AUTOMATIC INGREDIENT DOSING PLANTS

 

EVOLUTION OF PLANTS

FROM PREHISTORY TO THE 3rd MILLENNIUM

MACRODOSING

LARGE AMOUNTS OF INGREDIENTS FROM STORAGE SILOS

MEDIUM AMOUNTS OF INGREDIENTS FROM INDUSTRIAL BIG BAGS

MICRODOSING

SMALL AMOUNTS OF INGREDIENTS FROM BAGS

NANO DOSING

EXTREMELY SMALL AMOUNTS OF INGREDIENTS FROM SPECIFIC PACKAGING

DESIGN ASSUMPTIONS

1. BATCH DOSING

Forming a recipe implies the dosage of some granular or powdery ingredients. The recipe mixture is then transferred to other equipment for further processing (e.g. mixers, kneading machines and melters). The composition of the recipe mixture can be repeated or changed every time.

1.2. REQUIRED PERFORMANCES

1.2.1. ACCURATE DOSING OF EVERY INGREDIENT

Each ingredient is dosed according to the gain-in-weight or loss-in-weight principles, as better explained below. Accuracy is expressed as a per cent deviation from the theoretical weight. For example, suppose the required precision is ± 2% for an ingredient of which 100 grams need to be dosed. In that case, the real amount dosed at the end of the cycle must neither get below 98 grams nor exceed 102 grams.
Dosing accuracy can be either the same value for each ingredient or, due to economic, technological or qualitative reasons, a higher or lower value depending on the ingredient itself.
The dosing accuracy of each ingredient can be guaranteed to be ± 1 ÷ 5%.
Exceptionally <1%.

1.2.2. DOSAGE SCHEDULE

This value is expressed in number of batches/hour. A batch is defined as the recipe of each ingredient considering its most complex formulation regarding the number and/or amount of ingredients.

1.2.3. CROSS CONTAMINATION BETWEEN DIFFERENT RECIPES

This value is expressed as a percentage. It refers to the acceptable level of contamination occurring between recipes, i.e. either the total amount of ingredients of a recipe found in the dosage of the following one or the amount of dosed and weighed ingredients that is missing when they are discharged at the destination point. Residual amounts of the product may be stuck in the weighing recipe hopper, the service hopper or the transport equipment, and may contaminate the next recipe.
Cross-contamination between different recipes can be guaranteed to be <1 ÷ 3%.

 

2. CONTINUOUS DOSING

2.2. REQUIRED PERFORMANCES

One or more ingredients in powdery or granulated form require continuous dosing into the flow of the product concerned (e.g. during flavouring and surface salting processes). The product is dosed by loss-in-weight, either based on an external signal or calculated on the instantaneous weighing of the product flow. 
Dosing accuracy of each ingredient can be guaranteed to be ± 2 ÷ 5% of the theoretical quantity required. For example, suppose it is necessary to dose 1.5% of powder on a product flow between 500 and 1,000 Kg/h. In that case, the system continuously supplies an instantaneous quantity between 7,500 and 15,000 grams ± the established percentage quantity.
Accuracy can be exceptionally guaranteed to be <2% (if the product being dosed maintains constant physical characteristics over time).

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ANALYSIS OF THE CHARACTERISTICS OF THE PRODUCTS TO BE DOSED

To design an automatic dosing device or system, it is essential to know the physical properties of the product to be dosed. 
Our laboratory is perfectly equipped and able to determine:
- the bulk density of a product (grams/litre) 
- the angle of repose and/or flowability angle (“)
- humidity (%)
with maximum precision on an international scientifical basis.


 

 

Analyses allow designers to accurately identify:

THE FEATURES OF THE DOSING TOOLS AND THE NEED TO USE FLOW AIDS

As regards dosing screw equipment:
Type of loop to be used: continuous spiral screw, square thread centerless screws, round thread centerless screws, blade screws.
External diameter, internal diameter, pitch and rotation speed.

NB. In the case of ATEX execution, the peripheral speed of the spiral cannot exceed 1m/sec.
In the case of vibrating equipment:
Amplitude of vibration, angle of force and frequency.

