Uncontrolled release of energy is a major safety concern in any industry that utilises heavy machinery, mobile equipment and mechanical plant in the production cycle. Bringing to rest an uncontrolled moving object in a controlled manner is an engineering challenge that has both the potential to prevent catastrophic damage to equipment, and more importantly the potential to save lives.
The Technogrid Strain Energy Absorber is a novel solution to this problem, and was developed by Hamilton Stephenson and Gawie Mahne of Technogrid Pty Ltd.
Established in 1995, Technogrid Pty Ltd has been at the forefront of research and development for energy absorption devices. The solution was initially developed as a station stopper for loads on horizontal rails and was later developed to accommodate vertical applications such as shaft and inclined conveyances. Technogrid is represented in Australia through agent and distributor, Reliance Hexham, in NSW.
Technogrid is a ground-breaking invention that controls dangerous impacts by absorbing potential energy to allow the safe deceleration of large masses in a predictable and controlled manner, before damage to equipment, structures or people occurs. The energy is absorbed through the deformation of a metal grid of known design and characteristics through controlled stroke deformation.
Essentially, the Technogrids act as a controlled and purely mechanical crumple zone for any major impact. It is the last line of defense in a potentially catastrophic event where electronic safeguards fail to activate.
Technogrid comprises a series of multi-bar units connected in a staggered grid shape in such a way that an impact will cause the grid bars to yield and deform under a process of double curvature bending, undergoing a strain hardening that absorbs the impact energy. It is the yielding of the bars that allows the unit to open up and undergo stroke, with the strain hardening of the material absorbing impact energies in the order of 5000kJ all the way up to 40,000kJ. The impact energy is thus absorbed by the device instead of the surrounding structures or equipment.
Technogrid provides predictable outcomes because of the consistent relationship between energy absorbed, stroke and reaction force. The absence of moving parts results in a low maintenance requirement that amounts to a simple visual inspection.
The product is used in various industries world-wide, is highly customisable and has been adapted to suit a large variety of applications – to arrest track-bound equipment, or runaway protection for large equipment such as ship loaders or stacker/reclaimers, to arrest falling counterweights used on conveyors, arresting the energy of a bin or silo collapse, for cage and skip headframe overwind and shaft bottom underwind arresting, and as jack catch arresting.
Technogrid systems are single use only, and so after each full impact are replaced with new units ready for the next impact.
Counterweight Arresting in Conveyor Systems
Every bulk haulage conveyor utilises a hanging counterweight to maintain tension on the belt. In the event of belt or tension cable failure, the counterweight can fall creating a dangerous situation and potentially causing damage and long down times. The Technogrid counterweight arresting system can arrest a falling counterweight before the surrounding structure can be damaged.
Mine Shaft Overwind Arresting
Two of the major hazards associated with mine shaft operations are overwind and underwind, whereby the skip, cage or man carrier is allowed to be wound past the designated stop point due to some failure in the control and/or stopping/breaking mechanism. Without an arrestor system, the load continues upwards or downwards along the line of the shaft, which can result in the load being pulled into the head frame, the winding gear or the conveyance dropped to the bottom of the shaft, causing catastrophic damage and placing operator lives in danger.
To safeguard against this, Technogrids are installed in suitable positions inside the shaft with a light catch-frame where the conveyance can impact. In the event of an overwind, the catch-frame activates the Technogrid unit, which is pulled through a controlled stroke, absorbing the energy and bringing the conveyance to a stand-still. The stand still then causes the winding engine to trip out and cease winding.
Tailor-made Solutions
Since the relationships between material, stroke length and stopping forces are known, the design can be completely tailored to the desired application.
Technogrid size and shape can be customized to fit most spaces and absorb any impact as long as the framework is designed to put the grids into tension. In shafts, the units are designed to sit inside the head frame on either side of the conveyance. Steel strings extending from the units are then connected by anchor points onto the shaft’s steelwork.
The tailored design also takes into account requirements for higher/lower deceleration rates as required by design or regulations. In Australia, design standards permit 1g of deceleration force for man carriers, and 2g for production hoists, with 1g in the head frame.
The Importance of Mechanical Energy Absorption Devices
One of the worst known incidents in recent history of uncontrolled kinetic energy was in 1995 in South Africa, whereby a runaway locomotive breached the shaft gates and plunged into the shaft, resulting in more than 100 fatalities.
