Manufacturers of machined metal parts leave money on the table when leaving coolant on chips.

For example, if a manufacturer sends a typical scrap shipment of about 18,144 kg (40,000 lbs.) of coolant-laden chips to a recycler, about 20% of the weight is moisture, said Mike Hook, director of sales and marketing at Kalamazoo, Michigan-based Prab Inc., which makes equipment to move scrap metal chips and convert them to dry chips or compact briquettes. That equals about 3,629 kg (8,000 lbs.) of fluid, or roughly 3,785 L (1,000 gal.), because coolant weighs about 3.6 kg (8 lbs.) per gallon.

“That has to be disposed of by the recycler and hauled by the hauler,” he said. “And you lose all the value of that in terms of coolant that could be reused, so you have to buy 1,000 gal. of new coolant to replace it.”

Hook said scrap recyclers usually accept coolant-laden chips but back-charge a customer to handle and dispose of the fluid.

“Dry, reduced metal scrap is going to be the most valuable to the recycler,” he said.

Additionally, Hook said legislation makes a part manufacturer responsible for coolant from cradle to grave, so a hauler isn’t liable if coolant leaks or otherwise escapes from a container during transport.

Protecting the Planet

Not only is metalworking fluid a significant expense for part manufacturers and a rising one as the petroleum and other products needed to make it increase in cost, but the environmental protection regulations for scrap and fluid disposal continue to become stricter and pricier when violated, said Justin Viner, regional sales manager for Knoll America Inc. The Madison Heights, Michigan-based company, which is building a new headquarters in Dallas, North Carolina, also offers a wide range of equipment for central chip handling systems, including conveyors, pumps, coolant filtration, shredders, centrifuges and briquetters.

“The cleaner the chips are, the better it is to get rid of them,” he said, either by recycling or disposing of them.

Viner said an automated central chip handling system enables chip processing to be performed outside a production area, enhancing worker safety.

Using conveyors and sensors, he said the system is automated until the stage at which chips are dumped into containers.

“You can have robots even at that point to reduce personnel costs and remove the chips into containers,” Viner said.

Nonetheless, he said it’s easier to integrate an automated central system when machining centers are installed before rather than after.

“Sometimes it is an afterthought for companies,” Viner said.

Hook explained that creating a central system traditionally involved setting machine tools along a trench into which chips and fluid are conveyed to a centrifuge to wring out the fluid or to a briquetter to squeeze out the fluid and turn the chips into pucks before sending filtered fluid back to the machines and the scrap to trailers.

“It’s very simple and effective,” he said.

In addition to mechanical conveyors, Hook said material can be conveyed pneumatically to more efficiently transport it longer distances, which is especially
beneficial for newer modular shop layouts where companies adjust production processes based on changing workflow.

“The flexible automation makes a lot of sense,” he said.

Hook said electronic automation also plays a role in chip handling systems, allowing end users to communicate with partner organizations. This capability enables a system, for example, to tell a scrap dealer that bins are full and need to be collected.

Working with sister company KMC Global Controls & Automation in Kalamazoo, he said Prab offers an Industrial Internet of Things option for chip handling systems that monitors parameters, such as run times and downtimes, and sends data to customers so they can use it in Industry 4.0 initiatives.

“Some of this technology gets into predictive maintenance,” Hook said, “where we have sensors that will sense precursors to failure to make sure the equipment is serviced prior to it breaking down.”

Drying Out

Fundamental to an automated central chip handling system is a wringer/centrifuge or briquetter. Prab reports that its centrifuges and briquetters reclaim up to 99% of metalcutting fluids while saving space.

“Our equipment has proved to reduce scrap volume up to 90%,” said Marketing Coordinator Jack Gould. “The oil savings is a big part of it as well, especially with a centrifugal wringer system.”

He said briquetted pucks are slightly cleaner than loose chips, are easier to transport and enable more efficient re-melts. As a result, recyclers frequently pay more for pucks than dry chips. He offered the example of a customer, Martin-Baker America Inc., which received 17 cents more per pound for briquettes than loose chips.

“The briquetter can increase scrap value up to 25%,” Gould said. “That adds up quickly.”

Viner pointed out that some metals, such as magnesium, must be pressed because the material is flammable and compacting prevents chips from igniting. In addition, grinding slurry is well suited for pressing, he said. Knoll America offers the MicroPur reversible flow filter for separating superfine impurities from oils, and an ideal application is grinding carbide and high-speed steel cutting tools.

He said briquetting is suitable for central systems, which usually service at least 30 machines, rather than stand-alone machines.

Hook said companies that have their own re-melt facilities, such as die casters that both cast metal and perform secondary machining operations, can benefit from wringing chips in centrifuges prior to briquetting to increase melt efficiency.

“It doesn’t have to leave the facility,” he said, “and they can control their alloys and contamination very well.”

Breaking Down

“Prior to being processed into dry chips or compact pucks,” Gould said, “vertical-axis crushers and shredders are available to make bulky wads of turnings more manageable. A shredder reduces light to moderate wads of metal turnings into flowable chips.”

A vertical-axis crusher, however, reduces turnings and bulky wads into shovel-grade chips. Prab reports that a shredder reduces turnings volume up to four times at the source, and a crusher reduces scrap volume up to a 6-1 ratio.

“A shredder is an option for the company’s E-Series fully automated chip system, which is one of Prab’s more popular offerings,” Gould said. “We recommend it if you have nominal chip throughput.”

