Rock Box liners redesign for a Uranium Mine.
A uranium processing plant were experiencing premature failure of OEM Bisalloy 400 liners in the mill feed chute causing production delays.
Image 1. Rock Box on the mine. Tiles were used to substitute failed liners.
Castech Solution was asked to forward a proposal to increase the life of the liners in the rock box without having to modify the supporting structure.
After an initial site evaluation Castech Solutions was able to identify that the liners were operating under extreme erosive and corrosive conditions.
To improve the performance of the Chute, Castech Solution approached two aspects of the problem: Physical design of the liners and Material selection.
Prevent “racing” between mating liners
Taking advantage of the freedom of shape that castings allows, Castech engineers designed a saw tooth solution that staggers the mating joints minimizing the “racing” erosion of the original continuous joint line design. The saw tooth design is shown in Figure 2.
Image 2. Top view of the liner pattern designed .
The saw tooth design is orientated in the direction of the flow.
Variable thickness to balance the wear
Image 3 shows a section of one of the high wear liners. Thickness was increased in the high wear zones to balance the wear rate across the entire liner and increase service life. Also reducing the “throw away” material of the BIS 400 plate liners.
Image 3. Section of one of the high wear liners.
Thickness is increased in the area where the wear will be higher.
Reduce Change out time and improve safety
Designing the high wear liner mating edges with a reverse tapered allows these liners to be easily removed without having to remove the adjacent liners dramatically reducing the change out time and improving the safety for maintenance staff
Reducing erosive and corrosive wear
After analysing the typical impact and abrasive operating conditions and the pH levels of the process water, a High Chrome White Iron was specified. Cast Chrome Iron has a bulk hardness in excess of 600HB compared to the rolled steel plate at 400HB. Chrome Iron is also suitable to operate with pH levels of 3-9.5 compared to the 5-8 for the rolled steel plate. The recorded pH levels were 3-4.
The new liners were delivered as scheduled and installed with minimum disruption. Image 4 shows the liners during assembly.
Image 4. Liners on-site before installation (left). Rock box partially assembled (right).
Castech’s solution has extended the change out of the high wear liners from 5 weeks to >12 weeks. Change out times have been reduced to just 1/3rd.
This project demonstrates that:
- The freedom of shape provided by castings allows for an optimization of the geometry of the chute's liners that is specific for the working conditions of the chute.
- A combination of understanding the operating conditions and the properties of available wear material will result in extending wear life.
- Complex castings, both in terms of geometry and material grade, can be supplied from low-cost countries with consistent quality if the manufacturing process is closely monitored by an experienced company.