The automotive braking system is an important safety system for automobiles, and brake discs and drums are key security components in this system. They are one of the cast iron parts suitable for large-scale sand casting manufacturers in automotive components. China’s production base for automotive brake discs and brake drums accounts for over 90% of the country’s total production, including exports and supporting equipment from domestic and foreign OEMs. Since its launch in the market, there have been 10 enterprises and 45 molding lines in the three regions mentioned above using casting elements to replace coal powder and bentonite in the production of brake disc and brake drum castings, achieving satisfactory results.
1. Introduction to Casting Elements
Casting element is a new type of material independently developed and patented by ZHY Casting, which replaces coal powder, bentonite, and other additives. Casting element is its trade name. This material is made by mixing high-quality bentonite, high carbon environmentally friendly anti sticking sand material that replaces coal powder, powder, cellulose and other materials. It is a clay sand preparation reserve mixture that has both the characteristics of mixed soil and contains coal powder substitute materials, and the preparation method is different from mixed soil. Mixing clay sand with casting elements instead of coal powder and bentonite overcomes the problems of high harmful gas and solid emissions, easy spontaneous combustion of coal powder, and black pollution caused by mixing clay sand with bentonite and coal powder, and improves the performance of molding sand. The models and technical indicators of casting elements are shown in Table 1.
| Model | Blue absorption amount/(g/100 g) | Wet compression strength/kPa | Hot wet tensile strength/kPa | Micro volatility/% | Volatile matter/% | Bright carbon/% | Particle size 140 mesh pass rate/% |
| XZ50 | ≥20 | ≥70 | 2.8~3.3 | 10~12 | 15~23 | 6~8 | ≥90 |
| XZ60 | ≥22 | ≥80 | 3.0~3.5 | 10~12 | 14~22 | 5~7 | ≥90 |
| XZ65 | ≥25 | ≥85 | 3.0~3.5 | 10~12 | 12~20 | 4~6 | ≥90 |
| XZ70 | ≥27 | ≥90 | 3.0~3.8 | 10~12 | 11~19 | 4~6 | ≥90 |
| XZ75 | ≥28 | ≥95 | 3.2~3.8 | 10~12 | 10~18 | 3~5 | ≥90 |
| XZ80 | ≥30 | ≥95 | 3.2~3.8 | 10~12 | 9~18 | 3~5 | ≥90 |
| XZ85 | ≥30 | ≥100 | 3.2~3.8 | 10~12 | 8~16 | 3~4 | ≥90 |
2. Green, environmentally friendly, and low emission
(1) Reducing harmful gas emissions by using environmentally friendly high carbon materials such as polymer natural plant materials to replace coal powder as an anti sticking sand material in casting elements, thereby eliminating air pollution caused by coal powder and black pollution in the workshop. Table 2 shows the analysis and testing results of samples taken from the exhaust duct of the dust removal system of ZHY Casting’s sand casting manufacturers molding line brake discs, brake drum production line casting, and sand dropping department by Henan Provincial Testing Center. From the data in the table, it can be seen that the harmful gases produced by casting element sand are significantly lower than those of coal powder bentonite and clay sand.
