Brake Shoe Force Variation

2009 ◽  
Author(s):  
Scott Cummings
Keyword(s):  
Elevated Temperatures ◽  
Prevention Research ◽  
Brake Shoe ◽  
Potential Source ◽  
Temperature Detector ◽  
Defect Prevention ◽  
Force Variation ◽  
Freight Car ◽  
Research Consortium ◽  
System Designs

The Wheel Defect Prevention Research Consortium (WDPRC) has conducted a review and analysis of existing literature and existing data related to brake shoe force (BSF) variation in freight car brake rigging. This work was conducted to explore the sources of BSF variation, define the expected amount of BSF variation, and describe some of the existing brake system designs that may help reduce the amount of BSF variation. Wheel temperature is related to BSF due to the use of the wheel tread as a brake drum. Variation in BSF within a given railcar is one potential source of elevated wheel temperatures and thermal mechanical shelling (TMS) damage to the wheels. At elevated temperatures, wheels become less resistant to fatigue damage due to changes in the material mechanical properties and relief of beneficial residual stresses. Data recorded by a wayside wheel temperature detector shows that eliminating wheel temperature differences within individual cars could reduce the number of wheels reaching temperatures of concern for TMS by a factor of eight.

Brake Shoe Coefficient of Friction Variation

2009 ◽  
Author(s):  
Scott Cummings ◽  
Tom McCabe ◽  
Glenn Guelde ◽  
Dan Gosselin
Keyword(s):  
Coefficient Of Friction ◽  
Prevention Research ◽  
Brake Shoe ◽  
Test Matrix ◽  
Potential Source ◽  
Defect Prevention ◽  
Research Consortium

A series of dynamometer tests were conducted by the Wheel Defect Prevention Research Consortium (WDPRC) to quantify the amount of expected variation in brake shoe coefficient of friction (COF) and resulting wheel temperature throughout the life of an individual brake shoe. Variations in brake shoe COF within an individual railcar are one potential source of elevated wheel temperatures and thermal mechanical shelling (TMS) damage to the wheels. High friction composition and tread conditioning brake shoes were installed in the “as manufactured” condition with no wear-in or machining at the beginning of the test matrix which consisted of seventeen stop tests and twelve grade tests. For each brake shoe tested, the average COF and maximum wheel temperature were recorded during eleven identical light grade tests interspersed throughout the test matrix.

Service Wheel Temperatures and Car Condition in Relation to Thermal Mechanical Shelling

2008 ◽  
Author(s):  
Scott M. Cummings
Keyword(s):  
Real Time ◽  
Large Temperature ◽  
Prevention Research ◽  
Replacement Rate ◽  
Temperature Detector ◽  
Defect Prevention ◽  
Research Consortium ◽  
Possible Cause

The Wheel Defect Prevention Research Consortium (WDPRC) examined data from a wayside wheel temperature detector (WTD) located near the bottom of a grade in order to explore the root causes of hot wheels and thermal mechanical shelling. Not surprisingly, the data showed that most hot wheels, defined in this paper as a wayside WTD reading of 260°C (500°F) or greater, are found in trains descending the grade (descending trains), although they can be found in trains ascending the grade (ascending trains) as well. The majority of cars with hot wheels in ascending trains have the brakes applied at all wheel locations in the car, with unreleased or partially released hand brakes as a possible cause. While relatively few descending trains (15 out of 393) had many cars with hot wheels, these trains accounted for more than 20 percent of the descending cars with hot wheels, indicating that operational improvements could substantially reduce the quantity of hot wheels. Seventy-six percent of the descending cars with hot wheels had only a single wheel at or above 260°C (500°F). While the wheels in these cars are generally at higher temperatures than the wheels of other cars in the train, there were large temperature differences between individual wheel locations. Evidence of repeated hot wheel behavior was found in about 37 percent of the group of descending cars with hot wheels and about 20 percent of individual hot wheel locations. Two different car inspections were conducted based on the WTD data. First, a “near-real-time” inspection was conducted in which cars were quickly checked for obvious problems without removing them from the train. Next, an intensive inspection/test/teardown was conducted on bad actor cars, which showed repeated hot wheel behavior. Good actor cars, which repeatedly did not show hot wheels, were also present at the inspection/test/teardown for comparison. The cause of the hot wheels was not evident for the majority of cars at both inspections, however, bad actor cars were found to have twice the historical wheelset replacement rate of good actor cars.

