Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

Understanding the Characteristics of Turcite ®

It is only rarely that a marketing push succeeds so much that the brand name becomes synonymous with the product itself. When Turcite® B was first introduced, PTFE itself had been around for quite a while. Yet, so effective was the branding of this variant of PTFE that everything from the properties, to the composition to the colour merged under a single umbrella and became known simply as “Turcite®”. The material itself has become a mainstay in the industrial goods market with machine tool builders, re-conditioners and bearing manufacturers demanding it for their applications.

As the market expanded, new manufacturers developed their own variants under different brand names (ours being Lubring), which all succeeded in their own way. However, to this day, clients will initially demand “Turcite®” – following which there will be a brief discussion about the fact that our material is equivalent to Turcite®, but that we brand it under a different name. Usually the client is happy as long as the properties match and that the colour of the material matches the turquoise-green shade developed specifically for Turcite®.

We want to take a closer look at this material, because despite it’s widespread usage, there are always questions from clients regarding the application and installation of this material. We will look at the following aspects:

  1. What is Turcite® (Lubring)
  2. Where can it be used? What are the possibilities and limitations?
  3. How must it be installed?

 

What is Turcite® (Lubring)?

Quite simply – Turcite® is PTFE impregnated with fillers and additives that serve to enhance the wear properties of the material. It is used, most often in a sheet form, in thicknesses ranging from 0.5mm (0.02”) to 4mm (0.16”), although in some applications, it is also used as a bush and in more rare applications it is used as a thick plate.

Around the world, Turcite® is identified by its distinct turquoise (blue-green) shade. While some may mark this as another branding tactic, the pigment used is not a random choice. Studies of the wear properties across different PTFE-pigment combinations show that the specific pigment used in Turcite® (Lubring) sees a spike in the wear resistance of the material. It is clear that there was a significant amount of R&D done before the specific shade we use today was selected.

When we look at terminology, there are a few variants used around the world. Other than “Turcite”, we have had clients refer to the material as “Turkite”, “Turquite”, and “Torquite”. Clearly the original name itself has spread far enough and for long enough to spawn organic variations in different regions of the world.

Being based on PTFE, the material cannot be extruded like a normal plastic sheet and instead needs to be “skived” – the process most commonly used to make thin PTFE sheets. Also, the material will not easily adhere to other surfaces – another feature resulting from its PTFE base. Therefore a chemical etching is required on one surface of the material, so the sheet can be bonded to other articles.

In a broad sense, Turcite® (Lubring) offers the following key advantages:

  • Very low friction for reduced power loss
  • No stick-slip for positional accuracy / control
  • Good specific bearing loads
  • Low wear for long life
  • Excellent chemical resistance / fluid compatibility
  • Unlimited shelf life
  • High temperature resistance
  • Absorbs vibration during machining

 

Applications of Turcite® (Lubring)

Most commonly, Turcite® (Lubring) has been used in the machine tool industry where it serves to either replace or reinforce standard phosphor-bronze LM guideways. The material was earlier used primarily to recondition old machines in which the guideways had worn out. However, increasingly it is incorporated in new machines as well – owing to the higher life and lower maintenance required in comparison to metal guideways.

As mentioned above, Turcite® is also used as a bush – which needs to be specially moulded and machined as per the customer’s requirements. These bushes are usually replacements for metal bushes – especially in areas where the lubrication of the metallic bush is as issue. Turcite® – and in fact all PTFE grades – has self lubricating properties which means it can function deep within a sub-assembly taking enormous wear loads and does not need to be lubricated constantly to avoid damage.

However, the material is not an out-and-out replacement for metal. Being PTFE based, the material has a compressive strength limited to 150 Kgs per square cm (2,200 psi). This means that a single square foot of Turcite® can accommodate a load of up to 150 Tonnes – which is more than sufficient for most applications. However, it is also a soft material (Shore D Hardness: 50-60) – meaning that point loads and excessive squeezing of the material can cause deformation.

