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    Sobatech is the worldwide leader in designing, manufacturing & commissioning of Continuous Mixing Systems for the food industry. Sobatech is a passionate family business that helps food producers to simplify the mixing process, reduce labor and improve quality consistency.

    GENERAL LOSS-IN-WEIGHT FEEDER CHALLENGES - GRAVIMETRIC DOSING SOLIDS Sobatech doses its ingredients into the continuous mixing system by means of gravimetric feeding solutions. A gravimetric feeder doses the actual given weight of material per time unit. In such system, the motor automatically alters its speed when a change is detected in the material flow. This eliminates the need for manual adjustment, which ís required when using a volumetric feeder. Such a change in material flow can for instance be the result of the addition of new material or fluctuations in the material density.  In a continuous production process, the dosing of ingredients need to be accurate every split second. Therefore, it is recommended to only work with gavimetric dosing solutions as these are the most accurate and precise feeding solutions available. Sobatech works with so called loss-in-weight feeders which are gravimetric dosing systems and measure the weight reduction per time unit.  LOSS-IN-WEIGHT FEEDER CHALLENGES Generally, there are three challenges to take into consideration when it comes to loss-in-weight dosing. The influence of external forces on the weight sensing device (loadcells)  The controlling of the motor speed during refilling (gain in weight)  Powder bridging and arching in the dosing hopper  1. THE INFLUENCE OF EXTERNAL FORCES ON THE LOADCELLS Generally a loss in weight feeder interacts with the process by receiving and discharging material. Yet, it has to remain isolated from other process equipment in the plant for maximum weigh accuracy. Sophisticated digital filtering algorithms can be applied to recognize and ignore brief disturbances. However, the cumulative effect of ongoing disturbance degrade overall feeder performance. Loss in weight systems must often commit to extreme high dosing accuracies meaning that very small changes in total system weight have to be detected. This requires a very high resolution yet stable weighing system that is unaffected by environmental variations. In-plant shock and vibrations can corrupt the weight measurement, destroying the basis for feed rate control. What helps preventing this are: Flexible connections between the dosing unit and other parts of the system. Ensure that the dosing hopper has a stable mounting frame.  Use shock mounts to help isolate the feeding system and filter out the accelerations associated with the plant environment Eliminate strong air currents near the dosing unit 2. THE CONTROLLING OF MOTOR SPEED DURING REFILLING (GAIN-IN-WEIGHT) During hopper refill, system weight increases and clearly cannot be used as a basis for feed rate control.  There are two ways how to deal with this so called gain-weight-process. THE CONVENTIONAL METHOD The conventional method is to use a constant metering speed throughout the refill phase. the moment an increase in weight is sensed, the feeder maintains the RPM measured just before the refill process started. As in this method the material feed during refilling is maintained by keeping a constant metering speed, the feeder essentially functions volumetrically. When the refill phase is complete and the material has settled, the feeder senses the declining system weight and returns to gravimetrical operation with the metering speed once again being determined by the actual loss in weight. Depending on the process material compressibility, this traditional approach may or may not generate a sensed weight disturbance as the feeder returns to gravimetric operation. For an easily compressible material for which density changes significantly as a result of so called headload, feeder speed just before refill is somewhat higher that it should be after refill when the material being fed was compressed due to the applied weight of newly added material. As a result, when feeder speed is held constant at this higher speed, overfeeding may occur during refill, and feeder speed is abruptly reduced when gravimetric operation resumes. Such abrupt changes in feeder speed can occur resulting in a (sometimes extended) period of off-spec flow until the feeder settles at the new, proper speed.  THE ALTERNATIVE METHOD Some feeders avoid this shortcoming by memorizing the feeder’s recent weighing history and using that information to smoothly reduce feeder speed during the short refill period. This brings us to the alternative and at the same time best method for managing gain in weight. In this alternative method the feeders weight-to-speed ratio during gravimetric feeding is stored and that data is then used to control the feeder speed during volumetric feeding in the refill phase. In practice this means that the information that connects a certain filling level of the hopper to the corresponding screw speed is memorized. This way – the system can, even though it is dosing volumetrically during refilling, eliminate the effects of increased density as a result of compressibility of the refilling process. 3. FLOW THROUGH THE FEEDER PROBLEMS As the feeder tries to empty the powders below the blockage, the feed rate falls to zero; while the hopper net weight remains the same. Thereafter, feeder speed maxes out in its attempt to dose material that is no longer available. Then, weight loss drops to zero. In a trend line pattern typical of material buildup, weight loss per screw revolution declines more than expected over time as material builds up on the dosing screws. In response, feeder speed increases to compensate for the efficiency reduction. Too much build up could eventually trigger an alarm condition related to feeder speed or violation of weight loss per screw rotation limits. This condition could arise from any of several causes including a different ingredient supplier, changes in storage, temperature or transport practices. Generally, there are two types of flow through feeder problems. ARCHING (BRIDGING) Arching (bridging) occurs when an arch-shaped obstruction forms above the hopper outlet and stops flow.  It can be an interlocking arch, where large particles mechanically interlock to form an obstruction, or a cohesive arch.  A cohesive arch occurs when particles bond together due to effects of moisture, fines concentration, particle shape, temperature, etc. RATHOLING Ratholing occurs when discharge takes place only in a flow channel located above the outlet.  If the material being handled is cohesive, the material outside of this channel will not flow into it and may cake or agglomerate.   Solutions to prevent arching and ratholing from happening are vibrating units, air pads, and/or stirring devices. MORE INFORMATION? CONTACT US! [contact-form-7 id="2619" title="More information? Contact us!"]
