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What parameters should be paid attention to when selecting bronze bushings? To correctly select the size and tolerance of the bronze bushing, it is necessary to combine the matching conditions (such as load, speed, clearance requirements) and installation scenarios (such as shaft diameter, hole seat size), and pay attention to the matching of core parameters. The following is a detailed explanation from three dimensions: size determination, tolerance selection, and key parameters: 一. Size determination: "Shaft diameter + fit clearance" as the coreThe size of the bronze bushing must match the shaft diameter and the mounting hole seat. The core is to determine the three parameters of inner diameter (matching with the shaft), outer diameter (matching with the hole seat), and length: 1. Inner diameter (d): "dynamic matching" with shaft diameterBasic basis: The inner diameter of the bushing needs to be slightly larger than the shaft diameter (forming a matching clearance), and the size of the clearance depends on the working conditions:Low speed and heavy load (such as stamping equipment): a smaller clearance (0.01-0.03mm) is required to avoid local wear caused by shaking of the shaft and bushing;High speed and light load (such as fan shaft): a larger clearance (0.03-0.08mm) is required to reserve space for thermal expansion (the thermal expansion coefficient of bronze is higher than that of steel) to prevent high temperature jamming;Good lubrication scenario (such as oil bath lubrication): the clearance can be slightly larger (0.05-0.1mm); poor lubrication scenario (such as dry friction): the clearance needs to be strictly controlled (≤0.03mm) to avoid impurities from entering.Calculation formula: Recommended inner diameter d = shaft diameter + matching clearance, the shaft diameter accuracy is usually h6/h7 (tolerance zone of the shaft), and the bushing inner diameter tolerance is correspondingly selected H7/H8 (tolerance zone of the hole) to form a "clearance fit". 2. Outside diameter (D): "statically fixed" to the hole seat The outer diameter of the bushing needs to form a "transition fit" or "interference fit" with the mounting hole seat (usually cast iron or steel) to prevent the bushing from sliding in the hole seat:Light load, disassembly scenario: transition fit (such as bushing tolerance g6, hole seat tolerance H7), allow slight clearance or interference (±0.01mm);Heavy load, vibration scenario: interference fit (such as bushing tolerance r6, hole seat tolerance H7), interference amount 0.01-0.05mm (adjusted according to the diameter size, the larger the diameter, the greater the interference amount), to ensure that the bushing is firmly fixed. 3. Length (L): Balance "support stability" and "heat dissipation" Too short: insufficient support area, too large load per unit area, easy to cause bushing deformation;Too long: difficult to dissipate heat (although bronze has good thermal conductivity, long bushings are prone to high temperatures due to poor heat dissipation in the middle), and increased processing difficulty;Recommended ratio: usuallyL=(1.5−3)×d (inner diameter), special scenarios (such as slender shafts) can be increased toL=4−5d, but an oil groove design is required to assist heat dissipation.

