When I write my commentary pieces, I’m always trying to find unique subjects to discuss, since you can only address the importance of filtration so many times. And despite the threat of actual nice weather looming, it was only last month that I wrote about meteorological patterns, so I’ll leave that to the old men playing chess at the park. Sometimes, inspiration comes from real-life experiences, which is the case today.
Our company, Higginson Equipment Inc, makes hydraulic and pneumatic cylinders. But in 2013, we purchased a company called Amtec Hydraclamp, which manufactures high-pressure clamping primarily for the steel industry. And when I say “high pressure,” I don’t mean 5,000, 6,000, or even 8,000 psi. Our hydraulic clamps, nearly across the board, are rated for 10,150 psi.
Figure 1. Block not from high-pressure hydraulic clamp from Amtec Hydraclamp.
These high-pressure hydraulic clamps use either grease or oil and are primarily threaded in the center, functioning as hydraulic nuts. You simply thread the nut onto the arbor or bolt, twist it on by hand, and then loosen a hair before you pressurize. The thread ID may be ¼ or 16 in., and everywhere in between, so you’d be right to imagine these look like doughnuts (Figure 1). In reality, they are nuts with annular pistons that pull on threads to clamp or tension.
I’d like to say they’re more common than you think, but I’m biased. I’m certainly biased enough to feel they’re not nearly as popular as they should be, and my recent visit to some steel mills highlighted some applications where hydraulic clamps are perfectly suited, yet rarely used. These steel mills weren’t your local steel processing center, but more like “a few mills with combined steel-making capacity higher than the country of France.”
This unique application concerns the continuous caster, which is a multi-story section of the mill that transforms molten steel into solid semi-finished shapes by continuously pouring the liquid metal through a water-cooled mold and guiding it down a curved path of rollers as it solidifies into a continuous, glowing ribbon of steel. In my opinion, they are a technical marvel worthy of awe and admiration.
Part of the caster is the mold sections (Figure 2), where the molten steel is poured into to create the shape, which is maintained by the many roll segments below the mold as it also turns from vertical to horizontal in a continuous slab. Depending on the design, these caster molds and roll segments are held in place by bolts with mechanical nuts, which are then torqued using conventional methods, so long as those methods can handle 2,000 ft-lb.
Figure 2. Image shows the caster of the mold sections, where the molten steel is poured into to create the shape, which is maintained by the many roll segments below the mold as it also turns from vertical to horizontal in a continuous slab.
The point of torquing nuts is to establish that a minimum level of tension is applied to the bolts to ensure the molds and segments are fixed securely in place. However, the nuts are located at somewhat inconvenient locations to haul heavy torque guns, so as you would guess, these applications are perfectly suited to a hydraulic nut.
In fact, this application is perfectly suited for what we call a “block nut.” It contains a threaded piston ID, an outer body, and a block ring. Hydraulic pressure pulls the central section up to tension the thread to over 50 tons, and then the technician spins down the block ring to physically lock the piston in place. The technician then releases the hydraulic pressure, allowing the block ring to support the bolt under the correct tension indefinitely until the mold or segment requires maintenance again.
Because of the demanding nature of this application, the block nuts must withstand the environmental abuse of both high temperature and constant water exposure. The major components are electroless nickel-plated 4140 steel, which prevents corrosion in these extreme conditions, and the seal package must withstand the requisite 10,000 psi and ambient heat.
Before you ask, no, the hydraulic oil does not need to be fire-resistant. Because these nuts are pressurized only during maintenance, there is no flame-thrower potential, as can be found with high-flow hydraulic systems saturating the steel mill. And besides, the Viton seals used in many fire-resistant fluids is not an option due to its limited pressure-holding capacity.
We tend to limit our thinking to preconceived notions our experience and exposure have allowed, and despite my own familiarity with hydraulic clamps, it’s likely an unconventional application to you, the reader. Speaking of you, the reader … what unconventional hydraulic applications do you have experience with?
Filed Under: Components, News, Related Technologies
