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Lead Screws and Nuts

Lead Screws and Nuts by Reliance Precision Ltd.

Description

Reliance’s lead screw and nut assemblies provide a flexible, integrated solution for linear motion.  Available in a wide choice of sizes and styles, with options for custom designed end modifications, the range offers the flexibility to address a wide variety of requirements.

Lead screws are provided with leads from 0.3 mm to 92 mm, screw diameters from 3 mm to 19 mm and thread lengths of up to 4 metres, making them an effective solution, even for high linear speed applications. They are available in a range of materials and coatings, with a choice of cut or standard interfacing ends, or with the option of custom machined ends.  The screw thread form has been specifically designed for long life and quiet operation. It is manufactured using a rolled process, a highly consistent method of production resulting in a cost-effective, quality product.

The lead screw and nut assemblies have been designed specifically for motion control applications, rather than using adaptations of general purpose screws and nuts. There are 11 different nut styles, with a choice of mounts and also options for custom-designed nuts. Nuts are made from moulded plastic, which enables custom nuts to be produced with features of the drive system, such as bushings, carriages, pulleys and gears, integrated within the nut. This type of custom, multi-functional nut can offer a significant reduction in part count, reducing cost and assembly time in the overall mechanism.

The polyacetal nuts have a lubricating additive to provide longer life which, when combined with low friction lead screw coatings, can extend the life of a standard lead screw assembly by up to 300%. The assemblies are self-lubricating, making them ideally suited to medical and laboratory applications.

With lead accuracies up to 0.0001 mm/mm and positional bi-directional repeatability within 1.5 micron (0.0015 mm) on anti-backlash designs, the lead screw and nut assemblies are ideal for applications requiring precise, efficient linear motion.

Lead Screw Materials

Lead screws are rolled from a premium grade, corrosion resistant and non-magnetic 303 stainless steel. Other materials are available including 316 and 400 series stainless steel, precipitation hardened steels, aluminium and titanium. These materials are ideally suited for industries such as medical, vacuum, cleanroom, food and human contact, salt spray and cryogenics.

Lead Screw Coatings

Standard lead screw nuts are manufactured from self-lubricating plastics. We also offer soft TFE and hard BFE low friction coatings for the lead screw; lubrication to the screw/nut interface occurs by the nut picking up TFE particles from the coating as well as from migration of the internal lubricant from within the plastic nut.

We also supply lead screws with specialist nickel/TFE coatings and offer a choice of coatings used in medium vacuum applications (up to 10-5). Alternatively a BFE coating can be provided. This is a special proprietary hard coating which shares many of the benefits of TFE coating but offers exceptional durability in more aggressive environments and where reduced friction and a permanent coating is desired.

Although care should be taken to ensure that chips and voids do not occur in the coating, small voids have been shown to have little effect on the system performance. The lubricant, although solid, has some of the “spreading” ability of fluid lubricants. When machining bearing ends, soft fixtures are recommended to protect the coating.

TFE coated screws provide the maximum level of self-lubrication and should not be additionally lubricated or used in environments where oils or other lubricant contamination is possible.

Coatings, available for only a small additional cost, give the best results on wear life, coefficient of friction and torque to drive the lead screw assembly. To select a coating add -TFE or -BFE to the part number shown.

Lead Screw End Modifications

Lead screws are provided with the options of cut ends or a range of standard end modifications suitable for interfacing with ball bearings, circlips, couplings, pulleys and gears. Alternatively custom end modifications can be supported.

Modified, Custom and Multi-Functional Nuts

In addition to the standard nut types, custom configurations are available as well as simple modifications such as different mounting hole patterns or mounting threads, small dimensional changes or special materials.

Custom nut designs can offer multi-functionality, eliminating additional components, simplifying product manufacture, saving space and reducing cost. Multi-functional nuts can be produced using custom moulds and special machining to integrate components into the nut, such as guide bushings, carriages, timing pulleys, gears, syringe components, sensor mounts and flags, encoder features, clamps and many other complementary elements. In addition, custom designed nuts can offer quick release mounts, partial thread engagement, half nut construction or alternative shapes and geometries.

Special materials are available to extend the performance of the assemblies. We offer a range of Kerkite® composite polymers. Each member of the Kerkite® family is compounded with lubricants, reinforcements and thermoplastic polymers formulated to provide optimum performance in its target conditions and applications. In addition to the Kerkite® composite polymers, materials such as PEEK, polyester, Torlon, Vespel, PVDF, UHMW, Ertalyte® are available. Materials can be chosen for extreme temperature, chemical compatibility, autoclaving, agency approvals, special loadings and many other specific requirements.

Custom geometries and materials can be combined for a wide variety of product application requirements. Small quantities of custom nuts can be machined individually to suit specific requirements, alternatively large quantities can be moulded for reduced costs.

To achieve the most effective nut design we consider a combination of tolerancing and geometric shape of the nut. Tighter tolerances can be achieved by designing in geometric features to control important diameters, for example use of a ribbed feature on a bearing location diameter will reduce the need for tighter manufacturing tolerances.