GB2069748A - Making electrodes for lead accumulators - Google Patents

Abstract

The invention provides a process for the continuous production of positive armoured electrodes for lead-acid accumulators in which air pockets between the active substance and the casing and the formation of gas pockets during the electrochemical process in the cyclization of electrodes are prevented. This ensures good contact between the active substance and the casing. In accordance with the invention, a lead framework coated with active substance is encased in a synthetic fibre fabric cloth, pre-profiled by means of a pressure roller, finally compressed with a roller foot situated immediately in front of the stitching needles and then stitched by the double chain stitching method into a plurality of segments containing a central current tapping.

Description

SPECIFICATION Improvements in or relating to lead accumulators This invention relates to improvements in lead accumulators and more particularly to a process for the continuous production of positive armoured (protected) electrodes with a synthetic fibre fabric casing, in which the formation of gas pockets between the active mass and the casing is prevented.

Processes are already known in which positive electrodes subdivided in the form of small tubes are produced by introducing pulverous or granulated active mass into the tubes.

The electric current is obtained from lead cores situated centrally in the tubes. The tubular subdivi sion can consist of a fine-mesh synthetic fibre fabric or of perforated PC material in which a fibre glass reinforcement is generally embedded. The tubes can located adjacent one another and only interconnected by a tapping, or alternatively initially connected to form a fabric compartment. In general, 10 to 25 tubes are provided side by side. The purpose of this system is to prevent or at least greatly reduce deposit of residue occurring in the lead accumulator, particularly from the positive electrode, during charging and discharging with a consequent reduction in the ampere-hour capacity.

The above process has a number of drawbacks.

For example, not only production of the individual tubes but also production of the fabric compartments requires considerable apparatus. The operation of attaching the tubes or compartments to the lead frameworks is carried out manually. The introduction of the dry pulverous active mass generally involves a shaking or vibration process if the electrode is to be given the necessary density. The plates also have to be inserted in devices in which the pulverous mass is fed in vertically. This process generates considerable amounts of lead dust, and being a health hazard requires operators to take precautionary measures which impedes the process.

Such electrodes then have to be closed with a bottom strip and placed in a bath of sulphuric acid in order to provide them with the required quantity of same. The entire process is thus difficult to autosnate, involves a great deal of manual work and entails hazardous operations requiring protective measures.

As a result of these drawbacks the use of halfshells of microporous plastic was adopted for the casing. The active mass and also the lead electrodes interconnected at one end are initially introduced into separate half-shells, after which these latter, filled in this manner, are placed over one another and connected together with an adhesive. This method, however, has the disadvantage that the active mass must be introduced in a moist state, to prevent leakage thereof when the half-shells are being connected together. This moist mass, however, impedes the connection process by frequently adhering to the connecting surfaces, and preventing half-shells from being satisfactorily joined together.

This method does not enable the active mass to be given sufficient density to prevent formation of air and/or gas pockets. An accumulator battery is also known wherein glass fibre mats are provided between the pasted (mass-type) plates and separators and are pressed against the plates by longitudinal ribs of the separators. This construction however, has a particular disadvantage that the fibre glass mats become detached and the substance drops out prematurely. During cyclization of the electrodes the harmful gas pockets which impede diffusion of the sulphuric acid on the electrode are further produced on the loose parts of the fibre glass mats. An accumulator plate is also known in which the grid pasted with active mass is surrounded by a porous, electrolyte-resisting fabric connected round the plate and between the adjacent contact elements of the grid by stitching.This process produces continuous connected segments of the grid which surround the grid encased in the active mass. However this method of producing the electrodes is also incapable of preventing formation of the harmful gas pockets between the active mass and the casing, as it does not enable the said mass to be evenly compressed.

This process cannot be mechanized or directly combined with the pasting operation, as the plate, owing to its complicated structure, particularly the variant in which the active mass continues over and beyond the edge of the grid, can only be pasted by hand. Furthermore the stitching is effected in a different direction, so that this process cannot be automated and it therefore cannot be used in continuous production in the accumulator industry.

In order to obtain an evenly compressed active mass in positive armoured electrodes and to enable the latter to be produced more economically and uniformly, means have to be adopted for compression of the active mass and for production of these positive armoured electrodes in a continuous process.

The invention seeks to provide the conditions required for such compression of the active mass and continuous production of the positive armoured electrodes and to provide a process for the continuous production of positive armoured electrodes for lead accumulators.

A particular object of the invention is to provide a process for even compression of the active mass in order to avoid air pockets and the formation of gas pockets during the electrochemical process in the cyclization of electrodes and thus ensuring satisfactory contact between active mass and casing.

