Cast Iron Manhole Cover Process Control Technology: Melting and Control Methods
Release date:
Dec 01,2021
Source:
A. Melting Method (Ductile Iron Manhole Covers, Well Rings)
a. 1.5-ton dual-frequency electric furnace melting: pouring temperature ranges from 1400–1500°C
b. Weight per ladle of molten iron: 1500 kg per ladle
c. Rare earth magnesium alloy added at 1.4%–1.6%
B. Control Method
a. Check the tapping temperature once before each batch of molten iron is inoculated, maintaining the temperature within the range of 1400–1500°C.
b. After each batch of molten iron is inoculated, check the iron temperature once, ensuring it remains within the controlled range of 1360°C or higher.
c. Conduct five-element analysis on 1–2 samples of molten iron daily to ensure consistent control over casting material quality and the stable use of furnace charge recycling.
d. Each package of molten iron must be poured within a maximum of 10 minutes (after the spheroidization reaction); any delay beyond this time results in scrapping.
e. After each ladle of molten iron is poured, insert a pre-fabricated tag (etched with the specific sequence number of that ladle) into the sprue cup of the cast piece being poured, ensuring that different ladles are clearly identified and preventing any confusion between them.
f. At the final stage of each batch of molten iron pouring, a blank tensile test bar is produced as an inspection sample, which undergoes testing for mechanical properties, metallographic structure, and hardness.
g. When depositing the sand, stack it separately according to the license plates—do not mix sand from different batches—and await the results of the test rods and metallographic inspections.
h. After the test bar passes the mechanical performance inspection, notify the workshop to clean up. If any non-conforming batches are found, scrap them one by one according to the numbers indicated on the identification tags.
Testing Standards
A. Manhole cover inspection: Strictly follow the inspection standards.
a. Appearance: No obvious casting defects, with a clear pattern and legible lettering.
b. Flatness Inspection: Use a dedicated fixture to check the flatness of the manhole cover. Fabricate a fixture with a diameter matching the product’s dimensions and a depth of 37 mm—these dimensions should be precisely achieved through machining. Place the manhole cover inside the fixture; it should remain stable without any wobbling or audible noise. Additionally, the manhole cover must not protrude above the fixture, and the clearance between the cover and the fixture should be within 3 mm at the 37-mm depth.
c. Load-bearing capacity is assessed using a sampling method: During the press test, manhole covers are subjected to a pressure of either 360 kN or 210 kN to verify that the batch meets the required standards.
B. Well Ring Inspection
a. Appearance: No visible casting defects.
Control, inspection, molten iron, manhole cover, testing
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