Miks on pinna kareduse mõõtmine oluline enne pinnakatmist?

Karedus määrab, kui hästi kattekiht pinnale kinnitub (adhesioon). Korrektne karedus tagab optimaalse ankurdumise, mis tähendab pikemat katmisperioodi ja paremat korrosioonikaitset. Liiga sile pind ei anna piisavat mehhaanilist sidumist; liiga kare pind nõuab rohkem värviainet ja jätab katteta “tipud”.

Mis on Rz ja Ra ning kumba kasutada?

Ra on keskmise kareduse aritmeetiline väärtus; Rz on keskmiste kõrguste väärtus (5 kõrgeimat tippu + 5 sügavaimat orgu). Pinnakate tööstuses kasutatakse eelistatult Rz väärtust, kuna see korreleerub paremini adhesiooni ja materjalikuluga. ISO 8503 ja SSPC-VIS standardid viitavad Rz väärtustele.

Millised standardid reguleerivad pinna kareduse mõõtmist enne pinnakatteid?

Peamised standardid: ISO 8503-1 (standardsed profiilid terasele), ISO 8503-4 (stylus instrument meetod), ISO 8503-5 (replica tape meetod / Testex), SSPC-PA 17 (USA standard). Elister aitab valida sobiva mõõteseadme vastavalt kohaldatavale standardile.

/ / /

Hardness testers

When using protective coatings, it is necessary to measure the surface hardness before painting. The profile and roughness of the surface will directly affect the adhesion of the coating - a surface that is too smooth will not hold the coating, a surface that is too rough will require more material to fill the voids between the “peaks”.

Elcometer hardness testers are lightweight, portable measurement solutions for a wide range of surface roughness measurements in a variety of environments.

Methods for measuring roughness

Stylus profilometer - a mechanical sensor runs over the surface and measures the exact roughness profile; provides Ra, Rz, Rt values.
Combs (Testex Press-o-Film) - fast, barrier-free method, records surface profile using film; widely used in SSPC and NACE standards.
Digital hardness testers - automatic measurement and data transfer to ElcoMaster application

Application on steel structures

Cleaning the steel (e.g. after sandblasting) produces a surface profile that must meet the paint manufacturer's requirements. Too low a hardness (Ra 100 μm Rz) means wastage of material and potential “clean top” corrosion problems.

Frequently asked questions

Why is it important to measure surface roughness before coating?

Hardness determines how well the coating adheres to the surface (adhesion). Correct hardness ensures optimal anchorage, which means longer coating life and better corrosion protection. A surface that is too smooth will not provide sufficient mechanical bonding; a surface that is too rough will require more dye and leave uncoated “peaks”.

What are Rz and Ra, and which to use?

Ra is the arithmetic value of the average roughness; Rz is the value of the average heights (5 highest peaks + 5 deepest valleys). In the surfacing industry, Rz is the preferred value because it correlates better with adhesion and material consumption. ISO 8503 and SSPC-VIS standards refer to Rz values.

Which standards regulate the measurement of surface roughness before coatings?

Main standards: ISO 8503-1 (standard profiles for steel), ISO 8503-4 (stylus instrument method), ISO 8503-5 (replica tape method / Testex), SSPC-PA 17 (US standard). Elister can help you to select the appropriate measuring instrument according to the applicable standard.

Areas concerned

Elcometer 125 wetted surface reference plates

Elcometer 125 Waxed Surface Reference Plates are the reference standard for assessing the profile of a cleaned metal surface prior to painting or protective coating. The comparator allows a visual and tactile comparison of the profile of the wetted surface with four known profile values on the same plate. The Elcometer 125 is available in two versions, Grit (angular profiles produced by blasting with steel wool) and Shot (round profiles produced by blasting with steel balls). All profiles are recorded in microns and comply with international [...]

See product