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Dosage and weighing facilities

DOSING AND WEIGHING FACILITIES

In many productive processes, based on solid bulks, it is necessary to develop formulations, which require dosing of the different components involved.

According to the industrial process, the raw material used, the resulting final product and the quantities to be dosed, there are several techniques to perform the dosed weighing of the ingredients. These dosing processes can be carried out continuously or discretely (in batches), this will depend on how the process is designed.

Although in general the dosage is gravimetric, sometimes if the products are of very low density or precision in the dosage is not required, you can also perform the dosage in a volumetric way, but this one is unusual in solids dosage processes.

SOTECMA is specialist in bulk solids and dosing weighting systems.

At SOTECMA, we have extensive experience in both gravimetric and volumetric dosing processes regardless of whether the process is continuous or discrete.

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Elements of a Concrete Dosing Plant and other dosing systems

In any dosing process, as well as in the manufacture of concrete and other construction materials, it is necessary to have at least three basic equipment:

The silo or warehouse where the material to be dosed is stored
The equipment that extracts the material
Continuous weighing scale

There is a fourth element that is practically essential, which is the automation system, this is what guarantees us that the adjustments will be precise, and that the product obtained will have constant characteristics in all manufacturing batches. In the continuous and gravimetric dosing processes, a system that is not controlled automatically is not conceived.

1. Silos or storage tanks

Its size and shape will depend on the characteristics of the material we want to dose and the amount that is going to be consumed in a certain time.

The size must therefore be determined according to the consumption of the component to be dosed and the mode of supply (tank truck, open-box truck, big-bags or sacks). To clarify with an example, let’s imagine that the consumption is approximately 5 t / h, it is clear that this product should be supplied by truck and stored in a silo, but instead if the consumption were 50 kg / h, the normal thing is that was supplied in bags and stored in 200 or 300 liter hoppers.

The physical characteristics of the material (granulometry, abrasiveness, cohesiveness, corrosivity, humidity, temperature, flammability) are also important to take into account when designing these silos and storage tanks, both in the material with which they are manufactured and in the way to design them, and what is more important, the accessories that must be incorporated to guarantee the extraction of the material to be dosed.

2. Dosing equipment

This element is highly relevant in the dosing process, it is in charge of extracting the material to be dosed from the silo, transporting it and / or bringing it to the scale.

As in the case of silos, the type of dosing extractor, shape and size will depend on the characteristics of the material to be dosed and the flow that is required to be transported or supplied.

Among the most common dispensers are conveyor belt, screw conveyor, vibrating troughs and rotary valves. There are times that if much precision is not required, it can be dosed directly with hull or butterfly type gates, but in these cases control over the supply vein is difficult to perform.

At SOTECMA, we have an R & D & i department, with a pilot installation to test the products that offer more doubts about dosing. We also have an experienced, highly trained technical office to determine which is the best dosing system for Apply.

3. Weighing or measuring equipment

This element is the one that will indicate the weight or volume that we are providing with the dispenser and therefore will depend on its precision so that the dosage is more or less correct. Like the elements mentioned above, the design of the measuring equipment will depend on the behavior that the product may have and the amount to be dosed.

When it comes to liquids, the solution is usually simple, in most cases it is not necessary to weigh, the dosage is resolved with volumetric counters since the density is usually quite constant, of course, you have to take into account the characteristics physical and chemical fluid (corrosivity, temperature, viscosity) and flow rate to determine the type or size of the meter.

In the case of solids, except in rare cases the dosage is done gravimetrically, this requires that the container where the weighing is going to be carried out has a size and shape that will depend on physical factors (density, internal friction angle, angle of friction with the walls, moisture and cohesiveness), in addition to the chemical characteristics. It is important to know the maximum amount to weigh to determine the load cell capacity, this will condition the degree of appreciation of the scale and therefore its precision.

4. Automation and control system

To complete the dosing system, today, it is practically essential to have a good automatic program that manages the operation of the elements described above.

SOTECMA, has a control and automation department, where programs are developed, and electrical control panels are made to make it possible for the systems to work automatically, thereby guaranteeing good vein control and thus a good adjustment in weighing.

Types of solid and liquid dosing systems

They can be classified in two ways, depending on the way in which the measurement is carried out, they can be by weight (gravimetric) or volumetric, if we look at the type of process, they can be continuous or discontinuous (discrete).

Continuous gravimetric dosing

It is the most complex dosing process, it is generally only used for solids, for its execution it is required that the weighing equipment be dynamic, that is, the component is weighed as it is fed to the next process, which is usually mixing. Therefore the difficulty arises when designing this weighing element.

At SOTECMA, we have been developing continuous gravimetric dosing systems for more than 30 years, relying on dynamic weighing on a conveyor belt and the weighing dosing system with hopper. A utility model patented by SOTECMA more than 20 years ago and thanks to it is achieved greater precision. Due to its complexity, this type of dosage must always be carried out with an automatic control system.

We apply this type of dosage in our gravel-cement or cement soil plants, for the dosage of cement on the aggregate.

Discontinuous gravimetric dosing

It is the most used and precise dosing process since it allows us to weigh statically, thus allowing a good vein adjustment. It is easier to implement than the discontinuous one.

For any weighing system, the absence of vibrations and external actions that may interfere on the scale is essential, and more when it comes to dosing small quantities (below 10 kg), that’s why SOTECMA has developed and patented a high precision scale with a turning system for emptying and which is encapsulated to avoid the action of external agents.

In this case, the process can be carried out manually, starting and stopping the dosing equipment manually, but it is totally discouraged due to the risk of depending on the action of an operator who may forget to add a component, or repeating one or simply not stopping the dosing equipment in time by providing more of the component than required.

We apply this type of dosage in our dry mortar plants and concrete manufacturing plants, for the dosage of all the components that the mixture of this product requires.

Continuous volumetric dosing

It is used in both liquids and solids, for liquids the measurement can be quite precise in that the density is practically constant.

In the case of solids, the apparent density varies greatly depending on the granulometry and the degree of aeration of the product, and it is for this reason that this system is used only for processes where the proportion in weight of the various dosed components is not very precise.

We carry out this dosing system in our gravel-cement or soil-cement plants for dosing the water.

Discontinuous volumetric dosing

The only difference with the previous one is that the process is done in batches, but this does not mean more precision is achieved, the equipment used to measure is usually the same for both processes.

Dosing and weighing equipment

Within our range of equipment and the experience demonstrated in many years we highlight:

Micro-dosage of additives by volume and by weight.
Continuous cement and water dispenser for gravel-cement plant.
Dynamic weighing on conveyor belt.
Tipping precision scale weighing system. (Patented)
Portable solid additive dispenser for asphalt plants. (Patented)
Lime dosing silo for water treatment.
Complete chemical additive dosing systems for dry mortar and glue cement manufacturing plants.

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