On-site machining at Markland20 September 2010
Lawrence E Rentz and Karl Williams from Climax Portable Machine Tools report on the design of the portable milling machine that will be used at the Markland locks and dam in the US
This project details the design and development of a portable milling machine and the innovative process that will be used by the Army Corps of Engineers (USACE) to machine, drill and tap the four quoin blocks that are positioned between the Markland lock walls and doors. By using the portable milling to machine the quoins in situ, USACE will significantly shorten the machining time and reduce the overall costs of future repairs, making it possible to replace lock quoins more efficiently. This method of machining represents a paradigm shift in the way quoins are repaired or replaced, but promises to be a best practice for changing worn and corroded parts on other locks on waterways.
The Markland locks and dam are vital to the Ohio River navigation system in the US. Over the past five years, it passed an average of 55M tons of commodities annually. The project is located 5.6km downstream of Warsaw, Kentucky. USACE operates and maintains the locks on this inland waterway out of its Louisville, Kentucky District office. The main lock chamber has clear dimensions of 33.53m x 365.76m and the auxiliary lock 33.53m x 182.88m. Each lock has two doors – an upstream and downstream pair – which are 19.81m x 2.13m, each with two quoin blocks. In both cases the doors close against a slightly concave surface and seal up to prevent excess water from entering the locks. The pivot point in the door is slightly back and has support arms on the top and a pintle hemisphere at the bottom.
The Markland locks are more than 50 years old and because its doors’ quoin blocks are made of carbon steel material, they experience corrosion. This corrosion causes the door seals to close improperly resulting in a substantial amount of water leakage. As a stop-gap, USACE has traditionally repaired corroded quoin blocks by putting epoxy materials on the face of the blocks to build them back up so they meet the door again. Alternatively if these blocks were to be replaced, the Army Corps would cut out a very large piece of the concrete and remove that material, weld in new quoin blocks and then re-cast around the blocks with concrete, similar to original construction.
Because the old process could take months, USACE sought a better way to repair and replace the quoins and issued a request for proposals. Its first criteria was for the best technical and more efficient method for machining the carbon steel quoin blocks so that they could easily be unbolted and replaced with stainless steel ones that resist corrosion and last longer. Secondly, any new machining method had to enable USACE machinists to do the work in the shortest amount of time, eliminating the need for a long term shutdown.
A paradigm shift
Out of all the responses, USACE found in Climax’s proposal a paradigm shift to the current method used to repair quoins. Climax proposed to design and manufacture a portable, custom-made vertical milling machine that would enable USACE’s machinist’s to machine the quoins in situ. The machine would be delivered and set up at the Markland locks, then be attached to the lock wall. It would be capable of travelling up to 21.34m in height in a single pass, removing up to 63.5mm of metal material over multiple passes. The machine would also drill and tap the quoin blocks. Using this method, the entire job could be completed within a 17-day period.
In situ machining has been used successfully throughout the power industry and for infrastructure maintenance and repair when critical pieces of heavy equipment are too large or impractical to disassemble and ship offsite to a machine shop. Climax engineers were confident they could build a custom milling machine precise and powerful enough to do the work in the time allotted. They provided proof of similar successful in-situ machining projects such as line-boring the bushings on the wicket gates at the Hoover dam, then demonstrated how a similar machine operated, and was ultimately awarded the job.
At the Markland locks there are two different styles of quoin blocks – an extended design and an embedded design. The extended blocks are 203.2mm wide and protrude 76.2mm from the lock wall. The milling machine will remove metal 63.5mm x 203.2mm. It will also drill and tap holes as specified by USACE so the machinist can bolt the replacement pieces on.
The second style is a 254mm wide embedded block design that protrudes about 12.7mm from the wall. The milling machine will put a pocket into this area – cutting a 203.2mm x 63.5mm deep slot in the existing quoin block. Drilling and tapping will also be done so the replacement quoin blocks can be bolted into the lock walls.
The portable linear mill was specifically designed to work on both embedded and extended quoin blocks.
Designing the portable linear mill
Climax collaborated with USACE throughout the linear mill’s design process, conducting both a 30% design review and then another when the machine’s design plans were completed. In addition, alternative control and alignment systems were discussed and selected. There were some technical risks associated with being able to move the machine flat across sections of beds that had interlocking devices. These too were discussed to ensure that the final product fit the project’s needs.
The portable milling machine developed for USACE was modular for easy transportation and assembly at the job site. It consisted of six 4m long sections that connect end-to-end. The milling machine consisted of two separate sleds – a utility sled that houses the electrical and power components, and a machining sled. These sleds would be attached to each other. Dual rack and pinion drives using the NEXEN roller-pinion system were proposed to drive the machine vertically up and down the entire length of the lock doors. Servo-mechanisms were used for position control and to eliminate machining errors.
Its heavy duty beds are extremely rigid to provide precision milling within a +/- 7.6mm tolerance. A robust spindle design provides the power to utilize 203.2mm diameter cutter heads. Its user-friendly wireless controls included a wireless antenna that communicates to the device and a touch screen interface that is used to manage the entire machine’s programmed functions. The system operates for up to six hours, and a battery charger was also provided.
Testing and training
Before the portable milling machine could be delivered USACE required a factory acceptance test during which Climax had to demonstrate all the capabilities of the portable milling machine and its ability to meet all the functional requirements of the job. An extensive functional test requirement procedure was conducted by Climax at its facility. This procedure included a mock-up of the lock wall, test blocks and surrogate quoins that were machined to demonstrate how the portable mill would operate in the field.
During this time, USACE requested some changes to the machine such as revising the drilling and tapping head from a horizontal to a vertical orientation for better reach. These changes were easily made and the milling machine was retested and passed the stringent acceptance test.
At the same time, seven members of USACE’s team were also trained by Climax on how to set-up and safely operate the machine since they would be doing the actual work.
Completing the repair
All the components of the portable milling machine were delivered in June 2010. The machining is scheduled to take place in 2011.
USACE’s machinists will take about 7-8 days to set-up the machine, three days to do the actual machining, and 4-5 days to dismantle the equipment. To install the machine, USACE machinists will set down the first bed section on the concrete floor of the lock then drill and mount it to a concrete wall adjacent to the quoin blocks.
A laser system supplied with the machine will be used to indicate if and where the machine is out of alignment, and then a series of individual jacking screws will be used to adjust the mill to within a tolerance of 0.5mm to ensure that the beds are straight and flat. Once the first section of the mill is levelled up, other sections will be added and aligned until the machine is ready to operate. The operator will use the wireless controls to drive the milling machine vertically up and down, enabling them to hold a very tight +/-7.6mm overall machining tolerance over the entire 619.81m length of the door.
Efficient and cost-effective
The expected outcome of the repair is that USACE will have the ability to repair or replace the quoin blocks more efficiently and cost-effectively by just unbolting and replacing the blocks whenever wear and corrosion necessitate a change-out. In addition, replacing the carbon steel blocks with stainless steel ones that are more corrosion resistant will greatly extend the mean time between repairs and replacement.
The authors are Lawrence E Rentz, Vice President of Engineering/Quality and Karl Williams, Senior Design Engineer at Climax Portable Machine Tools.
More information can be found at www.cpmt.com or via email at [email protected]