Low Abrasion Resistance Research Articles

A study on crown and bridge resin using PNC-EMA monomer.

The present study investigated the development of crown and bridge resin using a new PNC-EMA monomer. MMA monomer has long been used for crown and bridge resins, but the polymer prepared with MMA monomer has certain demerits such as low mechanical strength and abrasion resistance. The authors prepared a polymer by mixing 3PNC-EMA monomer having a P=N bond in its skeleton, previously synthesized by ANZAI et al., with a monomer currently available on the market, in proportions of 14-70% (wt), using PMMA as the polymer. Both the compressive strength and hardness increased in accordance with increased amounts of the mixed 3PNC-EMA monomer, but water sorption reached 1.86 mg/cm2 when the mixed amount of 3PNC-EMA was 28%. The degree of abrasion decreased in accordance with the increase in the mixed amount of 3PNC-EMA, showing a value 1/3 that of PM MA, when mixed in a proportion of 70%.

The effect of carbide volume fraction on the low stress abrasion resistance of high Cr-Mo white cast irons

High chromium white cast irons display a number of advantages in abrasive wear applications. Their composition may be adjusted so that they contain moderate amounts of chromium yet solidify to produce massive chromium-rich carbides in an austenitic matrix of sufficient hardenability to be transformed to martensite with relatively simple heat treatment. In this study the role of carbide volume fraction (CVF) in developing abrasion resistance was investigated using a series of alloys with varying CVF but with constant matrix and carbide compositions. The low stress abrasion resistance of the alloys against quartz and Al 2O 3 was measured with a dry abrasive rubber wheel abrasion test. The abrasion resistance passed through a maximum at an intermediate CVF, near the eutectic composition, for the softer quartz, while the abrasion resistance increased monotonically with the CVF for tests against the harder Al 2O 3. Scanning electron microscopy showed that for quartz abrasion the reversal in the trend of wear versus CVF which occurred at the eutectic composition was caused by spalling and pitting of the massive primary M 7C 3 carbides in the hypereutectic alloys. This phenomenon did not occur in the Al 2O 3 abrasive tests, in which a monotonic increase in wear resistance with CVF was observed.

A study of abrasive wear mechanisms in cobalt-base alloys

Single-point scratch tests were used to investigate material removal mechanisms in two cobalt-base powder metallurgy alloys 6 and 19. Each alloy was produced with fine, medium and coarse chromium-rich M 7C 3 carbides in a cobalt-rich f.c.c. matrix phase. In a separate study, the low stress abrasion resistance was found to increase with carbide size. The present scratch test study was designed to simulate low stress abrasion conditions by using single quartz abrasive particles as scratch tools, and the results are compared with those from scratches made using regularly shaped diamond tools. Single- and multiple-pass scratches were made with several different loads using Vickers diamond pyramids and single quartz abrasive particles on metallographically prepared surfaces. Single-pass scratches were also made on preworn surfaces by using a Vickers diamond. Single-pass diamond scratches exhibited ploughing and extensive coarse slip bands in the matrix phase of metallographic specimens. Evidence of carbide deformation and of slip band cracking of the matrix material was observed also. Coarse slip bands were not observed on preworn surfaces. On both polished and preworn surfaces, thin layers of the matrix phase were often smeared over the carbides, and coarse carbides were extensively cracked. Multiple-pass diamond scratches on metallographic specimens exhibited thin detached layers of matrix material in the scratch groove and tongue-like extruded lips of material stretching away from the ridge. Particles of similar size and shape were found on the diamond pyramid. Scratch tests with quartz particles exhibited slip band cracking, smeared matrix material over the carbides and cracking and pulling out of carbides similar to observations with diamond tools. However, extensive ploughing and shear lip formation were not observed in quartz scratches, and wear debris particles in the scratch and on the tool were rounded and very much smaller than those produced by multiple-pass diamond scratches. Wear debris in multiple-pass quartz scratches were observed to pile up at the leading edges of the carbides, which protruded from the surface because of preferential wear of the matrix phase, as observed in low stress quartz abrasion. With both quartz and diamond tools, the material with the finest carbides (alloy 19A) exhibited large pits where cracks had traveled along the carbide-matrix interface and between carbides. Very little evidence of pulling out of carbides in the fine carbide materials was found.

