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Blending & Dosing - A Deep dive into the basics of blending versus dosing, controls, maintenance, process integration and more https://www.ptonline.com/knowledgecenter/blending Blending Basics Blending is an efficient, thorough and automated way to combine material ingredients, in pre-determined...

Blending & Dosing - A Deep dive into the basics of blending versus dosing, controls, maintenance, process integration and more https://www.ptonline.com/knowledgecenter/blending Blending Basics Blending is an efficient, thorough and automated way to combine material ingredients, in pre-determined proportions, and then mix them together in preparation for the production of plastic parts or products. In this section you'll discover: Why Blend? https://www.ptonline.com/knowledgecenter/blending/blending-basics/why-blend Every processor has a choice in how to feed material to their process in order to produce saleable product with the characteristics they require. In the past, most processors purchased materials that were pre-compounded into specialized pellets to produce the specific color and properties that they needed. It was a very simple process then, to simply feed these customized compounds into their process. However, the cost of these custom compounds were significantly higher than the cost of the individual raw ingredients. In addition, cost-conscious processors knew they needed to deal effectively with the regrind that was produced from their process and understood that simply discarding it or selling it to others for re-processing cost them money. They could very easily roll it back into their own process if they had a method for introducing it into the material stream at a repeatable, measured rate. In addition, since many processors changed the material, the color and the characteristics of the products they produced, keeping quantities of all the uniquely compounded materials they processed created an inventory nightmare. The solution? Blending and Dosing. By using a precision device for mixing materials together, as needed, inventories are reduced to only the necessary raw materials for the process, there is no costly pre-compounding step and reground material can be rolled directly into the process as required, with no disruption in the process flow. This results in significantly lower material costs, less inventory of materials, more efficient usage of reground material and, if the correct blending/dosing device is utilized, an increase in part or product quality and 100% repeatable results. How Blenders Work https://www.ptonline.com/knowledgecenter/blending/blending-basics/how-blenders-work Doser A doser simply meters one component (shown in red) into a machine throat or a blender, where it is joined with other materials. Dosing devices also known as Feeders or Metering Devices, generally provide for the introduction of a measured amount of material, typically an additive or color, to an existing flow or quantity of material, typically a base resin (virgin) and often, regrind. Dosing at the machine throat: Dosing can be provided as an add-on to an existing flow of material on the throat of a processing machine where it is triggered or speed-governed by the processing machine itself. In injection molding, as the machine cycles, a dose, calibrated to the shot size of the molding machine is introduced into the gravity flow of the other materials. In extrusion, as the machine operates continuously, constant dosing is provided at a certain rate, in step with the speed of the extruder. In some cases, multiple dosing devices may be connected to a single machine throat for the introduction of multiple additives, or simply to provide rapid changeover ease with redundant dosing units already installed. In other cases, materials like regrind may be dosed into the flow - in addition to - or instead of, additives. Often times, some form of mixer maybe installed below the dosing device to enhance the blending of the newly introduced additives with the base resins. The mounting frame for dosing devices of this type is critical to assure: This throat mounted dosing unit comes complete with a throat adaptor and a control that allows coordinated operation with extruders or injection molding machines. The ability to support the supply hopper(s) for base resins above it, as well as the dosing unit (typically installed into the side of the support frame) with solid connection to the throat of the processing machine below it. The ability to readily calibrate the dosing unit to accommodate the additive or material it will be metering. Calibration, is typically accomplished by a catch and weigh procedure, to align the performance of the doser to the material it is metering and the rate at which it will be metering. The frame device must create a void in the base material flow, so that the dosed additive can readily join the flow of material and not be displaced by its flood feed to the throat. The frame may be required to accept a mixing unit below it, without sacrificing structural integrity. Dosing units installed onto processing machine throats may operate either: Volumetrically...by providing doses of additive in measured volumes, by a rotating auger, or a perforated rotating disk, or some other less common means, or Gravimetrically - by weighing the additive as it is metered to assure delivery of additive by weight, not volume. Since most material recipes depend on materials being combined by weight, gravimetric dosing units are the clear choice for the highest precision and reliable dosing. Plus, they do not require calibration to align metering parameters with the delivery of additive. In many cases, gravimetric units are also the more expensive choice, but in recent years a number of new models have emerged that compete in price with the less precise volumetric units on the market. Easily installed and just as easy to remove for cleaning, this dosing unit is a modular compliment to the blender’s operation. Dosing Units in Blenders Dosing units are most popular as an important part of integrated batch or continuous blending systems, where they are relied upon to meter in lower quantity ingredients like color and similar additives. In this capacity, each dosing unit is governed by signals from the main blending control that monitors the need