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The process used to manufacture coated abrasives includes printing on the backing, a resin coating application, and electrostatic coating of abrasive grit. We will look at the 10 steps of the manufacturing process and the results that end in high-quality coated abrasives.
1. Printing
Printing is an important step in the manufacturing process as it lays out the information needed to identify the particular characteristics of the product. Backings will normally have product and company information printed on them. KLINGSPOR backings for instance will provide you with the following information:
- Company Name & Logo: KLINGSPOR and the KLINGSPOR spur symbol
- Material Name, Grit and Grit Grading Scale (P) and backing: I.E. CS412 P80 YX
- OC, A/S, W/P (optional)
- Batch or Material Control Number - 459
- Directional Arrows
- Point of Origin Statement: Made in Germany, the USA, Mexico, or Poland
Very few manufacturers print sizes on their belts, sheets, discs, etc. This is usually only done if the product is private-labeled in large quantities. When it is received as a jumbo roll, there is no way of knowing what size belts or other products will be made out of any particular material. This makes pre-printing a size virtually impossible. Pre-printing belt sizes on each belt would increase the time needed to manufacture the belts and the costs to the end user. Instead, sizes are printed on the labels that are attached to each “nest” of belts. (A bundle with a pre-specified number of belts is referred to as a “nest” of belts)
Material name, grit, grit grading scale, and backing provide 60% of the information needed to be certain you are using the correct abrasive grain, backing, and bonding. For example, CS412 is the material name, and P denotes that the abrasive grain used in this product is graded on the P or FEPA grading scale. 80 denotes the grit size and YX indicates that the backing is lightweight polyester. Depending on the material and whether the notations would apply, you may also see OC (open coat), A/S (anti-static), W/P (waterproof), or other similar markings. This provides another 25% of the information needed to make a complete cross reference.
Batch numbers are assigned when the jumbo roll is produced and are control and tracking numbers. At KLINGSPOR Abrasives, the batch numbers are normally 3 digits (like 459 above). The first two digits denote the week of the year (there are 52 weeks in a year) and the last digit reflects the last digit of the year. So using the info above and the present date as a reference, batch number 459 would tell us the material was made the 45th week of 2009. Batch numbers are important for raw material-type complaints as a way of tracking where a problem has arisen and where testing may need to be done.
When the conversion takes place where the jumbo rolls are made into their final forms, i.e. belts, discs, strips, sheets, etc., another identification number is added to the label that is placed on the product. This is the production date and uses three digits to identify the day of the year (based on 365 days per year) and an additional two digits to identify the year. An example would be 12324. The 123rd day of 2024.
Directional arrows are printed on the jumbo rolls for all materials that may be made into belts. Lightweight papers (A, B, or C) will not have arrows on them. D, E and F, as well as all the cloth-backed material, will have arrows. The arrow is used in the manufacture of lap-jointed belts. It informs the belt manufacturing line which end of the material will be the bottom of the lap and which end will be the top side of the lap so that skiving, or grit removal, is done to the appropriate end. After the belt is joined, the arrow informs the customer of the direction in which the belt must be run. THIS IS ONLY APPLICABLE FOR LAP JOINTED BELTS!
The arrow is printed on all jumbo rolls because we have no way of knowing what sizes or types of belts will ultimately be made from each roll.
It is very common for belts with the same material and grit but different sizes to use different joint types. For example, the standard pump sleeve material LS309JF will always have a #1 lap joint. But a 3 x 132 in the LS309JF will usually have a #4 butt joint. The same material, the same grit, but for a different size and application. So even though the arrow is on all belts, you only have to pay attention to it if the joint is an overlap joint.
Any belt with tape on the back, regardless of what the front looks like or the fact there are arrows on the backing, is a bi-directional belt! This can allow for extra life as the butt joint or tape-jointed belts can be run in one direction, removed, and put on to run in the opposite direction.
Finally, the backing of all materials and/or the boxes and labels will be printed to include the point of origin for manufacture of the material.
