Improvement of casting process for driving wheel of nodular cast iron

The drive wheel is an important part of a large crawler agricultural tractor. The material grade of nodular cast iron is GGG60-DIN1693. See the table for the mechanical properties of the material. The overall dimensions are ϕ 916 mm × 526 mm, 260 kg mass, gear structure, 19 teeth evenly distributed along the circumference, and the root of the teeth are isolated hot spots; Since the track is placed between the two teeth, the tooth is not allowed to have a mold angle; The internal quality of ductile iron castings is required to be level 2 for radiographic inspection, and the anatomical verification standard is 38.1 mm × The range of 38.1mm is allowed to be less than ϕ 12.7 mm shrinkage. The surface quality is required to be 38.1mm × Within the range of 38.1 mm, no more than 2 mm in diameter and no more than 5 pores are allowed. The parts are shown in Figure 1.

PerformanceTensile strength/MPaYield strength/MPaElongation (%)Hardness (HBW)
Standard requirements≥ 600≥ 370≥ 3%187-269

According to the product structure and characteristics of the driving wheel, the parting surface is selected at the center perpendicular to the axis of the part, and the parting is symmetrical. Since the tooth part does not allow the die angle, the core assembly process method is adopted for 19 independent teeth. The process scheme of sand core is shown in Figure 2. Each tooth is composed of 1 # and 2 # sand cores and assembled into 3 # sand cores, 3 # sand cores fall into 4 # and 5 # positioning sand cores and assembled into 6 # sand cores, and 6 # sand cores fall into the bottom box. With this process, the seam of nodular cast iron at the tooth is small, and it is easy to ensure the contour of the tooth of nodular cast iron.

The upper and lower sand molds are made of resin sand, and the 1 #, 2 #, 4 # and 5 # sand cores are made of hot-core box coated sand.

(1) The use of core assembly design can eliminate the angle of mold lifting in specific areas, and the seam of nodular cast iron is small.

(2) Multiple isolated hot spots use riser technology to effectively solve the defects of shrinkage porosity and shrinkage cavity in nodular cast iron, and the use of cold iron at the place far away from the riser to reduce the hot spot can effectively extend the feeding distance of the riser.

(3) The drying process of coated sand core can effectively reduce the gas generation of sand core and reduce the porosity defect.