Another limitation is with regards to insulation. Although the material has excellent temperature resistance (up to 260 Degrees Celsius/ 500 Fahrenheit), it does not have any electrical insulation.

In all, the industries for which we have supplied Turcite® (Lubring) include:

  • Automotives
  • Machine tool
  • Infrastructure
  • Nuclear power
  • Casting and forging
  • Textiles
  • Pumps and valves
  • Pipe liners

 

Installation guidelines for Turcite® (Lubring)

Preparation: The metal surface to be mounted with Turcite® (Lubring) can be prepared by the normal machining methods such as, grinding, milling, shaping, and planning. The surface roughness of all forms of preparation should be preferably between Ra = 1.6 µm and Ra = 3µm and not more than Ra = 6µm. Once roughened the surfaces can be cleaned with Trichloroethylene, Perchloroethylene or Acetone.

Bonding: For bonding of Turcite® (Lubring) the following resin adhesive can be used: Ciba Geigy's Araldite - Hardener - HV 953U; Araldite AW106. The Araldite should be applied both to metal and Slideway and be spread as uniformly as possible by means of a serrated spatula. To obtain the best dispersion of the adhesive, when spreading on the surface brush in the longitudinal direction; when spreading on the metal, brush in the transverse direction. The total quantity of bonding should be approximately 200gm per sq. mt.

Hardening: After mounting the slideway a clamping pressure of between 30-35 Kg/cm2 is recommended. It is important to keep the pressure constant during the hardening process. Due to the differences in the thermal expansion coefficient of the materials, maximum curing temperature should not exceed 40°C. The hardening time for various temperatures is: 20°C min 15 hours; 25°C min 12 hours; 40°C min 5 hours.

Finishing: After curing of the adhesive, the Turcite® (Lubring) can be machined by conventional means – if required. The choice depends on the machinery available viz.: grinding; grindstone.

Grinding: For grinding of Turcite® (Lubring) use the same speed as grinding cast iron, taking care that sufficient cooling is used with an ‘open ’stone. The grindstone should be preferably silicon carbide based with rubber or polyurethane binding; grain size 80-30. Alternatively aluminum oxide with rubber bonding may also be used for soft, fine grinding action, pre-polishing and pre-mating treatment. 

Oil Grooves: Turcite® (Lubring) pads can be machined with oil grooves using the same methods and cutting data as used for cast iron. The form and depth of the oil grooves are optional. However, the oil grooves should never pierce through the Turcite® (Lubring) Slideway. Oil grooves should be away from the edges by 6mm.

Metal Mating Surface: The metallic mating surface running against the Turcite® (Lubring) pad should be preferably Stainless Steel (SS) 304 with a grade #8 mirror finish. Against this material, Turcite® (Lubring) will have a coefficient of friction of between 0.1-0.12.

 

Conclusion

The recent surge in PTFE prices has obviously had a substantial impact on the price of Turcite® (Lubring). However, owing to the ambiguity surrounding the material’s composition (many clients know it simply as “Turcite®” and are unaware that it is PTFE based), there has been genuine confusion as to why the price has increased recently. While it takes time and patience to convince clients that the price of Turcite® is governed by the price of PTFE, it does serve as yet another reminder of how an effective branding campaign can truly give a product its own identity.

Turcite® is the registered trademark of Trelleborg Sealing Solutions

Oil Free Polymer Bearings - Fluoropolymer Formulations for Applications Needing Self-lubrication

Benefits of PTFE

From a friction/lubricity standpoint, neat fluoropolymers – such as PTFE (Teflon) - have long been accepted as an ideal non-lubricated bearing material for low speed applications at moderate temperatures. They are maintenance free, offer extremely low coefficients of friction without lubrication, and are immune to virtually all chemicals. Linear bearings and other wear parts are commonly made from PTFE, to take advantage of their low friction properties and chemical resistance. 

