Question 5 QMED05 - Machinist-Pump Technician

The Correct Answer is A. **Explanation for Option A (Wire brush):** A wire brush is the most appropriate hand tool for preparing metal surfaces with significant pitting for several reasons: 1. **Reaching Depressions:** The bristles of a wire brush are flexible and can effectively penetrate into small pits and depressions (like those caused by corrosion or pitting) that flat abrasives cannot reach. This action helps remove loose rust, scale, and contaminants trapped within the irregularities. 2. **Aggressiveness:** While not as aggressive as power tools, a good quality wire brush provides sufficient mechanical action to clean the complex contours of a heavily pitted surface, ensuring the primer or finish coat has a clean surface to adhere to. **Why the Other Options are Incorrect:** * **B) Sandpaper:** Sandpaper is primarily effective for smoothing relatively flat surfaces or light surface rust/contaminants. The paper and abrasive grains cannot conform deeply enough into significant pits, leaving contaminants trapped in the bottom of the depressions, which will cause premature coating failure. * **C) Chipping hammer:** A chipping hammer is designed for removing heavy, thick layers of mill scale or large, brittle rust formations (like barnacles of rust). Using a chipping hammer on surfaces with *pitting* would likely cause damage to the surrounding good metal and is not a practical method for achieving the required cleanliness profile for primer application. * **D) Hand scraper:** A hand scraper (or paint scraper) is used for removing loose paint or very loose, flaky rust from flat areas. Like sandpaper, it cannot effectively reach the bottom of significant pits and is intended for bulk material removal, not the detailed cleaning required for proper adhesion.