Cold Flow, otherwise referred to as creep, is the dimensional change over time of a material under a physical load.  All materials cold flow, to varying degrees, when a load is applied.    After the load is removed, Memory is the ability to return to its original dimensions while Compression Set takes place when the material does not  return to its original state.  Material wear, or loss of material, must not be confused with Cold Flow.  A product will weigh less after it wears, but will weigh the same after it Cold Flows, or simply changes its shape.  A typical value for comparing materials is given in pounds per square inch or p.s.i.  Therefore, the higher the PSI rating the more Cold Flow Resistant the material is. Material characteristics will vary with time, temperature, rate of loading, part density and wall thickness.

Coefficient of Friction, or C.O.F., is a value (number) used to compare how hard or how easy two materials will slide against each other.  Lubricated or greased “Steel-On-Steel” is around 0.1 while dry, or un-lubricated, “Steel-On-Steel” can be 0.5 to 0.8 or higher.  There are many factors that will effect the C.O.F. between two surfaces.  Some of these are of course lubrication, surface texture, material hardness, and the material itself.  Generally speaking, constant lubrication is required to maintain low frictional properties.  However, some plastics or polymers, like Nylon or UHMWPE, have a very low C.O.F. against a smooth steel surface even without any lubrication.  Other polymers, like a soft urethane, can have a very high C.O.F. unless lubricated.

Technically, the Molecular Weight is the average weight of a molecule in a material.  It is actually the “sum of the atomic weights of all the atoms in that molecule”. In laymans terms, the higher the Molecular Weight – the longer the molecular chains, and therefore the denser the material.  For instance Nylons and Polyethylenes can be processed into various molecular weights – low density – less than 50,000, medium – 50 to 100,000, high – 100,000 to 2 million, very high – 2 to 3 million and ultra-high densities from 3 to 6 million.  For instance the lowest polyethylene products range from candle wax and shrink film, to the medium and high densities of bottles and toys, to the ultimate Ultra High Molecular Weight Polyethylene, or UHMWPE.  The low molecular weight materials process very easily while the Ultra-High material is extremely difficult to produce.

ZefTek, Inc. uses our registered trademark, ZefTuf, as a “prefix” for the engineering grade materials we use in our product line. When UHMW’s, Polyethylenes, Urethane’s, Nylons and composites are selected, ZefTek Engineers will specify material properties and chemistry depending upon the products performance criteria.   From cold flow resistance, impact strength, and self lubrication properties to abrasion resistance and operating temperatures, each formulation is designed for the specific product solution.  Currently, some 25 different “Engineering Grade” formulations fall under the ZefTuf® name. When ZefTek analyzes a “problem area” and decides to improve on the application, we input all of our R&D efforts and our team selects the design and material we feel has the greatest chance for success.  Prototypes are lab and field tested and eventually become “standard production products”.