Automotive and bicycle engineering, industrial automation and robotics, medical science, consumer electronics and domestic appliances are just some of the sectors in which linear bearings are needed. The essential function of a linear bearing is to support and enable movement of an object along a straight (or occasionally curved) line. Think of the backward-forward adjustment of a car seat, the up-down motion control of a bike’s fork suspension, the precise positioning of factory cutting tools or medical imaging equipment, and the adjustment of a coffee machine’s spout for different cup heights.
In each case, users want the motion to be achieved smoothly, accurately and with little effort. Vibration and noise should be minimised, not only to avoid annoyance but to prevent vibration-related wear and damage. What’s more, the linear bearing should behave consistently in these respects, day after day, for many years. Depending on the application and sector, other important linear bearing characteristics may include low weight, compact size and the ability to function without generating or being affected by dust, dirt and debris. Manufacturers comparing linear bearings must also consider whether their choice will increase or decrease material and process costs relating to product assembly.
NORGLIDE® sliding bearings for linear motion address all these issues and more. Importantly, their inherent advantages can be optimised to create the ideal solution for each application by adjusting and prioritising specific properties according to each customer’s individual needs. This customisation is based on more than 140 different material combinations, as well as variations in material thickness, layer structures and bearing shape, geometry and dimensions.
NORGLIDE® linear bearings feature a layer of self-lubricated, low-friction PTFE which allows them to slide smoothly against contact surfaces. Their layered structure can be modified by using a choice of metals as reinforcement and different fillers for the PTFE compound, in configurations tailored to different applications.
They can be deployed in situations where ball bearings and other rolling elements have traditionally provided linear motion, and in others where ‘plain’ bearings are already commonplace. (Sliding bearings like NORGLIDE® are often referred to as plain bearings because they have no rolling elements or other moving parts.)
Although their detailed specification can vary enormously to meet specific needs, NORGLIDE® linear bearings fall into two main types according to their arrangement within engineered products.
In one type, the bearing is cylindrical and a shaft slides on the inner surface is the bearing. Here it is sometimes called a linear bush, a linear bushing or a linear sleeve bearing.
In the other type, the outer surface of the bearing slides against the inner surfaces of e. g. guide rails. Here it is sometimes called a slider or sliding pin.
The key to the sliding ability of NORGLIDE® linear bearings is PTFE’s low coefficient of friction and its self-lubrication. As the bearing slides, particles of PTFE rub off and form a lubricating (but dry) layer onto the mating surface. This means no grease or oil is ever needed.
To match the PTFE layer’s behaviour and performance with an application’s specific requirements, it can be compounded with a variety of fillers. These fine-tune characteristics such as bearing strength, coefficient of friction, creep (tendency to deform over time) and electrical or thermal conductivity.
In addition, different metals can be used to back the layered NORGLIDE® Bearing structure, to clad the metal backing against corrosion, or to form a structural interlayer. The choices in this respect match the bearing’s overall durability, strength and plasticity, in particular, to its task.
NORGLIDE® sliding bearings offer a wide range of properties ideal for linear motion, and each characteristic is adjustable to the individual application’s needs. Of fundamental importance is their low coefficient of friction for solid materials, which enables smooth movements with little effort and minimal stick-slip effect.
Crucially, there is no need for grease or oil as they are self-lubricating. While the friction in rolling bearings varies with the amount of lubricant, and with the effect of temperature and time on the lubricant’s performance, NORGLIDE® performs much more consistently – throughout its long life. It can also withstand an exceptionally wide temperature range, from -200 to +260⁰C.
The lubrication necessary for rolling bearings not only adds to material costs, maintenance labour expense and downtime but leads to gathering of dust and dirt which cause clogging and wear. By contrast, the PTFE elements of maintenance-free NORGLIDE® linear bearings act as a seal which keeps the sliding surfaces clean.
Thanks to their low coefficient of friction and the relatively large contact surface over which they spread their load, NORGLIDE® linear bearings can run on softer shafts. These may be made from aluminium or non-metallic materials which are lighter and less expensive than hardened or surface-treated steel, for instance.
The plasticity and formability of NORGLIDE® adds further advantages. First, it compensates for tolerances and misalignments in the shaft, rail or other associated components, making them less demanding and costly to manufacture. It makes assembly easier, with no need for the pre-tensioning and regular adjustment that rolling bearings require. In contrast to ball bearings, NORGLIDE® ensures that all components retain a close fit, with none of the unwanted play which would result in noise, vibration, wear and inefficiency. With NORGLIDE® you also avoid brinelling (damage caused to surfaces by ball bearings at their contact point).
NORGLIDE® linear bearings’ overall structure lowers vibration, reduces wear and extends product life. Load capabilities and pV (ability to withstand load pressure and speed) are high, and edge loading can be absorbed. An important characteristic of PTFE in this respect is that its coefficient of friction actually reduces with increased pressure. So, compared to roller bearings, the friction of NORGLIDE® Bearings are less sensitive to changing loads.
Weight and space savings are important in many applications. The relatively simple shape of NORGLIDE® linear bearings, with a single-piece construction and no rolling parts, makes them lighter and smaller than rolling bearing alternatives. They also simplify and speed up product assembly.
Another saving can be made in the amount of material needed for guide rails. With ball elements, the balls need to be in contact with both sides of the rail. In practice, this means that for an adjustment length of, say, 1 metre, each rail must be at least 0.5 metre. In a slider system, adjustment length depends only on the outer rail’s length, as the inner rail is attached to it. NORGLIDE® linear bearings’ infinite adjustability for length, along with their great flexibility of shape and size, contrasts sharply with the relatively fixed choices offered by rolling balls.
