Comparison of tensile strength of solder joints by infrared and conventional torch technique

Soldering in Dentistry: An Updated Technical Review

INTRODUCTION

The need to permanently join two or more pieces of metal using heat is a frequent condition in various fields of medicine such as dentistry. Welding, brazing and soldering are permanent joining techniques between different metals that require in-depth background knowledge in order to obtain predictable results.

AIM

This review examines the different methods of joining metals using heat and their fields of application.

DISCUSSION

It is possible to create permanent metal joints in various phases of the creation of final products that will be used on the patient. In several cases, welds are also made directly by the manufacturer during industrial processing. In dentistry, dental laboratories perform complex welds mainly on dental prostheses and orthodontic appliances during the production process. It is also possible to obtain intraoral welding carried out by the clinician inside the patient's oral cavity. Welding can be carried out using combustible gases, electric current, infrared light and laser light through different technical procedures which must be chosen according to the specific needs and the metals to be joined.

CONCLUSIONS

It is useful for the dentist and dental technician to know the different welding methods, including those carried out in the factory by the manufacturer, to better understand the physical properties and mechanical resistance of the components marketed for the construction of prostheses and orthodontic appliances. The enormous variety of conditions in which those who practice welding can find themselves therefore presupposes in-depth knowledge in this field in order to apply the most suitable technique.

Decreasing Shear Stresses of the Solder Joints for Mechanical and Thermal Loads by Topological Optimization

A methodology for obtaining the optimal structure and distribution for the gradient properties of a material in order to reduce the stress level in a soldered joint was constructed. The developed methodology was based on a combination of topological optimization methods (the moving asymptotes method) and the finite elements method; it was first implemented to solve problems of optimizing soldered joints. Using the proposed methodology, a number of problems were solved, allowing one to obtain optimal structural characteristics, in which a decrease in stress is revealed. Designing compounds using this technique will provide more robust designs. The proposed technique can be applied to a wide class of practical problems.

Effect of soldering techniques and gap distance on tensile strength of soldered Ni-Cr alloy joint

PURPOSE

The present study was intended to evaluate the effect of soldering techniques with infrared ray and gas torch under different gap distances (0.3 mm and 0.5 mm) on the tensile strength and surface porosity formation in Ni-Cr base metal alloy.

MATERIALS AND METHODS

Thirty five dumbbell shaped Ni-Cr alloy specimens were prepared and assigned to 5 groups according to the soldering method and the gap distance. For the soldering methods, gas torch (G group) and infrared ray (IR group) were compared and each group was subdivided by corresponding gap distance (0.3 mm: G3 and IR3, 0.5 mm: G5, IR5). Specimens of the experimental groups were sectioned in the middle with a diamond disk and embedded in solder blocks according to the predetermined distance. As a control group, 7 specimens were prepared without sectioning or soldering. After the soldering procedure, a tensile strength test was performed using universal testing machine at a crosshead speed 1 mm/min. The proportions of porosity on the fractured surface were calculated on the images acquired through the scanning electronic microscope.

RESULTS

Every specimen of G3, G5, IR3 and IR5 was fractured on the solder joint area. However, there was no significant difference between the test groups (P > .05). There was a negative correlation between porosity formation and tensile strength in all the specimens in the test groups (P < .05).

CONCLUSION

There was no significant difference in ultimate tensile strength of joints and porosity formations between the gas-oxygen torch soldering and infrared ray soldering technique or between the gap distance of 0.3 mm and 0.5 mm.

Comparative tensile strengths of preceramic and postceramic solder connectors using high-palladium alloy

STATEMENT OF PROBLEM

It is not known whether different high-palladium alloys of similar composition possess comparable tensile strength properties associated with connector soldering.

PURPOSE

The purpose of this study was to evaluate the tensile strength properties of 2 high-palladium alloys on soldered connectors under simulated pre-ceramic and post-ceramic soldering conditions.

