Innovations in grinding

FLSmidth is constantly moving ahead with new innovations to build better equipment and more efficient systems so that you can get the most out of your investment. With larger VXPmill stirred mills and the new Express Frame HPGR, milling is moving to new levels.

VXP5000 Vertical Stirred Mill

On August 20, 2013, FLSmidth Knelson hosted more than 25 clients—along with various FLSmidth employees—at its Vancouver, Canada, facilities to introduce FLSmidth’s new VXP5000 Vertical Stirred Mill.

Attendees included end-user customers, EPCMs and representatives from the University of British Columbia, which has performed fine and ultra-fine grinding research for FLSmidth using a VXP10 lab mill.

“The purpose of it was to showcase the VXP5000 mill,” FLSmidth application engineer Jack Meegan said. “It’s our largest mill, and right now it’s going through internal quality control factory acceptance testing. Bozshakol ordered a single mill, and we put it together at the shop site to make sure the components fit as they should. Because we’ve got it assembled—the whole mill except the motor—we figured we might as well have people 'kick the tires' and check it out.”

The event began with a round of presentations—topics included a general overview of the mill and its grinding parameters, new maintenance procedures, gravity concentrators and FLSmidth's field service offerings—followed by a visit to FLSmidth Knelson’s warehouse and manufacturing facility. The visitors were able to see firsthand some of the shop’s capabilities, which include production of the mills, gravity concentrators and vibrating screens, along with custom fabrications.

To cap it off, the customers were invited outside, where they saw the assembled mill and watched a demonstration of the VXP5000 mill’s maintenance capabilities.

“We wanted to give them exposure to what the mill is,” Meegan said. “They got to see it in person, and we did a quick maintenance procedure test in front of them so they could see how the maintenance features work. They also saw the Knelson concentrator equipment while they were on site.”

The VXP5000 mill differs from other stirred media mills in several ways. One is its small footprint, which is especially helpful on brownfield projects where equipment must be fit into an existing structure. Also, the lead time on mill orders is, in some cases, considerably less than what competitors can offer. The most noteworthy difference, though, is the mill’s operating speed.

"Mill speed is an important differentiator between the FLSmidth® VXPmill and the ‘low’ and ‘high’ speed stirred mills which operate below 3 m/s and above 15 m/s (impeller tip speed),” FLSmidth VXPmill product manager, David Rahal said. “It allows the VXPmill to be used in applications where the design constraints of the other mills limit their ability to operate at the optimum stress intensity for a given application. The VXPmill bridges the gap between these two extremes.”

Finally, the VXP5000 mill has a unique, newly designed maintenance procedure that increases safety by eliminating the worker's exposure to a suspended load while changing out the discs and spacers—a demonstration the clients were able to witness at the event in Vancouver.

Three VXP5000 mills have already been prepared for shipping to the MAK project in Mongolia, while another will soon be on its way to the Bozshakol plant in northern Kazakhstan—with commissioning scheduled for mid-2014.

Purpose Designed Frame for HPGR Mineral Application
Mineral high pressure grinding rolls (HPGRs) have come a long way since the early days of using the hydraulic roll press (HRP) and hydraulic roll crushers (HRCs) in the cement industry. One area of research focus has been the roll surface material. Traditionally, the cement roll surfaces were a smooth, hard-faced surface, suitable from both a wear point of view and production. Due to the abrasivity and slippage of the mineral ores in comparison to cement, though, these rolls were not meeting wear-life requirements or throughput in minerals or hard rock applications. Lifetime usage for the hard-facing surfaces in the cement industry is typically more than 12,000 hours with in-situ weld repairs (without removing the roller module). In minerals applications, the productivity was three weeks of operation, followed by one week of repair.

This extensive downtime led to the creation of the tungsten carbide studded roll surface for use in the minerals industry. Both wear life and throughputs were positively impacted. However, even though this new technology revolutionized roll surfaces for minerals applications, the studded wear liners did not make economical sense for the cement machines. Even with the advancement in wear life and roller surface technology, roller sleeves in high abrasive mineral applications last only nine months to a year on average before requiring a replacement. That differs greatly from the cement application, in which rollers are often repaired in-situ and do not require actual roll changeouts on a frequent basis. Due to the nature of the studded rolls, this in-situ repair is not possible. Mineral roll wear surfaces require a more frequent replacement than those seen in the cement plants. This also means an additional roller assembly modular set needs to be purchased.

Roll assembly modular sets can account for up to 35% of the machine cost, depending on the tungsten carbide grade and percentage coverage. Roll surface change-outs can take approximately 24 to 60 hours, depending on site location, tooling, planning, spare part stock and skill resources. This downtime greatly impacts production, and the manufacturing costs increase dramatically due to the high cost of tungsten carbide studs. On average, this accounts for 12–15% of the machine’s cost, compared to the cement industry’s cost of 3–6%.

With these considerations in mind, FLSmidth’s engineers revisited the HPGR frame design, aiming to ensure an optimal mineral ore product design. They not only looked into the roll changeout time requirements, but also the actual frame design and steel requirements.

The traditional FLSmidth® cement HRP L-gable has proven very effective for roll changeouts compared to other systems on the market. This unique system allows rolls to be lifted out of the machine without having to extract a top frame or incorporate an extended work platform. The L-gable incorporates a vertical side pressure beam and a portion of the top frame. It also utilizes a pinning system, which greatly reduces roll replacement time compared to the conventional hard bolting frames.

However, with plant sizes growing due to declining grades, more optimal flowsheets with reduced footprints are being implemented. The areas around the HPGRs are more compact, while chute-work and conveyors are less retractable than in the past. With this in mind, FLSmidth engineering created the FLSmidth® Express Frame, which is designed and built for the quick replacement of mineral application roll surfaces.

This purpose designed frame is optimized for mineral application functionality in the following ways:

  • In the Express Frame, the L-gable has been removed and the pinning system has been moved forward to make the bearing housing the vertical pressure beam. The removal of this L-gable, along with the reduced bearing house size, has drastically reduced the footprint and steel requirement.
  • The new design allows for far better maintainability of the roll surfaces.
  • The greater reduction in frame casting thickness makes it possible to use project specific local suppliers for replacement. This reduces delivery times and affords clients a better overview of the procurement of their equipment without intercontinental travel.
  • The shipping cost and associated taxes will be averted.
  • This innovative design offers a new taper pinning frame design. Removal of the tapered bushing creates more clearance space for inserting and removing pins.
  • The bearing housings are reduced in both size and configuration.
  • A wedge jacking system is utilized to take the load of the shaft and bearing housing for quick pin extraction and replacement.
  • This results in a reduced carbon footprint using fewer raw materials, as well as less weight in shipping and transport.

FLSmidth is proud to include the Express Frame as part of its standard Minerals HPGR offering.

CONTACT: David Rahal