Proceedings of SerbiaTrib '13

safe to use it in furter exploitation (to apply regenerationor the part) or should it be rejected. The size of expecteddeformation and residual stresses are also importantfactors in making such a decision [7-8]. Afterdetermination of the chemical composition of the basemetal and working conditions, it is possible to create thebasic conditions for the design of technologicalprocesses. Based on those facts and previouslyconducted detailed techno-economic analysis, themethod of regeneration should be chosen, taking intoaccount the local possibilities of the company. The basicrequirement is to obtain the required properties of theregenerated part and, ofcourse, the reliability of the partduring the estimated working life.To achieve the above requirements it is necessary tomake the proper selection of filler material for hardfacing.In some cases of reparation of working parts itis necessary to apply two or more kinds of additionalmaterial to insert an intermediate layer, the so calledbuffer layer, between the layer and the substrate. Thisreduces the large differences in the chemicalcomposition, structure and, consequently, the thermophysicalproperties, of the substrate and the deposit.Next follows the selection of the regeneration processparameters, resulting from the properties of the baseand filler metal, and form demands concerning the sizeand shape of regenerated parts. The final stage ofplanning, before the experimental surfacing, is theassessment of the necessity for implementation ofspecial measures and the previous, current andsubsequent heat treatment.For verification of the proposed technologies, thecomparative tests in laboratory and in workingconditions have been performed, and, in some cases,comparative test of imported parts, which were nothard-faced and the new-hardfaced parts. Laboratorytests are related to the microstructure, hardnessdistribution and tribological tests and working tests ofcomparing the working life of the new and repairedparts installed in the same machine [2-3,9].From the point of view of techno-economicanalysis, reparation welding technology is a complexset of different types of mandatory procedures, whichtake into account: the conditions of work, damageidentification, estimation of weldability, weldingprocess, filler material, welding and hard-facingregimes, heat treatment applied, model and real tests.Having in mind the complexity of the process, it isnecessary to determine the optimal technicaltechnologicalsolutions to bring the reparation processto a stage when it is possible to make a final decision,wheter to buy a new part or to repaire it.3. EXAMPLES OF IMPLEMENTED REPAIRSHere is considered the justification for applicationof the production and reparation hard-facing and it ispointed to profitabilityof repairs on examples ofdamaged forging hammer, forging press frame andlarge gear of eccentric presses. The subject matter is thereparatory welding and surfacing of the damaged orcracked forging hammers, broken and cracked frames,forging presses and large gear eccentric presses [10-11]. To determine the optimal technology of hardfacing,it was necessary to carry out tests on model andreal working parts. Test hard-facing and testing ofmodels have served to establish the initial reparationtechnology, and to "transfer" thus approvedtechnologies to the working parts, which are thenfurther checked under actual working conditions.This paper mainly deals with the techno-economicadvantages of the hard-facing technology, while thecomplete procedures of determining the optimaltechnology for each particular part were presented inpapers [2-3,5,9-11].3.1. Regeneration equipment’s for forginghammer and press frameFor regeneration of responsible parts with complexgeometries and large masses, made of material sutiblefor tempering, a detailed analysis of the working partsis required as well as the precisely proposed reparationtechnology.Hammers mallets and presses frames are exposed,during the long operation, to thermal fatigue due tocyclic temperature changes and to impact loads. Due tothe high costs and often to impossibility of purchasingthe new working parts, it is necessary to evaluate thepossibility of their repairs. Harsh working conditionssometimes lead to a complete fracture of the part andendangering the workplace safety. Figure 1 showsfracture of a forging mallet, which has originated fromfatigue crack propagation.Mallet of forging's hammer, shown in Fig. 2, andframe forging press, shown in Fig. 3, are primarilysubjected to impact compression loads, and, in partiallyto temperature gradient, that is thermal stresses causedby uneven temperature field [2,7-8]. After a long workof these parts, i.e., large number of repeated cycles onhammer mallet and on the press frame, visible crackswere observed, and on one portion of the frame and ona single occurred the complete fracture (Fig. 1 and 3).Taking into account that these are parts of largedimensions and complex shapes, and that componentsare subjected to dynamic and thermal loads, they aredimensioned on the basis of the increased safetydegrees; thus the special measures are required for themanufacturing and reparatory technologies, as well.Forging press frame is madeby casting in sand, from the medium carbon cast steel.On the other hand, pneumatic forging hammer mallet,as one of the most loaded mechanical parts, is made oflow alloyed steel for tempering.282 13 th International Conference on Tribology – Serbiatrib’13