Hammer-milling, particles

Particleboard or mat-formed composite board is one of the products that can use recycled wood as a raw material. According to questionnaires, recycled wood used in the particleboard industry is estimated to be 20% of the total chips, and the amounts have been increasing. Laboratory scale particleboards were made using recycled P-chip and S-chip to evaluate chip quality. The results showed that the quality of P-chip was equal to that of ordinary chip. Hammer-milled particle from low grade chips can be used as a core material of particleboard. A new type of structural board with three-layer construction was proposed to expand the use of recycled wood chips. 

Hammer milling was chosen for the preparation of the wood furnish. A laboratory scale hammer milling tool (Hosokawa Micron Co., H8-6), which has fifty-six hammer plates on its cylinder and has 15 mm opening screen, was used. Chips were crushed into particles at 4400 rpm. Particle-b was a hammer milled particle obtained from sound chip, P-chip. Expecting some decrease in the quality of the demolition wood, P-chip was subjected to one hour boiling treatment before hammer milling. Two lots of S-chip with some differences in quality were also hammer milled to prepare Particle-cl and Particle-c2 after 30-minute steaming at 0.5 MPa. 

After acid removal, scrap batteries are fed to a hammer mill in which they are ground to <5 cm particles. The ground components are fed to a conveyor and passed by a magnet to remove undesirable contamination. The lead scrap is then classified on a wet screen through which fine particles of lead sulfate and lead oxide pass, and the large oversize soHd particles are passed on to a hydrodynamic separator. The fine particles are settled to a thick slurry and the clarified washwater recirculated to the wet screen. 

Mech nic l Impact Mills. The mechanical types include cmshers, hammer mills, pin disk mills, turbine mills, and mills with air classifiers. Impact Crusher. Feed material is introduced through a feed opening onto a rotor moving at between 25 and 50 m/s (Fig. 11). The initial impact by the rotor causes some size reduction, and the material is accelerated up to the speed of the rotor and flung against the impact plates, where further size reduction occurs. It is possible to wear-protect these units quite well, so that abrasive materials can be handled. The final end particle size can be varied by the inclusion of an outlet grid to vary the residence time in the machine. 

HammerMills. One of the most versatile, economical, and widely used impact mills is the hammer mill (Fig. 12). Many variations are produced, with special types available for specialized appHcations, eg, quick screen change for animal feed, heavy duty for minerals, and light constmctions for woodchip. The principle employed is similar to that of the impact cmsher however, the rotation speed can vary from 20 up to 100 m/s with high speed fine-grinding versions. The oudet screen is used to vary the residence time, which in turn affects final particle size. The size of the end product is an order of magnitude finer than the size of the perforations in the outlet screen. 

The method used for grinding pressed cakes depends upon the nature of the cake, its purity, residual oil, and moisture content. If the whole cake is to be pulverized without removal of fibrous particles, it may be ground in a hammer mill with or without air classification. A 15-kW (20-hp) hammer mill with an air classifier, grinding pressed cake, had a capacity of 136 kg/h (300 Ib/h), 90 percent through No. 200 sieve a 15-kW (20-lm) screen-hammer mill grinding to 0.16-cm (Vi6-in) screen producea 453 kg/h (1000 Ib/h). In many cases the hammer mill is used merely as a preliminaiy disintegrator, followed by an attrition mill. Typical performance of the attrition mill is given in Table 20-25. A finer product may be obtained in a hammer mill in closed circuit with an external screen or classifier. 

The Lawrie Tea Processor (LTP) is used in Africa to macerate lightly withered leaf. A hammer mill, in which final particle size can be controlled by degree of wither and adjustment of the tungsten-carbide-tipped beaters, is essential. 

In the manufacture of PVC plastisol propellants, the usual care is taken to assure that all ingredients meet specifications for chemical composition, dryness, and particle size. Since PVC plastisol propellants do not involve chemical reaction in their curing process, however, the presence of certain impurities in the ingredients is far less critical than with those propellant systems that are solidified by polymerization reaction. Ammonium perchlorate, the most common oxidizer, can normally be procured from the supplier with the required low moisture content. If not, it is dried immediately before use. Tray dryers or other drying means may be used, depending upon the quantity of material. Normally, some or all of the oxidizer must be ground to achieve the desired mean particle size and particle-size distribuion. High speed hammer mills have proved... 

The particle size of grain processed in a hammer mill is affected mainly by the size of the screen used, although the speed of the hammer mill and the flow rate also affect it. 

Delumpers and hammer mills are frequently used to reduce the particle size of products, thereby creating a manageable physical form for ongoing processing, usually improving rates of dissolution or an even distribution of a product when blended in a mixture. 

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