The watches are made using double disk grinding technology from Supfina Grieshaber GmbH & Co. KG, while the brass plates which carry the various components of a clockwork mechanism are precision ground to a tolerance of microns in Planet machines. The cooling lubricant is then processed to the required filtration level of ≤ 5 μm.
The first stage in creating a bespoke design for a double disk grinding unit is a technical drawing of the component that the customer is looking to produce and for which a suitable machine is needed. Supfina’s applications engineers developed the necessary specifications for grinding wheels, cooling lubricants and grinding and cutting speeds. Next the company customises the machine to the customer’s particular process and plant specifications with application-specific transport disks and handling mechanisms for work piece feeding and removal. Depending on the thickness of the parts to be ground, the transport disks are made of glass fibre reinforced plastic or steel. For very thin parts, used extensively in the watch industry, with a lower limit of 0.5 mm for double disk grinding, the transport disk measures between just 0.3 and 0.4 mm and is laser cut from steel.
The machine selected was a Planet V4 with vertical grinding spindles, which was designed for finishing work piece diameters of up to 85 mm. The manufacturer commissioned Supfina to build a unit to produce plates with a roughness of 0.2 μm. To achieve the extremely smooth surface required, the cooling lubricant needed a filter fineness of ≤ 5 μm.
Supfina approached GKD and following laboratory testing the filter mesh construction and the number of filter disks were determined. GKD then configured the compact filter system MAXFLOW CS 1000-503 with a filter head comprising four static disks and a round tank system with integrated cooling coil for the test unit. The unit housing, filter disks and mesh are made of stainless steel. A filter disk package covered with multidimensional YMAX composite mesh, designed specifically for the given process, is installed vertically in the filter head. The filter disks are located in the crossflow as cooling lubricant emulsion contaminated with grinding waste and particles streams around them. With the required filtration level of ≤ 5 μm the filtration rate is 200 litres per minute. The clean tank has an integrated dirt tank with a tapered run-off that prevents a build-up of deposits at the bottom of the tank. The filter cake is detached from the disks by automatic backwashing and is pressed into a dry briquette by the integrated pressing unit and then discharged.