For Karl-Rudolf Vogel, Product Development Team Leader at Knoll, this is an efficient, economical filtration option. In this regard, Knoll relies on Heidland, a market leader in the field of making up technical fabrics for solid-liquid separation. "We have had excellent experience with Heidland belt filters for years. They are an integral part of our KF-E, VL and VLO technology," confirms Vogel. "We used to use single-layer fabrics, then we carried out tests with double-layer material. But it was only Heidland that succeeded in producing a double-layer filter belt that offers trouble-free passage for the cooling lubricant and also years of durability."

Heidland Managing Director Guido Rausse explains: "We have been using laminated polyester fabrics for many years for the filtration of cooling lubricants: a fine and a carrier fabric that are matched to each other." The special combination of the two fabric layers means that the free surface area is only imperceptibly reduced. The coolant can pass through the fabric barrier almost unhindered. The solid particles, however, are retained on the fabric surface by the fine screen mesh with a defined mesh size. "Our fabrics designed in this way have around 40 percent higher permeability compared to conventional single-layer fabrics or double-layer fabrics of the same filtration class," Rausse emphasizes.

A globally unique coating machine for laminated filter mesh, with which edge coatings of 20 to 200 mm can be applied fully automatically, also contributes to the high quality of its products. This PU coating prevents what is known as cross-filtration in a filter belt and protects the edge of the mesh from damage caused by loose or sharp-edged system components.

Experience in own production

Knoll also uses its filter systems in its own production, so it has its own experience with the Heidland mesh. For example, a large VLX 5000 filter is installed for the machines in the grinding department for HSS screw spindles, which contains an endless filter belt over 12 m long and 2 m wide. The cooling lubricant used here is an oil with a kinematic viscosity of approximately 20 ^mm2/s at an operating temperature of 25 °C. It must be reliably cleaned of the fine HSS chips and the particularly abrasive corundum grinding wheel abrasions.

Filter cake is gently blown off

The quality of the belt and the filter cake makes it possible to use nozzles instead of mechanical brushes or the like for cleaning. They lift the filter cake with exhaust air from the existing vacuum generation system so that it can be wiped off without contact. This protects the belt so that it does not have to be replaced every two years, as was previously the case, but has a service life of four years.

Team leader Vogel points out an additional advantage: "The filter cake is so ideally structured that it can be pressed afterwards - which is not necessarily the case with HSS chips. We therefore send it to a chip press that produces briquettes with a residual oil content of just 8 percent. This means a lower volume and more cost-effective disposal." Within two and a half years, this investment in chip processing had already paid for itself, including the wear parts.

According to documents from Knoll Maschinenbau /ag