Fence post selection the options

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New Star Pickets / Posts for Fencing and Electric Fencing a Informed Guide :

This guide is to assist farmers and users of Fence Posts and Star Pickets to be informed  on the benefits of alternative Star Pickets to the traditional Fence posts and the considerations  in making a choice between the various  options that are available the durability and comparison of the features of the posts in the Marketplace.

Fence posts traditionally timber types initially cut from adjacent timber stocks on or nearby fencing installations , with the advent of the Waratah lodging a patent for the steel star picket in 1926, there has been a progressive change to this as the mainstay. Initially this type of post became the benchmark , as other producers entered the market place with copies of the “Waratah” and the steel and manufacturing costs increased the quality and performance of the Steel post has been compromised to offer a low cost product.

Protective coatings and steel quality have been reduced lowering the performance of these alternative products well below a quality product.

New to the marketplace is the Plastic posts and the hybrid plastic posts and systems that employ reinforcements.

When a fence is used as a barrier for livestock whether with or without electrification when it is rigid the livestock are more secure in pushing through the fence , when the fence flexes and can move the livestock become insecure as the fear of entangling in the fence discourages livestock from pushing through the fence. When the fence does not flex and spring and move it will collect debury in floods and the fence will be loaded up and fail as the material builds on the fence , if it flexes and springs the material will be released and the likely scenario of fence loss is reduced .

SUMMARY:

Choosing the Fence post for environmental performance the outstanding product is the Fibopost XT with the lowest CO2 emissions and the recycled content with excellent insulation properties there is no requirement for insulators and the plastic posts all give the fencer the ability to construct versatile electric fences with outstanding performance .

The strength is superior to all other plastic posts comparing the materials is double in strength and many times stronger than the other plastic posts, when compared to steel the Fibopost is similar but as it is more flexible than the steel posts allowing a improved fence barrier .

Care should be taken in choosing PVC based fencing where there is a genuine risk of fire and the PVC could generate toxins TCDD's which can contaminate livestock and ground.

Cost advantages must be considered for electric fences a complete plastic post Fibopost XT does not require insulators or additional fittings for electric fences which means that any wire , mesh , ringlock or other systems can be electrified without cost of insulators.

As the plastic post is the insulator there are no developed leakages across the plastic insulators as they weather , salts and dust build up on the plastic insulators fixed to steel posts where in moist conditions rapid tracking or leakage can occur reducing the effectiveness of the electric fence.

Plastic posts will not rub the wires as they expand and contract .

Comparing Costs electric Fence

Steel post + insulators x 2-4 + wire or other conductor (braid / tape) + delivery of posts (weight 2.8 -4.0kg / 1800mm post) + rust and corrosion + CO2 emissions 0.4t CO2 / t steel Australian made

Fibopost XT + wire or other conductor (braid / tape) + delivery of posts (weight 0.9 -1.2kg / 1800mm post) + CO2 emissions 0.195t CO2 / t Fibopost XT

Therefore the steel costs more in insulation , rust , 3 times delivery cost and 4 times more expensive in CO2 emissions

Considerations when using Steel Star Pickets are:

Rusting , if the coatings Bitumen are not  hard or thick enough they will be weathered  off, abraded off during installation , if  the post is bent  to straighten during installation the coating barrier  on the post will  damaged and the  rusting / corrosion  with significantly increase , the base line for steel exposed is average rate of rust is 0.4 kg / yr / m² based in this and poor quality porous steel will corrode rapidly and be unserviceable  in less  than 2-5years pending the conditions.

In the production of the Steel Star pickets the holes are punched into the steel this can leave a sharp edge  and this is noticeable  around the holes  typically on one side  of the star picket, this is a serious problem where the wire  expands and contracts due to the  heating and cooling both overnight and during  daily variations the movement which can be significant in extremes. In a moderate climate with a + 200m strain of wire the movement could be up to 30mm . eve a small movement will cause protective coatings on the wires to be worn and the corrosion is then accelerated. Where  Timber posts were used and holes drilled through the posts the wires remain serviceable without rust or other issues +80years.

