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Linear bearings cope with the presence of glass dust

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HepcoMotion has supplied its GV3 linear bearings to a customer whose machines were suffering from premature bearing failures caused by the ingress of fine glass dust; the GV3 bearings have successfully eliminated the problem.

Linear bearings cope with the presence of glass dustCRT Heaven has created a cathode ray tube (CRT) screen splitting process that is claimed to be unparalleled in its speed, energy efficiency and reliability. However, the very nature of that process creates glass dust particles smaller than 5um in size that can – and did – play havoc with the system’s linear bearings. Dust infiltrated the ball races, causing premature failure of the bearings on the first ever CRT Angel machine. Now, having changed to HepcoMotion linear bearings, the problem has been eliminated.

This move to minimise downtime and maintenance was an important one, as the CRT processing technology is now in worldwide demand. As a result of recent trade shows, the company expects to install five of these machines in the coming months.

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 emerging products. The machine has an hourly throughput of 120 IT monitors and 80 CRTs of varying sizes from 6 to 42inches.

This technology is vital in the light of the European Waste Electronic and Electrical Equipment (WEEE) Directive that became law in 2007. CRTs are now classified as hazardous waste primarily because of their lead content, which can account for up to 25 per cent of their weight. Accordingly they cannot be sent to landfill, so televisions and monitors have to be dismantled so that the CRT glass tube and other components such as plastic casings, cables and printed circuit boards can be recovered.

Efficient glass reclamation

Government figures suggest that in the region of 5million CRTs are set to enter the UK waste stream per year over the next decade and beyond. The need for a cost-effective method of material reclamation is clearly evident and this 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 to cut the CRT below the frit line; this operation is therefore guided by a laser pointer. Initially the CRT passes between the diamond blades that cut it on two sides, and then it is rotated through 90 degrees for the remaining sides to be cut, thereby 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 for the door assembly. However, despite the efficient and complex extraction system the fine glass dust soon compromised the working of those bearings.

Problem

Project Manager Graham Hamshaw explains: “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. 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.”

Solution

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 fail catastrophically, so the powerful hydraulic drives were able 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, a further alternative was sought.

The HepcoMotion GV3 linear system was soon found to fit the bill in every sense. 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 the alternatives in composite aluminium and this rugged construction makes it suitable for this type of heavy-duty application. Another important feature of the GV3 is its innovative wiping action that actively expels the fine glass dust, preventing it from compromising bearing performance.

To remove any potential issues relating to bearing life, the decision was taken to retrofit HepcoMotion GV3 units on the first and already-installed CRT Angel machine. This work was undertaken in January 2007. Hamshaw states: “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. And that only failed as a result of impact when a foreign object was left in the machine. The operator did not 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. Hamshaw concludes: “There is no doubt that the longevity, performance and ease of installing and servicing these bearing assemblies has helped us to increase the productivity and reliability of the CRT Angel machines.”

For more information about the HepcoMotion GV3 system and to download a PDF catalogue, go to www.hepcomotion.com/db_pages/products/proddetail2.php?id=0001&cat=comp&c=.

 
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