vee bearings

Corrosion Resistant Linear Motion

combined roller bearing with TDC coating
~ kateharden

In some applications, it is necessary to specify corrosion resistant products (e.g. food, drink & pharmaceuticals) while in other applications it may be desirable but not essential (e.g. offshore, external use). While a few linear motion products are available in stainless steel, there are often high prices, long lead times & lower load capacities associated with specifying stainless steel.

So what options are there?

For light duty applications there are a few options available in stainless steel. For example miniature motion guidance, round shaft linear products and track guidance systems.

For heavy duty applications there is little choice but some products can be made corrosion resistant by the use of coatings. The most effective coating for linear motion systems is Thin Dense Chromium (TDC). TDC coating provides a hard finish which is able to withstand the high contact load between the bearing and its corresponding track.

Which Products are available?

Euro-Bearings Ltd can offer Combined Roller Bearings with TDC coating to provide a heavy duty corrosion resistant linear motion system. The bearings retain their load capacities (unlike stainless steel alternatives) and maintenance and downtime can be reduced. The TDC coating can also be applied to the rails (channel) and flanged clamps if desired. The combined roller bearings offer a versatile linear motion system which can be used in horizontal, vertical or cantilevered applications.

Euro-Bearings Ltd’s Combined Roller Bearings & Rails with TDC corrosion resistant coating

Another linear motion system to benefit from TDC coating is Vee bearings. While the Vee bearings themselves can be supplied in stainless steel, the T rail to suit the bearings is not so readily available due to the high costs associated with stainless steel. The rails can be TDC coated after any necessary fabrication work and the lead time can be as little as two weeks.

What should I choose?

Every linear motion application should be assessed individually. Use our flow chart to help select which product might be suitable, or ask our technical sales team for advice.

If corrosion resistance is required then consider the following products:

Light to medium duty –
Miniature Motion Guidance (Stainless steel)
Linear bearings & shafts (Stainless steel)
Track Guidance System (Stainless steel)
Exterior Slide System (Aluminium & Delrin)
Vee Bearings & Rails (Stainless steel or TDC coated)

Heavy duty –
Combined Roller Bearings (TDC coated) & Channel (TDC coated or Stainless steel)
Linear bearings & shafts (Stainless steel – small range & lead times are likely to be long)

Summary

Traditionally, corrosion resistance of linear motion products has been provided in the form of stainless steel. However, today, coatings such as Thin Dense Chromium can provide corrosion resistance to bearings without compromising on load capacities and incurring long lead times.

How to use Vee bearings and T-rails

~ kateharden

Our Vee bearings and T-rails offer the user a simple way of constructing smooth running linear systems with a high load capacity and, in the case of the stainless steel version, corrosion resistance too. For this example we are selecting the following parts:

4 pcs EV W3X ( Vee Bearings)

2 pcs MB3 (Metric bore Concentric bush)

2 pcs MB3X (Metric bore Eccentric bush)

2 pcs T-3 x 1000mm ( T-3 rails 1 metre long)

The first thing to do is to decide the width of the track and then choose what material the T-rail will be attached to. In this example (see drawing) we have selected a piece of steel or aluminum 50mm wide and 1 metre long. Let’s call this the “support”. The precision of the system is dictated by how accurately this support material is manufactured.

The Rail and Support

Drilling the T-rail is easy. The flats are not hardened, only the tip of the vee, so normal drilling techniques can be used. Our preference is to clamp the T-rail to the support material and to drill pilot holes through the T-rail into the support. This means the centres will match. Double check that the T-rail edges are still parallel. Then drill through holes in the T-rails and drill and tap the support.

Finally bolt the T-rail onto the support. We tend to use dome head machine screws. Make sure the screw heads do not interfere with the carriage or rail edges. Also make sure that the rail edges are parallel.

The Carriage and Bearings

In this example we are making a carriage 150mm x 150mm with 4 no. W3X bearings. So again, select the material, steel or aluminium, for the carriage. The hole centre positions for the bearings (dimension “A” on the drawing) can be calculated as:

A = Width of support + 2 x TE + 2 x A1

The value for dimension TE can be found here http://www.euro-bearings.com/veerails.htm (TE in this case is 6.35mm).

And the value for dimension A1 can be found here http://www.euro-bearings.com/veesizes.htm (A1 in this case is 19.05mm).

NOTE: Dimension TE is the offset of tip of Vee rail from the support material. A1 is the dimension from centre of bearing to bottom of Vee. In our example this is 50 + (2x 6.35) + ( 2 x 19.05) = hole centres 100.8mm.

The eccentric bush MB3X allows 1.07mm of lateral adjustment.

Drill the holes through the carriage plate at 100.8mm centres (in this case 8.2mm diameter clearance holes for the M8 bolts we will use to secure the bearings).

Insert the concentric bushes into 2 bearings and insert the eccentric bushes into 2 bearings. Firmly secure the concentric bushed bearings to one side of the carriage plate and tighten. Loosely assemble the eccentric bushed bearings to the carriage plate and slide the carriage onto the T-rails. Now adjust the eccentric bushed bearings by feel (or feeler gauge) to achieve the pre-load required. Slide the carriage back & forth to ensure there are no pinch points. It is recommended to use hex cap head bolts and nyloc nuts through each bearing bush.

IMPORTANT: Make sure the outer ring of the bearing is turning on the inner ring of the bearing and NOT on the bush. The bearing should be an interference fit onto the bush.

Euro-Vee Bearings

~ kateharden

euro-vee

EURO-VEE BEARINGS

Our Euro-Vee Bearings are available in 4 sizes which can take radial loads from 100kg up to 800kg. A cost effective linear sliding system can be built using our corresponding T Rail and Euro-Vee Bushings for applications requiring either vertical or horizontal movement.

The bearings are sealed and lubricated for life and so will tolerate being used in dirty environments. The Vee Bushings are used to mount these bearings. We have both concentric and eccentric bushings on stock, in both imperial and metric sizes.

A typical system would use a pair of rails with a minimum of four bearings acting as wheels for a carriage. Half the number of bearings would be mounted on the concentric bushings and the other half mounted on the eccentric type. All the bearings are held in position on their bushings by a bolt fixed through the centre of the bushing. By rotating the eccentric bushings it is possible to tighten the bearings onto (or off) the track. The eccentric bushings have a hex head so that they can be rotated with a spanner before their fixing bolts are tightened back up. The system should be designed so that the main loads are taken by the bearings on the concentric bushings.

The T Rail can either be drilled and bolted down (to a square edge) or it can be welded into position. The body of the rail is soft so it can be easily drilled. The top edge of the rail (where the bearing runs) is induction hardened and polished.

It is also worthing knowing that our Euro-Vee Bearings can be run on round (hardened and ground) linear shaft.

Example applications include:

  • packaging machinery
  • laboratory automation
  • woodworking machinery
  • vending machines
  • sliding doors (eg machine tool doors)

Our Euro-Vee Bearings are also available in stainless steel.