Bearing Strip
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Product Overview Bearing Strips are skived from material billets and are available in the standard thicknesses and widths. ERIKS Bearing Strip can be supplied in metre lengths. Length Calculation for Bearing Strip Once the bearing strip installed it is important that a ‘Gap’ is present between each end of the bearing strip. This feature is required to ensure:- |
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| For Bearing Strip used in Piston applications:- LB = (Π X (B - TH) / 1.01) – C For Bearing Strip used in Rod applications:- LB = (Π X (R + TH) / 1.01) – C Where:- LB = Calculated Bearing Strip Length (mm). B = Bore diameter (mm) R = Rod diameter (mm). TH = Bearing Strip thickness (mm) C = Gap constant: 0.8 (1.8 for PTFE based materials above 120°C) |
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Wear Ring/Machined Bearing Strip Design Guide
Bearing Design Options
Careful consideration needs to be taken when choosing the correct bearing material.
Factors influencing the design are load capacity, friction, temperature, service life and running velocity. As a general guide if wear and load bearing is paramount, then a Phenolic/fabric composite materials are favoured.
If low friction is important, PTFE based materials offer the best option.
Load Capability
To ensure minimal wear and optimum performance it is important to maintain the lowest possible unit load over the bearing. The bearing load can be estimated using the below illustrated calculation.
Influencing factors such as rod/piston deflection, bearing deformation and diametrical tolerancing need to be considered when considering bearing design. Other factors including external loads, geometrical tolerances (eccentricity, concentricity, ovality) and component weight also need to be recognised.
It is good practice to minimise bearing radial cross section as for a given load the thinner the radial cross section, the less the deflection. Lifetime requirements may contradict this.
Our experts can assist you in selecting the optimal configuration for your application if required.
Note: For small diameters, machined wear rings are
recommended to aid installation. Minimum Bearing Strip
Diameters: PTFE 8mm, Fabric 60mm.
Bearing Calculation
For the Bearing Load Calculation we assume the load distribution is uniform over a project bearing area. The bearing area may be approximated by using the following calculation.
Projected Bearing Area (Bpa) = Internal Bearing Diameter (Bd) X Bearing Axial Length (BL)
| e.g. | Internal Bearing Diameter (Bd) | = 50mm |
| Bearing Axial Langth (BL) | = 25mm | |
| Projected Bearing Area (Bpa) | = 1,250mm2 |
When the Projected Bearing Area (shaded red) has been approximated, the bearing pressure may be found by dividing the Total Force Load by the Projected Bearing Area. This will determine the minimum compressive strength (Cs) of the bearing material to be utilised.
If your design requires the incorporation of a safety factor, it is advisable to multiply the Total Force Load (FL) by the desired factor of safety (FOS), e.g. 2. The required bearing compressive strength can be calculated as follows;
| Cs | = | FOS X FL(Bd X BL) | |
| Cs | = | (2 X 3000N)(50mm X 25mm) | |
| Cs | = | 60001250 | = 4.8 MPa |
Material Selection
Calculating the required bearing material strength is important in determining the correct material to use. Listed below are additional criteria that need to be considered;
• Is the application rotary, reciprocating or static?
• What surface speed will the bearing see?
• Is lubrication present?
• What are the temperature extremes?
• What is the shaft/bore material, hardness and surface finish?
• Does the bearing have exposure to abrasive, erosive and chemically aggressive media?
The below table defines the properties of the standard materials available
| Material | Compressive Strength (max) | Max Surface Speed | Mating Surface | Size Availability | General Uses |
|---|---|---|---|---|---|
| Bronze Filled PTFE |
15 MPa at 25oC 12 MPa at 80oC 8 MPa at 120oC |
15.0 m/s | Steel Hard Chrome, Steel Hardened | Rings 8mm to 2600mm
Up to 4600 in Strip Form |
Light load, lubricated environment |
| Carbon Filled PTFE |
12 MPa at 25oC 9 MPa at 80oC 5 MPa at 120oC |
Stainless Steel, Hard Anodised Aluminium | Light duty, can run dry | ||
| Phenolic (Fabric Composite) |
300 MPa at 25oC (Static) 50 MPa at 60oC (Dynamic) |
1.0 m/s | Steel Hard Chrome, Steel Hardened | 10mm to 1500mm (Rod Dia) | Heavy load, lubricated environment |
Type of Cut
Angled cuts are recommended for use in reciprocating applications. Straight cuts are for rotary applications. Stepped cuts are used in special applications, e.g. for flow restriction.
Machined Wear Rings are application specific. Based upon application data, the appropriate dimensions and hardware tolerances will be calculated by our technical team for the entire sealing system.