There are four major pieces of equipment required in the TG&P process:
1. #1 Straightener
2. Turning Machine
3. #2 Straightener
# 1 Straightener:
The purpose of the number one straightener is to prepare the hot rolled or raw bar for the peeler. This means straightening the raw bar and removing the majority of rust from the surface of the bar in the process. The pre-straightener should have hydraulic cushioning to better handle the crooked incoming bars. The straightener has to be properly sized for the bars being processed. If the bars are too big for the straightener the mill post will not have sufficient stiffness to prevent excess "mill stretch". One cannot hold tight tolerance on an undersized straightener. On the other hand, if the machine is oversized, the over sized work rolls will not be able to properly work the bar. Straighteners work best when the range of diameters being process falls with in the design range of the straightening machine. Quality Bar's size 3 straightening machines are designed for the products being processed through the 3/4" to 3" line. Quality Bar's size 10 straighteners are designed for the products being processed in their 3" to 8" line. They are especially well designed to handle the higher alloy bars.
There are two types of straighteners, horizontal and vertical. The horizontal straightener has the straightening rolls side by side and the vertical machine has the rolls one on top of the other. In The vertical machine the force vectors are perpendicular to the ground with the separation forces being transferred directly down and into the foundation. Where as, with the horizontal machine the force vectors are parallel to the ground, parallel to the foundation bolts and working against the sides of the bolts. Quality Bar has had more success with its vertical machines.
The purpose of the turning machine is to peel away the rusty surface of the bar. Quality Bar's smaller line, orders hot-rolled bars 1/16" or .0625" over sized. The oversized material permits the turning machine to peel away .054 inches leaving .0085" to be removed by the # 2 straightener and the grinder. Quality Bars larger line orders hot-rolled bars 1/8" or .1250" oversized. The oversized material permits the turning machine to peel away .110" leaving .015" to be removed by the # 2 straightener and the grinder.
There are two types of turning machines, rough and finish. The rough has a heavier roller bearing in the spindle and the finish has a more precision bearing in the spindle. The rough machine can take a larger reduction where as the finish machine holds a closer tolerance. Quality Bar uses finish turners with the precision bearings.
Of the four major pieces of machinery in Quality Bar's automated production lines, the # 2 straightener has the most influence on producing a higher quality product. During peeling the bar is subject to intense bending forces. Tests show a bar coming out of the peeler can have a greater bend than before entering the peeler. In order for the grinder to do its job properly, the peeled bar must be straightened. Unlike the #1 Straightener, which should have a hydraulic cushion, the #2 Straightener has to maintain tighter tolerances and so should be mechanically backed up. Quality Bar only uses vertically backed up machines for their # 2 Straighteners.
Modern grinders are of the twin grip design and when properly sized, accurately aligned and well maintained, can hold tolerances in the low ten thousandths of an inch when using laser mics with digital read outs and with the correct grit in the grinding wheel. The grinder is responsible for the ovality and surface of the finished bar.
The key to better quality is receiving straight bars from the #2 straightener. Quality Bar uses the traditional Cincinnati twin grip for its larger line in conjunction with a belt polisher and on the smaller line uses the more expensive Schumag grinding machine which has polishing discs on the entry and exit side resulting in a finer, rounder and closer finished bar.