In 2003, Zhonghuan built a gravity casting production line and developed from an aluminum ingot raw material supplier to a professional aluminum casting manufacturer. Currently, we are equipped with more than 20 tilting gravity die-casting equipment, with an annual production capacity of 1.3 million sets of castings, and the weight of a single product ranges from 0.1kg to 100kg.
Gravity casting products are mainly used in automobiles and trucks, ships and oceans, engineering machinery, new energy equipment, impellers and robots, etc.
As a professional aluminum alloy casting company, we independently complete mold design, machining and assembly manufacturing. We have complete mold development capabilities and can provide customers with more flexible and efficient one-stop services. For castings with complex structures, the feasibility analysis and optimization of the plan can be realized through mold flow analysis. Completing design optimization before mass production can effectively reduce trial production costs and shorten the product cycle from design to mass production.

What is gravity casting?

Gravity casting is a permanent metal mold casting and is a mature process widely used in non-ferrous metal casting. The basic principle is to inject molten metal into a preheated metal mold, and only rely on gravity to complete filling and molding without applying additional pressure. Therefore, the molding is stable and the internal quality is controllable.
This process is suitable not only for the production of small and medium-sized batches of castings with complex structures, but also for products that require high air tightness, strength, and dimensional accuracy.

Zhonghuan is equipped with a tilting gravity casting machine, which makes the process flow more stable and efficient: first place the mold in a horizontal state, and pour the molten metal into the sprue basin; then the equipment slowly tilts according to the set program, allowing the molten metal to flow into the mold cavity in a low-speed, continuous, and smooth manner. This filling method can greatly reduce turbulence, air entrainment and inclusions, making the casting structure denser.
Due to the flexible gate and runner design, the mold can be reused, the product accuracy and surface quality are better than traditional sand casting, and the cost is lower than high-pressure die casting, gravity casting has become one of the ideal processes for the production of high-quality castings.

Three major stages of gravity casting

◉ Gravity casting preliminary stage

1. Mold preheating and pretreatment
The metal mold is first heated to the temperature specified by the process to eliminate casting defects caused by the mold temperature difference, and then the release agent and heat preservation agent are sprayed evenly, which not only ensures the smooth demoulding of the casting, but also extends the service life of the mold.
2. Sand core placement and mold assembly
For castings with complex structures and internal cavities or holes, the sand core made in advance is accurately positioned and fixed in the mold. After checking, the mold is closed to ensure that the mold is locked and sealed in place to avoid problems such as leakage and flash during pouring.
3. Molten metal smelting and processing
The aluminum alloy raw materials are put into the smelting furnace and melted. After degassing, slag removal, composition adjustment, temperature calibration and other processes, a molten metal with high purity, stable temperature and qualified chemical composition is obtained, ready for pouring.

◉ Gravity casting pouring molding stage

1. Tilt-type pouring and mold filling
Inject the qualified molten metal into the mold sprue cup, and control the mold to tilt slowly and steadily through the equipment, so that the molten metal flows smoothly into the mold cavity through the runner and inner gate under the action of gravity. The entire process has uniform flow rate, no turbulence, and no air entrainment, which can effectively reduce internal defects such as pores and inclusions.
2. Cavity exhaust and riser feeding
During the mold filling process, the air in the cavity is smoothly discharged through the exhaust groove and riser, and the high-temperature metal liquid naturally collects to the riser position. When the casting cools and shrinks, the molten metal in the riser continues to feed the casting to ensure that the casting has a dense structure and no shrinkage cavities.
3. Natural cooling and solidification
After the molten metal fills the mold cavity, the mold is kept stationary, and it cools and solidifies naturally according to the process time, so that the casting reaches sufficient strength and hardness, ensuring that it is not deformed or damaged when the mold is opened.

