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A checkweigher checklist

03 August 2022

A checkweigher can make a huge contribution to the smooth and efficient running of a packing line, so it is worth investing time to ensure a solutio that best meet your needs. Philip Grove outlines some key areas to consider. 

For many food manufacturers, a checkweigher is regarded as a reliable workhorse, the ‘policeman’ at the end of the line which helps to ensure adherance to regulations. However, the sophistication and features of many of today’s models mean that the checkweigher is able to take on a far more significant role on the production and packing line – in particular as many businesses embrace further automation as part of Industry 4.0.

For this reason, investing in a new checkweigher needs careful consideration to ensure the right model is identified to meet particular requirements. Outlined below are some of the key areas to take into account when assessing the options available.

Know your customers and your supplier
It is vital to fully understand the specific requirements of your customer base. In particular, while there are many national and international quality and weighing standards with which companies have to comply, several major retailers also have their own codes of practice for the manufacture of private label products.   

As well as the chosen machine being able to handle these various specifications and documents, it is important that the supplier is familiar with these relevant codes of practice. The supplier can then ensure that every machine is properly calibrated and has the required level of sensitivity; that the correct validation procedures are in place and carried out as required; that relevant checks are implemented after service or repairs; and that all the required paperwork is kept up to date.

Equally important, make sure the checkweigher can deal correctly with any out-of-specification packs. Software and hardware, such as Ishida’s RRC (Retail Reject Confirmation) system, can check and confirm that any rejected packs have been successfully removed from the line.

In competitive markets, the availability of detailed reporting functions on the checkweigher can be a benefit in delivering improved production efficiencies. Modern checkweighers can compile and assess a great deal of information to help assess a line’s Overall Equipment Effectiveness (OEE) by constantly monitoring it in terms of availability, performance and quality. The combination of these three elements provides an OEE percentage that identifies how efficiently the line is running, and can show this value for a factory, a production line, or a particular product at any time frame, in order to identify potential areas of improvement.

In one Ishida installation, for example, a pet food manufacturer packing around 700 cans of product every minute during an eight-hour shift saw a payback on investment of just a few months through the ability to better control the amount of raw ingredients that went into each can.

Continual monitoring by checkweighers can also flag up potential issues elsewhere on the line. This is particularly valuable in increasingly automated factories.

Speed versus efficiency
The checkweigher needs to be able to cope with the throughput on the lines but there are a number of other factors to consider. With many manufacturers now running more products over shorter runs, speed of set-up and changeover are equally important, so intuitive and easy to use controls are essential, with settings for different products inputted and stored for instant call up. 

It is also vital that the checkweigher maintains accuracy during production runs. Machines that can self-calibrate will auto zero at regular intervals to reset the weigh loadcell. Some models are also able to monitor the amount of product passing through the checkweigher and if there is not a long enough gap between products for auto zeroing to take place, a signal can be sent back up the line to slow down the product feed to create the necessary time.

Fast speeds do not always equate to the highest efficiencies; giveaway is amplified by the amount of product going through the line. If by lowering the overall speed, the amount of giveaway is significantly reduced, this will ultimately deliver a much better overall efficiency rate. This is particularly true for products with low target weights.

Some factory environments can be challenging, so it is important that the checkweigher is designed to cope with the most extreme conditions it is likely to face. A relevant ingress protection (IP) rating will help to identify a suitable model and is particularly important in highlighting a machine’s ability to cope with dust or water, as these are different hazards that require different handling. Seals that effectively withstand water ingress will not necessarily be as capable of preventing dust from entering critical parts and can therefore result in premature components failure.

Excessive vibration from elsewhere in the factory can also affect a checkweigher’s performance, so look out for features that help compensate for this. 

A compact checkweigher footprint will be invaluable in maximising factory space. Having an integrated metal detector is another space saving benefit. Give some consideration to the reject system; different types may be needed, depending on the products the checkweigher is handling. An overhead paddle, for example, is suitable for heavier weight packs, while lighter ones are more suited to pusher or air varieties. A tote reject bin design, as opposed to reject bins with doors, can be quickly exchanged to enable faster product changeovers.

The most important aspect of checkweigher selection is that the machine delivers a return on investment. It is therefore important to take into account not just its purchase price, but its ongoing reliability and performance and overall cost of ownership. As part of this, make sure you choose a knowledgeable and experienced equipment supplier with a ‘right first time’ approach that ensures that the checkweigher will deliver from the outset.

Philip Grove is product manager at Ishida Europe.

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