The dotted line from the earth to the moon represents your line of sight when looking at the moon. The large moon image shows what you would see at that point in the cycle. For the waning gibbous, third quarter, and waning crescent phases you have to mentally turn yourself upside down when imagining the line of sight.
Where can I find some general guideline for welding ventilation? For processes such as welding, brazing, soldering, and torch cutting, the primary purpose of ventilation is to remove air contaminants from the worker's breathing zone. Different ventilation strategies may be needed in each case to remove air contaminants from the welder's breathing zone. General guidelines have been published in CSA W117.2 Safety in Welding, Cutting, and Allied Processes, and ANSI Z49.1 Standard Safety in Welding and Cutting.
However, fusion welding processes, such as gas welding, arc welding, and gas metal arc welding are used in a large number of industries. Gas welding is a process by which the two pieces of metal are locally heated to beyond their melting point, at which time they effectively become one piece of metal.This can be done with or without an alloy rod. Metal inert gas and tungsten inert gas welding are examples of gas metal arc welding processes.ressure welding is a process in which external pressure is applied to produce welded joints either at temperatures below the melting point, which is solid state welding, or at a temperature above the melting point, which is fusion state welding.