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A Guide to Belt Checkweighers

The Key to Keeping Your Production Line Consistent, Efficient, & Safe

A checkweigher belt is a type of product inspection machine that ensures your product is the correct weight for quality control. These machines operate by running a product over a scale, if its weight is too heavy or light, the product will be removed from the line. This is usually accomplished with the help of a push-off rejector, which uses either an arm or a sharp blast of air to redirect the unfit product.

Checkweighers are designed with different length load cell conveyors so that the package can keep moving throughout the inspection process and not experience any delays along the way.

In this guide, we will cover all the basics of checkweigher belts so that you can make an informed decision on whether or not this equipment would be a good fit for your product or fit into your production line. The topics of this guide include:

- What size checkweigher belt do you need?
- The importance of the load cell and how to secure it
- Types of checkweigher belt rejects
- Common checkweigher features
- Why checkweighers are important for your production line
- Where checkweighers can fit into your production line
- Manufacturers to Buy From
- Questions you should ask before buying a checkweigher belt

What Size Checkweigher Belt do You Need?

Checkweigher belts come in a variety of belt sizes, ranging anywhere from less than three inches, 3-6 inches, and larger. So how do you determine which size you will need? This will completely depend on what size the product you’re running is. Knowing the exact dimensions of your product will help us find a checkweigher that will accurately read your product and fit in your line. The length of the weighing belt needs to be 1.5 times the length of the product so that there is enough time for the product to be recognized and weighed before another product enters the weighing area. If the belt width is too big or small for your product, you can end up with false readings or incorrect line spacing.

The Importance of the Load Cell and How to Secure It

Another element of the checkweigher belt that is dependent on the size of your product is the load cell. This is the device that converts weight or force into electrical signals that can actuate the measuring function of the checkweigher belt. The length of the load cell conveyor will impact the maximum product length and product spacing required. In addition to the product dimensions, you will also need to consider at what orientation your product will be moving through your belt.

Load cells are the most vital part of the checkweigher and are extremely sensitive. Any air movement or force around them can lead to false readings. It is for this reason that they should be well protected both during production and transportation.

If you’re moving your checkweigher belt for any reason, whether it be sending it back to SIGMA after renting it, selling it, or redeploying it between facilities, you must first ensure that the load cell is properly secured so that it will arrive safely. The instructional video below will teach you how to secure a checkweigher belt load cell so that it does not get damaged while on the move. Even after taking the needed precautions and securing your load cell, your machine will still need a reconfiguration after any type of movement. That’s just how fragile and important this component of the checkweigher belt is.

Types of Checkweigher Belt Rejects

After you have determined the correct size of checkweigher you will need, the next thing will be to consider the type of reject that will be compatible with your product. The reject is the part of the checkweigher that redirects unfit products from the production line. Having this option on a checkweigher is crucial in automating your production because it does not have to temporarily pause for product removal the way that checkweighers without a reject are programmed to do. With a reject, the machine will automatically move the product and allow for a more continual and automated process.

Some examples of checkweigher belt rejects include the following:

Flipper Reject
- Best for high-speed rejection of products up to 100g
- Also has the option to be fitted for two reject arms that can reject products in different directions. So that underweight products can go in one direction and overweight products in the other.

Photo source: https://www.mt.com/id/en/home/library/applications/product-inspection/checkweighing-product-sorting.html#ptabs_1ca0_tab_custom4_li

Air Jet Reject
- Best used for high-speed rejection for small and lightweight products up to 300 g
- Uses a sharp blast of air to remove the product

Photo Source: https://www.mt.com/id/en/home/library/applications/product-inspection/checkweighing-product-sorting.html#ptabs_1ca0_tab_custom1_li

Pusher Reject
- Best used for medium-speed applications for products weighing up to 3Kg
- Uses an arm to push the reject off

Photo Source: https://www.mt.com/id/en/home/library/applications/product-inspection/checkweighing-product-sorting.html#ptabs_1ca0_tab_custom2_li

Pneumatic Retracting Conveyor Reject
- Best used for small and un-packaged products
- The conveyor retracts causing the product to fall off of the line

Common Checkweigher Features

Below are some common features you will find on checkweighers. If you have any questions about which options will optimize your production and quality control. Please reach out to one of our equipment experts by clicking here.

Mechanics
- Various belt lengths and widths
- Additional conveyor belt
- Special working heights
- Support legs

Product Handling
- Lateral guide rails
- Rolling knife-edge
- Bridge plate between belts

Data Export
- USB port
- Paper roll printer
- Standard interfaces

Monitoring Functions
- Weight ranges
- Product flow control (left or right hand depending on how it will fit into your existing line)
- Pressure switch
- Fill level check/collector box (common for liquids)
- Emergency stop (various versions)
- Metal detector connection (these are commonly next to checkweighers in the production line)

Electrical Options:
- Lamp tower
- Signal horn

Sorting Options
- Pusher arm reject
- Air blow reject
- Free-standing hinged flap
- Flipper
- Second sorter
- Rejection bin

Why checkweighers are important for your production line

Some benefits of incorporating a checkweigher into your production line are as follows:

- They help you avoid costly fines with 100% weight inspection
- A checkweigher belt will help keep your operation stay synchronized
- Using one will ultimately lead to saving products and profits because the more accurate readings you have, the fewer products you have to waste
- Your production processes and efficiency will be improved
- Having the quality control process automated will save you labor and personnel costs
- Checkweighers help reduce the possibility of false rejects or having to rework any products
- Improve your overall equipment efficiency (OEE) and reduce your total cost ownership (TCO)
- Last but not certainly not least, this machine will help ensure you are maintaining your identity and credibility of your brand by checking that each product contains exactly the amount of what is shown on its label

Where Checkweighers Can fit into Your Production Line

So now that you’ve learned all about the importance of checkweighers and their elements, you’re probably wondering what one of these looks like in action.

Below is an example of three checkweighers that have been incorporated into an inhaler production line for the pharmaceutical industry. This line does a great job of showing the importance of having multiple checkweighers at different points in your production to make sure that your product is safe and that readings are accurate at every step of the packaging process.

Photo source: https://www.healthcarepackaging.com/machinery-materials/automation-robotics/article/21576900/pharma-packaging-lines-system-integration-for-18-modules#next-slide

Manufacturers to Buy From

Some common manufacturers of checkweigher belts that SIGMA sells are,
- LOMA
- Ishida
- Mettler Toledo
- Garrvens
- Alpha Checkweighers

Questions You Should Ask Before Buying a Checkweigher Belt

- What is the height and width of the conveyor?
- What is the load cell accuracy range?
- What are the minimum and maximum product weights?
- What are the minimum and maximum product lengths?
- What are the minimum and maximum product width?
- What is the conveyor belt speed?
- What was the last product ran on it?
- What type of product reject type does it have?
- What is the distance required between each individual product going across the weighing area?
- Is this a wash-down unit?
- What is the product flow?

Summary

In conclusion, a checkweigher belt is a piece of equipment that ensures the correct weight of a product for quality control. Some common reject methods on these machines are flipper, air, retracting conveyor, and push arm. Common industries that use checkweigher belts are food and beverage, pharmaceutical, and material handling/automotive.

To learn more about the kind of checkweigher belts we offer or to determine if one is right for your production and product, click the button below and one of our equipment experts will be more than happy to walk you through the process.

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