Linear bearings resist glass dust

The all-steel slideway on the GV3 is three times stiffer than composite aluminium alternatives and this rugged construction makes it ideal for this type of heavy-duty application.

CRT Heaven has created a cathode ray tube (CRT) screen splitting process that is unparalleled in its speed, energy efficiency and reliability.

The very nature of that process however creates sub-5 micron glass dust that can, and did, play havoc with the system's linear bearings.

Dust infiltrated the ball-race, causing premature failure of the bearings on the first ever CRT Angel machine.

A swift change to HepcoMotion linear bearings made the problem short-lived.

This move to minimise downtime and maintenance was an important one as this CRT processing technology is now in worldwide demand.

CRT Heaven deals with end-of-life televisions and monitors.

Its Angel CRT recycling system quickly and accurately separates the unleaded and leaded glass portions of the tubes, a process that allows the use of these raw materials in the manufacture of new CRTs and other products.

The machine has an hourly throughput of 120 IT monitors and 80 CRTs in sizes from 6 to 42in.

CRTs are now classified as hazardous waste primarily because of their lead content, which can account for up to 25% of their weight.

Accordingly they cannot be sent to landfill, so televisions and monitors have to be dismantled, allowing the recovery of the CRT glass tube and other components such as plastic casings, cables and printed circuit boards.

Government figures suggest that around 5 million CRTs are set to enter the UK waste stream per year over the next decade.

The need for a cost-effective method of material reclaim has prompted the introduction of the CRT Angel, a highly efficient machine that automates an important part of this process.

This is a process that involves precise measurement and control as the machine needs to handle a variety of CRT shapes and sizes.

Measurements are processed by the machine's PLC system which sets the automated cycle into one of six pre-programmed cut cycles to suit the CRT size.

The common feature of all CRTs is a conical rear portion that is bonded to the unleaded screen glass using a high lead oxide content glass frit.

To ensure efficient separation of the leaded and unleaded portion it is imperative cut the CRT below the frit line, an operation guided by laser pointer.

Initially the CRT passes between the diamond cutting blades cutting it on two sides and then it is rotated through 90 degrees for the remaining sides to be cut completing the separation of the two glass portions.

In adjacent enclosed and air extracted modules the cone or funnel glass is removed and ejected via a chute for bagging.

Concurrently the internal metal components are removed from the screen glass before the phosphor layer is vacuumed off and stored for disposal.

The screen glass is then also bagged for re-use as feed stock.

In the first installed CRT Angel machine ball-race linear bearing systems were used to facilitate the movement of the CRT through the machine, for the lateral traverse of the diamond cutting heads and the door assembly.

Despite the efficient and complex extraction system however the fine glass dust soon compromised the working of those bearings.

"The travel table bearings and the assembly that transports the CRT through the machine were those nearest the floor and therefore the most vulnerable to the build-up of glass", explained Project Manager Graham Hamshaw.

"Some of the CRTs also weigh in excess of 60kg and have glass that is 15mm thick".

"The combination of these factors meant the machine and its components needed to withstand significant forces".

Initially HepcoMotion Pacific bearings were the front runner in finding a suitable replacement for the ball race bearings.

Although they did show signs of wear in the aggressive environment they did not catastrophically fail, allowing the powerful hydraulic drives to perform their functions without a noticeable drop in machine performance.

However as their size and shape would have required structural changes to other parts of the machine an alternative was sought.

The HepcoMotion GV3 linear system was soon found to fit the bill.

It offered a similar profile to the flat rail and ball-race bearings already installed on the machine but promised far better performance in the aggressive, dust-laden environment.

The all-steel slideway on the GV3 is three times stiffer than composite aluminium alternatives and this rugged construction makes it ideal for this type of heavy-duty application.

Another important feature of the GV3 is its wiping action that actively expels the fine glass dust preventing it from compromising bearing performance.

The beraings were installed in January 2007.

"Now over a year down the line I am pleased to say that I have had to replace only one of the 48 journals that are on that machine", Graham Hamshaw continues.

"And that only failed as a result of impact when a foreign object was left in the machine".

"The operator didn't notice the obstruction as the machine continued to function perfectly".

Such has been the performance of the HepcoMotion GV3 system that CRT Heaven now uses it for the door assemblies, the cutter assemblies and the travel table".

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