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Steam treatment problems and solutions for iron - based powder metallurgy parts

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-09-19 08:32:00
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Every process of powder metallurgy parts must be inspected, unqualified products never into the next process, steam treatment is no exception. Some quality problems usually occur after inspection and treatment. The causes of common quality problems are analyzed below, and corresponding solutions are proposed.

Quality problemsPossible cause analysisCorresponding solutions
Brittleincrease,strength decreasesSteam treatment time is too long and oxidation layer is thickReduce steam treatment time
Too large steam pressure, too fast speed, and  too thick oxidation filmReduce steam pressure
Some parts have rust on surfaceThe heating in furnace is not uniform, and the steam has no good contact with some parts

Reduce furnace load capacity, or reduce feed capacity, or increase

the diameter of feed,  or improve the way of steam inlet

oxidation film is dark red, even porousHigh vapor pressure, too much Fe2O3Increase furnace load or reduce steam pressure
Too much local temperature, too much Fe2O3Lower the temperature, or improve the heating mode
Part’s surface is speckled, or uniform  oxide layer parts surface polluted before steam treatment, residual oil, cutting fluid, polishing fluid, etcAdd polishing, cleaning, drying and other processes

Steam treatment experience needs long-term exploration and accumulation. In addition to the factors listed in above table, the following details should be paid attention to ensure the qualified rate of parts.

For example, other conditions are exactly the same, products placed differently, steam treatment effect may not be the same. There are two kinds 

of products placing: orderly and random place. The orderly arrangement is to design equipment according to product size and shape. The products are arranged in layers and have a certain gap between each other, which provide a guarantee for the consistency and uniformity of steam treatment quality and avoids the collision between products. Load product inside a frame basket randomly, the position, clearance between each other is uncertain, can produce difference to steam flow mode inside furnace and temperature evenness, so affect steam treatment effect differently.

Second, steam pressure and flow rate. In actual continuous production, the temperature is basically set unchanged, generally in range of 550℃-570℃. Steam is generally generated by steam generator, and the inlet pressure will fluctuate to a certain extent. For example, if setting 0.40mpa, it will generally fluctuate between 0.25 and 0.45mpa, which is determined by steam generator itself. Control steam inlet flow, such as the requirement of 6m3/h, in fact, there will be certain fluctuations and errors, reduce the fluctuation error of inlet flow, can choose appropriate instrument range, improve instrument accuracy such as pressure gauge, flow meter. Increase the power and capacity of steam generator to reduce the fluctuation range of steam pressure and flow. At the same time to ensure the sealing of furnace, usually because of the warping or uneven of furnace cover edge affect furnace sealing, causes steam to come out from the edge and the pressure in furnace is unstable

Third, the furnace load, which needs to be very accurate controlled. As the steam treatment process is usually fixed, different furnace charging quantity will lead to different quality of products. Too much or too little, will make the product surface color and luster different, and even some surface red, not consistent size, which is due to the different amount of furnace loading lead to different contact area between steam and product, heating speed, atmosphere composition in furnace. 

In general, products should be arranged in an orderly manner, reduce the error of steam pressure and flow, and accurately control furnace loading, so as to better control products quality.

Keywords in the article: iron - based powder metallurgy parts
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