CHOOSING A LINEAR RAIL: 5 COMMON MISTAKES TO AVOID

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Matara has been producing linear rails for over 20 years. Drawing on this experience, Japh Humphries, the company’s UK Sales & Commercial Manager, identifies the five most common mistakes customers make when specifying and setting up a linear rail, to help others avoid going down the same costly path.

A linear rail is a common linear motion component that allows for the smooth movement of loads along one single axis. In order for a linear motion system to perform efficiently and to be cost-effective, it is essential for the linear rails and guides to be correctly specified and set up.

Mistake 1: Incorrectly calculating preload

Preload is the elimination of internal clearance between the linear rail and carriage. This makes the system more rigid by creating a load on the linear guide, which reduces deflection when an external force is applied. Common preload amounts for linear guides are 2, 5, or 8% of the dynamic load capacity. When specified accurately, preload reduces noise, vibration, heat generation and deflection. However, if the preload is not properly calculated or the mounting surfaces are not of a high enough precision to match that of the linear guide, attempting to apply preload can lead to friction – especially if the preload is too high – and reduce the overall performance of the linear automation system.

Mistake 2: Not taking tolerance into account

The goal of linear rails is to guide motion in a way that produces the least amount of friction between the carriage and the rails. If the rails or the bearings/balls of the carriage are not within the correct physical specifications, then friction can occur, resulting in heat, noise and/or damage to the parts. For linear rail specifications, tolerances must be accounted for in both the flatness of the mounting surface to which the rail is mounted and also how parallel the linear rails are to one another; any friction seen during operation is likely due to rail misalignment or incorrectly specified mounting tolerances.

Mistake 3: Treating mounting features as an afterthought

The purpose of mounting features, such as shoulders or alignment pins, is to support the linear rails to ensure that they perform to their specification. Mounting features add to the travel accuracy, speed and rigidity of the system and, therefore, its precision. Whilst linear rails are supplied straight, providing them with a stable support structure ensures that they remain both straight and parallel. Mounting features are specified by manufacturers to very precise dimensions, and these should be included as part of the linear automation system design from the outset.

Mistake 4: Failing to test a full run

Once assembled, linear automation systems such as linear guides must be tested across the full run of travel to ensure parallelism across the linear rails themselves. From one end to the other, the push force should show consistency to within 20%; if there is an increase in force, it may be that the linear rails need realignment. Without the correct level of alignment for the linear guide, it may lead to friction, deflection and noisy operation, not to mention a potential safety issue.

Mistake 5: Underestimating environmental factors

Demanding applications and locations, plus regular washdowns, take their toll on linear rails, frequently resulting in corrosion. This can be avoided, and maximum longevity can be achieved through the application of specialist coatings or epoxy paints. There is a good range of options here, including Armoloy TDC coating, which we use on our linear rail and provides corrosion protection equal to 440 series stainless steel, extending wear life by nearly 50% when compared with a typical hard chrome coating.

www.matara.com

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