Further developments for aluminium screw drives

Mechanics is a living science


Spurred on by the communicative partnership with customers and solution-oriented exchange, the designers at Eichenberger Gewinde have identified further developments for aluminium screw drives.

burning sparkler on green
The goal of technical progress is not only to achieve more but to do it better with new technologies and processes. The need to solve practical tasks is constant. The latest technologies or materials fertilise the field of mechanics and continually reformulate the requirements for these. Therefore mechanics is a living science. The opportunities that it offers are being successfully translated into reality by the Swiss thread specialist, which has succeeded in establishing itself in the drive engineering niche with its bespoke rolled screw drives. The potential of lightweight construction of even the simplest moving parts is unmistakeable – combined with a sophisticated thread form, the cold-formed aluminium lead screw is becoming the unsurpassable mechanical drive component, for example, in the vehicular door systems market.

Figure 2 Trailblazing: speedy aluminium high-helix lead screw, ø 16 mm / pitch 90 mm, left-hand thread.
Trailblazing: speedy aluminium high-helix lead screw, ø 16 mm / pitch 90 mm, left-hand thread.

A screw retrospective – and there is no end in sight
If the average consumer thinks of a screw and a nut, he probably imagines first of all a typical attachment element. Basically however there are two areas in mechanics in which a screw is used – attachment and motion. The invention of the screw drive is attributed to the Greek polymath Archimedes (287 – 212 BC). According to Pliny, from the 3rd century BC a very important use for the motion screw appeared. Roman wine presses worked with oak screws of impressive diameters. In order to achieve the required degree of efficiency, huge logs with a lead screw had to be ratcheted up so that the mash in the press basket could be placed under pressure
Along with the course of time the requirements of mechanical motion elements, that is, screw drives, changed and increased. For wherever a turning motion has to be converted into linear motion (or vice-versa), they are in use, at all levels of industry, even after 2,300 years of technological history.

Materials help to determine progress, even in screw drives
When it comes to mobility, billions of people on public transport put their trust in the reliability of rail- and commercial vehicles. In sustainable mobility concepts, energy efficiency, resource-saving, noise- and pollutant reduction all play a fundamental role.  However in current material research “cheaper, lighter, stronger” also determine the major trends. Weight savings, CO2 emissions and fuel consumption can also be lowered by aluminium, while longer ranges can be achieved. Aluminium offers light weight for equivalent stability, high load capacity and outstanding workability, which is of enormous interest to Eichenberger’s developers.

Typically Eichenberger: speedy aluminium high-helix lead screw, ø 20 mm / pitch 80 mm.
Typically Eichenberger: speedy aluminium high-helix lead screw, ø 20 mm / pitch 80 mm.

The centrepiece: door drive
The entry systems of vehicles of any kind, whether coaches, buses, fire service- or emergency ­vehicles, underground- or commuter trains, trams or high-speed trains, can easily lead to delays and unforeseen incidents. Therefore the condition of the automatic sliding door ­systems has a crucial influence on the safety and comfort of the passengers and also on profitability. High-speed trains reach spe­eds of over 300 km/h. Imagine the forces at work, including with regard to air resistance and wear. For example, resistance increases to the square of the speed. So when speed doubles, air resi­stance quadruples. The centrepiece of these door systems is formed by the linear drive. The aim of the designers from CH-Burg was to develop a more cost-effective solution for motion tasks within these drive units.

Innovations don’t fall from the sky
High exertion, robustness, precision and reliability have to be guaranteed with the smallest of available spaces. The doors should slide easily and quickly. In the event of a power failure the screw-nut system must not be self-locking. It is essential that in an emergency the doors can be opened by hand at all times. Far-reaching innovations are always the result of hard development work. Eichenberger succeeded in producing the special profile cold-rolled aluminium high-helix thread with a diameter of 20 mm and pitch of 80 mm.

Only when the various components (ideal raw material / alloy, immaculate cold forming, thread rolling dies manufactured specially for the rolling process at Eichenberger) are in perfect unison can the flow of material run optimally for a high pitch ratio of 80 mm. The Swiss thread specia­list is simultaneously able to offer development, production and quality control, so the flexibility in the production process or in the creation of ­prototypes, including thread rolling dies, is remarkably high. Powerful expertise is also indispensable when it comes to design of the tools for the female thread of the plastic nut. Thanks to these factors, production can be flexible and competitive even at an expensive site.

In the present case there is a continued development of the screws that are already used in sliding door applications. The new combination of the special hard-anodised 20 / 80 aluminium high-­helix ­lead screw and the plastic nut (nut material depending on application), is designed so that manufacture of the spindles in the cold forming production process is possible. It is well known that the thread-rolling process results in remarkable benefits with regard to bonding, roughness values and notch sensitivity.
With the special profile of the thread a completely different support takes place. The tipping point is captured via the external diameter of the spindle, which ensures frictionless operation and prevents jamming.

When it comes to weight savings, CO2 emissions and fuel consumption: speedy aluminium high-helix lead screw, ø 20 mm / pitch 80 mm.
When it comes to weight savings, CO2 emissions and fuel consumption: speedy aluminium high-helix lead screw, ø 20 mm / pitch 80 mm.

The plus points at a glance

The aluminium threads, already massively reinforced by the thread rolling, get an even more resistance-­capable surface via the further refining of the outer coat, or hard anodising. The result is additional reduction in the friction coefficient and very good sliding properties. These values, and of course protection against corrosion, are crucially responsible for a long service life.

What sounds so simple can only be managed with a treasury of experience col­lected over decades, high quality awareness and modern machinery. The dynamic ratio of the 20 mm diameter and 80 mm lead allows a very high movement speed. To achieve such a high nut speed, a single-start normal trapezoidal thread with 20 mm diameter would have to turn over 16 times more quickly. In addition to this, the low numbers of turns have a positive effect on wear and noise.

In terms of price the new innovation can really hold its own. Rational and rapid production is possible, which has a beneficial effect on the price, particularly with large unit quantities. For the Swiss thread roller, thread forms that lie outside the norm are the sought-after challenges. Customer- and solution-oriented diameters and leads can be implemented on request, including for aluminium screws.

Continued development for sliding door systems: cold-formed 20/80 aluminium special high-helix lead screws.

Development service provider
Eichenberger Gewinde AG is a company with clear goals: The rolling – as in cold forming – of threads and the manufacturing of lead screw assemblies (spindle and nut). Eichenberger supports “the customer’s” innovations through the use of state of the art production methods and by developing new dimensions.

  • Carry: Ball screw for applications where heavy loads must be moved with low energy consumption.
  • Carry Speedline: Wear-free high-helix ball screw for high moving speeds. The patented recirculating design combines low mass with a good price.
  • Speedy: The high-helix lead screw converts rotational motion into linear motion with high moving speeds. New: Some versions available in aluminium.
  • Rondo: The round thread lead screw with very quiet running New: Some versions available in aluminium.