A spline joint is a joint of a female and male surface (shaft-bore). Slots and grooves are used, which, as a rule, are located radially in the place of engagement. This connection has sufficient strength and ensures alignment of the shaft and the hole. The main advantage is that the part can move axially.
Splined connection: classification
As you know, there are several ways to fix two parts using a slot. In various conditions, different methods are used. There are involute splined joints. They differ from straight-line ones in the form of a tooth (lateral surface) and hollows. They have several undeniable advantages, such as the transmission of high torque (Nm) and high centering accuracy under heavy loads. If we talk about straight-line connections, then the main advantages are the simplicity of manufacture and low cost. There are also triangular slots, but they are used less often. Most often at the junction of fixed parts with a small torque. Quite often they find their application in thin-walled bushings. In them, the use of other types of compounds is not considered permissible for a number of technological reasons.
Key and splined connections
In some cases, a pulley or pinion must be secured to the shafts. If you also need a large torque transmission, then key and involute splined joints are used. As for the keys, prismatic are widely used, due to the ease of installation. The main issue is that sometimes you need to make it possible to move the part in the axial direction. In this case, a fit with a gap is used, and the key is attached to the shaft with screws. If it is necessary to create a reliable connection in a lightly loaded place, then a segment key, which has a short length, is well suited. The main difference between the slots is that they use a larger number of teeth and smaller protrusions. Connections are of 3 types: easy-disconnect, hard-disconnect and fixed. Every year, methods of processing parts allow you to achieve all the best results from a technological point of view. This is a high centering accuracy, interchangeability of failed parts, and more.
How were problems with the driveshaft solved?
Now let's look at the effectiveness of splined joints. In this case, the slot serves to change the shaft length, which is required to ensure the alignment of the units, the installation of which made inaccuracies. Grease is supplied to the thrust bearing and the actual slot by a grease nipple. Most often used is solidol. Since the length of the driveshaft is such that in many cases the lubricant does not reach all the working friction units, it is quite advisable to reduce the channels through which oil or other liquid enters. You can use transparent inserts. They will make possible visual inspection and timely supply of lubricant to the friction unit. In order for the sliding fork to serve as long as possible, a brass insert is used, which is tucked into the spline connection. Of course, this can significantly reduce the wear of the part. In principle, the splined joint of the driveshaft is reliable and easy to maintain, but it is not without drawbacks.
Centering Methods
There are several ways to center a straight-line spline connection. One of them is the outer diameter. To do this, the shaft is milled, and then polished on the outer diameter. By the way, this is the cheapest and most effective centering method. The sleeve is stretched mechanically. This method is used when the surface of the sleeve bore is not subjected to heat treatment or thermal improvement. If we talk about expensive methods, then this is centering along the inner diameter. The fact is that the shaft is milled and then ground on the side surfaces. The method applies only to preliminary heat treatment of the shaft and sleeve. To obtain a uniformly distributed load on each slot, centering on the sides is used. The bore and shaft are improved thermally. Most often, such centering is used for joints with high torque and considerable load.
A few important points
As already noted above, key and splined joints are used in order to prevent the rotation of two parts relative to each other. Before you install the part on the shaft, it is checked for strength, which allows you to choose the optimal technical characteristics, such as material, dimensions, weight. If we talk about the percentage prevalence of splines, then straight-line ones occupy about 80%, and only 10% of involute and triangular ones remain. Depending on the workload of the connection, a series of products is selected, which can be light, medium or heavy. It is important to pay attention to the presence of lubricant in the joint, especially if it is movable. The absence of mineral oil or solid material will cause the friction coefficient to increase several times . And this is increased wear of the connection and lower efficiency of the whole unit. Oil or solid oil is supplied by centralized automatic stations (if the number of nodes is more than 50 pieces) or mechanically.
Conclusion
An important point is the restoration of key and splined joints. Of course, it is sometimes easier to perform a replacement, but when this is not possible, then use the extension. If in simple words, then by welding, the original state of the product is restored. Most often, arc surfacing is used, followed by grinding (with high wear). Sometimes it happens that the designation of the splined joints does not allow for repairs. This happens when they are easily removable and not intended for regrinding. So that the node does not fail, it is necessary to exclude any beating in the connection. This can be achieved in several ways, for example, by installing special gaskets. That, in principle, is all that can be said about what a splined connection is and why it is needed.