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LOCK BOLTS AND THE LOW
MAINTENANCE MAINLINE FROG
AREMA 2007
CONFERENCE AND EXPOSITION
Chicago, Illinois September 9-12, 2007
Michael Roney Canadian Pacific Railway
Suite 500 Gulf Canada Square
401-9th Avenue SW
Calgary Alberta T2P 4Z4
403-319-7800 fax 403-205-9009
Luigi Pisano Canadian Pacific Railway
Suite 500 Gulf Canada Square
401-9th Avenue SW
Calgary Alberta T2P 4Z4
403-218-7770 fax 403-205-9009
Rocco DiRago Alcoa Fastening Systems
6150 Kennedy Road, Unit #10
Mississauga Ontario Canada
L5T 3J4
905 564-4825 fax 905-564-1963
Larry Mercer Alcoa Fastening Systems
P.O. Box 8117
Waco, TX, USA 76714
phone 254.751.5273 fax 254.751.5587
ABSTRACT
In April of 2005, Canadian Pacific Railway adopted lock bolts as the standard for
use in all mainline frogs. This followed seven years of experience with their use
in various special installations of frogs and diamond crossings. Lock bolts were
found to offer superior resistance to backing off under vibration, and have been
shown to require considerably lower maintenance when compared to
conventional threaded fasteners.
This paper explains how lock bolts produce consistent bolt tension as opposed to
the complex nut-thread-torque interaction that produces variation in clamp force.
This is related to comparative maintenance requirements recorded by
roadmasters and CPR field tests. Finally, this paper shares that swaging of lock
bolts to ensure the desired long term low maintenance regime that is demanded
of today's higher tonnage mainlines.
Key words: lock bolt, collar, swage
INTRODUCTION
Consistently obtaining the required preload (also called bolt tension, or clamp) in
high tensile bolts is a familiar and difficult problem. Many variables exist in field
applications which cause wide fluctuations in bolt tension, and the joint becomes
susceptible to slippage or fatigue failure. Various features and techniques
attempt to compensate for variation in bolt preload, but they cannot eliminate the
primary problem, which is using torque to induce bolt tension. Lock bolts avoid
this problem by being installed in direct tension. Preload is controlled by
component dimensions and hardness; torque is not a variable. Preload is
maintained by steel-to-steel press fit around the entire bolt thread, which allows
no relative movement from vibration, so lock bolts do not loosen.
Lock bolts have been used in the transportation industry for the last half century.
High, consistent clamp and fatigue strength make lock bolts ideal for structural
applications that are subject to high vibration and cyclical loading, such as rail
track. Basic physical and performance differences between lock bolts and
conventional bolts are presented, along with how this technology has been used
in rail track applications to extend service life. Best practices that have been
developed for rail track applications are also described.
LOCK BOLT COMPONENTS AND INSTALLATION TOOLING
Lock bolts are classified as an alternative fastener in the American Institute of
Steel Construction, Specification for Structural Joints Using ASTM A325 or A490
Bolts (1). Lock bolts are made from the same materials and are processed in the
same way as conventional bolts. Lock bolts have the same under-head bearing
areas as conventional bolts, but since they are installed by direct tension instead
of torque-induced tension, lock bolts may have a round head instead of a hex
head. Also, lock grooves (also called threads) can be either annular or helical.
Some lock bolts have a pintail section that breaks off and is discarded after
installation, while others do not have a pintail.
The nut counterpart of a lock bolt is the collar, although there are several
differences due to different functions. Both the nut and the collar are used to
develop bolt clamp and tensile strength, but the collar has no internal threads or
external hex wrenching surfaces. Instead, the collar is a tubular member that is
designed to lock into the bolt grooves as it is drawn into the swage cavity (similar
to a wire die) of an installation tool. Lock bolts and collars are shown in Figure 1.
An installation sequence is shown in Figure 2. For 1/2" through 1-3/8" diameter
lock bolts, the installation tool is powered by hydraulics. Low voltage electricity
from the installation tool is used to actuate hydraulic valves for pull (swage) and
return (eject) cycles. Installation tools are shown in Figure 3.
HOW LOCK BOLTS OBTAIN PRELOAD
Figure 4 compares clamp variation for a specified torque using different methods
of tightening (2, 3, 4). Methods based on torque are the least reliable, because
torque is an indirect creator of clamp, and only about 10% of the torsional energy
used in tightening a bolt goes into direct clamping force (5). Tension or
elongation based methods have more consistent clamp.
