SE463708B - PROCEDURES FOR PREPARING A LONG-TERM BATTERY GLASS - Google Patents

Description

15 20 25 30 35 ÄO 3.65 738 grinding in an area around the joint between the bonded edges or by cutting the strand. This was followed by a polishing step.

The present invention relates to the production of battery glass by hot welding technology. These battery glasses contain a liquid electrolyte and support a series of heavy electrodes. Once in place, the battery glasses are subjected to vibrations and sometimes to shock impulse forces and consequently the welds must have a significant strength and service life in order to remain usable for a long period of time.

To test the 'faultlessness and reliability of these welds, a number of methods have been developed. One method means that a very strong electromagnetic field is established over the weld, whereby it is determined whether dielectric disturbances occur. If there are small pores and / or cracks in the weld, the dielectric strength of the weld will be reduced and a spark will be generated when the electromagnetic field is established over the weld.

Another method for testing the faultlessness and reliability of welds means that a mechanical impulse force is generated against the weld in order to determine its breaking resistance.

In the battery glass industry, this is achieved by allowing a weight in the form of a spear to fall from a predetermined distance on the weld so that a very high point pressure differential is formed over the weld. Of course, other percussion methods can be used depending on the design requirements of the finished product. These methods for measuring the reliability and strength of welds have proven to be useful for many purposes as the ff fi šf fl l of a weld is of critical importance.

Using these and other known test methods, it has been found that the formation of hot welds by simply heating the edges of thermoplastic material to be bonded and subsequent pressing of the edges against each other so that the weld is formed results in a reduced tensile strength of the material at the weld; ie the tensile strength of the material at the weld can be 85% of the tensile strength of the starting material or lower.

In addition, the extent to which the dielectric test fails as determined by the generation of a strong electromagnetic field across the weld can be increased by as much as 100-fold compared to the extent to which the dielectric test fails for the starting material. Furthermore, the impact strength of such welds has when the materials have been tested by obtaining a spear weight; fall on the weld, proved to be significantly reduced in comparison with the starting material and the impact strength also varied considerably at different points along the welds and from one weld to another, thereby deteriorating the overall reliability of the weld. Furthermore, the bending strength, especially the bending strength during bending, for the weld around the welding shaft is significantly reduced.

Accordingly, the invention relates to the manufacture of battery glass by a process comprising bonding thermoplastic material to each other thereby improving the strength and reliability of the bond.

More particularly, the invention relates to a method of making an elongate battery glass having a first end portion which is open at the top thereof and which has an elongate open side and three elongate closed sides, the distance from the surface defining the open side to the opposite closed side being at least several times less than the distance from the top to the bottom thereof, and the end portion having a wall thickness which is substantially the same from the top to the bottom thereof; a second elongate end portion having an open side forming a mirror image of the first end portion wherein the first and second end portions are joined to form a battery glass at respective elongate ends, the method comprising forming the first end portion with an open side, which end portion is open at the top thereof and has an elongate open side, the distance from the open side to its opposite closed side being at least several times less than the distance from the top to the bottom thereof, and which end portion has a wall thickness which is substantially the same from the top to the bottom thereof; forming the second end portion with an open side exhibiting the same shape as the first end portion; heating the surfaces of the end portions defining the open side thereof to at least the melting temperature thereof; joining the end portions at respective heated surfaces so that a weld is formed, forming a strand of plastic material along the axis of the weld; which process is characterized by heating the strand to at least its melting temperature; extruding the heated strand against the weld until it is substantially flat; and 10 -15 20 25 BO 35 H0 U '7 f? The heating of the heated extruded strand to a temperature below the melting temperature is therefore sucked in by ambient air around the extruded strand, thereby forming a battery glass having a substantially homogeneous wall thickness.

Apparatus for carrying out the method comprises known equipment for heating and joining the edges of the thermoplastic materials so that a weld is formed. Such an apparatus comprises a strip of material which can be heated and cooled relatively quickly. The strip, which is preferably in the form of the weld joint, is supported by an insulating material which has a network of depressions over the entire surface thereof which supports the strip. The strip can be heated, for example by an electric current and cooled by sucking air from the area surrounding the strip through the network of depressions and out of there through a vacuum pump.

