Cure Feeder Problems in Twin-screw Compounding.

* The dilemma for compounders with starve-fed twin-screw extruders is how to keep the formulation constant within the extruder barrel. Compounders rely on feeders to meter polymers, fillers, and additives into the extruder to achieve specific properties in finished blends. Say that a compound specification calls for 36.

Cure Feeder Problems in Twin-screw Compounding. 1

1% filler with a tolerance of [ or -] 2.0%, but ash analysis of pellet samples from the extruder range from 34.5% to 40.

5% (see Fig. 1). Average filler content is within the target specification, but the distribution is too broad.

[FIGURE 1 OMITTED] If pellets are post-blended, this averages out variations in the material delivered from the feeder and will meet the ash specification (Fig. 2). While post-blending may solve this problem, it's not an economical approach to compounding.

Such feeding problems may appear randomly, periodically, or constantly--and each level of frequency indicates a different problem that requires a different solution. [FIGURE 2 OMITTED] Random feeder problems Product may randomly fail to meet specifications for ash analysis and/or mechanical properties when the feed rate from one or more feeders swings higher or lower, resulting in more or less material entering the extruder barrel. Imagine, for example, that a polymer feeder momentarily feeds above setpoint at the same time that a filler feeder is feeding below setpoint.

Cure Feeder Problems in Twin-screw Compounding. 2

These two materials fall together into the twin-screw extruder and are conveyed downstream as a "batch" that is below the target filler loading. Now imagine that after some period of time, these same two feeders swing to the opposite extremes, resulting in a "batch" falling into the extruder with a filler loading above target. The frequency at which the feeders vary, the amplitude of the variation, and the residence time in the extruder will determine the severity of this problem.

If the intervals at which feeders are varying are longer than the residence time for material in the extruder, the batch that is below the target filler content has little chance to mix with the batch that is above target. The "low-filler" batch will be in the pelletizer when the "high-filler" batch enters the extruder. The screw design for twin-screw compounders can be modified to increase backmixing somewhat, but there is no screw design that will cure this problem altogether.

This problem usually occurs when either belt feeders or screw feeders are run well below their design capacity. The solution is that the frequency of the feeder variation must be increased to fall within the residence time of material in the extruder. The more frequent the variation, the better.

With screw feeders, when the screw diameter and/or pitch is too large for the feed rate, the screw runs very slowly and produces low-frequency variations. This problem usually produces large feeder errors since the feeder controller is also trying to control the speed of the screw at the low end of its operating range. The screw diameter and/or pitch must be selected so that the feeder screw runs as fast as possible.

Consult the manufacturer of the feeder to identify alternate screw types. Belt feeders that are too wide will also run slowly. Again, slow belt speed makes the problem worse because the controller has difficulty in this range.

This is an easy fix. Adjust the discharge slide gates so that the feed material occupies only a small area of the belt. This will require the belt to run much faster.

Repeatability is the term used by feeder manufacturers to describe the amplitude of feeder variation. Gravimetric feeders are capable of maintaining [ or -] 0.5% repeatability at two standard deviations (2 sigma).

This applies to polymers fed in pellet form. Typically, however, most reinforcing and non-reinforcing fillers are powders and flow poorly, so their repeatability values are worse. Such fillers are usually metered by a primary weigh feeder into a side-feeder of a twin-screw extruder.

If the side-feeder is also run in a starve-fed mode, as suppliers usually recommend, feed-rate variations from the primary weigh feeder are transferred directly to the compounding extruder. If the screw speed of the side-feeder is reduced to the point where the screws are flooded, then only the speed of the side-feeder screws determines the feed rate into the extruder. So the side-feeder screws should run at a speed that keeps a constant level of material covering the screws--i.

e., when they are flooded. Note that repeatability is also a function of the sampling interval.