for material by the process it serves while it orchestrates the introduction of all material components. A much broader variety of dosing units are used in this application to meet the needs of demanding blending applications, from very small to very large throughputs and typically, ingredients are fed precisely by weight. Weighing is accommodated either in a single weighing chamber that is sequentially filled by all materials of the blend (gain-in-weight, batch type) or each ingredient bin is continuously weighed so that as material is continuously dosed, the loss of material in each bin can be tracked precisely to control the dosing rate and weight (loss-in-weight, continuous type). Blenders Blending systems are fully integrated, multi-material dispensing and mixing devices designed to precisely and consistently combine materials together prior to plastic processing and create a blended supply of material from a user-programmed set of parameters. Blenders can combine materials by volume (volumetric) or by weight (gravimetric) and may operate either continuously (typical for extrusion) or by batch (typical for injection molding). The use of a blender saves the processor money in valuable additive materials by assuring a consistent metering cycle that does not need to be over-dosed ‘just in case’. The blends are not created until they are required by the process demand and allow the processor to use lower cost materials and consume regrind more efficiently than more expensive, pre-compounded formulations. In addition, since the blender is dealing with all of the materials in a blend, some gravimetric blender controllers can actually keep track of material consumption for purchasing purposes. Continuous Blender Deceptively simple in appearance, this compact blender with touch screen control individually weighs up to 4 ingredients and blends them accurately. Continuous blenders are typically used in extrusion operations where the continuous operation of the blender is considered to operate in a fashion similar to the continuous operation of the extrusion line. These blenders typically operate with the ‘loss-in-weight’ principle, where the ingredients’ supply bins are constantly weighed and the metered quantities of each ingredient are measured by the loss-in-weight of each bin. As the extrusion speed increases of decreases, consuming more or less blended material, the blender reacts accordingly, increasing or decreasing the metering of each component, in step with the process speed. This process, although for years considered state of the art for extrusion, is elaborate and requires a highly complex control to operate reliably, plus a multitude of sensitive load cells (at least one for each ingredient). Care must be taken to assure the operation of each load cell is uninterrupted, or inaccuracies will occur. In addition, since the load cell measurements are impacted by the drain of material in each bin, the control needs to work in direct conjunction with the loading system(s) to make sure the re-supply of material is done at a predictable time to allow the control to re-adjust to the weight of loaded material. Typically, the blender switches to a ‘volumetric’ operation while the bins are replenished, affecting its accuracy momentarily. Metered materials are typically loaded into a main mixing chamber where they will reside for a period of time before being dispensed, usually by open flow, into the processing machine throat. Batch Blender Component batch blender installed on a blow molding machine, primarily to allow precision re-introduction of tabs and tails regrind. Batch blenders were originally designed to be machine mounted and to serve the needs of injection molders or to work offline, creating a supply of blended material for any type of processing. Their main advantages include low cost, simpler design, easy set-up and cleaning and high accuracy. Originally produced in volumetric configurations, batch blenders have been expanded to operate conventionally now as gravimetric units. They have found their way into many operations because of their simplicity, ruggedness and low cost. This includes very low throughput applications, once considered too minimal for sophisticated automation and even extrusion operations. In fact, some extrusion oriented models are capable of blending up to 8000 lb./hr. The batch blender provides a metering method for all materials in the blend, but unlike continuous blenders, the batch system uses metering devices better suited to the nature and volume of each ingredient and is not reliant on a similar method for all ingredients. Typical metering devices include timed flapper or plunger-style valves, rotating augers, and even minute metering corner valves that have the ability to trickle in tiny quantities of material at highly controlled and very repeatable rates. Many batch blenders feature a modular design which allows the manufacturer, or even the processor, to freely select and change the metering devices, based on the changing needs of their particular blending task. The dosing devices are programmed to meter one at a time into a common weighed chamber, which has the only set of load cells on the entire system. Due to advancements in batch blender controls, the traditionally sensitive load cells used on the weigh bin are able to ignore vibrations typical to injection molding by a sophisticated control logic that takes a number of weight readings and then uses its control logic to eliminate readings affected by vibration and then average the remainder for extremely accurate weight monitoring. As each is metered and deposited into the weighing chamber, its specific weight gain is sensed and calculated as a part of the desired blend of materials. Any inaccuracy is noted and the control modifies metering accordingly on the next metering cycle. Several metering cycles are typically included in each batch of blended material, so as time goes on, the blender actually becomes more accurate and self-corrects continuously throughout its operation. The materials are then discharged from the weigh bin into a mixing chamber, which is integrated into the system. There, the blend is homogenized continuously until use, or to a specification set by the processor. Blending Applications https://www.ptonline.com/knowledgecenter/blending/blending-basics/blending-applications 