Mixer loading
Under mixer feeding means the automatic supply of raw materials for industrial mixing, kneading and mixing processes.
If automatic feeding systems for bulk goods and liquids are used in the food , pharmaceutical , plastics and chemical industries, this offers these advantages:
- constant product quality through tightly tolerated production processes
- Reduction of production costs
- Freshness guarantee - "first in, first out" principle is implemented
- HACCP and food-compliant system design
- large variety possible thanks to short changeover times
- Raw material and batch traceability
- high availability through line-structured control concepts
- Compliance with regulations and guidelines, such as B. ATEX, EHEDG etc.
Since the feed technologies for dry substances and liquids in these mixed operations partially overlap or special solutions are required in the niches, the experience and know-how of the plant manufacturer is required.
Storage and delivery of large quantities
The delivery takes place in silo vehicles , which are coupled to silo filling lines, which blow the large quantities with pressure conveyor technology into the outside silos. In order to ensure that only flawless products are stored upon delivery, it makes sense to install sampling devices. In this case, the raw materials are only available for further processing after approval has been given by the laboratory. If the approval is not given, there is the option of discharging products and returning them to the silo vehicle. The outdoor silos are equipped with appropriate inspection systems, filters and level indicators. In the case of outdoor silos, round silos made of aluminum have largely prevailed. Painted normal steel silos are occasionally used (despite subsequent follow-up costs) or, for price reasons, partially GRP silos (made of plastic). Stainless steel silos, which are very expensive but also extremely stable in value, are used less often.
In the case of the outdoor silos, condensation often forms due to the temperature-controlled tank truck conveying air and solar radiation. Therefore, silos can be equipped with a head space drying system. In addition, appropriate structural explosion protection is provided for products that are prone to dust explosions.
The vibrating floor has largely established itself as a discharge system because it can be used universally. It has smooth surfaces and no mechanically moving parts and is therefore very easy to clean. Aeration floors are occasionally used, but these have the disadvantage that the loosening air has to be treated, otherwise condensation will form in the silo.
After the discharge device there are dosing devices for feeding the raw materials into the pneumatic conveying systems. A basic distinction is made here between two types of metering devices: sluices with a star-shaped rotor or metering screws with a screw thread that continuously transfer the products into the conveying line. In the case of suction conveying, the introduction of the product is much easier than in the case of pressure conveying, since there is no false lock air that has to be expensively removed via filters in order to ensure an even filling level in the lock or the dosing screw. Dosing screw systems are more complex, but offer the advantage of a higher shut-off accuracy due to the screw geometry and also make it possible to bridge distances in order to dose into different pipe guides. This is particularly interesting if you want to branch from one silo to several conveyor lines.
For indoor silos with smaller tonnages, in addition to round, rectangular or square silos are often used. Here, due to room height restrictions, ventilation floors with loosening are often used.
Delivery, emptying and storage of middle components
In the material preparation area, there are emptying stations for big bags and filling funnel stations for feeding sacks. Filling funnels with aspiration are used to feed the bags. After opening the hopper cover, aspiration begins, which ensures a low-dust task. After the bags have been emptied into the filling funnel, the raw materials are metered into pneumatic pressure conveying systems via metering devices and conveyed into indoor silos.
The same process takes place at the big bag loading stations. Big bags are moved into the big bag emptying station with a hoist and are docked dust-tight on a big bag connection system. The bulk materials are metered into a conveyor line via metering devices and conveyed into the internal silos. The interior silos are selected via a central, barcode-monitored coupling station.
Emptying systems for big bags
Since the trend towards medium-sized delivery containers continues to increase, more and more emptying systems for big bags are being used, with a double ring connection system in which the big bag's outlet is slipped over a pipe. A press-on cover creates a dust-tight connection; only then is the cord of the big bag opened. Dust can form, especially when the big bag is undocked and folded. There are preventive measures here, such as B. evacuating the big bag through an installed aspiration system. It ensures that the big bag is largely without product and air.
Control sieves of all incoming raw materials
Due to the new food hygiene regulation and the HACCP regulation, it makes sense to carry out control sieving when receiving the raw materials. These control sieving can take place after the discharge from the external silos, after the big bag emptying station or the filling funnel stations. Eddy current screening machines are preferably used. These have an inlet with a feed screw that transports the product into the sieve area, where the coarse material is automatically sieved out. The fines are fed directly into the pneumatic conveying through the fines outlet.