Figure 5 shows the relationship between tension and elongation which results
from tightening a bolt with torque and with direct tension. Both the ultimate
tensile strength and elongation for torque induced tension are about 15% lower
than for direct tension (6). These decreases occur because a torqued bolt is in
both tension and torsion during installation. Lock bolts keep their full strength
during installation because there is no torsional component.
Lock bolt preload occurs in three stages. First, before the collar swages onto the
bolt, considerable force is exerted on the application to pull out gap. During
swaging, the collar lengthens as it is reduced in diameter, so it stretches the bolt
and creates clamp. Finally, the collar dilates (similar to a nut) when the swage
anvil comes off, and preload drops a few percent. Minimum preload specification
for lock bolts is 70% of the minimum tensile specification for the corresponding
diameter of either A325 or A490 grade level.
HOW LOCK BOLTS MAINTAIN PRELOAD
The maximum recommended slope that is allowed for structural bolting is 1:20,
or about 3° (1). However, structural nuts and bolts are relatively hard and do not
conform to sloped surfaces, which allows embedment and/or slippage, and loss
of preload. Lock bolt collars are made from mild steel in order to flow into the
bolt grooves, and the base of the collar will also flow to fully seat against sloped
or contoured surfaces. Spot surfacing or special washers may not be necessary.
Figure 6 shows a collar that has fully seated on a 10° beveled surface, although
there is 1% to 2% loss of preload at installation per degree of slope.
Vibration is a dominant cause of bolt loosening in service. Deformed threads and
thread fillers attempt to overcome the inherent gap between nut and bolt threads,
but these are not reliable. Collars are designed to completely match the grooves
of lock bolts, including damaged threads, so there is no gap. Figure 7 compares
thread gap of conventional bolts and lock bolts. Because lock bolts have no gap
between bolt and collar contact points, there is no opportunity for any relative
movement or slippage.
If bolt tension is reduced, the influence of cyclical loading becomes greater, and
the bolt becomes susceptible to fatigue failure. In addition to maintaining bolt
tension better, lock bolts have modified threads which are shallower than coarse
threaded bolts, and have a larger root radius than fine threaded bolts. Lock bolts
therefore have a larger cross-sectional area plus less stress concentration, which
help to dissipate service loads better than conventional fine or coarse threaded
bolts.
LOCK BOLT USAGE AT CANADIAN PACIFIC RAIL
In April of 2005, Canadian Pacific Rail (CPR) adopted the use of lock bolts on all
mainline frog joints from 115LB, 132LB and 136LB rail frog configurations #9, 10,
11, 12,13,15,16 and 20. This decision was made after vigorous testing over a
seven year period across the CPR network. Lock bolts were found to offer
superior resistance to the fastener backing off under vibration and have shown to
require considerable lower maintenance requirement when compared to
conventional threaded fasteners.
(7) CPR operates over 24,000km (15,000 miles) of railway between Vancouver
on the west coast of Canada and New York on the east coast of the USA. In
western Canada, coal is transported over 1207km (750 miles) on a route
consisting of sharp curves and steep grades in unit trains with payloads of
13,250 metric tons (14,500 tons), powered by three 4400HP AC traction
locomotives. The route carries approximately 78 million gross tons (86MGT) per
year of mixed freight, grain, double stacked inter-modal container cars as well as
coal.
The route is predominately single track, running bi-directional traffic. With 46% of
the routing traversing curves sharper than 3492m radius (1/2 degree), 129km (80
miles) of curves less than 312m radius ( greater than 6 degree), and a maximum
curvature of 160m radius (11 degrees). Temperatures in the Thompson River
valley range from +43C (110F) to -34C (-30F). The rail in curves of 218m radius
(8 degrees) and sharper is predominately 68kg/m (136lb/yd) 350-390BHN head
hardened rail. Ties in curves are 274cm (9 ft.) long hardwood ties on 41cm (16
inch) rolled eccentric plates.
INITIAL CPR APPLICATIONS
For the past two years CPR has ordered all frogs with lock bolts. This decision
was made after extensive testing by CPR. The first tests were at the following
locations. A #13 136lb frog with lock bolts was installed at Sicamous, British
Columbia, on Canada’s west coast, at mile 44.4 in 1997 (Figure 8) with over 70
million gross tons at the time of the picture, with no bolt maintenance, tightening,
removal or replacement. In Pritchard, BC, at mile 103.8, in track since April,
1997, with an excess of 70 million gross tons at the time of the picture (Figure 9).
