Agribusiness & Food

Nestlé Singapore improves metal detection with flexible screw conveyor

Milo, the malt barley and cocoa drink, is a household name in Australia. Owned by Nestlé, the chocolatey beverage is also widely popular in Southeast Asia.

The company has operated a manufacturing plant in Singapore since 1912, producing and packaging the Milo powder in its iconic tins, as well as sachets that are formed and filled on a high-speed rotary filler.

Upstream of the sachet filler is a metal detector that scans the powder to identify contaminants. Detection of a contaminant, called a “strike,” triggers the metal detector to divert a portion of the powder stream into a collection bag. Workers then inspect the rejected powder to verify that the contaminant was removed and log the incident into a quality-assurance report. This had been a cumbersome process until a flexible screw conveyor smoothed the flow to the metal detector.

Agglomerated powder complicated detection 

The metal detector originally sat directly below the surge hopper that discharged the Milo powder through a butterfly valve. 

Sean Phua, technical engineer at the site said when the valve opened, often one large chunk of powder would flow through the metal detector which wasn’t fast enough to reject the 

As a result, some portion of the powder—and possibly the contaminant—passed through the metal detector and into a flexible screw conveyor that transferred it to the sachet filler. That would force operators to halt production.

With production halted, the operators would run the flexible screw conveyor in reverse to empty all the powder in flight. That powder, along with the rejected material, was then hand-sieved and dissolved with water to find the contaminant and “determine whether we had a real or a false strike. It was messy and the interruptions reduced packaging productivity,” Phua said.

He learned that the operation would improve if the powder could free fall into the metal detector in a steady stream. One possible solution would be to add a rotary valve under the surge hopper, but lack of headspace made that impossible, Phua said. 

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Instead, Flexicon recommended offsetting and raising the metal detector, allowing room to add a new flexible screw conveyor to feed powder to the metal detector in a steady, controlled flow. Flexicon Singapore provided the new conveyor to accommodate spatial constraints and throughput requirements.

The conveyor is 1.5m long and includes a spiral enclosed in a 90mm diameter outer tube made of ultra-high-molecular-weight polyethylene. The screw—the only moving part that contacts the product—ensures that the powder does not pack, cake or separate.

The conveyor includes a 150mm diameter inlet flange and charging adapter that connects under the surge hopper’s butterfly valve. From there, the powder is transported at a 41-degree angle and discharges into the metal detector through a 150mm diameter downspout. The conveyor’s 2.2 kW drive turns at a constant speed to transport about 720kg of powder per hour for 20 hours a day. Level sensors at the conveyor’s inlet and discharge are linked to the sachet filler’s controls, enabling both units to operate in sync. 

Regulated flow improves detection, cuts downtime

According to Phua, the new flexible screw conveyor has streamlined the operation. 

“All strikes are rejected before the powder enters the original flexible screw conveyor to the sachet filler, eliminating false rejections and manual clearing of powder from the conveyor,” he said.

His colleagues in the quality-assurance department welcome the improvement. 

“Because we have more positive rejection from the metal detector, quality assurance people have less worry about contaminants not being rejected.”

More reliable rejection boosts productivity by increasing sachet filler uptime and reducing incident reporting, while conserving product. 

“Previously, large chunks were being rejected. Now as a freefall, less powder is flowing, which reduces product loss by a good amount,” he said. 

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