Bronze bushings, steel bushings, and plastic bushings all play the role of friction reduction and support in mechanical transmission, but due to differences in material properties, their application scenarios and performance advantages have different focuses. The core advantage of bronze bushings is reflected in the balance of comprehensive performance, especially in terms of friction characteristics, adaptability and durability, which are significantly different from steel bushings and plastic bushings. The specific comparison is as follows: 一. Compared with steel bushings: the "low friction + maintenance-free" advantage of bronze bushingsThe core characteristics of steel bushings (such as bearing steel and carbon steel bushings) are "high strength and high hardness", but the friction characteristics and adaptability are weak. The advantages of bronze bushings are concentrated in the following aspects: 1. Better self-lubrication and anti-seizure performanceThe surface of the steel bushing is smooth but has no self-lubrication ability. It must rely on continuous lubrication (such as oil film, grease). If the lubrication is interrupted, it is easy to have "dry friction" with the shaft (mostly steel), causing rapid wear and even seizure of both;Bronze bushings (especially those containing lead and tin) contain free lubricants (such as lead particles) and have a low friction coefficient (about 0.05-0.15, which can reach 0.3-0.5 when the steel bushing is not lubricated). It is not easy to bite even if the lubrication is insufficient. It is suitable for scenes with intermittent lubrication or difficult lubrication (such as underwater and dusty environments). 2. Stronger protection for the shaftSteel bushings have high hardness (HRC50-60). When used with steel shafts, if there are impurities or installation deviations, the shaft surface is easily scratched due to "hard-to-hard" friction, increasing the shaft maintenance cost;Bronze bushings have moderate hardness (HB80-200) and are "soft wear-resistant materials". They will wear themselves first during friction, reducing damage to the shaft, and are especially suitable for precision shaft systems (such as machine tool spindles). 3. Better corrosion resistance and shock absorptionSteel bushings are prone to rust (need electroplating or coating protection, which is costly), and have strong rigidity and poor shock absorption. They are prone to noise and fatigue cracks under vibration conditions; Bronze bushings (such as aluminum bronze and tin bronze) are naturally resistant to seawater, fresh water and weakly corrosive media, and do not require additional anti-corrosion treatment. The material toughness is better than steel, and it can absorb part of the vibration energy and reduce operating noise. 二. Compared with plastic bushings: the "high load + temperature resistance" advantage of bronze bushingsThe core features of plastic bushings (such as PTFE, nylon, and polyoxymethylene bushings) are "lightweight, low cost, and low friction", but the physical properties are limited. The advantages of bronze bushings are reflected in their adaptability to extreme working conditions: 1. Stronger load-bearing capacity and wear resistancePlastic bushings have low compressive strength (usually 50MPa) for a long time, and the wear rate increases sharply with the increase of load;Bronze bushings (such as aluminum bronze) have a compressive strength of more than 600MPa, can withstand medium and high loads (50-300MPa) and impact loads, and have a wear resistance 5-10 times that of plastic bushings (especially in dusty and granular environments, plastics are prone to rapid failure due to scratches).2. Wider temperature resistance and environmental adaptabilityDue to the characteristics of polymer materials, plastic bushings are usually used at temperatures below 100°C for long periods of time (for example, nylon bushings will soften at temperatures above 80°C, and PTFE will decompose at temperatures above 260°C), and are susceptible to corrosion by grease and solvents (for example, gasoline will dissolve some plastics);Bronze bushings can work stably in a temperature range of -200°C to 300°C, are resistant to corrosion by media such as grease, acid, alkali, and seawater, and are suitable for harsh environments such as high temperature (such as metallurgical equipment), oil pollution (such as engines), and humidity (such as ships).3. Higher dimensional stabilityPlastic bushings are prone to dimensional deviations due to humidity changes (water absorption and expansion) or temperature fluctuations (thermal expansion and contraction), affecting the fit accuracy;Bronze has a low thermal expansion coefficient (about 18×10⁻⁶/°C, only 1/3 of nylon), and does not absorb water. It can still maintain a stable fit clearance in high and low temperature or humid environments, and is suitable for precision transmission scenarios (such as machine tool guides).三. The "comprehensive balance" of bronze bushings: adaptable to more complex working conditionsSteel bushings are suitable for "pure heavy load, low friction requirements, continuous lubrication" scenarios (such as fixed support of large machinery), plastic bushings are suitable for "light load, normal temperature, clean" scenarios (such as office equipment, small household appliances), and the advantage of bronze bushings lies in the comprehensive ability to take into account "medium load + medium speed + complex environment":It is neither dependent on continuous lubrication like steel bushings, nor limited by load and temperature like plastic bushings;Especially in scenarios with "unstable lubrication" (such as intermittent operation), "harsh environment" (such as moisture, dust), and "high requirements for shaft protection" (such as precision shaft systems), the durability and reliability of bronze bushings are more prominent. In summary, the core advantage of bronze bushings is the comprehensive performance of **"self-lubrication + medium and high load bearing + wide environmental adaptability + shaft-friendly"**, which makes it the "first choice for complex working conditions" in mechanical transmission, especially suitable for the middle ground that steel bushings and plastic bushings are difficult to cover.