Adding fillers to the resin blend improves long-term performance, especially under high temperature and load conditions.  A major reason for the application of plastic materials like PTFE, in sliding systems (like bearings) is their capacity to run – especially against metals – without lubrication. As such they surpass metals under conditions where the use of lubricants is impossible or undesirable. Also, if lubrication is possible, but full film lubrication is not achieved (e.g. at low speeds), PTFE maybe an attractive alternative for metallic running surfaces.

Additives such as Polyphenylene Sulfone (PPS) may be further added which would help the formulations to enhance the PTFE bearings last longer, handle higher loads, at higher temperatures, and resist cold flow under higher temperatures. Moreover, these gains are achieved without compromising the chemical resistance and/or lubricity of the bearing. The same PPS additives also improve bonding of PTFE to metallic reinforcement rings.

Past remedies have included reinforcing fibers and PAR or PI additives. Each has improved life and expanded the operating envelope of PTFE. Reinforcing fibers increase resistance to wear and cold flow, but only at the expense of lubricity. Fibers on the bearing surface can also mar metal parts that move against the fluoropolymer, increasing friction, heat and wear.

Formulated PTFE, on the other hand, provides more durable alternative to fibers in harsh environments, or those involving chemical exposure. Also, as a customized PTFE bearing material, it offers greater resistance to both wear and cold flow while retaining the lubricity and chemical immunity of neat fluoropolymers.

 

Some of the commonly used fillers of PTFE:

Practically any material that can withstand the sintering temperature of PTFE can be used as filler. Characteristics such as particle shape and size and the chemical composition of the filler greatly affect the properties of the compound. Through a proper combination of base resin and one or more fillers, compounds could be tailor-made for many end-uses. And compounding technology continues to develop and given the wider scope of this innovation, it is likely to go on doing so.

  • Improved resistance to cold flow or ‘creep’
  • Reduce wear and friction
  • Increased stiffness
  • Increased thermal conductivity
  • Increased thermal dimensional stability
  • Increased surface hardness
  • Increased electrical conductivity

 

Glass fiber is a widely used filler. It improves the creep resistance of PTFE both at low and high temperature. It is chemically stable (except to strong alkalis and hydrofluoric acid-HF).

Amorphous carbon is one of the most inert fillers, except in oxidizing environments where glass performs better. Addition of Carbon adds to the creep resistance, increases the hardness and raises the thermal conductivity of PTFE. Filled PTFE compounds with Carbon have excellent wear properties, more so when combined with Graphite. This combination of properties makes carbon/graphite compounds the preferred material for non-lubricated piston rings.

The use of a softer carbon has the additional advantage that it lowers tool wear during machining, thus allowing machining to very close tolerances. Also, Carbon-containing compounds have some electrical conductivity and are therefore antistatic.

The addition of Carbon fiber to PTFE changes its physical properties in the same way that Glass fiber does: Lower deformation under load, higher compressive and flex modulus and increased hardness.  Fillers with carbon fiber in PTFE have the advantage of higher thermal conductivity and lower thermal expansion coefficients than glass-filled ones with the same filler percentages, and they are lighter. They wear less in contact with most metals and are also less abrasive on the mating surface. The wear in water is particularly low. This makes carbon-fiber-filled PTFE an excellent bearing material, especially when lubricated with water. It is widely used in the automotive industry for bearings and seal rings, for example in water pumps and in shock absorbers.

Graphite is a crystalline modification of high purity carbon. Graphite-filled PTFE has one of the lowest coefficients of friction. It has excellent wear properties, particularly against soft metals, displays high load-carrying capabilities in high-speed contact applications and is chemically inert. It is often used in combination with other fillers.

Molybdenum disulfide adds to the hardness and stiffness of PTFE and reduces friction. It is normally used in low percentages and together with other fillers.

Calcium fluoride is suitable filler for PTFE in uses where it encounters chemicals that attack glass, such as hydrofluoric acid and strong alkalis.

