key connection - a peculiar kind of docking of two separable parts.It is important.In this case, the parts are connected using the auxiliary element - key.
Scope
In this regard, all quite simple.Keyed connection is used for splicing of the shaft and hub.Namely, to prevent their co-rotating during torque transmission.Also use these compounds, although not as widespread, to prevent shear flat parts.In the future, we have in mind only the first case.
Species
keyed divided into several groups:
1. Depending on the degree of mobility.This is an important characteristic.In this respect distinguished:
- movable connection.In this case, the guide or sliding key.
- fixed connection.
2. In the second group are considering a force which acts in conjunction.There are two types:
- tension.In this connection force is generated during assembly.It exists separately from the workload.
- unstressed.In this connection force is generated only if the workload.
3. The compounds are separated by type of used dowels.Namely:
- Parallel.
- Segment.
- cylindrical.
- Wedge.
- tangential.
further characterize each type of key separately.But first it must be said that these parts are mainly made of high-quality, medium-strength steels: 45, 50, 55. This is a known fact.In order to increase the strength of the dowels, bars for their manufacture are generally subjected to thermal treatment.It improves their quality.
Parallel key
This part is of three kinds.That is divided into guides, mortgages and moving.Due to the fact that the feather keys difficult interchanged because individual adjustment, they are not used in large production.It is their major disadvantage.Another disadvantage in this case is the ability to roll over during wear.
Woodruff
This form does not have these drawbacks, as the first.Therefore, they are easy to use in manufacturing.But they have a flaw that does not allow them to be widely used - it's a great cross-section of the shaft.It does not allow them to be installed on bends loaded sections of the shaft.
Cylindrical key
This is another important species.They are used mainly at the end portions of the shaft.When used, it is necessary that the combined materials are different in density and hardness.This prevents the wide use of this type of keys in large-scale production.
tangential key
This part consists of two parts.This kind of prismatic wedge that has a rectangular cross-section.Set tangential key pairs with an angle of 120-180 degrees.The advantage of these components is that their material in compression, and here there is a better form respective slot against the corresponding concentration of stresses.The downside of such a key, you can consider it a complex device.Apply these parts in heavy machinery.
The keys wedge
It is transmitted using friction forces.
plus the specified items:
- key connection in this case can withstand a small axial load.
- noted the good work under the influence of variable loads.
- Do not use the extra details that will keep the axial movement of the hubs.
drawback of this key are:
- The complexity of disassembly for repair.
- Strong offset from the center of the hub relative to the shaft axis.This is a significant fact.
- If you have a small length of the hub it is possible a significant bias, and it is possible runout part that is fixed (pulley, gear).
tolerances keyed
This definition is nemaloznachimym.To ensure the quality of the prescribed tolerances keyed.It is important to know.Defines GOST 2.308-79 keyed "Unified system for design documentation.Note the figures tolerances of form and position of surfaces. "This corresponds to the documentary base.
numerical parameters set tolerances arrangement with the following relationships: T (steam) = 0.6 T (w);T (sim0) = 4.0 T (w).
Where these designations include:
- T (w) - tolerance of the width of the groove keyed b.
- T (pairs) - specified parameter parallelism.
- T (sim) - the tolerance of symmetry in terms of the diameter.
The calculated parameters of the data definitions closer to the standard.Benchmark for this to GOST 24643.
landing keyed
precision alignment of parts provided by selecting this option.This is important.Tolerances define three types of compounds or landings.It is governed by standards.Next, we consider each type of detail.
free compound
This planting is used in difficult conditions to build the same load.It is used to obtain the moving subject compounds easy operation.
Normal connection
characterized it as an interference fit, it does not require frequent squabbles.It differs good conditions the assembly.
Tight junctions
determined they likely to produce about the same minor tightness in the appropriate splicing key to both parts (of slots).The assembly is used in a small amount of reverse loading.
Determination thereof
As mentioned above, the key is mainly made of high-quality and medium-strength steels (55, 50, 45).To increase the strength of this part blanks are usually subjected to a heat treatment that improves their quality.
When developing keyed connection, tentatively drawing up, the height and width of the part is used standard GOST 2336-7, taking into account the diameter of the shaft used.In this case, there is nothing complicated.The length of the key taken depending on the hub.Compare this with the norms of the standard.The correctness of the choice of certain key parameters checked using the calculation important key connection strength.In calculating this is no big deal.For example, the condition of the strength in this case is the following formula:
σsm = F1 / ACM ≤ [σsm].
There F1 - setting district forces on a pulley (H).AFM is the shear area (mm²).This value is determined by the following formula: (0,94h-t1) lp.
In this case lp = l-working length is a keys with rounded ends.This parameter is measured in millimeters.l - is keyed full length.
values in, h, t1 are standard sizes in accordance with GOST 23360 - 78.
[σsm] - setting allowable voltage to collapse (N / mm²).When using a cast iron hub [σsm] adopted within a certain range: 55 ... 95 N / mm².
Working key length is calculated as follows:
lp = 32 - 6 = 26 mm.
Determination of shear area:
AFM = (0.94 · 6 - 3.5) · 26 = 55.64 mm².
magnitude F1 accept for obtaining measurements.In this case F1 = 1200 H.
As a result, the calculation of the rated voltage will look like this:
σsm = 1200 / 55.64 = 21.56 N / mm².
This indicates that the condition of strength:
σsm = 21,56 & lt;[σsm] (55 ... 95 N / mm²).
Advantages key connection
This is seen as follows:
- designs reliable and durable.
- They are easily assembled and disassembled.
- low cost.
- They are easy to manufacture.
Disadvantages
In this context perceive the following:
- keyway weakened section of the shaft and hub.
- In many compounds observed misalignment.That is, the relative misalignment of the hub and the shaft half diametrical clearance.
- keyway In the corners of the high level of stress.
