Gentlemen:
Here's what I learned about piercing form steel service centers and associates in the company we had:
For those that have to pierce thick plate, the machine is set up with "ease-on" cutting oxygen. We made a servoed oxygen regulator that started with a lower pressure than the final operating pressure. After preheating the plate, cut oxygen came on and the machine followed a lead-in and ran slower than the final cutting speed as the cutting oxygen pressure built up to the normal pressure. This resulted in a ramped-down cut that exited the bottom of the plate before the end of the leadin, at which time the cutting speed and pressure were at full amounts. With the ramped-down cut, the dross shoots out the back away from the torch, and the tips stay in good condition.
To make the servoed cutting oxygen regulator, we used a separate pilot regulator, and made a replacement "dome" top to replace the normal tee handled spring pressure part of the oxygen regulator. The pre-regulator was set to the desired pressure, and its output taken over to the servoed regulator. A needle valve was placed in the line conveying the pre reg pressure to the dome to essentially delay the pressure buildup and thus the final cut oxygen pressure.
As I recall, piercing was limited to about 5" thick plates. For thicker plates, an oxygen lance was used. This consisted of a sacrificial steel pipe about 3/8 diameter and several feet long to which an oxygen pressure source with a ball valve was attached. The operator manually preheated the surface of the plate. and when it was at kindling temperature, he heated the end
of the lance while turning on the lance oxygen. The lance was now thrust down through the plate until is exited the bottom. It makes quite a shower of molten steel, usually contained by using a 5 gallon pail over the opening.
Regards,
J C  |