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.

The product range of the company, founded in 1955, is geared to all trends in customer requirements and machining tasks. The focus of machine development is on practical and economical solutions that guarantee the best possible production results for customers worldwide. Production takes place in Lemgo with around 280 employees; there are also locations in the Czech Republic, Poland and China. With an export share of around 80 percent and customers in over 90 countries, the edge band specialist is one of the leading global suppliers.

Glue application with precision

The latest developments include the QA 45 glue application system, which is available as an option from a certain machine size. It is characterised by, among other things, short heat-up times as well as fast changeover options and thus a high degree of flexibility when processing a wide variety of adhesives, edges and board materials. "With the system, we want to create the possibility of automating adhesive application. In this way, we offer our customers more ease of use. Otherwise, the adhesive is applied more or less by sight," says Ralf Garnjost, describing the original situation. "Our goal was to create an inexpensive, yet structurally sound solution that would stand the test of time in everyday operations."

Precise travel

"All the usual solutions tend to be susceptible to maintenance in everyday operation due to the difficult environmental conditions in woodworking," explains mechanical engineer in the design department, Thorben Fritz, who was largely responsible for the development of the adjustment unit. "Due to our many years of experience with tribo-optimised plain bearings from igus in our machines, we were convinced right from the start that we could guarantee precise format adjustment in the long term with lubrication-free machine elements." In the area of lead screw systems - up to ten axis units cover the most diverse work in an edge banding machine - the edge specialist has so far relied on brass nuts, which are, however, not backlash-free. Due to the existing backlash, the desired position is not always hit, the repeatability is poor.
 
With the help of the adjustment, the adhesive application on the edges is dosed. 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. "In contrast, we try to drive our axis systems with a relatively low torque." The low coefficients of friction of the new lead screw nut system provide the required low drive torque.

From trapezoidal to 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 for the company igus was to produce a custom-made special part with metric thread from a series product with a trapezoidal thread without sacrificing performance. "Since 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, Project Manager drylin TR lead screw drives.  After adapting the geometry of the nut in Cologne to the specifications of the company Brandt and appropriate samples were produced, various functional tests began in Lemgo. "We tested 40 000 strokes without sacrificing zero clearance," says Thorben Fritz. "This was the final proof that the anti-backlash function also works with metric threads." After a lead screw nut system was dismantled after a running time of nine months, and sent to Cologne for inspection, igus could also confirm 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 that 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 conversion to maintenance-free linear systems and plain bearing solutions