Color Distinction Between Drills Explained
In mechanical processing, hole processing accounts for about one-fifth of its total processing, of which drilling accounts for about 30% of the entire hole processing. Those of you working on the front line of drilling are likely familiar with drill bits. When purchasing a drill bit, you may encounter bits of different colors and materials.
So, what is the difference between drill bits of different colors? Does the color have anything to do with the quality of the bit, and which one is better?
Does drill bit color have anything to do with quality?
First of all, it is not possible to determine the quality of a drill simply by its color; the color is not directly related to the quality. Different colored bits are mainly the result of different processing methods.
Of course, you can make a general judgement based on the color, but even poor-quality drills can have their own color treatment to achieve the appearance of a quality drill.
What’s the difference between different colored bits?
High-quality, fully ground HSS bits often appear in white. Rolled bits can also be made white by finishing the outer round. The reason for the high quality is that, in addition to the material itself, the quality control of the grinding process is also very strict, so that the surface of the tool will not be burned.
Black is a nitrided drill bit. It is a chemical method to improve the durability of the tool by placing the finished tool in a mixture of ammonia and water vapor, after 540-560°C insulation treatment. Most of the black drills currently on the market are only black in color (to cover up burns or black skin on the surface of the tool), but the actual use has not been effectively improved.
There are three processes for producing drill bits, and black is rolled and the worst. White is clear-edged and milled. Unlike rolling, there is no high-temperature oxidation, so the grain structure of the steel is not damaged, and it is used to drill slightly harder workpieces.
The yellowish-brown drill, known in the industry as the cobalt-containing drill, is a kind of subterfuge in this drill industry. The cobalt-containing drill was originally white and produced by grinding. Later, when it was atomized, it became yellowish-brown (generally called amber), which is the best in circulation at present.
Another type of drill is M35 (Co 5%), which is gold. This kind of drill is called a titanium-plated drill and is divided into decorative and industrial plating. Decorative plating does nothing; it’s just nice and golden. Industrial plating is excellent, with a hardness of HRC78, which is higher than the hardness of cobalt-containing drills (HRC54).
How to choose a drill bit
Since color is not a criterion to judge the quality of a drill, how does one choose a drill?
From experience, white is generally a fully ground HSS drill and should be of the best quality. Gold drills are titanium nitride plated and can be either of good or poor quality. The quality of black drills also varies; some are made of poor carbon tool steel that is easy to anneal and rust, which is why blackening treatment is needed.
When buying a drill, look for the logo on the drill shank and the marking of the diameter tolerance. The marking should be clear, and the quality of laser or electric corrosion should not be poor. If the word is molded and the edge of the word is bulging, the drill is of poor quality because the bulging outline of the word causes the bit to be held with less accuracy than required. The word is of good quality if the edge is clear and intersects well with the cylindrical side of the bit’s stem.
Another thing to look at is the cutting edge of the drill tip. The fully ground drill has a good open edge, and the spiral face meets the requirements, while the poor quality drill is not very good at the back corner face.
I believe that through this article, you guys have a certain understanding of how to select a drill bit.
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Post time: Jul-14-2023
