Screw with Carbide Inserts
A screw is provided for an injection unit having an inner diameter surface and a raised outer diameter surface on the screw flights. Carbide inserts such as a carbide wire or a plurality of short carbide inserts are mounted to the outer diameter surface to reduce wear on both the screw flights and the inner surface of the extrusion barrel.
1 . A screw for an injection unit having an inner diameter surface and a raised outer diameter surface, wherein at least one carbide insert is mounted to a portion of the raised outer diameter surface.
2 . The screw of claim 1 , wherein the at least one carbide insert is mounted to the portion of the raised outer diameter surface by brazing.
3 . The screw of claim 1 , wherein the at least one carbide insert is preformed into its substantially final shape prior to mounting the at least one carbide insert to the raised outer diameter surface.
4 . The screw of claim 1 , wherein the raised outer diameter surface is formed on a substantially helical screw flight.
5 . The screw of claim 4 , wherein the at least one carbide insert is a carbide wire mounted around the substantially helical screw flight.
6 . The screw of claim 5 , wherein a groove is provided in the substantially helical screw flight to help locate the carbide wire.
7 . The screw of claim 1 when the at least one carbide insert is a plurality of short carbide inserts mounted in a spaced relationship along a screw flight.
8 . The screw of claim 7 , wherein the plurality of short carbide inserts is mounted in clusters spaced along the screw flight.
10 . The screw of claim 7 , where clusters are aligned longitudinally along the length of the screw over every second flight of the screw flight.
11 . The screw of claim 1 , wherein the at least one carbide insert is made of tungsten-carbide.
12 . The screw of claim 1 , wherein the at least one carbide insert is made of titanium-carbide.
13 . The screw of claim 1 , wherein the at least one carbide insert is made of tungsten-carbide-cobalt alloy.
14 . A method for preparing a screw for an injection unit having an inner diameter surface and a raised outer diameter surface comprising mounting at least one carbide insert to a portion of the raised outer diameter surface.
15 . The method of claim 14 , wherein the at least one carbide insert is mounted to the portion of the raised outer diameter surface by brazing.
16 . The method of claim 14 , wherein the at least one carbide insert is preformed into its substantially final shape prior to mounting the at least one carbide insert to the raised outer diameter surface.
17 . The method of claim 14 , wherein the raised outer diameter is formed on a substantially helical screw flight.
18 . The method of claim 17 , wherein the at least one carbide insert is a carbide wire mounted around the substantially helical screw flight.
19 . The method of claim 18 , wherein a groove is provided in the substantially helical screw flight to help locate the carbide wire.
20 . The method of claim 14 when the at least one carbide insert is a plurality of short carbide inserts mounted in a spaced relationship along a screw flight.
21 . The method of claim 20 , wherein the plurality of short carbide inserts is mounted in clusters spaced along the screw flight.
22 . The method of claim 20 , where clusters are aligned longitudinally along the length of the screw over every second screw flight.
21 . The method of claim 14 , wherein the at least one carbide insert is made of tungsten-carbide.
22 . The method of claim 14 , wherein the at least one carbide insert is made of titanium-carbide.
23 . The method of claim 14 , wherein the at least one carbide insert is made of tungsten-carbide-cobalt alloy.
24 . The screw of claim 1 , wherein the at least one carbide insert is mounted to the portion of the raised outer diameter surface by one of soldering, adhesives, mechanical fasteners or press fitting.