430 Modern Welding Copyright Goodheart-Willcox Co., Inc. This rail, with all its mechanisms, is called a gantry. Both rail and torches are moved on the X-Y (lateral and longitudinal) axes by electric servomotors. Once set up, these cutting machines are self- operating. However, the following initial adjustments must be carefully made by the operator: • Adjustment for the desired cutting rate (in/min or cm/min). • Adjustment of oxygen pressure to ensure a clean cut through the thickness of the metal without wasting gas. • Adjustment of the fl ames to ensure that each torch produces an identical cut. • Adjustment of the distance of the torch tip from the metal being cut to obtain the best results. In addition to properly setting up and adjusting the machine, the operator must periodically inspect and perform maintenance on its critical parts, such as cut- ting tips. 15.7 Safety in Oxyfuel Gas Cutting The appropriate protective clothing is necessary for oxyfuel gas cutting. Leather or slow-burning fabrics such as denim should be worn. Welders should wear leggings to protect against fl ying molten slag. Welding leggings are pieces of leather that cover the shin and top of the shoe to protect against splashes of molten metal and sparks. Welders should wear safety boots with high tops. Pants should have no cuffs. Pockets and clothing should be inspected for possible fl ammable materials, such as combs, plastic rules, matches, pencils, and other items. Face and hands must be protected from metal spatter by wearing a welding helmet and gauntlet gloves. Dangers can be greatly reduced through the careful and correct handling of oxygen and fuel gas equipment. Since cutting involves many potential hazards, every welder must follow approved proce- dures to eliminate these dangers. Cutting operations result in a considerable num- ber of fl ying sparks, which are globules (ball-shaped particles) of molten metal. Follow these guidelines to help prevent accidents during cutting operations: • Floors on which cutting is done should be concrete or other fi reproof material. • A heat-resistant material container should be placed under the cut to catch the hot liquid slag. • Workbenches and other necessary shop furniture should be made of metal or other fi re-resistant material. • Oil, paper, wood shavings, gasoline, lint, or other fl ammable materials should not be in the area where cutting is performed. • Objects being fl ame-cut may present additional hazards. Tanks and containers should be welded or cut only by an experienced welder. If a tank held unknown or combustible materials, it is generally necessary to pass an inert gas or steam through the tank in order to fl ush out any combustible gases in the tank. This safety procedure may take hours to complete prior to any attempted cutting operation. The tank may also be fi lled with water, except in the area of the work. In all cases, the tank must be vented to prevent the entrapment (holding) of potentially explosive gases. This work should only be done under the supervision of a qualifi ed safety engineer. A small amount of fl ammable material in such a container or tank can cause a powerful explosion. • Be certain of what material is to be cut before performing any OFC operation. Certain metals, such as magnesium, can burn with an explosive force if fl ame-cut. • A fi re extinguisher should always be at hand during oxyfuel cutting. It is recommended that a fi re watch be posted during cutting operations. • Be sure to understand and follow correct procedures for setting up and handling cylinders, regulators, hoses, and torches. These are explained in Chapter 14, Oxyfuel Gas Cutting Equipment and Supplies. • Check that ventilation systems are working. • Normal atmosphere contains about 21% oxygen by volume. As the oxygen content in an enclosed space is increased above this percentage, there is an increasing danger of a spark or fl ame causing a fi re or explosion. • Never use acetylene at a pressure greater than 15 psig (103 kPa). Acetylene becomes unstable above that pressure and may explode. A regular and careful safety review of OFC pro- cesses and equipment is essential. This includes routine safety inspections of PPE, hand tools, oxyfuel gas cut- ting outfi ts, motorized carriages, pipe beveling equip- ment and accessories, the gas supply system, cylinders, and the work area, as necessary. All welders must be familiar with the contents of ANSI Z49.1, especially Section 10, “Oxyfuel Gas Welding and Cutting Safety.” This document can be downloaded for free from the AWS.org website.