In operation, the strip of material is pressed after the weld has been formed against the weld formed during the welding step and heated to around the melting temperature of the plastic material. The heated weld joint area and the strip are then rapidly cooled by sucking ambient air over the joint area and the strip through the network of depressions. When the plastic material has cooled sufficiently, the strip is removed from the plastic material.

The two elongate end portions can be made by steps comprising injecting a plastic material into a mold, which shape defines a plastic material receiving cavity having the shape of the first open side end portion and having at least one injection hole for introducing plastic material into the cavity, wherein at least one injection hole is arranged between the top and the bottom of the end portion along the portion of the cavity defining the opposite closed side of the end portion. The invention is explained in more detail with reference to the accompanying drawings, in which Fig. 1 shows in simplified form a weld joint having a rounded strand formed on each side of the weld; Fig. 2 shows a simplified perspective view of an embodiment of the apparatus used to achieve improved hot plate welding; Fig. 5 shows a perspective view of a preferred embodiment of apparatus for achieving an improved hot plate weld; Fig. M shows an enlarged side cross-sectional view of the apparatus of Fig. 5; Fig. 5 shows an enlarged sectional view of a weld made by hot welding; Fig. 6 shows a cross-sectional view of a simplified apparatus using HO 5 _ -ng dtâö i.fU using the embodiment of Fig. 5; Fig. 7 shows two end sections which can be welded together to form a battery glass; Fig. 8 shows a side elevational view of the battery glass formed by welding the two end sections shown in Fig. 7; and Fig. 9 shows a plan view of the battery glass of Fig. 8.

Fig. 1 shows a cross-sectional view of a weld joint formed by heating the respective edges 10 and 12 of two pieces of thermoplastic material. After the respective edges have been heated to the melting temperature therefore or until they have become plastic, the edges are pressed against each other so that a weld joint is formed. The pressure on the molten plastic edges of the thermoplastic material which arises as a result of the edges being forced against each other gives rise to a rounded strand 11 on each side of the weld. The dashed lines 13 and 13 'near each edge 10 and 12 illuminate in a simplified manner the part of the thermoplastic material which has been reheated during the welding process. Welding defects determined by the above-mentioned spear impact test procedure often occur between and along the respective boundary lines 15 between the reheated portions 13 and the unheated portions 17 of the thermoplastic material.

Welding defects determined by the spear impact test procedure indicate that the thermoplastic material is more brittle and less stretchable than the starting material. Although reduced tensile strength for the material has been noted in the weld, fragility and reduced extensibility of the material at the weld in comparison with the starting material have more serious side effects with the welding process. In addition, the material at the joint is characterized by a much higher degree of failed dielectric tests regarding dielectric requirements in industry than the starting materials do.

Various reasons have been proposed for the variations in weld joint impact strength at the welded joints, namely (1) that the molecular weight distribution in the thermoplastic material may affect the weld joint impact strength and may give rise to the variations; (2) that the material has oxidized during welding and consequently become more brittle; and (3) that the crystalline structure of the material in and near the welding line has become coarser due to the welding heat. However, it has not been possible to determine that any or a combination of these effects would lead to a reduction in the impact strength of the thermoplastic materials at the weld.

According to the invention, it has been found that the impact strength of the material at the weld can be increased and that the error rate in the dielectric test of the material at the weld joint can be substantially eliminated, by (1) heating the material at the weld. to a temperature at least about the melting temperature of the thermoplastic material, possibly at elevated pressure, and by (2) rapid cooling of the heated joint to a temperature which is at least lower than the melting temperature. When two pieces of thermoplastic material are welded, as pointed out above, a strand appears along at least one side of the welded joint. This strand can be removed before the steps of heating and quenching, but preferably it is not removed.

