Emilia Wolowiec-Korecka

Precision Case Hardening by Low Pressure Carburizing (LPC) for High Volume Production

Abstract Traditionally, case hardening is based on carburizing in atmospheres and oil quenching; this is carried out in sealed quench furnaces and in continuous lines (pusher, roller or rotary furnaces). They are technologies and devices developed more than 50 years ago and, over the course of time, they have exhausted their development potential. At present, they hardly meet the incoming requirements of the modern industry regarding quality and replicability, integration and organization of production, and environment protection. A solution for weak points of traditional case hardening is the use of vacuum technologies and equipment. Vacuum carburizing increases the resulting precision and replicability, and the variety of vacuum equipment for heat treatment allows the adaptation to modern industry requirements. Two applications are described in the article. The first one – evolutionary – is based on the triple- chamber vacuum furnace for semi-continuous production as a wide alternative for traditional devices. The second system – innovative – is based on the true single-piece flow method. Both solutions have specific and characteristic properties that predispose them for different applications depending on quality requirements and organization of production.

2D-Finite element analysis of inlay-, onlay bridges with using various materials

Purpose: To compare the impact of different bridge constructions and different loads on stress distribution in bridges. Design/methodology/approach: The study was conducted on 96 computer models of both premolars and molars that simulated a missing second premolar restored with a bridge supported on crown inlays or onlays. Simulations were made of a bridge constructed from four different materials: Au alloy, Cr/Ni alloy as well as two kinds of glass fibre-reinforced composites: Targis Vectris and FibreKor /Sculpture. The study was conducted using the finite element method (FEM). The results were analysed with PQStat statistical software version 1.6. Findings: In none of the analysed cases did stresses appear capable of damaging the bridge construction. Reduced stresses were lower in glass fibre reinforced composite materials than in metal alloys. Practical implications: The force application point has a decisive influence on stress distribution in the hard dental tissue and in bridges. The highest stress values occurred at the loading of the pontic tooth. Originality/value: The force application point has a decisive influence on stress distribution in the hard dental tissue and in bridges. The highest stress values occurred at the loading of the pontic tooth.

Effect of chemical surface treatment of titanium on its bond with dental ceramics

Statement of problem. Airborne‐particle abrasion of titanium is a clinically accepted method of surface preparation. As a side effect of airborne‐particle abrasion, particles of the abrasive material get embedded into the surface. How particle presence or removal from the titanium surface affects the strength of the titanium‐ceramic bond is unclear. Purpose. The purpose of this in vitro study was to determine the effect of removing Al2O3 particles embedded into the surface by means of chemical surface treatment on the strength of the titanium‐ceramic bond. Material and methods. Titanium (TritanCpTi 1, Dentaurum, 99.5% Ti) disks were airborne‐particle abraded with 110 &mgr;m Al2O3 at a pressure of 0.4 MPa and an angle of approximately 45 degrees. The surface was etched chemically using 1 of 8 reagents, and the veneering ceramic applied and fired. The strength of the metal‐ceramic bond was determined using the shear strength test. Further, the effect of thermal fatigue on the bond strength was evaluated. The results were analyzed with 2‐way ANOVA and the Tukey honest significant difference (HSD) test (&agr;=.05). Fractographic investigations and microscopic tests were also performed to determine the quality of the titanium‐ceramic bond. Results. Effective etching of the titanium surface and removal of Al2O3 particles included a 30% water solution of HNO3 + 3% HF, a mixture of HNO3 + HF + glycerin, a 4% solution of HF in H2O2, and a 4% solution of HF in H2O. A statistically significant difference (of about 50%) in bond strength was found between the groups subjected to chemical etching and the control group (P<.05). Additionally, a statistically significant difference (about 25%) was found after thermocycling (P<.05). Conclusions. Removing the Al2O3 particles embedded into the titanium surface after airborne‐particle abrasion lowers the strength of the titanium‐ceramic bond (P<.05). Thermocycling also weakens the strength of the titanium‐ceramic bond, regardless of the surface preparation (P<.05).

The role of mechanical, chemical andphysical bonds in metal-ceramic bondstrength

Purpose: A review regarding the mechanisms of metal-ceramic join is presented. Design/methodology/approach: The impact of the air-abrasion parameters on the mechanical bond strength of the ceramic crowns was discussed. The presence of opaque on the chemical bond was analysed. Research of the influence of the difference in the coefficient of thermal expansion values on the metal-ceramic bond was included. The methods of testing the bond strength were analysed. Findings: The metal substructure-dental ceramic bond strength is affected by all types of bond. In bond strength, 3-point bending test and shear test are mainly used. Created samples simulate the ceramic crowns veneered on one side. The role of physical bond on ceramic crowns veneered around metal substructure is unknown. Research limitations/implications: The prosthetic restorations with the ceramic surrounding whole the metal substructure are commonly used. The impact of shrinkage in the cylindrical deposition of the ceramic on metal substructure should be analysed. Practical implications: Numerical analysis and FEM simulation can be helpful in the analysis of the physical bond between the metal substructure and the dental ceramic around it. Originality/value: The impact of the type of the bond to metal-ceramic bond strength is presented, taking into account the cognitive gap in the influence of the coefficient of thermal expansion on the cylindrical placement of ceramic on the substructure.

Low-pressure carburizing in a large-chamber device for high-performance and precision thermal treatment of parts of mechanical gear

This paper presents the findings of research of a short-pulse low pressure carburizing technology developed for a new large-chamber furnace for high-performance and precision thermal treatment of parts of mechanical gear. Sections of the article discuss the novel constructions of the device in which parts being carburized flow in a stream, as well as the low-pressure carburizing experiment. The method has been found to yield uniform, even and repeatable carburized layers on typical gear used in automotive industry.

Influence of number of fusions on mechanical properties of Ducinox alloy

Purpose: The purpose of the test was to specify influence of re-fusions of the nickelchromium prosthetic alloy Ducinox on its strength properties. Design/methodology/approach: The tests were carried out on the samples cast of the Ducinox alloy molten once, twice and three times. The hardness has been measured using the Vickers method; the tensile strength has been also specified. The samples designed for strength tests were subjected to X-ray control to find possible defects that would eliminate the samples from further tests. The last test was observation of fractures occurred as a result of the strength tests, under the microscope. Findings: Both hardness measurements and strength tests did not show statistically significant differences among individual groups of samples. Practical implications: Based on the results of the tests carried out, it can be found that re-fusion of the alloy Ducinox has no influence on its tensile strength. Thereby, in the dental technology practice, it is possible to add the casting scrap to pure metallic alloy without influence on strength of prosthetic element castings. Originality/value: This is an well-known method of analysis which is applied in many scientific fields. However in modern prosthetics it is new approach.

System of single-piece flow case hardening for high volume production

Purpose: Purpose of this paper is development of single-piece flow system to precision thermal treatment of parts of mechanical gear using a short-pulse low-pressure carburising technology (developed for a new large-chamber furnace). Design/methodology/approach: Sections of the article discuss the novel constructions of the device in which parts being carburised flow in a stream, as well as the low-pressure carburising experiment. Findings: The method has been found proper carburised layers on typical gear used in automotive industry. Research limitations/implications: The short-pulse low-pressure carburising technology needs further investigation to fully understand its all mechanisms. Practical implications: The device resulting from the experiment can be a fully robotised part of a production line which can be included in a system of automatic control of a production process. Originality/value: The device resulting from the experiment is only known solution on the world.