Most feeder manufacturers state feeder repeatability for one-minute sampling, which is okay since mean residence time in a conventional twin-screw compounding extruder is in the range of 30 to 60 sec. But high-speed, high-torque compounders with extruders running at screw speeds above 1200 rpm can push mean residence time below 10 sec. In these cases, feeder repeatability must be checked at intervals shorter than a minute.

The residence time in high-speed compounding extruders makes them extremely sensitive to feeder variations and prone to resulting quality problems. Periodic feeder problems If product periodically fails to meet specifications for ash analysis and/or mechanical properties, the culprit is probably the gravimetric feeder's refill cycle. Loss-in-weight feeders must be refilled during continuous operation, but they can't run in gravimetric mode while refilling.

As a result, actual feed rate varies from setpoint during and just after refill. Feeder makers have improved their controls to minimize this variation, but some is inevitable. Actual feed rate during and immediately after refill is usually above setpoint, though the system eventually stabilizes.

Common symptoms are momentary surges in filler loading accompanied by surges in extruder torque and sudden blockage of extruder screens. It is usually the poor flow characteristics of particulate fillers that create this problem. If these fillers are introduced into a side-feeder, reducing the speed of the side feeder just to the point of flooding will eliminate the problem.

Another cause of feeder surges is long refill intervals. If you refill the feeder more frequently with less material, it takes less time, so the feeder spends more time in gravimetric control. Constant feeder problems If product consistently fails to meet specifications for ash analysis and/or mechanical properties, the culprit is probably calibration of the feeder weighing system.

The ability of gravimetric feeders to introduce a specified amount of material depends on calibration of a scale or load-cell weighing system. If the weighing system is out of calibration, the feeder indicates it is feeding the specified amount, but it may not be. The solution is routine feeder-scale calibration, preferably using NIST-traceable weights.

A span value can be entered to adjust the scale reading to match the reference weight. Be sure to use reference weights with at least the same resolution as the feeder display. Leaking refill systems can also cause gravimetric feeders to feed the wrong amount of material.

If the refill system is leaking material into the feeder during continuous operation, the loss-in-weight feeder will compensate by feeding more material. The feeder controller will indicate that everything is okay, since it is feeding to setpoint. The easiest way to identify this problem is to decouple the refill valve from the feeder and make a visual observation.

An alternate method is to force the feeder to be refilled with the feeder stopped and look for an increase in weight on the load cells after the refill valve has closed. The weight on the load cell should not change with the feeder stopped. If the refill system leaks, fix it!

Adam Dreiblatt has over 20 years' experience troubleshooting twin-screw compounding extruders. For the past 10 years he has offered consulting and training through his own firm, Extrusioneering International Inc. in Randolph, N.

