting at a certain machine size. It features short warmup periods and fast setup options, and therefore high flexibility for processing various glues, edges and panel materials. "This system is designed to create options for automating glue dispensing. This provides our customers with increased operating convenience. Otherwise, glue dispensing is basically done by guess work, Ralf Garnjost describes the in-going position. "Our objective was to create a cost-effective, yet well conceived design solution that can be relied upon in daily use. “
In addition to the automatic cleaning function, the innovations on the new glue dispensing system include the clearance-free adjustments. The centerpiece of this adjustment mechanism is the anti-backlash nut, which was presented as a standard product at the Hannover trade show, Industry 2010. For several months, the glue dispensing system has been employing anti-backlash lead screw nuts for metric threads as a special development. Being lubricant-free, vibration and noise dampening, they ensure the utmost in precision.
"Due to the difficult environmental conditions, all other commonly available wood processing solutions tend to become maintenance-headaches", explains the mechanical engineering technician for the design group, Thorben Fritz, who was instrumental for the development of the adjustment device. "Our many years of experience with tribologically optimized plain bearings from igus® in our machines convinced us from the beginning that we could ensure accurate format adjustments over the long-term using lubricant-free mechanical components. " In the spindle system field – with one edge gluing machine with up to ten axis unit taking care of a variety of processing steps – the edge specialist has until now been relying on brass nuts, which are, however, not clearance-free. Due to the existing backlash, the desired position cannot always be found, resulting in poor repeat accuracy.
The adjustment unit performs the glue dispensing process along the edges. If the travel is inaccurate, deviations of several tenths occur, compromising the quality of the glue dispensing process. For this reason, the clearance-free adjustment was a particularly important criteria for the development. Classic solutions, such as counter-braced lead screw nuts were quickly dismissed. "These involve a host of design approaches, which are not only very elaborate, but also require a large drive torque for the actuator", elaborates Ralf Garnjost. "In contrast, we are attempting to operate our axis system at a relatively low torque. " The low friction values of the new lead screw nut system assure the required low drive torque.
But the clearance of the adjustment mechanism is not the only important issue, because low maintenance, reliability, fatigue strength and long service life all play an important role as well. The environment surrounding the edge-gluing machine is extremely dusty. If greased systems, such as ball screws, are employed, the wood dust and particles tend to smear and glue-bond. In this case, the region of the adjustment mechanism would need to be enclosed and would require on-going supplemental lubricant. This would result in regular maintenance, including in areas that are difficult to access. "This is clumsy and expensive, and it is why we relied on maintenance-free linear technology components from the get-go", Ralf Garnjost explains. These permanently ensure the required operational reliability.
The dust is accentuated by the high ambient temperatures, which can be as high as 200°C in the area of the melting glue. In the surrounding area of the glue dispensing system, temperatures can still be up to 80°C, which can impact the function of the mechanical components installed in the adjustment unit. But here as well, the long-term tests have not revealed deficiencies of any kind. The allround material, iglidur® J, ensures the necessary temperature resistance.
Before the development of the anti-backlash system, two counter-braced nuts ensured the necessary clearance, whereas today, the edge specialist can rely on only one component. The challenge for igus was to convert a series product with a trapezoidal thread into a customer specific special component with metric thread without compromising function. "Because we have been making lead screw nuts for nearly 15 years, we have the necessary experience to quickly and reliably implement custom made solutions of this type", states Dominik Hartmann, Project Manager, drylin® screw drives. After the nut geometry was adapted in Cologne according to the Brandt specifications, and the corresponding samples were made, various function tests were started in Lemgo.
"We tested 40,000 strokes, without compromising the clearance", Thorben Fritz states in retrospect. "This was the final proof that the anti-backlash function can also work on metric threads. "After the lead screw nut system was uninstalled after a good 9 months of operation and returned to Cologne for inspection, igus was able to confirm that the lead screw unit will operate without a measurable increase in clearance.
Ralf Garnjost elaborates on this. "However, in our system, the key is not the number of strokes, but rather the reliability of the adjustment system. The motion sequence of the glue dispensing system is relatively limited. This is not a continuous, but rather a dis-continuous motion. Nonetheless, the system must work at any time, and glue-bonding must be avoided. " Given the number of test cycles performed in advance, the edge specialist believes that the service life expectation of the complete adjustment mechanism will be several years of routine operation.
The clearance and low maintenance of the newly developed adjustment system impressed Brandt so much that the company is considering to convert all lead screws in its machines to the maintenance-free anti-backlash system. "This would position us to increase the reliability of our machines", Ralf Garnjost confidently expresses. The companies have been working together for a number of years.
Various tribologically optimized polymer bearing with special shapes have also proven their performance in the edge-gluing machines. "The lack of lubrication pays for itself in all areas. For us, lubrication and dust do not mix well anywhere. “
Presently, the company is also developing a special profile on the basis of the drylin® W linear guide, which is located at the relevant locations as a dimensionally equivalent unit to the previously employed recirculating ball bearing guides.
"This reduces the part count without making design changes", Ralf Garnjost summarizes. "This not only has a pay-back for the inventories, purchasing and assembly, but also simplifies the exchange of the corresponding parts during maintenance and repair. “