What special requirements do different heat treatment processes (such as quenching, annealing, and tempering) have for material trays/frames? Different heat treatment processes (quenching, annealing, tempering, etc.) have significant differences in temperature range, atmosphere, cooling method and workpiece state, so the performance requirements for the tray/frame also have different emphases. The following are the special requirements of the main processes for the tray/frame: 一. Quenching process: resistance to sudden changes and impactQuenching is a process in which the workpiece is heated to above the critical temperature and then rapidly cooled (such as water cooling, oil cooling) to obtain high strength. The core requirements for the tray/frame are thermal shock resistance and structural stability.Temperature characteristics: The heating temperature is high (usually 800-1200℃), and the temperature drops sharply during the cooling stage (the temperature difference can reach hundreds of degrees Celsius).Special requirements:Strong thermal shock resistance: It is necessary to withstand the thermal stress caused by rapid cooling to avoid cracking (such as ceramic trays are brittle and not suitable for quenching; metal trays need to be made of heat-resistant steel such as 310S, which has a stable thermal expansion coefficient and good resistance to sudden changes).Strong structure: The workpiece may impact the tray due to collision or deadweight during cooling, and the tray must have sufficient mechanical strength (such as the grid structure needs to be welded firmly to avoid deformation).Resistant to medium corrosion: If oil cooling is used, the tray must be resistant to oil stains and high-temperature oil erosion (metal materials are better than ceramics, and ceramics are easily affected by oil stains and their lifespan is affected). 二. Annealing process: high temperature resistance and creep resistanceAnnealing is to slowly heat the workpiece to a certain temperature, keep it warm for a period of time and then slowly cool it down. The purpose is to eliminate internal stress and soften the workpiece. The core requirements for the tray/frame are long-term high temperature resistance and dimensional stability.Temperature characteristics: The heating temperature is medium (600-1000℃), but the insulation time is long (several hours to dozens of hours), and the cooling rate is slow.Special requirements:High temperature creep resistance: Under long-term high temperature, the tray needs to resist slow deformation (creep) to avoid bending or collapse due to load-bearing (high nickel-chromium heat-resistant steel such as 310S has better creep resistance than ordinary heat-resistant steel and is suitable for long-term insulation).Uniform heat conduction: The tray material needs to have good thermal conductivity to avoid uneven heating of the workpiece due to local overheating (metal trays have better thermal conductivity than ceramics and are more suitable for annealing).Oxidation resistance: Annealing is mostly carried out in air atmosphere, and the tray needs to resist long-term high temperature oxidation (such as the formation of an oxide film on the surface of heat-resistant steel to protect the substrate). 三. Tempering process: medium temperature stability, low deformationTempering is to heat the workpiece to a lower temperature (usually 150-650℃) after quenching, and cool it after insulation to eliminate brittleness. The requirements for the tray/frame are relatively loose, but medium temperature stability is required.Temperature characteristics: low temperature and small fluctuation, medium insulation time.Special requirements:Dimensional stability: no need to withstand extreme high temperatures, but slight deformation caused by repeated use must be avoided (such as cast iron trays below 600℃ can meet the requirements and have lower costs).Easy to clean: After tempering, the surface of the workpiece may have oxide scale falling off, and the tray needs to be easy to clean (such as metal trays with smooth surfaces are better than porous ceramics to reduce residue accumulation). 四. Carburizing/nitriding process: corrosion resistance, no impurity pollutionCarburizing (900-1100℃) and nitriding (500-600℃) are processes for infiltrating carbon or nitrogen elements into the surface of the workpiece to increase the hardness. The core requirements for the tray/frame are chemical corrosion resistance and no secondary pollution.Atmosphere characteristics: There may be corrosive gases (such as CO, H₂S) produced by the decomposition of the penetrant (such as kerosene, ammonia) in the furnace, and it is necessary to avoid the reaction between the tray material and the penetrant to contaminate the workpiece.Special requirements:Strong corrosion resistance: It is necessary to resist the erosion of the penetrant (such as heat-resistant alloys Inconel and Hastelloy are resistant to sulfide corrosion, which is better than ordinary heat-resistant steel; ceramic materials have good chemical stability and can also be used).Low impurity release: The components of the tray itself cannot diffuse to the surface of the workpiece (such as cast iron with a high carbon content, which may cause excessive carburization of the workpiece and should be avoided).Structural permeability: Carburizing/nitriding requires that the gas evenly contact the workpiece, and the material tray should adopt a grid or porous structure (metal welded grid is better than closed ceramic tray to facilitate gas circulation). 