Twin screws and barrels

The ap extrusion company is an expert on the production and dimensioning of counterrotating twin screw extruders. These processing devices are interchangeable with all existing extruder brands and types that one can find on the market nowadays. An in-depth quality control takes place after the fabrication and before delivering the products.

AP extrusion's experience with screws' construction and with the running characteristics of twin screw extruders is combined with a very modern design and a simulation software that allows the optimisation of extruders' torsional. Only a right combination of the screw geometry and a correct material choice for screws as well as for barrels ensure a long durability for each processing advice. The ap extrusion company sets standards for the reduction of costs during the production.

Nitrified twin screws
For a lot of extrusion companies nitrified screws are standard. All ap extrusion screws are produced of high quality nitrified steel and get further deeply nitrified by a special plasma coating. Thanks to that technique the twin screws get a more robust surface and a very long durability.

Wear protection with Molybdenum Coating
It is ap extrusion's standard to apply a molybdenum wear protection onto the running surface. That system of wear protection needs 99 % pure molybdenum which is applied with a special Plasma spray process that was modified on purpose by the ap extrusion company. Thanks to that wear protection the durability can be increased by 180 % compared to conventional nitriding.

Screw temperature control
The screw temperature control can essentially affect extrudate's quality. One of the main components of screws' geometry is the decision between internal or external screw temperature control. Screw tempering with an internal closed water system is ap extrusion's standard. The system is maintenance-free and guarantees a high efficiency when a bigger output is produced. It regulates itself its melting temperature. The internal screw temperature control with thermal heat pipes constitutes an alternative offered by the ap extrusion company. For some types of double screws the oil cooling is still used. For those cases ap extrusion offers a profitable service.

Twin screw barrels
The ap extrusion company produces all types of twin screw barrels, suitable with all types of gearings - conic as well as parallel twin screw extruders. Those twin screw barrels are made of high-quality steel and are extra nitrified until a depth from 0.7 to 0.9 mm. The surface's rigidity is accurately controlled to be between 58 and 60 HRc in order to guarantee a long durability. Finally, the twin screws get precise drilled and honed.

Barrel heating
The accredited standard of barrel temperature control is reached by well-engineered, air cooled special heating elements. That system has the advantage to be almost maintenance-free. Furthermore it enables to control the temperature in an easier way during the processing. The air cooled system suits very well to climatically hot conditions. A more frequent alternative is a temperature control with the help of oil or water. The cooling liquid is conducted around the barrel and has a tight contact with the cooling pipes. In that case water is very efficient, but it requires a special temperature control device. The maintenance of an oil cooling, especially the function of the valves, depends on the cleanness of the oil. Therefor high diligence is required.

Bi-metal barrels and TC twin screws
The ap extrusion company recommends the use of screws that are coated with tungsten carbide combined with a bi-metal barrel, especially when using recipes with a high proportion of fillers. Bi-metal barrels have a very good wear protection. It is about 3 mm thick. That wear protection combination increases the durability compared to a standard nitrified system by more than three times.