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Why Coatings Fail: No Worries with Byers Bush

Posted on: October 28th, 2014 by byersbushblog

As a top powder coating and sandblasting company in the area, we need to understand why special coatings fail so we do not make the same mistakes. We have learned throughout our experiences in the industry that improper anchor patterns are the most frequent reasons for early failure.

What is an Anchor Pattern

An anchor pattern is the industry term that defines the roughness of the surface that is sandblasted. These anchor patterns are microscopic, blasted down to a MIL which is 1/1000th of an inch. The MIL is easy to remember because paint coatings use the same measurement. When coatings are used, a specific MIL is usually required to the coating to stick permanently to the surface. The different coatings require different MILS, so sandblasters need to know how clean to get the surface and coaters need to know the technical information about the coating and its required MILS. When shops take a guess at the MILS and the product profiles, they usually make mistakes that result in coatings coming off too quickly.

Manufacturer’s Data Provide Formulas for Blasting

Most coatings will come with manufacturer’s data so shops do not need to guess at the required MILS, but in some cases, shop employees need to be able to do some math to figure out the proper anchor patterns. There is a general rule of thumb that shop employees need to understand.

Rule #1

The first rule is that anchor patterns need to be between 25 percent and 30 percent of the thickness of the film when it is dry, but it should never be more than the dry thickness of the primer coat. The only exception to this rule is if extra coats are going to be applied right away.

Rule #2

The second rule is that MILS that are wet are going to be a different thickness than the MILS that are dry. Coatings are notorious for shrinking and the percentage of solids in the coating will make a difference in the amount of shrinkage that occurs. The best sandblasting anchor patterns are going to be shallower that the coatings are when they dry.

Rule #3

The third rule of anchor patterns involve the materials, especially the steel, that is being sandblasted. The chemical makeup and the hardness of the steel needs to be taken into consideration, as well as the abrasive that is being used. The history of the steel is also important to know, considering that the prior use could have weakened the steel. The blast nozzle, especially the angle and distance to the surface, and the details of the sandblasting like the size, velocity, and shape need to factored into the formula.

Determining Surface MILS and Blasting Material

Sandblasting shops need to understand the behaviors of their surfaces as well as the math behind anchor patterns. MIL profiles can be anywhere from 1 MIL to 5 MILS in steps of .5 MILS between them. There are charts that shops can use to get baseline data when the anchor pattern is unknown for a particular project. The profiles include different grits, meshes, shots, and slag.

Quality Control

At Byers Bush we use a product called Ebonygrit on our projects. This fine grit allows us to meet the needs of our customers’ blasting needs. This product creates low amounts of dust, so we can pay close attention to the anchor patterns and reduce the risk of any early failure.

If you need powder coating or sandblasting services in the South-Central Ontario, please give us a call at 905-625-4334.

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