ASTM D5977-03(2007)
(Specification)Standard Specification for High Load Rotational Spherical Bearings for Bridges and Structures
Standard Specification for High Load Rotational Spherical Bearings for Bridges and Structures
ABSTRACT
This specification covers bridge bearings that consist of a spherical rotational element, where a stainless steel convex surface slides against a concave carbon steel plate covered with woven or sheet polytetrafluoroethylene (PTFE). The function of the bearing is to transfer loads and to accommodate any relative movement, including rotation between a bridge superstructure and its supporting structure, or both. The requirements of spherical bearings with a standard horizontal load (a maximum of 10 % of vertical) are discussed. The bearings are furnished in three types: fixed spherical bearing which is for rotation only, unidirectional sliding spherical bearing which is for rotation plus movement in one direction, and multi-directional sliding spherical bearing which is for rotation plus movement in all directions. The materials to be used in producing the bearings include: steel, stainless steel (flat sliding surface and convex surface), woven fabric polytetrafluoroethylene, and sheet polytetrafluoroethylene. The following different test methods shall be performed: proof load and rotation tests for fixed and expansion bearings, coefficient of friction test for expansion bearings only, PTFE (woven or sheet) bond test for expansion bearings only, and physical property test of both PTFEs for fixed and expansion bearings.
SCOPE
1.1 This specification covers bridge bearings that consist of a spherical rotational element, where a stainless steel convex surface slides against a concave carbon steel plate covered with woven or sheet polytetrafluoroethylene (PTFE). The function of the bearing is to transfer loads and to accommodate any relative movement, including rotation between a bridge superstructure and its supporting structure, or both.
1.2 This specification covers the requirements of spherical bearings with a standard horizontal load (a maximum of 10 % of vertical).
1.3 The requirements stated in this specification are the minima necessary for the manufacture of quality bearing devices. It may be necessary to increase these minimum values due to other design conditions.
1.4 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 The following safety hazards caveat pertains only to the test method portion, Section 7, of this specification: This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D5977 −03(Reapproved 2007)
Standard Specification for
High Load Rotational Spherical Bearings for Bridges and
Structures
This standard is issued under the fixed designation D5977; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope A240/A240MSpecification for Chromium and Chromium-
Nickel Stainless Steel Plate, Sheet, and Strip for Pressure
1.1 This specification covers bridge bearings that consist of
Vessels and for General Applications
a spherical rotational element, where a stainless steel convex
A572/A572MSpecification for High-Strength Low-Alloy
surfaceslidesagainstaconcavecarbonsteelplatecoveredwith
Columbium-Vanadium Structural Steel
woven or sheet polytetrafluoroethylene (PTFE). The function
A588/A588MSpecification for High-Strength Low-Alloy
of the bearing is to transfer loads and to accommodate any
Structural Steel, up to 50 ksi [345 MPa] Minimum Yield
relative movement, including rotation between a bridge super-
Point, with Atmospheric Corrosion Resistance
structure and its supporting structure, or both.
A709/A709MSpecification for Structural Steel for Bridges
1.2 This specification covers the requirements of spherical
D638Test Method for Tensile Properties of Plastics
bearings with a standard horizontal load (a maximum of 10%
D792Test Methods for Density and Specific Gravity (Rela-
of vertical).
tive Density) of Plastics by Displacement
1.3 The requirements stated in this specification are the D1457 Specification for Polytetrafluoroethylene (Ptfe)
Molding and Extrusion Materials (Withdrawn 1996)
minima necessary for the manufacture of quality bearing
devices.Itmaybenecessarytoincreasetheseminimumvalues D1777Test Method for Thickness of Textile Materials
D2256Test Method for Tensile Properties of Yarns by the
due to other design conditions.
Single-Strand Method
1.4 The values stated in inch-pound units are to be regarded
2.2 AASHTO Standard:
as the standard. The values given in parentheses are for
AASHTO Standard Specifications for Highway Bridges
information only.
2.3 AWS Standards:
1.5 The following safety hazards caveat pertains only to the
C.2.2-67Metalizing withAluminum and Zinc for Protection
test method portion, Section 7, of this specification: This
of Iron and Steel
standard does not purport to address all of the safety concerns,
D.1.5ANSI/AASHTO/AWS Bridge Welding Code
if any, associated with its use. It is the responsibility of the user
of this standard to establish appropriate safety and health
3. Classification
practices and determine the applicability of regulatory limita-
3.1 The bearings are furnished in three types, as follows:
tions prior to use.
