Patent Application
20140119153
The invention relates in general to extruders for rubber processing, and more particularly to an extruder screw.
It is known in the art to extrude visco-elastic materials such as rubber, using a screw extruder. It is known in the art to utilize a feedbox to feed slabs of rubber compound into the extruder. One problem that may occur is that the slab of rubber will shear off due to slab feed tension, commonly referred to as slab “bite off”. This typically occurs when low strength compounds are utilized, particularly tread compounds. The problem is worsened by the “scissors” action on the screw flights against the feed roll and feedbox. If the feed strip breaks, it will result in workers having to clean out the feed box. Thus it is desired to have an improved extruder screw that overcomes the slab bite off problem.
Feed Hopper—typically a cone-shaped slab feed “chute” which attaches to the top of an extruder feedbox. The feed hopper establishes folds in the compound slab feeding into the extruder.
Feedbox—that area of an extruder, where the screw is exposed to accept a rubber slab feed. Typical cold feed extruders have a driven feed roll assembly which forms a pinch area with the screw flights and serves to pull slab compound through the feed hopper and fill the screw flights. The feed roll assembly is usually a hinged assembly, which can be opened for cleaning and greater maintenance access to the screw and feedbox.
Cold Feed Extruder—a piece of machinery for processing visco-elastic materials, including rubber. This machine accepts cold compound in slab form, warms the compound and moves the compound from the feedbox to the end of the barrel, by means of a rotating mechanical screw.
The invention will be described by way of example and with reference to the accompanying drawings in which:
The extruder 12 has a screw 18 that is rotatable in a cylindrical barrel 20. The cylindrical barrel has an internal channel for housing the screw. The screw has an elongate cylindrical body 13 having at least two helical screw flights 30,32 mounted thereon. The screw is typically rotated by power means such as a motor and gearbox (not shown). The screw has a first discharge end forming a nose 19 and a second terminal end 21, typically having shallow flights 25 for keeping compound out of the splined screw-to-gearbox interface (not shown). The barrel 20 has a feed opening 22 at an entrance end 24 of the extruder. The feed opening is connected to a feed hopper 23.
The rear end 21 of the extruder screw has been modified as shown in
Experiments were conducted with a notched extruder screw over a range of speeds. It was observed that the notch reduced the number of misfeeds. It was also observed that directing the rubber into the feedbox area occupied by the rolling ball of compound could still cause a misfeed, but the action of the screw notch had the unexpected result that the feed was able to restart itself without any intervention. Complete clean-out of the extruder feedbox is typically required to re-establish normal compound feeding, with traditional extruder screws lacking the screw notch.
While certain representative embodiments have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention.
