Cast iron inner container concentric circle polishing process
By using concentric polishing technology and high-temperature nitriding treatment for the cast iron inner liner, the problem of dotted black pits after polishing of the cast iron inner liner was solved, improving the finished product qualification rate and service life, and achieving uniform heating and rust prevention of the inner liner.
Patent Information
- Application Number
- CN202610292237.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-11
- Publication Date
- 2026-04-10
AI Technical Summary
The existing polishing process for cast iron liners results in dotted black pits after high-temperature nitriding, leading to a low finished product qualification rate and high cost, making it difficult to meet the requirements for mass production of uncoated cast iron liners.
The cast iron inner liner adopts a concentric circle polishing process, which includes multiple polishing processes such as rough polishing, fine inner polishing, fine outer polishing, pot mouth treatment, nitriding and oiling maintenance, forming a regular and uniform concentric circle texture. Combined with high-temperature nitriding treatment, it enhances the rust prevention effect.
It effectively reduces the defects of dotted black pits, improves the physical non-stick effect and heating uniformity of the inner liner, and increases the finished product qualification rate and service life of uncoated cast iron inner liners.
Smart Images
Figure CN121821024A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of kitchen appliance inner pot processing technology, specifically to a surface polishing process for an uncoated cast iron rice cooker inner pot and an electric pressure cooker inner pot. Background Technology
[0002] As core cooking components, rice cooker and pressure cooker inner pots are currently manufactured using cast iron as the material for uncoated inner pots. However, cast iron cookware, without additional coatings, is prone to corrosion due to its metallic properties. Rust prevention is particularly important for cast iron during processing and in daily use. Currently, high-temperature nitriding is the primary rust-prevention process for uncoated cast iron rice cooker inner pots. However, high-temperature nitriding of cast iron inner pots has a fatal flaw: prolonged high-temperature nitriding easily produces pitted black specks, resulting in low finished product quality but high production cost. The surface smoothness and texture regularity directly affect the product qualification rate, heating uniformity, non-stick effect, rust prevention effect, service life, and overall product compliance rate after long-term, batch high-temperature nitriding. Traditional inner pot polishing processes mostly involve bright surface machining or sandblasting. This type of polishing method for cast iron liners has drawbacks in high-temperature nitriding technology. If the nitriding time is too short, the nitrided layer may not penetrate deeply enough, leading to rust and oxidation of the nitrided layer after a short period of use. If the nitriding time is too long, it can result in pinpoint black pitting, causing an excessive number of defective products. The cost is too high, making it difficult to meet the requirements for high-quality finished products in mass production of uncoated cast iron liners.
[0003] In view of the above, the inventors propose the following technical solution. Summary of the Invention
[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a concentric circular spiral texture polishing process for uncoated cast iron rice cooker inner pots and electric pressure cooker inner pots. This solves the problem that the existing cast iron inner pot polishing process results in dotted black pits after high-temperature nitriding, leading to a low product qualification rate. It hides the dotted black pit defects and improves the physical non-stick properties and heating consistency of the inner pot.
[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a concentric polishing process for cast iron inner liners, comprising:
[0006] Step S1: Inner liner casting and pretreatment;
[0007] Step S2: Rough polishing. The inner liner is rotated at a high speed of 800-1500 r / min, and the polishing wheel is rotated at a high speed of 2500-3000 r / min. The polishing wheel is controlled to move from the center of the bottom of the inner wall of the inner liner to the edge by a feed speed of 5-8 mm / s, forming a concentric circle trajectory on the inner wall of the inner liner.
[0008] Step S3: Fine internal polishing treatment. The inner liner is rotated at a high speed of 1500-2000 r / min, and the polishing wheel is rotated at a high speed of 2800-3200 r / min. The polishing wheel is controlled to move from the center of the bottom of the inner wall of the inner liner to the edge by a feed speed of 1-3 mm / s, forming a concentric circle trajectory on the inner wall of the inner liner.
[0009] Step S4: Fine external polishing. Turn the inner pot over so that the opening of the inner pot faces downwards and fix it. Rotate the inner pot at a high speed of 1300-1800 r / min and the polishing wheel at a high speed of 2800-3200 r / min. By controlling the polishing wheel to move from the edge of the pot opening to the center of the bottom of the inner pot at a feed speed of 1-3 mm / s, the outer wall of the inner pot is polished.
[0010] Step S5: Pot rim treatment;
[0011] Step S6: Nitriding treatment;
[0012] Step S7: Clean after nitriding;
[0013] Step S8: Apply oil for maintenance.
