Cross belt sampler: mechanical design of the World’s largest hammer sampler for bauxite export contractual requirements

Automated, mechanical cross belt (hammer) samplers remain popular because they are easy to retrofit into brown fields applications or green fields projects when cross stream samplers are not always designed into the plant layout from initiation. Cross belt samplers require less headroom and are easy to retrofit onto existing conveyors. Despite disputes about possible delimitation and extraction errors resulting from hammer samplers, they are not excluded for use from ISO sampling standards (13909 - Coal and Coke and 8685 - Bauxite) but are excluded from others (3082 - Iron ore). Possible errors can be mitigated by applying “know-how” into the bespoke design of a hammer sampler for installation on a specific conveyor belt system. This paper discusses the design details of a primary stage hammer sampler for a Bauxite ship-loading sampling plant. The design requirements of 10 000 metric ton per hour ship loading rate, 100mm particle top size, 1800mm wide conveyor travelling at 5.4m/s, results in a hammer sampler that takes up to a 260kg increment with each cut. The application requires more torque and at faster responses than that delivered by 10 Bugatti Chiron’s combined and is (to my knowledge) the largest of its kind requiring a unique high-torque-at-low-rotational-speed drive system where conventional geared motors could not achieve the necessary output performance. Even though the sampler is the primary stage to a complete operational sampling plant, the emphasis is on the power requirement calculations, the mechanical design, components, materials and features of this unit that makes it not only mechanically operational but also intended at high sampling precision levels prescribed by the Theory of Sampling (TOS). Despite a small statistical bias detected for the sampling system (not the hammer sampler only), the sampling plant performed within the maximum tolerable bias specified for the commercial trade application and is fit for purpose.