利用六方BN改进切削性的一个成功范例

为了满足用于铝合金发动机体中的粉末冶金轴承盖切削加工的要求，开发了含六方BN的粉末组成。除要求强度外，为了对发动机体组合件能够有效地进行镗孔，材料的切削性能还必须和铝合金相一致。本文介绍了材料性能，概述了切削性试验，以及静态与动态强度试验的结果。     

一种直列式6缸发动机主轴承盖的开发

将粉末冶金用于铝合金发动机汽缸体意味着对材料切削加工性能的一种挑战.除了要求静态与疲劳强度之外,为了能够对发动机汽缸体组件进行有效地镗孔,材料的切削加工性状还必须和铝合金相容.为了满足这项应用提出的要求,开发了含有六方氮化硼的粉末配方.这项重要发展包括材料选择、切削性评价,以及静态与动态强度试验.为确定轴承盖最关键的部位进行了有限元分析(FEA).轴承盖是在经过金相检验、尺寸变化测定、静态与疲劳试验之后,进行制造与鉴定的.对制造工艺提出并实行了一些改进.轴承盖顺利地进行了切削加工,并通过了用户的发动机试验.此后,这些轴承盖在数以百万件计地进行生产.     

用于常规粉末冶金工艺的生坯切削加工

生坯切削加工的好处已众所周知，如切削刀具的寿命较长，能够用可烧结硬化粉末制作形状复杂的零件等。零件生坯强度高可防止在运送过程中生坯开裂与损坏。但是，用常规粉末冶金工艺不易达到所要求的高生坯强度(约大于20MPa)。因此，生坯切削加工尚未得到广泛应用。用魁北克金属粉末公司(QMP)新开发的高生坯强度(high green strength，简称HGS)聚合物润滑剂。正在消除使用生坯切削加工的限制。这种润滑剂的一个杰出特性是其对温度的敏感性。在压制温度55℃下整个坯件就能获得高生坯强度，这用冷压很容易达到。若将零件生坯压制到密度6．8g／cm^3，随后经固化处理。甚至可将生坯强度增高到48MPa左右。这样高的生坯强度使得用常规粉末冶金工艺制造的零件都能进行生坯切削加工。本文介绍了用正时链轮进行生坯切削加工试验的一些结果。使用的材料是由QMP ATOMET 4601与HGS润滑剂组成的可烧结硬化的粉末混合料。先用冷压将链轮压制到密度约6．8g／cm^3，再对用压制的生坯与经固化处理的生坯进行切削加工(在齿的中间车槽)。结果表明，HGS润滑剂，特别是固化处理后，可赋予生坯足够高的强度，以进行装卡与切削加工作业。切削加工表面光滑且棱边完好。由可烧结硬化粉末制作的可生坯切削加工的链轮，能省掉热处理，大大延长刀具寿命以及改善尺寸公差。     

粉末冶金零件生坯切削加工性能研究进展

综述了粉末冶金生坯切削加工技术的进展,指出其关键在于提高生坯强度以达到可加工的要求;分析了切削参数控制与刀具磨损和零件质量的关系,以及对生坯样品加工性能、烧结性能等的影响。通过预烧结、温压等工艺提高了钨基合金粉末冶金生坯的强度,并对其进行了切削加工试验。结果表明,经预烧结或温压的生坯均可进行装夹与切削加工,而预烧结生坯的加工性能更好,其加工表面光滑且棱边完好;采用生坯切削加工技术,可延长粉末冶金零件生产中的刀具寿命,节约成本,提高效率。     

轿车变速器的粉末冶金齿轮

粉末冶金齿轮由于材料中残留有孔隙,和用切削加工铸锻材料制造的零件相比,强度与耐磨性较差,不适用于重负载应用.通过横向辗压,利用选择性表面致密化,可显著改进粉末冶金齿轮的强度与耐磨性.这篇论文阐述了用压制、烧结、选择性表面致密化、表面硬化及根据要求的品质水平可能还有最后珩磨,制造轿车变速器的粉末冶金螺旋齿轮.研究了各种参数,诸如材料组成、横向辗压与热处理的工艺参数对致密化与硬度深度、孔隙形态、显微组织、齿轮齿廓、DIN品质以及表面粗糙度的影响.初步研究是在3轴的总成成对试验台架上进行的,其表明粉末冶金齿轮具有高负载承载能力.     

