Non-Retractable Louvres & External Venetian Blinds - Basic (C) Profile
Non-Retractable Louvres Basic 80C L1 E
Basic wind loading models use ladder braid to control the slat or louvre and this ladder braid methodology is taken directly from internal venetian blinds. The ladder braid is a woven polyester with extruded ladder strings on which the blind slat is either rested upon or placed between. The blind slat is then tilted by moving the ladder string either up or down by means of a bearing with associated lifting tape and motor.
The disadvantage of ladder braid is that the polyester fibres stretch which causes the top blind slats to be closed while the bottom blind slats are not and therefore uneven solar heat reflecting and light penetration is present in the blind. This disadvantage can be overcome by adding kevlar/aramid, non stretch fibres, into the ladder braid.
However all such reinforced ladder braid are not of equal quality. The kevlar/aramid polymer is extremely “slippery” and to prevent the ladder braid from slipping from the kevlar/armid string requires very technical weaving methods to be employed otherwise the result is not stable and the ladder braid will still stretch over time as the braid slips from the kevlar/aramid.
Unless the kevlar/aramid reinforcing has been double over locked before being introduced into the ladder braid weaving process and then again over locked within the polyester ladder braid during weaving the ladder braid will stretch.
The fixing of the blind slat to the ladder braid and ladder string is achieved by a number of methods yet unfortunately there is no guaranteed method to prevent the blind slat from slipping around the ladder string either because of wind loading or braid stretching.
Slat rotation stability is attempted by either a single or double over lock of the top, bottom or both ladder cross strings. Over lock of the ladder cross string is achieved in two ways, by a plastic stabiliser pressed into he underside of the convex slat which engages with the ladder cross string or punching one or two “clover leaf” engagement tabs into the slat next to the lift tape punched hole.
Both methods are primitive in engineering design and will lead to ladder string rotation control failure. Historical testing has proved that the plastic stabiliser disconnects from the slat under Australian climatic conditions and since the punched “clover leaf” tab cannot be “drawn” to provide a rounded edge, the “clover leaf” tabs , being a sharp raw metal edge, will cut through the 1-2mm thick cross ladder string over time caused by wind vibration of the slat.
Similarly if the slat lift tape hole is punched and NOT DRAWN to provide a rounded edge, the exposed sharp raw metal edge, will cut through the lifting tapes of the entire external venetian blind at a service life of 6-7 years, caused by wind vibration of the lift tape against the sharp raw edge of the punched lift tape hole. When manufacturers/assemblers of external venetian blinds use such primitive engineering this failure of lift tapes will necessitate the external venetian blind to be removed and refitted with new lift tapes.
All wire guides are not of equal: wire guide cable is either untreated, galvanised or stainless steel. Given Australia’s highly corrosive coastal salt air and humidity rust is a major issue ALL SURE SHADE ® blind wire guides are stainless steel coated for both blind and surface abrasion. The SURE SHADE® wire guide is coated with PA12 , a high performance superior polymer which features high toughness, very high resistance to grease, oil, water, saline solution & organic solvents and stress cracking. It has a low co efficient of sliding friction and has a high abrasion resistance even when running dry and also has noise & vibration damping qualities.
The blind slat profile SURE SHADE ® Basic 100F is 100mm wide and can only be controlled by ladder braid and has flexibility of movement under wind load or use. This excessive flexibility of the blind slat has a significant drawback as the slat can either rotate around the ladder string or distort and flatten against the glazing in the wind causing excessive instability, movement, noise and block out of light.
All 100F Sure Shade slats are manufactured with lift tape holes that are punched and DRAWN to present a smooth round edge to the lift tape.
Slat rotation is over come by either a single or double over lock of the ladder cross string across the required number of slat as dictated by the location and wind loading. (caution : see above discussion for limitation of blind ladder string service life)
Lack of slat rigidity also necessitates that the ladder braid be closely placed along the length of the blind slat as the slat flexibility will cause the slat to sag if the ladder braid is spaced too far apart.
The side to side movement control of the blind slat is achieved by a wire guided through the end of each slat, which allows very easy fixing and minimal visual obstruction but, as is common to ALL wire guide installations, cannot provide wind stability and has these major defects ;
- Wind loading will cause the blind wire guide to vibrate, resonate and shake the blind slats causing considerable noise. (similar to rigging on a boat in the wind)
- Due to the single convex/concave blind slat design light block and sun glare cannot be achieved with wire guide as there will always be approximately 20% light coming through the slats even when the slats are fully closed.
- Wind will cause the blind to sway sideways and move forward and backwards hitting walls and the glazing when under wind load. In summary the SURE SHADE ® Basic 100F L3 W offers high solar heat block out at a very cost effective price where wind loading and light block out is not an issue.
The SURE SHADE ® Basic 80C L1 E can gain some wind stability when wire guidance is replaced with Zamac pins, riveted to alternate slats (left and right), which engage with an extruded aluminium side guide. The side guide has plastic side inserts to reduce noise and provide easy movement yet the possibility of the 80C slat rotating in the ladder string is only reduced and cannot be eliminated. (caution : see above discussion for limitation of blind ladder string service life)
We trust this informative and detailed background to the industry is of educational value and provides the necessary information for informed debate and selection criteria for the correct and appropriate engineered solution and slat profile most suitable to provide a functional project with future viability.
Of equal importance is that we have committed ourselves to make a difference in the”climate debate” and have instituted a range of greatly reduced square metre prices, ($250 to $470 + GST) that enable all projects from “spec homes” to high value building towers and projects to benefit.
The Sure Shade range of quality products are engineered to provide improvements to either existing concepts and products or provide the uniqueness and “world first” of the Sure Shade 120S.
While Australians lament the “death of Australian manufacturing” we have invested in the design, development, engineering and manufacture plant and machinery for a true “world first” solar radiation protection suite of products.