Whilst it may be fair to assume these incidents are rare due to today’s sophisticated equipment and rigorous standards, they happen far more regularly than expected because sophisticated systems can also fail.
In 2009 at an Australian mine, a failure in the breaking mechanism caused a kibble to undergo freefall, dragging another kibble up into the head frame. This resulted in a reported $200m in associated damage costs and production loss.
Last month, there was reported three overwind incidents in South Africa alone. One particular incident involved a kibble which was overwound into the head frame, causing the ropes to snap. Once the ropes snapped, the kibble underwent freefall after the jack catchers failed to fully arrest the fall, resulting in three fatalities and one injury.
Several weeks later, a personnel-carrying conveyance with five people was overwound into the head frame at low speed causing the ropes to detach and allowing the cage to be restrained in the headframe. Luckily, the detaching hook engaged and prevented the conveyance from falling back down the shaft resulting in no injuries.
The third incident involved an overwind event in a shaft where the Technogrids are installed. The load came into contact with the Technogrid assembly at a speed of 4m/s, and the Technogrid successfully deployed. Upon inspection, it was observed that the Technogrid system had only used 10% of the available energy capacity, successfully preventing major damage to the winding equipment and shaft. The unit did not need to be immediately replaced as it had 90% remaining capacity and was still well within safe working limits, thus there were no significant resultant production lost costs due to downtime as the winding plant could continue to operate immediately regulatory clearance was issued. The replacement catch straps and Technogrid unit could then be procured with standard delivery periods and with significant cost savings as no manufacturing overtime was incurred.
International Reach
Technogrid systems are currently installed all over the world – Freeport (Grassberg) mine in Indonesia, Mosaic’s Pot Ash mines in Canada, Rio Tinto’s Oyu Tolgoi in Mongolia, as well as North America, South America, Africa and Australia.
In the past four months, Technogrid systems have successfully arrested counterweight freefall in four belt failure incidents in Namibia, South Africa, Canada and South America. Three custom systems are currently installed in Australian operations.
Quality Assurance and Testing
Technogrid Pty Ltd has engaged the CSIR (Council for Scientific and Industrial Research) to perform static tests whereby the Technogrids are pulled to destruction. Results are then provided to Technogrid Pty Ltd and verified against in-house testing and data.
More recently, a 6.5m dynamic drop test tower was commissioned in Cape Town, specifically to perform dynamic tests for an upcoming project in Australia. In a standard dynamic testing scenario, more than 1000 points of data are collected over 500 milliseconds to verify stroke diagrams and measure performance.
According to Technogrid Director and engineer, Hamilton Stephenson, the CSIR static tests are used “to ensure the product meets minimum requirements and in-house dynamic tests are used to further improve real-world performance”.
Other Safety Devices
Technogrid Pty Ltd is now established as one of the world leaders in energy absorption safety devices and has a variety of energy absorption devices on offer that utilise strain energy absorption and double curvature bending principles in their design.
The product offerings include Multiple Impact Buffers, Hydraulic Shock Absorbers for port cranes and overhead cranes, Cellular Buffers used on long travel and cross travel on overhead cranes, and adjustable rail fixing systems.
Moving Forward
Technogrid Pty Ltd is currently heavily invested in research and development.
“I have been in the energy absorption game since 1992, and Technogrid have been going for 22 years and we are still discovering and developing incredible new ways of absorbing energy. Hence the R&D program,” Hamilton said.
“Every single application is different. You might do four technical solutions in a week, and not one will ever be the same. One engineer may recommend a longer stroke, whereas another might recommend a little bit more energy capacity. It’s all a matter of optimising the solution to its application.”
Conclusion
As technology, systems and equipment have become more sophisticated over time, it is easy to forget that sometimes the simplest solution is the most effective.
As far as simple solutions go, it doesn’t get much more effective than the Technogrid: a purely mechanical bolt-on attachment with no-moving parts and no maintenance requirement other than that of a visual inspection. The Technogrid is the last line of defence against uncontrolled kinetic catastrophe – a global product with a myriad of applications that can minimise downtime costs and production losses, but most importantly, it can save lives.
More information:
Reliance Hexham
0413 648 502
www.reliancehexham.com.au
