Ball mill steel balls are classified according to the manufacturing process: casting and forging

The ball mill steel balls on the market can be divided into two types according to the manufacturing process: casting and forging, but their wear resistance is different. Because of the crushed material, the steel ball needs good wear resistance and sufficient toughness. Usually, alloy steel, high manganese steel, cast iron and ferrochrome are used for forging or casting, and it is more economical to equip with the corresponding heat treatment process. , Ball mill steel balls can be divided into:
1. Forged steel balls: low carbon alloy steel balls, medium carbon alloy steel balls, high manganese steel balls, rare earth chromium molybdenum alloy steel balls;

2. Cast steel ball: low chromium cast ball, medium chromium cast ball, high chromium cast ball.

Which steel ball is the best on the market now? Let us analyze it now:

1. Forged steel balls:

Good surface quality, good impact resistance, strong toughness, good wear resistance, not easy to break and lose round. That is, the metal is heated to a temperature of 700-1300°C, and the forging machine is used to apply pressure to the metal blank to cause plastic deformation to obtain a processing method for forgings with certain mechanical properties, certain shapes and sizes. One of the two major components of forging (forging and stamping). Forging can eliminate defects such as loose as-cast during the smelting process and optimize the microstructure. At the same time, due to the preservation of complete metal flow lines, the mechanical properties of forgings are generally better than castings of the same material. For the important parts of related machinery with high load and severe working conditions, forgings are mostly used except for simpler shapes that can be rolled, profiles or welded parts. In addition, for forging steel balls to be wear-resistant, the most wear-resistant materials must be selected, such as national standard 60Mn, 65Mn, or high-efficiency wear-resistant alloy steel materials independently developed by some companies, and it is recommended to use steel produced by national super large steel plants. The quality of the materials produced in different steel plants is also different, and the quality of forgings is 80% dependent on the quality of the material. For example, the use of high manganese steel has good impact resistance, strong toughness and good wear resistance. , Not easy to break. Forged steel balls are favored by users because of their low price, economy and durability. For example, international mining giants Rio Tinto, BHP Billiton, and Anglo Gold all use forged steel balls.

Features of forging production:

(1) Forging the heated metal material into various shapes of tools, mechanical parts or blanks is called forging. Forging can change the internal structure of metal materials, refine crystals, and improve their mechanical properties.

(2) Forging production must use heating equipment, forging equipment and many auxiliary tools.

(3) Forging equipment mainly includes steam hammer, air hammer, die forging hammer, mechanical hammer, splint hammer, spring hammer, belt hammer, crank press, friction press, press, reaming machine, roll forging machine, etc.

2. Cast steel balls:

Low and medium chromium cast balls have poor wear resistance and high crushing rate. Although they are cheap, the overall cost performance is not high, so they are not recommended here. High chromium cast ball has excellent hardness and is a high-quality wear-resistant material. It has been widely used in dry ball mills in the cement industry. However, high chromium cast balls have poor toughness and are prone to breakage in ball mills with a diameter of more than 3 meters. The price is higher.

Influence of cast steel ball material: Generally speaking, the harder the steel ball, the greater the wear resistance. To improve the wear resistance of the steel ball, it is necessary to increase its hardness, but as the hardness increases, the impact toughness of the steel ball will decrease. At the same time, the hardness of the steel ball must also take into account the material and hardness of the liner, not too high (Damage the liner), and should not be too low (not wear-resistant). Therefore, how to balance the suitable hardness and good impact toughness of steel balls is the key to improving the wear resistance of steel balls.

The commonly used materials for steel balls are: low carbon alloy, high manganese steel, high chromium cast iron, high carbon and high manganese alloy steel.

Low-carbon alloy steel balls have good toughness and low price. Under the same working conditions, their service life is more than twice that of low-chromium cast balls;

High manganese steel has good toughness, good manufacturability and low price. Its main feature is that under the action of greater impact or contact stress, the surface layer will quickly produce work hardening, and its work hardening index is 5-7 times higher than other materials. The wear resistance has been greatly improved;

High chromium cast iron is a kind of wear-resistant material with excellent abrasion resistance, but its toughness is low, brittle and broken easily and expensive.

High-carbon and high-manganese alloy steel is mainly alloy structural steel containing chromium, molybdenum and other elements, with high hardness and good toughness. Its matrix structure has martensite, bainite or bainite + martensite composite structure. The hardness of the steel ball is about HRC60, and the impact toughness is ≥15J/CM2. Under the same working conditions, its service life is at least one time longer than that of the high manganese steel ball.

