Innovative Screw Feeder Design For Pulp Processing in the Paper Making Industry

Screw Feeder For Pulp and Paper

When ATAC (Analytical Technology & Control Ltd.) was faced with overcoming the problem of screw feeder leaks and excessive maintenance caused by handling corrosive chemicals, they turned to Ajax Equipment to manufacture an improved screw feeder. The screw feeder uses a 'pull' type drive to eliminate leaks and provide maintenance free service.

Since 1986, ATAC has manufactured chemical dissolving units for Silox (previously R. V. Chemicals and Clariant), a leading manufacturer of reductive bleaching agents. The Silox process involves transferring a specially formulated hydrosulphite powder blend, trade names HY-BRITE and Hydros, from a returnable container to a dissolving unit to produce a bleach solution. The units are in continuous use in many paper mills in the U.K. and Europe for bleaching wood pulp and recycled fibre, and also in the china clay and textile industries. Until 1994 these dissolving units used screw type volumetric powder feeders from other manufacturers to control the rate of chemical powder addition to the dissolving process, with varying degrees of success. Although normally a free flowing chemical powder, hydrosulphite is highly reactive with oxygen and moisture and as such, tends to form concretions within crevices in the equipment, particularly in rotating shaft seals, causing premature seal failure and powder leakage. The reactive nature of the powder was also the cause of much external corrosion of the steel chasses and other mechanical components in these original feeders. The general dissatisfaction with the proprietary feeder designs available at the time lead ATAC to contact Ajax Equipment.

"From the outset, it was clear that Ajax had both the willingness and expertise to produce a purpose designed volumetric screw feeder to meet our client's particular requirements. This has lead to Ajax screw feeders being used exclusively in all subsequent builds," says Malcolm Stevenson, Development Engineer, ATAC.

Screw Feeder Design Innovations

Screw feeder design innovations have been the inlet flow geometry and cantilevered screw arrangement. The inlet features an insert to prevent sheer, providing excellent mass flow and ensuring good pick up by the screw. A cantilevered screw arrangement creates a 'pull' type of drive mounting, where the geared motor is positioned at the outlet end of the casing. Combined with a box-shaped outlet permitting an unrestricted discharge from the feeder and preventing cross over of the powder to the seal protecting the screw motor, the screw feeder is maintenance free.

The Ajax screw feeder is available with a range of screw diameters (50, 75 and 100mm) with flexible speed drive to provide the maximum flexibility and sensitivity of output control. The feeder can deliver between 1.8 to 28 kg per minute of HY-BRITE powder to the dissolving unit. Internally the screws are Teflon coated to prevent damage to the hydrosulphite powder and build up of the powder in the feeder body. Because of the sensitivity of the HY-BRITE, the feeder is seldom opened or cleaned.

The quality of the trial unit is important believes Simon Bennett, Business Development Manager for Silox. "The quality and performance of the unit must be right for companies to feel confident enough to move beyond the trial stage after 3 - 4 months to a fully dedicated HY-BRITE dosing unit. We have been very pleased with the Ajax screw feeder unit. During the past 5 years we've had no problems with any of the Ajax screw feeders," he said.

For more information on AJAX's screw feeders please visit our Screw Feeder page or call AJAX on 44 (0)1204 386723.

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