How do powder metallurgy bearings improve wear resistance?
Method:
1. Vulcanization treatment of powder metallurgy products
(1) Intention of vulcanization treatment
When the vulcanization treatment is used as a friction reduction data in powder metallurgy finished products, the use of iron-based oil-impregnated bearings is the most widely used. The Du bushing made of sintered oil-impregnated bearing (containing 1%-4% of graphite) is simple in technology and low in cost. It can replace bronze and babbitt in the case of PV<18~25 kg·m/cm 2 · second. Information. However, under the working conditions of heavy solid lubricating bearings, if the sliding speed on the conflict surface is too high and the unit load is large, the wear resistance and life of the sintered parts will be agilely reduced. In order to improve the anti-friction function of porous iron-based anti-friction parts, reduce the conflict coefficient, and improve the operating temperature to expand its application range, the use of vulcanization treatment is a worthwhile approach.
Sulfur and most of the sulfides have a certain smooth function with powder metallurgy bearings. Iron sulfide is an outstanding solid smoothing agent, especially in the presence of dry conflict, the presence of iron sulfide, with excellent resistance to seizure.
Powder metallurgy iron-based finished products can be immersed in a considerable amount of sulfur by using capillary pores. After heating, sulfur can form iron sulfide with iron on the outer surface of the pores. It is evenly distributed throughout the finished product and plays an outstanding smoothing effect on the conflict surface. And can improve the cutting function. After the vulcanization, the finished product looks smooth and has a smooth appearance.
After the porous sintered iron is vulcanized, the most outstanding effect is that it has an excellent dry collision function. Under oil-free smooth working conditions (ie no oiling or oiling), it is a satisfactory self-smoothing material and has excellent anti-seizure properties, reducing the axis of the shaft. In addition, the conflicting nature of such data is not the same as the usual anti-friction information. Usually the data is followed by the addition of the specific pressure, and the conflict coefficient does not change much at the beginning. When the specific pressure exceeds the certain value, the conflict coefficient is added sharply. However, the porous sintered iron after the vulcanization treatment has a collision coefficient which decreases with a larger specific pressure than the specific pressure. This is a valuable feature of friction reduction data.
The sintered iron-based oil-impregnated bearing after vulcanization can work smoothly below 250 °C.
(2) Vulcanization treatment technology
The technology of vulcanization treatment is relatively simple and does not require special equipment. The technology is:
The sulfur is placed in a crucible and heated and melted. When the temperature is controlled at 120 to 130 ° C, the fluidity of sulfur is good at this moment, and if the temperature is too high, it is disadvantageous for impregnation. The sintered product to be impregnated is preheated to 100 to 150 ° C, and then the finished product is immersed in molten sulfur, immersed for 3 to 20 minutes, and the unpreheated product is immersed for 25 to 30 minutes. The impregnation time is determined by the density of the finished product, the wall thickness and the amount of immersion required. The impregnation time with low density and thin wall thickness can be less; vice versa. After the dipping, the finished product is taken out and the remaining sulfur is drained. Finally, the impregnated finished product is placed in the furnace, maintained by hydrogen, and can also be maintained with charcoal and heated to 700-720 ° C for 0.5 to 1 hour. At this moment, the sulphur and iron immersed to form iron sulfide. Regarding the finished product having a density of 6 to 6.2 g/cm 3, the sulfur intrusion amount is about 35 to 4% (percent by weight). The heating is performed in order to make the iron immersed in the pores of the part constitute iron sulfide.
The sintered product after the vulcanization treatment can be subjected to oil immersion and finishing treatment.
(III) Examples of application of vulcanization treatment
1. Flour Mill Bushing The bushing is installed at two ends of two rolls, for a total of four sets. The roll pressure is 280 kg and the rotational speed is 700 to 1000 rpm (P = 10 kg / cm 2, V = 2 m / sec). The original tin bronze bushing was used, and the oil ring was smooth. Now it is replaced by porous sintered iron with a density of 5.8 g / cm 3 and a S content of 6.8%. It is not necessary to use the original smooth device. It only needs to drip a few drops of oil before driving, and the operation time is 40 °C for 40 hours. Milling flour 12,000 kg, the bushing is still working normally.