After these results, CPR decided to expand testing to 100 main line frogs, with
lock bolts to be installed over several years. Fifty two of these joints were
tracked (Figure 12). An unpublished frog tracking report was prepared by
Moffatt Supply. The tracking took place from 1997 to 2003, and was updated in
2005. Fifty two RBM frog joints in the #13 configuration with 115 and 136lb/yd
saw individual tonnages as high as 120 million gross tons and a total tonnage
over all frogs of over 3 billion gross tons. Regular maintenance on all these frogs
was greatly reduced, with less welding and no bolt replacement or tightening.
RECENT CPR TRACK PERFORMANCE
Since April of 2005, over 600 frogs of various configurations from # 9 to #20 in
115lb to 136lb/yd have been installed in CPR track. All cases have proven to
reduce maintenance and increase longevity of frogs. Lock bolts in the 1-3/8 inch
diameter, in lengths from 7 inches of grip to 20 inches of grip, were proven to
increase service life of frogs as well as reduce maintenance during typical frog
life. To date, all new CPR frogs are ordered with lock bolts. These new frogs are
assembled with Lock Bolts at the Progress Rail frog shop in Winnipeg, Manitoba,
Canada.
In addition, several TMS crews are now equipped with installation tools (Figure
10) to install lock bolts in existing frogs. Conventional threaded fasteners in the
heel part of the frog are removed and replaced with lock bolts (Figure 11),
extending the life of existing frogs. In December, 2005, CPR installed lock bolts
in four # 9 136LB RBM frogs in the high coal haulage corridor of British
Columbia. This particular test, at the Page subdivision, has resulted in Canadian
Pacific Rail approving and endorsing the field use of lock bolts for replacement of
conventional threaded fasteners on heels of frogs. This procedure has resulted
in reduced bolt maintenance as well as extended frog life.
CONCLUSION
Lock bolts have many features that make them especially suitable for rail track
applications. High, consistent preload, seating on sloped surfaces, vibration and
fatigue resistant features combine to give lock bolts superior performance. Rail
track experience has shown that the use of lock bolts on frog joints will extend
the typical life of mainline frogs, while reducing maintenance during its service
life. In an environment of high tonnages, difficult terrain, extreme temperatures
and higher expectations on existing work crews, lock bolts offer a viable solution
to fastening rail joints for both new components as well as in field track repair.
BIOGRAPHICAL SKETCH
Larry Mercer has been a Product Engineer for Alcoa Fastening Systems in
Waco, TX, for the last ten years. He joined the organization in 1979 when it was
Huck Manufacturing Company, and has held the positions of Project Engineer
and Manager of Heat Treat and Plating. Larry holds a Bachelor of Science
degree in Metallurgical Engineering from the University of Oklahoma.
Rocco DiRago has been the Canadian Sales Manager for Alcoa Fastening
Systems in Mississauga Ontario Canada since 2005. He joined the organization
1988 as an account manager. Rocco has been instrumental in promoting the
use of lock bolts in track for the mining industry surface and underground track
as well as Toronto Transit (TTC) for all street car surface track as well as class 1
rail roads main line track. Rocco holds a Business Administration degree from
Dawson College in Montreal as well as a Bachelor of Commerce degree from
Concordia University also in Montreal.
Michael Roney is General Manager, Track Maintenance, at Canadian Pacific
Railway.
Luigi Pisano is Track Design for Canadian Pacific Railway.
REFERENCES
1. Research Council on Riveted and Bolted Structural Joints, "Structural Joints
Using ASTM A325 and A490 Bolts", Publication S 314, Sections 2(d) and
3(a), 1978, American Institute of Steel Construction, New York.
2. Rodkey, E., "Making Fastened Joints Reliable…Ways to Keep 'em Tight",
Assembly Engineering, March, 1977, pp. 24-27.
3. Irving, R., "Who Knows How Tight Is Tight?", Iron Age, October, 1968,
pp.85-92.
4. Munse, W., "An Evaluation of Huck Bolts for Use in Steel Structures",
University of Illinois, a report to Huck Manufacturing Company, February,
1960.
5. Brenner, H., "Standard Threaded Fasteners", Standard Handbook of
Fastening and Joining, 3rd Edition, McGraw Hill, 1997, ISBN 0-07-048589-
5, Section 1-18.
6. Kulak, G., Fisher, J., Struik, J., "Bolts", Guide to Design Criteria for Bolted
and Riveted Joints, 2nd Edition, Wiley, 1987, ISBN 0-471-83791-1, pp. 39-
41.
7. Canadian Pacific Railway 100% Effective Friction Management Strategy
Peter Sroba PEng Principal Engineer National Research Council Canada
Kevin Oldknow PhD Field Application Engineer Kelsan Technologies Corp.
Russ Dashko PEng Manager Track Standards Canadian Pacific Railway
Michael Roney PEng General Manager Track Maintenance Canadian
Pacific Railway.
