Method for forming wood fibres

A method of forming wood fibres for use in the production of a riding surface comprises feeding wood chips having a length, in the grain direction, of from 18 mm to 35 mm, to a milling machine adjusted to break the wood chips into wood fibres, the lengths of the fibres produced by the milling machine being substantially in accordance with the following percentages, by volume, of the total volume: ______________________________________ Wood fibre length Percentage of Total Fibre ______________________________________ 0 mm-5 mm 10%-20% 5 mm-15 mm 40%-55% 15 mm-35 mm 35%-50% ______________________________________ It is found that a surface formed from a compacted layer, several inches deep, of fibres produced by the above method has excellent characteristics for horse riding and these characteristics are not unduly affected by variations in weather conditions.

BACKGROUND OF THE INVENTION 
The invention relates to the production of wood fibres for use in the 
construction of all-weather horse riding surfaces. 
As is well known, the characteristics of conventional horse riding 
surfaces, such as turf and sand, vary according to the weather conditions. 
Also such surfaces are liable to serious damage, rendering them 
temporarily unusable, under extremes of weather conditions such as severe 
frost. To overcome these disadvantages it has been proposed to construct 
an all-weather riding surface from a thick layer of wood fragments, since 
such a surface is less susceptible to variations in weather conditions. 
Generally such riding surfaces have been formed from mixed wood residues 
from timber processing plants and have comprised a mixture of wood 
shavings, chippings, fibres and sawdust in variable proportions. It has 
been found, however, that an improved and more consistent surface may be 
provided by forming the surface from a more consistent mixture of wood 
fibres, and the present invention provides a method and apparatus for 
forming wood fibres in a mixture having desirable characteristics for use 
as a riding surface. 
SUMMARY OF THE INVENTION 
According to the invention a method of forming wood fibres for use in the 
production of a riding surface comprises feeding wood chips having a 
length, in the grain direction, of from 18 mm to 35 mm, to a milling 
machine adjusted to break the wood chips into wood fibres, the lengths of 
the fibres produced by the milling machine being substantially in 
accordance with the following percentages, by volume, of the total volume: 
______________________________________ 
Wood fibre length 
Percentage of Total Fibre 
______________________________________ 
0 mm-5 mm 10%-20% 
5 mm-15 mm 40%-55% 
15 mm-35 mm 35%-50% 
______________________________________ 
It is found that a surface formed from a compacted layer, several inches 
deep, of fibres produced by the above method has excellent characteristics 
for horse riding and these characteristics are not unduly affected by 
variations in weather conditions. 
The wood chips may be produced by the preliminary step of feeding timber 
into a wood chipping machine adjusted to produce said wood chips having a 
length, in the grain direction, of from 18 mm to 35 mm. 
Preferably the mean length of the wood chips is substantially 25 mm. 
In order to produce the proportions of fibre lengths referred to above it 
may be necessary to adjust the moisture content of the wood chips before 
subjecting them to the milling process, and the method may therefore 
comprise the further step of adding liquid to the wood chips, before 
milling, to adjust the moisture content thereof. Preferably the moisture 
content is adjusted to be in the region of 45%. 
The milling machine may be of a known form comprising a plurality of 
coaxially rotating elements each having mounted at the periphery thereof a 
plurality of hammers which, as the discs rotate, cooperate with a closely 
encircling peripheral surface to break the wood chips into fibres before 
passing the fibres through a screen. The screen preferably has a 25 mm 
mesh size. 
Preferably at least a major proportion of the timber from which said wood 
chips are formed is hardwood. Preferably also at least a proportion of the 
timber from which said wood chips are formed comprises whole natural 
timber including bark. 
To reduce the cost of transport of large quantities of wood fibres produced 
according to the invention, the milling portion of the method is 
preferably carried out at the site where the riding surface is to be 
constructed. A mobile apparatus for use in carrying out the above method 
may be provided, the apparatus comprising a wheeled support on which are 
mounted a hopper for receiving wood chips having a length in the grain 
direction of from 18 mm to 35 mm, a milling machine, a motor driving the 
milling machine, a conveyor delivering wood chips from the lower end of 
the hopper to the milling machine, and a conveyor delivering wood fibre 
from the outlet of the milling machine. 
The wheeled support may be self propelled or may comprise a trailer vehicle 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The mobile apparatus shown in FIG. 1 comprises a trailer vehicle 10 for 
coupling to a tractor vehicle and comprising a horizontal platform 11, 
rear road wheels 12, and front support legs 13 which are lowered to 
support the front end of the trailer when it is disconnected from the 
tractor vehicle. 
