Continuous weighing solids
Loss-in-Weight vs. Gain-in-Weight
Producing a correct and consistent product starts at the feeding of the seperate ingredients. There are two ways to dose powder ingredients: (1) volumetrically and (2) gravimetrically.
A volumetric dosing system doses a given volume of material per time unit. The dosing speed of a volumetric feeder should be selected manually, which may vary based on the nature of the raw material input. A volumetric feeder is open-loop in a sense that it does not correct to variations in the material density.
A gravimetric dosing system doses the actual given weight of material per time unit. The weight is measured by using load cells; the foundation of the entire system. The motor automatically alters its speed when a change is detected in the material flow. By running feeders in gravimetric mode, possible underlying variations n bulk density or screw flight loading are automatically corrected for and an extreme high dosing accuracy is achieved.
LOSS-IN-WEIGHT VS. GAIN-IN-WEIGHT
Sobatech only works with loss-in-weight dosing systems which are gravimetric feeder solutions; the most accurate weighing solutions available. The systems ensure an accurate flow of ingredients during both loss-in-weight (normal operation) as well as gain-in-weight (during refilling). The feeders are located on digital load cells that constantly measure the weight reduction per time unit. Based on that information, the speed of the dosing screws is constantly controlled.
OPEN SOURCE SOFTWARE
Sobatech developed its own tailor made open source software to control the feeder-pumps and other hardware involved in the continuous dosing of the ingredients. Put differently, in Sobatech’s continuous mixing systems there are no hidden programs nor protected passwords. The complete system is open and accessible to the customer.
Sobatech offers two different dosing systems for gravimetrically dosing the powder ingredients: (1) The gravimetric weighing belt and/or (2) The gravimetric weighing hopper.
1. THE WEIGHING BELT
A weighing belt operates by continuously weighing a moving bed of material on a short conveyor belt and controlling that belt speed to result in the desired flow rate at discharge.
Unlike most loss in weight feeding systems whose physical size must typically be increased to accommodate higher flow rates, weight belt feeders can achieve high rates while remaining compact. The system is flexible in regards to the quantities it can dose; it can feed between 20 and 10.000 kg of powder per hour.
There is an open connection between the receiving hopper and the weighing belt system meaning that the challenges of compressibility related to the gain in weight process do not apply to this system.
The gravimetric weighing belt is mounted on a stable u-frame that is by means of shock mounts connected to the platform. The weighing belt is by means of flexible hoses connected to the homogenizer (phase 1 mixing). In the homogenizer the powders are injected by the liquid ingredients and thereafter enter the actual continuous mixer (phase 2 mixing).
2. THE WEIGHING HOPPER
The well-known gravimetric dosing hoppers are located on loadcells that constantly measure the weight reduction per time unit.
The gravimetric weighing hoppers are offered in a variety of different sizes and designs. Please contact one of our team members to learn which design fits your process best.
The hopper design shown on the top of this page is called the flat bottom dosing hopper and has significant advantages in relation to the gain in weight (refilling) process. As the location of the dosing screws is different from the location of refilling – compressibility of powders is, as a result of an increased headload, minimized. This allows for an accurate dosing result in both loss-in-weight operation as well as gain-in-weight operation.
The gravimetric dosing hopper is mounted on a stable u-frame that is by means of shock mounts connected to the platform. The outlet of the hopper is by means of flexible hoses connected to the homogenizer (phase 1 mixing). The powders fall through the homogenizer into the actual continuous mixer.