Lead screw nut application in edge banding machine

Dryspin machine with control panel and close-up of the internal mechanical assembly.

Technical data:
► What was needed: Lifelong zero clearance of the adjustment unit and thus precise glue application without maintenance
► Requirements: No sticking due to the fine wood dust, high precision, absolute freedom from lubrication and maintenance, flexibility in production
► Products used: Anti-backlash trapezoidal lead screw nut, stainless steel trapezoidal threaded spindle

► Success for the customer: Brandt was so impressed by the clearance and maintenance-free nature of the newly developed adjustment system that it is considering converting all of the spindles in the machines to the maintenance-free anti-backlash system. "This will allow us to further increase the reliability of the machines," says Ralf Garnjost confidently. Various tribo-optimised polymer bearings in special shapes are also proving their worth in the edge banding machines. "The absence of lubricants pays off in all areas. lubrication and dust don't mix at any point."

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Lubrication and clearance-free dryspin® screw drives ensure precise glue application

What happens when fine and ultra-fine wood dust meets lubricant? Adhesions are inevitable. The functionality of woodworking machines can be permanently impaired. In its new development of a glue application system for edge banding machines, a medium-sized company therefore relies on lubricant- and maintenance-free screw drives with anti-backlash-lead screw nut, which ensure zero clearance of the adjustment unit and thus precise glue application for the life of the machine.

"The variety of furniture products continues to increase and consumer wishes are becoming ever more diverse. For these reasons, our customers want the greatest possible flexibility in production," explains Ralf Garnjost, mechanical engineer and head of design at Brandt Kantentechnik GmbH in Lemgo. Whether sophisticated shopfitting, batch size 1 production for individual requirements, living room and bedroom furniture or functional office furnishings: the edgebanding technology specialist, a member of the globally active Homag Group, offers the right solution for every requirement profile. "Our modular system with customised machines for all customer requirements and processing tasks ranges from the simple entry-level machine for the carpenter around the corner to the highly automated edge banding machine," summarises Ralf Garnjost.

Founded in 1955, the company's product programme is geared towards all trends in customer requirements and machining tasks. The focus of machine development is on practical and economical solutions that guarantee customers worldwide the best possible production results. Production is carried out by around 280 employees in Lemgo, with additional sites in the Czech Republic, Poland and China. With an export share of around 80 per cent and customers in over 90 countries, the edgeband specialist is one of the world's leading suppliers.

Glue application with precision
One of the latest developments is the QA 45 adhesive application system, which is available as an option from a certain machine size. It is characterised, among other things, by short heat-up times and quick changeover options and therefore a high degree of flexibility when processing a wide variety of adhesives, edgebands and panel materials. "With this system, we want to make it possible to automate adhesive application. This allows us to offer our customers greater ease of use. Adhesive application is otherwise done more or less by eye," says Ralf Garnjost, describing the initial situation. "Our aim was to create an inexpensive yet sophisticated solution that would prove its worth in day-to-day operations."

dryspin spindle nut with threaded spindle for linear guidance.

In addition to the automatic cleaning function, the innovations of the new glue application system include a clearance-free adjustment, which was realised in cooperation with the company igus® SE & Co. KG, Cologne. The centrepiece of this adjustment is the anti-backlash-lead screw nut, which was presented as a standard product at Hannover Messe Industrie 2010. "Backlash" refers to the backlash caused by the axial play in a screw drive.

The anti-backlash-lead screw nut offers many advantages:
► Reduction of backlash over the entire service life
► Permissible wear is guaranteed
Non-lubricated and extremely dirt-sensitive screw drive
► No adhesion of dirt and dust to lubricants

Anti-backlash spindle nuts for metric threads have been used in the glue application system for several months as a special development: lubrication-free, vibration- and noise-damping, they ensure maximum precision.

Precise travel
"Due to the difficult environmental conditions in woodworking, all other conventional solutions tend to become susceptible to maintenance in everyday operation," explains Thorben Fritz, mechanical engineer in the design department, who was largely responsible for the development of the adjustment unit. "However, thanks 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 spindle systems - up to ten axis units cover a wide variety of tasks in an edgebander - the edgebanding specialist has so far relied on brass nuts, which are not clearance-free. Due to the existing backlash, the desired position is not always achieved and repeatability is poor.

The adhesive application on the edges is metered with the aid of the adjustment. If the travel is not exact, deviations of several tenths occur, which results in a reduction in the quality of the adhesive application. For this reason, clearance-free adjustment was particularly important in the development of the application system. Classic solutions such as lead screw nuts braced against each other were quickly discarded. "These are a variety of design approaches that are not only very complex, but also require a relatively high drive torque from the actuator," explains Ralf Garnjost. "In contrast, we try to drive our axis systems with a relatively low torque." The low coefficient of friction of the new spindle-lead screw nut system ensures the low drive torque required.

Several dryspin threaded spindles, nuts and support parts on a wooden table.

However, it is not only the zero clearance of the adjustment that is important, but also the issues of freedom from maintenance, reliability, durability and long service life. The atmosphere around edge banding machines is extremely dusty. If greased systems such as ball screw drives are used, wood dust and particles smear and stick together. In this case, the adjustment area must be encapsulated and continuously relubricated. Regular maintenance, even in places that are not easily accessible, would be the result. "This is complicated and expensive, which is why we opted for maintenance-free linear technology components right from the start," explains Ralf Garnjost. They ensure the necessary operational reliability in the long term.

The high ambient temperature, which can be up to 200 °C in the hot melt adhesive area, also adds to the dust. In the area surrounding the adhesive application system, these temperatures can be as high as 80 °C, which can affect the functionality of the machine elements installed 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.

General conversion to maintenance-free linear systems and plain bearing solutions

Brandt was so impressed by the clearance and maintenance-free nature of the newly developed adjustment system that it is considering retrofitting all of its machines with the maintenance-free anti-backlash system. "This will allow us to further increase the reliability of the machines," says Ralf Garnjost confidently. The companies have been working together for a number of years. Various tribo-optimised polymer bearings in special shapes are also proving their worth in the edge banding machines. "The absence of lubricants pays off in all areas. lubrication and dust do not get along at any point."

A special profile based on the linear guide drylin® W is also currently being developed, which is dimensionally identical to the recirculating ball bearing guides previously used at the relevant points. "We save on parts without making any major design changes," concludes Ralf Garnjost. "This not only pays off in terms of warehousing, purchasing and assembly, but also simplifies the replacement of the relevant parts in the event of maintenance and servicing."

igus machine module with multiple precision drive and guiding elements in an industrial setup.

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