When designing a dosing system, the first thing is to understand if you need a volumetric or a gravimetric feeder. The first represents an economic feedeing solution, easy to maintain and it can be quickly integrated (or removed). A gravimetric feeder, or loss-in-weight feeder, is a self-calibrating system, that doesn’t need manual adjustment. It allows a total control over your product quality and it ensures a much more efficient and cost-effective process.
Both can be used in batch and continuous processes.
Screw feeders or spiral feeders can be either continuous feeders or batching units. Continuous feeding is characterized by releasing a constant amount of product over a set time (kg/h).
Over a set time, the batching unit must release a set quantity of product over a series of programmable cycles. Depending on the type of product and the application, you can opt for a batching element with a flexible rotating spiral or a screw feeder with central shaft. By varying the rotation speed of the spiral or screw feeder, a corresponding variation of flow is obtained: the precision obtainable is therefore volumetric.
The speed control can be achieved manually, usually with gear motors controlled by inverters or, more rarely, by mechanical or hydrostatic variators.
Gravimetric feeders, similar to volumetric feeders, may also operate on a continuous or batch basis. In this case, measurement is optimized with precision weighing. During weighing operations load cells are used to detect the variation in weight of the measured product. In the control panel a weighing processor is inserted which, by means of the signals coming from the load cells, suitably manages the rotation speed of the spiral or screw conveyor.
In the case of continuous dosing, control of the speed is generally obtained automatically with PID regulation via vectorial inverter or brushless motor.
Depending on requirements controllers can be set up to manage multiple components and recipes. Systems can be designed for Loss-in-Weight dosing or Gain-in-Weight systems.
An important accessory used with Gimat’s powder feeders are the bin dischargers, used below hoppers and tanks for the discharge of powder, milled and mixed substances.
These bin dischargers become necessary and are particularly advantageous in the presence of products that clog with low fluidity, or if the installation is in a confined space. They allows to feed the dosing screw in a constant and uniform way over time.
These are particularly suited for moving and dosing granular products in bulk in piles or fragile substances that could be damaged if moved on a spiral or screw conveyor. The vibration is obtained with electromagnets. They are widely used in the chemical, pharmaceutical, food and plastic industry, installed on the packaging machines. Thanks to a special controller with vibrating feeders, it is possible to set the capacity and thus regulate the dosage of the ingredients in an accurate and reliable way.
The vibrating base in the “engine” of this type of doser and is selected on the basis of the customer’s needs.