But the quenching and tempering heat treatment of the steel ball is the key. After the quenching and tempering heat treatment, not only the overall toughness is required to reach 12 joules/CM2, but also considerable plasticity and wear resistance are required. However, the general casting process can only reach 3-5 joules, resulting in breakage The rate is higher, even for high chromium cast balls, so forgings are recommended when the working conditions are strong. The manufacturing process of the steel ball is also a key factor in determining its service life. If there are defects in the surface or internal manufacturing of the steel ball, such as shrinkage holes, cracks, transcrystallization, etc., it will not only reduce the performance of the steel ball, but even cause the steel ball to break. Therefore, reasonable forging, casting and heat treatment processes must be formulated in the production of steel balls. For example, for high chromium cast iron balls, vertical pouring and reasonable use of external cooling iron should be adopted, and the casting temperature should be strictly controlled. This can make the steel balls have a good solidification sequence and feeding conditions in the casting, and then obtain a dense internal structure. And weaken the phenomenon of coarse grains. The heat treatment process of the steel ball determines the realization of its mechanical properties and the distribution of carbides. Since the composition of the steel ball contains a certain amount of chromium and other alloying elements, how to make these alloying elements form hard point carbides is also a factor considered when formulating the heat treatment process. In short, formulating a reasonable production process and strict quality inspection methods are the prerequisites for ensuring the performance of steel balls.

Investigate and analyze the gap between domestic and foreign spring steel wires

Spring steel wire is the main raw material of spring, and its quality mainly determines the quality of the final product. The unconventional development of China’s automobile industry not only provides rare development opportunities for the spring manufacturing industry, but also creates a market pull for spring raw materials. The development of spring technology will inevitably raise higher and higher requirements for their raw materials. The spring industry hopes that the domestic metal product industry will keep pace with the times and propose more high-quality and low-cost materials for spring production.
From the perspective of users of spring steel wires, there is still a big gap between domestic spring steel wires and similar foreign products.

A. Steel wire raw material quality Baosteel is a leading domestic enterprise, but compared with the famous Kobe Steel, there is still a gap in bloom technology, harmless treatment of inclusions, and uniformity of overall materials.

B. Production of variable cross-section materials for suspension springs and oval-shaped cross-section materials for valve springs. Domestic companies have no ability to produce them and can only give up the market.

C. In terms of mechanical properties, the strength range of the same batch of domestic steel wire materials, even the same disk material, fluctuates greatly, which makes it difficult to control the outer diameter, free length and shrinkage of the spring during production. The stability of mechanical properties of imported steel wire is obviously better than that of domestic steel wire.

D. Steel wire products foreign companies have used peeling and eddy current flaw detection technology, most domestic steel wire manufacturers do not have the corresponding equipment, or the testing technology is not enough.

E. The two indexes of surface defects and decarburization, which have the greatest impact on the fatigue life of the spring, cannot reach the level of similar foreign products.

F. The development of new steel grades is the weakest link for domestic enterprises. So far, the development of new suspension spring materials and ultra-pure valve spring materials is still blank, and there is no development plan in the near future.

Talking about high-strength spring steel with plasticity and corrosion resistance

Spring steel mainly has good elasticity, and because it works under dynamic load environmental conditions, the most important material for manufacturing springs should have high yield strength; it should not cause plastic deformation when subjected to heavy loads; should be High fatigue strength, long service life under repeated loads; and sufficient toughness and plasticity to prevent sudden brittle fracture under impact force.
As economic and environmental pressures continue to grow, the automotive industry continues to improve to reduce weight. For example, the weight of the coil spring has been reduced from 4kg in 1975 to 2kg today, a half reduction. This is mainly due to improved design and increased hardness (the current hardness is 52~56HRC). The higher strength can not only reduce weight but also improve the resistance to bending deformation, but also provide the possibility for the new design of the suspension system. However, higher hardness means increased sensitivity to surface defects during fatigue and corrosion fatigue. Indeed, the fracture of high-strength suspension springs is mainly caused by corrosion pits. Therefore, in order to ensure reliability, in addition to improving strength, it should also have good plasticity (impact toughness) and corrosion resistance.

