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SEAMLESS PASTING BELTS | --> A belting performance

Battery manufacture appears to be more of a craft than a precise engineering science.
Take lead acid battery plate pasting for example. At 5 ELBC, the Editor Gerry Wolf (GW) met with Giovanni Terzaghi (GT) of Termar to learn something about belt pasting.
This reported dialogue is an account of that meeting.

GW: Our Let's Learn series said it all really. Improve on quality, composition of raw materials, their formulation, the training of staff and testing of product and you can make a better battery that lasts longer. So where does pasting fit into that equation?

GT: A silent revolution occurred in the pasting process by the introduction of seamless belts for automatic pasting machines. The electrical characteristics and life of lead storage batteries depend gretly on the structure and phases present in the active material which, in turn, result from the composition and properties of the pastes.
To enable plates to deliver their rated capacity in batteries, plates must be pasted with weight of paste in the weight range specified.
The paste applying operation is the process during which the properly mixed paste is applied to grid panels of the proper composition and stiffness. The pasting belt plays an important role in this process.
Control of the weight, thickness and density of the resulting pasted plate will determine process ability of the plate in the battery assembling area. All of these characteristics combine to determine how the plate will perform in the finished battery.

GW: So what are the advantages of belt pasters versus the competitive systems (fixed orifice, continuous pasting with steel belts, extruding pasters, etc)and why is belt pasting still so popular?

GT: The belts pasters are a more forgiving type of system than say, the fixed orifice or steel belt pasters. The tolerances of casting a grid do not need to be held as close, because the belt will give a little when the thickness of the plate is on the high side.
The need for operator skills are not as high or demanding with a belt paster as with some of the other types of machines. The overhead costs for a belt paster are not as high as fixed orifice or continuous cast lines.
On some systems you have to soften or add water to the mix to paste the plate but with a belt paster this is not required.

GW: And what are the shortcomings of belt pasters?

GT: The only shortcoming I see with a belt paster is that you have to change the belts on a regular basis

GW: How can belt pasters be improved? Better running, better operating practice? And how much difference does the belt material make?

GT: Obviously you have to employ a good preventative maintenance programme to keep the machine running as it was designed to run. Secondly changing from traditional cotton belts to Industrie Tessili Bresciane (I.T.B.) seamless belts will certainly improve the paster's performance, and as you can see for yourself, I've got customer endorsement to that effect.

I.T.B. seamless pasting machine belts have been developed in close cooperation with battery makers, taking into consideration all the problems connected with the pasting process. Pasting machine manufacturers and pasting process engineers pointed out the following problems and requirements to design an ideal belt:

  1. Traditional pasting belts are woven open-ended. The two fabric ends are then sewn and glued to get a ring shaped belt. They have therefore a weaker seam zone.
  2. The belt must have the same strength in all its points while traditional cotton belts may have a seam break zone.
  3. The belt must have the same thickness and surface smoothness throughout its circumference to give a better pasting and improved active material distribution on battery grids.
  4. Water absorption must be uniform in every point. No glue should be used for seam purposes in the belt.
  5. The belt must run straight on the pasting machines and not move towards one side or another. It must be perfectly cylindrical. The belt should be dimensionally stable to avoid textile structure distortions. The belt life time should be extended as much as possible to reduce the amount of down time on the pasting lines to replace the belts.

GW: So when did you produce the first seamless belt?

GT: About fifteen years ago, I.T.B. and Termar technicians recognised the need for an improved product to replace the traditional cotton seamed belt.

We designed the seamless belt consisting of a unique textile composite structure: two ply woven fabric at the
external pasting surface and non-woven synthetic mat with longitudinal reinforcing fabric at the internal surface.
We then selected the most suitable raw materials, and have developed and perfected an appropriate manufacturing process to build a reliable production capacity to meet pasting process engineers' most strict requirements.
A unique composite was so created by combining a textile cotton material which is smooth and absorbent with reinforcing fabrics (able to give the requested tensile strength and controlled elongation) by a synthetic non-woven mat (flexible and elastic).
The resulting composite structure depends on the yarns' physical and chemical composition.

GW: And the advantages?

GT: Well, that's obvious really. Belts come out "endless" from the weaving looms and need no further seam or splice, so no further joining or gluing is necessary.
The belt, which is made of cotton and synthetic fibres, has the same strength in all its points and the well-known "seam break zone" no longer exists. The belt has the same thickness (about 9mm) and surface smoothness throughout its circumference and that means a better pasting and an improved distribution on battery grids. Water absorption is uniform in every point of the belt since no glue is used for seam purposes.
The belt runs straight on the pasting machine and does not move towards one side or the other because it is perfectly cylindrical. I.T.B. seamless belts are heat-set at high temperature under a remarkable stretching load.
Their dimensional stability is therefore excellent throughout their whole life. Length and width do not change even under heavy working conditions, so the belt can work very taut, but in no case do they create slipping under heavy working machine rolls. I.T.B. belts are also protected against abrasion by means of a patented material which we have specially developed for this.
The result of all the above is the that belt lifetime proved to be three to four times as much as the traditional spliced belts.

GW: Regarding close tolerance plates, can you give typical values on weight thickness and pasted weight and can you compare old belt pasters with manual hopper control versus more recent belt pasters with traditional cotton belts or seamless belts?

GT: As far as close tolerance and thickness of the plates, this depends on the manufactures. Most plates that are run on an automotive paster are from 0.95 to 1.10mm thickness with a ±0.05 to ±0.10mm tolerance.

