Mechanical Housings Design of a housing begins when the other elements of a mechanism have been already designed in every detail: with the shafts and axles and their supports, with all dimensions of the parts and their motion paths. Then can be defined the dimensions of the bearing bosses, the possible location of partings and hatches, and other elements of the housing.

This design procedure gives the idea that, a housing is one of the components of a mechanism, as the shell is an integral part of a tortoise’s skeleton. Without this part the mechanism doesn’t exist. This is the difference between a housing and a guard; the latter is just to isolate the mechanism from the surroundings.

The housing is almost always the biggest part of a mechanism. It is usually made as a closed box, so that the rest of the parts are mounted inside it. In this respect, the housing also serves as a guard. The housing is fixed part of a mechanism that serves to attach it to some foundation or substructure or to another unit.

Though the mobility or immobility of the housing may be just a matter of definition, its movement in space should be taken into consideration. When the housing moves, all the parts of a mechanism (including the oil) are exposed to inertia forces, which can essentially change the load of the parts and the lubrication conditions.

Serving as a guard, the housing isolates the mechanism from the surroundings to create conditions inside that are comfortable for the mechanism. On the other hand, the housing isolates the surroundings, including the personnel, from the mechanism, so that we are protected from hearing the noise and from being sprinkled with hot oil; besides, we can’t easily put our fingers into it. This is an important function of the housing; nevertheless, it is not an envelope but one of the parts of a mechanism.

Therefore, with respect to stress and strain analysis, the housing deserves attention no less than any other machine element. The problem is that housings usually have a complex spatial shape. It can be analyzed by “engineering methods”. This method, however, requires a certain level of experience and feeling of how the housing deforms under load; otherwise, the simplifications may be done incorrectly, and the results of the calculation may be far from satisfactory.

Obligatory requirements a housing should meet: Housing must be designed so as to enable assembly operations and the control of parameters to be checked after assembly. That means, the housing should have partings or sufficiently sized openings that enable convenient assembly and control of the mechanism. Sometimes the mechanism must be periodically inspected while in service to check the condition of wearing parts (like gear teeth or bearings).

For this purpose, the housing should be provided with inspection hatches in needed places. The hatches may reduce the strength and rigidity of a housing; thus, their dimensions should not be large but enough to enable the actions they are made for. In relatively small mechanisms, it may be preferable to dismantle the mechanism for inspection and in that way avoid the inspection hatches.

2. Housing should have exact dimensions where it is in contact with other parts. This accuracy should be achieved in production and then remain within permissible limits while the housing is exposed to mechanical and temperature influences. Change in dimensions can relate to elastic and plastic deformations under load or to thermal expansion, or it may be caused by structural changes in the material. Metals, with high strength, high modulus of elasticity, and stable structure, are preferable to other materials. Therefore, housings are almost always made from metals.

3. In addition, some other requirements may be important, such as • Heat conductivity of the housing material (to enable more effective heat extraction from inside to outside) • Ability to damp noise and vibrations • Low weight • Ability to withstand aggressive environments, such as seawater, and others.

MATERIALS FOR HOUSINGS Because housings are intricately shaped, they are mostly cast, and usually the surfaces that fit to other components are machined. One of the material is gray cast iron. It has good castability and machinability, increased corrosion resistance, and good wear resistance. But gray cast iron is brittle and sensitive to overload and impact load; therefore, it is not recommended in dangerous applications.

External components of a housing The mounting: Are intended for attachment of the housing to a base or foundation. Lifting elements: These are hooks or protrusions for holding when lifting. Seals: Are designed to prevent communication between the inside the housing and the surroundings, all locations where this communication may take place must be sealed.

The consequences of seal failure determine the requirements of the seal specification. For example, if an oil-lubricated mechanism works in a clean room, the ingress of air inside the housing is admissible. Leakage of oil from the housing is unpleasant, but if it is one drop a day, it can be bearable. If such a mechanism works in a food production line and has contact with food, no oil leakage from the housing can be permitted, and no ingress of the product into the housing can be allowed.

The same applies to a submerged mechanism: oil leakage pollutes the water, and water ingress into the housing is likely to damage the mechanism. The most stringent sealing requirements are necessary if the housing contains substances that are dangerous for the environment or personnel. In these cases, more than one stage of sealing is used as a rule.

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