Brake Shoes and Thermal Mechanical Shelling

2008 ◽  
Author(s):  
Scott M. Cummings ◽  
Tom McCabe ◽  
Dan Gosselin
Keyword(s):  
Test Results ◽  
Brake Shoe ◽  
Test Parameters ◽  
Defect Prevention ◽  
Potential Benefits ◽  
C 50 ◽  
Force Time ◽  
Research Consortium ◽  
Test Individual ◽  
Dynamometer Test

The Wheel Defect Prevention Research Consortium (WDPRC) conducted a review of existing brake shoe tests to explore the combinations of brake shoe force, time, and wheel/brake shoe coefficient of friction (COF) needed to achieve the temperatures of concern for thermal mechanical shelling (TMS). Data was found involving normally expected brake shoe forces applied to a dynamometer wheel and a variety of test parameters and procedures. All temperatures were measured using a sliding thermocouple pressed lightly against the wheel tread. All testing reported involved new brake shoes that may have different COF properties from used brake shoes. Tests included brake shoe tests conducted in accordance with the Association of American Railroads (AAR) M-926 specification, constant horsepower tests, and simulated stuck brake tests. Tread conditioning brake shoes were investigated, as well as high friction composition brake shoes. Findings from these tests include the following: • Tread conditioning brake shoes produced lower wheel tread temperatures compared to high-friction composition brake shoes. The magnitude of this difference varied depending on the test conditions; • In the dynamometer test most closely simulating revenue service conditions, 37 kW (50 hp) was required to heat wheels above 316°C (600°F); • Different models of high-friction composition brake shoes produced similar wheel temperatures under the parameters of the AAR M-926 tests. The range of average wheel temperatures produced by different models of high-friction composition brake shoes was only about 28°C (50°F) at any point during the test; • Individual brake shoes of the same model usually produced consistent results with respect to wheel temperature. Two exceptions to this statement were observed in the AAR M-926 test results. In a laboratory dynamometer test involving service damaged wheels, the WDPRC was unable to produce any measurable reduction in wheel tread defect size through the application of tread conditioning brake shoes. However, four service trials of tread conditioning brake shoes showed potential benefits in using tread conditioning brake shoes to reduce the number of wheelsets removed for tread damage.

Wheel Spalling Literature Review

2008 ◽  
Author(s):  
Scott M. Cummings ◽  
Cameron P. Lonsdale
Keyword(s):  
Literature Review ◽  
Analytical Model ◽  
Analytical Models ◽  
Prevention Research ◽  
Multiple Sources ◽  
Slide Test ◽  
Defect Prevention ◽  
Train Speed ◽  
Adhesion Level ◽  
Research Consortium

As a means of determining the conditions under which a patch of martensite (and eventually a spall) is formed on a wheel tread, the Wheel Defect Prevention Research Consortium (WDPRC) has conducted a review of wheel slide test reports and analytical models for the prediction of contact patch temperature due to wheel slide. The relative merits of the analytical models are discussed and applied to the known/assumed conditions, i.e., speed, axle load, and wheel/rail coefficients of friction (COF) for each of the wheel slide tests. The accuracy of the analytical models is evaluated with respect to test data under a variety of conditions from multiple sources. After selecting the most appropriate analytical model, wheel slide temperature predictions are given for empty cars at a variety of speeds and wheel/rail COF levels. It is concluded that the potential exists to create martensite on sliding wheels with almost any realistic combination of axle load, wheel slide duration, train speed, and wheel/rail adhesion level. Additionally, sources of wheel spalling are discussed with a focus on misapplied hand brakes and malfunctioning air brake systems. Multiple authors noted the presence of tread damage on one wheel of a wheelset with no damage at the corresponding circumferential location of the mate wheel. The accompanying theories to explain this seemingly counterintuitive finding are restated in this literature review. At the end of the paper, the actions of the WDPRC to reduce wheel spalling are briefly outlined.

Inspections of Tread Damaged Wheelsets

2008 ◽  
Author(s):  
Scott M. Cummings ◽  
Don Lauro
Keyword(s):  
Impact Load ◽  
Damage Mechanism ◽  
Location Data ◽  
Root Cause ◽  
Frequent Use ◽  
Crack Band ◽  
Defect Prevention ◽  
Research Consortium ◽  
High Level ◽  
Contact Position

Inspections of 163 wheelsets conducted by the Wheel Defect Prevention Research Consortium (WDPRC) have produced critical information in identifying the high-level root causes of tread damage. While the overall wheel tread damage problem appears to be split fairly evenly between shelling and spalling, the type of tread damage on a wheelset is strongly linked to the type of car from which it was removed. Coal car wheels, which generally run in heavy axle load, high-mileage service with minimal yard handling, are almost exclusively subject to shelling damage with little spalling damage. On the other hand, mixed freight cars, such as tank cars and covered hopper cars, tend to run in lower mileage service with more yard handling, resulting in fewer loading cycles under lighter stress and more frequent use of hand brakes. Not surprisingly then, wheels from these types of cars were observed to have a mix of spalling and shelling damage, with spalling being the predominant damage mechanism. Nearly every high impact wheel (HIW) inspected showed either spalling, shelling, or some combination of the two. As expected, wheel impact load detector (WILD) readings and radial tread run out data were found to be related. Rim thickness deviations and rim lateral face deviations were not found to be important contributors to shelling. The lateral tread location of radial run-out deviations and crack bands could be an important clue in discovering the root cause of shelling. Radial run-out data and crack band location data shows that shelling damage is most prevalent outboard of the tapeline. This is the expected wheel/rail contact position of a wheel in the lead wheelset position of a truck, while riding on the low (inside) rail of a curve. Many of the wheels that were removed for wear causes were found to have noncondemnable shelling and spalling, indicating that tread damage is more prevalent than repair records would indicate.

