Tufram – UK

TUFRAM® is a surface treatment method developed to improve the surface properties of aluminium and itsalloys. The process combines the properties of hard anodising and coating with fluorocarbons resulting in improved properties in a number of aspects:

  • High hardness
  • High corrosion resistance
  • Non galling properties
  • Close dimensions
  • Good electrik isolation
  • High wear resistance
  • Low coefficient of friction
  • Non-stick properties
  • Uniform coating thickness
  • No post machining

There are various coatings within the TUFRAM® family, all featiring the combination of properties but each of them optimised to one, or some, of them.

TUFRAM® L – 4
Highest hardness and wear recistance combined with good friction properties.

TUKRAM® H – 0*
Good non-stick properties, hardness and wear resistance

TUFRAM® R 66*
Best non-stick properties aspecially against rubber and urethane.

TUFRAM® C-22
Highest corrosion resistance combined with hardness and wear resistance.

Tufram® FC-12
Best dry lubrication by a combination of MoS2 / PTFE coating, together with high hardness and wear resistance.

TUFRAM® HCD-31
High hardness and wear resistance with good friction properties combined with hight dielectric strength, >2000 V at 50 um coating thickness in dry environment.

* The fluorocarbons used in the process are approved for the use in food and drug industry bu the US Food & drug Administration and the USDA.

HARDNESS
Aluminium oxide, which the TUFRAM® coating mainly consists of, is next to diamond the hardest non-synthetic material, in its hardest form, >VHN 2000, and a hardness of well over VHN 1000 in its softer structural form. The hardness in the coating is however lower due to a certain microporosity. Depending on coating thickness and aluminium alloy coated, the hardness varies between VHN 400 and VHN 600.

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Schematic illustration of TUFRAM® coating

The coating has good adhesion and will not peeloff as it is built up by chemical conversion of thesurface of the substrate material. Due to the high hardness of the coating TUFRAM® -treated parts can stand higher local loads than uncoated aluminium pieces. However, extreme loads can cause cracking of the TUFRAM® coating.

Wear resistance
The hardness of the aluminium oxide, of which the hard anodised layer consists is, as above mantioned, much higher than the Vickers hardness, that can be measured in the coating.

Because of this, the TUFRAM® coating shows considerably better resistance against abrasive wear than other materials and coating with much higher hardness. TUFRAM® coatings have better abrasive wear resistance than for instance case hardened steel and hard chromiumcoatings. Best wear resistance is achieved on material with low surface roughness. The figure below shows the difference in taber abraser wear test which is a method for evaluating abrasive wearresistance.

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Weight loss per 10.000 cycles at Taber wear test with wheel CS-17 and 1,000g load

Sliding properties
To produce the TUFRAM® coating fluorocarbons and other organic materials are used tocoat and impregnate the hard anodised layer giving it its unique combination of durable dry lubrication and wear resistance. Characteristic of all TUFRAM® coatings is their ability to prevent stick-slip, i.e. the difference between static and dynamic coefficient offriction is very small. The table below shows static cofficient of friction under dry conditions between different TUFRAM® coatings and steel, respectively, to another surface with the same coating.

Coefficient of friction

to steel to one another
TUFRAM®L-4 0,14 0,11
TUFRAM®H-0 0,15 0,13
TUFRAM®FC-12 0,21 0,19
Ytox® (hard anod. Al) 0,22 0,17
Anodised Al 0,30 —–
Hard chromium 0,23 0,18

After running-in and at higher loads TUFRAM® FC-12 has a dynamic coefficent of friction of approx. 0,10 to steel and approx. 0,05 to one another.

At wearsituations in which normally adheesive wear appears, TUFRAM® coatings prevent wear even on uncoated mating surface. Pin-on-disc tests have been performed under dry conditions with a steel pin in contact with a TUFRAM® coated disc. In the graph below, the endurance of the dry lubrications is shown for the, in this respect, most interesting TUFRAM® coatings. The graph is showing the number of cycles before coefficient of friction 0,3 is reached vs the load.

Corrosion resistance
TUFRAM® coatings provides a much better protection against corrosion than coventional hard anodising. TUFRAM® C-22 and R66 show little or no effect of corrosion after more than 2000 h Salt Spray Test in accordance with ASTM B117, TUFRAM® L-4, and HCD-31 will stand for more than 240 h. TUFRAM® R66 should be used in strong alkaline or acid solutions (pH>9 or pH<3) if there are no efficient inhobitors in the solution or ifthe exposure is at low temperature for a short time. In order to achieve the best corrosion protection pieces to be coated shold have no sharp edges, if possible all radii should be 10x the coating thickness. Also in blind holes, corners and at similar shapes the coating build-up can be disturbed.

Temperature range
TUFRAM® coatings provide exellent friction and slide properties within a wide temperature range. All types stand continuous use from -200ºC to +350ºC. At higher temperatures decompositions of the fluorocarbons in the coating will take place.

Change of dimensions
At hard anodising the coating is formed by conversion of the surface of the aluminium. As the aluminium on the surface is used for the formations of the coating the dimensional growth is not as big as the coating thickness.

Depending on the aluminium alloy the dimensional growt can vary between 35 and 50% of the coating thickness. Diameter of threads which are coated will increase with approx. twicethe coating thickness. Depending of the hight hardness of the coating, the possibilities to adjust dimensions of threads ans close tolerances on coated parts, are limited.

Applicable Aluminium Alloys
Chemical compositions of the aluminium alloy to be coated has a great influence on the properties of the coating and on maximum coating thickness. Also the color of the coating is affected by the alloyng elements and the coating thickness. There are no possibilites to dye the coatings. The table below gives some guidance for a proper choice of alloy.

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Specification at order
In order to be able to meet your expectations of thecoating, we need your helpwith some information.Yor order and drawings must therefore contain information about:

  • Customer name
  • Reference name
  • Delivery address
  • Means of transportation
  • Produce name
  • Produce number
  • Number of pieces
  • coating method
  • Coating thickness
  • Tolerances
  • Maskin off, if any
  • Critical surfaces
  • Surfaces for contacts (jig marks)
  • Type of alloy

Examples of applications
TUFRAM® opens new doors to your design work and give you possibilities for more cost efficient constructions. TUFRAM® is used in a wide range of applications. Below a few examples.

Manufacture Valve body, Cylinder housing Bearing, Motor housing, Transformator body, Shaft, Drying wheel, Cog-wheel, Cylinder, Piston
Vehicle Brake piston, Valve body, Fork tube, Rotor, belt wheel, Master cylinder
Pumps Housings, Impellers, Diffuser, Fittings, Lid, Bushing, Piston, Mambrane lid, Slide-valve, Shaft
Plastic Weld pad, Forming tools, Cores, Feeding screw, Press pad
Packing Guide, Cylinder, Roll, Forming pad, Pallet, Link, Flap
Food stuff Frying table, Form, Knife, Baking-plate, Funnel, Scraper,Tube
Defence Gable, Shield, Magazine lock, Bushing, Locking, Housing, Piston, Igniter holder, Rotor, Housing
Aircraft Shield, Driving housing, Cog wheel.