Studies have found that reducing the carbon content can improve corrosion resistance, impact toughness and plasticity. However, in order to obtain the same strength when the carbon content is reduced, the tempering temperature must be lowered, and the carbon content should be controlled as far as possible to 0.45 ~ 0.55wt%; silicon can improve the yield strength and toughness, but in the process of heat treatment Silicon is also easy to cause decarburization. Therefore, the content of silicon should be controlled at 1.6~2.1wt%; the addition of Cr, Ni, Cu can be adjusted to control the morphology of corrosion pits to improve corrosion resistance and corrosion fatigue resistance, and obtain the required hardenability And keep enough low cost to ensure the economy of new steel grades; the microalloying elements Ti, V, Nb can make the steel have finely dispersed carbonitride precipitates. These precipitates, especially those containing V, are beneficial Obtain higher hardness and yield strength. Nb, Ti and a small amount of V help control the grain size during the austenitization process and obtain a fine structure, thereby improving toughness, corrosion resistance and bending resistance.

The biggest challenge in designing high-strength steel for spiral springs is to ensure that they have high hardness, while having good plasticity and corrosion fatigue resistance and reasonable cost. Kobe Steel and ASCOM Metal jointly developed a new type of high-strength spring steel (HRC>55). The design idea of ​​this kind of steel is: adding controllable alloying elements and microalloying elements to improve the fatigue, corrosion fatigue and bending deformation resistance of steel. Combining the effects of these elements on hardness, corrosion resistance, corrosion pit morphology, hydrogen embrittlement resistance, toughness and cost, the content of alloying elements can be precisely controlled.

Compared with SiCr steel, this type of steel has excellent hydrogen embrittlement resistance, toughness and corrosion resistance, and can meet the needs of higher quality springs that can improve corrosion fatigue resistance under high stress (1300MPa). The difference in the chemical composition of these steels allows users to choose the best composition combination by adjusting cost, corrosion fatigue and toughness according to their needs.

Spring steel definition

Spring steel refers to steel specially used for manufacturing springs and elastic elements due to its elasticity in the quenched and tempered state. The elasticity of steel depends on its elastic deformation ability, that is, within the specified range, the elastic deformation ability makes it bear a certain load, and no permanent deformation occurs after the load is removed.

Spring steel should have excellent comprehensive properties, such as mechanical properties (especially elastic limit, strength limit, yield ratio), elastic reduction properties (that is, elastic reduction resistance, also called relaxation resistance), fatigue properties, hardenability , Physical and chemical properties (heat resistance, low temperature resistance, oxidation resistance, corrosion resistance, etc.). In order to meet the above performance requirements, spring steel has excellent metallurgical quality (high purity and uniformity), good surface quality (strict control of surface defects and decarburization), precise shape and size.

According to the GB/T 13304 “Steel Classification” standard, according to basic performance and service characteristics 1, spring steel belongs to mechanical structural steel; according to the quality grade, it belongs to special quality steel, that is, the steel that requires strict quality and performance control during the production process . According to our country’s custom, spring steel belongs to special steel. When making spring steel, the technical requirements are relatively high, and the technical excellence directly determines the quality.

Several protective layers about hardware springs

Several protective layers about hardware springs
Hardware springs are generally electroplated to obtain a metal protective layer. Because the electroplating protective layer can not only protect from corrosion, but also improve the appearance of the spring. Some electroplated metals can also improve the working performance of springs, such as increasing surface hardness, increasing wear resistance, improving thermal stability, and preventing radiation corrosion. But if it is purely for the corrosion of the spring, the electro-galvanized layer and the electro-cadmium layer should generally be used. Nickel-plated spring

Zinc and cadmium plating of the spring is carried out in a cyanide electrolyte. In the electroplating process, in addition to zinc or cadmium plating, part of the reduced hydrogen penetrates into the plating layer and the crystal lattice of the base metal. This causes internal stress and makes the plating layer and spring on the spring brittle, also called hydrogen embrittlement. Due to the high strength of the spring material and the large deformation of the hardware spring during forming, it is particularly sensitive to hydrogen embrittlement. If the hydrogen is not removed in time, it will often cause the spring to break, in order to eliminate some defects generated in the electroplating process To improve the physical and chemical properties of the spring, extend the service life of the spring, and increase the corrosion resistance of the coating, post-plating treatment must be carried out, that is, hydrogen removal treatment. The hydrogen removal treatment is carried out immediately or within a few hours after electroplating. Heat the electroplated spring at a temperature of 200-215°C for 1 to 2 hours (or more than 2 hours) to achieve the purpose of hydrogen removal.