1. Regrind Problem: Process produces rejected or start-up parts/product that must be discarded or sold at a loss as regrind. A common challenge to processors, trying to ensure maximum return on their raw material investment, is the production of rejects, either at start-up during process refinement, or as a part of the process (sprues, runners, edge trim, tabs and tails, etc). Most processors simply cannot endure the cost of rejected waste. Although selling this reground material can offset the cost to some degree, the best solution is to roll the regrind back into the process as quickly and as accurately as possible. Solution: Regrind Dosing/Blending The processor can easily determine the amount of regrind they can expect (compared to virgin material), the accuracy required when combining these two ingredients into the process and whether or not the supply of regrind will vary measurably during processing. Once these simple determinations are made, an appropriate dosing or blending device may be selected to assure a repeatable, accurate mix of the two materials. Dosing: For very small amounts of regrind, a dosing device (volumetric or gravimetric) may be easily installed on the feed throat of the processing machine to meter regrind into the flow of virgin material, in pace with the processing rate. Typical features include the ability to meter only when the processing machine is accepting material (injection molding) or constant feed rates that are tied to the pace of the processing machine (extrusion). If needed, a mechanical or static mixing device can be added below the dosing mechanism to homogenize the mixed materials, before entering the feed throat. Blending: For larger, or varying amounts of regrind, a blending device allows for automating the process of combining the two materials and includes a mixing process. Both virgin and regrind quantities are now measured by timed loading, dispensing or metering, and levels are monitored by the control in the event that material variations occur. Often times gravimetric load cells are employed so that minute changes can be sensed and accommodated automatically for the highest level of accuracy. Typically, these blending devices also include the ability to add additional additive dosing devices to them so that the measurement of all ingredients of the process are automatically controlled by a single blending unit. Color/Additive Introduction: Process requires the precise use of small quantities of (expensive) color or other additives. In order to achieve the necessary product characteristics, additives are required for the final product to be produced. Pre-blending these additives manually with quantities of virgin, possibly along with regrind is time consuming, inaccurate and ingredients may be poorly mixed or even separate again prior to processing. Typically, in order to be sure that the necessary processing characteristic (i.e. color correctness) is achieved, more of the costly additive than is required is typically introduced. The process suffers from high cost, inaccuracy and poor repeatability. Solution: Additive Dosing/Blending Once the processor simply determines the amount of additive(s) required and the nature of those additives (powder, pellet) an appropriate automated device can be selected to blend the materials together, accurately, repeatedly and in-step with the process. Dosing: For simple introductions of one or two additives, a dosing device (volumetric or gravimetric) may be easily installed on the feed throat of the processing machine to precisely meter the additive(s) into the flow of virgin and or virgin/regrind materials, in pace with the processing rate. Typical features include the ability to meter only when the processing machine is accepting material (injection molding) or constant feed rates that are tied to the pace of the processing machine (extrusion). If needed, a mechanical or static mixing device can be added below the dosing mechanism to homogenize the mixed materials, before entering the feed throat. Blending: To fully control all of the materials required for the process, a blending device allows for automating the process of combining all materials and includes a mixing process. Virgin, regrind and the smaller, critical quantities of additives are now measured by timed dispensing or auger metering and all levels are monitored by the control in the event that material variations occur. Often times gravimetric load cells are employed so that minute changes can be sensed and accommodated automatically for the highest level of accuracy. A wide range of metering devices for the smaller additive amounts have been developed to allow not only extreme precision in the process, but to eliminate the need to “over-dose” to assure proper coloring. This sophisticated, yet simple to operate device, keeps track of all material dynamics to assure an accurate blend being delivered to the process with each and every cycle. Inaccurate dosing at the machine throat due to material variations or, the calibration process too time consuming. Processors who have employed dosing devices at the processing machine throat may seek to further improve their process by moving to a higher level of accuracy. Calibrating the dosing device prior to starting the process for each new additive or job may be found to be time consuming or challenging for shop level workers. Inaccuracy and over-dosing are typical results. In addition, simple dosing may not accommodate variations in the regrind supply nor address variations in the additive’s flow characteristics. Solution #1: Gravimetric Dosing The use of a dosing unit that actually weighs the metered material permits rapid start-ups with only infrequent calibration of the unit itself to assure its weight measurements are accurate. Thereafter, only inputting the required feed rate into the dosing control is required. The gravimetric device assures that the proper dose of additive is provided by weight, with each and every metering cycle. Solution #2: Gravimetric Blending A blending device allows for automating the process of joining all materials and includes a mixing process. And because of its gravimetric load cells, all variations in the process are accommodated automatically for highly accurate, consistent results. Virgin, regrind and the smaller, critical quantities of