Above: Compeo kneader

compounders can combine 2, 3, 4 and even 6-flight screw elements to optimise shear and distribution

In addition, the Compeo series employs a new

discharge unit in the form of a counter-rotating twin screw extruder that provides forced conveying and uniform pressure build up. Buss says this is particularly suitable for processing of sticky and/or abrasive products for underwater pelletising, especially in combination with melt filtration or direct extrusion. It provides multiple possibilities regarding configuration of process parameters, the company says, and together with the broad operating temperature range and conical twin screw discharge characteristics makes the Compeo machine suitable for many applications.

Right: Buss says it has

developed new cable com- pounding processes on Compeo extruders in its test labs, which it is now rolling out to customers

Test to market The Compeo and LSHC process technology have been developed within the Buss test centre over the past 2-3 years, during which they underwent several industrial scale trials, says Robert Hollosi, Process Engineer. “We are now investing significant effort to establish these technologies in the market. This means working very closely with customers, as well as partners, in order to fine tune our latest developments for the most demanding applica- tions. In parallel, we are working on expanding the Compeo series for both very low and high capaci- ties. There is a market need for both a new and more flexible laboratory machine, as well as for very high outputs, especially for PVC and HFFR.” Loviat cites the example of a project completed last year for a customer produc- ing a sensitive and highly filled PVC compound that required outstanding dispersion and exhibited thixotropic behaviour making it particularly difficult to pelletise. “This compound could not be produced in a satisfactory way by any other methods, such as twin screw extrusion,


because of degradation, bad filler dispersion or pelletising issues. The Compeo could produce the compound successfully, due to the smooth but effective mixing made possible by a combination 2- 3- and 4 flight screw configuration. In addition, the efficient conveying characteristics of the conical twin screw discharge solved the pelletising issues encountered with gear pumps and single screw extruders. The machine was sold, start-up performed at the end of last year without any major issues, and a second machine for this customer is now under discussion,” he says. “We have also developed a process with one of our industrial partners for the production of a compound to be used in appliance cables, such as phone chargers and household electric devices. Cable material for this application should be flexible, robust, flame retardant and heat resistant,” he says. Loviat says to achieve the required flexibility an

EVA grade with a high VA content is used as the raw material. The high MFI grades used are more typically employed as hot melts and are not suitable for traditional cable compound produc- tion. For this reason, the process usually is divided into two steps: in the first the melt is partly crosslinked to modify the rheology; in the second step the partly crosslinked product is compounded to the final cable compound. “In this project we managed to streamline the

production process by combining the partial crosslinking and compounding into one single step. The result was a ready-to-use, highly flexible cable compound containing close to 70% of flame retardant (ATH),” Loviat says. “This final material exhibits high flexibility, outstanding mechanical properties and can be used either as a thermoplas- tic or thermoset cable compound by applying the appropriate post-treatment.” Future developments at Buss in the short term



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