Microscopic evaluation of the thickness of sealants used in orthodontic bonding

Placement of a resin sealant on the enamel surface prior to orthodontic bracket bonding has been suggested as a means of providing protection against demineralization, particularly at known sites of plaque accumulation. The duration of protection is influenced by resin sealant thickness and distribution. The object of this study was to determine the thickness of polymerized sealant at the vulnerable bracket/resin periphery. Six groups of ten extracted caries-free teeth were bonded with metal brackets using six commercially available bonding materials and their respective sealants. Scanning and light microscopy were used to map sealant distribution and measure sealant thickness at the bracket/resin periphery. Results showed a wide range of sealant thickness, from 0 to 228 μm, with considerable intraproduct variation. It was concluded that thin resin films, with their low abrasion resistance, cannot be expected to provide long-standing protection against demineralization.

Problems with Polymers in Dentistry

AbstractDespite the important contributions made by polymers in dental treatment procedures, many shortcomings of these materials are apparent. Rigid type denture base polymers (commonly P.M.M.A.) have low impact and abrasion resistance and lack radiopacity. Resilient polymers used as denture liners may bond poorly to the denture base and suffer changes in physical properties in use. Early problems of colour stability, high polymerisation and thermal contraction, low surface hardness and poor abrasion resistance of the first polymeric filling materials have been only partly overcome by the introduction of polymer/ceramic composites.In dental cement applications, present bonding systems include unfilled dimethacrylates, which do not attach to dentine. A system based on polyacrylic acid, or copolymers thereof, is believed to bond chemically to the calcium in tooth structure, but the bond to dentine is poorer than that to enamel and also the hydrolytic stability is suspect.

Reinforcing Silicas and Silicates

Abstract Since the first intensive literature review on silicas and silicates was published, significant new technology for their use in rubber has developed. Usage in the rubber industry has broadened considerably, and increases in their consumption have occurred during the ensuing fifteen years. From the “soles and heels” fillers of the 1950's, the usage of precipitated silicas and silicates since has gained significantly in quality components of tires and mechanical goods. Potential applications in the immediate future are no longer limited by the “good, but second to carbon black” performance that has prevailed for the past twenty-five years. Besides the traditional unique properties of tear resistance, hardness, stiffness, flex resistance, heat resistance, low modulus, and neutral color imparted to rubber by silicas and silicates, it is now possible to add adhesion, low heat buildup, high resilience, high modulus, and high abrasion resistance. This is part of the new technology which has developed that provides an alternative type of filler to meet the demanding needs of tire components, conveyor belts, automotive mounts, gaskets and seals, and other quality rubber compounds previously inaccessible to silicas. The present review covers the period 1960–1975. Because of the volume of available literature, it became necessary to be quite selective, in a way perhaps that may seem arbitrary. Nevertheless, coverage will be confined largely to that relevant to more general rubber uses. Silicone rubber technology was not covered because of its highly specialized and generally proprietary nature. The definitions used in the previous review were expanded somewhat. Silicas and silicates (henceforth, “silicas”) germane to this review were generally restricted to those which are synthetic and amorphous. However, the size limitations were relaxed somewhat to include those having a specific surface area greater than 25 m2/g or an average particle diameter less than 100 nm. Natural products (e.g., clays, diatomaceous earth, sand, etc.), as well as their modified forms, were excluded.

Traction-Abrasion Relationships of Tread Compounds Containing New Reinforcing Blacks

Abstract Abradibility and braking force coefficient (BFC) were determined on compounds of various elastomers and fillers, using a modified Lambourn abrader. Butyl rubber showed the highest BFC and butadiene rubber the lowest, with SBR intermediate. While the effect of carbon black type is not as large certain types of carbon black imparted not only improved traction (“wet” BFC) to tread compounds but also increased wear resistance, in contrast to other methods of improving traction which invariably lead to lower abrasion resistance. The laboratory relationship was confirmed on actual tires on a special trailer and on a test fleet car.