为生坯加工用强化生坯强度的润滑系统的开发

粉末冶金零件烧结后往往面要切削加工，以达到压制时无法成形的设计特征或窄小的尺寸公差。可是，随着高性能材料出现，鉴于这些材料烧结后表观硬度与强度高，采用生坯切削加工可减低切削加工费用与增强竞争性，因此，是一种很有吸引力的生产工艺。现在，采用新润滑系统可使零件在烧结前进行切削加工，这些新润滑系统和常用润滑剂相比，都是一些能大大增高零件生坯强度的聚合物润滑剂。在切削加工时，较高的生坯强度可减低生坯开裂和／或棱边剥落的危险。这篇论文对由新聚合物润滑系统或常用EBS蜡润滑剂压制的烧结硬化材料FLC-4608的脱模特性与生坯特性进行了比较。这种比较是用实验室与生产规模压机压制成形的密度为6．7～7．1g／cm^3的横向断裂试样和油泵齿轮进行的。还报告了油泵齿轮烧结后的性能和零件间性能的均一性。     

引进高性能粉末冶金高速钢丝锥的应用剖析

日前,陕西某机械厂从国外进口一种粉末冶金高速钢丝锥,在应用中发现了一些值得深思的技术问题.有些机械零件非常精密,在制造过程中要求材料必须在热处理之后进行切削加工,这样可以避免因热处理变形的影响,从而才能保证对零件的高精度要求.但是由于材料在热处理之后,强度和硬度等性能大幅度提高,因此极大地增加了切削加工的难度.在这种情况下则必须使用高性能的刀具.     

中国成为全球粉末冶金汽车零件最大的集散地之一

<正>目前,粉末冶金已经被业界公认为是一种绿色、可持续的制造技术。例如在持续性功能方面,粉末冶金的最终成形能力与材料利用率很高,可使全部能源消耗最小化。与传统工艺(热加工+冷加工)的铸造或锻造+切削加工相比,粉末冶金工艺制造同一零件只需要采用较少的几道工序,即能完成工序较多、较复杂的工艺。在材料可持续性方面,粉末冶金的最终成形能力是其主要优势。例如成形一个齿状零件,传统切     

TEC-3X钻头获得了2006年欧洲粉末冶金协会优秀粉末冶金奖荣誉奖

Hilti AG公司制作的TEC-3X钻头获得了2006年欧洲粉末冶金协会优秀粉末冶金奖荣誉奖。TEC-3X钻头是世界第一种被投入大规模生产的功能梯度硬质合金零件,TEC-3X钻头是经过轴向压制、液相烧结后制成的,硬质合金材料的性能根据钻头各部位对功能的不同要求逐渐变化。TEC-3X钻头的钻孔速度和使用寿命比传统方法制造的钻头略有提高,而TEC-3X钻头的强度则有了明显的提高。这种新开发的粉末冶金技术也适用于制造其他一些对零件的不同部位有不同性能要求的粉末冶金制品,例如切削和耐磨零件等。信息摘译自欧洲粉末冶金协会网站http://www.epm…     

用于汽车自动变速器的温压涡轮毂

温压是一种可将增高密度与选择高使用性能材料相结合的技术。增高密度有助于提高零件的力学性能,以及整体使用性能。将密度增高与高使用性能相结合,可使制造的零件的使用性能超过相应的铸锻材料产品,同时可制成具有最终形的零件,从而显著减低生产成本。因此,自动变速器的涡轮毂就成为了温压的一个理想对象。这篇论文将评述,将用于高扭矩自动变速器的常规锻件切削加工的涡轮毂转换为用一次压制/一次烧结制造的粉末冶金涡轮毂。粉末冶金涡轮毂使用的材料是FD-0405。在试验室对这种扩散合金化材料进行了评价,和报告了几个密度水平的力学性能。温压可使高应力的内花键区全面达到高密度。为了证明粉末冶金零件的适用性,进行了广泛的力学与零件的特定试验。     

