Impact Resistance of Materials for Guards on Cutting Machine Tools—Requirements in Future European Safety Standards

Guards on machine tools are meant to protect operators from injuries caused by tools, workpieces, and fragments hurled out of the machine’s working zone. This article presents the impact resistance requirements, which guards according to European safety standards for machine tools must satisfy. Based upon these standards the impact resistance of different guard materials was determined using cylindrical steel projectiles. Polycarbonate proves to be a suitable material for vision panels because of its high energy absorption capacity. The impact resistance of 8-mm thick polycarbonate is roughly equal to that of a 3-mm thick steel sheet Fe P01. The limited ageing stability, however, makes it necessary to protect poycarbonate against cooling lubricants by means of additional panes on both sides.     

Evaluation and Optimization of Handle Design Parameters of a Grass Trimming Machine

The grass trimming machine is a widely used agricultural machine for cutting grass by the roadside and in other areas in Malaysia. Hand-arm vibration (HAV) syndrome is very common among workers operating power tools and performing similar work for extended periods. Grass trimming involves the use of a motorized cutter spinning at high speed, resulting in high levels of HAV among its operators. The existing D-shape handle causes HAV-related stress and operational load in operators. This research proposes a new design of a handle of the grass trimming machine. When this new design was compared with the old one, it was found that the new handle resulted in 18% lower HAV. To find the lowest HAV, 3 critical parameters of the new handle (length, angle and material of the cap of the handle) were optimized using the Taguchi quality tool. Appropriately selected parameters of the new handle significantly reduced the occurrence of HAV among grass trimmers.     

Safety of stationary grinding machines – impact resistance of work zone enclosures

Guards on machine tools are intended to protect persons from being injured by parts ejected with high kinetic energy from the work zone of the machine. Stationary grinding machines are a typical example. Generally such machines are provided with abrasive product guards closely enveloping the grinding wheel. However, many machining tasks do not allow the use of abrasive product guards. In such cases, the work zone enclosure has to be dimensioned so that, in case of failure, grinding wheel fragments remain inside the machine’s working zone. To obtain data for the dimensioning of work zone enclosures on stationary grinding machines, which must be operated without an abrasive product guard, burst tests were conducted with vitrified grinding wheels. The studies show that, contrary to widely held opinion, narrower grinding wheels can be more critical concerning the impact resistance than wider wheels although their fragment energy is smaller.     

信息技术与高职英语教学整合应用探析

把信息技术融入高职英语教学已经成为高职院校英语教学的普遍现象。从高职英语教学现状分析入手,结合学习的联结理论和建构主义理论,论述了信息技术是高职英语教学改革的必然性。详细分析了信息技术在高职英语教学中具有的显著特点和优势,以及信息技术与高职英语教学的整合模式,即情景教学模式、学生主体模式和交互学习模式。在此基础上分别从教师、学生两个角度深入探讨了在英语教学中应用信息技术应该注意的一些问题。通过这些深入的探讨应该看到随着更先进的信息技术引入教育领域,高职英语课堂将更具有吸引力,教师的教学空间将更加开放和富有创意,学生的自主学习将更加宽广和富有弹性。     

Local Sustainability Indicators

Local Environment has established a bit of a niche in local sustainability indicator studies. In 1997 it published the important debate between Jeb Brugman and Graham Pinfield, which highlighted that sustainability indicators and their role are contested issues (Vol. 2, Nos 1-3). In 1999 it produce a first special issue on the topic (Vol. 4, No. 2). As the editors identified, this special issue probed ‘deeper into aspects of indicator selection, methodology, theory and practice’. The papers presented there began to discuss a theme that is developed further in this special issue, that of the relationship between the objective and the subjective in indicator development and use. Our special issue brings together three full papers and a commentary presenting research and information from the USA, Sweden, France and Austria. In this editorial we are going to review the growth of interest in sustainability indicators and the changing way in which they are viewed and briefly comment on some recent indicator projects that we have been involved in.     

The importance of experience in the interpretation of conspecific chemical signals

Foraging bumblebees scent mark flowers with hydrocarbon secretions. Several studies have found these scent marks act as a repellent to bee foragers. This was thought to minimize the risk of visiting recently depleted flowers. Some studies, however, have found a reverse, attractive effect of scent marks left on flowers. Do bees mark flowers with different scents, or could the same scent be interpreted differently depending on the bees’ previous experience with reward levels in flowers? We use a simple experimental design to investigate if the scent marks can become attractive when bees forage on artificial flowers that remain rewarding upon the bees’ return after having depleted them. We contrast this with bees trained in the more natural scenario where revisits to recently emptied flowers are unrewarding. The bees’ association between scent mark and reward value was tested with flowers scent marked from the same source. We find that the bees’ experience with the level of reward determines how the scent mark is interpreted: the same scent can act as both an attractant and a repellent. How experience and learning influence the interpretation of the meaning of chemical signals deposited by animals for communication has rarely been investigated.     

提高材料利用率的有效途径

从运用数冲编程技巧、改进加工方案和改进结构设计三方面阐述了提高利用率的方法。     

数控机床的故障诊断

针对数控机床的故障特点，主要介绍了数控机床机械类故障和电气类故障的诊断程序和诊断方法。     

腈纶装置烘燥机自燃的原因及预防措施

分析了上海石化腈纶事业部金阳装置二步法纺丝后处理使用的第二烘燥机在高温高热状态下运行,设备内部经常发生自燃现象的原因和预防措施。