Key points
While the inverted cone of a multihead weigher may be recognisable at a glance – and from a distance, the differences between one system and another may not be. Those elements of bespoke design are often of critical importance and are constantly evolving.
Machine speeds are frequently talked about in terms which are more notional than real-world – or useful. But in some cases, they can be extremely relevant. Last month, Yamato Scale Dataweigh introduced the F3 Frontier Produce Weigher, capable of handling 80 packs per minute (ppm) of unprocessed potatoes when filling 2.5kg bags, or 100ppm filling 1kg packs.
“Twelve tonnes an hour is really going some,” says UK sales manager Steven Spencer. “With main-crop potatoes, especially, these businesses want to pack very fast and very accurately. It’s because of the costs involved, and supermarket demands on price. That’s what’s driving the marketplace.” On the previous machines, says Yamato, top speeds were closer to 55 or 60ppm.
“The other major advantage is the accuracy achievable with multiheads,” says Spencer. This reduces giveaway, which in turn gives better payback and return on investment than other weighing systems, according to the company.
In the case of the F3 Frontier, the equipment is given the IP67 hygiene rating, which is standard across most of Yamato’s machines. But with a move to higher-value, processed potatoes, speed criteria become less important, while hygiene requirements increase.
Accordingly, the CCW-RV multihead that Ishida Europe installed at German potato processor Friweika has the highest possible rating against water ingress: IP69K. This high level of resistance is required in part because the potatoes are conveyed around the plant using flowing water, but also because starch deposits (which contain corrosive fruit acids) build up quickly, calling for frequent wash-downs.
Ishida marketing manager Torsten Giese points out that this high rating does not mean that poorly-trained temporary workers can be let loose on the system with a high-pressure hose.
“High-pressure cleaning requires special guidance. But this RV model does allow for quicker hose-down, leading to a reduction of around 20% in cleaning downtime,” he says.
The 10-head weigher at Friweika packs up to 2.5t of potatoes an hour, according to Ishida.
When Ishida launched the RV in 2013 as its ‘top-of-the-range’ system, it made much of the higher speed capability (around 15% higher than its predecessor). But it also focused on the high levels of accuracy and ‘close-to-zero’ giveaway. However, speed is not always the key issue.
Equipment effectiveness (Return to top)
Giese says: “There’s a lot of talk about increasing speeds by so much, but that’s not as critical as efficiency, availability, performance and the number of rejects. Overall equipment effectiveness is the important measure.”
While multiheads are commonly positioned above vertical form-fill-seal machines, customisation is often needed in order to feed alternative packing systems. This was the case with Ishida’s Friweika installation, where the cooked potatoes are deposited in trays thermoformed in-line. Different arrays of four or six tapered depositing heads are used depending on whether 500g, 2kg or 5kg packs are being produced, with a single mobile funnel feeding each head.
Another Ishida multihead is being used to fill trays at Martini Alimentare in Italy. Here, breaded products such as chicken nuggets are dosed from the 20-head weigher at speeds of around 120ppm, though the manufacturer's eventual target speed is 160ppm. “These speeds are being achieved using a following head, which deposits product in the tray in-flight,” Giese explains.
“There are more trays on the market now,” he adds. “That is not least because consumers can pay up to three times as much for product displayed in a tray.” This tendency, along with the trend towards smaller trays (and smaller portion sizes generally), is requiring the development of some ingenious, high-speed depositing systems.
Spencer says: “We’ve been heavily involved with suppliers of thermoforming machinery such as Multivac. We can design our Frontier technology, for instance, to have multiple discharge points. So you can fill three rows of six trays at 10 or more cycles a minute, requiring 180 weighments a minute.” Yamato’s multipoint discharge system can be used for pots as well as trays, where product can span soup mixes, porridge oats, noodles and pasta.
The opposite end of the weigher can be equally important when it comes to tailoring the installation to a given application. “In fact, I’d say that 80% of the challenge with a tricky product is in getting it as far as the hoppers,” says Giese.
With grated cheese, for example, the problems associated with accurate metering of the product have been exacerbated by rising prices in the supply chain. “We’ve been able to improve the stroke on our vibratory feeders by using piezoelectric sensors which help to predetermine the amount of product deposited in each basket,” says Spencer. “Giveaway becomes very small compared with even a few years ago.
“By using a different loadcell, and improving product metering prior to the weigh cell, our customers are seeing a 1.6% or 1.7% improvement in yield. But we’ve also improved accuracy. We’re probably looking at a 2% increase in accuracy on our latest Omega range.”
For products such as leaf salads, Ishida has refined its pulse width modulation for the vibratory radial infeed. This applies direct rather than alternating current to allow the selection of a wider range of frequencies. “The machine can identify the best combination of time and amplitude, or this can be adjusted manually,” Giese explains.
The finish on multihead parts, from infeed to outfeed, is equally important. For products which stick or cling, Teflon remains an option, while Ishida offers its C4 ‘easy-motion’ finish.
Weighing and dosing (Return to top)
In some cases, single machines will be required to weigh and dose a range of products. A division of the Co-op in Switzerland has a recently-installed 14-head RS weigher from Ishida which handles 70 different products, from small grains and pulses to nuts and dried fruits. Change parts include an enclosed dispersion table with apertures for small-grained product such as quinoa, and a C4-coated dispersion table for product such as dried fruits, with steeper angles to make sticking even less likely.
On the Co-op machine, hoppers are plastic to reduce high noise levels. The same can be true for frozen vegetables, says Ishida.
For other products including cereals, there is a risk that electrostatic charge can build up. Materials can be specified to reduce those risks.
When it comes to breakfast cereals, it is often no longer a case of handling different products in sequence, but together, in parallel, on the same machine. As Spencer explains: “A box of Special K, for example, will include three main types of component: the fibre, which tends to be low-density; freeze-dried fruits, which account for around 12% of the target weight; and sultanas and raisins, which form another 12% or so.”
The relatively low-value cereal and higher-value fruit (especially freeze-dried) are treated very differently. “Controls on the yield of the fruit have to be tight,” says Spencer. Designed for volume, the linear feeds for the cereal might be wide and flat. “But for the fruit, you would use a V-shaped pan, because it is more precise.”
Just as importantly, piezoelectric feedback on the infeed for these more expensive products will maximise yield for the customer, says Yamato.
It first introduced the system of ‘memory buckets’, which sit below the weighing buckets and allow mixing, back in the 1980s. “The company developed software to discharge at different times to ensure that the product in the bag was a true mix of the components,” says Spencer.
Like Ishida, bagging line supplier tna sees multihead suppliers coming under pressure from the drive for smaller pack sizes. European sales director James Hosford says: “Over the last 10 years, bags have reduced in size to facilitate convenience and portion control. At the same time, manufacturers are required to meet consumer demand for greater variety and product choice.”
This means that the improved performance expected of multiheads includes changeover times as well as speeds, without loss in accuracy, he says. According to tna, which sources its multiheads from Yamato, twin scales can be a good solution. “By combining two packaging machines and two weighers, manufacturers can achieve up to 400 weighments per minute all with a reduced footprint,” says Hosford.
Despite the existence of robotic grading systems, multiheads appear to be unchallenged in a growing number of segments, and able to build ever more sophistication into balancing speed against accuracy, flexibility, changeover times and overall efficiency.