Improved survival in stage III melanoma patients with GM2 antibodies: a randomized trial of adjuvant vaccination with GM2 ganglioside

PURPOSE: To perform a double-blind randomized trial with American Joint Commission on Cancer (AJCC) stage III melanoma patients for the following reasons: (1) to confirm our previous finding that patients with antibodies against the melanoma differentiation antigen GM2 have an improved prognosis, and (2) to demonstrate clinical benefit from GM2 antibody induction. PATIENTS AND METHODS: One hundred twenty-two patients with AJCC stage III melanoma who were free of disease after surgery were randomized: 58 to receive treatment with the GM2/BCG vaccine, and 64 to receive treatment with bacille Calmette-Guèrin (BCG) alone. All patients were pretreated with low-dose cyclophosphamide (Cy). RESULTS: GM2 antibody was detected in 50 of 58 patients treated with GM2/BCG and seven of 64 patients treated with BCG alone. With a minimum follow-up period of 51 months, there was a highly significant increase in the disease-free interval (P = .004) and a 17% increase in overall survival (P = .02) in these 57 antibody-positive patients, confirming our earlier experience. Exclusion of all patients with preexisting GM2 antibodies (one in the GM2/BCG group and five in the BCG group) from statistical analysis resulted in a 23% increase in disease-free interval (P = .02) and a 14% increase in overall survival (P = .15) at 51 months for patients treated with the GM2/BCG vaccine. However, when all patients in the two treatment groups were compared as randomized, these increases were 18% for disease-free interval and 11% for survival in the GM2/BCG treatment group, with neither result showing statistical significance. CONCLUSION: (1) Vaccination with GM2/BCG induced immunoglobulin M (IgM) antibodies in most patients. (2) GM2 antibody production was associated with a prolonged disease-free interval and survival. (3) Comparison of the two arms of this trial as randomized fails to show a statistically significant improvement in disease-free interval or survival for patients treated with GM2/BCG vaccines.     

Prediction of change in mitral valve area after mitral balloon commissurotomy using cine computed tomography

RATIONALE AND OBJECTIVES: Mitral balloon commissurotomy (MBC) can successfully increase the mitral valve area (MVA) in mitral stenosis, but the outcome is variable. In multicenter studies, qualitative echocardiographic scores obtained before MBC are only weakly predictive of the increase in MVA after MBC. METHODS: To evaluate whether the change in MVA after MBC can be predicted by evaluating mitral valve morphology using cine computed tomography (CT), we studied 12 women with mitral stenosis and 11 female control subjects. RESULTS: In the patients with mitral stenosis, MVA increased from 1.13 +/- 0.24 to 1.93 +/- 0.56 cm2 (P < .0001) after MBC. A standard echocardiographic score assessment of mitral valve morphology before MBC was not associated with the change in MVA after MBC in these patients (P > .20). However, the total mitral valve morphology score evaluated by cine computed tomography was strongly associated with the change in MVA after MBC (r = -.87; P < .0005). In addition, the individual morphologic characteristics of mitral valve mobility (P < .0025), leaflet thickness (P < .05), and subvalvular disease (P < .05) were significant predictors of the change in MVA after MBC. CONCLUSION: Cine computed tomography may be useful for predicting immediate increases in MVA in patients after MBC and may be helpful for preoperative assessment of these patients.     