J. He can be reached by e-mail at .

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Micro Weighments of Compound Ingredients.
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Micro weighments of compound ingredients The first remotely controlled, automatic weighing system installed for rubber compounding took place around 1955, with the weighing equipment consisting of mechanical scale levers connected to dial indicators having potentiometer assemblies mounted on the dial spindles and simple Wheatstone Bridge circuitry activating electro mechanical relays for material feeding control. That first system, and several which followed, included the automation of the feeding and weighing of carbon black and oils, with the polymer stocks being manually loaded on a belt conveyor mounted on a mechanical/dial scale. The control for sequencing the weighing and mixer charging cycles was accomplished through a motor driven cylinder having adjustable wiper contacts to control the variable parameters of the system. Initially, no attempt was made to automate the micro ingredients. 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This term is used in reference to the weight sensor/transducer element in the system and defines the smallest usable increment that a weight signal can generate to be used for display and control. * Repeatability. It is one thing to be able to provide an automated system that gets the accuracy factor under control some of the time, but a successful system is only acceptable when accuracy is present just about all of the time. The ability of a system to hit accuracy targets consistently is called repeatability. * Net weighing. This is used in batch weighing when one or more than one material is fed into a hopper mounted on a load sensor/transducer assembly with automatic re-zeroing of the system between individual material weighments. This technique is in contrast to loss-of-weight or weight by subtraction which is described in more detail later. Original attempts at micro ingredient automation Since several types of carbon black were fed by screw feeders and successfully automatically weighed in a common weigh hopper connected to the back of a mixer through a down spout, the original attempts at micro ingredient weighing used a smaller version of that same concept. The only difference was that the down spout came into the side of the mixer because of physical layout constraints. Several serious problems became evident rather quickly using this net weighing technique, including the limited number of materials which could be handled, the fact that some of the materials such as sulfur and zinc oxide stuck to the sides of the weigh hopper and the down spout, the resolution limitation of one part: 1,000 resulting in minimal accuracy, the effects of vibration on the mechanical sale equipment, plus the expense of having one of these systems per mixer, led to the evident conclusion that this was not a viable way of automating micro ingredient weighing. From these early automation attempts, the problems started to come into focus in the categories of accuracy, materials handling and cost. Introduction of load cell technology One major improvement in the instrumentation aspect of the system was made available through the introduction of electronic strain gage load cells instead of mechanical levers and dials. This resulted in resolution capabilities of one part: 5,000, with the ability to provide electronic damping and filtering for better vibration control. This new technology provided some "quantum jumps" in the area of accuracy, one of the focus target problem areas to be resolved. Load cell instrumentation also opened up new possibilities in the area of formula input control through the use of analog to digital and digital to analog devices. Digital thumbwheels and punched cards became the acceptable mode for formula control, and data recording became a reality. The other two problem areas of micro ingredient automation, however, namely the materials handling aspect and a total system cost, were not helped with this upgrade in instrumentation. Attempts at solving the materials handling problems With the development of low melt index sheet material which could be used to make bags, the idea occurred that putting the micro ingredients into this type of bag and dropping the entire bag into the mixer would eliminate a lot of the sticking problems originally experienced in the common weigh hopper concept tried initially. This led to the realization that filling bags at a central location would enable one system to serve multiple mixer lines which would help the cost justification for an automated system. But this left the challenge as to the best way to fill the bags. Preparation of master batch pre-blends was tried with the pre-blended batch being transported to a single scale which would be used to fill the bag through a single filling spout. An operator standing at the filling spout placing empty bags and sealing the filled bags was used originally. The next step was the attempt to replace the operator with an automatic bag handling system. One type using bags connected through a tab and pulled from a box in a fan-fold pattern was used, and the next attempt was the use of a form/fill/seal system where tube stock was taken from a roll, a bag formed and filled with the pre-blend and sealed forming the bottom of the next bag. From a bag handling point of view, these machines worked very well. However, the old problem of materials handling reared its ugly head again. The pre-blended batches were not absolutely homogeneous as they came out of the preblender, and transporting the batches from the blender to the filling station caused segregation, and