Mounted at the rear end of the platform 11 is an open-topped hopper 14 for 
receiving wood chips. An endless belt conveyor 15 extends upwardly from 
the lower, discharge end of the hopper 14 so as to deliver wood chips from 
the hopper into the upper feed inlet 16 of a milling machine 17. The 
milling machine 17 will be described in greater detail with reference to 
FIG. 2. 
The milling machine 17 is driven by means of a transmission, indicated at 
18, from a power unit 19 which may comprise a diesel engine mounted on the 
platform 11. 
A further endless belt conveyor 20 extends upwardly away from the outlet 
from the milling machine 17 so as to deliver wood fibres from the milling 
machine to a collection vehicle or storage pile adjacent the apparatus. 
Referring to FIG. 2, the casing of the milling machine 17 provides a 
downwardly inclined conduit 21 which leads from the feed inlet 16 into the 
upper part of a cylindrical milling chamber 22. Rotatable within the 
chamber 22 are a plurality of coaxial parallel beaters 23 each comprising 
a central square hub plate 24 secured to a shaft 25 and having mounted at 
the periphery thereof four equally spaced hammers 26 which extend radially 
outwards to a point just clear of the encircling peripheral wall of the 
chamber 22. The hammers 26 cooperate with the encircling wall surface to 
break into fibres the wood chips which are delivered into the feed inlet 
16 from the above-mentioned conveyor 15. 
The lower half of the peripheral wall of the chamber 22 is in the form of a 
screen 27 so that when the fibres have been broken down to a sufficiently 
small size they pass through the screen 27 into an outlet tray 28 from 
which they are picked up by the aforementioned conveyor 20. 
In use of the above described apparatus, wood chips having a length, in the 
grain direction, of from 18 mm to 35 mm, and preferably of substantially 
25 mm, are delivered to the hopper 14 from where they are delivered by the 
conveyor 15 to the milling machine 17. Liquid may be added to the wood 
chips at any stage before they pass into the milling machine 17 to adjust 
the moisture content thereof until it is preferably in the region of 45%. 
The moisture content and make-up of the wood chips, the size of the screen 
27, and the characteristics of the milling machine 17 are so selected that 
the lengths of the fibres produced by the milling machine are 
substantially in accordance with the following percentages, by volume, of 
the total volume. 
______________________________________ 
Wood fibre length 
Percentage of Total Fibre 
______________________________________ 
0 mm-5 mm 10%-20% 
5 mm-15 mm 40%-55% 
15 mm-35 mm 35%-50% 
______________________________________ 
It is found in practice that a 25 mm mesh size is suitable for the screen 
27. 
The wood fibres produced by the described method are particularly suitable 
for use in the construction of horse riding surfaces for training and/or 
racing. In constructing such a riding surface a layer of wood fibres is 
deposited on a flat polyester membrane formed with drainage holes, the 
surface on which the membrane is laid having been well compacted with two 
to three inches of brick rubble or ballast. Although the membrane may be 
laid in the bottom of a shallow channel or other shallow excavation, it is 
preferably laid on the surface of the ground within a surrounding 
upstanding wall of timber or concrete. It will be appreciated that this 
greatly reduces the difficulty and cost of laying the surface. After 
laying the fibres on the membrane and within the surrounding wall to a 
depth of about nine inches (23 cms), the surface is raked level and 
watered and compacted with a heavy roller. 
During use of the surface the smaller fibres migrate to the bottom of the 
layer and provide a compact and firm base layer over wich extends a more 
open top surface which therefore readily drains and which is resistent to 
frost. 
The described apparatus, being mobile, allows the method of producing wood 
fibres according to the invention to be carried out at the site where the 
riding surface is to be constructed. In this case the mobile apparatus is 
taken to the site at which the riding surface is to be laid, and wood 
chips of the required size are obtained from the nearest local wood 
chipping plant, using local timber at least a major proportion of which is 
preferably hard wood, the chips being formed from lengths of whole natural 
timber including bark. It is found that the use of such timber for the 
chips improves the characteristics of the final riding surface. 
Any suitable method and apparatus may be used for producing wood chips 
having the required length, in the grain direction, of from 18 mm to 35 
mm, and preferably 25 mm. However, one suitable known form of wood 
chipping machine comprises a rotating disc having chipping blades mounted 
around the periphery thereof, the timber being fed in the direction of its 
grain at an angle to the axis of rotation of the disc.