Alumina or aluminum oxide is an excellent electrical insulator and is used to improve mechanical properties of compounds. As it is very hard, machining of the sintered part should be avoided whenever possible

In recent years, Polymeric fillers with sufficient heat stability to be used in PTFE have become available. Some remarkable properties have been obtained with polymer-filled compounds, particularly with respect to friction against soft metals.

Factors influencing tribological properties:

  • Load
  • Velocity
  • Sliding Movement-rotating/reciprocating
  • Degree of coverage
  • Ambient temperature
  • Filler-Percentage nature morphology
  • Preparation method of the finished part
  • Running-in conditions
  • Mating Surface
  • Material-surface roughness
  • Lubrication - Environment
  • Entrapped wear debris

 

The “pv” factor

The performance of PTFE bearings depends on the load and speed conditions to which they are submitted in the final application

The “pv” value is the product of the load “p” and the speed “v” and represents the reference factor for dry operating conditions.

By working within the recommended limits for the pv value, the temperature generated by friction, between the surfaces reciprocally sliding against each other, is assured to be well within the desired operating range.

In case the recommended pv limits are exceeded in dry operating, higher wear rates can be expected. In order to avoid that it is recommended to provide lubrication or a proper cooling of the bearing.

The limit ‘pv” values for dry operating of Fluoropolymer, PTFE bearings are:

  • For continuous use without any noticeable wear traces 0.35 N/mm2.m/s
  • For short time 1.7 N/mm2.m/s.

The specific load

The specific load limit for these bearings should not exceed 7 N/mm2. Load induces a deformation during the time, which is also function of the bearing wall thickness and that can negatively influence the bearing performance.

Higher values, up to 7 N/mm2, can be adopted by reducing the wall thickness using, for example, solutions obtained from tapes of thin thickness made through peeling of the desired formulated fluoropolymer cylinders.

The sliding speeds

The maximum sliding speed in dry conditions is 2 m/s. Higher speeds can be adopted provided lubrication or a proper cooling of the bearing is adopted.

Absence of lubrication

In many applications, lubricating two moving parts that are sliding against each other can pose a tough problem, because of the nature of the application itself, or for economical cost reasons. It is therefore essentially important, in such cases, to have the possibility to select bearings able that operate completely dry, offering in the meantime a proper performance level.

PTFE compounds do not need to be lubricated; that is one of their main attractions in use for bearings. Yet there can be circumstances where a lubricant or a process liquid is in contact with the surface. Almost without exception, the coefficient of friction of compounds is decreased by the presence of a lubricant, whether it is water, a lubricating oil or a solvent, but – perhaps surprisingly – the wear rate goes up in the presence of a lubricant. The reason, however, is simple. Under non-lubricated, dry conditions a very thin layer of PTFE is transferred to the mating surface and acts as an effective by lubricant. But the presence of liquid prevents or hinders this PTFE transfer. The degree to which it nevertheless happens depends on the nature of the liquid.

Water greatly increases the wear rate of PTFE compounds especially that of glass-filled types. Carbon/graphite compounds show the best performance. When surfactants are added to the water, and the surface tension is decreased to less than 27/dyne/cm1 the wear rate decreases sharply.

Generally PTFE formulated bearings, can operate:

  • For continuous use in dry conditions, up to 0.35 N/mm2 m/s, without any noticeable wear traces
  • For continuous use in dry conditions, up to 0.70 N/mm2 m/s, with extremely reduced wear rates
  • For intermittent use in dry conditions, up to 0.70 N/mm2 m/s.

The coefficient of friction

The dry coefficient of friction of formulated oil-free PTFE bearings depends on the load and speed conditions, as well as on the grade of finish and on the nature of the counter surfaces. It is generally comprised in the range between 0.04 to 0.28. If lubrication is available, the coefficient of friction is further reduced to a value around 0.02 to 0.04.

The (mating) counter-surfaces

Oil free bearings give the best performances in contact with hard counter surfaces. The bearings, if formulated correctly, adapt equally well against softer surfaces, such as the stainless steel, copper and aluminum alloys or plastic materials.

