December 14, 2018

Automotive Polishing: What is a High Cut Rate?

Automotive polishing prioritizes speed and quality, whether correcting fresh aftermarket paintwork or dust nibs on a brand-new vehicle from the OEM assembly line. These two properties are seemingly at odds in the realm of abrasive polishing compounds. Faster removal rates are typically associated with a poor surface finish due to the comparatively coarse particles of higher cut products. This highlights the ongoing challenge of modern automotive polishing: how to achieve an optimal intersection between aggressive cutting action and improved surface finish.

How Does Automotive Polishing Work?

Automotive polishing compounds are usually comprised of abrasive particles suspended in a fluid, paste, or gel compound. This mixture is applied to a vehicle’s bodywork and a dual action (DA) orbital or rotary buffer is used to remove uneven clear coat, gradually leveling the surface. The liquid phase of the product may enhance the overall finish of the polishing process, but the suspended abrasives are responsible for the cutting action. 

The cutting action of an abrasive refers to the rate at which it removes material from a vehicle’s surface, otherwise known as the material removal rate (MRR). This is influenced by particle size, with larger and coarser particles conventionally believed to exhibit faster material removal rates – or high cut rates.

This is certainly the direction taken by traditional abrasives, but advances in particle size distribution (PSD), microstructure, and morphology manipulation have enabled a new generation of materials that eclipses the conventional method.

Automotive Polishing: Cut Rate vs Surface Finish

High cut rate automotive polishing compounds typically sacrifice surface uniformity for the most aggressive cutting action possible. This is desirable for leveling the surface of paintwork to remove significant defects such as sanding scratches, swirls, and holograms. The drawback of this rapid removal is that it can impart new imperfections that must be removed through subsequent polishing steps using compounds with a less aggressive abrasive.

Polishing products with a high removal rate usually comprise coarse abrasive particles. These are typically comprised of ceramic oxide materials such as alumina (Al2O3), which is one of the hardest and most durable engineered materials on the planet. Calcined alumina is broadly used in automotive polishing products, with particle size distributions (PSDs) centered around a larger particle generally offering a higher rate of removal. This performance also relies on the unique microstructure of the particles, such as the available cutting-facets of individual crystals: more cutting facets generally translates to a higher cut.

This can be problematic when it comes to loading abrasive particles into a slurry. Coarse particles may impart an improved cutting action, but their larger geometries inhibit the number of particles that can be loaded. Reducing the particle load is associated with an increase in the length of time required to reach the optimal surface level, which nullifies one of the primary benefits of high cut rate automotive polishing products.

Saint-Gobain Surface Conditioning: IDEAL Automotive Polishing

Saint-Gobain Surface Conditioning offers three standard abrasives suitable for automotive polishing products and an innovative alumina powder for aftermarket polishes. Our two primary high removal rate abrasives (HRRA), IDEAL Cut and IDEAL Super, feature PSDs centered around 5 microns. We carefully engineer these products to eliminate overly coarse or fine particles from the mixture, allowing solids loading to be minimized in the polishing compound. [we do not adjust solids loading, this is what the customer does when they load our product into their compound]  Conventional abrasives require up to 50% loading to achieve sufficiently high cut rates. Ideal products can perform to exceptional standards with solids loading as low as 5%.  Historically, leveling and finishing a paint system required as many as 4 steps.  However, IDEAL automotive polishing particles encompass an innovative abrasive technology that begins with a high cut rate and morphs into an improvised state during use conditions. This ensures an excellent surface finish in only 1-2 steps.

If you would like any more information about our engineered abrasive particles for automotive polishing products, read our previous blog post Saint-Gobain Surface Conditioning: Alumina Abrasive Particles for Automotive Polishing. Or, contact us if you have any questions.