as a result, there was no way to assure the correctness of the proportions of the materials that were fed into the bags. Using a net weigh scale above the filling spout of these automatic bag handling machines did not eliminate the materials handling problem of the blended materials sticking in the weigh hopper and bag spout. Loss-of-weight control About the same time as the introduction of low melt bags, and automatic bag handling, a new weighing concept was developed called loss-of-weight. Although you are probably familiar with this term, briefly it means that a weigh hopper and feeder assembly are mounted on a scale platform, the weigh hopper is filled from an overhead supply bin, and after taring-out (re-zeroing of the total load), the feeder runs to weigh-out (or weigh by subtraction) the required batch amount. The primary advantage of this type of weight control is that there is no weigh hopper or contacting surface to which any materials can stick after they are weighed, resulting in much better weighing accuracy of the material being handled. The problem of having one filling spout with an automatic bag handling system, however, did not eliminate the segregation and non-homogeneous blend problems already mentioned. All this solution did was put a more accurate amount of unknown quantities of the blend into the bag. At this point in the development of loss-of-weight feeding, there were still some disadvantages, one being the very large dead load to live load ratio of the hopper and feeder equipment related to the actual ingredient quantity to be weighed. This required that some method of off-setting this dead load through a mechanical device be developed, so that a load cell of a capacity close to the maximum weight required for any given batch could be used. By this time though, load cell technology and instrumentation had increased to the point where resolution capabilities of 1:10,000 were available so the technology trend was in the direction of providing better accuracy. Another disadvantages of using loss-of-weight control was the fact that each ingredient needed its own supply bin, re-fill feeder and scale system which drove the pricing of a multiple ingredient system to the point where it was hard to cost justify. Although the accuracy factor in an automated system was heading in the right direction, the demands of some of the chemicals to be used in the feeder/scale combinations available were such that these systems were still not up to a level where all of the requirements could be satisfied. Because of the material handling characteristics of most of the ingredients to be used, auger type feeders are required. Conventional type feeders using two speed drive control provides a turn-down ratio (fast feed rate to slow feed rate) of only approximately 50:1; and although the feeder ran slower at the dribble rate, the volumetric through-put does not change, resulting in a large amount of material to be concerned with at the conclusion of the weighing. Granted, this factor is not as critical in loss-of-weight control as it is in net weighing, but it is still a significant factor considering the inertia of a weighing system during feeding and material flow cut-off on completion of the weighment. The "now" generation of transducers and feeders Everything discussed so far was background information leading up to the equipment available today, which has the capability of meeting all of the challenges including accuracy, materials handling and cost, which have been eluding complete solutions until now. First let's consider the transducers which are being used. Vibrating wire or strain gage types still have limitations in the 1:10,000 part range of resolution, and although there is a gyro based transducer available, which has much higher resolution capability, it is very difficult to implement in a dynamic weighing application. This leads us to a transducer now available called magnetic force restoration type. This device starts at a null balance point and as a load is applied, the current required to drive the transducer coil back to that null point can be measured very precisely resulting in a weight sensor having usable resolution and display capability of 1:120,000. This type of transducer is available now, built into a scale platform sized 600 x 750 mm (23.6" x 29.5") for example, which is large enough for the mounting of a hopper/feeder assembly resulting in a loss-of-weight scale with a capacity of 240 kilograms (529.2 pounds) which can be read to the nearest 2 grams (.004 pounds or .064 ounces). In addition, due to the flexure design included in this scale platform, it is possible to pre-load this scale with up to 65 kilograms (143 pounds) to offset the "dead load" of the hopper and feeder assembly without eroding the live load capacity and readability as previously mentioned. With this new technology, the weight signal from this scale platform can be readily converted into an RS232 format for interfacing with just about any microprocessor or micro computer type device. However, in order to take advantage of this new level of weight sensor/transducer capability, it is necessary to use a new feeder design which has a much higher turn-down ratio than those previously available. Since auger type feeding is still required (because of the handling characteristics of the ingredients being handled), the use of two speed drive control with two different diameter augers is the answer. Running both augers at the high feed rate for the major portion of the feed cycle, and then running only the small diameter auger at a much lower rate for the dribble feed cycle results in turn-down ratios approaching 500:1, eliminating the previously described