The hydrogen removal is generally carried out in an oven. The effect of hydrogen removal is related to temperature, time, and residence time after plating. Generally speaking, if the temperature is high, the heating time is long, and the pause time after plating is short, the hydrogen removal effect is good. Therefore, select a higher temperature for removing hydrogen from the spring.

Metal protective layer, in addition to the above-mentioned zinc and cadmium plating, there are copper plating, chromium plating, nickel plating, tin plating, silver plating, zinc-titanium alloy plating, etc. The spring designer can choose the plating layer according to the spring working occasion.

Zinc is relatively stable in dry air, hardly changes, and is not easy to change color. A white film of zinc oxide or carbon zinc carbonate is formed in humid air. This dense film prevents further corrosion. Therefore, the galvanized layer is used as the anti-corrosion protection layer of the spring under normal atmospheric conditions. All springs that are in contact with solutions such as sulfuric acid, hydrochloric acid, caustic soda, and working in humid air such as sulfur trioxide, should not be coated with zinc. Galvanized spring

Generally, the galvanized layer is passivated after plating. Passivation can improve the protective performance of the coating and increase the appearance of the surface.

In oceanic or high-temperature atmospheres, springs in contact with seawater, and springs used in hot water at 70°C, cadmium is relatively stable and has strong corrosion resistance. Cadmium coating is brighter and more beautiful than zinc coating, softer, and has better plasticity than zinc. The coating has less hydrogen embrittlement and is most suitable for springs as a protective layer. But cadmium is scarce, expensive, and cadmium salt is highly toxic, which is very harmful to the environment. Therefore, it is restricted in use. Therefore, most of the springs used in aviation, navigation and electronics industries use cadmium plating as a protective layer.

In order to improve the corrosion resistance of the cadmium coating, passivation treatment can be performed after plating.

The thickness of the zinc and cadmium coatings determines the level of protection. The thickness should generally be selected according to the working environment during use. The thickness of the zinc coating is recommended to be selected within the range of 6-24/μm; the thickness of the cadmium coating is recommended to be selected within the range of 6-12μm.

60Si2Mn spring steel plate enterprise

The Ministry of Industry and Information Technology indicated that the important method is to eliminate outdated production capacity. In 2012, it will further eliminate outdated production capacity, study and affirm and implement the annual mission and obligations. 60Si2Mn spring steel plate organizes a review and inspection, and perfectly defines the environmental protection and energy consumption norms of outdated production capacity. The large-scale suppression, volume reduction or equivalent replacement mechanism promotes the use of market means to eliminate outdated production capacity, and synthetically implements the obligation to eliminate outdated production capacity during the 12th Five-Year Plan.
“While eliminating outdated production capacity, the state should strengthen the evaluation and review of industrial investment and energy conservation, strictly control the’two highs’ and the conscious expansion of industries with excess production capacity, and add power to waste from the source.” The aforementioned officials of the Central Economic and Information Commission analyzed this newspaper. , “I hope that the energy-saving evaluation and review system will only be perfect and play a restraining role like an environmental assessment.”

Miao Wei pointed out that in 2012, we will also strengthen the innovation of energy saving and consumption reduction techniques, organize the implementation of 9 key energy conservation projects, 10 comprehensive application projects, and 7 clean consumption projects that are affirmed in the plan, and enhance the individual crux of energy conservation and emission reduction skills and equipment development and demonstration. And promotion.

In addition to the above-mentioned projects, the upcoming energy-saving and low-carbon activities of thousands of enterprises will also help the industrial energy-saving purpose of centrifugal ductile iron pipes. An expert close to the National Development and Reform Commission leaked to this report, “This behavior is currently under design and is expected to be officially launched next year.”

In practice, the contribution rate to industrial energy conservation during the “Eleventh Five-Year Plan” period is negative. Previously, Deputy Minister of Industry and Information Technology, Su Bo, once said underground that during the “Eleventh Five-Year Plan” period, the energy consumption of 60Si2Mn spring steel plate industry accounted for the proportion of the overall energy consumption of the whole society, from about 70.9% in 2005 to about 73% in 2010; The proportion of energy consumption in large and high energy-consuming industries in the overall industrial energy consumption has risen from about 71% in 2005 to about 77%. “These two rises will put a lot of pressure on industrial energy conservation in the 12th Five-Year Plan.” .