2, roller cone drilling small shaft sleeve roller drill is an important thing in oil drilling, the top of this oil has a sliding sleeve, subject to great pressure (pressure P = 500 kg force / cm 2, speed V = 0.15 m / sec ), and there is a fierce sensation and impact.
Second, the oil immersion treatment of powder metallurgy products
Powder metallurgy porous anti-friction finished oil immersion oil is an important process, which can add the corrosion resistance and improve wear resistance of powder metallurgy products, and extend the service life. The iron-based oil-bearing bearing is immersed in oil after being sintered, and the smooth oil enters the finished pore. When the shaft rolls, the movement conflicts with the sleeve, heat is generated, the bearing temperature rises, the oil expands and expands, and the oil flows out from the pore to the shaft and the shaft. The oil supply is actively supplied between the sets, and the oil film formed has a smooth anti-friction effect. Immersion oil also prevents the finished product from being oxidized.
The oil method can be divided into normal oil immersion, heat immersion oil and vacuum oil immersion.
Usually immersed in oil: soak the cleaned and sintered product into the oil (usually 20 to 30 oil). The oil is immersed in the pores of the finished product under the capillary force effect of the finished product. This method has low oil immersion power and long oil immersion time. It takes several hours and is used in finished products with low oil content.
Heating immersion oil: The cleaned sintered product is immersed in hot oil at 80-120 ° C for 1 hour. Because the finished product is heated, the air in the connected pores expands, causing a portion of the air to be swept away. After cooling, the remaining portion of the air is shortened, drawing oil into the pores. Because the hot oil has good fluidity and high smoothness, more oil can be immersed in the finished product. The oil immersion method has a higher power than the usual oil immersion rate.
Vacuum immersion: Put the cleaned sintered product into a vacuum box, seal it to -720 mm Hg, then put the oil into the vacuum box, then heat to 80 ° C for 20 to 30 minutes. Since the air in the finished communication pores is extracted, the oil can be immersed in the finished product within 10 minutes. This method has high oil immersion power and high speed.
Another way of this method is to first extract the air in the vacuum box with the finished product, then pass the preheated oil into the vacuum box, cover up the finished product, and then connect the vacuum box to the atmosphere. That is, it is immersed quickly into the pores of the finished product.
Third, waxing
Generally, the powder metallurgy products have porous characteristics, and the touch interface with air is large, and it is prone to rust, especially in the coastal rainy area, the air humidity is high, and the corrosion of the finished product is more serious. In some cases, not only the appearance of the finished product is corroded, but also the appearance of the internal connected pores is corroded, which seriously affects its function and even causes scrapping.
In order to avoid and reduce the corrosion of iron-based products, it is necessary to apply wax after the oil immersion to block the touch between the finished product and the outside world. In this way, the long-distance delivery of the finished product or the retention of the longer time (according to the regulations, the finished product shall not rust within six months), will not cause rust.
The waxing technology of the powder metallurgy finished product is that the wax is placed in the upper wax cylinder, heated to 60-80 ° C, the wax is melted, the cleaned finished product is immersed in the wax liquid, and immediately taken out, that is, coated on the finished product appearance. A layer of uniform wax, cool and can be packaged.
The wax liquid is composed of white wax and petroleum jelly, and it has different proportions according to the season. The intent of Gartholin is to improve the fastness of the wax after it is dried and not to crack. When the temperature is high, Vaseline can be added less, and when the temperature is low, the Vaseline ratio can be appropriately improved. Usually, Vaseline is 20% and white wax is 80%.
Fourth, packaging
The suitable packaging is to maintain the powder metallurgy finished product in the process of storage and transportation without damage or metamorphosis, which is the final process in the production of powder metallurgy. If the packaging is not good, it will cause the loss of the final product, it should be said that it is very regrettable.
The method of packaging is: after the finished product is coated with wax, it is packed in anti-rust paper, and a number of pieces are packed into a box, and each box should be put on the certificate and operation manual. The name and address of the manufacturer, the name, type and quantity of the manufacturer, the product scale and standards are indicated outside the box. It is not possible to misplace and mix different standard types of goods. Then put a number of boxes into a box, it is necessary to put moisture-proof paper around the box, the weight of each box can not exceed 50 kg. The name and address of the manufacturer, the name, type, standard and quantity of the manufacturer shall be indicated outside the box. Together, the packing date should be marked, and the symbol “Be careful, pay attention to moisture” should be attached.