Paul,

U should talk to TUNRA in Newcastle re getting your product tested for all size ranges and moisture contents > output to be advice on the bridging dims and wall angles...(for various wall linings).

With their advice, U can then ponder on how to deal with your problem.

U may wish to consider a few trials.

Adding an anti bridging shedder over the top of the hopper and crosswise to the bombay doors amy relieve the consolidation prssure in the material and help prevent the bridging that is being seen in the photo.

The fact that some of the hopper / wagin has discharged and some has not should be raising question as to why > what is different on the left hand side of your photo.....wagon construction or material.

To stop fines dribbling out...U will need to seal the doors better....overlapping lips.

Also, if U have bombay doors - do theyling open with a big bang and help dislodge the material??

Are the bombbay doors double acting ie hinged wall insert inside that changes the wall angle?

We transport limestone/clay in rail wagons...no probs. if the time in the wagon is not too long > avoid consolidations. TUNRA did the testing for our wagons.

Our sister plant transports finsihed cement in rail wagons with bottom discharge..some spillage but not much.

Cheers

James ■

Dear Mr. Paul,

It is not clear whether you have captive wagons for your needs or you are receiving various materials in national railway wagons, as decided by railway authorities in far off location (mine).

1) If you are having captive wagons for your needs, then there is possibility that you can have control on choice of wagons for particular grade of material. If so, you can think of providing UMHW polymer liners in outlet zone of wagons meant for iron ore fines. Such liners are good for flow improvement; but the same are not ideal for impact resistance.

2) If you are not having captive wagons then you will be receiving material in railway wagons arriving at mine from different location. In such situation, you will not be in a position to apply special liners at outlet zone. In this situation you can think of attaching vibrator on wagons which will improve the flow. Such device for imparting vibration to the wagons, is possibly manufactured by manufacture of wagon tipplers. You can contact such manufacturers for possible available device. Needless to say that the application of such device will be subject to the approval of the wagons owner (national railways i.e. general network serving the country).

In India I have not come across such problem, because mostly wagons for iron ores have been designed by Indian Railways to suit the material and these are mostly used by giant iron ore organisations in India.

Solution also depends on, whether the discharge is occurring when wagon is in slow motion or whether it is standstill.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Paul,

I suspect Tunra will tell you to introduce chamfers in the corners to reduce the arching stress in the corners and apply a UHMW.

The same can be said for the longitudinal abrupt change from vertical to shallow angle. By introducing a transition between similar to a radius, the arching stress is lowered in this region.

Certainly UHMW sheeting will help a great deal. Not all UHMW has the same abrasive properties. So, take care in this regard. Poly-Hi Solidur have a truck bed sheeting called Quicksilver that has, I susppect, excellent propoerties for this type of installation.

If the fall distance is significant, such that the plastic is gouged, then you might need to go to a bimetal. There are bi-metals that have similar friction properties to UHMW, however they are significantly more expensive. They will last many times UHMD.

If you need further assistance, give a call.

Lawrence Nordell

www.conveyor-dynamics.com ■

With Tunra, U will get answers to what data U tell them. If the moisture content, size dist. etc changes/varies, then they need to know this to get a ranging solution.

With plastics, we do not use but I understand that sealing the edges against material ingress appears to be the key - to stop bulging etc.

Our bombay doors have an internal flap which has a separate hinge located futher up the wagon....so, this flap acts as the real floor...when the outside doors close, the flap seals up in the middle. When the main doors opens, these flaps follow by gravity, material weight....due to the hinge being up further, the flaps form a better sloping floor for discharge. Sounds odd but that is the way there are.

We do have issues with buildup...this is created by the dust suppresion sprays during loading - the sprays wet the uncovered wagon walls and this can lead to build ups acc.

If U can not get the wagon to discharge naturally, then U will have to revert to forced means which is not preferred.

Cheers

James ■

Placement of chamfers in the vertical end corners, made of UHMW, may be sufficient to release the material at the ends. Try installing a 300 mm wide vertical sheet that increases the corner arching angle from 90 degrees to 135 degrees. This will require a reinforcing steel sheet behind the UHMW.