The exact heating temperature depends on exactly which thermoplastic materials have been welded and can for example be as low as 150 ° C for branched polyethylene and can be up to 480 ° C when the thermoplastic is a high density polyethylene thermoplastic.

This means that the exact heating temperature depends on the melting temperature of the thermoplastic materials, ie the temperature at which it turns into molten form. As a practical guide, the exact heating temperature can be determined for a specific thermoplastic by selecting the temperature at which sufficient melting occurs within a time period of up to about 25 seconds.

Pressure is applied to the weld during the heating step or after the heating step. high for the material at the weld to be completely flat.

The pressure must be sufficient In practice, the pressure can vary greatly depending on the device and the temperatures used and can vary from 0.1 h to 0.62 MPa. If the string is formed, the pressure must be sufficient to force out the string. If the string formed at the weld does not face the weld until it is substantially flat. According to a preferred embodiment, pressure is preferably applied during the heating step and the combined effect of the heat and pressure conditions is sufficient to extrude the string until it is substantially flat. After the pressure treatment, the heated weld is rapidly cooled immediately. Rapid cooling comprises rapid cooling of the heated weld to a temperature which is at least lower than the melting point of the thermoplastic material, and preferably to a temperature at which the thermoplastic does not exhibit adhesive properties. The rapid cooling step is performed so that the material at the weld joint will solidify again.

The rapid cooling must take place immediately tryck ter pressure treatment u? 10 15 20 25 50 35 H0 ~ 1 g-IAA ¿tÜÄ) fïiü or hot pressure treatment of the weld. This means that rapid cooling according to the invention does not include that the pressure-treated or hot-pressure-treated weld joint is allowed to cool under ambient conditions. Namely, it has surprisingly been found that rapid cooling after the steps involving melting of the two thermoplastic edges and joining these edges under pressure, ie immediately after the formation of the weld, in practice really means that the weld has improved properties with respect to dielectric properties, impact strength and depression flexural strength around the weld shaft. Rapid cooling can be carried out, for example, by immersing the treated joint in water.

To eliminate the problem of reduced tensile strength, low impact strength and high relative error rate in the dielectric test and the problems due to a rounded strand extending along the longitudinal length of the weld, an apparatus shown in its simplest form in Fig. 2 was used. Fig. 2 shows an insulating strip 19, which according to a preferred embodiment is made of a ceramic material or a high-temperature plastic, such as Torlon, which is a polyamide. A strip 21, preferably of titanium alloy 6AlüB having a thickness of 0.30 mm and a width of 25 mm is arranged over the insulating strip 19. As can be seen from the figure, the insulating strip 19 has the double function of an electrically insulating material and heat-insulating material and as a mechanism for rapid cooling of, among other things, the strip 21.

In the annealed state, the strip 21 has an electrical resistivity of about 180 uncm, excellent corrosion resistance and a tensile strength of 90 MPa at room temperature. The high strength of the alloy is suitable for it to withstand the local compressive forces generated when it first comes into contact with the rounded weld bead. The high strength is also suitable due to forces that arise on the titanium strip when it is exposed to high temperatures. For example, when the titanium strip is heated to 230-26000, its length increases due to thermal expansion. In contrast, the plastic material outside the welding zone, i.e. the area 13, can substantially prevent the area of the strand at the heated strip 21 from expanding or contracting along the weld during the process including crushing the strand and cooling the formed smoothed strand.

Consequently, the longitudinal expansion and contraction can 10 15 20 25 BO 35 NO fl; '? fee% í) d 7liu tion of the heated strip 21 give rise to a shear stress between the strip 21 and the welding strand material. This could give rise to cracks in the surface of the plastic material and possible throwing of the plastic object formed by the welding step.

Accordingly, the titanium alloy strip 21 is subjected to a longitudinal tensile stress at room temperature which slightly exceeds the maximum thermal stress which occurs during heating and cooling. The tension is kept constant during the heating of the belt 2l with known technology. through screws 55 and 56 as shown in Fig. 6.

