Ⅰ. Introduction to the slider

1. Universal rolling shaft is one of the important parts of steel rolling mill, which can transfer a large torque. In large and medium-sized rolling mill in our country, blooming mill must ensure that its greater work Angle makes rolling get bigger gap adjustment range, which is commonly used in cross slider type universal rolling shaft.

2. In the process of use, because of the limitation of structure and the special working conditions, the sliding block often produces early serious wear, short service life, and becomes one of the main vulnerable parts.

3. In the early days, aluminum bronze material was selected for the slide block. After continuous development, high manganese aluminum bronze, high force brass and other materials were adopted.

Aluminum bronze ZCuAl10Fe3

Aluminum bronze is characterized by high chemical stability, corrosion resistance to acid, alkali, vapor and other corrosive substances, at the same time has a certain wear resistance and process performance, but it is easy to produce refractory oxide alumina in the casting, casting is more difficult, and in the actual use of aluminum bronze slider wear resistance and strength can not meet the requirements, we put our eyes on high manganese aluminum bronze body.

High manganese aluminum bronze ZCuAl8Mn13Fe3

High manganese aluminum bronze has high strength and hardness, good wear resistance and casting performance, high density of alloy, good corrosion resistance, high mechanical properties, high corrosion fatigue strength, but in the process of use there will be serious heating phenomenon and high hardness on the workpiece body produce greater wear, then there is a high force brass material slider.

High strength brass ZCuZn25Al6Fe3Mn3

High strength brass has very high mechanical properties, good casting performance, good corrosion resistance, can be welded, suitable for high strength, wear resistant parts, such as bridge support plate, nut, screw, wear plate, slide and turbine, manganese can significantly improve the process performance, strength and corrosion resistance of brass. Aluminum can improve the strength of brass to a great extent and improve their stability against corrosion, but the plasticity is significantly reduced. But in the process of use also found the shortcomings of high force slider, although high force brass strength and hardness are high, but because the material contains a lot of zinc, iron, manganese, aluminum and other elements are easy to cause hard and brittle products, low plasticity, can not meet the use of rolling mill, and ultimately contributed to the production of tin bronze slider.

Tin bronze 12-2 CuSn12Ni2

Tin bronze is characterized by high wear resistance, mechanical properties, casting properties, ductility, plasticity, as well as good corrosion resistance, and is one of our most commonly used nonferrous alloys. The content of tin in the alloy is generally no more than 13% (rarely up to 15%), and too high will reduce its plasticity. In addition to tin, tin bronze generally contains a small amount of zinc, lead, phosphorus, nickel and other elements. Zinc improves the mechanical properties and fluidity of low tin bronze; Lead can improve the wear resistance and machinability of bronze, but reduce its mechanical properties. Nickel can refine the grain of bronze and improve its mechanical properties and corrosivity. Phosphorus can improve the toughness, hardness, wear resistance and fluidity of bronze. Tin bronze containing phosphorus, called phosphor bronze, has better properties than ordinary tin bronze. Tin bronze is generally used for casting wear-resistant parts (such as bearing bush, shaft sleeve, slide block) and corrosive gases such as acid and alkali vapor contact.

Ⅱ. Sliding block product types

1. Our company is specialized in casting and processing sliders, and is in a leading position in casting sliders technology and processing level. According to the national standards of the People's Republic of China "Casting copper and copper alloy GB/T 1176--2013", "Copper and copper alloy Castings GB/T 13819--2013", the casting and processing of customer products.

2. Our company now produces slide block products material: brass ZCuZn38, high force brass ZCuZn25Al6Fe3Mn3, aluminum bronze ZCuAl9Fe4, ZCuAl9Fe4Ni4Mn2, high manganese aluminum bronze ZCuAl8Mn13Fe3Ni2, tin bronze ZCuSn12Ni2. Wide range of material, large production.

3. Tin bronze ZCuSn12Ni2 material, for our company's special ingredients, special process, in the use of slider products have been recognized by customers, tin bronze ZCuSn12Ni2 material slider, with high wear coefficient, high temperature resistance, good casting performance, high plasticity, strong ductility and other advantages.

4. Our company's products are sold in Beijing Shougang, Laigang, Baosteel, Tisco, Shan Steel and other domestic companies, the product material and physical detection performance has a good range, give long-term cooperation, has reached a consensus.

Ⅲ . The improvement process of slide block

1. The casting process of our company is steel mold casting. The advantages of steel mold are fast cooling speed of the casting, good internal structure density, no slag, slag, porosity and other defects.

