Predetermined breaking point
A predetermined breaking point is a point determined by a special structure, shape or construction (usually a material taper) that predictably breaks when stressed or overloaded. This can be a notch, a perforation or a scratch track, for example. The component is decisively weakened by the notch effect .
Replaceable elements are also often used for overload protection, such as: B. Shear pins in couplings . These parts are smaller than the rest of the system. I.a. these parts are available as spare parts for household appliances . You can usually exchange them without specialist knowledge, e.g. B. small outboard motors , lawn mowers and kitchen machines.
The goal is, for example, that pressure, torque or force are limited and in this way greater damage to the overall system is avoided ( e.g. slipping clutch or torque wrench ). On the other hand, predetermined breaking points on packaging are used for more convenient opening.
With snap-off blades, predetermined breaking points serve to facilitate removal of the blunt blade section; an unused and sharp blade section is released for use.
Break cutting at predetermined breaking points is used industrially as a manufacturing method. One example is the scribing of PCBs along its final shape before it automatically benefits are stocked.
If you scratch the peel before peeling an orange, you will create predetermined breaking points that will make it easier to remove the peel without tearing.
The term must be clearly distinguished from the intentionally constructed weak point in connection with planned obsolescence . It is assumed that manufacturers build weak points in their products to promote sales in order to artificially shorten the lifespan of the product and to stimulate the sale of other products (for example, women's stockings, sweaters, zippers, light bulbs or undersized components that cannot withstand long-term use ).
Examples
Breaking points can be found in many other areas:
- On beverage cans and other packaging they provide a convenient and clean opening.
- In the case of security stickers / seals or price tags , unauthorized removal should be prevented: predetermined breaking points have the effect that the label cannot be torn off as a whole, but tears when an attempt is made to remove it.
- On castings or stamped parts, the connections to several components are designed as predetermined breaking points in order to be able to separate the components easily and without damage from the excess material (sprues, closed punching waste) (e.g. model construction, removable openings in housings and junction boxes).
- Pressure and vacuum containers are sometimes protected by rupture discs .
- Champagne bottles have predetermined breaking points in order to be able to "saber" them with a champagne saber.
- Bollards with predetermined breaking points are used in inner-city streets . If they are hit by a vehicle, the bollard breaks off at this point. The damage to the vehicle remains minimal.
- Chocolate bars have predetermined breaking points to make them easier to break into bite-sized pieces.
- Soil cultivation equipment such as plows or heavy cultivators often have shear bolts that act as predetermined breaking points in the event of overload.
- In aviation, shear bolts and predetermined breaking points should prevent the aircraft structure from being damaged; The main landing gear of an aircraft should break away when the load is too high in such a way that it cannot damage the wing and thus the fuel tanks with their high risk potential, while during the testing of the Boeing 707 in 1954 the engines were fixed in such a way that they, if they got out of hand, should fall away.
- Predetermined breaking points on aluminum electrolytic capacitors ensure that the damage caused by an explosion in the event of overload remains within limits.
- Egg grenades have indentations on the surface so that when they explode they will tear into many splinters.
- The brake and clutch levers on some motorcycles have predetermined breaking points so that the lever does not break off completely in the event of a fall and can then still be used to operate the machine.
- In the case of blind rivets , the pull pin is equipped with a predetermined breaking point. At the end of the riveting process, the pin tears off there and a connection is made without a protruding wire.
- Often, tablets are also provided with a notch as a predetermined breaking point, so that they can be neatly divided into smaller portions so that pieces of the same size as possible are created.
- Lanyards tear if they get stuck at a given point so that the person wearing the lanyard is not strangled.
- Collars for cats often have predetermined breaking points so that the animal does not suffocate if it gets caught with the collar.
- There are predetermined breaking points in nature too. For example, the branches of the broken willow break off; These are often torn off by floods and then take root again when they are washed onto the bank elsewhere.
- The tail of sand lizards also has a predetermined breaking point where the tail end can be thrown off in case of danger.
- In the case of cutting dies made of cardboard (e.g. handicraft sheets, Advent calendar) or paper (e.g. postage stamps) or toilet paper on a roll, perforation of the material leads to predetermined breaking points.
- In a broader sense, predetermined breaking points can also be found at
- Fuses predetermined breaking points - but for the electrical current : they can be designed as a component or as a narrow point of a conductor run and interrupt the current by melting due to their self-heating ( electrical heat ).
- Toughened safety glass . When damaged, the glass shatters into small, rather round fragments instead of pointed, more dangerous splinters.
- as a pressure relief valve
Individual evidence
- ↑ Planned obsolescence
- ↑ Boeing's Jet Stratoliner , Popular Science, Number 165, Jul. 1954, p. 121
See also
Web links
- Breaking points - a safety risk? (in the glider area)