五. High-temperature sintering process (such as powder metallurgy): ultra-high temperature resistance, low pollutionHigh-temperature sintering is a process of heating the powder body to below the melting temperature to make it dense (the temperature often reaches 1000-1700℃). The core requirements for the tray are ultra-high temperature resistance and cleanliness.Temperature characteristics: extremely high temperature (partly exceeding 1500℃), and may be carried out in vacuum or inert gas.Special requirements:Ultra-high temperature resistance: Need to withstand high temperatures above 1600℃ (such as silicon carbide ceramics, graphite trays, graphite needs to be combined with inert gas to prevent oxidation).No adhesion: The workpiece (such as powder metallurgy parts) is easy to adhere to the tray at high temperature, and the tray surface needs to be smooth or coated with an isolation layer (ceramic material is better than metal and is not easy to metallurgically bond).Low volatility: In a vacuum environment, the tray material needs to be free of volatiles (such as alloy elements in metal trays may volatilize and pollute the workpiece, ceramics are more suitable). Email: cast@ebcastings.com

What is the highest temperature they can withstand? The need for heat treatment trays to withstand high temperatures is determined by their core role in the heat treatment process, and the maximum temperatures that trays of different materials can withstand vary greatly, as follows: 1. Direct contact with high temperature environmentHeat treatment (such as quenching, annealing, tempering, carburizing, etc.) needs to be carried out in a high-temperature furnace, and the temperature is usually above 500℃. Some processes (such as high-temperature sintering and brazing) even exceed 1000℃. As a carrier for the workpiece, the tray must be placed in the furnace throughout the process and must withstand the high temperature environment in the furnace. Otherwise, it will be deformed, melted or oxidized due to high temperature, causing the workpiece to fall, contaminate or fail the process. 2. Ensure structural stabilityThe material will soften, creep (slowly deform) or oxidize at high temperatures. If the tray is not resistant to high temperatures, it will bend, crack, collapse and other problems. It will not only affect its own service life, but also cause unstable stacking of workpieces due to structural failure, causing uneven heating, collision deformation and other quality problems. 3. Adapt to temperature fluctuationsDuring the heat treatment process, there may be fluctuations in temperature rise and fall (such as rapid cooling during quenching). The tray needs to withstand the thermal stress caused by the sudden temperature change to avoid breaking (such as ceramic trays) or cracking (such as cast iron trays) due to poor thermal shock resistance of the material. Material Type Specific Material Maximum Temperature (℃) Remarks Metal Material Ordinary heat-resistant steel (304) 600-800 Suitable for medium and low temperature heat treatment High nickel-chromium heat-resistant steel (310S) 1200-1300 Long-term use temperature recommendation ≤1100℃ Heat-resistant alloy (Inconel) 1100-1200 The creep resistance is better than that of ordinary heat-resistant steel Cast iron (grey cast iron/ductile iron) 500-600 Easily oxidized and embrittled above 600℃ Ceramic Material Alumina ceramics 1600-1700 Pure alumina ceramics have better high temperature resistance Silicon carbide ceramics 1600-1800 Thermal shock resistance is better than that of alumina Other Materials Graphite 2000-2500 Need to be used in vacuum or inert gas (easy to oxidize above 500℃ in air) SummaryHigh temperature resistance is the core performance requirement of heat treatment trays. The maximum temperature they can withstand depends on the material: metal trays are usually 600-1300℃, ceramic trays can reach above 1600℃, and graphite trays can withstand temperatures above 2000℃ (protective atmosphere required). When making actual choices, a comprehensive judgment must be made based on the specific heat treatment temperature, insulation time, and environment (such as whether it is exposed to corrosive gases) to avoid failure due to insufficient material temperature resistance. Email: cast@ebcastings.com

