No breakage of femoral prosthesis stems made of hot-forged cobalt-base or titanium-base alloys has been reported since 1972, in spite of their being loosened and severely overstressed. The minimum requirements imposed on fracture-resistant femoral prosthesis stems were established in laboratory tests and studies lasting several years. The results of these time-consuming and costly efforts have been confirmed by the nonoccurrence of fatigue fractures in more than 350 000 original Mueller and Weber hip joint prostheses with stems made of hot-forged, high-strength Co-Ni-Cr-Mo Protasul-10 alloy, one of the future-oriented alloys used for biocompatible and highly stressed long-term implants. Straight-stem hip prostheses made of hot-forged Ti-Al-V alloy in combination with ceramic Biolox ball heads give promising results, as has been demonstrated by extensive laboratory tests. This must be further confirmed, however, in long-term field studies.
Loosening of the anchorage in the bone is a problem in hip-joint arthroplasty which up to now has not been entirely solved. In the loosened condition, anchorage stems of artificial joints are subject to alternating overload which causes rupture if the fatigue strength is exceeded by the stress amplitude. At Sulzer a hip-joint anchorage stem made from wrought CoNiCrMo alloy Protasul-10 has been developed which has substantially higher fatigue strength than stems made from stainless steel of grade AISI-316L or CoCrMo cast alloy. It is therefore essentially safe from fatigue cracking and this offers the possibility of significantly easier removal in case of re-operation after loosening. This paper deals with some rules to be observed in choice or development of materials for long-term implants subject to fatigue. The results of laboratory investigations on the fatigue behaviour of cobalt-base alloys for surgical implants are discussed.
Since loosened femoral component stems are subjected to severe stresses, the material of which the stem is made becomes over-stressed and this may eventually result in an absolutely undesirable fatigue fracture of the loosened stem. Extensive static stress measurements performed along the lateral aspect of simulated loosened stems of various hip prosthesis types yield load/stress curves for determining the safety factor for the structural strength of the stem design. Decisive for the safety against fracture of a loosened femoral prosthesis stem is, ultimately, the dynamic pulsating fatigue test at up to 5 × 106 load cycles in Ringer's solution. Under the given test conditions as many as 2000 hip prosthesis stems have been subjected to 5–10 million load cycles over the last ten years, and minimum requirements have been laid down for the fracture-safety of these components under conditions of loosening in the body. The experience gained over a period of ten years with more than 500 000 series-produced fracture-proof anchorage stems strongly suggest that these test conditions should be standardized nationally and internationally.
The flow of gases with powder in the countercurrent to the charge materials occurs in many chemical processes. In the shaft metallurgical devices, the physical and chemical processes take place also in the countercurrent system. An important issue is that there are no disruptions of the flow in this multiphase system. Under real operating conditions of the device, the powder is generated within the process and its source is the charge or it is inserted to the device within the process procedure.In this system, a problem of bed particle suspension appears. That is why the author undertook investigations on the gas -powder flow in the descending bed. A physical model of this system was constructed. The experiments were performed and the influence of gas velocity, a type and size of the bed and powder particles as well as the powder concentration in the gas was established. Conditions when the descending bed suspension occurs were defined. In the case of physical model with glass materials, the suspension of bed did not occur. Therefore, investigations using beds of high alumina materials, blast furnace pellets and iron powder were performed. The results are presented below. When the bed of glass spheres was replaced with the bed of alumina spheres, a considerable increase in the volume of powder held up in the bed the gas flow resistance were observed. The surface properties of bed particles changed and better conditions for powder holdup were created. The actual gas velocity in the bed increased due to void fraction reduction.Replacement of the glass powder with the iron powder caused a change in the powder density, its surface properties and the shape factor. Greater amounts of the iron powder were held up in the bed and the gas flow resistance increased.Comparing the alumina particle bed -iron powder system to the blast furnace pellet bed -iron powder system, changes in the surface properties of bed particles and the void fraction of bed changed. The study results were the basis for defining conditions of the descending bed suspension.Keywords: descending packed bed, gas -powder flow, powder holdup, bed suspension Przepływ gazów z pyłem w przeciwprądzie do materiałów wsadowych występuje w wielu procesach chemicznych. W szybowych agregatach metalurgicznych procesy fizykochemiczne zachodzą także w układzie przeciwprądowym. Istotnym jest by w tym wielofazowym układzie nie dochodziło do zakłóceń przepływu. W warunkach rzeczywistych pracy agregatów pył jest generowany podczas przebiegu procesu a jego źródłem są materiały wsadowe lub jest wprowadzany do agregatu w ramach procedury procesowej. W układzie takim pojawia się problem zawieszania cząstek złoża. Stąd autor podjął badania przepływu gaz + pył w złożu schodzącym. Skonstruowano model fizyczny układu. Przeprowadzono badania z analizą wpływu prędkości gazu, rodzaju i wielkości kawałków złoża, cząstek pyłu, ilości pyłu w gazie. Określono warunki, w których dochodzi do zawieszania schodzącego złoża.W przypadku modelu z materiałów szklanych do zawieszania złoża nie ...
The flow of gases in metallurgical shaft furnaces has a decisive influence on the course and process efficiency. Radial changes in porosity of the bed cause uneven flow of gas along the radius of the reactor, which sometimes is deliberate and intentional. However, holdup of solid particles in descending packed beds of metallurgical shaft furnaces can lead to unintentional changes in porosity of the bed along the radial reactor. Unintentional changes in porosity often disrupt the flow of gas causing poor performance of the furnace. Such disruptions of flow may occur in the blast furnace due to high level of powder content in gas caused by large amount of coal dust/powder insufflated as fuel substitute. The paper describes the model test results of radial distribution of static pressure and powder hold up within metallurgical reactor. The measurements were carried out with the use of 3D physical model of two-phase flow gas-powder in the moving (descending) packed bed. Sinter or blast furnace pellets were used as packed bed while carbon powder or iron powder were used as the powder. Wide diversity within both static pressure distribution and powder distribution along the radius of the reactor were observed once the change in the type of powder occurred.
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