Application Example: Pet Food Processing Incorporating Screw Feeders, Weigh Belt Feeders, and Liquid Loss-in-Weight Feeders

Coperion K-Tron feeders are used for a variety of applications within the pet food manufacturing process. Screw feeders (both volumetric and loss-in-weight), liquid loss-in-weight, and weigh belt feeders are used for metering and high accuracy feeding of ingredients into a mixer (batch or continuous), an extruder, and before the packaging line.

Meal Batching and Blending:

When creating pet meal blends in the industry , two types of operations are used. In a continuous approach, various components including meat and grain meals, vitamins, minerals and other ingredients are fed to a continuous mixer. This approach is used with weight belt feeders, provided the number of ingredients is limited. When working on a batch basis, a more economical option is to use a Gain-in-weight (GIW) batch design for these same dry ingredients, using volumetric feeders for the ingredient feed and a separate hopper on load cells for the GIW verification.

Coperion K-Tron Smart Weigh Belt (SWB) feeders are available in closed frame (shown here) or open frame models.
Coperion K-Tron screw feeders are designed in sanitary construction for ease in cleaning, with options for 3A requirements.


All ingredients are fed either onto a conveying line or direct to the mixer by gravimetric weigh belt feeders or screw feeders depending on the material characteristics and feed rate requirements. Each of the feeders is outfitted with some sort of reload or refill device, which can include pneumatic conveyors or simple gravity drop bins complete with level indicators. The mixture leaving the mixer is often labeled the "mixed meal". It is then loaded into another feeder and fed with the pigment direct to the extruder, usually utilizing either single or twin screw feeders. 

Coperion K-Tron Smart Weigh Belt Feeder Advantages

  • Typical rates: 20 – 40,000 kg/hr (44 - 88,000 lb/hr)

  • Less height requirement at equivalent accuracies of screw feeders

  • Coperion K-Tron SmartConnex control capabilities to allow for a variety of programming options including ingredient control and recipe management

  • Improved Belt cleaning design as well as reduced maintenance requirements

  • Trapezoidal inlet design allows for improved material flow from feed storage bin

  • Optional second weigh bridge with continuous online taring ensures that neither dust nor product build-up on belt has any effect on overall accuracy 

  • Models available in open frame or closed frame designs for ease of accessability, cleaning and maintenance 

  • Minimal product damage or attrition due to gentle action of weigh belt

Extrusion Feeding and Proportioning: Application Details

The mixed meal is fed directly to the extruder.


The feed of the mixed meal to the extruder can be with either volumetric or gravimetric feeders. Volumetric feeders are typically used only with meal that is “preconditioned”, or optimal for screw feeding flow, without a possibility of bridging or buildup.

However, the addition of other proportioned ingredients such as water, steam, animal fat, and molasses can change the flow properties of the mix considerably.

Managing the delivery of the dry feed to the extruder is most important to tight ingredient and moisture control. If these key process parameters are not controlled, improper extrusion can result, costing manufacturers significant costs in wasted product.

In order to achieve an acceptable degree of dry feed accuracy, (± 1% of the maximum delivery rate), a high precision feeder system based upon weight is imperative. Volumetric feeding systems to an extruder can often vary as high as ± 6% accuracies due to such factors as bridging and improper flow of the premix to the screws.

Utilization of Coperion K-Tron’s loss-in-weight algorithm and smart refill techniques ensure that a consistently high accuracy of dry ingredient feed can be maintained. Once a predictable dry feed delivery system is utilized, then the other ingredient feeds (such as moisture addition or alternate liquid addition) can be managed by coordinating them to the dry feed system on a ratio basis.

Advantages of Coperion K-Tron's Patented SFT Weighing Technology

  • Unsurpassed and unequalled repeatability and stability
  • Advanced single wire weighing technology
  • High resolution weighing and powerful on board digital signal processing ensure precision feeding even at short intervals or in vibration-prone plant environments
  • Fast measurement speed
  • Resolutions as high as 1:4,000,000 in 80 ms 
  • Direct digital weighing with electronic temperature compensation
  • Built in overload and underload protection
  • Hazardous area models available for European (ATEX) and North American (NEC) standards

Learn more about Coperion K-Tron's feeder accuracy: Coperion K-Tron Accuracy Statement  

Flavor Enhancing and Particle Blending
Application Details:

Addition of animal fats and flavors after drying and before packaging


The cooked and “baked” nugget by itself rather unpalatable. Typically various animal fats and flavors are gravimetrically mixed onto the product after drying and before packaging. Due to the higher cost of these ingredients, and a definite need for overall quality control, the use of weigh belts, loss in weight feeders and KTron PID pump control systems are of utmost importance. As stated above, Coperion K-Tron’s unsurpassed repeatability and stability in feed accuracy through the use of the patented SFT load cell design are critical for control of cost and quality.

Application Details: Packaging

After the extrusion and drying step the product is cut, dried and weigh metered prior to feeding to the packaging line


After the dried product is weigh metered, it is often times sprayed with liquids prior to going to the packaging line. The addition of these liquids can be done two ways. For a more economical approach, the Coperion K-Tron control system with PID can be integrated with a liquid flow meter (like those by MicroMotion).

The liquid pump delivery is controlled by the PID function to provide moisture control which is proportioned gravimetrically. This same arrangement can also be used for addition of the water and or steam to the extrusion steps mentioned above. As an alternative, and in cases where even tighter control of liquid addition is necessary, a liquid loss in weight feeder combined with a positive displacement pump is used to meter the liquids sprayed onto the product.

In the case of a varied product mix, e.g. multiple colors and/or shapes, each line of dried and sprayed product is sent to its own individual weigh belt feeder, where it is metered and sent to a horizontal conveying line, and then on to the packaging machine. The percentage of each individual component is managed by the recipe controls integral to the Coperion K-Tron Smart Connex control system.

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