Old belt pasters with manual hopper roll control and traditional seamed cotton belts have pasted weight tolerance of ±7 grams per plate. Modern pasters from MAC (USA) and SOVEMA (Italy), with improved hopper control and equipped with I.T.B. seamless belts can achieve paste weight control of less than ±3 grams and minimise paste waste.

GW: There's quite a difference on the price of your belts compared to ordinary cotton isn't there?

GT: The cost of a traditional cotton belt for an automotive paster is about US$90 while the equivalent I.T.B. seamless belt is US$300. The enormous price difference has been a shock for many buyers since our first commercial offer in 1981, but a quick calculation may show how the extra cost of seamless belt can be repaid by (i) less down time, (ii) saving of paste through better weight tolerances and (iii) much longer life time.
For example, a battery manufacturer producing one million SLI batteries of various sizes needs 68 million plates, i.e. 34 million panels (double plates). Using traditional cotton belts, the manufacturer may need over 70 belts while using I.T.B. seamless belts they may need only 30. There is an initial extra cost of seamless belts. However, the pasting line down time for replacing the belt is 30 times per year with seamless belts and 70 times with cotton belts, so there is a saving of about 40 hours per year in down time.
The correct use of a seamless pasting belt as well as good operation and a good paster maintenance programme can save tens of thousands of dollars in reduced paste waste, energy and health care cost. It has been estimated at a saving of US$60,000 a year with only 3 grmas of paste saved per plate.
Another evident saving of paste is noticed when comparing traditional seamed cotton belts with I.T.B. seamless ones. For a battery manufacturer producing one million SLI batteries per year and the hypothesis that 1 panel using every 16 can be overpasted in the last third of the cotton belt life time (because of the wearing of the seaming zone), you have about one million panels overpasted. If the overpasting is 3 or 4 grams per panel, the manufacturer loses 3 to 4 tons of active material per year.
Longer life time of I.T.B. seamless pasting belts is today a proven fact all around the world, as they are used by over 240 battery plants in 82 countries. The life time of seamless belts proved to be at least 3 times that of the traditional cotton belts with a good average of 1.1 million panels pasted per belt. In 1995 I.T.B. belts helped the battery industry to produce over 140 million SLI batteries around the world.

GW: It's hard to argue with that. So what belts are there on offer?

GT: Battery manufacturers can choose among several producers of traditional seamed cotton belts or I.T.B. seamless ones. Seamless belts can be offered in any size with no actual limits in length or in width.

GW: So how do you get the best out of your belts?

GT: There are a few points you have to observe:

  1. The Paste
    Belt pasting machines operate best with crunchy paste because it has excellent cohesion to itself and it will not penetrate the belt. This assures longer belt life. The crunch of the paste is increased by: (a) increasing the acid addition - increasing the specific gravity (b) decreasing the speed of the mixer. When the paste coming from the mixer is too hot - over 38° C (100° F) - the moisture in the paste will evaporate and change the consistency of the paste. This can affect the operation of the machine as well as the performance and life of the belt. To facilitate a good machine operation, it is also recommended that the paste be about 18 to 22 reading on a globe penetrometer. If paste sticks to the belt, tighten the squeeze roller to remove more moisture from the belt. If paste sticking or pulling persists, the paste is too wet or the belt is too old and saturated with hard oxide and must be replaced
  2. The squeeze roll
    The squeeze roll is used to squeeze water out of the belt. It also presses the belt against the drive roll to avoid belt slippage and to aid in belt guiding. It is ideal to have sufficient moisture in the paste to provide a flow of water out of the belt. If the squeeze roll is adjusted too tight because of stiff paste, the belt may stretch excessively. Also, stiff paste will not stick well to the grids. Again, use paste and a cut-off wire when necessary.
  3. Belt cleaning
    For good plates and long belt life, the belt must be cleaned and flushed until clean water comes out of it at the squeeze roller. Also, inject water to the underside of the belt next to the rollers. This water will be forced through the belt by the squeeze roll and flush out the paste and oxide. If residual paste in the mixture is allowed to harden, it will damage the water absorbency of the belt and it will also crack the belt fibres. Therefore, keep the belt wet all times when the machine is not in use.
  4. Belt life-time
    Under good operating conditions an I.T.B. belt can easily paste over 1.1m panels. Once a belt is saturated with paste and the surface is too smooth and too hard, little can be done except install a new belt. When the top surface of a belt has worn smooth, the oxide will tend to stick even when the moisture content in the belt is correct. In this case belt life can be extended considerably by placing a steel cut-off wire (piano wire) diagonally across the belt surface to separate the plates. When the pasting belt is new, the use of the piano wire is not recommended. If paste begins to pull from the panels, the wire can be added. The "plate finishing rolls" (located at the exit end of the paster) wrapped with a cheese cloth or tobacco cloth will absorb moisture from the pasted panels to the upper and lower pasted panel surfaces. This extra added surface texture has been found to add to the plate's initial cranking performance. Also, when the belt pulls paste, look for the following:
    a) belt or paste is too wet
    b) belt scraper is not cleaning the belt
    c) squeeze roller is not tight enough to remove enough water from the belt
    d) belt is saturated with paste and has lost the property to absorb water

GW: Finally, what's the future of pasting. What is your opinion on the survival of belt pasting?

GT: I believe that belt pasters will be used for many years to come for it is a good, low overhead way of making lead battery plates. In addition, the continuous improvements in seamless pasting belts allow battery makers to produce plates with low cost, good flexibility and close tolerances.

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