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+--- Thread: V2 terra motor snapping bolts (/showthread.php?tid=5120)
V2 terra motor snapping bolts - Timdin - 13-10-2014
Hi. Fitted a pair of metal gates on v2 terra motors 2 years ago . Fitted similar set ups many times and always found v2 to be decent. A month after installation the shear bolt in the top of the motor snapped. I put it down to a weak bolt or something minor changed the bolt and all was fine for another month & it snapped again. Have now returned to these gates about 15-20 times . I have tried many different options including stops, high tensile bolts and even tried welding arm to motor ! Running out of options now and customers as peed off as me & considering action to get their money back! Any ideas greatly appreciated
RE: V2 terra motor snapping bolts - thm - 14-10-2014
I don't know what a V2 terra operator is but from what you say it should be for swing gates (an uderground one?). If yes, then the most likely cause of your problems would be wind force.
Let us assume that each leaf is 2.2 m wide and 1.8 m tall.
The total surface of each leaf is 2.2 x 1.8 = 3.96 m²
A uniformly distributed pressure over the leaf gate causes the same torque in reference to the gate leaf hinges as the summed force would cause if acting on the center of the leaf. The center of the leaf is at 2.2 / 2 = 1.1 m from the hinges.
If the wind pressure is 40 Kgf/m² (kilograms of force per square meter - see http://www.sussex.ac.uk/weatherstation/technical/Windforce.html ) then this would cause a total of 3.96 x 40 = 158.4 Kgf of total force acting on the leaf surface.
The torque that this force creates in reference to the hinges is 158.4 x 1.1 = 174.24 Kgf*m
This is the torque that the operator has to overcome by producing more torque of its own in order to move the gate. This also is the torque that the operator has to be able to withstand if it is to hold that gate leaf closed without being damaged itself.
Most swing gate operators are in the 20 to 80 Kgf*m of produced torque range. I don't have the numbers but I would guess that most components of an operator would be designed for a safety factor or 3 to 5 (meaning they wouldn't fail until the torque acting on the operator is at least 3 to 5 times the torque it produces).
In reference to our example, no ordinary operator will be able to move it against a wind exerting 40 Kgf/m² (and by a wide margin). It is also quite probable that the weakest (and, logic says, less robust) operators will be damaged by such a wind.
It may well be that the shear pin you describe is intentionally designed to fail first in order to protect the rest of the operator.
When one faces problems with wind the only real solution is modifying the gate so that it allows wind to go through as unimpeded as possible.
It also helps a lot if one properly installs a sturdy electric lock (for example, in double leaf gates, an electric lock should be installed low on the primary leaf and lock the gate to the ground or mid-height on the primary leaf and lock it to the secondary leaf in combination with the installation of a mechanical spring bolt, low on the secondary leaf). This ensures that, when the gate is closed, most of the loading is resisted by the lock and not by the operators. In addition, the gate users should be cautioned not to operate the gate when the wind is strong.
PS1: in case of double leaf gates where the secondary leaf has a shoulder on which the primary leaf rests when the gate is closed (which is the most typical case), the situation is worse for the operator installed on the primary leaf as it is also partially loaded by the wind force acting on the secondary leaf and with the full gate length as the distance. That is the reason it tends to fail sooner than the other operator.
PS2: in our experience, linear electromechanical operators are more suitable than electrohydraulic operators when strong wind is a problem (provided of course that usage frequency is not high enough to necessitate an electrohydraulic operator) or other types of operators.
The common misconception that electrohydraulic operators are stronger is based on the fact that most people focus on the linear force of the operator (on average, electrohydraulic operators produce substantially more linear force) and not on produced torque which is the product of linear force by acting distance. An electrohydraulic operator producing 2F linear force which acts at a distance D right to the axis of the hinges produces exactly the same torque on the gate as an electomechanical operator producing F linear force which acts at a distance 2D right to the axis of the hinges (=2FD). It is torque that matters and not the linear force.
The problem is that, for linear operators, the acting distance D is a function of the distance of the rear pivot from the hinges, the fully extended and fully retracted length of the operator and the opening angle (for a given installation, the torque will still vary as we open the gate and the geometry changes). That makes it impossible for the manufacturer of a linear operator to just state the torque the operator produces and be done with it. The manufacturer must state all the above (suggested installation distances from axis of hinges, fully extended and fully retracted length (or stroke) and linear force. Then it takes some analysis to get a graph of torque as a function of opening angle and understanding how strong the operator really is. I could post a graph or two if anyone finds that interesting. The bottom line is that, unfortunately it is not easy to provide one descriptive number that says how strong a linear operator is. Contrast this to underground operators that just state the produced torque and how easy it is to conclusively compare various underground operators on that metric.