3.1.1 Fixed Spherical Bearing—Rotation only.
3.1.2 Uni-Directional Sliding Spherical Bearing—Rotation
2. Referenced Documents
plus movement in one direction.
2.1 ASTM Standards:
3.1.3 Multi-Directional Sliding Spherical Bearing—
A36/A36MSpecification for Carbon Structural Steel
Rotation plus movement in all directions.
A167 Specification for Stainless and Heat-Resisting
Chromium-Nickel Steel Plate, Sheet, and Strip
4. Material Specifications
4.1 Steel—The steel used for all major plates shall be
structural steel conforming to Specifications A36/A36M,
This specification is under the jurisdiction ofASTM Committee D04 on Road
and Paving Materials and is the direct responsibility of Subcommittee D04.32 on
Bridges and Structures.
Current edition approved Dec. 1, 2007. Published January 2008. Originally The last approved version of this historical standard is referenced on
approved in 1996. Last previous edition approved in 2003 as D5977–03. DOI: www.astm.org.
10.1520/D5977-03R07. Available from American Association of State Highway and Transportation
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Officials (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM http://www.transportation.org.
Standards volume information, refer to the standard’s Document Summary page on Available from American Welding Society (AWS), 550 NW LeJeune Rd.,
the ASTM website. Miami, FL 33126, http://www.aws.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5977−03 (2007)
A588/A588M, A572/A572M,or A709/A709M, as required. 4.4.1 The thickness of the sheet PTFE shall be a minimum
AllexposedsurfacesshallbezincmetalizedaccordingtoAWS of ⁄8in.(3.17mm)andshallberecessedatleastone-halfofits
C.2.2-67 (with no chipping), having a minimum thickness of 6 thickness.
mil (0.152 mm) or treated with other project-approved coating 4.4.2 ThePTFEfortheprincipalslidesurfaceandforguide
systems such as coal tar or inorganic zinc paint. The dry film bars shall conform to the physical requirements listed in Table
thickness (DFT) of the approved paint system must be speci- 2.
fied by the owner.
5. Design Requirements
4.2 Stainless Steel:
NOTE 1—To Designer: The bearing details shall be designed in
4.2.1 Flat Sliding Surface—The sheet stainless steel used as
accordance with the requirements of the current edition with interims of
the mating sliding surface to the woven fabric PTFE or sheet
the AASHTO Standard Specifications for Highway Bridges or other
governing design procedures.
PTFE in the sliding spherical bearings shall conform to
Specification A167 or A240/A240M, type 304, 20-µin. (0.5-
5.1 Rotational Elements:
µm) rms finish.
5.1.1 The spherical radius shall be determined such that the
4.2.2 Convex Surface—The solid stainless steel plate or
resulting geometry of the bearing is capable of withstanding
sheet stainless steel used as the mating rotational convex
thegreatestratioofthehorizontalloadtoverticalloadunderall
surfacetothewovenfabricPTFEorsheetPTFEshallconform
loading conditions to prevent the unseating (separation at the
to Specification A167 or A240/A240M, type 304. The surface
edges) of the convex/concave elements.
shallbemachinedtoasurfacefinishof20-µin.(0.5-µm)rmsor
5.1.2 Unseating of the curved spherical surfaces relative to
less.
each other shall be prevented by transferring horizontal forces
through specifically designed restraints or by control of the
4.3 Woven Fabric Polytetrafluoroethylene (PTFE)—The
spherical radius.
woven fabric PTFE shall be made from virgin PTFE oriented
5.1.3 Acceptable spherical radius control shall be given
multifilament fibers with or without a high-strength backing.
when the configuration of the woven fabric PTFE concave
4.3.1 The thickness of the woven fabric PTFE in the free
radius follows the following design:
state shall be a minimum of ⁄32 in. (2.38 mm) when measured
in accordance with Method D1777.
ratio# tan α (1)
4.3.2 ThethicknessofthebondedwovenfabricPTFEunder
the application of vertical load shall be a minimum of the
where:
following:
ratio = worst case ratio of horizontal to vertical loads.
(1) ⁄16 in. (1.59 mm) from 0 psi (0 N/mm ) to 3500 psi
(24.1 N/mm ).
d/2
2 α 5 arcsin 2 designrotation (2)
S S DD ~ !
(2) ⁄64 in. (1.19 mm) from 3501 psi (24.1 N/mm ) to 4500 Rmax
psi (31.0 N/mm ).
