What is a GTU doing on a 24m conveyor? Kevlar belts were, once upon a time, used on stacker booms to reduce the SCREW take up travel and simplify the frequent splicing operations. If you use steel chord belts for 24m centres the life will be very short and the replacement time will be disproportionately long.

Without more insight into the proposed system I don't understand the effectiveness of a 'sacrificial' belt. Whether effective or not, it shouldn't be steel chord. Have further words with your designer. Maybe he can explain why the introduction of a short belt will increase the life of a long belt. The problem is clearly at one of the loading points. If you can load it properly 2nd time then you can load it properly 1st time. Or What?

If the multiplicity of belts is being used to accelerate material to a final speed the loading criterion is still the same.

"CEMA 6th edition recommends not exceeding 110% of the “critical maximum belt speed without causing material lift off”." Now there's something which I never paid attention to before. Recommending not to exceed 110% of the critical value rather nullifies the criticality: by definition. But don't worry, you're not the first to use a chocolate teapot. ■

Hello,

Inform whether you intend to use sacrificial belt conveyor for increasing speed or it is mainly for material of very aggressive lumps (relatively big lump, higher density, sharp edge). In first case, you can increase the speed by simple curved chute or belt conveyor. In second case, one small (of reasonable length) conveyor with thick belt covers will bear the impact due to non-ideal feed situation and then will load onto main conveyor more gently. For meaningful reply, mention the name of material, bulk density, belt velocity of the main conveyor and the main conveyor length.

Ishwar G. Mulani

Author of Book : Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book : Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Originally Posted by I G Mulani

Hello,

Inform whether you intend to use sacrificial belt conveyor for increasing speed or it is mainly for material of very aggressive lumps (relatively big lump, higher density, sharp edge). In first case, you can increase the speed by simple curved chute or belt conveyor. In second case, one small (of reasonable length) conveyor with thick belt covers will bear the impact due to non-ideal feed situation and then will load onto main conveyor more gently. For meaningful reply, mention the name of material, bulk density, belt velocity of the main conveyor and the main conveyor length.

Ishwar G. Mulani

Author of Book : Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book : Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com

Although a little late in posting a response, I offer a general comment on the use of "Sacrificial Belts" (SACBELT).

Many years ago engineers installed "A Sacrificial Belt" (SACBELT) to feed an overland belt conveyor (OLC). This was done for two basic reasons:

1. Allow inspection and removal of potential damaging trap metal/wood/et.al. where the SACBELT was fitted with metal detectors and magnetic removal equipment. Futhermore, human inspectors would study the slow-wide belt via platforms along side the short length and/or with cameras. This practice still continues on some installations. The term Sacrificial refers to both wear and puncture risk from sharp metal objects such as shovel teeth, drill bits, roof bolts and netting, support timber, et. al. Modern chute design is based on a geometry that does not allow the tramp metal to get sufficient leverage to puncture the belt or that limits/eliminates wear and dust behavior. These can all be quantified by modern Discrete Element Method (DEM) programs such as ROCKY.

2. Speed up the product delivered, to an intermediate speed, matching half the OLC, in the anticipation it would lower the OLC wear and facilitate reduced cover thickness. Today most engineers do not use this practice. It is far more efficient, less costly and more reliable to use the feed chute geometry to place material onto the OLC at its operating speed. DEM has changed the way engineers treat this later feature. DEM has proven very accurate when the engineer is gifted in its use and the DEM code has proven accurate in simulating particle mechanics behavior for the site specific properties and variances.

Unlike comments from some in this forum that target criticism of DEM, stating it is not accurate, we take great effort to promote the use of DEM as an accurate engineering tool to do just what the sacrifcial belt was originally designed for. We offer a challenge to the nay sayer, pick any chute you have experience with and claim DEM cannot do what you do with your special tool. We will publically submit a design that does the proper job and either will equal or better your special concept using our DEM code ROCKY. Either we will go down in flames or you will cease to continued objections of DEM that are found without merit. Of course you must be able to identify the specific material properties and offer field/lab observations that led you to corrective action, and design details of the chute(s) before and after your mods. All free of charge. ■

Hello,

Use of auxiliary or speed-up belt conveyor just to create more speed for feeding, is a second preference option.

Looking to such system, there is one original discharge equipment along with its floor (i.e. second floor), then there is speed up conveyor (short or not short) on its supporting floor / platform (i.e. first floor), and then there is main outgoing conveyor at ground floor. Considering minimum 2.15 m (7 feet) head room and minimum 0.25 m (10 inch) floor thickness; the height difference between original equipment and outgoing conveyor is (2.15 + 0.25 ) x 2 = 4.8 m.