The eddy current screening machine was further developed. In the new variant, the feed side is decoupled from the sieve side, which offers many advantages: An additional metering element can be dispensed with, which results in a lower overall height; an individual setting of the speed to the respective product is possible; In addition, this machine can be dismantled when installed using quick-release devices, so that the screen basket can be inspected quickly and easily without having to dismantle the machine.
Conveying, dosing and weighing of large components
Compared to mechanical conveyor systems such as screws , spiral conveyor screws and the like, pneumatic conveyor systems have largely prevailed.
Suction conveyor systems are particularly useful where there is a need to convey from many product feed points (silos) to a few delivery points (mixers). The product infeed is extremely easy and dust-free with suction, as there is no overpressure. The fan is always located at the end of the system and creates a vacuum, which is used to suck the material through the lines. The raw material is not polluted by "warm" conveying air.
Pressure conveying systems are useful wherever a product feed point (e.g. feed hopper) is to be conveyed over long distances to many discharge points (silos). Since the product has to be metered in against the air flow, sluices or pressure vessels are required for product feed. The product delivery, however, is easier. The fan is always located at the beginning of the system and generates the pressure with which the conveyed material is blown through the lines.
A combination of suction and pressure conveying systems is mainly useful where there is a need to convey from many product feed points (silos, big bag emptying stations, filling hoppers) to many delivery points (mixers).
For sensitive raw materials, impulse conveying systems have recently been increasingly used, which work at a speed of 1 to 4 m / s (normal flight conveyance: 20 m / s), thus conveying much more gently and using less energy. But they are much more expensive due to the outlay on equipment.
Decisive for the achieved weighing and dosing accuracy are the dosing devices in the product feed, which were described above, such. B. feeders, locks and screw systems. In convenient systems, these metering devices are frequency-controlled, ie the flow rate is thinned out shortly before the target weight is reached (approx. 1:10) so that very high levels of accuracy are achieved.
In the following three variants of suction weighing systems are described (there are similar variants for pressure weighing systems):
One-pipe system
With the single-pipe system, a conveyor line leads from all product feed points - be it filling hoppers, big bag feed stations or external / internal silos - to the conveyor scales. Due to the different distances between the product loading points (e.g. silos), there are different product follow-ups that can affect the weighing and metering accuracy and must be taken into account in the control.
Multi-pipe system
In the multi-pipe system, a conveying line is led from each product feed point to a valve switch with a fresh air or fine metering valve, which is connected to the conveyor scales. This system has the advantage that the product overrun from the valve switch is always the same, so that a higher level of accuracy is achieved than with the one-pipe system.
Central weighing system
For reasons of performance, a central weighing system is ideal for many delivery points and several delivery points. With this solution, the individual components in the multi-pipe system are conveyed from the product loading points to a central conveyor scale, which is equipped with an electromechanical weighing device, and weighed there. The weighed batch is transferred to a secondary container and from there it is conveyed to several consumers (kneader, mixer, etc.) by pressure conveyance. In order to achieve high throughput rates, the next batch is already being put together in the central scale.
A horizontal material flow is recommended for new buildings, since the individual raw material tasks are on the same level as the mixer. Of course, this has a decisive effect on the investment costs. With vertical material flow , raw material components are delivered on level 0, while the mixer is e.g. B. is on level 2 or 3. The raw materials delivered at ground level (on level 0) must be transferred to the closed system with as little dust as possible and then transported to level 2 or 3. The suction weighing technology has clear advantages, as it works with much less dust than pressure pneumatics. The product feed is also much easier, as there is no false air and there is therefore no need for airlock ventilation.
Suction weighing systems
The recipes are becoming more complex and consist of more and more components. The suction weighing systems are predestined for this, as you can get to one point with a large number of lines. The pressure conveyor technology with pre-containers above the scales is much less favorable. The conveying behavior of the raw materials and the flow velocities should be known. Since the weight ranges of the components are very different, one moves on to assign these corresponding conveyor lines with different accuracy classes. In the case of mixer feeds, there is often a suction weighing system for large components in the range of over 80 kg, one for medium components between 20 and 80 kg and one for smaller quantities between 2.5 and 50 kg. Since the container sizes of the conveyor scales are exactly matched to the respective electromechanical weighing systems, it is possible to operate with higher accuracy with smaller systems, since the pipeline cross-sections are correspondingly smaller. Under certain circumstances it can make sense to assign the conveyed goods to specific lines (e.g. light lines: flour , salt , etc., dark lines: cocoa ). If contamination is not permitted, separate feed systems must be provided for the various conveyed goods. There is also the option of pre-weighing small quantities and then conveying them to a collective scale.