additives are now measured by timed dispensing or auger metering and then weighed so all measurements are constantly corrected by the control in the event that material variations occur. The device needs only infrequent calibration to assure its weight references are accurate, and then each processing job or material variation requires only the inputting of the required rates into the control for set-up. Compare Blender Technologies https://www.ptonline.com/knowledgecenter/blending/blending-basics/comparing-blender-technologies Comparing Blender Technologies; Volumetric vs. Gravimetric What’s the best way to meter material? By volume or by weight? Although blender technology was originally developed to using volumetric principles, in recent years, higher precision gravimetric blenders have emerged as superior, simpler to use, with more model available and comparable in cost to lower accuracy volumetric models. Comparisons between the two are: Operation: Volumetric units control metering devices by time only, with a presumption that the metering device has been manually calibrated to relate the volume of material metered to the time the dosing device is operating. Once calibrated, the dosing device is presumed to deliver a relatively consistent volume of material per second. Gravimetric (batch) blenders also meter based on time. However every dispense cycle is verified by weighing the dose and the control system is designed to ‘self-correct’ on subsequent doses, based on the weighed results. This self-correcting operation makes no presumption on accuracy, but actually measures the metering results and adjusts as needed for very high accuracy. Set-up for Operation: Volumetric blender controls are basically a series of timers and sensors designed to make presumptions of metering quantity (loosely related to material weight) and the user sets the timers according to the necessary volume of each material desired. Primary to the function however, are the initial step(s) of calibrating the metering device(s) used, to the material being metered, by time-consuming catch and weigh exercises and charting the results. This is a critical step that requires skill and manual math to assure the timer settings inputted into the blender control will deliver the correct volume of each material based on time. Gravimetric blenders require no calibration for set-up. Since each dose of material is weighed as a part of its normal operation, the blender automatically provides its own form of “catch and weigh” exercises as a normal part of each blending cycle. As a result, the user can directly input specific weight or even ratio percentage settings into the control with no translation into time settings. Operation, although complex inside the control, is actually significantly simpler for the user. Accuracy: Volumetric blenders meter by timed sequences of volume doses with a presumption that the volume of the metered material does not change significantly enough to alter the results and that the material supply will never falter or be interrupted by bridging or other common flow problems. In cases where flow is consistent and the material mass does not change and/or the need for accuracy is not crucial, a volumetric blender, once set-up correctly can deliver what could be termed a fair level of accuracy. Unfortunately, the presumption mentioned above is often trumped by unexpected material problems. Volumetric blenders need to have consistent, free-flowing materials to work at all. Any change in the flow-ability of the material drastically affects the already marginal accuracy because the screw runs for X seconds and has no clue about whether any material was delivered – let alone, how much. Gravimetric batch blenders use weight readings to verify virtually every single metered dose of all materials, with no assumptions. If a material does not meter due to flow blockage or is momentarily altered, the gravimetric blender will accommodate in subsequent cycles to assure that the blend delivered, is done so based on the desired weight. All variations in flow, mass, time, etc. are accommodated and corrected in weigh blenders to deliver what could be called the highest practical accuracy available for an automatic blending system. Comparing Blending Alternatives You have several choices when it comes to how you will introduce materials into a blend suitable for your processing requirements. Oddly enough, the method that seems least expensive may be the most expensive in the long run so you need to examine the choices carefully to see what is best for your operation. Scoop & Weigh The “scoop & weigh” method is labor intensive and typically a very inaccurate process, meaning that you have no real control over your blending costs or accuracy. Human error can run rampant. Typically, colorants are used in higher quantities than necessary, leading to higher costs than necessary but what if colorants or performance additives are shorted? Then, product performance and appearance can vary greatly – leading to dissatisfaction among customers. Comparing technologies Keeping an inventory of unique formulations burdens your bottom line and your warehouse. Summary: Lowest initial investment Labor intensive High level of errors No mixing unless a machine-mounted mixer is used Excessive use of high-cost additives Poor quality control High reject rate Customer dissatisfaction Buy Pre-Mixed/Custom Compounded Material Purchasing all materials pre-mixed or custom compounded is not only costly but you are putting the blending of your ingredients into the hands of a supplier over whom you have no control. Typically, you are investing in high volumes of a number of unique materials that require extensive inventory space and record keeping. Plus - changes in your process or material needs requires extensive planning and testing of revised material formulations. Comparing technologies A proportional mixing valve simple shuttles conveying valves back and forth during loading to approximate the introduction of regrind in with virgin material. Summary: No equipment investment Highest material cost Highest level of material inventory Ingredient blending out of your control High level of record-keeping Specification change may stick you with unused material Extensive testing required for changed formula Proportional “Mixing” Valves Proportioning