Steve Saxion
Dimension Bond
Chicago, Ill.

A bonded film in cross section reveals the layered structure that forms the insulating barrier for GFTP parts. The substrate ( bluegray) is covered with nanosized reinforcement particles (pink) in a binder material. The black and dark gray layers above the reinforcement particles are films that reduce friction and wear.

A bonded film in cross section reveals the layered structure that forms the insulating barrier for GFTP parts. The substrate ( bluegray) is covered with nanosized reinforcement particles (pink) in a binder material. The black and dark gray layers above the reinforcement particles are films that reduce friction and wear.


Glass-filled engineering thermoplastics (GFTPs) can replace metals in many applications. GFTPs are lightweight, stiff, strong, and inert to most process fluids and corrosives. And they can be molded to accurate, finished dimensions without secondary operations. But parts made from the materials can act like sandpaper when they rub against mating components and counterfaces. The culprit: glass fibers protruding from the plastic surfaces.

Previous approaches to improve surface properties of GFTP parts have had mixed results. Conventional dry-film lubricants, for example, lower surface friction but are sheared by glass fibers protruding above the plastic. Coatings that rely on thermal curing are typically processed at elevated temperatures that degrade most plastics. Further, coatings don't adhere well to the glass portion of the composite.

But a process of direct-bonding wearresistant films to both plastic and glass from Dimension Bond, Chicago, Ill., solves the abrasion problem. It directly bonds one of several bearing-grade films to such glass-filled GFTP thermoplastics as nylon, PBT, PET, PPS, and PPO. Film-to-GFTP bonding takes place without the elevated temperatures of conventional coatings.

The films are made of multiple, laminar layers of matrix resinous bonding materials and nanocomposites. One formulation has the wear properties of bronze with a top layer of pure PTFE. The film cross section is similar to that of a bronzefilled, DU-style bearing with a PTFE top layer. Other formulations exceed the wear rate of bronze but with lower inherent dry friction. Wear rate is three to four-times that of bronze-PTFE bearing materials.

Film thickness depends on the application but ranges from 0.0005 to 0.009 in. To some extent

the percent of glass filler determines the amount of glass protruding through the surface. Films must cover the glass projections and extend to some additional "insurance" depth. An engineering rule of thumb says to cover the surface with a first layer 1.5 3 taller than the glass projections. To this first layer are bonded top layers that lower friction, boost wear resistance, or both. Final bonded-film thickness is typically 0.0011 to 0.009 in.

WHERE BONDED FILMS MAKE SENSE
Bonded
Total fil
Relative wear
film
thickness
life versus
Applications
designation
(in.)
bronze/PTFE
L36
0.0007 to 0.003
12
Rack-and-pinion rod support
 
Shaft-end bearings and guides
 
Wheels
 
Hubs
 
Supports for heavy loads against
 
smooth, ground counterfaces and O-rings
 
Elastomer-seal counterfaces
 
and mating surfaces
L23
0.0007 to 0.0045
7
Electrical switches
 
Pump components
 
Thrust faces
 
Printer parts with high
 
cycle and surface speeds
L9
0.0005 to 0.007
14
Automotive and apliance components
 
Water-conditioner parts
 
Solenoid bobbins with lower quality,
 
rough counterface surfaces
Can be applied to glass-filled engineering plastics such as PBT, PPS, PET, PPO, PEEK, acetal, nylon, polyester, polycarbonate, and others.