The meaning of Holdon® and its principles of functionality
Why the name Holdon®?
“Hol” is a village in which the original clip was invented – whilst in Swedish “don” means “tool” or ”device”. Everything we do is aimed at finding smarter solutions to fasten sheet formed objects such as banners, tarps, films, textiles, boards or even sign plates to the surroundings. ...
Having this niche of what many would call oddities makes us focus on solving things most suppliers would leave to others. We have simply put our self in such a small narrow niche that we are forced to think far deeper into the problems of fasteners than what could be considered normal. This corner is a chance further explain how Holdon® products works and how we believe they shall be used, it may sometimes be obvious to us but it might not be for everyone. Thus this corner is intended to broaden a little on the info given on packing’s, webpages and distributors marketing material.
The principle of the clip is that the harder you pull the harder it grips. The principle of the clip is patented. The self-tensioning principle applies when pulling the wedge via its hole in the end of wedge, pulling in the sleeve part of the clip will not work, we often see test been carried out by simply grabbing the clip and pull the whole clip - this will not work since the wedge need slide in - and it will if you pull via a cord or hook applied to the hole in the wedge. Remember; the clip only works if pulled as it will be in real life - via a cord or similar attached to hole in wedge.
Another consequence of the wedge principle is that you need push wedge in to get an initial bite - once done the initial bite will cause the wedge slide in and tighten the grip more and more as you pull in cord. This principle is very different from most other clips visible on the market. Many other clips are attached by a once and forever tensioning caused by twisting a screw or pushing a sliding compressing sleeve, etc. - these clips will thus only have its initial grip.
The fact that Holdon® clips outperform other clips is not only due to the working principle it also depends on the choice of material. The material need be UV-resistive, long time stable and stiff, yet not brittle. This trade off balance is made by using compounds of nylon and glass fiber - there are however thousands of brands and compositions each having their specific pros and cons - we continuously monitor this market and whenever possible we tune performance by changing the resin mix. Having the base in polyamide we are rather insensitive to UV deterioration - the UV problem is much related to simpler plastics like polypropylene.
Applying the clips to fabrics we very often get the question how many are to be used on a certain material etc. Our general advice on this is as follows; A fabric/tarp awning material has certain tear strength in itself. When this tear strength is exceeded the material will tear apart regardless what fastening item was used. So rather than thinking on clips contra eyelets the spacing has to do with the material strength.
Some physics and maths for the interested ones;
The shear wind force on a banner hanging perpendicular to the wind and only held by cords in eyelets is ca 60 grams per square meter at a wind speed of 1 m/s. A banner having a surface of 5 square meters will then only be pulled with a force of 0.3 kg. In such a condition it is easy to just use a few fastening points. Unfortunately the wind force is increasing proportional to the square of the wind speed. If we 10-fold the speed of wind to a modest 10 m/s we will increase the force on the banner by a factor 100 to a total of 30 kg. This is the force pulling the banner in the direction of the wind. Unfortunately we cannot pull in the other direction to hold the banner - we can only hold the banner in the direction from eyelet to fastening point. You can compare this to stretching a horizontal cord and hanging a weight on the middle of the cord. You need stretch just a little to get cord almost straight but you must stretch with much more force to get the cord almost straight again.
To be able hold the banner in the wind we thus need release the tension a little to get a reasonable angle on the cord contra the wind direction. The simplest way achieve this is to tension the banner with elastic bungee cords. If we accept the angle to be 80-85 degrees rather than 90 degrees the pulling force needed will still be 10 times more than the pulling force on the banner. We thus need pull the banner with a total force of 300 kg at a modest 10 meter per second. If we just used eyelets or clips in the corners we would then get 75 kg per fastening point. This is no problem to the clip as such but most materials are likely to break, and we have failure. In reality we will not balance the forces perfectly due to wind jerks etc and this will cause ripped fabrics or causing Holdon® clips to slide off.
Should we increase the wind from a modest 10 m/s to a storm at 25 m/s the shear wind force will increase with a factor (25/10)2 to 187 kg. To get a reasonable holding force we need accept the banner to bulge into a bubble form. The bungee cords will give in to achieve this and if we go down to a 45 degrees angle of the cord contra wind direction the pulling force needed will be ca 1.5 times the wind force = 280 kg. To hold 280 kg we need distribute that load on a number of fastening points. Each point has a max loading that is decided of the weakest chain in the series of material - eyelet/clip - bungee cord. If we have an example where the bungees are the weakest point carrying 20 kg we will need 14 fastening points - corresponding to 80-85 cm spacing.
In practice; Use clips in the same way you would have used eyelets. Eyelets or clips are not as important for the long time durability as the choice between cords and bungees. You can read more about this subject in detail, in my upcoming post.
Staffan Gunnarsson, MD
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