[0014] Furthermore, in the above technical solution, in step S2, the polishing wheel speed is controlled at 2800 r / min, the feed speed is 6 mm / s, the inner liner speed is 1300 r / min, and the surface roughness of the inner liner after rough polishing is controlled at 3.2-6.3 μm.
[0015] Furthermore, in the above technical solution, in step S2, the polishing wheel is a 75# alloy wheel, the contact pressure between the polishing wheel and the inner liner surface is 1.5-2.0MPa, and the 75# alloy wheel is controlled to move from the center of the bottom of the inner liner to the edge of the inner liner wall to polish, remove casting defects and oxide layer from the surface of the blank, form basic concentric circle thread texture, and the surface roughness is 4.5μm.
[0016] Furthermore, in the above technical solution, in step S3, the polishing wheel speed is controlled at 3000 r / min, the feed speed is 2 mm / s, the lower plate speed of the inner liner is 1500 r / min, and the surface roughness of the inner liner is reduced to 0.2-0.8 μm after fine polishing.
[0017] Furthermore, in the above technical solution, in step S3, the polishing wheel is a 150# steel wire wheel, the contact pressure between the polishing wheel and the inner liner surface is 1.5-2.0MPa, and the 150# steel wire wheel is controlled to move from the center of the bottom of the inner liner to the edge of the inner liner wall for fine polishing, so that the polishing texture of the inner liner wall maintains a complete concentric circle thread texture and the surface roughness is 0.5μm.
[0018] Furthermore, in the above technical solution, in step S4, the polishing wheel uses a 120# abrasive belt, the rotation speed of the 120# abrasive belt is controlled at 3000 r / min, the feed speed is 2 mm / s, the rotation speed of the inner liner is 1500 r / min, the contact pressure between the polishing wheel and the surface of the inner liner is 1.5-2.0 MPa, and the surface roughness is 0.5 μm.
[0019] Furthermore, in the above technical solution, in step S5, a YG6X cutting head is used on a lathe with a rotation speed of 300 r / min to flatten the inner liner opening plane, and a YG6X cutting head is used on a lathe with a rotation speed of 250 r / min to perform fine flattening on the outer edge of the inner liner.
[0020] Furthermore, in the above technical solution, in step S6, the inner liner is placed in a carburizing furnace, and after the air is vented, the carburizing furnace is heated to 600°C for 24 hours of high-temperature nitriding to form a sufficient nitriding layer.
[0021] Furthermore, in the above technical solution, step S7 involves first wiping away surface dust with a scouring pad and removing the tiny protrusions on the surface of the nitrided layer to make the concentric circle texture more delicate, then rinsing it with tap water and preheating it to 150°C for drying.
[0022] Furthermore, in the above technical solution, the pretreatment in step S1 includes: fixing the inner liner on the spindle fixture of the CNC spinning equipment, using a high-pressure air gun to remove metal debris and oil stains from the surface of the blank; and performing heat treatment on the blank, with the temperature controlled at 60-80℃ and the time at 15-20min, to reduce surface stress deformation caused by temperature difference during the polishing process.
[0023] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:
[0024] 1. This invention employs a multi-stage polishing process—"rough polishing—fine internal polishing—fine external polishing—pot mouth treatment—nitriding—cleaning after nitriding—oiling and curing"—to create a regular and uniform concentric circle texture on the surface of the cast iron inner liner. The surface roughness of the inner wall is 120 mesh, and the texture depth is controlled within ±0.4mm. This effectively reduces the excessive number of defective products caused by dotted black pitting defects, significantly improving the physical non-stick effect and heating uniformity of the inner liner. It also increases the yield rate of uncoated cast iron inner liners after long-term high-temperature nitriding in batch processing.
[0025] 2. Pot rim treatment: Since neither rough polishing nor fine polishing can reach the pot rim, a YG6X cutter head is used on a lathe with a speed of 300 r / min to flatten the inner pot rim. The outer edge of the inner pot is finely flattened using a YG6X cutter head on a lathe with a speed of 250 r / min.
[0026] 3. Nitriding for rust prevention: The inner liner is nitrided at high temperature with gas after fine polishing, which upgrades the ferric oxide on the surface of the cast iron inner liner to magnetite. After nitriding, a sufficient nitriding layer is formed to enhance the rust prevention effect of the cast iron inner liner.
[0027] 4. Cleaning after nitriding can remove surface dust and tiny bumps on the nitrided layer, making the concentric circle texture more delicate.
[0028] 5. Applying oil for maintenance not only enhances the rust prevention performance of the inner liner but also further optimizes the surface texture and extends the service life of the inner liner. Attached Figure Description
[0029] Figure 1 This is a cross-sectional schematic diagram of the present invention.
