INSPECTING HEAT TREATED PARTS

TITLE: INSPECTING HEAT TREATED PARTS

OBJECTIVE: When you have completed this Learning Element ,

you will be able to:

- perform inspection methods in detecting

different heat treatment defects.

EQUIPMENT , MATERIALS , AND AIDS YOU WILL NEED

QUANTITY UNIT DESCRIPTION

1 piece Hardened guide post

1 piece Hardened Punch

1 piece Hardened die

1 piece Dial indicator with stand

1 unit Surface plate

1 set Dye penetrant

1 unit tester

RELATED LEARNING ELEMENTS

INTRODUCTION

Die parts which undergo heat treatment are subjected to high temperature and then rapidly cooled. With such thermal shock it is possible that die parts come out warped and distorted and worse , cracked. In order to preclude additional cost through wasteful and useless machining time , it is required to detects right after completing the heat treatment process.

THE MOST COMMON DETECTS OF HEAT TREATED PARTS ARE :

-Warpage

-Distortion

-Cracks

-Hard surface but has some soft spots

-Lack of hardness of surface

WARPAGE AND DISTORTION

1. For flat parts , warpage can be easily detected by laying workpiece on top of the surface plate . Used the dial indicator to find the “wind” on the surface. Determine the amount of the wind and find out if it lies within the allowance provided.

NOTE : If not , consult your instructor for disposition of said part .

2. For cylindrical parts , mount the said part between the centers in a small lathe and with the use of the surface gage on the dial indicator , find the out-of-straightness.

CRACKS

3. Surface of discontinuities such as cracks can be detected by the following methods:

3.1 Magnetic Particle Testing

This is very well known non-destructive inspection for detecting the presence of flaws, cracks, and other discontinuities that are open to the surface but too fine to be seen with the naked eye.

NOTE : See L.E. on Magnetic Particle Testing

3.2 Dye Penetrant Inspection

Dye Penetrant inspection is the best method for finding cracks exposed to surfaces of magnetic non-porous materials . Her e, the penetrant remaining in the crack after the removal of the penetrant provides the indication by contrast with an unbroken background.

It is a process for finding discontinuities open to the surface in an essentially non-porous solid .It is best adapted to inspection of all types of surface cracks , porosity , laminations , lack of bond at exposed edges of joined materials.

The principles of the penetrant inspection is quite simple. It consist of three basic steps : (1) application of the penetrant to the surface under inspection , (2) removal of excess penetrant , and (3) the application of a developer.

CHECKING FOR CRACKS

4. Pre-clean and dry the surface to be inspected.

5 Drop penetrant using a medicine dropper. Apply penetrant , allowing sufficient dwelling time for the penetrant to enter the discontinuities through capillary action.

6. Removing excess penetrant by wiping with cloth.

7. Apply developer , to absorb or draw the penetrant entrapped in the discontinuity to the surface thereby increasing flaw visibility.

8. Inspect areas for presence of coloredpenetrant.

HARDNESS TESTING

9. The most common method of finding the hardness of heat treated parts is by means of the Rockwell Hardness Tester . Basically , the increment in depth due to the increment in load is the linear measure that forms the basis of Rockwell Hardness Testing .

FUNDAMENTALS

10. The basis operation of the Rockwell Hardness Tester is as follows :

- a small indentation by a diamond cone is first seated firmly by applying a minor load of 10 kg.

- with the indicator on the dial set at zero , a major load of 150 kg. is then applied to produce a deeper indentation.

- removal of load causes the indicator to point hardness number at the C scale .

USING THE ROCKWELL HARDNESS TESTER

11. Load 150 kg. weight holder behind the tester.

12. Set the diamond indentor.

13. Set the work on the anvil .

14. Elevate the work supporting the anvil by turning the handwheel just enough to set the workpiece on the anvil near the indentor.

15. Make initial indentions by elevating the anvil with the workpiece against the indentor. Stop raising the table if the small indicating pointer indicates the preload condition.

16. Set the dial to zero and apply the major load of 150 kg.

17. Watch the indicating pointer until it comes to rest; and then remove the load by turning back the handle.

With the load removed , the indicating pointer will now indicate the Rc on the “C” scale .

LOCATING THE SOFT SPOTS

18 . Place 1 liter of warm water in a container.

19. Place 1 liter of muriatic acid in the container.

NOTE: Always pour acid on water , not t he other

way around.

20. Immerse the workpiece.

21. After (5) minutes , get the workpiece and wash with water . Wipe dry .

NOTE: Use rubber gloves in handling the workpiece .

22. Areas appearing as lighter gray color are soft spots.