Final answer:
When a weld bead is not properly shielded, it can be caused by impurities in the environment, incorrect welding parameters, or poor technique. This can result in defects like porosity, inadequate penetration, or oxidation. It is important to ensure proper shielding to maintain the integrity of the weld and avoid these issues.
Step-by-step explanation:
When a weld bead is not properly shielded, it can have several causes. One common cause is the presence of impurities in the welding environment, such as dirt, grease, or moisture. These impurities can prevent the shield gas from adequately protecting the weld bead and can result in defects like porosity or inadequate penetration. Another cause can be incorrect welding parameters, such as improper gas flow rate or voltage settings, which can lead to insufficient shielding.
For example, if the gas flow rate is too low, the shield gas may not completely cover the weld bead, leaving it exposed to the air and causing oxidation. On the other hand, if the voltage settings are too high, the arc may be too intense, which can blow away the shield gas and leave the weld bead unprotected. Additionally, poor welding technique or insufficient operator skill can also contribute to a lack of proper shielding.