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In this issue we cover a number of topics including KATO CoilThread® - our inserts that reduce installation time by 40%, some key definitions that are used within the industry and a guide to Roller Shutter Door Springs. We are also pleased to announce our forthcoming release of our online Engineers Knowledge Hub.

We hope you enjoy this issue. If you have any questions that you would like us to answer then please click here.
KATO CoilThread® - Our world leading Tangless® inserts can be used to reduce installation and removal times by up to 40% for the assembly team.
KATO CoilThread® comes in either Tanged or Tangless® versions and is used in various sectors including Automotive, Rail, Defence, Aerospace and Medical Device Development. The Tangless® insert was designed to reduce installation time, eliminate the need for tang removal and thus give debris free installations of Wire Thread inserts. They also provide full traceability and are fully compliant with the key aerospace and military standards.
Lightweight materials are essential for Aerospace and other high performance applications. Wire thread inserts make it possible to take advantage of these while maintaining the strength of the bolted joint. A simple design table makes it easy to select the correct insert for the application, ensuring that the bolt remains the weakest part of the design. Threaded inserts create permanent, wear-resistant thread that exceeds the strength of most parent materials.

Both the Tanged and Tangless® threaded inserts are made from cold-rolled stainless steel wire (AS7245), work hardened to a tensile strength above 200,000 psi and a hardness of Rc 43-50. The finished surfce is extremely smooth which helps to virtually eliminate friction-induced thread erosion. The stainless steel that is used to make KATO CoilThread® can resist harsh environmental conditions and is suitable for many applications. KATO CoilThread® can withstand temperatures ranging from -320F to 800F (-195.6C to 426.7C).

Inserts can be used to repair threads, or designed into the component to reinforce and protect them. Other threaded inserts exist, but Wire Thread Inserts provide the strongest and lightest joints in these lightweight materials. For a constant wall thickness they enable the designer to create the smallest, and therefore lightest, component. An additional benefit is that the stress is distributed more evenly along the length of an insert than a tapped thread, which reduces the chance of stripping and fatigue failures.

Advanex produce the KATO CoilThread® in both Metric and Unified sizes with both the Tanged and Tangless® available in M2 to M12 Metric ranges and the Unified in 2-56 to 3/8-16 size range. The entire range is available both "free running" and "locking" styles with five standard lengths and materials range from standard stainless steel through Nitronic™, Inconel™ and Phosphor Bronze as well as plating options including Cadmium, Dry Film Lube and Silver.

When using KATO CoilThread® a tapped hole is prepared using a standard drill bit which is then countersunk. The hole is then tapped using an STI (Screw Thread Insert) tap. The Tanged or Tangless® insert is then installed into the tapped hole. In a free state, the insert is bigger in diameter than the tapped hole. The inserting tool "pre-winds" the insert to a smaller outside diameter allowing it to enter the tapped thread. When the insert is released from the tool, the insert springs outward, anchoring itself into the tapped hole. With Tanged inserts the tang would then need to be removed at this stage for the thread to be ready to use.

For Tangless® inserts the installation process is simple. Thread the insert onto the tools' mandrel. The unique bi-directional design means no time is needed to orientate the insert. Align the insert with the tapped hole and press the trigger on the electric tool. After that it's automatic – the insert goes in, the tool comes out and the job is finished. For Tanged inserts it is more costly to install an insert into a blind hole, break-off, remove and account for the tang. Some customers estimate this cost as high as 30p per tapped hole. Loose tangs not removed can cause costly damage and production down time to expensive electronic and mechanical components.

Additionally Tangless® inserts are easily removed without damage to the customer's expensive parts, unlike conventional Tanged inserts, allowing easy service of components or the separation of dissimilar materials at the products "end of life". It is also possible to adjust the installation depth of a Tangless® insert if it were installed too deep. This adjustment is not possible with Tanged inserts.
The free running and locking, bi-directional inserts provide strong permanent internal threads, which resist heat and corrosion. For high volume production KATO CoilThread® can be supplied in reels of plastic tape known as Strip Feed Inserts. This reduces the need for manual positioning of the inserts.

A range of tooling has also been developed for insertion and extraction. The tooling range is available in hand, air and electric versions depending on customers' needs and demands.

Click here for further information.
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 (Not an integrated operational brake; it must work independently of the motor.)
  • 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.

Which Hand?

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.

The illustration below will help to clarify. '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.

Spring Lubrication

Once fitted, the springs should be given a liberal coating of grease to ensure smooth operation of the shutter.

Multiple Springing

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.

Gearing Questions

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.

Technical Advice

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.
We are busy putting together our Engineers Knowledge Hub. This will be an online resources tool that will contain lots of useful information such as articles of spring finishes, spring ends, reducing particulate, data sheets for certain products and a glossary for the key terms used within the industry.

We will let you know when it is ready to use.
If you have any ideas about what could be featured please click here.
Spring index (w)
Ratio of mean coil diameter (D) to wire diameter (d).

Stress Correction Factor (k)
Factor that is introduced to make allowance for the fact that the distribution of shear stress across the wire diameter is not symmetrical.

Stress range
The difference in operating stresses under minimum and maximum forces.

Stress relieving
Low-temperature heat treatment designed to relieve the detrimental stresses induced by the manufacturing processes.

The distance between the minimum and maximum working positions of a spring.

Torque (M) also known as Moment
The product of the distance from the spring axis to the point of load application, and the force component normal to the distance line. Usually expressed in N.mm

Torsion Spring
A helical spring which provides rotational energy or torque. The material in such a spring is stressed in bending. A torsion spring can have two separate sets of coils in which case it is known as a double torsion spring.

Total number of coils (nt)
The total of all active and inactive coils.

Shot peening
Impacting the surfaces of the spring with pellets to induce compressive stresses and thereby improve fatigue life.