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ENVELOPES
Teflon coated moulds are one of the latest developments, leading to more evenly flowing rubber, giving a more consistent quality throughout the production
course, the simplest method is to made is the use of Teflon coated
manually record use but the technology today is available to barcode and track the life of every envelope just as a mature retreader will do with every casing. This will allow the retreader to access accurate curing data, help analyse the cause of problems and of course ensure proper inventor y rotation.
Just as more and more truckers are looking at the cost of tyres on a cost per kilometre basis, retreaders need to look at envelopes on a cost per cure basis. Equally, there is always the temptation to buy cheap, but Sandberg
suggests that cheap and often is less efficient than making that quality purchase. By proper tracking of envelope use, through scanning perhaps, and knowing how many cures an envelope has done, the retreader can work out the cost per cure.
“One of the most
common questions is:
How many cures can I
expect? The answer,”
says Sandberg,
“depends upon several
factors, the cure
method, the length of
cure time and
temperature, the type of sealing rings used, tread pattern and of course the envelopes used. In Robbins’ experience retreaders can expect to get up to 20 percent improvement in envelope life through implementing some basic techniques as outlined previously. “If there is one thing that most retreaders could do to improve efficiency at a single stroke, it is to ensure that they have sufficient envelopes in stock. It is a one-time expense with a repeated payback.”
Changes at Robbins
There have been some changes at Robbins since it became part of the Hexpol Group. The Muscle Shoals plant has become a dedicated moulded products facility with a new plant leadership team and all staff have been retrained in all production processes and the company has made improvements to the production process.
This has seen aggressive investments in tooling and presses with associated increased production quality inspection to tightened standards.
One example of the improvements
moulds that give an easy release, the rubber flows more evenly and no lube is used when stacking envelopes so they do not stick together, and it is also easier to install sealing rings on new envelopes.
On the envelopes, a new skirt
bead is 43 per cent thicker and has an enhanced tapered bead that is resistant to abrasion created defects. All Robbins envelopes are embossed with the Robbins’ R- logo. Additionally, ever y envelope is tested on a spreader immediately after moulding. This
be allowed to slip, or the efficiency of the envelopes will drop. Sandberg concedes that even with the best of care, damage will arise from time to time, and when it does he recommends using dedicated repair products to maximise envelope life and avoid tyre miss-cures. Robbins supplies easy to use, long lasting repair materials for envelopes from stock. A great deal of envelope damage comes from the spreader and its operation. It looks like a simple job, but Sandberg recommends that operators are properly trained to avoid overspreading the envelope and improper mounting of the tyre in the envelope,
“Once the envelope has been applied to the tyre, the valve should be oriented to the correct position and once on the j-hook, the tyre should not be rotated as this could damage the envelope.” It has been stated that cooling the envelope is important. Robbins recommend storing the envelopes where they can cool, or, they suggest having a cooling area, perhaps aided by a fan, where envelopes can be cooled prior to storage. They should not be stored on the floor but in dedicated racking where they can be laid flat,
not folded.
“There is a temptation to use any available space, and sometimes envelopes can be found stored under the autoclave, which is a really poor practice as they are exposed to a constant heat and in less well managed plants the area under the autoclave can become a dumping ground for all sorts of contaminants. So, it is best to have a proper storage area for tubes and envelopes.
“Having said that storage is important, it is also worth ensuring that the storage is suitable. Metal bins are not a good idea, and folding envelopes can distort them and create weak points. Of course, over stretching envelopes to fit tyres larger than they should be used for is another common practice but one that is short-sighted as it can lead to damage. Equally as damaging to profitability is over-using envelopes past their maximum useful life as this can lead to failures in the autoclave and a rejected retread, which is more expensive than a new envelope.”
The challenge for the retreader is, if all of the above is to be maintained as a standard, is how to control the use of envelopes? Of
enhances the quality control and minimises the returns on not-to- standard envelopes.
There have been changes to the inner envelopes too with an improved consistency in thickness specifications; an improved bead to ensure a great seal; and improved wall thickness to make them more wear resistant and more capable of withstanding the pressures of the j-hook. Each flap is moulded with the proper tyre size enabling a ready match to the correct tyre.
Robbins is also refining its post- production lubrication of envelopes and there is continued refinement of outer and inner envelopes. Bar coding and RFID recording is under development and the company has an all new website www.robbinsllc.com Robbins is a stable US company that is part of a strong financial Group offering the market the widest possible range of sizes. Its field representatives and its call centre offer a quick response with the best available quality products for the retreader.