He said the system can process a variety of workpiece materials at a rate of 113 kg (250 lbs.) per hour for aluminum chips, 272 kg (600 lbs.) per hour for brass, 340 kg (750 lbs.) per hour for steel and 363 kg (800 lbs.) per hour for cast iron.

“The E-Series system is compact enough to be moved with a forklift,” Gould said. “They’re used for smaller plug-and-play applications.”

Hook said Prab also offers the Bundle Breaker, a pre-processing piece of equipment with dual rotating cylinders to shred apart stringy wads of chips, turning and bundles. That capability is particularly beneficial when long, stringy ribbons of material become tied together while a solid piece of metal is held inside.

“The biggest challenge in the automatic scrap handling business is in parts, bar ends and contamination making it into the scrap flow,” he said.

Hook said if a relatively large chunk of solid metal is introduced into a centrifuge spinning at, say, 1,700 rpm, damage to the wringer is likely.

“You basically turn it into a projectile at that point in time,” he said.

Parting Ways

Prior to shredding or crushing, Hook said chip wads frequently go through a solid separator, and Prab provides four different types that use air, vibration or a combination of both.

“Even though crushers or shredders can oftentimes handle or even process some of the solids,” he said, “as you can expect, anytime a sold piece meets a high-torque piece of equipment, no matter how fast the clutch disengages or overload kicks on, there’s always the potential for damage.”

In addition to separating solids from chips and turnings, Hook emphasized it’s important to have some sort of separation technology to avoid one type of workpiece material being processed with another type and causing cross contamination. The simplest, most widely used is magnetic separation, which separates ferrous from nonferrous materials. When there is a significant difference in the density of metals being processed, density separation is possible. In addition, eddy current separators are available for nonferrous materials.

“However,” he said, “by the time you get to that level, you might be better off having dedicated systems to do your higher-percentage materials.”

One way to reduce the amount of coolant on chips is to apply substantially less by machining with a minimum-quantity lubrication
system. Viner said Knoll America offers AerosolMaster 4000 ATS and 4000 Cryolub MQL systems for almost all machining processes with geometrically defined cutting edges, such as on machining centers, process lines and turning, milling, drilling and sawing machines.

“I don’t think it has been adopted enough yet,” he said, “but it will eventually. The chips are a lot cleaner when they come out.”

In the meantime, manufacturers of chip handling systems continue to refine and enhance their
equipment.

“We have incorporated many more features into our equipment to make them less user-intensive and less maintenance-intensive so systems can generally be set up to run without manual intervention,” Hook said. “The only time intervention is required is when something goes amiss.”

For more information from Prab about chip handling systems and from Sandvik Coromant about chip management, view video presentations at cteplus.delivr.com/2n8aq and cteplus.delivr.com/272pe

Chip Control Through Oscillation

Prior to processing chips in a chip handling system, it’s beneficial to control how chips are formed so they flow through the system without being caught in conveyors or needing to be crushed or shredded into a manageable size. This capability is especially helpful when thread turning, which tends to generate long, stringy and tangled turnings. The chips not only take extra work to process but tend to coil around robots, chucks, tools and components.

In addition, chip control when thread turning has become increasingly challenging as more part manufacturers machine more near-net-shape forgings, such as ones made of low-carbon steel for automotive applications, and only remove a small amount of material, said John Winter, product manager of East U.S. for Sandvik Coromant Co.

“You need a certain chip thickness as you’re processing the part in order to gain chip control,” he said.

To overcome these issues, the Mebane, North Carolina-based toolmaker developed the OptiThreading software module for its cloud-based CoroPlus Tool Path software. Winter explained that the module creates CNC threading code based on the cutting data parameters to mechanically control the chip and provide the correct number of passes with evenly distributed cutting forces.

He said the code enables toolpaths that deliver controlled, oscillating movements that go in and out of a cut on all passes except the last one, which is a straight, conventional toolpath.

“Even in the final pass when you are creating that full chip form,” Winter said, “you still are managing the chip.”

The resulting chips are 50.8 mm (2") to 101.6 mm (4") long.

“That chip is manageable enough that it should get through the chip hopper,” Winter said.

Because OptiThreading creates high cutting forces on a tool as it moves in and out of a cut, he recommends using only CoroThread 266 indexable-insert thread turning tools. The tool body features the iLock interface, a locking mechanism that provides insert security by preventing it from moving in the pocket.

“The CoroThread 266 has a rail within the shim that goes right into the back of the insert and supports it and keeps it from moving,” Winter said. “You get a better-quality thread.”

He said the cutting movement during the OptiThreading process extends tool life because wear is spread over a larger area of an insert instead of one spot when conventional thread turning. Also, having pocket security enables an insert to handle a heavier load and reduce the number of passes, depending on the thread size, finish specification and the number of passes required.

The process is suitable for external and internal threading. Winter said internal threading can be the more problematic of the two because chips tend to ball up more when they’re inside a part. To overcome that issue, he recommends a pull threading operation when using OptiThreading to flow chips out of the part instead of staying inside.

He said tool grades are available for threading a variety of workpiece materials, including steel, stainless steel, iron, brass and heat-resistant superalloys. Sandvik Coromant even successfully tested the process on drawn over mandrel steel tubing. DOM is a metalforming process that starts with an electrically welded formed tube, which is cold-drawn through a die and over the sides of a mandrel.

“I don’t know anyone who can get chip control when threading that material,” Winter said.

— Alan Richter