step Drill Bit is a drill bit that has the tip ground down to a different diameter. The transition between this ground diameter and the original diameter is either straight, to form a counterbore, or angled, to form a countersink.
The advantage to this style is that both diameters have the same flute characteristics, which keeps the bit from clogging when drilling in softer materials, such as aluminum;. Most of these bits are custom-made for each application, which makes them more expensive.
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Fork Chong Reservoir once contaminated ( August 14th photo) Xinhua News Agency reporter Chen Haining
What is chromium residue?
Chromium is a silvery white hard metal that is slightly lighter than iron and contains trivalent and hexavalent compounds. Chromium compounds are toxic, with hexavalent chromium being the most toxic. Chromium slag is an industrial waste produced during the production of metallic chromium and chromium salts, and it is a highly toxic hazardous waste. Chromium slag has yellow, black, and ytterbium colors, and is mostly powdery.
Chromium residue chemical composition:
Silica accounts for 4 to 30%
Al2O3 accounts for 5 to 10%
Calcium oxide accounts for 26 to 44%
Magnesium oxide accounts for 8 to 36%
Diiron trioxide accounts for 2% to 11%.
Chrome oxide (Cr2O6) accounts for 0.6-0.8%
**** (Na2Cr2O7) accounts for about 1%.
The main minerals contained in chromium slag are periclase (MgO), calcium silicate (2CaO•SiO2), brucite (4CaO•Al2O3•Fe2O3), and 1~10% residual chromite.
Chromium residue hazards:
In the absence of reducing agents, the aqueous solution of **** contains highly toxic hexavalent chromium ions. Due to the specific needs of the production process, as long as the chromium has not been converted into a fixed product and becomes an insoluble form, these chromium will become ionic chromium, and will quickly become extremely toxic hexavalent chromium when dissolved in water. When chromium slag is stored in the open air, a large amount of hexavalent chromium ions are leaked and leaked into the earth's surface with rain after long-term stormwater showering, contaminating groundwater, contaminating rivers and lakes, and damaging farmland, aquatic products and human health. .
Hexavalent chromium ions are very toxic to human health. Its compounds have a strong oxidizing effect and are harmful to the human digestive tract, respiratory tract, skin and mucous membranes. Even worse, chromium has a carcinogenic effect, and the main cause of chromium carcinogenesis is the lungs.
News link:
On August 12th, the network uploaded a total of more than 5,000 tons of heavy toxic chemical waste chromium slag from Yuezhou Town, Qujing City, Yunnan Province. Due to illegal dumping, poisonous water was directly discharged into the Nanpanjiang River. This news immediately attracted the attention of many Internet users, and quickly became the hot topic and microblogging hot spot of certain forums. Posts said: Qujing, Yunnan Province has 5,000 tons of chromium slag poured into the reservoir, causing the reservoir deadly hexavalent chromium exceeding 2000 times. Afterwards, Yunnan will discharge 300,000 cubic meters of contaminated water into the Nanpanjiang River, the source of the Pearl River. The Zhujiang River Basin sketch of the post specifically pointed out that the Nanpanjiang River is the source of the Pearl River, and the Pearl River originated in Qujing and was injected into the South China Sea at the Modaomen near Guangzhou.
On August 10, Feng Wei and other reporters from the Yunnan Information Daily conducted an investigation and interview on the dumping site of chromium slag, Yuezhou Town, Qilin District, Qujing. Feng Wei said that there are some pine trees near the piles of waste, and they are all dead.
Huang Jie, head of Yunnan Environmental Protection Bureau deputy director, and Yunnan Environmental Protection Supervision Corps captain, told an interview with the Yangcheng Evening News that two months ago, a chemical plant's slag-driver secretly stole 1000 tons in the mountains of Yuezhou Township. Chromium residue, a local dead pool was contaminated and 100 cubic meters of water in the pond was contaminated. Has been governing.
According to He Hua, the propaganda minister of Qujing Municipal Party Committee, the drinking water of local villagers is tap water, and the tap water source is very far away from their village, so it has no effect on drinking water. The director of the Qujing City Environmental Protection Bureau, Yang Shuxian, also said, “It is because of the long distance from the local people drinking drinking water sources that they have not yet had an impact on the safety of people’s drinking water, nor have they found that chromium slag pollution has caused casualties. So far there have been a total of 75. Goats, a horse, and a cow died because they drank a lot of highly toxic water under the chromium residue."
It is reported that on the 14th, an expert group composed of the Zhujiang Water Resources Commission of the Ministry of Water Resources came to Qujing for illegal sampling of chromium waste. 
