Cameron Portelli, Senior Mechanical Engineer, shares his expertise with Australian Bulk Handling Review.
Limitations to the parameters at which belt support failure occurs have been found experimentally in the past. Kinder Australia however, aims to predict a specification limit for its belt support systems to ensure that it will survive and push the boundaries in terms of belt speed and capacity.
A failure from insufficient support is unheard of within Kinder Australia. All of its “impact” rated systems have fully supported rails. Only the K-Sure Support uses a slider surface that is not fully supported. This system is not considered for severe impact loading, only as a slider surface for 1000TPH maximum systems and lump up to 50mm. However, there is much to be learned of how a dynamic system can reduce impact loads in the pursuit of belt preservation.
A dynamic belt support system consisting of UHMWPE slider rails supported by steel plate had measurement devices fitted to analyse friction heating and impact loading.
Temperature data showed a 7°C difference measured over 20mm, which was less than expected. Such friction heat losses may be attributed to convection from the sides of the slider rails, quite feasible given the slider width in the centre is made up of three segments, allowing for much surface area that can interact with some potentially turbulent air due to the moving conveyor belt.
A superior slider material has been observed in a Kinder installation since 2011. An increase in belt speed or capacity insists that it either use rollers in the centre (Combi system), use a slider material with better properties or a combination to reduce friction. This can also be necessary in slow moving feeder belt applications, where the pressure across the transfer is very high. To ensure there were no drive power issues or overheating of slider materials, Kinder Australia opted to use both a centre roller and proprietary K-Glideshield product at the wings as slider surfaces.
K-Glideshield is a unique composite engineered plastic that has far superior mechanical and thermal properties when compared to all grades of ultra high molecular weight polyethylene (UHMWPE) which lends itself to be the preferred and to date only suitable material for higher capacity and/or speed belt support applications.
|Dynamic friction coefficient
|Service Temperature °C
Table 1 – Slider material comparison data
From Table 1, comparisons between K-Glideshield and UHMWPE materials can easily be made:
- At least 25 per cent less friction induced heat will be produced due to the lower friction coefficient.
- Heat that is generated will be able to move through the entire section of K-Glideshield rail over 50 per cent faster.
- Any heat that must be stored by the K-Glideshield rail will be permitted due to the much greater service temperature.
Therefore, both belt speed and capacity of conveyor systems can be pushed much further if a system warrants a slider bed solution. Both lower friction heat will be generated and the slider materials capacity for temperature is greater.
Kinder Australia have collaborated with clients that wish to push boundaries installing belt support systems in ever greater belt speed and capacity conveyor systems. Case studies that exceed the allowable temperature of the slider material have given the company invaluable data which it can apply as limits for future systems. Calculations have shown the heat transfer properties of a slider system depends on the system being analysed, whether a conventional impact bar system, dynamic slider system, K-Sure Belt Support System, or a Combi system.
A maximum heat flux with unit ‘watts per square meter’ method is a practical shortcut to avoid numerical solutions for unknown properties such as convection heat transfer. We can also account for “reasonable” levels of allowable wear in the slider rail material using this method. This method omits the friction factor, to keep the limitation factor (p value) comparable across all materials, which allows us to impose limits for the different materials and system type combination.
Some interesting K-Sure Belt Support case studies arose when comparing this subset. This shows some successful case studies in green and failures that occurred in red.
Using the above data, Kinder Australia can accurately recommend a slider material or advise another heavier duty system.
While Kinder Australia have not experienced a structure failure, there are opportunities to decrease the impact forces to protect the belt. One such solution developed by Kinder Australia was the K-Shield Dynamax Impact Idler, the first of which was commissioned originally for belt protection then went on to increase the conveyor belt system uptime, requiring fewer unscheduled shutdowns to replace failed rollers and idler frames.
This site has seen shutdown cycles for belt replacement move from six to nine months out to 12 months. This minimum 30 per cent belt life improvement makes savings on a belt change that is reportedly a $250k exercise (as of 2019, likely much more now), not to mention the opportunity to allocate the labour elsewhere on site for shutdown works. With roller and idler frame sets lasting four to six weeks prior to the Dynamax Idler install, requiring unscheduled shutdowns of the conveyor for replacement, they are now having no such issues and able to complete multiple shut cycles before offering any preventative maintenance on these items.
Impact force measurements were taken from our K-Shield Dynamax Impact Cradle. We can observe the recorded data, as one load cell was used per spring (independent). It was also possible to observe the impact loading live on site via the control box.
With so much data taken over many weeks, it was necessary to seek data of interest. For Kinder this was the peak readings. On many occasions, it noted that higher force readings were recorded on the lead in and lead out torsion springs. Due to the six-spring layout, this leads Kinder to believe that under lump impact the trough panel is rotating about the centre springs.
As this was Kinder’s first attempt at data capture in a load zone application, further improvements will be made to the data collection system for another attempt at baseline data and subsequent belt support system installation. A summary of these improvements are:
- Ensure baseline data can be obtained accurately.
- Consider other load cell types and data capture that can produce higher frequency data collection to ensure peaks are accurately captured.
- Improve temperature capture to achieve more reliable data closer to the heat source.
- Installation to a harder/denser rock or ore carrying system.
Another case study pushed the innovation boundaries to further soften, control and allow adjustment of the spring configuration, as well as incorporate some other improvements from other belt support systems. Kinder’s client opted to incorporate a tapered chute on this troughed system. They realised the issue of skirting related wear to the belt and opted to spread this over a greater area. This further pushed Kinder Australia to come up with a completely bespoke system to ensure the dynamic section too followed the tapered shape of the chute.
- Combi design to remove a significant quantity of friction.
- Polyurethane isolation bushes incorporated to all impact loaded rollers.
- Pre-tension of one torsion spring to further dial in the dynamic system behaviour.
- Completely independent dynamic sections to ensure springs are less likely to work together producing a higher (harder) spring rate.
- Spring assembly is more open, making build up issues less likely.
- Lead in rollers ensures excessive pressure on slider rails will not occur.