The most iron-based powder metallurgy process manu

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Iron based powder metallurgy process manufacturing machine clamp indexable turning tool bar

powder metallurgy is a process technology that makes metal materials, composite materials and various types of products by making metal powder or using metal powder (or the mixture of metal powder and non-metallic powder) as raw materials, forming and sintering. The application of powder metallurgy technology can obtain materials and parts with special properties and which cannot be produced by general technology, and the material utilization rate is high, the processing volume is small, and it has considerable economic benefits. It has been widely used in machinery, automobile, metallurgy, light industry, instrumentation, electrical appliances, national defense and other industries and fields

Zhuzhou Metallurgical Tool Factory, a factory run by our college, began the production of iron-based powder metallurgy products in 1970, and formally produced machine clamp indexable turning tools and welding turning tools in 1974, achieving good economic benefits

I. production process of iron-based powder metallurgy tool bar

iron-based powder metallurgy tool bar belongs to Fe-Cu-C series materials, and the main raw material is iron oxide scale left by steel mills after rolling. The whole production process is mainly divided into three main stages: milling, molding and machining

1 pulverization

a. water washing puts the iron scale into water for cleaning, which is generally carried out in the mixing tank or cleaning tank, in order to remove the impurities soluble in water or floating on the water

b. drying put the washed iron scale in the drying furnace or drying oven, heat it to 500 ~ 800 ℃, remove the moisture and combustible impurities in the iron scale, promote the further oxidation of the iron scale, enhance the magnetism of the iron scale, and improve the magnetic separation effect

c. magnetic separation uses the magnetic characteristics of iron oxide scale. Through multi-stage magnetic separation, impurities are further removed and the iron content of iron scale is increased

d. ball milling and sieving this process can refine the particle size of iron scale, increase the contact surface area between iron scale and reducing agent (CO or H2) for the next reduction process, and improve the diffusion speed of reducing gas in the iron scale. The granularity of iron scale should be controlled between 40 ~ 60 mesh

e. reduction the purpose of this process is to remove the oxygen molecules in fine Fe3O4 or Fe2O3, so as to produce spongy iron powder. At present, charcoal, coke and anthracite are commonly used as reducing agents in China's pulverized coal production. Their physical and chemical properties and application effects are shown in the table below. Table physical and chemical properties and application effects of common reductants

reductant moisture

% volatile matter

% ash

% fixed carbon

% sulfur

% porosity

% reduction process parameters temperature (℃) time (H) charcoal 3 ~ 1010 ~ 200.5 ~ 2.570 ~ 80 70 ~ coke 2 ~ 81 ~ 68 ~ 1470 ~ 800.5 ~ 1.530 ~ anthracite 3 ~ 51 ~ 54.5 ~ 885 90.50.5 ~ 1.52 ~

it can be seen from the table that charcoal has the strongest reduction ability, followed by coke, Anthracite is the worst. Because charcoal has the largest porosity, the largest area to participate in gasification reaction and the largest activity. In addition, the volatile matter content in charcoal is high, and its main components are H2 and various carbon silicon compounds, and H2 is the best catalyst in the process of carbon fixation and reduction. Therefore, the iron powder produced with charcoal as reductant has the best quality, but the cost is high, and the charcoal resources are limited

when the reduction temperature is higher than 570 ℃, the process of reducing oxide by solid carbon is divided into three stages: Fe2O3 when the temperature drops below 4 ℃ - → Fe3O4 - → float (Fe · Fe3O4) - → Fe, its chemical reaction formula is

3fe2o3 + CO = 2fe3o4 + CO2, △ h298=-15050 calories

Fe3O4 + CO = 3feo + CO2, △ h298=5030 calories

FeO + CO = Fe + CO2, △ h298=-3150 cards

2 forming

pressing tool bar blank ball mill the reduced sponge iron slices to make iron powder with different particle sizes. According to the requirements of tool bar material, add some metals and nonmetals in an appropriate amount, and mix evenly to form a metal mixture with iron powder as the matrix. Then put the mixture into the die and press it to produce the tool bar blank. The pressing density of the blank is required to be 6.8 ~ 6.9g/cm3; The blank shall be free from delamination, crack and edge drop

the sintering process of sintering tool bar is relatively complex, which plays a key role in product performance. Gas desorption, lubricant volatilization, recovery recrystallization, Austenite Formation, aggregation recrystallization, particle bonding, alloying, partial metal or alloy melting, pore concentration and elimination will occur in the sintering process. Austenite decomposition into pearlite, graphite precipitation, cementite decomposition and liquid phase recrystallization will occur when the tool bar is cooled after sintering. The density of the sintered tool bar is 6.9 ~ 7.5g/cm3, and the hardness is greater than 150HB

