Posted by Mark Rossi on 16th Apr 2018
Achieving the best performance from your PCD scrapers is a result of two factors: PCD pressure and RPM. The pressure exerted on the PCD bits must be sufficient to penetrate through the material being removed. The RPM must allow the PCD bits to maintain good contact with the surface without creating unnecessary stress on the bits. (Note: This article only deals with PCD scrapers. If you would like information on regular concrete grinding tools, see Concrete Grinding Tools 101.)
Before we dive into the first factor, let’s do a quick refresher on PCD scrapers.
About PCD Scrapers
A PCD scraper is a diamond tool designed to remove surface materials from concrete. This could be an epoxy coating, a flooring adhesive, or an overlay.
Technically speaking, a PCD scraper is a tool that incorporates a polycrystalline diamond bit (or multiple bits) to function as scraping devices. They can have anywhere from one to four polycrystalline bits per tool and can be used for scraping a range of surface materials.
PCD scrapers are far superior to scrapers that use metal scraping bits because the hardness of the diamond cutting tip retains its shape much longer, ensuring consistent performance. Metal scrapers dull quickly and lose their performance.
In order to determine the penetrating force a PCD scraper will deliver, you need to calculate the pressure exerted on the individual PCD bits.
Two properties must be known to calculate PCD pressure:
- The head pressure of the grinder
- The total number of PCD bits in the set of tools
The formula for calculating PCD pressure is: head pressure divided by the total number of PCD bits.
Table 1 is an example of the type of table you should create. It should contain all your grinders and show the PCD pressure for single, double and quad PCD scrapers. This will provide you with a valuable reference when considering which tool will be right for your job. You can handwrite the chart or create one in a spreadsheet.
The column chart is a visual representation of the data in table 1.
Armed with your PCD scraper data, let’s see how it relates to different types of surface materials. Having a basic understanding of these materials is essential for selecting the correct PCD scraper.
High Strength (50 lbs per PCD+)
The highest penetrating force will be required to remove rubberized coatings (elastomeric membranes). Use the PCD scrapers to remove 99% of the coating because it will be very difficult or impossible to grind off the coating with a traditional grinding tool.
A high quality epoxy or urethane coating (over 30mils) bonded to extra hard concrete will also require high pressure. Remove 70-80% of the coating with the scrapers; the remaining amount should be relatively simple to grind off with a 20 or 35 grit metal bond tool.
Medium Strength (25-35 lbs per PCD)
Moderate pressure will be required to remove most cementitious overlays and epoxy or urethane coatings (over 30mils) bonded to medium or soft concrete. It’s rarely encountered, but some very old, thick black mastics fall into this category, while most would be considered low strength. Remove approximately 85% of the material with the scrapers (95% for the black mastic); remove the remaining amount with a metal bond grinding tool.
Low Strength (11-17 lbs per PCD)
Low pressure will be required to remove carpet, vinyl tile (and other flooring adhesives), gypsum underlayment, and flaking or poorly bonded coatings. Remove approximately 85% of the material with the scrapers, remove the remaining amount with a metal bond grinding tool.
Tool Operating Speed
PCD scrapers should be run at low RPM, normally between 1-4 on a grinder’s speed dial. The grinder head must run smoothly with as little vibration or jumping as possible so that the scrapers can maintain good contact with the surface. PCD scraping bits are brittle and will be degraded or broken by the unnecessary stress caused by high RPM, excessive vibration, or jumping.
To find the best RPM, start at the slowest speed and progressively increase the RPM until the grinder begins to vibrate or shake. Then, reduce the speed to the level where it was running smoothly. You should not exceed 900 RPM even if the head remains smooth and vibration free. If the floor conditions change, adjust the grinder RPM to maintain smooth vibration-free running.
Scraping vs Grinding
Scrapers and traditional grinding tools should not be used in the same way. A grinding tool should remove the surface layer of concrete and leave a new, clean surface. A scraping tool should remove 80-90% of the materials on the surface (except rubberized coatings) and then be followed by a grinding tool.
Weigh Your Options
When selecting a PCD scraper for your project, follow these four steps:
- Determine if the material you are removing will require high, medium, or low pressure
- Select the PCD scraper that will deliver the pressure required
- Establish the correct RPM for the conditions, adjusting as necessary
- Continually evaluate the PCD scraper performance, making changes as required
You are now equipped with the knowledge to improve your productivity, reduce your labor, and confidently tackle any heavy removal project. PCD scrapers are an immensely powerful option if used correctly; don’t let them go to waste.
You can find all the PCD scrapers you will need here: GS Series
Knowledge is power, success is a result of the effort you put in, and comfort zones are for retirement. Today is the day. Advance your business. Outthink the competition. Don’t sit idle.
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