valves are attached to self-contained loaders or to vacuum receivers (in a central resin conveying system). They have two valves that are timed to open and close to layer materials into the loader or receiver as it is loaded by vacuum. They are typically used to introduce some approximate percentage of regrind into virgin material, but they are actually best suited for simply allowing the consumption of regrind generated during processing. No real mixing takes place unless you install a separate mixer. This works if the appearance and properties if your end product are not critical and if your process can tolerate all of the regrind generated, as it is generated. But, results of this type of “blending” is extremely erratic and should be avoided if quality control is important in your process and products. Comparing technologies Cascading is a primitive, chancy method for mixing materials together. Summary: Low equipment investment May be OK to introduce regrind if product quality and appearance not critical Timed material proportions are approximate No mixing unless machine mount mixer used Cascading “ Blenders” Cascading blenders depends on the feeding of ingredients, usually from up to four hoppers, into a series of angled chutes. As the ingredients fall through the chutes, they intermingle to become “blended”. The materials are metered into the chutes using either vibratory or screw feeders but since there is no weighing of the ingredients and therefore little control over the actual blending, the system is victim to all of the inaccuracies of any volumetric blending process. Only the mixing section is simplified through the use of a cascading system, vs. a powered, typically rotating mixing section. Summary: Moderately low equipment investment Gravimetric blenders feed ingredients by volume Inaccurate feed rates result in product defects Inaccurate feed rates increase additive costs Mixing is haphazard using cascading method Comparing technologies It doesn’t just look like an antiquated process; it is. Manual procedures have no place in a modern factory. Dosers A Doser, also referred to as a Feeder is designed to introduce minor ingredients into the flow of a main ingredient at the throat of a processing machine. Common components include a throat adaptor, mounted below the machine’s main material supply hopper, a speed-adjustable DC motor connected to a metering auger and a machine interface control. Dosing is controlled either by a trigger signal from an injection molding machine or it may operate continuously with its speed is governed by the extruder it feeds. Volumetric dosers rely solely on free flowing materials and careful calibration to achieve a modest level of accuracy. Gravimetric dosers typically operate in a ‘loss of weight’ mode to accurately monitor and continuously correct the desired dosing level by measuring the weight of the additive supply hopper. Comparing technologies Gravimetric dosers scaled the accuracy of gravimetric blenders down to a single, stand-alone additive feeder, at a very attractive price point. Dosers typically do not provide any mixing to the combination of materials that they create, unless a separate machine-mounted mixer is added below, or in place of its throat adaptor. Summary: Moderate equipment investment Volumetric dosers: Relatively inaccurate For free flowing materials only Operate on time, to introduce approximate volume of material Increased labor costs due to tweaking of dispense rates Inaccurate feed rates result in product defects Inaccurate feed rates increase additive costs Gravimetric dosers: High accuracy of ± 0.1% “Loss in weight” method reduces material costs and rejects Can dose materials with poor flow characteristics Accessories available for difficult materials Volumetric Blenders Comparing technologies Volumetric blenders meter by time and volume, with no regard to the actual weight of the ingredients. Typically OK if the proportions of regrind and additives are not critical to the quality or appearance of your end product. May consist of two or more volumetric feeders mounted over a bin with or without a mixer. Sometimes material falls through a cascading “blender” (see picture). The image shows two feeders attached to a “cascading blender” (see above). There is no weighing of components. Each component of the blend must be calibrated to assure a working knowledge of volume to weight ratios for properly setting up the blender. Volumetric blenders are basically timing devices that assume a certain volume of an ingredient, added over time will yield a certain weight in the mix. This is typically inaccurate to some degree. Using more virgin or more additives than necessary impacts product cost, quality and decreases profitability. Summary: High investment, considering its marginal accuracy Depends on timed dispensing of free-flowing materials Increased labor costs due to tweaking of dispense rates Relatively low accuracy Poor control over material costs Higher reject rates May be useable where product quality not critical Gravimetric Blenders Comparing technologies Machine mounted gravimetric blender, fed from an overhead material supply. Gravimetric blenders hold batch weight to within ± 0.1%, by weight, so you can rest assured that ingredient proportions are uniform. In addition, once set up, and the recipe is entered, most gravimetric blenders automatically calibrate and run “hands-free” to ensure proper proportions and mixing of ingredients. Advanced controls allow complete documentation of the blending process as a further level of quality control. The results of using gravimetric blenders are dramatic. Summary: Highest initial cost Quick recovery of investment costs Hands-free operation reduces labor costs Gravimetric dispensing within ± 0.1%, by weight Significant reduction of additive costs Increased product quality and customer satisfaction Faster changeover times with removable hoppers Machine mount units reduce floor congestion Advanced controls provide complete documentation Controls for Blenders Online Video: See how easy it is to enter blending data with this example of a modern blender control. The impressive advancements in control technology for industrial equipment have not been overlooked in the latest generations of controls for automatic blenders. Acknowledging that the dialog between man and