How do Multi-Head Weighers Work?

Accuracy is crucial when filling dry products into flexible packaging, especially in the USA, where a minimum weight system is used.

This means that the net weight of the product must, as a minimum, meet the stated weight on the package labeling. Any product above the stated weight is being given away, so manufacturers strive to keep this to a minimum.

Multi-head Weigher. Image Source Wikipedia CC by SA

One key technology that enables precise weighing and packaging of products is the multi-head weigher. These machines have revolutionized the packaging industry by providing rapid and exact weight measurements for a variety of products. This article delves into the intricacies of multi-head weighers, exploring how they work and their significance in modern packaging applications.

Table of Contents

1. Introduction to Multi-head Weighers

2. Components of a Multi-head Weigher

3. How Multi-head Weighers Work

4. Types of Products Suitable for Multi-head Weighers

5. Advantages of Using Multi-head Weighers

6. Considerations for Implementation

7. Final Thoughts

Introduction to Multi-head Weighers

Multi-head weighers are automated weighing systems commonly used in the packaging industry to accurately measure and dispense products into bags, containers, or packages. They are especially prevalent in the food industry for packaging items like snacks, candies, nuts, frozen foods, and more. The technology enhances productivity by combining speed with precision, reducing product giveaway and ensuring consistent package weights.

Components of a Multi-head Weigher

Understanding how a multi-head weigher functions begins with familiarizing oneself with its main components:

Infeed System: Delivers the product to the weigher, often using vibration to ensure even distribution.

Pool Hoppers (Feeder Pans): Temporarily hold the product before it moves to the weigh hoppers.

Weigh Hoppers (Weigh Pans): Individual pans equipped with load cells to measure the weight of the product.

Discharge Chutes: Guide the weighed product into the packaging machine or container.

Control System: A computerized unit that calculates the optimal combination of weights from the weigh hoppers to achieve the target weight.

Support Structure: The framework that holds all components together, ensuring stability and alignment with the parent packaging machine.

How Multi-head Weighers Work

The operation of a multi-head weigher involves a series of coordinated steps:

Step 1: Feeding the Product

The product is fed into the weigher via the infeed system. This system may include vibratory feeders or conveyors that distribute the product evenly across the top of the weigher.

Step 2: Distribution to Pool Hoppers

From the infeed system, the product enters the pool hoppers (feeder pans). These hoppers serve as buffers, temporarily holding the product and ensuring a consistent flow to the weigh hoppers.

(Image Source: WeighPack)

Step 3: Transfer to Weigh Hoppers

The product moves from the pool hoppers to the weigh hoppers. Each weigh hopper is equipped with a load cell that measures the weight of the product it contains.

Step 4: Calculating the Optimal Combination

The control system plays a critical role here. It receives weight data from all weigh hoppers and uses algorithms to calculate the combination of hoppers that, when combined, will be closest to the target weight without going under or over predefined tolerances.

For example, if the target weight is 100 grams, the system might find that combining the contents of weigh hoppers 1, 3, 10, and 12 (which contain 25.1g, 23.9g, and 36.0g, and 15.0, respectively) will total 100 grams.

Step 5: Discharging the Product

Once the optimal combination is determined, the selected weigh hoppers discharge their contents simultaneously into the discharge chute. The product then moves into the packaging machine or directly into the packaging container.

Step 6: Replenishing the Weigh Hoppers

After discharge, the empty weigh hoppers receive more product from the pool hoppers, and the cycle repeats. This continuous process allows for high-speed operation with minimal downtime.

Products Suitable for Multi-head Weighers

Multi-head weighers are versatile and can handle a wide range of products, particularly those that are:

Granular or Particulate: Items like rice, beans, nuts, and seeds.
Irregularly Shaped: Snack foods, candies, and certain frozen foods.
Sticky or Oily: Dried fruits or marinated products (with specialized coatings on contact surfaces).
Fragile: Products that require gentle handling to prevent breakage, such as chips or biscuits.

This video is a good example of how versatile these weighers are. A MULTIPOND system weighing mussels, before packing them into small cans.

Advantages of Using Multi-head Weighers

Implementing multi-head weighers in packaging lines offers several benefits:

High Accuracy

By calculating the best combination of weights, multi-head weighers achieve precise package weights, reducing product giveaway and ensuring compliance with weight regulations.

Speed and Efficiency

These weighers can perform hundreds of weighings per minute, significantly increasing packaging line throughput.

Versatility

They can handle a variety of product types and sizes, making them suitable for different packaging applications without extensive modifications.

Reduced Labor Costs

Automation minimizes the need for manual weighing and packaging, reducing labor costs and human error.

Data Collection and Integration

Modern multi-head weighers come with control systems that can collect data on production, integrate with other machinery, such as the parent packaging machine, and support Industry 4.0 initiatives.

Considerations for Implementation

While multi-head weighers offer many advantages, there are factors to consider when implementing them:

Initial Investment

The upfront cost can be significant, especially for high-end models with advanced features.

Product Characteristics

Very sticky products with a high moisture content or that are prone to clumping may require specialized equipment or additional handling systems.

Maintenance and Training

Regular maintenance is essential to keep the weigher operating efficiently. Staff may require training to operate and troubleshoot the equipment effectively.

The combination of weighing and packaging machines is a sophisticated system, often needing quite specialized knowledge to keep it running at its best.

Space Requirements

Multi-head weighers can be sizable, so adequate space must be allocated in the production area.

Weighers are usually mounted above the filling machine, as shown here, so it is important to have sufficient overhead clearance for the system and product handling.

Final Thoughts

Multi-head weighers have become an integral part of modern packaging operations, offering unparalleled speed and accuracy. By understanding how these machines work and the benefits they provide, businesses can make informed decisions about integrating them into their packaging lines. With proper implementation and maintenance, multi-head weighers can significantly improve efficiency, product consistency, and overall productivity.