For example, this stress can be produced. In this way, each point along the alloy strip 21 remains in substantially the same position with respect to the strand during heating and cooling, and consequently the length of the heated section of the strip 21 remains substantially constant. Since a voltage at room temperature of about 2U MPa is necessary to provide the necessary voltage on the strip, which voltage is significantly reduced at high temperature, the strength of the strip 2l must be quite high.

It is obvious that a tensile strength limit of 90 MPa is more than sufficient for the stress values induced in the strip 21.

As shown in Fig. 1, the heated strip 21 together with its insulating carrier 19 is pressed against the string 11 so that it is caused to melt and becomes plastic. The string is pressed and flattened against the welding area. During this operation, the molten thermoplastic material will adhere to this strip 21. After the strip has cooled to below the melting point of the thermoplastic material, the adhesion of the strip to the thermoplastic material ceases and the strip can be removed from the material.

It has been found that the welded joint which has been heated according to the invention must be cooled rapidly in order for the benefits including improved tensile strength, improved strength and improved dielectric properties to be achieved for the material at the weld joint. Accordingly, a plurality of holes 23 are received in the strip 21, each of the holes communicating with the other holes through a channel 25 formed in the insulating carrier 19. According to one embodiment, cool air is blown through the channel 25 and out through the holes 23. and around the heated thermoplastic material as illustrated by the arrows in Fig. 2. Thereby the thermoplastic material and the strip are rapidly cooled whereby the desired crystalline structure is achieved, i.e. the flattened thermoplastic material has a smooth, closed surface having a very low dielectric relative error rate. 10 15 20 25 30 35 HO 708 Ch! 9 136. - - ° t - The reshaped weld strand forms a flat additive layer of material which is laminated to the starting material. FolJaktll8e fl Fe U. - «- - - '' 't essentially ceras the possibility of a small crack 1 sve sen which would give rise to undesirable' leakage.

Figures 3 and H show a preferred embodiment of the apparatus used according to the invention. As shown there, for example, an insulating Teme 29 made of ceramic or a high temperature resistant plastic has a groove 35 formed through the center thereof sanding a plurality of transverse grooves. 33 of relatively small size 'up the strip 29. Over the play formed along the length of that insulation. the insulating strip 29 is a heating strip or a heating strip 'placed 31 which is preferably made of the titanium alloy 6AL4V having a thickness of 0.30 mm and a width of 25 mm- This strip is exposed as previously pointed out in connection with the embodiment shown in Fig. 2, initially when writing those which are greater than the room temperature for a voltage at which the maximum voltage due to the heating is kept in place and in the same position with respect to the thermoplastic strand for the strip to undergo during the heat equalization operation.

In the embodiment shown in Fig. 3, ambient air is sucked in through the grooves 33 by means of a vacuum pump (not shown) which establishes a reduced air pressure of 0.2 atm. By sucking in cool ambient air through the grooves 33, a more homogeneous distribution of air around the strip 31 and the flattened string is achieved and consequently a more homogeneous cooling of the strip 31 and the flattened thermoplastic material.

The groove 35 should have a relatively smaller width to form a carrier for the strip 31, and consequently the groove must be deep for the intake air from each of the grooves 33 to be led to the vacuum pump. In addition, the grooves 33 should be wide enough to provide a large cooling surface for the strip 31 but should not be so wide that the strip 31 does not receive adequate support.

According to a preferred embodiment, the grooves 33 are 1.7 mm wide and only 0.17 mm deep, each groove being separated by a 0.5 mm wide portion. This groove structure is designed to keep the bending stress in the strip 31 low and at the same time to provide a relatively large area between the strip and the cooling air. During the heating cycle, at the same time, the grooves can act as insulators which prevent a large heat transfer to the insulators 29. The central channel 25 is deep and narrow so that it has a very small surface area relative to the strip 31. which could induce transverse bending stresses while at the same time having a sufficiently large cross-sectional area for the air from the grooves 33 to be led to the vacuum pump.