2. Maker Coat
The maker coat is the first layer of adhesive bonding that is applied to the backing. The purpose of the maker coat is to provide a seat for the grit that will be attached in the electrostatic coating process. It is what adheres the grit to the backing. Most of the bonding agents today are synthetic resins and are phenolic which ensures a sturdy, heat-resistant connection of the abrasive grit and the backing.
3. Electrostatic Coating
Electrostatic coating is a process in which a plate with a negative charge is placed above the backing (which has the maker coat applied), and a plate with a positive charge below a loose grain conveyer containing abrasive grit. The grit has been graded several times to obtain the appropriate size. This results in a separate charge being created between the two plates that pulls loose grit up from the conveyor and onto the backing in such a way that each abrasive grain is consistently oriented on the backing with a broad base against the backing and a sharp end pointing out. This is the most common method for coating backings with abrasives in use today.
There is another method of grain coating called gravity coating, which simply drops the grit through the use of gravity onto the backing without orienting it as the electrostatic method does. This method is still sometimes used today for coarser grits but would be most ineffective for any finishing grit. This process may be modified to alter how much grit is applied to the backing, determining whether a product is a closed coat, semi-open, or fully open coat.
This is done by inserting a filtering screen between the maker coat and the loose grit conveyor that will only allow 50 - 70% of the backing to be coated in grit.
4. Curing
After the maker coat has been applied and the electrostatically placed grit has been added, the material is run through curing ovens to ensure a good bond between the grit and the backing. You can have the best grit and backing in the world, but if they do not remain connected, the products will not be effective.
Curing oven times and temperatures vary depending on the types and sizes of grit, the backing, and the type of bonding agents used. Once this initial curing is completed, you are ready to add the second layer of adhesive bonding, which is the size coat.
5. Size Coat
The second layer of adhesive bonding, referred to as the size coat has two main purposes. The first is to tie the individual grains on the abrasive backing together to act as a unit instead of as individual grains. The other function of the size coat is to act as a heat shield for the grit. As previously discussed, most of the bonding agents in coated abrasives are phenolic resins, which after curing, are heat resistant.
Too much size coat or too little size coat can cause performance and finishing issues. Too much size coat and the grit won't be able to cut, instead creating a shiny effect on the abrasive's surface. It can often result in burning of both the abrasive and the workpiece. This is called glazing.
Too little and the abrasive grains won't act as a unit and will shed individually under pressure. Glazing and shedding are primary indicators that something may have gone wrong during the application of the size coat.
The application of the size coat is also where several optional steps may occur. These would include but not be limited to the addition of dyes, stearates, and lubricants. The size coat is a critical part of the making process that can have far-reaching effects on both the life and finishing properties of the coated abrasives.
6. Curing (Again)
After the size coat is applied, another curing step needs to be implemented to ensure the bonding agents cure completely.
7. The Jumbo Roll
After the second curing, the material is wound into jumbo rolls. These rolls vary in width depending on the material backing and its most common use. The jumbo rolls may be as narrow as 37 inches or as wide as 65 inches with lengths ranging from 50M to 2000M.
8. Flexing
Flexing is a process by which a base cloth material, in our case either the J or X weight cotton backings, may be made more pliable. When a material is flexed, such as the J-Flex or X-Flex, the base material (J OR X) is run over a series of stainless steel rollers set up at 45 or 90-degree angles to crack the bonding. By cracking the bonding, you enhance a material's flexibility. However, by this same process, you also provide a doorway for heat to get to the grit. For that reason, flexed products will exhibit lower life than non-flexed materials. Flexing is necessary for the sanding of contoured parts, and should only be used when a degree of conformability to a profile or contour is required. Otherwise, life is sacrificed without any return.
9. Storage
After all processes to the material are accomplished it is put into storage until it is required to fill orders.
10. Conversion
Conversion is the manufacturing of belts, sheets, discs, flapwheels etc. from jumbo roll materials.