Figure 1
Figure 2
COLLAR PINTAIL
LOCK BOLT WITH PINTAIL
PINTAIL-LESS LOCK BOLT
A B C D
Figure 3
Figure 4
PRELOAD VARIATION BY TYPE AND METHODTYPE METHOD VARIATION Torque Impact Wrench ± 45% Torque Feel ± 35% Torque Torque Wrench ± 30% Tension Turn of Nut ± 15% Tension Load Indicating Washer ± 10% Tension Elongation Measurement ± 5% Tension Swaged Lock Bolt ± 5%
A
B
Figure 5
Figure 6
Figure 7
Std. Bolt
Nut
Gap Contact length
B
No Gap
Lock Bolt
Collar
A
CAPTIONS FOR FIGURES
1. Typical lock bolts and collars.
2. Lock bolt installation sequence. (A) Lock bolt is placed in hole, and collar is
placed onto lock bolt. (B) Installation tool engages and pulls on lock bolt.
(C) Tool swages collar onto lock bolt grooves. (D) Pintail breaks off of lock
bolt and tool pushes off of collar.
3. Hydraulic installation tools for 1-3/8" lock bolts. (A) Lock bolt with pintail.
(B) Pintail-less lock bolt.
4. Bolt tightening methods based on tension have less variation than methods
based on torque.
5. Bolt tension and elongation based on method of tightening. Torque-induced
tension has lower tensile strength and elongation than tensile-induced
tension during the tightening process.
6. Flanged collar that has fully seated on a 10° bevel after swaging.
7. Thread gap comparison. (A) No gap exists between the swaged collar and
crest, pressure and relief side of the lock bolt thread. (B) Nut thread
contacts bolt thread along the pressure side of the thread. Gap at the crest,
root and along the thread relief side allows for relative movement and
loosening from vibration.
Figure 8
#13 #13 SicamousSicamous BC mile 44.4 1997.BC mile 44.4 1997.
Over 70 million gross tons at time of picture.
Figure 9
Pritchard BC mile 103.8 in track April 97Pritchard BC mile 103.8 in track April 97
These were first test frogs for CP with C50L product frogs exceeded expected life and fasteners required no maintenance during life of frog.
Figure 10
Figure 11
Figure 12
Tracking Report-Canadian Pacific Railway Lock Bolted Frogs
Prepared by: Moffatt Supply at request of CP Rail October 2005
Manitoba Canada
Gord Lowen Brandon Manitoba mile 2.5 Brandon West Broadview Sub
Installed August 14,2001 #13-136LB Tonnage 72 million ytd.
Gord Lowen Brandon Manitoba Brandon East
Installed Feb. 1,2002 #13-136LB Tonnage 70 million ytd
Gord Lowen Brandon Manitoba Mile 57 Hargrave Sub
Installed December 10,2002 #13-115LB Tonnage 38 million ytd
Gord Lowen Brandon Manitoba Mile 118.4 Whitewood Sub
Installed December 18,2002 #13-115lb Tonnage 38 million ytd
Gord Lowen Brandon Manitoba Mile 31.7 East Oak Lake
Installed October 2003 #13-115lb Tonnage 35 million a year
Gord Lowen Brandon Manitoba East Rotave
Installed October 2002 #13-115 tonnage 35 miilion per year
Gus Sezesny Carberry Manitoba Chater
Installed November 2002 #13-115lb Tonnage 30 million ytd
Gus Sezesny Brandon Manitoba Mile 94.1 Sydney
Installed October 2003 #13-136lb Tonnage 33 million
Ontario Canada
Doug Gilberton Kenora Ontario Dryden West
Installed June 2003 #13-136lb tonnage 40 million year
Doug Gilberton Kenora Ontario East River
Installed November 2003 #13-136lb Tonnage 40 million year
Doug Gilberton Ignace Ontario Summit Lake
Installed November 2003 #13-136lb Tonnage 40 million year
Saskatchewan Canada
Albert Major Regina Sask. Mile 30.05 Wocseley East Storage
Installed November 2001 #13-115lb Tonnage 70 million year
Albert Major Regina Sask. Mile 31.18 Wocseley West Storage
Installed November 12,2001 #13-115lb Tonnage 70 million ytd
Ken Leys Moose Jaw Sask. Madrid
Installed October 21 2001 #13-136lb Tonnage 135 million ytd
Tim DiMarco Swift Current Sask. SC Sub Caron West 2 installed here.
Installed December 2001 #13-136lb Tonnage 114 million ytd each.