Other benefits of NORGLIDE® Bearings and their materials include non-absorption of water and high resistance to corrosion. NORGLIDE® configurations can be specified both to protect the bearing’s own metal reinforcement and to protect materials with which the bearing comes into contact. NORGLIDE® Bearings can also be conductive or non-conductive depending on the application and, where required, can be specified with the necessary conductive properties to support e-coating.
Spout height adjustment in a high-quality coffee machine presents a simple illustration of linear motion and the comparative suitability of alternative bearing solutions for achieving it. The spout assembly is manually pushed up or down to reach the right height for different cup sizes.
A cheap moulded plastic sliding bearing gives an unsatisfying stick-and-slip motion. A ball bearing may give a much better feeling initially, but gravity and other factors will eventually affect its performance and readjustment will be needed to restore smooth and quiet movement. In addition, grease in the bearing may deteriorate in hot and humid conditions, leading to annoying squeaks. Grease-free, damp-proof, heat-resistant NORGLIDE® linear bearings are the obvious solution.
Avoidance of grease in mechanisms, and a move away from the need for lubrication in general, is a wish for many businesses. This is just one of the many reasons why all major automotive manufacturers, for example, now use NORGLIDE® Bearings somewhere in their products. Where ball bearings are used instead, users must either accept the need for regreasing and readjustment or live with the squeaking and rattling. Bearings for linear motion are needed, for instance, in sliding seats, centre consoles and headrest.
For car makers, minimising NVH (noise, vibration and harshness) and BSR (buzz, squeak and rattle) is a growing priority which NORGLIDE® Bearings can address. End users have become increasingly demanding in terms of a quiet, smooth, positive driving experience. To some extent this is influenced by the growth in popularity of electric vehicles: with no engine noise, other sounds have become more noticeable. Due to the relatively thick PTFE layer NORGLIDE® is able to better dampen vibrations and allow clearance-free but smooth sliding elements. This quiets down the noise level inside the vehicle cabin. NORGLIDE® Bearings also contribute to lowering vehicle weight, helping manufacturers in responding to demands for higher energy efficiency and lower CO2 emissions. Extension of product life, by minimising corrosion and vibration-related damage, is another area in which NORGLIDE® can improve sustainability.
In the bicycle market, a typical NORGLIDE® linear motion bearing application is in the front forks of bikes with suspension mechanisms. A cylindrical sliding NORGLIDE® Bearing can be used to ensure smooth performance with no slip-stick effect, squeak or rattle. At the same time, it creates a perfect seal against water. Avoiding corrosive and vibration-generated damage and wear is important to cyclists, as is minimising weight.
When it comes to factories and warehouses with automated and often robotic equipment, the scope of bearings for linear motion is extremely varied. They can be found in machines and robots used for product assembly, material handling, packaging and palletising, for instance. Precise positioning of workpieces for machining tasks such as drilling and cutting may also depend on linear bearings. There are similar requirements for accuracy of position and movement in 3D and other printing machinery.
NORGLIDE® Bearings have a distinct advantage in ‘clean’ applications like food and drink processing and packaging, laboratory work and positioning of medical imaging equipment. They do not pollute sterile environments with lubricants and they are unharmed by washdown water and detergents.
At the same time, they are ideal for ‘dirty’ workplaces such as mining, foundries and fabrication workshops which generate dust and debris. Unlike rolling bearings, they have no moving parts to become clogged.
This list could go on to cover everything from sliding drawers and doors in the home to turbine brakes for wind farms in the energy industry. Each can gain from the remarkable range of NORGLIDE® linear bearing properties.
NORGLIDE® Bearings for linear motion are custom-designed, configured and manufactured according to the requirements of each individual application and order. We work closely with the customer at all stages to understand and meet those needs precisely.
When deciding on the right bearing configuration, there are various issues to consider around the load it will carry. How heavy is it? Where is it applied and how is its weight distributed? Does the load vary, and by how much? At what speed and acceleration rate will it move? These factors have implications for a bearing’s functioning and longevity.
Other important variables include the level of control and precision required and the ideal amount of adjustment force needed to move the load. For a given load or range of loads, the friction level should be engineered such that adjustment is neither too difficult – leading to stick-slip motion – nor too quick and uncontrolled.
At present there are more than 140 possible material combinations for NORGLIDE® Bearings. These, together with variations in material layer thickness, configuration of other layers, and overall bearing shape, provide the basis for creating the ideal set of characteristics for any given application.
PTFE’s properties can be adjusted by using different fillers to reduce cold flow, improve load capability or create electrically conductive or non-conductive materials.
The fillers selected affect factors including coefficient of friction, corrosion resistance and wear resistance of the bearing but also of mating materials (ability to use softer shafts). The choice between electrically conductive or non-conductive materials helps to support e. g. during a painting process or to divert electrostatic charge.
A metal backing layer made from aluminium, steel or stainless steel can be added to reinforce the bearing. The steel backing layer, if selected, can be cladded with aluminium or coated with zinc for corrosion protection. Sizing capacity can be increased by adding a metal interlayer.
Last but not least, the shape, geometry and dimensions of the NORGLIDE® linear bearing can be modified almost infinitely for its specific purpose. Examples include clearance or interference fit with mating components, and addition of flanges, fingers, tabs and holes as required.
Whatever your linear motion challenge, we can solve it with customised NORGLIDE® Bearings. To get in touch and talk to us, engineer to engineer, use our contact form or email us at: email@example.com.