[0030] Figure 2 This is a schematic diagram of the polishing trajectory of the present invention.
[0031] Figure 3 This is a diagram illustrating the actual effect of the invention. Detailed Implementation
[0032] The present invention will be further described below with reference to specific embodiments and accompanying drawings.
[0033] A concentric circular thread texture polishing process for cast iron inner pots, including but not limited to those used in rice cookers and electric pressure cookers.
[0034] See Figures 1 to 3 The diagram shown is a schematic of the inner liner structure produced by a concentric circle polishing process for cast iron inner liners. This polishing process includes:
[0035] Step S1: Inner pot casting and pretreatment. First, the HT-150 gray cast iron blank is melted into molten iron at 1800℃ and cast into an inner pot blank for a rice cooker or electric pressure cooker. Then, the inner pot is fixed on the spindle fixture of a CNC spinning machine. A high-pressure air gun is used to remove metal debris and oil stains from the surface of the blank. The blank is then heat-treated at a temperature of 60-80℃ for 15-20 minutes to reduce surface stress deformation caused by temperature difference during polishing.
[0036] Step S2: Rough polishing. The inner liner is rotated at a high speed of 800-1500 r / min, and the polishing wheel is rotated at a high speed of 2500-3000 r / min. The polishing wheel is controlled to move from the center of the bottom of the inner wall of the inner liner to the edge by a feed speed of 5-8 mm / s, forming a concentric circle trajectory on the inner wall of the inner liner.
[0037] Step S3: Fine internal polishing treatment. The inner liner is rotated at a high speed of 1500-2000 r / min, and the polishing wheel is rotated at a high speed of 2800-3200 r / min. The polishing wheel is controlled to move from the center of the bottom of the inner wall of the inner liner to the edge by a feed speed of 1-3 mm / s, forming a concentric circle trajectory on the inner wall of the inner liner.
[0038] Step S4: Fine external polishing. Turn the inner pot over so that the opening of the inner pot faces downwards and fix it. Rotate the inner pot at a high speed of 1300-1800 r / min and the polishing wheel at a high speed of 2800-3200 r / min. By controlling the polishing wheel to move from the edge of the pot opening to the center of the bottom of the inner pot at a feed speed of 1-3 mm / s, the outer wall of the inner pot is polished.
[0039] Step S5: Pot opening treatment. On a lathe, use a YG6X cutter head and set the speed to 300 r / min to flatten the inner pot opening. On the outer edge of the inner pot, use a YG6X cutter head and set the speed to 250 r / min on a lathe to perform fine flattening.
[0040] Step S6: Nitriding treatment. Place the inner liner in a carburizing furnace. After venting the air, heat the carburizing furnace to 600°C for 24 hours of high-temperature nitriding to form a sufficient nitriding layer.
[0041] Step S7: Clean after nitriding. First, use a scouring pad to wipe away the surface dust and remove the tiny bumps on the surface of the nitrided layer to make the concentric circle texture more delicate. Then, rinse with tap water and preheat to 150℃ to dry.
[0042] Step S8: Oiling and curing. Set the inner drum speed of the automatic oiling machine to 800 r / min and apply edible oil evenly. After drying at 300℃ for 20 minutes, the entire process is complete.
[0043] In step S2, the polishing wheel speed is controlled at 2800 r / min, the feed speed is 6 mm / s, the inner liner speed is 1300 r / min, and the surface roughness of the inner liner after rough polishing is controlled at 3.2-6.3 μm, and the texture depth is controlled at ±0.6 mm.
[0044] In step S2, a 75# alloy grinding wheel is used for polishing. The contact pressure between the polishing wheel and the inner liner surface is 1.5-2.0 MPa. The 75# alloy grinding wheel is controlled to move from the center of the bottom of the inner liner to the edge of the inner liner wall to polish, remove casting defects and oxide layer from the surface of the blank, form basic concentric circle thread texture, and the surface roughness is 4.5 μm.
[0045] The spiral texture moves from the center of the bottom of the inner liner to the edge of the inner liner wall for polishing, and the polishing texture of the inner liner wall forms a basic concentric spiral texture.
[0046] In step S3, the polishing wheel speed is controlled at 3000 r / min, the feed speed is 2 mm / s, the lower plate speed of the inner liner is 1500 r / min, and the surface roughness of the inner liner is reduced to 0.2-0.8 μm after fine polishing, and the texture depth is controlled within ±0.4 mm.
