Research on the casting process of spiral series thick ductile iron parts

1 Structural characteristics of castings

Spiral series products are a series of small batches and multiple models, with many product types, weight ranging from 500~2000 kg, belonging to thick ductile iron castings, the main wall thickness is 20 mm, the maximum wall thickness is 100 mm, the wall thickness distribution of castings is uneven, the distribution of hot joints is more complex, and the product structure is shown in Figure 1. The casting requires that no casting defects are allowed after processing, which constitutes a difficulty in the casting process.

Figure 1 Spiral series product structure

2 Test protocol

Spiral series products are the company’s new development products, casting profile size: 1450 mm× 850 mm×380 mm, weight: 200~1500 kg, QT400-18-LT material, the casting is required to be UT (according to DIN EN 12680-1 Grade 1) and MT (according to DIN EN1369 Grade SM 3) flaw detection, the casting can not have visual appearance defects after processing. In this paper, the characteristics of the spiral structure are analyzed and combined Its operability in the actual production process, the quality of the casting, the needle The bottom injection process scheme of cold iron and riser is used to solve the problems of shrinkage and slag defects of the spiral.

3 Test results and analysis

3.1 Optimize the process design, simplify the modeling and reduce the modeling cost

(1) For different models in the range of 200~1500 kg
The spiral is unified with a gating system of one specification (shown in Figure 2),
Not only can the number of molds be reduced, but the mold production can be further reduced
Moreover, it can simplify the molding operation and avoid repeatedly switching the pouring system
(2) Due to the high cost of new sand boxes, for multiple products such as spirals
Most of the products produced in small batches use substitute sand boxes, workers
When designing the gating system and the outer mold, it is a movable structure
The sample can be selected by adjusting the position of the gating system and the outer mold
The size of the sand box should be smaller, and the amount of sand should be reduced to reduce the cost of molding.

3.2 Optimize the mold structure and reduce the mold cost

Spiral series products belong to small batches of multi-model products, molds
The utilization rate is low, and the requirements for the life of the mold are low, in order to reduce the mold production
Optimize the mold structure and take the following measures:
(1) The mold structure includes metal mold structure, steel and wood structure, and wood
Mould structure, this series of products adopts the lowest cost wood mould structure. (2) The outer mold without a pattern plate is used, and the outer mold with a pattern plate is compared with the pre-mold
Save 50% of tooling costs. Put the solid shape and extension on the fetal membrane
Spread the block (shown in Figure 2) and use the fetal membranes to achieve upper and lower parting. The modeling steps of the outer mold of the shapeless plate are: the solid mold and the expansion loose block are placed On the tire mold – solid mold, expansion block and tire mold are placed as a whole
On the mold board – place the sand box and fill the sand to make the lower type – after the lower type is cured Flip – take out the tire mold – sprinkle the particle size 100 ~ on the parting surface
140 Purpose Parting Dry Sand – Place the sand box and fill the sand to make the upper mold – Upper
After curing, the mold is demolded to obtain a cover box – take out the solid mold and expand the activity Block — demoulding to obtain the bottom box.

Fig. 2 The outer mold structure of the shapeless plate of the spiral series products

(3) Considering that there are many product models, there is often a phenomenon of mold borrowing, and the mold is split into a basic mold pattern and an expansion mold block, so that when borrowing a mold, only the expansion mold block needs to be replaced without a new base mold mold, which greatly reduces the mold production cost.

3.3 Optimize the casting process and solve the problem of spiral inclusion

On the one hand, to control the source of inclusions and improve the purity of molten iron, the main measures are as follows: (1) control the time from tap to pouring within 10 minutes to prevent inoculation decline and reduce the generation of oxidation slag (; 2) Put a piece of asbestos on the surface of the molten iron before pouring, which can adsorb the oxidized slag on the surface of the molten iron and reduce the slag of the molten iron from entering the sprue basin; (3) The filter plate (as shown in Figure 3) is placed before the inner sprue to filter and block the molten iron entering the cavity, and the filter specification is 150×150×20, and the quantity is 2. On the other hand, to reduce the impact of inclusions, the main thing is to control the loose sand in the cavity or the gating system, and improve the cleanliness of the cavity, and the specific measures are as follows: (1) clean and polish the local virtual sand or sharp angle sand in the cavity before closing, so as to avoid bringing molten iron into the pouring; (2) The inner runner adopts a ceramic pipe (as shown in Fig. 3) to reduce the risk of sand washing into the cavity during the sprue; (3) Using the bottom injection pouring system, the molten iron is flushed smoothly from bottom to top, even if there is oxidation slag in the molten iron or there is loose sand in the cavity, it is easy to float and discharge through the overflow of the riser and outlet sheet.

3.4 Optimize the casting process to solve the problem of dispersion and shrinkage in the local position of the spiral

Analyze the structure of the casting, place risers and cold iron at the hot joint part to reduce or eliminate the shrinkage defects of the casting, and the specific measures are as follows: (1) increase the insulation riser at the thick part of the box surface of the casting cover (as shown in Figure 3), and make up and shrink the thick part of the casting, among which there are 4 insulation risers on the top round table, the insulation riser size is ø200 mm×200mm, the riser neck size is ø100 mm×50 mm, and the top surface of the flange is 1 insulation riser, the insulation riser size is ø100 mm×100 mm, and the riser neck size is ø50 mm×20 mm。 (2) Cold iron (as shown in Figure 3) is placed at the hot joint part of the casting and important processing positions to quench the casting to reduce the tendency of shrinkage and loosening. (3) Adopt low-temperature open pouring scheme and selection of gating syste Inner sprue cross-section 4×ø40 mm, cross-sprue cross-section 2× (40/50)mm×40 mm, sprue cross-section ø60 mm, pouring temperature according to (1330±10)°C.

Figure 3 The process scheme of the spiral series products

3.5 Spiral process validation

(1) Optimize the bottom injection casting process of cold iron and riser, which is effective
The ground reduces the tendency of the casting to be loose. Shrinkage porosity is simulated by solidification It was found that the hot joints of the castings were widely distributed and dispersed, and the shrinkage of the castings was loose The rate is controlled at around 1%, as shown in Figure 4.
(2) “1+2+4” is used in three batches of experiments to carry out the experimental pieces
MT and UT flaw detection meet the technical requirements of customers, and the experimental pieces are processed The appearance of the post-casting is free of any casting defects.
(3) In actual production, the process has been solidified and realized in batches
Mass production, using this casting process scheme, more than 150 castings of similar structure of 35 kinds have been produced, and the quality of the castings is stable and the finished products have been delivered.

Fig. 4 Solidification of spiral castings simulates shrinkage porosity distribution

4 Conclusion

(1) Optimize the bottom-injection flat pouring process scheme of cold iron and riser,
It can solve the problems of shrinkage porosity and slag defects of the spiral to a large extent.
(2) The combination of riser and cold iron is adopted, which is conducive to reduction
Low tendency to shrinkage in castings.
(3) Control the purity of molten iron and the cleanliness of the cavity, which can be larger
To a certain extent, the problem of casting slag defects is solved.