feed rate problems as the point of cut-off. Empirically it has been found that the accuracy of a weighing, when the proper size and type feeder is mounted on a properly sized scale platform, will be not more than plus or minus 3 divisions of the resolution. From this input, you can see that it is not possible to expect accuracies in the range of up to 10 kg. (22.05 lbs.) to plus or minus 6 gms. (.01 lb.). With the materials handling problems being resolved, the accuracy capabilities being available to meet today's compounding requirements and on the basis of using low melt bags as the best method of assuring that the right quantity of the right material gets into the compound, the only thing left is the best way to fill the bags. Figure 1 shows the optimum system which incorporates all of the current technology. Although only three loss-of weight stations are shown, an unlimited number of stations is possible, since they are located in a row along both sides of a container conveyor which can be as long as required. Each scale platform is mounted on a portable stand, so that they can be positioned as required, and if necessary different capacity units can be moved into position as formulas vary. In addition, on each scale platform there are inverted V tracks, and under each hopper/feeder assembly there are V-grooved wheels, enabling any hopper/feeder to be placed at any scale station. With this arrangement, the minimum number of scales can be used (this is where the cost savings occur) and a large number of hopper/feeder assemblies can be kept stored in a convenient location and put into place as required. Keeping a hopper/feeder dedicated to a particular material also saves time in cleaning and eliminates the possibility of contamination if one hopper/feeder unit is used for more than one material. Under the discharge nozzles of the feeders which have been wheeled into place, there is a conveyor assembly consisting of equally spaced containers into which the empty bags are placed. The spacing of the loss-of-weight feeder assemblies will coincide with the center lines of these containers; the conveyor will be controlled in such a manner that they will be automatically indexed one increment at a time. When the indexing cycle is complete, each scale weighs-out its required quantity directly into the bag, with the formulas being retained in memory in the micro computer which runs the entire system. With the number of scale platforms equal to the maximum number of ingredients ever put into any compound, and portable hopper/feeder units equal to the total number of ingredients ever used, moving these assemblies into the proper position gives unlimited flexibility and ingredient combinations. With this type of micro ingredient weighing system, one operator stands at the end of this container conveying assembly to place empty bags into the containers as they are positioned in front of him, and he also takes out the filled bags as the arrive, heat seals them and places them on a pallet or into a tote type container for delivery to the mixer stations. Although not shown on the reference drawing, dust control is built into the system by placing dust "pick-up" points at the feeder discharge location at each scale station. Of course with today's digital technology, anything that happens on the bag filling line can be recorded, and as a further safe guard, rugged industrial proximity switch identification can be provided so that the system will not run unless the materials that are called for in the formula are in fact in position on the scale platforms. As a final check that the proper amount of material has been introduced into each mixer batch, the filled bags can be placed on to an automatic bag indexing conveyor at the side of the mixer inlet hopper, and a scale platform can be located at the discharge end of that conveyor to catch and check-weigh the bag weight just prior to its being discharged into the mixer hopper. 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Fears Over Twin of Collapsed Genoa Bridge in Venezuela
Fears Over Twin of Collapsed Genoa Bridge in Venezuela
Maracaibo (Venezuela) (AFP) - Venezuelans are concerned over the safety of a "twin" viaduct of the collapsed Morandi bridge in Genoa, Italy, after a fire on the concrete structure caused a major blackout.The 8.6 kilometer (five mile) General Rafael Urdaneta viaduct links second city Maracaibo with the rest of Venezuela.Designed by Italian structural engineer Riccardo Morandi, it predates by five years his 1967 bridge in Genoa that collapsed this week causing the death of 39 people.Experts are preparing a report on the condition of the Venezuelan structure following the fire last Friday which destroyed an electricity transformer, forcing the closure of the bridge and leaving millions without power for several days.Marcelo Monot, former director of a private engineering company in the surrounding state of Zulia, said no maintenance had been carried out on the viaduct's reinforced-concrete piers for more than two decades.Also, "the weighing system has not worked for years, so it is not calculating the weight of the cargo vehicles, which represents a risk," he said.Experts from the University of Zulia, as well as engineering and construction specialists, are preparing a report on the condition of the bridge."We will not issue any irresponsible diagnosis . or fall into sensationalism," Enrique Ferrer, president of the Chamber of Construction, told AFP.- Crumbling infrastructure -He said the report would seek to "calm the population" about the 56-year-old viaduct's condition.Venezuelans have long been concerned about the country's crumbling infrastructure after a slump in oil-prices coupled with corruption and mismanagement brought the economy to a standstill, causing chronic food and medicine shortages.The Maracaibo bridge, inaugurated in 1962, remained closed between Friday and Monday and was only partially re-opened by Wednesday.The incident heightened concerns over the structural integrity of the bridge and left the surrounding Maracaibo and San Francisco areas, home to four million people, without power for several days.The government claimed the fire was caused by sabotage, a recurrent explanation offered for the repeated failures of an electricity grid ravaged by lack of maintenance and spare parts.
