Electric motor is the main and most expensive part of any household appliance. Meat grinder is no exception. The reliability of its protection significantly affects the duration of service life that is an important criterion for choosing a meat grinder.
The motor heats up quickly during operation. Engineers are constantly improving methods of solution this problem.
For example, cooling the stator windings of vacuum cleaner motor is carried with the help of air that sucked from the room. In addition, vacuum cleaners have the holes in the housing for sucking air flow due to the Bernoulli Effect. Moreover, small additional impeller on the motor shaft creates additional air motion. As a result, vacuum cleaners have a very effective forced cooling.
Traditional methods of cooling with the help of air flow are not possible in a meat grinder due to slow auger rotation. Therefore, protection against overheating is mainly carried out with the help of cyclic operation. Some manufacturers are silent about this of marketing considerations. This information is usually contained in the instruction.
Standard modern meat grinder withstands continuous operation for a maximum of 15 minutes. Some inexpensive models provide continuous operation only during 5 minutes. Then, the device requires a pause in work for a natural engine cooling. Also, the duration of such cooling is often substantially longer compared to operation duration and reaches 15-20 minutes. Of course, such work is especially inconvenient for processing a large amount of meat. Therefore, the organization of protection against overheating significantly affects the model usability.
Meat grinders without special protection
Steel gears easily withstand mechanical overload, for example, at hit of a large bone into auger. Therefore, the possibility of engine overheating is very high. Some models have plastic gears with low mechanical strength that quickly break during overload. In this case, the repair requires replacement of relatively inexpensive plastic part. This protection is used by such well-known companies as Philips, Tefal, Moulinex, Kenwood and Zelmer.
But, of course, their purchase and replacement are not very convenient.
Locking the motor
This method uses the cogwheels, couplings, caps and other plastic details as protection elements. They are made of plastic that is destroyed in case of mechanical overload (for example, at jamming an auger). Rotation stop protects the expensive motor reducer from overload. Of course, coupling replacement is much cheaper than a motor repair.
It’s usually located between the screw and the gear shaft. Of course, the presence of such a spare plastic coupling in kit device is its advantage.
Thermal fuses are the most common type of household appliances protection from overload. Today, they protect thermoelectric heating elements, transformers, motor windings, etc. Thermal fuses interrupt the power supply circuit when the temperature exceeds the allowable value.
Thermal fuses are divided into disposable and reusable.
Disposable fuses are burn out after triggering and require replacement.
Reusable fuse represents a bimetallic plate. Curved bimetallic plate connects the electrical contacts of the power supply circuit. Interruption between contacts occurs due to different values of the coefficient of thermal expansion at exceeding the allowable temperature. The thermostat is reset after cooling a device. In summer, the thermostat is activated at a lower engine load due to the high ambient temperature.
Some manufacturers equip their models by special electronic device that provides a soft start and protection against overload and overheating. This solution is most effective, but greatly increases the model cost.
The video shows the replacement of plastic clutch and coupling in Bosch meat grinder.