Roller Shutter Door Guide
Advanex – Shutter-Door
Roller Shutters And The Law
Since 2005 and the introduction of BS EN 13241-1, it’s been mandatory to have at least two methods of preventing a door from falling on all shutters, except in certain circumstances. In practice this means a door must have any two of the following:
- An Electric Motor
- A Safety Brake
- A Spring or Springs
There are a couple of exceptions, -doors with downward forces under 200N (20Kg) are exempted, and shutters used over windows (i.e. where there will be no people accessing the area underneath) need not comply.
Choosing A Suitable Spring
We publish springing charts for most popular barrel/lath combinations. Simply read off the spring numbers from the square that’s in line with your door height (always ‘the ‘Under Stops’ height on our charts), and the width (the ‘cut lath’ length). The chart gives you the reference number of the appropriate spring or springs, together with the total number of turns to be applied.
If the door size you want to make doesn’t appear on the chart, or if you’re using an unusual lath or barrel size, please ring us for advice. This also applies if you are using more than one lath type (for example if you are planning to install a section of perforated lath as a viewing panel in an otherwise solid door), or if your shutter is to include a wicket door.
One of the principle points of confusion is the ‘handing’ of shutter springs. It’s usual for door manufacturers to call a spring ‘right hand’ if it is to be installed on the right hand side of the door. However, spring-makers refer to the ‘helix’ direction, as in a screw thread. A right hand spring has a right hand helix, and is commonly installed at the left hand side of the door. Starting at the tang either end of the spring and following the wire around, if it goes in a clockwise direction, it’s a right hand spring.
‘Reversing’ The Spring
If the correct hand of spring is not available, it’s possible to ‘reverse’ the hand of a spring by putting an extra block on the shaft, and fitting the spring anchor near to the end, rather than in the centre. So, for example, if you have the gearing installed on the right hand side (looking from inside), but you only have a left hand helix spring available (which would normally be installed on the right hand side), you could reverse the spring as follows. Instead of attaching the left side tang of the spring to the end-block, install a spring anchor just inboard of the end block on the left, and attach the left hand end of the spring to it. Then install an extra block at a suitable position along the shaft, and attach the right hand tang to this. The spring will then wind up when the door is lowered, and will therefore work correctly.
Installing The Spring(s)
Our springs are supplied slightly open coiled, to allow for the extra turns applied when the springs are wound up during the operation of the door. Whilst there is sufficient space between the coils to allow for the recommended maximum number of turns, care must be taken to ensure that the springs aren’t compressed during installation. To avoid this possibility, we recommend that you stretch the springs slightly when fitting them.
Heating of Tangs
It is normal to heat the tangs of the springs to secure them, once they have been passed through the holes in the block or spring anchor. The heat applied makes bending of the tang much easier. In doing so, great care must be taken to ensure the wire is not overheated, as this can cause embrittlement. The spring tangs should be heated to no more than a dark, cherry red. Keep the heat to the inactive part of the spring, i.e. that part of the tang that has been passed through the hole in the casting, as the heat is detrimental to the spring properties of the wire. Form the bend whilst the tang is still showing the cherry red colour. Make sure the spring sits centrally on the shaft, particularly at the spring anchor end, as this is static relative to the rotating shaft, and it’s been known for a badly centralised spring to wear right through the tube.
Once fitted, the springs should be given a liberal coating of grease to ensure smooth operation of the shutter.
Sometimes it’s necessary or desirable to fit more than one spring. For shutters exerting a force of more than 200N at the bottom rail, but less than 400N, it’s a good idea to install two springs. In that way, the shutter is compliant with the anti-drop regulations.
For heavier doors, it’s common to use two springs. In this case, it’s normal to have one spring of each hand. It’s not always the case that the springs are the same strength; different strength springs may be required to effect a suitable balance.
Very large doors sometimes need in excess of two springs. Sometimes it’s possible to fit three springs in a row, but frequently on these occasions, it’s necessary to ‘nest’ smaller- diameter springs inside larger ones. Ring us to arrive at the best possible solution, in these cases.
It’s the door manufacturer’s responsibility to decide what ratio of gearing to incorporate into the door. A spring can’t compensate for an inappropriately geared door, as it’s the gearing that dictates the amount of effort required to haul the door up and down. Larger doors often need double reduction gearing, otherwise the amount of effort required to operate the door will be excessive. The downside of low gearing is that it takes longer to open or close the door, but it’s a better situation than having a door that is too heavy to operate. We aren’t door manufacturers, but if you’re stuck, we may be able to offer advice about the level of gearing appropriate for your door.
There are numerous situations that occur infrequently, and can cause the door manufacturer to look for advice on springing. Don’t hesitate to contact us for help on these occasions; we have many years of experience in springing doors, and we’re happy to offer our assistance in solving your problem.