EURO PM2011 congress & exhibition Authors: C. Besleaga, ECONET PROD, Bucharest, RomaniaPM in Barcelona-Expanding PM Possibilities R.M. Negriu, ECONET PROD, Bucharest, Romania9th – 12th October 2011 I.C. Popescu, ECONET PROD, Bucharest, RomaniaCCIB Congress Centre, Barcelona, Spain S.G. Badea, ECONET PROD, Bucharest, RomaniaEPMA – European Powder Metallurgy Association M. Stefanescu, ECONET PROD, Bucharest, Romania APPLICATIONS OF PM THE CHAIN EXCAVATOR OF A RAILWAY MACHINE

1.Abstract

One of the most important devices of the cleaning machines which are used for maintenance of the railway is the chain excavator. This device works under the sleepers and excavates the crushed stone (ballast) for cleaning, sorting and reusing. The chain excavator is loaded in tension, bending, shock, abrasive wear, being the most stressed device of the machine. The usual materials for elements which compound the chain excavator are steel alloys with Mn, Cr, Mo. Using the hard or extra hard materials like tungsten carbide and other, manufactured using PM technologies, in high stressed zones, can improve the fatigue life of the chain and the machine. Using MEF and CAD simulation methods, the 3D stress’ system and displacements, fatigue life and other important data and conclusions are obtained. These simulations are used for optimizing the shapes of the chain excavator.

5.Conclusions

Because of the factors that lead to the wear and the deterioration of the crushed stone degradation occurs by contamination and clogging of the stone prism, with the reduction of elasticity and permeability, with the formation of very hard objects, similar to the hardness of the stone (Fig. 1).

2. Introduction

Fig.1. The clogging of the stone prism very hard bodies

To restore the qualities of elasticity and permeability of the crushed stone prism, in terms of efficiency and technical-economic efficiency, re-using the corresponding crushed stone from the railway, technological mechanized operations of excavation of the crushed stone, cleaning, sorting, selection and waste elimination are performed. These technological mechanized operations are realized by the ballast cleaning machine, one example being MCB-450 (Fig. 2).

Fig.2. Ballast cleaning machine type MCB-450 and the excavation subassembly: 1 –excavator chain; 2 - the chain wheel drive; 3 - guide / chute climb chain; 4 - guide / chute descending chain; 5 – cross piece; 6 - rotation (training) direction of the chain; 7-work movement; 9- screen; 10 – rail; 11 –clean crushed stone; 12 - sand and gravel substrate; 13 - ground (soil); 14 – clogged crushed stone

Through our experimental research we identified the parts of the chain excavator type MCB-450 which are stressed at intensive wear. In the case of scrapers type MCB-450 we propose an improving through using of PM technology to decrease the wear.

From analyzing the results obtained through the finite element method results: the equivalent tensions state from the elements of the chain do not exceed the allowable values of the equivalent tensions except locally, in the contact regions between the elements and the stones from the crushed stone prism; it is possible that the breakage of the elements may occur for stress at lower equivalent tensions that the maximum allowed, if there are material defects of relative critical dimensions at the local level tensions [10]; the maximum equivalent tension values from the contact region between the crushed stone prism and the elements of the chain explain the phenomenon of wear by cutting off small pieces of metal from that element. The analysis and the simulations performed using the finite element method lead to the finding of solutions for increasing the life spam of the excavator chain. The manufacturing of the scraper through methods specific to powder metallurgy and the shape optimization have been tested and represent a solution that must be generalized mainly because of the economical advantages obtained.

The manufacturing of scraper shovels with a gradient of mechanical and physical characteristics of the material is in the experimental phase. The optimal technological solution will be validated through a big enough number of experiments, for a convincing economical analysis.

Fig.3. Spare parts of chain excavator: 1- joint bolt; 2- connecting chain link; 3- scraper; 4- safety bolt of scraper; 5- left scraper shovel; 6- right scraper shovel; 7- safety part; 8- safety bolt (screw) of joint bolt; 9- nut; 10-washer

3. The wear phenomena of the main elements of the excavator chain

Fig.4. Defections and wear of the elements of the excavator chain: a- zones of fracture; b- defective casting; c- wear of scraper

4. The CAD- MEF analysis

Fig.6. The tension state in two extreme cases from the analyzed cases

4. The usage of PM at the scrapers of the excavator chain

Fig.7. Scraper corner made from composite material with WC and gradient of material: ● hardness measurements points; a and b zones with different properties; X- checked zone.

Fig.8. Scrapers manufactured with the help of PM technology

After the analysis and of the performed simulations by using the finite element method, we concluded that the life spam of the excavator chain can be increased through the following methods:- improving the material utilized for the scraper and the optimization of its shape;- manufacturing the scraper shovels and the connecting chain links through a technology which will ensure a gradient of material and characteristics favorable to wear resistance.