VOL. 14 July ISSUE YEAR 2013
in Vol. 14 - July Issue - Year 2013
Finishing & Safety
A tumbling barrel: very low risks
A round-tub vibrator: low risk level
Complex centrifugal finishing systems: medium and comfortably controllable risk level
In recent years, the discussions and press releases about Security levels in construction and engineering have steadily grown. Regulations like the EU machinery directive 2006/42/EG are influencing the mechanical engineering branch more and more. It is not always easy to maintain a solid view on legal requirements concerning the safe construction and documentation of machines.
Older techniques of surface finishing like tumbling in drums and simple forms of mass vibratory finishing were established in the industries many decades ago. At first view, it seems simply clear that a drum or vibratory working bowl bear nearly no fundamental dangers for any user. Furthermore, that impression is strengthened by the fact that most people have never heard of a serious accident caused by a simple machine like a drum or a vibrator. Nevertheless, the situation today needs a closer look.
Modern production environments have changed. Automation and interlinked systems are becoming more and more important. When you combine a simple Vibrator with another machine, for example automatic loading and unloading systems, new risks are appearing at the user level. Some of the most important risks at this sector are the dangers of squeezing, pushing and pinching. These risks are typical for automatically released movements of machine parts.
Risks are much more numerous when you look at centrifugal finishing machines. Here, fully automatic batch treatment and the more complex modular designs of these machines are leading also to a more complex risk level situation. On the one hand, you have in most cases more risks as in vibratory finishing systems, on the other hand, these risks are often much more severe.
All manufacturers are obliged to make a risk analysis of their machines. Every kind of possible danger has to be spotted first and then it has to be evaluated in two dimensions. Probability of occurrence and the severity of the possible hazard are the two fundamental parameters to define the risk figure of each risk. The international EU norm EN1050 provides detailed instructions of how to build up a risk analysis.
Most people are astonished that a simple round-tub vibrator can also be a risky machine when it is not used as it should be. Incorrect transport measurements for example can bear a great risk, because a vibrator is a heavy machine. The unbalanced motor inside the machine is a risk when it is operated with an open engine cover. The quick rotation of the imbalance weights can cut off a human hand. Many more smaller and sometimes hidden risks like body vibration and extremely loud sound can be identified.
The most dangerous risks at centrifugal finishing systems are the pivoting movements of the storage hoppers, of working bowls, and of hydraulic feeding units. These movements have enormous kinetic energy and can threaten a human life. Though the motions are always relatively slow and easy to anticipate, an untrained or fully inattentive machine operator could be surprised by them and be squeezed between the components.
Different protective devices are used to prevent such accidents. Protective mats and cabins are examples for a machine stop or an access-prevention mechanism. Nevertheless, a door sensor and a protective mat can be bridged and so a great risk can reappear. Time and output pressure mislead people to ignore possible risks. Equipment that is more modern applies light sensors, which are deeply integrated into the machine’s PLC programming and security structure. The devices are combining highest programmable security features with absolute optical accessibility.
It is good that legal institutions are auditing companies to create more security awareness for employees and also for managers. And this is important for the side of the machine manufacturer and the applier of the technique as well. Both are responsible. The designer of the machine has to construct it safely, from the first design conception up to the last detail. The management has to accept higher costs for a better and longer construction process and a safer machine with higher quality standards, independent of market price calculations. The operator of a machine has to train his employees and should create a corporate culture where the manipulation of security features due to time and output pressure is not accepted as a legal means of avoidance.
Sometimes we should not complain about the current time trends with always more and new regulations. Some of them are really important and well thought out, based on bad experiences in the past, even when things have so far, gone quite well for many years. Technical innovation should always be accompanied by an evolution of security measures for ourselves. And that is not a new insight: "The prevention of accidents must not be regarded as a provision of the law, but as a dictate of human obligation and economic reason." – Werner von Siemens, 1880.
Good Vibrations by Mathieu Geuting, Spaleck Oberflächentechnik
GmbH & Co. KG, Germany