When the Steel posts are driven in the tops of the posts sharpen due to the impact and these  edges harden and become  a hazard that is now  well recognised and many jurisdictions require that he posts are capped to prevent injuries from  this.

Steel is unforgiving and these steel pickets are not recommended to be used in roadside work zones as they are not frangible , the same applies to applications where animals apply pressure to fencing systems. When Steel bends it stays bent !

Steel posts are very conductive and provide a excellent electrical connection to ground , this means that very good quality insulators with very good insulation properties must be used to  prevent  leakage from the  electric fence across the small distance of the typical insulators to the metal post.

Posts manufactured in established industrial countries emit around 0.4t CO2 / t steel, and in developing countries (China)  0.9t CO2 / t steel , neither of these number take into consideration  the cost of delivery to the farm or fencing site of the posts.

Electrical insulation ZERO

Ultimate Tensile Strength MPa 350-500

Considerations when using Timber Post are:

Whether the  wires are threaded through holes in the post or stapled to the posts there is no rubbing or loss on the wire causing wire premature rusting and corrosion.
Timber posts are subject to rot , termites and other bugs that are particular to specific species.

Copper Chromium Arsenate(CCA) treated timber leaches chemicals . In New Zealand CCA treated timber for new or replacement construction must be discontinued from 1 July 2010. Many other jurisdictions are phasing out the use of this type of post.

Timber posts are expensive and careful consideration should be given to utilising this precious resource in  fencing  and other post applications that will not realise the benefits to the environment of this resource.

Timber posts actually store carbon and then have a negative carbon value -10.0t CO2 / t timber. but of course this is reversed where the post is burnt or disposed of and the carbon is released.

Considerations when using Plastic Posts (thermoplastic) :

First the consideration of the material used in the manufacture of the post is the most important consideration and the plastic posts have been divided into the most  common materials.
Plastic posts have a distinct advantage that they do not rust or corrode like Steel.
All Plastic posts should have holes to match steel or timber post hole spacing , this provides a basis for the wires to be spaced and matched to existing fencing systems.

FIBOPOST XT  recycled modified PET glass reinforced Fence Post :

This post utilises a proprietary manufacturing method where the PET polymer is modified and reinforced with orientated fibreglass and formed into a variety of different posts.

As Fiboplas materials have a   Deflection Temperature  223 - 255ºC combining this  with  high melting temperature 280ºC makes this material ideal in respect of temperature and is suitable below -20ºC.
Installation of these Fiboposts is different than steel and care should be taken as energy can build up during the driving resulting in significant flex ( see driving notes shipped with the product)
Fibopost XT products  are difficult to burn and usually require continuous application of flame to maintain a burn.  Flammability, UL94 typical  V-0
Fibopost XT will not shatter but are frangible. While 4WD and construction and mining equipment can run over the post they will not puncture the tyres
Electrical insulation - Dielectric Strength nominal PET 40kV/mm
CO2 emission's  Fiboplas XT products   0.055t CO2 / t Fibopost XT (note that CO2 emissions were generated for the original  waste material)
FIBOPOST XT prevents waste going to the landfill, being burnt or even shipped overseas the material is processed where the waste is created.  1 t Fibopost XT saves 6.2 cubic metres of landfill space
Ultimate Tensile Strength MPa 300
       

PVC  Fence Posts (Polyvinyl Chloride rigid )

The most common fence type utilising PVC is the post and rail type fencing there are a number of products also used as posts for typical electric and wire fencing applications.
When PVC burns it  produces TCDD Tetrachlorodibenzodioxin is classified as carcinogenic class I which is the highest step in the classification of the IARC (International Agency of Research of Cancer). In Farming enterprises this product can enter the food chain rapidly .  Flammability, UL94 typical  V- 0
PVC can become brittle when incorrectly formulated without the correct UV stabilisers and when aged on impact shatter and splinter on impact  or extreme flexing ( consider PVC down pipes on the side of buildings they are perfectly functional but  a impact on aged  pipes will cause them to shatter and splinter . This obviously is a issue in any fencing application .
Where the PVC is reinforced or modified the aging and impact issues are greatly improved .
When selecting plastic fence posts it is imperative that the post can perform in extreme temperatures , a measure of this is the heat deflection temperature that is  at given temperature the post will flex just because of the temperature : Deflection Temperature PVC typical 78ºC
Electrical insulation - Dielectric Strength nominal 17kV/mm
CO2 emission's  PVC products   2.0t CO2 / t PVC + production of Post emissions
Ultimate Tensile Strength MPa 42

