By David Reed, UT EditorMunich, Germany-Krauss-Maffei Kunststofftechnik GmbH, a leading German polyurethane processing equipment maker, is offering a hard-metal version of its PSM mixing heads for polyurethane spray moulding. This will allow makers of the highly filled-and often highly abrasive-acoustic deadening products such as backing layers for mats and carpets used in the automotive sector, to use the spray process in place of the current closed-mould systems. And this, in turn, reduces costs by eliminating the need for heavy moulds and mould carriers capable of delivering high clamp forces, Krauss-Maffei says. Furthermore, although the acoustic layers are less than 1.5 mm thick, metering machines must be capable of delivering very high shot weights since the parts frequently have large surface areas.Using the new unit, based on Krauss-Maffei's MK 10 P-2KV spray mixing head, the highly filled compounds widely used in the backing layers for mats and carpets used in the automotive sector can be sprayed into open moulds.This has a number of advantages, Krauss-Maffei says. The mould costs significantly less because it has only one half (positive or negative), and no clamp is required. The PU/barium sulphate (barytes) compound can be sprayed into the open half-mould to produce layer thicknesses between 0.5 and 3 mm and weights between 1000 and 6000 g/m2. Additional layers can be sprayed directly onto the acoustic layer. In this way, components with a complex, multilayer structure can be made in a one-step process. Component thickness can be changed easily, even during a production run, while keeping the thickness and weight of acoustic layers to the necessary minimum also results in weight savings.And mould-changing times are also cut substantially, Krauss-Maffei adds. However, the fillers used are usually high-density materials, such as barium sulphate, in concentrations as high as 70 percent weight which, Krauss-Maffei points out, can be highly abrasive.But the new head can handle this, Krauss-Maffei claims. The design combines the MK 10 P-2KV high-pressure linear mixing head with an application-specific spray adapter capable of delivering higher output than conventional spray mixing heads. The new wear-resistant mixing head can also be successfully used to spray other PU compounds using fillers such as Wollastonite, mica or chalk, Krauss-Maffei concludes."
