Surface Analysis of a Common Rail Injector

On the components of an injector for a diesel engine surface  parameters were analysed by means of optical 3D measuring technology. For this purpose, the tip of the nozzle needle, the valve body and the valve plate are measured at the relevant points and profile-based as well as area-based roughness parameters are calculated.

Roughness measurements on the nozzle needle seat

The nozzle needle of a common rail injector is to be examined at the seat surface. In this context, the roughness is to be determined in a profile-based manner according to DIN EN ISO 4287/4288 and DIN EN ISO 13565 as well as in an area-based manner according to DIN EN ISO 25178. Due to the geometry of the nozzle needle, the measuring section of 1.5mm prescribed for this surface is not available. In this case, a shorter profile can be used for the analysis, if the measuring section and the filtering are indicated.

The amplitude parameters according to ISO 4287 obtained from a profile section only allow for a limited analysis of the surface as they can only be determined along a line in each case. Structural components which are located outside of this line will not be taken into account. This can result in faulty analysis results. Therefore, the analysis software MountainsMap® offers a function for automatically creating several profile sections which are distributed across the entire measured surface area. (See left)

Areal Analysis (SK parameter) according to DIN EN ISO 25178

For characterising different structures of the surface with respect to their tribological behaviour, the material ratio curve (Abbott curve) is used. This curve describes the surface material ratio Smr as a function of the depth of a section plane through the surface.  At the highest point of the structure, the material ratio is 0% and at the lowest point it is 100%.

Examination of the Surface for Droplets

The surface shows several droplets. These droplets can affect the funtionality of the component. For better evaluation one  droplet was analysed in detail.

Measuring device and method

The measurements are carried out with the compact standard measuring system ConfoSurf CLV150. This measuring system is equipped with the 2-in-1 scanner module Confocam C1+ and allows for two measurement methods in one system: form measurements are taken in the measuring mode "focus variation" due to the high flank angles. Roughness measurements are taken in the confocal measuring mode "structured lighting". This patented technology is based on confocal measurement technology and can even measure reflective surfaces without any problems.