LUBRON TF spherical bearings are widely used in structural applications to accommodate thermal, seismic and mechanical expansion and rotation.
LUBRON TF bearings provide exceptionally low coefficient of friction and high load capability for heavy duty and structural applications. Constructed of woven PTFE fabric liners permanently bonded to metal or composite substrates, LUBRON TF bearings are available in many configurations, including journal bushings, thrust washers, expansion bearing plates, self-aligning plain spherical bearings, multi-rotational spherical bearings and disc bearings.
- Sleeve Bearings
- Flange Bearings
- Thrust Bearings
- Spherical Self Aligning Bearings
- Expansion Bearing Plates
- Radial Bearing Plates
- Spherical Bearings
- Aerospace & Defense
- Hydro Power & Water Control
- Machinery & Heavy Equipment
- Power Generation
Typical applications include highway bridges, railroad bridges, light rail transit, offshore oil platforms, airports, sports arenas, convention centers, and air pollution.
LUBRON TF bearings are designed to accommodate unidirectional and omni-directional sliding movement in a single plane, and are recommended for applications subject to limited angular misalignment. LUBRON TF expansion bearing assemblies typically consist of an upper sole plate and a lower bearing plate, and are available either unguided or guided.
LUBRON TF bearings provide an exceptionally low coefficient of friction and heavy load capability, and are fabricated, tested and inspected in accordance with the latest ASTM, ASHTO and State DOT standards, plans and specifications. LUBRON TF expansion bearings have been performing flawlessly in a variety of rigorous structural applications for more than 25 years.
LUBRON TF woven PTFE fabric liners offer the most advanced design and construction available for high load and low coefficient of friction applications. LUBRON TF’s proprietary construction provides full support of the individual PTFE fibers and ensures a rigid bond of the fabric to the bearing substrate, two basic requirements that DuPont specifies for the successful use of Teflon as a bearing surface. The effective entrapment of the PTFE and glass fibers with high strength bonding resins eliminates cold flow and minimizes heat buildup. Low shear stresses and 100% supported bearing surfaces are two important advantages LUBRON TF bearings offer over other mechanically locked systems.
LUBRON TF spherical bearings offer the most advanced design and construction available for high load and low coefficient of friction applications. Sliding surfaces are permanently bonded with a woven PTFE fabric liner. Unlike PTFE resin sheets used in other types of bearings, woven PTFE fabric liners prevent cold flow and compressive creep leading to bearing failure. LUBRON TF’s proprietary construction provides full support of the individual PTFE fibers and insures a rigid bond of the fabric to the bearing substrate, two basic requirements that DuPont specifies for the successful use of Teflon as a bearing surface. The effective entrapment of the PTFE and glass fibers with high strength bonding resins helps prevent cold flow and minimizes heat buildup. The high molecular orientation of PTFE fiber gives it approximately 25 times the tensile strength of PTFE resins, making PTFE woven fabrics particularly suitable for heavy load applications. Low shear stresses and 100% supported bearing surfaces are also two important advantages LUBRON TF bearings offer over other mechanically locked systems.
LUBRON TF expansion and spherical bearings shall be designed in accordance with the following requirements unless otherwise specified by the Project Plans, Specifications and Special Provisions:
- Expansion bearings and spherical bearings shall accommodate the maximum total vertical load required unless otherwise specified. Maximum vertical load is assumed to be the total dead and live loads.
- The projected area of the woven PTFE surface shall be designed for a working stress under full vertical load unless otherwise specified.
- Expansion bearings shall be designed to resist the maximum horizontal load, or at least 10% of the maximum vertical load, unless otherwise specified.
- Expansion bearings shall be designed to accommodate the total movement as specified. Unguided and guided sole plates shall completely cover the expansion plate in all longitudinal and lateral operating positions with a minimum 1/2" (12.7 mm) distance from the edge of the sole plate sliding surface to the edge of the bearing plate for every direction of movement.
- All welded and bolted connections shall be designed to resist the maximum horizontal load, or at least 10% of the maximum vertical load, unless otherwise specified.
- Spherical bearings shall be designed to accommodate the maximum allowable concrete stress.
- Spherical bearings shall provide full multi-directional rotational capacity and accommodate an angular vertical displacement of at least 2º (.035 radians) unless otherwise specified.