Abrasive wear of tungsten carbide—cobalt composites. I. Rotary drilling tests

Studies have been made of the wear mechanisms operative during rotary drilling of abrasive rock using tungsten carbide-cobalt tools of varying abrasion and fractire resistance. For rock drilling grades, containing from 8 to 12% cobalt, wear occurs both by cobalt erosion and by gross fracture of the carbide skeleton. Although fracture is likely to account for the greater proportion of the weight loss, the wear rate is larger for composites having the greatest fracture resistance and lowest abrasion resistance. The apparent anomaly suggests that the two observed mechanisms may be stages in an overall mechanism.

The Effect of Abrasion Resistance and Thermal Properties of the Cemented Carbide Cutting Tool Grade on the Flank Wear Characteristics

Correlation of the wear characteristics with abrasion resistance factor—1/(vol. loss) in a standard test—has been established in a low speed range where the temperatures involved in the cutting action are relatively low. It was found that a lower abrasion resistance factor produced, (in specified time and cutting conditions except speed, which was a variable), higher flank wear at a range of low speeds—20 to 100 SFPM or 6 to 55 per min—but, when speed is increased, other properties than abrasion resistance are involved, i.e., hot hardness characteristics and thermal conductivity coefficient are able to withstand higher velocities. Speed versus thermal conductivity coefficient curve was established where the cutting time and flank wear levels were constant. Feed and depth of cut were also constants. The investigation demonstrated that thermal conductivity coefficient of the cutting grade material is very significant and plays a major role in its ability to resist transfer of heat from the cutting zone to the flank of the tool, and thus no reduction of hardness due to temperature. This phenomenon results in the ability of the tool to perform in high speed range.

The Role of Zinc in the Corrosion Protection of Offshore Structures

As a protective coating, zinc can be applied by hot dipping or by continuous, low-cost galvanizing of sheet and strip. Additional protection can be readily achieved by painting. On-site application can be achieved by zinc spraying, or by using zinc rich paint. Zinc-containing paint has proved particularly effective for offshore structures exposed to atmospheric corrosion. Coatings with inorganic vehicles give outstanding abrasion resistance, and such coatings, having over 80% zinc in the dry film, are giving good protection after twenty years. Those based on organic vehicles should have over 90% zinc in the dry film for maximum protection. They require somewhat less meticulous surface preparation, and provide a more flexible coating, but they have lower abrasion resistance.

Construction material assessment from quarry sites at Chaktan-Ghasa-Kaligandaki River area, western Nepal

Construction material assessment is the crucial part of the hydroelectric power projects. The quality and quantity of the construction materialis the major concern when exploring construction material. Four quarry sites (Q1, Q2, Q3 and Q4) were identified and assessed for both quantityand quality. Distribution of rock quarry sites was taken for quantitative assessment of reserves. The rock samples were obtained from the sitesand were analysed for physical, mechanical and petrographic features. Rock types in quarry sites were schistose marble (in Q1), augen gneiss(in Q2), and banded gneisses (in Q3 and Q4). The analytical results showed that water absorption values were < 1% in all the samples, but wasthe highest in Q2 (0.92%). Contrarily, Q2 possessed the least specific gravity among the samples. Sodium sulphate soundness values rangedfrom 0.21 to 0.77, which was the highest in Q2. Samples Q1, Q3 and Q4 yielded Los Angeles Abrasion value below 45%, whereas Q2 gave57.5%. Similarly, Q2 also yielded the least value (1.82 MPa) of point-load strength index tested along the foliation. Augen gneiss (Q2) showedthe low abrasion resistance and soundness to freeze and thaw because of weak bonding between platy and other constituents of the rock , whereasschistose marble and banded gneisses yielded better resistance to abrasion and freeze and thaw, and possessed better strength perhaps due towell bonding among the mineralogical constituents due to the presence of appreciable amount of carbonate minerals.DOI: http://dx.doi.org/10.3126/bdg.v14i0.5442Bulletin of the Department of Geology Vol.14 2011, pp.77-82