With regards to the finish of the counter surfaces, values between an average roughness Ra=0.2-0.6µm is recommended. Further, it is not advisable that the maximum roughness value should exceed Ra=0.8 µm.

Material and surface roughness of the mating surface are important variables in predicting wear. Against hardened steel, the general wear pattern remains the same, although the wear rate is usually lower. Soft metals should be used in combination with less abrasive fillers. Bronze or copper alloys should not be used in contact with bronze-filled compounds.

Both friction and wear increase as surface roughness increases. Where the mating surface is rough, compounds with abrasive components like glass or ceramic perform better as they tend to polish the opposing face. This also explains why initial wear on a clean surface is usually different from wear after an initial running-in period. The wear rates indicated refer to “steady state” conditions after such a running-in period.

 

High temperature applications

PTFE bearings can be used both at very low temperatures (-2600C) and in high temperatures (+2600C) – an exceptionally extreme range where normal lubricants would fail.

For high temperature applications, the coefficient of thermal expansion of the formulated PTFE bearings should be adequately considered.

Adopting proper formulation is therefore important, so that the customized polymeric matrix responds to thermal variations. These bearings modify their original tolerances and dimensions much more than metals.

Also, if appropriate precautions are not taken in the design phase, it can cause high mechanical stresses, for example in case of press fit installations in metallic housings, with consequent damages to the bearing assembly.

In applications where a wide temperature range is predictable, the use of tape bearings made from PTFE formulations provides the ideal solution.

A peculiar characteristic of these bearings is that, in case of anomalies in the application that could generate extreme conditions of load or temperature, they do not break, but simply deform, thus avoiding seizure or unwanted debris with consequent damages to other parts of the machine.

Environment

The environment also affects the wear properties of PTFE compounds. At very low moisture levels in air (40ppm or lower) wear rates increase. This is particularly the cause for compounds containing graphite, as this material tends to disintegrate when no moisture is present. The nature of the ambient gas also has an influence. Wear rates in nitrogen and helium is reported to be lower than in air.

Entrapped wear debris

During the process of wear, debris is formed, consisting of particles of the filler, of PTFE, and of the mating surface. Thus, wear rates can be lowered if the geometry of a bearing allows debris to expelled from the bearing. This can be done by machining radial grooves in a bearing surface. This is particularly effective with bronze-filled compounds

Space and weight saving

With respect to the conventional metallic bush, or ball bearings, oil-free PTFE bearings offer substantial saving of installed weight. In comparison to ball or roller bearings, PTFE bearing offer a consistent reduction of the radial space required.

Basic considerations on the operating and the design of oil-free PTFE bearings.

Summarizing, the adoption of oil free PTFE bearings offer the following advantages:

  • Dry running capability/self-lubricating properties
  • Low coefficient of friction
  • Low relative abrasiveness
  • Resistance to high loads
  • Operating temperatures from -2600 C up to 2600 C
  • Thermal dissipation and antistatic properties
  • Dielectric properties
  • Chemical inertness and non-toxicity
  • Dimensional stability
  • Flexibility and fatigue stress resistance
  • Vibrations dampening/low noise running
  • Low drying characteristics

Typical Applications segments of Fluoropolymer PTFE Bearings

Applications

Design Considerations

Product typology

Benefits

Cars and their components

  • Low coefficient of friction
  • High wear resistance
  • Vibration and noise absorption
  • Reduction of weight
  • Bearings and bushings also of special conformation
  • Weight and cost saving versus metallic solution.
  • Long life/reliability

Textile machines and components of the textile industry

  • Dry operation
  • Low coefficient of friction and high wear resistance in high sliding speeds conditions
  • Operating in wet environment
  • Chemical resistance
  • Resistance to abrasion caused by dusty environments
  • Low dirtying
  • Standard and ad hoc bearings and bushings
  • Lining of flexible rapiers
  • Sealing elements
  • Parts of special conformation
  • Plain PTFE and formulations offer the most suitable solution to customize the specific application requirements with standard or tailor-made products

