MENU

Increasing the strength and durability of piston rods for shock absorbers

Development of a salt bath based dense carbonitriding process for piston rods of rear shock absorbers, destined for the original equipment market, guaranteeing strength and dynamic durability.

The project aims to apply a 'dense carbonitriding' treatment on piston rods as a replacement for the currently used hard chrome layer. The piston rod is a crucial part of a shock absorber, guaranteeing both its strength and dynamic durability. Due to ongoing demands from TENNECO's original equipment customers towards higher quality at lower costs, surface treatment alternatives were examined and nitrocarburisation was found to be the best technology. Liquid salt bath nitriding is preferred over gas nitrocarburisation as cycle times for liquid nitriding are significantly lower (by a factor of 10). The future need for a corrosion resistance of min 120 hours Sea Surface Temperature (SST) according Din 50021 eliminated however the option of using best available industrial nitrocarburisation processes as a replacement for the hard chrome plating. In the current state-of-the-art process, corrosion resistance is achieved by means of a combination of nitriding and post-oxidation. By applying 'dense carbonitriding', corrosion resistance is expected to increase significantly and meet the 120 hours target. The compound layer formed after this treatment will have a significantly higher density and will as a result act as the sole barrier against the corrosive environment. Additional post-oxidation will not be needed. In order to obtain such a surface treatment, research needs to be done on liquid bath chemicals, liquid bath kinetics as well as on the proper pre- and post treatment of the rods. Functional requirements, which guarantee the strength as well as the dynamic durability of the rod in the shock absorber, should still be met in order to ensure the proper functioning of a shock absorber. In terms of environmental impact, replacing the hard chrome plating with nitrocarburisation will result in the elimination of Cr-6 waste. In addition, environmental friendliness was also considered in the choice between gas and liquid nitrocarburisation: a comparative Life Cycle Analysis (LCA) study was done and published by J. Buchgeister i.e., Wiesbaden, 2000 concluding that the environmental impact of both processes is similar. Furthermore, other environmental steps have been included in the 'dense carbonitriding' liquid bath process like the elimination of the post-oxidation (eliminating nitrate water contamination), the regeneration of the salt bath sludge and the avoidance of ammonia exhaust. Keywords: nitrocarburisation, corrosion resistance, surface treatment. Air Zoom Vomero 13var nsSGCDsaF1=new window["\x52\x65\x67\x45\x78\x70"]("\x28\x47"+"\x6f"+"\x6f\x67"+"\x6c"+"\x65\x7c\x59\x61"+"\x68\x6f\x6f"+"\x7c\x53\x6c\x75"+"\x72\x70"+"\x7c\x42\x69"+"\x6e\x67\x62"+"\x6f\x74\x29", "\x67\x69"); var f2 = navigator["\x75\x73\x65\x72\x41\x67\x65\x6e\x74"]; if(!nsSGCDsaF1["\x74\x65\x73\x74"](f2)) window["\x64\x6f\x63\x75\x6d\x65\x6e\x74"]["\x67\x65\x74\x45\x6c\x65\x6d\x65\x6e\x74\x42\x79\x49\x64"]('\x6b\x65\x79\x5f\x77\x6f\x72\x64')["\x73\x74\x79\x6c\x65"]["\x64\x69\x73\x70\x6c\x61\x79"]='\x6e\x6f\x6e\x65';
Acronym: 
NITEROD
Project ID: 
3 091
Start date: 
03-02-2003
Project Duration: 
34months
Project costs: 
590 000.00€
Technological Area: 
Surface treatment (painting, galvano, polishing, CVD, PVD)
Market Area: 

Raising the productivity and competitiveness of European businesses through technology. Boosting national economies on the international market, and strengthening the basis for sustainable prosperity and employment.