Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING

Successful Grinding: Starting with the Basics
(Part 2 of 2)
By Norman Hooper • July 2010

Part 1 of this article examined tie, fastener and surfacing maintenance practices, as they relate to the planning and quality of rail grinding procedures.

Experience has shown that an efficient and cost-effective rail grinding program requires attention to basic track inspection and maintenance procedures. This includes attention to “hot spots,” such as joints, welds and road crossings.

Figure 1 shows a rail joint at the end of its life. Note the broken joint bar, crushed ties, battered joint and broken tie plate. These conditions generate significant dynamic impact to traction motors and roller bearings.

Regulation for the inspection of joints in CWR is aimed at finding loose bolts and broken joint bars. In addition to finding loose or broken bars, maintenance personnel should try to determine what caused them. Are the rail fasteners in place? Are the joint bolts the right size and properly torqued? A mixture of 7/8- and 1-inch bolts when the standard is 1-1/8-inch is an invitation to a 10-mph slow order (or worse) when the bolts loosen or fail. While there's no safety regulation compelling the use of a 6-hole bar in CWR with all of the right bolts installed to the correct torque, it’s good practice to ensure long life for the joint.

Equally important is ensuring that there is proper drainage and support at rail joints. A series of joints (temporary or otherwise) that are too close together is an invitation to poor surface and a rough ride.

A joint in track will start to develop rail flow between the two rails. The amount of rail flow increases, and some surface cracking starts. The flowed rail material is brittle and poorly supported and it begins to crack out. As the flow advances and increases over time, small chips begin to break out (see Figure 2). The surface discontinuity imparts a dynamic load into the joint structure. Eventually, larger pieces of the rail head break out.

As the ends of the rails are battered, the uneven rail surface causes a dynamic load that destroys the ties and ballast below. As rail end batter increases, secondary batter forms along the rail due to dynamic load response from vehicle suspensions. This results in a weak spot in the track structure and a failed joint, with loose or missing bolts, or a broken bar (see Figure 3). The problem can’t be fixed by rail grinding; it needs basic timely joint maintenance. Slotting, an almost a forgotten art in CWR territories and on most shortlines, is a very effective method of joint maintenance.

If joints must be left in CWR territory, railways should use good ties, proper bars/bolts and slot the rail flow. Grinding cannot solve the batter and secondary batter issues of joints; it takes basic maintenance.

Weld Dipping
Weld dipping in CWR creates many of the same issues as rail flow. Good sub-support and regular grinding (approximately 0.004 inches of regular metal removal, while the growth is slow) is the solution. Weld dipping follows an exponential growth pattern; mild dips increase in depth at a greater and greater rate, and batter grows longitudinally from the weld. The depth of batter (weld dip) on thermite welds is often such that grinding is not a viable, cost-effective option, and a plug must be installed. Secondary batter also can occur in a dip over a shop flash-butt weld. Secondary batter will grow more quickly at dip areas with poor tie support. If weld dipping is not addressed by regular grinding, the batter grows, ties deteriorate and cause secondary batter on the rail surface.

Road Crossings
Maintenance grinding is also required at road crossings. Generally, rail wear in crossings is two to three times the rate of wear in the adjacent rails. Road vehicles pick up the lubrication or contamination that's on the rails and increase the local friction, corrosion and wear rate. In heavy haul, softer older standard carbon rails will not stand-up, which is why active road crossings should have premium rails installed. Many crossing also have tie-quality and drainage issues that reduce rail support. Most crossings are not regularly ground for profile or rolling contact fatigue (RCF) because of the restriction of the pavement or mudrail.

As a result, RCF takes a toll at crossings. Figure 4 shows a crossing in 45-mgt territory with a predominance of 286K unit coal trains. The rail is older, 265/270 Brinell hardness (Bhn) that was rolled in the mid ‘80s. It is referred to as “Tootsie Rail” — a hard outside (work hardened surface) with a soft center. Sectioning did not reveal any internal defects in the head area; the steel is just too soft/weak to withstand the dynamic loading. Timely grinding would have delayed the failure.

A “best practice” to achieve the most from a rail grinding budget and the lowest life cycle cost of rail is to use current technology to determine grinding locations and profiles. Excellent measurement and analysis tools are available that can be used to cost/benefit justify additional resources.

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