CW Checkweigher

What does the CW do on the line?

The CW sits between two conveyors after the packing or cartoning machine and weighs each item individually without disturbing the flow of the line. The measured value is compared with the target weight and the lower and upper tolerance limits defined for that product. A pack within the limits carries on; a pack outside them is taken off the line automatically. How rejection is arranged is decided with the order, according to the pack’s weight, shape and the layout of the line.

Every weighing is also a count. The CW keeps separate totals for packs weighed, correct packs, packs over the upper limit and faulty packs, and it calculates the average pack weight. At the end of a shift you therefore see not only how many packs were rejected but also how far above or below target the filling ran on average. That second figure is the starting point for cutting product giveaway.

Is a part missing from the box? Checking contents by weight

One of the CW’s main uses is products where many parts go into the same box. Think of a white-goods accessory pack, a hand-tool set, or a small appliance packed with its manual and fixings. Forgetting a part on the assembly line is a common mistake, and it goes unnoticed until the customer opens the box. When the whole box is weighed, a missing part shows up as a drop in total weight; the product reaches the consumer complete and the manufacturer’s reputation is protected.

Whether this approach will work can be worked out in advance. For example, if a complete box weighs between 2,390 and 2,410 g and the lightest part in it weighs 30 g, a box missing that part weighs 2,380 g at most. Setting the lower limit at 2,385 g separates incomplete boxes reliably from normal ones. If the lightest part were a 4 g washer, an incomplete box would land between 2,386 and 2,406 g and mix with the normal range; catching such a part by weight would not be dependable. The rule is simple: the part you are looking for must be clearly heavier than the weight spread between complete boxes. You can establish the real spread of your boxes by weighing a few dozen samples and send it to us before deciding. Remember that packaging adds to this spread as well: carton weight can vary from one supplier to another, and that difference has to be allowed for when comparing against the lightest part.

Product records, tolerances, reports and user rights

The CW stores 100 product records. Each holds the pack name, configuration details, target weight, upper tolerance and lower tolerance. When the product on the line changes, the operator picks the right record from the list without re-entering any values. For a plant packing dozens of different products on one line, this reduces a product change to a few taps and lowers the chance of running with the wrong values.

When setting tolerances, keep two different goals apart. If fill weight is being checked, the lower limit is set with the quantity declared on the pack and the spread of the filling machine in mind. If contents are being checked, the limits are chosen from the weight of the lightest part, as in the example above. The upper limit carries information too: an extra part in the box or two items riding on top of each other shows up as an over-limit pack.

Counter values are shown on the panel and can be exported as a report directly to a USB stick or a PC. From these reports the quality department reads how many packs were weighed for a given day or product, how many were rejected and where the average sat. When a customer complaint comes in, the records for that period are far firmer ground than handwritten notes.

One of the most frequent problems with checkweighers is tolerances being loosened without authority: opening the limits when rejects rise hides the problem instead of solving it. To guard against this, the CW offers three user levels, administrator, supervisor and operator, with up to 20 users defined. A common set-up lets operators only select products and leaves tolerance and record changes to the higher levels; which action is open to which level is agreed together during commissioning.

Vibration filter, installation site and food-line options

Weighing a moving pack is harder than weighing on a quiet scale; motors, neighbouring machines and the pack’s transfer onto the belt all add noise to the signal. The CW has a strong vibration filter that suppresses these fluctuations. Even so, for good results the installation point should be kept as far from vibration as possible: a press, compressor or vibratory feeder should not share the same frame, and the floor should be solid. Seeing photos of your line and its layout dimensions before installation makes it easier to choose the right spot.

For lines working close to open or packed food, the CW can optionally be built in stainless material with a hygienic frame design. On an assembly line carrying dry, boxed products, the standard construction is usually enough. Telling us how the line is cleaned and which product passes over it is enough to pick the right option.

CW or MCW?

Both models serve the same purpose: verifying pack weight. The CW is conceived as a full inspection station that weighs packs on the line and rejects wrong weights automatically, and it is the first model considered where the line has room for it. The MCW is designed for short, compact lines where space is tight. Share your line length, pack dimensions and items per minute and we will work out together which model fits.

The first question in deciding is how much of the line can be given over to the checkweigher; the second is where rejected packs should go. If there is room and wrong-weight packs are to leave the line by themselves, the CW is the natural choice. If only a short gap is left on an existing line, the MCW is considered. The speed and accuracy that can be reached are calculated for both models from pack size and line speed, which is why we work with your line’s data rather than a general figure. We reply to quotation requests within 3–4 hours.