machines that blend resins and additives can be confusing, blender manufacturers have strived to reduce the inputs, computations and specialized knowledge required by the user to a minimum. Today’s blenders do the thinking for you. All the user has to do is to input the desired variables, and the control does the rest. Here are some examples of typical blending controls: PLC: Many manufacturers have entered the blending market utilizing ‘off-the-shelf’ programmable logic controls, due to their flexible design capabilities. The growth in popularity of PLC’s in industrial applications has generated a multitude of interfaces for the PLC user, ranging from detailed I/O programming, requiring special skills and equipment, to touch screens, requiring only rudimentary knowledge of the blender operation. In general, PLC’s perform the functions required for blending adequately and buyers are often comforted by the historic reliability of this class of product. However, PLC abilities in weight readings and fast responsiveness are often not suitable for today’s full featured, sophisticated and highly accurate blenders. In addition, being a generic control device, the PLC must be custom programmed extensively for blending applications and the functions required often demand a very high premium price in I/O and a fairly large control cabinet size. Touch screen controls for PLC driven blenders have made the products relatively easy to use, but typically lacking in the depth of their features and response speed, and as a result, the accuracy of the overall product. Proprietary Controls: Many manufacturers have concluded that in order to perform the functions required of a sophisticated blending device, the controls must be created from scratch and be dedicated to the functions of blending. Such controls are optimized for all of the functions of time, weight readings, number of inputs and outputs, etc. and are designed to be instantaneous in their operation, for speed and accuracy of blending. Using this approach, proprietary controls for blenders are typically ‘loaded’ with features not found on PLC’s and they can typically be modified readily via simple software changes; not add-ons nor new firmware. Adding reliability to the list of ‘must-haves’ for these proprietary controls makes them the logical choice for today’s buyer and today’s full featured blenders. A number of user interfaces are available for custom designed blender controls: Comparing technologies Your recipe calls for a percentage, and the blender asks for a percentage: What could be simpler? Thumbwheels: Reducing the number of inputs that must be provided by the user (allowed by the sophistication of the controls themselves) has led to the offering of thumbwheel input switches that require the user to only input the percentages of each ingredient desired. This interface methodology is intuitive and simple and literally, the control does the rest. Unless the user wishes to change other basic parameters, IE: blending time, the type of metering device being used, etc., once inputs are provided via the thumbwheels, an “ON” switch may be flipped to begin blending. Thumbwheels are typically provided for the more basic models of blenders, combining up to 4 materials. Keypads: Users wishing to store their blend combinations, or for larger blenders that combine more than 4 materials, will benefit from blending controls with keypad entry. These simple labeled buttons tap into the brains of the control and allow more sophisticated access to the operation of the blender. A small multi-line display, menus and selection codes are common and although they are not as simple to use as thumbwheels, the keypad control method unlocks deeper functions, recipe storage, operational variations, etc. Some popular blenders utilize both thumbwheels and keypads for multiple levels of sophistication and commonly, multiple levels of user access; IE: everyday or engineering level. Touch screen: In an attempt to simplify the user experience with blenders, manufacturers have taken advantage of the latest advances in touch screen controls and the public acceptance of them. Touch screens can provide not only simplified input logic, like thumbwheels, but also exhibit pictures and allow for deeper access to the blender when needed; all on one screen. The range of use of touch screens is extensive. Some mimic the popular thumbwheel concept by sporting images of thumbwheels that may be manipulated on the touch screen. User acceptance is instantaneous and the intimidation level is very low for everyday users. Yet the same screen can convert to more sophisticated use with a simple touch of another area of the screen. Other manufacturers employ central images on the screen, allowing the user to select what item (mixing chamber, metering device, etc) they wish to control. Once selected, that portion is either highlighted or expanded for more control choices. Comparing technologies Some manufacturers employ only touch screens for their blenders while others offer the touch screen as an upgrade to existing thumbwheel-controlled blenders. Comparing technologies Something familiar. This touch screen mimics thumbwheels for ease of use Dosing Basics A Doser, or Feeder is designed to introduce minor ingredients to the flow of main ingredients at the throat of a processing machine. You'll also find information about: Doser Technologies The history of dosing Gravimetric color dosing Gravimetric payback Liquid Dosing Learn about liquid dosing Applications Blending/Dosing Answers Question: Is there a recommended way to clean a blender when preparing for a new recipe? Response: Many processors develop their own methods for cleaning, and most approaches are based on how thoroughly they need to be cleaned. For instance...read more Putting Blender Accuracy To the Test – Published November 01, 1999 by Jan H. Schut https://www.ptonline.com/articles/putting-blender-accuracy-to-the-test When you look at competing claims for gravimetric batch blenders, the issue is accuracy. Virtually all makers of the equipment claim similar accuracy, but the numbers appear to mean different things to different people. You need to know what counts for you and how to test accuracy with your own resin and regrind. Blender accuracy is very much in the eye of the beholder. Hard data are rare, as is any firm definition