Wrights offers samplers for quarrying and cement

The Wrights Dowson Group, alongside Intersystems, develops and supplies powder, liquid and industrial automatic samplers, particularly within the quarrying and cement sector.

Early in the 1980s, Wrights Dowson identified a growing need for a controlled, traceable, quality assessment of a range of 'in-process' bulk materials.

In 1988, Wrights Dowson became a distributor for Intersystems, a North American equipment manufacturer, for its complete range of industrial samplers.

According to Wrights Dowson, automatic sampling is defined as the use of a mechanical device to remove a representative sample from a product flow and direct it either to a manual collection point or into an automatic collection cabinet.

The automatic collection system provides for preset adjustable timers controlling the number or duration of samples.

There is an inbuilt control flexibility that provides for a manual operation override and the facility to change the collection receptacle, type and quantity to suit specific applications.

Once the sampling parameters have been determined and the equipment selection matched to the requirements, the equipment must be fit for purpose in three areas.

First, a representative sample must be obtained at the same frequency by the same method and at the same location.

The second aspect is a repeatable sample; this is where it becomes vital that the samples are collected in the same way at a predetermined time cycle.

Third, the quality of the sample is not only about representation and repeatability, but the equipment must be rugged, fit for purpose and easily operated and maintained.

The reference to the ASTM standard is to highlight the fact that sampling of cement and aggregate has been defined by the society in North America and has also been adopted by other countries, thereby providing a common quality assessment template.

The ASTM standard defines the following sampling conditions: Condition A = Stop Belt is a basic instruction that relates to the removal of a sample, manually or mechanically, from a belt in a failsafe stop position; Condition B = Crosscut; Condition C = Strip; and Condition D = Quartering, which is the least representative way to take a sample because it is an old method, which is rarely, if ever, used.

The procedure was to take a front-end loader scoop up some material from a product pile, dump the material on the ground, then a QC operator would take a quarter section of the pile on the ground, assume it as being representative and endeavour to carry out an analysis confronted with all the vagaries of particle separation.

There are automatic options available and ASTM Condition B and Condition C are fully met by the range of equipment supplied by Intersystems and the Wrights Dowson Group.

When carrying out an investigation in the use of sampling, the cement and aggregates sector is confronted with the issues of sampling requirements and the adoption of the requisite standards.

It must be determined what materials are being processed and why are they being sampled, where is the most suitable location for sampling and by what specific method should the samples be obtained.

Typically, Condition B = Crosscut will entail sampling being carried on belt conveyors for raw materials in quarries such as limestone and in raw meal plants at gravity chutes, hoppers and spout locations.

In conveyor terms, to meet ASTM Condition B, it is necessary to know the conveyor incline, belt width, belt speed and throughput, together with an awareness of the following factors: belts from 600mm to 1,800mm; where they are mounted on the belt; 35-degree idlers; sample cutters (3 x standard particle); and tip speeds of 6.0m/s.

It is worth noting that the sample cutter never touches the belt.

In the cement industry, Condition B also relates to use in gravity chutes and spouts and typically supports the sampling of raw meal.

The Intersystems equipment widely specified in the industry is the type-GRA/-GRE cross-cut sampler or a GRES derivative where sloping wall chutes are used.

For an ASTM C = Strip sampling condition, the equipment is closely defined for use with clinker and finished cement with the samplers located in gravity spouts, pneumatic conveying lines, air slides.

The operating specification allows for material sampling up to 75mm; the arm actuation is either by air or hydraulic control with a stroke range of 300mm to 1,370mm.

The sample arm rotates through 270 degrees.

A range of industrial samplers, such as PS, PT, HD-PRT and PRT, are used for strip sampling, while the GRS/GRE models cover the demand for cross-cut sampling.

The aggregate and cement sector continues to be exposed to new technology and developments in particle sampling and analysis are no exception.

However, since it uses the latest in ultrasonic or shape analysis techniques, it could be questioned as to whether it is the complete answer.

In Australia, the materials board recently issued the AS 1141.11.2 standard, detailing the use of a vision-sizing system (VSS), such as a high-speed video camera linked to a computer, which ultimately provides a typical particle size distribution analysis in such a way that it produces comparable results to laboratory sieving.

Vision-sizing equipment installed at a quarry in New South Wales works in conjunction with a belt sampler operating to the Australian standard (AS 4433), which removes the required sample from the belt for electronic vision analysis.

There is a written claim that the moisture content can also be obtained from a VSS, but whether the chemical content and density is also obtained in the same way is yet to be determined.

It appears to have taken a long time to move into the electronic era, but there is still a requirement for an electro mechanical device such as the Intersystems RS to present the sample.

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