Casting Inspection | Non Destructive Testing | Destructive Testing | Mechanical Engineering

发布日期:[12-07-26 18:58:43] 浏览人次:[]

Inspection of Castings:

A large number of methods have been developed to inspect castings for defects that may occur during their production. Such inspections may be in process inspections or finished product inspections.

01-ndt testing-ndt inspection-non destructive inspection-ndt systems

In process inspections are carried out before a lot of castings have been completed to detect any flaws that may have occurred in the process so that corrective measures can be taken to remove the defect in the remaining units. Finished product inspections are carried out after the castings have all been completed to make sure that the product meets the requirements specified by the customer.

Defective castings may be salvaged or completely rejected to be re-melted for their material content depending upon the nature and extent of defect. The inspection methods may also be divided into destructive or non-destructive categories depending upon the magnitude of damage done to the casting during inspection. Destructive methods generally relate to sawing or breaking off of parts of the castings at places where voids or internal defects are suspected. Castings may also be damaged during strength tests.

Destructive tests suffer from the disadvantage that the saw cuts may miss the flaw or the sample may not represent the behavior of the entire lot. Because of these reasons non-destructive tests are generally more commonly relied upon than destructive tests.

Some of the prominent non destructive methods are described below:

Visual Inspection:

01-visual inspection-inspection of casting

It consists of inspecting the surface of the casting with naked eye or sometimes with a magnifying glass or microscope. It can only indicate surface defects such as blow holes, fusion, swells, external cracks, and mismatch. Almost all castings are subjected to certain degree of visual inspection.

Dimensional Inspection:

01-visual inspection-inspection of castings-dimensional inspection

Dimensional inspection is carried out to make sure that the castings produced have the required overall dimensions including allowances for machining. It may sometimes be necessary to break a part of the casting to take measurements of inside dimensions.

Sound Test:

This is a rough test to indicate a flaw or discontinuity in a casting. The casting is suspended from a suitable support free of all obstructions and tapped at various places on its surface with a small hammer. Any change in the tone produced indicates the existence of a flaw. The method cannot indicate the exact location and extent of the discontinuity.

Impact Test:

01-impact test - impact testing machine-inspection of castings - destructive testing

In this test the casting is subjected to a blow from a hammer of known weight striking or falling on the casting. Defective castings fail under the impact of the blow but the method is very crude and unreliable.

Pressure Test:

01-hydrostatic pressure testing

This test is carried out on castings required to be leak proof. All openings of the castings are closed and a gas or fluid under pressure is introduced in it. Castings having porosity leak under this pressure. The leakage may be detected by submerging the casting in a water tank or using a soap film if the press

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