[0047] In step S3, a 150# steel wire wheel is used for polishing. The contact pressure between the polishing wheel and the inner liner surface is 1.5-2.0MPa. The 150# steel wire wheel is controlled to move from the center of the bottom of the inner liner to the edge of the inner liner wall for fine polishing, so that the polishing texture of the inner liner wall maintains a complete concentric circle thread texture and the surface roughness is 0.5μm.
[0048] In step S4, a 120# abrasive belt is used for polishing. The rotation speed of the 120# abrasive belt is controlled at 3000 r / min, the feed speed is 2 mm / s, the rotation speed of the inner liner is 1500 r / min, the contact pressure between the polishing wheel and the surface of the inner liner is 1.5-2.0 MPa, and the surface roughness is 0.5 μm.
[0049] In summary, the specific polishing process steps are as follows:
[0050] Step S1 Inner pot casting: Raw HT-150 gray cast iron: melted into molten iron at 1800℃ and cast into the inner pot of rice cooker or electric pressure cooker.
[0051] Step S2: Rough polishing: Use a 75# alloy grinding wheel on the polishing machine. Control the rotation speed of the upper 75# alloy grinding wheel to 2800 r / min, and the rotation speed of the lower wheel with the inner liner fixed to 1300 r / min. The contact pressure between the polishing wheel and the inner liner surface is 1.5-2.0 MPa. Control the 75# alloy grinding wheel to move from the bottom center of the inner liner to the edge of the inner liner wall to polish, remove casting defects and oxide layer from the surface of the blank, and form basic concentric circle thread texture. After rough polishing, the surface roughness of the inner wall of the inner liner is 80 mesh, and the texture depth is controlled within ±0.6 mm.
[0052] Step S3: Fine internal polishing: Using a 150# steel wire wheel on the polishing machine, control the speed of the upper 150# steel wire wheel at 3000 r / min, and the speed of the lower wheel fixing the inner liner at 1500 r / min. The contact pressure between the polishing wheel and the inner liner surface is 1.5-2.0 MPa. Control the 150# steel wire wheel to move from the center of the bottom of the inner liner to the edge of the inner liner wall for fine polishing. After fine polishing, the surface roughness of the inner liner wall is 120 mesh, and the texture depth is controlled within ±0.4 mm.
[0053] Step S4 Fine external polishing: Use a 120# sanding belt on the polishing machine, control the speed of the upper 120# sanding belt to 3000 r / min, fix the inner pot with the inner pot opening facing down on the lower turntable, set the speed of the lower turntable to 1500 r / min, and set the contact pressure between the polishing wheel and the surface of the inner pot to 1.5-2.0 MPa. Control the 120# sanding belt to move from the edge of the pot opening to the center of the bottom of the inner pot, and then move from the bottom of the inner pot to the edge of the pot opening to polish the outer wall of the inner pot.
[0054] Step S5: Pot opening treatment: Using a YG6X cutter head on a lathe, with the inner pot fixed on the turntable and the speed set to 300 r / min, the inner pot opening plane is machined flat. The outer edge of the inner pot is finely flattened using a YG6X cutter head on a lathe with the speed set to 250 r / min.
[0055] Step S6 Nitriding treatment: The finely polished inner liner is subjected to high-temperature nitriding at a gas nitriding temperature of 600℃ for 24 hours to upgrade the ferric oxide on the surface of the cast iron inner liner to magnetite. After nitriding, a sufficient nitriding layer is formed to enhance the rust prevention effect of the cast iron inner liner.
[0056] Step S7 Cleaning after nitriding: After nitriding, first wipe off the surface dust with a scouring pad, then use a cloth wheel polishing device. Set the cloth wheel polishing speed to 2800r / min and the lower plate of the inner liner to 1400r / min. Control the cloth wheel polishing to move from the center of the bottom of the inner liner to the edge of the inner liner wall to clean, remove the tiny protrusions on the surface of the nitrided layer, and make the concentric circle texture more delicate. Rinse with tap water and preheat and dry at 150℃.
[0057] Step S8 Oiling and Curing: Apply cooking oil evenly to the inner drum of the automatic oiling machine at a speed of 800 r / min, and wipe it evenly. Dry it at 300℃ for 20 minutes to complete the entire process.
[0058] Of course, the above description is only a specific embodiment of the present invention and is not intended to limit the scope of the present invention. All equivalent changes or modifications made to the structure, features and principles described in the claims of the present invention should be included in the scope of the claims of the present invention.
