The "thin shell art" of precision casting reshapes the efficiency and quality of metal forming

1、 Overview of Shell Casting Technology

Shell casting, also known as shell mold casting, is a precision casting process that forms a thin shell cavity on a metal template using resin sand. Its core characteristics are "thin shell, high strength, and excellent precision", widely used in the production of high complexity castings in fields such as automobiles and aerospace.

Process principle:

Heat the coated sand (resin sand) and adhere it to the surface of the preheated metal template to form a thin shell sand mold with a thickness of 5-15mm. After high-temperature curing, demold and assemble it into a complete mold cavity for pouring.

2、 Shell casting process flow

templates preparation

Material: Metal template (cast iron, steel or aluminum alloy), surface polished to Ra ≤ 0.8 μ m to ensure the smoothness of the mold cavity.

Design: including pouring system, exhaust channel, considering parting surface and demolding slope (usually 0.5 ° -1 °).

Preparation of coated sand

Formula: Quartz sand (AFS 50-80)+Phenolic resin (2.5-4%)+Urotropin curing agent (10-15% of the resin).

Mixing: Sand, resin, and curing agent are heated to 60-80 ℃ in a sand mixer to evenly coat the sand particles with resin.

Shell forming

Template preheating: Heat to 200-300 ℃ and activate resin viscosity through thermal conduction.

Sand covering: The template is inserted into the sand box, and the coated sand covers the surface of the template by gravity or air pressure, forming an initial sand layer.

Hardening: Maintain the template temperature at 180-250 ℃, and the resin crosslinks and solidifies within 30-60 seconds, forming a semi shell shape.

Demolding: The ejection mechanism separates the shell and template to obtain a single-sided shell (usually requiring the production of upper and lower halves of the shell).

Shell assembly

Adhesive: Use thermosetting adhesive to bond the upper and lower shell shapes together, forming a complete cavity.

Reinforcement: Fill the exterior with dry sand or metal casing to prevent cracking of the shell during pouring.

Pouring and Cleaning

Pouring: Metal liquid (such as cast iron, aluminum alloy) is filled at low pressure to reduce turbulence.

Cooling: After the casting solidifies, the shell will break and the shell will automatically disintegrate, causing the casting to come out.

Post processing: Shot blasting cleaning to remove residual sand particles and burrs.

3、 Core advantages of shell casting

High precision and surface quality

The dimensional accuracy can reach CT5-CT7 (± 0.1-0.3mm), and the surface roughness Ra 6.3-12.5 μ m is close to the level of investment casting.

Suitable for mass production of complex geometric components such as gears and impellers.

Efficient Materials and Energy

The thickness of the sand shell is only 1/5-1/10 of traditional sand molds, and the amount of resin used is reduced by more than 50%.

The pouring temperature can be reduced by 20-50 ℃, which significantly saves energy.

High process flexibility

The shell has high strength (tensile strength ≥ 3.5MPa) and can produce thin-walled parts with a wall thickness of 1.5mm or more.

Support automated production lines, with a cycle time of 60-120 types/hour.

Shell casting occupies a unique position in the field of precision casting due to its characteristics of "thin shell lightweight, high quality and high efficiency". With the integration of new materials and digital technology, their application boundaries will continue to expand, providing better solutions for high-end manufacturing.