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Hot Riveting Preserves Historic Value of Bunker Mill Bridge

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    April 3, 2014 | 9:43 am
    KALONA, Iowa - Work on the historic Bunker Mill Bridge continues, and this past week, some onlookers got a chance to get hands-on with its restoration. Nels Raynor, owner of Bach Steel in Michigan, led a demonstration of hot riveting in downtown Kalona. It's a lost art that Rayor is trying to preserve.

    "There's not a lot of people left who have drove a hot rivet before," Raynor explained, as he and his team fabricated replacement parts for the bridge.

    Raynor first heats the steel rivets in a small forge on the back of his pickup.

    "We can get it up to about 2,300 degrees," Raynor said.

    Then, there's a 20-second window to thread and drive the rivet with a special gun, before it cools. It's not a difficult process, as many people in the crowd found out after getting a chance to drive a hot rivet. However, it's easy to see why hot riveting is no longer a common method for tying steel beams together.

    "It's pretty labor-intensive," Raynor told us.

    It's also easy to understand the old-fashioned appeal of hot rivets. Once driven, each one is unique, and they look nice, too, according to Doris Park.

    "They're handsome," Park said of the rivets. "Oh, I love it. I love that stuff. I've always wondered how they put those big rivets in."

    As Raynor points out, threaded bolts and nuts are no match for the strength and durability of a rivet. "When we're done with that rivet, it expands in that hole and fills that whole void, so it attaches itself to all the material."

    Meaning once these pieces are re-fastened to the bridge, it will be stronger than ever.

    "It's such a beautiful bridge," Park said. "It's going to be a wonderful asset to the community and I think everybody's going to love having the bridge."

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