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The heart and soul of all ferrous wire drawing is the maintenance of the wire drawing blocks. They control the surface quality of the wire, drawing speeds, bundle size and method of packaging. There is no one procedure for all types of ferrous wire drawing, but there are some standard guidelines worth following.
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A step may also be required on a single-taper block if the wire initially climbs smoothly but falters as the bundle weight increases. Usually, the wire backs down and overlaps at the radius prior to achieving full bundle size. Many stripper blocks and some intermediate blocks use steps to compensate for the shrinking inside diameter of the coil as the wire cools and contracts. The wire becomes so tight that it seizes to the face of the block and makes it increasingly difficult to push the wire up into the accumulated bundle. The step should be smaller than the smallest wire being drawn to prevent overlap while approaching full bundle conditions. Normal steps range from 0.240 to .125 in. per side. When adjusting taper to increase bundle size, each case must be considered separately. Many hard surfacing or block repair companies either do not have the capacity or are unwilling to grind double tapers and compromise by grinding a 1/2° or 3/4° straight taper. That often results in startup problems and jumping wire on the block.
Troubleshooting
Block performance problems are often blamed on the radius, but its only function is to get the wire to start climbing. A general rule is that the radius should be slightly larger than the largest wire to be drawn. If you have a wide range of wire diameters, use a 45° ramp 1 to 1.5 in. long instead of a radius with small radii (i.e., 1/4 in.) at both ends. The wire enters about two-thirds up the 45° and creates the lift of the radius over a wider range of wire sizes.
Cooling - be it air, water or mist - is critical to block performance, so make sure that clogged water jets are repaired and leaking water seals are rebuilt. A standard practice is to turn off the water at startup to facilitate wire climbing. That, however, can also cause a block to crack, especially narrow gap-cooled blocks, decreased diameter blocks and those that have been hard surfaced by a sub-arc method. Rust and hydrocarbon buildup can also reduce the effectiveness of a water-cooled block, so the block interiors should be grit-blasted and coated with a rust preventative paint. Also make sure that the brass air pipes are intact and the water seal is still intact. A worn shaft or bore can cause a block to wobble. Excessive wobble will cause a jerking effect at the die and prevent a smooth wire flow. The fit between the bore and the shaft should be .005 in. or less. The larger the wire and die pull, the more likely it is that gripper damage can occur. There are special gripper heads available to reduce this problem although you can try wrapping a basic head with heavy rubber or old carpet and secure it with wire. Then tell the operator to start the wire slowly, since the point of initial contact is where most contact occurs.
Another problem is
galling, where some of the wire surface becomes embedded on the block.
You can remove it with an emery paper flap wheel mounted on a disc
grinder, but carefully check from the radius up the face of the block.
Wire overlap another potential concern, is often caused by die alignment.
Most die boxes can be adjusted so that the wire will enter at the draw
line parallel to the floor. A level placed on the wire can be used to
correct this. There are many other areas, such as the type of block hard
surfacing used, that can greatly affect block performance, but being aware
of the above-mentioned factors is a good place to start.
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