4.3.3 The woven fabric PTFE shall be mechanically inter-
where:
locked and epoxy-bonded to the substrate using a system that
d = projected diameter of the woven fabric
prevents migration of the epoxy through the fabric. The use of
PTFE,
a mechanical interlock system along with the epoxy increases
design rotation = design rotation of the bearing (in
thebondstrength,providingaredundancyforthepreventionof
degrees), and
migration of the PTFE material. Any edges, other than the
Rmax = maximum allowable radius to prevent
selvedge (woven edge), shall be oversewn so that no cut fabric
uplift within the bearing during the worst
edges are exposed.
horizontal to vertical load case.
4.3.4 The individual PTFE filaments used in making the
5.1.4 Calculationsshowingdeterminationoftheradiusshall
wovenPTFEfabricshallconformtothephysicalrequirements
be submitted for approval.
of Table 1.
5.1.5 The radius of the convex plate shall be less than the
4.4 Sheet Polytetrafluoroethylene (PTFE)—The sheet PTFE
radiuscalculatedforthewovenfabricPTFE(concaveplate)by
shall be virgin material (not reprocessed) meeting the require-
a value equal to the thickness of the PTFE.
ments of Specification D1457. The PTFE shall be resistant to
5.1.6 The concave surface shall face down whenever the
acids, alkalis, petroleum products, and nonabsorbtion of water.
resulting center of rotation is not detrimental to the system
It shall be stable for temperatures up to 500°F (260°C) and
geometry. See Fig. 1
shall be nonflammable. When used in PTFE surfaces used for
guide bars only, filler material shall be composed of milled
glass fibers or carbon.
A
TABLE 2 Physical Property Requirements for Sheet PTFE
Physical Properties Test Method Requirement
Ultimate tensile strength, min, psi (MPa) D638 2800 (19.3)
TABLE 1 Physical Property Requirements for Woven PTFE
Ultimate elongation, min, % D638 200
Specific gravity, min D792 2.12
Physical Properties Test Method Requirement
A
Ultimate tensile strength, min, psi (MPa) D2256 24 000 (165.4) 15 % glass-filled PTFE may be used for guide bar surfaces (Specification
Ultimate elongation, min, % D2256 35
D1457).
D5977−03 (2007)
5.3 Woven Fabric PTFE Concave or Sliding Surfaces, or
Both:
5.3.1 The woven fabric PTFE shall be mechanically inter-
locked to the steel substrate. An epoxy bond system shall be
used for additional security. After completion of the bonding
operation, the PTFE surface shall be smooth and free from
blisters, bubbles, and evidence that any epoxy has migrated
through the woven fabric PTFE.
5.3.2 The area of the woven fabric PTFE shall be designed
for a maximum average working stress of 4500 psi (31.0
N/mm ).
5.3.3 The maximum edge pressure on the woven fabric
PTFE shall not exceed 10000 psi (68.8 N/mm ).
5.4 Sheet PTFE on Concave or Sliding Surfaces, or Both:
5.4.1 ThesheetPTFEshallbepurevirgin,unfilled,meeting
therequirementsofSpecificationD1457.ThesheetPTFEshall
berecessedtoone-halfofitsthicknessandepoxybondedtothe
FIG. 1 Views of a Spherical Bearing
steel substrate. The PTFE surface shall be smooth and free
from blisters or bubbles after completion of the bonding
operation.
5.1.7 The minimum thickness at the center of the concave
5.4.2 The area of the sheet PTFE shall be designed for a
spherical element shall be ⁄4 in. (19 mm).
maximum average working stress of 3500 psi (24.1 N/mm ).
5.1.8 The minimum thickness at the edge of the convex
1 5.4.3 The maximum edge pressure on the sheet PTFE shall
spherical element shall be ⁄2 in. (12.7 mm).
not exceed 5000 psi (34.4 N/mm ).
5.1.9 Vertical and horizontal cl
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:D5977–96 Designation: D 5977 – 03 (Reapproved 2007)
Standard Specification for
High Load Rotational Spherical Bearings for Bridges and
Structures
This standard is issued under the fixed designation D5977; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 Thisspecificationcoversbridgebearingsthatconsistofasphericalrotationalelement,whereastainlesssteelconvexsurface
slides against a concave carbon steel plate covered with woven or sheet polytetrafluoroethylene (PTFE). The function of the
bearing is to transfer loads and to accommodate any relative movement, including rotation between a bridge superstructure and
its supporting structure, or both.
