Paper pulp scrubbers generally comprise sieves provided either with slots or holes, these sieves being made of stainless sheet metal such as stainless steel.
Piercing holes through such sheet metal does not raise any manufacturing problems, but matters are different when having to make narrow calibrated slots, the edges of which are usually flared, at least on one face of the metal sheet, according to specified configurations and angles.
Indeed, the width of such slots is in the approximative range from 0.15 mm to 1 mm for sieves, the size of which may range, for cylindrical sieves, from 0.25 m to 1.50 m diameter with 0.30 m to 1.50 m height or length.
In the present practice, these sieves are made either by milling or sawing a sheet of metal, or else by placing side-by-side parallel thin bars forming a grid, these bars being assembled by welding with cross-members in the form of binding hoops which are perpendicular to said bars.
This latter method of manufacture presents major drawbacks, due to the presence of the welds which are fragile because of occurrences of crystallization of the stainless metal which these welds bring about and which have the further drawback of weakening the chemical resistance of the metal.
Moreover, such scrubbers generally include rotors carrying vanes or foils which move close to the surface of the sieve for generating pressure drops and pressure surges for helping in the cleaning out of the sieve and for preventing the slots from becoming plugged by an accumulation of fibers. These rotors run at a high speed, giving rise to very large tangential strains on the bars. These strains tend to tip the bars over when they are arranged along the generating lines of a cylindrical sieve, this being the more frequent case. They also subject the welds to alternating strains which cause these welds to break.
The object of this invention is to overcome these problems.