Packaging and packing machines

  • Dry operating
  • Low coefficient of friction
  • Food compatibility
  • Reduction of installed weight
  • Standard and d hoc bearings and bushings
  • Parts of special conformation
  • Dry operating capability
  • Non-toxic
  • No risk of contamination the handled products and of the plastic films used for packaging

Machines of the food industry

  • Dry operating
  • Food compatibility / chemical inertness
  • Abrasion resistance
  • Mild counter surfaces
  • Standard and ad hoc bearings and bushings
  • Parts of special conformation
  • Special seals
  • Dry operating capability
  • Non-toxic
  • No risk of contamination the handled products
  • Low relative abrasiveness

Machine tools

  • Low coefficient of friction/ non-stick-slip
  • Tapes 1.5mm thick, etched for bonding, for slide ways lining
  • Very low coefficient of friction in the specific operating conditions

Dry reciprocating compressors

  • Non-lubricated or wet operating conditions
  • High wear resistance
  • Compression resistance
  • Piston rings
  • Cup seals
  • Bearer rings
  • Long lasting
  • Self-energizing qualities
  • Fatigue resistance

Valves and solenoid valves

  • Low deformation under load
  • Chemical resistance
  • Dimensional stability
  • Valve seats
  • Solenoid valve shutters
  • Resistance to deformation under load also at high temperatures
  • Chemical inertness

Bearing and sliding pads

  • Low deformation under load
  • Absence of stick-slip
  • Weathering resistance
  • Long lasting life
  • Sheets and tapes cut to size 2.5 mm thick, etched for bonding
  • Resistance to deformation under load Stick-slip free operating
  • Long life without appreciable wear

 

Wear testing

For the proper selection of dry running materials, tribological data on the material combinations in question are required. The tribological behavior of a material in given situations may strongly depend on their actual composition and structure. Since a general theory to predict this behavior from the first principles is not available, tribological characterization of the material must be based on experimental results.

The standard pin-on-disc friction / wear testing apparatus performed all the tests under identical conditions. A sample disc is spun under controlled conditions of temperature and velocity while a hard pin bears down on it under a known load. Loss of material due to the load is measured periodically to quantify a wear rate.

Pure PTFE, eight PTFE compounds and a Polyimide compound were tested according to the pin-on-disc test principle against normalized plain carbon steel discs. All specimens were manufactured under processing parameters corresponding to those used to make a commercial quantity of Fluoropolymer PTFE bearings material with 10-30 percent additive levels.  Specific loads were in range of 1 to 4 N/mm2, sliding velocity (v) from 0.1 to 2.5m/s; sliding distance amounted to 180km.

The wear factors (k) of most compounds were found to be in the range from 0.2 to 0.7. The dependence of k and f on the operational conditions is an important consideration in selection of the various compounds.

To measure the effect of surface roughness on service life test materials were tested against two different levels of surface roughness: 1 and 2 µm Rz

Usually, no damage occurred to the steel-mating surface. Glass fiber and bronze fillers however tend to scratch finely the disc at high load and speed. Carbon fiber and carbon graphite containing PTFE compounds may cause slight changes in the surface condition of the normalized steel. The presented data allow for the tribological comparison of the compounds under consideration and may contribute to the tribological proper selection of dry running materials. From these tests a few first comments can be made: the tested glass filled compounds and the bronze filled compound show high friction and wear at elevated speeds while showing relatively low friction and wear at low speeds. These compounds would therefore perform better as slowly running slide bearings than as high-speed compressor seals. The opposite is true for the carbon fiber filled compounds; they show relatively low friction and wear at elevated speeds.