Su Bo indicated that in the future, the country will further improve the entry barriers for energy consumption, environmental protection, and comprehensive utilization of resources in heavy and chemical industries, strictly implement the energy-saving evaluation and review system for industrial investment projects, and strengthen the establishment of name target governance for industries with excess capacity; strict control The newly added talents in industries with excess capacity such as iron and steel, cement, and plate glass have curbed the conscious development of high-energy-consuming and high-purification industries such as traditional coal chemical industries.

The main factors affecting the clamping force of the collet

The spring chuck seems to be a simple process device, but there are many main factors that affect the clamping force.
The main factors affecting the clamping force of the collet and summary:

1. Axial force. As shown in the figure, the axial pulling force exerted by the pull rod on the collet. In the use of the spring chuck, the axial force can be applied in different ways, but the principle of action is basically the same. Obviously, a large axial tension will produce a large clamping force, and vice versa. Generally, the axial tension of the tie rod can be adjusted by the operator.

2. In the use of the collet chuck, the designed locking angle (or head inclination) will determine the index that the clamping force can reach after expansion, which is usually determined by the machine tool manufacturer and the collet manufacturer. When the new design of the spring chuck is still being explored, the designer recommends that the user use the existing spring chuck structure in consideration of economy and reliability. The standard taper (or head inclination) has been determined by the design according to the type of machine tool (such as lathe, etc.), use conditions (dynamic and static) and purpose (workpiece and tool).

3. The total friction between the workpiece (or tool) and the collet will directly affect the clamping force. A small friction value will result in a small clamping force and vice versa. The collet chuck supplier can take various measures to overcome the relative rotation or axial movement between the collet chuck and the workpiece (or tool). For example, the inner hole of the collet chuck deliberately creates a serrated shape or micro-hard alloy Die is immersed in the clamping surface etc.

4. The conical surface of the spindle and the collet chuck friction at the locking angle. The friction force also directly affects the clamping force of the collet on the workpiece. If the friction force is too small, the clamping force is not enough. Too much clamping force will accelerate the wear of the spring chuck. During use, the collet chuck should be loosened frequently to exchange workpieces. For example, when it is used on a turning machining center, a thin layer of lubricant should be sprayed on the surface of the inner hole of the collet chuck when loosened. Conditional use of coolant is better for lubrication, because the coolant provides a flushable collet, and the lubrication effect is good. In particular, regular application of coolant to the locking angle can reduce long-term wear and increase clamping force. Some more materials with better lubricating effect can also be used, including high-quality grease or wax-based materials with EP (Extreme Pressure) characteristics. It seems a little strange that some smart operators have great difficulty in processing and when the general cooling and lubricating effect is not good, they choose the lipstick used by ladies, which is said to be effective.

my country’s spring industry presents three major development trends in the future

Some experts in the spring industry in my country believe that with the development of the main engine, the spring product market in my country will also grow simultaneously. It is estimated that by 2010, the sales of the whole industry will exceed 4 billion yuan, and the proportion of the automobile and motorcycle industries in the spring market will be More than 50%. At the same time, in order to adapt to market changes, the spring industry will show new development trends in the next few years:
-A new combination appears. In the next few years, my country’s spring industry will still be dominated by small companies, but some advantageous companies start from the market and business strategy, use the capital, technology and talent advantages in their hands to merge and acquire some companies to obtain the necessary production factors and market resources , Most of the state-owned and collective enterprises in the spring industry will be transformed into joint-stock or private enterprises.

——Price competition turns to technology and quality competition. With the increasingly fierce market competition, the profit margins of the spring industry have become smaller and smaller. In addition, the OEMs have higher and higher requirements for the quality of accessories. Enterprises can no longer rely on simple price reductions to win the market. Technology and quality have become the key to competition.

From July 1, 2006, my country’s auto parts tariffs will be reduced to 10%, and the final prices of suspension springs, valve springs, stabilizers and other products for the automotive industry will gradually be in line with international prices, and for mini vehicles , The products supporting the van have undergone fierce market competition. The current price has a certain degree of competitiveness compared with the international market, but the quality level cannot compete with similar products. The prices of other products, especially those for motorcycles and some small springs, are already lower than the international market prices. Therefore, the price of similar foreign products poses no threat to us, and the competition is mainly manifested in quality.