Light-microscopical investigation of the distribution of extracellular matrix molecules and calcifications in human dental pulps of various ages

Human glioma cell line KG-1C contains GM3 ganglioside as its sole glycolipid. The degree of M2590 antibody binding to GM3 was found to be regulated by the cell density; the percentage of positive cells in FACS analysis decreased from approximately 20% to close to none as the cells increased their density from sparse to confluent. The contents of GM3 with different cell densities were consistent, being more than 0.4 micromol/g of the cellular weight, which was high enough to be recognized by the antibody. Trypsin treatment of the cells did not increase antibody reactivity. The extracted GM3 retained its antigenicity, being intensely stained with M2590 on a TLC plate; there was no change in chromatographic mobility either, indicating no modification of its chemical structure. The fluorescent microscope disclosed scattered dot-like staining of GM3, particularly at the periphery of the cells. We were able to expose cryptic GM3 fully within 12 h by dispersion of the cells to a sparse density. Surface labeling of GM3 with the use of limited sodium periodate oxidation of sialylated residue equally labeled GM3 either from the confluent cells or the sparse cells. Disassembly of actin filaments with cytochalasin B (10 microM) partially exposed cryptic GM3 of confluent cells, indicating reversibility of the crypticity. All together, the results indicate that cryptic GM3 actually exists on the cell surface, hidden from the surface not by other molecules but by other mechanisms associated with the cellular architecture. We are beginning to explore the possibility of selective localization of GM3 in small caves or folds of the cell membrane produced upon cell-to-cell contact.     

N-formimidoyl-thienamycin: in vitro activity in bacteria with resistance to beta-lactam antibiotics or gentamicin

The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of N-formimidoyl-thienamycin were determined for 25 strains each of Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens and Pseudomonas aeruginosa which were resistant to gentamicin and/or acylureido penicillins or cefotaxime, cefoperazone or moxalactam, and for 38 strains of the group D streptococci. The drug was very active against the most frequently encountered gram-negative resistant causative organisms of nosocomial infections. The MIC ranged from 0.25-1 mg/l for multiresistant Enterobacteriaceae, and from 0.5-4 mg/l for multiresistant P. aeruginosa. The group D streptococci (enterococci) showed a low MIC (median: 0.75 mg/l); the median of the MBC was greater than 64 mg/l, however.     

Prospective randomized trial of meropenem versus cefotaxime and metronidazole in the treatment of intraabdominal infections

BACKGROUND: The empiric antibiotic treatment of intraabdominal infections is in constant evolution. Monotherapy appears to be a desirable goal because of the simplicity of its administration, lack of toxic effects and wide spectrum. PATIENTS AND METHODS: A multicentre, prospective, randomized, open study was carried out to compare two antibiotic regimens in the treatment of intraabdominal infections in patients undergoing surgery. Ninety-eight consecutive patients were randomly allocated into two groups. One group (GM, n = 51) received meropenem (1 g/8 h) and the other (GCM, n = 47) a combination of cefotaxime (2 g/8 h) plus metronidazol (0.5 g/8 h). Clinical and bacteriological responses were assessed at the end of treatment and at 2-4 weeks. RESULTS: The severity of patients as assessed by the APACHE II score was similar in both groups (GM: 7.2 and GCM: 8.1). Three patients in each group could not be evaluated due to premature interruption of treatment or deviation from the protocol. The mean duration of treatment was 7.4 days in GM and 7.9 days in GCM. A satisfactory clinical response was obtained in 95% of patients in both groups. 31 patients (61%) in GM and 26 patients (55%) in GCM were bacteriologically evaluable. Bacteriological erradication was achieved in 94% of patients in GM and in 92% of patients in GCM. CONCLUSION: Meropenem is a good alternative for single antibiotic therapy in intraabdominal infections of moderate severity.     

Correlation between in vitro and in vivo activity of amoxicillin against Streptococcus pneumoniae in a murine pneumonia model

