By Andy Becker
|To fabricate the turbine housing, a Portable Machine Works had to prepare two skids — a large one and a smaller one as a sub-base skid — and several sets of mounting pads in various sizes and shapes. The smaller skid had mounting pads on the top and bottom, in order to mount on top of the larger skid to hold a gas turbine. |
Portable machine tools like milling machines, boring bars and flange facers, are being used to supplement stationery tools in modern machine shops, so shop owners are able to expand their service offerings and compete for more projects. Ongoing research and development to incorporate the most-in-demand features — precision, durability, rigidity, and ease of use - make these machine tools comparable in performance to stationery tools. At the same time, the added benefit of portability makes them ideal for on-site machining anywhere.
For many years, machinists experienced with top-quality portable milling machines have relied on them for on-site machining, especially in manufacturing sectors like shipbuilding and electric power supply. They have found that they are a cost-effective solution for heavy equipment repair and maintenance, saving time and eliminating the costs of disassembling components and shipping them to a shop for repair. Moreover, these operators recognize that the portable machine tools prove their worth when they allow a shop to take on jobs that otherwise would have been extremely challenging or nearly impossible to do.
For example, a fabrication shop in Texas took a contract from a supplier of power-generation technologies to build a metal housing and large skids for a first-of-its kind, small gas turbine — essentially an innovative “power plant in a box”.
The shop manager wanted to do all the fabrication at its own location, mount the finished assembly on large metal skids and ship it to the project site. Knowing that a stationery mill likely couldn’t do the machining required for the huge skid components of this project, he wanted to explore other possible options. Climax Portable Machine Tools manufactures custom machining solutions, so the shop operators placed a call for information about designing and supplying a specialized milling machine to do the job.
After an in-depth discussion with the project fab manager, and to address his desire to supervise the work, Climax concluded that the most cost-effective way to machine these skids and related components was to do it on-site using portable linear mills. Because Climax manufactures precision machine tools but doesn’t do the actual machining, they referred the fab shop’s project manager to Steve Harrell at Portable Machine Works, a full-service company in Prairieville, LA, with machine shop and field-service operations. Climax was confident that Harrell's machinists — who are experienced at using both stationary and portable machine tools — could meet the criteria set by the fab manager and the shop’s customer.
A winning combination
The project called for machining two skids - a large skid measuring 16 ft. x 60 ft., (4.9 m x 18.3 m) and a 6 ft. x 6 ft. (1.8 m x 1.8 m) sub-base skid —as well as several sets of mounting pads in various sizes and shapes. The smaller skid had mounting pads on the top and bottom, and was to mount on top of the larger skid to hold a gas turbine.
In order to eliminate vibrations that might damage the turbine, all the skids and mounting pads had to be machined to extremely tight tolerances of 0.002 inches (0.051 mm), so that the skids would lay flat and parallel to each other and the mounting pads would match and mate properly when the components were assembled.
Although Harrell’s company owns several Climax machines, they were being used for other projects. So, he rented two Climax LM6000 portable linear mills and a PM2000 portable mill. These are modular, rugged, precision machines capable of meeting the close tolerances typically demanded in the power industry.
Harrell’s crew, under the supervision of his field service manager, Dave Pettit, then set up operation in the fab shop and got to work.
A view of the turbine skid during the machining process.
To machine the skids, the crew welded the LM6000s in place using gussets to support the milling machines. They then located the base plate onto the gussets and proceeded with the milling operation. The larger skid included 28 equipment pads of various sizes and shapes, ranging from 2 in. x 2 in. (50.8 mm x 50.8 mm) to a large midplate 8 ft. x 6 ft. pad (2.4 m x 1.8 m). They used the linear mill to machine the seven equipment pads for the smaller skid, too. The smaller Climax PM2000 portable mill was used on the 2 in. x 2 in. (50.8 mm x 50.8 mm) equipment pads that were mounted on the perimeter of the larger skid. The modular design and portability of these mills allowed the machinists to move and mount them to the pads easily, to machine them down to a desired height and flatness.
Once the skid was finished and the gas turbine placed on the skids, it was walled inside an enclosure. The finished fabrication is a turbine package that is modular, mobile, and easy to set up at a plant.
Saving time, expanding business
Laser tracking technology, used in combination with the machining operation, allowed Portable Machine Works machinists to monitor and maintain tight tolerances of 0.002 inches (0.051 mm) over the entire length of the skids and pads. In addition, as they became more familiar with the project and all the capabilities of the milling machines, the machinists found ways to shorten completion time. The initial skid machining project took two machinists just three weeks to complete, but they’ve since completed many more of these “turbine in a box” projects. With each new project the machinists have been able to cut the machining time a bit further. Currently, it takes only 12 days to complete the task.
Pettit believes there is no machine shop capable of machining these large skids using a stationary tool. And the precision and versatility of the portable milling machines allowed the fabricator to meet the requirements of its customers, keep the entire operation in-house, and maintain its high quality standards.
Through the expertise of its machinists and the efficiency and precision of the tools they use, Portable Machine Works was able to meet the stringent specs set by the fab shop’s customer, and to do so in a cost-effective and timely manner. The turbine manufacturer was very pleased with the work, and has subsequently received numerous orders for these systems, for which Portable Machine Works continues to be the subcontractor of choice. For its part, Portable Machine Works believes the linear mills have more than paid for themselves by making a seemingly impossible job possible, strengthening its relationship both with Climax as well as its customer.
Portable machine tools have become invaluable at tackling challenging machining projects that can’t be done by stationery machines. They make it possible for many field service companies to operate efficiently in a variety of environments. But, even more than that, portable machines are making it possible for machine shops to expand their services and compete for business in new industries.
Andy Becker is vice president of Business Development for Climax Portable Machine Tools