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Auger Filling Accuracy

October 30th, 2021

Achieving greater accuracy with auger fillers is a concern with virtually all applications.Whether filling to a desired weight setpoint, or by volume alone, the less product given away and consistently predictable fills are often the elusive ”holy grail” sought after by owners and operators of auger filling machinery. In an attempt to attain greater accuracy, the following will try to identify and analyze some of the major factors affecting accuracy, as well as list some of the common remedies available to correct accuracy problems.

FACTORS AFFECTING FILLING ACCURACY

Among the most important factors affecting auger accuracy are the following: 

A detailed discussion of each of these factors follows. A graphical comparison of the relative affects of each of these factors appears at the end, along with a summary chart identifying possible remedies for inaccuracies resulting from each of these sources.

· Product Density
· Tooling & Machine Accessories

· Temperature & Humidity
· Mechanical Efficiency. Filler
· Product Infeed Supply Efficiency

PRODUCT DENSITY

Inherent to its design, an auger dispenses a specific amount of product for each revolution. Accordingly, if the density; that is the mass of product per physical volume: changes, differing amounts of product will be dispensed in each revolution. Changes in density can result from a variety of causes. Certain products may change density due to the affects of temperature and humidity, or when the product gets aerated from transport and conveying. Others from the actual processing methods used in production (e.g., milled products). Other common causes of density changes include misuse of agitation blades, inadequate head pressure in the product supply hopper, and excessive auger speed that unintentionally changes density during the fill.


Methods used to normalize density for better accuracy include: 

The actual methods of remedying density problems, however, vary according to the specific application. Other sources of inaccuracy, such as use of incorrect filling accessories may inadveliently cause density changes in the product.

Horizontal Screw Feeders

The use of a small, horizontal screw feeder mounted immediately over the filler’s hopper from the infeed supply is another method of “re-densifying“ product prior to filling the hopper.

Head Pressure

Maintaining a steady reliable head pressure of product in the hopper is one of the more common and simple solutions to improving accuracy by maintaining a consistent density. This can be as simple as increasing the frequency at which the hopper is resupplied with product.

Hopper Venting 

Equalizing the pressure in the hopper by venting it to atmospheric pressure is a common method of achieving better density, especially when the product supplied has become aerated through conveying or other causes.

Infeed System Redesign

If the product changes density (e.g., becoming aerated) before reaching the auger filler, a change in the infeed product supply may be suggested to correct density problems.

 

TOOLING & ACCESSORIES

Another source of inaccuracy with augerfillers is the use of incorrect inappropriate or misadjusted filling machine tooling and accessories. Generally, auger filling machines can be equipped with two variations of tooling, depending on the general flow characteristics of the product being dispensed. The Free Flow configuration isused with products such as sugar, salt, bread crumbs, etc., and comprises a Straight Auger & Funnel, Spinner Plate (secured with a left-hand nut), Collector Funnel assembly, and slow speed agitator blade. A Non-Free Flow configuration, for products such as bakery mixes, carbon, ortalc typically includes a Self Feeding Auger fitted with a Drip Washer (and secured witha left-hand screw), and a Lip Funnel. Depending on the product and filling application, either a high speed and/or slow speed agitator blades may be used to move product into flights of the auger.These two configurations are shown in the following. 

Accuracy problems can occur when toolingis substituted for products with the opposite flow characteristics (i.e.. free flow productwith non-free flow accessories and vice-versa). Incorrectly sized tooling may alsobe a source of inaccuracy. Worn and damaged tooling, even if not visible to the naked eye, may also result in gradually deteriorating levels of accuracy with your auger filler. Obviously, the remedy for these types of inaccuracies is to use the recommended type and size of tooling appropriate to thespecific type of product and amount of fill:and to carefully maintain and regularly inspect tooling for wear, damage, or misalignment.

TEMPERATURE & HUMIDITY

Changes or extremes in temperature and humidity like changes in density or using the wrong accessories can also he a source of in accuracy with the auger filler. Often a previously accurate running filer may start to drift because of changes in the ambient environment. Environmental changes can often distort the basic flow characteristics of the product which inturn may lead to using wrong or inappropriate accessories. Extremes in temperature & humidity can addi-tionally affect other components of the filer thatmay result in a seeming loss of accuracy. Straingage loadcells used in scale equipment, as well as other, associated electronic components, canbe adversely affected by extremes in heat humidity, and especially condensation resulting from rapid changes in temperature and humidity.

FILLER MECHANICAL EFFICIENCY

The type of filling machine can also be a sourceof inaccuracy. The standard clutch/brake designemployed in the great majority of auger fillersdoes offer a high torque rate with quick accelera-tion/deceleration profile, however the possibilityof clutch/brake coasting and spillage, especially as the machine ages, will affect accuracy overtime. Accuracy problems deriving from coasting and slippage can be remedied through a consistent, regular preventative inspection and replacement program. Other designs, such as Stepper motors and Servo motors may offer greater accuracy, but only for specific types of products, or at a much greater cost.

PRODUCT INFEED SUPPLY EFFICIENCY

Among the more common sources of inaccuracyencountered with auger filler is how the tiller’shopper is supplied with product, rather than howaccurately the tiller dispenses. Inefficient productinfeed systems can prohibit an auger filler from ever attaining accuracy, despite proper tooling, controlled temperature & humidity, or the latest high-tech auger drive system. Infeed systems that terminate a distance above the filler almost ensures that consistent, reliable head pressure in the hopper never occurs. By the time product is called for, the accumulated product located between the filler and infeed system has already been delivered, often at a different density that was originally in the hopper. Often, however, this problem can besolved through use of an intermediateinfeed system, such as a horizontal or vertical screwfeeder used to feed the hopper ofthe auger filler directly. Unvented infeed system can additionally be a source of accuracy problems - building up air pressure in the hopper of the filler. Venting the hopper back through the infeed system is often the simplest method to eliminate this problem. Uncontrolled infeed systems lead to expected accuracy and density problemsas well, although possible remedies willvary, according to nature of the system.Other infeed inefficiencies can result from lack of attention to proper shutdown and startup procedures. After a shutdown, previously accurate filler may suddenly act of control, due to an accumulation of product that was allowed to sit in the hopper for the length of the shutdown. Orderly, coordinated cleanout before shutdown can easily be implemented to eliminate these “monday morning” inaccuracies.

COMPARISON

The pie chart below identifies the relative affects of each of the factors that may account for inaccuracies of auger fillers. Note that several of these sources are interrelated and changing one aspect may directly or indirectly influence another. 

 

ACCURACY IMPROVEMENT CHART 

POSSIBLE SOURCE

REMEDIES

Product Density  

Hopper Venting, Infeed System Redesign. Horizontal Screwfeeders, Regulate Head Pressure

Tooling & Accessories

Inspect tooling for wear and damage; check for proper configuration

Free Flow 

Straight Auger & Funnel, Spinner Plate, Collector Funnel Assembly, Slow Speed Agitation

Non-Free Flow 

Self Feeding Auger & Drip Washer. Lip Funnel, High/Slow Speed Agitation

 

Temperature & Humidity  

Control for extreme fluctuation

Filler Efficiency

Inspect clutch brake for wear and damage

Infeed Supply Efficiency:

 - Infeed system too far away
 - Unvented system
 - Uncontrolled
 - Other

 

Intermediate Infeed System
Vent hopper through the Infeed System
Control System redesign
Proper shutdown and start-up procedures



 

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