Doug Jensen, Application Engineer, Norton | Saint-Gobain Abrasives
The numerous and diverse applications for the use of abrasive belts naturally require different belt joining designs and technology. There are hundreds of grinding, polishing, and sanding applications that abrasive belts are used for which require various belt widths and lengths, with one of the smallest being 1/8” wide by 12” long and one of the largest being 128” wide by 157” long. As you can imagine, the applications these belt sizes are used on are vastly different from one another.
This smaller belt size would generally be used on hand held pneumatic tools, with horsepower ratings as low as 0.5 HP and are used for deburring/polishing intricate parts or other applications with relatively low material removal requirements. We often see them used on internal component parts for land based turbines, aircraft jet engines as well as on many types of castings made from various types of metals that have areas that are difficult to reach with other types of abrasive tooling.
On the other hand, the larger belt size is obviously used on very robust stationary equipment. Industrial engineered panel manufacturers (particleboard, medium density fiberboard, oriented strand board) are the primary users of these very large abrasive belts. They are used on sanding equipment that typically has eight heads with four heads sanding one side of the panels and four heads sanding the other side of the panels. They utilize abrasive grit size sequencing with coarser grit sizes being used for the majority of the total amount of required material removal, medium grit sizes to upgrade the finish, and fine grit sizes to impart the final finish requirement. Horsepower on this type of equipment can be as high as 250 HP or more.
Given these extremely different coated abrasive belt applications and the many applications in between, how do abrasive manufacturers decide what belt joining design would work best on each application? Historical internal and external testing data help to determine what the “standard” joint design should be on a given abrasive belt application. However, it is not uncommon for a standard joint to fail on an application it was designed for use on. In some cases, the failure mode type may already be known so there may be an alternative joint design that is already established as a backup for a given application. In other joint failure cases, further study of the particular application must be done to determine what the root cause of the failure was so that a non-standard joint design can be selected for testing, or a new or hybrid belt joint may need to be designed.
Norton utilizes three primary joining tapes for the vast majority of “standard” abrasive belt applications, but has several other joining tapes that are used for unique applications and/or for the new or hybrid joint designs previously mentioned. Most of these joining tapes are based on a clear polyester film backing with nylon reinforcing fibers. The diameter of the nylon fibers determines the tensile strength of each individual tape design, with larger diameters obviously having higher tensile strengths - as well as being thicker - than smaller diameters with lower tensile strengths.
These tapes are used in different widths and at different joint angles as needed. Abrasive belt joints that utilize any of these joining tapes are referred to as “butt” joints. The reason for this name is because the two ends of the coated abrasive panel, that will become an abrasive belt, are butted together prior to the joining tape being applied. Lap joints, although rarely used any longer, do not use joining tape. As their name implies, lap joints are made by lapping over the ends of the coated abrasive panels to create a belt. The ends of these panels are prepped, in a similar manner as butt joints, which allows them to be joined with adhesive and press operations as described below.
The three standard tapes which Norton uses for joining are color coded, as are some of the other tapes (with different colors), in red, white, and blue. We utilize these three tape designs by abrasive belt grit size categories. Red tape (thinnest and lowest tensile strength) is used for fine grits, white tape (slightly thicker and higher tensile strength) is used for middle grit sizes, and blue tape (thickest and highest tensile strength) is used for coarser grit sizes.
Belt joint tape on print side
Joining tape, treated with adhesive, is applied to “abrasive panels” which become abrasive belts after joining. The panels have been cut to the appropriate dimensions (width and length) for the belt size needed and the area where the tape is to be applied has been prepped and adhesive has been added to promote tape adhesion and joint strength. Most abrasive applications require the joining tape be applied to the print side (or back side) of the abrasive belt. For this type of joint, the prep is done by sand or glass bead blasting the joining area which removes what we refer to as backfill from this area exposing the cloth backing.
Other types of abrasive applications require the joining tape to be located on the abrasive side of the belt. For this joint type the abrasive grain and resin system, which holds the grain in place, is removed with diamond wheels to expose the cloth backing. This type of joint design is primarily used in the engineered panel industry and it leaves an area on the face of the abrasive belt, slightly wider than the joining tape, with no abrasive grain. Because this industry only uses steel contact rolls and platen heads on their sanding equipment, this joint type runs well. However, it cannot be used on rubber contact rolls as compression of the rubber under sanding/grinding load will allow the joining tape to make contact with the parts being processed which will cause the joining tape/abrasive belt to rupture.
The joining tape is applied to the panels during press operations where hydraulic or roller presses are used to apply pressure and heat to the belt joining area. The heat used in this process is supplied through press bars that are a primary component of these presses. The heat supplied activates the adhesive system, which has been applied to the joining tape and prepped area of the panels. Although the abrasive belts are on the press for only a few moments, when they are removed they can be handled and packaged within a few minutes without harm to the belt joint. However, depending on environmental conditions, the adhesives used could take as long as twenty-four hours to fully cure.
For more information on the content of this article or questions about coated abrasives, please email the author.
Automated wide belt press