Accelerating a flying saw to tube and pipe mill speed

Tube and pipe mill builder ASMAG Group used a linear drive for a flying cutoff system and doubled its acceleration. This increased the time available for cutting, allowing shorter cut lengths while improving cut quality and saw blade service life. ASMAG

How fast is fast enough? That’s hard to say. In the automotive realm, the fastest cars are terrifyingly fast. Lamborghini boasts that its Aventador LP 780-4 Ultimae achieves a top speed of 220 miles per hour. The Rimac Nevera is quite a bit faster than that at 258 MPH. Certainly both of these top speeds are more than enough for most drivers, but next year’s models will probably be faster still.

Top end isn’t everything, of course. Acceleration is essential too. Heart-pounding, gut-wrenching, tire-smoking acceleration. It’s just a matter of stomping on the accelerator when the traffic light turns green. Why not? Blistering acceleration can be a bigger thrill than an outrageous top speed.

The Aventador takes 2.9 seconds to reach 100 km/hr. (62.14 MPH), meaning that it accelerates at 31.4 feet per second². The Rimac Nevera can reach 60 MPH in just 1.85 sec., an acceleration of 47.6 ft./second². That’s a difference of more than 50%. What gives? A key difference in the two vehicles is one of technology: The Aventador burns gasoline; the Nevera is electric.

A similar change in technology enabled equipment manufacturer ASMAG GmbH, Scharnstein, Austria, to upgrade its flying saw, doubling its acceleration.

A Flying Saw Takes Off

Acceleration is critical on many machines, especially flying cutoff systems. Whether the cutting is done with a saw blade or a shear system, the drive system on a flying cutoff has to be a minor marvel of engineering to keep up with a modern welded tube or pipe mill.

Cutting is the easy part. The motion is the difficult part. The carriage has to exceed the speed of the mill, which might run at 650 ft./min. The saw has to accelerate from a stop to match the mill’s speed, make the cut, rapidly decelerate to a stop, then travel in the opposite direction to return to the start position. While the carriage is returning to the start position, traveling backward, tube is still moving forward through the mill at 650 FPM, so the carriage’s return speed has to be about twice that of the mill’s speed.

These actions are extremely kinetic, so such systems have to be extremely robust. The entire unit has to be as light as possible so it can accelerate and decelerate rapidly, yet durable enough to withstand endless accelerations, decelerations, and abrupt stops.

Like high-performance automobile manufacturers, flying cutoff manufacturers do all they can to improve such systems so they can cover the specified distance in shorter times. Improving a system’s acceleration means that the mill can run faster or, if the mill’s speed remains the same, the cutting system can cut the tube to shorter lengths. Other factors concern cut quality and the service life of the saw blade; having more time to make the cut improves both.

Of course, these manufacturers design these systems to have the smallest possible footprint, which means the carriage has to get up to speed, make the cut, and come to a stop over the shortest possible distance. At modern line speeds, such saws don’t have a lot of time to make a cut.

“If the mill runs at 330 feet per minute, and the pipe producer has to make cut the product into 20-foot lengths, the saw has only 1.2 to 1.5 seconds to make the cut,” said Klaus Heinzl, a sales manager for ASMAG.

By using an alternate drive technology, ASMAG gave the flying saw concept a kick in the seat of the pants, providing substantially more time to make the cut.

“The new saw design accelerates about twice as fast as its predecessor,” Heinzl said. The new design is a departure from the standard drive system, rack and pinion, replacing it with a linear drive system. As the name implies, a linear system’s motion is in a straight line. While a rack (linear gear) and pinion (circular gear) system also provides linear motion, it’s driven by the rotation of the pinion, so it’s not a strictly linear action. Also, the friction between the two gears chews up a lot of power. A linear actuator slides on guides for a smoother, essentially frictionless action.

“There’s virtually no wear on the system,” Heinzl said. “The motor slides between two magnets with a very small clearance, about 0.020 inch,” he said.

It also uses an aluminum actuator and an aluminum gearbox, which helps to keep the system’s weight down.

“A cutting carriage made with rack and pinion technology accelerates from 23 to 32 ft./second². ,” he said. “The new saw’s acceleration is almost twice that at 62 ft./second².” It provides about 2 sec. to make the cut. That doesn’t sound like much of a difference, but compared to 1.2 sec., it provides two-thirds more cutting time if the cut length remains the same. Using the longer cycle to make shorter cuts can allow a tube or pipe producer to eliminate a secondary cut-to-length process, Heinzl noted.

The saw system’s length depends on the model. For cutting diameters up to 2.5 in. OD, the unit is approximately 20 ft. long. For cutting tubulars up to 5 in. OD, the saw’s length is 23 ft. The saw carriage’s travel distance varies from 17.5 ft. to 12 ft., depending on the model and features.

What’s Inside?

Getting a good grip on the tube helps with cut length accuracy, but the gripping process does much more than that.

First, a flood system distributes the coolant to rinse any chips from the incoming tube and the grippers. Eliminating the chips improves the grip, reducing the potential for the tube to slip. Chips also create unnecessary vibrations, shorten the blade’s service life, and mar the tube’s surface if they get caught between the tube and the clamps. Second, the gripping system itself is not magnetic, but mechanical (and, like the linear actuator, wear-free).

The outcome is a cut length accuracy on par with that of a stationary saw cutting stationary parts: ± 0.020 in. over a 6-ft. cut length.

The cut’s quality depends on factors such as the blade speed and feed rate. While the blade speed is stable, the feed rate isn’t. To optimize the cut quality, the blade starts at a baseline speed, then rotates faster as the cut progresses, then decreases before the blade exits the cut.

Getting a saw like this to run smoothly means coordinating a large number of motions, accelerations, and decelerations, many of which are extremely brief with rock-solid timing. The machine also has to take into account the presences of chips and coolant. The design of the machine prevents debris from getting to the actuator and guides, and a machine cover—which is locked when the saw is in operation—prevents the coolant and fines from traveling into the shop. The cover also incorporates some soundproofing to keep the noise to a minimum.

Installation

The company knows no tube or pipe producer wants to shut down its moneymaker for a few days to install a new peripheral. To that end, when this saw is delivered, it’s nearly ready for installation. The setup process doesn’t include any of the common steps, like installing and connecting the PLC, adding the covers, and mounting the cooling unit.

“It’s delivered as a single item,” Heinzl said. “Lift it with a crane, set it in position, and it’s almost ready to go,” he said. Whereas commissioning a conventional unit often takes two to three days, this one requires just a couple of connections—electricity and coolant—and little else.