How to Assemble NORGLIDE^® Bushings

The process described here, though idealized, includes the most important steps for installing NORGLIDE^® Bearings or Bushings into a housing bore. If and in which order the individual steps have to be made depends on material type, application and technical feasibility, and should be discussed with our application engineers.

Installation

How to feed the bushing to the installation point

The degree of automation decides on whether the bearing is inserted by hand or by machine. With tangle-free bearings, a combination of vibration feeder and gripper can be used. Long distance between feeder and installation point are overcome by “shooting” the bearing pneumatically through profile tubing.

 

How to insert the bushing into the housing bore 

Bearings with loose fit in the housing bore do not necessarily need a mandrel for installation. For NORGLIDE^® Bearings with metal backing > 0,4 mm and interference fit in the housing a installation mandrel is required. For the layout of the mandrel it should be considered to guard the sliding layer from damaging.

 

How to prevent movement of the bushing

To prevent bearing movement during all subsequent forming operations, a so-called “down-holder” is used which grips the axial flange and fixes the bearing. A dead stop (spacer) prevents squeezing of the flange.

 

How to size the inside diameter 

The bushings inside diameter can be modified by sizing. This leads to a reduced overall tolerance field. As sizing may cause an increase of bushing length, this step is always executed before 2nd flange forming. Details are shown below.

 

How to form the 2nd flange 

Usually flanging is done in two steps; first step: 45° (Image B), second step: 90° (Image C). In particular cases, if the geometry of housing bore, pin and NORGLIDE^® material allows, the second flange can be formed in a single step.

For further details, please contact our technical expert for guidelines regarding design and dimensioning. 

Sizing of a NORGLIDE^® Bushing

Manufacturing tolerances, or variations, are an everyday occurrence for many of our customers. That is why Saint-Gobain engineers work hard to ensure our customer’s systems work consistently.

NORGLIDE^® Bearings, in combination with a sizing procedure, can help to minimise this issue. For bearing applications, assembly options range from clearance fits to interference fits (also known as press fits). With a clearance fit, there is some space between the shaft and bearing. With an interference fit, the shaft diameter is slightly larger than the inner diameter of the bearing. The latter makes for a tight fit and higher torque. While the PTFE in a NORGLIDE^® Bearing still provides low friction even in a tight interference fit, adjustment of the level of interference – by sizing – can be used to fine-tune the torque.

Sizing, as shown in Figure 1, is achieved by pushing a sizing pin through the bearing during assembly. The pin has a projection, known as an olive, which is wider than the inner diameter of the bearing. Using a sizing pin of a controlled outer diameter, the bearing is plastically deformed, transforming the bearing's inner diameter into a specific and significantly more consistent value. This leads to a more consistent inner diameter than even the housing alone.

A similar device can be used to create flanges. Flanging pins are available with or without an olive, depending on whether or not the bearing is to be sized at the same time.

Figure 1: Schematic representation of the sizing procedure. The sizing pin features an olive which has a larger outer diameter than the required inner diameter due to the elastic behaviour of the bearing's sliding layer. The pin is inserted into the bushing to plastically deform the PTFE sliding layer into the specified thickness. It is important for Saint-Gobain engineers to work closely with customers so we can ensure an effective sizing procedure is implemented.

The sizing process detailed above will not be effective on all bearings, however. NORGLIDE^® SM, SMALC, SALC, M and MP Bushings all incorporate a metal stretched mesh or metal fabric layer within the PTFE compound that helps the sizing process by allowing plastic deformation of this layer. Figure 2 shows the possible control of the inner diameter using increasing sizing pin diameters with NORGLIDE^® SM Bushings. The level of sizing that is achievable depends on the total stiffness of the bushing material. It should be noted that due to the thickness of the deformable layer, there is a limit to the highest wall thickness reduction possible which is why it is important to work closely with our customers to ensure the initial problems are understood so an effective, custom-made solution can be provided.

Figure 2: An example case of wall thickness reduction after increasing sizing pin calibrations for NORGLIDE^® SM Bushings of dimensions: thickness = 1 mm, length = 17 mm, inner diameter = 12 mm. The sizing steps were performed at 50 µm intervals. The width of the shaded area indicates the range in standard deviation from the average values.

For further details, please contact our technical expert for guidelines regarding design and dimensioning.

Tolerance stack-up

In the case where a bearing is placed between the shaft and housing, the bushing inserted into the housing will have an inner diameter tolerance equal to that of the housing tolerance plus twice the bushing wall thickness tolerance. This can lead to a third element in the system adding to the tolerance stack-up.

The worst case scenario of tolerance stack-ups occur when a housing and a shaft are at equal and opposite extremes of their tolerance ranges – simply, the smallest inner diameter of the housing with the largest diameter of the shaft as one example. This can lead to excessive torque for a particular assembly whilst the other extreme, large housing diameter and small shaft diameter can lead to low or no torque.

Interested in finding out more?

Interested in finding out more? Contact us to speak to an engineer about how you could use NORGLIDE^®.