Checkweighing in Flow Wrap Applications
The challenges of high-speed weighing of small, wrapped packages
Flow wraps, also known as flow packs, are one of the most common packaging types in food manufacturing due to the ability to cover a wide variety of product sizes and shapes. They are used in many food applications - from meat packaging to individually wrapped chocolate bars.
However, precise inline checkweighing can become increasingly challenging as you start weighing smaller flow packs at increasingly higher production speeds. That’s why it's so important to choose the right checkweigher equipment provider and a checkweighing system that is designed to achieve the precision weighing results you need for high-speed flow wrap applications.
Learn more about the trends and challenges of flow wrap packaging in our “Dynamic Checkweighing in Flow Wrap Applications” application note, which will discuss:
- Production and packaging trends
- Challenges of high-speed weighing in flow-wrapped products
- Requirements for accurate weighing of packaged food
- The METTLER TOLEDO checkweighing solution using Flashcell™
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What are flow wraps, and how are they used in packaging?
Flow wraps (also flow packs) are a widely used packaging format used in the manufacture of many products. Globally, there is a clear growth trend for flow packs, and by using them, manufacturers can save a lot of plastic.
These efficient packages still need to be properly weighed – which can be challenging – but proper setup and placement of systems is more than enough to deliver accurate weighing results.
What types of products use flow wrapped packaging?
The 'flow pack' is an efficient solution for fresh meat packaging because it reduces the use of plastic immensely.
Compared to other formats, flow wraps have a number of other benefits, including:
- Saving more space on the production line, as flow wrapping systems can be more compact
- Can be made from mono or fiber-based materials, helping to protect the environment
- Support a wide range of packaging applications, in either vertical or horizontal configurations
What is an overview of product packaging trends?
Packaging has shifted from slow coiling machines to high-speed flow packers. Horizontal flow-wrapping machines pack products such as chocolate bars at high-throughput, which is around 500 to 600 parts per minute (ppm), although maximums of over 700 ppm are possible. Another trend appearing in packaging is a movement towards small and lightweight packaging units as a way to more efficiently utilize production space.
What should manufacturers look for in an inspection solution for flow wrapped packages?
- Reliable product handling and inspection at high speeds
- Compliance with pre-package goods legislation (e.g. MID) for single items
- Minimize false reject rates at high speeds
- Small footprint of production machines due to limited line space
- Maximize automation to reduce operational costs
What are the challenges for dynamically weighing flow wrapped products?
As flow pack manufacturers sell single items in supermarkets, they need to comply with legislation regulating pre-packaged goods. To stay within required tolerances, manufacturers need consistent product weights. This means either performing manual spot checks or using dynamic in-line weighing. With fast production speeds and a trend toward automation already present, manufacturers typically elect for automated in-line weighing using a checkweigher. The ideal insertion place is right after the horizontal flow-wrapper.
The trend towards faster packaging speeds and shorter, lighter products means the potential for more challenges which can negatively impact the weighing process. Additionally, limited line space presents another potential difficulty. Generally, the smaller and lighter a package is, the more difficult it is to weigh that package accurately. The package shape itself adds to the difficulty: the sealed edges and inherent instability can cause product handling issues which in turn impact the accuracy of the weighing result.
To sum up the challenges of weighing flow-wrapped products:
- Smaller, fast-moving products are not on the weighing conveyor for long, meaning the system has less time (only around 30 to 35 milliseconds) to weigh the product
- The sealed edges of flow packs can cause product handling and sorting issues
- The shorter weighing time places higher requirements on electronics and software, as faster data processing is required
- Smaller, lighter products mean that the weight tolerances are much stricter, and the accuracy of the weighing result needs to be higher
What is needed to get an accurate weighing result in a high-speed application?
While our solution does support high-speed applications, there are certain requirements that must be met in order to secure an accurate weighing result:
- Proper sealing of flow wraps: the top sealed seam must be flat. Otherwise, the air drag is too high, and the product generates lift as it travels
- Bottom sealing must be flat: crinkled seals prevent the product from staying still during the weighing process. When a product moves during the process, it cannot be accurately weighed
- Homogeneous chocolate molding: if the chocolate enrobing is not done correctly, the product surface is not homogeneous which can result in product movement