If the ends are sloped, the same chamfers should be continued down from the vertical corners along the sloped valley angles to the doors with UHMW.

Treating the corners may be all that is required. Placing UHMW along the end slopes will help in conjunction with the corner chamfers.

The edges James speaks of are also important. Rough edges allow an anchor for wet fines to cement to the walls. Try to minimize these rough corners when cutting, fitting, finishing, and/or fill them with a plastic on both vertical and horizontal edges.

Sealing the edges of the added liners will help prevent corrosion from setting in behind the liners in the reinforcing steel or rail car walls.

The whole process can be adequately modelled using DEM. Sensitivity to flow can be calibrated to you actual conditions. This is a more accurate approach than a theoretical treatment. It minimizes the redesign of the rail car and maximizes the net volume left for transport. However, Truna is a good institute. You will get good value in their skills.

Lawrence Nordell

www.conveyor-dynamics.com ■

Paul,

Our company has experience using applied vibration to aid in the discharge and flow of difficult materials from rail cars.

We offer the following points to consider:

1) It must be certain that the hopper section is completely discharging and flowing.

2) The take-away system must have the capacity to handle the material as it flows from the rail car.

3) Applied vibration from the Railside Car Shaker can reduce the materials cohesive strength and it's sliding friction from inside the rail car which will aid in breaking down rat holes and bridging. However, the hopper section must be clear and flowing properly.

4) As the rail cars are emptied and the rail car mass is reduced, the Railside Car Shaker offers better results for the reduction of material rat holes and bridging.

5) We have had success with rat holes, bridging and the discharging of "heels" (the material retained on the end plates) in rail cars.

The Railside Car Shaker offers the following advantages:

1) Permanently mounted next to track at the discharge location.

2) Precludes the need to enter the rail car to add liners. This is most important if the rail cars are non-captive.

3) Can definately speed up the unloading time of rail cars. However, if the material does not flow when the rail car doors are opened, there may be other challenges to address before the Railside Car Shaker can be applied.

Our experince has been with US rail cars. The smaller rail cars used in Europe and in Asia may respond better to the operation of the Railside Car Shaker.

Visit www.navco.org to see the Railside Car Shaker.

Sincerely,

Ross M. Jamison ■

Dear Paul

Recently we have carried out a project where we are discharging bottom discharge wagons for Lignite. Since Lignite also contains very high moisture (total about 30 %, surface moisture about 15 %), we are facing similar problems i.e. bridging of material in wagons.

I would suggest you for 2 actions, which has reduced our problems to great erxtent.

1) We have provided Polymer liners in the complete hopper. In one of the answer I see that some one have suggested you for these liners but lot of apprehensons are also mentioned. please note that these liners are excellent in reducing friction, they have good abrssion resistent and also they can bear impact without any problem.

2) Secondly we are emptying the wagon in 2 stages, one in normal course, then we close the bottom gates and then take other wagons for emptying, during the process of movement and jerks it takes, usually the bridging dislodges, and while returning, balance material from the wagon is cleared.

I hope the above may be of some help to you. In case you want to consult further, you may write direct mail to me at jpg@holtecnet.com

JPGupta ■

Paul,

I have done some significant study work on the dicharging of rail wagon for fine coals.

The short version of the issue relates to moisture levels, impact compaction of bottom layer and consolidation through vibration.

Given that the last issue is difficult to change, moisture levels and the way the wagons are loaded are the better solution trails.

If I can help you in any way, please don't hestiate to contact me on trevor.learey@anglocoal.com.au.

Regards,

Trevor. ■

Hello Paul,

Depending on how many cars you have to contend with, it may be practical to install UHMW polyethylene sheets (Solidur has a good line) and augment it with hopper vibrators (such as those produced by Martin Engineering). The vibrators will need to be plugged in for the unloading process.

