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Perfect edges

Lubricant and clearance-free lead screw nut system ensures precision glue dispensing on an edge-gluing machine

What happens when fine and the finest wood dust encounter the lubricant? Adhesion is inevitable. The functionality of woodworking machines can be permanently impaired. For this reason, a medium-sized company relies on lubrication-free and maintenance-free lead screw drives with anti-backlash nuts in its new development of an adhesive application system for edge banding machines, which ensure lifelong zero clearance of the adjustment unit and the precise application of glue.

"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.

Anti-backlash lead screw nuts for metric threads as a special development for a glue dispensing system. Anti-backlash' lead screw nuts for metric threads as a special development in the adhesive application system. These ensure the utmost precision for this clearance-free adjustment drive.

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 custom production of the drylin® lead screw units Anti-backlash lead screw nut. The custom-made drylin® lead screw drives, anti-backlash lead screw nuts

Precision glue dispensing

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. “

Besides the automatic cleaning function, one of the innovations of the new glue application system is a clearance-free adjustment. At the heart of this adjustment is the anti-backlash nut, which was presented as a standard product at the Hannover Messe Industrie 2010. In the glue application system, anti-backlash lead screw nuts have been used for metric threads as a special development for several months: lubrication-free, vibration and noise-dampening, they ensure maximum precision.

Precision travel

"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.

polymer linear bearings from the construction kit Various polymer plain bearings and polymer linear bearings from the construction kit in special configurations prove their functional capabilities in the edge-gluing machines.

With the aid of the adjustment, the adhesive application is dosed at the edges. If the travel is not accurate, there are deviations of several tenths, which reduces the quality of the adhesive application. For this reason, clearance-free adjustment was very important in the development of the application system. Classic solutions such as lead screw nuts braced against each other have been quickly discarded. "These are manifold design approaches that are not only very complex, but also require a relatively high drive torque of the actuator," explains Ralf Garnjost. "However, we try to drive our axis systems with a relatively low torque. " The low coefficient of friction of the new lead screw nut system provide the required low drive torque.
 
However, it is not just about the zero clearance of the adjustment, but also the issues of zero maintenance, reliability, durability and long service life that play an important role. The atmosphere around the edge banding machines is extremely dusty. If greased systems such as ball screw drives are used, wood dust and particles come and accumulate on them. The range of adjustment would have to be encapsulated in this case and continuously relubricated. Regular maintenance, even in less accessible places, would be the result. "That is cumbersome and expensive, which is why we have relied on maintenance-free linear technology components right from the start," explains Ralf Garnjost. They permanently ensure the necessary operational safety.
 
Added to the dust is high ambient temperatures, which can be up to 200°C in the hot melt adhesive range. In the surroundings of the glue application system, they still amount to up to 80°C, which can influence the functionality of the installed machine elements in the adjustment unit. But even here, no complaints were found in endurance tests. The all-round material iglidur® J provides the necessary temperature resistance.

View of an edge-gluing machine of the Ambition 1600 series, View of an edge-gluing machine of the Ambition 1600 series,

From a trapezoidal to a metric thread

Before the development of the "anti-backlash" system usually two mutually braced nuts ensured the necessary zero clearance, the edge specialist today uses only one component. The challenge was to produce a custom-made special part with metric thread from a series product with a trapezoidal thread without sacrificing performance. "As we have been manufacturing lead screw nuts for almost 15 years, we have the necessary experience to implement such special solutions quickly and reliably," says Dominik Hartmann, Product Manager drylin® lead screw drives. After adapting the geometry of the nut in Cologne to the specifications of Brandt and appropriate samples were produced, various functional tests began in Lemgo.

"We tested 40,000 strokes without sacrificing zero clearance," says Thorben Fritz. "That was the definitive proof that the anti-backlash function works on metric threads as well. " After a lead screw nut system was dismantled after a running time of nine months, and sent to Cologne for inspection, it could be confirmed that the lead screw drive works without a measurable increase in clearance.
 
Ralf Garnjost adds to that. "However, our application does not depend on the number of strokes, but on the reliability of the adjustment system. The movement sequence of the glue application system is relatively limited. It is not a continuous, but a discontinuous movement. Nevertheless, it must be ensured that it always works and no adhesions occur. " With regard to the number of cycles tested in advance, however, the edge specialist assumes that the service life expectancy of the complete adjustment unit in everyday operations is several years.

General setup and maintenance-free linear systems and plain bearing solutions

The freedom of clearance and maintenance of the newly developed adjustment system has convinced Brandt so much that it is thinking of converting all lead screws in its machines to the maintenance-free, anti-backlash system. "That way we can further increase the reliability of the machines," says Ralf Garnjost with confidence. The companies have been working together for a number of years.
In the edge banding machines, various tribo-optimised polymer bearings are also proving themselves in special shapes. "Freedom from lubrication pays off in all areas. For us lubrication and dust are incompatible at all points." “
 
In addition, a special profile based on the drylin® W linear guide is currently being developed, which has the same dimensions as the previously used recirculating ball bearing guides.

Newly developed glue-dispensing system. Newly developed glue-dispensing system.

"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. “


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