Plastic instead of recirculating balls - Linear guides for mechanical deburring
 

Profile

• What was needed: Plastic plain bearings
• Requirements: Strong mechanical load, strong vibrations, much dust
• Industry: Mechanical engineering
• Success for the customer: A low-wear product with good sliding properties

 
Machine deburring of metal parts places high demands on the drives and above all on the guide elements of the milling motors. High rigidity is required and the guides must be designed for high feed rates. Purely theoretically, these are ideal operating conditions for recirculating ball bearing guides - if it weren't for the high dirt and dust loads. A machine manufacturer therefore decided to use plastic plain bearings, with success.
 

Automatic edge milling machine for intercoolers.

Problem

The two main axes for the milling process are equipped with recirculating ball linear guides. This also seems to be the right choice for the high speeds. However, things look different with the vertical guides for the two milling motors and the sawing unit, which also perform the feed stroke of around 25 mm. These guides are heavily stressed because they have to absorb the forces occurring during milling and counteract them accordingly. In addition, the fast running motors generate extreme vibrations. Finally, at this point, in the immediate vicinity of the machining process, there is a high level of contamination from aluminium swarf and dust.

Solution

All these factors speak rather against recirculating ball bearing guides. Therefore the designers at the engineering office looked for an alternative solution. They decided on the drylin® T plastic plain bearings from igus®. In this bearing, a carriage with sliding elements made of the abrasion-resistant high-performance polymer "iglidur® J" travels in a guide profile made of hard anodised aluminium. This is a perfect glide surface, as it is approximately three times more resistant to abrasion than steel mating surfaces.
 
Good sliding properties
Due to the very good sliding properties, the system also has a quiet operation. It is also insensitive to corrosion and dirt. The so-called "dry operation" is decisive for these specifications. As the drylin® T plain bearings do not require lubrication, the sliding elements act like wipers and simply push chips and dust off the glide bar. That such good sliding properties are nevertheless achieved is due to the high-performance polymer iglidur® J. In this highly abrasion-resistant material developed by igus®, the lubricants are permanently "incorporated". The linear guide drylin® T is successfully used today, especially in dirty environments. In woodworking machinery, for example, in paper and textile processing and in packaging machines. Even in environments where water, alkalis, or acids are added to most ball guide systems, the linear guide will last.
 
No signs of wear and tear
This cannot be taken for granted, because the machine is subject to hard wear and tear. Each year, the guide units have to complete around 300,000 strokes - under vibrations, heavy mechanical loads and in an environment contaminated by aluminium swarf and dust. A little wear would be quite understandable, but nevertheless the drylin® guides still run without bearing clearance after three years and now 900,000 strokes.