- The projected area of the woven PTFE surface shall be designed for a maximum working stress of 3.5 ksi under full vertical load unless otherwise specified. Diameter of the concave spherical recess is generally used to determine projected surface area.
- Spherical bearings shall be designed to resist the maximum horizontal load, or at least 10% of the maximum vertical load, unless otherwise specified. Guided and fixed bearings shall be designed to insure the stability of the bearing components under maximum horizontal load and minimum vertical load conditions. Minimum vertical load is assumed to be the total dead load only.
- Spherical bearings shall be designed to accommodate the total movement as specified. Unguided and guided sole plates shall completely cover the concave bearing plate in all longitudinal and lateral operating positions with a minimum 1/2” (12.7 mm) distance from the edge of the sole plate sliding surface to the edge of the bearing plate for every direction of movement.
- All welded and bolted connections shall be designed to resist the maximum horizontal load, or at least 10% of the maximum vertical load, unless otherwise specified. Spherical bearings shall be designed to accommodate uplift when required.
HIGH LOAD CAPACITY
LUBRON TF expansion bearings are generally designed to accommodate bearing loads of 3.5 ksi (24 MPa) to 10 ksi (69 MPa), and can withstand loads in excess of 60 ksi (414 MPa) without cold flow.
The high molecular orientation of PTFE fibers gives it approximately 25 times the tensile strength of PTFE resins, making PTFE woven fabrics particularly suitable for heavy load applications.
The coefficient of friction for PTFE fibers is the lowest of all known fibers. The static coefficient of friction is only slightly higher than the dynamic value, minimizing stick-slip. LUBRON TF expansion bearings typically exhibit coefficients of friction of less than 4.0%, depending on the bearing load, temperature, velocity, finish and hardness of the mating surface.
LOW WEAR RATE
LUBRON TF bearings have a very low rate of wear, which is defined in terms of volumetric loss of material over time. Volumetric wear is approximately proportional to the unit load multiplied by the distance traveled, and is generally expressed as follows:
where W=wear depth, in (cm)
P=bearing pressure, psi (kg/cm2)
V=surface velocity, ft/min (m/min)
T=elapsed time, hr
K values for LUBRON TF bearings have been drived from independent testing, and can be used to determine the amount of wear that will occur over a period of time. For most applications, a value of K=9.1 x10-10 in3-min/ft-lb-hr is appropriate, which would be equivalent to 0.00045 inches of wear after 100,000 inches of travel at 3.5 ksi (24 MPa).
HIGH SHEAR RESISTANCE
LUBRON TF woven PTFE fabric liner is permanently bonded to the substrate metallic surface, and will resist a minimum 25% of the allowable vertical load in horizontal shear between the adhering elements as tested in accordance with Federal Specification MMM-A-175 Method 1033.
LUBRON TF bearings have excellent thermal stability and are recommended for continuous operation from -148ºF (-100ºC) to 500ºF (260ºC) and intermittent exposure up to 550ºF (288ºC). Coefficient of friction generally decreases with an increase in surface temperature.
EXPANSION BEARING COMPONENTS
The lower component consists of a woven PTFE fabric liner permanently bonded to carbon steel or stainless steel. The upper side of the bearing plate is permanently lubricated and maintenance-free. For guided expansion bearings, two sides of the bearing plate which slide against the guide bars may also be permanently lubricated and maintenance-free. The PTFE fabric liner is interwoven with secondary bondable glass fibers, impregnated with thermosetting resins, and bonded under temperature and pressure to the metallic substrate. The PTFE fibers predominate on the bearing surface, and provide low tangential shear stress and high wear resistance. The PTFE fabric liner varies in thickness from 1/32" (0.8 mm) to 3/32" (2.4 mm) depending on the application, and will accommodate edge loading and angular misalignment up to 1/32".
The upper component, with a stainless steel sliding surface, consists of 1/8" (3.2 mm) thick ASTM A240 Type 304 stainless steel sheet full seam welded to carbon steel. Sole plates are also available in solid stainless steel or with a carbon steel sliding surface hard dense chromium plated in accordance to Federal Specification QQ-C-320B Class 2 with a Rockwell C60 hardness. Guided sole plates shall have guide bars secured to the sole plate by welding or high strength fasteners. The distance between the guide bars, as measured perpendicularly to the bars along the full length of the sole plate, shall have a tolerance of 1/32" (0.8 mm) of the nominal dimension. The sole plate and guide bar sliding surfaces shall be polished to a maximum 20 microinch (0.5 micrometer) finish.
