What is a Metering Rod? How a Small Part Plays a Big Role

Written by Wes Buschman

Metering rods are precision instruments used to accurately meter the amount of liquid coating applied to papers, films, foils, and other substrates.

Customarily, excess coating (referred to as the pre-coat flood) is applied to the substrate prior to making contact with the metering rod. The metering rod removes excess coating, leaving a precisely metered layer on the substrate.

Industries where metering rods are used include:

  • Paper Mills
    • Metering rods are used in Rod Metering Size Presses to surface size both the front and back of the paper. The rod accurately controls the volume of starch and/or other coatings. In these applications, the sizing agent is metered onto a transfer roller which transfers the coating to the moving paper web.
  • Paperboard Mills
    • Smoothing rods are used to apply Kaolin clay coating to both single and duplex coated board.
  • Linerboard Plants
    • Linerboard plants use metering rods to apply a variety of color and functional coatings to liner and medium. Examples include the application of white coating prior to a printing operation and barrier coatings that keep grease and moisture from penetrating the sheet.
  • Converting Plants
    • Metering rods are used in converting coating operations for a vast array of purposes, such as applying adhesive to tape, silicone release, or laying down tint on window film treatments.

The first metering rods, originally called “equalizer bars” or “doctor bars,” were introduced in the early 1900s by Charles W. Mayer. This is why metering rods are sometimes referred to as Mayer rods.  Other terms for metering rods include metering bars, “meyer” rods, mayer bars, mayer coating rods, coating rods, smoothing rods, sizer bars, and whole host of other variations.

The first metering rods consisted of a round steel rod tightly wrapped with wire. The area created by the valleys between wires determines the amount of coating that is metered. A typical wire-wound metering rod is shown in Figure 1.

By changing the diameter of the wire used to wrap the rod, coating application volume can be easily changed and accurately controlled; the larger the wire, the larger area between wires, which allows more coating to pass through the windings and stay on the substrate.

The ease with which coating weights can be quickly and accurately changed simply by using a different size wire is one of the main reasons metering rods remain a popular method to meter coatings over 100 years after their introduction.

Figure 1 – Typical Wire-Wound Metering Rod

In the early 1980s, Thomas Buschman revolutionized the metering rod industry by introducing precision rollformed (sometimes called grooved) metering rods. Instead of wire wrapped around the rod, a precision thread is cold formed into the surface of the metering rod as shown in Figure 2.

Like wire rods, application volume is controlled by the area of the valleys between thread peaks. Unlike wire, the shape of the thread profile can be engineered and manipulated to control rod performance variables. While wire-wound rods are still in use today, grooved metering rods offer many advantages over their wire-wound cousins.

Figure 2 – Typical Roll Formed Metering Rod

Since we introduced roll-formed metering rods in the 1980s, Buschman has continuously worked to improve this technology and leads the world in customized thread profiles.  Today we have over 25 different thread shapes and often custom engineer new profiles to meet demanding applications.

Contact us today to learn how Buschman metering rods can optimize your coating application.

 

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Senior Manager
Multinational Paper Mill in Australia

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“The quality of Buschman’s products is excellent. In the ten years we’ve been purchasing coating rods from them, we’ve had maybe two or three issues and they are minor issues. For the number of coating rods we purchase, that’s incredible. Their quality has been so high and they work so well with us that we don’t even consider looking at other vendors for our coating rod needs.”

Purchasing Manager
Leading Packaging Paper Producer in Southern US

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“The number one reason we work with Buschman is the product quality. The second reason is service. If we are running low on product, they’ll turn the world upside down to get us what we need. Buschman delivers product performance and customer service.”

Coated Products Manager
Prominent Packaging Paper Producer in Northern US

Buschman Delivers Consistent Quality

“It’s all about the quality of the rod we’re using to meter the product onto the paper. Without the proper rod application, your coating isn’t going to lay properly. Buschman has a quality product that performs the way it’s supposed to and they get it to us when we need it. They consistently meet all our expectations.”

Coated Products Manager
International Packaging Paper Producer

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“Since we’ve opened the doors here, we’ve worked and had a great partnership with Buschman. They are a very highly reputable company and we’re proof of that as a happy customer. We have a lot of trust and faith in Buschman, so we just give them gold stars.”

Production Manager
Large Multinational Packaging Paper Plant

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“We’ve used Buschman for well over ten years. Buschman goes above and beyond: The quality of materials, the finished goods, the on-time deliveries. They go out of their way to get us the product we need.”

Coating Manager
Large Converter in Northern US