1.The broken screw should be repaired according to the actual diameter of the
barrel. A new screw should be manufactured based on the designed outer
diameter tolerance according to the normal clearance with the barrel.

2. The thread surface of the worn screw with shrinking diameter should be hot
sprayed and painted with abrasion-resistant alloy after treatment, and then be
ground to designed dimension. This repair is generally finished in a rofessional
spray painting factory, and usually costs less.

3. The thread of a worn screw should be bead welded with abrasion- resistant
alloy. It should be bead welded for 1-2mm thick according to the degree of
wear and then be grounded to designed dimension. The abrasion-resistant
alloy is made of materials like C, Cr, Vi, Co, W and B, which can improve the
screw's resistance to wear and corrosion. Generally, this repair will cost much
in a professional bead welding factory. Thus it is usually not adopted unless
otherwise specified.

4. Hard chromium plating on surface can also be used for the repair of screw.
Chromium is resistant to wear and corrosion, but hard chromium plating easily
fall off.

The inner surface of a barrel has higher hardness than a screw. Thus it is not
as easily worn as the screw. If the inner diameter of the barrel is increased as
time goes by, the barrel might be scraped. Methods:
1. If there is still a certain nitriding layer in the barrel with diameter increasing
due to wear, bore a hole inside the barrel, grind the barrel to a new diameter,
and then make a new screw according to this diameter.
2. Trim the inner diameter, cast the inner side with alloy again at 1-2mm thick,
and then process it to the designed dimension.
3. Generally, the homogenizing section of a barrel is easily worn. For that, trim
the involved section (5-7D long) via boring, and install a nitrided alloy steel
sleeve. The diameter of inner hole should be determined based on that of
the screw. Normal fit clearance should be reserved for professing.