Expansion Bearing SIZING GUIDE
To accommodate maximum horizontal movement, the required sole plate sizes for standard bearing plate sizes can be determined using the following Tables.
Using the appropriate bearing design load and maximum vertical load, select the proper bearing plate size and corresponding sole plate size. The maximum bearing movement, dimensions "E" and "F", must be added to dimensions "C" and "D" respectively.
SPHERICAL BEARING COMPONENTS
Concave Bearing Component
Square or round plate with a concave spherical recess designed to accommodate rotation and angular deflection. For unguided and guided spherical bearings, both the concave recess and the upper side of the concave bearing plate shall be permanently lubricated with a woven PTFE fabric liner. Two sides of a guided concave bearing plate shall also be permanently lubricated. Fixed spherical bearings shall be permanently lubricated on the concave surface only. The woven PTFE fabric liner shall have a thickness not less than 0.020” (0.5 mm) or greater than .125” (3.2 mm) after compression.
Convex Mating Component
Round plate with a convex spherical surface designed to accommodate rotation and angular deflection. The convex plate shall be machined from solid stainless steel, or alternatively fabricated using carbon steel with a minimum 3/32” (2.4 mm) thick stainless steel weld overlay or hard chromium plated in accordance with Federal Specification QQ-C-320B Class 2 with a Rockwell C hardness of not less than 60. The convex surface shall be polished to a maximum 20 microinch (0.5 micrometer) finish. The convex plate shall be recessed into and/or attached to the base plate with a full fillet weld around the entire perimeter of the convex plate.
Upper plate affixed to the superstructure. Unguided and guided sole plates shall be machined from solid stainless steel, or alternatively fabricated from carbon steel with a minimum 16 gauge (1.6 mm) thick stainless steel sheet full perimeter welded to the carbon steel plate or hard chromium plated in accordance with Federal pecification QQ-C-320B Class 2 with a minimum Rockwell C60 hardness. The sliding surface shall be polished to a maximum 20 microinch (0.5 micrometer) finish. Guided sole plates shall have two guide bars connected to the lower side of the sole plate to restrict movement in one horizontal direction with corrosion resistant sliding surfaces.
Base Plate (Masonry Plate)
Lower steel plate to be affixed to the supporting substructure.
Anchor bolts and welded studs are generally furnished for affixing the bearing assembly to the superstructure and supporting substructure.
SPHERICAL BEARING SIZING GUIDE
The size of the spherical bearing is determined by the allowable design load and the maximum vertical and horizontal loads which occur. Design loads should be selected to suit the appropriate state and federal design codes. Bearing size may also be influenced by the maximum allowable concrete stress and other factors limiting the bearing load. LUBRON TF spherical bearings are designed to resist horizontal forces acting in any direction. A maximum horizontal load equal to 40% of the minimum concurrent vertical load is recommended for most application. To accommodate maximum horizontal movement, the required sole plate size for standard size bearings can be determined using the following size charts. Using the appropriate bearing design load and maximum vertical load, select the proper bearing plate size "A" and corresponding sole plate size "C" and "D". The maximum bearing movement, dimensions "E" and "F", must be added to dimensions "C" and "D" respectively.
All materials used in the manufacture of LUBRON TF expansion bearings shall meet the following requirements unless otherwise specified in the Project Plans, Specifications and Special Provisions:
Structural steel shall conform to the requirements of ASTM A36, ASTM A709 Grade 36 (250), ASTM A709 Grade 50 (345), ASTM A572 Grade 50 (345), ASTM A709 Grade 50W (345W) or ASTM A588 Grade A.
Stainless steel shall conform to the requirements of ASTM A240 Type 304 or Type 316.
Hard chromium plating shall conform to the requirements of Federal Specification QQ-C-320B Class 2.
High strength bolts and studs shall conform to the requirements of ASTM A325 Type 1 or ASTM A449 Type 1 unless otherwise specified. Heavy hex nuts shall conform to the requirements of ASTM A194 Grade 2H or ASTM A563 unless otherwise specified, and hardened steel washers shall conform to the requirements of ASTM F436 unless otherwise specified.
