Centrifugal Casting Process
Centrifugal Casting Introduction
Centrifugal casting is a metal forming process that utilizes centrifugal force as its core driving force. Molten metal is poured into a high-speed rotating mold, where it is evenly distributed along the inner wall of the mold under centrifugal force, cools, and solidifies, ultimately forming a hollow cylindrical, annular, or tubular casting.
This process is widely used in machinery manufacturing, piping engineering, and the automotive industry due to the high density, excellent mechanical properties, and high production efficiency of the castings. It is also an important forming method for metal parts related to tool storage bags (such as tubular supports, connectors, and wear-resistant bushings).
Centrifugal Casting Process
The core logic of centrifugal casting is “mold rotation → molten metal filling → centrifugal force densification → cooling and solidification → demolding and processing”. The process framework is the same for different process types (horizontal / vertical / inclined), with differences only in details such as mold installation and pouring method.
Suijin Machinery provides standard process flows for large-scale industrial production, while also offering optimized solutions for small-batch customization.
Step 1: Mold Preparation and Inspection
Ensure the mold’s inner wall is smooth, dimensions are within specifications, and there are no defects affecting casting quality; check the mold’s structural safety to prevent malfunctions during high-speed rotation.
Operating Procedures :
- Mold Selection:Select the mold according to the casting type (tubular mold for horizontal centrifugation, ring mold for vertical centrifugation). The material is typically high-strength alloys such as H13 mold steel and Cr12MoV (small molds suitable for tool storage bag accessories generally have an inner diameter of 5-50mm and a length of 100-500mm).
- Dimensional Verification:Use calipers and micrometers to check the mold’s inner diameter, length, and wall thickness tolerances (error ≤ ±0.05mm) to ensure the casting’s dimensional accuracy.
- Defect Inspection: Inspect the mold’s inner wall visually or with an endoscope to remove burrs, scratches, sand adhesion, and other defects (inner wall roughness must be ≤ Ra3.2μm).
- Structural Inspection:Tighten mold flanges, bearings, rotating shafts, and other connecting components to ensure there is no looseness (centrifugal force is extremely high during high-speed rotation; looseness can easily lead to mold breakage).
Step 2: Mold Preheating and Coating
Preheating the mold prevents cracking caused by sudden cooling of the molten metal; applying a release agent reduces adhesion between the casting and the mold, improving surface quality.
Operating Procedure:
- Mold Preheating: Use electric heating, gas heating, or infrared heating to raise the mold temperature to 150-350℃ (temperature varies depending on the material: 150-200℃ for cast iron, 250-350℃ for stainless steel); the temperature must be uniform to avoid localized overheating or undercooling (a thermometer can be used for monitoring);
- Applying Release Agent: After preheating, evenly spray a release agent (common types: graphite powder suspension, water glass + talc coating, special ceramic release agent) onto the inner wall of the mold, controlling the coating thickness to 0.1-0.3mm;
- Secondary Drying: After spraying, continue to maintain the temperature for 10-20 minutes to ensure the release agent is completely dry (to prevent moisture evaporation that could cause porosity in the casting).
- Technical points: The release agent must be evenly applied without any missed spots or accumulation; small molds for tool storage bag accessories can be coated using automatic spraying equipment to ensure consistent coating.
Step 3: Mold Installation and Speed Adjustment
Fix the mold and adjust it to the optimal speed to ensure uniform distribution of molten metal under centrifugal force.
Operating Procedure:
- Mold Installation: Fix the preheated mold onto the spindle of the centrifugal casting machine. For horizontal centrifugation, ensure the mold axis is completely aligned with the spindle (verticality error ≤ 0.02 mm). For vertical centrifugation, ensure the mold is placed horizontally (horizontality error ≤ 0.01 mm).
- Speed Calculation: Calculate the optimal speed based on the casting’s inner diameter and metal density.
- No-Load Testing: Start the centrifugal casting machine and run it unloaded for 5-10 minutes to check the mold’s rotational stability (vibration value ≤ 0.1 mm/s). Pouring can proceed only after confirming no abnormalities are found.
- Safety Precautions: During testing, the safety door must be closed, and operators must stay away from the rotating area. The speed must not exceed the mold’s rated limit (usually 1.2 times the calculated value).
Step 4: Metal Smelting and Composition Testing
The process involves melting raw metal materials into a molten metal that meets specific requirements, ensuring a uniform composition and the absence of impurities.
