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ROSA-sistemi Cross roller linear guideway GR1120

GR linear system bearings could utilize either cross rollers or balls as rolling elements. The two will differ substantially in load ratings. The ratio is approximately 10 to 1 in favor of rollers, depending upon the dimention under consideration.

Balls are more advantageous in case of presence of impurities and/or misalignment as it happens when the structure, to which rails are anchored, is not sturdy enough to support them and rails are not therefore placed in their correct position.

Such systems offer good load rating with respect to the cross section, lenght and relative stroke. They utilize different cages and end pieces depending upon the application.

Technical characteristics

The rails are made of special alloyed steel and through-hardened to a hardness value of 60 ± 2 HRC. The precision relative to the parallelism variation between the raceways and the reference surface are dependent upo the quality selected (10 micron/1600 millimeters for the “standard” quality, 5 micron/1600 millimeters for the “selected” quality).

It is important to state that all the elements are individually checked during all manufacturing phases before the final inspection. Also, a non-destructive check is performed to assure the absence of internal cracks which may have been generated during heat treating. Such micro-cracks could drastically affect both the precision and the life of the rails.

The advantages obtained by employing rolling systems can be summarized as follows: 

• Very sensitive movement (friction coefficient of 0.003) 

• Lack of start-up frictional losses (stick-slip) 

• Minimum wear 

• High load carrying capacity 

• Maximized precision 

• Availability in stock of all models included in the catalogue

In our production program we have a full range of standardized cross roller tables with lengths ranging from 25 to 1010 mm and widths of 30 to 145 mm; with load ratings from 250 N to 48100 N. The structural members of the tables are made of cast iron (G25), naturally aged, or of steel. A range of anticorodal tables is also available; their light mass makes it possible to reduce inertial forces.

Manufacturing tolerances

1. Standard quality

2. Selected quality

The rails are through-hardened to 60 ± 2 HRC. The material is alloy steel (DIN 1.2842). Each rail is accurately checked during all the manufacturing phases and it is subjected to a final inspection where the geometry, hardness, surface texture of raceways and adjacent surfaces are thoroughly checked.

The rail hardness is of major importance since its variation has a direct influence on the life expectancy of the system. 

It is important to know that the best working conditions (Fd = 1) corresponds to a hardness value of 58 HRC minimum. For hardness lower than 58 HRC, the theoretical load rating should be multiplied by the corresponding hardness factor. Therefore, if a rail with a hardness of 55 HRC and theoretical load rating of 3000 N is used, its load rating will be C = 3000 x Fd which corresponds to 3000 x 0.78 thus 2340 N.

Temperature

The temperature also has a great influence on the system life. For temperatures above 80°C the factor Ft should be introduced. The table shows the most common factors if the theoretical load rating of a recirculating ball unit RK 6100 is 715 N such a rating will be reduced to 536,25 N (715 x 0.75) if the temperature rises to 250°C. Permissible operating temperatures is between -40°C and +80°C.

Acceleration

If all the conditions of the system have been verified, values up to 50 m/sec² are allowed.

Speed

Linear systems utilizing GR type rails could be used for speed up to 50 m/min. If higher speeds are sought, our engineering office should be consulted

Sealing and protection

It is absolutely necessary that the linear system is protected from impurities of either solid or liquid nature.

Multi-piece ways

For systems requiring longer than standard catalogue rails, multipiece ways can be provided. To accomplish this, the individual rails are head-ground and ground simultaneously to the required length. By doing so, there will be no difference in precision and smoothness. In case of shipping of multi- piece system, the individual rails will be numbered to allow proper mounting.

Lubrication

The rolling systems are usually lubricated with a thin oil film applied during assembly. This lubrication method allows the better utilization of the precision and smoothness characteristics of such an arrangement. However, should the application dictate it, oil-drip, oil-mist can be used. 

(Type CLP or LP with viscosity from ISO V6 15 to 100 like DIN 51519)

Preload

Usually the preload is applied with set screws placed in correspondence of the mounting screws by using appropriate dynamometric spanners. A system could also be preloaded by means of a tapered gib, a wedge of cylinder, though all of these methods are more complex and require a more accurate execution of the supporting structure. Such accuracy may not be achievable or even wanted by the user. 

The preload setting is usually dictated by the application and can very between 2% and 20% of the dynamic load rating C of the system examined.

Rosa-Sistemi_Linear-bearings-and-precision-tables.pdf