3 machining and heat treatment

machining properly machine the sintered tool bar blank. The main processes are: milling, drilling, tapping, Tong repair, etc., so as to ensure the appearance size and fitting accuracy of the tool bar

the hardness and strength of the heat treatment tool bar have an important impact on ensuring the service performance of the tool bar. In order to ensure the strength and hardness of the tool bar, a specific heating time and temperature must be used in the heat treatment process. The hardness of the tool bar after heat treatment is 38 ~ 42hrc, and the bending strength is 1102 ~ 1190n/mm2

surface oxidation treatment generally adopts low-temperature alkaline blackening, that is, the knife bar is heated and oxidized in a certain concentration of alkali and oxidant solution, so that a layer of magnetic Fe3O4 film is formed on the metal surface according to the cleaning operation. The oxidation process is: Fe - → nafeo2 - → na2fe2o4 - → Fe3O4, Its chemical reaction formula is

3Fe + NaNO2 + 5naoh - → 3na2feo2 + NH3 + H2O

6na2feo2 + NaNO2 + 5H2O - → 3na2fe2o4 + NH3 + 7naoh

na2feo2 + na2fe2o4 + 2h2 - → Fe3O4 ↓ + 4naoh

the main purpose of surface oxidation is: ① rust prevention; ② Increase the appearance and luster of the surface; ③ Eliminate the stress effect during quenching

II. Analysis of the cutting force of the tool bar

at present, the tool bar is usually manufactured by forging or casting process, and whether the tool bar manufactured by powder metallurgy process can withstand the impact of cutting force is analyzed and compared below

under normal working conditions, the cutting force borne by the turning tool of C620 lathe is:

main cutting force pz=200 × t × s=200 × five × 0.3=300kg

when the cutting depth t=5mm and the feed rate s=0.3mm/r

radial force py ≈ 0.4pz=0.4 × 300kg=120kg

axial force PX ≈ 0.25pz=0.25 × 300kg=75kg

total turning force p= (px2+py2+pz2) =331.7kg

the corresponding bending strength value is: σ Bb=3pl/2h2b=31.63n/mm2 (p=331.7kgf in the test, sample span l=80mm, height h=24.8mm, width b=19.8mm)

according to the formula calculation data, considering various special situations in the cutting process, the strength value is set as ≥ 1050n/mm2 when formulating the production standard. The strength value of our iron-based powder metallurgy tool bar is measured to be 1102 ~ 1190n/mm2. It can be seen that the tool bar manufactured by powder metallurgy process has sufficient safety factor and reliable bearing capacity

III. conclusion

compared with the traditional forging and precision casting process, the production of turning tool bar by powder metallurgy process has broad development prospects and better economic benefits. Its advantages are as follows:

1 Because all of them are pressed by molds, the overall dimensions and geometric angles of the products are basically the same. As long as the mold manufacturing accuracy is high 9 Multiple languages are switched randomly: Simplified Chinese, traditional Chinese, English. The production process is strictly controlled. Many profiles and angles can be exempted from machining processes, giving full play to powder metallurgy. Therefore, the measurement of deformation must be raised to a certain height to realize the advantages of less or no cutting of gold products, which is suitable for mass production. Compared with processing the cutter bar with high-quality steel, it can save 30% of materials, reduce the processing cost by 60%, and improve the work efficiency by three times

2. The main raw material of powder metallurgy tool bar is iron oxide scale, which can save a lot of high-quality steel

3. The powder metallurgy tool bar has small elastic deformation and strong anti vibration performance, which is conducive to reducing the surface roughness of the workpiece and improving the accuracy and quality of the product in the cutting process

4. In the process of heat treatment, the deformation of the tool bar is very small, which is conducive to ensuring the geometric accuracy of the tool bar after machining. (end)

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