We studied the relationship between in vitro bacteriological parameters [minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and killing rate, defined as the reduction in the inoculum within 1, 3 or 6 hr] and in vivo activity of amoxicillin against 12 strains of Streptococcus pneumoniae, with penicillin MICs of < 0.01 to 16 micrograms/ml, in a cyclophosphamide-induced neutropenic murine pneumonia model. Dose-response curves were determined for amoxicillin against each strain, and three quantitative parameters of in vivo amoxicillin activity were defined, i.e., maximal attainable antimicrobial effect attributable to the drug [i.e., reduction in log colony-forming units (CFU) per lung, compared with untreated controls], dose required to reach 50% of maximal effect and dose required to achieve a reduction of 1 log CFU/lung. We demonstrated a highly significant correlation between the dose required to reach 50% of maximal effect and MIC (Spearman r = 0.98, P < .0001) or MBC (Spearman r = 0.95, P < .0001) for amoxicillin against strains of S. pneumoniae with a wide range of amoxicillin MICs (0.01-8 micrograms/ml). Significant correlations between the dose required to achieve a reduction of 1 log CFU/lung and MIC (Spearman r = 0.98, P < .0001) or MBC (Spearman r = 0.95, P < .0001) were also observed. In contrast, there were no significant correlations between the maximal attainable antimicrobial effect attributable to the drug and MIC, MBC or killing rate or between killing rate and the dose required to reach 50% of maximal effect or the dose required to achieve a reduction of 1 log CFU/lung. We conclude that in vitro susceptibility test results (MICs and MBCs) correlated well with in vivo amoxicillin activity against pneumococcal strains, including highly penicillin-resistant strains, in this animal model. Furthermore, these data suggest that the estimated MIC breakpoints for amoxicillin against S. pneumoniae would be 2 micrograms/ml for intermediate-resistant and 4 micrograms/ml for resistant, although this remains to be confirmed in clinical studies.     

GM and KM immunoglobulin allotypes in a Spanish Pyrenean population: Val d'Aran

Four hundred and thirteen unrelated individuals (202 autochthonous and 211 non-autochthonous) of Val d'Aran (Catalan Pyrenees) have been analysed for the GM and KM immunoglobulin genetic system using the inhibition haemagglutination method. This population was defined by eight GM haplotypes (GM*3 23 5*, GM*3 5*, GM*1,17 21,28, GM*1,2,17 21,28, GM*1,17 5*, GM*1,17 5,6,11,24, GM*1,17 10,11,13,15 and GM*1,17 10,11,13,15,16) inferred from the 17 observed phenotypes. The Val d'Aran population frequencies conform to Hardy-Weinberg expectations. The frequencies of phenotypes and haplotypes show a definite homogeneity between the autochthonous and non-autochthonous people of Val d'Aran and 11 other Pyrenean populations (Mauléon, Macaye, St. Jean Pied de Port, Vallée de L'Ouzom, Gavarnie, Barèges, Luz St. Sauveur, Esparros, Camurac, Capcir and Pays de Sault) that have already been studied for the same allotypes. A factorial correspondence analysis was performed for the 12 autochthonous Pyrenean populations, showing a high frequency of the GM*3 23 5* haplotype in the three Pyrenean regions (Western, Central and Eastern), while the GM*1,17 21,28 haplotype is mainly found in the Central region, GM*3 5* in the Eastern and Western zones, and the GM*1,2,17 21,28 is mainly present in the Central and Eastern populations. The results show a relative regional homogeneity, so there is no evidence of a frequency gradient in the Pyrenean populations for the GM and KM genetic systems. It may, however, be noticed that the Central Pyrenean populations form a group, with one population (Vallée de l'Ouzom) isolated from the rest, probably because of its particular model of inheritance by which the heritage is passed to the first born without sex consideration. It has been possible to point out some differences in the genetic structure of the autochthonous and non-autochthonous Val d'Aran population and to place the autochthonous Aranese group among its Pyrenean neighbours.     