MATERIAL AND METHODS

Eighty cylindrical castings were fabricated (Rx Naturelle Plus alloy and Option alloy). The 40 castings for each alloy were subdivided into 2 groups of 20 each. In the first group, castings for each alloy were randomly paired and soldered with presolder (SMG2) to produce 10 preceramic test connector specimens for each alloy. In the second group, castings were similarly paired and soldered with postsolder (490 fine) to produce 10 postceramic test connector specimens for each alloy. Each soldered connector was subjected to tensile force until failure in a universal testing machine. Statistical analysis using a Wilcoxon rank sums test was performed (alpha=.05)

RESULTS

No significant difference was found between the mean tensile failure stress for Rx Naturelle Plus preceramic solder (344.7 +/- 77.6 MPa) compared to Option preceramic solder (411.5 +/- 112.8 MPa) (P =.1202). However, the mean tensile failure stress for Rx Naturelle Plus postceramic solder (260.8 +/- 223.7 MPa) was significantly lower than the Option postceramic solder (312.6 +/- 120.8 MPa) (P =.0407). Not only did Rx Naturelle Plus postceramic solder connectors show evidence of lower strength, but also an increased variation among specimens.

CONCLUSIONS

Rx Naturelle Plus solder connectors provided better strength with the preceramic as opposed with the postceramic connectors. For postsolder connectors, Rx Naturelle Plus alloy had less acceptable strength and a wider variation, suggesting it is more technique sensitive than Option alloy connectors.

Effects of three soldering techniques on the strength of high-palladium alloy solder joints

STATEMENT OF PROBLEM

Little information is available on the optimum technique for soldering high-palladium alloys, which have gained considerable popularity for prosthodontic applications.

PURPOSE

The objective of this study was to compare the flexural stress at the proportional limit of four noble dental alloy specimens soldered with torch, oven, and infrared-techniques.

MATERIALS AND METHODS

The high-palladium alloys studied were Legacy XT (Jelenko), Freedom Plus (Jelenko), and IS 85 (Williams/Ivoclar). A gold-palladium alloy, Olympia (Jelenko), served as the control. Thirty round bars, 18 x 3 mm, were cast from each alloy, cut in half, aligned, and joined using Olympia Pre solder (Jelenko) for the gas-oxygen torch and the infrared technique and Alboro LF solder (Jelenko) for the oven technique. Each soldered bar was subjected to three-point bending, and the maximum elastic stress or strength of the solder joint was calculated at the proportional limit. Data were analyzed by two-way ANOVA and the Ryan-Einot-Gabriel-Welsch (REGW) multiple range test at the 0.05 level of significance.

RESULTS

There was no significant difference between torch and oven-soldering, but both were significantly different from the infrared technique. ANOVA showed a significant difference between alloys, but this difference could not be detected with the REGW test. SEM examination of the fracture surfaces revealed grooves associated with the path of crack propagation. X-ray energy-dispersive spectroscopic analysis failed to detect copper in the solders, and there were no significant changes in the solder compositions after the melting procedures.

CONCLUSIONS

All three techniques can yield satisfactory solder joints in high-palladium alloys. These joints should be well-polished to achieve optimal strength.

Laser welding of a cobalt-chromium removable partial denture alloy

STATEMENT OF PROBLEM

The electric alloy brazed joints of removable partial denture alloys have failed frequently after routine usage.

PURPOSE

A technique providing higher joint strengths was investigated. This investigation compared the tensile strengths of electric-brazed and laser-welded joints for a cobalt-chromium removable partial denture alloy.

MATERIAL AND METHODS

Twenty-four cobalt-chromium standard tensile testing rods were prepared and divided into three groups of eight. All specimens in the control group (group 1) were left in the as-cast condition. Groups 2 and 3 were the test specimens, which were sectioned at the center of the rod. Eight specimens were joined by using electric brazing, and the remaining specimens were joined by using laser welding. After joining, each joint was ground to a uniform diameter, then tested to tensile failure on an Instron universal testing machine. Failure loads were recorded and fracture stress calculated. Statistical analysis was applied.

RESULTS

The student-Newman-Keuls test showed a highly significant difference between the joint strengths of the as-cast control specimens, the electric-brazed and laser-welded joints.

CONCLUSIONS

The tensile strengths of the as-cast joints were higher than those for the laser-welded joints, and both were higher than the electric-brazed joint strengths.

Tensile strength of soldered gold alloy joints

STATEMENT OF PROBLEM

Little information is available about the mechanical properties of soldered gold alloys after they have undergone various heat treatments.

PURPOSE

This study investigated the influence of heat treating on the strength properties of soldered joints of two gold alloys (NC Type IV and Sofard), which can be age-hardened at intraoral temperature.

MATERIAL AND METHODS

Dumbbell-shaped specimens were cast with each gold alloy and were cut at the center of the connecting bar for soldering. The two halves of the casting were then soldered with two different gold-based solders (Maingold and Degulor). Three different heat treatments were performed on the soldered gold alloy assemblies: solution heat treatment (ST) at 700 degrees C for 5 minutes (treatment A); aging at 37 degrees C for 7 days after ST (treatment B); and aging at 250 degrees C (Sofard) or 400 degrees C (NC type IV) for 15 minutes after ST (treatment C). The tensile strength, elongation and microhardness were evaluated after each heat treatment.

