video notes oxyfuel/plasma cutting

Course Overview and Scope

  • Objective: entry-level skills in oxyacetylene welding, brazing, and cutting with demonstrations and exercises across joints, positions, and materials.
  • Covered joints/positions: flat, horizontal, vertical, overhead; square groove butt joints; single V butt joints; various plate/thicknesses (e.g., 3/16 inch mild steel) and pipe (e.g., 2 inch Schedule 80).
  • Applications: welding, brazing/braze welding, cutting, heating, scarfs/gouging; flame cutting demonstrated manually and on a straight-line track.
  • Materials shown: mild steel plate, pipe, copper tubing.
  • Assessment: quizzes, visual inspection, destructive testing based on industry standards.

Oxyacetylene Processes at a Glance

  • Oxyfuel welding: coalescence by heating with a flame to melt base metal and filler metal to form weld metal.
  • Oxyfuel cutting: heat metal to ignition (~1600^ ext{°F}) and use a jet of pure oxygen to cut through the metal.
  • Brazing/Braze welding: filler metal melts above the base metal temperature but below the base metal melting point; no base metal melting.
  • Soldering: filler metal melts below the base metal melting point; capillary action used to join.
  • All rely on oxygen–acetylene flame; changes in gas pressures, torch tips, and filler metals tailor the process.

Historical Context and Process Overview

  • Early development: acetylene–oxygen flame became exceptionally hot (~6{,}000^ ext{°F}) around the late 1800s–1920s, enabling modern welding and repair.
  • Oxyacetylene system uses a cylinder of compressed oxygen and acetylene, regulated for safe working pressures; traditional use expanded to cutting, brazing, brazing welding, and heating.
  • Modern oxyfuel equipment emphasizes safety, portability, and adaptability for various flame applications.

Safety, Hazards, and Regulatory Compliance

  • Key hazards: fumes/gases, electric shock, arc radiation, fire/explosion, falling objects, burns, eye damage.
  • Standards: AWS/ANSI Z49.1 safety in welding, cutting, and allied processes; OSHA regulations; MSDS requirements.
  • Risk control: hazard communication, ventilation, proper PPE, hot-work permits, confined-space precautions, and housekeeping.
  • Eye/face protection: safety glasses with side shields; filter lenses by task (e.g., #4–#8 shade references); helmet with proper lens shade and cover plate.
  • PPE basics: flame-resistant clothing, gauntlet gloves, leather jacket/apron for heavy welding, sturdy footwear (high-top), and hearing protection where needed.
  • Hazards in confined spaces: oxygen depletion, hazardous fumes, toxic gases; require ventilation and sometimes SCBA/respirators.
  • MSDS: sections cover manufacturer, hazards, physical/chemical data, fire/explosion data, fumes/gases, health effects, and PPE requirements.

Gas Cylinders, Regulators, and Hoses

  • Oxygen: stored in cylinders up to high pressure (e.g., 2{,}200~ ext{psi}); green hoses, right-handed threads.
  • Acetylene: stored under pressure with acetone in porous material, lower safe pressures (below 15~ ext{psi} for use in systems); red hoses, left-handed threads on some connections.
  • Cylinder handling: upright storage with caps on, secured during use; keep oxygen and fuel-gas cylinders apart; never store in same location.
  • Regulators: single-stage vs. two-stage (two diaphragms); they reduce cylinder pressure to working pressure.
  • Leaks/maintenance: inspect all connections, replace damaged hoses, do not lubricate threads, use leak tests before operation.
  • Connections: do not mix fittings; identify left-handed vs. right-handed threads; check valves must be installed to prevent flashback.
  • Hoses: typical lengths 25~ ext{ft}; protect hoses from heat and sparks; avoid oil/grease contamination around gas systems.

Torch Setup, Flame Types, and Light-Off

  • Flame types (start-up):
    • Carburizing (reducing) flame: inner cone, feather, outer envelope; adjust by balancing acetylene/oxygen to get a longer feather.
    • Neutral flame: most common for welding; balanced inner cone and feather.
    • Oxidizing flame: excess oxygen; hotter and harsher, used for brass/bronze brazing in some cases; not typical for mild steel.
  • Key flame indicators: inner cone, feather length, outer envelope; flame size indicates tip orifice and gas pressures.
  • Flame adjustment procedure: light with acetylene first, then introduce oxygen; adjust until smoke disappears and a stable flame with three zones is observed. Use a neutral flame for general welding.
  • Starting/shutdown: acetylene valve first to extinguish, then oxygen; to shut down, close acetylene then oxygen and purge lines; back out regulator screws when done.
  • Six essential factors for quality welds: flame adjustment, joint preparation, torch angle, travel speed, inner cone distance, and filler metal addition.