2. In the smelting process, the use of current batching method, customer-centric, according to customer requirements to provide material and drawing size, to meet the requirements.

3. Use medium frequency electric furnace melting, extract sample and test block, pre-furnace detection and physical performance detection, and make material report, and casting. With processing equipment, the first car in annealing out, and then finishing, the process flow is reasonable.

4. In the high force brass ingredients, improve the content of copper, reduce the content of aluminum, iron, manganese, zinc, while maintaining a certain strength to improve the plasticity and ductility of the slide; In the tin bronze 12-2 ingredients, keep copper and nickel in the upper limit of the composition standard, improve the role of plasticity and grain refinement, and the first to add phosphorus and lead elements, the former can improve the toughness, hardness, wear resistance and fluidity of the bronze, the latter can improve the wear resistance and workability of the bronze, the comprehensive performance is far greater than the conventional tin bronze 12-2 material. For our independent research and development of the sliding block material.

5. In order to solve the problem of coarse grain in the internal structure of the slider, we contacted various universities and institutes engaged in the research of copper alloys, and suggested adding rare earth alloys into copper alloys according to our actual situation through a series of demonstration and experiments. Rare earth elements have three main functions in copper alloys: purification, metamorphism and alloying. The interactions of rare earth elements with impurity elements such as oxygen, hydrogen, sulfur, phosphorus, tin, bismuth and lead in copper are shown in Tables 1 and 2.

Table 1 Study results of thermodynamic properties of rare Earth elements with oxygen and sulfur elements in copper molten liquid (1200℃)

Table 2 Melting points of compounds formed by certain impurities and rare earth elements

5.1 Deoxidation: rare earth metals interact with hydrogen to form Reh-type stable hydrides, thus controlling the hydrogen in copper solution and preventing the possibility of "hydrogen embrittling" during plastic processing.

5.2 Impurity removal: rare earth is highly chemically active and can be combined with many fusible components to form refractory binary or multicomponent compounds.

5.3 Metamorphism: First of all, rare earth can eliminate dendritic zone and refine grain sharply. Moreover, rare earth compounds with high melting point can be distributed in a dispersed state, thus improving their plasticity and strength and reducing surface cracks and defects. Secondly, rare earth can transform some strip, sheet or even block impurities in metals and alloys into dots or spheres, so as to improve or enhance their mechanical properties and machining properties. Finally, the impurities can be evenly distributed throughout the crystal, improving the metal properties.

To sum up, adding rare earth to copper and copper alloys can produce four effects:

(1) Form high melting point compounds with oxygen, sulfur, lead, lead and so on into the slag, playing the role of impurity removal and purification;

(2) Form stable compounds with hydrogen, soluble in copper in solid solution state, although can not reduce the content of hydrogen, but played a role in hydrogen fixation, so as to avoid causing "hydrogen embrittance ";

(3) change the form and distribution of some impurities, improve the metallographic structure;

(4) there is obvious metamorphism, so that the processing, mechanics, welding, wear and corrosion resistance and other properties improved

5.4 Refining microstructure: the influence of rare earth on the microstructure of copper and copper alloys is mainly reflected in refining grains, reducing or eliminating columnar crystals, and expanding the equiaxed crystal region.

5.5 Change the shape and distribution of impurities: reduce or eliminate the dendritic crystal and columnar crystal in the alloy structure, so that some impurities in the alloy strip, sheet or even block (such as Pb, Bi, etc., some of which can form low melting point eutectic) into point or ball, so as to improve or enhance the mechanical and processing properties of copper and its alloys. Make some harmful impurities in the alloy (such as S, P, Pb, Bi, etc.) from concentrated distribution in dendrites or grain boundaries, change to more uniform distribution in the whole crystal, so that the impurities in the metal micro-volume to achieve redistribution, or influence the macrosegregation of some impurities, resulting in the improvement of various properties. Reduce the amount of harmful impurities at low melting point on the grain boundary of the alloy, so as to weaken the high-temperature tempering brittleness of the alloy.

5.6 Machining properties: The casting properties of copper and copper alloys can be improved by adding an appropriate amount of rare earth metals to copper alloys. The specific performance can improve the segregation or reverse segregation phenomenon of the alloy, significantly increase the high temperature elongation of the copper alloy, improve the hot working performance, reduce or eliminate the phenomenon of hot rolling cracking, can greatly improve the machining performance, especially reduce the surface roughness, burr and tool wear.

