GB2083519A

GB2083519A - Horticultural Enclosures

Info

Publication number: GB2083519A
Application number: GB8121274A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-07-12
Filing date: 1981-07-10
Publication date: 1982-03-24

Abstract

A horticultural enclosure comprising transverse members (1) and longitudinal members (7) connected to form a sub-frame, a connector (8) to make rigid joints between the sub-frame members, a cover (3) of flexible sheet material to stretch over the sub-frame, the cover being tensioned longitudinally by its own elasticity and secured by releasable clips (2) to the transverse members of the sub-frame and tensioned transversely by prestressing the longitudinal members (7) of the sub-frame and securing the cover (3) by releasable clips (2) to the longitudinal members (7). End covers are provided which may progressively unclipped to increase ventilation. <IMAGE>

Description

SPECIFICATION Horticultural Enclosure This invention relates to horticultural enclosures and more particularly, but not exclusively, to a portable cloche.

The present invention aims to provide a horticultural enclosure of simple construction in which the benefits of Dutch Lights and 'Barn type' cloches are combined and by employing modern materials, to produce a portable structure.

The basic structures are preformed modules which can be used singly or clipped to each other to form a tunnel of unlimited length.

In prior art the enclosures known as 'Dutch Lights' and the 'Barn type' cloche employ glass as the cladding material. This material has the ability to allow solar radiation to pass freely to inside the enclosure whilst acting as a barrier to infra-red radiation from inside to outside of the enclosure.

The disadvantages of glass are that it is costly, heavy, brittle and cannot be easily fitted to a frame. Modern plastics materials have been and are being developed which have some or all of the properties of glass and being flexible, cannot break. It would be advantageous if any of the plastics materials could be selected solely with a view to its end use or its basic cost. For example, Polyvinyl chloride film is the most expensive but has a close resemblance to glass for transmission.

Polythene is the least expensive but will give only poor, it any, protection against frost. The cladding could be selected to suit the crops being grown.

For example:- If half hardy or some hardy plants have to be overwintered then a PVC cover should be selected. The cheaper polythene would be selected however if the frame was intended to be used for spring planting.

Other advantages of using the enclosure are that netting could be used for retaining bees for pollination in an enclosed space and the newer cladding materials such as E. V. A. and Melinex could be used. In addition the enclosure could be clad with netting to protect the crops from birds.

In prior art, selection of a cladding material has been limited by its mechanical and physical properties. For example, if the structure is made firm by fitting a tubular frame into welded pockets, thus tensioning the cover, then the cladding must be able to be welded by High Frequency welding techniques. This limits the choice of cladding to Polyvinyl Chloride (PVC) film. The welding of PVC for horticultural enclosures is not entirely satisfactory. The reason for this is that the High Frequency field generated for the weld leaches out the plasticizer around the weld area. The end result of this reaction is that although the weld appears to be satisfactory it becomes brittle and therefore subject to 'cold crack' at temperatures around the freezing point.

This loss of plasticizer can sometimes be limited by tuning the welding press for high power and, or, high frequency and therefore short time cycles.

These partially corrective measures result in a weld which is difficult to monitor because of the tight limits. Weld failure due to 'cold crack' in winter could be a disaster for growers. With present knowledge, 'cold crack' caused by brittleness in welded areas at around OOC will always give an unreliable product.

In the case of polythene being selected, as it cannot be satisfactorily welded, it usually has to be secured by tension over hoops and the edges buried in soil. Such a structure cannot be easily transported to cover another crop, neither can access to crops be easily obtained. In addition longitudinal tension is obtained by bunching the ends which are pegged to the ground. Perfect sealing is seldom obtained and the small gaps give rise to high velocity draughts through the tunnel in a 'chimney' effect. This leads to a high percentage of plant failure.

When the growing season commences in late February the solar altitude angle is around 260 at latitude 530 which represents average conditions for the Midlands. For maximum solar heat gains the transmission structure should be at an angle normal to the sun and therefore 240 to the vertical (included angle) on the north/south axis.

It can be seen that the pitch of the roof is far less important than the inclination of the walls.

According to the invention, there is provided a horticultural enclosure comprising a rigid tubular sub-frame with firm joints, any type of selected cladding material, providing it is flexible, to cover the sub-frame, cladding clips which tension cover both longitudinally and transversely, ventilation holes in bottom of walls and fixed holes in ridge to allow convected ventilation, ends which clip on the sub-frame such that they can be progressively unclipped to obtain increasing increments of extra ventilation.

In a preferred embodiment of the invention the enclosure is a module of convenient length with gable shaped ends and inclined walls. The pitch of the roof is kept to a minimum to allow uniform height for plants to grow inside the enclosure but sufficient to allow water to run off to irrigate under the enclosure by capillary action.

For maximum solar heat gains, the roof is pitched at 120 to the horizontal. The wall angle is 240 to the vertical. These angles generate a shape which gives a tall ridge height thus leading to maximum heat gains and retention. This angle is also useful in that wind pressure will tend to force the structure to the ground rather than lift it.