of what accuracy means. "About accuracy, we all pretty much say what Maguire says," admits the marketing head of a competing blender manufacturer. Maguire Products wasn't the first to market a weigh blender, but it was first to capitalize on a huge injection molding appetite for inexpensive batch blenders that could tally resin ingredients to calculate part cost. The market evolved with other suppliers following Maguire's lead, either by private-labeling or imitating its product. But in the past few years, as increasing numbers of extrusion processors also bought batch blenders, new competitors came in, brashly claiming better quality--particularly mixing quality. One of those, Process Control Corp., last year introduced the first test protocol to verify mixing quality. Maguire and its competitors typically claim their batch weigh blenders are accurate to ±0.1% to 0.25%. "When pressed for an explanation, it is rare that any blender manufacturer knows the basis for its accuracy claim," writes Steve Maguire, president of Maguire Products. (He declined to be interviewed for this article but did submit documents on the subject.) "It's a confusing subject because there is no accepted standard in the plastics industry to express blender accuracy. I personally believe that marketing pressure requires that we all make claims at least equal to our competitors without really knowing how they are derived." A claim of ±1% accuracy, for example, could mean that a blender set to dispense 4% color concentrate actually delivers from 3% to 5% colorant, which would be ±1% of the total batch weight. Or, it could mean 3.96% to 4.04% colorant, which would be ±1% of the 4% target ratio. "We do better than the latter, reaching 3.99% to 4.01% delivered, or 0.25% of target," says Maguire. "If asked to deliver 10%, we reach 9.99% to 10.01%. This is ±0.1% of requested target." AEC/HydReclaim reports metering accuracy of up to 0.1% per component for free-flowing ingredients and "total machine accuracy up to 0.25%." Maguire adds, "It would be more meaningful to discuss average error in grams per batch and then compare this to the batch size. These are more meaningful numbers. But customers do not ask for that. They ask for 'percent accuracy.'" Another measure of accuracy concerns not weighing precision, but mixing uniformity. Accurate weighing may ensure that a batch as a whole contains within 0.1% of the target amount of additive. But mixing quality could lead to differing amounts of additive being present in each increment that enters the feed throat of a molding machine or extruder. That's what Process Control found in its testing of a "leading model" of blender (which Maguire identifies as a Maguire WSB-44). The test involved taking sequential plug-flow samples of a batch and counting colorant pellets. Blend homogeneity was reported as two standard deviations divided by the mean of all measurements. Process Control found that the leading model "benchmark commercial blender" gave 50% variation in blend homogeneity. By the same test, Process Control's new Guardian Blender, engineered for more thorough mixing, reportedly gave 6.3% variation in blend homogeneity. Maguire argues that for Process Control to have obtained such poor results on the Maguire, it must have bypassed the mix cycle altogether and just let dispensed material pour through the blender. Process Control insists that it ran all equipment following Maguire's instruction manual. Counting pellets Last summer, Process Control submitted its Guardian blender to outside evaluation by Plastics Product Review magazine (published in Traverse City, Mich.), which performs independent product testing and does not accept advertising. Plastics Product Review used Process Control's plug-flow-tube test protocol. The magazine plotted a flow chart of the percentages of colorant observed in a series of shots and found it hovered between 3.5 and 4.5% when 4% was set as the target. That amounts to a 14% variation. Blenders from Mould-tek, Conair, and Maguire were to have been evaluated next. All three companies agreed to submit blenders for testing but so far have not done so, says Plastics Product Review editor Adam Schultz. Conair explains that it isn't opposed to giving the magazine a blender for comparative testing. It just wants to be sure of the test criteria, test materials, and its blender performance. Conair's AutoWeigh name is on some 4000 blenders built around Maguire components and controls. Conair has started to conduct its own accuracy tests on the AutoWeigh blender, says product manager Gary Hovis. Conair is using a plug-flow test similar to that used by Process Control. Testing isn't yet completed. No more law of averages? The heart of the testing controversy is averaging. For years, blender makers totaled gravimetric weights over 20 to 30 or more batches and averaged them. Averaging works fine to calculate part cost, but it doesn't ensure part-to-part uniformity, critics say. "If you put your hand in freezing water and then in boiling water, the average would be quite comfortable," sniffs William Orozco, international sales manager of Mould-tek Industries. Opponents argue that averaging makes any blender look good if the time line is long enough. Process Control CEO Joe Robertson says his batch weigh blender doesn't need averaging to make it look good because it is accurate within one batch. Meanwhile, Maguire states that all makes of blenders "achieve 0.1% accuracy only over time, only with pellets that are fairly uniform in shape and weight, only if the hopper material is level and held steady (for uniformity) and internal parameters are set correctly." Customer tests with real-world materials typically show a "variation of ±3% within any given portion of the blended batch," Maguire claims. Its dispensing software compensates for errors in one batch by metering more or less in the next batch. According to Maguire, variation isn't significant because a blender's mixing hopper holds two to four batches, and an extruder screw can hold three to four times the volume of the mixing unit, or roughly 12 batches. Plastics Product Review had previously rated Maguire's Micro Blender in January 1998, giving it high marks for quality, but using Maguire's averaging approach. The magazine took three lots of 30 batches each, a total of 90 batches, and recorded 