RESULTS

The hardness values of Sofard significantly (p < 0.05) increased during aging at 37 degrees C (treatment B) and produced adequate strengths of the soldered joints, especially with the harder solder (645.7 MPa: Degulor [222 VHN] vs. 493.3 MPa: Maingold [165 VHN]).

CONCLUSIONS

The results of this study indicated the possibility of strengthening soldered joints in the oral environment, thus eliminating the necessity for any additional hardening heat treatment.

Mechanical and elemental characterization of solder joints and welds using a gold-palladium alloy

PURPOSE

This study was conducted to determine whether newer infrared or laser welding technologies created joints superior to traditional furnace or torch soldering methods of joining metals. It was designed to assess the mechanical resistance, the characteristics of the fractured surfaces, and the elemental diffusion of joints obtained by four different techniques: (1) preceramic soldering with a propane-oxygen torch, (2) postceramic soldering with a porcelain furnace, (3) preceramic and (4) postceramic soldering with an infrared heat source, and (5) laser welding.

MATERIAL AND METHODS

Mechanical resistance was determined by measuring the ultimate tensile strength of the joint and by determining their resistance to fatigue loading. Elemental diffusion to and from the joint was assessed with microprobe tracings. Scanning electron microscopy micrographs of the fractured surface were also obtained and evaluated.

RESULTS

Under monotonic tensile stress, three groups emerged: The laser welds were the strongest, the preceramic joints ranged second, and the postceramic joints were the weakest. Under fatigue stress, the order was as follows: first, the preceramic joints, and second, a group that comprised both postceramic joints and the laser welds. Inspection of the fractographs revealed several fracture modes but no consistent pattern emerged. Microprobe analyses demonstrated minor diffusion processes in the preceramic joints, whereas significant diffusion was observed in the postceramic joints.

CLINICAL IMPLICATIONS

The mechanical resistance data conflicted as to the strength that could be expected of laser welded joints. On the basis of fatigue resistance of the joints, neither infrared solder joints nor laser welds were stronger than torch or furnace soldered joints.

A comparison of infrared- and torch-soldering of Au-Pd and Co-Cr metal-ceramic alloys using a high-fusing solder

PURPOSE

The purpose of this study was to compare the bond strengths and fracture modes of soldered joints formed by infrared and gas-oxygen torch heating of a high-fusing, gold-based solder in two metal-ceramic alloys.

MATERIALS AND METHODS

Pairs of half-dumbbell-shaped specimens of either an Au-Pd or a Co-Cr alloy were positioned with a 0.25-mm gap and were joined using a high-fusing, gold-based solder by either gas-oxygen torch heating or infrared heating. The resulting specimens were subjected to a heat treatment that simulated ceramic firing. Each specimen was fractured in tension at a loading rate of 0.5 cm/min, and its bond strength was measured. The halves of the specimen were rejoined using the other heating method and were heat treated, and the specimen's bond strength was again measured. Fractured cross-sections were examined at a magnification of 40x to determine the following: the fracture mode (adhesive, cohesive, or mixed); the percentage of adhesive fracture; the presence or absence of voids, porosities, or flux inclusions; and the percentage of the cross-section that was discolored.

RESULTS

Three-factor analyses of variance showed that neither the heating method, the particular specimen tested, nor the order of testing significantly affected the bond strength (P < .05). For each alloy, significantly fewer infrared-heated joints than torch-heated joints contained voids, porosities, or flux inclusions visible at 40x (chi 2 test, P < .05). All fractures were either entirely cohesive in the solder or mixed cohesive and adhesive. When infrared heating was used, entirely cohesive fractures occurred more frequently in the Au-Pd alloy specimens than in the Co-Cr alloy specimens (chi 2 test, P < .05). The coefficients of variation of the bond strengths for the infrared-heated joints were smaller than those for the torch-heated joints.

CONCLUSIONS

Although the two heating methods produced solder joints that had strengths that were not significantly different, infrared-heated joints showed less scatter in bond strengths. It was suggested that, in the hands of most technicians, fewer infrared-heated joints would contain defects visible at a magnification of 40x. The presence of such defects may increase the probability of in vivo failure caused by cyclic stresses.