几种典型机床调整垫铁的接触刚度

机床床身的静刚度是由结构刚度和接触刚度组成的。从总体设计观点来看,可以利用机床基础和垫铁刚度,使床身—垫铁—基础三者共同作用,有效地改善床身的刚度。实践证明,在基础具有一定刚度的条件下,增加基础与垫铁、垫铁与床身之间的接触刚度,可成倍地提高床身的刚度。而接触刚度是通过垫铁、地脚螺栓将基础和床身连在一起实现的。因为垫铁是支承机床重量、工件重量和切削力的重要部件,在外力作     

重型精密机床床身安装与调整时的刚度问题

床身是重型精密机床的主要基础件。床身导轨是其它部件的测量基准。因此,正确、合理地安装与调整床身,刘提高重型精密机床的刚度,保证精度及其稳定性具有决定性作用。机床刚度包括:动刚度、静刚度(综合刚度)、热刚度。一般认为,机床的刚度主要决定于设计与制造部门,而对安装与调整对刚度产生的影响则认识不足,往往因此严重地影响机床的精度及其稳定性。     

大型机床横梁的变形及修复方法

横梁、立柱、工作台、床身、顶梁是组成大型龙门式机床的五大件,它们构成了机床的基础和骨架。机床的其它部件,在这些大件的导轨上移置和滑动(除顶梁外)。机床的工作精度,在很大程度上取决于这些大件的精度和刚度。龙门式机床——龙门刨床、龙门铣床、龙门磨床、龙门座标镗床等的横梁部件,由于:1.它在工作时承受复杂的空间载荷;2.结构和尺寸的限制,如跨度大等,使它的静刚度和动刚度均不理想;3.横梁导轨在经常使用的部位,由于刀架(或铣头)的重量和切削时扭转力矩的作用,使某些导轨面局部磨损。因而在制造时采取了必要的工艺措施,使某些导轨面具有精度储备量,相应地进行恢复或提高精度的大修时,也必须全面考虑这些问题。要为每台机床制定正确的修复工艺,尽量保证在修复过程中不至于返工。     

高压水泵的故障诊断与处理

分析锅炉给水泵机组振动超标的故障现象，应用频谱分析技术和动刚度理论，对泵轴瓦振动过大的和电机基础共振问题进行诊断，确定故障部位，做到有针对性检修、消除故障，解决了给水泵机组长期存在的问题。     

用“生产法”测定机床和部件的刚度

用“生产法”测定机床及其部件的刚度所根据的原理是误差复映规律,由于现行的误差复映系数的定义不确切,因而由此得出的测定结果也不确切。本文在对误差复映系数和机床精化系数进行了分析后,提出了准确测定机床及其部件刚度的“生产法”。     

机床的振动及防治

为了提高机床的整体运作效率,需要对机床振动问题进行控制。针对机床的振动及防治进行分析,提出相应优化措施。     

国外机床滚动轴承主轴组的发展近况

机床主轴组的刚性和转速对机床的加工性能和生产率有决定性影响。一般说来,机床主轴的刚性越好,转速越高,则机床的生产率也越高。为了提高机床主轴组的刚性,世界各国进行了大量的研究工作,总的趋势是向着高刚度高转速方向发展。液体静压轴承正是为满足这一要求研制和发展起来的。液体静压轴承具有良好的阻尼特性,如果设计合理、制造精良,可以获得很高的支承刚度、良好的轴心运动轨迹、很广的转速范围、较长的使用寿命,从而提高机床的加工能力和加工精度。无论是对新机床产品的设计制造或老旧设备的改造,液体静压轴承都受到了应有的重视,显示出一定的优越性;但是,任何事物总是一分为二的,按照目前的技术水平,液体静压轴承要求有外加供油系统,这不仅增加了制造或改造的     

直齿圆柱齿轮振动模型的建立

本文建立了直齿轮传动的振动方程,方程中考虑了轮齿啮合刚度的周期变化和啮合当量综合误差,并对轮齿啮合刚度和啮合当量误差进行了数学上的处理,使振动方程既不失一般性又得到了简化。按此方程对直齿轮传动的振动进行分析和计算,其结果可靠。     

75MW汽轮发电机组轴向振动分析

对一台75MW汽轮机组出现的异常轴向振动进行了测试并深入分析,指出轴承座刚度不足是引起轴向振动的主要原因,通过轴承座加固等方法解决了机组振动故障。     

多级立式离心泵振动高问题解决方法及应用

某核电站一期2台1000 MW机组共有4台ACO低加疏水泵。自工程安装调试以来，该电站1#、2#机组ACO电机非驱动端均存在振动高的问题。通过对泵组支架刚度、转子质量不平衡、泵组水泥基础、振动频谱等的分析，确认振动高根本原因为泵支架刚度不足。经项目组分析调研，最终的处理方案为轻型电机及配套电机支架。更换后泵组振动明显降低，振动数值达到卓越水平，成功解决了ACO泵组振动高的问题，保障机组的安全稳定运行。     

