Railway Track & Structures - February 2008 - (Page 18) TTCI R&D Figure 2, left, shows total metal loss and natural wear in ground and unground rail. Figure 3 shows metal loss by rail type. contact angle. • No grind (control) zone: This zone was not to be ground unless not doing so would compromise safety, or necessitate the removal of the rail. The rail was not ground in 515 mgt of traffic. The experiment was conducted in a six-degree curve with five inches of superelevation. The typical train speed of 40 mph results in a cant deficiency of about 1.7 inches. The gauge face of the high rail was lubricated with lithiumbased molybdenum disulfide (MoS2) grease and the top of the low rail was lubricated with 90w oil. Traffic was split nearly equally in each direction. Metal loss Preventive grinding increased metal loss. There was approximately 77 percent more total metal loss on the high rail of the preventive grind zone than on the high rail of the unground zone and approximately 240 percent more on the low rail (the high-contact stress zone is excluded because it is an atypical practice, and heavy metal removal was required to achieve the desired profiles). The metal removed by grinding was the primary reason for the increase; natural wear rates were similar in the unground and preventive grind zones, Figure 2. The harder rails wore less than the softer rail. The DHH 370 rail showed slightly more metal loss and more wear than the higher hardness rails. Figure 3 shows results for the high rail. There was less of a difference on the low rail where the amount of metal removed by grinding far exceeded metal loss from natural wear. Results The results of this test were consistent with the results of previous grinding tests on premium rail at FAST. Clean highhardness premium rail is resistant to RCF and to development of transverse defects. When adverse wheel profiles are avoided, and conditions that produce high vehicle dynamic forces are addressed, the need for grinding can be greatly reduced. Under the conditions at FAST, namely: • Conformal, uniform wheel/rail contact conditions, no severely hollow wheels • Consistent, overbalance speed with limited braking and acceleration • Lubrication on the gauge face of the high rail and on the top of the low rail • Dry climate The premium rails in the unground zone developed only light, isolated RCF in 515 mgt of traffic and there were no rail breaks initiating in the head of the rail. Figure 1 shows the condition of the unground rails. 18 Railway Track & Structures February 2008 Effects: high-contact stress profiles High-contact stress profiles were ground on both the high and low rails of one zone after 150 mgt. The upper gauge corner of the high rail and the field side of the top of the rail were heavily ground to produce an exposed gauge corner and a narrow contact band on the top of the rail. The field side of the top of low rail was heavily ground to narrow the contact band, and to move it toward the gauge side of the rail (inhibiting vehicle curving). Figure 4 shows profiles illustrating these grind patterns. These profiles were maintained when the rail was ground at approximately 30 mgt intervals. WRTOL analysis of the modified profiles predicted an increase in contact stress and a concentration of the stresses. The high rail of the high-contact stress zone showed more RCF than the high rails of either of the other two zones, but it did not become problematic. The RCF was not on the gauge corner, but on the head of the rail. The low rail of the high-contact stress zone showed RCF similar to that in the preventive zone. The presence of lubrication, as was on the gauge corner of the high rail and the top of the low rail at FAST, can have a mitigating effect on RCF. Other studies have shown that top-of-rail lubrication can reduce RCF.1 A further illustration of this is a comparison of the condition of the unground low rail in this curve, with that of the unground low rail in an unlubricated (but contaminated) five-degree reverse curve at FAST. The premium rail in the unlubricated curve developed significant RCF after 265 mgt. The unground rail in the lubricated curve was in good condition after 515 mgt. Conditions: preventive grind zone The grinding in the preventive grind zone is similar to what many railroads practice, i.e., light metal removal at regular intervals. This grinding practice was effective in removing shallow cracks and checks from the surface of the high rail. The surface condition of that rail was better than the high rails in the other two zones. On the low rail, the eightinch crown radius concentrated contact in the center of the rail and resulted in slightly more RCF than was observed on the unground low rail. www.rtands.com http://www.aar.com http://www.rtands.com
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