Mixing Equipment

 Batch Mixers 

These mixers produce concrete batch  by  batch  with interval. Two types of batch  mixers are commonly used i.e. Pan type and Drum Type. Pan  mixers are suitable for mixing lean and dry mixes in which the mortar trees to stick to the drum. They are commonly used  in precast concrete plants where their greater bulk size and less convenient discharge do not pose much problem.  In this mixer the blades are fixed to an assembly so that they agitate the concrete throughout the stationary pan as the vertical drive shaft rotates. 

Drum mixers are classified into two types namely  tilting  and non-tilting type. The shape of the drum the angle and size of blades, the  angle at which the drum is held, affects the efficiency of the mixer. Tilting drum is considered more efficient than non  tilting type. IS 1791-1968 designates concrete mixers by a number  which represents its  nominal mix batch capacity in liters. 

The types of mixers and their  sizes are: 

1. Tilting (T) : 85T, 100T, 140T, 200T 
2. Non-tilting  (NT): 200 NT, 280 NT, 340 NT, 400NT, 800NT 

These are shown in Figure 

Tilting Mixer

 Non Tilting Mixer

For  a 1:2:4 mix  you may choose a  200 litres capacity mixer while for  a 1:3:6 mix 280 litres capacity will be suitable.

Continuous Mixer 

In this  type of mixer the materials are fed into a mixing  drum by means of special conveyors. The concrete is mixed as it passes through the drum to the discharge end. The concrete is proportioned by adjusting the relative speed of different conveyors. Therefore proportioning is actually by volume  and hence to produce uniform concrete it is essential to  have a uniform source of aggregate and constant moisture content of sand to avoid distortions due to building. Continuous mixers are useful  where a continuous supply of concrete is desired as in step-forming and in mass concrete.