0.4% accuracy. But after the magazine subsequently reviewed Process Control's blender, it now uses that company's plug-flow method to test blending accuracy. Until recently, blender suppliers tended to avoid testing. John Hotchkiss, v.p. of engineering at Process Control and chairman of the blender subcommittee of the Society of the Plastics Industry's Machinery Division, says he tried four years ago to get the subcommittee to draft accuracy standards, but the rest of the committee was not interested in pursuing it. Factors in accuracy Up to now, blender-accuracy claims have tended to focus on dispensing accuracy. That depends on load cells, batching software, and dispensing mechanisms such as air-actuated slide gates, pinch valves, auger feeders, and vibratory feeders. Load cells themselves are pretty accurate: Maguire says its 3-kg load cells are accurate to 0.025 g, or one pellet. Its controller reportedly has "software resolution" of four pellets. On the other hand, Maguire warns, "Vibration is always an issue, and accurate readings when vibration is present require more time." Mould-tek claims superior metering accuracy based on its pinch-valve dispensing and precise computer control. A bar closes off a rubber flange, like fingers dispensing a pinch of salt. The valve is fully open until 80-90% of target weight is dispensed, then it feathers open and shut rapidly until the target is reached. Each dose is weighed by the quick-acting load cells of Mould-tek's RLTS (real-time live scale) system. A number of factors in the process can affect blender accuracy: resin type, pellet size, density, flow characteristics, regrind type and level, batch size, and throughput rate. Oversized, heavy, or irregular particles can cause difficulty in mixing in the blender. Color masterbatch pellets tend to be heavy and often of a different size from virgin, which can hinder uniform mixing. Easy-flowing particles can cause errors by rushing too fast through slide gates, while sticky resins clump and bridge. AEC/HydReclaim says auger feeders are most accurate for both slippery and sticky resins. But augers pulsate: The first half turn delivers two-thirds of the material, and the second half turn delivers the rest. Regrind affects accuracy in several ways. When regrind content varies, software calculates changing amounts of virgin and adjusts the level of colors and additives. But as the color fraction gets smaller, it's hard to measure accurately. Geometry of the regrind particles affects accuracy, too. "Film regrind is impossible in a batch blender," notes Conair's Hovis. "Sheet and bottle regrind can be used, but only with adaptations for extra mixing." Blender size and throughput affect accuracy both directly and indirectly. Blenders range from 10 lb/hr for lab models up to 10,000 lb/hr for central blending In general, bigger blenders are more accurate. Slide gates may be accurate to ±2.5 grams with an optimal resin, but percentage accuracy depends on batch size--2.5 g is 0.25% of a 1-kg batch or 0.014% of an 18-kg batch. Central blenders have the disadvantage that material must be conveyed to processing machines by airvey system or gaylords. This transport can cause demixing. Blender vibration also demixes and can upset load cells momentarily, causing metering errors. Blenders aren't equally accurate at all throughputs. HydReclaim's biggest batch blender, model OS-100, for example, has a throughput range of 50 to 5000 lb/hr. Blenders are generally more accurate at dispensing larger amounts. Yet some blenders double their output by following a gravimetric batch with several rapid volumetric batches, which aren't weighed, so accuracy decreases. The number of ingredients affects batching cycle time and accuracy. More components take more time to dispense and raise the risk of error. Maguire has software that manages up to 12 components. HydReclaim doesn't build a batch weigh system for more than six components. Beyond that, HydReclaim recommends using a continuous weigh blender instead. The accuracy debate has focused attention on blender mixing effectiveness. Some suppliers are already addressing the issue. For example, AEC/HydReclaim introduced a new agitator design, called the Opti-Mixer, which is a whorl of interwoven paddles with holes in them to improve blend homogeneity. Meanwhile, Conair uses a ribbon-style mixer for hard-to-mix materials whose particles have different sizes or geometries, like mixing thermoformed sheet regrind with virgin pellets. This year, Conair also introduced the XB Series extrusion blender, which has a reverse-flighted auger mixer and components from TSM Control Systems, an Irish blender maker that has an office in Atlanta. It pulls material from the edge of the hopper to the center and positively feeds material to the outlet. "This is a superior mixing method for all materials and especially for ones that tend to demix," Conair's Hovis asserts. What accuracy do you need? How should you approach suppliers' claims and counter-claims? Look carefully at what's really being measured--metering accuracy, mixing, or weighing--and how important that is to your process. Not everyone may find the accuracy dispute relevant. For example, Steve Maguire remarks, "With over 13,000 units sold, if we had a mixing problem, our customers would tell us, not just our competitors." He adds that "extruders do an excellent job of mixing. One color pellet can disperse across 20,000 natural pellets." So differences in blenders may or may not produce perceptible differences in product color or quality. On the other hand, Process Control points out that an accurately dispensed and homogeneously mixed blend could save you money on costly additives. Different processes require different levels of accuracy in metering and mixing. "Generally the people doing injection molding aren't as picky as the people doing extrusion, and not nearly as concerned with [blender] accuracy," says Fred Eichhorn, electrical engineering manager at Novatec Inc. Automotive molders are exceptions, he says. "They'll quite often bring their own materials and go to different blender manufacturers and run tests. Engineers will sit around and literally count pellets from a 5-lb batch to see which blender is more accurate." Revision History Rev: Effective Date: ECO No: Originator: Reason for Change: 00 tbd N/A AMG Initial Release