Outlook

Linear drives, transmissions and actuator mechanisms have broad requirements for bearings capable of handling low speeds and high loads with zero maintenance. Examples are found in control linkages, clutch and shift mechanisms, shaft containment and housings. Self-lubricated PTFE bearings have proven to successful in thousands of such applications. With PPS improving wear resistance, dimensional stability and cold flow resistance, oil-free PTFE bearings are now ready to take on even more severe-service applications.

Recent achievements have important implications for designers of linear actuators, low-speed transmission, or gearboxes that incorporate linear, thrust, or plain rotary bearings. This implies that drive and bearing designers can take full advantage of the exceptional lubricity and chemical resistance of PTFE and other Fluoropolymer in higher-load and preload situations.

Solar Tracker Bearings - Cost Benefits from Injection Moulding

Our foray into Solar Tracker Bearings over the past few years has not come without a fair share of learnings.

While, the initial assumptions we had regarding the bearing design and polymer grade selection have not altered much, we have had to revise our understanding of the manufacturing process significantly.

Primarily, a solar tracker bearing needs to conform to a few parameters in order to be suitable for the application involved:

  1. Lightweight – this is essential because the more load the bearing places on the solar tracker mechanism, the higher the inefficiency of the system. Solar energy is sensitive to net energy losses within the system and the bearing should not be a drag on energy

  2. Low coefficient of friction – the smoother the motion of the bearing, the easier the system can move. Again, if it requires extra load to rotate the bearing within its casing, it leads to a new energy loss

  3. UV resistant – since the bearing is being used in a solar application, it is essential that the polymer does not degrade over the 15-20 years that the system is expected to be operational

  4. Load resistant – while different projects have different parameters on how much load the bearing needs to take, it is safe to assume that a single solar tracker bearing would need to withstand somewhere between 700-1200 Kgs of load without experiencing any fatigue or deformation over time

  5. Low cost – with most projects needing about 1000-2000 sets of bearings per megawatt, there is a high volume of bearings needed for a single project. One reason that standard pillow block bearings are not used in these projects is that they are prohibitively expensive in comparison to the polymer bearing assemblies
     

Below, we look at some of the key learnings along the above metrics and evaluate how our understanding has changed and allowed us to offer a more tailored and effective solution for this product.

  Existing designs Poly Fluoro designs Benefits
Weight Machined from rods, so parts tend to be bulky Injection moulded using special lattice structure Injection moulding offers significant weight reduction of up to 40%
Grade of polymer UHMWPE or PA6 Special blend of thermoplastic with PTFE PA6 has high moisture absorption, while UHMWPE is not injection mouldable in its standard form. Poly Fluoro uses special blends to give a low moisture absorption polymer that has the benefits of PTFE's self-lubricating properties
UV resistance Usually black pigment Uses HALs HALs offer a far superior resistance to UV radiation over the long term
Coefficient of friction 0.15-0.2 0.1 Using a thermoplastic-PTFE blend allows us to reduce coefficients of friction to within 0.1 and possibly below
Load capacity 700-1100 Kgs 700-1100 Kgs Poly Fluoro designs offer the same load capacity, but at much lower part weights
Cost 1X 0.6X The use of injection moulding allows us to lower material consumption, machining cost and gives a much higher productivity overall. This brings the cost down significantly

 

To summarise – we too had initially opted for the machining route in making these bearings. However, we find that using injection moulding allows us the freedom to lower the part weight, improve the blend of the polymer grade being used and increase productivity, thereby reducing cost while enhancing the effectiveness of the part.

The downside to injection moulding is that it requires a significant up-front cost in making the mould. However, our understanding is that the mould cost is effectively recovered within the first 1500-2000 sets of bearings made. In other words, a project that requires many thousands of bearings would recover the cost quite quickly. Furthermore, since the life of the mould is anywhere between 150,000 and 200,000 sets of bearings, solar companies would save significantly by standardising a bearing design and using this across multiple projects.
 

Poly Fluoro Ltd. is currently making solar tracker bearings under the brand name: HelioGlide. We offer standard sizes of bearings which can be incorporated even in smaller projects, where the total requirement may not be high.