——Products are developing towards lightweight and high reliability. Roughly estimated, in 2010, the annual demand for suspension springs in China’s automobile industry was about 8 million pieces, and the annual demand for valve springs was about 30 million pieces (excluding motorcycles and diesel engines). The technical development trend of these two springs is generally lightweight (high stress) and high reliability. For the current special-shaped cross-section suspension springs and valve springs, due to high material prices and complex manufacturing processes, the production cost is higher than that of round-section springs. Therefore, there is no sign that special-shaped cross-section springs will completely replace round-section springs.

Automotive elastic components: few leaf springs

As we know, the elastic components of the independent suspension of passenger cars mostly use coil springs, and the elastic components of non-independent suspension mostly use leaf springs. Because of the simple steel structure and reliable use, leaf springs are widely used, such as some off-road vehicles, pickups or vans. However, most buses and trucks use leaf springs.
As the name suggests, leaf springs are made of steel plates, which are also called leaf springs. In order to make full use of the material, the leaf spring is made into a form close to the stress beam. It has two types, one is equal thickness, the width is narrow at both ends and wide in the middle. The traditional multi-piece leaf spring is of this type. This type of leaf spring is composed of multiple steel plates with different lengths and the same width. Nowadays, most buses and trucks use this type of leaf spring.

The other is equal width, the thickness is thin at both ends and thick in the middle. The common small-leaf leaf spring is of this type. The small-leaf leaf spring refers to a variable-section leaf spring with only 1 to 4 pieces. The variable-section leaf spring refers to the thickness of the center along the length of the steel plate and gradually thinner at both ends, or Leaf spring with gradual change in width and thickness. It is mostly used in light vehicles, and now some large and medium passenger cars tend to use this type of leaf spring.

The middle part of the leaf spring is fixed on the axle by U-shaped bolts (also called riding bolts), and the curling lugs at both ends are hinged on the bracket of the frame with pins. In this way, the axle and the body are connected by the leaf springs, which play the role of buffering, damping, and transmitting force. The steel plates of multiple leaf springs are superimposed into an inverted triangle shape. The uppermost steel plate is the longest, and the lowermost steel plate is the shortest. The number of steel plates is related to the weight of the car and the shock absorption effect. The more steel plates, the thicker and shorter. The greater the spring rigidity. However, when the leaf spring flexes, the pieces will slide and rub against each other to generate noise. Friction can also cause spring deformation, causing uneven driving. Therefore, in cars with low load capacity, few leaf springs appear to eliminate the defects of multiple leaf springs.

Some small-leaf leaf springs use only one leaf spring. Compared with multiple leaf springs, apart from reducing noise and no friction, they can also save material, reduce weight, facilitate layout, reduce the height of the vehicle, and have good ride comfort.

The section of the steel plate of the small leaf spring changes greatly, and the section from the middle to the two ends is gradually different, so the rolling process is more complicated. In order to reduce the weight and the difficulty of the rolling process, a fiber reinforced plastic (FRP) has appeared in recent years to replace the steel plate, which can reduce the weight by more than half. This fiber-reinforced plastic is made of glass fibers and polymerized together with polyester resin. According to calculations, the weight of a general single leaf spring is about 11-20 kilograms, and the weight of each pair of fiber-reinforced plastic springs is about 4 kilograms, and the driving is stable and the noise is very low. (end)

Main factors and countermeasures affecting the bright annealing quality of stainless steel strip