企业核心能力的刚性特征及其超越

自“核心能力”被提出以来，该概念仿佛成了企业的“万能金钥”。然而，我们却不能忽视这一事实，核心能力容易走向其反面，形成刚性。核心能力刚性抑制了企业创新，严重削弱了企业创新的能力。本文首先提出了核心能力刚性的定义，然后分析了核心能力刚性的载体，进而对核心能力刚性的本质即路径依赖现象从三个角度进行了阐述，最后讨论了核心能力刚性特征的克服。     

Positional rigidity: low performance and resource acquisition in large and small firms

Past research has given contradictory answers to the question of how strategic change is linked to firm size and performance. This paper resolves the contradictory predictions of performance feedback theory and threat rigidity theory by positing that small and large firms have distinct responses to performance because of differences in risk aversion and internal rigidity. To examine these differences, it is necessary to distinguish risk taking from rigidity in the strategic position, which is accomplished by separate analysis of the amount of resource acquisition and the difference of acquired and existing resources. Analysis of data from the shipping industry supports the predicted interactions of firm size and performance. Copyright © 2010 John Wiley & Sons, Ltd.     

Diversification,coordination costs,and organizational rigidity: evidence from microdata

This paper examines the impact of coordination costs and organizational rigidity on the returns to diversification. The central thesis is that coordination costs offset economies of scope, while organizational rigidity increases coordination costs, further constraining economies of scope. The empirical tests of this proposition identify the effects of coordination and organizational rigidity costs on business unit and firm productivity, using novel data from the Economic Census on taxicab and limousine firms. The key results show that coordination and organizational rigidity costs are economically and statistically significant, while organizational rigidity itself accounts for a 16 percent decrease in paid ride‐miles per taxicab in incumbent diversifiers, controlling for the other costs and benefits of diversification and incumbency. The findings suggest that coordination costs, in general, and organizational rigidity costs, in particular, limit the scope of the firm. Copyright © 2010 John Wiley & Sons, Ltd.     

Durability Versus Concentration as an Explanation for Price Inflexibility

We document the extent of price rigidity across United States manufacturing industries in the 1980s and early 1990s and compare rigidity across different phases of the business cycle. We measure price rigidity in three ways – each under four different sets of assumptions. We take an approach that relies on disaggregated data; we look at price patterns for over 4000 individual manufactured commodities. Both durability and seller concentration are found to be important factors explaining differences in price rigidity across industrial product classes. Using our data, we replicate the regression results found in Carlton (1986) that were based on actual transaction prices from the 1960s.     

开式压力机刚度多目标优化设计

本文采用 Powell 直接搜索法和序列无约束极小化技术(SUMT),对开式压力机的刚度进行了多目标优化设计,所得结果表明,采用本文介绍的优化方法对提高开式压力机的精度效果明显。     

通用平面连杆机构动态模拟软件的研究

介绍了一种用C语言编制通用平面连杆机构动态模拟软件的方法。它以杆组概念为基础,具有广泛的通用性,使用者只需按菜单提示在键盘上选用各类杆组搭接机构即可,随后的运动分析及动态模拟主程序便可自动生成。     

车床床身刚度的有限元法计算

本文介绍采用有限元法计算车床床身的静刚度。该计算是在 M—160大型计算机上用 SAP—V 程序进行的。本文给出的计算结果即变形图可作为车床床身结构设计方案比较之用。     

Are prices ‘sticky’ online? Market structure effects and asymmetric responses to cost shocks in online mortgage markets

We analyze daily mortgage rates posted by online lenders at the price comparison site, Microsurf. While cost shocks occurred almost daily in our sample, quoted mortgage rates are surprisingly rigid: Only 16% of the posted rates represent changes. However, firms that adjusted rates in response to cost shocks did so quite rapidly; about 98% of a cost shock was passed through within 2 days of the cost shock. Duration analysis reveals that the observed rigidity in rates systematically depends on market structure: Online mortgage rates are 30% to 40% more durable in concentrated markets than in markets where there are many competitors. We also find that rates posted online tend to exhibit downward stickiness; rate adjustments in response to cost increases are about twice the corresponding adjustments for cost decreases.     

集总方法及其在蒸汽热裂解动力学模型中的应用

复杂反应体系集总动力学方法在石油炼制过程中已得到广泛应用,介绍了集总方法在催化裂化、催化重整和催化裂解复杂反应体系中的应用,并结合建立大庆重质原料蒸汽热裂解集总动力学模型的经验,提出了用集总方法建立复杂反应体系动力学模型具体方法的几点经验和建议。     

环氧树脂E-20/甲醇醚化氨基树脂体系固化反应动力学

本文利用差示扫描量热法（DSC）研究了不同升温速率下环氧树脂E-20/甲醇醚化氨基树脂（MEAR）体系固化反应动力学;采用Kissinger、Ozawa法计算得出体系固化表观活化能分别为35.67kJ/mol、40.27kJ/mol;用Crane公式求出反应级数为0.95,表观频率因子为1.12×10^4s^-1。根据固化反应产物红外光谱分析了反应机理,在200℃以下,烷氧基甲基（=NCH2OCH3）与环氧基团反应是主反应,烷氧基甲基基本不与羟基（-OH）反应。