GREEN SAND PLANT MACHINES

GREEN SAND PLANT MACHINES: STATE OF THE ART

Sand preparation has often – and wrongly – been considered secondary to other main
issues, such as moulding or casting plant. Investments have often been aimed at
increasing productivity (“to make more flasks”) and capacity of furnaces (“to fill the
flask”). This right corporate policy has often created problem to the sand plant, that
has more or less brilliantly withstood all these changes.
Sand plant (goals)
The modern sand plant must satisfy three fundamental requirements:
− production of high quality sand;
− guarantee of constant quality in time;
− production of a constant high quality at the lowest cost possible. 
Production of high quality sand:
What does “high quality sand” mean?
High quality sand must have the following characteristics:
− compactability that allows a good moulding and consequent shakeout, without
causing any defects due to moisture excess / deficiency;
− strength that allows to produce moulds resistant to handling, core laying and
casting, and that does not cause any problems during shakeout; 
BELLOI & ROMAGNOLI 2
− temperature below 45 – 48°C and without any sudden variations, as higher values
hinder the correct activation of additives (with consequent higher bentonite
consumption with equal strength) and increase water demand, causing defects on
castings;
− permeability that enables the evacuation of gases from the mould without causing
any blowholes.
Of course, it is necessary to control also other characteristics, such as moisture,
bentonite and fines content, etc.. However, if above-mentioned features are kept in a
limited range, the whole sand system will be stabilized.
In our experience, we have never found two foundries using the same sand
parameters, even if production typologies were almost the same.
This “uniqueness” is absolutely normal and justifiable. In fact, sand is a means to
obtain high quality castings and every foundry must optimize its own castings by
producing a distinctive type of sand.
This specificity is not only due to different casting types, but also to the usage of
different moulding systems (high pressure, shot, shock wave, manual).
So, there is not one sand which is fit for all, but there are many sands of different
qualities that satisfy every single requirement.
Guarantee of constant quality in time
It is of the utmost importance to maintain the same sand quality in time. In fact, if the
“right” quality of sand allows to obtain a better casting, quality constancy in time
extends such advantage to “all castings”.
Constant quality at low cost
Of course, it is extremely important to make the first two conditions available at the
lowest possible cost so as to obtain from the sand plant the efficiency and the cost
abatement which render our product more competitive.
The attainment of this goal is pursued on two levels: first of all, a constant quality of
sand leads to a reduction of rejects, unpoured flasks, sandblasting times, broken
flasks and to an improvement of casting “skin”.
For instance, the muller must have just one motor to reduce energy losses and to
ease maintenance; the rotary sand and casting drum is to be considered as a
multifunction machine, as it allows to cool both sand and castings at the same time
and to pre-sandblast castings; besides lowering temperature, the cooler must
homogenize sand and enable the controlled removal of fines and a preventive
moisturizing.