Automation

Plan metal detection and conveying systems carefully

February 3, 2011
/ Print / Reprints /
ShareMore
/ Text Size+
Processors that buy metal detection systems without due consideration to e conveying systems could find integration more difficult.


Potato salad undergoes final metal inspection before going out the door. Plastic conveyor immediately in front of and behind the metal detector prevents interference to the detection system, which could create false indications. Source: Dorner.
An essential part of any food inspection process is the ability to quickly and effectively remove questionable product from the process flow. And a key component of that inspection process is metal detection. Integrating a conveying system with a metal detection system is not so difficult if it is well planned from the get-go.

Recently, AJ Naber, Dorner Manufacturing senior design engineer, designed a retractable-tail metal detection conveyor for a frozen French fry manufacturer. “Based on the configuration of the existing processing line, a retractable conveyor was the best fit for this application,” says Naber. The conveyor primarily runs in the extended position, and as French fries successfully pass through the metal detector, they continue on the extended conveyor to a take-away conveyor. When the metal detection system detects metal within the flow of French fries, the retractable-tail conveyor pulls back and creates a gap to allow the product to fall onto a second conveyor for disposal, adds Naber.

While this was a fairly complex application, others can range from a basic stop-on-detect-requiring operator intervention-to varying degrees of complexity, says Naber. Stop-on-detect is the simplest and generally least expensive option available.

Nevertheless, many processing lines need more automation, which requires some type of reject mechanism beyond human intervention. Push-on-detect, air blast and diverter arms are some of the common reject mechanisms on metal detection conveyor systems, says Naber.

  • Push-on-detect involves a pusher mechanism mounted to the side of the conveyor. The pusher face is actuated when the metal detector flags a product for rejection.
  • Air blast operates similarly to push-on-detect. However, rather than a pusher, a flagged product is removed from the conveyor by a blast of air. This works with lightweight products requiring a more finite reject.
  • Suited for bulk materials, a diverter arm swings out across the width of the conveyor belt to guide flagged product to a reject lane or bin for disposal.

The area within the metal detector through which product travels is known as the aperture. Within the aperture there needs to be room to accommodate both the conveyor and the product, says Naber. Most metal detectors require a metal-free zone of approximately 1.5 times the aperture height. This constraint presents a challenge because everything on the conveyor system within this metal-free zone needs to be made from plastic.

The stainless steel conveyor frame also needs to be split to run plastic through the aperture and within the metal-free zone. “That’s why it’s important to properly size a metal detection system to the application,” advises Naber. “I recommend considering all supporting equipment including the conveyors and reject method when selecting a metal detector for a processing line. Think of the metal detector and supporting conveyor line as one integrated component.”

Selecting a metal detector with an aperture that may be too big for the product may also limit space where accessories can be mounted to the conveyor frame. “Remember, a larger aperture casts a larger metal-free zone around the entire system,” says Naber. And if the metal detection system is located in a fairly confined space, available space on the frame to mount the reject mechanisms may be limited. From an engineering standpoint, it’s always a challenge to make the system as sanitary and compact as possible while still achieving what the application requires.

“Ultimately any design we make needs to be safe, and often, safety and sanitation don’t go hand in hand. Ideally we want as little human intervention in the reject mechanisms as possible, so we’ll add various guards to eliminate access to dangerous areas. However, with every component that is added to the conveyor, you can decrease its overall level of sanitation,” says Naber. “It’s a balancing act. Our job is to design a metal detection conveyor system that’s very sleek, smooth and uninterrupted, but at the same time provides the highest level of safety.”

No two metal detection conveyor systems are identical. However, when specified properly, they can serve an integral role toward adding value and efficiency to any production line.

For more information, contact AJ Naber, Dorner Manufacturing, 262-369-1258.

Did you enjoy this article? Click here to subscribe to Food Engineering Magazine.

You must login or register in order to post a comment.

Multimedia

Videos

Image Galleries

Fabulous Food Plant: Paramount Citrus

Learn more about this fabulous food plant in Food Engineering's article, found here.

Podcasts

Burns & McDonnell project manager RJ Hope and senior project engineer Justin Hamilton discuss the distinctions between Food Safety and Food Defense as well as the implications for food manufacturers of the Food Safety Modernization Act.
More Podcasts

THE MAGAZINE

Food Engineering Magazine

Food engineering magazine 2014 april cover

2014 April

Catch a preview of the Powder and Bulk Show in this April 2014 edition of Food Engineering. Also, be sure to check out a coffee stick making a real stir and a major advancement in the the pet food industry.
Table Of Contents Subscribe

THE FOOD ENGINEERING STORE

Food-Authentication-Flyer-(.gif
Food Authentication Using Bioorganic Molecules

This text provides critical tools and data needed to augment routine food analysis and enhance food safety by aiding in the detection of counterfeit, and potentially deleterious, foods.

More Products

Clear Seas Research

Clear Seas ResearchWith access to over one million professionals and more than 60 industry-specific publications,Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.

Food Master

Food Master Cover 2014Food Master 2014 is now available!

 

Where the buying process begins in the food and beverage manufacturing market. 

Visit www.foodmaster.com to learn more.

STAY CONNECTED

FE recent tweets

facebook_40.pngtwitter_40px.pngyoutube_40px.pnglinkedin_40px.png