SELF-CLEANING DOUBLE SCREW

NECESSITY OF USING LUMP BREAKERS, EXTRACTORS OR FLOW AIDS

LUMP BREAKER SYSTEMS

FLAT BOTTOM EXTRACTORS

PNEUMATIC FLUIDIZER

PNEUMATIC HAMMER

DOSING TECHNOLOGIES

GAIN-IN-WEIGHT DOSING OF ONE OR MORE INGREDIENTS

Serbatoio Pesatura Scale per impianto di dosaggio e pesatura ingredienti

FIGURE 1 - DIAGRAM OF A GAIN-IN-WEIGHT DOSING SYSTEM

It is the most common configuration for dosing systems based on “batch” operation, when the recipe consists of many ingredients and needs to be formed in a set time (number of dosages per hour). 
Dosing stations usually comprise:

A. A tank mounted on load cells and entirely isolated by flexible membranes. It is employed for weighing of ingredients which are dosed one after another by equipment specifically adapted to the characteristics of the product and the quantity to be dosed.

B. A system of valves enables to completely unload the dosed recipe and, at the same time, to perfectly isolate the weighed tank from interferences caused by the transport system located under the shipping hopper, which is used to transfer the batch towards the point of use.

C. Another hopper (service hopper) acts as a buffer for the loading on the (generally pneumatic) transport circuit, so as to transfer the recipe to its destination and use point. 
This service hopper allows to completely isolate the weighing process from possible interferences caused by any leaks from the rotary valve into the pneumatic circuit, and to separate the weighing and the shipping cycles and save batch processing time. While the dosing process is carried out, the system conveys the previously dosed recipe which has been transferred by gravity from the weighing hopper to the service hopper.

D. A (generally pneumatic, suction) conveying system transfers the complete recipe to the next use point.
Standard dosing accuracy is guaranteed to be <± 3%; cross-contamination between recipes is generally guaranteed to be <1.5%. Picture 2 in the following page displays a 15 batch/h dosing system for 23 components and 3 final destination points. 

 

Schema unifilare impianto dosaggio ingredienti

SINGLE-LINE DIAGRAM OF AN INGREDIENT DOSING SYSTEM WHICH PRODUCES 15 BATCHES/H FROM:

16 BAGGED PRODUCTS; 2 PRODUCTS FROM SILO; 5 PRODUCTS FROM BIG BAG, WITH 3 DESTINATIONS

LOSS-IN-WEIGH DOSING OF ONE OR MORE INGREDIENTS

Dosatori per dosaggio in continuo polveri

This technology is particularly suitable in the case of continuous dosing or when it is necessary to carry out a high number of cycles per hour: the ingredients can be dosed simultaneously, because the products can converge to a single point, but are weighed separately during dosage. 
Each ingredient is dosed by subtracting the weight of the product located in the hopper; therefore, although all the ingredients flow towards the same point, they can be dosed simultaneously. This technology thus allows to dose a large number of ingredients in the time required to dose the ingredient which requires a longer dosage time due to its quantity being dosed or the required extreme accuracy.
The diagram below schematises a dosing system for flavouring powders for the production of dry pet-food.
The flavour ‘A’ (in a big bag) is pneumatically conveyed towards a batch doser and a vacuum mixer.
The flavour ‘B’ (in bags) is pneumatically conveyed towards a continuous doser placed on a continuous in-line mixer.
On both lines, it is possible to dose the flavour ‘C’ (in bags), which is loaded manually.
On the continuous line, dosage precision is guaranteed to be +/- 3%.
On the “batch” line, precision is <+/- 1%.

CONTINUOUS DOSING OF FLAVOURING POWDERS IN A DRY PET-FOOD PRODUCTION LINE

BATCH DOSING OF FLAVORING POWDERS IN A VACUUM MIXER FOR DRY PET-FOOD

DOSING ACCURACY

Each ingredient is dosed according to the gain-in-weight or loss-in-weight principles. Accuracy is expressed as a per cent deviation from the theoretical weight. For example, if the required precision is ± 2% for an ingredient of which 100 grams need to be dosed, the real quantity dosed at the end of the cycle must neither get below 98 grams nor exceed 102 grams.
Dosing accuracy in an automatic system is obviously the design parameter to which the greatest attention should be devoted; especially in the food and/or pharmaceutical industry, it is necessary to deal with products that are essential for the success of the formulation or are even dangerous for the health of the consumer in case of over- or underdosing.

