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Steam process flow of iron - based PM parts

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-09-12 08:22:00
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1. Steam treatment process

The process of steam treatment is generally: 1) polishing -2) oil degreasing -3) water washing -4) drying -5) steam treatment -6) oil immersion -7) inspection. In addition to oil, including ultrasonic cleaning, rust cleaning. Cooking oil is to remove water inside parts, to prevent some parts from rust. Some processes can be saved according to actual condition, step 1 ~ 5 for pretreatment, main purpose of pretreatment is to remove grease, rust, cutting fluid, polishing fluid from surface increase the surface activity, in order to guarantee steam treatment quality, step 6 is the post-processing, main purpose is anti-rust, step 7 is for inspection, ensure steam treatment conform to the requirements.

The specific process of steam treatment is: put appropriate amount of workpiece into the fixture, load in the furnace when temperature reached 350 ~ 370℃, after 10 ~ 15min (estimated workpiece temperature above 150℃ to avoid steam condensation) electric heating, and then pass into the steam. At this time, the exhaust valve should be fully opened, maintain inlet pressure at 0.2 ~ 0.3MPa in order to remove the air in furnace, adjust the exhaust valve after exhausting 10 ~ 15min. Increase steam pressure to 0.3 ~ 0.5mpa, and the air inlet pressure to 0.4 ~ 0.6mpa. Then directly increased the temperature to 540 ~ 570℃, and the insulation time is determined according to the amount of furnace loading and experience. The steam pressure remains constant during insulation. After insulation completed, the exhaust valve should be opened immediately, and the air inlet pressure can be appropriately increased. Power off, cool the furnace to 300℃, stop steam input, and taking out for air cooling. If the amount of furnace loading is large and the oxidation film color is light after one treatment, the second steam treatments can be taken to deepen the color and improve the surface quality.

Attention should be paid to: charging must be reasonable firstly, this is the quality premise, then degreasing cleaning must be complete, the last line of clean water must be neutral water, followed by the charging process after cleaning, operation must quickly and steam is piped in, before inlet steam again, must rule out the sewage pipe, avoid defects attach on parts.  Finally, in order to ensure safety, it is best to cut off steam inlet and power first and then release.

2. Quality inspection of steam treatment

An oxidation film has been formed on the part surface after steam treatment. In order to ensure film quality, it should be tested, including appearance test, wear resistance test, corrosion resistance test, and so on. Qualified parts processed according to requirements, unqualified parts, analysis of the reasons, and polishing or do other treatment once more, re - steam treatment.

Appearance inspection refers to look with one's eyes to check part surface presenting uniform black or microstrip blue black under sufficient light condition. However, due to the chemical composition of parts, and the time and temperature of steam treatment are different, the color will be slightly different. No non-oxidized, speckles, rusts, attached sediments and red attachments are allowed on the surface of all parts. Surface corrosion is not allowed. Please refer to "electroplating manual" and " chemical protective coating appearance of black metal", etc.

After steam treatment, samples shall be randomly selected from the inspection batch according to GB/T 12609-2005 "sampling procedure for electrodeposited metal coating and relevant fine decoration count inspection". The quality of oxide film is tested according to application conditions and customer requirements, based on relevant standards, uniformity and thickness of film can be tested by scanning electron microscope. Wear resistance can be used NOS-ISO 1 wear testing machine, using Q/ ojs0001-1995 standard. The binding force is also known as the porosity of oxidation film. Dropping 5% neutral copper sulfate on workpiece’s smooth surface, it is qualified that if copper color is not displayed within 15min, while the rough surface and edge are qualified if copper color do not displayed within 5 minutes. Salt spray test was used for corrosion resistance [11]. At 25℃, using 0.05% sodium chloride solution as corrosive agent, spraying salt  fog once for 30 min.

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