The main factors affecting the quality of bright annealing of stainless steel strip are: the composition and purity of the protective gas, the heating and cooling system, the degreasing and dehydration of the steel strip, and the production process of the steel strip before BA treatment. The composition and purity of the protective gas used in the production of BA panels are the primary conditions for bright annealing. BA uses H2 and N2 as protective gas. Shi is a strong reducing agent, such as Cr2O3+3H2-2Cr+3H2O, so the higher the concentration of the protective gas neutral line, the better the brightening effect. Due to the high price and explosiveness of the game, the mixture of nitrogen and hydrogen was widely used in the past, adding 1% to 5% of pure nitrogen (volume fraction); or using 75% and 25% from (volume fraction) Ammonia decomposition gas. With the advancement of technology, in order to improve the surface quality and production capacity of stainless steel strips, pure hydrogen is widely used as protective gas on large bright furnaces, and ammonia decomposition gas is generally used for protection on some small furnaces due to the preparation of protective gas. Gas, ammonia decomposition gas contains 75% practice (volume fraction), and its brightening effect and productivity are also very good.
As the treatment temperature and dew point decrease, the oxidation temperature decreases. For example, the oxidation (Cr2O3) that occurs at 1000°C can be reduced by the treatment temperature with a higher dew point of -30°C, but it will be oxidized again when the temperature of the steel strip drops to 600°C. Therefore, under the condition of constant dew point, increasing the treatment temperature, or decreasing the dew point temperature under the condition of constant treatment temperature, can achieve better brightening effect. In order to obtain 3~4 BA board, when it is greater than 85% (volume fraction), the dew point can be -35℃; but when it is 55%-75%h2 (volume fraction), the dew point temperature should be lowered to below -40℃ . The dew point of the protective gas is directly related to the gas moisture content. Since the reaction of 2Cr+3H2O2–Cr2O3+3H oxidizes the surface of the steel strip, the protective gas dew point should be controlled within the range of -40~-60℃, and the moisture content (mass fraction) should be 1.21%-0.23%. Similarly, the residual oxygen content (volume fraction) of the protective gas should also be less than 0.001%. Determined by the Cr/Cr2O3 equilibrium temperature, the quality of the BA plate has a great relationship with the cooling rate of the steel strip after heating. At the normal processing temperature, in the heating process from room temperature to high temperature, although oxidation occurs in the range of 300-800°C, it is quickly reduced when the processing temperature is reached. Only the oxidation that occurs during the cooling process after the treatment can no longer be reduced. Therefore, rapid intensive cooling is extremely important. The cooling rate should be about 20°C/s below 800°C; the cooling method is to spray protective gas directly from the bottom up to the surface of the treated steel strip.

Current status of the spring industry: exports to overseas markets may be weakened

China’s spring industry currently has more than 700 large-scale spring production enterprises, and 10 professional spring research institutes have been established. The entire spring industry employs more than 80,000 people. There are 21 major categories of products produced in the spring industry, with more than 1,600 varieties, and an annual output of about 4 billion pieces.
For the spring industry, there has been a passive situation of oversupply of low-grade ordinary springs and high-end products in short supply for a long time. Driven by key investment in the development of agricultural machinery, construction machinery, general machinery, environmental protection machinery, automobiles and other host industries, the output of springs will increase. The most important thing is that the structure of spring products will change, the proportion of high-tech products will greatly increase, and the number of export products will also increase to a certain extent. It can be seen that in the next few years, my country’s spring market will maintain a relatively ideal growth space.

Automobile industry: The automobile and engine industry is the largest market in the spring industry, accounting for 50% of the industry’s total industrial output value. The automobile industry, especially the car industry, is growing rapidly. The trend of cars entering the family is increasing year by year, and the demand for high-end springs is increasing. With the increase of global environmental awareness, the development and putting into use of environmentally friendly vehicles also kicked off the curtain. In addition, the country’s increased investment in infrastructure construction will inevitably drive the development of trucks and provide a market for springs.

Spring exports to overseas markets may be weakened

According to customs statistics, in the past two years, China exports about 22,000 tons of springs each year. Most of them are leaf springs, and coil springs only account for a small part of them. The product structure is dominated by household hardware springs, and the destination is Hong Kong and Taiwan. A small amount of mold springs and auto parts springs are exported to Japan, Europe, America, and Southeast Asia, but they have not really entered OEM supporting facilities. In recent years, in order to reduce procurement costs, some American automobile companies have shifted the procurement of auto parts including springs to China, setting a precedent for Chinese springs to enter the US OEM supporting market. With the establishment of China’s status as a major manufacturing country and the improvement of technology and product quality in the spring industry, the spring export market has a bright future. It is estimated that by 2005, the proportion of export spring products in the industry output value will reach about 5%, and the export value will increase to 70 million US dollars.

According to statistics, the export of spring products in industrialized countries accounts for about 15% to 20% of the industry’s output value. From a long-term perspective, there is a large potential market for my country’s spring exports. Chinese spring companies should take specific actions based on their own conditions, such as strengthening cooperation with foreign companies and introducing advanced foreign technology to improve product quality, enhance competitiveness, create well-known brands, expand the international influence of products, and seize a larger international market Share.

The impact of Simmons’ bankruptcy on spring companies is absolutely profound, and it is also a wake-up call for those hardware companies that manufacture springs. It will take time to verify whether Simmons will come back to life. let us wait and see.