Technical Blog

Fast, Accurate Profile Rail Linear Guides - which design is best suited for your application?

Profile rail linear guides are the most sought after linear guides when machine designers are looking for fast, accurate control over the linear movement of heavy loads.

What is a Profile Rail Linear Guide?

Also known as a square rail, they provide an increase of rigidity and stiffness over round-rail linear guides, as well as offering high load capabilities in a small, concise package.  Profile-rails can differ in rigidity, load capacity, travel accuracy, smoothness of operation and speed. They also come in various sizes and mounting configurations.

Profile-rail architectures vary in the shape and arrangement of the rolling elements. The primary options are:

  • Double-back profile-rail with ball bearings
  • Double-back profile-rail with roller bearings
  • Double-face profile-rail with ball bearings

 

Double-back profile rail with ball bearings

This design uses two sets of ball bearings running back-to-back inside the rail, providing high moment load capacities.

Support comes from a ball-conforming groove on both the inner and out races. The ball-track groove is a slightly larger radius than the balls themselves, cradling the bearings as they are flattened under a load. The bearings slightly expand the contact area between the balls and the races.

These profile-rail linear guides are ideal for applications such as high-industrial automation, machine-tools and precision measuring due to their rigidity and load-bearing capacity.

Double-back profile rail with roller bearings

Cylindrical rollers replace the ball bearings in this profile-rail. This provides stability over the convex balls, which only have a single-point contact area making them more susceptible to deforming under pressure. The rollers, in comparison, have a broad contacting surface along the length of the roller itself. 

For demanding applications, roller bearing elements offer even greater advantages. They are much more space-efficient so they can deliver higher load capacities in small footprints.

Double-face Profile-rail with ball bearings

This design uses four bearing tracks which are deployed face-to-face on the top of the profile-rail instead of inside it. This bearing arrangement results in equal load-carrying capabilities in all directions. The rails are much more receptive of mounting surface in-accuracies, but compromise on rigidity and moment load capacities.

Double-faced profile-rails can deliver a smoother operation with lower installation costs and are suitable for applications involving packaging equipment and food processing.

Exploring trade-offs for Profile Rail Linear Guides

It is important to consider trade-offs when deciding which profile-rail architecture is correct for your application. The different types of trade-offs include:

  • Rigidity
  • Capacity
  • Accuracy
  • Smoothness
  • Size
  • Durability
  • Cost

In order to choose a bearing suitable for your application you need to determine the mass of the load, location of the load, required acuracy, desired travel life and system mounting contraints.

Bear in mind, there is a risk of over-specifying. If you select a guide with too much rigidity it can increase preparation costs due to the reduction of the allowable installation tolerance. If the mounting surface is not prepared correctly the linear guide will run rough and will need to be replaced more often, thus inscreasing installation time and cost.

Installation Issues of Profile Rail Linear Guides

Poor installation can affect all variables including stiffness, capacity and smoothness. Profile-rail designs are particularly sensitive to flatness errors so if the rails are not alligned perfectly they will bind up under travel which can shorten the rail life.

Surfaces must be prepared carefully. In applications where two rails run parallel, a single mounting plate should be used to tie all four carriages together, allowing them to move together in unison.

Other possible installation issues include the flange getting in the way, therefore alternative mounting confiurations need to be established. The location of the mounting holes may not be standard size so a special plate may need to be designed. The choice of material is another issue that a design engineer may face. Most profiles are available in carbon-steel or stainless-steel for corrosive environments but there are also chromium-plate options, which also provide some corrosive prevention.

Noise is another issue with profile-rail linear guides. Generally, ball-based designs are prone to noise but ball-space and ball-chain based technologies are available to reduce noise levels by 30-40%.

For further information take a look at the Linear Guides we have available.

Have any questions? Call us on +44 (0) 1403 792 300 or email sales@heason.com.

Article published on: 30/06/2016