Understanding Nylon Abrasive Filament Brushes (Nylox)

Understanding Nylon Abrasive Filament Brushes (Nylox)

This article published in Manufacturing Engineering - March 1999

Nylon abrasive filament (NAF) brushes solve many deburring, edge radiusing, and finishing problems. Their compliancy and filament nature accommodate part contours, prevent damage to value-added components, and make them ideal candidates for robotic and automated workstations. These brushes replace tedious hand operations, provide consistent quality, improve productivity, shorten cycle times, improve part finishes, generate precise edge radii, and lower finishing costs.
A nylon abrasive filament brush deburring and edge radiusing an automotive transmission valve body.

Where Used. Applications include deburring, edge radiusing, and finishing of blanked steel components, carbide inserts, aluminum aircraft parts, and automotive components; including camshafts, cylinder heads, wheel rims, and transmission housings and valve bodies. Another important application is deburring. NAF brushes have provided automated deburring solutions for many complex part shapes. These tools evolved over the past decade to cope with the increasingly stringent requirements of state-of-the art manufacturing. Shorter cycle times, tighter part tolerances, improved part finishes, precise edge radii, and lower deburring costs are achieved by employing NAF brushes in CNCs, robots, and other automated deburring setups.

Made of heat-stabilized nylon filaments impregnated with abrasive grain, the brushes work like flexible files. Conforming to part contours, they wipe and file across part edges and surfaces in an action that deburrs, blends edges, and surface-finishes parts.

Filament configurations include round crimped, round straight, or rectangular. Rectangular filaments, having a larger cross section, are stiffer and more aggressive than round filaments. They also provide greater abrasive contact with the work surface.

Nylon, an ideal material for brush filaments, has excellent toughness and fatigue properties as well as moisture, abrasion, and chemical resistance compared to other polymers. Its good memory (ability to return to its original position after deformation) lends itself to brushing.
Configurations of nylon abrasive filament brushes are wheel, disk, cup, tube, and end.

Of the nylons used in the production of nylon abrasive filaments, Type 612 offers the most heat resistance and is preferred in industrial applications. Normal percentage of abrasive grit weight to total filament weight is 20-40%.

Common Grits. Abrasive grits commonly used in nylon filaments are silicon carbide and aluminum oxide. Silicon carbide has excellent hardness, toughness, and sharpness, and is cost-effective for use with nylon filaments. The silicon carbide used in these filaments has less than 0.1% iron oxide and no free iron, therefore they can be used on nonferrous metals, such as aluminum, without corrosion caused by iron contamination.

Tougher than silicon carbide, aluminum oxide is less likely to fracture, and is used for finishing softer metals. It's also used when risk of carbon contamination raises concern in hi-tech applications, especially in the aircraft, aerospace, and biomedical fields. Filaments with cubic boron nitride (CBN) and diamond abrasives are also available. Although diamond and CBN are harder than silicon carbide, their high cost (almost 100 times more than silicon carbide) prevents their widespread use. Further, the softer nylon filaments wear away long before expensive, harder abrasives wear out.

Abrasive grits in round filaments generally range in size from 46 to 600; grit sizes available in rectangular filaments vary from 80 to 320. Grit sizes represent the mesh number used in abrasive particle separation. Smaller grit numbers relate to coarser grit particles. In round filaments, grit size decides filament diameter (coarser the grit, larger the filament diameter). Rectangular filaments, regardless of grit size, are offered in 0.045 X 0.090" (1.1 x 0.3 mm).
Although grit sizes range from coarse (46) to fine (600), NAF brushes do not remove material rapidly like grinding wheels or coated abrasive products. They only remove very small amounts of material, changing surface characteristics and improving microfinish, and are considered surface-finishing tools.
The manner in which abrasives are held govern their material removal and surface-finishing capabilities. As a test, researchers ran an 80-grit coated abrasive belt and an 80-grit rectangular NAF wheel brush on a surface mirror-finished to 4 痣n (0.1 痠) Ra to compare their finishes. The belt made deeper scratches and removed larger amounts of material compared to the NAF brush. Checking the finish showed that the belt generated a 100 痣n (2.54 痠), Ra finish. Even with aggressive rectangular filaments, the NAF brush only produced a 30 痣n (0.76 痠) Ra finish.
Brush configurations include wheel, disc, cup, end, and tube. They are used on automated equipment such as CNC machines, robots, and other specially designed automated set-ups. They are also used on manual and semiautomated equipment such as air and electrical portable tools, bench/pedestal grinders, buffing and polishing lathes, drill presses, and milling machines.

