20,000 km Without Relubrication
Ball rail systems and ball screw assemblies should be productive and require little maintenance. Bosch Rexroth has now looked into how technical progressis affecting lubrication intervals. The results are impressive.
By Sebastian Pfeuffer
Quality components are worth the money—all automation specialists, mechanical engineers, and plantengineers who value lasting performanceand low-maintenance operations know this.For the linear guides and screw drives used,this means that the relubrication intervalsshould be as long as possible. Ideally, the basic lubrication should last the full life of thelinear motion product, making it practicallymaintenance-free.
Why Lubricate At All?
Essentially, linear motion componentsare lubricated to reduce the friction betweenthe rolling elements and tracks to minimizewear. This is achieved with a film of lubricant that forms during motion. Whether orwhen relubrication is required depends onthe particular loads involved. Tables anddiagrams provided by manufacturers showwhat distance a runner block, for example,can travel maintenance-free under a specificload and normal environmental conditions.With screw drives, the number of revolutions is given instead.
Because lubrication intervals become longer with each technical development, theyare reviewed from time to time. During thelatest practical tests under various operatingconditions, the linear motion technologyexperts at Bosch Rexroth determined thecurrent values. Basically, three factors decide how long the lubrication intervals are:
During the check, Bosch Rexroth lookedat the ball rail systems BSHP and the ballscrew assemblies BASA in particular. Bothproduct groups are designed for optimumrunning, with rolling elements that movefrom the load zone into the load-free return zone in an optimum manner. Thisway, the BSHP ball runner blocks achievethe best possible values when it comes toprecision, friction forces, and friction forcefluctuations. In the nuts of the ball screw assemblies, deflectors at the transition to theload zone ensure optimum guideway andsmooth-running rolling elements.
Both the ball rail systems BSHP and the
ball screw assemblies BASA benefit from a
continually improved surface and the geo-
metric accuracy of the tracks. As a result,
the lubrication intervals are longer, but at
the same time the load ratings are higher
and the range of maintenance-free applica-
tions is greater.
Factor 2: The Lubricant
The job of any lubricant is to separaterolling elements and tracks, to minimizefriction and to prevent corrosion. Variouslubricants can be used for linear motionapplications. The most important ones aregrease, liquid grease, and lubricant oil.Within the first group, the grease fromBosch Rexroth is particularly attractivefrom an economic point of view becauseit is permanently effective at the specificpoint of contact between the rubbing surfaces and allows particularly long lubrication intervals. The solid consistency alsoreduces the ingress of dirt and makes sealing or stripping elements more effective.
The liquid grease recommended byBosch Rexroth is easily moved and is therefore often used in central lubrication systems. Lubricant oils have even better flowcharacteristics. They can dissipate morefriction-induced heat but can also leakout more easily. The technical documentation or the product catalog from BoschRexroth provides information about whichlubricants are approved for which productand are suitable for which operating conditions. In case of doubt, the relevant country unit can provide further advice.
Factor 3: Operating and Environmental Conditions
Whether long lubrication intervals are
possible with a preferred linear component
depends not only on the operating con-
ditions, such as load and travel speed—it
depends on the environment too. For ex-
ample, relubrication is necessary earlier or
more often if the environmental conditions
are characterized by high temperatures or
vibrations or if the linear motion compo-
nents are frequently in contact with cool-
ing lubricants, dust or chippings during
operation. If relubrication is necessary,
the lubricant connections should be po-
sitioned according to the
recommendations in the
product catalogs. After
all, easy accessibility
makes maintaining the
machine easier later on.
As part of its flexible design, the BSHP ball runner blocks are accessible from eight locations.
A Good Basis: Basic Lubrication
If linear motion components are to function correctly, the lubrication intervals specified in the product catalog as well as thequantity and specifications of the lubricantmust be observed. Mechanical and plantengineers who have stringent requirementsregarding the life cycle of their machinesshould pay particular attention to the basiclubrication. The linear guides and the ballscrew assemblies from Bosch Rexroth arenormally given basic lubrication in the factory using the optimum lubricant.
Pester pac automation GmbH, a successful packaging machine manufacturer, is oneof the companies taking advantage of thisbenefit. “The ready-to-install linear guidesand ball screw assemblies save time andmoney when installing and commissioning systems. In addition, they offer longermaintenance intervals and require almostzero maintenance,” explains Hans Haug,head of development at pester pac automation GmbH. “Together with Bosch Rexroth’sglobal presence, this is an important assetfor our international customers.”
Lubrication Intervals Up to Four
With its decades of production experi-
ence, Bosch Rexroth has now optimized its
ball guide rails and ball screw assemblies
so much that the lubrication intervals with
grease lubrication are up to four times lon-
ger. As a result of limit value shifting, many
applications with smaller loads can be
achieved with minimal maintenance. Test
results revealed that the lubrication inter-
vals for the latest ball rail systems BSHP in
the sizes 15 to 45 have now doubled. The
runner blocks can now cover distances of
up to 20,000 km—the same distance as
from Germany to New Zealand—with the
200 Million Revolutions Without
The latest generation of ball screw assemblies BASA with diameters up to 40 mmachieves up to 200 million revolutions—upto four times the previous values—with basiclubrication. For size 32 with a 64 mm lead,this equates to a distance of around 12,800km—the same distance as from Germanyto Hawaii. Clear comparisons like these godown well with users, according to Managing Director Martin Albrecht from albrechtElektrotechnik, an automation specialistand manufacturer of special machines. “Themaintenance-free linear motion technologyfrom Bosch Rexroth is an important uniqueselling point when competing in the international market.”
Go Easy on Your Budget and
Because lubrication intervals are nowup to four times longer, many applicationsat machine manufacturers such as albrechtElektrotechnik and pester pac automationGmbH now require no relubrication. Asa result, lubricant consumption falls andoperating costs are reduced. The ball railsystems now require only half as much lubricant, while the ball screw assemblies useonly a quarter of the previous amount ofgrease. The new lubrication requirementsnot only conserve valuable resources —they reduce operating costs, increase availability and help to protect the environment,an important sales argument.
For more, visit newequipment.com/21158603Ball rail systems BSHP achieve a high level of precision, lowerfriction forces, and quieter running under load. Pictured Right:With extra rolling elements and a preloaded single nut, ballscrew assemblies BASA achieve higher load ratings in spite oftheir short design. Credit: Bosch Rexroth