Multi-head weighers make for faster packaging, but not at the expense of accurate measurement. The potential savings are considerable, reports Michelle Knott.
Giveaway is the little bit extra that often makes its way into finished packs of goods, whether it is a tray of chicken legs, a bottle of tablets or a box of detergent. It’s rarely at a level where it provides any appreciable advantage for customers, but for manufacturers, giveaway can add up to a significant drain on profits.
With a large throughput of small packs, even a fraction of a gram can make a huge difference, according to Torsten Giese, marketing manager with Ishida Europe: “Let’s say you can save 0.4g on a 30g bag of sweets. Now imagine you’re producing one million packs a day...”
Where giveaway is the problem, a modern multi-head weigher may be the solution. Multi-head weighers are probably most familiar to those working in food production. However, their ability to speed up packing and portioning operations dramatically, combined with their unrivalled accuracy, means they are increasingly cropping up elsewhere.
Let’s say you can save 0.4g on a 30g bag of sweets. Now imagine you’re producing one million packs a day...
Torsten Giese, marketing manager with Ishida Europe
“Multi-head weighers are used extensively within the food industry – from frozen foods to confectionery, bagged salads and pet food. They can also be used on detergent powders, sugars, tea and coffee, as well as more obscure items such as plastic pipe fittings and plastic clips,” confirms Andrea Spencer, commercial operations manager at Yamato Scale Dataweigh UK.
Multi-head systems rely on a number of different weigh heads, most commonly arranged in a circle but sometimes sitting in a row. The circular arrangement is typical where a central, automated dispersal system can be relied on to deliver product fairly evenly to each weigh head, whereas a linear arrangement may be more practical in applications where an operator needs access to manually feed the system.
Each weigh head has its own precision load cell. The system uses smart electronics to calculate the weight in each small hopper and combine several of these together to deliver precisely the overall weight required.
In a typical circular set-up, product feeds into the top of the weigher, where a dispersal system – often but not always a vibrating or rotating top cone – distributes the product into a series of linear feed plates that transfer it radially, out to the weigh heads.
Smooth operation
According to Giese, the speed and accuracy of a multi-head weigher depends on having the right combination of load cells and electronics, as well as having a distribution system that can deliver product smoothly to the hoppers.
“You get what you pay for,” he says. “If the value of the product is very high, such as a spice like saffron, really it’s worthwhile investing in a top of the range multi-head weigher.”
Spencer agrees that a combination of factors must be just right to deliver optimum results: “Feed systems to multi-head weighers are key. If you have poor, inconsistent feed then the weigher cannot function correctly. The number of buckets used on a given weigher is determined by the speed that the customer wants to run at and the target weights they want to achieve. The electronics are obviously key.”
Exactly how much added speed and accuracy the latest multi-head solutions can deliver also depends very much on the application, but here are a few examples.
Herbs and spices are the focus of a recent installation by multi-head weigher supplier Multipond which provided a new system for Polish spice processor Prymat Group.
Prymat produces around 2,000 tonnes of spices each month, including some with a very low bulk density, which makes accurate weighing especially tricky. The new 16-head weigher handles 100,000 packs a day 30% faster than the company’s previous system. At the same time, giveaway has been reduced from 6% to less than 1%, according to Prymat.
For UK-based Big Bear Confectionery, increasing throughput on its packaging line was the top priority. Last year the company installed a Yamato multi-head weigher and Yamato checkweigher combination, which have been instrumental in boosting production by an extra 7,000 packs per shift, says Big Bear.
The 14-head Omega multi-head weigher from Yamato features a six-litre capacity and can reach speeds of up to 110 packs per minute on retail packaged Big Bear products, and 12 packs a minute on the larger 4.5kg packs.
A combination of speed and accuracy enabled Ishida and its Belgian agent, BRN, to tailor handling systems to improve throughput and reduce giveaway on yeast tablets for Belgian firm Blankedale.
Feed systems to multi-head weighers are key. If you have poor, inconsistent feed then the weigher cannot function correctly
Andrea Spencer, commercial operations manager, Yamato Scale Dataweigh UK
As part of a wider redesign of the company’s packing line by BRN, a 10-head Ishida weigher is fed by an infeed conveyor with accumulation control, which regulates the amount of product at the entrance to the filling carousel in order to maintain a steady throughput.
It also includes a servo-driven starwheel that presents different pack formats underneath the weigher, a vibrating unit to reduce the fill level, and an outfeed conveyor to carry filled packs across to Blankedale’s existing labelling and lid application systems.
Blankedale previously used a counting machine instead of a weigher, but this was so slow that it achieved no more than 15 packs per minute for 100g jars.
In contrast, the new system can deliver up to 50 packs per minute. In addition, the Ishida weigher is accurate to within 0.8% of the target weight, compared to around 3% with the old system.
Different combinations
A key challenge for the Blankedale installation was the discharge of the weighed tablets into the various packs. In particular, the 40g jar has a small 29mm opening relative to its volume, so filling could not be achieved using a traditional timing hopper and distribution system.
Instead, the Ishida weigher incorporates an innovative feature that minimises blockages by staggering the product discharges from the selected weigh hoppers in each combination.
In addition, BRN installed a special parabolic transfer chute, the shape of which maintains the flow of product and reduces blockages to practically zero.
So far, so good. But there are some applications where a multi- head weigher will not be the right solution. For instance, Giese says that a multi-head weigher may not be the best approach for packing certain products in precise numbers, as in packs of prescription pharmaceuticals, for example. If the weight of each tablet is slightly off-spec, errors will build up so that beyond a certain number, the weigher may deliver, say, 14 or 16 tablets instead of the targeted 15.
“You cannot weigh liquids on multi-heads, the key criteria are for a product that is basically dry (frozen is fine) and will move through the machine,” says Spencer. “If a customer’s output is not very high then again the use of multi-heads would be questionable,” she adds, chiefly because low-output processes might struggle to accumulate sufficient savings in terms of giveaway and improved productivity to achieve an acceptable payback.
