Minster Press - bolster regrind, Carnaud Metal Box
To remove the effects of fretting corrosion on metal can conversion presses - used for partially cutting throughlids to produce a ring pull - Metalock Engineering has developed a grinding machine to regrind in-situ the lowerbed face to an extremely fine tolerance over a large surface area.
The majority of can making presses throughout the world are made by The Minster Machine Company of Ohio,USA. For several years now Coventry based Metalock, has been refurbishing the lower bed faces on Minsterpresses throughout Europe, the Middle and Far East. These machines operate 24 hours a day all year roundand a typical 100 tonne press will have a lower die bed length of 1270mm(50in.) up to 760mm wide(30in.) towhich the bolster and die is bolted. To ensure that the penetration dimensions required for the ring pull tofunction are consistently achieveable, the lower die bed must be parallel to the upper moving ram to within0.040mm(0.0015in.) over length and width. The material used for can lids is 0.203mm(0.008in) to0.229mm(0.009in) thick and after penetration, only 0.0762mm (0.003in) to 0.102mm(0.004in) ±0.0152mm(0.0006in) remains around the scored appperture.
Even though the bolster and and die are firmly bolted to the lower bed, the constant vibration and heavypressure causes slight relative movement and fretting corrosion, the evidence of which is a reddish browndeposit of iron oxide when the parts are separated. Over a long period this corrosion affects the parallelism ofthe upper and lower bed faces and regrinding is required.
Metalock has developed a special system with a moveable carriage that bolts to the edges of the lower bed,and following accurate alignment facilitates the lower bed surface regrind. Usually removal of up to 15thousandths of an inch is all that is needed to restore the overall flatness and parallelism to within the 0.040mm(0.0015in) required.
Recently Metalock undertook refurbishments on two 100 tonne presses for Carnaud Metal Box in Carlisle, UK.Although the beds are not skimmed every time, CMB machines are overhauled on an annual basis. On thisoccasion the machines were being upgraded with new rams, slides and bolsters so the opportunity was takento regrind the beds and restore the press frames to as near new conditions as possible.
Metalock’s insitu grinding machine for metal canconversion presses, used to press ring pulls,restores the overall flatness and paralellism withthe upper ram to within 0.04mm TIR on a lowerbed die of 1270mm by 760mm.