The angle also allows the modules to be stacked for storage.

According to the invention the sub-frame can be clad with a cover of any type of flexible material. The cover is secured to the sub-frame by clips. The clips are extruded PVC tube material l.C.I. R7/760 with a slot formed along its length.

The PVC tube is not circular but rather an elipse shape thus ensuring, when pushed on to steel tube, that pressure is applied uniformly around the circumference of the steel tube. The jaws are formed by cutting the slot so that the sides are inclined outwards from the vertical. This ensures that the trailing edges of the jaws contact the cladding when the clip is pushed on to the tube thus preventing tearing of the cladding.

The tensions are imposed on the cover by the application of the classical mathematical formula for friction of a cord or belt around a cylinder, i.e.

where T2=tension in the cover Tension at longitudinal edge of clip e=constant 2.7 18 y=coefficient of friction between cover and sub-frame 0=angle of wrap around the tube of subframe To obtain maximum tension T2 in cover, the clip has been given maximum pressure, normal to tube, without tearing the cover at the corners of clips. To prevent tearing, the corners of the clips are radiused. The clips ensure an angle of wrap of a minimum of 2600.

It has been found that clips of 30mm length spaced at 200mm will yield a tension pull T2 of almost ultimate strength of a horticultural grade polyvinyl chloride cover.

Many, if not all, flexible plastics which can be used to clad the sub-frame have what is known in the art as 'tack' additive. An example is Storey Bros. Velbex EB5 1 3AB. This 'tack' ensures that the coefficient of friction 8 is high and explains why the tensions in the cladding can almost reach the ultimate strength of the material used.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view of a sub-frame Figure 2 is a perspective view of a preferred method for the sub-frame joints Figure 3 is a perspective view of a sub-frame joint employing proprietary components Figure 4 is an enlarged view of a clip Figure 5 shows a sub-frame with a cover fitted thereon Figure 6 is a perspective view of a clip on end for use with the enclosure of Figure 5 Figure 7 is a perspective view of a separate end piece Figure 8 is a perspective view of the preferred method for anchoring the enclosure to the ground Figure 9 is a perspective view of a high embodiment with an access flap Referring to Figure 1, the sub-frame for an enclosure, in this case a 'barn type' cloche, comprises end hoop 1, preferably made from zinc plated steel with internal corrosion protection.

These hoops 1 are spaced apart by the members 4. The shape of the hoops 1 and number of tie members 4 can be altered to provide any required configuration. The joints 3 must be of a rigid type.

Cross members 5 are fitted, if desired, to secure the bottom of the clip on end cover.

Alternative methods of making the sub-frame can be used. For example, the frame can be made from solid rod and the joints welded, or from solid rod and knock-in joints.

Referring now to Figure 2 which shows the preferred method of making rigid joints for the enclosure, the body 2 has a diameter such that it will slide easily into tube 1. The sliding action is assisted by inclined plane 3. Spaced equidistant along body 2 are rings 4. The rings 4 have the face adjacent to tube 1 inclined to form a 'sawtooth' shape. The collar 5 has a diameter greater than the outside diameter of tube 1. On the side opposite to body 2 the collar has a profile which is shaped in a radius 7. This radius is such that it fits around the outside diameter of tube 8.

Located centrally in radius side of collar 5 is spigot 6. The spigot 6 has then enlarged and cone shaped.

The component is made by the injection moulding process and preferably from a material with a high coefficient of friction such as neoprene.

To make the joint, the tube 8 has a hole drilled through one side in the required position. The diameter of the hole is greater than the minor diameter of cone 6 but smaller than the major diameter of cone 6. The component is fitted to tube 8 by forcing the coned spigot into the drilled hole. The wall of tube 8 is now trapped between collar radius 7 and flat face of coned spigot 6.

Body 2 is slid into tube 1 and forced over rings 4. The inclined plane of rings 4 allow the end of tube 1 to locate up to collar 5. The rings 4 resist any effort to remove tube 1 from component due to the right angled face of the rings 4.

Whilst this method of making rigid joints is preferred, due to the simplicity of preparation and fitting, other methods can be used.

For example in Figure 3, tube 1 is part of an end hoop of Figure 1. Radius washer 2 'CUPID' (trade mark) together with body connector 3 'CUPID' (trade mark) are fitted to tube 1 by closing tucker 'POP' (trade mark) rivet 4 in hole 5 of tube 1. Body connector 3 must be of sufficient outside diameter to receive tube 6 with a tight knock-in fit.

A further example of a suitable joint is the 'PLASTI-LOC' (trade mark) which is very firm. Its disadvantages are that tools are required for assembly, both sides of the tube have to be drilled and one side indented.

Referring now to Figure 4 which shows a clip with its elipse shape 1 and radiused corners 2.

The jaws 3 must have an angle such that traiiing edges 4 contact the cladding before the loading edges when clip is pushed on to tube.

Referring now to Figure 5, the cover 3 is shown in position related to the sub-frame 1 of Figure 1.

