Stonebox Vs Curved Hood & Spoon ??
Dear Mr. Siddharth,
Rockbox use has been practiced for many years as you rightly suggest wearing hard and sharp stone-on-stone. Then the Queensland Port Authority experimented with washed coal using a version of the modern hood and spoon to improve ore flow control, load station spillage, and dust control. Tasman Warajay ( http://www.flexco.com/tw-transfer-chutes.html ). You must read beyond the Flexco sales hype of their technical superiority. Tje Queensland experiments lead others to investigate and capitalize on this concept.
Conveyor Dynamics, Inc. (CDI) designed and applied the first curved spoon, for hard rock in 1994-1995 at the Palarbora open pit copper mine. The chute was designed to overcome the 3 year belt wear life on a 16 degree incline belt, transporting 6500 t/h of primary crushed copper (-300 mm x 0) operating at 4.1 m/s. The curved spoon increased the 1800 mm (ST-6600 N/mm) belt life from 3 years ( 18 mm top cover) to roughly 24 years ( estimated to be closer to 30 years from site wear measurements). The spoon initial cost was close to $50,000 for the white iron liner castings. The belt replacement cost was over 2.5 million USD. About half the liners were replaced every 35-50 million tons or about every 1.5 years of service for half liner replacement.
Based on this measure of belt life increase by 8 times, in rough terms, means more than $20 million belt savings in 20 years vs. liner costs of $500,000 over the same periond, excluding time to replace each and loss of production. The savings may be ~$20 million over 20 years or roughly $1 million USD per year not including NPV.
In addition, belt cleaning was improved by eliminating belt cover surface damage, reducing maintenance and improving safety. Spillage of ore exiting the skirts was dramatically reduced, especially large rock tumbling off the belt. Rock was centralized and locked against backward rotation, impact idler damage was almost eliminated, skirtboard damage and spittle fly rock was highly improved, noise and dust were much improved. The belt survived over the last 8 years with neglible wear (< 3 mm of 18 mm belt cover rubber) before the in-pit crusher & conveyor operation was terminate.
Palabora realized the biggest savings, from the curved spoon, in eliminating belt punctures and the risk of a large belt rip. The original belt had many hundreds of punctures from shovel teeth, drill rods, crusher liner damage, and from rock entrapment at the tail pulley from rocks bouncing over the tail scraper/plow.
Now many hard rock installation have used this model. Some hard rock installations do not apply pen-to-paper that acknowledge the ROI, I believe this is mainly due to the Consultant not being equipped to analyze the benefits. We see these benefits from using modern Discrete Element Modeling (DEM) such as with ROCKY:
http://www.conveyor-dynamics.com/rocky.htm ■
Re: Stone Boxes Vs Chute Liners
Hello Shri Joglekar Siddharth,
Stone box is shelf type plate in chute where accumulated material itself provide flow surface to material stream. This reduces the wear of chute plate in this zone.
Keeping actual stone pieces in shelf is hazardous as same may go along with material at some time, as foreign body in material, which will be seriously objectionable.
Shelf (or if you name stone box), retards the material and helps to prevent excessive speed of material, while landing in / on equipment (conveyor, crusher, screen, etc.).
The shelf (stone box) is sometime part of chute to achieve desired flow velocity (projected value) in chute, particularly vertical chute of more height.
Regards,
Ishwar G Mulani.
Author of Book : Engineering Science and Application Design for Belt Conveyors.
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: parimul@pn2.vsnl.net.in ■
Wear Boxes
There are various reasons why ‘stone boxes’, variously called ‘rock boxes’ and ‘wear boxes’, are not used every time instead of plain chutes or liner plates. The main reason is that plain chutes are quite adequate for many applications and, with hard wearing liner plates if needed, are simple to construct and take up less headroom than when friction losses on the rough surface of a ‘wear box’ demand a steeper inclination to guarantee flow. ‘Wear boxes’ are also useful at changes of direction in a chute handling abrasive product and receiving a free fall flow stream, to avoid high wear due to impact. They normally comprise a pocket that fills with the material being handled, so that later flow impinges on a bed of like material and is deflected without wearing the main chute material. A succession of ledges in a straight chute can similarly protect the base of the chute from direct contact with sliding material but, as indicated, the slope must be steep enough to allow the flow to pass and there is also likely to be a degree of attrition from the dynamic shear taking place.
A balanced assessment is therefore necessary, to decide whether the extra fabrication cost and space is justified against the potential wear effects and maintenance costs. ■
Re: Stone Boxes Vs Chute Liners
Dear Mr.Joglekar Siddharth,
If different types of materials are handled in a same conveyor stream, a very slight mixing of materials is possible every time. If this is not causing any worry to the end users or customers, there should be no problem of having stone boxes. A well constructed stone boxes can avoid material clogging, eliminate chute damages and improve belt's life.
Regards, ■
Re: Stone Boxes Vs Chute Liners
Hello Mr. Siddharth Joglekar,
Following is some more information about stone box:
1) This is not used for material like coal. They say it is prone to create spontaneous fire of the coal, due to repetitive impact energy being dissipated in the material lying on shelf / stone box. This is practice in all power stations in India, and it is likey to have relevance to the practice in Europe, etc. It can also not be used for material like Sulphur.
2) This is also not used for material like grain or food items where material lying here for a longer time will be objectionable (will rot).
3) If the conveyor is handling different type of material like iron ore, coal, etc. then the prudence is to avoid it for reason of contamination.
Regards,
Ishwar G Mulani.
Author of Book : Engineering Science and Application Design for Belt Conveyors.
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: parimul@pn2.vsnl.net.in ■
Stone Boxes vs Chute Liners
I have read about stone boxes which are placed at a particular region of a chute which is prone to excessive wear. once the lining gets damaged the material instead of hitting the walls of the chute enters a stone box which as the name suggests is filled with stones, once material fills the stone box entirely, the stone box acts as a self protecting lining and material falls on to the conveyor. I'd like to know under what circumstances do we use a stone box. why cant we use stone boxes at every chute? ■