| Detection name | Standard code | Standard method | Testing items | 2023/03/06 1st | 2023/03/06 2nd | 2023/03/06 3rd | 2023/03/07 1st | 2023/03/07 2nd | 2023/03/07 3rd |
| SO2 | HJ57-2017 | Constant potential electrolysis method | Measured concentration | 6 | 6 | 6 | 3 | 3 | 3 |
| SO2 | HJ734-2014 | Gas chromatography-mass spectrometry | Emission rate | 0.0598 | 0.0597 | 0.0596 | 0.0301 | 0.0300 | 0.0299 |
| Naphthalene | HJ734-2014 | Gas chromatography-mass spectrometry | Measured concentration | 0.014 | 0.016 | 0.015 | 0.009 | 0.011 | 0.014 |
| Naphthalene | HJ734-2014 | Gas chromatography-mass spectrometry | Emission rate | 0.0001 | 0.0002 | 0.0001 | 0.0001 | 0.0001 | 0.0001 |
| Phenol | Note 1 | Gas chromatography | Measured concentration | Not detected | Not detected | Not detected | Not detected | Not detected | Not detected |
| Phenol | Note 1 | Gas chromatography | Emission rate | — | — | — | — | — | — |
| P-xylene | HJ734-2014 | Gas chromatography-mass spectrometry | Measured concentration | 0.010 | 0.017 | 0.010 | 0.008 | 0.013 | 0.008 |
| P-xylene | HJ734-2014 | Gas chromatography-mass spectrometry | Emission rate | 0.0001 | 0.0002 | 0.0001 | 0.0001 | 0.0001 | 0.0001 |
| Ortho xylene | HJ734-2014 | Gas chromatography-mass spectrometry | Measured concentration | 0.016 | 0.026 | 0.016 | 0.012 | 0.011 | 0.012 |
| Ortho xylene | HJ734-2014 | Gas chromatography-mass spectrometry | Emission rate | 0.0002 | 0.0003 | 0.0002 | 0.0001 | 0.0001 | 0.0001 |
| Toluene | HJ734-2014 | Gas chromatography-mass spectrometry | Measured concentration | 0.064 | 0.082 | 0.055 | 0.048 | 0.011 | 0.014 |
| Toluene | HJ734-2014 | Gas chromatography-mass spectrometry | Emission rate | 0.0006 | 0.0008 | 0.0005 | 0.0005 | 0.0001 | 0.0001 |
(2) Reducing solid emissions from sand treatment, dust removal, and discarded old sand are the main solid emissions for modern sand casting manufacturers. The effective solid powders (bentonite, coal powder, casting elements, etc.) and the failed solid powders that have been burned during high-temperature casting are the main sources of dust for sand casting manufacturers. The solid powder of new sand and core sand entering the sand treatment system causes the amount of old sand in the entire sand treatment system to exceed the capacity of the system, and the excess amount of human waste is the main source of discarded old sand. The reduction of burning loss rate of solid powder during high-temperature casting of casting elements is used to reduce the mud content of molding sand and adjust the performance of molding sand. The addition of new sand is reduced, and under normal operating conditions of sand treatment, the amount of dust removal and discarded old sand is reduced, resulting in a decrease in solid emissions.
ZHY Casting, the sand casting manufacturers, produces brake discs and brake drum castings using one sand treatment line shared by three Japanese imported horizontal unboxing injection molding lines. After using casting elements, the amount of auxiliary materials added decreased from 0.74% to 0.44%, and the mud content of the molding sand decreased. Not only did it not require the addition of new sand, but also in order to maintain the mud content at the original process requirement of 10%~12%, 0.3% of dust removal ash was reused, reducing solid emissions by 80%. The pre – and post process sand mix of sand casting manufacturers is shown in Table 3.
| Material Name | Old sand/kg | New sand/kg | Bentonite/Kg | Coal powder/kg | Casting Element/Kg | Dust removal ash/kg |
| Original process | 2700 | 4 | 14 | 6 | 0 | 0 |
| Current process | 2700 | 0 | 0 | 0 | 12 | 9 |
3. The Performance of Casting Elements in Clay Sand
ZHY Casting used experimental research methods to compare the indicators of XZ80 casting elements and other similar materials, and studied the process performance of controlling the total mud content of clay sand by mixing casting elements, bentonite, and coal powder, in order to evaluate the performance of casting elements in mixing clay sand. Through comparative research, it can be concluded that: ① the blue absorption and volatile matter of 1g casting element are the same as 11.271g of bentonite I and coal powder, and 1.248g of bentonite II and coal powder II; ② The changes in wet compressive strength and permeability of clay sand containing casting elements with casting elements and moisture are the same as those of bentonite and coal powder clay sand with changes in bentonite and moisture The wet compression strength and permeability of clay sand containing casting elements are higher than those of clay sand containing equivalent bentonite and coal powder without controlling the total mud content; ④ The wet compressive strength of clay sand containing casting elements, which accounts for 13% of the total mud content of molding sand, is higher than that of clay sand containing equivalent bentonite and coal powder. The permeability is slightly higher or equal to that of clay sand containing equivalent bentonite and coal powder.
