Testing of Mechanical Properties of Castings

The conventional mechanical performance testing is carried out at room temperature. The testing items usually include tensile strength, yield strength, elongation after fracture, reduction of area, deflection, and impact absorption. (Or impact toughness) and hardness. Tensile strength, yield strength, elongation after fracture, and reduction of area are measured on a tensile testing machine; impact absorption or impact toughness is measured on an impact testing machine; deflection and bending strength are measured by transverse bending test methods; hardness is measured by Kind of hardness tester.

1. Tensile test.

The tensile specimens of gray cast iron are machined by cylindrical single cast test bars or attached cast test bars. The diameter of the single casting test bar is 30mm, and it is poured in the same batch as the casting in the vertical casting dry sand mold. The diameter of the parallel section is 20mm±0.5mm. When the bending strength and deflection are used as the acceptance conditions of the mechanical properties of the casting, the bending test can be carried out, and the bending sample directly adopts the as-cast blank test bar with a diameter of 30mm±1mm. The shape, size and surface quality of tensile test specimens, bending test specimens and as-cast blank test bars, tensile test and bending test methods, technical requirements for the testing machine, and calculation and processing of measurement results shall all comply with industry standards.

2. Impact test.

The impact test is used to determine the impact absorption energy when the impact sample is broken under the secondary impact load. The impact testing machine should meet the requirements of GB/T3808-2002 "Inspection of Pendulum Impact Testing Machines" and should be periodically verified by the national metrology department. Impact samples are divided into V-notch impact samples, U-notch impact samples and non-notch impact samples. Gray cast iron adopts unnotched cylindrical impact specimens, which are machined from as-cast blank test bars with a diameter of 30mm. The nominal scale is 420mm×120mm. The casting method of the blank test bar, the technical requirements of the impact specimen, the technical parameters of the impact testing machine, the test conditions and methods should meet the requirements of GB6296-1986 "Impact Test Method for Gray Cast Iron". Impact samples of brittle and hard materials such as white cast iron can be unnotched as-cast blank samples, or unnotched samples that have been annealed and processed by machining and heat treated in the same furnace with the casting. The shape, size and technical requirements of the sample are determined by supply and demand. Other cast metals and alloys are U-shaped impact specimens (usually used for cast metals and alloys with large notch sensitivity) or V-shaped impact specimens are used as the strike sample.

3. Hardness test.

There are two common methods for determining the hardness of castings: Brinell hardness method and Rockwell hardness method. Hard and brittle casting alloys are usually measured by the Rockwell hardness method, and other casting alloys are generally measured by the Brinell hardness method. For cast alloys with uniform metallographic structure such as cast steel, there is a certain conversion relationship between Rockwell hardness, Brinell hardness and tensile strength. Refer to GB/T112-199 "Ferrous Metal Hardness and Strength Conversion Value" and GB /T3771-1983 "Copper alloy hardness and strength conversion value".

It needs to be pointed out that the terminal inspection of casting quality is only the last checkpoint to prevent unqualified castings from leaving the factory. The key to ensuring the quality of castings lies in enhancing the quality awareness of all employees within the enterprise, strengthening quality supervision and management over the entire production process of castings, stabilizing the production process, organizing civilized production, and adopting advanced production technology and equipment as much as possible, equipped with sufficient Effective inspection methods for process quality and casting quality.