Metrology Lab

Metrology lab – Talyrond and shadow graph

For this lab analysis was put on the operating cylinder of the brake system. With further inference to this claim this lab was assigned to give an experience of a component inspection. Due to this, the first place to start was a visible inspection. From this inspection the piston housed in the cylinder was immediately found to be defective as it had NDT paint on its main surface. Due to the nature of the pistons movement during operation, (vertical displacement through the chamber) the metallic dye was understood to have rendered the part unusable, and therefore in need to replacement. The reasoning behind this was that during operation the piston needs to be smooth in order to slide through the operating cylinder without the risk of getting stuck. With the Paint on the surface of the piston this smoothness was compromised further to that, as the piston was housed tightly into the cylinder the risk of a malfunction improved drastically.  Continuing on with the visual inspection, the surface of the piston was also found to have various scratches on the surface in addition to that, the housing cylinder also has mild cases of deformation on the surface of the metal.  Although it was assumed that the operating cylinder was already unusable if this was a real maintenance task, for experience sake a metrology test was still conducted on the piston.

Procedure – Talyrond inspection (surface roundness)

·         The piston was removed from the operating cylinder as the cylinder could not fit into the talyrond machine. The piston was then placed into the central housing of the machine. When placing the piston in extra care had to be taken to make sure that the piston was centred and not leaning to one side to eliminate the risk of systematic error.

·         After placing the piston centrally into the apparatus, the jaws of the machine were then closed in simultaneously, this was also important to centre the piston.

·         The height of the needle was then adjusted to match the location of the most visible scratch on the piston.

·         Once locked and held into position the needle of the talyrond machine was then adjusted, using the thimble that gauged the distance between the needles head and the piston surface.

·         Looking at the distance visualised on the PC monitor, the distance between the needle and the component was set to a separation of 0 micro metres.

·          Once In contact with each other, the test was then simulated and the piston was rotated with the spindle of the talyrond machine gauging the deviation of the part, using the zero value as reference point.

·         After the doing roughly 3 revolutions on the component the results were then shown on the computer screen highlighting the deviation from a perfect circle reference generated on screen.  

·         This test was the simulated over 5 times at varying heights in order to surmise the components surface roundness. In addition to this, repeating the test was imperative to remove anomalous results, and so each time the test was started the component was re-centred therefore making the results more accurate.

Results

From the Talyrond inspection, results on the surface roundness of the piston were found. Evidence and analysis of these results may be highlighted from 4 key pictures that were taken during the test.

 

 

From these initial images of the test simulated at the same height as the scratch on the piston, the deformation of shape was clearly shown.  Using the perfect red circle generated by the software as the reference point, the green circle representing the surface of the piston is shown to be relatively round up until a certain point where there is a sharp dip shown. This dip highlighted the deformation that the scratch had placed on the piston as the ball of the machine lost contact with the cylinder. In addition to that, general expansion of the piston was also shown through these tests as the circle was shown to grow outside of the reference point at certain locations. This deformation could have been caused by the metal of the piston expanding after working at constant high temperatures. 

For this form of NDT the tip of the talyrond machine was ruby. The reasoning behind this was associated to the properties of Ruby. Primarily Ruby is considered a strong stone can easily be manipulated into a round shape. Bearing this in mind, this property allowed it to last for a long time, whilst being effective at its job. In addition to that, the property for it to be easily manipulated gave it the edge over diamond, as that would be more costly to cut and shape as diamond tools would need to be used to cut the stone.

Shadow graph

This form of NDT (non-destructive testing) was needed to inspect the elements of the brake operating cylinder. The reasoning behind this was that the cylinder was too big to fit into the jaws of the talyrond machine, this meant another form of testing had to be used to see if its surface was damaged.  The shadow graph was able to provide a more in depth visual of the cylinder, highlighting any cracks and deformations.

Procedure

·        The cylinder was placed on the top of the shadow graph machine and the machine was turned on producing a light that created a shadow projection of the cylinder.

Shadow graph machine

·        On the screen of the machine, the profile of the cylinder was then focused to give clearer view of the component.

·        By altering the positioning of the cylinder, varying angles of projections could be formulated essentially giving a more in depth view of the cylinder than the visual inspection.