Few things can bring a machine to a grinding halt (literally!) like a jammed linear bearing. Metal shavings, sawdust, glass powder – all can shorten the useful life of linear guides dramatically. The use of proper bottom and end seals can prevent a great deal of maintenance headache. While not necessary in every circumstance, seal options should always be considered!
Seals For Linear Guides
Most linear guides have 3 different seals that make up the contamination protection system. These are the end seal, bottom seal, and inner seal. In addition to these 3 seals, a metal scraper can be added to either or both ends of a linear guide for additional protection. The end seal is an external NBR (Nitrile Rubber – also known as Buna-N) seal that is attached to the end of the carriage. The seal edge contacts the profile of the rail and protects against contamination that is resting on the rail. The inner seal and bottom seal are internal to the carriage. They contact the top of the rail and the sides of the rail, respectively. The inner seal protects for contamination from inside the holes in the rail and the bottom seal protects from anything along the sides of the rail or bottom of the carriage.
What Are My Options?
With our linear guides there are many seal options to consider. They range from no seal at all to bottom and end seals specially designed for high-debris environments. When specifying one of our guides, the seal option is the 4th designation. For example, the part number “MSA 25 E ZZ FC N” calls bidirectional seals and metal scrapers.
These options and product codes are listed below:
- Standard Option:
The standard for our MSA, MSB, MSR, SME, and MSG linear guides is the “SS” bidirectional end seal & bottom seal. For MSC and MSD series linear guides, the “RR” Low friction end seal and bottom seal is standard. For the majority of applications these seal offer an effective solution.
- Heavy Contamination:
For applications that require protection from large amounts of debris on the linear guides “DD” double end seals are typically the best option. Options with metal scrapers such as the “ZZ” and “KK” are good options for machines such as plasma cutters where metal debris may stick to the rail or where the guides will run through metal chips.
- Fine Abrasive Dust:
New for 2015, we now have the “HD” high-dust seal as an option. It is specifically designed with CNC wood routers and similar applications in mind. Both the end and inner seals have been improved to keep the finest sawdust out. The “HD” option is only available for MSA sizes 15-35 and MSB sizes 15-20.
- Low Friction:
For applications that need the lightest resistance possible “LL” low friction end seals with no bottom seal are a good option. If even the low drag of an “LL” is too much, our linear guides can be used with no seal at all, only a metal scraper. This should only be used if there is to be absolutely NO debris.
Last Points For Consideration
There are a few considerations to take into account when selecting seals that are sometimes overlooked. The length of the seal, resistance of the seal, and rail caps or cover strips for the rail are all important factors when designing in linear guides. These topics are covered in detail in this document and can be found in the back of our catalog (pages B202-B212).
- When choosing a seal option for linear guides always be sure to consider the additional length it will require! For example, on an MSB 35 linear guide the “KK” double seals and scraper option will add 15mm to the overall length of the carriage.
- End seals add fairly significant resistance – with proper lubrication end seals can add anywhere from 2 – 65N of resistance (depending on series). While this additional resistance is typically negligible, it is still worth considering.
- Good contamination protection for linear guides isn’t just limited to the seals on the carriage! The mounting holes in the rail can collect a significant amount of debris in them. While the inner seals offer protection from this debris, it’s better to eliminate this build-up altogether using rail caps or cover strips. Rail caps are plastic disks that are tapped into the rail holes after mounting and the cover strip is a thin steel strip that is fixed to both ends of the rail after mounting.
Hopefully you found this guide informative. If you have any questions or would like more information, please feel free to contact us here.