Once you have established that an auger filler is the proper method for filling your powder product, you then need to consider what type of closure method will be used to insure a clean cutoff of your product based on its flow characteristics. It is critical that the auger filler machine both produce an accurate dose but also a distinct “charge” from cycle to cycle. If you choose the wrong closure type, you may lose both accuracy and run into issues with product being caught in the horizontal seal.
The first option is a Short Auger with a Spinner Plate.
This concept is based off of a product's angle of repose. All powders have this and it is defined as the maximum slope, measured in degrees from the horizontal, at which loose solid material will remain in place without sliding. In this solution the auger spins and feeds product and when the appropriate dose is achieve the auger stops and the product collects on the spinner plate until the next cycle. The spinner plate is sized to stop the powder falling over the sides of the plate when the auger has stopped, taking into account the powder's angle of repose. This approach is the simplest method and often achieves very clean cut-offs without having to use more complex closure technologies. Products that often work well with this type of system are granulated free flowing products such as instant coffee, dry yeast, coffee beans, salt and granular sugar.
The second option is a Long Auger with Drip Washer or Sieve
A Long Auger with Drip Washer or Sieve creates a slight back pressure to prevent product dribble into the seal. Products that often use this type of closure are non-free flowing powder products such as whole milk powder, flour, ground coffee, or cake mix. Like the spinner plate mentioned above, there are no moving or mechanical parts involved with this type of solution and is a relatively simple and effective way to create a clean cutoff.
The third Option is a Long Auger with a clam shell closure.
A third option which is designed for products whose angle of repose is quite severe is a Long Auger with a clam shell closure. The clam shell closure uses a mechanical means to physically close and retain any product that may trickle out of the auger during the gap in the filling cycle. This option is useful for free flowing powder products such as spices, cement, additives, tea, and skim milk powder.
Click here to see outline drawings of the three auger filling options.
An additional technology that is available which can be useful and used in combination with the options above is a product compression unit or sometimes described as a vacuum auger system. Ideal for free-flowing powders for air removal, the product compression is accomplished via air extraction. This process also reduces dust generation during the filling process and better product handling with no drip between cycles. One ancillary benefit is that by compacting or condensing the product it can sometimes lead to a reduction in the overall package size and thus provide substantial film savings.
A simple bench test for evaluating the flow characteristics of powders is to insert a pencil or pointed narrow dowel into the top of a container of powder and then remove it. If the hole you created collapses on itself, then the powder would be considered free flowing. If, however, an impression of the pencil or dowel remains, then the powder is non-free flowing. Partial collapse might indicate a powder where a specific drip washer or sieve is required at the end of the auger tooling.
Auger manufacturers typically can evaluate and test your product to determine the optimal solution for you and your product. In the end, the decision of the type of auger filler machine closure that is chosen is important for an efficient, accurate and reliable vertical form fill seal bagging operation.