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Sampling & Inspection

continuously weighing the material as it travels across a predetermined length of conveyor belt above the weigh carriage (weight per unit length). This is then combined with the measured belt speed to give the throughput weight per unit time (typically in units of tonnes per hour). Finally the integrated on-

going totalised weight is cal- culated. Throughput capa- bilities of such weighers typically range from less than 5t/h up to 12,000t/h. Belt weigher accuracy

depends on a number of fac- tors, including the number of rollers on the weigh car- riage, the weighing technol- ogy used and the uniformity of the material being weighed. Accuracies of better than

±0.5% can be achieved for free flowing materials. Moisture content measuring systems used in conjunction with the belt weighers can further improve accuracies. Belt weighers play an-

other important role at ports and terminals on giant mo- bile stacker/reclaimers. In

these applications, the weighers are fitted within the moving booms and therefore operate in one of the most arduous and hostile environments imaginable with little time for mainte- nance. Although the weighers

form a relatively small part of the giant equipment, their importance cannot be under- estimated. Any downtime is costly and very inconven- ient, and as a result, reliabil- ity is vitally important.

Resometric weighers

A high proportion of belt weighers use strain gauge load cells to support the weigh carriage and although these provide good service- ability, they can prove unre- liable over time in harsh out- door environments. To overcome this draw-

back, UK-based Procon En- gineering has continued to develop its unique Resometric belt weighers. These robust weighers have proved to be significantly more reliable than conven- tional load cell based units in arduous applications.

The units provide a

unique combination of fea- tures that ensure the key fac- tors influencing belt weigher performance are maintained in service over long periods of time. The digital force trans-

ducer has no moving parts and the resonator is pre- loaded to a standard level by the applied force from the weigh carriage. As the force varies with the load passing over the carriage rollers, the resonant frequency changes in proportion to applied load. This change in frequency

is processed by the electron- ics and combined with the belt travel speed to provide an accurate weight reading per unit time. Unlike fixed inclination

weighing applications, the belt weighers on the stacker/ reclaimers are subjected to constantly changing angles of operation. This would normally

introduce

significant cosine weighing errors due to the apparent change in the suspended weigh carriage mass. To automatically com-

Procon Engineering’s Resometric belt weighers can provide accurate results even when mounted on the tilting boom of a stacker/reclaimer

The PowderProof automated sampler from Bürkle with pneumatic drive

pensate for the changing an- gles of operation, the weigh- ers are fitted with Procon’s proprietary Astatic Mass Zero Compensation sys- tems.

Accurate calibration

Last year Siemens Industry Automation Division intro- duced a higher-capacity ver- sion of its Milltronics MWL Weight Lifter mechanical calibration system for belt scales within the Milltronics MSI, MMI, MBS, MCS and MUS product ranges. The compact calibration

system, which is now avail- able for heavier loads up to 340kg, mounts under the conveyor belt and stores the calibration test weights above the calibration arms of the belt scale. The user can easily lower the refer- ence weights manually with a crank handle and safely apply them to the belt scale, without having to lean into the conveyor or remove any protective guards. Adaptable to any applica-

tion, the maintenance-free, easily installed MWL cali- bration system is available for use with flat bar or inte- gral round bar style calibra- tion weights. Each weight and weight

WCN sub form (124x178) 15/1/09 08:00 Page 1

holder is stamped with its exact weight to avoid cali- bration errors. Combined with a Milltronics belt scale, speed sensor and integrator, the Milltronics MWL is able to provide very efficient calibration. This constantly ensures high accuracy and

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reliability of the belt scale system.

New range

Kersting GmbH, based in Brilon, Germany, specialis- ing in both manual and in- stalled samplers, has just in- troduced a new range of in- stalled powder samplers. This latest equipment, mar- keted under the SiloTasty and InlineTasty trade names, has been designed to meet the growing demand for ver- satile and low-cost sampling systems. The new Tasty series,

which is manufactured from food-grade materials such as 316 stainless steel and Teflon polymers, can be used with all free flowing powders as well as granules up to a particle size of 8- 10mm. A special welded flange

is supplied by Kersting with each sampler to allow the unit to be installed by the customer. All connections are based on the Triclamp system. These simple de- vices can be installed on silo cones, gravity chutes, down- pipes and on pneumatic con- veying pipelines. Sampling takes place

when the hand lever is en- gaged. Thanks to the Triclamp connectors these

samplers can be easily dis- assembled, allowing mainte- nance and cleaning to be car- ried out quickly and without tools. There is a choice of options for sample collec- tion including bag holder, endless liner system or cus- tomised bottle connector. A ball valve is available to en- sure reproducible samples of equal 0.4-litre quantities. The Inline Tasty for

pneumatic conveying appli- cations has been success- fully tested for operational pressures up to 5 barg.

Special development

Another leading German manufacturer of dry bulk samplers, Bürkle based in Bad Bellingen, has intro- duced a new drive assembly for its popular PowderProof automated sampler. This device, suitable for

use with both powders and granules, can now be used with a rechargeable battery drive as well as with a pneu- matic power source, which is very useful if there is availability of a compressed air connection at the sam- pling location. A further advantage of

compressed air operation is that it can be safely em- ployed in potentially explo- sive zones which would pre-

Inspectorate Colombia at Cerrejon complex

Inspectorate Colombia last year secured a five-year extension of Cerrejon’s contract under which In- spectorate inspects and certifies over 32 mtpa of high quality thermal export coal through the Cerrejon mining complex in the north eastern part of Co- lombia. Cerrejon is the largest

open pit coal mine in the world and the leading coal producer in Colombia. Under the contract, In-

spectorate operates auto- matic sampling systems and quality control during the processes of explora- tion, production and ship- ment of coal. In addition, through

rapid laboratory analysis techniques it provides feedback on key quality parameters within a two- hour period and before the coal is loaded onto trains. The coal is then trans-

ported via rail to Puerto Bolivar located 150 km from the mine site. The

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port is capable of loading more than 300 ocean-going vessels from handysize to capesize per year. Coal is stockpiled at

the port and Inspectorate operates the automatic sampling station to certify the coal quantity and qual- ity that is loaded into ves- sels. 64% of the coal is destined for the European market, 20% USA, 3% South America, and 13% other destinations. Inspectorate says that a

thorough quality processs, well-trained personnel, HSE programmes, ISO 9000 certification and ISO 17025 accreditation are the key elements that al- lowed it to win an exten- sion of this contract. Inspectorate Colombia

has worked uninterrupted since 1993 as the only in- dependent inspection service provider for Cerrejon’s mine and is the industry leader with a 65% market share in the country.

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