4. Application in the production of brake discs and brake drums
The test results of the above casting elements in clay sand are consistent with the results obtained by more than 10 sand mold casting manufacturers in their production practice using XZ80 casting elements to replace bentonite and coal powder in the production of automotive brake discs and brake drum castings. Under the condition that the sand is required to achieve the same wet compression strength and anti sticking effect, the actual amount of casting elements added is lower than the amount of bentonite and coal powder added. Under the same amount of coal powder added to bentonite, the comprehensive performance of molding sand is improved, and the quality of castings is improved and enhanced. The following is a specific case analysis.
Case 1: A sand casting manufacturers used four horizontal unboxing injection molding lines imported from Japan to produce automotive brake discs and brake drum castings, using coal powder and bentonite. The casting yield was 93%, with porosity defects accounting for about 80% of the total waste. Sand casting manufacturers have taken measures to achieve the annual target of a 95% casting yield, such as increasing pouring temperature, increasing vent area, reducing sand core gas generation, replacing carburetors and inoculants, improving scrap steel quality, and increasing sand particle size, all of which have had little effect. After using casting elements, the sand was recycled for more than a month. While the process requirements for sand compaction rate, wet compression strength, effective bentonite content, ignition reduction, volatile matter, etc. remained unchanged, the amount of casting elements added was less than the sum of original bentonite and coal powder. The mud content of sand decreased from 11.5% to 13% to 10% to 12%, and the moisture content decreased from 3.4% to 3.8% to 3.0% to 3.5%. The amount of casting porosity waste was significantly reduced. Later, under the advice of the casting element application guidance engineer, the compactness rate of the sand at the sand outlet of the sand mixer was reduced from (38+2)% to (34+2)%, and the moisture content of the sand was reduced to 2.8%~3.3%. There were no problems such as increased sand hole defects and decreased mold performance in the castings. The number of casting porosity and waste products was further reduced, and the final product rate remained stable at 95%~96%.
Case 2: The sand casting manufacturers uses two heavy straight split box less injection molding lines imported from Japan to produce automotive brake discs and brake drum castings. The sand mold size is 500mmx400mmx250mm, and 360 types per hour are specifically used to produce non core single disc brake discs (solid discs) and non core brake drums. Each type has one piece, with a sand iron ratio of 6:1, using coal powder and bentonite. There is a contradiction between increasing the wet compression strength of molding sand and increasing the collapsibility of the mold during the production process. The reasons are as follows:
(1) Vertical molding molds do not have sand box support and conveyor carts. The entire string of sand molds arranged on the conveyor grid is pushed forward by a hydraulic system. The wet compression strength of the sand is slightly lower, and it will be squeezed or crushed during the pushing process. Cleaning up broken sand molds and restoring normal production is labor-intensive and affects production efficiency. To ensure the smooth production process, it is necessary to control the wet compression strength of the molding sand to be higher.
(2) Vertical production of brake discs and brake drums does not require the core to be lowered, and the rough holes in the castings are directly cast from the sand tire, which can improve the production efficiency of vertical production and save costs. However, the residual strength of clay sand is higher than that of resin sand, and its collapsibility and sand production are lower than that of resin sand. Compared with the rough holes formed by resin sand cores, the rough holes formed by casting have more sand after sand drop, and the rough holes are severely sticky, which increases the workload of subsequent cleaning. To improve the collapsibility and sand production of molding sand, and reduce the occurrence of rough pores with sand, it is necessary to lower the wet compression strength of molding sand, which in turn increases the risk of mold crushing. The wet compression strength and collapsibility are contradictory. To solve the above problems, sand casting manufacturers adopt the method of adding more bentonite to improve the wet compression strength and compaction rate of the sand, and at the same time, adding more coal powder to improve the dispersion and sand production of the sand. But as the mud content and moisture content of the sand increase, the collapsibility and sand production of the sand become worse, and the problem of rough holes with sand and serious sand sticking in the casting becomes more serious. At the same time, other parts of the casting also have an increase in sand, and the sand treatment system is severely depleted. Under normal circumstances, for mixed personnel without core sand, the sand iron ratio is 6:1, and adding 1.5% -3.0% new sand can maintain the sand balance of the sand treatment system. Due to a shortage of inventory, sand casting manufacturers add up to 5% to 10% of new sand. Sometimes, in order to reduce costs, they often purchase old sand discharged from brake discs and brake drum molding lines from other sand casting manufacturers to replenish their inventory.
