MINE HOISTS
The safety brake is designed to deploy automatically in the event of a slack-rope or rope-break suspension failure . When such an event occurs , actuation and operation is performed by redundant mechanical systems , automatically arresting and holding the cage securely in place within the shaft . Suspension failure events generally cause no permanent damage to any of the Cage Guardian Safety Brake components , and the cage can then be retrieved and redeployed .
Built for control , longevity , reliability and low maintenance , the Cage Guardian™ Safety Brake is designed for use on conveyances running on tubular or top-hat-shaped steel guides and uses a self-contained brake path rather than relying on shaft guides for full braking performance . The Cage Guardian Safety Brake is an economic solution compared to multi-rope redundancy ( Blair multi-rope hoists with compensating sheaves or multi-rope Koepe hoists ), where multiple ropes are used to negate the requirement for a safety catch while operating on steel guides . Additionally , users can enjoy the security of proven equipment , because every brake is free-fall tested and certified before it is installed .
A new overwind protection system
Overwinding might become a serious issue , in case when all emergency systems have failures .
In the worst -case-scenario, heavy accidents would be the result if a loaded cage crashes into the shaft .
To avoid the worst case scenario , Germany based OLKO-Maschinentechnik GmbH recently developed and tested a new overwind protection system called Energy Absorption System ( EAS ). The conceptual idea was to invent a new system like a crash box - similar to an impact absorber in vehicle - which absorbs energy through the deformation of the crash box material . The system allows the mine operator to easily replace damaged parts of the overwind protection system and hence reduce shutdown times in the unlikely event of an accident caused by overwinding .
Early on , various materials , absorption processes and designs suitable for absorbers were tested . After analysing suitable geometrical designs of the crash structures and their absorption rates using force curves , extensive static and dynamic experiments were conducted in order to find the optimal material for the application . The experiments included foam , honeycomb and sheet structures as well as various metals , plastics and composite materials and many more . The result : composite materials showed very good linearity in terms of energy reduction and a high continuity in terms of the force progression .
All the results of the experiments were combined and a design concept was contrived . Stacked absorption plates should be destroyed using a plow , continuously absorbing the kinetic energy of the system .
In order to verify these results , gained on a small scale , a drop tower was designed . Using the drop tower , different combinations of drop mass , material thickness and plow width were investigated , while the drop height remained constant . After each test the low penetration depth into our material was measured und the specific energy absorption rates were calculated as well as the theoretical velocity at the point of impact . Additionally , v / t measurements were performed using special high-speed camera technology and coinciding accelerometers were used to validate the results .
OLKO ’ s Carsten Schmidt , Deputy Managing Director , told IM : “ The results of these experiments aligned closely with our expectations and theoretical calculation , mainly : linearity and low scatter of energy absorption and retardation ; plus optimised Specific Energy Absorption rate .” He says the patented EAS overwind protection system offers an alternative to established solutions offering several advantages - little weight of the system and absorption material , no limitations in regard to necessary energy absorption rates and shorter downtimes as damaged parts can easily and cheaply be replaced .
IM
AUGUST 2022 | International Mining 23