Handling of the rubber compound after the mixer

• Usually the compound is required in either sheet or strip form after mixing process. This can be obtained in several ways One or several mills

Dump extruder

Dump extruder with roller die

• The extruder itself could be either a single screw extruder or more recently a bi-conical twin screw extruder.
• After the extruder or calender in the mixing line there is an air cooling section. The purpose of the cooling is to prevent pre-vulcanization reaction and prevent sheets from adhering to each other.
• Before cooling sheets run through anti-stick bath, which prevents sheets from sticking to each other. Other way to prevent rubber sheets from sticking to each other is to put a plastic sheet between the rubber layers.

Sheeting Mills

• The sheeting mills are the oldest and most commonly used follow-up devices.
• Milling is not to be recommended in this day and age except where a batch identity has to be maintained.
• Mills are to be recommended for most general rubber goods applications, but controlled and careful operation must be maintained to give consistent product.

Dump Extruder

• Forming extruders instead of sheeting mills are increasingly used as follow-up equipment of larger mixers of fully automated mixing systems with low personnel requirements.
• The use of dump extruders is not totally confined to the tyre industry but they are certainly found more often in this sector than any other.
• The extruders are used to manufacture an endless strip after the mixing operation.
• The compound pieces fall from the internal mixer through a big funnel onto the end of the screw where they are pressed into the screw flights by a hydraulically operated ram.
• The cylinder and the screw are cooled intensively.
• Either a wide strip is extruded through a sheet die or a thick walled tube that is then automatically slit exits then as a wide strip.
• Often twin rolls are used after the extruder (extruder with roller die).

Twin Screw Dump Extruder

• Twin screw dump extruders introduced recently by several manufacturers benefit from the ability to operate without pushers, the large biconical screws easily pulling the batch between them and driving it forward through the die.
• Normally twin rolls are used on the front of the twin screw machine to give a sheet, but as pressures are low the sheet edges can be poor. The advantage of this type of machine in comparison with a single screw unit is the lack of temperature rise in the stock due to lack of energy put into it, and the claimed ease of self-cleaning. The removal of the requirement for maintenance on pushers is also thought of as a benefit by maintenance engineers.