The raw materials and got directly from the dredger is transported hydraulically via the segment pipes or pipelines to the sand treatment plant for subsequent beneficiation.
The sand treatment plant processes sand for the manufacturing of hollow glass/table wares by classification in a rising stream of water. The materials which is mainly got as sand pulp delivered to the storage “silo A” through the mesh vibrator. The flow of operation is shown below:
Vibratory mesh Silo “A” Cone “A” Screen house Classifier
Cone “B” Floatex Separator Turn Table Silo “B”
Vibratory mesh
The vibratory mesh can also be called a vibratory filter or screen due to the dual functions of screening and filtering. The vibratory mesh is constructed on top of the silo “A”.
A vibrator is attached to the mesh and also a spring, during which the sand pulp flows into it from the dredger, screens and filters the sand. The size of the mesh is 2.5mm.
It implies that those particles larger than the mesh size will remain at the top of the mesh and with the aid of the vibration is shaken off through the outlet and they are rejected as “rice gravel”.
Screen house
The screen house consists of the primary, secondary and auxiliary screens. The primary screen is 2.0mm is size while the secondary and its auxiliary screen is 1.2mm in size.
The upper part of the screens has barriers which help in retarding the velocity of sand flowing through by reducing the quantity of reject thereby increasing efficiency of the screens. Particles which are retained by the screen are rejected.
Effect of grain size and shape
In judging the value of a glass sand, the grain size and its shape are of considerable importance long before these factors had been recognized. It has been noticed that some sands melted down quickly than others and therefore require less fuel to produce a given quantity of glass.
Careful study led to the observation that the grains of rapidly melting sand were neither too large nor too small. To ensure an even size of sand grains, the producers undertake to put the sand through a series of screens to remove the oversize grains. The former retard melting process and may appear in the product as stones.
The fine sand dust may cause lumps which fail to mix with the fluxes during melting. Sharp and regular sand grains offers more surface to the fluxes than the rounded grains.
It is generally believed that angular grains melt quicker. However, very pure sands makeup a well rounded grains, have been found to give excellent results for
the water and clay mixture. The sand flow down to the floatex tank and its pump to the turn table or dewatering table for dewatering.
Effect of iron
When iron is present a limonite mixed with clay, it may be largely removed by washing. Cream coloured, yellowish and brown sand contain limonite. The depth of colour depends on the amount of minerals present. Hematite impacts a reddish brown colour to sand. The colour given by sand depend on the oxidation state of iron. Ferrous iron gives the glass a bluish green flint which is not nearly a noticeable. For this reason, it may be advised to maintain oxidizing condition during melting. This is obtained by adding arsenic or sodium nitrate to the batch.
Since bluish green and yellow are complementary. The presence of both ferrous and ferric iron in small amounts may result in colourless glass. Magnesium, selenium, cobalt and nickel are added to glass batches to mask the colour due to iron.
Percentage of iron permissible in glass
KIND OF GLASS PRODUCED % IRON OXIDE PERMISSIBLE
Bottles green or brown 1 – 2
Window glass 0.3 – 0.5
Plate glass 0.1 – 0.25
Mirror glass 0.05 – 0.15
Flint glass 0.05 – 0.15
Lead glass 0.02 – 0.03
Brown optical glass 0.03 – 0.04
Optical glass 0.02 – 0.03
Aluminum may increase the durability of glass if present in small amount and also the resistant qualities in glass.
Dewatering table
The function is to dewater or demoisturize the processed sand for subsequent transportation due to the fact that wet sand cannot be used directly for glass production.
The dewatering table or as it is called turn – table is mounted systematically on cone “B” by a shaft which rotates it. The sand from the floatex separator before getting to the table is further classified by the cyclone which feeds the table to reduce the initial water content.
At the bottom of the turn – table in cone “B”, the shaft is connected to a vacuum tank and a dryer which when on operation dewaters the sand and the excess recycled to cone “B”, during which the screw conveyor evacuate the sand to the short conveyor belt and then the short conveyor feeds the longer one.
Silo “B”
This is final destination of the sand and it is the finished product that is ready to be transported to the factory. The sand here is fed manually to tippers and when not available, it is emptied and stockpiled in the quarry before needed. When the sand is needed, pale loaders are used in feeding the tippers. The nature of manual feeding of the tippers directly from the silo is with the aid of a fixed chain block pulley.