Ventilation holes 5 in bottom wall of covers allow convected ventilation through ridge holes 4. It has been found that 1 Omm holes at 1 O0mm centres, give adequate ventilation to prevent diseases.

The enclosure is assembled by fitting tie members 7 to hoop 1. If the joints 8 are of the preferred or 'CUPID' (trade mark) type, the tie members 7 are knocked into hoop 1. If of the 'PLASTILOC' (trade mark) type, the tie members 7 are secured by screws into hoops 1. Either type gives a rigid self supporting structure for the subframe.

Selected type of cover 3 is placed centrally over the sub-frame. The cover 3 is then secured to the sub-frame by clips 2 along the bottom tie member 7. Clips 2 are placed from the centre outwards at 200mm centres. The enclosure is then lifted on to the other side and the cover 3 pulled as tightly as possible and then clipped at the centre. Working out to each side the cover is given transverse tension. The ends are then pulled tight and clipped, thus giving longitudinal tension.

Referring to Figure 6 which shows an end piece 3 clipped to the end of the enclosure, piece 3 is cut from the selected type cover to enclosure and shape, leaving 25mm overlap around sides and roof. The bottom has a flap 6 which is 1 OOmm wide. To secure the end piece, the original clips 2 are removed, one at a time, and reclipped over both enclosure cover and end piece. It is best to work From the bottom upwards.

The flaps 6 can either be clipped to a cross member or a tube 1 laid on the flap transversely.

Tube 1 is then secured with pegs 7.

To obtain controlled additional ventilation during hot days, the end piece is unclipped from the top downwards. It can be stopped at any desired increment.

Referring to Figure 7 which shows a rigid end piece which may be fitted in place of the clip on end piece in Figure 6.

Hoop 1 and cross tube 5 are formed similarly as in Figure 1 but without the tie bars. The preferred cover 3 is cut to shape with a 25mm overlap, tensioned, and clipped to frame 1.

In use, the end piece in Figure 7 is placed adjacent to ends of enclosure Figure 4 and held in place by pushing legs 7 into the sail. Following usual practice, the ends are secured by rods 4.

When the modules are placed with the ends adjacent then one end is unclipped and made to overlap the joint between the modules. The end can then be reclipped.

The structure is anchored to the ground as shown in Figure 8 by adopting the method used in tents. That is canopy clip 1 under the bottom tube member, an elastic band 2 hooked in the clip and a long tent peg 3 to secure the enclosure.

Referring to Figure 9 which shows the same basic structure but with the height raised for taller crops such as tomatoes, the basic enclosure 1 is fitted to extension legs 2 which are swagged into the enclosure legs 3. The cover is clipped to the frame as in the 'Barn type' cloche. For this type of enclosure access from the side is essential. Flap 4 is cut so that it can be unclipped for access and reclipped when required. The same device can also be used for barn type cloches. The top of the cover can also be cut to gain access from the top by removing the clips from part of the cover. The shape and dimensions of the enclosures can be altered to suit requirements. Irrigation can be by means of capillary action from outside to inside or if desired proprietary mist sprays can be fitted to the ridge member, thus irrigating by normal methods.

Claims

1. A horticultural enclosure comprising a tubular sub-frame with fixed joints, any selected type of flexible cover to clad the sub-frame, cladding clips which tension cover both longitudinally and transversely, ventilation holes in bottom of walls and fixed holes in ridge to allow convected ventilation, end pieces which clip on to sub-frame such that they can be progressively unclipped to obtain increasing increments of extra ventilation.

2. An enclosure as claimed in claim 1 wherein end hoops are spaced apart by tie bars with rigid joints.

3. An enclosure as claimed in claim 1 wherein the cladding material is polyvinyl chloride.

4. An enclosure as claimed in claim 1 wherein the cladding material is polythene.

5. An enclosure as claimed in claim 1 wherein the cladding material is polypropylene.

6. An enclosure as claimed in claim 1 wherein the cladding material is Melinex.

7. An enclosure as claimed in claim 1 wherein the cladding material is woven.

8. An enclosure as claimed in claim 1 wherein the cladding material is a net.

9. An enclosure as claimed in any preceding claim wherein the cladding material is secured by clips.

10. An enclosure as claimed in claim 1 wherein ventilation holes are provided at bottom of walls and pitch of roof.

11. An enclosure as claimed in claim 1 wherein cladding flaps are provided at ends.

12. An enclosure as claimed in claim 1 wherein the top of the walls are inclined inwards 200 to 250 from the vertical.

13. An enclosure as claimed in claim 1 wherein the roof is pitched 100 to 140 from the horizontal.

14. An enclosure as claimed in claim 1 wherein the enclosures can be stacked one inside the other.

1 5. An enclosure as claimed in claim 1 wherein the cladding material is Papronet.

1 6. A horticultural enclosure substantially as herein described with reference to and as shown in Figures 1, Figure 2 and Figure 5 on the accompanying drawings.