Operator-guided, manual weighing of small quantities
An operator-guided, manual weighing center is useful if very small quantities, such as additives or flavorings, etc., are to be weighed, which, however, cannot be fully automated due to their consistency (physical properties) or their proportion of the recipe (quantity and frequency). However, it is precisely these small quantities that have a decisive influence on the recipe. They must therefore not be fed into the mixing process in an uncontrolled and undocumented manner.
A maximum of three scales with different weighing ranges can be connected to one workstation. A printer is used to print material accompanying documents - also with barcodes - on paper or labels . The raw materials are identified using a barcode reader. The operator reaction takes place via keyboard or externally via buttons. Depending on the application, the weight display can be designed to increase or decrease. The large actual value displays are supported by a bar display, which also shows in color when the tolerance window has been reached.
Fully automatic weighing stations
This version is the ideal solution for weighing a large number of ingredients with a very high batch frequency. The system is particularly suitable where difficult products such as B. flavorings , enzymes , additives , colorants, etc. should be automated. The parallel weighing achieves a frequency of over 100 batches per hour without contamination and mixing, since each batch is in a separate container. Containers with a barcode are used instead of the linearly movable collecting vessel. These are carried out via a timing belt under the dosing points and collect the small components that are automatically weighed to the gram. A different recipe can be assigned to each container. The unambiguous barcode identification of the filled small containers ensures that the correct small component is transferred to the correct mixer; at the same time, contamination is excluded.
Handling of liquid components
Large quantities are delivered in silo vehicles and stored in tanks - lying or standing. Depending on the consistency of the raw materials used, these tanks must be heated or insulated. This also applies to liquid components delivered in containers or drums. The feed to the mixer can be done volumetrically via flow meters or - more safely - via gravimetric weighing systems. Depending on the requirements, the delivery lines can be insulated or heated. For fluids that flow well, such as B. water, additive weighing systems are used. These are container weighing systems in which the liquid components are dosed and weighed in the appropriate composition via coarse / fine dosing valves. Fats and poorly flowing oils are tempered and filled into containers of negative weighing systems, from which they are then negatively weighed. Pressure is often used to support the exit. With gravimetric systems you can be sure that all liquid components are transferred to the mixing process in the correct amount and with the required tolerance.
Significance of process IT in relation to system availability
The process control and visualization technology has a special task in the loading process, especially when recipes need to be changed frequently, quick reactions to changed market trends or capacity expansions are pending. Maintenance and cleaning programs ensure a preventive inspection, timely fault reports ensure quick troubleshooting. This enables the system availability to be increased significantly. In modern mixed operations, the sensitive issues of ease of cleaning and flexibility are closely linked. However, they are to be considered project-related and individually. Therefore, an exact specification sheet and a specification sheet derived from it are required for an optimal system design. A target costing study (on life cycle costs) shows that the follow-up costs for the conversion and cleaning during operation are a significant factor that should not be disregarded in all investment decisions.
EU regulation EU 178/2002
The EU regulation EU 178/2002 allows process technology and process IT to grow closer together from January 1, 2005. Full automation naturally requires the most modern IT concepts that meet these regulations. All process steps - from production to packaging and shipping - must be made transparent. The focus is on consumer protection and proof of origin as well as risk minimization for the manufacturer. The requirements are high, it is about quality control across all processes in the supply chain, i.e. from the receipt of raw materials through the manufacture of the product to delivery. All processes and results must be available for testing. Because batch tracking does not end with production: A warehouse management system provides information on storage and retrieval as well as storage locations. For this reason, batch tracking and tracing have a strong influence on both process engineering and process IT.
All processes involved in the "mixing" value chain must be optimally coordinated. The solutions and process stages are as diverse as the mixed products. Due to the high degree of automation in the bulk solids processing industry, it is important - regardless of how many raw materials are used and how large the product variety is - that the automatic feed systems can be seamlessly integrated into the overall "mixing" process without interface problems, which is the basis for top quality mixtures is created.