BL-S786, a new parenteral cephalosporin. II. In vitro antimicrobial activity comparison with six related cephalosporins

BL-S786 was compared by in vitro studies with 6 other parenteral cephalosporins (cefamandole, cefazolin, cefoxitin, cephaloridine, cephalothin and cephradine). The following parameters were assessed: Comparative MICs against a wide variety of bacterial isolates, MIC/MBC comparisons and the effect of inoculum size on the MIC. BL-S786 showed the greatest antimicrobial activity against K. pneumoniae, C. diversus and Salmonella species; was equal to cefamandole against E. coli, E. agglomerans and P. mirabilis; and was second to cefamandole against Shigella, E. tarda, C. freundii, E. cloacae, E. aerogenes and the pathogenic Neisseriae. Essentially no activity against Serratia and Pseudomonas species was observed. Compared to the other cephalosporins tested BL-S786 showed poor activity against staphylococci and streptococci. For most species tested, the MBC of the various cephalosporins was the same or within one dilution of their respective MICs. However, for Enterobacter and indole-positive Proteus species, the MBC of BL-S786 and cefamandole was usually larger than or equal to 8-fold higher than the MICs. Cefoxitin, on the other hand, showed little MIC/MBC variations against indole-positive Proteus species. Inoculum size had only a small effect on the MICs against most gram-negative species--in some instances greater than 64-fold increases in MIC resulted by increasing inoculum size from 10(5) to 10(7) organisms per ml.     

Reduction of myocardial infarct size in vivo by carbohydrate-based glycomimetics

One of the foremost mechanisms involved in the pathogenesis of myocardial reperfusion injury is the adhesion of neutrophils within the myocardium. The initial neutrophil-endothelial cell interactions are mediated by the selectin family of adhesion molecules. Blockade of this group of adhesion molecules, through the use of synthetic carbohydrate analogs to the selectin ligand sialyl Lewisx and glycomimetics, has been beneficial in reducing neutrophil influx and infarct size. In the present study, glycyrrhizin (GM1292), a natural structural glycomimetic, was analyzed for the ability to decrease myocardial infarct size after regional myocardial ischemia/reperfusion. To determine the structural requirements for optimal cardioprotective activity, two additional compounds related to glycyrrhizin, GM3290 and GM1658 (glycyrrhetinic acid), were studied. The molecular structures of the latter two compounds differ in the number of glucuronic acid residues in their respective molecules. Open-chest, anesthetized rabbits were subjected to 30 min occlusion of the left coronary artery followed by 5 hr of reperfusion. Vehicle or glycomimetic (10 mg/kg/hr) was administered intravenously immediately before the onset of reperfusion and every hour during the reperfusion period. Myocardial infarct size in rabbits treated with GM1292 (two glucuronic acid residues) and GM3290 (one glucuronic acid residue) was reduced significantly when compared with vehicle-treated animals (P < .05). GM1658, which lacks glucuronic acid residues, did not provide a protective effect in vivo. The data suggest that GM1292 and GM3290, which contain carbohydrate moieties, are effective in reducing the degree of myocardial injury after an acute period of ischemia/reperfusion.     

The clinical relevance of static disease (no change) category for 6 months on endocrine therapy in patients with breast cancer

This study reports on the clinical relevance of the static disease (SD) category in 255 breast cancer patients on endocrine therapy. All patients had received first- and second-line endocrine therapy and were assessed for response by the International Union Against Cancer (UICC) criteria. We did not include patients who received first-line endocrine therapy but did not or have not yet proceeded to second-line hormone therapy, e.g. died from rapidly progressive disease, started chemotherapy for rapidly progressive disease, remained in long-term remission on first-line endocrine therapy. We analysed survival from initiation of first-line endocrine therapy by the remission criteria, i.e. complete response (CR), partial response (PR), static disease (SD) or progressive disease (PD), achieved on that therapy. Patients were divided into those with metastatic breast cancer (MBC) and non-metastatic disease. There was no significant difference in survival from starting first-line endocrine therapy between patients who obtained CR, PR or SD: all three groups of patients survived significantly longer than patients who showed PD within 6 months (all P < 0.0001 except CR versus PD [MBC] which was P < 0.002). Equally, for second-line endocrine therapy there was no difference in survival between patients who obtained CR, PR or SD: all three groups (CR, PR and SD) survived significantly longer than PD (all P < 0.0003 except for CR versus PD which was P < 0.003 for non-metastatic and P < 0.059 for MBC). Durable SD appears to be a clinically useful criteria of therapeutic remission.