Claims
1. A concentric polishing process for cast iron inner liners, characterized in that, include: Step S1: Inner liner casting and pretreatment; Step S2: Rough polishing. The inner liner is rotated at a high speed of 800-1500 r / min, and the polishing wheel is rotated at a high speed of 2500-3000 r / min. The polishing wheel is controlled to move from the center of the bottom of the inner wall of the inner liner to the edge by a feed speed of 5-8 mm / s, forming a concentric circle trajectory on the inner wall of the inner liner. Step S3: Fine internal polishing treatment. The inner liner is rotated at a high speed of 1500-2000 r / min, and the polishing wheel is rotated at a high speed of 2800-3200 r / min. The polishing wheel is controlled to move from the center of the bottom of the inner wall of the inner liner to the edge by a feed speed of 1-3 mm / s, forming a concentric circle trajectory on the inner wall of the inner liner. Step S4: Fine external polishing. Turn the inner pot over so that the opening of the inner pot faces downwards and fix it. Rotate the inner pot at a high speed of 1300-1800 r / min and the polishing wheel at a high speed of 2800-3200 r / min. By controlling the polishing wheel to move from the edge of the pot opening to the center of the bottom of the inner pot at a feed speed of 1-3 mm / s, the outer wall of the inner pot is polished. Step S5: Pot rim treatment; Step S6: Nitriding treatment; Step S7: Clean after nitriding; Step S8: Apply oil for maintenance.
2. The concentric polishing process for a cast iron inner liner according to claim 1, characterized in that: In step S2, the polishing wheel speed is controlled at 2800 r / min, the feed speed is 6 mm / s, the inner liner speed is 1300 r / min, and the surface roughness of the inner liner after rough polishing is controlled at 3.2-6.3 μm.
3. The concentric polishing process for a cast iron inner liner according to claim 2, characterized in that: In step S2, a 75# alloy grinding wheel is used for polishing. The contact pressure between the polishing wheel and the inner liner surface is 1.5-2.0 MPa. The 75# alloy grinding wheel is controlled to move from the center of the bottom of the inner liner to the edge of the inner liner wall to polish, remove casting defects and oxide layer from the surface of the blank, form basic concentric circle thread texture, and the surface roughness is 4.5 μm.
4. The concentric polishing process for a cast iron inner liner according to claim 1, characterized in that: In step S3, the polishing wheel speed is controlled at 3000 r / min, the feed speed is 2 mm / s, the lower plate speed of the inner liner is 1500 r / min, and the surface roughness of the inner liner is reduced to 0.2-0.8 μm after fine polishing.
5. The concentric polishing process for a cast iron inner liner according to claim 4, characterized in that: In step S3, a 150# steel wire wheel is used for polishing. The contact pressure between the polishing wheel and the inner liner surface is 1.5-2.0MPa. The 150# steel wire wheel is controlled to move from the center of the bottom of the inner liner to the edge of the inner liner wall for fine polishing, so that the polishing texture of the inner liner wall maintains a complete concentric circle thread texture and the surface roughness is 0.5μm.
6. The concentric polishing process for a cast iron inner liner according to claim 1, characterized in that: In step S4, a 120# abrasive belt is used for polishing. The rotation speed of the 120# abrasive belt is controlled at 3000 r / min, the feed speed is 2 mm / s, the rotation speed of the inner liner is 1500 r / min, the contact pressure between the polishing wheel and the surface of the inner liner is 1.5-2.0 MPa, and the surface roughness is 0.5 μm.
7. The concentric polishing process for a cast iron inner liner according to claim 1, characterized in that: In step S5, a YG6X cutting head is used on a lathe with a rotation speed of 300 r / min to flatten the inner liner opening. The outer edge of the inner liner is finely flattened on the lathe with a YG6X cutting head at a rotation speed of 250 r / min.
8. The concentric polishing process for a cast iron inner liner according to claim 1, characterized in that: In step S6, the inner liner is placed in a carburizing furnace. After the air is vented, the carburizing furnace is heated to 600°C for 24 hours of high-temperature nitriding to form a sufficient nitrided layer.
9. The concentric polishing process for a cast iron inner liner according to claim 1, characterized in that: In step S7, first use a scouring pad to wipe away surface dust and remove the tiny protrusions on the surface of the nitrided layer to make the concentric circle texture more delicate, then rinse it with tap water and preheat it to 150°C to dry it.
10. A concentric polishing process for cast iron inner liner according to any one of claims 1-9, characterized in that: In step S1, the pretreatment includes: fixing the inner liner on the spindle fixture of the CNC spinning equipment, using a high-pressure air gun to remove metal debris and oil stains from the surface of the blank; and performing heat treatment on the blank, with the temperature controlled at 60-80℃ and the time at 15-20min, to reduce surface stress deformation caused by temperature difference during the polishing process.