According to the embodiment shown in Figs. 2 and 3 and H, when electricity is passed through the strips 211 and 31, it becomes hot enough for the strand 11 shown in Fig. 1 to be transferred to around or above the melting temperature thereof. The carrier 20 for the insulators 19 or 29 and the strip 21 or 31 press the heated strip against the strand so that the strand is flattened against the welding area until it is substantially flat. The reheated welding material is then bonded to the plastic in the welding area as illustrated in Fig. 5 so that an improved weld is formed. The joint in Fig. 5 is not shown to scale in order to make it clear how the smoothed strand forms a thin extra layer of bonded plastic material at the welded joints.

Fig. 6 shows a simplified cross-sectional view of an apparatus specially designed for the manufacture of battery glass and based on the embodiment of Fig. 3. The strip 31 is arranged over the insulating material 29 which in turn is supported on a steel frame 60 which defines an closed room S. The room S is connected to a vacuum pump 3H and opens into the channel 35 which in turn is connected to the grooves 33. A current source 36 is connected to the strip 31 through a line 38 for connecting electrical current thereto. When the vacuum pump is in operation, it sucks air under reduced pressure over the strip 31 and the weld joint area and both of these are cooled. A copper coating 57 (For simplicity shown on an enlarged scale) is provided on the strip 31 in such areas of the strip 31 that do not come into contact with the plastic material to prevent overheating of the strip in such areas.

The strip 31 must be kept under tension as indicated above with reference to Fig. 2. Screws 55 and 56 schematically illuminate a device for achieving this tension; but obviously there are many equivalents that can be used instead.

When the screw 56 is tightened, one end of the strip 31 is wound up, whereby the necessary tension on the strip 31 is provided. As can be seen from Fig. 6, the insulating material 29 on which the strip 31 is supported is arranged on a flat surface. However, the surface supporting the insulating material need not be flat but may have a surface which corresponds to the surface of the thermoplastic workpiece at the weld. 10 15 20 25 30 35 U0 11 _ _ f. ~ v m fl iï, - 'Û! 4 'f) Ö / l U Thus, if two thermoplastic pipes are welded together, the surface can be annular or cylindrically shaped. A device comprising a notch and a cylinder acts on the frame 60 so that contact is made with the weld H1.

A second apparatus 58 is schematically illuminated on the opposite side of the weld H1 by the plastic material 14 and serves to heat and level the formed strand on the other side of the weld H1.

Example Using the apparatus shown in Fig. 6, the embodiment illustrated in Figs. 3 and H was applied to make a battery glass of a propylene copolymer blend of the type shown in Figs. 7-9.

The elongate battery glass of Figs. 8 and 9 includes two end portions 37 and 39, as shown in Fig. 7, each of which is open at the top and which has an elongate open side and three elongate closed sides. The distance from the surface defining the elongate open side of each end portion to its opposite closed side is at least several times less than the distance from the top to the bottom thereof. In general, the distance between the open side and the opposite side is about 1 / H to 1/10 of the distance from the top to the bottom of the portions 37 and 39. Each end portion 37 and 39 has a wall thickness which is substantially the same. from the top to the bottom thereof; that is, no taper or surface reduction occurs from top to bottom and each of the end portions 37 and 39 forms a mirror image of the other portion. The end portions 37 and 39 are heat-welded at respective elongate end portions so that the battery glass illustrated in Fig. 8 and Fig. 9 is formed. The process for manufacturing the battery end portions 37 and 39 is set forth in USP U 118 265 to which reference is hereby made.

The main requirements for a battery glass are that it is resistant to battery acid, does not show leakage, essentially shows exact dimensions, is resistant to shrinkage when the battery overheats, has high impact resistance to be exposed to accidents during battery manufacturing and use thereof, has a homogeneous width and length from top to bottom, ie no surface reduction occurs, has straight sides that do not bend out or in and has a capacity to bend and / or deform during handling to prevent cracking of the battery glass. As pointed out earlier, when the respective edges of the end portions 37 and 39, which are illustrated in Fig. 7, are heated to the melting temperature and then bonded together to form a weld, the molten plastic material is formed: : strings 11 on the inside and outside of the glass of the type illustrated in Figs. 1 and 8 and 9.

