Page 220 - Materials Chemistry, Second Edition

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Recycling of Municipal Solid Waste Rejects
then transferred to the mold according to the required shapes and applications.
The mold will be placed in a hydraulic press to be pressed into bricks, inter-
locks, table toppings, wheels, manholes, road ramps, and other products as
will be discussed later. The manufacturing process of rejects (silica-plast) prod-
ucts consists of the following steps and as shown in Figure 6.1:

• Sieving the rejects to remove organic wastes and returning the organic
waste to the composting process.
• Agglomerating the rejects (contaminated plastic waste).
• Sieving of sand to remove oversize grain.
• Mixing the agglomerated rejects with sieved sand and heating the
mix indirectly to the required temperature.
• Pouring the hot mix into molds and pressing it in a hydraulic press
to reach the required density and shape.
• Cooling the product.

The hot mix can be easily molded into any form and any decorative shape
according to the shape of the mold. The key issue behind this technology is
the continuous mixing of sand and plastics to guarantee homogeneous dis-
tribution of materials and good quality products. Reject technology consists
mainly of the following machines:

• Sand screen
• Reject screen
• Agglomerator
• Indirect flame furnace
• Hydraulic press to form the products according to the mold shape
• Overhead crane
• Conveyor system

The two key machines used in reject technology are the agglomeration
machine and the indirect flame furnace. Details of both machines will be
given in the following sections.

Agglomeration machine
The agglomeration machine shown in Figure 5.13 consists of a cylinder with
four stationary and four rotating knives as shown schematically in Figure 6.2.
Two pulleys are used to transmit the motor power to the disk with the rotat-
ing knives. Plastic is fed to the machine through the upper lid. The disk con-
taining the four knives rotates via the power transmitted from the motor. The
four stationary knives on the cylinder are used in association with the rotat-
ing knives to shred/agglomerate the plastics into small pieces. A door is used
near the bottom of the machine for the release of the product “agglomerates”.