When designing a sow mold, it is necessary to combine the thermodynamic properties of metal casting, the service life of the mold, and the quality requirements of the ingot, and focus on the following process parameters: 一. Cavity size and structural parameters•Cavity volume and size: It is necessary to match the weight (usually hundreds to several tons) and shape (such as rectangle, trapezoid) of the target ingot to ensure that the depth and width of the cavity match the volume of the molten metal to avoid incomplete or wasteful ingot molding due to dimensional deviation. •Cavity slope (draft slope): To facilitate demolding, the side wall of the cavity needs to be designed with a certain slope (usually 0.5°-2°). Too small a slope is prone to mold sticking, and too large a slope may affect the dimensional accuracy of the ingot. •Fillet and edge processing: The bottom and corners of the cavity need to be rounded (R angle) to reduce stress concentration and avoid cracks in the mold due to thermal shock; at the same time, prevent shrinkage or cold shut at the corners of the ingot. 二. Thermal and cooling parameters •Wall thickness design: The mold wall thickness needs to be calculated based on the melting point of the casting metal (such as aluminum about 660℃, copper about 1083℃) and heat capacity to ensure that it can withstand the thermal shock of high-temperature molten metal and control the heat dissipation rate through reasonable wall thickness (too thick will cool too slowly, too thin will be easy to deform). •Cooling system layout: If forced cooling (such as water cooling) is used, the position, diameter and spacing of the cooling channel need to be designed. The channel needs to avoid the stress concentration area of ​​the cavity and keep a reasonable distance from the cavity surface (usually ≥50mm) to ensure uniform cooling of the ingot and reduce defects such as shrinkage cavities and cracks. •Thermal expansion compensation: Considering the solidification shrinkage rate of the molten metal (such as the shrinkage rate of aluminum is about 1.3%-2%) and the thermal expansion coefficient of the mold itself, reserve compensation in the cavity size design to avoid ingot size deviation or mold locking. 三. Metal liquid flow and filling parameters •Gate and runner design: The gate position should avoid the metal liquid directly impacting the bottom of the cavity (to prevent splashing and oxidation), and the runner cross section should match the metal liquid flow rate to ensure uniform filling speed (generally controlled at 0.5-1.5m/s) and reduce slag rolls and pores. •Vent structure: Design venting grooves (width 0.1-0.3mm, depth 0.5-1mm) at the top or corner of the cavity to avoid air encapsulation and pores when the metal liquid is filled, and prevent incomplete filling due to gas back pressure. 四. Mechanical performance parameters •Mold strength and rigidity: According to the weight of the ingot (such as 500kg-5 tons) and the static pressure of the molten metal (calculation formula: pressure = molten metal density × height × gravity acceleration), select the appropriate material (such as cast steel, ductile iron) and design the reinforcing rib structure to prevent the mold from deformation or cracking. •Mold release mechanism matching: If mechanical or hydraulic mold release is used, it is necessary to reserve the installation space of the mold release device (such as the ejector hole, the position of the hydraulic cylinder) to ensure that the mold release force (usually 1.5-2 times the weight of the ingot) acts evenly on the bottom of the ingot to avoid damage to the ingot or mold. 五. Material and surface treatment parameters •Material thermal fatigue resistance: For the cyclic process of repeated heating (such as aluminum liquid 660℃) and cooling of molten metal, select materials with moderate thermal conductivity (such as cast steel thermal conductivity of about 40-50W/(m・K)) and high thermal fatigue strength to reduce thermal cracking. •Surface treatment process: Improve surface wear resistance and anti-adhesive aluminum performance through nitriding (hardness up to 50-60HRC), shot peening or coating (such as ceramic coating), reduce demoulding resistance, and reduce erosion and wear of the mold surface by molten metal. These parameters need to be comprehensively optimized in combination with the characteristics of specific casting metals (aluminum, copper, zinc, etc.), production efficiency (such as the number of castings per hour) and quality standards (such as internal flaw detection requirements for ingots), and ultimately achieve the goal of long mold life and high ingot quality. Email: cast@ebcastings.com