Fibers From Crystalline Hydrocarbon Polymers1

Properties of fibers derived from crystalline polymers of ethylene, propylene, 4-methyl- 1-pentene, and styrene are presented and contrasted. Polyethylene fiber properties depend markedly on the crystallinity or density of the polymer; although high-strength fibers can be made from linear polyethylene, resiliency properties are poor, tensile properties are highly time-dependent, and endurance under sustained loading is very poor. On the other hand, polypropylene fibers have good stress-endurance properties, excellent recovery from high extensions, and fair-to-good recovery properties at low strains; recovery at 'low strains is shown to depend on the extent of fiber orientation and annealing. Anoma lies in the change of the sonic modulus of polypropylene yarns during extension and relaxation are noted and interpreted in terms of structure changes in the crystalline phase. The high melting temperature of 235°C for poly(4-methyl-1-pentene) appears to be due to its low entropy of melting, and fibers from this polymer are characterized by low tenacity when tested at elevated temperatures. Crystalline polystyrene fibers have relatively good retention of tenacity at elevated temperatures and are characterized by excellent resiliency at low strains, good wash-wear characteristics in cotton blends, and low abrasion resistance.

Laboratory Testing of Tread-Stock Abrasion Resistance at Constant Transmitted Power. I. Comparison of Road and Laboratory Data at Various Severities

Abstract Laboratory abrasion data were obtained on various tread vulcanizates over a large range of severities, including the region equivalent to the low severity encountered on straight, smooth California highways. The constant transmitted power principle was used as a severity criterion for comparison of abrasion of different tread vulcanizates. Load, wheel angular velocity, and ambient temperature were held about equal to those prevalent during road tests. These data were compared with road tests on the same vulcanizates, conducted on tires tested on courses varying from low to high severity. The laboratory data and the California low severity test data show a high degree of correlation for BR vs SBR (50 HAF) over the entire range of severities tested. The loss rate-severity plots for BR and SBR show a crossover point, with the BR showing the higher abrasion resistance at the higher severities. The BR shows a substantially higher abrasion resistance than the SBR on the Texas straight highway course. This is in opposition to the California data, which shows a substantially lower abrasion resistance of the BR compared to SBR on the straight highway course. The abrasion rates for BR and SBR in Texas, California, and laboratory tests are consistent if the severity of the Texas course is assumed to be equivalent to a linear combination of at least two California or laboratory severities. A plausible cause of the difference between California and Texas results is the difference in pavement surface texture. This viewpoint is shown to be consistent with abrasion patterns observed on tires in the California and Texas straight highway tests. The laboratory data and California test data on NR relative to SBR are consistent at the high severities, and for laboratory data extrapolated into the low severities from the high severity data. However, the actual laboratory data taken at low severities are more erratic and show consistently higher loss rates than those observed in the California freeway test. It is postulated that this may be the result of increased susceptibility to thermal oxidative degradation of the NR surface, caused by relatively longer exposure in the laboratory than on the road at a given severity. The investigation described in this paper lends a great deal of encouragement to the usefulness of laboratory abrasion testing for the screening of treadstock vulcanizates. The ability to obtain abrasion results under carefully controlled conditions of transmitted power, temperature, load and wheel angular velocity allows results to be investigated confidently as a function of conditions in the instrument, or of the polymeric properties. These investiagtions can be quite fruitful in eventual understanding of the polymer behavior or of the mechanism of abrasion. An important observation has also been the large variations in tire test results on different courses of assumed equal severities. Thus, the laboratory abrasion test can also assume the position of a guide to more effective road tests.

Abrasion Resistance of Multifilament and Staple Yarns Tested on Modified Walker Abrader

Nine multifilament yarns and 18 staple yarns were tested on a modified Walker Abrader using the same low tension for all yarns. To correct all filament yarns to the same fineness (100 den.), multiple strands of filament viscose 100/40 were tested, and a correction factor was obtained. In the same manner, multiple strands of Kuralon 80/2 were tested to obtain a correction factor for staple yarns. The Walker Abrader results for staple yarns were also corrected to 100 den. After the results had been corrected, acetate filament yarn was found to have the lowest abrasion resistance and nylon filament yarn the highest abrasion resistance among the filament yarns. In the staple yarns, acetate 20/1 had the lowest abrasion resistance, and Dacron 60/2 (worsted) had the highest abrasion resistance. Comparing staple and filament yarns, acetate staple 20/1 had the lowest abrasion resistance, and nylon 100/40/2.5 filament had the highest abrasion resistance. In general, the abrasion resistance of filament yarns was greater than the abrasion resistance of staple yarns.