DOSING ACCURACY is influenced by two different technical elements that nonetheless interact with each other to determine the final result. 
 

WEIGHING

In either gain-in-weight or loss-in-weight dosing, the equipment (a tank or the entire device) needs to be instantaneously weighed and monitored to control the increase or decrease of the product being dosed. Our 40-year experience and neverending development allow us to achieve the most advanced result in this field.

BENDING LOAD CELLS

In either gain-in-weight or loss-in-weight dosing, the equipment (a tank or the entire device) needs to be instantaneously weighed and monitored to control the increase or decrease of the product being dosed. Our 40-year experience and neverending development allow us to achieve the most advanced result in this field.

3 LOAD CELLS EQUIDISTANT FROM THE CENTER OF BARYCENTER

LOAD CELL LEVELING SYSTEM

Load cells are faultlessly efficient if they work on a perfectly flat surface and are free from any parasitic constraints.
In addition to the above, the system used by CRISTIANO TORRE Engineering guarantees self-centering and safety when overturning. 

FOOD-GRADE DOUBLE COATED FLAT SHEET, 0.4 MM THICKNESS

FLEXIBLE INSULATION BETWEEN THE FIXED PARTS AND THE WEIGHED UNIT

Particular attention is devoted to flexible connections which isolate the weighed unit from the fixed components, i.e. the tools used for dosing and the equipment to which the weighed amount is conveyed.

The use of inadequate flexible connections leads to significant interferences on the weighing accuracy and cross-contamination between recipes.

AUTOMATIC CHECK ON THE EFFICIENCY OF THE WEIGHING SYSTEM

IIn an automatic plant, production batches follow one another with no human intervention.
During automatic processing, some components may be affected by faults or anomalies, which in turn may determine serious errors during ingredient dosing. 
This inconvenience can result in severe economic damage, since all the batches which are involved in succession are made unusable. 
All the weighing hoppers employed by TORRE company comprise an automatic system which monitors the overall efficiency.
This monitoring process is carried out by a management software on a periodic basis or even at the end of every batch. It consists in applying sample weights on the scale and in verifying the correspondence of the signal, triggering an alarm if necessary. 

COMPLETE EMPTYING - CROSS-CONTAMINATION

Every ingredient batch needs to be completely emptied without leaving any internal residues which may lead to cross-contamination and dosing errors in the subsequent batch.
All weighing hoppers are internally polished with surface roughness < 0,6 µ.
Particular attention is devoted to the access doors used for inspection and cleaning, to ensure perfect internal flatness and avoid any roughness or cracking.
To ensure greater safety, all the weighing and service hoppers are equipped with a silenced pneumatic hammer. After the emptying process, a single pneumatic hammer blow removes all the dust which is stuck on the walls due to static electricity.

PROCESS AUTOMATION

Our 40-year experience in collaboration with a leading company allows us to offer a ‘turnkey’ service. It includes a system management software which is completely customised and connected to existing company systems through Ethernet data exchange.
The ease of intervention on recipes for modification, implementation, etc. is guaranteed by a customised interface that allows to simply and intuitively interact with the production process.
Traceability of all operations
Software for automatic calibration of the ‘IN-FLIGHT WEIGHT’ for each ingredient in each recipe

BATCH DOSING OF FLAVORING POWDERS IN A VACUUM MIXER FOR DRY PET-FOOD

DOSING TOOLS

An essential condition to ensure accurate and fast dosing is the choice of a suitable dosing tool.

Our 40-year experience with a variety of products allows us to make the most appropriate choices to achieve the target result.

The most common tool for powdery products is undoubtedly the Archimede’s screw in the configuration that best suits the characteristics of the product to be dosed.

For instance: dosing a very poorly-flowing product using a continuous spiral screw with a solid shaft leads quickly to an agglomeration problem, which, in turn, blocks the dosing process. In this case, it is necessary to use a square thread centerless screw. Great attention needs to be devoted to the hygroscopicity of the product. It is often necessary to install an additional dehumidification system which continuously monitors this parameter.

A DOSING TOOL AFTER USING CALENDULA POWDER

SQUARE THREAD CENTERLESS SCREW

MUNTERS DEHUMIDIFICATION UNIT

Products with coarser and more flowing granulometry are dosed employing electromagnetically controlled vibrating channel dosers.

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