Welding Setup and Shutdown Procedure (Orientation)

  • Regular setup procedure: gather equipment; inspect area; select tip size and filler rod; verify safety.
  • Gas/torches: secure gas filters, remove caps but keep caps handy; purge passages by opening valves slightly to clear debris; ensure leak-tight connections before lighting.
  • Lighting: adjust flames to neutral; light with striker; verify proper flame before welding.
  • Shutdown: extinguish flame, close valves, relieve pressure, detach hoses, and store equipment properly.

Flame Cutting Principles and Mechanized Cutting

  • Flame cutting principle: heat metal to ignition, then use a jet of pure oxygen to sustain oxidation and cut through the metal.
  • Combustion triangle: fuel, heat, oxygen; all must be present for combustion.
  • Steel ignition temp ~1{,}600^ ext{°F}; requires high-purity oxygen adjustments.
  • Manual cutting torches: two main types (cutting-only and combination for cutting/welding/heating); cutting tips vary with metal thickness and fuel gas.
  • Tips and orifices: acetylene tips with fewer preheat orifices due to higher flame temperature; oxygen tips/holes control cutting stream.
  • Mechanized cutting: straight-line track cutters ride on a track; oxygen flow controlled by on/off lever; travel speed set for a smooth cut with small vertical lines and squared edges.
  • Cut quality indicators: smooth surface with minimal edge droplets; improper flame or travel speed results in uneven edges, excessive drops, or incomplete cuts.

Worksite Safety: Permits, Ventilation, and Housekeeping

  • Hot-work permits: required for welding/cutting in hazardous areas or areas not designated for hot work; provide checklists and emergency contacts.
  • Fire protection: fire extinguishers accessible; keep flammables away from the work zone; use fire-resistant curtains/shields to protect nearby workers.
  • Ventilation: required to control fumes and gases; natural, general mechanical, and local exhaust ventilation types; in confined spaces, monitor air quality and provide respirators if needed.
  • Air contaminants: fumes from fluxes, paints, oils, solvents; metals like zinc, lead, cadmium, beryllium; proper ventilation reduces exposure.
  • Housekeeping: keep area clean; store electrode stubs in containers; secure lit torches when not in use; protect trailing hoses; avoid sparks near combustibles.
  • Confined spaces: lookouts required; lifelines or harnesses in extreme cases; check atmosphere with appropriate equipment before entry.

Maintenance and Common Hazards

  • Regular inspection and maintenance: machines, hoses, leads, and clamps; only trained personnel should repair welding equipment.
  • Electrical safety: use properly grounded equipment; disconnect switches; avoid damp work areas; keep leads untangled and away from the arc.
  • Oxygen hazards: oxygen supports combustion; avoid oil/grease contact; never transfer gases between cylinders; use correct regulators and fittings.
  • Acetylene hazards: unstable at high pressures; ensure acetylene is handled at safe pressures and never stored or used inappropriately.
  • Eye and skin protection: ultraviolet/infrared arc radiation; use proper PPE and maintain clean weld areas to minimize hazards.
  • Noise and flying particles: use hearing protection as needed; wear eye protection for all grinding/welding/cutting operations.

Quick Reference: Key Safety and Setup Facts

  • Oxygen pressure can reach up to 2{,}200~ ext{psi} in cylinders; acetylene is used at much lower pressures (≤15~ ext{psi}) in typical applications.
  • Flame temperatures: approx. 6{,}000^ ext{°F} for the flame;
  • Steel ignition for cutting occurs around 1{,}600^ ext{°F}; high-purity oxygen is required for efficient cutting.
  • Hoses: commonly 25~ ext{ft}; color-coded (green = oxygen, red = acetylene).
  • Safety culture: always be observant, use MSDS, and enforce hot-work permits and ventilation; report injuries and unsafe conditions immediately.