Brushing Benefits. The NAF brushing process offers several benefits to the end-user:
During use, sharp new abrasive grains are constantly being replaced as nylon wears against the work surface. This provides constant brushing action throughout the brush life. Brushes accommodate various part contours due to their compliance and filament nature. Compliance accommodates small errors in part positioning and slight variations in part or burr sizes, making them good candidates for robotic and automated workstations. It also prevents damage to value-added components, and hence minimizes/eliminates scrapping of components, unlike rigid tools. Automation is practical, thereby making deburring and edge-radiusing processes less labor intensive and time consuming. Due to the use of automation, medical conditions such as carpal tunnel and tendinitis can be prevented. No coolant is required under normal conditions, therefore no waste is produced by the operation, leading to a clean and dry working environment. Dedicated equipment is not needed because the brushes can be used on standard production machines, robots, and automated workstations. Operations are possible in a single setup, thereby eliminating the need for additional part handling or refixturing. No part preparation or post cleaning is required. Generally NAF brushes are a cost-effective replacement for tedious manual methods, non-woven abrasives, mass media finishing, buffs and compounds, abrasive flow/jet machining, air blasting, and thermal and electrochemical deburring methods.

Deburring Solutions. Effective deburring solutions can be engineered by controlling brush and process parameters that affect brush aggression and performance. Here are some guidelines to customize these parameters to suit your specific application.

Filament Configuration. Use rectangular filaments for all applications except when reduced aggression is required, especially when processing softer metals such as aluminum and brass. Round filaments provide added conformability to accommodate part contour. Larger, rectangular cross-sections cannot get into the edges of small holes/slots and other features on parts. Filaments with 80-grit abrasive grains provide the most aggressive brushing to enhance productivity.

Grit Size. Use 80 grit for all applications except when reduced aggression is required, especially when processing delicate parts and softer metals such as aluminum and brass; generating minimal edge breaks; producing a desired surface finish; or when smaller filament cross-sections offered in other round filament grit sizes are more suitable to get into the edges of small holes/slots and other features on the part.

Abrasive Type. Silicon carbide is best for all general applications. Use aluminum oxide only in cases where silicon carbide causes part discoloration or raises contamination concerns in certain nonferrous applications.
Diameter and Trim Length. They depend on the size and shape of the workpiece, and process/ equipment constraints including available spindle speeds and maximum brush diameter. Machine guard clearance or space limitations between brush face and work surface determine this diameter. Wheel brush diameters are sometimes chosen based on trim lengths. Generally, larger diameter wheel brushes have longer trim lengths. This longer trim is required to adapt to contoured parts and for parts requiring greater wiping and filing action. In many cases, each wheel-brush diameter is available with various trim lengths to create different degrees of conformabilities and brushing characteristics.

Process Parameters. Depth of Interference (DOI) is analogous to depth of cut in machining. It depends on trim length and spindle speed. Longer trim can accommodate greater DOI. Slower spindle speeds allow greater DOI part geometry, contoured parts require greater DOI to allow filaments to adapt to contours and wipe and file across all edges and surfaces.
Spindle Speed. It depends on brush diameter, DOI, and part geometry. Spindle speed, along with brush diameter, dictates surface speed. Usually, NAF brushes operate at surface speeds below 3500 sfm (17.8 m/sec) to prevent overheating and smearing the nylon onto the work surface. Higher speeds can be accommodated by using coolants.