Operating Procedures:
- Raw Material Preparation: Select raw materials according to the casting material (e.g., pig iron, scrap steel, and inoculant for cast iron; stainless steel billets for stainless steel). Raw materials must be clean and free of oil and rust (to avoid affecting the purity of the molten metal).
- Metal Smelting: Use equipment such as a medium-frequency induction furnace or electric arc furnace for smelting, controlling the smelting temperature (cast iron 1300-1380℃, stainless steel 1500-1550℃, aluminum alloy 680-720℃). Add deoxidizers (e.g., ferromanganese, ferrosilicon) during smelting to remove impurities.
- Composition Analysis: Quickly analyze the chemical composition of the molten metal (e.g., carbon, silicon, manganese content) using a spectrometer to ensure compliance with industry standards (e.g., cast iron parts for tool storage bags must comply with GB/T 9439-2010 standard).
- Slag Removal: After successful smelting, allow the molten metal to stand for 5-10 minutes to allow impurities and slag to float to the surface, then remove them using a skimmer (to prevent impurities from entering the casting and causing defects).
Step 5: Pouring Operation
While the mold is rotating at high speed, molten metal is smoothly poured into the mold to ensure complete filling and uniform wall thickness.
Operating Procedures:
- Pouring Preparation: Confirm that the mold rotation speed is stable at the set value and the molten metal temperature meets the requirements (pouring temperature 20-50℃ lower than melting temperature);
- Pouring Methods:Horizontal Centrifugal: Use “end-pouring” or “rain-type pouring,” continuously injecting molten metal along the gating gate at one end of the mold (flow rate controlled at 0.5-2L/s, adjusted according to casting length), avoiding impact on the inner wall of the mold;Vertical Centrifugal: Use “center-pouring,” injecting molten metal into the mold through the central runner, ensuring uniform distribution along the circumference;
- Filling Control: Observe the filling of the molten metal during pouring (through the mold observation window or infrared thermometer) to avoid flow interruption and overflow; adjust the filling time according to the casting length (usually 5-15 seconds for small tubular fittings);
- Shrinkage Treatment: After pouring, if the casting wall thickness is large (>20mm), a small amount of molten metal can be added at the gating gate to prevent shrinkage cavities during cooling.
Step 6: Cooling and Solidification Control
To control the cooling rate to ensure uniform solidification of the molten metal from the outside in, reducing internal stress and defects.
Operational Procedures:
- Cooling Methods:Natural Cooling: Small castings (such as tool storage bag bushings) can cool naturally with the mold for 5-15 minutes.
Forced Cooling: Large castings or high-melting-point metal parts (such as stainless steel pipes) use water cooling (spraying water onto the outer wall of the mold) or air cooling (blowing compressed air), for 15-60 minutes. - Cooling Control: The cooling rate must be matched to the material (5-10℃/min for cast iron, 3-8℃/min for steel) to avoid cracking due to excessive speed or loose structure due to insufficient speed.
- Heating Stage: When the surface temperature of the casting drops to 300-400℃, forced cooling can be stopped, and the casting should be held in the mold for 5-10 minutes to release internal stress.
- Technical Points: The mold must be rotated during the cooling process (until the casting is completely solidified) to prevent uneven wall thickness caused by gravity.
Step 7: Demolding and Preliminary Cleaning
Safe demolding, removing risers, burrs, and other excess structures.
Operating Procedures:
- Demolding Timing: When the casting has completely solidified and the temperature has dropped to 200-300℃ (touchable by hand), stop mold rotation and activate the demolding device (ejector rod for horizontal centrifugal casting, hydraulic lifting platform for vertical centrifugal casting);
- Safe Demolding: Small castings can be removed manually with assistance; large castings require a crane to prevent deformation due to collision;
- Preliminary Cleaning: Use an angle grinder and sander to remove risers, burrs, and other imperfections (risers on tool storage bags are usually small and can be removed in one go); use a wire brush to clean the surface of the casting to remove any remaining release agent and oxide scale.
Step 8: Subsequent Processing and Quality Inspection
Machining improves precision, and inspection identifies defects to ensure the castings meet usage requirements.
Operational Procedures:
- Machining
- Quality Inspection
- Rust Prevention Treatment
Suijin Casting Solution
The core of centrifugal casting lies in three main stages: precise control of mold rotation, molten metal filling, and cooling and solidification. Each step requires matching the material properties and casting structure (e.g., for small parts, emphasis should be placed on mold precision, coating uniformity, and automated pouring to ensure consistency in mass production). Through standardized process operation, dense, dimensionally accurate hollow metal castings can be stably produced, providing a highly durable and cost-effective molding solution for metal parts in tool storage bags.