Ball cage displacement: Questions and answers

Fortunately, this phenomenon is rather rare, but the reason for a KKV can be very versatile. This article will take a closer look at this topic. Our linear technology specialist Beat Schwizer from HA-CO Motion AG, Altendorf (CH) provides answers to the most important questions. 

What are the applications for ball cage-guided telescopic slides? 

Worldwide, more than 99% of all telescopic splints are used as spherical cage-guided splints. as sheet metal telescopic rails such as our Accuride products. These mass products are very lucrative in terms of price and are therefore industrially produced in very high quantities! The rails are used in a variety of ways: Furniture a all Cage Displacement

Ball cage displacement (KKV) can occur with telescopic slides as well as with linear guides. Fortunately, this phenomenon is rather rare, but the reason for a KKV can be very versatile. This article will take a closer look at this topic. Our linear technology specialist Beat Schwizer from HA-CO Motion AG, Altendorf (CH) provides answers to the most important questions.

What are the applications for ball cage-guided telescopic slides?

Worldwide, more than 99% of all telescopic splints are used as spherical cage-guided splints. as sheet metal telescopic rails such as our Accuride products. These mass products are very lucrative in terms of price and are therefore industrially produced in very high quantities!

The rails are used in a variety of ways:

• Furniture and especially in the kitchen industry
• In mechanical engineering: packaging machines, covers for machine tools, inspection and testing machines ...
• In automation as feeders, in storage buffer towers, assembly machines ...
• In intralogistics for shuttles and high-bay warehouses, for load carriers ...
• In medical technology for drawers, feeders, buffer storage ...
• In the accessory units in the industry for drawers, carcasses, storage units ...

How do you notice a ball cage shift?

The telescopic rails / drawer rails can no longer be pulled out completely, i.e. the maximum stroke according to the data sheet is no longer reached. The ball cages of the telescopic rails are not force-guided, i.e. all individual parts within the rail are not pulled out synchronously. This can lead to a KKV due to the design and installation. 

It is then necessary to extend to the maximum extension length. In this way, the ball cages are realigned. This is achieved by pulling the drawer all the way to the end stop. Undressing can be stricter or easier and again depends on various factors. After repeated repetition several times, the telescopic rails run smoothly again and without displacement.

Why can KKV occur?

This is not so easy to answer. There are umpteen different factors that can have an influence, and a combination of several of them is also possible. Evaluating the exact reason can be very time-consuming! Below we have tried to list some reasons, but it is always necessary to take a closer look at the corresponding application:

• Vibrations: They occur during transport and occur on machines / vehicles. They can also affect the application from a compressor, motor, etc
• Unequal loading: One of the two rails is subjected to greater load
• Dirt: Causes one rail to jam more than the other.
• Installation of parallels: If the rails are not installed in parallel, they can easily jam. There are different parallels that have to be looked at, e.g. are the rails from body to drawer in the same axis, etc.
• Installation dimensions: If the installation dimensions are not correct and the rails are compressed, jamming can occur again. 
• Very wide drawers: When the drawers are wider than deep. This increases the possibility of a one-sided burden.
• Drawers that are too weakly designed (rigidity): This can cause the drawers to bend and this results in torque on the telescopic rails. This rotational load also reduces the service life of the telescopic rail, as there is also a risk of jamming here. 
• Handle: If the handle is not attached to the middle of the drawer, different forces can act on the rails.
• Installation position: A vertical installation position (telescopic rail provided) is required. 
• Installation position horizontally: With a few telescopic rails, the rails can also be put down/installed horizontally. The deflection is much greater and can also have a detrimental effect. 
• Reduced stroke: If the drawer is often not pulled out to the end stop, this promotes cage displacement. 
• Temperature differences: Can change various parameters and lead to a jam. 
• Fast displacement movements: this in combination with other points can have an intensifying effect

Are there ways to prevent ball cage displacement with installed rails?

As a first measure, the above-mentioned conditions must be controlled and improved. In most cases, this reduces the susceptibility to errors and thus increases the runnability of the rails. 

Furthermore, we have the possibility to use slightly smaller balls (0.01mm and more) with very few guides / telescopic rails. This increases the play in the rail and the ball cage can be easily pushed back into the correct position. 

Unfortunately, this is not possible with the sheet metal telescopic rails and thus with most rails due to mass production.

Are there alternatives to the ball-cage-guided telescopic rails?

With the help of roller telescopic rails, the problem of CISO is circumvented. With such telescopic rails, ball cage displacement can never occur due to their design. The harmless vertical installation of roller telescopic rails is another advantage.

In addition to the roller guides, telescopic rails can also be built with recirculating ball guides. Again, there are no shifts and they can also be used vertically. Thanks to the stiffer and more resilient guide systems, other designs and applications can be achieved here.

Unfortunately, in addition to all the advantages, it also has disadvantages. For example, these rails are a lot more expensive, can sometimes absorb less load, especially with the rollers, and have a larger cross-section than the ball versions.

Does HA-CO have these alternatives in its range?

Such rail systems are special products and therefore we do not offer them as standard. But we have already been able to carry out some projects for customers. The experience in design and calculation is correspondingly extensive. However, since this is always customer- and application-specific, increased consulting effort is required here. This distinguishes us as a system supplier from standard dealers.