1.2 This specification covers the requirements of spherical bearings with a standard horizontal load (a maximum of 10% of
vertical).
1.3 Therequirementsstatedinthisspecificationaretheminimanecessaryforthemanufactureofqualitybearingdevices.Itmay
be necessary to increase these minimum values due to other design conditions.
1.4 Thevaluesstatedininch-poundunitsaretoberegardedasthestandard.Thevaluesgiveninparenthesesareforinformation
only.
1.5 The following safety hazards caveat pertains only to the test method portion, Section 7, of this specification: This standard
does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this
standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
A36/A36M Specification for Carbon Structural Steel
A167 Specification for Stainless and Heat-Resisting Chromium-Nickel Steel Plate, Sheet, and Strip
A240/A240M Specification for Heat-Resisting Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for
Pressure Vessels and for General Applications
A572/A572M Specification for High-Strength Low-Alloy Columbium-Vanadium Structural Steel
A588/A588MSpecification for High-Strength Low-Alloy Structural Steel with 50 ksi [345 MPa] MinimumYield Point to 4 in.
[100mm]Thick 588/A588M SpecificationforHigh-StrengthLow-AlloyStructuralSteel,upto50ksi[345MPa]Minimum
Yield Point, with Atmospheric Corrosion Resistance
A709/A 709MSpecification for Carbon and High-Strength Low-Alloy Structural Steel Shapes, Plates, and Bars and
Quenched-and-Tempered Alloy Structural Steel Plates for Bridges 709/A709M Specification for Structural Steel for
Bridges
D638 Test Method for Tensile Properties of Plastics
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D1457 Specification for Polytetrafluoroethylene (PTFE) Molding and Extrusion Materials
D1777 Test Method for Measuring Thickness of Textile Materials
D2256 Test Method for Tensile Properties of Yarns by the Single-Strand Method
2.2 AASHTO Standard:
This specification is under the jurisdiction ofASTM Committee D-4 on Road and Paving Materials and is the direct responsibility of Subcommittee D04.32 on Bridges
and Structures.
Current edition approved July 10, 1996. Published September 1996.
This specification is under the jurisdiction ofASTM Committee D04 on Road and Paving Materials and is the direct responsibility of Subcommittee D04.32 on Bridges
and Structures.
Current edition approved Dec. 1, 2007. Published January 2008. Originally approved in 1996. Last previous edition approved in 2003 as D5977–03.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
, Vol 01.04.volume information, refer to the standard’s Document Summary page on the ASTM website.
Annual Book of ASTM Standards, Vol 01.03.
Available from American Association of State Highway and Transportation Officials (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001,
http://www.transportation.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5977 – 03 (2007)
AASHTO Standard Specifications for Highway Bridges
2.3 AWS Standards:
C.2.2-67 Metalizing with Aluminum and Zinc for Protection of Iron and Steel
D.1.5 ANSI/AASHTO/AWS Bridge Welding Code
3. Classification
3.1 The bearings are furnished in three types, as follows:
3.1.1 Fixed Spherical Bearing—Rotation only.
3.1.2 Uni-Directional Sliding Spherical Bearing—Rotation plus movement in one direction.
3.1.3 Multi-Directional Sliding Spherical Bearing—Rotation plus movement in all directions.
4. Material Specifications
4.1 Steel—ThesteelusedforallmajorplatesshallbestructuralsteelconformingtoSpecificationsA36/A36M,A588/A588M,
A572/A572M, orA709/A709M, as required.All exposed surfaces shall be zinc metalized according toAWS C.2.2-67 (with no
chipping), having a minimum thickness of 6 mil (0.152 mm) or treated with other project-approved coating systems such as coal
tar or inorganic zinc paint. The dry film thickness (DFT) of the approved paint system must be specified by the owner.
4.2 Stainless Steel:
4.2.1 Flat Sliding Surface—ThesheetstainlesssteelusedasthematingslidingsurfacetothewovenfabricPTFEorsheetPTFE
in the sliding spherical bearings shall conform to Specification A167 or A240/A240M, type 304, 20-µin. (0.5-µm) rms finish.
4.2.2 Convex Surface— The solid stainless steel plate or sheet stainless steel used as the mating rotational convex surface to
the woven fabric PTFE or sheet PTFE shall conform to Specification A167 or A240/A240M, type 304. The surface shall be
machined to a surface finish of 20-µin. (0.5-µm) rms or less.
4.3 Woven Fabric Polytetrafluoroethylene (PTFE)—The woven fabric PTFE shall be made from virgin PTFE oriented
multifilament fibers with or without a high-strength backing.