Polyethylene - “PE” Fence posts (LDPE , HDPE , UMPE)

The Polyethylene group makes up a large variation of products both recycled posts and virgin posts , although posts most commonly are recycled materials of this type to keep them competitive in the market place .
As PE materials have a very low Deflection Temperature  typical ranging from 40-90ºC combining this  with very low melting temperatures ranging from  100-130ºC.
Consideration of fire rating must be considered as the PE products  burn rapidly and will melt and fuel a fire rapidly, most often the PE products are not rated for fire due to there flammability
To increase the performance of the PE products often fillers are added to improve the stiffness . When timber or saw dust is added water absorption will increase  and the effectiveness of the post as a insulator is decreased or even compromised.
Recycled PE posts will be difficult to drive into the ground  due to the flex and absorption of the impact of drivers , it should be considered to dig a hole for the installation of this type of post, although driving them in is  common in some soil types.
Electrical insulation - Dielectric Strength nominal LDPE 17 – 27kV/mm , HDPE 17 – 30kV/mm and  UMPE +35kV/mm
CO2 emission's  PE products   1.8 - 2.2t CO2 / t PE (virgin resins) + production of Post emissions
Ultimate Tensile Strength MPa 10-43

Reinforced PE  posts not common but their performance is dependant on the reinforcement employed in the design of the post.

Polypropylene glass reinforced  Fence Posts


The Polypropylene group makes up small group of posts where the  glass reinforcement increases the properties of the Polypropylene resin
As PP/Glass materials have a  Deflection Temperature PP/glass typical ranging from 138-150ºC combining this  with  low melting temperatures ranging from  134 – 174ºC consideration  must be given to utilising this post in extreme temperatures.
Consideration of fire rating must be considered as the PP products  burn rapidly and will melt and fuel a fire rapidly, most often the PP products are not rated for fire due to there flammability but glass filled rated  Flammability, UL94 typical  HB (the lowest rating)
PP is a excellent absorber of energy so is very difficult to drive into the ground , it is best to pre drill holes so that the post is not damaged during the installation .
PP/glass posts will not shatter and are frangible.
Electrical insulation - Dielectric Strength nominal PP/glass 40kV/mm
CO2 emission's  PP/Glass products   5.0t CO2 / t PP/glass (3.7-7.75 t CO2 / t PP/glass) + production of Post emissions
Ultimate Tensile Strength MPa 60-125


Polyethylene Terephthalate (PET)  Fence Posts:

The PET resin posts are small group that are  not reinforced and are often injection moulded to specific sizes , due to the crystallinity which varies from amorphous to fairly high crystalline .
 As PET materials have a   Deflection Temperature PP/glass typical 150ºC combining this  with  high melting temperatures ranging from  255-280ºC makes this material ideal in respect of temperature.
Care should be taken on the installation of these products as they can be brittle and shatter under impact with very sharp pieces resulting.
Consideration of fire rating must be considered as the PET products  are difficult to burn and usually require continuous application of flame to maintain a burn.  Flammability, UL94 typical  V-0
PET posts will shatter on impact often resulting in sharp pieces and are frangible.
Electrical insulation - Dielectric Strength nominal PET 50kV/mm
CO2 emission's  PET products   5.0t CO2 / t PET  + production of Post emissions
Ultimate Tensile Strength MPa 26- 155

The information contained in this guide is provided in good faith and is believed to be accurate at the date of issuance. FiboplastInd. Pty Ltd makes no representation of the accuracy or comprehensiveness of the information and to the the full extent allowed by law excludes all liability for any loss or damage related to the supply or use of the information in this guide. The user is cautioned to make their own determinations as to the suitability of the information provided to the particular circumstances .

©Fiboplast – Andrew Wytkin March 2011
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