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Many operations require the ability to blend materials at very high volumes, previously thought to be beyond the scope of automatic blending equipment. These operations require special equipment for the high volume, a diversity of ingredients and a wide range of throughputs.

Historically, devices that serve this need have been custom fabricated to the specifications required by individual users and have been very limited in their application. For instance, a blender made for extrusion that combined large amounts of virgin and regrind, plus lesser amounts of distinctly different ingredients like wood flour, stabilizers and color might be custom fabricated to meet these needs. Thereafter, this device may be found to have very limited possibility variations due to the very specific combination of vessels, metering devices and controls that had been specifically created to fill this need.

Today however, large volume blenders for up to 12 components are far more common and are constructed in a modular fashion, similar to their smaller, on-the-machine cousins. Their modular construction permits lower purchase price due to the mix and match capability of all of its components. Metering devices, holding vessels and even control variations are all possible, allowing the supplier and even the user himself to define the necessary variations for their specific combination of high volume blending specifications. Modular design of components and flexible controls has opened the door for many high volume processors to the efficiencies of automated blending.

Important Elements of a High Volume Blender

High volume blenders must meet the needs of its users in several important ways.

Large Capacity Blending:

The blender must first possess the ability to blend large volumes since throughput (5000 lb./hr. or more) will be high and batch amounts of up to 12 ingredients must be included in each blended quantity of material. This is typically a simple matter of scale, but accepted designs must incorporate this kind of blending capability in a conservative footprint, in order to be practical. Some operations may require installing the blender directly onto an extruder throat or possibly even an injection molding machine, so size should be no larger than necessary. The ability to thoroughly blend diverse ingredients like pellets, powders, flour and regrind into a homogenous output is essential. As a result, a suitable blending motor and agitator system must be integrated to assure homogeneity and no separation. The use of 3 phase power for high volume blenders is common, to accommodate the power of the mixing motor.

Choice of Metering Capabilities:

Text Box:High volume blending applications need high volume material metering capabilities, and also lesser, perhaps even trace volume capabilities. Diversity in the ingredient characteristics are also typically an issue. As a result, a high volume blender should be able to accommodate up to at least 4 high volume components and as many as 8 lower volume ingredients; each possibly being a powder, pellet, flake, wood flour or regrind element.

Metering capability can be provided in many forms. Some popular and precise methods include:

• material dispensing knife gates (high volume)
• low flow pivot valves (low volume)
• Auger feeders with bridge breakers for powder or wood flour (low to high volume)
• Auger feeders (low volume)

See Blender Accessories for more.

Each of these devices should be accommodated in a modular high volume blender frame to easily match the needs of the process and the ingredients to be combined. The storage vessels above each of these metering devices must also match the throughput needs (high or low volumes) of each ingredient. Flexible blender design permits the interchange of these devices easily for evolving process needs.

12 Component Controls:

Combining and blending up to 12 ingredients into a precise mixture can be a daunting task, even if done carefully by hand. Expecting a single control to perform this function repeatedly and flawlessly in a manner that is easy to use and understand by the average worker may seem impossible. Today, sophisticated and easy to use blending controls (link to 7.0) are hard at work around the world doing just that. These modern controls require only simple percentage inputs for each ingredient of the blend, along with some blending preferences (duration of mix time, etc.) and they take it from there. Often, the inputs are very simply made, via thumbwheels or touch screens; a far cry from complex PLC programming of the past. Once energized, the blender control takes charge, sequentially operating each metering device and reading the increasing weight on load cells in the weighing bin. Corrections are made as a normal part of the operation as the blender continuously updates its readings and its accuracy. All this is done automatically.

In addition, it is common that larger volumes of material are traced by consumption. Rich reports, detailing yield results are commonly available and are constantly updated with each new blending batch, via Ethernet, USB or serial communications. Recipe storage, multiple languages, password protection and many more features are now standard on controls that make easy work of complex blending tasks.

Gravimetric Precision

Many of the features of modern, high volume blenders are really only possible with the use of gravimetric load cells on the metering weigh bin to track the performance of the material metering devices in use. Weighing each ingredient separately, as they are introduced, makes these high volume blending systems the ultimate in precision and ease of use. Unlike systems that utilize multiple sets of load cells (one set on each metering device), the use of a single load cell, set on the common weigh bin, simplifies not only the operation, but also set-up. In addition, this simple design choice allows the blender to be modular, by permitting the common weigh bin to be fed by virtually any kind of metering system.

High Volume Blending Applications

High volume (5000 lb./hr. or more) blending applications typically require not only higher quantities of material, but also a diversity of ingredients with a wide range of throughputs.

In the past, these types of applications have driven the need for custom built machinery, but as the products produced by such processes become more common, the market has responded with more standardized equipment.

High volume blending applications have become more common since the blending of wood flour (sawdust) and plastic regrind are now popular for the production of products like:

• Pallets
• Fencing
• Siding
• Plastic Lumber
• Alternative structural supports
• Drainage components

Key for Plastics Processors

A super-sized gravimetric blender of innovative design is required for plastics processors with very high-throughput production lines. Such a blender must be capable of precisely and efficiently dosing large quantities of hard-to-handle bulk powders like additives and wood flour.

A blender for these applications must be equipped to accommodate more ingredients than standard blenders. Ideally, it will have several removable hoppers and various dispensing methods, suitable for ingredients with different properties. Removable hoppers also allow the ingredients to be changed quickly for end products that have different properties or colors.

The basic operation of a high-volume blender is basically the same as other blenders. Ingredients are dispensed sequentially into a weigh chamber; the batch then falls into a mixing chamber. The dispensing devices include vertical valves (for resin pellets and regrind) and auger feeders (for powders, granules, and pulverized materials). Because the hoppers are interchangeable, it is easy to accommodate variations in batch recipe.

This kind of blending system should enable companies with the greatest volumes to achieve the same exceedingly fine control over ingredient consumption and batch consistency that smaller blenders have long made available to other processors.

A blender of this caliber may be supplied with a microprocessor controller but a high quality touch screen with Ethernet capability is desirable. In either case, the controller should automatically make small corrections from batch to batch, including adjustments to compensate for variations in extrusion rate or bulk density, maintaining overall batch accuracy to within ± 0.1%.

In the case of costly additives, this level of precision eliminates such wasteful practices as over-coloring to compensate for process variations or for the unreliability of alternative feeding equipment. In addition, because the blender doses colorants and additives in accordance with their weight as percentages of natural resin and automatically adjusts for the presence of these materials in regrind, it eliminates double-dosing. Even for a low-volume operation, the savings in colorant costs alone can yield payback on the cost of the blender in ten to twelve months; for high-throughput operations.