Effect of Residual Stress, Temperature and Adhesion on Wheel Surface Fatigue Cracking

2008 ◽  
Author(s):  
Daniel H. Stone ◽  
Scott M. Cummings
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Residual Stresses ◽  
Contact Stress ◽  
Fatigue Cracking ◽  
Fatigue Tests ◽  
Operating Conditions ◽  
Defect Prevention ◽  
Class C ◽  
Research Consortium

The Wheel Defect Prevention Research Consortium (WDPRC) conducted an analysis pertaining to the fatigue cracking of wheel treads by incorporating the effects of residual stresses, temperature, and wheel/rail contact stress. Laboratory fatigue tests were conducted on specimens of wheel tread material under a variety of conditions allowing the analysis to properly account for the residual stresses accumulated in normal operating conditions. Existing literature was used in the analysis in consideration of the effects of contact stress and residual stress relief. This project was performed to define a temperature range in which the life of an AAR Class C wheel is not shortened by premature fatigue and shelling. Wayside wheel thermal detectors are becoming more prevalent on North American railroads as a means of identifying trains, cars, and wheels with braking issues. Yet, from a wheel fatigue perspective, the acceptable maximum operating temperature remains loosely defined for AAR Class C wheels. It was found that residual compressive circumferential stresses play a key role in protecting a wheel tread from fatigue damage. Therefore, temperatures sufficient to relieve residual stresses are a potential problem from a wheel fatigue standpoint. Only the most rigorous braking scenarios can produce expected train average wheel temperatures approaching the level of concern for reduced fatigue life. However, the variation in wheel temperatures within individual cars and between cars can result in temperatures high enough to cause a reduction in wheel fatigue life.

Fatigue Testing of Microalloyed AAR Class C Wheel Steel

2006 ◽  
Author(s):  
Cameron Lonsdale ◽  
Steven Dedmon
Keyword(s):  
Yield Strength ◽  
Elevated Temperatures ◽  
Fatigue Testing ◽  
Research Work ◽  
Past Research ◽  
Fatigue Tests ◽  
Wheel Steel ◽  
Fatigue Properties ◽  
Freight Car ◽  
Class C

Railroad wheels guide a freight car along the rails while supporting mechanical loads, and also serve as the brake drum in the air brake system of a freight car. Since a 36-inch diameter freight car wheel experiences approximately 560 revolutions per mile, and since many North American freight cars accrue 100,000 miles per year in service, fatigue properties of steel are very important. Further, elevated tread temperatures resulting from tread braking are known to significantly reduce the yield strength of the wheel steel at the tread surface. This paper describes fatigue testing of AAR rim quenched Class C wheel steel manufactured with microalloy additions. Small amounts of selected alloy elements were purposely added to develop a wheel steel with improved high temperature yield strength. Rotating bending fatigue tests, conducted at a well-known professional testing laboratory, were performed at ambient and elevated temperatures using complete stress reversal (R = -1) cycling. Stress-life (S-N) curves were constructed and the microalloy steel results were compared to existing fatigue data, and to results for typical Class C steel with no microalloy additions. Past research work is briefly reviewed. Test results are discussed with emphasis on the implications for service performance of wheel steel.

Reactivity of Isoprenic and Analogous Hydrocarbons towards Thiocyanic Acid and Dithiocyanogen

1946 ◽  
Vol 19 (1) ◽  
pp. 34-35
Author(s):  
Ralph F. Naylor
Keyword(s):  
Thermal Decomposition ◽  
Hydrogen Sulfide ◽  
Hydrogen Cyanide ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Amorphous Powder ◽  
Hydrogen Halides ◽  
Potential Source ◽  
Thiocyanic Acid ◽  
Methyl Thiocyanate

Abstract By analogy with hydrogen halides and hydrogen sulfide it is reasonable to expect thiocyanic acid to react with olefins, and it has been reported by Kharasch, May, and Mayo that it will add to isobutylene at room temperature to give a mixture of tert.-butyl thiocyanate and isothiocyanate. Under similar conditions in the present work, the only product that was obtained from cyclohexene and thiocyanic acid was a small quantity of an amorphous powder, probably mainly a perthiocyanic acid, formed by elimination of hydrogen cyanide from three molecules of thiocyanic acid. This tendency towards decomposition of the reagent prevented the use of elevated temperatures, and when methyl thiocyanate (a potential source of SCN and Me radicals by thermal decomposition) was heated at 170° with 1-methylcyclohexene and a little benzoyl peroxide (as catalyst), it underwent but slight reaction, the drop or two of product giving analytical values which suggested that it might be an impure adduct. Attempts to catalyze the addition of thiocyanic acid to, rubber included the use of ultraviolet irradiation, and of aluminum chloride or ferric chloride as catalyst. The most successful of these attempts was with ultraviolet light, but even then the product contained only 1.95% of sulfur, which represented 6% addition to the double bonds of rubber.

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