Product Introduction

The cylinder block is the most important part of construction machinery - extruder, and its function is to convert hydraulic energy into mechanical energy. At the end of 2013, our company produced a thick large-section cylinder block for a company in Guangdong, as shown in Figure 1. The casting material grade is QT600-3, the net weight is about 13500kg, the maximum external dimension is 1980mm×1330mm×1130mm, the cylinder size is Φ840mm×800mm, and the main wall thickness is 330mm. The customer puts forward the following mandatory requirements: ① The acceptance of the cast test block must meet the following requirements: tensile strength Rm≥600MPa, elongation A≥3%; ② The bottom of the cylinder body, the bottom and the cylinder wall R shall not have shrinkage or pinholes and other defects; ③ The inner wall of the cylinder is carried out by derivatives grinding, and the hardness is 200-250HB; ④ After processing, 25MPa water pressure test is carried out, which lasts for 10min without leakage or sweating; ⑤ Magnetic powder inspection, do not allow the existence of casting defects that affect the strength, such as slag inclusion, sand inclusion, porosity.

Technical principle and performance index

Using reasonable forming type cold iron, reasonable pouring system, high quality raw materials, appropriate copper and antimony content ratio and strict process control, we can produce thick large-section cylinder block that meets customer requirements.

(1) The performance of 70mm standard cast test block: tensile strength Rm: 532-578MPa, yield strength Rp0.2:372-415MPa, elongation after breaking: 12.5-16.0%, hardness: 175-189HB, spheroidization rate: 90-96%, graphite size: 6 grade, pearlite volume fraction: 25-35%, ferritic volume fraction: 65-75%.

(2) The nodulation rate of the bottom and top body of the cylinder base is more than 94% in the metallography, and the number is 300 /mm2, the difference is small, and the hardness difference is also small, indicating that the material uniformity of the cylinder base body is very good, and it is not easy to crack when it is subjected to huge pressure during use.

(3) Destructive test of the cylinder seat: cut at the crack failure R position, color detection, no defects were found, especially shrinkage and slag inclusion; Metallographic spheroidization rate of 93%, quantity of 300 PCS /mm2; At the same time, the yield strength Rp0.2 was sampled and the result was 329-367MPa.

Creativity and advancement of technology

(1) No matter which location is sampled, the spheroidization rate of the casting is relatively high, reaching 90%, and the number of graphite balls is also relatively high; This not only ensures the density of thick and large section castings, but also reduces the tendency of shrinkage and loosening.

(2) The rational use of the formed cold iron can not only improve the spheroidization rate and increase the number of graphite spheres, but also improve the pearlite volume fraction to ensure a high hardness.

(3) A reasonably designed pouring system can not only ensure fast and stable filling, but also effectively avoid the slag entering the mold and reduce the generation of slag inclusion defects.

(4) The use of high-quality raw materials, such as high purity pig iron, carburizing agent, nodulating agent, and the use of synthetic ductile iron melting process to provide high-quality iron liquid for the production of thick and large section ductile iron casting.

(5) The appropriate amount of w (Cu) and w (Sb) ensures that the pearlite volume fraction of the casting matrix is 65% ~ 85%, so as to ensure that the thick and large section casting has good comprehensive mechanical properties.

Maturity, scope of application and safety of the technology

In addition to the mature stage, the technology is suitable for the casting production process to improve product quality. After the use of customers, it has been proved that the service life has been significantly improved from the original 18-24 months to more than 48 months.

Application and existing problems

Through the combination of reasonable casting process and melting process, the production of a single thick large section cylinder block, after testing the technical indicators are in line with customer requirements. For the future production of similar castings to accumulate valuable experience. In the continuous experiment process, it is found that cracking oil leakage or non-crack oil seepage failure often occurs at the R position of the circular arc connecting the cylinder bottom and the cylinder wall, and the service life of the cylinder seat is often 18-24 months, resulting in greater economic losses. After dissecting the failure site (where the wall thickness is greater than 85mm), metallographic analysis (FIG. 1) showed that the nodularity rate was 90%, the graphite size was grade 5, and the number of graphite balls was 100 /mm2. Yield strength Rp0.2 is 285MPa. The analysis shows that although the R-position graphite ball is round, it is small in number and not dense enough, and the yield strength of 285MPa can not withstand the huge pressure generated when the cylinder is working, and eventually it fails due to oil leakage or oil seepage.

Awards over the years

The technology has obtained the invention patent certificate issued by the State Intellectual Property Office.

Detection Systems

Copper Silica Sol Investment Casting

We are the manufacturer of "Cylinder ductile iron parts", if you need more information please contact us!