New Machines to Weigh ICDS Kids - the Times of India
New Machines to Weigh ICDS Kids - the Times of India
Trichy: Childhood malnourishment adversely affects physical and mental growth. Improper and inadequate diet results in poor growth of children. Government-run anganwadis aim to address this issue by improving the nutritional content of foods served to children enrolled there. Anganwadis have now planned to use electronic weighing machines for proper monitoring of children's growth. An official of the Integrated Child Development Scheme (ICDS), which manages the anganwadis, said electronic weighing machines would help better monitoring of children's growth. So far, the 1,808 anganwadis in Trichy district lacked an accurate weighing system to check the growth of children up to six months of age. "ICDS aims to ensure healthy children in society. We will use electronic weighing machines from a couple of days at all the centres," said A Thameem Munisha, ICDS project officer in Trichy. As many as 1,808 electronic weighing machines have been procured for Rs 10,84,800. Bar weighing scales are currently being used at anganwadis to weigh children of different age groups. While bar weighing scale is necessary to weigh babies above six months of age, those below this age can be weighed accurately using electronic weighing machines. Munisha said they are following the new growth chart prescribed by the World Health Organisation (WHO). "The new growth chart enables us to have clear information about babies' growth. We have advised our staff to closely watch the growth of newborns with the facilities available," Thameem said. Records indicate that anganwadis in Trichy district have 133 severely underweight babies, 28,399 moderately underweight babies and 112,513 normal babies. Despite substantial government investment, the number of nourished children is yet to fall. It is said schemes are not being fully utilised by the beneficiaries because of various hurdles. Interestingly, the ICDS promotes adoption of underweight children to improve their lot. "Our staff, public and NGO have adopted severe underweight children in the district so that more attention could be paid for their growth. The programme is working out well. We hope continuous effort will gradually reduce the number of malnourished children," said Munisha.Download The Times of India News App for Latest City .
The License Plate Recognition System By TGW Team Officially Put Into Use in February 2021
The License Plate Recognition System By TGW Team Officially Put Into Use in February 2021
In December 2019, a Thai company specializing in logistics truck weighing system contacted the TGW team to improve and improve the data omissions, false data, and statistical efficiency of the existing weighing platform during the operation process. The problem of information lag caused by low and unsettled expenses. According to the person in charge of the Thai company, such a problem has existed for decades. They have been looking for a brand-new intelligent system, hoping that the system can be connected to the weighing system to integrate vehicle information, weighbridge data, operational meta-information, etc. A large amount of data is integrated into a management database system, and the central management system conducts unified deployment and management of vehicles and personnel, thereby further improving the flow rate of the weighbridge system in the actual logistics transportation system, thereby greatly increasing the income of the enterprise.   After three months of preliminary demand communication and business negotiation, the two parties reached an agreement to start the docking of a large-scale integrated system of vehicle information identification, personnel information identification, and weighbridge data at the end of March 2020. After 5 months of day and night communication and program interoperability, this comprehensive vehicle data synchronization system has been basically completed and entered the commissioning stage. After entering the debugging stage, the chief engineer of TGW program, Mr. Zhu, discovered that in the process of transferring data, because the language of the Thai computer operating system was inconsistent, some files of the dynamic library could not be synchronized and updated in time, and proposed the ideal operating state of the program. A new adjustment has been made. Therefore, the TGW team recommends that customers change the English operating system in time, and realize the smooth operation of the Thai operating software under the English system, and finally completed all technical debugging on the eve of the Spring Festival in 2021.   At the end of February 2021, the Thai company announced the smooth operation of the entire system and officially put it into use, and promised to hand over the company’s 20 logistics, transportation and other major projects in Bangkok to the TGW team, just because this team uses responsibilities and Professionals have solved the problems that have plagued them for 10 years.  
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