Later, sand casting manufacturers used casting elements to replace coal powder and bentonite. The amount of casting elements gradually decreased, and the final amount was reduced to half of the original amount of bentonite and coal powder. The wet compression strength, mud content, and compaction rate of the sand returned to normal, and the molding line remained stable and normal production. The sand mold was no longer crushed or cracked during the pushing process, and its collapsibility and sand production were improved. The problem of rough holes with sand and serious sand sticking was solved, The workload of the cleaning process is reduced, and the shot blasting time is shortened. Adding 1.5% to 3% of new sand can maintain the balance of sand volume in the sand treatment system, without the need to add more new sand and supplement old sand.
Case 3: The sand casting manufacturers used three horizontal unboxing injection molding lines imported from Japan to produce automotive brake discs and brake drum castings. In order to improve production efficiency, they used partition sand cores to change the original one type of two pieces to one type of four pieces (double-layer molding process). The amount of broken core sand entering the sand increased from an average of 2% to 7%, reducing the toughness of the sand, increasing its brittleness, decreasing its mold performance, increasing the number of scrap molds, and significantly increasing the defects of sand flushing and sand inclusion in the sand holes of the castings, In order to solve the above problems, sand casting manufacturers have adopted measures to increase the effective bentonite content and add 0.1% to 0.3% during sand mixing α Starch is a measure to extend the mixing time, but the flowability of the molding sand decreases, leading to clogging of the sand barrel and insufficient sand injection during production. Only 1% -3% new sand can be added during the mixing process to reduce the adverse impact of loose core sand on the toughness of the molding sand. This not only increases the amount of bentonite and coal powder added during sand mixing, increases production costs, but also increases the discharge of waste sand. After using casting elements instead of coal powder and bentonite to mix molding sand, sand casting manufacturers gradually restored the toughness and molding performance of the sand, eliminated the need to add new sand, reduced the scrap rate of sand flushing, sand holes, and sand inclusion in castings, and the finished product rate of castings was close to the single-layer process level.
Case 4: A sand mold casting manufacturer used three Japanese imported horizontal parting and unboxing injection molding lines to produce automotive brake discs and brake drum castings. When mixing sand, artificial sodium bentonite and high-quality coal powder were used. It was found that during the production of brake disc castings with larger diameters, there are often peeling, rat tail, vein patterns, and slight sand sticking defects near the small end root. After the single layer sand removal drum of the casting is used for sand removal, some sand blocks cannot be broken and scatter on the scale conveyor along with the casting. When packaging the mold, it often causes deformation of the mold and produces casting waste.
The high-quality bentonite in the casting element has been modified and reprocessed, resulting in high thermal wet tensile strength and good reusability. High carbon materials and C-starch, which replace coal powder, can effectively reduce the hot pressing stress of small sand, reducing expansion defects such as peeling, rat tails, and veins in the casting. By using casting elements, the strength and toughness of the molding sand are improved, and the sand mold is not easily damaged when subjected to mechanical effects such as casing and pressing iron. Sand casting manufacturers use casting elements to replace bentonite and coal powder, with a 54% reduction in the amount added compared to the sum of bentonite and coal powder. When mixing sand, no new sand is added, and the effective bentonite content of the molding sand remains basically the same as before. The reduction in burning is 0.3%~0.5%. The defects of peeling, rat tail, and veining in brake disc castings are completely solved, and the amount of sand blocks that cannot be broken and the deformation of castings caused by casing is greatly reduced. The initial inspection scrap rate of castings is reduced by 60%.
5. Conclusion
Casting element is a green, environmentally friendly, and efficient shaping material that has been successfully applied in many domestic brake disc and brake drum production enterprises. The addition of casting elements is less than the sum of coal powder and bentonite, resulting in a reduction in harmful gas and solid emissions. The moldability, collapsibility, and flowability of molding sand have been improved. Defects such as porosity, sand holes, sand sticking, peeling, rat tail, veins, and deformation in castings are reduced. Casting elements provide new choices for energy conservation, consumption reduction, quality improvement and upgrading for casting enterprises.