5.7 Mechanical properties: The mechanical properties of copper and copper alloys are mainly improved by rare earth in the aspects of hardness, strength, plasticity and so on.

5.8 Oxidation resistance and corrosion resistance: Si, Al and RE elements are infiltrated into copper alloys at 850℃ by chemical heat treatment, and surface films with improved oxidation resistance are formed on the surface of copper alloys, and the corrosion resistance of copper and copper alloys is improved to varying degrees after the addition of rare earth.

5.9 Wear resistance: Rare earth and copper elements can form intermetallic compounds with high hardness and uniform distribution, which become the resistance of dislocation movement; Moreover, rare earth can effectively improve the existence form and distribution of inclusions, reduce the possibility of weakening grain boundaries, and reduce the probability of cracking along grain boundaries under load, thus improving the wear resistance.

Ⅳ. Slide wear failure situation analysis

1. Because of the restrictions of the slider structure and the special working conditions, the slider often produces early serious wear and short service life. Because there is a clearance between the slider, the offset head and the pin shaft, the slider is not in contact with the whole length of the surface at work, but at one end of the local tilt state contact, in the transfer of torque, due to the existence of the working Angle, the slider will swing around the pin shaft reciprocating, producing wear state.

2. The wear of the working surface of the slider is divided into adhesive wear, stripping wear, abrasive wear, plastic flow, four wear states.

3. The early wear failure of the slide block is the result of the combined action of several wear forms. Adhesive wear and scale-like stripping wear are the two main wear mechanisms. The above wear is mainly caused by the following aspects:

(1) Dry friction and poor lubrication are the main causes of adhesive wear under high contact stress;

(2) under the given working conditions of universal contact, the copper sliding block without self-lubrication and steel flat head pair are used. Under the condition of no oil, the complete welding of copper and iron is also the main cause of adhesive wear;

(3) The contact characteristics of the slider and the flat head during working time are not fully considered. The slider and the flat head contact in a small area on the edge at the early stage of working, so that the larger driving torque is borne by the narrow contact area, and the local contact stress is too high, resulting in serious early wear of the end of the slider;

(4) the slide block wear to a certain extent is not replaced in time, so that the gap is too large, increases the unit pressure and intensifies the impact, so that the wear is more serious.

Ⅴ. The improvement measures of the slide block

1. Reasonable selection of sliding block materials: through the above analysis, we believe that one of the key problems to solve poor lubrication and reduce sliding block wear is reasonable selection of sliding block materials, the material selection of sliding block should meet the following requirements:

① The working surface has high wear resistance;

(2) must have good self-lubrication, wear resistance at the same time, the wear of the spouse parts should also be smaller;

③ with a certain strength and impact toughness;

The surface of the workpiece should have a good ability to embed foreign bodies.

2 According to the wear of flat head and fork head hole, adjust the size of sliding block accessories: universal shaft work, sliding block wear at the same time, flat head and fork head hole should also produce wear, this wear makes the new sliding block in the connecting shaft assembly gap increase, speed up the wear of sliding block.

Ⅵ. Improve the lubrication conditions of universal joint shaft

1. Change the structure of the oil groove. When the universal shaft is lubricated by grease, the reasonable configuration of the oil groove is very important. Reasonable oil ditch can reduce the damage to the working surface.

2. Use oil cap sealing lubrication technology. In order to prevent the manually injected grease from being thrown out when working, reduce the lubrication effect.

3. Strengthen maintenance: Correct maintenance is one of the key measures to ensure that the slider reaches the expected service life, to choose the oil with good extrusion performance, and regular lubrication, when the flat head wear should be repaired in time or modify the size of the spare parts of the slider, to ensure the minimum assembly gap, to avoid the early wear of the slider due to too large assembly gap.

Ⅶ. Conclusion

1. Through the analysis of the working and mining conditions of the sliding block universal joint shaft, the sliding block works under the condition of low speed and heavy load, resulting in its early wear failure is mainly caused by adhesive wear accompanied by plastic flow and abrasive wear and other forms of interaction.

2. There are many ways to improve the life of the universal shaft slider, such as reasonable selection of the material of the slide block, the size of the spare parts of the slide block should be adjusted according to the wear amount of the flat head and fork hole, change the structure of the oil ditch, and improve the lubrication conditions of the universal shaft by using the oil cover closed lubrication.