Rail car vibrators, as already mentioned, are another option - but you mentioned that you have four different styles of cars, and this could present a problem.

Good luck with your project. ■

Paul,

Product moisture appears to be the cause of your discharging problems. Our company specialises in covering systems for rail wagons. Our systems range from simple manual systems to fully automated systems and all systems are easily attached to wagons with nil or minor modifcations. We protect a wide range of materials such as base minerals, woodchip, fertilizers, sugar, grainsl etc. Our systems can be readily applied to bottom discharge or tippler wagons. Our system provides complete elimination of moisture during transit, eliminates dust losses and significant fuel savings from enhanced wagon aerodynamics.

Please call me to discuss.

Regards

John Cruikshank

Ecofab Australasia

Ph: 61 7 3356 5826

jrc@ecofab.com ■

Worthwhile to trial vibrator before getting into a project ti install railside or similar vibrator.

Ideally the hopper cars will have pockets on the hopper walls already attached to slip vibrator head into - but probably not.

For a test, a vibrator can hang down against the wall - with support hooked over the car wall top.

Vibrators can be destructive to old corroded railcars

- observe - you may have to limit force & time to avoid damage.

Never leave running a long time - especially after the car is completely empty. ■

Paul,

The flow condition of iron ore fines is definitely dependent upon the moisture content. Your description of the leakage potential indicates that the material is loaded in a dry state, so weather is the culprit in changing its condition. The 'flowability' of the material will initially decrease as the powder gets wet but it will eventually attain a worst flow condition. Thereafter, additional moisture weakens the bulk until is becomes a weak paste and then a free running slurry in a super-saturated condition. The 'setting' or 'caking' that occurs when damp product dries out is a different, and usually a more serious, issue. This is caused by the formation of strong crystal bridges between the articles and the bulk strength can attain very high values the demands strong mechanical action to break up.

Presumably, rain covers are out of the question, although some bright spark may be able to construct a simple, tarpaulin roller-reefer that fits over the end wall at each end of the wagon.

However, addressing the discharge potential of poor flow material the design of liners and inserts demand a degree of technical expertise, particularly when the condition of the material is highly variable. 'Arches' and 'Ratholes' will not be overcome by lining the contact surfaces with low friction material unless the wall inclination is steep enough to make the material slip when it would not do otherwise, and even then they are not a guaranteed cure for initiating flow. The 'cliff' face shown in the photograph represents the unconfined face of a bed where the adjacent material has moved out. This is a different situation as the static product is resting on the sloping face of the end of the wagon, where it also presumably converges from the sides as well. Low friction liners on these sloping walls and gully plates that eliminate the sharp corners and slightly increase with effective angle should make a major improvement in this region for discharging the residual mass. Vibration or car shakers can aid discharge once the central region has cleared but its a brutal way compared with gravity flow, if this can be achieved.

TUNRA are exceptionally placed to advise on the gravity flow potential and measure the relevant bulk property values. Some information on inserts is available from tech@ajax.co.uk with ideas on flow geometry that may be appropriate.

Lyn Bates ■

Hello Paul,

Something different to consider.

Mikalen has a patented new side/bottom discharging container that has been designed for the transport of difficult to handle bulk material like mineral concentrate. The units are half-height boxes (1200mm high) and stackable with two compartments that discharge simultaneously to either side of the track. The "Tiltainer" as it is called has ISO standard dimensions so can be mounted on a container transport wagon. Operation of the hydraulic tipping mechanism causes the compartment to rotate about an upper central hinge so that the floor and back wall come into alignment at a tipping angle of about 50 degrees. Consolidated material at the bottom of the load is disturbed by the opening of the floor and promotes discharge. The internal surfaces can be made of s/s 3cr12 or lined with tivar, shakers can be applied and "music note" compressible seals keep the fines in. There would be a capital cost of about $40k per unit for these but they could be procured through a lease back arrangement like most other containers.

Should the idea sound interesting please email me at mikalen@bigpond.net.au for further details

Regards

John Hanna

Managing Director ■