    DOSING ACCURACY - Correct weighing of the ingredients is essential for reaching the required product quality. If the various raw materials are not dispensed in the correct quantities to begin with, it will never be possible to produce a correct product. For that reason, the dosing of all solid & liquid ingredients into the continuous mixer is constantly monitored. The line stops and gives an alarm signal if a dosage deviates from the set value (the time and % of the deviation are adjustable). But, what is dosing accuracy and how do we measure it? REPEATABILITY VS. LINEARITY To fully define feeder accuracy it is important to look at two seperate principles of feeder performance. Only when evaluating a combination of these factors, one can make substantiated statements on dosing accuracy. Lets start at the repeatability factor. REPEATABILITY The repeatability measurement is made by taking a series of carefully timed consecutive samples from the discharge stream, weighing them, and then calculating the +/- standard deviation of sample weights expressed as a percentage of the mean value of the samples taken. Simply said, repeatability is the ability to return to the same position multiple times under identical conditions. However, it is important to understand that the repeatability numbers reveal nothing at all about whether the feeder is delivering, on average, the targeted rate. It only says something about how much on average your weights deviate from the total average of your samples. LINEARITY Then we have the linearity factor which is evenly important as the repeatability factor – the linearity factor says something about how much your data, within the operating range of the dosing system, on average deviates from your set value. The so called operating range is the range of flow that a dosing system is able to measure with acceptable accuracy. Basically linearity is the percentage of your setpoint. However, only looking at this number does not say sufficient about your dosing accuracy. For a real-world example, let’s consider a basketball player. If the player is linear, he’ll always get the ball close to the hoop. If his shooting is repeatable, he’ll always shoot to the same location (hopefully, in the basket). The best players are both accurate—hitting the basket—and repeatable—doing it every time. [caption id="attachment_2745" align="alignnone" width="189"] not repeatable and not linear[/caption] [caption id="attachment_2747" align="alignnone" width="186"] repeatable and linear[/caption] [caption id="attachment_2749" align="alignnone" width="186"] repeatable but not linear[/caption] PRACTICAL EXAMPLE Lets now go to a reallife example in relation to the continuous dosing of raw materials that will help explain why it is important to look at both factors, linearity and repeatability when talking about dosing accuracy. Imagine you have a set value of 100 kg/hr and a mean (average) process value of 100.220 kg/hr. In that case your dosing system seems very accurate as it has a linearity percentage of 0.22% (!). However, when looking at the repeatability factor – it might be that the spread of your weights is quite large. If you look at the graph below you can see that eventhough your average value is really close to your set value - there are many moments in time that your system is performing off spec. [caption id="attachment_2743" align="alignnone" width="883"] Measuring feeder accuracy[/caption] In other words, when talking about dosing accuracy – it is crucial to evaluate both your linearity as well as repeatability. Our experience shows that our and many feeding solutions on the market are nowadays so advanced that they can have a repeatability of 0.5%, at for example 2 sigma (meaning that 95.5% of your weights fall within +/-0.5% bandwith from your mean) and a linearity number of 0.25% meaning that within the operating range of your feeder your weights deviate +/- 0.25% from your set value. This results in a product quality that is extremely consistent and completely independent of human error. Please note these numbers are based on laboratory conditions and do not account for possible external factors that have to be taken into consideration and act upon when commissioning the production line. Do you have any questions in relation to dosing accuracy or other processes involved in the continuous production of (food) products? Ask them below.  Continuous regards, Team Sobatech More information? Contact us! [contact-form-7 id="2619" title="More information?"]  [video width="1920" height="1080" mp4=""][/video]
    Naegele Inc. Bakery Systems Partners with Sobatech to Offer Continuous Mixing Equipment to North American Market - To meet the increased demand for continuous, Sobatech decided to expand its international network of local representatives. Today we are proud to officially announce that Naegele Inc. Bakery Systems will be our new continuous representative for the North American Market. As a result of the increased food and quality demand, continuous mixing is becoming more popular every day. “Interest in continuous processing is growing rapidly as food manufacturers seek new ways to increase throughput and product quality while keeping costs down,” said Mike Philip of Naegele Inc. Bakery Systems. Since 1994, Naegele Inc. Bakery Systems has provided the highest quality professional services and support to their clients from new product development to plant automation. Naegele is a family business and the exclusive provider of top-tier bakery equipment and technology with complete technical support throughout all phases of a project from conception to equipment selection through implementation. Sobatech’s continuous mixing equipment complements the existing portfolio of Naegele allowing customers to one-stop-shop providing additional convenience and efficiency. Naegele proofs to be a partner with thorough knowledge of both market and technology. We are proud to join forces with Naegele Inc. Bakery Systems and look forward to serve the increased demand for continuous production of freshly baked goods, cereals, long-life bakery products, convenience foods, meat substitutes, confectionary and snacks. To learn more, visit Neagele online  or follow the company on social media: Facebook, Twitter, YouTube, LinkedIn More information? Contact us! [contact-form-7 id="2619" title="More information?"]     

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