The above height difference of 4.8 m (say net 3.8 m) can create any of the required velocity of discharge. For vertical free fall of 2.8 m, the velocity = Squareroot of (2 x 9.81 x 2.8) = 7.41 m/s. The last inclined leg having vertical height 1 m and sloping length say around 1.4 m can be utilized to create velocity in particular direction. The figures etc. are for explaining and not to be treated as a solution. The vertical chute along with radial curved chute will have better result. The designer can look into this option.

Serious misunderstanding is created by fictitious depiction of main conveyor, then auxiliary (sacrificial) conveyor just stacked above it, and then feeding equipment again stacked onto the auxiliary conveyor; disregarding supporting floors, material trajectory and resulting chute work at junction of these equipments. I have drawn the attention to this option. The point is that earth gravity is doing same job freely and with ‘never fail’ assurance, then why to have equipment (its price, running expense and maintenance liability).

Designer can opt for auxiliary belt conveyor if height below the feeding equipment is so critical that even 2.4 m saving matters. In this case, auxiliary (sacrificial) conveyor head end has to rise-up to discharge onto main conveyor. Designing of auxiliary conveyor (sacrificial conveyor), is part of the system engineering and conveyor design etc. is as per usual practice.

Subject caption is about steel cord belt for short conveyor but I have provided above information in context of the basic issue. Finally system arrangement depends upon the material lump size, bulk density and aggressiveness of lump. Long length cross country conveyor is rarely used to convey big size lumps (material is usually crushed to around 125 mm size prior to feeding cross country conveyor).

Note: My reply was formulated few hours back. So it may be repeating some of the points by earlier respondents in the meantime.

Ishwar G. Mulani

Author of Book : Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book : Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

This thread started as questioning the advantages a 24m long belt with a GTU. That was answered regarding perceived downtime alone and further replies have mentioned the use, or otherwise, of accelerating conveyors. Most importantly the thread admits that the loading needs improvement.

I personally see DEM as 'raising the bar' in many aspects of bulk handling although I have been given very short shift by the people in Edinburgh.

"DEM has proven very accurate when the engineer is gifted in its use..." Well yes: but therein lies a state of dependency. What happens in the newer generation and those engineers starting to familiarise themselves with DEM. What happened to 'user friendly'; 'plug and play' etc.?

For example, in the particular case of this thread I can appreciate that DEM will help to improve the loading situation considerably. However the actual wear rate of the belt seems as vague as ever and the uninitiated amongst us have to fall back on good transfer chute design, with or without DEM, and belt length and service guidelines, courtesy of belt manufacturers. I can accept that the material transfer is improved quantifiably, beyond recognition. I am just struggling with the quantification of belt wear after the muck hits the belt. No doubt the centuries of man-hours will pay off quite soon and I, for one, look forward to seeing the fruits of the work done by the learned colleagues. Perhaps the wear is already accurately predictable in its own right. Its just that if it is: it isn't publicised enough as it deserves. ■

Dear John:

I am at a lost to know what happened to a prior post to you on this. I hope it does not appear in the night.

DEM can predict wear on belts, chute liners, and a multitude of other materials. Like all material science endeavors, you need to calibrate the device of interest and materials to be used. Wear is not a simple scientici phenomenon. Tearing, gouging, shearing, abrading, and other rheologies need to be understood. In lieu of this approach we try phenonological methods - measure and quantify according to knowable features such as: time, force, temperature, strain, elasticity, plasticity, fatigue, yielding, according the individual materials et. al. For belts we have DIN, ASTM, .... abrasion tests and we have a multitude of belt types, and load station geometries, idler configurations, cover rubbers and rheologies, ore properties and rock shapes, chute geometires, rock velocity, angle of impact, etc.

Over time we have been able to assess the phenomological information and establish a reasonable picture of rubber damage for many installations. Furthermore, we are accurately able to compare various geometries to assess the differences in wear mechanics from simple abrasion and gouging actions on the rubber.

CDI has published a number of papers on field measurements and theory of wear. Other interested parties have also published in this area. Have you read any? Usually, the measurements and theory are in good agreement within the first magnitude or to better than 90% accurate. This can provide a magnitude or up to a quantum difference in wear life (i.e., 2 year vs. 20years), such as Palabora. We have watched the 10,000 t/h Los Pelambres copper ore operation with rockbox and curved spoon survive primary crushed (-300 mm) sharp rocks transfering at about 7 m/s. The multi-flight conveyor chutes went into service in late 1999. The belt lasted more than 13 years of wear service. This would roughly be 400-500 million tons. I know Kennecott Copper overland belts lasted about 250 million tons of similar primary crushed rock transfer on the two main belts. When the Palabora belt was retired, based on the curved spoon, it transfered about 200 million tons on a 1.1 km long belt, going up a 16 degree incline, at 4 m/s and still have most of its belt life left. These facts have been published. ■