Evolution of the trapezoidal thread: new igus standard from Treotham achieves 82 percent efficiency

Harmonised lead screws and lubrication-free lead screw nuts extend service life by 30 percent

Even tried and tested structures have potential for improvement. One example is the classic trapezoidal thread, which igus has refined. Thanks to a special geometric interaction between the lead screw nut, which requires no lubrication or maintenance, and the metal lead screw, dryspin technology promises a long service life, improved efficiencies, low wear and less movement noise. Now dryspin lead screw technology is available in eight new installation sizes from Treotham.

Trapezoidal threads have been mechanical engineering classics for decades. The machine elements convert rotary motion into linear motion – in such applications as window and door drives, format adjustments in production plants and laboratory technology. However, almost every classic has potential for improvement. “We have tackled a market standard, and are able to say that we can do even better”, says Thorben Hendricks, Head of the dryspin Lead Screw Drive Business Unit at igus. The motion plastics specialist relies on optimised interaction between the metal lead screw and the plastic lead screw nut geometries.

30 percent longer service life, 82 percent efficiency

At igus, the nut’s thread flanks are larger than those of classic trapezoidal threads, as is the width of the lead screw. This is a small change, but it has major consequences: enlarging the thread flank results in more high-performance plastic being used for power transmission. This means more material that is tribologically optimised, i.e. regarding friction and wear. “The asymmetry has enabled us to extend the service life so that it is about 30 percent longer than that of symmetrical trapezoidal threads”, Hendricks says. Optimising the flank angle also increases the amount of energy supplied that can actually be used. We have flattened the flank angles of the lead screw nut and lead screw. This gives us above-average efficiency – up to 82 percent at high pitches.”

 Lead screws work almost noiselessly and with low vibration

However, the new dryspin thread technology is not only durable and efficient, but also quieter than many conventional trapezoidal threads. This is due to the fact that the tooth flanks are not angular, but rounded, reducing the contact area between lead screw nut and lead screw. This leads to less vibration, which can take the form of rattling or squeaking. Hendricks remarks: “The rounded tooth flanks allow the lead screws to move without vibration and almost silently. The lead screw manufacturing tolerance is tighter than that specified in DIN 103 7e, ensuring more precise operating behaviour and allowing for much higher speeds in the application.”

Eight installation sizes added to the dryspin lead screw technology portfolio

igus began establishing its own lead screw technology on the market in 2013, initially as an alternative to high helix threads. Now there are eight new installation sizes – harmonised lead screws and lead screw nuts, including dimensions with low pitches that enable quick one-to-one replacement of installed trapezoidal threads. The new lead screws are available with pitches of 6.35×6.35 RH, 8×40 RH, 10×3 LH, 12×25 LH, 14×4 RH, 16×5 RH, 18×4 RH and 20×10 RH from Treotham. The lead screws are made of stainless steel or aluminium; the lead screw nut material can be selected from seven high-performance plastics and several geometries – from a cylindrical design with flange or spanner flats to a version with spring pre-load.