4.3.1 The thickness of the woven fabric PTFE in the free state shall be a minimum of ⁄32 in. (2.38 mm) when measured in
accordance with Method D1777.
4.3.2 The thickness of the bonded woven fabric PTFE under the application of vertical load shall be a minimum of the
following:
2 2
(1) ⁄16 in. (1.59 mm) from 0 psi (0 N/mm ) to 3500 psi (24.1 N/mm ).
2 2
(2) ⁄64 in. (1.19 mm) from 3501 psi (24.1 N/mm ) to 4500 psi (31.0 N/mm ).
4.3.3 ThewovenfabricPTFEshallbemechanicallyinterlockedandepoxy-bondedtothesubstrateusingasystemthatprevents
migration of the epoxy through the fabric. The use of a mechanical interlock system along with the epoxy increases the bond
strength,providingaredundancyforthepreventionofmigrationofthePTFEmaterial.Anyedges,otherthantheselvedge(woven
edge), shall be oversewn so that no cut fabric edges are exposed.
4.3.4 TheindividualPTFEfilamentsusedinmakingthewovenPTFEfabricshallconformtothephysicalrequirementsofTable
1.
4.4 Sheet Polytetrafluoroethylene (PTFE)—ThesheetPTFEshallbevirginmaterial(notreprocessed)meetingtherequirements
of Specification D1457. The PTFE shall be resistant to acids, alkalis, petroleum products, and nonabsorbtion of water. It shall be
stable for temperatures up to 500°F (260°C) and shall be nonflammable. When used in PTFE surfaces used for guide bars only,
filler material shall be composed of milled glass fibers or carbon.
4.4.1 The thickness of the sheet PTFE shall be a minimum of ⁄8 in. (3.17 mm) and shall be recessed at least one-half of its
thickness.
4.4.2 The PTFE for the principal slide surface and for guide bars shall conform to the physical requirements listed in Table 2.
5. Design Requirements Design Requirements
NOTE 1—To Designer: The bearing details shall be designed in accordance with the requirements of the current edition with interims of theAASHTO
Standard Specifications for Highway Bridges or other governing design procedures.
5.1 Rotational Elements:
5.1.1 The spherical radius shall be determined such that the resulting geometry of the bearing is capable of withstanding the
greatest ratio of the horizontal load to vertical load under all loading conditions to prevent the unseating (separation at the edges)
of the convex/concave elements.
Annual Book of ASTM Standards, Vol 08.01.
Available from American Welding Society (AWS), 550 NW LeJeune Rd., Miami, FL 33126, http://www.aws.org.
TABLE 1 Physical Property Requirements for Woven PTFE
Physical Properties Test Method Requirement
Ultimate tensile strength, min, psi (MPa) D 2256 24 000 (165.4)
Ultimate elongation, min, % D 2256 35
D 5977 – 03 (2007)
A
TABLE 2 Physical Property Requirements for Sheet PTFE
Physical Properties Test Method Requirement
Ultimate tensile strength, min, psi (MPa) D 638 2800 (19.3)
Ultimate elongation, min, % D 638 200
Specific gravity, min D 792 2.12
A
15 % glass-filled PTFE may be used for guide bar surfaces (Specification
D 1457).
5.1.2 Unseating of the curved spherical surfaces relative to each other shall be prevented by transferring horizontal forces
through specifically designed restraints or by control of the spherical radius.
5.1.3 Acceptable spherical radius control shall be given when the configuration of the woven fabric PTFE concave radius
follows the following design:
ratio #tan a (1)
where:
ratio = worst case ratio of horizontal to vertical loads.
d/2
a5 arcsin 2 ~designrotation! (2)
S S DD
Rmax
where:
d = projected diameter of the woven fabric PTFE,
design rotation = design rotation of the bearing (in degrees), and
Rmax = maximum allowable radius to prevent uplift within the bearing during the worst horizontal to vertical load
case.
5.1.4 Calculations showing determination of the radius shall be submitted for approval.
5.1.5 TheradiusoftheconvexplateshallbelessthantheradiuscalculatedforthewovenfabricPTFE(concaveplate)byavalue
equal to the thickness of the PTFE.
5.1.6 The concave surface shall face down whenever the resulting center of rotation is not detrimental to the system geometry.
