Visual Inspection

Manufacturing defects, Form and Surface Imperfections

Significance and Test Method

The industrial production of elastomer parts takes place in batch processes. Once moulded and vulcanised, the possibilities for reworking the parts are limited or even impossible. The form and dimensions are fixed and surfaces can only be slightly reworked.

In most cases, post-processing is limited to deflashing. Therefore, the final check by means of a visual inspection is an important part of the manufacturing process.

Cost Pressure and Manufacturing Defects

Often, manufacturers of standard parts face strong cost pressure; high production capacities in short time are key to their success. Therefore, moulding and vulcanisation processes are pushed to the limits of technical feasibility. However, rubber is a rather difficult material to process. The highly viscous materials do not melt. Thus, they are injected into the usually hot moulds with enormous pressure. Moulds are quickly filled and parts demoulded, and the vulcanisation process is kept as short as possible. Thus, during elastomer production, a wide variety of mould and surface defects can occur.

On the Track of Manufacturing Defects

Final inspection as an important part of elastomer production is carried out using different methods. Depending on the type of component and the desired quality level, either random samples or all parts of a production lot are inspected. Optical inspections vary from manual visual inspections to automatic inspection machines with numerous cameras..

Different quality criteria apply to the form and surface quality of rubber parts and seals. For O-rings, ISO 3601-3 defines acceptance criteria for the surface quality. Since 2010, this standard has replaced the previously common O-ring standard DIN 3771-4. The form and surface imperfections defined in this O-ring standard can also be applied to other sealing rings, for which unfortunately there are often no specific standards available. Other technical rubber parts are tested in accordance with part-specific standards, factory standards or individual specifications.

At Elastomer Institut Richter we usually use our light microscopes for visual inspections.