According to this invention, the lead frameworks, together with a base consisting of synthetic fibre fabric and the moist active mass, is passed between a pair of rollers and is pasted from above. The lead frameworks, to which the currenttappings are stitched on, are encased in a protective cloth of synthetic fibre after the pasting process and are passed through a pressure roller apparatus in order to press the synthetic fibre fabric firmly against the moist pasted lead frameowrks, after which they are subjected to the pressure of a pre-profiled pressure roller, serving to compress the active mass and also to produce the connection between the said mass and the casing of the lead frameworks, and are conveyed into a stitching apparatus, where the pasted and encased lead frameworks, by means of a roller foot, immediately preceding the stitching needles, are finally profiled for the stitching process, and thereafter subdivided, by firm mechanical uniform stitching, into parallel segments which are situated lengthwise and which contain a central current tapping.

Example The production of positive armoured electrodes for lead accumulators according to the invention is carried out as follows. A lead framework suitable for the stitching process and cast in accordance with the ampere-hour capacity required is suspended on discharge rails by means of a feed magazine and placed individually on a transport table. By transport rollers exerting pressure it is conveyed to a pasting roller, where it is pasted with the moist active mass from above. The lead framework is accompanied in this process by a protective cloth of synthetic fibre fabric forming a base. This synthetic fibre fabric cloth can be supplied, underneath the pasting level, from a continuous roll, or alternatively prefabricated pieces of fabric are automatically folded around the said moist plate.

When the protective cloth of synthetic fibre fabric is taken from the continuous roll it is cut off with a red hot wire and the surplus portion automatically placed around the top of the plate by a turning device, so that the pasted plate is now encased on both sides. The plate, which is conveyed onwards by chains after the pasting process, is now arranged to pass through a pressure roller apparatus by which the synthetic fibre fabric is firmly pressed against the moist pasted plate from both sides. By means of a pre-profiled pressure roller the positive armoured electrode is now conveyed into a stitching apparatus. A uniform mechanical stitching process is commenced by auxiliary lugs which are provided on the side of the lead frameworks and which produce a signal in a light barrier to operate the stitching apparatus.

In this process the plate is subdivided on both sides into 10 to 25 segments, situated parallel to one another and arranged longitudinally, at a distance of about 1 cm apart, the number of segments corresponding to that of the cores of the lead frameworks.

The stitching process is advantageously carried out by the double chain stitch method and is terminated by a second light barrier control system, the sections of stitching provided from the foot of the positive armoured electrodes to the current tapping and being commenced adjacently at the same level or in off-set positions. Because the stitching needles are situated close together and that a stitching foot situated immediately in front of the stitching needle is constructed as a roller foot for the final profiling of the armoured electrodes prior to the stitching process, together with the special shape given to the lead framework, these features ensure that in the stitching of the synthetic fibre fabric and of the active mass the latter will be given the required even density. Satisfactory contact is thus ensured between the active mass and the casing, thereby avoiding air pockets and the formation of gas pockets during the electrochemical process in the cyclization of electrodes. Each longitudinal segment which has been completely stitched and profiled by the stitching process contains a core of the lead framework, which performs the current tapping function. The positive armoured electrode thus produced can now be placed, in the same manner as a positive starter electrode, in appropriate locations to mature.

Claims (7)

1. A process for the continuous production of positive armoured electrodes for lead accumulators wherein lead frameworks having current tappings secured thereto are arranged in conjunction with a base comprising a synthetic fibre fabric and a moist active mass to pass between a pair of rollers and are pasted with active mass whereby the frameworks are encased in a protective cloth of synthetic fibre s fabric, the encased frameworks being passed through a pressure roller apparatus to press said fibre fabric firmly against the moist pasted lead frameworks which are then pressed by a pre-profiled pressure roller to compress the active mass and form a connection between said active mass and the fibre fabric casing of the frameworks, conveying the frameworks into a stitching apparatus to be finally profiled by a roller foot and then stitched such that the pasted, encased frameworks are subdivided into longitudinal, parallel segments by uniform mechanical stitching whereby the segments are each arranged to include a central current tapping.

2. Process in accordance with Claim 1,wherein the stitched sections are arranged from the foot of the positive armoured electrodes to the current tapping and are commenced adjacent to one another and at the same level or in off-set positions.

3. Process in accordance with either preceding claims, wherein the active mass is finally compressed for the stitching process by the roller foot situated immediately preceding stitching needles in the stitching apparatus.

4. Process in accordance with any preceding claim, wherein the synthetic fibre fabric is already carried along, as a base, in the course of the pasting process.

5. A positive armoured electrode produced by a process in accordance with any preceding claim.

6. A lead accumulator incorporating a positive armoured electrode produced by a process in accordance of any of Claims 1 to 4.

7. A process for producing positive armoured electrodes substantially as herein described with reference to the example.