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BEARINGS & LINEAR MOTION FEATURE ar R guide do you need?


For a smelting plant application, this piece of an aluminium ingot handler utilises profile guides


They can, for example, bolt from top or bottom and offer multiple methods to cover and protect bolt holes from debris, including cover strips, plastic rail plugs and metal rail plugs. When more flexibility is required, round shafts


have the advantage. They can be configured in many ways to facilitate holding the ends of the shaft and can even provide structural support in a larger assembly. To increase mounting flexibility, options include implementing flats or reduced shaft diameters, or drilling through the case on the shaft either on centre or radially. Their self-aligning design is also more forgiving of poor parallelism and variations in rail height.


Solid Particulate SaFeguarding Solid particulates such as metal, wood chips, extremely fine glass, ceramic dust or flour get into moving parts and impact wear and performance. Particulates can fall onto round or profile rails or may be airborne. Guide manufacturers address dust and particulate handling through sealing and wiper designs that protect against solid contaminants that land onto bearing surfaces. Getting a robust seal on a profile rail is


medical industries, as well as for harsh environments like food processing. Higher loads may require hardened shafting. This can be accomplished with advanced coatings, which can extend component life 200-fold. Coating options are comparable for both round


and profile rails and, in both cases, increased corrosion protection may involve trade-offs with hardness. Armaloy chromium coating, for example, provides moderate corrosion resistance and a hardness of 78 HRc, while austenitic stainless steel, such as 300 series, is more corrosion resistant but more expensive, and has HRc hardness levels only in the 20s. Austenitic stainless steels are typically only recommended to be used with plain-style bushings. Martensitic stainless steel, such as 440C, also offers improved corrosion resistance over carbon steel but can achieve hardness levels in the 50s and thus can be used with Ball Bushing Bearings. Other factors may come into play when


considering coating options. Stainless steel, for example, is a good choice for food-grade environments or where users might be concerned about flaking off of the plating. Ergonomic considerations or guarding can also


improve a system’s ability to handle excessive fluid. Orienting the guide in a way that will minimise fluid penetration into bearing surfaces or that will promote run-off will also improve fluid handling. Profile rails are more compact, so they can provide more flexibility if standard mounting geometries are possible. The quality of the mounting surface finish is key to having the most flexibility during profile rail installations. To further facilitate installation flexibility, profile rails are available in different mounting configurations.


www.designsolutionsmag.co.uk


challenging because wipers must conform to the ball tracks, which are ground in the rail and may increase drag – in fact, twice as much drag as with round linear bearings. Low-drag wiper designs for profile rail carriages help to minimise this problem but do not eliminate it. Profile rails might use scrapers to remove


heavier particulate or bellows to shield raceways from any dust or particulate accumulation. Round rails have natural debris-shedding capabilities due to the curvature of their shafts. Although profile rail tracks are hidden from direct access, they do not necessarily shed debris.


extreme temPeratureS Extreme temperatures tend to have the greatest effect on plastic components, such as seals and recirculation mechanisms. Temperatures above or below the lubrication’s rating can cause components such as base oil, thickener and additives to separate and reduce. Fluctuations in temperatures can cause condensation, which leads to corrosion as well as thermal expansion and contraction in steel and aluminium. Round rails can


provide all-steel or stainless steel bearings with no plastic


components. Both steel and stainless steel provide a wider operating temperature profile, but the stainless steel bearings have less load capacity than steel. Also, the plastic end caps and recirculation tubes in profile rail often prevent them from being used in extreme temperatures.


Vibration and Shock reSiStance Constant torque and movement can weaken a component over time and cause failure. Shock loading, as with an instantaneous impact load, affects all bearings. The heavier the load, the greater the problem, and because profile rails can handle heavier loads, shock is more of an impact force. In all cases, however, the rail is scaled to the capacity of the normal load and not to the shock load. The greatest impact is with heavy machinery, where the shock is more detrimental just because of the pure mass involved. Profile rails are also more tolerant of heavy


impacts since they offer various preload options, which can make them more resistant to other impacts that don’t affect the rolling element. Round rails are less tolerant of impact


due to their natural clearance fit. They do, however, outperform profile guides when a fluid driving force is applied to the rail because they are less likely to pull up on race areas than are profile rails.


the Final Verdict The decision on whether to use round or profile rail depends on the application. As always, begin by establishing your motion profile and the essential performance characteristics. Then evaluate your options according to their advantages or disadvantages for each environment. Profile and round rails can both be used in


wet, corrosive, dusty and high-shock/vibration environments, as long as the considerations are made for their design differences, accessories and overall precision and load requirements. Where precision beyond the capability of round


rails is essential in hazardous environments, coatings may be specified, or the designer will have to factor in the operational limits and incremental costs of the profile rails. Profile rails may have some advantages in


wet environments because their compact size provides more flexibility in mounting to avoid moisture,


but if forgiving


tolerances, nonstandard geometries or end-


supported configurations


are required, round rails have the clear advantage. There are many useful online tools available that help users weigh the tradeoffs among various hazardous conditions.


Thomson www.thomsonlinear.com/en/index


Motion www.motion.com


Exploded view of a profile rail carriage assembly showing integrated sealing and contamination protection components


SEPTEMBER 2026 DESIGN SOLUTIONS 29


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