Tim DiMarco Swift Current Sask. SC Sub Mortlach East
Installed December 2001 #13-115lb Tonnage 110 million ytd
Tim DiMarco Swift Current Sask. SC Sub Parkberg West
Installed December 2001 #13-115lb Tonnage 110 million ytd
Tim DiMarco Swift Current Sask. SC Sub Secratan East
Installed December 2001 #13-115lb Tonnage 110 million ytd
Tim DiMarco Swift Current Sask. SC Sub Chaplin West
Installed December 2001 #13-115lb Tonnage 110 million ytd
Tim DiMarco Swift Current Sask. SC Morse East
Installed December 2001 #13-115lb Tonnage 110 million ytd.
Tim DiMarco Swift Current Sask. SC Sub Morse West
Installed December 2001 #13-115lb Tonnage 110 million ytd
Tim DiMarco Swift Current Sask. SC Sub Rush Lake West
Installed December 2001 #13-115lb Tonnage 110 million ytd
Tin DiMarco Swift Current Sask. SC Sub Waldeck West
Installed December 2001 #13-115Lb Tonnage 110 million ytd
Tim DiMarco Swift Current Sub Aikens
Installed December 2001 #13-115lb Tonnage 110 million ytd
Tim DiMarco Swift Current SC Sub Enfold west
Installed September 2001 #13-115lb Tonnage 50 million per year
Gord Brudevold Maple Creek Sask. Mile 5.5 Java
Installed November 2001 #13-115lb Tonnage 120 million ytd
Gord Brudevold Maple Creek Sask. Mile 15 Steward West
Installed November 2001 #13-115lb tonnage 120 million ytd.
Gord Brudevold Maple Creek Sask. Mile 13.3 Seward East
Installed November 2001 #13-115lb Tonnage 120 million ytd
Gord Brudevold Maple Creek Sask. Mile 138.5 Antalope
Installed November 2001 #13-115lb Tonnage 120 million ytd
British Columbia Canada
Roger Dubielewicz Invermere Fairmount South Siding
Installed June 2001 #13-115lb replaced due to broken wing rail October 2002
Bill Cowie Salmon Arm BC Mile 55.5 Canoe east Power Switch
#13-136lb
Bill Cowie Salmon Arm BC Mile 63.5 Salmon Arm West Power Switch
#13-136lb
Bill Cowie Salmon Arm BC Mile 70.5 Tappen North Crossover Switch
#13-136lb
Bill Cowie Salmon Arm BC Mile 88.2 Squalix West Power Switch
#13-136lb
Bill Cowie Salmon Arm BC Mile 93.6 Chase east Power Switch
#13-136lb
Bill Cowie Salmon Arm BC Mile 93.63 Chase East #1 Track
#13-136lb
Vic Parr Kamloops BC Mile 120.4 Northbend
Installed November 2001 #13-136lb Tonnage 85 million ytd.
Vic Parr Kamloops BC Mile 31.8 Walbachin East
Installed June 2002 #13-136lb Tonnage 125 million ytd
Vic Par Kamloops BC Mile 33.5 Walbachin West
Installed October 2004 #13-136lb Tonnage 100 million year
Dave Ryles Mission BC Mile 2.1 Cascade
Installed October 2001 #13-136lb
Stan Sadek Golden BC Glenogle
Installed December 2003 #13-136lb
Ed Palasy Revelstoke BC Mile 94.11 Flat Creek Mountain Sub
Installed August 1997 #13-136lb
Ed Palasy Revelstoke BC Mile 119.83NT Greely X over Mountain Sub
Installed August 15 2001 #13-136lb
Ed Palasy Revelstoke BC Mile 123.22ST White X Over Mountain Sub
Installed September 2003 #13-136lb
Ed Palasy Revelstoke BC Mile 123.26NT White X Over Mountain Sub
Installed April 9 2003 #13-136lb Tonnage 100 Million year
Ed Palasy Revelstoke BC Mile 14.68-3 Valley East Shuswap Sub
Installed December 5 2003 #13-136lb Tonnage 100 million per year
Ed Palasy Revelstoke BC Mile 22.45 Taft East Shuswap Sub
Installed December 15 2003 #13-136lb Tonnage 100 million per year
Ed Palasy Revelstoke Mile 44.00 Storage Track Shuswap sub
Installed November 21,2003 #13-136lb Tonnage 100 million per year.
Terry Rota Revelstoke BC
Installed November 2004 #13-136lb Tonnage 100 million per year
Stan Sadek Kamloops BC Mile 48.5 Ashcroft west Frog #248
Installed October 2003 #13-136LB Tonnage 100 million per year.g