After the weld joint including the strands has been cooled, the insulator 29 and the belt 21 are arranged as illustrated in Fig. 3 along both the inside and the outside of the welding area against the strands formed during the initial welding step using an apparatus of the type illustrated in Fig. 6.

The titanium alloy strip 21 is then heated for a time interval ranging from 2.5 seconds to more than 20 seconds while being pressed against the strings. Thereby the strands melt and are flattened towards the heated welding area 13 "as illustrated in Fig. 1 whereby a flat weld is formed as illustrated in Fig. 5. The strip 21 and the flattened strand are then cooled by sucking air of room temperature through the grooves and through the channel formed in the insulating strip 29. After the flattened string has cooled sufficiently to no longer adhere to the strip 21, the strip and the insulating carrier are removed, whereby the finished welded battery glass is obtained.

It has been found that when longer heating and cooling times are used, the point impact strength of the welds increases. However, it has also been found that if longer heating cycle times are used, the battery glass falls, especially at the upper end next to the open end of the glass, ie the glass curves inwards or outwards to an unacceptable extent. The casting that occurs during long heating times obviously depends on the shrinkage that occurs in the plastic material after it has been heated to the melting point. The material in the area above which the strand is flattened is thus brought to a temperature at or near the melting point thereof and consequently shrinks during cooling, when on the other hand the surrounding material which has not been reheated does not shrink.

A method for eliminating the throwing problem means that the welded battery glasses are preheated to 80-90 ° C before the equalization process. This causes the whole glass to shrink slightly upon cooling and consequently the difference in shrinkage between the material adjacent to the weld and the remainder of the battery glass is significantly reduced. However, this method is undesirable in a production line because the extended cooling cycle required in preheated glasses significantly increases the total manufacturing time of the battery glasses. It has therefore been discovered that by using a very short heating time of 3-4 seconds and heating the titanium alloy strips to a higher temperature, an improved weld exhibiting high point impact strength can be achieved without any significant throw. The degree of casting is further reduced by using a method comprising sucking in relatively cool ambient air under the strip 31, whereby the battery glass material adjacent to the strips is cooled. This causes a narrower zone 10 of heated plastic material to be subjected to shrinkage which in turn reduces the distortion of the walls of the battery glass due to shrinkage. Consequently, by using a relatively short heating time cycle and sucking in air from the area surrounding the heated plastic material, the total time cycle for treating the weld can be kept lower than 30 seconds.

Claims (1)

H 708 <5 (ml Claims claimed for the manufacture of an elongate battery glass having a first end portion (37) which is open at the top thereof and which has an elongate open side and three elongate closed sides, the distance from the surface defining the open side to the opposite closed side being ¿at least several times less than the distance from the top to the bottom thereof, and the end portion having a wall thickness which is substantially the same from the top to the bottom thereof; a second elongate end portion (39) having an open side forming a mirror image of the first end portion, the first and second end portions joining to form a battery glass at respective elongate ends, the method comprising forming the first end portion (37) with an open side, which end portion is open at the top thereof and has an elongated open side, the distance from the open side to its opposite closed side being at least one several times smaller than the distance from the top to the bottom thereof, and which end portion has a wall thickness which is substantially the same from the top to the bottom thereof; forming the second end portion (39) with an open side having the same shape as the first end portion; heating the surfaces (10, 12) of the end portions defining the open side thereof to at least the melting temperature thereof; joining the end portions at respective heated surfaces (10, of plastic material formed along the axis of the weld; and 12) so as to form a weld (41) forming a strand (11) which method is characterized by heating the strand to at least its melting temperature ; extruding the heated strand against the weld until it is substantially flat; and rapid cooling of the heated extruded string to a temperature below the melting temperature therefore by sucking ambient air around the extruded string thereby forming a battery glass having a substantially homogeneous wall thickness.