When you are faced with the choice of door hinges, the first thing you look for is the load capacity stated by the manufacturer. Often the danger lies in stopping exclusively at this numeric value without examining its meaning.
Weight and load capacity are not the same thing
The weight of a door is the value, expressed in Kg, which is obtained by positioning the door on a weighing scale. When it comes to load capacity of hinges instead, you have to make reference to the inter-relation of multiple elements and in particular the following:
- the nominal weight of the door;
- the ratio of height to door width;
- frequency usage of the door.
All CE marked hinges, that is, all those hinges which are produced, tested and certified according to EN 1935 regulations provide as follows:
- a standard door 2000 mm (h) x 1000 mm (w) and a distance of 1540 mm between hinges;
- mass (or weight) of the test port based on the category that you want to achieve;
- use of two hinges, one load-bearing (in the case of concealed hinges both hinges are load-bearing);
- 200,000 opening cycles, for use on doors.
From these assumptions, then it starts every consideration related to load capacity when you have to define the appropriate handling of a specifics door hinge system. Therefore, unless indicated in the technical documentation of the hinge, you should check that the declared capacity is actually related to the above.
It is also good to know that, leaving constant the weight of the door:
- an increase in the height of the door (and therefore the distance between hinges) has a neutral or positive effect on the load capacity of the hinges;
- an increase in the width of the door has a negative effect on the load capacity of the hinges;
- It is not absolutely true that mounting 3 hinges you a 50% increase in load capacity nor that installing 4 hinges capacity even doubles.
How many hinges carry the load of the door?
We tend to think that if two hinges carry 40 kg, 80 Kg doors can be handled by installing 4. Dispel so once and for all the myth that most hinges are installed on a door, more the load capacity increases in proportion.
Hinges that carry the weight of a door and which are affected by the greatest efforts are always two:
- the top hinge holds up in traction (F1);
- the bottom hinge holds up in thrust (F2);
- both hold up the vertical thrust, i.e. the force of gravity (G).
That said, it’s easy to see why product families have developed over the years, with incremental capacity in order to support increasingly large and heavy doors properly. Hinge systems which, with the necessary technical measures and dimensions, are able to offer a complete solution to most application requirements. All without sacrificing aesthetics.
Using a correctly sized hinge system has the advantage to avoid many unnecessary processes, which tend to weaken the door and frame structure and that are then visually unpleasing.
The problem of panel warping and door hinges
The phenomenon of the door warping seems to be a fairly common problem. Unfortunately, there are few companies that can provide accurate data on the percentage of warped doors. On the other hand, to be sure, three hinges are installed, with the third central, to have one more anchored point.
What are the causes of warping? According to the companies, possible causes which lead the interior doors to have these problems are:
- high humidity (e.g. bathing areas);
- high temperature between rooms (living and sleeping areas);
- radiators too close to the door;
- using poor quality wood materials and coatings;
- failure to comply with the timing of gluing and drying of the different components of the door.
If a port warps for any of these reasons, the effect will be uniform over the entire surface of the door and it will not be a phenomenon visible only on the right side rather than just on the left one.
How many anchored points are on the lock side? For internal doors just one, the lock itself, and it is in operation only if the door is closed! Nevertheless, it seems that the lock side, as if by magic, the doors remain upright.
It is likely to think that if a door warps for any of the reasons mentioned above, on the hinge side the door panel will grow a belly in the center, while on the lock side door ends will bend toward the side opposite to the seal.
So adding a third hinge in the middle, it does not solve the problem completely.
How hinges behave when a door warps? When a door warps, it is as if it shortened and, depending on the system of hinges used, what happens may give inspiration.
If you use two body hinges, male and female, usually the lower hinge female is detaches from male a few millimeters as it is free to lift up. As a further consequence of this effect, the total weight of the door will load on the top hinge.
If using pivot hinges at the ends of the door, usually the upper hinge female is detached from the male for a few millimeters as it is free to get downward.
Conversely, if you use 3 rings with through plug systems or with recessed or concealed hinges, the door is “continuously” attached to the frame thanks to a sturdy locking system (this, of course, greatly depends on the quality of the hinge and the materials used). The door is tight, held in tension between the two hinges and therefore the phenomenon of warping, at least on the hinge side, is reduced or not even takes place.
In addition, using this last typology of door hinges, you avoid the typical flag waving affecting two body hinges where time and wear of the hinges cause door horizontal drop.
Using only two hinges, it means saving when you process, install and purchase hardware. Be warned though: the two hinges must be designed in such a way that they can carry alone the weight of the door.