See Fig. 1
5.1.7 The minimum thickness at the center of the concave spherical element shall be ⁄4 in. (19 mm).
5.1.8 The minimum thickness at the edge of the convex spherical element shall be ⁄2 in. (12.7 mm).
5.1.9 Vertical and horizontal clearance between the rotating (attached to the superstructure) and non-rotating (attached to the
substructure) spherical bearing components, including fasteners, shall be no less than ⁄8 in. (3.17 mm) when rotated to 150% of
the design rotation.
NOTE 2—To Designer: The spherical PTFE pad may be damaged at 150% of the design rotation.
5.1.10 The concave radius shall be machined to a tolerance of−0.000,+0.010 in. (−0,+0.25 mm).
5.1.11 The convex radius shall be machined to a tolerance of−0.010,+0.000 in. (−0.25,+0 mm).
FIG. 1 Views of a Spherical Bearing
D 5977 – 03 (2007)
5.2 Stainless Steel Sliding Surface :
5.2.1 Thethicknessofthestainlesssteelsheetshallbe11gage,withamanufacturer’sminimumthicknessof0.059in.(1.5mm).
5.2.2 Fixing of the Stainless Steel Sheet—The stainless steel sheet shall be attached to its backing plate by continuous fillet
welding along its edges. It is essential that the stainless steel sheet remain in contact with the base metal throughout its service
lifeandthatinterfacecorrosioncannotoccur.Theattachmentofthestainlesssteeltoitsback-upplateshallbecapableofresisting
the frictional force set up in the bearing. Welding must be in accordance with ANSI/AASHTO/AWS D1.5.
5.2.3 The backing plate shall extend beyond the edge of the stainless steel sheet to accommodate the weld; also, the weld must
not protrude above the stainless steel sheet. TIG welding of the stainless steel sheet is highly recommended to achieve this
connection.
5.2.4 The flat horizontal stainless steel sliding surface shall cover the PTFE surface completely in all operations, plus one
additional in. (25.4 mm) in all directions of movement. For a guided bearing with which there is no transverse movement, this
requirement does not apply in the transverse direction.
5.3 Woven Fabric PTFE Concave or Sliding Surfaces, or Both:
5.3.1 The woven fabric PTFE shall be mechanically interlocked to the steel substrate.An epoxy bond system shall be used for
additional security.After completion of the bonding operation, the PTFE surface shall be smooth and free from blisters, bubbles,
and evidence that any epoxy has migrated through the woven fabric PTFE.
5.3.2 The area of the woven fabric PTFE shall be designed for a maximum average working stress of 4500 psi (31.0 N/mm ).
5.3.3 The maximum edge pressure on the woven fabric PTFE shall not exceed 10000 psi (68.8 N/mm ).
5.4 Sheet PTFE on Concave or Sliding Surfaces, or Both:
5.4.1 The sheet PTFE shall be pure virgin, unfilled, meeting the requirements of Specification D1457. The sheet PTFE shall
be recessed to one-half of its thickness and epoxy bonded to the steel substrate. The PTFE surface shall be smooth and free from
blisters or bubbles after completion of the bonding operation.
5.4.2 The area of the sheet PTFE shall be designed for a maximum average working stress of 3500 psi (24.1 N/mm ).
5.4.3 The maximum edge pressure on the sheet PTFE shall not exceed 5000 psi (34.4 N/mm ).
5.4.4 The surface of the PTFE sheet to be epoxy bonded shall be etched using the sodium naphthalene or sodium ammonia
etching process.
5.5 Sheet PTFE Guiding Surfaces :
5.5.1 Attachment of the sheet PTFE to the steel substrate of the guiding surface shall be performed by epoxy bonding and
mechanical fastening. The mechanical fastening shall consist of a minimum of two stainless steel screws (Specification A304)
locatedonthecenterlineofthestripofPTFEandlocated ⁄2in.(12.7mm)fromeachendofthePTFEstrip.Thetopofthescrews
shall be recessed a minimum of 50% of the amount of protrusion of the PTFE above the steel substrate.
5.5.2 The surface of the PTFE sheet to be epoxy bonded shall be etched using the sodium naphthalene or sodium ammonia
etching process.
5.6 Guide Bars:
5.6.1 Each guide bar shall be manufactured from a monolithic piece of steel. Guide bars may be made integral by machining
from the solid shape or fabricated from solid bars that are welded, bolted, or recessed into the guiding plate, or some combination
thereof.
5.6.2 Guided surfaces shall be faced with opposing strips of stainless steel and sheet PTFE. No metal-to-metal contact shall be
permitted. The shee
...
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