◉ Gravity casting post-removal and processing stage

1. Open the mold and pick up the parts
After the casting is completely solidified, open the mold and use tools to take out the casting smoothly to avoid bumping or straining the surface of the casting.
2. Cleaning the pouring riser
Remove excess gates, risers and flash burrs from the casting, and perform preliminary grinding and cleaning of the surface to restore the smooth appearance of the casting.
3. Subsequent finishing and inspection
Carry out machining, heat treatment, surface treatment and other processes according to product requirements, and finally pass inspection items such as dimensional inspection, air tightness inspection, mechanical property inspection, etc. After passing the inspection, the product will be put into storage or delivered.

Advantages and Limitations of the Gravity Casting Process

-- Advantages of Gravity Casting Process

1. Product accuracy and surface quality are better
Compared with traditional sand casting, gravity casting has stable molding, high dimensional accuracy, small tolerances, and better surface finish. It can significantly reduce subsequent machining allowances and reduce production costs.

2. The casting has high internal density and good mechanical properties
Relying on smooth mold filling and riser feeding, the internal structure of the casting is dense, without obvious pores and shrinkage defects, and the strength and toughness are outstanding. After T6 heat treatment, aluminum alloy castings can withstand pressure up to 100kg/cm², which is suitable for products with high pressure-bearing performance requirements.
3. High production efficiency and reusable molds
The mold is made of heat-resistant metal and can be used repeatedly. There is no need to make a single mold like sand casting. The production process is simpler and suitable for stable mass production.
4. The applicable product range is flexible and can be used for large and complex parts.
Compared with high-pressure die casting, gravity casting can produce larger, heavier, and more complex castings without being restricted by high-pressure equipment and has a higher degree of molding freedom.
5. Lower mold investment cost
Compared with the expensive investment in molds and equipment for high-pressure die casting, gravity casting molds have a simple structure, lower cost, shorter investment return period, and outstanding cost performance.
6. Can be used with sand core to achieve complex inner cavity structure
The process supports built-in sand core molding, which can easily produce castings with porous, complex inner cavities and special-shaped structures, and is applicable to a wide range of industries.

-- Limitations of the Gravity Casting Process

1. Mold cost is higher than sand casting
Gravity casting molds need to be made of heat-resistant alloy steel. The initial investment is higher than that of sand molds. They are more suitable for medium and large batch production. The cost of small batch trial production is higher.
2. Molding speed is lower than high pressure die casting
Relying on natural gravity filling and cooling, the production cycle is slightly slower than high-pressure die casting, and it is not suitable for ultra-high-speed, ultra-large batch production of small parts.
3. Applicable metal materials are limited
Limited by the heat-resistant temperature of the mold, the process is mainly suitable for low-melting point non-ferrous metals such as aluminum alloys, zinc alloys, and magnesium alloys, and cannot be used for high-melting point materials such as cast iron and cast steel.
4. There are certain requirements for the wall thickness of castings
Although complex structures can be produced, too thin walls are prone to insufficient pouring, and the molding ability for extremely thin-walled parts is slightly lower than high-pressure die casting.

Our Gravity Casting Material Range

• National standards (GB/T standards): ZL104, ZL101A, ZL102
• International standards (ISO standards): EN AC-42100, EN AC-44200, EN AC-44300
• American Society for Testing and Materials standards (ASMT standards): A356, A360, A413
• Japanese standard (JIS standard): ADC12
• British Standard (BS Standard): LM6, LM9, LM25
• French standards (NF/EN standards): A-S7G, A-S13, A-S9G
• Russian standards (GOST standards): AJ19, AJ19-2, AK9

Material	China (GB/T)	International Standards (ISO)	USA(ASTM)	Japan(JIS)	Germany (DIN/EN)	UK(BS)	France (NF/EN)	Russia (GOST)	Italy (UNI/EN)	India (IS)
Cast aluminum alloy	ZL101A	ENAC-42100	A356.0	AC4C	ENAC-42100	LM25	A-S7G	АЛ9	EN AC-42100	A356.0
Cast aluminum alloy	ZL102	EN AC-42000	A413.0	AC3A	EN AC-44200	LM6	A-S13	АЛ9-2	EN AC-44200	AC3A
Cast aluminum alloy	ZL104	EN AC-44300	A360.0	AC4B	EN AC-44300	LM9	A-S9G	АК9	EN AC-44300	A360.0