PTFE (polytetrafluoroethylene) surfaces shall consist of unfilled PTFE woven fabric made from oriented multi-filament 100% virgin PTFE fibers and other reinforcing fibers. The resin in the filaments shall be virgin PTFE material (not reprocessed) meeting the requirements of ASTM Designation D4441 Type VI (superceding ASTM Designation D1457). The PTFE fabric shall have a minimum thickness of 1/32" (0.8 mm) and a maximum thickness of 3/32" (2.4 mm) after compression.
Welding of expansion bearing components shall be performed in accordance with the requirements of ANSI/AASHTO/AWS D1.1, AWS D1.5 or AWS D1.6 unless otherwise specified. Welding of the expansion plate shall be permitted providing welding procedures are established which restrict the maximum temperature reached by the bonded area to less than 300°F (150°C) as determined by temperature-indicating wax pencils or other suitable means.
Corrosion protection including painting and metallic coating of all exposed carbon steel plates and fasteners shall be performed in accordance with Project Plans, Specifications and Special Provisions.
Expansion bearing assemblies shall be tested if required in full compliance with the Project Plans, Specifications and Special Provisions. Testing shall be performed in-house or by an independent testing laboratory subject to the approval of the Project Engineer. Bearings which do not fully satisfy all the testing and inspection requirements shall be replaced or repaired to the satisfaction of the Project Engineer.
Quality Assurance requirements for the manufacture and inspection of expansion bearing assemblies shall be in strict accordance with the requirements ISO 9002. Every phase of manufacture shall be monitored by Quality Control personnel to ensure that all materials and workmanship meet or exceed the requirements of the Project Plans, Specifications and Special Provisions.
We offer a variety of engineering services from the selection of bearing materials to in-house testing of bearing assemblies to simulate load, movement, velocity, temperature and other environmental conditions present during the actual operation of LUBRON TF bearings. Bearing design, AutoCAD drawing preparation, testing, consulting and on-site engineering services are available upon request.
Our leadership and reputation for service and product knowledge has been achieved through a strong commitment to total customer satisfaction. Every LUBRON TF bearing is guaranteed to perform reliably and trouble-free, and every effort is made to accommodate our customer’s delivery requirements in the shortest time possible.
Information for ordering LUBRON TF expansion bearing assemblies shall include the following:
- Type of bearing (unguided or guided)
- Maximum total vertical load (dead & live)
- Maximum allowable concrete bearing load
- Maximum longitudinal and transverse movements
- Bearing offset if required
- Anchorage required
- Corrosion protection required
- Proof testing required
LUBRON Self-Lubricating Bearings for Structural Applications
LUBRON SL bearings are widely used in structural applicatons for loads up to 8,000 psi. Available in a variety of high strength bronze alloys, LUBRONB SL bearings are permanently embedded with solid lubricants contained in trepanned or circular recesses.
LUBRON TF woven PTFE fiber bearings are designed to provide the lowest possible coefficient of friction for high load structural applications. Interwoven with secondary glass fibers and bonded under pressure and temperature to carbon steel or stainless steel substrates, LUBRON TF bearings are capable of static loads up to 60,000 psi.
LUBRON TR resin slide bearings provide an economic alternative for low friction applications with loads up 2,000 psi. LUBRON TR slide bearings consist of PTFE resin sheets bonded to either a combination of carbon steel, stainless steel, elastomer, or fabric pads. For higher loads, LUBRON TR bearings are als
LUBRON TF spherical bearing assemblies offer simple mechanical design, heavy load capability and high rotational capacity. Spherical bearings can accommodate large loads by virtue of its geometry. A more uniform load distribution under the spherical bearing makes it possible to reduce the overall dimensions. Spherical bearings are designed to permit horizontal movement and vertical rotation, as well as complete structural freedom of rotation about any horizontal axis. Vertical rotation can belarge, limited only by the geometry of the bearing. Rotational movements of the superstructure are accommodated by the sliding of the concave and convex spherical surfaces, which allow rotation in any direction with a minimum of resistance. Multi-Directional LUBRON TF multi-rotational spherical bearing assemblies typically consist of an upper sole plate, concave bearing plate, convex mating plate and a lower base or masonry plate, and are available either unguided, guided or fixed. Spherical bearings offer superior reliability compared to other types of high load multi-rotational (HLMR) bearings. Spherical bearings are characterized by their insensitivity to temperature changes, no permanent restoring moment load after rotation of the superstructure, and larger admissible rotation angles.